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Class II cavity preparation
1. Class II Cavity Preparation
Presented by,
Sreelekshmi J
Intern
KVG Dental College
2. INTRODUCTION
Dental Caries is “an infectious microbiological disease of the teeth
that results in localized dissolution and destruction of calcified
tissues.”
- STURDEVANT
Tooth preparation is defined as the mechanical alteration of a
defective, injured or diseased tooth to best receive a restorative
material that will re-establish a healthy state for the tooth, including
esthetic corrections where indicated, along with normal form and
function.
- STURDEVANT
3. CLASSIFICATION FOR CAVITY
PREPARATION
Black’s Classification:
Class I cavity – for caries involving pits, fissures and
defective grooves.
Locations
Occlusal surface of molars and premolars
Occlusal two-third of buccal and lingual surfaces of
molars
Lingual surfaces of anterior tooth
4. Class II cavity – for caries lesions found on the proximal
surfaces of the bicuspids and molars.
5. Class III cavity – Carious lesions found on the proximal surfaces of anterior
teeth that do not involve or necessitate the removal of the incisal angle.
Class IV cavity – Carious lesions found on the proximal surfaces of anterior
teeth that involve the incisal angle.
6. Class V cavity – Carious lesions found at the gingival third of the facial
and lingual surfaces of the anterior and posterior teeth.
Class VI cavity (Simon’s modification) – Carious lesions involving cuspal
tips and incisal edges of teeth.
7. PRINCIPLES OF CAVITY PREPARATION
The steps in cavity preparation are:
Initial cavity preparation stage
- Outline form and initial depth
- Primary resistance form
- Primary retention form
- Convenience form
8. Final cavity preparation stage:
- Removal of any remaining infected dentin
- Pulp protection
- Secondary resistance and retention form
- Finishing of enamel walls
- Final procedure – Cleaning, varnishing and conditioning
9. Outline Form and Initial Depth
Placing the preparation margins in the positions they will occupy in the
final preparation.
Preparing an initial depth of 0.2 – 0.8 mm pulpally of the DEJ position.
Principles involved:
1. All friable and/or weakened enamel should be removed.
2. All faults should be included.
3. All margins should be placed in a position to afford good finishing of
margins of restoration.
10. Features:
1. Preserving cuspal strength.
2. Preserving marginal ridge.
3. Minimizing faciolingual extension.
4. Using enameloplasty.
5. Connecting two close faults of the tooth which are less than 0.5 mm
apart.
6. Restricting depth of penetration into dentin to a maximum of 0.2 mm for
pit and fissure caries and 0.2 to 0.8 mm for the axial wall of smooth
surface caries.
11. Primary Resistance Form
It is defined as that shape and placement of the preparation
walls that best enable both the restoration and the tooth to
withstand, without fracture, masticatory forces delivered
principally in the long axis of the tooth.
Principle:
1. To use the box shape with a relatively flat floor.
2. To restrict the extension of the external walls.
3. To have a slight rounding (coving) of internal line angles.
4. In extensive tooth preparations, to cap weak cusps and
envelope or include enough of a weakened tooth.
12. 5. To provide enough thickness of restorative material.
6. To bond the material to tooth structure when appropriate.
Features:
1. Relatively flat floors
2. Box shape
3. Inclusion of weakened tooth structure
4. Preservation of cusps and marginal ridges.
5. Rounded internal line angles.
6. Adequate thickness of restorative material.
7. Reduction of cusps for capping when indicated.
13.
14. Primary Retention Form
Shape or form of the conventional preparation that resists
displacement or removal of the restoration from tipping or
lifting forces.
Features:
1. Occlusal dovetail in the case of proximo-occlusal cavities
where only one proximal surface is involved.
2. Proximal box of Class II design is divergent gingivally to
contribute to the retention form.
15. Convenience Form
Shape or form of the preparation that provides for adequate
observation, accessibility and ease of operation in preparing
and restoring the tooth.
Obtaining this form may necessitate extension of distal,
mesial, facial or lingual walls to gain adequate access to the
deeper portion of the preparation.
Occlusal divergence of vertical(longitudinal) walls of tooth
preparations for Class II cast restorations.
Extending proximal preparations beyond proximal contacts.
16. Removal of any remaining infected
dentin
In the case of a small carious lesion, the infected dentin would be
completely removed as the above mentioned principles are achieved.
However, when a large carious lesion exists, some amount of infected
dentin still remains in spite of following the above procedures. In such
cases the infected dentin has to be removed.
17. Pulp Protection
When thickness of the remaining dentin is minimal, heat generated by
injudicious cutting can result in a pulpal burn lesion, an abscess formation
or pulpal necrosis.
A water or air-water spray coolant must be used with the high speed
rotary instrument.
Liners or bases can be used to protect the pulp or to aid pulpal recovery
or both.
Zinc oxide eugenol and Calcium hydroxide liners in thickness of 0.5 mm
or greater have adequate strength to resist condensation forces of
amalgam.
18. Bases are used in thicker dimensions beneath permanent restorations to
provide mechanical, chemical and thermal protection to the pulp.
Several materials such as zinc phosphate, zinc oxide eugenol, calcium
hydroxide, polycarboxylate and resin modified glass ionomer have been
used under amalgam restorations.
A shallow composite restoration may not need a base, but in deep cavities
use of resin-modified glass ionomer base is recommended before final
restoration with composite.
19. Finishing the Enamel Walls
It is further development of specific cavosurface design and
degree of smoothness that will bring about the maximum
effectiveness of the restorative material being used.
Purpose:
1. To place the margins on sound tooth structure.
2. To have smooth walls and rounded angles.
3. To facilitate placement and finishing of the restorative material.
4. Placement of taper or bevel for the appropriate restorative
material.
20. Cleansing of the Cavity
The operating field should be kept clean and adequately
isolated by the use of rubber dam, cotton rolls and high vacuum
evacuation equipment should be used.
Conditioning of the cavity may be done in certain cases like
bonding systems for amalgam and composite restorations.
21. Modifications of Class II Cavity
preparation in primary teeth
Due to the presence of broad contact areas, the gingival floor of
the proximal box should be wide so as to place the margins in self-
cleansing areas.
The box should however converge occlusally with the buccal and
lingual wall paralleling the external tooth surface.
The walls of the proximal box should meet the occlusal walls in a
straight line to avoid any stress points.
The walls of proximal box should not be flared as it would lead to
unsupported enamel.
22.
23. The isthmus should not exceed 1/3rd the intercuspal width in primary
molars.
The axiopulpal line angle must be either rounded, tunnelled or
grooved for sufficient bulk of the restoration.
The strength of amalgam at the isthmus area can be increased by an
adequate depth of the preparation.
Retention can be improved by a ‘U’-shaped retention groove along the
dentinoenamel junction of the proximal box.
The weakened cusp is reduced to the level of the pulpal floor of the
occlusal preparation. Mesiodistally the cusp should not be reduced
more than 1/3rd the crown’s mesiodistal length.
24. Since the enamel rods, at the cervical area of the tooth, are oriented
occlusally the gingival seat should not be beveled, rather should
follow the enamel rod inclination.
If the depth of the lesion is farther gingivally, the axial wall should
follow the contour of the external surface. This will prevent pulp
exposure from occurring.
Care should be taken to avoid the mesiobuccal pulp horn from
exposure in the case of small first molars. Since the contact with the
canine is a point contact, the proximal box extension and the gingival
flare can be minimized.
The proximal box should allow the passage of an explorer tip between
its margins and adjacent tooth in all three directions, buccally,
gingivally and lingually.
