Occlusal Surface Morphology and pH Cycling Effect on Enamel Demineralisation

Methods: Enamel blocks were prepared from the labial surfaces of bovine incisors and coated in acid-resistant varnish on five sides leaving the polished enamel surface exposed. Adjacent block pairs were then fixed at planar angles 180° ≤ q ≥ 20° and subject to net demineralisation in a pH cycling system. Demineralisation conditions proceeded for 6h (2mM Ca, 2mM P, 1M Lactate Buffer pH 4.6, 0.03ppm F, 40mL) between which conditions were altered to favour remineralisation (1.5mM Ca, 0.9mM P, 0.13M KCl, 20mM HEPES Buffer pH7, 0.05ppm F, 20mL, 18h). Following a 7 day cycle, parameters of integrated mineral loss (ΔZ) and lesion depth (LD) were measured using transverse micro-radiography (TMR) and considered in relation to groove depth.

Results: Average mineral loss (R) was found to correlate positively with absolute aperture. Moreover, lesion character was influence by groove angle. Wide angles (180° ≥ q > 90°) resulted in evenly distributed mineral loss as compared to acute angles (90° ≥ q ≥ 20°) where both LD and ΔZ we shown to decreased exponentially on recession from the peripheral edge albeit to a minimal extent. Thus, acute groove structures were less susceptible to chemical dissolution within this model.

Conclusions: These results contrast those obtained in vivo where demineralisation is localised at the narrowest point of the occlusal groove. Thus, the role of residual plaque in caries development is corroborated further and the need for refinement of physiologically relevant in vitro systems is emphasised.