Effects of acid-etching on the tensile properties of demineralized dentin matrix.

OBJECTIVES: Little research has been done to evaluate the effects of acids commonly used in adhesive dentistry, on the tensile properties of the demineralized dentin matrix. The purpose of this study was to evaluate the effects of a number of acidic conditioners on the ultimate tensile strength (UTS) and modulus of elasticity (E) of human coronal dentin matrix. METHODS: Small hour-glass shaped (for UTS) or l-beam shaped (for determination of E) were prepared from mid-coronal dentin of extracted human third molars. After protecting the ends with varnish, the middle of the specimens was completely demineralized in 0.5 M EDTA (pH 7). UTS was determined by tensile stressing to failure. Modulus of elasticity was calculated from stress strain curves. The results were analyzed by ANOVA and Student-Neuman-Keuls test at the 95% confidence level. RESULTS: Brief (ca. 1-2 min) exposure of demineralized dentin matrix to acids had no measurable effects on its tensile properties. Ten-minute exposures to 2.5% and 17.5% nitric acid lowered (p < 0.05) the UTS compared to phosphate buffered saline (PBS)-exposed controls. Exposure of the decalcified dentin to 10% citric acid containing 3% ferric chloride, 10% citric acid, 37% phosphoric acid or 17.5% nitric acid containing 3% ferric chloride for 10 min had no effect on UTS. None of these acids consistently lowered stiffness. SIGNIFICANCE: The results indicate that relatively long exposures to acids are required to alter the tensile properties of demineralized dentin. It is unlikely that the brief exposures to acids that are used in adhesive dentistry would acutely weaken the physical properties of demineralized dentin. However, long-term studies should be done to determine if such treatment increases the susceptibility of the matrix to hydrolysis.     

Effects of water and water-free polar solvents on the tensile properties of demineralized dentin.

OBJECTIVES: The aim of this study was to test the null hypothesis that the tensile properties of demineralized dentin are not influenced by the hydrogen bonding ability of anhydrous polar solvents. METHODS: Dentin disks 0.5mm thick were prepared from mid-coronal dentin of extracted, unerupted, human third molars. 'I' beam and hour-glass shaped specimens were prepared from the disks, the ends protected with nail varnish and the central regions completely demineralized in 0.5M EDTA for 5 days. Ultimate tensile stress (UTS) and low-strain apparent modulus of elasticity (E) were determined with the specimens immersed for 60 min in water, methanol, HEMA, acetone or air prior to testing in those same media. Apparent moduli of elasticity were measured on the same specimens in a repeated measures experimental design. The results were analyzed with a one-way ANOVA on ranks, followed by Dunn's test at alpha=0.05. Regression analysis examined the relationship between UTS or E and Hansen's solubility parameter for hydrogen bonding (delta(h)) of each solvent. RESULTS: The UTS of demineralized dentin in water, methanol, HEMA, acetone and air was 18(7), 29(7), 31(6), 41(13) and 146(27)MPa, x(SD), n=10. Low-strain E for the same media were 11(7), 43(12), 79(21), 132(31) and 253(115)MPa. Regression analysis of UTS vs delta(h) revealed a significant (p<0.0005, r=-0.69, R(2)=0.48) inverse, exponential relationship. A similar inverse relationship was obtained between low-strain E vs delta(h) (p<0.0001, r=-0.93, R(2)=0.86). SIGNIFICANCE: The tensile properties of demineralized dentin are dependent on the hydrogen bonding ability of polar solvents (delta(h)). Solvents with low delta(h) values may permit new interpeptide H-bonding in collagen that increases its tensile properties. Solvents with high delta(h) values prevent the development of these new interpeptide H-bonds.     

Collagen cross-linking and ultimate tensile strength in dentin

Several studies have indicated differences in bond strength of dental materials to crown and root dentin. To investigate the potential differences in matrix properties between these locations, we analyzed upper root and crown dentin in human third molars for ultimate tensile strength and collagen biochemistry. In both locations, tensile strength tested perpendicular to the direction of dentinal tubules (undemineralized crown = 140.4 +/- 48.6/root = 95.9 +/- 26.1; demineralized crown = 16.6 +/- 6.3/root = 29.0 +/- 12.4) was greater than that tested parallel to the tubular direction (undemineralized crown = 73.1 +/- 21.2/root = 63.2 +/- 22.6; demineralized crown = 9.0 +/- 3.9/root = 16.2 +/- 8.0). The demineralized specimens showed significantly greater tensile strength in root than in crown. Although the collagen content was comparable in both locations, two major collagen cross-links, dehydrodihydroxylysinonorleucine/its ketoamine and pyridinoline, were significantly higher in the root (by ~ 30 and ~ 55%, respectively) when compared with those in the crown. These results indicate that the profile of collagen cross-linking varies as a function of anatomical location in dentin and that the difference may partly explain the site-specific tensile strength.     

Anisotropy of tensile strength of root dentin

An effect of dentinal tubule orientation on mechanical properties of dentin has been difficult to demonstrate. We have tested the hypothesis that ultimate tensile strength (UTS) of dentin is affected by tubule (and hence collagen fibril) orientation. The UTS of human root dentin was investigated by direct tensile and diametral testing of specimens of known orientation prepared from extracted teeth. Dumbbell-shaped samples were machined for direct tensile testing (load parallel or perpendicular to tubule direction) and cylinders for diametral testing (load at 0 degrees, 45 degrees, 67.5 degrees, and 90 degrees). Fractured surfaces were examined by SEM. UTS was lowest when the tensile force was parallel to tubule orientation, and greatest at 90 degrees to tubule orientation (fracture parallel to tubule direction). SEM views of fractured surfaces suggested that microstructure contributes to fracture patterns. At least for properties involving disruption of the collagen matrix, root dentin shows a definite anisotropy.     

Cytotoxicity test of dentin bonding agents using millipore filters as dentin substitutes in a dentin barrier test

Objectives

The purpose of this study was to find proper dentin substitute for standardized dentin barrier test and perform the cytotoxicity test of commercial bonding agents with the proper substitute.

Materials and methods

The three-dimensional cells attached to dentin disc or millipore filters as the dentin substitute were tested in a dentin barrier test by perfusion. MTT assay was performed as an evaluation method for the cell survival rate. The cytotoxicity test of serial phenol dilution by bovine dentin disc was done to determine a standard toxic material, and the test of this proper phenol by using various millipore combinations was performed to find the suitable dentin substitute. Also, the cytotoxicity test of bonding agents was performed by this standardized substitute. The cell viability was expressed as percentages of untreated group.

Results

Phenol concentration of 0.05 % was selected as the standard toxic material. The different combinations of millipore filters—two sheets of 0.45 μm, two sheets of 0.22 μm, and the combination of 0.65, 0.45, and 0.22 μm—showed similar cytotoxicity to natural dentin discs by 0.05 % phenol (p?>?0.05). The millipore combination of 0.65, 0.45, and 0.22 μm that had structural similarity to natural dentin discs was used as the substitute for cytotoxicity test of bonding agents. The toxic level of Adper Prompt L-Pop using the selected substitute was significantly the highest among four kinds of dentin bonding agents (p?<?0.05). Also, the dentin barrier test by the substitute showed constant results compared with the one by the natural dentin disc.

Conclusions

The millipore filter combination of 0.65, 0.45, and 0.22 μm could be used as the substitute for the cytotoxicity test of materials applied to dentin.

Clinical relevance

Dentin barrier test by standardized substitutes would be helpful for considering the potential toxicity of dentin bonding agents prior to clinical adaptations and reducing the variations of natural bovine dentin that has individually different characteristics.     

Relation between incremental lines and tensile strength of coronal dentin

In one aspect, this study examined the tensile strength of coronal dentin, as a function of the location of incremental lines, in two types of teeth: human molar versus bovine incisor. In another aspect, tensile strength in coronal dentin was examined with tensile loading in two different orientations to the incremental lines: parallel versus perpendicular. There were four experimental groups in this study: HPa, human molar dentin with tensile orientation parallel to the incremental lines; HPe, human molar dentin with tensile orientation perpendicular to the incremental lines; BPa, bovine incisor dentin with tensile orientation parallel to the incremental lines; BPe, bovine incisor dentin with tensile orientation perpendicular to the incremental lines. Tensile strengths of the parallel group (HPa and BPa) were significantly higher (p<0.05) than those of the perpendicular group (HPe and BPe). Effect of structural anisotropy, contributed by the incremental lines, was thus confirmed in coronal dentin. However, there were no differences in anisotropy effect between the two tooth types.     

The inductive properties of human dentin and cementum

Studies of the inductive properties of human dentin and cementum have yielded differing results. Comparisons are difficult to draw because of variations in time, donor tissue, host immunologic status, implant site, decalcifying agents and degree of decalcification. Analysis of the many experiments intimates that the answers may lie in the use of citric acid and/or the degree of decalcification. The direction of future investigations is suggested.     

牙本质屏障细胞毒性试验的研究进展

牙本质屏障细胞毒性试验能较好地模拟临床实际,在评价牙体充填材料及与牙本质直接接触材料细胞毒性方面有很大的价值,具有替代动物试验的可能性,并已广泛应用于相关材料的毒性研究。该文就此试验中细胞的选择与培养、试验装置和牙本质片的选取等主要关键技术点做一综述。     

The direct tensile test of composite resins using the small specimen--effect of the preparation of specimen, the size of specimen and the testing condition on the tensile properties

The direct tensile test of composite resins using the specimen with the gauge length 10 mm has been developed by authors. In this study smaller specimens with the gauge length 5 mm and 2 mm were also investigated. As the gauge length became smaller, tensile properties such as the proportional limit, the proof stress, and the tensile strength showed the tendency to become higher. The effect of strain rate on the tensile properties appeared clearly when using the specimen with the gauge length 2 mm. The small specimen was found to have many advantages for the preparation, the cost of material and the handling during the tensile test.     

The effect of local interfacial geometry on the measurement of the tensile bond strength to dentin

The local detail of the geometry of the adhesive interface can have a significant effect on the measurement of dentin bond strengths and may be a contributory factor in the discrepancies among data in the published literature. The potential effect on the dentin bond strength due to modifications of the local stress distribution at the adhesive/dentin interface has been assessed. Tensile bond strength measurements for specimens with and without an adhesive flash were carried out and compared with the stress distribution at the adhesive interface determined by finite element stress analysis. The results showed that when the adhesive was constrained to the interface only, the tensile bond strength was 3.10 MPa, which increased to 6.90 MPa when a flash of adhesive was present. For a realistic measurement of dentin bond strength, the adhesive should be constrained to the interface only. Extension of the adhesive beyond the interface will result in an artificially high value for the dentin bond strength. A standardized method for the measurement of dentin bond strength is urgently needed, but must take these as well as all other known factors into account if results from different testing centers are to be directly comparable.     

The influence of design and production on the structural integrity of tensile test specimens and stated values for mechanical properties

Two sizes of tensile test specimens were produced, the smaller of them by several techniques each incorporating a particular casting variable. All castings were subsequently subjected to radiographic evaluation and mechanical testing. An attempt has been made to relate the application of each variable to the degree of metal integrity produced in the specimens and ultimately to mechanical behaviour.     

Effect of the dentin smeared layer on tensile strength of cemented posts

The tensile strengths for post lengths of 4 and 7 mm were compared in vitro with 3 different cementing media. In one group, the post preparation was rinsed with 5.25% NaOCl and in the other with 17% EDTA followed by 5.25% NaOCl. The EDTA-NaOCl flush had a profound effect when unfilled resin was used to cement the posts. A 4 mm post cemented with resin in the EDTA-NaOCl group was one and one-half times as retentive as a 7 mm post cemented with zinc phosphate and twice as strong as the 7 mm post with polycarboxylate cement. The 7 mm post cemented with the resin after the EDTA-NaOCl rinse was twice as resistant to displacement as the 7 mm post cemented with zinc phosphate and three times stronger than the polycarboxylate cement.     

Density of dentinal tubules affects the tensile strength of root dentin.

OBJECTIVES: The aim of this study is to count the dentinal tubules in the coronal and middle-apical third of root dentin of teeth extracted due to the progression of periodontal disease, and to compare the Ultimate Tensile Strength (UTS) of the same areas. The research hypothesis was that root dentin areas with different densities of dentinal tubules would also show different UTS values. METHODS: From 10 caries free maxillary central, lateral incisors and canines, extracted for periodontal reasons from three patients, cylindrical specimens approximately 10 mm long were prepared parallel to the long axis of the root and then divided into two parts using a low speed diamond saw one from the coronal third of the root, (Group 1) and one from the middle-apical third of the root (Group 2). The density of the dentinal tubules of the specimens of the two groups was measured by means of a scanning electron microscope and the UTS of the specimens was measured by a microtensile test. One way ANOVA was used to assess the effect of specimen location (coronal specimens vs. middle-apical specimens) on UTS. The differences in the density of dentinal tubules between coronal and middle-apical specimens were also subjected to statistical analysis using one-way ANOVA. RESULTS: UTS values of middle-apical specimens were found to be significantly (p < 0.05) higher than those of coronal specimens. The results of the one-way analysis of variance showed that the number of dentinal tubules of the samples from the coronal part of the root groups was significantly higher than that of samples from the middle-apical part (p < 0.05). SIGNIFICANCE: These results suggest that high values of tensile strength of the dentin are associated with low densities of dentinal tubules and that apical areas of root dentin are more resistant to tension than coronal ones.     

The effect of diabetes on the tensile bond strength of a restorative dental composite to dentin

Odontology - This study was performed to evaluate the effect of diabetes mellitus (DM) on the tensile bond strength (TBS) of dental composite resin bonding to enamel and dentin of extracted human...     

Viscoelastic properties and residual strain in a tensile creep test on bovine temporomandibular articular discs

This study was designed to evaluate the creep characteristics and residual strain of bovine temporomandibular joint (TMJ) discs in tension. Twenty discs were divided into three specimens each: central, lateral and medial regions. Tension of 1.0 MPa was applied and sustained for 20 min to the specimens from 10 right-side discs, and tension of 1.5 MPa to specimens from 10 left-side discs. After the period of tension for creep, the specimens were removed from the tension devices and restoration observed for 20 min. Time-dependent creep curves showed a marked change in strain during the initial 5s. The essential time delay in strain ceased after 2 min, and strain reached an almost steady level after 3 min. At a tensile stress of 1.5 MPa, a strain of 14.5% on average was produced after 20 min creep in the central specimens; peripheral specimens showed strains of 12.4% on average. There were significant differences in strain between the central and peripheral specimens. The residual strain after 20 min restoration was 0.93% on average and there were no significant regional differences. This creep feature could be well represented by a generalized linear viscoelastic model. It was concluded that the regional differences in viscoelasticity might be caused by the complicated articulating functions of the TMJ, and that the residual strain caused by sustained stress could be an important factor in disc deformation.     

葡萄籽提取物对脱矿牙本质极限拉伸强度及树脂-牙本质粘接强度的影响

目的:探讨葡萄籽提取物(grape seed extract,GSE)短暂预处理脱矿牙本质对其极限拉伸强度及树脂-牙本质即刻微拉伸粘接强度的影响。方法:以乙醇、丙酮、蒸馏水为溶剂配制不同浓度的GSE溶液,以溶剂为空白对照,无预处理为阴性对照,5%戊二醛为阳性对照,每组样本15例。GSE预处理脱矿牙本质后,测试牙本质极限拉伸强度及树脂-牙本质微拉伸粘接强度,观察粘接断裂面微观形貌并分析断裂模式。结果:GSE预处理组牙本质极限拉伸强度均呈浓度和时间依赖性增加。应用Single Bond 2粘接时,无论何种溶剂,10%或15%GSE预处理组微拉伸粘接强度显著高于空白对照组(P<0.05);而用Prime&Bond NT粘接时,仅15%GSE水溶剂组和10%GSE丙酮溶剂组微拉伸粘接强度显著高于空白对照组(P<0.05)。交联预处理对水和乙醇溶剂的Single Bond 2粘接时微拉伸粘接强度的改善作用比用水和丙酮溶剂的Prime&Bond NT粘接时更为显著。粘接试件断裂均以混合破坏为主,预处理组试件断裂多发生在混合层顶部,而阴性和空白对照组断裂多位于混合层底部。结论:GSE短暂预处理脱矿牙本质可改善其机械性能,增强混合层,并提高树脂-牙本质即刻微拉伸粘接强度。     

The influence of chemical structure on the properties in methacrylate-based dentin adhesives

Objectives

The objective of this study was to investigate the influence of the chemical structure of methacrylate monomers used in dentin adhesives on degree of conversion (DC), water sorption, and dynamic mechanical properties.

Materials and methods

Experimental adhesives containing 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane (BisGMA), 2-hydroxyethyl methacrylate (HEMA), and co-monomer, 30/45/25 (w/w) were photo-polymerized. Ethyleneglycol dimethacrylate (EGDM), diethyleneglycol dimethacrylate (DEGDM), triethyleneglycol dimethacrylate (TEGDMA), 1,3-glycerol dimethacrylate (GDM), and glycerol trimethacrylate (GTM) were used as a co-monomer. The adhesives were characterized with regard to DC, water sorption, and dynamic mechanical analysis and compared to control adhesive [HEMA/BisGMA, 45/55 (w/w)].

Results

DC and water sorption increased with an increase in the number of ethylene glycol units in the monomer. Experimental adhesive containing GDM showed significantly higher storage moduli (p < 0.05) in both dry and wet samples than experimental adhesives containing EGDM or DEGDM. The rubbery moduli of adhesives containing GDM and GTM were found to be significantly greater (p < 0.05) than that of the control. Adhesives containing GTM exhibited the widest tan δ curves, indicating the greatest structural heterogeneity.

Significance

The hydrophilicity, functionality and size of monomers in dentin adhesives affected the water sorption, solubility, crosslink density and heterogeneity of the polymer network. The experimental adhesives containing GDM and GTM showed higher rubbery moduli, indicating higher crosslink density accompanied by a decrease in the homogeneity of the polymer network structure.     

In vitro tensile bond strengths of amalgam to treated dentin.

Since amalgam traditionally relies on undercuts in the tooth preparation for retention, extensive tooth structure must be removed for amalgam core build-ups. In contrast, the ideal build-up material would achieve its retention by directly bonding to tooth structure. This study compared tensile bond strengths of amalgam to dentin using All-Bond Liner-FX with three different dentin pretreatment conditions and Amalgambond according to the manufacturer's directions. One hundred and twenty dentin samples were tested. Groups 1-3 used All-Bond Liner-FX as a bonding agent. Group 1 received a 15-second application of 10 percent phosphoric acid on the dentin; Group 2 received the recommended dentin conditioner; and Group 3 received no dentin pretreatment. Group 4 used Amalgambond as the bonding agent after a 10-second application of 10 percent citric acid/3 percent ferric chloride. Analysis of the data was conducted using both ANOVA and the Weibull statistic. Results of the analysis of variance indicate that there were no statistical differences among mean tensile bond strengths for the three dentin pretreatment conditions using All-Bond. All (30) of the Amalgambond specimens debonded prior to testing. The All-Bond fracture data was well described by the Weibull function as evidenced by the high coefficient of determination (R2 = 0.98-0.99). Fracture analysis indicated that all of the Amalgambond failures were adhesive at the Amalgambond-amalgam interface. All-Bond fractures were mixed cohesive/adhesive failures indicating similar bonding to amalgam and dentin.     

Anisotropy of tensile strengths of bovine dentin regarding dentinal tubule orientation and location

The purpose of this study was to investigate the effects of the location and orientation of dentinal tubules in the tooth on tensile strengths of the dentin. Dumbbell-shaped specimens of 12 groups from various locations and dentinal tubule orientations were prepared. The tensile test was performed in distilled water at a temperature of 37 degrees C. The tensile strengths of the parallel to the orientation were significantly greater than those of the perpendicular to the orientation; the tensile strengths of the radicular dentin were significantly greater than those of the coronal dentin. Nevertheless, in the radicular dentin, the tensile strengths of the perpendicular to dentinal tubules differ with respect to tensile forces. These results suggest that tensile strength of the dentin varies according to the location and orientation of dentinal tubules in the tooth.     

Influence of load cycling and tubule orientation on ultimate tensile strength of dentin

PURPOSE: The purpose of this study was to evaluate the effect of mechanical load cycling and tubule orientation on the ultimate tensile strength of crown and root dentin. MATERIALS AND METHODS: Twenty bovine teeth were cleaned and their incisal surfaces reduced, resulting in a flat surface 4 mm above the cementoenamel junction. The teeth were divided into 4 groups: G1 = control (no mechanical load cycling); G2 = 1,000,000 load cycles at 50 N; G3 = 1,000,000 load cycles at 100 N; G4 = 1,000,000 load cycles at 200 N. Sections of 0.5+/-0.1 mm thick were cut mesiodistally and the slabs further trimmed to 0.5+/-0.1 mm in an hourglass shape, according to the tubule orientation (parallel and/or perpendicular to the long axis of the tooth) in the root and crown, with a fine diamond bur to produce a cross-sectional surface area of 0.25 mm2. All specimens were then subjected to ultimate tensile strength testing at a crosshead speed of 1 mm/min. Means and standard deviations were expressed in MPa. The bond strength data were analyzed with three-way ANOVA and Fisher's PLSD test (p < 0.05). RESULTS: Ultimate tensile strength values did not differ statistically significantly between the loaded group and the control. However, statistical differences existed between root and coronal dentin (p < 0.001) and between parallel and perpendicular orientation of tubules (p < 0.001), where root and sections parallel to the tubules presented higher values than coronal and perpendicular, respectively. These differences were not related to mechanical loading. CONCLUSION: There was no effect of in vitro load cycling on ultimate tensile strength of dentin. Differences presented between ultimate tensile strength of crown vs root dentin and parallel vs perpendicular to the tubule orientation can be influenced by differences in the amount of organic and inorganic content as well as composition of the dentin matrix. It is important to consider these aspects when predicting the quality and durability of restorations according to the types of dentin and tubule orientation to be restored.