Naturally occurring secondary caries was described in the early 1970s as being formed by two components: the primary surface lesion (outer lesion) and the cavosurface lesion (wall lesion). These findings were subsequently confirmed by others over the remainder of that decade.
It is well-recognized that natural and in vitro (artificial) caries begin within the enamel or root surface adjacent to the restorative material. The presence of crevices, microspaces or voids at the cavosurface and along the cavity wall–tooth interface becomes of importance once the caries process is established in the enamel or root surface adjacent to the restoration.
It has been well-established that the crevice size adjacent to a restoration is not a predictor of whether secondary caries has occurred or will occur. However, the presence of crevices in individuals at moderate-to-high risk of caries development, based on prior caries experience and/or current caries risk factors, is of special concern for secondary caries development. While the vast majority of caries-free or low-caries–risk individuals have noncariogenic bacteria in their dental plaque, those individuals with moderate-to-high caries risk possess cariogenic bacteria that place them at particular risk of secondary caries development.
It is well-recognized by academically oriented clinician-researchers that the cavosurface (wall) lesion in secondary caries (natural or in vitro) is due initially to microleakage along the interface between the cavosurface and restorative material. This allows for percolation of acidic byproducts into the microspace and potential dissolution and widening of the microspace between the cavosurface and restorative material, allowing ingress and colonization by cariogenic bacteria in susceptible (moderate-to-high caries risk) hosts.
A variety of methods have been used to study secondary caries formation and progression adjacent to coronal and root surface restorations within the laboratory setting. In vitro carieslike systems have been employed to better understand the role of various restorative materials (adhesive and nonadhesive), cavity-sealing agents (adhesive and nonadhesive), caries preventive agents (fluoride, calcium-phosphate minerals, amorphous calcium phosphate [ACP], ACP-casein phosphopeptide, heavy metals) and remineralizing agents (calcium-phosphate fluoride solutions, rinses, gels, toothpastes). Such in vitro studies have repeatedly demonstrated the beneficial effects of preventive and remineralizing agents on primary surface caries (outer lesions) and the cavosurface lesion (wall lesion due to microleakage).
Results from laboratory studies are always couched with a realization that the clinical situation may be vastly dissimilar, due to the multiplicity of factors involved in secondary caries formation. However, several clinical studies have shown that the addition of fluoride to amalgams and the use of atraumatic restorative techniques (glass ionomers) demonstrate remarkable secondary caries reduction in children from third-world nations and developing countries.
In the primary and permanent dentition of children, it has been shown that, when glass ionomers and amalgam Class II restorations are compared, there is a remarkable reduction in caries occurrence in the proximal surfaces of adjacent teeth, as well as reductions in secondary caries.
With all laboratory studies, it is not possible to reproduce the clinical milieu associated with oral diseases, such as caries, gingivitis and periodontal disease. The purpose of laboratory studies is to provide a certain level of insight into the potential that a specific procedure, technique, medicament or material may have on oral diseases.
The difficulties with clinically based studies of caries, gingivitis and periodontal disease are well-documented in the dental literature. The lack of funding by government and private sources is also well-known to academically oriented clinicians-researchers.
If the potential of a dental restorative material or caries preventive agent can be provided to the general dental practitioner in an informative, timely and cost-effective manner, then a laboratory study has met its primary goal as a means to be an effective initial screening process: no more, no less.
References to document the above statements are found in the references listed below.1–7
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