Longevity of posterior composite restorations: Not only a matter of materials
Introduction
Direct restorations have been largely employed to restore posterior teeth due to their low cost and less need for the removal of sound tooth substance when compared to indirect restorations, as well as to their acceptable clinical performance [1], [2], [3], [4]. Despite the fact that both amalgam and composite resin are considered suitable materials for restoring Class I and Class II cavities, some advantages can be related to composite restorations such as better esthetics; their adhesive properties, resulting in reduced preparation size [5]; and reinforcement of the remaining dental structure [6]. A clinical study has shown that painful vital teeth with incomplete fractures can be treated successfully by replacing the amalgam fillings with bonded composite restorations [7]. On the other hand, posterior composite restorations have been shown to produce higher failure rates due to secondary caries [8], [9]. However, although used in many practices around the world, amalgam is facing its demise, leaving resin composite as the most likely material for posterior restorations for widespread use in the near future.
Even though acceptable survival rates are achieved with Class I and II restorations in dental health care, the replacement of failing restorations is still a relevant issue. Dentists still spend a significant amount of time replacing restorations, contributing to the repetitive restorative cycle described by Elderton [10]. Factors related to the patient, operator, tooth, cavity size, and materials have been reported in the literature as potentially relevant for restoration failures [2], [3], [8], [11], [12], [13], although evidence of this is still limited.
Despite the considerable differences in properties among commercial composites as found in laboratory analysis [14], [15], [16], [17], [18], [19], [20], in vitro tests are limited in predicting the clinical survival of composite restorations. Due to the constant influx of new posterior restorative materials on the market and the need for manufacturers to prove the clinical safety of their new materials, there has been an emphasis on relatively short-term clinical studies with a limited number of restorations, mostly placed in low-risk patients. In those studies, differences in performance are seldom found, as most materials perform well on a short-term basis, with a few exceptions [21], [22].
To estimate how long posterior composite restorations last, long-term studies are needed to identify modes of failure and possible reasons for these failures. In a comparative amalgam–composite study after 5 years, no differences in performance were found; after 12 years, however, the composite showed significantly better performance [12]. Given the considerable differences between (non-bonded) amalgam and composite and the fact that, after 5 years, no differences in performance were observed, it is not likely that the majority of composite restorations will show different longevity when investigated before at least 5 years of clinical service. Because of limited observation times of most clinical studies [4], limited information is available on the performance determinants and reasons for the failure of posterior composite restorations in the long term. Although the rapid evolution of composites makes it difficult for long-term evaluations to be conducted using materials still available in the market, the good results shown with previous and presently available materials in clinical studies [3], [4], [12] foster the question of whether new materials are actually improvements, and the authors tend to conclude that this is not likely. This means that, based on the available long-term studies, especially studies with observation times exceeding 5 years, an expectation regarding the long-term behavior of posterior composite restorations can be made. In the present article, we aim to review and discuss, with an emphasis on the available long-term literature, the longevity of posterior composite restorations, and the main factors associated with restoration failures.
Section snippets
Selection of papers
To investigate the longevity of composite restorations as reported in clinical studies in the dental literature, a PubMed search for articles that evaluated longitudinal data for posterior resin composite restorations published between 1996 and 2011 was performed. The terms used in the search were ‘posterior composite restorations’ and ‘survival’ or ‘longevity’ or ‘failure’. After selecting only papers reporting clinical longevity studies of composite restorations with evaluation periods of at
Clinical
Clinical related factors play an important role in restoration longevity and causes of failure. Several studies have indicated that the position of the tooth in the mouth or the tooth type directly affects restoration longevity, with restorations in premolars showing better performance than those in molars [2], [3], [24], [25], [26]. One paper reported a risk of restoration failure twice as high for molars compared to premolars [24]. One study with a 22-year observation time found the risk of
Main reasons for failure
Table 2 shows the main causes of failure reported by the studies included in this review (Table 1). The two main causes of failure identified were fracture (restoration or tooth) and secondary caries. In a previous review, it was shown that early failures were more closely related to fractures, while studies with long periods of observation showed a trend to find more caries-related failures [1]. However, according to the present review, the same conclusion cannot be drawn since most long-term
Repair as an alternative to replacement
Failed restorations or restorations presenting small defects are routinely treated by replacement by most clinicians. Because of this, for many years, the replacement of defective restorations has been reported as the most common treatment in general dental practice, and it represents a major part of oral health care in adults [100]. When a restoration is replaced, a significant amount of sound tooth structure is removed and the preparation is enlarged [100], [101]. Moreover, the general cost
Overall considerations
Due to their esthetic properties and good clinical service, composites have become the preferred material for direct posterior restorations. When ‘gold standard’ hybrid composites are used, an AFR between 1% and 3% can be expected depending mainly upon factors other than material properties. The main reasons for the failure of posterior composite restorations are secondary caries and fracture. The failure of restorations related to the wear of these materials in the posterior region seems,
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