modifications of class 2 cavity preparations

MODIFICATION OF CLASS 2

CAVITY PREPARATION

Presented By: Shashank Mishra Guided By : Dr. Sandip Metgud Dr. Deepali Agarwal

CLASS 2 ,DESIGN 2 (MODERN DESIGN

)

INDICATION

Moderate to small size proximal caries.

Cavity not exceeding one fourth the intercuspal distance.

A class 2 in stress concentration area.

A patient with good oral hygiene, low plaque and caries index.

A lesion where after removal of carious dentin sufficient bulk in the buccal and lingual wall present.

GENERAL SHAPE :

OCCLUSAL PORTION :

Outline resembles class 1 design 1 or 2 , except they should have some dovetail formation which may be toward one side only.

PROXIMAL PORTION:

These preparation assume an only unilateral inverted truncated cone shape

LOCATION OF MARGIN

OCCLUSAL PORTION :

Resemble those seen in class1 design 1

Proximal portion Gingival margin may be located anywhere on the

proximal surface,provided

1. It is gingival to the contact area

2. Cavity preparation include all carious and undermined tooth structure.

ISTHMUS PORTION facial and lingual margins at the isthmus are placed on

corresponding surfaces of inclined plane and the remaining areas of marginal ridge. Because of the limited cavity width , the universal sweeping curves of facial and lingual margins occlusally will always reverse in isthmus portion (in S-shaped form) to include contact area.

INTERNAL ANATOMY

A. occlusal portion : similar to class 1 design 1.

Proximal portionMesio-distal cross-section :

Similar to the conventional design, except that rarely gingival margin may be located on cementum. All line angles are rounded, with exception of gingivo-axial line angle, which

should be kept sharp.

facio – lingual cross section

It is very similar to the conventional design With following variations -- Buccal and lingual dentinal retention grooves will

be present

The axial depth of modern design cavity is much less than that of the conventional design .

Preparation modifications:

In tapered teeth (bell shaped teeth )

in line with the axio-pulpal line angle facially and lingually a groove is prepared on each of the facial and lingual walls respectively.

. After preparing a Class II cavity preparation, if there presents an intact marginal ridge, crossed by a fissure, or carious groove, all that is needed is a proximal extension in the form of slit .

Slit : a long, narrow cut or opening.

This “ slit “ may open proximally on the same level as the pulpal floor , or with an occlusal step .

Instrumentation for Class II , Design 2

Procedure

Procedural steps are similar to those described for Design 1, with exception that smaller instruments are used.

Eg. In gaining access and gross removal use a 168 bur, instead of a 699 bur. In preliminary and final shaping use the smallest sizes of chisels . The proximal retention grooves , which are mandatory here, are created with smaller gingival marginal trimmers or angle former.

○CLASS II , DESIGN 3 (CONSERVATIVE

DESIGN)

Involvement This preparation is designed to involve

primarily the proximal surface(s) and a very limited part of the occlusal surface , not extending beyond the adjacent triangular fossa .

Indication

The decay is restricted to the proximal surface only and the occlusal surface is completely sound.

• Low stress bearing area .

• There is sufficient bulk of remaining tooth structure to place substantial buccal , lingual and gingival retentive grooves .

• Patient exhibits good oral hygiene and low caries and plaque indices

General shape

These preparations appear proximally as a one-sided inverted truncated cone which is located totally proximally

with the exception of its tip, which involves part of the adjacent occlusal triangular fossa

LOCATION OF MARGIN

OCCLUSAL PORTION

located on the occlusal inclined planes of the involved marginal ridge

Proximal portion : Appear exactly like modern design .

Internal anatomy :

1. Mesio-distal cross section

The gingival floor may assume one of two forms

a. If the gingival margin is present at the gingival third of the proximal surface , the floor will be formed of 3 planes –

1. an inner dentinal plane in the form of a groove.

2. middle transistional dentinal phase 3. an outer enamelo-dentinal plane

following the direction of the enamel rods and inclining gingivo-proximally.

. If the gingival margin is located at the middle third proximally the gingival floor will be formed of 2 planes –

1. an inner dentinal plane in the form of a groove.

2. straight plane formed of enamel and dentin

Facio-lingual cross section This view shows the axial wall to be perfectly convex. The facial and lingual walls , If their margins are at the facial or lingual thirds of the proximal surface ,It will be formed of 3 planes : 1. an inner dentinal plane in form of groove . 2. a transitional dentinal plane. 3. an outer enamel –dentinal plane following the direction of enamel rods proximo-buccally and lingually.

If their wall ends at middle third it will be composed of 2 planes : 1. inner dentinal groove plane . 2. outer , straight enamel –dentinal plane , perpendicular to the tangent of the axial wall

INSTRUMENTATION

PROCEDURES: Using a ¼ round bur , start a tunnel on the occlusal inclined

planes of the marginal ridge to be involved in the preparation, connecting this tunnel with the lesion, widening and breaking it in the same way as was done in preparation of previous 2 designs.

If part of the marginal ridge is lost , two lateral grooves may be prepared on the buccal and lingual behind the portion of marginal ridge to be removed

CLASS 2 DESIGN 4( SIMPLE DESIGN)

Involvement : The proximal surfaces only

Indications The decay is restricted to contacting

or proximal surfaces without undermining the corresponding marginal ridges

There is a diastema

• the adjacent tooth is missing facilitating direct access to the lesion.

The affected tooth is rotated or inclined.

• The proximal lesion occurs on tapered teeth with wide gingival embrasures facilitating facial or lingual access to the lesion

The proximal lesion is located very gingivally at or apical to, the CEJ, accompanied by gingival recession(senile decay), making accessibility to the lesion from the facial or lingual direction possible

General Shape

Generally, it should follow the shape of the contact area and the proximal surface. Usually it will assume a trapezoidal or rhomboidal shape.

Locations of margins

If there is no proximally contacting tooth (diestema) , there is no specific location of margins , for the entire proximal surface is essential self-cleansable.

If the lesion is apical to the contact area(senile decay ), the occlusal and gingival margins will be in the gingival embrasures.

Internal anatomy

a. Facio –lingual cross section

The axial wall is seen to be flat to slightly convex facio-lingually .

(interrupted line)

The buccal or lingual wall , on the access side will be a one-planed enamel dentinal wall following the directions of the enamel rods.

Occlusogingival cross section

The gingival floor may be seen to occur in one of the two ways

If the gingival margin is located on cementum , cementum should be removed

gingival floor should be completely formed of dentin and in 2 planes : an inner one formed of a groove and an outer one perfectly straight and flat

If the gingival margin is present on enamel, it will be formed of 3 planes : inner dentinal groove , a dentinal transistional plane and an outer plane of enamel and dentin

Instrumentation for class II design 4

Prerequisites : These are similar to previous designs , with the exception that

wedges are used if they will interfere with access.

Procedures : a. Gaining access and gross removal

From the access side, using a round bur ¼ the size of the proximal preparation with axial pressure and lateral dragging. Remove decayed and sound tooth structure within the outline.

b Preliminary shaping This is done using the base of an inverted cone

bur . With buccal access ,at the future location of the lingual wall ,form the lingual wall in gingivo-

occlusal movements .

• At the gingival floor location ,use the same part of the bur moving it in a bucco-lingual direction to form the gingival floor .

• Then using the side of the bur , in an occluso-apical direction , form the buccal wall .

The occlusal wall could be formed with a tapered fissure bur , using bucco-lingual strokes.

If access is from the lingual, the exact reverse of the previous steps are followed.

Final shaping is accompanished in several steps. The different planes for the buccal and lingual walls can be

formed using a hatchet and wedelstaedt chisel .

Similarly different planes for the gingival and occlusal walls could be formed using a Wedelstaedt chisel from buccal or hatchet from lingual

CLASS II DESIGN 5

Involvement : Part of the proximal surface, with a very limited access area on the facial or lingual surface .

Indications There are two shapes for this design , each with certain indications.

Shape A– facial and lingual surface will not have dovetail form.

1. The cavity will have 4 walls , with retentive grooves in atleast 2 of them.

2. Small to medium sized proximal lesions.3. Restoration subjected to normal displacing forces.4. Marginal ridge is intact.5. Lesion does not involve the contact area.6. Good oral hygiene.

In shape B - the facial or lingual access will have a locking feature in the form of a dovetail, unilaterally cut in the occlusal direction.

1. Final cavity preparation will not have 4 surrounding walls and either one wall or no wall is bulky enough to accommodate a groove.

2. For medium to large sized proximal lesion.

General shape

The proximal part of this cavity will have no specific shape , however , it will appear either trapezoidal .

One- sided dovetailed shapedovetailed shape

a box or rectangular shape

Gingival margin present in gingival embrasure

Occlusal margin located in gingival

embrasure

The proximal margins are far enough onto the facial or lingual surface to include the axial angle and ¼ th of the facial or lingual surface.

Locations of margins

Internal Anatomy

Occluso –gingival cross section

The axial wall will appear flat

occlusogingivally

The occlusal and gingival walls , if both are located on cementum or dentin, will be formed of 2 planes – an internal dentinal grooved plane and an external dentinal plane which is perfectly flat and

opening straight proximally.

If the occlusal margin is located on enamel it is always at the gingival third of the surface .The resultant inclination

axio-gingivally creates a needed

undercut.

Two distinct axial walls , i.e. One proximal and

another facial or lingual (access side). Both are perfectly flat

.

If the facial or lingual wall on the non-access side has its margin on enamel, it will be composed of 2 planes: an inner dentinal

plane at right angle to proximal axial wall for resistance and retention and outer enamel-dentin plane in direction of

enamel rods

Facio-lingual cross section

In a very apically located lesion, part or all of this

facial or lingual walls will be completely formed of dentin,

always at a right angle to the axial wall.

The mesial and distal wall on the access side is always one planed. It is formed

of enamel and dentin following the

direction of enamel rods.

Facio-lingual cross section

Instrumentation

a. Gaining access and gross removal :

with a tapered fissure bur using axial pressure and lateral dragging , on the access side, cut the access window which usually will be in sound tooth structures.

Access window in the sound

tooth structure

From this access preparation introduce the same tapered fissure bur proximally using axial and lingual pressure and occluso-gingival dragging.

Axial and lingual

pressure

Buccolingual

direction

a. Preliminary shaping : this is done using the tip and side of a 700 or a 169 bur which creates definite surrounding walls, and to formulate the proximal axial wall. Retention grooves if indicated , may be cut using a ¼ round bur, dragged along the axio-gingival and sometimes axio-occlusal line angle

with pressure gingivally and occlusally.

.

a. Final shaping occurs when the different planes of surrounding walls are formed using a hatchet for the access cavity and axial wall and a gingival marginal trimmer for the non-access side walls and gingival walls . Defining and rounding of line and point angles is done using a Wedelstaedt or hatchet chisels.

hatchet GMT Wedelstaedt

Cavity finish is accomplished using the same instruments but with lighter and more frequent applications

CLASS II , DESIGN 6

Involvement : The occlusal, proximal(s) and part of the facial and/or lingual surfaces.

Indications:

1. The cusp length is double or more its width , either throughout or at certain portions of cusp.

2. A cusp is completely missing .

3. A foundation for cast restoration is required.

4. Teeth have a doubtful prognosis endodontically and periodontically.

5. A badly broken down tooth needs to be prepared prior to endodontic or orthodontic treatment

General shape The occlusal and proximal portions have the

same locations of margins as in designs 1 or 2 . The facial and/or lingual parts are rectangular in outline.

RECTANGULAR IN OUTLINE

Locations of margins The occlusal and proximal portions have

same location of margins as design 1or 2. With only partial mesio-distal replacement

of cusp, the margin should not end at the tip of cusp rather it should be located mesial or distal to it.

• Similarly if margins come near groove , the groove is involved in cavity preparation

Cuspal elements , or parts of them , which will

accomodate amalgam must be cut flat, i.e. In the form of a table with right

angled cavosurface margins.

Reduce cusps or parts of a cusp until there is minimum length:width ratio of 1:1. If

length:width ratio is different at different levels tables can be prepared at

these different levels.

The junction between tables should be rounded.

Cusps or parts of it to be replaced or covered with amalgam should be reduced at least 1.5-2 mm from the opposing cuspal elements in both static and dynamic contacts. This will accomodate sufficient amalgam

bulk to resist loading.

Internal Anatomy

It is always advisable to have a retention form , for e.g. External box or groove, adjacent to the

tabled cusp

• Undermined or thinned enamel should be tabled .

• Never place pins on tables which will accommodate amalgam cusps.

Class II Design 7 (Combination of Class II with Class V)

Shape A

The junction between the Class II and Class V via the proximal, crossing the axial angles.

Involvement

The occlusal, proximal and part or all of the gingival third of the facial and/or lingual surfaces with the intervening part of the axial angles

Indications

a. When at a location apical to the contact area, an occluso-proximal lesion joins a senile decay lesion via decalcification, or a defect that has spread laterally beyond the regular cavity preparation.

b. A class V lesion undermines enamel or directly involves tooth structure of the adjacent axial angles in a tooth having a proximo-occlusal lesion.

c. Surface defects or decalcifications at the axial angles of the tooth are continous with a proximo-occlusal cavity preparation apical to contact area.

If the cavity extension will unilaterally involve the facial or lingual axial angle only, will be

“L shaped”.

If cavity extension is bilateral it will be “invered

T-shaped”.

General shape

Location of margins

The occlusal margins and main parts of the proximal margins will be exactly like Design 1 and 2.

In the extensions, facially and/or lingually the gingival margin will seldom be located

subgingivally but will be even with free gingiva or

supragingival.

•The occlusal margin in the extension will be apical to the contact area.• In unilateral L shaped design there is one occlusal wall.

The facial and/or lingual margins of the extensions will be located past the axial angle on facial or lingual surfaces.

In bilateral inverted T design there are 2 occlusal walls.

Shape B

The junction between class II and class V is through the occlusal via the buccal and/or lingual grooves.

Involvement : the proximal, occlusal , facial and/or lingual surfaces.

Indications

1. Class V lesion connects with an occluso-proximal lesion via a facial or lingual fissured groove.

2. Surface defects or decalcifications on facial or lingual surface .

3. Class V is continuous with Class 1.

General shape

Occlusal and proximal portions are exactly as design 1 and 2. The facial and / or lingual parts are inverted T-shaped.

Internal AnatomyThe connection between the occlusal and facial or lingual portion is in the form of long arm of inverted T.

Class II Design 8

Involvement

Two or more surfaces of an endodontically treated that does not require post retention .

Indications

1. The remaining tooth structure after endodontics can support and retain an amalgam restoration.

2. The tooth has a sufficient pulp chamber to accomodate retaining self – resisting amalgam bulk i.e. A minimum 2 mm thickness in three dimensions.

3. The post-endodontics pulp chamber has at least two opposing intact walls.

4. The tooth contains sufficiently large root canals to accomodate retaining resisting amalgam bulk at its occlusal 1/3rd (i.e. Minimum 1.5 mm thickness )

5. A foundations is needed for a reinforcing restorations (cast restoration)

6. There is sufficient remaining tooth structure to permit the preparation of flat planes at right angles to occluding forces.

7. There has been successful root canal therapy leaving an intact subpulpal floor.

8. The tooth does not show any signs of cracking or crazing.

Large root canals that can accomodate an

amalgam thickness of 1.5 mm should have the

root canal filling removed to a 3-4 mm

depth .

Excavate from the entire pulp chamber any residual root canal filling materials or debris. Bare dentin should be exposed on

the surrounding walls and subpulpal floor

General shape

The outline will appear exactly as described for Design 6.

Internal anatomy

Each flat portions of the tooth preparation eg. Tables or ledges should be opposed by a similar flat component for proper reciprocation, to immobilize the restoration and evenly distribute stresses.

•Any external boxes for retention should not perforate to the pulp chamber or cause thinning in the intervening walls.• In preparing tables and ledges allow sufficient reduction depths to provide enough thickness of amalgam to serve as a foundation for a reinforcing cast restoration.

In the bulky portion of the surrounding walls of the pulp chamber, cut flat

ledges to receive most of the occlusal loading , thereby minimizing

stresses on the subpulpal floor during such loading .

If possible “square up” surrounding walls provided this action will not perforate to the surface , furcation , or

thin tooth structure to the extent of making these areas non-resistant .

Retain any residual pulpal floor , placing

ledges in it and making it as flat as

possible.

Instrumentation for Class II, Design 8

The occluso-proximal cavity preparation and capping of cusps , short of pulp chamber and root canal preparation, is done in same way as described for Designs 1 and 6 .

For intrapulpal and intraradicular prepartion the following procedure may be done : Ledges and shelves may be prepared using 555 and 556 burs in apical pressure

and lateral dragging .

APICAL PRESURE

Intraradicular preparation is started by removing the specified lengths of the indicated root canal material using hot gutta-percha pluggers,peeso reamers or bibevelled-sided reamers.

Then the specified length of the canal is widened and side-paralleled using large tapered, then cylindrical fissure burs (704,558).

Following this , the junction between pulp chamber and root canal preparations should be rounded using round burs. Finally , all junctional parts of the cavity preparations are rounded using a round bur or a very sharp gingival marginal trimmer

References

Operative Dentistry – Modern theory and Practice – Marzouk.

Art and Science of Operative Dentistry – Sturdevant.

Fundamental of operative dentistry – j.summit

Textbook of endodontics- Nisha garg

Thank You