Synergistic degradation of dentin by cyclic stress and buffer agitation

Abstract

Secondary caries and non-carious lesions develop in regions of stress concentrations and oral fluid movement. The objective of this study was to evaluate the influence of cyclic stress and fluid movement on material loss and subsurface degradation of dentin within an acidic environment. Rectangular specimens of radicular dentin were prepared from caries-free unrestored 3rd molars. Two groups were subjected to cyclic cantilever loading within a lactic acid solution (pH=5) to achieve compressive stresses on the inner (pulpal) or outer sides of the specimens. Two additional groups were evaluated in the same solution, one subjected to movement only (no stress) and the second held stagnant (control: no stress or movement). Exterior material loss profiles and subsurface degradation were quantified on the two sides of the specimens. Results showed that under cyclic stress material loss was significantly greater (p≤0.0005) on the pulpal side than on the outer side and significantly greater (p≤0.05) under compression than tension. However, movement only caused significantly greater material loss (p≤0.0005) than cyclic stress. Subsurface degradation was greatest at the location of highest stress, but was not influenced by stress state or movement.

Sclerostin inhibits odontogenic differentiation of human pulp‐derived odontoblast‐like cells under mechanical stress

“…Runx2 is a transcription factor which regulates many odontogenic genes and is highly expressed in the reparative odontoblast-like cells (Han et al, 2014). As a fundamental aetiology of NCCLs, mechanical stress is supposed to be a potential inducing factor of sclerotic dentin formation (Bartlett & Shah, 2006;Orrego et al, 2015;Tanaka et al, 2003). Hence, we established in vitro MS model imitating in vivo mechanical stress to explore the involvement of odontoblasts in reactive dentin formation.…”

“…Runx2 is a transcription factor which regulates many odontogenic genes and is highly expressed in the reparative odontoblast-like cells (Han et al, 2014). As a fundamental aetiology of NCCLs, mechanical stress is supposed to be a potential inducing factor of sclerotic dentin formation (Bartlett & Shah, 2006;Orrego et al, 2015;Tanaka et al, 2003). Hence, we established in approach, our research focused on mechanosensory reactions of odontoblasts, which are actually the cells that secrete dentin matrix in the stage of terminal differentiation and perceive mechanical stimuli by cell process and branches (Magloire et al, 2009;Ruch et al, 1995).…”

“…Sclerotic dentin is a variant of reactive dentin and is mainly located beneath NCCLs, which result from multifactorial pathogenies including erosion, abrasion, and stress-corrosion (Orrego, Romberg, & Arola, 2015). Mechanical stress induced by incorrect toothbrushing and large occlusal loading is a pivotal underlying aetiology of NCCLs (Bartlett & Shah, 2006;Tanaka, Naito, Yokota, & Kohno, 2003), and should be a potential inducing factor of sclerotic dentin formation.…”

Degradation in the fatigue crack growth resistance of human dentin by lactic acid

“…The fatigue crack growth exponent ( m ) increased by 30% and 23% for the middle and outer regions, respectively, which signifies the increase in sensitivity of the material to the stress intensity. The greater severity to middle dentin is attributed to the higher mineral-to-collagen ratio [40,52,53] and more extensive acid degradation. The crack growth resistance of dentin is location-dependent, and deep dentin exhibits the lowest toughness overall due to the limited degree of extrinsic toughening [5].…”

“…An S. mutans colony increases in number at pH levels between 4.5 and 5.5 [38], whereas a pH below 4.5 causes instability and disruption [34,38]. Thus, a lactic acid solution with pH=5 was considered a clinically relevant model and is consistent with the acid environment used in previous investigations [31,40]. The lactic acid solution was prepared by adding 7.45 ml of 0.1M lactic acid to 950 ml of deionized water.…”