Materials and methods
Unerupted, human third molar teeth were extracted from patients in the Bristol area aged between 18 and 30 years, of either gender. Teeth were prepared by cleaning and sterilizing in sodium hypochlorite, followed by embedding in epoxy resin and minimally grinding the buccal aspect of the tooth to produce an optically ̄at area of root dentine or enamel as described by West etal. (2000). Baseline surface pro®les of the dentine and enamel specimens were recorded twice by pro®lometry, with a tolerance of