access opening

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Introduction After the establishment of a diagnosis and treatment plan ,the first part of treatment directly applied to the is the access cavity preparation, also known as the endodontic entry. Canal preparation may be divided into two phases: the coronal portion and the intraradicular portion. The coronal phase ,which is the access cavity ,must give direct access to the root canals and the apical foramina so that these areas may be cleaned and shaped during the intraradicular phase Defination According to schielder access cavity is defined as a round, tapered, evenly spaced preparation with minimal opening to the apical foramen.

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Page 1: Access Opening

IntroductionAfter the establishment of a diagnosis and treatment plan ,the first part of treatment directly applied to the is the access cavity preparation, also known as the endodontic entry.

Canal preparation may be divided into two phases: the coronal portion and the intraradicular portion.The coronal phase ,which is the access cavity ,must give direct access to the root canals and the apical foramina so that these areas may be cleaned and shaped during the intraradicular phase

DefinationAccording to schielder access cavity is defined as a round, tapered, evenly spaced preparation with minimal opening to the apical foramen.

Rules for Access Preparation

1. The objective of entry is to give direct access to the apical foramina, not merely to the canal orifices.

2. Access cavity preparations are different from typical operative occlusal preparation. The typical occlusal cavity preparations used in operative dentistry are based on the topography of occlusal grooves ,pits and fissures and on the avoidance of underlying pulp.

3. The likely interior anatomy of the tooth under treatment must be determined.

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4. Endodontic entries are prepared through the occlusal or lingual surface – never through the proximal or the gingival surface. The typical occlusal cavity preparations used in operative dentistry dentistry are based on the topography of occlusal grooves , pits, and fissures and on the avoidance. The access cavity preparation includes uncovering the roof of the pulp chamber and providing direct access to the apical foramina by the way of pulp canals.

5. As part of the access preparation, the unsupported cusps of posterior teeth must be reduced. Endodontic therapy requires the removal of much of the central portion of the treated tooth, greatly reducing to stress . All unsupported cusps must be reduced by trimming with a tapered fissure carbide or diamond stoneuntil a definite clearance in occlusal and lateral movement is obtained.

6. Removal of all defective restorations and caries before entry into the pulp chamber

7. Delay of Dam placement until difficult canals have been located and confirmed.8. A proper access cavity has a tapering walls and is widest at the occlusal

surface .In such preparations occlusal forces do not push the temporary restoration into the cavity and disrupt the seal .At least 3.5 mm of temporary filling material is needed to provide an adequate coronal seal.

Components of Root Canal System

The entire space in the dentin where the pulp is housed is called the root canal system. The root canal system is divided into Pulp chamber located in the anatomic crown of the toothPulp or root canal (s) found in the anatomic rootOther features are pulp horns, accessory, lateral, and furcation canals; canal orifices; apical deltas and apical foramina Accessory canals are minute canals that extend in a horizontal ,vertical or lateral direction from the pulp to the periodontium .Formed by the entrapment of the periodontal vessels in hertwig’s epithelial root sheath during calcification.They serves as avenues for the passage of irritants, primarily from the pulp to the periodontium.73.5% - apical third of the canal; 11.4% in the middle third; 15.1% in the cervical thirdAccessory canals also occur in the bifurcation or trifurcation of multirooted teeth .Furcation canals form as a result of the entrapment of periodontal vessels during the fusion of the diaphragm which becomes the pulp chamber floor .In mandibular molars these canals occur in three distinct patterns

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F.Haznedaroglu et al, (2003) conducted the on the incidence of patent furcal accessory canals in permanent molars of a turkish population . Incidence of Patent furcation canals on the pulp chamber floor range from 68% in mandibular and maxillary first and second molars. They concluded that the exposure of accessory canals in the furcal area of molars to5.25% sodium hypochlorite for 1hr with agitation would make the canals patent by dissolving soft within them

But Clinically this not possible because this much concentration of NaOCl will make the dentin weak.So in an in vivo situation ,accessory canals can be obliterated or calcified or remain as viable channels containing normal tissue. In this way it does not contribute to the spread of disease.

The coronal aspect of the tooth should be adequately sealed other wise accessory canals can become contaminated by ingress of fluids and bacteria from the periodontium ,or by oral fluids ,when exposed in a periodontal pocket

Apical Root Anatomy The apical root anatomy is based on three anatomic and histologic landmarks in the apical region of a root:Apical constriction (AC)

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Cementodentinal junction (CDJ)Apical foramen (AF)AC is considered the part of the root canal with the smallest diameter .It is also the reference point clinician use most often as the apical termination for shaping , cleaning, and obturation.

The anatomical location of the apical constriction cannot be clinically determined with accuracy. It has been recorded as far as 3.8 mm from the anatomical apex .in one SEM study(Gutierrez 1995)

A fact should be remembered when determing the length of the toot canal during root canal procedures that the measurement based on root length rather than canal length would carry the filing beyond the apical foramen and into the periapical tissue.

Finally even in cases in which necrosis and bacteria went beyond the foramina the apical limit of the procedures will be the apical constriction.

D.Ricucci (1998) Apical limit of root canal treatmentation and obturation ,A histological study ,IEJ ; 31, 394-409

The CDJ is the point in the canal where cementum meets dentin ;point where pulp tissue ends an periodontal tissue begin.

AF is the circumference or rounded edge , like a funnel or crater , that differentiates the termination of the cemental canal from the exterior surface of the root.

AF does not normally exit at the anatomic apex but rather offset .5 to 3mm

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The diameter of apical foramen increases with age 502micrometers in individuals – 18 to 25 years681micrometers individuals - over 55 years

In 88% of cases the root apex and the AF of the central incisors and canines are displaced distolabially ,whereas those of the lateral incisor are displaced distolingually

Dummer’s classification of apical canal anatomyType A – Traditional single constriction

Type B – Tapering constriction

Type C – Multiconstricted

Type D – Parallel constriction

Isthmus

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An isthmus is a narrow, ribbon – shaped communication between two root canals that contains pulp or pulpally derived tissue.It is also known as corridor, a lateral interconnection, or a transverse anastomosis .They should be found , prepared and filled

during surgery, because they can function as bacterial reservoirs. The incidence of

isthmus is greatest in the apical 3-5mm.

Kim et al identified five types of isthmi Type I Two or three canals with nocommunications.Type II Two canals with a definite connectionbetween them.Type III Three canals with a definite connectionbetween themType IV Canals extend into the isthmus area.Type V Is a true connection or corridor throughout the section.

Weller et al. found that the highest incidence of isthmi in the mesiobuccal root of maxillary first molars occurred 3–5mm from the root apex.

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Canal ConfigurationAccording to Weine Type I- Single canal from the pulp chamber to the apex Type II – Two separate canals leaving the chamber but merging short of the apex to form only one canal Type III – Two separate canals leaving the chamber and exiting the root in separate apical foramina Type IV - One canal leaving the pulp chamber but dividing short of the apex separate and distinct canals with separate apical foramina

CANAL CONFIGUARATION (WEINE- 1969 )

According To Vertucci Type I – A single canal extends the pulp chamber to the apex. Type II - Two separate canals leaving the chamber but merging short of the apex to form only one canal. Type III – One canal leaves the pulp chamber and divides into two in the root :the two then merges to exit as one canal. Type IV – Two separate ,distinct canals extend from pulp chambers to the apex.

Type V -One canals leaves the pulp chamber and divides short of the apex into two separate, distinct canals with separate apical foramina

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TypeVI-Two separate canals leaves the pulp chambers ,merge in the body of the root and re divide short of the apex to exit as two distinct canals.TypeVII - One canal leaves the pulp chamber, divides and then rejoins in the body of the root , and finally re divides into two distinct canals short of the apex

Type VIII - Three separate distinct canals extend from the pulp chamber into the apex

Vertucci’s canal configurations ( 1984)

According Gulabivala and coworkers Type I – Three canals joining in to one Type II – Three canals joining into two canals Type III – Two canals separating into two canals. Type IV – Two canals joining into ,redividing into two , and terminating as one canal Type V – Four canals joining into two canals Type VI – Four canals extending from the orifice to apex Type VII – Five canals joining into four canals

Gulabivala’s canal configurations(2001)

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.

Evaluation of Cementoenamel Junction And Occlusal Anatomies

MORPHOLOGY OF THE PULP CHAMBER:Two categories of anatomic patterns were observed:

1. Relationships of the pulp chamber to the clinical crown.2. Relationships of orifices on the pulp chamber floor.

Relationships of the pulp chamber to the clinical crown. Law of centrality – Floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ.

Law of concentricity - The walls of the pulp chamber are always concentric to the external surface of the tooth at the level of CEJ.

Law of cemento enamel junction (CEJ) – The CEJ is the most consistent, repeatable landmark for locating the position of the pulp chamber.

First law of orifice location :The orifices of the root canals always located at the junction of the walls and the floor.

Second law of orifice location : always located at the angles in the floor-wall junction.

Third law of orifice location : always located at the terminus of the root developmental fusion lines.

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95% of the teeth Conformed to these laws. Slightly fewer than 5% of mandibular second and third molars did not conform because of the occurrence of C- shaped canals

Relationships of the pulp chamber floor The floor of pulp chamber is always a darker color than the surrounding dentinal walls.

Color difference creates a distinct junction where the floor and the walls of the pulp chamber meet .

The orifices of the root canals are always located at the junctions of wall and floor.

The orifices of root canals are located at the angles in the floor wall junction.

The orifice lay at the terminus of developmental root fusion lines, if present .

The developmental root fusion lines are darker than the floor color.

Law of symmetry 1: Except for maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial distal direction through the pulp chamber floor.

Law of symmetry 2: Except for maxillary molars , the orifices of canals lie on a

line perpendicular to a line drawn in a mesial distal direction across the center of the floor of the pulp chamber.

Cemento Enamel Junction is called the “North star” for locating the pulp chamber.

In an event that instrument impingement occurs owing to severely curved root or an extra canal, extend only that portion of the wall to free the instrument, a cloverleaf appearance may evolve as the outline form. Hence luebke termed this as SHAMROCK PREPARATION.

Armamentaria

Magnification And Illumination

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Digital operating Microscope is the preferred means of magnification and illumination

Locating the hidden canals Management of calcified canals

Optimum magnification for endodontic practice ranges from 8 x – 24 x magnification. ( Kim et al)

Surgical loupes

The high magnification is needed to locate the hidden canals, detect microfractures, distinguish between pulp chamber floor & dentin, to identify isthmus & other small anatomic entities of which recognition & treatment are important for endodontic therapy success.

16x – 24 x for microfracture detection

Classification of access cavity preparation instrumentsINITIAL PENETRATION.

Round carbide burs No. 2, No. 4, No. 6, No. 8 Round diamond burs No. 2, No. 4 Tapered carbide fissure burs No. 57. Transmetal bur – metal restoration

ROUND CARBIDE BURS

No.2 - mandibular anteriors maxillary premolarsNo. 4 - maxillary anteriors, mandibular premolarsNo. 6 – maxillary molars

SAFETY TIP TAPERED DIMOND & SAFETY TIP TAPERED CARBIDE BURThese are the safer choices for axial wall extensions. Also used to reduce cusp tips. Used extensively for initial penetration of access cavities. Used to remove caries & to create external outline shape . Fissure carbide burs or diamond burs with round cutting end can also be used. The advantage of this burs over round carbide is that they also can be used for axial wall extensions of the access cavity preparation. However , when this burs are used by inexperienced clinicians, their cutting ends can gouge the pulpal floor & axial walls. Round diamond burs are needed when endodontic access must be made through the porcelain or ceramometal restorations

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Diamond burs are less traumatic to porcelain without fracturing or cracking it.They should always be used with water spray to control heat build up in porcelain restorations

After penetrating the porcelain the clinician should switch to carbide bur for metal or dentin penetration, because of this bur greater cutting efficiency.

UNROOFING THE PULP CHAMBER Specialized

Endoaccess bur Endo z bur Transmetal Ultrasonic tips ; CPR 2 D – 5 D BUC 1 Endo Z bur

Safe ended tungsten carbide bur used to taper and smooth the access cavity preparation. Non-cutting tip prevents gouging on the floor of pulp chamber. Endo access burUnroof the pulp chamberCombined 2 actions at one time, the round cutting tip for easy & fast penetration to the pulp, while conical diamond body needed for straight line access.

Canal orifice enlarging instruments Traditional Gates - Glidden burs Peeso reamersSpecialized Ultrasonic tips ; CPR 2 D – 5 D BUC 1- 3 Rotary - profile orifice shaper k3 ni ti rotary system

Endodontic pathfindersTraditional

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Endodontic explorer DG – 16 CK - 17 Muller bur LN bur

Specialized Micro openers Ultrasonic tips

GG instruments are manufactured in a set and numbered 1 to 6 (with corresponding diameters of 0.5 to 1.5 mm).The number of rings on the shank identifies the specific drill size .GG drills are side-cutting instruments with safety tips; they can be used to cut dentin as they are withdrawn from the canal .

Gates - Glidden is available in two lengths 32 mm - 19 mm (Shank) 28 mm - 16mm (shank) Blade length 3-4 mm GatesGlidden drills may be used safely and to their fullest potential at 750 to 1500 rpm

Peesoreamers

Used for preparation of post space.Sizes 1 to 6.Diameter range from 0.7 to 1.7.Non cutting tip.Careless use can lead to perforations. Available in two lengths

32 mm 28 mm

Endodontic pathfindersEndodontic pathfinder is defined as an endodontic instrument used for tracing the course & exploring root canals.

Endodontic explorerDG 16

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CK 17

Position of this instrument in the orifice reveals the angle at which canals depart the main chamber. Locates canal orifices

Muller Bur• Helps in locating calcified canals.• Extra shank of these burs moves the head of the hand piece away from tooth thus

improving visibility. LN Bur

• Helps in locating calcified canals.

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• Extra shank of these burs moves the head of the hand piece away from tooth thus improving visibility.

• Ultrasonic tips• Traditionally access cavities have been refined with burs that are designed

primarily for operative procedures. Recently a combination of access refinement tips & magnification has revolutionized the basic concept of access cavity preparation.

Profile Orifice Shapers: sizes 4,3,2,1Enlargement of coronal two –third#.12 tapered rotary endodontic files have been used for the Flaring and blending procedure

X-Gates - Unique X-Gates that combines gates glidden drills 1-4 in a single instrument ,flare the orifice to get direct and straight access to canals Use with a brush cutting action. The shaft of the X-Gates should be arched so the cutting flutes selectively cut dentine on the outstroke and to intentionally relocate the canal away from an external root concavity. 800-1000 rpm

Advantages of ultra sonic tips over burs

No hand piece head to obscure vision.

Size of ultra sonic tips is smaller than the smallest burs, therefore dentin can be brushed off in smaller increments with greater control.

The process allows for exposure of any missed or hidden canals or recesses containing necrotic pulp tissue without cutting down the tooth structure.

Unroofing” the pulp chamber – For young and large pulp chamber. “Un covering” the floor of pulp chamber - for receded and calcified pulp chamber.

Production of cavitation within the cooling water that flows over the tip of ultra sonic instruments. ‘Cavitation’ may be described simply as bubble activity in a liquid, which is capable of generating enough shock waves to cause disruption of remnants of necrotic pulp tissue and any calcific deposits.

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Access refinement tips;

Uncovering the floor of the pulp chamber can be accomplished with the help of CPR 2D or BUC 1 tips.

BUC 2 tip can be used to remove pulp stones until the dark colored dentin becomes visible. The unveiling of the dark colored dentin is of critical importance as it dictates & guides the extension of access cavity.

Ultrasonic refining tips can be used for delineating the outlines of the root canal orifices, so that the overhanging dentin deposits are removed & the orifices are exposed.

The ultrasonic tips can be used to dig & follow the sclerosed canals until patency is achieved, however this procedure is restricted to coronal aspect of root trunk & require radiographic assessment

Vibratory tips; Used in case of endodontic retreatment. The tips of these instruments are spherical or flat and are placed against the post to transmit vibration. Also used to remove root canal obstructions after troughing. Ex: VT ( sybron Endo), Osada Enac ST 09 & CPR 1.

Bulk removal tips; Designed primarily to remove dentin and core material quickly and expedition before subjecting the root canal obstruction to vibratory or troughing procedures. Ex; BUC 1 and CPR 2D.

Troughing tips; Troughing tips are used to create sufficiently deep trough around posts and root canal obstructions to maximize the benefits of subsequently applied vibratory or extraction forces. Ex; CPR 3D, 4D, 5D used in coronal, middle and apical one third of root canals respectively.

Anterior Access Cavity PreparationInitial out line form The clinician should begin in the centre of the lingual surface of the anatomic crown. A #2 or #4 round bur or a tapered fissure bur is used to penetrate through the enamel and slightly into the dentin It is 1/2 or 3/4 of the final sizeThe bur is directed perpendicular to the lingual surface

Penetration Of Pulp Chamber Roof – Continuing with the round or tapered fissure bur, clinician changes the angle of the bur from perpendicular to the lingual surface to parallel to the long axis of the root

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Penetration into the tooth is accomplished until roof of the pulp chamber is penetrated :and frequently a drop in effect is felt when this occurs

Complete Roof Removal – Once the pulp chamber has been penetrated ,the remaining roof is removed with a round carbide bur with a withdrawal stroke. Identification of all canal orifices – After pulp chamber has been unroofed, the canals orifices are located with the endodontic explorer. The endodontic explorer is preferred over the rotating bur as it offers two angles of approach Removal of lingual shoulder and orifice and coronal flaring- It is the lingual shelf of dentin that extends from the cingulum to a point approx 2mm apical to the orifice. It is removed with a tapered safety-tip diamond or carbide bur or with Gates Glidden burs. Placed 2mm apical to the canal orifices and inclined to the lingual during rotation to slope the lingual shoulder Using GGs drills – small – large circumferential filing motion ,flaring each canal in sequence. for flaring rotary nickel titanium orifice openers can be used. Straight Line Access Determination – It is evaluated by inserting into the canal the largest file that fits passively to the apical foramen .The file is inserted gently and withdrawn as the clinician feels for canal binding or deflection If deflection is detected the clinician reevaluate the adequacy of lingual shoulder- inadequate removal will lead the file to deflect in a facial direction

Morphological Measurement of Human Anterior Teeth

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Measurement A – The distance from the cusp tips to the lingual CEJ .Measurement B- The distance from the buccal to the lingual CEJ.Measurement C – The distance between the midpoint of the cusp tip to the lingual CEJ and the midpoint of the buccal to the lingual CEJ Measurement D – The distance from the midpoint of B to the labial surface of the toothMeasurement E – It is the sum of distances C and D

Points To PonderThe measurement C is the estimate depth of an endodontic accessMeasurement D is an estimate of the safety margins from proper access to perforationThe risk of perforation is much greater if it is closer to CEJ.For all anterior teeth , measurement C is about 40% of measurement E. In furcated teeth, it is about 60% of the equivalent measurement E.Level of ceiling of pulp chamber in anterior teeth is more occlusal to the CEJ

Access Cavity Design For Maxillary Anterior Teeth

Lingual cingulum access

The initial point of entry was the lingual surface of the crown, just coronal to the cingulum. With the bur at right angles to the long axis of the tooth, the opening was enlarged until the cavity was extended minimally to remove the entire pulp chamber roof cervico-incisally and mesiodistally.

G.Mann et al 2001, Effect of access cavity location and design on degree and distribution of instrumented root canal surface in Maxillary anterior teeth, IEJ ;34,2001

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Lingual conventional access

The initial point of entry was the centre of the lingual surface of the crown with the bur at right angles to the long axis of the tooth. The opening was enlarged holding the bur at right angles to the long axis of the tooth until the cavity extended cervically to a point just above the cingulum, incisally to within 2 mm of the incisal edge and mesiodistally to remove the entire pulp chamber roof

Incisal straight-line access

The initial point of entry was just short of the incisal edge in the lingual surface of the crown, with the bur held parallel to the long axis of the tooth. The opening was enlarged holding the bur parallel to the long axis until the cavity extended cervically to the centre of lingual surface, incisally to involve half the bucco-lingual width of the incisal edge and mesiodistally to include the entire pulp chamber roof.

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Cingulum access cavities preserve incisal tissue, but should a crown be required this would be lost anyway.

An incisal cavity, on the other hand, preserves the dentine in the cingulum area, important for adequate retention and resistance form of a crown.

Straight-line access also involves removal of no more dentine than the conventional palatal approach. The encroachment on the incisal edge and concerns about aesthetics should be unfounded considering the quality of available modern composite restorative material. In some cases, straight-line access may even require a labial approach (Clements & Gilboe 1991).

The lingual conventional access cavity provides a design which falls between the other two, leaving the incisal edge intact but allowing reasonably good contact of the file with the canal walls. This more conservative design may prove to be comparable with the straight line access when combined with the added effects of chemical cleansing, and therefore may be considered more appropriate if aesthetics of the remaining tooth structure are a consideration. Overall, however, it seems that the straight line access cavity has many merits, including better planing of canal walls, less restriction of the instruments coronally, and therefore better apical control, and finally preservation of the important dentine in the cingulum area

Tooth Morphology

Maxillary Cental Incisor

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Avg length 23.3mmLateral canals 23%Distal curve 8%2 degree mesial axial inclination29 degree lingual axial angulationNewly erupted has three pulp hornsThe external out line is rounded triangularThe width of triangular base is determined by the distance between the mesial and distal pulp horns

Cervical- ovoid Middle- ovoid to round Apical third- round

Maxillary Lateral Incisor

Average Length 22.8mmLateral canal – 26% ,more frequentDistal curve – 53% - most common16 degree mesial angulation29 degree lingual axial angulation2 or no pulp horns may be present

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External out line is rounded triangle or an oval depending upon the prominence of mesial and distal pulp hornsRoot canal is conicalIn cross section ovoid in cervical third, ovoid in middle third, round in apexApical foramen is centered located in the anatomic apex in 22%

Maxillary CanineAvg length – 26mm21 degree palatoaxial angulation in the alveolusPulp chamber is wider labiopalatally and secondly one pulp horns is present corresponds to single cusp External outline form is oval or slot shapedThe incisal wall meets the lingual surface of the canine in a butt joint to provide adequate thickness for a restorative materialRoot canal is wider labiopalatally

Cervical- ovoid

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Middle third- ovoidApical third- round

Mandibular Central and Lateral Incisors

Avg length central 20.5mmLateral 22.6mmCentral incisor smallest tooth in the arch Pulp chamber is flat mesiodistallyRoot canal is wide labiolinguallyLingual shoulder must be eliminated as it conceals the orifice of second canalPulp outline is wider labiolingually

Christen John et l(2005) conducted the study on the effect of mesiodistal chamber dimension on access preparation in mandibular incisors .As the person ages the chamber recedes , looses its coronal flare and become oval in shape and as consequence access goes from triangular to oval .He concluded that normal access preparation of mandibular incisor s of patients older than 40 yr of age be limited to an oval preparation of less than 2mm mesiodistal width.

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One study determined that a relationship existed between the crown size and incidence of bifid root canals (expressed as MD/FL) .Double root canals occur more often in teeth with a smaller index .The shape of the access opening is long oval.

Cervical- slightly ovoidMiddle- ribbon shaped due to flatness of the root .It is this area where bifurcation occurs or peroration occurs due to over instrumentsation Apical third- round

Mandibular Canine

Avg length – 25mmLateral canals 9.5%Distal curve -20%13 degrees Mesial inclination115 degree lingual axial angulationOccasionally has two root canals located labially and lingually

Variation Pineda and Kuttler (1972), Green(1973) and Vertucci (1984) reported that 15% of mandibular canines presented with 2 canals with one or two foramina

Laurichesse reported 2% of mandibular canines presented with one root and two canals.

C.D Arcangelo et al (2001) Root canal treatment in mandibular canines with two roots: a report of two cases- case rport ,IEJ,34

Cervical- ovoidMiddle- ovoidApical third- round

Posterior Access Cavity Preparation

Initial External outline Form –

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The pulp chamber of posterior teeth is positioned in the centre of the tooth at the level of the CEJ In Max Premolars this point is on the central groove between the cusp tips .In mandibular premolars ,crowns are tilted lingually relative to their roots ,so the starting location is half way up the lingual incline of the buccal cusp on a line connecting the cusps tips Mandibular 2nd premolars have less lingual inclination so the location is one- third the way up the lingual incline of the buccal cusp .For mandibular molars the correct location is central groove halfway between these mesial and distal boundaries. The bur is directed perpendicular to the occlusal table and its shape is about one half to three forth its final size.

Penetration of the Pulp Chamber Roof- Continuing with the same bur there is change in the angle of penetration from perpendicular to the occlusal table to an angle appropriate for penetration . In case of premolars the angle is parallel to the long axis of roots. And in molars it is toward the largest canal.

Complete Roof Removal – A round bur,a tapered fissured bur, or a safety –tip diamond bur is used to remove the roof of the pulp chamber.The safety tip diamond bur or carbibe bur is passed between the orifices along the axial walls to remove the roof, taper the internal walls and create the desired external shape simultaneously

Identification of all canal orifices- The access cavity should have all orifices positioned entirely on the pulp floor and should not extend into an axial wall. Extension of an orifice into an axial wall will create a “mouse hole effect” which indicates internal under extension and impedes straight line access.Removal of the cervical dentin bulges and orifices and coronal flaring- In posterior teeth the internal impediment are the cervical dentin bulges and natural coronal canal constriction Cervical bulges are removed with safety tip diamond bur or carbide burs .After shelf has been removed ,the orifice and constricted coronal portion of the canals can be flared with GGs drills in a sweeping upward motion with a lateral pressure.

Maxillary First Premolar

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The pulp chamber is wider buccolingually. Palatal orifice is wider than buccal orifice because of its mesial concavity .May have one, two or three root and canals – most often two. Access preparation is oval or slot shaped .

The buccal extension is 2/3rd to 3/4th up the buccal cusp incline .The palatal extension is approx halfway up the palatal cusp incline

A” Represents the distance from the floor of the pulp chamber to the point of the furcation

“B” Represent the distance from the celing of the pulp chamber to the closest point of the furcation

“C” It is the distance from the midpoint of a line connecting the two cusp tips and the closest point to the furcation

“D” Represents the distance from the midpoint of a line connecting two cusp tips to the pulp chamber ceiling.

“E” Represent the height of the pulp chamber

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The reported measurements in this study give us general guide lines for a more quantitative approach to endodontic bicuspid access .The cusp tip to ceiling height is 6.94mm. For both molars and bicuspids, the measurement from the chamber ceiling to furcation is statistically the same but quite variable and this variability is related to the calcigication which is highly random event occurring over the lifetime of an individual.In furcated bicuspids , the cusp tip to pulp chamber ceiling height is approx 7.0mm .Affixing a mark or stop of the bur at 7 or 7.5mm from the cutting tip will enable the dentist to drill in to the middle of the pulp chamber of molars and bicuspids without risk of perforation

Maxillary Second PremolarAvg length – 21.5mmRoot curvature – distal

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It usually has single root and can have two root canals parallel to each other.

Variations

Studies have demonstrated a lower incidence of 3 root canals between .3% - 2%

J .A. Soares et al (2003) reported a case maxillary second premolar with 3 canals and 3 independent roots . The anatomy of maxillary premolar with 3 roots canals , mesiobuccal,distobuccal,and palatal , is similar to that of adjacent maxillary molar and therefore called as small molars or “radiculous”

A two dimensional image of 3 dimensional root canal system, its interpretation reveals external and internal anatomic details that suggest the presence of extracanals or roots Whencver there abrupt straightening or loss of a radiolucent canal in the pulp cavity in the pulp cavity , an extracanal should be suspected in the same root or in other independent roots

In straight on radiograph s of maxillary premolar sieraski found that whenever mesiodistal width of the mid root image is equal to greater than the mesiodistal width of the crown ,the tooth most likely had 3 roots.

In the treatment of 3-rooted maxillary first and second premolar , buccal orifices are close to each other and it has a T- shaped access opening

Mandibular First Premolar

Mandibular first premolar has a 30 degree lingual tilt of crown to the long axis of the root .Wider buccolingually

Cervical line – oval Middle third - roundIf two root canals then it round from the chamber to the foramen

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Mandibular Second Premolar

Root canal is often round .Crown has smaller lingual inclination, less extension up the buccal cusp incline Lingual half is more fully developed ;so lingual access extension is half up the lingual

cusp incline. It can have two lingual cusp of equal sizes then access form is centered

mesiodistally line connecting the buccal cusp and the lingual groove between the lingual cusp tip

Variation L.Holtzman (1998) reported a case of root canal treatment of mandibular second molar with four rootcanals. ,IEJ ,31,364-366

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Maxillary First MolarLargest tooth in volume. Cervical outline form has a rhomboid shape, with rounded corners. ,mesiobuccal angle is an obtuse angle;distobuccal angle is an obtuse angle; and palatal angles are right angles .The palatal canal orifice is centered palatally, distobuccal orifice is positioned within the acute angle and MB-1 is buccal and mesial to the distobuccal orifice .

MB-2 is located palatal and mesial to the MB-1 within 3.5mm palatally and 2mm mesially of the MB-1

Molar Triangle – A line drawn to connect the three main canal orifices (MB orifice, distobuccal orifice, and palatal orifice) forms a triangle ,known as the molar triangle .Palatal canal is longest and has largest diameter .Curves buccally at the apical third

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Palatal canal is flat and wider mesiodistally .DB is oval and becomes round as it approaches to apical third .MB canal is oval and wider buccolingually . Concavity exist on the distal aspect of the MB root which makes it thin .Care not to instrument the wall excessively because a strip perforation may resultMB-2 orifices 84% molars.

Apical canal configurations for mesiobuccal root of maxillary first molar

AUTHOROne canal(%) Two canals(%) Three canals (%)

vertucci 82 18

Pineda & kuttler 51.5 48.5

Wiene et al 86 14

Thomas et al 73.6 26.4 0.4

VariationsF.Maggiore et al 2002 reported case of maxillary first molar with six canals . the tooth has trifurcation in the palatal canal in the apical third and 3 separate foramina , two distinct canals in the MB root and single canal in DB

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Maxillary Second Molar3main orifices (MB,DB, P) forms a flat triangle .MB canal orifice is located more to the buccal and mesial ; DB located between the MB and palatal orifice. Floor is convex .If 4 canals are present then access preparation has a rhomboid shape.

Cervical - ovoidApical- round

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If 3 canals are present, the access cavity is a rounded triangle with base to the buccal. If 2 canals are present then outline form is oval and widest in the buccolingual dimension

Mandibular First MolarThe two-rooted mandibular first permanent molar tooth usually has three canals.

The major variant in this group is the mandibular first molar with three roots. The major variant in this tooth type is the presence of an additional third root; a supernumerary root which can be found lingually. Thiss macrostructure, which is first mentioned in the literature by Carabelli (1844), is called Radix entomolaris (RE) (Bolk 1915).

This has a frequency of less than 5% in Caucasian(UK, Dutch, Finnish, German, other European), African (Bantu, Bushmen), Eurasian and Indian populations, whereas in those with Mongoloid traits, such as Chinese, Eskimo and American Indian populations, it occurs with a frequency of five to more than 40% .

Classification of Radix Entomolaris

Type I: a straight root/root canal; type II: initially curved entrance of the root canal and the continuation as a straight root/root canals; type III: initial curve in the coronal third of the root canal and a second buccally orientated curve starting from the middle third; the radix entomolaris may also have a pronounced curve in the apical part of the root

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Curzon (1974) suggested that the ‘three-rooted molar’ had a high degree of genetic penetranceThe additional root is usually located on the lingual aspect and has a Vertucci type I canal configuration (Sperber & Moreau 1998) DL root often has sharp apical hook toward the buccal .

R. J. G. De Moor 2004 The radix entomolaris in mandibular first molars: an endodontic challenge;IEJ,2004

MB Orifice commonly is under the MB cusp whereas the ML orifice just lingual to the central groove S.Middle mesial canal sometimes is present in the development groove between the MB and ML cusp .The incidence of an MM canal ranges from 1% to 15% .The access cavity for the mandibular first molar is trapezoid .3 root canal are oval in cervical and middle third and round in the apical third. MB canal has a significant curvature in the buccolingual plane- not apparent in the radiograph , detected by the precurve pathfinder instrument.

58% - 4 root canals (2 mesial and 2 distal)42% - 3 root canals (2 mesial and 1 distal)

Mandibular Second Molar2 roots – 71 % 1 root – 27 % 3 roots – 2%

Mesial root have 69.2% type II canal configuration

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C- Shaped Canal

C- shaped molar is so named for the cross sectional morphology of the root & root canal. Instead of having several discrete orifices , the pulp chamber of the c- shaped molar is a single ribbon shaped orifice with a 180 degree arc starting at the mesiolingual line angle & sweeping around three buccal to end at the distal aspect of the pulp chamber.

C – shaped root and canal was first reported by “Cooke and Cox” (1979)It was first reported in maxillary molar2 basic groupsThose with single ribbon like, c- shaped canal from orifice to the apex.Those with 3 or more distinct canals below the usual c - shaped orifice. Second form is more common

Ethnic variation - more common in Asians than Caucasians.Studies on mandibular second molars have shown a high incidence of “C” shaped roots and canalsEtiology – Failure of the Hertwig’s epithelial root sheath to fuse on lingual or buccal root surface is the main cause of C-shaped root which contain the c-shaped canal . It can also be formed because of coalescence because of deposition of cementum with time.

Melton’s classificationProposed in 1991 based on their cross sectional shapeCategory I: Continuous C-shaped canal running from the pulp chamber to the apex defines a C – shaped outline without any separationCategory II: the semicolon – shaped orifice in which dentin separates a main C-shaped canal from one mesial distinct canalCategory III: refers to those with two or discrete and separate canals:

subdivisionI,C –shaped orifice in the coronal third that divides into two or more discrete and separate canals that join apically.Subdivision II – C-shaped orifice in the coronal third that divides into two or more discrete separate canals in the midroot to the apex .Subdivision III ; C-shaped orifice that divides into two or more discrete and separate canal in the coronal third to the apex .

Fan’s Classification (Anatomic Classification)

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Fan et al in 2004 modified Melton’s classification into following categoriesCategory I (C1) – The shape was an interrupted “c” with no separation or divisionCategory II (C2): the canal shape resembled a semicolon resulting from discontinuation of the “C” outline but either angle α or β should be no less than 60 degreeCategory III(C3) :2or 3 separate canals and angles,α and β should be no less than 60 degreeCategory IV (C4): only one round or oval canal in that cross sectionCategory V (C5): no canal lumen could be observed

Fan’s Radiographic classificationFan et al, classified C- shaped roots according to their radiographic appearance into 3 types: Type I – conical or square root; there is mesial distal canal that merged into one before existing as the apical foramenType II – There was mesial and distal canal, and the two canals appeared to continuous on their own pathway to the apexType III – mesial and distal canal, one canal curved to and superimposed on the radiolucent line when running towards the apex and other canal appeared to continue on its own pathway to the apex

Challenging Access Preparation

Heavily Restored TeethRestorative materials and full veneers crown rarely reproduce the original tooth anatomy .Crown root angulations is altered when large restorations or crowns correct the occlusal discrepancies

Restorative materials block the passage of light into the internal aspects of the tooth resulting in poor visibility during preparation .Complete removal of the large amalgam, composite resin or GIC restorations is the wisest course .It allows the clinician better visibility of the internal anatomic structures and increased light penetration .Clinician can check for the recurrent caries or fracture lines on the pulp chamber walls or floor

Another reason to remove the restoration is to prevent pieces of the restorative materials from falling into the root canal. Creation of the access through an intact full or partial veneer crown should be done with cautionClinician’s best approach is to stay as centered in the tooth as possible using all available clinical and radiographic information. Metal veener crowns best penetrated with sharp carbide bur. Round diamond bur and copious water spray to penetrate with porcelain and transmetal bur used to penetrate the metal copings

Teeth with calcified canal

Chronic inflammatory processes (caries, medications, occlusal trauma) often cause narrowing of the root canal system

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Teeth with severe pulp calcifications may present problems with negotiating root canals .The clinician should search for root canal orifices only after preparing the pulp chamber and cleaning and drying its floor (70% denatured ethanol is useful for drying the floor and enhancing visibility) Clinician should keep in mind that root canal orifices are located at the angles formed by the floor and walls and the end points of developmental grooves For locating the calcified root canals stain the pulp chamber floor with 1% methylene blue dye performing with the sodium hypochlorite “champgne Bubble” test and searching for canal bleeding points.As the search moves apically, two radiographs must be taken, one from straight – on direction and other from an angled direction. Small piece of lead foil placed at the apical extent of the penetration can provide a radiographic reference.

When canal is located , a small K-file (no 6,8 or 10) coated with chelating agent should be introduced into the canal to determine patency. It should be used with in short up and down movements and in a selective circumferential filing motion with most of the lateral pressure directed away from the furcation. This enlarges the coronal canal and moves it laterally to avoid the furcation.

Methods of assessing root canal anatomy1) Decalcification with Indian ink, haemotoxylin blue2) In vitro radiopaque gel infusion & radiography.3) Scanning electron microscopic examination.4) Sectioning of tooth

Radiographic 1) Conventional2) Cone\ image shift3) Mirocomputed tomography

ConclusionThe endodontic access cavity is an essential component of the endodontic triad upon which all subsequent canal preparation and filling is based. It is probably the most frequently underemphasized aspect of endodontic therapy. This results in great clinical frustration and poor immediate and long-term results for the practitioner. The access cavity must provide clear and unobstructed access to each and every orifice and must be designed in such a way so as not to interfere with the often difficult intracanal procedures to follow. An understanding of root development, chamber, and canal anatomy will allow the practitioner to more easily debride and seal each canal through proper access cavity preparation.