ReviewQuantifying and qualifying surface changes on dental hard tissues in vitro
Introduction
Tooth surface loss (TSL) is an increasingly recognised problem.1 We are therefore seeing an increase in the number and complexity of in vitro studies investigating factors that modify effects at the tooth surface.2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 Often studies only quantify the amount of tooth loss; there are relatively few attempts to describe or qualify the remaining surface beyond descriptors such as hardness, or producing a visual representation of the sample surface. Quantified results are often considered fundamental in order to compare laboratory measurements. Surface quality is reported less often, but has the potential to account for particular surface characteristics that determine how future loss may progress. The aim of this paper is to provide a narrative review that illustrates the more commonly used in vitro methods (both historical and contemporaneous) that are available for measuring surface loss and surface change. Equally important are in vivo measurements, but discussion of these is not within the scope of this paper; they are reviewed elsewhere.31, 32
Section snippets
Data sources
An initial search (March 2009) was carried out using Scopus abstract and citation database with the keywords: ‘dental’ AND ‘erosion OR abrasion’ AND ‘surface change OR surface loss’ AND ‘vitro’ (1975–2009). This resulted in 69 papers which were reviewed and the methods critically appraised. Bibliographic material from the papers was then used in order to find other appropriate sources.
The effects of scale
With direct visualisation33 of the tooth surface, accurate tissue loss is very difficult to determine. Even when tissue loss is identified, the remaining surface's textural characteristics cannot be accurately described. Clinically, more advanced techniques such as stereoimagery34 may provide a clearer, more accurate explanation of the patterns of surface loss. These techniques, however, still fail to qualify the surface change that occurs.
Micro- and nanoscopic techniques
Polarised light microscopy (PLM) was originally used
Bearing parameters
In 1933, Abbott and Firestone defined the ‘bearing area curve’.95 The bearing curve has been used to assess engineered surfaces in medicine96 (mainly that of femoral stem wear). Its use to monitor erosion was first mentioned in 199797 and, more recently, it has been used to describe the native enamel surface.98 The bearing curve represents the cumulative distribution of the lengths of individual plateaux, normalised by the total assessment length. If this ratio was plotted against sample
Discussion
It is clear that tooth surface change is a complex process that can be measured in a variety of ways. No single technique provides a comprehensive assessment of the remaining tooth surface, and each technique suffers its own limitations (whether that is sample destruction, the inability to assess certain characteristics of the remaining surface, or difficulty in interpreting the results). What is also clear is that way in which surface change is reported by each of the techniques gives little
Conclusion
Despite a variety of available in vitro tests for measuring surface changes, the roughness average (Ra) is still the main reported measurement within dental studies. Using the same set of profilometric data, it is proposed that additionally reporting bearing area parameters will allow a further and more meaningful description of the surface quality.
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