Functional tooth mobility in young pigs.

Mobility is a fundamental characteristic of mammalian teeth, and has been widely used to determine individual tooth prognosis. However, the direction and extent of tooth movement under functional loads are unknown. This study investigated maxillary molar mobility, alveolar bending, and periodontal space (PDL) fluid pressure during mastication and masseter muscle contraction in young pigs, along with PDL space measurements. Twelve three-month-old farm pigs were instrumented with some or all of the following: (1) ultrasonic crystals, one implanted into the pulp chamber of a deciduous maxillary molar and additional crystals glued onto its buccal and palatal alveolar plates; (2) rosette strain gauges affixed to the buccal and palatal of alveolar ridges; (3) a pressure transducer inserted into palatal alveolar bone facing the PDL. Tooth mobility, alveolar bending, and fluid pressure were simultaneously recorded during unrestrained feeding and subsequent masseter muscle stimulation. The PDL widths were measured using micro-CT. The results indicate that during the power stroke of mastication, (1) the molar displaced buccally and apically (192 ± 95 µm) regardless of the side of chewing; (2) compressive bone strain was greater on the buccal than on the palatal alveolar plate; and (3) PDL pressure increased during the power strok (3.63 ± 0.80 kPa). Masseter contraction produced similar results but with generally lower values. The PDL widths were larger than the range of tooth mobility, and showed no correlation with the mobility. Thus occlusal function causes buccal tipping and intrusion of maxillary molars with concomitant compression of the buccal alveolar plate and raised pressure within the PDL space.