Journal of dental biomechanics最新文献

Unlabelled: The purpose of the study was to compare Quasi-Static (QS) and harmonic (CSM) methods of indentation testing. Bone sections were obtained from mid-femoral diaphyses of dogs which received a pair of calcein labels. Labeled (n = 35) and unlabeled (n = 112) osteons were identified. Indentation modulus (IM) and hardness (H) for the CSM method were collected during the entire loading cycle to peak depth, while IM and H for QS method were calculated at a peak depth of 500 nm.

Results: The mean (SD) of the IM and H for labeled osteons were as follows: QS IM = 15.3 GPa (3.85) versus CSM IM = 14.7 GPa (3.58); P = .52 and QS H = .39 GPa (.171) versus CSM H = .42 GPa (.146); P = .32. The mean (SD) of the IM and H for unlabeled osteons were as follows: QS IM = 21.5 GPa (2.80) versus CSM IM = 20.6 GPa (2.53); P = .054 and QS H = .64 GPa (.117) versus CSM H = .70 GPa (.120); P = .017. There was no difference in IM and H for the two methods, except for H of the unlabeled osteons. In addition, for the CSM method, IM at 100 nm, 200 nm, 300 nm, 400 nm and 500 nm were not statistically significant different (P = .06). Bone is viscoelastic at an organ level. However, this component of its behavior was not detected at the length scale examined.

An understanding of functional responses in oral bone is a crucial component of dental biomechanics. The purpose of this study was to investigate the potential biological remodelling response during mastication on the mandibular pre- and post-insertion of a fixed partial denture (FPD). A series of three-dimensional (3D) finite element analysis (FEA) models were presented pre- and postextraction to determine the biomechanical responses to masticatory loading in the anterior mandible. Equivalent strains were analysed at lingual/buccal and mesial/distal areas of the premolar to molar region and quantified to anticipate bone remodelling response. Mandibular bone incorporating an FPD experienced substantially greater stress/strain magnitudes than that prior to placement of fixed prosthodontics, which is suggestive of engagements of bone remodelling. The results suggest similar outcomes to those reported clinically. Developing a simulation reflecting the outcomes of restorative treatment can provide meaningful insight into restorative treatment planning, clinical outcomes, and fixed prosthodontics designs.

The dentino-enamel junction (DEJ) connects enamel, that covers the outer surface of a tooth, to a thicker underlying dentin. The DEJ is a critical interface that permits joining these materials that have widely dissimilar mechanical properties. AFM-based nanoindentation and Raman microspectroscopy were used to define the width and composition of human molar DEJ. Indentation elastic modulus and hardness of enamel, dentin, and DEJ were determined along lines of indents made at 2 μm intervals across the DEJ. Indents made at maximum loads at each end of the indent lines were used to make visible markers allowing Raman microspectroscopy at 1 μm intervals across the DEJ, while using the nanoindent markers for orientation and location. Functional DEJ width estimates were made based on results from nanoindentation and Raman microspectroscopy. DEJ width estimates ranged from 4.7 (±1.2) μm to 6.1 (±1.9) μm based on hardness and 4.9 (±1.1) μm to 6.9 (±1.9) μm based on modulus. DEJ width based on Raman peak intensity variations were 8.0 (±3.2) μm to 8.5 (±3.1) μm based on the phosphate peak, and 7.6 (±3.2) μm to 8.0 (±2.6) μm for C-H stretching mode. These estimates are in the range of DEJ width estimates reported using nanoindentation.

The mechanical strength of the periodontal ligament (PDL) was first measured as force required to extract a tooth from its socket using human specimens. Thereafter, tooth-PDL-bone preparations have extensively been used for measurement of the mechanical response of the PDL. In vitro treatments of such specimens with specific enzymes allowed one to investigate into the roles of the structural components in the mechanical support of the PDL. The viscoelastic responses of the PDL may be examined by analysis of the stress-relaxation. Video polarised microscopy suggested that the collagen molecules and fibrils in the stretched fibre bundles progressively align along the deformation direction during the relaxation. The stress-relaxation process of the PDL can be well expressed by a function with three exponential decay terms. Analysis after in vitro digestion of the collagen fibres by collagenase revealed that the collagen fibre components may play an important role in the long-term relaxation component of the stress-relaxation process of the PDL. The dynamic measurements of the viscoelastic properties of the PDL have recently suggested that the PDL can absorb more energy in compression than in shear and tension. These viscoelastic mechanisms of the PDL tissue could reduce the risk of injury to the PDL.

Many developments have been made in the field of resin composites for dental applications. However, the manifestation of shrinkage due to the polymerization process continues to be a major problem. The material's shrinkage, associated with dynamic development of elastic modulus, creates stresses within the material and its interface with the tooth structure. As a consequence, marginal failure and subsequent secondary caries, marginal staining, restoration displacement, tooth fracture, and/or post-operative sensitivity are clinical drawbacks of resin-composite applications. The aim of the current paper is to present an overview about the shrinkage stresses created during resin-composite applications, consequences, and advances. The paper is based on results of many researches that are available in the literature.

Orthodontic lingual root movement (torque) is an important aspect of treatment biomechanics and is typically achieved by torsion of a rectangular wire within the orthodontic bracket slot which introduces a force couple. The magnitude of the force moment achieved by wire torsion may be influenced by deformation of the orthodontic bracket. A device utilizing an optical image correlation technique has been developed to accurately quantify bracket slot dimensional changes during application of wire torsion. Simultaneous torque moment magnitude, degrees of wire twist, and bracket slot dimension data can be gathered. Bracket tie wing elastic deformation when loaded was demonstrated and plastic deformation was also observed with a single rotation of the wire.

Objectives. The aim of this study was to assess the influence of resistance to sliding on expression of superelastic properties of NiTi wires. Methods and Materials. A three-point bending test was performed for 0.014 NiTi wire engaged in self-ligating (Damon, SmartClip, In-Ovation) and conventional brackets (Victory) ligated with regular and reduced friction modules (Slide). The wire was deflected in the buccal direction and allowed to straighten. The maximum load, unloading plateau and unloading capacity were registered. Results. The lowest activation load was required in the active self-ligating group (In-Ovation 2.2 ± 0.4 N) and reduced friction module group (Victory/Slide 2.9 ± 0.4 N), followed by the passive self-ligating systems (Damon 3.6 ± 0.7 N, SmartClip 3.7 ± 0.4 N). Higher activation load was obtained in the conventionally ligated group (Victory/module 4.5 ± 0.4 N). Unloading plateau phase with the load magnitude ranging from 1.27 ± 0.4 N (In-Ovation) to 1.627 ± 0.4 N (Slide) was distinct in all groups but one (Victory). Conclusions. Higher friction at flanking points reduces the net force delivered by the wire. Unloading plateau phase of NiTi load-deflection curve disappears in the conventionally ligated group thus indicating to an incomplete expression of NiTi superelastic properties. A rigid passive bracket clip amplifies resistance to sliding in an active configuration and produces a permanent deflection of the wire.