Effect of staining beverages on color and translucency of CAD/CAM composites.

This study investigated the color (ΔE) and translucency changes (ΔTP) of CAD/CAM composites after exposure to staining solutions using both spectrophotometer and shade-matching device. Direct (Filtek Z350XT [ZT]), indirect (Shofu Ceramage [CE]) and CAD/CAM (Shofu HC Block [HC], Lava Ultimate [LU], Vita Enamic [EN]) composite specimens measuring 12 × 14 × 1.5 mm were fabricated, divided into five groups (n = 8), and immersed in cola, tea, coffee, red wine, distilled water (control) at 37°C for 7 days. Color parameters were determined with both spectrophotometer and shade-taking device at baseline and 1 week. Delta E (ΔE) with white and black backgrounds, and Delta TP (ΔTP) were computed. Statistical testing was performed with ANOVA and Tukey post hoc test (P < .05). Mean ΔE (white) values ranged from 0.20 ± 0.06 to 12.26 ± 1.95 while mean ΔE (black) varied from 0.22 ± 0.11 to 14.21 ± 2.37. Mean ΔTP values ranged from 0.13 ± 0.17 to -3.87 ± 2.16. CAD/CAM composites fared better in red wine than direct and indirect materials. Clinically perceptible color changes (ΔE > 3.3) were observed for almost all materials when exposed to wine, coffee and tea. Direct, indirect, and CAD/CAM composites are all susceptible to various degrees of discoloration and translucency changes after exposure to staining beverages. Red wine caused the most discoloration and translucency changes. Limitations of these materials must be considered when placing an aesthetic restoration. CLINICAL SIGNIFICANCE: Direct, indirect, and CAD/CAM composites are all susceptible to various degrees of discoloration and translucency changes after exposure to staining beverages. Red wine generally caused the most discoloration and translucency changes. Although CAD/CAM composites were more color stable than direct and indirect materials when exposed to red wine, color changes were still clinically perceptible.

Rapid identification of elastic modulus of the interface tissue on dental implants surfaces using reduced-basis method and a neural network.

This paper proposes a rapid inverse analysis approach based on the reduced-basis method (RBM) and neural network (NN) to identify the "unknown" elastic modulus (Young's modulus) of the interfacial tissue between a dental implant and the surrounding bones. In the present RBM-NN approach, a RBM model is first built to compute displacement responses of dental implant-bone structures subjected to a harmonic loading for a set of "assumed" Young's moduli. The RBM model is then used to train a NN model that is used for actual inverse analysis in real-time. Actual experimental measurements of displacement responses are fed into the trained NN model to inversely determine the "true" elastic modulus of the interfacial tissue. As an example, a physical model of dental implant-bone structure is built and inverse analysis is conducted to verify the present RBM-NN approach. Based on numerical simulation and actual experiments, it is confirmed that the identified results are very accurate, reliable, and the computational saving is very significant. The present RBM-NN approach is found robust and efficient for inverse material characterizations in noninvasive and/or nondestructive evaluations.

Digital moiré interferometric investigations on the deformation gradients of enamel and dentine: an insight into non-carious cervical lesions.

OBJECTIVES: The objective of this study was to evaluate the biomechanical basis of non-carious cervical lesions by examining the patterns of deformation (strain) in the enamel and dentine. METHODS: The digital moiré interferometry is optics based non-destructive, whole-field experimental technique that provides whole-field strain information. Diffraction gratings (with a frequency of 1200 lines/mm) were transferred onto sagittal sections of human teeth, which were subsequently loaded compressively for loads ranging from 10 to 200 N at the incisal edge of the tooth. The acquired digital moiré fringe patterns were used to determine the in-plane deformation pattern in the enamel and the dentine in the direction parallel to the long axis (axial direction) and in the direction perpendicular to the long axis (lateral direction) of the tooth. RESULTS: It is observed that the enamel displayed marked strain gradients in the lateral direction, while the coronal dentine experienced marked strain gradients in the axial directions during compression. With the increase in applied loads, the strains in the enamel increased at the cervical edge (above the cemento-enamel junction) on the facial side, while the strains in the dentine increased below the cemento-enamel junction on the facial side. CONCLUSION: The enamel and dentine displayed unique in-plane deformation patterns in the axial and the lateral directions of the tooth. These experiments support the hypothesis that occlusal loading will contribute to cervical loss of dental hard tissues.

Dental education in Singapore--from the past to the future.

Dental education in Singapore has come a long way since the founding of the Dental School in 1929. With an initial intake of 7 students, the Faculty has over the years produced more than 1700 graduates. Its early years were fraught with physical constraints and recruitment problems. With a dedicated core of leaders and good planning, the dental school has overcome many of these shortcomings. The King Edward VII College of Medicine played a significant role in the early years of the school's development. Many a student of the past era has pleasant memories that bind and bond them to the SGH Sepoy Lines campus. Acquiring full Dental Faculty status in 1966, the progress of dental education took on a new urgency and stature. The basic medical science subjects were taught to the dental students by our medical colleagues at Sepoy Lines and now continue to be tutored at the Kent Ridge campus. With the shift of the Faculty in 1986 to Kent Ridge (NUS-NUH), together with the implementation of the changed curriculum in 1990 and 1997, the Faculty of Dentistry remains at the forefront of pedagogy and technology to train the future generation of dentists for Singapore.

Finite element analysis of an osseointegrated stepped screw dental implant.

An osseointegrated stepped screw dental implant was evaluated using 2-dimensional finite element analysis (FEA). The implant was modeled in a cross section of the posterior human mandible digitized from a computed tomography (CT) generated patient data set. A 15-mm regular platform (RP) Branemark implant with equivalent length and neck diameter was used as a control. The study was performed under a number of clinically relevant parameters: loading at the top of the transmucosal abutment in vertical, horizontal, and 45 degrees oblique 3 orientations. Elastic moduli of the mandible varied from a normal cortical bone level (13.4 GPa) to a trabecular bone level (1.37 GPa). The study indicated that an oblique load and elastic moduli of the cortical bone are important parameters to the implant design optimization. Compared with the cylindrical screw implant, the maximum von Mises stress of the stepped screw implant model was 17.9% lower in the trabecular bone-implant area. The study also showed that the stepped screw implant is suitable for the cortical bone modulus from 10 to 13.4 GPa, which is not necessarily as strict as the Branemark implant, for which a minimum 13.4 GPa cortical bone modulus is recommended.

Finite element analysis of four thread-form configurations in a stepped screw implant.

The purpose of this study was to determine the optimal thread form configuration for an experimental stepped screw implant. Two-dimensional finite element analysis was applied to model the experimental stepped screw implant in a standard cross-section of the posterior human mandible digitized from a CT-generated patient data set. Four different thread form configurations: v-thread (V), thin-thread (T), and two square-thread forms of 0.24 mm (S1) and 0.36 mm (S2) thread width were compared under oblique load in normal cortical bone condition. The support-type constraint position changed from middle to the base of the bone segment. In middle support-type constraint position only the thin-thread (T) model demonstrated significantly different stress distribution from the other three models, however, in base support-type constraint position T and S1 models demonstrated significantly different stress distribution from the other two models. The results implies that v-thread (V) or large square-thread (S2) are optimal thread form for the experimental stepped screw implant. While, minimal support constraints allow clearer differentiation of the stress picture between the different stepped screw types at the trabecular bone-implant interface.