Dentin bonding systems: the latest generation.

Abstract

SUMMARYSeveral points should be kept in mind regarding the content of this paper. First, laboratory data may not be an accurate predictor of clinical success, particularly with regard to dentin bonding agents. Methods to evaluate bond strength and bond integrity through marginal leakage studies are not conducted on comparable models. Bond strength is measured on a one‐dimensional model, whereas leakage is assessed on a three‐dimensional model. A system may show creditable bond strength values, but may allow leakage. The problem does not necessarily lie in the model, but in the current resin formulations. It has been shown that shrinkage of the resin during polymerization may not disrupt the dentin‐resin bond in a one dimensional physical test model, but may be of significant magnitude to do so in a three‐dimensional one. The latter is similar to that encountered in the clinical situation and may help to explain the lack of clinical success with earlier systems. These systems showed creditable bond strength data, but all exhibited gap formation and leakage when three‐dimensional preparations were evaluated. Insufficient data are available in the area to draw any conclusions regarding the latest generation of bonding agents, which produce greater bond strengths and may resist disruption from polymerization shrinkage.The second point to be made is that laboratory investigations have seldom taken into account the physiologic status of dentin encountered clinically. This tissue together with the pulp are morphologically and physiologically inseparable. Of special interest is the role of dentinal fluid and the hydration state of dentin. Only recently have models been developed to study the influence of dentinal fluid flow on adhesion to dentin. The hydration state of collagen significantly affects its cohesive strength. Such influences may have been underestimated. It may be particularly pertinent with this latest generation of bonding agents since pretreatment opens tubules and would consequently increase fluid flow.The third point relates to the integrity of the dentin‐resin bond and, indeed, the integrity of the hard‐ and soft‐tissue tooth complexes as a whole. Laboratory tests may involve thermal cycling to stress the integrity of a bond, but very seldom has cyclical physical stress been introduced. Class V erosion lesions may provide the ultimate challenge to a bonded restoration for the lesion itself is believed to be the result of tissue degradation through localized stress concentration. More research is needed in this important area. The dental tissues deform microscopically under load, a property important to their survival, for example, cusps flex. It may seem a noble idea to bond a bulk of resin to enamel and dentin in order to strengthen the anatomic unit, but it must be remembered that the physical properties of current restorative materials do not match those of dentin and enamel, which differ even between themselves. There is much research, both laboratory and clinical, yet to be done.