Method and materials
Unerupted, human third molar teeth were extracted from patients aged between 18 and 30 years, of either gender. Teeth were soaked in 50% sodium hypochlor- ite, scraped of any remaining debris, washed in distilled water, sonicated in 70% ethyl alcohol and finally rinsed again in distilled water. The teeth were sec- tioned longitudinally, placed in polyurethane vacuum packed moulds filled with epoxy resin* and left for 24 h cure. The buccal aspect of the tooth was mini- mally ground with an automatic lapping and polishing unit with decreasing coarseness of discs, to produce an optically flat area of root dentine or enamel. Baseline surface profiles of the dentine and enamel s