Fundamentals of Fixed Prosthodontics. James C. Kessler
Tunnel preparation and glass ionomer can be used to restore an incipient lesion on the proximal surface of a posterior tooth.
Fig 6-4 Root caries restored with glass ionomer.
Fig 6-5 Rampant caries can be brought under control with glass ionomer.
Tooth preparation size for incipient lesions has diminished in recent years as the popularity of the concept of “extension for prevention” has waned. This move toward less destructive preparations has been augmented by the development of smaller instruments and stronger amalgams. Nonetheless, even a minimal preparation for an amalgam restoration significantly weakens the structural integrity of the tooth.9
Complex amalgam
Amalgam augmented by pins or other auxiliary means of retention can be used to restore teeth with moderate to severe lesions in which less than half of the coronal dentin remains (Fig 6-9). Amalgam used in this manner can be employed as a definitive restoration when a crown is contraindicated because of limited finances or poor oral hygiene. It can be used in the restoration of teeth with missing cusps or endodontically treated premolars and molars—teeth that ordinarily would be restored with mesio-occlusodistal (MOD) onlays or other extracoronal restorations. In such situations, amalgam is used to replace or overlay the cusp to provide the protection of occlusal coverage. Although amalgam produces good strength in the restored tooth,10 ideally a crown should be constructed over the pin-retained amalgam, using it as a core, or foundation restoration.
Fig 6-6 Composite resin is commonly used to restore Class III and Class V lesions on anterior teeth.
Fig 6-7 Indirect inlays of composite resin can be used for proximo-occlusal restorations on posterior teeth.
Fig 6-8 A simple amalgam restoration placed in an MOD preparation on a molar.
Fig 6-9 A complex amalgam restoration replaces a missing cusp on a molar.
Fig 6-10 A metal inlay is used to restore a molar.
Fig 6-11 Ceramic inlays can be used to restore posterior teeth.
Fig 6-12 An MOD onlay for a maxillary premolar.
Metal inlay
Teeth with low esthetic requirements and small- to moderatesized lesions can be restored with metal inlay restorations (Fig 6-10). Although usually made of softer gold alloys, metal inlays also can be fabricated of etchable base metal alloys if a bonding effect is desired.11,12 The preparation isthmus should be narrow to minimize stress in the surrounding tooth structure. Premolars should have one intact marginal ridge to preserve structural integrity and minimize the possibility of coronal fracture.
The additional bulk of tooth structure found in a molar permits the use of this restoration type in an MOD configuration. The indications for this type of restoration are much the same as those for an amalgam because this restoration only replaces lost tooth structure and will not protect remaining tooth structure. Because of the amount of destruction of tooth structure required by this restoration, it is not recommended for incipient lesions.
Ceramic inlay
Ceramic inlay restorations are used to restore teeth with smallto moderate-sized lesions that permit a narrow preparation isthmus in an area of the mouth where the esthetic demand is high. Premolars should have one intact marginal ridge, but MOD ceramic inlays can be used in molars (Fig 6-11). This type of restoration can also be etched to enhance bonding, and there is some evidence that the structural integrity of the tooth cusps may be stabilized by bonding.13 The relatively large size of the cavity preparation required for this restoration precludes its use in the treatment of incipient lesions.
Mesio-occlusodistal onlay
This design can be used for restoring moderately large lesions on premolars and molars with intact facial and lingual surfaces (Fig 6-12). It will accommodate a wide isthmus and up to one missing cusp on a molar. If a cast metal restoration is needed on a premolar with both marginal ridges compromised, it should include occlusal coverage to protect the remaining tooth structure. This restoration also can be considered an extracoronal restoration because of the occlusal coverage that overlays and protects the tooth cusps.
The MOD onlay does not have the necessary resistance to be used as a fixed partial denture retainer. Although ordinarily fabricated of a gold alloy, this restoration design has been used with cast glass and other types of ceramics. Ceramic MOD onlays should be used very cautiously. Without generous occlusal thickness, these restorations are susceptible to fracture.
Extracoronal Restorations
If insufficient coronal tooth structure exists to retain the restoration within the crown of the tooth, an extracoronal restoration, or crown, is needed. It may also be used where there are extensive areas of defective axial tooth structure or if there is a need to modify contours to refine occlusion or improve esthetics.
Partial coverage crown
This is a crown that leaves one or more axial surfaces uncovered (Fig 6-13). Therefore, it can be used to restore a tooth with one or more intact axial surfaces with half or more of the coronal tooth structure remaining. It will provide moderate retention and can be used as a retainer for short-span fixed partial dentures. If tooth destruction is not excessive, a partial coverage crown with a minimally extended preparation and carefully finished margins can satisfy moderate esthetic demands in the maxillary arch.
All-metal crown
The all-metal conventional crown can be used to restore teeth with multiple defective axial surfaces (Fig 6-14). It will provide the maximum retention possible in any given situation, but its use must be restricted to situations where there are no esthetic expectations. This will usually limit it to second molars, some mandibular first molars, and occasionally mandibular second premolars. Because less tooth structure must be removed for its preparation than for crowns with a ceramic component, and because its fabrication is the simplest of any crown, this restoration should remain among those designs considered in planning single-tooth restorations