Supragingival Minimally Invasive Bonded Onlays: The Replacement for Full Crowns
The indication for supragingival minimally invasive bonded onlays is simple: Any situation where the need for a full crown would have been identified and the tooth has not yet been cut for a crown. It is always preferable to make restorative dentistry healthier by retaining a supragingival margin and preserving tooth structure. Nevertheless, this is a departure from the popular view and traditional recommendations for bonded onlays. Bonded onlays have been indicated for simple cases that fulfill strict requirements, such as sufficient tooth structure available (Figure 5.1a–c), acceptable tooth color (Figure 5.2a–c), ideal location in the arch (Figure 5.3a–d), existing supragingival margin (Figure 5.4a–d), ideal occlusion (Figure 5.5a–g) [1,2,3,4,5]. When these requirements are not fulfilled, traditional full crowns have been indicated. With such strict recommendations, it is not surprising that well over 95% of teeth needing an indirect restoration end up being prepared for full crowns .
Indirect restoration should be reserved for badly damaged and weakened teeth. Less damaged teeth should be repaired with direct composite restorations. Direct composites can serve the patient very well. They allow for tooth structure preservation, are less costly for the patient and have excellent durability (Figure 5.6) . Additionally, experience and clinical studies show that direct composites can perform as well as or may outperform indirect inlays . For this reason, I do not recommend the use of indirect inlays. Only when the tooth is badly damaged, including badly weakened or missing cusp or cusps, or in the case of a fracture, is the option of an indirect onlay preferred to a direct composite. While it is possible to restore such teeth with a direct technique, it is more difficult and time consuming to perform a free-hand reconstruction of the morphology of a tooth’s occlusal surface, and the results are usually less than ideal. Additionally, some degree of fracture resistance is added by constructing the occlusal surface with a higher-modulus, strong, restorative material, such as porcelain. Very large composites, as in the case with very large amalgams, are less durable and predictable [9,10,11]. Endodontically treated posterior teeth should have full occlusal coverage  but are ideal for supragingival minimally invasive onlays, which preserve more of the already badly compromised tooth (Figure 5.7a,b) .
Clinical experience and the literature show that different outcomes can be expected from restoration, depending on the amount of remaining tooth, extension of the caries, old restorative material or fracture, as well as other circumstances. For these reasons, modifications and different types of preparation and restoration should be considered . Posterior teeth requiring an indirect restoration can be divided into three major categories:
- simple partial and full coverage on vital teeth;
- complex partial and full occlusal coverage requiring buildups on vital teeth; and
- complex full coverage on endodontically treated teeth or teeth with vertical fractures.
In cases where one or more of the cusps are undermined, fractured or missing, and must be onlayed (Figure 5.8a–d), a direct restoration would not be indicated. Simple cases have ideal, natural, tooth color, and the amount of remaining tooth structure, especially the periphery of the enamel, is sufficient, the final preparation is more than 2 mm from the pulp, and the existing margins are supragingival. Using a supragingival protocol would allow the margins to remain supragingival, without the need for dentin sealing or buildups. These are the cases that most experts recommend for bonded onlays. Currently, however, these cases are usually treated with full crowns (Figure 5.9a–e) . Full-mouth rehabilitation is also well suited for simple onlay preparation. Many of these cases are in patients with severe occlusal wear, and, although some experts consider severe occlusal wear a contraindication to bonded onlays , condemning these patients to a mouth full of crowns, much experience shows that bonded onlays cases have excellent results in such patients (Figure 5.10a–e).
Badly damaged vital teeth require dentin sealing and some type of buildup, such as where the caries is very close to the pulp, where large undercuts and a weak cusp or cusps need to be reinforced, and cases where the caries is deep at the cervical margin area, and where enamel margin preservation techniques or margin elevation technique must be performed (Figures 5.11a–c, 5.12a–d). As these teeth are vital, color is usually not generally an issue. Traditionally, these cases have been recommended for crowns. Nevertheless, with the advances in adhesion, and materials, and by implementing a supragingival protocol, these cases can be very successful with partial coverage supragingival restorations.