Retention of a restoration is markedly influenced by the type of luting cement, and restorations cemented with an adhesive lute require much higher forces to dislodge them. Advances in adhesive techniques have added another mode of treatment in addition to more conventional techniques. Resin-based composite materials may be reliably bonded with similar resin-based luting cements, which may also be for luting ceramic restorations following etching and silane treatment of the ceramic fitting surface. Base metals may be bonded to tooth structure with bi-functional polymeric resins, for example phos-phonated esters of Bis-GMA (bisphenol A-glycidyl methacrylate), and gold may also be reliably bonded to tooth structure following heat-treatment18 (to produce a chemically active oxide layer on the fitting surface of the restoration). Although long-term studies are limited, there is clinical evidence that indirect restorations bonded to tooth structure survive well in the oral environment19.
Adhesively bonded restorations may permit preservation of tooth structure when compared with more destructive traditional options. For example, the use of bonded restorations to prevent cusp fracture rather than reducing and overlaying cusps. Adhesive techniques are also very useful when retention is at a premium and when a traditional preparation would involve removal of a large amount of healthy tooth structure or may result in exposure of the pulp.
Adhesively retained restorations often prove useful in restoring defects caused by tooth wear/non-carious tooth tissue loss (NCTTL). Anterior NCTTL typically occurs on palatal surfaces and these may be restored with cobalt-chromium or gold veneers cemented with resin. This technique is relatively easy. Maximal coverage up to and including the incisal edge is provided to increase retention and aid placement. Thin metal palatal veneers can also be used in conjunction with labial resin composite to increase tooth length. Posterior NCTTL can also be restored with adhesively retained gold castings, which are useful when space is limited.
There are also situations in which adhesive restorations may prove useful when traditional alternatives give limited options. A common example is the situation of an upper premolar that has a large restoration spanning from one proximal surface to the other across the occlusal surface and has suffered a cusp fracture. The most conservative traditional treatment option would be to place a core and a partial-coverage, three-quarter gold crown. However, the visibility of gold is not very aesthetic and is often unacceptable to patients. The traditional aesthetic alternative would be to place a full-coverage metallo-ceramic crown with ceramic on the visible parts of the tooth; however this would require removal of a significant amount of tooth structure. The use of an adhesive restoration would allow for an aesthetic onlay/inlay to be directly bonded to the remaining tooth structure with little additional preparation.
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