Mechanical Properties Of Teeth Research Articles

In Vitro Investigation into the Effect of Cryopreservation on the Mechanical Characteristics of Dental Hard Tissues.

Previous research has reported on hidden damage within the dentin introduced by cryopreservation, but the effect on the mechanical properties of the hard tissues at tooth level remains unclear. The main objective of this study is to investigate the effect of cryopreservation on the mechanical properties of teeth. A matched sample of 234 premolars of 117 children (9 ≤ age ≤ 16 years), bilaterally extracted for orthodontic reasons, were included. For each child, one tooth was randomly allocated to the cryopreservation group and the contralateral tooth was assigned to the control group. Static compression tests were performed to determine load to failure, stiffness, and toughness. In a subgroup of 20 teeth, a cyclic preloading or chewing simulation was performed. Additionally, the fracture mode was determined, and the microstructure of the fractured surfaces was examined using a scanning electron microscope (SEM). Linear mixed model analyses could not detect a statistical difference in the mean load to failure (p = 0.549), mean toughness (p = 0.968), or mean stiffness (p = 0.150) between cryopreserved and non-cryopreserved teeth. No significant difference in load to failure after cyclic preloading was detected between groups (p = 0.734). SEM analysis revealed comparable fracture characteristics between groups. It is concluded that cryopreservation does not affect the mean load to failure, stiffness, or toughness of teeth, indicating that hidden damage in the dentin is not critical at tooth level.

Finite element analysis relating shape, material properties, and dimensions of taenioglossan radular teeth with trophic specialisations in Paludomidae (Gastropoda)

The radula, a chitinous membrane with embedded tooth rows, is the molluscan autapomorphy for feeding. The morphologies, arrangements and mechanical properties of teeth can vary between taxa, which is usually interpreted as adaptation to food. In previous studies, we proposed about trophic and other functional specialisations in taenioglossan radulae from species of African paludomid gastropods. These were based on the analysis of shape, material properties, force-resistance, and the mechanical behaviour of teeth, when interacting with an obstacle. The latter was previously simulated for one species (Spekia zonata) by the finite-element-analysis (FEA) and, for more species, observed in experiments. In the here presented work we test the previous hypotheses by applying the FEA on 3D modelled radulae, with incorporated material properties, from three additional paludomid species. These species forage either on algae attached to rocks (Lavigeria grandis), covering sand (Cleopatra johnstoni), or attached to plant surface and covering sand (Bridouxia grandidieriana). Since the analysed radulae vary greatly in their general size (e.g. width) and size of teeth between species, we additionally aimed at relating the simulated stress and strain distributions with the tooth sizes by altering the force/volume. For this purpose, we also included S. zonata again in the present study. Our FEA results show that smaller radulae are more affected by stress and strain than larger ones, when each tooth is loaded with the same force. However, the results are not fully in congruence with results from the previous breaking stress experiments, indicating that besides the parameter size, more mechanisms leading to reduced stress/strain must be present in radulae.

Characterization of Phosphorus Species in Human Dentin by Solid-State NMR.

The rat has been considered as an appropriate animal model for the study of the mineralization process in humans. In this work, we found that the phosphorus species in human dentin characterized by solid-state NMR spectroscopy consist mainly of orthophosphate and hydrogen phosphate. Some orthophosphates are found in a disordered phase, where the phosphate ions are hydrogen-bonded to structural water, some present a stoichiometric apatite structure, and some a hydroxyl-depleted apatite structure. The results of this study are largely the same as those previously obtained for rat dentin. However, the relative amounts of the various phosphorus species in human and rat dentin are dramatically different. In particular, stoichiometric apatite is more abundant in human dentin than in rat dentin, whereas the converse is true for disordered-phase orthophosphates. Furthermore, spatial proximity among all phosphorus species in human dentin is identical within experimental error, in contrast to what observed for rat dentin. Although it is not clear how these spectroscopic data could relate to the hierarchical structure or the mechanical properties of teeth, our data reveal that the molecular structures of human and rat dentin at different growth stages are not exactly the same.

The effect of cadmium exposition on the structure and mechanical properties of rat incisors.

Alterations in the structure and mechanical properties of teeth in adult Wistar rats exposed to cadmium were investigated. Analyses were conducted on two sets of incisors from female and male specimens, that were intoxicated with cadmium (n = 12) or belonged to the control (n = 12). The cadmium group was administered with CdCl2 dissolved in drinking water with a dose of 4mg/kgbw for 10 weeks. The oral intake of cadmium by adult rats led to the range of structural changes in enamel morphology and its mechanical features. A significant increase of cadmium levels in the teeth in comparison to the control, a slight shift in the colour and reduction of pigmented enamel length, higher surface irregularity, a decrease of hydroxyapatite crystals size in the c-axis and simultaneous increase in pigmented enamel hardness were observed. The extent of these changes was sex-dependent and was more pronounced in males.

Interrelationships Between Morphometric, Densitometric, and Mechanical Properties of Teeth in 5-Month-Old Polish Merino Sheep.

Interrelationships between morphological, densitometric, and mechanical properties of deciduous mandibular teeth (incisors, canine, second premolar) were investigated. To perform morphometric, densitometric, and mechanical analyses, teeth were obtained from 5-month-old sheep. Measurements of mean volumetric tooth mineral density and total tooth volume were performed using quantitative computed tomography. Microcomputed tomography was used to measure total enamel volume, volumetric enamel mineral density, total dentin volume, and volumetric dentin mineral density. Maximum elastic strength and ultimate force of teeth were determined using 3-point bending and compression tests. Pearson correlation coefficients were determined between all investigated variables. Mutual dependence was observed between morphological and mechanical properties of the investigated teeth. The highest number of positive correlations of the investigated parameters was stated in first incisor indicating its superior predictive value of tooth quality and masticatory organ function in sheep. Positive correlations of the volumetric dentin mineral density in second premolar with final body weight may indicate predictive value of this parameter in relation with growth rate in sheep. Evaluation of deciduous tooth properties may prove helpful for breeding selection and further reproduction of sheep possessing favorable traits of teeth and better masticatory organ function, leading to improved performance and economic efficiency of the flock.

On the importance of aging to the crack growth resistance of human enamel

With improvements in oral health and an overall increase in quality of life, the percentage of fully or largely dentate seniors is increasing. Understanding the effects of aging on the mechanical properties of teeth is essential to the maintenance of lifelong oral health. In this investigation the effects of aging on the fracture toughness of human enamel were evaluated from incremental crack growth experiments performed on tissue of donor teeth representing “young” (17⩽age⩽25) and “old” (age⩾55) age groups. Results showed that the old enamel exhibited significantly lower resistance to fracture than that of the young tissue in two orthogonal directions of crack growth. For crack growth transverse to the enamel rods, the fracture toughness of the old enamel (0.37±0.15MPam0.5) was nearly 70% lower than that of tissue from the young teeth (1.23±0.20MPam0.5). Based on results from a mechanistic analysis of crack growth, the reduction in fracture resistance is attributed to a decrease in the degree of extrinsic toughening. The practice of restorative dentistry should account for these changes in tooth tissues in the treatment of senior patients. Statement of SignificanceThe mechanical behavior of enamel has been studied for over 3 decades. Due to the limited volume of tissue available for evaluation, past work has been largely based on indentation methods. In this investigation we have evaluated the resistance to fracture of human enamel using a conventional fracture mechanics approach and incremental crack growth. We compared the fracture resistance of cuspal enamel obtained from the teeth of representative “young” and “old” donor groups. Our results show that there is a substantial reduction in the resistance to fracture with age, that it is anisotropic, and that the degradation is more severe than that which occurs to dentin. As such, we feel this work is a significant contribution to the field.

In-vitro evaluation of various solvents for retrieval of mineral trioxide aggregate and their effect on microhardness of dentin

Aim:Organic acids have the potential to decrease the strength of mineral trioxide aggregate (MTA) during retreatment. However, this might cause alterations in dentin composition and structure. The aim of this study was to assess the efficacy of chemicals on surface microhardness of white MTA (WMTA) and dentin.Materials and Methods:White MTA-Angelus® was mixed and packed into tooth molds. Six experimental groups (n = 15) were formed and exposed to 2% carbonic acid, 2% chlorhexidine gluconate, 5.25% sodium hypochlorite, 10% citric acid, 20% tartaric acid, and normal saline for 10 min and 20 min intervals on 1 and 21 days of setting, respectively. Vickers microhardness of WMTA and dentin for each specimen was measured before and after exposure. Data were subjected to repeated-analysis of variance (ANOVA) and post-hoc tests.Results:Carbonic acid was effective in significantly reducing the surface hardness of WMTA on both 1 and 21 days; followed by citric and tartaric acid (P < 0.05). Two percent chlorhexidine gluconate and NaOCl were effective on 1-day set WMTA. All chemicals, except 2% chlorhexidine, decreased microhardness of dentin significantly (P < 0.05) at 20 min interval.Conclusion:Cautious use of these chemicals not exceeding 10 min is mandatory to prevent significant alterations in mechanical properties of tooth during MTA retrieval.

Effects of CO2 laser debonding of a ceramic bracket on the mechanical properties of enamel

To investigate the effects of CO(2) laser debonding of a ceramic bracket on the mechanical properties of tooth enamel. Fifty-three human premolars were used in this study. The temperature changes of cross-sectioned specimens during laser irradiation were monitored with an infrared thermographic microscope system. Different laser output settings (3, 4, 5, and 6 W) were compared. The shear bond strength of brackets after laser irradiation was measured for specimens bonded with a conventional etch and rinse adhesive or with a self-etching adhesive, and the adhesive remnant index score was calculated. The hardness and elastic modulus of cross-sectioned enamel after laser irradiation were investigated by the nanoindentation test. Data were compared by one-way and two-way analysis of variance, followed by the Scheffé test. The temperature of enamel increased by about 200 degrees C under CO(2) laser irradiation with a relatively high output (5 and 6 W), and a temperature increase of about 100 degrees C to 150 degrees C was seen under laser irradiation with a low output (3 and 4 W). The bracket shear bond strength decreased under all laser irradiation conditions. The hardness and elastic modulus of enamel were not affected by CO(2) laser debonding. CO(2) laser debonding may not cause iatrogenic damage to enamel.

The mechanical anisotropy on a longitudinal section of human enamel studied by nanoindentation

Nanoindentation has been widely used for probing the mechanical properties of tooth, especially for characterizing its complex hierarchical structures. Previous studies have confirmed the anisotropic mechanical behaviors caused by the alternated orientations of enamel rods and the alignment of fibril-like hydroxyapatite crystals, but the longitudinal section of enamel, which was composed of parallel-arranged rods, was regarded as a homogeneous continuum as always. In this study, nanoindentation combined with SEM was carried out with the indenter rotating on the longitudinal section of enamel to evaluate the relativity between the nano-mechanical properties and the orientation of indentation impressions. It has been shown that the enamel presented different elastic modulus and hardness with different angles of indenter on its longitudinal section, and its anisotropy was also confirmed by the remarkable asymmetric morphologies of impressions. We observed that the parallel arrangement of crystal fibrils and enamel rods might trigger the expansion of the micro-cracks in preferred orientation, and result in scalene triangle indentation impressions, altering contact areas as well as inconsistent mechanical behaviors. Consequently, it is considered that the longitudinal sections of enamel should be modeled as anisotropic.

Effect of Fluoride on Mechanical Properties of Teeth Demineralized by Use of Orthodontic Appliances

ABSTRACTThe risk of dental caries increases with the use of orthodontic appliances, and it does not only depend on a patient's oral hygiene. Caries cause teeth enamel demineralization close to the orthodontic bracket. The hardness of the teeth consequently decreases, and they become brittle and loose. The type of adhesive used to fix brackets may or may not reduce enamel demineralization. Previous studies have shown that a resin-modified glass ionomer (RMGI) inhibits demineralization. The purpose of this work is to evaluate the effect of a fluoride-releasing bracket on mechanical properties of dentin and enamel on regions adjacent to orthodontic brackets bonded with RMGI and composite resin cements. The remineralization effect due to fluoride on teeth was assessed by measuring hardness and reduced elastic modulus on dentin, enamel and dentin-enamel junction (DEJ) around the bracket area by nanoindentation methods. Nanoindentation was performed using a TriboScope from Hysitron. For this purpose two sets of polished samples were prepared: one sample was a cut along a longitudinal section and the other one along a cross-section of a tooth with orthodontic treatment using RMGI. Anisotropy in the mechanical properties of the teeth is observed along each direction.

Effect of Fluoride on Mechanical Properties of Teeth Demineralized by Use of Orthodontic Appliances

ABSTRACTThe risk of dental caries increases with the use of orthodontic appliances, and it does not only depend on a patient's oral hygiene. Caries cause teeth enamel demineralization close to the orthodontic bracket. The hardness of the teeth consequently decreases, and they become brittle and loose. The type of adhesive used to fix brackets may or may not reduce enamel demineralization. Previous studies have shown that a resin-modified glass ionomer (RMGI) inhibits demineralization. The purpose of this work is to evaluate the effect of a fluoride-releasing bracket on mechanical properties of dentin and enamel on regions adjacent to orthodontic brackets bonded with RMGI and composite resin cements. The remineralization effect due to fluoride on teeth was assessed by measuring hardness and reduced elastic modulus on dentin, enamel and dentin-enamel junction (DEJ) around the bracket area by nanoindentation methods. Nanoindentation was performed using a TriboScope from Hysitron. For this purpose two sets of polished samples were prepared: one sample was a cut along a longitudinal section and the other one along a cross-section of a tooth with orthodontic treatment using RMGI. Anisotropy in the mechanical properties of the teeth is observed along each direction.

Effect of Nd:YAG laser irradiation on the hardness and elastic modulus of human dentin.

The purpose of this study was to investigate the changes of hardness and elastic modulus of human dentin after Nd:YAG laser irradiation. The application of Nd:YAG laser in dental hard tissues has been widely studied. However, little information is available about the mechanical properties of teeth after Nd:YAG laser irradiation. The human dentin was irradiated by Nd:YAG laser through a 400-microm optic bare fiber. The parameters in laser delivery were 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec. Both the hardness and elastic modulus were obtained using an Instron microhardness tester and Vickers indenter. The indentations were then examined under a scanning electron microscope. The hardness and elastic modulus of irradiated human dentin in the energy of 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec were 44.7 kg/mm(2) and 22.8 GPa, and 46.9 kg/mm(2) and 21.4 GPa, respectively. These values were significantly lower than that of non-irradiated dentin by the Student's t test. Our study demonstrated that Nd:YAG laser irradiation would reduce the hardness and elastic modulus of human dentin.

The Effect of Sodium Hypochlorite Irrigant Concentration on Tooth Surface Strain

The effect of root-canal irrigation with different concentrations of sodium hypochlorite (3%, 5.1%, 7.3% NaOCI) on the mechanical properties of teeth was investigated in vitro. Root canals of 13 extracted, human premolars, denuded of enamel, were prepared with nickel-titanium rotary instruments (Quantec) to a standard size by using saline irrigation. An electrical strain gauge was bonded to the cervical aspect of each tooth. The 10 experimental teeth were subjected to 5 successive, 30-minute periods of irrigation. The irrigants were used in the following order: (a) saline; (b) 3.0% NaOCI; (c) 5.1% NaOCI; (d) 7.3% NaOCI; (e) saline. Three control teeth were irrigated with saline only for all five periods. After each irrigation, the teeth were cyclically loaded to 110N while the surface strain was measured. Changes in strain of the test teeth after each irrigation regimen followed broadly similar patterns that were different from the control teeth. There was no difference, however, in the strain recorded after irrigation by the different irrigants within the experimental group.

Indentation damage and mechanical properties of human enamel and dentin.

Understanding the mechanical properties of human teeth is important to clinical tooth preparation and to the development of "tooth-like" restorative materials. Previous studies have focused on the macroscopic fracture behavior of enamel and dentin. In the present study, we performed indentation studies to understand the microfracture and deformation and the microcrack-microstructure interactions of teeth. It was hypothesized that crack propagation would be influenced by enamel rods and the dentino-enamel junction (DEJ), and the mechanical properties would be influenced by enamel rod orientation and tooth-to-tooth variation. Twenty-eight human third molars were used for the measurement of hardness, fracture toughness, elastic modulus, and energy absorbed during indentation. We examined the effect of enamel rod orientation by propagating cracks in the occlusal surface, and in the axial section in directions parallel and perpendicular to the occlusal surface. The results showed that the cracks in the enamel axial section were significantly longer in the direction perpendicular to the occlusal surface than parallel. The cracks propagating toward the DEJ were always arrested and unable to penetrate dentin. The fracture toughness of enamel was not single-valued but varied by a factor of three as a function of enamel rod orientation. The elastic modulus of enamel showed a significant difference between the occlusal surface and the axial section. It is concluded that the cracks strongly interact with the DEJ and the enamel rods, and that the mechanical properties of teeth are functions of microstructural orientations; hence, single values of properties (e.g., a single toughness value or a single modulus value) should not be used without information on microstructural orientation.