Biomechanics of a bone–periodontal ligament–tooth fibrous joint

Abstract

This study investigates bone-tooth association under compression to identify strain amplified sites within the bone-periodontal ligament (PDL)-tooth fibrous joint. Our results indicate that the biomechanical response of the joint is due to a combinatorial response of constitutive properties of organic, inorganic, and fluid components. Second maxillary molars within intact maxillae (N=8) of 5-month-old rats were loaded with a μ-XCT-compatible in situ loading device at various permutations of displacement rates (0.2, 0.5, 1.0, 1.5, 2.0 mm/min) and peak reactionary load responses (5, 10, 15, 20 N). Results indicated a nonlinear biomechanical response of the joint, in which the observed reactionary load rates were directly proportional to displacement rates (velocities). No significant differences in peak reactionary load rates at a displacement rate of 0.2 mm/min were observed. However, for displacement rates greater than 0.2 mm/min, an increasing trend in reactionary rate was observed for every peak reactionary load with significant increases at 2.0 mm/min. Regardless of displacement rates, two distinct behaviors were identified with stiffness (S) and reactionary load rate (LR) values at a peak load of 5 N (S5 N=290–523 N/mm) being significantly lower than those at 10 N (LR5 N=1–10 N/s) and higher (S10N–20 N=380–684 N/mm; LR10N–20 N=1–19 N/s). Digital image correlation revealed the possibility of a screw-like motion of the tooth into the PDL-space, i.e., predominant vertical displacement of 35 μm at 5 N, followed by a slight increase to 40 μm at 10 N and 50 μm at 20 N of the tooth and potential tooth rotation at loads above 10 N. Narrowed and widened PDL spaces as a result of tooth displacement indicated areas of increased apparent strain within the complex. We propose that such highly strained regions are “hot spots” that can potentiate local tissue adaptation under physiological loading and adverse tissue adaptation under pathological loading conditions.

<em>In situ</em> Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

“…Once the PDL-space is minimized and as the PDL undergoes strain hardening, hard tissue interactions between the tooth and bony socket arise at the interradicular region resulting in a steeper load to displacement slope. In addition to material recovery, the backlash of the loading device can be exploited to investigate the viscoelastic nature of the PDL without altering the joint as was done in other studies 16,25 .…”

“…The reactionary response can be from softer and/or harder constituents. The dominance of the softer constituent over the harder can be identified by loading incrementally and imaging, followed by digitally correlating the no load to loaded conditions to identify strain-dominated regions within the bone-PDL-tooth complex 13 .…”

“…Methods specific to the tooth organ biomechanics include the use of strain gauges [1][2][3] , photoelasticity methods 4,5 , Moiré interferometry 6,7 , electronic speckle pattern interferometry 8 , and digital image correlation (DIC) [9][10][11][12][13][14] . In this study, the innovative approach includes noninvasive imaging using X-rays to expose the internal structures of a fibrous joint (mineralized tissues and their interfaces consisting of softer zones, and interfacing tissues such as ligaments) at loads equivalent to in vivo conditions.…”

Multiscale visualisation of tooth-periodontal ligament-bone fibrous joint function

“…Freshly harvested specimens were prepared for in situ mechanical testing as described previously [14,15,18]. Biomechanical testing was done on human specimens obtained through the Willed Body Program at UCSF.…”

Adaptive properties of human cementum and cementum dentin junction with age

“…When changes in function occur within physiological limits, an adequate PDL-space of 150–380µm is thought to provide an optimum biomechanical function [1, 2]. Optimum function is limited to joints where no significant change in overall displacement of the tooth into the alveolar socket in response to simulated loads is observed [3]. However, inevitable adaptation due to innate age related physiology can manifest as observable differences in tissue properties and their interfaces that makeup the dentoalveolar complex [4].…”