Tooth Mobility and PDL Space Width in Pigs

Objectives: Tooth movement is governed structurally by the health of periodontal tissue, and functionally by occlusal loads and forces of masticatory muscles. The extent of tooth mobility is clinically used to determine the prognosis for teeth. However, the range of tooth movement and its direction under functional loads are largely unknown for either periodontal health or disease. The objective of this study was to investigate in vivo tooth displacement during mastication and masticatory muscle stimulation in pigs and its relationship to the periodontal ligament (PDL) space width.
Methods: Sonomicrometry was used to measure tooth mobility in periodontal healthy two-month-old farm pigs (n=6). Arrays of 2mm ultrasound crystals were implanted in the pulp chamber (mesial side) of the last deciduous maxillary molar and in the surrounding buccal and palatal alveolar bone. Pigs were allowed to chew, and then re-anesthetized while stimulating electrodes were placed in the jaw muscles. The masseter muscles were stimulated with gradually increasing voltage to supramaximal. Micro CT (µCT) images were analyzed to measure PDL space width for the mesial roots in the buccal, palatal, mesial, distal and apical directions.
Results: Tooth displacements ranged from 20-800µm averaging about 300µm for both mastication and masseter stimulation. The reported measurements are expected to be higher than the actual mobility mainly because the crystals were calibrated in water. PDL space width measurements for the mesial roots were similar, averaging 350-400µm in all directions except for width at the root’s apex, which at about 600µm was significantly larger (p<0.001) than the other directions and closest in extent to the maximal tooth displacements observed.
Conclusions: Functional tooth mobility caused by muscle contraction is extensive, approximating the entire width of the periodontal space. The molar typically moved away from both the buccal and palatal alveolar bone, which suggests an intrusive movement during power stroke of mastication.