09.amalgam cavity designs

Cavity Designs For Amalgam

Restoration

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Nomenclature

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Cavity Line angle Point angle

Class l 8 4

Class 2 11 6

MOD 14 8

Class lll 6 3

Class lV 11 6

Class V 8 4

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There are many angles in a cavity

prepared cavity such as:

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Cavosurface angle

This refers to the angle

of the tooth structure

formed by the junction

of a prepared wall and

the external tooth

surface.

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Cavosurface margin

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Cavity

Simple cavity: only one tooth

surface is involved.

Compound cavity: two surfaces

are involved.

Complex cavity: three or more

surfaces are involved.

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Simple

Compound8

Classification of cavity

G.V .Black classification

Class l – pit and fissure restoration

-Restoration on occlusal surface of premolar and

molars

-Restoration on occlusal two thirds of facial and lingual surfaces of molars

-Restoration on lingual surface of maxillary incisors

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Class ll –Restoration on proximal surfaces of

posterior teeth

Class lll - Restoration on proximal surfaces of anterior teeth that do not involve the incisal angle

Class lV -Restoration on proximal surfaces of anterior teeth that do involve the incisal angle

Class V – Restorations on the gingival third of the facial or lingual surfaces of all teeth

Class Vl – Restoration on the incisal edge of anterior teeth or the occlusal cusp heights of posterior teeth

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Class 1

Class 2

Class 1

Class 2

Class 3

Class 4

Class 5

Class 6

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The four sizes of carious lesions

Size 1. Minimal involvement of dentine just beyond treatment by remineralization alone.

Size 2. Moderate involvement of dentine. sound,. That is, the remaining tooth structure is sufficiently strong to support the restoration .

Size 3. The cavity is enlarged beyond moderate.The remaining tooth structure is weakened to the extent that cusps or incisal edges are split,

Size 4. Extensive caries with bulk loss of tooth structure has already occurred.

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Principles of

tooth preparation

for amalgam

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Outline Form

means extending the preparation margins to the place they

will occupy in the final preparation

Removal of all carious and defective pits and fissures to

healthy tooth structure

Removal of all unsupported enamel rods

To avoid ending preparation margins in high stress areas

like cusp tip and crest of the ridges

Placing margins on sound tooth structure.

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Steps establish the external outline form to extend all margins into sound

tooth tissue.

Maintain the initial depth of 1.5 mm, this is approximately one-half of

the length of the cutting bur. should be, at least 0.2 to 0.5 mm in dentin

to provide adequate strength to resist fracture due to occlusal

forces

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Extend the margin mesially and distally but do not involve marginal

ridges. These walls should have dovetail shape to provide retention to

the restoration

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While working towards mesial and distal surface, orient

the bur towards respective marginal ridge. This will

result in slight divergence of mesial and distal walls

which helps to provide dentinal support for marginal

ridges

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The isthmus width should be as narrow as possible

The deep pit and fissure defects less than 0.5 mm apart

should be included within the outline form.

The external outline form should have smooth curves,

straight lines and rounded angles. All unsupported and

demineralized enamel should be removed.

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Primary Resistance Form

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The shape given to a prepared tooth

cavity imparting strength and durability

to the masticatory dislodging forces of

a dental restoration and remaining

tooth structure.

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Cavosurface margin

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Resistance form

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Reverse curve

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Primary retention form

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Class l designs

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Class l, design 1

Caries penetration into dentin does

not exceed 0.5-1mm

Width- I/4 intercuspal distance

Low caries index

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Molar outline Premolar outline

General shape

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Mesio distal cross section

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•Pulpal Floor mesio-distally is flat and

perpendicular to the long axis of the tooth

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Pulpal floor of

Lower premolar

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Class l, design 2Indication ; caries cones in dentin extend 1mm or more

from the DEJ

Pulpal floors have different levels33

Mesiodistal cross section

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Class l, design 3

Indication ; in occlusal one to two thirds of facial

and lingual surfaces of molars and on lingual surfaces

of anterior teeth

General shape

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Internal anatomy

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Class l, design 4

Applied to molars involving their occlusal surfaces,the

grooved part of the facial or lingual surfaces

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--Pulpal wall elevated occlusaly

--Use in mandibular first molar

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Class l, design 5 : Indications Occlusal surface, most of the facial or lingual surface

involved

Occlusal surface is not conducive to retention of restoration

Location of margins

In occlusal cavity mesial

and distal margins located at

Corresponding axial angles

Gingival margins

–gingival third of the facial

or lingual Surface

Pulpal floor – internal boxes (mesial third)39

Mesio distal cross section

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Class l, design 6 :Includes occlusal surfaces of molars or premolars

as well as portion of facial, proximalor lingual surface in form of a table of an entire

cusp or section of cusp (marginal ridges )

Gingival margin should extend to allow

Occlusal clearance of 1.5-3 mm from

Opposing teeth

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Class l, Design 7

Involves occlusal , facial and lingual surfaces of

molars and premolars

Pins and posts are indicated

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Class l, design 8 Endodontically treated tooth

Pulp chamber is retention form

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Out line form

• Extent of caries

• Extent for convenience

• Location of gingiva

• Convexity of proximal surface

• Location and extent of contact areas

Resistance form

Occlusal loading and its effects

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Small cusps

Tensile stress

Compressive stress

Large cusps 46

Axial wall

Design features for the protection of mechanical integrity of

restoration

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Reverse curve

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Class ll, Design 1

Moderate to large size proximal

Lesion with occlusal surface cavity

promotes the cavity width of cavity to

exceed 1/4 0f intercuspal distance

Conventional design

Indications

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Proximal box

Inverted truncated shape

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Tunnel preparation

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Class ll, Design 2 (moderate design )

Indications•Moderate to small sized proximal lesions

•In stress concentration area

•Width not exceeding 1/4 of intercuspal distance

General shapewidth 53

Bucco lingually

Mesiodistally54

Class ll, Design 3 (conservative design )

• Involves primarily proximal surface and very limited part

of occlusal Surface, not extending beyond adjacent

triangular fossa

•Sound occlusal crossing ridges

•Minimal loading areas

General shapeInternal anatomy55

Gingival margin

Middle third Gingival third

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Class ll, Design 4 (Simple design )

•Proximal surface only

•Indications; Decay restricted to contacting or proximal

surface without undermining marginal ridges

Diastema or adjacent tooth is missing

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Bucco-lingual

Cross section

Occlusal-gingival

Cross section

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Class ll, Design 5

Part of proximal surface ,with a limited access area on facial

or lingual surface

Indications :

1)Do not have dovetail2) Have dovetail

•1)Preparation will have 4 surrounding walls

•small proximal lesions

•Marginal ridge intact

•Does not involve contact area

2) Preparation will not

have surrounding walls

•medium proximal lesion

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Class ll, Design 6

The occlusal ,proximal and part of the facial or lingual

surfaces

Indications ; Cusp is missing

Badly broken down teeth

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Class ll, Design 7

Shape A : junctions between the class ll and class V via, the

Proximal , crossing the axial angles

Shape B : via buccal / lingual groove

Shape A Shape B

(Combinations of class ll with class V )

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Class ll, Design 8

Two or more surfaces of an endodontically treated tooth

does not require post retention

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Class lll Amalgam is usually not indicated for anterior teeth due to

its esthetic , but distal surface of the cuspid is a unique

location

General principles are similar to class llcavity

preparation but with emphasis laid on in areas of preparation

1 esthetic concern

2 extension for access

3 stress consideration enamel rod direction

Incisal access63

Designs of cavity preparation at the distal slope of

the cuspid

Indications;

1 The lesion does not involve or undermine the distal

slope of cupid

2 bulky walls will remain, incisally, after removal of

Undermine tissues

3 the labials axial angle is intact

4 the restoration will be directly loaded by vertical forces

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Internal anatomy ;

Axial convex

Depth - .5 from DEJ

Retention points :

Depth 1 to 2 mm in dentin

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Class lV

Indications :

•Incisal angle is undermined

•Labial and lingual walls intact

Labio lingual cross section

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Modifications

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Class V cavityInvolvement :smooth surfaces apical to height of contour

on facial and lingual surfaces of all teeth eg ; erosion,

abrasion , hypoplasia, aplasia

Resistance and retention

To minimize the effects of displacing

forces forces grooves occlusal and

gingival walls are essential

- cementum completely removed

- Gingival margins follow the curvature of

the furcation

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•lesion are confined to

gingival third of the

facisal or lingual third

of the facial or lingual

surface

- axial angles intact

- no furcation

involvement

Class V design 1

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Class V ,design 2

Lesions on facial or lingual gingival third have

involved axial angle

Lesion on facial or lingual gingival third are

apical to contact area

General shapeMesiodistal cross section

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Mesio distal

Occluso gingival 72

Class V Design 3

Indications;

Lesion on gingival third facially or linguallly is continuous

with isolated decalcifications or lesions occlusal to height of

contour

Bilateral extension 73

Class V Design 4

Multiple lesions in gingival third with sound tooth

structure separating them

General shape 74

Class V Design 5

Internal

anatomy

Involves bifurcation or part of it

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Class VI

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Retention coves

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Retention locks

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Tooth preparation for pin amalgam

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Pin location

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Cavosurface angle

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Enamel –amalgam junction

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Conclusion

Although composite resins and crown and bridge

restorative dental techniques receive much attention,

amalgam will continue to be the most extensively used

restorative material for many years to come .

If it is used with care in minimal cavities, the restoration,

the tooth and the occlusion will all last longer!

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