Cavity Preparation for Caries Restoration
Caries are the decay of the tooth structure. They can be restored using different dentistry methods. In this article, there is a brief discussion on cavity preparation for caries restoration. Let us examine them.
Modifications of cavity preparation in primary teethAll the principles of cavity preparation of permanent teeth also hold good for the primary teeth. However, a few factors have to be taken into consideration while restoring the primary teeth. These include the following:
- The smaller tooth dimension of the deciduous dentition
- The thin enamel covering the teeth
- Broad contact areas
- Proximity of the pulp chamber to outer tooth surface
- Narrow occlusal table
Class I cavities
- Due to the narrow occlusal table present the isthmus should not be more than 1/3rd the intercuspal distance in the case of a small carious lesion.
- The depth should not be more than 0.5 mm into the dentin.
- The pulplal floor must be flat. Any remaining caries lesion should be removed using round bus.
- Use of preventive resin restoration is advocated rather than the conventional cavity preparation which includes all pits and fissures.
Class II cavities
- 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 cleaning 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 weak points.
- The walls of proximal should not be flared as it would lead to unsupported enamel.
- The isthmus should have just adequate width that is it should not exceed 1/3rd the intercuspal width in primary molars.
- The axiopulpal line angle must be either rounded, tunneled 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 amelodentinal junction of the proximal box.
- When the cavity margins exceeded that of an ideal preparation particularly in the case of a mandibular first primary molar, it is recommended that an overlay of the distobuccal cusp be prepared. 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 lenth.
- Since the enamel rods, at the cervical area of the tooth are oriented occlusally the gingival seat must not be beveled, rather it 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 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 margin and adjacent tooth in all three directions, buccally, gingivally and lingually.
Class III cavity
- When the contact is open, the outline is triangular with base towards the gingival aspect of the cavity.
- Gingival cavity wall is inclined occlusally to parallel the enamel rod direction.
- Retention pills can be placed at the axiobucco gingival and axio linguo gingival point angles.
- A dovetail may be placed in the middle one third of the lingual surface of the tooth. This helps in gaining access to the carious lesion and in facilitating retention of the restoration.
Young permanent first molarsThe following special morphological considerations should be kept in mind while preparing a cavity in a young permanent first molar.
- The first permanent molars erupt between the age of five and six years and this is the age group wherein caries is a common problem. These are often first of the permanent teeth to become carious.
- The result of various developmental interference will often result in failure of the enamel to unite completely and smoothly in the middle of the occlusal surface and there will be potential for faults and defects in the occlusal enamel, even before eruption.
- The occlusal surface of any tooth is particularly susceptible for plaque accumulation within a defect because of the heavy pressure to which this surface is subject to during mastication. Such fissures can be as far as 1.5 to 2mm deep into the enamel and it is possible for them to penetrate right through to dentin.
- They may range in width from 100 to 500 micrometers and will often be wide at the entry, narrow down to less than 200 micrometers and then open wider again at the dentin.
- In many cases, the fissures are made up of a series of pits of considerable depths rather than one continuous fissure.
- The result of this convoluted anatomy may be compaction of bacteria laden plaque into the depths of the fissure leading to active demineralization down the walls and into dentin with minimal visible evidence on the occlusal surface. In communities that have systemic fluoridation the enamel is often very hard and does not breakdown until it is severely undermined. This means that caries that has progressed through to the dentin can progress all the way to pulpal involvement without any visible breakdown on the occlusal surface.
- The enamel rods within a fissure are not always as regular in pattern as those elsewhere around the crown of a tooth. Those at the shoulder around the entry to a fissure are often gnarled and irregular and will not always accept a regular etch pattern. In the depths of a fissure there may be a layer of enamel rods lying parallel to the surface rather than at right angles.
- There is a likelihood of a carious lesion on the distal of the deciduous second molar extending some damage on to the mesial of the adjacent permanent tooth. The carious lesion may become visible and available for treatment at the time the deciduous tooth is exfoliated.
Kinetic cavity preparation
- KCP which used fined particles of powder fired at high speed in a controlled manner instead of the traditional high and low speed drills.
- Advantages of this technique are that no vibrations or pain sensation and also no need for anesthesia in most cases.
- This truly allows us to multiple quadrant dentistry so as to decrease the number of patient visits and better time utilization.