Quantifying in vivo Tooth Mobility

Objectives: Teeth move within their sockets in response to environmental stressors and loads. Clinically, the extent of tooth mobility is used to determine the prognosis for teeth and to establish treatment plans. However, the direction and extent of tooth movement under functional loads, such as clenching, are unknown for either periodontal health or disease. The objective of this study was to investigate the tooth displacement caused by in vivo stimulation of masticatory muscles in healthy pigs, chosen as the animal model because of their masticatory similarity to humans.
Methods: Sonomicrometry was used to measure tooth mobility in two-month-old farm pigs (n=6). Arrays of 2mm ultrasound crystals were implanted in the pulp chamber of the third deciduous maxillary molar and in the surrounding buccal and palatal alveolar bone. After restoration of the molar crown, stimulating electrodes were placed in the jaw muscles. The ipsilateral and contralateral (relative to the instrumented molar) masseters were stimulated separately and bilaterally with voltage that was gradually increased to supramaximal. In addition, the ipsilateral masseter and medial pterygoid were co-stimulated to mimic working side muscle activity.
Results: Tooth displacements ranged from 15-110µm. Buccal displacements were typically larger than palatal displacements and ipsilateral contractions had a greater effect than contralateral contractions. For ipsilateral masseter contraction, the pulp chamber moved an average of 66µm (SD=34), usually in a direction away from the buccal bone. Extent of movement tended to be greater for combined ipsilateral masseter and medial pterygoid (85µm), but direction of displacement was not consistent among animals.
Conclusions: Functional tooth mobility caused by muscle contraction is extensive, approaching half the width of the periodontal space. The deciduous molar typically moved away from the buccal alveolar bone. Movements are three-dimensional.