I.  Clinical Detection of Tooth Structure and Dental Restorative Materials

A.  Identification of Tooth Structure and Restorative Materials

Many areas of tooth structure and types of restorative materials are easily identified. At times during an examination or scaling, however, it will be difficult to distinguish between exposed dentin and a recent, well-placed composite resin restoration. In such instances, the restorations can be overlooked, and an inappropriate polishing procedure may result.

Table 14.1 was developed as a guide for the hygienist to differentiate between tooth structure and restorative materials and between the different types of restorative materials.

1.  An Example

Using Table 14.1 to distinguish between dentin and a glass ionomer restoration, several statements may be made: both may appear radiopaque. In addition, dentin feels smooth to the explorer, whereas glass ionomer feels rough.

A detectable margin also differentiates these two materials. If a sharp explorer were to pass over these two surfaces, a variance in sound would be noted, with the dull sound being peculiar to the glass ionomer. The sound referred to as sharp or dull is slight and, in all probability, is a combination of auditory and tactile sensations perceived by the operator. Another way to explain this concept is that most clinicians would agree that enamel has a certain hardness and smoothness to it, whereas restorations may have a different texture and feel.

Using only the criteria listed in Table 14.1, rapid identification can be made. If the hygienist is unaware of the presence of the restoration and scales from the dentin surface of the tooth (in an area of gingival recession) onto the composite with heavy pressure, damage could be done to the restoration. A careful analysis of the restorative materials used on the patient must be carried out before initiating any form of treatment.

2.  Other Criteria to Aid in Identification

a.  Radiographic Characteristics

The shades of gray between the extremes of radiolucency and radiopacity aid the trained clinician in identifying tooth structures and materials. This information is discussed in Chapter 15, Radiographic Appearance of Dental Tissues and Materials.

b.  Visual Appearance

Tooth enamel is the only natural material in the oral cavity that is translucent to visible light. Dentin has more color (yellow) and is much more opaque. In recent years, considerable efforts have been made to develop tooth-colored restorative materials that transfer light in a manner similar to that of tooth structure. This was discussed in detail in Chapter 5, Direct Polymeric Restorative Materials. These characteristics are evident in both ceramic materials and resin; the restorations made from these materials are difficult to be detected by casual observation. At times, an experienced clinician will detect a restorative material because it looks very homogenous in appearance rather than the slight variations present in enamel and dentin.

c.  Surface Smoothness

In respect to surface smoothness, it could be stated that all exposed tooth surfaces in the oral cavity should be smooth. When a surface is smooth, it is free of irregularities. An explorer passed over this type of surface will glide freely with the change in contour and will not meet resistance.

One of the goals of the hygienist is to produce smooth surfaces on both natural tooth structure and restorative materials. Less plaque and debris accumulate on smooth surfaces.

d.  Sound and Touch

A sharp explorer can be one of the most helpful diagnostic tools available to the astute hygienist. Passage of the tip of the explorer at right angles to the surface with minimal pressure and force will transmit two distinct sensations to the hygienist.

e.  Location

The location of the restoration can make the identification of tooth-colored restorations difficult. Depending on the material used, the age and marginal integrity of the restoration, the junction of the enamel, and the restorative material are often visually indiscernible. For this reason, the clinician should make the most of radiographs and proper transillumination with the mouth mirror to identify the exact location of the restoration before using any instrument.

B.  Management of Restorative Dental Materials during Scaling and Polishing

After the dental hygienist has identified the patient’s various restorative materials, the selection of cleaning agents, instruments, and specific techniques is made. Polishing agents, instruments, and procedures are designed to aid the clinician in producing highly polished surfaces on the teeth, restorations, and appliances.

Smooth surfaces on tooth structure and restorative materials are less receptive to bacterial colonization and dental plaque formation. Coronal polishing, which may take place after scaling and root planing, must be accomplished in a way that is not damaging to the tooth and restorative materials. Fairly common examples of detrimental procedures include production of excessive heat during polishing, excessive use of abrasives, damage to the margins of cast restorations, and the use of high-speed instrumentation.

1.  Production of Excessive Heat during Polishing

Heat is generated when an abrasive rubber cup and handpiece is used against a natural tooth surface. Rotating a bristle brush, rubber cup, or rubber wheel on a thumbnail readily demonstrates how quickly excessive heat can be generated by speed or pressure. Adding mouthwash, water, or glycerin to make a slurry when abrasives such as silex or tin oxide are being used will reduce the amount of heat that is produced.

Prophylaxis pastes supplied in unit doses are moist so that less heat is produced. It only takes once or twice for a patient to jump during polishing for the clinician to learn that excessive heat has been generated. The cause could be the cup is left on the tooth too long, too much pressure is applied, or too much speed is used by the clinician.

Temperatures of 140°F or greater will alter the surface characteristics of an amalgam restoration because of a release of mercury. This will result in accelerated corrosion and marginal breakdown.

2.  Excessive Use of Abrasives

Excessive use of abrasives can be injurious to patients in several respects. Improper use of an abrasive agent and a rubber cup at the gingival margin can cause trauma to or removal of the surface epithelium in that area.

As is discussed in Chapter 16, Polishing Materials and Abrasion, abrasive agents can be harmful because of the following factors:

• Particle size of the polishing agent
• Number of particles applied per unit of time
• Speed of the application
• Amount of pressure applied

It is for these reasons that selective polishing has become an accepted alternative treatment to polishing with abrasives.

A study of the surface roughness of restorative materials after polishing with polishing pastes showed that many restorative materials were rougher after polishing. Gold, amalgam, and microfilled composites were used in this study. It must be remembered that for cast gold restorations, such as inlays, onlays, or crowns, the final polish applied in the dental lab provides the smoothest surface these restorations will have during patient service. Many polishing agents can create fine scratches in several restorative materials because of speed, pressure, and particle size. The hygienist should make a dedicated effort to use a polishing agent containing the smallest abrasive particle that will remove surface stain and attached plaque.

3.  Damage to Margins of a Cast Restoration

A third way in which damage could be incurred on a restored surface during scaling is by opening a margin of a cemented casting. This particular type of restoration is likely to have a detectable margin. More so than gold foil or amalgam restorations, cemented castings (inlays, onlays, and crowns) will have a “cement line” margin. A properly mixed cement should have a film thickness of less than 40 microns. The margins of cast restorations are delicate, and they have been adapted to the preparation by the dentist. Margination is the process of using hand instruments from cast metal to tooth, to adapt the margins of the gold casting to the tooth preparation. Because the longevity of the cast restoration depends, in part, on the condition of the margin, it is critical that the margin be identified. When scaling in the area of a cast restoration, the dental hygienist should alter his or her scaling technique so as not to jeopardize the margin of any cemented casting.

Figure 14.1A illustrates the casting in place and a thin, fragile gold edge over the beveled margin (the sloping or angled edge of the preparation) of the tooth. A potential position of a curette scaler is shown in Figure 14.1B, and Figure 14.1C depicts the results of an applied working stroke. The scaler has engaged the gold edge and lifted the gold up and away from the tooth. The margin of the restoration is now “open.” Note that destruction of the marginal integrity can lead to recurrent decay, which can be seen in Figure 14.1D.

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