Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs.
We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression.
An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a well-behaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele.
Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors. Neurology® 2012;78:690–695
X-linked myotubular myopathy (MTM) is a severe neuromuscular disease of infancy caused by mutations of MTM1, which encodes the phosphoinositide lipid phosphatase, myotubularin. The Mtm1 knockout (KO) mouse has a severe phenotype and its short lifespan (8 weeks) makes it a challenge to use as a model in the testing of certain preclinical therapeutics. Many MTM patients succumb early in life, but some have a more favorable prognosis. We used human genotype–phenotype correlation data to develop a myotubularin-deficient mouse model with a less severe phenotype than is seen in Mtm1 KO mice. We modeled the human c.205C>T point mutation in Mtm1 exon 4, which is predicted to introduce the p.R69C missense change in myotubularin. Hemizygous male Mtm1 p.R69C mice develop early muscle atrophy prior to the onset of weakness at 2 months. The median survival period is 66 weeks. Histopathology shows small myofibers with centrally placed nuclei. Myotubularin protein is undetectably low because the introduced c.205C>T base change induced exon 4 skipping in most mRNAs, leading to premature termination of myotubularin translation. Some full-length Mtm1 mRNA bearing the mutation is present, which provides enough myotubularin activity to account for the relatively mild phenotype, as Mtm1 KO and Mtm1 p.R69C mice have similar muscle phosphatidylinositol 3-phosphate levels. These data explain the basis for phenotypic variability among human patients with MTM1 p.R69C mutations and establish the Mtm1 p.R69C mouse as a valuable model for the disease, as its less severe phenotype will expand the scope of testable preclinical therapies.
While the Apex chert is one of the most well-studied Archean deposits on Earth, its formation history is still not fully understood. Here, we present Raman spectroscopic data collected on the carbonaceous material (CM) present within the matrix of the Apex chert. These data, collected within a paragenetic framework, reveal two different phases of CM deposited within separate phases of quartz matrix. These multiple generations of CM illustrate the difficulty of searching for signs of life in these rocks and, by extension, in other Archean sequences. Key Words: Apex chert—Carbonaceous material—Raman microspectroscopy—Paragenetic analysis—Archean. Astrobiology 12, 160–166.
Myotubular myopathy (MTM) is a severe congenital muscle disease characterized by profound weakness, early respiratory failure and premature lethality. MTM is defined by muscle biopsy findings that include centralized nuclei and disorganization of perinuclear organelles. No treatments currently exist for MTM. We hypothesized that aberrant neuromuscular junction (NMJ) transmission is an important and potentially treatable aspect of the disease pathogenesis. We tested this hypothesis in two murine models of MTM. In both models we uncovered evidence of a disorder of NMJ transmission: fatigable weakness, improved strength with neostigmine, and electrodecrement with repetitive nerve stimulation. Histopathological analysis revealed abnormalities in the organization, appearance and size of individual NMJs, abnormalities that correlated with changes in acetylcholine receptor gene expression and subcellular localization. We additionally determined the ability of pyridostigmine, an acetylcholinesterase inhibitor, to ameliorate aspects of the behavioral phenotype related to NMJ dysfunction. Pyridostigmine treatment resulted in significant improvement in fatigable weakness and treadmill endurance. In all, these results describe a newly identified pathological abnormality in MTM, and uncover a potential disease-modifying therapy for this devastating disorder.
A pooled analysis was conducted of 1257 toddlers who received a fourth dose of Haemophilus influenzae type b-Neisseria meningitidis serogroups C and Y-tetanus toxoid conjugate vaccine (HibMenCY-TT) or Hib conjugate vaccine (Hib polysaccharide conjugated to N. meningitidis outer membrane protein) coadministered with measles-mumps-rubella (MMR) and varicella (VAR) vaccines (NCT00134719/NCT00289783). Noninferiority of immunological responses to MMR and VAR was demonstrated between groups and incidences of MMR- and VAR-specific solicited symptoms were similar, indicating that HibMenCY-TT can be coadministered with MMR and VAR.
Haemophilus influenzae type b; Neisseria meningitidis serogroups C and Y; MMR; varicella; vaccination; toddlers
It was hypothesized that applying the polymer-induced liquid-precursor (PILP) system to artificial lesions would result in time-dependent functional remineralization of carious dentin lesions that restores the mechanical properties of demineralized dentin matrix. 140 µm deep artificial caries lesions were remineralized via the PILP process for 7–28 days at 37°C to determine temporal remineralization characteristics. Poly-L-aspartic acid (27 KDa) was used as the polymeric process-directing agent and was added to the remineralization solution at a calcium-to-phosphate ratio of 2.14 (mol/mol). Nanomechanical properties of hydrated artificial lesions had a low reduced elastic modulus (ER = 0.2 GPa) region extending about 70 μm into the lesion, with a sloped region to about 140 μm where values reached normal dentin (18–20 GPa). After 7 days specimens recovered mechanical properties in the sloped region by 51% compared to the artificial lesion. Between 7–14 days, recovery of the outer portion of the lesion continued to a level of about 10 GPa with 74% improvement. 28 days of PILP mineralization resulted in 91% improvement of ER compared to the artificial lesion. These differences were statistically significant as determined from change-point diagrams. Mineral profiles determined by micro x-ray computed tomography were shallower than those determined by nanoindentation, and showed similar changes over time, but full mineral recovery occurred after 14 days in both the outer and sloped portions of the lesion. Scanning electron microscopy and energy dispersive x-ray analysis showed similar morphologies that were distinct from normal dentin with a clear line of demarcation between the outer and sloped portions of the lesion. Transmission electron microscopy and selected area electron diffraction showed that the starting lesions contained some residual mineral in the outer portions, which exhibited poor crystallinity. During remineralization, intrafibrillar mineral increased and crystallinity improved with intrafibrillar mineral exhibiting the orientation found in normal dentin or bone.
A major goal in bone engineering is the creation of large volume constructs (scaffolds and stem cells) that bear load. The scaffolds must satisfy two competing requirements—they need be sufficiently porous to allow nutrient flow to maintain cell viability, yet sufficiently dense to bear load. We studied the effect of scaffold macroporosity on bone formation and scaffold strength, for bone formed by human bone marrow stromal cells.
Rigid cubical hydroxyapatite/tricalcium phosphate scaffolds were produced by robo-casting. The ceramic line thickness was held constant, but the distance between adjacent lines was either 50, 100, 200, 500, or 1000 μm. Cultured human bone marrow stromal cells were combined with the scaffolds in vitro; transplants were placed into the subcutis of immunodeficient mice. Transplants were harvested 9, 18, 23, 38, or 50 weeks later. Bone formation and scaffold strength were analyzed using histology and compression testing.
Sixty transplants were evaluated. Cortical bone increased with transplant age, and was greatest among 500 μm transplants. In contrast, maximum transplant strength was greatest among 200 μm transplants.
Lamellar spacing within scaffolds regulates the extent of bone formation; 500 μm yields the most new bone, whereas 200 μm yields the strongest transplants.
The soft zone in dentine beneath the dentino-enamel junction is thought to play an important role in tooth function, strain distribution and fracture resistance during mastication. Recently reported asymmetry in mechanical properties with tooth side may point at a basic property of tooth function. The aim of our study was to test if this asymmetry was reflected in the nano- and micromechanical properties of dentine.
We investigated the mechanical properties of dentine on the buccal and lingual side of nine extracted human teeth using nano- and microindentation. Properties were analysed on the natural log scale, using maximum likelihood to estimate the parameters. Two-sided 0.05-level likelihood ratio tests were used to assess the influences of surface (buccal versus lingual) and dentine depth, measured from the DEJ in crown dentine and from the CDJ in root dentine.
Results showed the well known gradual increase in mechanical properties with increasing distance from the DEJ. Coronal dentine showed higher elastic modulus and hardness on the lingual side of teeth for all measurements, while root dentine was harder on the buccal side. Due to the subtlety of these effects and the small number of teeth studied, results failed to reach statistical significance. Results suggest that dentine nano- and micromechanical properties vary with tooth side in agreement with recent literature using macroscopic methods. They also reveal that buccal-lingual ratios of hardness are in opposite directions in crown and root dentine, suggesting compensatory functions.
human teeth; tooth; mantle dentine; dentino-enamel junction; soft dentine; nanoindentation; microhardness; elastic modulus; hardness; atomic-force microscopy
A discrete choice experiment (DCE) is a preference survey which asks participants to make a choice among product portfolios comparing the key product characteristics by performing several choice tasks. Analyzing DCE data needs to account for within-participant correlation because choices from the same participant are likely to be similar. In this study, we empirically compared some commonly-used statistical methods for analyzing DCE data while accounting for within-participant correlation based on a survey of patient preference for colorectal cancer (CRC) screening tests conducted in Hamilton, Ontario, Canada in 2002.
A two-stage DCE design was used to investigate the impact of six attributes on participants' preferences for CRC screening test and willingness to undertake the test. We compared six models for clustered binary outcomes (logistic and probit regressions using cluster-robust standard error (SE), random-effects and generalized estimating equation approaches) and three models for clustered nominal outcomes (multinomial logistic and probit regressions with cluster-robust SE and random-effects multinomial logistic model). We also fitted a bivariate probit model with cluster-robust SE treating the choices from two stages as two correlated binary outcomes. The rank of relative importance between attributes and the estimates of β coefficient within attributes were used to assess the model robustness.
In total 468 participants with each completing 10 choices were analyzed. Similar results were reported for the rank of relative importance and β coefficients across models for stage-one data on evaluating participants' preferences for the test. The six attributes ranked from high to low as follows: cost, specificity, process, sensitivity, preparation and pain. However, the results differed across models for stage-two data on evaluating participants' willingness to undertake the tests. Little within-patient correlation (ICC ≈ 0) was found in stage-one data, but substantial within-patient correlation existed (ICC = 0.659) in stage-two data.
When small clustering effect presented in DCE data, results remained robust across statistical models. However, results varied when larger clustering effect presented. Therefore, it is important to assess the robustness of the estimates via sensitivity analysis using different models for analyzing clustered data from DCE studies.
Discrete choice experiment; Intra-class correlation; Statistical model; Patient preference
This study sought to gain insights into the steps leading to remineralization and mechanical recovery of hydrated dentin. Mechanical recovery in water was hypothesized to result from effective mineral matrix binding and to occur from the innermost regions outwards due to increased number of nucleation sites. Partially demineralized (0.05 M acetate, pH=5.0, 8 hrs) dentin was remineralized using calcium and phosphate solutions of 10.1 or 9.8 degree of saturation (DS) for hydroxyapatite (pH=7.4) for 4, 8 or 24 hours. Remineralization used a constant solution composition approach, which allowed for a continuous mineral growth with relatively constant thermodynamic driving forces. Rates of crystal growth rates (R) were calculated using concentrations of calcium and phosphate. Before and after de- and remineralization specimens had their surface and cross-section elastic moduli measured using AFM-nanoindentation in water. DS=10.1 provided higher R and higher mechanical recovery at the surface (p<.0001). Cross-sectional measurements showed that subsurface mechanical recovery occurred from the innermost demineralized areas gradually outwards for both groups with no statistical differences at different DS, thus suggesting that remineralization is driven by mineral growth within nucleation sites with preserved collagen fibrils. Further, mechanical recovery appeared to initially obey a heterogeneous pattern which vanished with time. This study provides evidence of mechanical recovery of hydrated dentin after remineralization and novel insights into the steps leading to mechanical recovery of carious dentin.
Dentin; remineralization; mechanical properties; nanoindentation; caries
This study sought to gain insights into the surface structural and mechanical changes leading to remineralization of dentin. Remineralization was compared between a continuous remineralization approach and a non-buffered static approach using solutions of the same initial composition. Artificial carious lesions were treated for 5 days and analyzed every twenty-four hours using nanoindentation in water, SEM, AFM. The continuous approach yielded a recovery of mechanical properties of up to 60% of normal dentin whereas the static approach lead to a recovery of only 10%. Image analysis revealed that the static approach yielded the formation of areas suggestive of an apatite precipitate on the surface of the dentin matrix. In contrast, surface precipitate was absent using the continuous approach suggesting that mineral formed within the lesion and re-associated with the collagenous matrix. This study provided evidence that mechanical recovery of dentin in near physiological conditions is attainable through the continuous delivery of calcium and phosphate ions.
Dentin; remineralization; collagen; hydroxyapatite; mechanical properties; nanoindentation; AFM
Recent literature suggests that the scalloped structure of the dentino-enamel junction (DEJ) is critical for DEJ stability. Aim of our study was to see if there are differences in scallop size and shape with tooth type.
Enamel of extracted permanent human teeth was demineralised using EDTA. After fixation and dehydration the scallops of the DEJ were investigated in a scanning electron microscope. Scallop area and shape (circularity) were measured for molars, premolars, canines and incisors.
Scallop area showed main effects for tooth type and specimen, while, due to high variability in third molars, there was also an interaction effect (repeated measures two-way ANOVA, p < 0.05). Differences between tooth types were statistically significant, suggesting that posterior teeth showed larger scallops compared to anterior teeth. Differences in shape (circularity) were not statistically significant.
Our results suggest that teeth which are subject to higher masticatory loads (posterior teeth) show larger and more pronounced scallops. These findings might be of interest for improving other interfaces joining dissimilar materials.
dentino-enamel junction; interface; tooth structure; biomimetic model; teeth; scanning electron microscopy
The imperative to further constrain extractive uses of natural resources will strengthen as resources degrade through over-use or exposure to climate changes. Here, we explore an approach to increase the support for marine conservation among coral reef fishers. We explore the proposition that resource dependency in the Egyptian Red Sea can act as a barrier to conservation. We administered face-to-face surveys to 49% of the fishing industry to: (i) identify the level of compliance to the local marine protected area (MPA), (ii) assess the level of dependency on marine resources in the region and (iii) examine the relationship between resource dependency and conservation attitudes. Only 11.4% of fishers were aware of the MPA. Fishers were mostly limited in their social flexibility and livelihood options. Results suggest that resource dependency is highly and negatively correlated with conservation attitudes suggesting that management efforts need to seriously focus on reducing dependency if conservation goals are to be met.
Human dimensions; Social resilience; Attitudes; Resource dependency; Compliance; Marine protected areas
It was hypothesized that the coronal cementum containing collagen forms a weak junction with enamel unlike the well integrated DEJ and CDJ.
The hypothesis was investigated in two parts: 1) Evaluate the structure, chemical composition and mechanical properties of coronal cementum and its junction with enamel using scanning electron microscopy, micro-X-ray computed tomography, and atomic force microscopy. The chemical composition and mechanical properties were determined by evaluating the spatial variations of inorganic (PO43− ν1 mode at 960 cm−1) and organic (C-H deformation at 1452 cm−1; C-H stretch at 2940 cm−1) contents using Raman microspectroscopy and elastic modulus and hardness values using nanoindentation. 2). Estimate the strength and evaluate the microstructure of coronal cementum interface with enamel using SEM and MicroXCT™.
Results & Conclusions
Coronal cementum is heterogeneous because it is a combination of laminar acellular afibrillar cementum and acellular extrinsic fiber cementum with relatively higher organic content. It integrates micromechanically via a scallop-like weak interface with enamel unlike the biomechanically efficient DEJ and CDJ and is continuous with primary root cementum. A single tooth could exhibit all three types of cementum enamel junctions; an overlap, butt and a gap depending on the sectioning plane. The elastic modulus of coronal cementum (11.0 ± 5.8 GPa) is significantly lower (p < 0.05; Student’s t-test with 95% confidence interval) than primary cementum (15.8 ± 5.3 GPa).
coronal cementum; atomic force microscopy; interface; structure; chemical composition; mechanical properties; cementum enamel junction
The objective of this article is to critically evaluate the methods that are used to assess outcomes of remineralization of dentin. Currently, the most used assessment methods fall either into quantitative analysis of the mineral content of the remineralized structures or dry measurements of their mechanical properties. Properties obtained from the dehydrated organic dentin matrix may not reflect the true mechanical behavior of the remineralized tissue under physiological and hydrated conditions. Here we seek to clarify the biomechanical aspects of remineralization of dentin, pointing out the effects of hydration and dehydration on the mechanical properties of treated tissues. We also emphasize that a more appropriate endpoint to evaluate the effectiveness of remineralization in dentin should be associated with the recovery of the mechanical properties of the hydrated tissue, which is presumed to correlate well with its overall functionality.
Biomechanics; Caries; Dentin; Mechanical properties; Nanoindentation; Remineralization
This work seeks to establish comparisons of the physical properties of rat and human cementum, root dentin and their interface, including the cementum–dentin junction (CDJ), as a basis for future studies of the entire periodontal complex using rats as animal models. In this study the structure, site-specific chemical composition and mechanical properties of cementum and its interface with root dentin taken from 9- to 12-month-old rats were compared to the physiologically equivalent 40- to 55-year-old human age group using qualitative and quantitative characterization techniques, including histology, atomic force microscopy (AFM), micro-X-ray computed tomography, Raman microspectroscopy and AFM-based nanoindentation. Based on results from this study, cementum taken from the apical third of the respective species can be represented as a woven fabric with radially and circumferentially oriented collagen fibers. In both species the attachment of cementum to root dentin is defined by a stiffness-graded interface (CDJ/cementum–dentin interface). However, it was concluded that cementum and the cementum–dentin interface from a 9- to 12-month-old rat could be more mineralized, resulting in noticeably decreased collagen fiber hydration and significantly higher modulus values under wet conditions for cementum and CDJ (Erat-cementum = 12.7 ± 2.62 GPa; Erat-CDJ = 11.6 ± 3.20 GPa) compared to a 40- to 55-year-old human (Ehuman-cementum = 3.73 ± 1.81 GPa; Ehuman-CDJ = 1.5 ± 0.71 GPa). The resulting data illustrated that the extensions of observations made from animal models to humans should be justified with substantial and equivalent comparison of data across age ranges (life spans) of mammalian species.
Cementum; Interfaces; Structure; Chemical composition; Animal model
Caries Detector staining reveals 4 zones in dentin containing caries lesions, but characteristics of each zone are not well-defined. We therefore investigated the physical and microstructural properties of carious dentin in the 4 different zones to determine important differences revealed by Caries Detector staining. Six arrested dentin caries lesions and 2 normal controls were Caries-Detector-stained, each zone (pink, light pink, transparent, apparently normal) being analyzed by atomic force microscopy (AFM) imaging for microstructure, by AFM nano-indentation for mechanical properties, and by transverse digital microradiography (TMR) for mineral content. Microstructure changes, and nanomechanical properties and mineral content significantly decreased across zones. Hydrated elastic modulus and mineral content from normal dentin to pink Caries-Detector-stained dentin ranged from 19.5 [10.6–25.3] GPa to 1.6 [0.0–5.0] GPa and from 42.9 [39.8–44.6] vol% to 12.4 [9.1–14.2] vol%, respectively. Even the most demineralized pink zone contained considerable residual mineral.
dentin; caries; mineral; mechanical properties; atomic force microscopy
The objective of this article is to critically evaluate the methods that are used to assess outcomes of remineralization of dentin. Currently, the most used assessment methods fall either into quantitative analysis of the mineral content of the remineralized structures, or dry measurements of their mechanical properties. Properties obtained from the dehydrated organic dentin matrix may not reflect the true mechanical behavior of the remineralized tissue under physiological and hydrated conditions. Here we seek to clarify the biomechanical aspects of remineralization of dentin, pointing out the effects of hydration and dehydration on the mechanical properties of treated tissues. We also emphasize that a more appropriate endpoint to evaluate the effectiveness of remineralization in dentin should be associated with the recovery of the mechanical properties of the hydrated tissue, which is presumed to correlate well with its overall functionality.
Dentin; remineralization; mechanical properties; nanoindentation; biomechanics; caries
Caries Detector staining reveals 4 zones in dentin containing caries lesions, but characteristics of each zone are not well-defined. We therefore investigated the physical and microstructural properties of carious dentin in the 4 different zones to determine important differences revealed by Caries Detector staining. Six arrested dentin caries lesions and 2 normal controls were Caries-Detector-stained, each zone (pink, light pink, transparent, apparently normal) being analyzed by atomic force microscopy (AFM) imaging for microstructure, by AFM nano-indentation for mechanical properties, and by transverse digital microradiography (TMR) for mineral content. Microstructure changes, and nanomechanical properties and mineral content significantly decreased across zones. Hydrated elastic modulus and mineral content from normal dentin to pink Caries-Detector-stained dentin ranged from 19.5 [10.6-25.3] GPa to 1.6 [0.0-5.0] GPa and from 42.9 [39.8-44.6] vol% to 12.4 [9.1-14.2] vol%, respectively. Even the most demineralized pink zone contained considerable residual mineral.
dentin; caries; mineral; mechanical properties; atomic force microscopy
To evaluate dentin tubule numerical density variations below the CEJ.
Three human non-carious permanent canines were sectioned parallel to the CEJ to obtain dentin disks 1 mm thick whose surfaces were 1 mm and 2 mm below the CEJ. Each disk was sectioned into quarters resulting in four segment locations: facial, lingual, mesial, and distal. The outer (PDL side) and inner (pulp side) surfaces of the specimens were shaped to expose dentin with SiC papers and polished. Numerical tubule density was determined from SEM images. All data were statistically analyzed using a three-way ANOVA.
The dentin tubule density (number/mm2) ranged from 13,700 to 32,300. Dentin tubule density was relatively uniform at 1 and 2 mm below the CEJ and increased by a factor of about two from the outer to the inner surface, which was significantly different (P<0.0001).
The tubule density variations at the cervical root did not present the marked changes.
Cemento-Enamel Junction (CEJ); Cervical lesions; Density; Dentin hypersensitivity; Dentin tubules; Root dentin; Scanning Electron Microscopy (SEM)
Postmating, prezygotic phenotypes, especially those that underlie reproductive isolation between closely related species, have been a central focus of evolutionary biologists over the past two decades. Such phenotypes are thought to evolve rapidly and be nearly ubiquitous among sexually reproducing eukaryotes where females mate with multiple partners. Because these phenotypes represent interplay between the male ejaculate and female reproductive tract, they are fertile ground for reproductive senescence – as ejaculate composition and female physiology typically change over an individual's life span. Although these phenotypes and their resulting dynamics are important, we have little understanding of the proteins that mediate these phenotypes, particularly for species groups where postmating, prezygotic traits are the primary mechanism of reproductive isolation. Here, we utilize proteomics, RNAi, mating experiments, and the Allonemobius socius complex of crickets, whose members are primarily isolated from one another by postmating, prezygotic phenotypes (including the ability of a male to induce a female to lay eggs), to demonstrate that one of the most abundant ejaculate proteins (a male accessory gland-biased protein similar to a trypsin-like serine protease) decreases in abundance over a male's reproductive lifetime and mediates the induction of egg-laying in females. These findings represent one of the first studies to identify a protein that plays a role in mediating both a postmating, prezygotic isolation pathway and reproductive senescence.
Overview of the Disease
IncidencePrognosisCurrent General Therapy Standards
StagingLymph Node ExcisionStage III DiseaseStage II DiseaseMolecular MarkersAccomplishments During the Year
Cytotoxic ChemotherapyChemotherapy Plus Targeted TherapySpecial PopulationsBasic Science—BiomarkersMethodologyWhat Needs to Be Done
Application of the AccomplishmentsControversies and DisagreementsFuture Directions
Comments on ResearchObstacles to Progress
The dentino-enamel junction (DEJ) connects enamel, that covers the outer surface of a tooth, to a thicker underlying dentin. The DEJ is a critical interface that permits joining these materials that have widely dissimilar mechanical properties. AFM-based nanoindentation and Raman microspectroscopy were used to define the width and composition of human molar DEJ. Indentation elastic modulus and hardness of enamel, dentin, and DEJ were determined along lines of indents made at 2 μm intervals across the DEJ. Indents made at maximum loads at each end of the indent lines were used to make visible markers allowing Raman microspectroscopy at 1 μm intervals across the DEJ, while using the nanoindent markers for orientation and location. Functional DEJ width estimates were made based on results from nanoindentation and Raman microspectroscopy. DEJ width estimates ranged from 4.7 (±1.2) μm to 6.1 (±1.9) μm based on hardness and 4.9 (±1.1) μm to 6.9 (±1.9) μm based on modulus. DEJ width based on Raman peak intensity variations were 8.0 (±3.2) μm to 8.5 (±3.1) μm based on the phosphate peak, and 7.6 (±3.2) μm to 8.0 (±2.6) μm for C–H stretching mode. These estimates are in the range of DEJ width estimates reported using nanoindentation.
We investigated the influence of dentin tubule direction and identifiable zone of carious dentin on the microstructure and the thickness of the hybrid-like layer (HL) formed by self-etch and etch-rinse adhesive systems.
An etch-rinse and a self-etching adhesive were bonded to dentin carious zones divided into groups with parallel or perpendicular orientation relative to the dentin tubules at the resin-carious dentin interface (N = 5/variable). Bonds were prepared to each of the four zones of carious dentin apparent after staining with Caries Detector: pink, light pink, transparent and apparently normal Six non-carious third molars were controls. The microstructure and thickness of the HL were determined by SEM.and compared using three-way ANOVA and Tukey's multiple comparisons (p<0.05).
Etch-rinse controls gave thicker HLs than self-etching systems; ; orientation did not affect thickness for the self-etch system. Perpendicular orientations gave thicker HLs than parallel for the pink zone bonded with the etch-rinse system. For both adhesives, HL thickness in the pink zone were significantly greater than in light pink for the perpendicular group, but no significant differences were found among other variables. HL microstructure was more granular and rougher for the etch rinse than for the self etching system. Pores and cracks were obvious in the more demineralized zones, Resin tags were shorter and irregular in the transparent zone and often were completely absent in the outer demineralized zones (pink, light pink).
Microstructure of bonded interfaces varies markedly depending on adhesive system, tubule orientation and carious zone.
dentin bonding interfaces; dentin caries; microstructure; SEM; hybrid layer thickness