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It has been reported that bond strength can be reversed to prebleached levels with the application of 10% alpha-tocopherol in a 2-hour time frame or by delaying bonding for 2 weeks. This study evaluated the effectiveness of a 5-minute application of 20% alpha-tocopherol to reverse the deleterious effects of nonvital bleaching on consequent bond strength. Thirty third molars were assigned to the following 3 groups: unbleached, bleached, and bleached followed by treatment with alpha-tocopherol. The bleached groups were exposed to sodium perborate (2 g/mL) for 7 days. The postbleach treatment group was subsequently treated with 20% alpha-tocopherol for 5 minutes, and then all groups were restored with composite resin. After 24 hours of storage at 37°C and 100% humidity, restored tooth specimens were sectioned into 1-mm 2 dentin-composite beams. Six beams from each tooth were subjected to microtensile bond strength testing. Representative beams were further evaluated with Raman microspectroscopy and scanning electron microscopy. The mean bond strength values (MPa) for each group were as follows: unbleached control group = 26.2, bleached control group = 20.3, and post-bleach treatment group = 18.5. A 1-factor analysis of variance and Tukey post hoc test (α = 0.05) indicated that bleaching had a detrimental effect on bond strength and that short-term alpha-tocopherol treatments did not improve postbleach bond strength. Raman microspectroscopy and scanning electron microscopy revealed no noted improvement for the post-bleach treatment group.The application of 20% alpha-tocopherol in a clinically relevant time frame was not effective in counteracting the deleterious effect of bleaching on bond strength. Bonding procedures should be delayed after tooth bleaching., (Copyright © 2019. Published by Elsevier Inc.)

Objectives: The aim of this paper is to determine the interrelationship between the microstructure - in terms of chemical composition and crystallinity - to the microhardness of coronal dentin., Methods: Dentin microhardness was tested by a novel reference point indenter and compared to the traditional Knoop hardness method. Micro-Raman spectroscopy was used to determine the chemical composition and crystallinity of dentin., Results: From the occlusal groove to the border of the coronal pulp chamber, dentin hardness decreased from superficial dentin (SD) to deep dentin (DD). Mineral/organic matrix ratios (phosphate/CH and phosphate/amide I) also decreased from SD to DD; however, this change was significant (P<0.05) in the phosphate/amide I ratio only. The phosphate/carbonate ratio decreased significantly by varying position from SD to DD. The degree of the crystallinity, as measured by the full width at half maximum (FWHM) of the peak at 960cm -1 , decreased significantly going from superficial to deep dentin., Significance: For the first time, the interrelationship between the microstructure and the mechanical properties of coronal dentin was determined by using the novel reference point indentation technique and micro-Raman spectroscopy. We hypothesize that the decrease in hardness from superficial to deep dentin can potentially be explained by decreased mineral content and increased carbonate content, which is also associated with decreased crystallinity. Collectively, there is a positive association between dentin hardness and mineral content and a negative association between dentin hardness and carbonate content., (Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.)

Objective: To understand radiotherapy-induced dental lesions characterized by enamel loss or delamination near the dentine-enamel junction (DEJ), this study evaluated enamel and dentine nano-mechanical properties and chemical composition before and after simulated oral cancer radiotherapy., Design: Sections from seven non-carious third molars were exposed to 2 Gy fractions, 5 days/week for 7 weeks for a total of 70 Gy. Nanoindentation was used to evaluate Young's modulus, while Raman microspectroscopy was used to measure protein/mineral ratios, carbonate/phosphate ratios, and phosphate peak width. All measures were completed prior to and following radiation at the same four buccal and lingual sites 500 and 30 μm from the DEJ in enamel and dentine (E-500, E-30, D-30 and D-500)., Results: The elastic modulus of enamel and dentine was significantly increased (P ≤ 0.05) following radiation. Based on Raman spectroscopic analysis, there was a significant decrease in the protein to mineral ratio (2931/430 cm(-1)) following radiation at all sites tested except at D-500, while the carbonate to phosphate ratio (1070/960 cm(-1)) increased at E-30 and decreased at D-500. Finally, phosphate peak width as measured by FWHM at 960 cm(-1) significantly decreased at both D-30 and D-500 following radiation., Conclusions: Simulated radiotherapy produced an increase in the stiffness of enamel and dentine near the DEJ. Increased stiffness is speculated to be the result of the radiation-induced decrease in the protein content, with the percent reduction much greater in the enamel sites. Such changes in mechanical properties and chemical composition could potentially contribute to DEJ biomechanical failure leading to enamel delamination that occurs post-radiotherapy. However, other analyses are required for a better understanding of radiotherapy-induced effects on tooth structure to improve preventive and restorative treatments for oral cancer patients., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The dental basement membrane (BM) is composed of collagen types IV, VI, VII, and XVII, fibronectin, and laminin and plays an inductive role in epithelial-mesenchymal interactions during tooth development. The BM is degraded and removed during later-stage tooth morphogenesis; however, its original position defines the location of the dentin-enamel junction (DEJ) in mature teeth. We recently demonstrated that type VII collagen is a novel component of the inner enamel organic matrix layer contiguous with the DEJ. Since it is frequently co-expressed with and forms functional complexes with type VII collagen, we hypothesized that type IV collagen should also be localized to the DEJ in mature human teeth. To identify collagen IV, we first evaluated defect-free erupted teeth from various donors. To investigate a possible stabilizing role, we also evaluated extracted teeth exposed to high-dose radiotherapy--teeth that manifest post-radiotherapy DEJ instability. We now show that type IV collagen is a component within the morphological DEJ of posterior and anterior teeth from individuals aged 18 to 80 yr. Confocal microscopy revealed that immunostained type IV collagen was restricted to the 5- to 10-µm-wide optical DEJ, while collagenase treatment or previous in vivo tooth-level exposure to > 60 Gray irradiation severely reduced immunoreactivity. This assignment was confirmed by Western blotting with whole-tooth crown and enamel extracts. Without reduction, type IV collagen contained macromolecular α-chains of 225 and 250 kDa. Compositionally, our results identify type IV collagen as the first macromolecular biomarker of the morphological DEJ of mature teeth. Given its network structure and propensity to stabilize the dermal-epidermal junction, we propose that a collagen-IV-enriched DEJ may, in part, explain its well-known fracture toughness, crack propagation resistance, and stability. In contrast, loss of type IV collagen may represent a biochemical rationale for the DEJ instability observed following oral cancer radiotherapy., (© International & American Associations for Dental Research.)

Unlabelled: According to previous reports, adverse effects of tooth bleaching on bond strength can be reversed by delaying bonding for 1-3 weeks or by applying 10% sodium ascorbate (SA) for 3 hours or more. This study evaluated the effectiveness of the short-term application of 35% SA to counteract the effects of a 7-day 35% hydrogen peroxide (H2O2) bleaching regimen on bond strength., Methods: Forty extracted third molars were mounted and sectioned to obtain a flat dentin surface and then randomly assigned into 4 groups: group 1: restored, no bleach; group 2: bleached, bonded immediately; group 3: bleached, treated with two 1- minute 35% SA applications before bonding; and group 4: bleached, treated with two 5-minute 35% SA applications before bonding. For bleach treatment in groups 2-4, flattened dentin surfaces were exposed to H2O2 for 7 days at 37°C. Subsequent to respective treatments, dentin surfaces were built up with composite (TPH3 and Prime &Bond NT, Dentsply Caulk, Milford, DE). After 24 hours of storage (100% humidity, 37°C), the specimens were sectioned into 1-mm(2) dentin-composite beams. Four beams from each tooth (n = 40/group) were subjected to microtensile bond strength testing., Results: Results were as follows: group 1: 18.1 ± 8.1MPa, group 2: 11.3 ± 5.7MPa, group 3: 11.2 ± 5.2MPa, and group 4: 12.6 ± 6.1MPa. A 1-factor analysis of variance and the Tukey post hoc test (α = 0.05) indicated that bleaching had a detrimental effect on bond strength and that short-term SA treatments after bleaching did not significantly improve bond strength., Conclusions: The application of 35% SA in a clinically relevant timeframe was not effective at reversing bleaching effects on bond strength. Bonding procedures should be delayed following tooth bleaching., (Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Although mature enamel is predominantly composed of mineral, a previously uncharacterized organic matrix layer remains in the post-eruptive tissue that begins at the dentin enamel junction and extends 200-300 μm towards the outer tooth surface. Identification of the composition of this layer has been hampered by its insolubility; however, we have developed a single step method to isolate the organic enamel matrix relatively intact. After dissociative dissolution of the matrix with SDS and urea, initial characterization by Western blotting and gel zymography indicates the presence of type IV and type VII basement membrane collagens and active matrix metalloproteinase-20. When combined with data from transgenic knockout mice and from human mutations, these data suggest that the enamel organic matrix (EOM) and dentin enamel junction may have a structural and functional relationship with basement membranes, e.g. skin. To clarify this relationship, we hypothesize a "foundation" model which proposes that components of the EOM form a support structure that stabilizes the crystalline enamel layer, and bonds it to the underlying dentin along the dentin enamel junction. Since we have also co-localized an active matrix metalloproteinase to this layer, our hypothesis suggests that, under pathologic conditions, MMP-mediated degradation of the EOM could destabilize the enamel-dentin interface.

The inner enamel region of erupted teeth is known to exhibit higher fracture toughness and crack growth resistance than bulk phase enamel. However, an explanation for this behavior has been hampered by the lack of compositional information for the residual enamel organic matrix. Since enamel-forming ameloblasts are known to express type VII collagen and type VII collagen null mice display abnormal amelogenesis, the aim of this study was to determine whether type VII collagen is a component of the enamel organic matrix at the dentin-enamel junction (DEJ) of mature human teeth. Immunofluorescent confocal microscopy of demineralized tooth sections localized type VII collagen to the organic matrix surrounding individual enamel rods near the DEJ. Morphologically, immunoreactive type VII collagen helical-bundles resembled the gnarled-pattern of enamel rods detected by Coomassie Blue staining. Western blotting of whole crown or enamel matrix extracts also identified characteristic Mr=280 and 230 kDa type VII dimeric forms, which resolved into 75 and 25 kDa bands upon reduction. As expected, the collagenous domain of type VII collagen was resistant to pepsin digestion, but was susceptible to purified bacterial collagenase. These results demonstrate the inner enamel organic matrix in mature teeth contains macromolecular type VII collagen. Based on its physical association with the DEJ and its well-appreciated capacity to complex with other collagens, we hypothesize that enamel embedded type VII collagen fibrils may contribute not only to the structural resilience of enamel, but may also play a role in bonding enamel to dentin., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Introduction: Ultrasonic instruments are available for a variety of endodontic uses. Few published evaluations exist that compare the dentin cutting efficiency of endodontic ultrasonic tips. Furthermore, previous comparison studies often did not take into account 2 critical factors: clinically relevant downward forces and linear movement during use., Methods: Four different round-tipped ultrasonic tips were compared (n = 5 per tip group): BUC-1 (Obtura Spartan, Fenton, MO), BL-2 (B&L Biotech, Bala Cynwyd, PA), BL-3 (B&L Biotech), and START-X #2 (Dentsply Maillefer, Ballaigues, Switzerland). The tips were attached to a testing apparatus that applied a 15-g axial force and a linear movement during instrumentation of a human dentin specimen. Instrumentation was completed at the manufacturers' recommended power settings, and 3 of the tips were also compared at an equal power setting. Instrumentation consisted of 20-second cycles for a total of 6 minutes. Dentin specimens were weighed at baseline and after 2, 4, and 6 minutes of instrumentation. The dentin cutting efficiency was measured by the change in weight of dentin specimens to the nearest 0.1 mg., Results: A 1-factor analysis of variance and Tukey post hoc analysis of cumulative dentin removal (after 6 minutes of instrumentation) revealed a statistically significant difference among the 4 ultrasonic tips (P ≤ .0001) at the recommended PS, with the BUC-1 tip removing significantly more dentin across time. At an equal power setting, the BUC-1 was significantly more efficient than the BL-3; no difference was found between the BUC-1 and the BL-2., Conclusions: Within the limits of this study, the BUC-1 showed the greatest dentin removal. Adding a linear movement and a clinically relevant axial force allows better generalization to clinical applications., (Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Introduction: Pointed ultrasonic tips can be used for several applications including troughing around intracanal obstructions. With the variety of pointed ultrasonic tips available, the purpose of this in vitro investigation was to compare the dentin cutting efficiency of 4 commonly used pointed ultrasonic tips., Methods: The ultrasonic tips (n = 5 tips/group) included in the study were the following: CPR-3D (Obtura Spartan, Algonquin, IL), BL 6A (B&L Biotech, Bala Cynwyd, PA), PUENDO2 (Dentsply Tulsa Dental Specialties, Tulsa, OK), and WH1 (eie2, San Diego, CA). The tips were attached to a testing apparatus that produced linear movement and a 15-g axial force during instrumentation of a human dentin specimen. For all tips, instrumentation was completed at the same power setting, which fell within the power setting range recommended by each manufacturer. Dentin specimens were weighed at baseline and after 6 minutes of instrumentation to measure dentin loss to the nearest 0.01 mg. A qualitative analysis of the shape and surface topography of new and used ultrasonic tips was performed via scanning electron microscopy., Results: A 1-factor analysis of variance and Tukey post hoc analysis of dentin removal revealed a statistically significant difference between the 4 ultrasonic tips (P < .05). The CPR-3D removed more dentin than the other 3 tips, whereas the BL 6A removed more dentin than the WH1. Scanning electron microscopic analysis revealed the CPR-3D as having the least change to tip shape and topography as compared with the other tips., Conclusions: Within the limits of this study, CPR-3D showed the greatest dentin removal, which may be linked to the stability of the CPR-3D tip shape and topography., (Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Objective: To investigate the ultrastructure and chemical composition of the dentine-enamel junction and adjacent enamel of minimally processed third molar tooth sections., Design: Undecalcified human third molar erupted teeth were sectioned and etched with 4% EDTA or 37% phosphoric acid prior to visualization by scanning electron microscopy. Confocal Raman spectroscopy was carried out at 50 μm and more than 400 μm away from the dentine-enamel junction before and after mild etching., Results: A novel organic protein-containing enamel matrix layer was identified for the first time using scanning electron microscopy of etched bucco-lingual sections of crowns. This layer resembles a three-dimensional fibrous meshwork that is visually distinct from enamel "tufts". Previous studies have generally used harsher solvent conditions which likely removed this layer and precluded its prior characterization. The shape of the organic enamel layer generally reflected that of sheath regions of enamel rods and extended from the dentine-enamel junction about 100-400 μm into the cuspal enamel. This layer exhibited a Raman CH stretching peak at ∼2931 cm(-1) characteristic of proteins and this signal correlated directly with the presence and location of the matrix layer as identified by scanning electron microscopy., Conclusions: The enamel protein layer was most prominent close to the dentine-enamel junction and was largely absent in cuspal enamel >400 μm away from the dentine enamel junction. We hypothesize that this protein containing matrix layer could provide an important biomechanical linkage between the enamel and the dentine-enamel junction and by extension, with the dentine, of the adult tooth (246 words)., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Aim: To evaluate the sealer/dentine interface associated with an epoxy resin sealer using the combination of Goldner's trichrome stain (GTS) and scanning electron microscopy (SEM) to verify the use of the experimental methodology., Methodology: Extracted human maxillary incisors (6) were subjected to root canal treatment. Subsequent to pulp removal, canal instrumentation and smear layer removal using EDTA and NaOCl, teeth were randomly and equally assigned to a 'wet' or 'dry' group. The 'dry' group was desiccated (95% ethanol/suction/paper points/air-drying), whilst the 'wet' group was treated with a saline rinse/suction/single paper point. Canals were then filled with an epoxy-based resin sealer and warm vertical gutta-percha compaction. After 7-day storage at 37°C, roots from each group were sectioned into apical, middle and coronal horizontal subsections that were cut and split into paired halves and evaluated with GTS or SEM. With GTS sections, hybrid layer and sealer tubular penetration were measured (n=15 measurements/intracanal location/condition) and evaluated using a two-factor repeated measures analysis of variance. The SEM qualitative analysis of paired sections was included as a complementary confirmation of GTS analyses., Results: In dry and wet groups, there was no conspicuous sealer/dentine interface hybrid layer, irrespective of canal location. However, dry specimens exhibited more uniform sealer distribution with deeper tubular penetration in the coronal and middle third (P<0.05). In contrast, there was decreased sealer distribution and tubule penetration in the apical third, regardless of moisture condition (P<0.05)., Conclusions: The experimental methodology (combination of GTS and SEM) can be used to evaluate the intracanal resin sealer/dentine interface. The pilot data indicated that thorough drying of the root canal system may result in improved epoxy resin sealer distribution and deeper resin sealer tubular penetration, especially in the coronal and middle thirds of root canals., (© 2010 International Endodontic Journal.)

Objective: The purpose of this study was to determine the loss of efficacy over time of the Buc-1 ultrasonic tip in dentin blocks., Study Design: An ultrasonic handpiece was mounted to the loading arm of a universal testing machine and a downward force of 15 g was applied in 20-sec cycles for a total of 30 min of instrumentation. Efficacy was measured by the change in weight of the dentin block to the nearest 0.01 mg after 2, 10, 20, and 30 minutes of instrumentation (n = 5 tips)., Results: Dentin removal decreased significantly between 2 and 10 minutes of instrumentation with no further significant decrease after 20 or 30 minutes (1-factor analysis of variance: alpha = .05)., Conclusion: The evidence suggests there is a significant decrease in dentin removal efficacy of the Buc-1 tip after 10 minutes of instrumentation. Continued instrumentation for up to 30 minutes showed no further decrease in efficacy., (Copyright (c) 2010 Mosby, Inc. All rights reserved.)

Introduction: The objective of this study was to compare the efficiency of 4 ultrasonic tips to remove dentin from sectioned third molars., Methods: The 4 groups (n = 5) were as follows: ET-18D, BUC-1, TUFI-2, and P5. A P5 Newtron XSTM ultrasonic unit was used. A universal tester applied a downward force of 15g, previously determined in a pilot study, in cycles of 20 seconds for a total of 4 minutes of instrumentation time. Efficiency was measured by change in weight of the dentin specimen measured to the nearest 0.01 mg after 2 and 4 minutes of instrumentation., Results: There was no statistically significant difference in dentin removal between measurement times for any tip (P>.05). There was a statistically significant difference in dentin removal as a function of tip type (P=.0001), with the BUC-1 tip removing significantly more dentin across time., Conclusions: On the basis of the results, the BUC-1TM tip removes dentin more efficiently than the other tips tested., (Copyright (c) 2010 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.)

Objective: BisGMA, a widely used component in dentin adhesive has very good mechanical properties after curing, but is relatively hydrophobic and thus, does not adequately infiltrate the water wet demineralized dentin collagen. Developing techniques that would lead to optimum infiltration of the hydrophobic component into the demineralized dentin matrix is very important. The purpose of this study was to evaluate interfacial morphological and chemical characteristics of the resultant adhesive-dentin interface when the ethanol wet bonding technique is used with hydrophobic adhesives., Materials and Methods: The occlusal one-third of the crown was removed from six unerupted human third molars; a uniform smear layer was created with 600 grit SiC. The dentin surface was etched with 35% phosphoric acid for 15s before applying BisGMA/HEMA model adhesive using either water wet or ethanol wet bonding technique. Five-micro-thick sections of adhesive/dentin interface specimens were cut and stained with Goldner's trichrome for light microscopy. Companion slabs were analyzed with SEM and micro-Raman spectroscopy., Results: The presence of ethanol in the demineralized dentin increased adhesive collagen encapsulation as indicated by trichrome staining. The SEM results confirmed that the ethanol wet bonding improved the quality of the interface. Micro-Raman spectral analysis of the dentin/adhesive interface indicated there was a gradual decrease in penetration of BisGMA component for specimens using water wet bonding, while relatively homogeneous distribution of the hydrophobic BisGMA component was noted in the interface with ethanol wet bonding., Significance: Wet bonding with ethanol instead of water permits better BisGMA infiltration improving the quality of interface. We speculate that the higher infiltration of hydrophobic BisGMA and better collagen encapsulation observed from the specimens using ethanol wet bonding would lead to more durable bonds because of improved resistance to hydrolytic attack.

The dentin-enamel junction (DEJ) plays an important role in preventing crack propagation from enamel into dentin. This function stems from its complex structure and materials properties that are different from either dentin or enamel. The molecular structural differences in both mineral and organic matrix across the DEJ zone were investigated by two-dimensional confocal Raman microspectroscopic mapping/imaging technique. The intensity ratios of 1450 (CH, matrix)/960 (P-O, mineral) decreased gradually to nearly zero across the DEJ. The width of this transition zone was dependent on the intratooth location, with 12.9 +/- 3.2 microm width at occlusal positions and 6.2 +/- 1.3 microm at cervical positions. The difference in width was significant (P < 0.001). Concurrently, spectral differences in both organic and inorganic matrices across the DEJ were also noted. For example, the ratios of 1243 (amide III)/1450 (CH) within the DEJ were lower than the values in dentin; however, the ratios of 1665 (amide I)/1450 (CH) within the DEJ were higher than those values in dentin. In addition, the ratios of 1070 (carbonate)/960 (phosphate) within the dentin were lower than the values in the DEJ. Raman images indicated that the distribution of the above ratios across the DEJ zone were also different at occlusal and cervical positions. The results suggest that the intratooth-location-dependent structure of the DEJ may be related to its function. Micro-Raman spectroscopic/imaging analysis of the DEJ provides a powerful means of identifying the functional width and molecular structural differences across the DEJ.

Use of composite restorations continues to increase, tempered by more potential problems when placed in posterior dentition. Thus, it is essential to understand how these materials function under stress-bearing clinical conditions. Because mastication is difficult to replicate in the laboratory, cyclic loading is frequently used within in vitro evaluations but often employs traditional fatigue testing, which typically does not simulate occlusal loading because higher stresses and loading frequencies are used, so failure mechanisms may be different. This investigation utilized relevant parameters (specimen size, loading frequency) to assess the effects of cyclic loading on flexural mechanical properties and fracture morphology of (coronal) dentin, composite, and dentin-adhesive-composite "laminate" structures. Incremental monitoring of flexural modulus on individual beams over 60,000 loading cycles revealed a gradual increase across materials; post hoc comparisons indicated statistical significance only for 1 versus 60k cycles. Paired specimens were tested (one exposed to 60k loading cycles, one to static loading only), and comparisons of flexural modulus and strength showed statistically significantly higher values for cyclically loaded specimens across materials, with no observable differences in fracture morphology. Localized reorganization of dentin collagen and polymer chains could have increased flexural modulus and strength during cyclic loading, which may have implications toward the life and failure mechanisms of clinical restorations and underlying tooth structure., (Copyright 2008 Wiley Periodicals, Inc.)

In clinical practice, dentists must frequently bond adhesives to caries-affected dentin substrates, but the bond that characteristically forms with these substrates does not provide the durability necessary for long-term clinical function. The purpose of this study was to characterize and compare the interfacial chemistry of adhesive with caries-affected and noncarious dentin using micro-Raman spectroscopy. The results indicated that the differences in the Raman spectra between noncarious and caries-affected dentin could not be accounted for by simple decreased mineralization. Both the structure of collagen and mineral in the caries-affected dentin has been altered by the caries process. The differences in structure and composition not only interfered with acid-etching process but also subsequent resin monomer penetration. It was shown that the interface between the adhesive and caries-affected dentin was wider and more complicated than that of the adhesive and noncarious dentin. As a result of adhesive phase separation, a structurally integrated hybrid layer did not form at the interface with either caries-affected or noncarious dentin. Using chemical imaging techniques, this study provides the direct evidence of adhesive phase separation at the interface with caries-affected dentin. Although our group previously reported adhesive phase separation at the interface with noncarious dentin, the chemistry of caries-affected dentin leads to greater variability and a more highly irregular composition along the length and breadth of the interface., (Copyright 2006 Wiley Periodicals, Inc.)

The calculation of the scalar compressive and shear anisotropy factors developed for single crystal refractory compounds has been adapted to the anisotropic elastic stiffness coefficients determined by a number of ultrasonic measurements of bone based on transverse isotropic symmetry. Later, this work was extended to include the ultrasonic measurements of bone based on orthotropic symmetry. Recently, the five transverse isotropic elastic constants for both wet and dry human dentin were determined using resonant ultrasound spectroscopy. The five transverse isotropic elastic constants for wet bovine enamel and dentin had been calculated based on modeling of ultrasonic wave propagation measurements and related data in the literature. The scalar compressive and shear anisotropy factors have been calculated from both these sets of data and are compared with a representative set from those published previously for both human and bovine bone and both fluoro- and hydroxyl-apatites.

Purpose: The purpose of this study was to analyze a resin cement/dentin interface by comparing the diffusion of a resin cement into dentin surfaces pretreated with a self-etching primer with or without pretreatment by conventional acid etching., Materials and Methods: Dentin surfaces of 8 unerupted human third molars were treated with a self-etch primer (Panavia 21) with or without conventional phosphoric acid pretreatment. Panavia 21 resin cement was applied according to manufacturer's instructions. Dentin/resin cement interface sections from each tooth were examined with scanning electron microscopy and micro-Raman spectroscopy., Results: When the self-etch primer was used following conventional acid pretreatment, the resin cement did not penetrate to the depth of the zone of demineralized dentin, leaving a substantial area of exposed dentin matrix at the dentin/cement interface. In contrast, there was substantial resin cement diffusion throughout the demineralized dentin when the self-etch primer was used without acid etching pretreatment., Conclusion: The in vitro evaluation of resin cement penetration throughout the zone of demineralized dentin is an important step in identifying sites of exposed dentin matrix that may promote postoperative sensitivity and may leave the dentin/resin cement interface vulnerable to premature degradation under clinical conditions. In this study, the self-etch primer used alone produced substantial resin cement penetration and left no exposed dentin matrix at the dentin/resin cement interface.

It is commonly reported that acid etchants remove the smear layer, but to date, there has been no chemical evidence to support these observations. The purpose of this study was to determine the molecular structure of acid-etched carbide- and diamond-bur-created smear layers. This project tested the null hypothesis that such smear layers are totally removed with current etchants. Smear layer/demineralized/mineralized dentin interfaces were analyzed at 1- m intervals by micro-Raman spectroscopy. Features associated with the organic component were substantially broadened with loss of fine structure, and mineral peaks were clearly evident in the spectra of acid-etched smear layers. The organic features in the spectra of the EDTA-treated smear layer showed relative intensity ratios similar to demineralized dentin without contribution from the mineral phase. The disorganized collagen within the smear layer was not removed but was denatured by the acid treatment; the mineral was trapped in this gelatinous matrix and shielded from complete reaction.

Purpose: The purpose of this study was to compare the penetration of a resin cement into dentin surfaces pretreated with self-etching primer with or without conventional acid etch., Materials and Methods: Dentin surfaces of 8 unerupted human third molars were treated with self-etch primer (Panavia 21; Kuraray Co, Ltd, Osaka, Japan) with or without conventional acid etch treatment. A resin cement (Panavia 21) was applied according to manufacturer's instructions. Dentin/resin cement interface sections from each tooth were examined with light microscopy and scanning electron microscopy. In the light microscopy sections, exposed protein at the dentin/cement interface was stained a distinct red with Goldner's trichrome., Results: The resin cement did not penetrate the depth of the zone of demineralized dentin when the self-etch primer was used in combination with conventional acid etch treatment. Inadequate resin cement penetration leaves a substantial area of exposed protein at the dentin/cement interface. In contrast, there was complete resin cement diffusion throughout the demineralized dentin when the self-etch primer was used without acid etching., Conclusions: Combining conventional acid etch treatment with a self-etching primer/resin cement system resulted in incomplete resin cement penetration and exposed protein at the dentin/cement interface.