Methods: An epoxy model was prepared to reproduce the morphology of the human adult mandible. Variable loads were applied on targeted teeth via a stainless steel post and magnitudes were measured with load cells. Displacement analysis was performed by electronic speckle pattern interferometry (ESPI). Experiment 1: Loading was applied to each of four teeth (1st premolar to 2nd molar) individually and displacement analysis was performed on the mandible's buccal-side around the loaded tooth. Experiment 2: Loading was applied to the first and second molars simultaneously, with displacement analyses performed on the buccal and lingual mandibular surfaces around the loaded teeth.
Results: Experiment 1: The ESPI fringe patterns of the four teeth examined differed. In the molar region, the center of the fringe pattern i.e. the most strongly focused site of stress, existed on the cervical side. In the premolar region, the fringe center was located on the lower apical side. Experiment 2: In the buccal side, the fringe center was half moon-shaped, centrally located between the two teeth, and vertically at the midpoint of the results for the individually loaded teeth, showing a dispersed appearance of stress by the two teeth in a joint manner. In the lingual side, the stress focused around the branching site of each tooth independently.
Conclusion: Molars have two roots and the stress focuses around the root furcation site; but premolars have one root and stress is focused more apically. The difference between the buccal and lingual side results may be due to the shape of bone, being thicker on the buccal side and relatively thin on the lingual.