DENTAL HISTOLOGY AND PRIMARY DENTAL CARE Saving Pulps––—A Biological Basis. An Overview

Many new technologies with potential application to dentistry are on the horizon, including tissue engineering, gene and growth factor therapy, although there are a number of problems to overcome1 before these might be introduced clinically. However, the dentine-pulp complex has strong natural regenerative capacity and exploitation of these biological repair processes can allow current approaches to restorative dentistry to be optimised.2 Our understanding of these biological processes has significantly advanced with appreciation that many of the cellular and molecular processes of tooth development appear to be recapitulated during dental tissue repair.3 Importantly, dentine seems to be far less inert than previously recognised and contains many components capable of stimulating pulpal cell responses. Growth factors, especially those of the Transforming Growth Factor-beta (TGF-β) family, are important in cellular signalling for odontoblast differentiation and stimulation of dentine matrix secretion. These growth factors are secreted by odontoblasts4 and deposited within the dentine matrix5,6 where they remain protected in an active form through interaction with other components of the dentine matrix.7 Carious demineralisation of the dental tissues can lead to their release as can application of cavity-etching agents and restorative materials like calcium hydroxide.8,9 Once released, these growth factors may play key roles in signalling many of the events of tertiary dentinogenesis, a response of pulp-dentine repair. Consideration of how these biological processes are influenced by current restorative treatment may influence treatment outcomes. A high proportion of restored teeth show symptoms requiring endodontic treatment and 60% of all restorations are replacements for failed restorations.10 Thus, current restorative treatment regimens still have limitations and it is important to re-evaluate all aspects of cavity preparation and restoration to identify those factors most likely to increase the success of restorative treatment. In this review, we have investigated human pulpal responses to a range of common restorative materials and have part icularly focused on factors that might influence restoration longevity. The clinical diagnosis of secondary caries is by far the most common reason for replacement of restorations,10 but the scientific basis for the diagnosis is meagre.11 However, restoration fai lure may arise from surgical trauma and bacterial microleakage into cavity margins.12 Thus, we have also examined the relationships between bacterial microleakage and restorative materials, as well as pulpal inflammation and pulp necrosis. The importance of the remaining dentine thickness (RDT) beneath cavity preparations to pulp injury has long been recognised, although the quantitative relationships between cavity RDT, cavity dimensions, or restorative materials and pulpal injury and repair remain uncertain. Understanding and being able to predict pulpal reactions to cavity preparation and restoration events has many advantages for the practitioner, one of the most obvious being the ability to make treatment decisions which exploit the natural repa i r responses o f the too th . Deviations from the expected pulp responses to restorative treatment DENTAL HISTOLOGY AND PRIMARY DENTAL CARE