[Morphological evaluation of the cut enamel surface on the tooth crown]

The Preparation of rest seat and guiding plane is an essential part of the prosthetic restoration for partial denture treatments. Although these preparations are confined within the outer enamel surface, cut surfaces are left exposed after completion, which involve potential risks of caries. This study observed the morphological change of the cut surface of the enamel in vivo.

The prominent areas of bucco-lingual surfaces of the volunteers' third molars to be extracted, were cut with a dental turbin. The prepared tooth was then left for while (3, 6 months) in the oral cavity, and subsequently extracted. Either cut and non-cut surface were observed by SEM,TEM, HRTEM. In addition, salivary buffer test and cariostat test were introduced.

In most subjects, salivary buffer test showed "middlespillage" with "high buffer", and cariostat test showed "attention area". The observation of SEM showed that the enamel prism was not broken although cut and non-cut surface of the enamel were covered with bacterial flora. The observation of TEM and HRTEM revealed that the apatite crystal had dissolution and broken in both cut and non-cut area.

Comparative study of cut and non-cut surface of the enamel showed that the apatite crystal had dissolution and broken in two stages.