Loading rate response of a diseased bone-tooth fibrous joint

Functional loads and/or disease over prolonged time can alter joint biomechanics. Objective: The effect of disease was investigated by mapping the displacement response of a tooth to loads at different loading rates using a ligature-induced periodontitis model. Methods: 4-0 silk ligatures soaked with lipopolysaccharide (L2880, Sigma) were placed within diastema flanking left and right second maxillary molars of 6-week-old rats for 12 weeks. Control rats were flossed in the same regions over the same period. Second molars of intact maxillas were loaded at a displacement rate of 0.2mm/min (MT500CT, Deben UK Ltd.). Form and resorption-related changes of mineralized tissues were identified via microXCT (Xradia, Inc.). Results: Increased alveolar bone recession was observed in diseased rats (634.9±196.9µm) compared to controls (389.7±145.6µm). Distal surfaces of diseased roots exhibited greater resorption compared to corresponding mesial surfaces, as well as respective distal surfaces of controls. Measurements of periodontal ligament (PDL)-width revealed increased coronal distal (183.0±43.3µm) and interradicular (158.1±34.1µm) PDL-widths in diseased compared to control (146.8±37.2µm, 103.2±12.9µm, respectively). Under whole-organ loading, diseased molars exhibited decreased force per unit displacement compared to control (Fig. 1). Stiffness values from force-displacement curves of diseased molars for maximum loads of 5, 10, 15, and 20N, exhibited lower stiffness values (0.2±0.1, 0.4±0.1, 0.4±0.1, 0.5±0.2 N/µm) compared to control molars (0.3±0.1, 0.4±0.1, 0.5±0.1, 0.5±0.1 N/µm) (Fig. 2).  More importantly, lower force caused the same displacement in a diseased complex compared to a higher force for a control complex. Conclusion: Bacterial insult alters the overall biomechanics of the fibrous joint as exhibited through increased displacement response to load due to lower stiffness values and increased degrees of freedom in the coronal aspects of the complex.