Tooth Mobility, Periodontal Ligament Space, and the Alveolus During Periodontal Health, Disease, and Disuse

Thesis (Ph.D.)--University of Washington, 2016-07

Teeth move during mastication and this mobility is structurally governed by the periodontium (including PDL and alveolar bone) supporting the teeth and functionally by the forces that are generated during mastication and transferred to the teeth via the masticatory muscles. The extent of this 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, disease, or disuse. The objective of this study was to investigate in vivo tooth mobility during mastication and masticatory muscle stimulation in pigs and its relationship to the periodontal ligament (PDL) space. A periodontal disease model was created and these diseased pigs were compared with healthy controls. However, it was not possible to create a pig disuse model, so instead quality of the alveolar bone supporting the molar teeth was assessed in a rabbit disuse model. The assessment of magnitude and direction of mobility of molar teeth during mastication and masticatory muscle stimulation utilized ultrasound signaling in the form of small implantable piezoelectric transducers placed inside and around the maxillary molars of young pigs. Periodontal disease was induced over 8-week period using silk ligatures with a cocktail of four bacteria. µCT images were used to quantify the PDL space around the molars and histology was used to observe the general organization and pattern of the PDL fibers during health and disease. µCT images were also used to assess the alveolar bone density of the molar bearing region of the alveolus during disuse conditions in rabbits. Tooth mobility ranged from 20-322µm for both mastication and masseter stimulation. Mobility did not differ between healthy and diseased pigs. PDL space width measurements were in the range of 116-1690µm around the root circumference and at the furcation locations and did not differ for health and disease. The PDL space at the root’s apex, was larger ranging from 329-1,833µm and was greater in diseased teeth. These results show that functional tooth mobility caused by masticatory muscle contraction is extensive, approximating the entire periodontal space especially at the furcation. The molar typically showed intrusive and lateral (either buccal or palatal) movements during mastication. The intrusive movements appeared to be limited by the height of the PDL space at the furcation of the molars. Although it was not possible to characterize the functional tooth mobility during disuse conditions, bone density was significantly reduced (P < 0.05) after unloading via muscle paralysis, which could affect the tooth mobility. Future studies are needed to further investigate the functional tooth mobility during disuse.