The incidence of non-carious cervical lesions (NCCLs) has been increasing. The clinical performance of resin composites in NCCLS was previously unsatisfactory due to their non-retentive forms and margins lying on dentin. In order to address this problem, a lot of effort has been put into developing new dentin adhesives and restorative techniques. This article discusses these challenges and the criteria used for evaluating clinical performance as they relate to clinical studies, especially long-term clinical trials. Polymerization contraction, thermal changes and occlusal forces generate debonding stresses at adhesive interfaces.
In laboratory studies, we have investigated how these stresses can be relieved by various restorative techniques and how bond strength and durability can be enhanced. Lesion forms, restorative techniques, adhesives (adhesive strategies, bond strengths, bond durability, and the relationship between enamel and dentin bond strengths) were found to have a complex relationship with microleakage. With regard to some restorative techniques, only several short-term clinical studies were available.
Although in laboratory tests marginal sealing improved with a low-viscosity resin liner, an enamel bevel or prior enamel etching with phosphoric acid, clinical studies failed to detect significant effects associated with these techniques. Long-term clinical trials demonstrated that adhesive bonds continuously degraded in various ways, regardless of the adhesion strategy used.
Early loss of restoration may no longer be the main clinical problem when reliable adhesives are properly used. Marginal discoloration increased over time and may become a more prominent reason for repair or replacement. Reliable and standardized criteria for the clinical evaluation of marginal discoloration should be established as soon as possible and they should be based on evidence and a policy of minimal intervention.
Non-carious cervical lesions (NCCLs), which may be caused by erosion, abrasion and/or occlusal stress (‘abfraction’), are commonly observed in clinical practice . Restorations for NCCLs are necessary to relieve hypersensitivity, to prevent further tooth structure loss, and to improve esthetics. Unfortunately however, the longevity of resin-based composite restorations for NCCLs was previously unsatisfactory compared to that of anterior approximal restorations . The main reasons for failures were loss of the restoration, secondary caries and/or marginal discoloration . This is probably because NCCLs have a non-retentive cavity shape and margins lying on dentin or cementum, which are unfavorable for bonding. In addition, the dentin in NCCLs tends to be sclerotic. Duke et al. have suggested that the more sclerotic that dentin becomes, the more difficult it is to establish adhesion. When we started our laboratory studies, it was speculated that the prevalence of NCCLs would likely increase as a nation’s population ages and as the survival times of teeth increase. For the benefit of public oral health, the clinical longevity of restorations for NCCLs requires an urgent improvement. In order to get more insight into this clinical problem, we first performed a series of laboratory studies on clinical placement techniques of cervical resin composite restorations by means of microleakage tests and then we have been conducting clinical trials . The aim of this article is to discuss the challenges we faced in the clinical placement and evaluation of cervical resin composite restorations as they relate to clinical studies, especially recently published, long-term clinical trials .