Learn-A-Prep II as a Predictor of Psychomotor Performance in a Restorative Dentistry Course

This investigation assessed whether early student performance with a dental handpiece on a didactic training aid known as the Learn-A-Prep II (LAP II) was predictive of performance on subsequent practical examinations in a preclinical restorative dentistry course. Eighty-one first-year students were given initial handpiece training and formative feedback using the LAP II and were then instructed to independently prepare four LAP II patterns within the pattern lines and at a specified depth. Performance on the LAP II was compared with the summative assessment on two subsequent amalgam preparation practical examinations given at the middle (Class II) and end (Complex) of the course. Pattern preparation within the lines did not significantly improve the likelihood of receiving an A or B on the Class II practical (p=0.53) or on the Complex practical (p=0.37). Students who had an acceptable depth on the LAP II were 3.73 times more likely to receive an A or B on the Class II practical than those students who did not have acceptable depth (p=0.03). Performance at an acceptable depth did not significantly improve the likelihood of receiving an A or B on the Complex practical (p=0.15). The LAP II may aid in identification of students who would benefit from early intervention with additional focused instruction

Distribution of Matrixmetalloproteinase-2 in Human Coronal Dentin

It has been reported that matrixmetalloproteinase-2 (MMP-2) is present in dentin, but its distribution and significance in human dentin are not well understood. OBJECTIVE: To identify MMP-2 and determine its distribution in human coronal dentin. METHODS: Immunohistochemistry was used to investigate the distribution of MMP-2 in coronal dentin. Freshly extracted human premolars and 3rd molars (age range 12-30) were fixed with formaldehyde, demineralized with 10% EDTA (pH=7.4) and embedded in paraffin. Five [micrometer] serial sections were made and subjected to analysis using a monoclonal anti-MMP-2 antibody with an avidin-biotin-complex method. Immunoreactivity was visualized with 3,3'- diaminobenzidine substrate and observed under light microscopy. ImageJ software was used to calculate the relative amount/distribution of MMP-2. Based on immunohistochemical results, crowns of freshly extracted human 3rd molars (age range 15-32) were sectioned, pulp and predentin tissue was removed, dentin matrix was extracted with EDTA and guanidine- HCl, pH7.4, and subjected to Western blot analysis with monoclonal anti-MMP-2 antibody and zymography. RESULTS: Immunohistochemical analysis revealed immunoreactivity for MMP-2 throughout human coronal dentin. However, intense immunoreactivities were identified in a 90-200 [micrometer] zone adjacent to the pre-dentin as well as a 9-10 [micrometer] wide zone adjacent to the dentinoenamel junction (DEJ). Biochemical strategies detected MMP-2 as ~66 and ~72 kDa proteins (mature and proform of MMP-2, respectively). Furthermore, gelatinolytic activity was detected in the extracts. CONCLUSION: The results indicate that MMP-2 may be involved in extracellular matrix organization and dentin mineralization in predentin matrix. In addition, its concentration in the zone immediately adjacent to the DEJ and the retained enzymatic activity after demineralization suggest that MMP-2 may play a role in the spread of early dentin caries along DEJ. Supported by NIH grants DE10489, DE015876 and the UNC School of Dentistry

Are All Dentiform Teeth with Simulated Caries the Same? A Six-Year Retrospective Study in Preclinical Operative Dentistry

Dentiform teeth with simulated caries (DTSC), frequently used in preclinical courses, should show no variability in the amount of simulated caries from tooth to tooth. However, the level of caries variability among DTSC is currently unknown. The aim of this study was to assess the variation in simulated caries levels in one group of DTSC and determine whether variation among DTSC impacted the preclinical performance of dental students. In the study, 80 commercially available mandibular first molar DTSC with simulated mesio-occluso-distal caries were sectioned in coronal (n=40) and sagittal (n=40) planes where the caries depth/width was greatest. Section images were analyzed for variation in levels of simulated caries using image-processing software. Three years of practical performance data using DTSC were compared with three years of practical performance data using dentiform teeth without simulated caries, for a total of six years (students' performance on two exams, Practical 1 and Practical 2). The results showed that 70% of the coronally sectioned teeth had manufacturing defects that resulted in caries overextension at the dentino-enamel junctions (DEJs). Overextensions were found at the DEJ in 41.3% of the sagittally sectioned teeth. There was a statistically significant decrease in Practical 1 performance of the students who used DTSC as compared with students who used teeth without simulated caries (p=0.0001); there was no statistically significant difference on Practical 2 performance. Of the DTSC evaluated in this study, 56.6% contained manufacturing defects, and more than 80% were found to have excessive caries variation. Prediction of which DTSC will have caries overextension is not possible. Students preparing DTSC that contain caries overextension are therefore at increased risk of receiving undeserved negative summative assessment on practical examinations

Distribution and relative activity of matrix metalloproteinase‐2 in human coronal dentin

The presence of matrix metalloproteinase-2 (MMP-2) in dentin has been reported, but its distribution and activity level in mature human coronal dentin are not well understood. The purpose of this study was to determine the MMP-2 distribution and relative activity in demineralized dentin. Crowns of twenty eight human molars were sectioned into inner (ID), middle (MD), and outer dentin (OD) regions and demineralized. MMP-2 was extracted with 0.33 mol·L−1 EDTA/2 mol·L−1 guanidine-HCl, pH 7.4, and MMP-2 concentration was estimated with enzyme-linked immunoabsorbant assay (ELISA). Further characterization was accomplished by Western blotting analysis and gelatin zymography. The mean concentrations of MMP-2 per mg dentin protein in the dentin regions were significantly different (P=0.043): 0.9 ng (ID), 0.4 ng (MD), and 2.2 ng (OD), respectively. The pattern of MMP-2 concentration was OD>ID>MD. Western blotting analysis detected ∼66 and ∼72 kDa immunopositive proteins corresponding to pro- and mature MMP-2, respectively, in the ID and MD, and a ∼66 kDa protein in the OD. Gelatinolytic activity consistent with MMP-2 was detected in all regions. Interestingly, the pattern of levels of Western blot immunodetection and gelatinolytic activity was MD>ID>OD. The concentration of MMP-2 in human coronal dentin was highest in the region of dentin that contains the dentinoenamel junction and least in the middle region of dentin. However, levels of Western blot immunodetection and gelatinolytic activity did not correlate with the estimated regional concentrations of MMP-2, potentially indicating region specific protein interactions

Immunohistochemical localization of matrixmetalloproteinase-2 in human coronal dentin

While it is known that matrixmetalloproteinase-2 (MMP-2) is present in dentin, its distribution and role in human dentin formation and pathology are not well understood

Characterization of Genipin-Modified Dentin Collagen

Application of biomodification techniques to dentin can improve its biochemical and biomechanical properties. Several collagen cross-linking agents have been reported to strengthen the mechanical properties of dentin. However, the characteristics of collagen that has undergone agent-induced biomodification are not well understood. The objective of this study was to analyze the effects of a natural cross-linking agent, genipin (GE), on dentin discoloration, collagen stability, and changes in amino acid composition and lysyl oxidase mediated natural collagen cross-links. Dentin collagen obtained from extracted bovine teeth was treated with three different concentrations of GE (0.01%, 0.1%, and 0.5%) for several treatment times (0–24 h). Changes in biochemical properties of NaB3H4-reduced collagen were characterized by amino acid and cross-link analyses. The treatment of dentin collagen with GE resulted in a concentration- and time-dependent pigmentation and stability against bacterial collagenase. The lysyl oxidase-mediated trivalent mature cross-link, pyridinoline, showed no difference among all groups while the major divalent immature cross-link, dehydro-dihydroxylysinonorleucine/its ketoamine in collagen treated with 0.5% GE for 24 h, significantly decreased compared to control (). The newly formed GE-induced cross-links most likely involve lysine and hydroxylysine residues of collagen in a concentration-dependent manner. Some of these cross-links appear to be reducible and stabilized with NaB3H4

Characterization of Genipin-Modified Dentin Collagen

Application of biomodification techniques to dentin can improve its biochemical and biomechanical properties. Several collagen cross-linking agents have been reported to strengthen the mechanical properties of dentin. However, the characteristics of collagen that has undergone agent-induced biomodification are not well understood. The objective of this study was to analyze the effects of a natural cross-linking agent, genipin (GE), on dentin discoloration, collagen stability, and changes in amino acid composition and lysyl oxidase mediated natural collagen cross-links. Dentin collagen obtained from extracted bovine teeth was treated with three different concentrations of GE (0.01%, 0.1%, and 0.5%) for several treatment times (0–24 h). Changes in biochemical properties of NaB3H4-reduced collagen were characterized by amino acid and cross-link analyses. The treatment of dentin collagen with GE resulted in a concentration- and time-dependent pigmentation and stability against bacterial collagenase. The lysyl oxidase-mediated trivalent mature cross-link, pyridinoline, showed no difference among all groups while the major divalent immature cross-link, dehydro-dihydroxylysinonorleucine/its ketoamine in collagen treated with 0.5% GE for 24 h, significantly decreased compared to control (P< 0.05). The newly formed GE-induced cross-links most likely involve lysine and hydroxylysine residues of collagen in a concentration-dependent manner. Some of these cross-links appear to be reducible and stabilized with NaB3H4

Distribution and relative activity of matrix metalloproteinase‐2 in human coronal dentin

The presence of matrix metalloproteinase-2 (MMP-2) in dentin has been reported, but its distribution and activity level in mature human coronal dentin are not well understood. The purpose of this study was to determine the MMP-2 distribution and relative activity in demineralized dentin. Crowns of twenty eight human molars were sectioned into inner (ID), middle (MD), and outer dentin (OD) regions and demineralized. MMP-2 was extracted with 0.33 mol·L(−1) EDTA/2 mol·L(−1) guanidine-HCl, pH 7.4, and MMP-2 concentration was estimated with enzyme-linked immunoabsorbant assay (ELISA). Further characterization was accomplished by Western blotting analysis and gelatin zymography. The mean concentrations of MMP-2 per mg dentin protein in the dentin regions were significantly different (P=0.043): 0.9 ng (ID), 0.4 ng (MD), and 2.2 ng (OD), respectively. The pattern of MMP-2 concentration was OD>ID>MD. Western blotting analysis detected ∼66 and ∼72 kDa immunopositive proteins corresponding to pro- and mature MMP-2, respectively, in the ID and MD, and a ∼66 kDa protein in the OD. Gelatinolytic activity consistent with MMP-2 was detected in all regions. Interestingly, the pattern of levels of Western blot immunodetection and gelatinolytic activity was MD>ID>OD. The concentration of MMP-2 in human coronal dentin was highest in the region of dentin that contains the dentinoenamel junction and least in the middle region of dentin. However, levels of Western blot immunodetection and gelatinolytic activity did not correlate with the estimated regional concentrations of MMP-2, potentially indicating region specific protein interactions

Characterization of Genipin-Modified Dentin Collagen

Application of biomodification techniques to dentin can improve its biochemical and biomechanical properties. Several collagen cross-linking agents have been reported to strengthen the mechanical properties of dentin. However, the characteristics of collagen that has undergone agent-induced biomodification are not well understood. The objective of this study was to analyze the effects of a natural cross-linking agent, genipin (GE), on dentin discoloration, collagen stability, and changes in amino acid composition and lysyl oxidase mediated natural collagen cross-links. Dentin collagen obtained from extracted bovine teeth was treated with three different concentrations of GE (0.01%, 0.1%, and 0.5%) for several treatment times (0–24 h). Changes in biochemical properties of NaB3H4-reduced collagen were characterized by amino acid and cross-link analyses. The treatment of dentin collagen with GE resulted in a concentration- and time-dependent pigmentation and stability against bacterial collagenase. The lysyl oxidase-mediated trivalent mature cross-link, pyridinoline, showed no difference among all groups while the major divalent immature cross-link, dehydro-dihydroxylysinonorleucine/its ketoamine in collagen treated with 0.5% GE for 24 h, significantly decreased compared to control (P< 0.05). The newly formed GE-induced cross-links most likely involve lysine and hydroxylysine residues of collagen in a concentration-dependent manner. Some of these cross-links appear to be reducible and stabilized with NaB3H4