Georgi Todorov, Diyan Slavchev, Dobromira Shopova,

Ilian Hristov, Tanya Bozhkova

PRACTICAL GUIDE

FOR INTRODUCTION TO

PROSTHETIC DENTAL MEDICINE

Part І – Fixed dental prosthetics

Part II – Model cast dentures

Part III – Articulators

Medical University – Plovdiv

2018

CONTENTS

INTRODUCTION .......................................................................................... 5

Part І - FIXED DENTAL PROSTHETICS .......................................................... 7

1. TERMINOLOGY ..................................................................................... 7

2. CASTING GYPSUM MODELS .............................................................. 8

3. CONSTRUCTIONAL REQUIREMENTS FOR PARTIAL CROWN

PREPARATION ............................................................................................. 9

4. PREPARATION OF A CANINE FOR A PARTIAL CROWN STEPS .. 10

5. PARTIAL CROWN PREPARATION OF A PREMOLAR, STEPS .... 11

6. MONOLITHIC PINLEY ........................................................................ 13

7. PLASTIC CROWNS .............................................................................. 17

8. ADAPTA SYSTEM BRIDGE PROSTHESIS ....................................... 19

9. WAX DIPPING TECHNIQUE .............................................................. 31

10. MODEL CASTBRIDGE PROSTHESIS ............................................ 32

11. BRIDGE PROSTHESIS WITH SELECTIVEOPEN RETAINERS .. 38

12. WAXING A COPING FOR A METAL CERAMIC CROWN .......... 39

13. RESIN-BONDED FIXED PARTIAL DENTURES ........................... 40

Part II - TECHNOLOGICAL PROTOCOL FOR MODEL CAST DENTURES

............................................................................................................................. 49

1. CLASSIFICATION OF PARTIAL EDENTULISM ................................ 49

2. ELEMENTS OF A MODEL CAST DENTURE ...................................... 51

3. METAL FRAMEWORK ........................................................................... 51

4. CLASPS. SPECIFIC REQUIREMENTS .................................................. 59

5. MAIN CLASP TYPES .............................................................................. 61

6. PLANNING AND CONSTRUCTION OF A MODEL CAST DENTURE

69

7. LABORATORY PROTOCOL FOR MODEL CAST DENTURES......... 71

Part III - ARTICULATORS ................................................................................ 78

INTRODUCTION

This current practical guide is in accordance with the program of

Preclinical Practical classes of Prosthetic Dentistry based at the Department of

Prosthetic Dentistry at the Faculty of Dental Medicine (FDM), Plovdiv. This

practical guide is an improved and expanded version of the previously released

edition in 2013. This guide has been translated and published in English to aid

English-studying students at FDM-Plovdiv.

The first part of this guide entails the technology of fixed prosthesis in

steps and as a thorough review.

The second part of this guide outlines the peculiarities and stages

concerning the model cast denture only.

The third part demonstrates the main construction principles and elements

of articulators.

The practical guide demonstrates the materials, supplies and equipment that

are required for each practical class in order to acquire the overall technological

and laboratory protocol for each construction. Arrangement, concepts and

terminology are consistent with the Glossary of Prosthodontics Terms.

I would like to acknowledge and express my greatest gratitude to the

leadership team; Prof. St. Ivanov and Prof. Y. Kalachev for their continual

support, critical remarks, and relentless advice. Also, I would like to the

assistants from the department of Prosthetic Dentistry ; Dr. V. Doshev, Dr. M.

Rusev, Dr. St. Hristov, Dr. St. Yankov, Dr. St. Alexandrov, Dr. T. Bozhkova

and Dr. D. Shopova, as well as the students Georgi Chachevski, Rateb Al

Macawi and Manisha Shafi. Special thanks to the dental laboratory team for

their continual support and participation.

The management would like to thank for their help and dedication Assoc.

Prof. Diyan Slavchev, for the development of the additional part named

"Articulators” and Dr. Ilian Hristov for “Resin-bonded fixed partial dentures.”

Prof. d-r G. Todorov, PhD

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Part І - Fixed dental prosthetics

1. TERMINOLOGY

Dentition defects – The loss of one or more teeth up to a condition where

only one tooth remains in the dental row any violation in the integrity or the

occlusal-articulation balance of the masticatory system; any cause for esthetic

and functional changes or pathological conditions.

Full crown – A restoration which completely covers the natural tooth

crown by removing its contours, functional surface and morphology in

accordance with strict technological, functional and constructional requirements.

Partial crown – Restores only part of the crown through preparation in

accordance with specific technological and constructional requirements.

Depending on their purpose partial crowns can be:

a) Restorative

b) Retainers

In English books restorative partial crowns are referred to as inlay,

onlay, overlay, pinlay; they are used to restore hard tissues, missing as a result

of caries or mechanical trauma; their preparation follows specific constructional

presets.

Partial retainer crowns are used to attach fixed dentures like bridges and

splints to their respective abutment teeth; for this type of abutment the vestibular

surface of the natural crown is kept intact, while the other surfaces are reduced

in the process of preparation; grooves, pinlay retentions and channels are used to

improve retention; more commonly known modifications include the half

crowns, three-quarters and four-fifths crowns.

Fixed dental prosthesis – a construction which replaces one or more

absent teeth; it is permanently affixed to the remaining teeth; the masticatory

force is distributed physiologically – denture → tooth →periodontium→ bone.

Elements of a bridge prosthesis:

Abutments – the teeth to which the bridge is affixed to; it’s is their

periodontium that bears the masticatory force;

Pontic – the artificial teeth which replace the missing natural teeth; it

restores the anatomical, functional and esthetic integrity of the dentition; it

connects to the retainers;

Retainers –through them the pontic is fixed on to the abutments with the

use of cement; all types of metal, combined and metal ceramic crowns can be

used as retainers

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The connection between the pontic and retainers can be achieved through:

soldering

autogenous welding;

monolithic casting

Path of insertion

The path of insertion is an imaginary line which describes the path of

insertion and removal of the bridge; it determines the characteristics of the

process of preparation.

Retention, resistance, taper1

Retention - prevents removal of the restoration along the path of insertion

or long axis of the preparation

Resistance prevents dislodgement of the restoration by forces directed at

an angle, an apical or occlusal direction; and important element of retention is

the existence of two opposing vertical surfaces that we envision and create

during the process of preparation.

Taper – counteracts the rotational and tipping horizontal force

2. CASTING GYPSUM MODELS

Models of the mandibular and maxillary tooth arches are cast from ordinary

laboratory gypsum. Rubber models with specifically placed plastic teeth are

used for this purpose. The placement of the teeth corresponds to the type of

dental construction that is required for the practical courses.

Models for partial crown preparation are cast using special impression

forms of canines and premolarsin a 1:3 scale (fig.1).The same are used as

models for sculpting classes during the first semester (fig. 2).

Fig. 1. Phantom models

1 These (characteristics, features, conditions) apply to crowns as well

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Fig. 2. Gypsum models for partial crowns

Two layered plaster casts with removable dies used for the making of

model cast, metal ceramic and Adapta system bridges are cast from closed

mouth impressions. (fig. 3)

Fig. 3. Silicon closed mouth impression

3. CONSTRUCTIONAL REQUIREMENTS FOR PARTIAL CROWN

PREPARATION

The path of insertion for partial crowns depends on the tooth group. For

premolars the path of insertion is parallel to the longitudinal axis of the tooth while

for frontal teeth it is parallel to the incisal half of the vestibular surface. (fig. 4)

Fig. 4. Path of insertion: a) for premolars; b) for frontal teeth

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These requirements are followed during the preparation of grooves for

partial crowns:

Resistance against rotational forces is achieved through the “keyhole

effect”; it is achieved through tipping the bur in the lingual direction and

thus giving the groove a smooth roundness (fig. 5b);

The grooves walls are V-shaped, slanted and offer good resistance (fig. 5a);

A groove placed too far to the lingual surface does not allow for volume

and wideness of the metal (fig. 5c);

A groove with an undermined vestibular enamel surface can easily be

fractured (fig. 5d);

During the preparation of natural teeth access to the approximal walls is

achieved through the use of a diamond needle bur, moved along the longitudinal

axis of the tooth in an up-down motion similar to that of a “sewing machine”.

Fig. 5. Requirements for the channel walls: a) incorrectly V-shaped; b) correctly

rounded; c) incorrect lingual placement; d) incorrectly undermined vestibular wall

4. PREPARATION OF A CANINE FOR A PARTIAL CROWN STEPS:

(fig. 6)

Smoothing the approximal walls with a modeling knife without crossing

the vestibular visual border;

The lingual surface is reduced with a modeling knife within the

boundaries of 0.5 to 0.75 mm;

In the cervical area the lingual preparation is finished with a

supragingival margin;

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The incisal edge is shaped with a modeling knife in the form of a

horizontal groove which follows the spear shape of the canine;

A modeling knife is used to shape the cutting tooth, while the horizontal

groove follows the spear shape of the canine;

Keeping the established requirements for groove retentions in mind

(from page 4), the approximal grooves and the one on the incisal edge

are made П-shaped;

After the preparation and isolation with plant oils, a parallelism and non-

retention check is made with the use of a plaque of plasticized pink wax.

Fig. 6. Preparation of a canine for a partial crown

5. PARTIAL CROWN PREPARATION OF A PREMOLAR, STEPS:

(fig. 7)

Fig. 7. Preparation of a premolar for a partial crown

0.5 – 0.75mm are removed from the approximal walls with the use of a

modeling knife

The vestibular preparation is made in a way which prevents the

excessive shortening of the approximal wall in the lingual direction

The lingual wall is reduced by 0.5-0.75 mm ;

The lingual contours of the tooth are kept; this however does not apply

the lingual parts of the approximal walls;

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In the later stages the parallelism of the approximal walls with be further

developed, in some cases it will extend in the vestibular direction;

On the occlusal surface the lingual cusp is reduced with 0.5-0.75mm

The vestibular cusp is reduced only in it’s lingual half; the

aforementioned requirements for preparation of the approximal walls are

followed for the positioning of the cusp’s occlusal margin;

In the cervical zone of the tooth a supragingival margin is placed on the

reduced approximal and gingival walls;

In the medio-distal sulcus, on the occlusal surface, a V-shaped channel is

formed; the same becomes a П-shaped form consisting of two vertical

grooves in the approximal walls

After the preparation is complete the tooth is sealed with plant oils ; it is

then checked for parallelism and any undesired retentions with the use of

a plasticized plate of pink wax;

After the preparation is complete, a П-shaped handle is made from zinc

wire with flat nose pliers (fig 8).

Fig.8 Placing a П-shaped handle

a) on a canine; b) on a premolar

b)

5.1. IMITATION WAXING WITH PINK BASEPLATE WAX

Pink baseplate wax is used to test the preparation’s quality. The criterion

for a successful test is the effortless removal of the wax without it fracturing or

deforming.

Additional wax is added on to the baseplate until it reaches a thickness of

0.7-0.8 mm, after which the wax is sculpted and modeled.

The ends of the П-shaped handle are heated on a alcohol burner and

inserted into the imitation wax model of the partial crown (fig. 9 and fig. 10).

13

Fig. 9. Wax model of a partial crown (canine)

Fig. 10. Wax model of a partial crown (premolar)

6. MONOLITHIC PINLEY

This type of restoration is only performed on highly damaged, devitalized

teeth with a properly carried out root canal treatment. After the cementation of

the tooth stump, the reconstructed tooth is treated as if it were intact and

prepared for a crown.

The monolithic pinley construction consists of a crown and root part.

The amount of destroyed and missing hard tissue and the assessment of the

integrity of the remaining walls, dictate how the crown part will be prepared.

The general intent is to preserve as much of the hard tissue as possible. If

possible the preparation has to facilitate the so called “ferrule effect” which

protects the crown from fracture. (fig. 11)

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Fig. 11. Preparation of the so called “ferrule effect”.

6.1. ROOT CANAL PREPARATION

The root part of the pin stump is prepared with calibrated mechanical burs.

The root pin reaches up to 3-4 mm into the root canal, taking up 2/3 of its

volume. This way the ratio of root pin to crown length becomes - 2:1, thus

creating the most favorable lever ratio (fig. 12). As for the pin’s diameter, the

advised width in the middle root section is 1.5-2.0 mm smaller then the one is

the cervical area. The diameter of the pin in the cervical zone must not exceed

the width of the tooth wall, on any side (fig 13). This size would prevent the

forming of any unequal force distribution reactions between the post and the

hard tissues, which could lead to fractures. The preparation for the pin has a

slightly ellipsoidal shape (fig.13) which is more preferable then the round

configuration.

Fig. 12. 2:1 ratio of the pin to the crown

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Fig. 13. Different diameter of the pin

6.2. PINLEY PRERATION ON A PHANTOM MODEL

The preparation of the plastic canine begins at the crown part and continues

with the root .

The preparation of a ring type supragingival margin can be seen on figure

14. The margin is 1.5 mm wide and is created with the goal of maximum

preservation of hard tissues.

Fig. 14a. Pin stump reparation

(preservation of hard tissues

through the ferrule effect)

Fig. 14b. Bur types used for the root canal

preparation

In the next step, the root is gradually prepared while following the

specifications listed in part 7.1. (fig. 14b)

The creation of step-like indentations, edges or any alteration of the

passage of the root canal, during the process of preparation are absolutely

unacceptable.

The quality of the preparation can be checked with the use of a plate of

plasticized baseplate wax rolled up like a fuse. The wax is inserted and pressed

16

into the canal forming an impression of it. It is then extracted, analyzed and if it

shows any flaws or mistakes, they are corrected through further preparation.

After the preparation process is complete, enough steel wire is prepared for

the needed depth and adjusted at around 2 sm above the crown part.

The method of adjusting and transforming the wire into a sprue pin is

shown on figure 15.

Fig. 15. Pin stump (preparation of the root part)

The root canal is sealed with plant oil after which the rolled up, plasticized

wax is inserted in. The adjusted pin is heated on a spirit burner and then tightly

and firmly inserted into the canal. The crown is modeled to look like a canine in

smaller scale without an equator or interdental contacts (fig.16). Repeated

addition of wax and reshaping of the crown part is allowed. It is however

unacceptable to make contacts with the neighboring or opposing teeth. With all

of these procedures completed, the modeled tooth stump is ready to be invested

and cast from a metal alloy.

Fig. 16. Pinley; wax modeling; finished crown part

17

The finished construction is cleaned and adjusted. Polishing is allowed only

for the crown part, while the pin is just cleaned (fig. 17).

Fig. 17. Investing and finished pin stump

7. PLASTIC CROWNS

The plastic crown is built onto an adjusted pin stump of a canine. The

crown has to have an even thickness of 1.5 mm to everyone of its walls as well

as a rounded margin.

After the stump is sealed with plant oil, the crown part is modeled from

clear, colorless wax. The next step is restoring the crown’s anatomical and

functional features – occlusal surface, contact points – equator, cervical details.

The finished crown is then removed and inspected (fig. 18). As the

crown is ready for investment, a flask is prepared. The bottom half of the flask is

filled with gypsum paste and the crown is placed in the middle, with its

vestibular surface facing up (fig. 20). The crown is angled so that the incisal

edge is on the same level as the flask while the cervix is in a lower level. The

gypsum surface is smoothened and then sealed. After it hardens the upper half of

the flask is mounted, sealed and filled with gypsum paste. After 20-25 min the

flask is boiled for about 3-5 min which causes the wax to plasticize. The flask is

then opened and the melted wax is washed off with boiling water. Warm

gypsum surfaces are sealed with Ysodent.

18

Fig. 18. Plastic crown (pin stump; wax-up)

Fig. 19. Plastic crown wax-up

Fig. 20. Investment of a plastic crown

The plastic is mixed following the manufacturer’s instructions after which

a period of time has to pass until the initial polymerization. After roughly 15

min the plastic paste is ready to use. The paste is ready when it no longer sticks

to your fingers and stretches into fibers when you attempt to pull it apart.

19

The base dye is applied and covered with wet cellophane after which the

flask is assembled and fastened to a mechanical press. After the flask is opened

the excess plastic is removed. During this process extra plastic will be removed

around the incisal edge and cervical area, which will then be replaced with a

different color plastic. It is then once more covered in wet cellophane, fastened

and placed in cold water where the process of polymerization can continue.

After its completion the crown is carefully extracted gypsum cast, processed,

cleaned and polished.

8. ADAPTA SYSTEM BRIDGE PROSTHESIS

8.1. CASTING A TWO LAYERED GYPSUM MODEL –

STEPS, SPECIFICS

A two layered, two step impression of the prepared teeth (fig. 21) is taken

with a standard impression tray (fig.22). The heavy body is mixed first and then

later corrected with light body silicon.

Fig. 21. Prepared abutments – 23 and 26

Fig. 22. A single jaw silicon impression

20

An Adapta system bridge is constructed using a working cast with

removable dies, which can be effortlessly removed multiple times without

causing damage to the model.

A parallel fixator can be used to ensure that the two dies are parallel

(fig.23). It consists of a base, perforated plate, a frame and guiding spokes. The

model is oriented and fixed onto the horizontal plate (fig. 24) and with the use of

the guiding spoke the corresponding opening on the perforated plate is selected.

The guiding spoke has to find its way to the center of the negative impression of

the tooth stump (fig. 25), that defines the most appropriate opening.

Fig. 23. Parallel fixator Fig. 24. The guiding spoke searches for the

corresponding opening of the perforated plate

A small brass pin with a retentive tail is attached to the spoke and placed in

the center of the stump, staying about 1 mm from the bottom of the impression.

Fig. 25. Guiding- spoke in the center of the die

21

The number of pins corresponds to the number of dies. Two pins will be

required for the purposes of the practical course (fig. 26).

Fig. 26. Stationed pins

After rotating the perforated plate at 1 , a small amount of hard gypsum is

added, reaching the borders of the impression and a bit more is added at around

5-8 mm from the cervical area (fig. 27). The entirety of the occlusal area is

covered in hard gypsum, including the intact teeth. The model is then returned

through a counter rotation of the perforated plate again at 1 . The pins are then

returned to the positions in the impression, indicated by the guiding spokes.

Fig. 27. Rotating the perforated plate at 180

о

22

Special retention nails are placed medially and distally from the pins (fig.

28), following the rule that they must be placed outside of the cutting range.

Fig. 28a. Application of hard gypsum is small portions

Fig. 28b. Returning the perforated plate and placing the retention nails

8.2. WORKING CAST WITH REMOVABLE DIES

After the hard plaster sets, the cast is released from the horizontal base

plate. The plaster around the pins is isolated and a socket for the cast is created

out of ordinary laboratory gypsum.

After the plaster setting process is complete, a flat saw is used to make two

converging notches at around 0.5 – 1.0 mm medially and distally from the

stump’s cervical area. The cuts reach the border where the plasters meet.

23

A modeling knife is used to press on the pin and free it from the model’s

socket. And that concludes the process of making a working cast with

removable dies. This type of model is an important part of the Adapta system.

A milling cutter with a diameter of 2-3 mm is used to further prepare the

vestibular and lingual walls of the dies for the placement of the margin (fig. 29).

A 1.5 – 2.0 mm deep groove is formed underneath the margin.

Fig. 29. Making converging notches with a flat saw

8.3. ADAPTING THERMOPLASTIC FOIL –

REQUIREMENTS

Special thermoplastic materials, which burn without a trace are adapted

over the die to form the cap.

Two types of foil are used:

Carrier foil–it is made of polyethylene or polypropylene, has a diameter

of 35 mm and thickness of 0.6 mm. It serves as a base for the wax up of

the cap, which will be made on top of it.

Spacer foil – it is made of celluloid, has a diameter of 35 mm and a

thickness of 0.1 mm. From a technological stand point a spacer lacquer

can be applied directly on the die (above the cervical area). The spacer

foil’s job is to save space for the cement needed to fix the construction.

With the help of a special holder with metal rings, the two foils are heated

evenly and plasticized over an alcohol burner. The foils are placed in the holder

so that the spacer is on top and the carrier is above the flame. Signs of the proper

conduction of the plasticization process are the foils becoming transparent and

slightly drawn, it is however considered a failure if they are overheated, burned

or warped by the temperature alone.

24

Fig. 30. Forming a die with a spherical milling cutter (a)

Finished die (b)

The plasticized foils are pressed into a moulding filled with moulding

material – a mixture of silicon and phenanthrene rubber. It is pressed until it

sinks above the gingival margin and held in the moulding material for 30

seconds (fig. 31).

Fig. 31. Plasticization of the two foils

The two newly formed caps are separated, cut to size and positioned in the

following way:

The spacer is cut to around 1- 1.5 mm above the gingival margin;

The carrier is cut to around 0.5 – 1 mm above the gingival margin;

The two caps are placed back on the die (fig. 32);

25

Fig. 32. Plasticization of the two foils

Melted cervical wax is used to fill in the circular space between the

carrier foil and the preparation border (fig. 33);

Another test removal of the cap is made to test the quality of the wax’s

application.

Fig. 33. Modeled cervical wax rim

8.4. (CROWN) CAP WAX-UP

The wax-up is performed on the carrier foil with attention towards

expressing the crown’s specific details such as the equator, occlusal surface and

approximal contacts. The wax layer should have a minimal thickness of at least

0.4mm.

26

The bridge construction which will be produced in these practical courses

intends the use of teeth 23 and 26 as abutments. They will be prepared as per the

requirements for a blend and all – metal crown.

Requirements for a blend crown (performed on the canine)2

The palatal and approximal wax is modeled in keeping with the

aforementioned conditions;

The wax on the vestibular wall is removed all the way to the carrier foil;

its thickness is above 0.4 which is the minimal required thickness for

metal alloy casting.

A window is modeled on the vestibular wall, while the wax on the

incisal edge (occlusal surface) is kept to ensure a minimal defensive rim

for the plastic incrustation; the approximal surfaces are reduced to only

point or surface contacts;

The modeled vestibular window is covered in a thin layer of acetone

varnish and sprinkled with plastic pearls which are about 0.4 mm thick

and burn without a trace. The pearls are spaced 1mm apart without

coming into contact with each other (fig. 34).

Fig. 34. Plastic pearls for a full metal crown on a canine

Requirements for the pontic:

Approximaly connects to the wax-up of the retainers;

2When making a full metal crown for 26 a vestibular window is not created

27

The vestibular contours are shaped like a window which comes in slight

contact with the alveolar ridge; the shape or the window depends or the

type and amount of missing teeth;

The lingual wall is made oblique, convex and rounded like the true

hygienic profile;

Pearl retentions or П-shaped wire retentions can be used for the

vestibular window (fig. 35).

Fig. 35. Finished wax-up

8.5. PREPARATION FOR INVESTING, CASTING,

CLEANING AND POLISHING

The placing of the sprue pins is done in accordance with the rules for

diameter, length and positioning of the pins (fig. 36). The alignment of the sprue

pin has to coincide with the longest diameter of the wax element (fig. 37). The

next step is forming the crucible with a diameter larger than that of the widest

part of the wax object.

Fig. 36. Positioning the sprues

28

Fig. 37. The wax prototype with removable dies

The process of casting is carefully executed in accordance with the rules

for choosing a proper mold, investing, removal of the sprues, vaporizing the wax

and the technological steps involved in working with the specific metal alloy

(fig. 38).

Fig. 38. Standard crucible (a); casting mold (b)

The cleaning, sanding and polishing of the bridge construction is performed

under the established rules and methods (fig. 39).

29

Fig. 39. Cast bridge prosthesis (a); cleaned and polished (b)

8.6. ESTHETIC INCRUSTATIONOFACRYLIC PLASTIC

After the casting is finished, the surfaces that are going to be covered in

acrylic plastic are not going to be polished. They are instead going to be

carefully cleaned of any leftover investment material or oxidization. A special

color modifier or opaquer is applied to the cleaned surfaces to prevent the

metallic color from being seen through the slightly transparent plastic layer.

Every other surface not intended for esthetic incrustation is polished. The

vestibular surface of the blend crown and the pontic both receive a special

coating of a color neutralizing varnish, such as Conalor (Spoofa). These

varnishes come in a variety of hues including pink and can successfully

neutralize the metallic color of the underlying alloy. A small brush is used to

apply the varnish. After that it can either be allowed to polymerize in the

presence of warm air or it can be held high above the flame of an alcohol burner

(fig. 40).

Fg. 40. Application of Conalor

Colorless clear wax is used to model the profile and vestibular wall of the

pontic and blend crown (fig. 41).

30

Fig. 41. Wax up for the plastic incrustation

The bridge construction is then invested in plaster and placed within a two-

part casting flask. The bridge is placed in the drag with all of its wax covered

parts facing up and its metallic parts submerged in gypsum. Boiling water is

used to remove the wax after which the plaster surfaces are isolated.

Appropriately colored acrylic plastic is placed on the isolated surfaces and

then the flask is closed and pressed. The polymerization process then passes

through its established temperature and time regime.

Finally the plastic is cleaned and polished, and with that the Adapta system

bridge construction is complete (fig. 42).

Fig. 42. Finished bridge construction

The advantages of this technical process are:

It’s built using a cast with removable dies;

Good adaptation and forming of the foils;

31

Easy to model and control even after removing the dies;

Can easily be removed and placed back without changing the position;

Dies imperfections can easily be corrected;

The parallelism or the guiding brass pins allows the simultaneous

extraction and returning of the dies in the model;

The possibility of switching the thermoplastic forming stage with a wax

dipping technique;

The Adapta system runs the risk of deforming the wax-up when it is

removed from the dies because of its thin wax walls; this is countered by

simultaneous removal after the placement of the sprues, which serve as a

makeshift reinforcement.

The plaster cast with removable dies, the easy waxing and forming and the

ability to repeatedly remove and return the dies without altering their position

are the main advantages of this technological process.

9. WAX DIPPING TECHNIQUE

The steps leading up to the production of the gypsum cast with removable

dies remain the same. The substantial difference is the replacement of

thermoplastic foils with a wax heater tank set at a fixed temperature regime

which keeps the wax in a perpetual liquid state (fig. 43).

Fig. 43. Heater tank with melted wax.

32

After it is isolated the dies is dipped in melted wax for about 1-2 seconds

while carefully making sure the wax reaches about 1-2mm above the preparation

border (fig. 44). The dipping process is followed by two very specific motions,

done for about 1 second – dipping then tilting the dies towards the tank’s wall

and extracting after rotating it to ensure that the last drop of wax flows towards

one of the approximal walls.

This process is then followed by waxing. After which it is followed by

investing and casting using the established methods and technological steps.

10. MODEL CASTBRIDGE PROSTHESIS

The main technological principle of this method is that the wax-up is

performed on a model made of investment material. This method allows for the

wax construction to be directly cast without ever having to remove it from the

model. This way the risks accompanying the removal and investment of the

construction can be avoided.

The protocol for a model cast bridge consists of the following technological

steps:

10.1. MAKING A CAST OUT OF DENTAL STONE

A cast is made out of dental stone. A small knife is used to trim the

gingival margin without affecting the preparation area. That way a ring margin

can be formed without vertical trimming (fig. 44).

Fig. 44. Horizontal trimming without affecting the preparation border

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10.2. PREEMPTIVE MODELING (PREPAIRING THE MODEL

FOR DUPLICATION)

Preemptive modeling is used to create distance between the dies walls and

the cap, as well as the pontic and gingiva.

A specific wax that is harder to melt is added to several locations:

On the dies and it’s shaped like a smaller version of the crown which

stays at around 0.5mm away from the opposing teeth and the

neighboring teeth’s approximal contact points;

The thickness of the wax layer determines the thickness of the layer of

cement after fixation;

Wax is not added above 1-1.5mm from the cervical area, above the

preparation border (fig. 45);

On the crest of the alveolar ridge at the edentulous area to insure the

minimal amount of space between the pontic and gingiva;

In any retentive areas of the model ensuring an easier cast duplication

(fig. 46)

Fig. 45. Preemptive modeling

Fig. 46. Preemptive modeling

34

10.3. MASTER CAST DUPLICATION

A reversible thermoplastic hydrocolloid is used for the job. The impression

material goes from a sol into a gel state which enables it to be poured into a

special flask (fig. 47). The model is positioned inside the drag while carefully

leaving enough space for the cope. The drag has a special ring-like slot for the

П-shaped cope and its openings.

Fig. 47. Model positioned for duplication

The heated gel state impression material is poured through the flask’s

openings (fig. 48). After is cools down the drag is released which leaves us with

the П-shaped cope, duplicated material and the gypsum model (fig. 49). With

the help of a small modeling knife the cast is released leaving an unharmed

negative impression of the cast in the duplicated impression material.

Investment material is prepared and poured into the impression. The end result

after its casting is a perfectly duplicated model, made of investment material.

Fig. 48. Pouring the duplicated impression material

35

Fig. 49. Duplicating the master cast

While the classic method requires reversible hydrocolloid and specific

technological steps there is another method which requires silicon.

Unlike the impression silicone, adaptive silicone is not thixotropic, and

allows it to better recreate finer details. After polymerization the duplicated

silicone displays a hardness of 10 – 35 on the Shore scale while the impression

silicone measures up to around 65 – 85. These silicones have very high elasticity

– 99.92% - 99.98%, which insures there are no permanent plastic deformations

and allows for repeated casting.

Investment material is very fragile and brittle which in turn means that the

duplicated model is as well. It is precisely because of this that the model is

hardened through dipping it in a heated wax – colophony mix. The result is a

protective layer of colophony which gives the model a specific light brown color

(fig. 50).

Fig. 50. Hardened model: a) before hardening; b) after

36

10.4. WAXING THE BRIDGE CONSTRUCTION

The wax-up of the hardened duplicated model includes:

Retainers – are modeled like ordinary all metal or blend crowns with a

wax dripping technique or through plasticizing a wax plate with a

thickness of 0.5 – 0.8 mm; the thickness depends of the type, positioning

and individual features of the retainers; in practice the two methods are

often combined; the wax plate is folded around the dies and pressed after

which the crown details are modeled through dripping; the occluso-

articulational contacts for the opposing teeth and the interdental contacts

for the neighboring teeth are carefully recreated without adding to the

area around the preparation border; an integral part of the waxing

process is the accurate recreation of the tooth’s equator, positioning, size

and details related to the group it belongs to;

Pontic – its profile and general shape depend on its position and the type

of construction it’s going to be; it’s modeled directly on the crest of the

alveolar ridge because the space between the pontic, gingiva and the dies

walls is guarantied trough the preemptive modeling and the preparation

phase for the model duplication; the wax-up has to adhere to the

established requirements for contacts, profile, occlusal relations, specific

details, and the vestibular fenestration for the esthetic incrustation (fig. 51)

Fig. 51. Finished wax-up

10.5. SPRUE PLACEMENT AND INVESTMENT

Plastic and wax sprues are used for model casting. They burn without a

trace and are oriented towards a standard crucible. The choice of casting mould,

the number and placement of the sprues depends on the size of the construction,

the number of retainers and the profile of the pontic. The technological process

37

allows for the use of plastic crucibles and a double casting mould with a

removable bottom. When casting a whole model and not just the wax-up a

specific mould of appropriate size and diameter is required.

The duplicated model is cast from the same substance as the investment material.

The mould is filled with investment material and is then left to set. Afterwards the

mould is gradually heated to a temperature and regime specific to the type of metal

alloy which is going to be used. Through this process the sprues and wax melt and

vaporize leaving space for the casting channels and the casting form in the shape of the

negative impression of the finished wax-up. The manufacturers of the investment

material give out specific instructions for the duration, temperature, specifics and

heating intervals of the mould.

10.6. CASTING, CLEANING AND POLISHING

Model casting is always done using high frequency casting machines.

These machines are actually mechanical centrifuges that work through high

frequency centrifugal casting. The mould is fixed horizontally on one end of the

machine while a counterweight is fixed on the opposite end (fig. 52). The alloy

is melted is a special flame-resistant melting pot through a high frequency

induction current, outside of the crucible. Since these machines do not use an

open flame, the oxidization is brought down to a minimum and because of this

there is no need to use a flux. After the alloy has melted the centrifuge activates

and automatically starts spinning. Through the centrifugal force the melted alloy

flows from the crucible through the casting channels and almost instantly fills

the casting form.

Fig. 52. High frequency casting machines (castomat)

38

If noble alloys are used the mould is left to cool at room temperature after

the casting.

When casting chrome cobalt molybdenum alloys it’s important to keep an

eye on the color of the cast as it goes from red to gray black. Immediately after,

the mould is submerged in cold water and then the cast is freed from the

investment material.

The final cleaning of the construction involves sandblasting, cutting and

removal of the sprues, pickling as well as electro-chemical treating. The final

polishing is done according to the established rules for metal surface polishing.

The incrustation of acrylic plastic follows the same principles and

technological steps as in the Adapta system protocol (9.6.).

11. BRIDGE PROSTHESIS WITH SELECTIVEOPEN RETAINERS

11.1. DISTINCTIVE FEATURES

SO- retainers connect with the pontic and cover the lingual, occlusal and

approximal walls of the abutments. They do not require preparation of the

abutments because they are fixed on to the enamel through the use of composite

resins. Instead of covering the whole occlusal surface SO – retainers are open in

the opposing contact spots. These areas are uniquely individual and so are

chosen specifically for every person. These conditions apply to the lingual

surface as well, where spots for potential opening are marked, opened and

formed according to the occlusal proportions. Approximal separation is not

required for SO-retainers.

11.2. TECHNOLOGICAL PROTOCOL FOR SO-RETAINERS3

The following steps are used in the construction of an SO-retainer for a

first premolar with a second premolar pontic:

A model is cast from hard gypsum;

The intact lingual, occlusal and distal surfaces are isolated (alginate

solution, plant oil, water glass);

A thermos-plasticized plate of wax with a thickness of about 0.6-0.8 mm

is folded and press around the aforementioned surfaces;

3These steps are tailored to a first molar SO- retainer which will be used for a construction

during the courses in the third semester; a jacket crown will be prepared for the first molar

abutment.

39

The wax plate is cut, leaving only the occlusal and lingual walls fully

covered, while having the approximal walls covered differently;

When observing from vestibular side, the border of the distal approximal

wax-up should not be visible because it should flow into the pontic while

the medial, approximal border should reach as close as possible to the

contact point with the canine;

Removal of the wax around the gingival margin, so as to ensure the SO-

retainer’s border stays about 1.5mm above the gingiva ;

The occlusal wax is plasticized and the occludator is closed, this way the

antagonists are pressed and sink into the heated wax;

The wax is thinned in the contacts spots and in some cases even

punctured, this marks the areas for the selective occlusal openings;

The openings are formed until they are smooth and flow freely into the

occlusal plaster surface without any margings;

The result is an even wax layer which follows the occlusal contours and

topography; it comes into full contact with the antagonists without

affecting the articulation or traumatizing the gingival tissues.

11.3. MODELING THE PONTIC

A true hygienic profile will be modeled for the pontic. It will almost reach

the alveolar ridge without coming into full contact with it or pressing on and

damaging the gingiva. This profile ensures good phonetic and sound articulation

while keeping its surfaces open to the effects of the saliva, tongue and

toothbrush. Its esthetic qualities however are quite unsatisfying.

12. WAXING A COPING FOR A METAL CERAMIC CROWN

The crown will be constructed on a lower first molar which has been

prepared onto a working cast with removable dies. The coping’s modeling will

follow the “dipping technique” technological steps shown in the Adapta system

bridge protocol.

The dies is covered in isolating varnish up to the cervical line and is then

left to dry. After which it is dipped in the tank of heated wax until the wax

reaches the same line.

After 1- 1.5 seconds, the dies is extracted and the excess wax is removed

with a modeling knife at about 1.5mm above the preparation border. The area

40

below is filled with cervical wax and a reinforcing collar is modeled over it for

added durability.

The following procedures are used to model and shape the reinforcing

collar:

It’s made only on the lingual and less visible part of the approximal

walls; the vestibular side and the bigger parts of the distal and medial

side are left only with cervical wax;

It’s about 1-1.5mm high and 0.8 mm thick;

After the metal coping has been cast a margin is shaped which gives the

crown additional mechanical durability;

Technological safety for the dental technician is assured when casting

with a reinforcing collar; with the help of tongs the collar can serve as a

handle while the technician applies the ceramic material;

The collar can be of great help in the removing of a crown by serving as

a stable margin on which to balance the calibrated mechanical

instrument (fig. 53).

The wax coping is modeled with smooth, rounded outer contours while

being careful not to make any sharp edges or angles which might lead to

a build-up of internal pressure and subsequent cracks or fractures of the

ceramic.

Fig. 53. Reinforcing collar: a) schematic; b) finished bridge

13. RESIN-BONDED FIXED PARTIAL DENTURES

One of the major disadvantages of the conventional fixed partial denture is

the removing of “healthy” enamel and dentin needed for the abutment

preparation. Various solutions of this problem have been proposed through the

years. The development of acid etching of enamel for improving retention of

41

resin have been described by Buonocore (1955). Ibsen first described the

attachment of an acrylic resin pontic to an unprepared tooth using a composite

bonding resin. To facilitate bond strength various authors proposed different

solutions, like extended “wings” over the abutment teeth, electrochemical pit

corroding technique, use of silane coupling agents etc.

13.1. CLASSIFICATION (by Shillingburg, H. et al.)

The following classification reveals only the differences in metal

framework treatment technique. These types of fixed partial dentures have

continued to develop throughout the years.

Rochett bridge

Marylend bridge

Cast mesh FPD

Virginia bridge

Selectively opened partial retainer (by prof. Popov, N.)

ADVANTAGES

1. Low cost

2. No anesthesia

3. Supragingival margins

4. Minimal or no preparation needed

5. Possible rebonding

6. Time saving

DISADVANTAGES

1. Irreversible

2. Uncertain longevity

3. No space correction

4. No alignment corrections

5. Impossible temporization

INDICATIONS

1. Caries-free abutment teeth

2. Incisor replacements

3. Single posterior tooth replacements

4. Splints

CONTRAINDICATIONS

1. Extensive caries

42

2. Nickel sensitivity

3. Deep overbite

13.2. TOOTH PREPARATION

The early use of acid-etched resin-bonded FPD was recommended to be

done without any tooth preparation. This is actually the major advantage of this

method! Although many authors advocate this, still others prefer to do some

small preparations to improve the stability and longevity of these constructions.

Fig.54. Case 1 A missing upper left central incisor

Fig. 55. Palatal view

The framework is outlined on the die with a pencil. There are several marks

that show very clearly the contact points with the antagonists. Pay attention that

this FPD withstands approximately 1 mm away from the gingival margin!

43

Fig. 56. The wax pattern

The holes in the wax pattern are quite visible. These are the spots of the

preliminary contacts with the antagonists that should be avoided (Selectively

opened partial retainer, by prof. Popov).

Fig. 57. Vestibular view

The mechanical retention can be seen. It is needed for the future aesthetic

coverage (in this case made from acrylic resin). The vestibular surfaces of the

frontal teeth are absolutely intact. This fact guarantees the aesthetic look of the

bridge.

Fig. 58. a) The bridge ready for

investing and casting; b) The bridge already casted from

metal

44

Fig. 59. a) The same FPD-vestibular

view;

b) The bridge finished and polished-

palatal view

Fig. 60. Case 2 Periodontal splint (Rochette)

The framework is outlined on the die with a pencil. The perforated retainer

became the standard design for years to come.

Fig. 61. The wax pattern

The splint withstands 1mm away from the gingival margin and from the

incisal edges.

45

Fig. 62. The splint ready for investing and casting

Fig. 63. The splint already casted from metal; The splint finished and polished

Fig. 64. The FPD from Case1 and Case 2 – vestibular view

As it can be seen from this figure the vestibular surfaces of the abutment

teeth are intact. This emphasizes the natural look of the restorations. All metal

parts of the bridges are covered and they are not visible from this point of view.

46

Fig. 65. Case3 A missing first molar

This case will be restored with a help of a Maryland bridge.

Fig. 66. The framework is outlined on the die with a pencil

Fig. 67. Here a minor tooth preparation is needed

These are the areas around the tooth equator. If there are any old

restorations, they can be removed as well and their cavities can be used for

additional retention.

47

Fig. 68. The wax pattern

Fig. 69. The bridge ready for investing

Fig. 70. The bridge already casted from metal

48

Fig. 71. The bridge finished and polished

Fig. 72. A vestibular view of the Maryland bridge.

13.3. 14.3. CONCLUSION

Although their indisputable advantages, the problem with the reliability of

the bond strength still exists. That’s why it is recommendable the Resin-bonded

FPD to be used as long-term provisional restorations or for intermediate

replacement of a missing teeth.

49

Part II

Technological protocol for model cast dentures (elements, characteristics, thorough protocol)

A detailed overview and analysis of the protocol, elements,

classifications and terminology necessary for the planning of model cast

dentures.

1. CLASSIFICATION OF PARTIAL EDENTULISM

There are many classifications, however the most rational and relatively

accurate is the one proposed by Edward Kennedy in 1925. The classification is

based on principles of topographic anatomy and contains four main classes.

Kennedy class I – describes bilateral partially edentulous (fig.73)

Fig. 73. Kennedy class I

Kennedy class II – unilateral partially edentulous areas with missing

premolars and molars (fig. 74) (unilateral free-end saddles, one sided posterior

edentulous area)

50

Fig. 74. Kennedy class II

Kennedy class III –a unilateral edentulous area with natural teeth anterior

and posterior to it (fig. 75)

Fig. 75. Kennedy class III

Kennedy class IV – a partially edentulous area which encompasses the

frontal teeth (fig. 76).

Fig. 76. Kennedy class IV

51

2. ELEMENTS OF A MODEL CAST DENTURE

A model cast denture consists of the following elements:

Metal framework;

Denture saddles;

Mastication complex;

Stabilization and retention components

3. METAL FRAMEWORK

Every component of the metal framework, depending on its function is

give a name or term in special literature, which is specific and clearly answers to

the principles of classification and terminology.

The terminology and the sequence of technological steps used in the

making of model cast dentures coincides with the Glossary of Prosthodontic

Terms, which is updated every two years and published in the Journal of

Prosthetic Dentistry.

METAL FRAMEWORK COMPONENTS

3.1. CONNECTIVE ELEMENTS

Model cast dentures have a major (large) and minor (small) connector4.

In Cyrillic these connectors are listed as biugels (Russian specialized literature).

In this practical guide every component of the metal framework is listed with a

specific term established in the specialized terminology.

Purpose of the connective elements:

To serve as a connective link in the metal framework;

To replace part of the denture base;

They offer reasonable reduction and better tolerance;

They do not disrupt the phonetic, tactile or taste perception;

To transfer and redistribute the masticatory forces.

Distinctive features of connectors:

they don’t have their own counteractive effect which is why they are

used in combination with clasps and stabilization components;

they’re waxed up and cast along with the rest of the metal framework;

they have to be rigid and non – flexible;

4 connector – connection, connecting part

52

they mustn’t press on or exact any pathological reaction with the

gingiva;

they have to be placed at about 5 – 6 mm from the free gingival groove;

the peripheral margins have to be smooth, comfortable and seamlessly

flow into the gingiva, without any protruding edges;

if any additional bulk is required, the underlying tissues and topography

have to be taken into account;

they have to be smooth, even and polished so that they do not retain any

food debris.

3.2. MAXILLARY MAJOR CONNECTOR

Every design of the maxillary connector requires special modeling around

its border for the so called undercut line (notch, margin). They’re also referred

to as finish lines and are made through trimming (in the lines, borders) with a

round bur. The trimming stops at around 6- mm superior to the abutment teeth’s

gingiva and has a width and depth of 0.5 – 1 mm. These lines prevent the

buildup of food debris underneath the maxillary major connector (biugel).

Types of maxillary major connectors:

single palatal strap (fig. 77);

Fig. 77. Maxillary major connector – single palatal strap

53

transversal plate (palatal plate type) (fig. 78);

Fig. 78. Maxillary major connector – transversal plate

circular form (circular strap) (fig. 79);

Fig. 79. Maxillary major connector – circular strap

U-shaped palatal connector (horseshoe) (fig. 80);

Fig. 80. Maxillary major connector – U – shaped palatal connector (horseshoe)

54

complete palatal connector (fig. 81);

Fig. 81. Maxillary major connector – complete palatal connector

phonetic neutral zone connector (PNZ by G. Georgiev) (fig. 82)

Fig. 82. Maxillary major connector – phonetic neutral zone connector

3.3. MANDIBULAR MAJOR CONNECTOR

Mandibular major connectors are long, relatively narrow and rigid without

being too bulky so that they can be comfortable for the patient. It’s imperative

that they do not obstruct the frenulum or reach the bottom of the oral cavity.

They also do not require undercut finish lines like the maxillary major

connectors. Their cross-section has a “half pear shape” (fig. 3).

55

Fig. 83. Mandibular major connector – “half pear” shape (profile)

The connector stays in front of and under the tongue. During mastication it

follows the vertical “sinking” motions of the saddle which correlate with the

susceptibility of the mucosa. If the mandibular major connector lies directly on

top of the mucosa it will press on it and eventually traumatize it. This can be

prevented through preemptive waxing in this area before the model is

duplicated. Depending on the susceptibility of the mucosa a distance of around

0.8 – 1.2mm is ensured between it and the mandibular major connector.

Types of mandibular major connectors:

Lingual bar (so called biugel) (fig. 84);

Fig. 84. Mandibular major connector – lingual bar (biugel)

56

Lingual plate (fig. 85)

Fig. 85. Mandibular major connector – lingual plate

Lingual bar with a continuous bar indirect retainer (fig. 86)

Fig. 86. Mandibular major connector –

lingual bar with a continuous bar indirect retainer

Labial bar (fig. 87)

Fig. 87. Mandibular major connector – labial bar

57

3.4. SECONDARY, MINOR CONNECTORS connect all the

components of the cast denture to the major connectors. Their characteristics,

positioning and features have very specific borders, requirements and

geometrical principles and therefore will not be discussed in an introductory

level course.

3.5. SUPPORTING ELEMENTS – BAR TYPE PRECISION

ATTACHMENT

These specific components primarily serve a supporting function with a

minor blockage effect and no notable retention. Their purpose is to transfer and

redistribute the masticatory forces away from the saddles (fig. 88). They serve as

stabilizers against the deformation of longer lingual bars, like for example in

unilateral posterior free-end saddles by Kenedi class II (fig. 89).

Fig. 88. Bars attachments transferring pressure away from the synthetic teeth

(by Filchev, Ralev)

Fig. 89. Bars attachments counteracting the deformation of lingual bars

(by Filchev, Ralev)

58

3.6. SUPPORT ELEMENTS – (KIPMEIDERS; LINGUAL/PALATAL

BARS; SUPPORT BARS)

They are also called counter rotators and work similarly to the bars

attachments – mainly a support function with a relative blockage effect. They

offer resistance against rotating forces which tend to separate the saddle from

the prosthetic field (fig. 90). Support bars are modeled like an extension to the

metal plate which medially reaches the frontal teeth or ends as an occlusal rest

on the lingual surface of the frontal teeth. If these cases are inapplicable then a

viable substitute counter to the rotational forces comes in the form of frontal

extensions to the palatal side arches.

Fig. 90. Support bars offering resistance against rotational forces

(by Filchev, Ralev)

3.7. STABILIZING AND RETENTION COMPONENTS

The stability of the denture on the prosthetic field during a period of rest is

called retention.

The immovability of the denture during mastication with a minimal chance

of displacement is called stability.

Removable dentures require a relative freedom of movement in the

direction of insertion and removal. This creates specific requirements for the

stabilizing components and their ability to perform the following functions:

59

Retention – resistance against upward forces from the prosthetic field

toward the masticatory field;

Support (transference of masticatory pressure) – resistance against vertical

forces from the masticatory plane towards the prosthetic field;

Stability (blockage) – resistance against all horizontal forces – forward,

backward and sideways

Stabilization and retention components can be classified in two main

groups:

Clasps – consists of a monolithic body with retentive arms; one end of the

clasp enters the denture base or is connected to the metal framework; the other

has special retentive arms which encircle the abutment tooth.

SPECIAL STABILIZING COMPONENTS

They consist of two parts which connect to each other through a male and

female part (patrix and matrix) and are used in combined prosthesis; the

movements of the denture are blocked, reduced or free depending on the

configuration of the male and female part.

4. CLASPS. SPECIFIC REQUIREMENTS5

Clasps fulfill the roles of retention, support and blockage. With model

cast dentures however, the clasps are designed to make firm, direct contact

without displacing from the abutment. This is achieved by the clasp’s retentive

arms which encircle the tooth.

The forth role of cast clasps is called encircling – resistance against the

forces seeking to dislodge the clasp from the abutment.

If the clasp encircles less than 180о of the tooth’s circumference then the

construction can be dislocated. If however the clasp encircles more than 180о

then the dislocation effect is significantly reduced (fig. 91).

5 The specified requirements apply to (pertain to ) cast clasps (only) as components of model

cast dentures

60

Fig. 91. Encircling a) over 180

о; b) under 180

о (circumference of the tooth)

An important factor for the successful encircling is the position of the

tooth in the tooth row.

Depending on the position the options are:

A tooth within the tooth row – 180о encirclement;

For a tooth at the end of the tooth row – up to 270о envelopment;

A singular tooth (which is not positioned within the tooth row) requires

315о envelopment.

Clasps are made through bending and casting. When using the one-piece

casting technique the clasps are planned, modeled and cast along with the metal

framework following the rules for model casting.

In 1916 N. Nesbitt introduces a simple and easy method of casting clasps

from gold alloys. In order to reach the modern technological methods for cast

clasps a lot of suggestions had to be made regarding alloys, investment

materials, wax prototypes and casting machines.

In 1956 in Frankfurt a Main collective of dentist, dental technicians,

constructors and metallurgists critically analyzed the cast clasps used at the time.

61

They note an insufficient durability and constructional weakness of the clasps in

the areas of the body and exit point from the denture base. A new system is

patented which consists of five types of clasps with much wider retentive arms,

a body and elements positioned supra – equatorially and encompassing up to ¾

of the crown. The new clasps have a rigid connection with the framework which

allows for greater loadbearing and stability during mastication. The patent is

submitted by the “Ney Company” – USA, and the system becomes known as

“Ney system clasps”. In the next chapter we’re going to look at the main clasp

designs and the various versions of the most frequently used clasps.

Tooth equator

If we place a graphite rod in contact with one of the tooth surfaces and then

without changing its angle make a full rotation around the tooth, a line will form

which is referred to as a tooth equator.

If the rod is parallel to the long axis of the tooth then the resulting line will

be its anatomical equator.

If the rod is not parallel and instead perpendicular to the masticatory plane

then the resulting line is the clinical equator.

When the rod’s direction correlates with the path of insertion and removal

of the denture (regardless of its relation to the anatomical axis or the masticatory

plane) the line we end up charting is the prosthetic equator.

5. MAIN CLASP TYPES

Currently the main clasp types described in our and foreign specialized

literature revolve around the following designs6:

“G” clasp (double –arm clasp)

Used for premolars, very rarely for molars;

Used for posterior teeth;

For Kenedy Class I and II;

Unsuitable for tilted teeth;

Teeth with a short crown and a shallow undercut zone;

Interdental shortening towards the support arm;

Springy, unstable support arm.

6 Specialized literature shows different versions of model cast clasps and the Ney system (five clasps)

is a part of them

62

Fig. 92. “G” clasp (double arm clasp)

“E” clasp (Aker clasp, Ney system clasp №1)

Used for premolars and molars;

For class III and rarely for class IV;

Easy planning;

Used on teeth bounding the defect, which is why they have to be close to

the denture base, to the framework;

Different from the ring which leaves the distal area of the abutment free

(see ring clasp);

Not esthetic.

Fig. 93. “E” clasp (Aker clasp, Ney system clasp №1)

Single arm, Back-Action clasp

For lower molars and premolars;

Class I, II, IV;

Clasp with a reverse action;

Rigid support, positioned right next to the base, without using the

interdental space;

63

Is not used one-sidedly;

Very long, with a larger and wider arm;

Elasticity, springing effect;

Differs from the № 4clasp (see Ney system).

Fig. 94. Single arm (back – action) clasp

Ring claps – 7/8 clasp

Upper and lower singular molars, 315о encirclement;

For inclined, rotated teeth and retentive ridges;

Long clasp arm, elasticity, danger of deformation during insertion and

removal;

Encircles 7/8 of the tooth;

Is not used one-sidedly;

The end of the clasp can traumatize the cheek.

Fig. 95. Ring clasp (7/8; molar clasp; single arm clasp)

Bonvil clasp (double “E” clasp)

Used in an intact row;

Used on pathologically mobile teeth (splinting);

64

A four arm clasp – four retentions, double support;

The body is positioned in the interdental space;

Disrupts the occlusion;

Requires precise preparation of the support bar;

Unhygienic, traumatizes the mucosa and the cheek;

Difficult insertion and removal.

Fig. 96. Bonvil clasp (double “E” clasp)

Modified Bonvil clasp

Combines the E clasp with a ring clasp;

Good positioning with remaining posterior teeth;

Used with inclined or retentive aporoximal walls;

Not esthetic;

Splinting effect;

Four part clasp;

Easier to insert and remove than the Bonvil clasp.

Fig. 97. Modified Bonvil clasp

65

NEY SYSTEM CLASPS

Clasp № 1

Universal; fulfills all requirements;

It can be used on every tooth providing it has a suitable equator;

It has a short and stable body closely connected with the stabilizing and

supporting parts of the clasp arm;

The retentive part of the arm reaches the approximal surface on the far

opposite side of the defect;

The stabilizing and retentive parts encircle the tooth on both sides,

blocking almost all horizontal movements of the denture;

The supporting part lays above the equator and encompasses up to ¾ of

the wall near the defect, which is a result of the position of the equator;

It has reduced application on inclined teeth;

Esthetically unsatisfactory – the clasp is visible while smiling and talking;

The clasp has singular support and dual stabilization and retention (fig. 98)

Fig. 98. Ney system clasp № 1

a – support; b – stabilizer; c – retention (by Filchev, Ralev)

Clasp № 2

Its equator positioning is the exact opposite of clasp № 1, in other words

the undercut areas are close to the saddle and the supra equatorial areas

are further away;

66

It’s used on small and narrow teeth;

The clasp looks like it’s dived into three parts – support part, two T-

shaped clasp arms and an extended connector to the other parts;

The elongation has higher elasticity and spring effect;

There are three versions of the № 2 clasp, depending on the positioning

of the equator (fig. 99).

Fig. 99. Ney system clasp № 2 (by Filchev, Ralev)

Clasp № 3

Combined;

For different vestibule – lingual positioning of the equator;

The first arm resembles clasp № 1 and the second one resembles clasp № 2;

The opposing stabilizing and retention arms cross each other;

The rigid occlusal rest ensures a reliable support while the clap’s arms

ensure good retention and stabilization;

Not esthetic;

singular support and double crisscrossing retention and stabilization (fig. 100)

67

Fig. 100. Ney system clasp № 3 (by Filchev, Ralev)

Clasp № 4

Single arm;

In consideration with the transversal compensation curve the posterior

teeth are inclined – vestibular for the upper and lingual for the lower;

because of this the equator is projected high up on one side, occlusally

with the possibility of a retentive arm;

and on the other side the equator is positioned low, cervically with a

wide undercut zone, suitable for a stabilizing arm;

The stabilizing part is positioned high above the equator with an occlusal

rest aproximally (without disrupting the occlusion) and continues into a

long retentive arm on the other side;

The clasp has a singular support, stabilizer and retention (fig. 101)

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Fig. 101. Ney system clasp № 4 (by Filchev, Ralev)

Clasp № 5

Circular, ring – shaped, molar clasp;

5/6 clasp with a massive body, positioned approximally, connected with

an occlusal rest, transitioning into an elongated stabilizing arm above the

equator. It reaches the other approximal wall after which it transitions

into a second occlusal rest and a long retentive arm;

This way the circle almost fully closes, reaching about 5/6;

The stabilizing arm is enhanced further with the use of a bar, positioned

gingivaly, connecting the second occlusal rest with the frame saddle;

Double support, singular stabilization and retention, that is why this

clasp is never used on its own but is instead always combined with

another mutually complimenting clasp.

Fig. 102. Ney system clasp № 5 (by Filchev, Ralev)

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6. PLANNING AND CONSTRUCTION OF A MODEL CAST

DENTURE

With model cast dentures most of the masticatory force is absorbed by the

abutment teeth. In order to avoid the consequences of the increased load bearing,

it’s important to:

To ensure that there are enough abutment teeth, on which to place

the support and retention components;

Ensuring a minimal possibility of vertical rotation of the posterior

unbound saddle

Blocking or reducing the pathological horizontal displacement of the

denture.

The denture saddle is what we call the part of the partial denture base

which encompasses and lies on top of the edentulous alveolar ridge.

The support line is the line imaginary which connects the support arms of

the model cast clasps.

The part of the prosthetic field bounded by several support lines is called

the supporting field.

The stability of the denture and the supporting field are in directly

proportional – the bigger the field the more stable the denture.

6.1. STABILIZATION WITH A UNILATERAL UNBOUND DEFECT

The goal is to at lease ensure a triangle supporting field with a maximum

size (fig.31). Support line AB crosses the prosthetic field diagonally and serves

as an axis of rotation, which requires the placement of supportive –retentive

elements in the area of point B.

The perpendicular line from the end of the prosthetic saddle (unilateral

unbound defect) to the support line AB is the pathological, rotating axis

around which the denture rotates.

The perpendicular line from point B to the support line AB serves as the

counter rotational axis of resistance BE.

The stability of the denture is in proportional to the length of the counter

rotational axis of resistance. It’s imperative the axis of resistance is at least as

long or longer than the pathological axis.

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Fig. 103. Triangular support field in a unilateral unbound defect

(by Filchev, Ralev)

6.2. STABILIZATION IN A BILATERAL UNBOUND DEFECT

With this type of defect there is isn’t any possibility for a triangular

support field. A transversal support line which connects the symmetrical

homonymous teeth on both sides of the tooth arch is projected across the

prosthetic field (fig. 104).

Fig. 104. Transversal support line in an unbound bilateral defect

(by Filchev, Ralev)

The linear cross sectional placement of supportive – retentive elements,

known as the principle of single line relation, is most effective when the

support line (transversal) is perpendicular to the sagittal plane.

Even better for the abutment teeth is the principle of double line relation,

which dictates the creation of a second support line (fig. 105), on two anterior

symmetrical teeth which is, if possible parallel to the first support line. Thus a

rectangular support field is created and despite its smaller size it still exceeds the

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effect of the singular support line. The supporting elements of the frontal

support line act as precision attachments against the vertical rotations of the

denture saddles, with a tendency to remove them from of the prosthesis field.

Fig. 105. Principle of double line relation

7. LABORATORY PROTOCOL FOR MODEL CAST DENTURES

The framework is modeled on a gypsum cast. An initial analysis is then

conducted without too much detail regarding the type of clasps that are going to

be used, the abutment teeth or the placement of the clasp arms. For the purpose

of effortless placement and removal of the denture the equators, the sub- and

supra equatorial as well as the undercut zones are analyzed.

7.1 DENTAL SURVEYOR

An instrument known as a dental surveyor is used for the analysis,

planning and construction of the model cast denture. It consists of a platform, a

vertical column with a cross arm, which ends with a vertical spindle. The

spindle ends in a chuck, to which various surveying instruments can be attached,

like for instance the spring loaded attachment used for measuring (fig. 106).

Under the vertical attachment there is a mobile cast holder attached to a ball

joint on top of the platform. The cast holder can be shifted to any angle or

simply locked in a horizontal position.

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Fig. 106. Dental surveyor – general design

The gypsum cast is fixed onto the cast holder and with the use of the

graphite rod in the vertical attachment, the equator of the teeth can be measured.

When the cast holder is in the horizontal position and the graphite is

perpendicular to the masticatory plane then the measurement shows the clinical

equator. If the undercuts or supra equatorial zones are not satisfactory or

unsuitable for clasp placement then the cast holder can be repositioned (fig. 107)

through the ball joint.

The goal is to find an equator with undercuts suitable for a clasp’s retentive

arm or supra equatorial zones suitable for the blockage or support parts of the

clasp.

The change in angle allows us to find a more viable undercut or supra

equatorial zone but it also changes the path of insertion and removal (a

prosthetic equator is measured) (fig. 107).

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Fig. 107. Different angulation of the model through the cast holder

The angle must not exceed 35°, as any higher angulation would make

placement of the denture virtually impossible. An angle over 45° will increase

the pathological forces during mastication and lead to the inevitable overbearing

of the abutment teeth.

7.2. UNDERCUT DEPTH

Steps, rules, determining according to the Ney system

The laboratory analysis begins with determining the undercuts, which is

done with a surveyor, graphite and undercut surveyor attachments.

Created in 1956 the Ney system offers a set of steps and requirements for

determining the undercuts for its 5 clasp types. The method is consistent,

specific, and objective and doesn’t leave any room for intuitive adjustments or

questions.

The undercut gauges are cylindrical metal pins, which end in disks of

varying sizes (fig. 108). The distance from the pin’s wall to the edge of the disk

for the first gauge is .25 mm, for the second it’s .5 mm, for the third – 0.75

mm. The necessary depth for clasps 1, 2, and 3 is 0.50; for clasp № 4 – 0.25 and

for clasp № 5 – 0.75.

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Fig. 108. Disks for undercut measuring (undercut gauges)

Instead of using graphite a disk corresponding to the chosen clasp is

attached to the surveyor. First the shaft of the gauge is placed in contact with the

abutment tooth then the vertical column is repositioned until the disk comes in

contact with the wall of the abutment tooth (fig. 109). If its edge comes within a

minimal distance of 0.5 mm from the gingiva then the space is considered viable

and marked with a pencil (fig. 110). This point is where the tip of the clasp’s

retentive part will reach.

Fig. 109. Defining the undercut and the contour of the clasp

75

Fig. 110. This is where the tip of the clasp’s retentive part will reach

If the established parameters are not met even when the protocol steps and

regulations have been followed, the model’s angulation is adjusted and newly

analyzed, tested and the new parameters are once again checked until a suitable

position is found.

This procedure is done by the technician under the supervision of the

dentist especially when repeated alteration of the cast holder’s potion is

required. A new position is found which accounts for all of the abutments and

thus increases the viability and serves as criteria for assurance and success.

The next step is fixing the surveyor, replacing the gauge with graphite and

measuring the abutment’s equators (fig. 111).

Fig. 111. The equators are marked with graphite

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With the use of a pencil, the clasps are drawn (form, trajectory, position)

onto the teeth. The position, form, details, features of the saddles, connectors

and the plate are all drawn onto the model until we’ve completely formed the

framework (fig. 112).

Fig. 112. The framework is drawn with a pencil

7.3. PREPAREING THE MODEL FOR DUPPLICATION

The following steps are carried out:

The walls of the abutments are modeled with special (high melting point)

wax, with borders under the clasp markings;

The undercuts of all teeth are filled without exception;

The surveyor’s graphite rod is switched for a modeling knife used to

ensure that the wax- up is parallel;

The mucosa is isolated with wax, up to a thickness of 0.1 mm at the

torus, 0.25 mm at the connectors and 1 mm under the saddles.

7.4. MODELING THE CLASPS AND FRAMEWORK

(from profile wax)

The following rules and steps are kept in consideration:

Waxing is not performed through dripping or with melted wax;

The wax prototype is made from a wide selection of pre-prepared

elements with varying shapes, widths and seizes (fig. 113);

Wax profiles are used to assemble the framework onto the duplicated

model.

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Fig. 113. The framework is modeled from profile waxes

7.5. SPRUE PINS AND INVESTMENT

7.6. CASTING, CLEANING, POLISHING AND FINISHING

(steps 7.7 and 7.8 are identical to the steps for model cast bridges)

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Part III

ARTICULATORS (elements, characteristics, classification)

Search for creating more transcendent prosthetic dentures pushes scientific

intellection towards creation of devices that resemble to maximum extent the

movements of the lower jaw.

The first apparatus for apposition of both upper and lower jaw was

proposed by F. Pfaff in 1756 y. The reproduction of occlusal relationships only,

were not satisfactory in manufacturing of new dentures.

Evans is considered to be the inventor of the modern articulator. In 1840 he

proposed a device that reproduces not only the occlusal, but the articulating

relations as well. Edgar Stark and Richmond Heiss (1889) patented the first

articulator with descending condylar paths.

Nowadays there is a great variety of devices that reproduce the movements

of the lower denture and TMJ. They are all based on different theories. The most

popular ones are:

Theory of movement of the lower jaw around an axis

Theory of movement of the lower jaw around a sphere

Theory of movement of the lower jaw around a cylinder

Theory of movement of the lower jaw around a cone

Theory of movement of the lower jaw around a helicoids

Each of these theories has contributed to the development of the

articulators, but still cannot satisfy entirely the upcoming requirements towards

the most precise and complex movements of the lower jaw.

In the English-Bulgarian dictionary the term articulate means –

anatomically: with jaws and technically: hinged. Obviously the term articulator

means a device that looks like a jaw and has a hinged axis. Generally speaking

the articulator is a complex apparatus, which has to reproduce the finest neuro-

muscular movements of the lower jaw. Posselt considers that it is not the jaws,

but the neuro-muscular reflex that leads the TMJ in action. A terminal axis could

be created by manipulating the patient, but this could rather be a starting point

for programming the articulator.

A detailed view of the TMJ, describes it as incongruent (incongruity

between the joint pit and the joint head in ratio 2.5-3 :1 (fig.1).

79

а b

Fig. 1. Congruent (a) and incongruent joint (b)

This anatomic peculiarity, practically allows simultaneous movements in

three perpendicular axes x y z (fig. 2 and 3).

Fig. 2. 3-D view of a skull, with an

accentuation on the TMJ

Fig. 3. TMJ with axes of rotation

This phenomenon of the movement of the TMJ is typical for humans only, from

all mammals and for some primates. It is because of the very well defined groups of

teeth (incisors, canines, premolars and molars).

Classification of the articulators

There is a great variety of articulators’ manufacturers. All of them pretend

that their device is unique. Very often they even don’t define which group their

apparatus belongs to. The only thing they mention is the definition: articulator.

x

y

z

y

z

80

This classification does not pretend to be full and comprehensive. It has a

guiding role and it is an introduction to the great variety of articulators.

The Glossary of prosthodontic terms, presents a classification describing

the abilities of the mechanical devices arranged in four classes.

Class – I. Simple mechanical devices. They register only the static position

between the upper and lower jaw.

Class – II. They allow horizontal and vertical movements, without

reproducing the movements of the lower jaw.

Class – III. Mechanical devices, reproducing the path of condyl guidance

by means of mechanical analogs of TMJ. They can reproduce completely or

partially the possible movements.

Arcon type

Non-arcon type

Class – IV. Mechanical device that can accept any data from 3-D digital

registers, allows individual position of the models according to the TMJ and

complete simulation of the movements of the jaw.

Adjustable

Non-adjustable

They are defined as completely individualized.

ARTICULATORS

Articulators with

mechanical axis

Made of wire

Made of brass

Articu-

lators

with

intermedi

ate values

Articulators with

individual values

Non-arcon

Virtual (Digital

CAD/CAM)

Arcon

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Articulators with mechanical axis only, fixing occluso-articulation

interrelations between the upper and lower jaw, allowing vertical movements

(fig. 4).

а b

Fig. 4. Wired (a) and brass (b) articulator with mechanical axis only.

The peculiarities of the movements of the lower jaw are corrected in the

patient’s mouth with the help of articulating paper by trimming the hindering

spots. The dentures made with the help of occludator have reduced functional

effectiveness, that’s way it is recommendable in such cases occludators not to be

used.

The most frequently observed problems, when using these devices are the

preliminary contacts that may cause traumatic occlusion.

The articulators with “mean values” are probably the most commonly used.

It is because of the comparatively easy work and assembly of the models. The

necessary values are preliminary pledged in the apparatus. The dentures made

with them are compliant with the mean values of the articulator.

As a prototype of these devices, Gisy’s articulator “New-simplex” has been

pointed out. It is based on the theory of movement of the lower jaw around

cylinders. It has been presented in 1910 y., with mean values, non-arcon type,

angle of condyle guidance 330, based upon Bonvill

’s triangle and incisal path

inclination 600. Fig. 5 modified Gisy

’s articulator.

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Fig. 5. Gisy

’s articulator 1912

Fig. 6. Aticulator with mean values

83

Fig. 7. Articulator „KaVo PROTARevo“ with individual values

Fig. 8. Virtual articulator – adjustments

The virtual articulators are most commonly used in the CAD /CAM

technology, to simulate the movements of the lower jaw, during manufacturing

the prosthetic constructions. In these articulators, the necessary values can be

preliminary pledged in certain limits, or to be totally individually

preprogrammed. They are considered to be the most precise and accurate,

simulating completely the movements of the lower jaw. They are absolutely

individual.

The unifying element of all kinds of articulators is Bonvill’s triangle, based

on the theory of movement of the lower jaw around an axis. The plaster models

84

are assembled according to this triangle. This geometric figure is formed by

connecting the lower incisal point and the highest points of the two heads of the

condylar processes. The bisectrix of this triangle is exactly 8.5 cm. Its basis is

considered to be the anatomic axis of rotation of the two heads of the condylar

processes.

Fig. 9. Bonvill

’s triangle

The real mechanical axis is situated 2.5 cm behind and under the anatomic

axis of rotation. The point of the chin describes an arch, when the lower jaw

opens. At the same time the highest point of the condylar head also moves along

an arch over the articular tubercle. When drawing perpendiculars towards the

two arches, their intersecting point marks the mechanical axis of rotation. That’s

why the mechanical axis of the articulator should be 11 cm away from the lower

incisal point.

Fig. 10. Scheme of Bonvill

’s triangle situated in an articulator.

Triangle ABC and bisectrix AD=11cm

8,5см

А

В

С

D

85

MECHANISM OF THE ARTICULATOR

The detailed mechanism and instructions for exploitation should be read in

details according to the manufacturer and the model. There are certain

differences, when working with articulators of one and the same manufacturer,

but from different models.

Fig. 11. General view of an articulator

Basically the articulators consist of:

1. A lower shoulder which resembles the lower jaw and the mandible

model is fixed.

2. An upper shoulder, where the maxilla model is fixed and the mechanical

axis of rotation is situated.

3. A mechanical joint.

4. A mechanism for individual adjustment.

5. Molds for including the upper and lower model.

6. An incisal plate (table).

7. An incisal pin.

8. A pin for supporting the upper shoulder during practical work.

These are the basic elements of every articulator, without the details of the

certain model. The variety of articulators is enormous and it is impossible to be

described with details, as well as the way of use of every one of them.

In the course of practical work with articulators, specific terms acquired

popularity and international recognition are been used.

86

TERMINOLOGY

Arcon articulators, here the mechanical joint is very much alike the TMJ. It

consists of spherical part that resembles the condylar head (always made of

metal) and a plate resembling the glenoid fossa (fig. 11). They can be made of

metal or highly rigid plastic material. In case this plate is been made of plastic, it

can be easily replaced (when worn-out), but when it is been made of metal, this

replacement is very difficult. Sometimes the whole articulator has to be replaced

with a new one. It is believed that the dentures made with the help of these

articulators are very precise as well as the occluso-articulating relationships

between the upper and the lower jaw, the sagittal and trasversal movements are

concerned.

a – Anatomic

TMJ

b – Scheme of an

arcon joint

c – View of a

metal arcon joint

d – View of a

plastic arcon joint

Fig. 11. View of different joints

Non-arcon articulators. The variety in this group of articulators is

enormous. There are two basic options.

1. Type one. The mechanic joint looks like the one of the arcon

articulator, but its metal plate is different. There is no anatomic

curvature of the articular tubercle. That means that the plate is

absolutely flat fig. 12.

A – Type one B – Type two

Fig. 12. Non-arcon joint

87

2. Type two non-arcon joint is characterized with a rather complex

mechanism, consisting of two metal discs, placed one into another. The

inner disc is been drilled and inside this hole a cylindrical body is placed,

with the help of which the movements are made fig. 12. As a variation of

the non-arcon articulators is a joint with the shape of a horseshoe that is

opened in the distal direction. The sliding movements can be done with

the help of a cylindrical or spherical body fig. 13.

Fig. 13. Non-arcon articulator

On fig. 14 the differences between the arcon and non-arcon articulators can

be seen.

Fig. 14. Arcon and non-arcon articulator

88

Angle of condylar inclination.

Fig. 15. Incisal inclination A, Condylar inclination B.

This is the angle between the horizontal plane and the path the head of the

condylar process, passes from the beginning of the articular tubercle to its basis

(condyl path) fig.15. It is relatively constant and is 35-400 in elder individuals

with preserved dentition. The values of this angle change amongst 10-500,

depending on the age and the condition of the dentition. In totally edentulous

patients, this angle is around 330.

Angle of incisal inclination.

The distance that the lower incisors pass along the palatal surface of the

upper is called sagittal incisal path fig. 16 and the angle with the horizontal

plane is called angle of incisal guidance fig. 15. Its values are approximately 40-

500. The paths and the angles of the incisal and condyl guidance are in very

close relationship. This condition is absolutely obligatory to achieve balance in

the articulation, that’s why they are a very important biomechanical landmark

for the construction of the articulators (23).

А

Б

89

Fig. 16. Sagittal incisal path

Bennett’s angle

This angle is very important for the transversal movements of the mandible

(to the left and to the right). The head of the condylar process rotates vertically

around the y axis and slightly outwards. On the balanced side several rather

complex and simultaneous movements alongside the three axes x,y,z are been

done. Alongside the axis y the head of the condylar process rotates slightly

inwards, which is demonstrated with movement of the mandible to the left and

to the right respectively. Alongside the axis x, the head of the condylar process

also rotates, which is demonstrated with the opening of the mouth. Alongside

the axis z the head of the condylar process slides a little bit along the articular

tubercle. The transversal movements of the mandible continue till the moment

when on the working side cuspids of the same name are in contact (lateral

occlusion), and on the balanced side - vice verse. The deviation of the mandible

from central position to side occlusion is defined as Bennett’s angle fig. 17. Its

value is approximately 15-170.

Fig. 17. Bennett’s angle Fig. 18. Facebow

90

Facebow.

The facebow fig.18 is a device that serves for transferring the skull-based

position of the maxilla and the individual hinge axis of the patient to the

articulator.

Pantograph

This is a fixed to the facebow device, absolutely necessary for transferring

individual data. Graphite styli pointed perpendicularily towards small vertical

and horizontal tables attached in the vicinity of the hinge axis on each side of the

pantograph are used. There are also two tables attached to the anterior member

of the bow, one on either side of the midline fig. 19.

Nowadays digital devices are been widely used fig. 20.

Fig. 19. Mechanical pantograph

Fig. 20. Digital pantograph

91

Application of the articulators

Basically the articulators are been applied in the prosthetic dentistry for

manufacturing the full volume of prosthetic constructions, starting from inlays

to total dentures, as well as implant-supported appliances.

Nowadays the articulators are been applied in the orthodontics, as well as

for planning some surgical procedures for resection of jaws etc.

A dentist, who uses an articulator in his practice demonstrates remarkable

knowledge and striving for perfection.