Modulus Of Dentin Research Articles

Alteration of dentin–enamel mechanical properties due to dental whitening treatments

The mechanical properties of dentin and enamel affect the reliability and wear properties of a tooth. This study investigated the influence of clinical dental treatments and procedures, such as whitening treatments or etching prior to restorative procedures. Both autoclaved and non-autoclaved teeth were studied in order to allow for both comparison with published values and improved clinical relevance. Nanoindentation analysis with the Oliver–Pharr model provided elastic modulus and hardness across the dentin–enamel junction (DEJ). Large increases were observed in the elastic modulus of enamel in teeth that had been autoclaved (52.0 GPa versus 113.4 GPa), while smaller increases were observed in the dentin (17.9 GPa versus 27.9 GPa). Likewise, there was an increase in the hardness of enamel (2.0 GPa versus 4.3 GPa) and dentin (0.5 GPa versus 0.7 GPa) with autoclaving. These changes suggested that the range of elastic modulus and hardness values previously reported in the literature may be partially due to the sterilization procedures. Treatment of the exterior of non-autoclaved teeth with Crest Whitestrips™, Opalescence™ or UltraEtch™ caused changes in the mechanical properties of both the enamel and dentin. Those treated with Crest Whitestrips™ showed a reduction in the elastic modulus of enamel (55.3 GPa to 32.7 GPa) and increase in the elastic modulus of dentin (17.2 GPa to 24.3 GPa). Opalescence™ treatments did not significantly affect the enamel properties, but did result in a decrease in the modulus of dentin (18.5 GPa to 15.1 GPa). Additionally, as expected, UltraEtch™ treatment decreased the modulus and hardness of enamel (48.7 GPa to 38.0 GPa and 1.9 GPa to 1.5 GPa, respectively) and dentin (21.4 GPa to 15.0 GPa and 1.9 GPa to 1.5 GPa, respectively). Changes in the mechanical properties were linked to altered protein concentration within the tooth, as evidenced by fluorescence microscopy and Fourier transform infrared spectroscopy.

An Evaluation of the Effect of Non-Setting Calcium Hydroxide on Human Dentine: A pilot Study

To evaluate the effect of non-setting calcium hydroxide (NSCH) on the hardness and elastic modulus of dentine from extracted permanent premolar human teeth. 30 freshly extracted single rooted human premolar teeth were decoronated and the roots then sectioned longitudinally into equal halves. In the experimental group a thin layer of NSCH was applied whilst the control group had no medicament. After 1, 3 and 6 months, nanoindentation was used to assess dentine hardness and the modulus of elasticity. Scanning Electron Microscopy (SEM) was used to visualize the depth of penetration of NSCH into the dentinal tubules. SEM images showed that there were no structural changes in the dentine slabs that had NSCH application after 1, 3 or even 6 months. However, penetration of NSCH into the dentine tubules was seen at both 3 and 6 months with a significant reduction in the hardness of dentine observed at 3 (p<0.02) and 6 months (p<0.01). The modulus of elasticity was significantly lower (p<0.01) at 6 months. It appears that there is a significant reduction in the hardness of dentine with increasing periods of calcium hydroxide application. Prolonged application of NSCH could have a detrimental effect on dentine, making the dentine more prone to fracture.

Comparative assessment of time‐related bioactive glass and calcium hydroxide effects on mechanical properties of human root dentin

Suspensions of micro- or nanoparticulate SiO(2)-Na(2)O-CaO-P(2)O(5) bioactive glasses could potentially be used as dressings in traumatized front teeth with open apices as an alternative to Ca(OH)(2). These materials have a disinfecting capacity similar to Ca(OH)(2), but bear the advantage of bioactivity. However, because bioactive glasses initially act as alkaline biocides just as Ca(OH)(2) does, they may also negatively affect mechanical dentin properties over time. This was assessed in the current study using standardized human root dentin bars. Specimens were immersed in 1:20 (wt vol(-1)) suspensions of nanometric bioactive glass 45S5 or calcium hydroxide for 1, 10, or 30 days. Control specimens were immersed in pure saline for 30 days (n = 20 per group). Subsequently, modulus of elasticity (E) and flexural strength (FS) of the specimens were determined. Results were compared between groups using one-way anova and Scheffé's post-hoc test. Ca(OH)(2) caused a significant (P < 0.001) 35% drop in mean flexural strength values compared to the control treatment after 10 days. No further change was observed between 10 days and 30 days. Bioactive glass caused a 20% drop in mean flexural strength as compared to the control after 10 days. However, this difference did not reach statistical significance (P > 0.05). No effects of either material on dentin modulus of elasticity values were observed. It was concluded that the calcium hydroxide suspension affected the dentin more than the bioactive glass counterpart; however, the effect was self-limiting and probably restricted to superficial dentin layers, as suggested by the mere decrease in flexural strength but not in modulus of elasticity values.

Change in elastic modulus of bovine dentine with exposure to a calcium hydroxide paste

Objective To determine the effect of calcium hydroxide [Ca(OH) 2] paste exposure on the elastic modulus of bovine dentine. Methods Dentine sections (4 mm × 4 mm × 1 mm) were obtained from freshly extracted bovine incisors and placed in dishes containing a 1-mm deep layer of Ca(OH) 2 paste or physiological saline as a control. An ultrasonic device was used to measure the sonic velocities of the longitudinal and shear waves, and the elastic modulus was calculated. Data were examined by analysis of variance followed by the Tukey H.S.D. test in order to compare different storage times. Results Exposure to Ca(OH) 2 paste significantly increased the mean elastic modulus of the dentine from 16.3 to 22.1 GPa. By contrast, the elastic modulus of the control dentine, which was exposed to physiological saline, remained constant. Conclusion These results demonstrate that exposure to Ca(OH) 2 paste increases the elastic modulus of dentine, thereby making it more prone to fracture.

Changes in stiffness of demineralized dentin following application of collagen crosslinkers

It is thought that increasing the strength of the dentin matrix using crosslinking agents may improve both the strength and the durability of resin-dentin bonds. The purpose of this study was to evaluate the effect of two collagen crosslinking agents (glutaraldehyde, GD and grape seed extract, GSE) on the modulus of elasticity of demineralized dentin. Sound molar fragments were fully demineralized and divided into five groups according to the type and concentration of crosslinking agents: 2.5% GD; 5% GD, 25% GD; 0.65% GSE; 6.5% GSE. Specimens were immersed in their respective solution and tested at baseline, 10 min, 30 min, 1 h, 2 h, 4 h. The elastic modulus of dentin was significantly affected by the treatment (p < 0.01) and exposure time (p < 0.01). There was a statistically significant interaction between the two factors evaluated (treatment vs. time p < 0.01). Mean baselines values varied between 4.8 and 6.2 MPa in water; after 4 h of treatment the values increased between 34.9 and 242.5 MPa, that were treatment time and agent dependent. The use of these collagen crosslinkers to increase the stiffness of demineralized dentin, was both concentration and time dependent.

Elevated TGF-β2 signaling in dentin results in sex related enamel defects

Initiation of enamel formation requires reciprocal signaling between epithelially and mesenchymally derived cells. Objective In this study, we used a transgenic mouse model which drives overexpression of an activated form of TGF-β2 under control of the osteocalcin promoter, to investigate the role of TGF-β2 in the dental mesenchyme, on enamel formation. Design Dentin and enamel were imaged by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dentin mechanical properties were characterized for hardness and elasticity, following nanoindentation with a modified AFM. Pores found in enamel were quantified and compared using image analysis software (Scion Image™). Results The elastic modulus of dentin was significantly reduced in the male TGF-β2 overexpressor mice as compared to male wildtype mice, with no significant differences between female mice. Similarly, there were significantly more pores in enamel of the male transgenic mice as compared to male wildtype mice, with no significant differences between female mice. In situ hybridization of the continuously erupting incisor confirmed that osteocalcin expression was limited to the odontoblast cell layer at all stages of tooth formation. Conclusion TGF-β2 overexpression in the dentin matrix, results in sex-linked differences in dentin and enamel formation.

Determination of elastic modulus of demineralized resin‐infiltrated dentin by self‐etch adhesives

The purpose of this study was to determine ultrasonically the changes in elastic modulus of demineralized adhesive-infiltrated dentin. Dentin disks were obtained from bovine incisors and shaped into a rectangular form. The specimens were immersed in single-step self-etch adhesives, then stored in distilled water and run through thermal cycles between 5 and 60 degrees C. The longitudinal and shear wave sound velocities and the elastic modulus were determined using ultrasonic equipment composed of a pulser-receiver, transducers, and an oscilloscope. After 24 h of storage, the elastic modulus of mineralized dentin was 16.9 GPa and that of demineralized dentin was 2.1 GPa. The immersion of demineralized dentin in adhesives significantly increased the elastic modulus to 3.3-5.9 GPa. After 30,000 thermal cycles, the elastic modulus of dentin was 32.4 GPa, whereas that of demineralized adhesive infiltrated dentin was 3.1-4.1 GPa. Thermal stresses did not cause adhesive-infiltrated demineralized dentin to deteriorate, as measured by elastic modulus.

The Importance of Intrafibrillar Mineralization of Collagen on the Mechanical Properties of Dentin

It is widely held that the hardness and modulus of dentin increase in proportion to the mineral concentration. To test this belief, we measured hardness and modulus of normal dentin and an altered form of dentin without gap-zone mineralization in wet and dry conditions by AFM nanoindentation to determine if the modulus and hardness scale linearly with mineral concentration. Mineral concentrations in the mid-coronal location of the normal and altered dentins were 44.4 vol% and 30.9 vol%, respectively. Surrounding the pulp of the altered dentin was a region of higher mineralization, 40.5 vol%. The indentation modulus of normal dentin was 23.9 (SD = 1.1) GPa dry and 20.0 (SD = 1.0) GPa wet. In mid-coronal regions of the altered dentin, the indentation modulus was 13.8 (SD = 2.0) GPa dry and 5.7 (SD = 1.4) GPa wet. In the more mineralized regions of the altered dentin, the modulus was 20.4 (SD = 1.8) GPa dry and 5.3 (SD = 0.8) GPa wet; the properties of the altered wet dentin did not correlate with mineral concentration. The results of this study raise doubt as to whether mineral concentration alone is a sufficient endpoint for assessing the success or failure of remineralization approaches in restorative dentistry.

AFM-Based Nanomechanical Properties and Storage of Dentin and Enamel

ABSTRACTThis study evaluated the affects of 2 different solutions, e. g. deionized water and Hanks' Balanced Salt Solution (HBSS), on nanohardness and elastic modulus of dentin and enamel from human third molars at storage times of 0, 1, 7, 14 and 28 days using a modified AFM (Triboscope). The pH values of the solutions were monitored throughout the test periods. Storing the specimens in deionized water resulted in a large decrease of mechanical properties, e.g. the reduced elastic modulus of dentin decreased from 24.0 ±1.5 GPa to 21.0 ±1.6, 8.6 ±1.1 and 5.2 ±1.1 GPa for storage times of 1, 7 and 14 days, respectively. Mechanical properties of dentin and enamel dropped by more than 12% after one day and more than 50% after a week when stored in deionized water. The observed changes in mechanical response were attributed to a superficial demineralization process during storage. In contrast, storing teeth in HBSS did not significantly alter the mechanical properties of dentin or enamel over the time studied.

A new imaging technique for measuring the surface strains applied to dentine

Objectives: To investigate possible variation in directional material properties of dentine in relationship to tubule orientation using a new optical imaging technique.Method: The optical imaging technique records photometrically a grid pattern formed by using a transmission electron microscope grid as a template on the polished surface of the dentine. The grid pattern is silhouetted onto the sample surface using standard techniques. Compression (c) and diametral compression (dc) tests were undertaken using a servo hydraulic testing machine (MTS model 810) acting on rectangular blocks of dentine with dimensions 1.5×1.0×1.0mm (for c) and cylindrical samples with dimensions 2.1mm in diameter and 1–1.5mm thick (for dc), respectively. The samples were cut using a diamond wheel and miniature lathe and the cut surfaces polished. Images due to a changing load profile were captured and stored as digitised files on a computer for later analysis. The precision is mainly determined by the pixel resolution of the charged-coupled device camera.Results: Preliminary results show the value of elastic modulus of dentine (10.4±2.9GPa) to be similar to those previously reported in the literature. Very small localised strains at the surface of a sample can be observed qualitatively and measured quantitatively by reference to the line spacing (∼85μm). Maximum strength varied with tubule orientation and (compressive/tensile) stress.Conclusion: Very small samples of dentine may be investigated for strain in more than one direction using the imaging technique described. These results may be more appropriate for finding relative directional change rather than obtaining the elastic properties of the dentine.

The elastic modulus of dentine determined by static and dynamic methods

The purpose of this investigation was to determine a static elastic modulus of dentine using a three point beam test and a dynamic modulus in the frequency range of 0·1 Hz and 10 Hz across a temperature range of 27–37 °C. At body temperature, the mean static modulus was 8·6 GPa, (standard deviation 0·86 GPa). The dynamic test produced a range of modulus values. At 0·1 Hz the modulus ranged from 14·3 to 15·2 GPa; for 1·0 Hz the range was 14·6–15·5 GPa and for 10 Hz the range was 14·9–15·8 GPa. The results are of value in the design and analysis of restorative materials.

Experimental determination of the rigidity modulus, poisson's ratio and elastic limit in shear of human dentine

The rigidity modulus of dentine determined by the torsion of rectangular prisms was 0.62GN/m 2. This led to the calculation of Poisson's ratio values of −0.025 to 0.26 which are very low. If Poisson's ratio is 0.00, then the bulk modulus is 1 3 Young's modulus, i.e. 4 GN/m 2. The proportional limit in shear is much lower than in torsion, and elastic deformation forms only a small region of the total deformable region in shear.