Secondary caries in situ: minimal gap size and MMP inhibitor

Recent research has shown that secondary caries can develop in smaller gaps
than originally thought. In the in situ study of Kuper et al. (2014) it was
shown that even in a gap of 68 µm secondary caries wall lesions could develop,
compared to the originally assumed gap size of 225 µm (Thomas et al., 2007) or
400 µm (Kidd et al., 1995). However, not in all volunteers wall lesions
developed in all gaps. It was observed that high caries risk patients showed
more often wall lesions in smaller gaps than low caries risk patients. So it is
hypothesized that wall lesion development may exhibit a threshold for gap size,
possibly depending on the caries risk of the patient. The first rationale of
this study is to investigate what the threshold gap size is for secondary
caries development and whether the caries risk of patients influences this
threshold.
The other aim of this study is to investigate the role of MMP-inhibitors on
secondary caries development. Matrix metalloproteinases (MMP*s) are present in
saliva, dentin, and dentinal fluid and may be capable of degrading
extracellular matrix components. They can cause loss of collagen in the
adhesive hybrid layer under composite restorations (Visse and Nagase, 2003) and
therefore play a role in the secondary caries pathogenesis. There are multiple
in vitro and in vivo reports showing that the longevity of the adhesive
interface is increased when nonspecific enzyme-inhibiting strategies are used.
Different chemicals (i.e. chlorhexidine, galardin and benzalkonium chloride)
have been successfully employed as therapeutic primers. Therefore, the second
rationale of this study is to investigate the effect of chlorhexidine as
MMP-inhibitor on the development of secondary caries in situ.

Aims of this in situ study are: i) to investigate whether there is a threshold
in gap size for secondary caries to develop and additionally to link the level
of secondary caries formed with the caries risk of the volunteers, and ii) to
evaluate the role of MMPs inhibitor (2% CHX) in the secondary caries lesion
development and progression.

a mono-center, double blind in situ study, with split-mouth design

The burden for participating volunteers exists of wearing a removable appliance
in which the tooth samples are placed during a period of 3 weeks, for 24 hours
per day. Swallowing one of the tooth samples is a relative risk. Securing the
tooth samples in the slots of the appliance with the help of composite material
in an undercut has proven to minimize this risk in earlier studies
(NL33528.01.11).