Clinical challenges and the relevance of materials testing for posterior composite restorations
Introduction
Dentists have used composite materials to restore posterior teeth for approximately 30 years [1]. The development of resin-based materials with inorganic fillers came with great promise for a substitute for dental amalgam. It was soon learned that composite was not a true replacement material for amalgam. The first composite materials exhibited rapid loss of anatomic form due to wear when placed in stress-bearing areas [2], marginal staining, and bulk discoloration [3]. These problems were due almost entirely to the properties of the materials [4]. Dentists also found the materials difficult to work with. The fast-curing two-paste chemically activated composite had to be packed quickly into the cavity and could not be built in layers. Rotary burs and abrasives were required to properly shape the restorations; this was a technique the dentists of this time were not accustom to using and special cutting instruments designed for the task were not available. Patients often complained of sensitive teeth, rough surfaces, and discoloration or their restorations.
The mantra of finding an amalgam replacement led dentists to use composite materials as if they were ‘white’ amalgam. The usual matrix bands and condensation techniques used for amalgam restorations were employed for class II composite restorations and the most consistent problem dentists faced was establishing a tight proximal contact. Composite is not condensable (despite the names of some commercial products) and during placement the matrix band does not adapt to the adjacent tooth to establish contact. Creating correct anatomic contours and polishing the final surface, although more difficult than carving amalgam, was achievable in light-activated systems. More time was needed to place posterior composite restorations and thus demanded a higher fee. The extra time required to place composite was consumed by adhesive bonding steps, shaping and polishing with rotary instruments, and control of moisture. Dentist quickly learned that this new posterior restorative material was more technique-sensitive and moisture contamination during placement could not be tolerated. Secondary caries is often cited as a reason for replacement of composite restorations [5], [6], [7], [8], [9] and it is assumed that polymerization shrinkage and loss of adhesive bonding are the causes [10]. Anecdotal reports by dentists indicated that composite restorations were more likely to develop secondary caries and failed much sooner compared with amalgam restorations. Many dentists were discouraged from placing posterior composite restorations because of these concerns. It is important to mention that there was little formal training in the placement of posterior composite restorations in dental schools until the 1990s. Only in the past 5 years have the majority of dental schools included classes I and II composite restorations in the operative dentistry curriculum [11], [12], [13], [14], [15], [16], [17], [18]. Many continuing education programs on esthetic dentistry appeared in the early 1990s attempting to fill the educational void. With a highly technique-sensitive material like composite, clinical outcomes are usually dependent on the dentist's level of training in using the material and knowledge of the material's properties.
Composite restorations must withstand a harsh environment that varies from patient to patient. Mastication forces, occlusal habits, abrasive foods, chemically active foods and liquids, temperature fluctuations, humidity variation, bacterial byproducts, and salivary enzymes all contribute uncontrollable factors that affect composite restoration longevity [19], [20], [21], [22], [23], [24].
This paper reviews what is known regarding the clinical challenges for posterior composite restorations and attempts to dispel some of the dogma that surrounds this restorative treatment. The clinical relevance of laboratory tests is explored from the perspective of solving the remaining clinical challenges of current materials and of screening new materials.
Section snippets
Clinical evaluation of posterior composite restorations
Composite restoration quality is evaluated using a system of clinical parameters developed by Gunnar Ryge [25], [26], [27] while working in the United States Public Health Service in San Francisco and are known as the USPHS Criteria or Ryge Criteria. These criteria were also adapted by the California Dental Association for quality evaluation and are also referred to as Modified USPHS Criteria or USPHS/CDA Criteria Table 1. Most of the existing information on posterior composite restoration
Material-related challenges
It is useful to categorize the challenges that affect clinical outcomes as those related to the material properties, those related to the dentist, and those related to the patient. The composite materials available today have solved the major clinical challenges related to the stability and durability of the material in the oral environment. The excessive wear loss observed in early studies of posterior composite restorations was caused by a combination of factors related to filler composition,
Clinical relevance of laboratory tests
Determining the relevant laboratory tests to predicted clinical performance of posterior composites is not a simple task. As described above, the clinical challenges are multifactorial and there are likely significant interactions among the factors. We do not have a good understanding of the clinical factors and the magnitude of their effect in predicting long-term performance. There is a general lack of hypothesis-driven clinical trials to explore factors that may predict performance. Clinical
Summary and recommendations
The current composite materials have solved many of the clinical challenges that dentists observed relative to stability and durability of posterior composite restorations. Clinical data indicate that the two main challenges are secondary caries and bulk fracture. Polymerization shrinkage has been implicated in marginal discoloration, post-operative pain, and secondary caries. There are no clear clinical data to make this implication for post-operative pain and secondary caries. It is suggested
References (65)
- et al.
Observations on a composite resin for class II restorations: three-year report
J Prosthet Dent
(1973) - et al.
Reasons for replacement of restorations in permanent teeth in general dental practice
Int Dent J
(2000) - et al.
The teaching of posterior composites: a worldwide survey
J Dent
(1989) The teaching of posterior composites: views of recent UK graduates
J Dent
(1989)- et al.
Teaching class I and class Ii direct composite restorations: results of a survey of dental schools
J Am Dent Assoc
(1998) - et al.
The teaching of Class I and Class II direct composite restorations in European dental schools
J Dent
(2000) - et al.
Teaching of posterior composite restorations in Japanese dental schools
Int Dent J
(2000) - et al.
Influence of enzymes and plaque acids on in vitro wear of dental composites
Biomaterials
(1996) - et al.
The effects of alcoholic beverages on composite wear
Dent Mater
(2000) - et al.
Evaluating the clinical quality of restorations
J Am Dent Assoc
(1973)