|SECTION V||RESTORING EACH CLASS OF CARIES|
In 1908, Dr. G.V. Black developed a comprehensive method for preparing and restoring teeth by defining five classes of carious lesions using Roman numerals I through V.16 All lesions that begin in defective pits and fissures are in class I, whereas classes II, III, IV, and V include different types of smooth surface caries. His five classifications are still appropriate when considering principles of cavity preparation for conventional tooth preparations, although now these principles may be modified depending on the restorative material used. For the most part, the terminology and principles to consider when restoring each of Black’s classes of decay presented and illustrated in this section relate to conventional tooth preparations. However, a few modified preparation principles for restoring with composite resin will also be discussed. Before treating each tooth, keep in mind that the dentist has confirmed that the tooth has a healthy periodontium with adequate bony support and that the maintenance of the tooth is an integral part of the overall patient treatment.
1. Class I Caries: Defined and Diagnosed
Class I carious lesions can form in deep enamel pits and fissures that are difficult or impossible to keep clean (Fig. 10-11A, B, D, and E). Detecting class I lesions clinically requires visual inspection and tactile evaluation, that is, feeling for a soft spot. Careful visual analysis of a clean, dry, well-lighted occlusal surface will reveal this type of caries as a carious fissure or pit if it is surrounded by chalky enamel that has lost its translucency compared to the adjacent enamel (Fig. 10-11A). Some dentists prefer to confirm caries within these suspicious defects by probing with a very sharp explorer. When the dentist presses the explorer into the defect with moderate to firm pressure, and upon removal, senses a resistance known as tug-back, this helps to confirm the presence of softness and therefore caries within the defect. However, the firm use of the explorer for the detection of pit and fissure caries should be used with caution. One study suggests that the confirmation of decay based on tug-back may not always be accurate (there might not be decay, just a deep groove), and excessive force could actually damage fragile enamel rods on the tooth.17 Also, the explorer tip may inoculate caries-free teeth with harmful bacteria. Besides, even in the absence of obvious tug-back, loss of translucency of enamel around a pit or fissure may be considered to be reliable evidence of caries. It is especially important to avoid undue pressure with the explorer point into an obvious large lesion with exposed dentin as seen in Figure 10-11B and E since it could be quite painful.
The shape of a class I lesion in cross section within enamel is somewhat triangular in shape with the apex of the triangle barely visible on the enamel surface and its wide base located along the DEJ. Once into dentin, the decay spreads out at the DEJ because dentin is less mineralized than enamel. The spread within dentin forms a triangular shape with its wide base along the DEJ and its apex toward the pulp following the dentinal tubules (Fig. 10-12A and B). That is, the shape of the spread of class I caries through enamel and into dentin is like two triangles with their bases touching at the DEJ.
A class I lesion is usually not detectable on a radiograph until it has spread considerably into dentin because the lesion is superimposed between the thick buccal and lingual surfaces of enamel, which show up whiter (radiopaque), thereby masking the darker color of caries. By the time the cavity is visible on the radiograph (Fig. 10-12C), the size of the preparation required to remove all of the decay would be considerably deeper (toward the pulp) than if the decay had been detected during a good clinical examination when the lesion was smaller. Thus, early class I decay is best diagnosed during a thorough, systematic clinical examination of clean, dry teeth using good lighting and the judicious use of a sharp exploring point. There are new technologies designed to detect caries, but researchers disagree about their accuracy and effectiveness.
2. Class I Caries: When to Restore or Apply Sealants
Some class I lesions are difficult to differentiate from noncarious, deep enamel defects. If there is a hole with obvious tug-back, or the enamel surrounding the defect is chalky or less translucent, a restoration is indicated. However, if tug-back is slight but there is no accompanying evidence, the dentist might consider periodically reevaluating the area during recall appointments, especially if the patient is older and has a low caries rate, since tug-back can occur when probing in deep fissures even when caries is not present.
An alternative to waiting is to apply a dental sealant. A sealant is a “flowable” resin that is applied over noncarious but caries-prone, unprepared pits and fissures. Pit and fissure sealants can be used to prevent class I caries in deep caries-prone pits and fissures, especially on recently erupted teeth of a young patient, such as the permanent molars as they erupt around 6 and 12 years of age. These sealants have been shown to be an effective means of preventing caries from forming in these pits and fissures.18–20 An initial sealant application on all permanent molars and premolars requires only 15 to 20 minutes per child.21
The dentist should not wait until class I caries is obvious on a radiograph since by that time the lesion would be quite large.
3. Class I Preparation and Restoration: Terminology
After removing occlusal decay, the conventional class I preparation using amalgam can be compared to a room with no ceiling that has four vertical walls and a horizontal floor (sometimes called a fifth wall). The four vertical walls are named after the closest tooth surfaces, namely, buccal, mesial, lingual, and distal; the horizontal floor is called the pulpal floor (or wall) because it is over the pulp (abbreviated as B, M, L, D, and P in Fig. 10-13A). The term that describes the junction of the walls of the preparation with the unprepared tooth structure is called the cavosurface. The cavosurface, therefore, is the outline that encircles the preparation.
A line angle in the preparation is the junction or line formed where two walls join. There are eight internal line angles in a conventional class I preparation (if the preparation is confined to the occlusal surface and is not extended into a carious buccal or lingual groove). These are named by combining the terms for the two walls that join to make up each line angle, changing the suffix of the first word from “al” to “o.” The junction of the pulpal floor and distal wall is the distopulpal line angle. All possible line angles in a class I occlusal preparation include four that are horizontal (distopulpal, mesiopulpal, buccopulpal, and linguopulpal) and four that are vertical (mesiobuccal, distobuccal, mesiolingual, and distolingual).
Finally, there are four point angles in a class I preparation, each formed by the junction of three walls (as in the corner of a room where two walls meet the floor). Point angles are named after the three walls that form them: mesiobuccopulpal (abbreviated M-B-P in Fig. 10-13A), mesiolinguopulpal, distolinguopulpal, and distobuccopulpal. Since the junction of walls in a preparation is often rounded, line angles and point angles are most often areas rather than distinct, sharp points.
A class I restoration is properly identified by naming the surfaces involved and material used. For example, an amalgam on tooth #14 involving the occlusal surface with a lingual extension would be abbreviated OL-A, #14 (Fig. 10-14C). The letter O represents the occlusal portion of the preparation, the L represents the lingual extension, and the letter A represents the restorative material, amalgam. If composite had been used, the representation would have been OL-C, #14. A lower right third molar with an occlusal amalgam and buccal extension would be an OB-A, #32. A buccal or lingual pit restored with composite would be a B-C or L-C, followed or preceded by the tooth number.
4. Class I: Applied Principles of Initial Tooth Preparation
If there is a only a minute amount of decay in a groove, the dentist may make a very small preparation, possibly confined to enamel and not extending into adjacent, noncarious grooves, which can be restored with a small amount of composite resin followed by a sealant to protect abutting deep grooves. This restoration is called a conservative resin restoration (previously called a preventive resin restoration). A sealant and a conservative resin preparation are shown in Figure 10-15. Conservative modified preparations can also be formed using an air abrasion system where abrasive particles are blown forcefully toward the tooth to remove a minimal amount of tooth structure. Some principles of cavity preparation apply to this modified tooth preparation such as providing retention, obtaining access to the decay, and extending to sound enamel. Retention is obtained by flowing an initial layer of bonding agent, similar to a sealant, into the irregularities of the microscopically roughened enamel.22,23
Amalgam may also be chosen to restore larger, stress-bearing class I preparations on occlusal surfaces (Fig. 10-14).
a. Outline Form and Initial Depth (Class I)
When using amalgam, the outline form may be extended to include those pits and fissures adjoining the defects with suspected decay, especially when the patient is young, has a high caries rate, and/or exhibits poor oral hygiene. However, sealants may also be used to protect adjacent pits and fissures. Examples of several amalgam preparations that have been extended into all major grooves can be seen in Figure 10-16.
b. Primary Resistance Form (Class I)
When amalgam is used on a stress-bearing surface, a minimum total preparation depth (of 1.5 to 2 mm) is recommended due to the brittleness of amalgam in thinner layers (Fig. 10-13B). The buccal and lingual cavity walls each form almost a right angle with the uncut tooth at the cavosurface that permits a good bulk of amalgam that abuts against a strong enamel surface (Fig. 10-13C). When restoring with composite, a modified preparation does not require a flat, evenly deep pulpal floor.
c. Retention (Class I)
Retention for amalgam in an occlusal preparation is provided by forming a slight convergence of the buccal and lingual preparation walls toward the occlusal surface (Fig. 10-13C). For modified composite preparations, retention is also provided by acid etching the enamel to produce microscopic irregularities on the surface that can be filled with a first layer of flowable bonding agent.
Amalgam may be chosen for larger stress-bearing class II restorations using a conventional preparation, but when esthetics are important, composite resins can be chosen using modified preparations, possibly in conjunction with sealants to protect, rather than cut into, adjacent susceptible pits and fissures.
1. Class II Caries: Defined and Diagnosed
Class II decay forms on the smooth proximal surface of posterior teeth just cervical to the proximal contact (Fig. 10-17A and B). It forms due to inadequate plaque removal in the hard-to-reach interproximal surfaces. Judicious use of dental floss to frequently remove bacterial plaque between posterior teeth is one method for preventing (and with fluoride, possibly reversing) class II caries.
Clinical detection of a small class II lesion in the mouth without the aid of radiographs is often difficult due to the inability to visualize or probe the areas where it forms. A loss of translucency of the enamel on the overlying marginal ridge may be the first clinical evidence of class II caries (Fig. 10-18). As a carious lesion increases in size, it may appear as a dark, cavitated area (hole) that can be detected by a using a thin probe (explorer) into the interproximal space. A very large class II lesion may actually undermine the marginal ridge, causing the entire ridge of enamel to break off during mastication (Fig. 10-17D).
Radiographic detection of an incipient class II lesion (i.e., a lesion that is just beginning and still quite small) is most predictably accomplished by using bitewing radiographs because a class II lesion is normally visible on the radiograph before it can be detected clinically. A class II lesion is seen as a narrow triangular shadow within enamel just cervical to the proximal contact (Fig. 10-19A and the distal of tooth #20 in Fig. 10-19B). Unlike the spread pattern of class I caries, the wide base of its triangular shape is located at the enamel surface, and it tapers to its apex toward the DEJ. When the lesion gets large enough to spread into dentin, the spread pattern is the same as for class I caries: it is triangular in shape with a base that spreads out along the DEJ and an apex that follows the dentinal tubules toward the pulp (seen on the distal of tooth #12 in Fig. 10-19C and in cross section in Fig. 10-19A and D).