Discontinuities in the human bone–PDL–cementum complex

Abstract

A naturally graded interface due to functional demands can deviate toward a discontinuous interface, eventually decreasing the functional efficiency of a dynamic joint. It is this characteristic feature in a human fibrous joint i.e. bone-tooth complex that will be discussed through histochemistry, and site-specific high resolution microscopy, micro tomography, X-ray fluorescence imaging and wet nanoindentation techniques. Results demonstrated two causes for the occurrence of 5-50 μm narrowed PDL-space: 1) microscopic scalloped regions at the PDL-insertion sites and macroscale stratified layers of bone with rich basophilic lines, and 2) macroscopic bony protrusions. Narrowed PDL-complexes illustrated patchy appearance of asporin, and when imaged under wet conditions using an atomic force microscope (AFM), demonstrated structural reorganization of the PDL, collagen periodicity, organic-dominant areas at the PDL-cementum and PDL-bone entheses and within cementum and bone. Scanning electron microscopy (SEM) results confirmed AFM results. Despite the narrowed PDL, continuity between PDL and vasculature in endosteal spaces of bone was demonstrated using a Micro XCT™. The higher levels of Ca and P X-ray fluorescence using a microprobe were correlated with higher elastic modulus values of 0.1-1.4 and 0.1-1.2 GPa for PDL-bone and PDL-cementum using wet nanoindentation. The ranges in elastic modulus values for PDL-bone and PDL-cementum entheses in 150-380 μm wide PDL-complex were 0.1-1.0 and 0.1-0.6 GPa. Based on these results we propose that strain amplification at the entheses could be minimized with a gradual change in modulus profile, a characteristic of 150-380 μm wide functional PDL-space. However, a discontinuity in modulus profile, a characteristic of 5-50 μm narrowed PDL-space would cause compromised mechanotransduction. The constrictions or narrowed sites within the bone-tooth fibrous joint will become the new “load bearing sites” that eventually could cause direct local fusion of bone with cementum.

Tooth movements are guided by specific contact areas between the tooth root and the jaw bone: A dynamic 3D microCT study of the rat molar

“…Based on these large variations it is not surprising that the contacts between the bone and the tooth are in specific locations and not in others. Variations in PDL thickness have also been observed in bovine teeth (Bosshardt et al, 2008) and in humans (Hurng et al, 2011;Mandel et al, 1986;Toms et al, 2002b). We can therefore predict that their movements are also guided by contact areas.…”

Effect of proteoglycans at interfaces as related to location, architecture, and mechanical cues

“…Examples of entheses in the articulating musculoskeletal joints include, the ligament–bone and tendon–bone fibrocartilaginous interfaces (Benjamin & McGonagle, 2009). Within the oral and craniofacial systems, the ligament-alveolar bone and ligament–cementum fibrous interfaces of the dentoalveolar fibrous joint (Ho et al, 2010; Hurng et al, 2011; McCulloch, Lekic, & McKee, 2000) are responsible in part for the overall mechanics of fibrous joints. Because of the mismatch in elasticity at the ligament–cementum and cementum–dentin interfaces, from a pure engineering perspective strain concentrations should exist at the attachment sites and interfaces within load bearing joints (Ho et al, 2013; Qian et al, 2009).…”

“…PGs have been identified within mineralized tissues as well as the mineral-free periodontal ligament (PDL) (Ababneh, Hall, & Embery, 1998; Ababneh, Hall, & Embery, 1999; Ho, Marshall, Ryder, & Marshall, 2007; Matheson, Larjava, & Hakkinen, 2005). PGs were also identified at the PDL–bone, PDL–cementum interfaces (Ho et al, 2010; Hurng et al, 2011; Lukinmaa, Mackie, & Thesleff, 1991). Previous studies from our laboratory have identified hygroscopic regions of the PDL–bone, PDL–cementum interfaces alluding to the presence of SLRPs (Ho et al, 2010; Hurng et al, 2011) and subsequently have identified SLRPs at the attachments sites (Chiu et al, 2012).…”

“…PGs were also identified at the PDL–bone, PDL–cementum interfaces (Ho et al, 2010; Hurng et al, 2011; Lukinmaa, Mackie, & Thesleff, 1991). Previous studies from our laboratory have identified hygroscopic regions of the PDL–bone, PDL–cementum interfaces alluding to the presence of SLRPs (Ho et al, 2010; Hurng et al, 2011) and subsequently have identified SLRPs at the attachments sites (Chiu et al, 2012). Additionally, the presence of chondroitin sulfated GAGs was confirmed at a similar region, but at an interface between mineralized tissues, cementum and dentin within the complex of human molars (Ho, Balooch et al, 2004) (Yamamoto et al, 1999).…”

Biomechanical adaptation of the bone-periodontal ligament (PDL)-tooth fibrous joint as a consequence of disease

“…However, a shift in homeostasis can cause modeling of the soft and hard structural elements (Giannobile et al, 2003), subsequently leading to an overall disturbance in organ biomechanics (Lee and Lin et al, 2013). Such shifts are often a result of perturbations (periodontal disease, parafunctional loads, and therapeutic load) to physiologic tooth mobility, which over prolonged loading can cause abnormal tooth displacement within the alveolar socket (Hurng et al, 2011). …”