Yu-Chih Chiang

Polymerization composite shrinkage evaluation with 3D deformation analysis from μCT images

OBJECTIVES The aim of this study was to develop a method to experimentally determine and visualize the direction and amount of polymerization shrinkage. METHODS We modified a composite to include 1.5 wt% traceable glass beads. A cylindrical cavity (6mm diameter, 3mm height) was restored with this traceable composite, with and without dentin adhesive, and digitized with high-resolution micro-computed tomography (microCT). Image segmentation was performed to extract the glass beads from the acquired 3D microCT images (uncured and cured). Afterwards, each glass bead was subjected to local rigid registration. The resulting displacement vectors were used to examine and calculate the changes. RESULTS In unbonded restorations, the displacement vectors were oriented inwards to the center of mass, although not perfectly. Bonded restorations exhibited two contraction patterns: either toward one side of the cavity or toward the top-surface of the restoration. The displacement vector length values (mean/SD) for the bonded group (46.8 microm/10.0 microm) was significantly higher (p<0.01) than unbonded group (31.3 microm/8.5 microm), and the histogram curve was flatter (skew/kurtosis: 0.10/-0.56) as compared to the unbonded group (skew/kurtosis: 0.03/-0.26). SIGNIFICANCE The proposed method can visualize real 3D displacement vectors generated by polymerization shrinkage. The bonding quality and cavity geometry are critical for the direction of polymerization contraction. This method has the potential to validate current models concerning the amount and orientation of shrinkage vectors.

A Novel Mesoporous Biomaterial for Treating Dentin Hypersensitivity

An ideal material has yet to be discovered that can completely treat dentin hypersensitivity; however, calcium phosphate precipitation has exhibited potential value for the treatment of dentin hypersensitivity by the occlusion of dentinal tubules. We hypothesized that a novel mesoporous silica biomaterial (nano CaO@mesoporous silica, NCMS) containing nano-sized calcium oxide particles mixed with 30% phosphoric acid can efficiently occlude dentinal tubules and significantly reduce dentin permeability, even with the presence of pulpal pressure. This highly supersaturated Ca2+-and HPO4 2−ion-containing NCMS paste was brushed onto dentin surfaces, and the ions diffused deeply into the dentinal tubules and formed a CaHPO4·2H2O precipitation with a depth of 100 μm. The results of the dentin permeability tests showed that the novel mesoporous material exhibited a significant reduction in dentin permeability (p < 0.05), even under simulated pulpal pressure, as compared with our previously developed material, DP-bioglass, and a commercial desensitizing material, Seal & Protect®.

A Mesoporous Silica Biomaterial for Dental Biomimetic Crystallization

The loss of overlying enamel or cementum exposes dentinal tubules and increases the risk of several dental diseases, such as dentin hypersensitivity (causing sharp pain and anxiety), caries, and pulp inflammation. This paper presents a fast-reacting, more reliable and biocompatible biomaterial that effectively occludes exposed dentinal tubules by forming a biomimetic crystalline dentin barrier. To generate this biomaterial, a gelatin-templated mesoporous silica biomaterial (CaCO3@mesoporous silica, CCMS) containing nanosized calcium carbonate particles is mixed with 30% H3PO4 at a 1/1 molar ratio of Ca/P (denoted as CCMS-HP), which enables Ca2+ and PO4(3-)/HPO4(2-) ions to permeate the dentinal tubules and form dicalcium phosphate dihydrate (DCPD), tricalcium phosphate (TCP) or hydroxyapatite (HAp) crystals at a depth of approximately 40 μm (sub-μ-CT and nano-SEM/EDS examinations). In vitro biocompatibility tests (WST-1 and lactate dehydrogenase) and ALP assays show high cell viability and mineralization ability in a transwell dentin disc model treated with CCMS-HP (p<0.05). The in vivo efficacy and biocompatibility analyses of the biomaterial in an animal model reveal significant crystal growth (DCPD, TCP or HAp-like) and no pulp irritation after 70 days (p<0.05). The developed CCMS-HP holds great promise for treating exposed dentin by growing biomimetic crystals within dentinal tubules. These findings demonstrate that the mesoporous silica biomaterials presented here have great potential for serving as both a catalyst and carrier in the repair or regeneration of dental hard tissue.

Effect of resin shades on opacity of ceramic veneers and polymerization efficiency through ceramics

OBJECTIVES The aim of this study was to assess the effect of different resin cement shades on the opacity and color difference of ceramics and to determine the polymerization efficiency of the resin cement at different shades after curing through ceramics. METHODS Two different ceramics (IPS e.max Press and IPS Empress(®)CAD, Ivoclar Vivadent) were used for this study. A light-cured veneer luting resin (Variolink Veneer, Ivoclar Vivadent) in four different shades of HV+1, HV+3, LV-1, and LV-3 was used for the colorimetric measurements. The color and spectral reflectance of the ceramics were measured according to the CIELab color scale relative to the standard illuminant D65 on a reflection spectrophotometer (ColorEye7000A, USA). Color differences (ΔE values) and the contrast ratios (CR) of the different groups of samples were calculated. In order to analyse the polymerization efficiency of the resin cements, the micromechanical properties of the resins were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). The results were analysed using one-way ANOVA and Tukeys HSD post hoc tests (SPSS 18.0). RESULTS The one-way ANOVA test showed that the values of ΔE and CR of the different specimen groups were significantly different (p<0.05). Group 1 (20.7 ± 0.5) (IPS-CAD without resin cement) exhibited the highest and group 10 (14.8 ± 0.5) (e.max:HV+3) exhibited the lowest ΔE value. Significant differences in the micromechanical properties were identified among the tested resin cements in different shades (p<0.05). CONCLUSIONS Resin cement shade is an important factor for the opacity of a restoration. Furthermore, the resin shade affects the micromechanical properties of the underlying resin cement.

Repair of silorane-based dental composites: Influence of surface treatments

OBJECTIVE The purpose of our study was to evaluate the effects of surface treatment on the microtensile bond strength (MTBS) of repaired silorane-based composites (Filtek Silorane (Silorane), 3M ESPE). METHODS The surfaces of the aged Silorane blocks (6 mm × 6 mm × 5 mm) were ground with 320-grit SiC paper. The subsequent surface treatments were: no treatment, bonding agent, acetone, acetone+bonding agent, ethanol, ethanol+bonding agent, silane and silane+bonding agent. Another group made from Silorane without repair served as positive control. New Silorane was bonded onto the treated samples. The MTBS test was performed (1mm/min) with beam-shaped sticks (1.0 mm × 1.0 mm × 10 mm) before and after fatigue simulation (FS). The Weibull moduli for the MTBS data were also calculated. The fracture modes were examined with an optical microscope. The aged specimens after grinding were observed in a SEM and the percentage of uncovered filler surface in relation to the whole surface was calculated. RESULTS There were no significant differences between the no treatment group and the acetone only or ethanol only groups. Bonding agent improved the MTBS and the Weibull modulus. Although the SEM image revealed only 5.1% of uncovered filler surface, silane improved the MTBS. The groups with silane and bonding agent had the highest strength values except two groups and showed a fairly large number of cohesive failures. However, after FS, the differences between almost all groups were insignificant. FS increased the MTBS of almost all groups. SIGNIFICANCE The application of silane and bonding agent enhanced the initial repair strength.

A novel chitosan-γPGA polyelectrolyte complex hydrogel promotes early new bone formation in the alveolar socket following tooth extraction.

A novel chitosan-γPGA polyelectrolyte complex hydrogel (C-PGA) has been developed and proven to be an effective dressing for wound healing. The purpose of this study was to evaluate if C-PGA could promote new bone formation in the alveolar socket following tooth extraction. An animal model was proposed using radiography and histomorphology simultaneously to analyze the symmetrical sections of Wistar rats. The upper incisors of Wistar rats were extracted and the extraction sockets were randomly treated with gelatin sponge, neat chitosan, C-PGA, or received no treatment. The extraction sockets of selected rats from each group were evaluated at 1, 2, 4, or 6 wk post-extraction. The results of radiography and histopathology indicated that the extraction sockets treated with C-PGA exhibited lamellar bone formation (6.5%) as early as 2 wk after the extraction was performed. Moreover, the degree of new bone formation was significantly higher (P < 0.05) in the extraction sockets treated with C-PGA at 6 wk post-extraction than that in the other study groups. In this study, we demonstrated that the proposed animal model involving symmetrical sections and simultaneous radiography and histomorphology evaluation is feasible. We also conclude that the novel C-PGA has great potential for new bone formation in the alveolar socket following tooth extraction.

Erosive potential of soft drinks on human enamel: An in vitro study

BACKGROUND/PURPOSE Most soft drinks are acidic in nature. Regular consumption of these drinks may result in dental erosion. The aim of this in vitro study was to evaluate the erosive potential of different soft drinks in Taiwan by a novel multiple erosive method. METHODS Four commercially available soft drinks in Taiwan were selected for this study. The properties of each product were analyzed to measure their pH, titratable acidity, and ion contents. The erosive potential of the soft drinks was measured based on the amount of loss of human enamel surface following its exposure to the soft drinks tested for different periods (20 minutes, 60 minutes, and 180 minutes). The enamel loss was measured using a confocal laser scanning microscope. RESULTS The pH values of the soft drinks were below the critical pH value (5.5) for enamel demineralization, and ranged from 2.42 to 3.46. The drink with ingredients of citric acid and ascorbic acid had the highest titratable acidity (33.96 mmol OH(-)/L to pH 5.5 and 71.9 mmol OH(-)/L to pH 7). Exposure to all the soft drinks resulted in loss of human enamel surface (7.28-34.07 μm for 180-minute exposure). The beverage with the highest calcium content had the lowest erosive potential. CONCLUSION All tested soft drinks were found to be erosive. Soft drinks with high calcium contents have significantly lower erosive potential. Low pH value and high citrate content may cause more surface enamel loss. As the erosive time increased, the titratable acidity to pH 7 may be a predictor of the erosive potential for acidic soft drinks. The erosive potential of the soft drinks may be predicted based on the types of acid content, pH value, titratable acidity, and ion concentration.

Application and development of ultrasonics in dentistry

Since the 1950s, dentistrys ultrasonic instruments have developed rapidly. Because of better visualization, operative convenience, and precise cutting ability, ultrasonic instruments are widely and efficiently applied in the dental field. This article describes the development and improvement of ultrasonic instruments in several dental fields. Although some issues still need clarification, the results of previous studies indicate that ultrasonic instruments have a high potential to become convenient and efficient dental tools and deserve further development.

Tension-compression viscoelastic behaviors of the periodontal ligament.

BACKGROUND/PURPOSE Although exhaustively studied, the mechanism responsible for tooth support and the mechanical properties of the periodontal ligament (PDL) remain a subject of considerable controversy. In the past, various experimental techniques and theoretical analyses have been employed to tackle this intricate problem. The aim of this study was to investigate the viscoelastic behaviors of the PDL using three-dimensional finite element analysis. METHODS Three dentoalveolar complex models were established to simulate the tissue behaviors of the PDL: (1) deviatoric viscoelastic model; (2) volumetric viscoelastic model; and (3) tension-compression volumetric viscoelastic model. These modified models took into consideration the presence of tension and compression along the PDL during both loading and unloading. The inverse parameter identification process was developed to determine the mechanical properties of the PDL from the results of previously reported in vitro and in vivo experiments. RESULTS The results suggest that the tension-compression volumetric viscoelastic model is a good approximation of normal PDL behavior during the loading-unloading process, and the deviatoric viscoelastic model is a good representation of how a damaged PDL behaves under loading conditions. Moreover, fluid appears to be the main creep source in the PDL. CONCLUSION We believe that the biomechanical properties of the PDL established via retrograde calculation in this study can lead to the construction of more accurate extra-oral models and a comprehensive understanding of the biomechanical behavior of the PDL.

Effects of various periodontal ligament elastic moduli on the stress distribution of a central incisor and surrounding alveolar bone.

BACKGROUND AND PURPOSE Previous studies investigating the effects of core or post on the fracture strength of teeth often omitted the periodontal ligament (PDL) because its physical properties are difficult to reliably quantify. This study investigated the effects of various PDL elastic moduli on the stress distribution around a central incisor and surrounding alveolar bone using 3-dimensional finite element stress analyses. METHODS Four 3-dimensional finite element models of an upper central incisor and the dento-alveolar complex were established. Five models were constructed, including: no PDL, as well as a PDL with elastic moduli of 6.9 MPa, 68.9 MPa, and 1750 MPa. Two loading conditions were simulated, one with protrusive force and one with intrusive force. Protrusive loading was generated using a point force of 200 N at 45 degrees inclination to the longitudinal axis of the incisor applied on the lingual side. Intrusive loading was generated using a point force of 200 N applied perpendicular to the incisal edge. RESULTS The absence of a PDL had detrimental effects on the surrounding bone, because the applied stress remained concentrated at the bone crest and cervical third of the root. A PDL with a lower elastic modulus, on the other hand, helped to alleviate the magnitude of stress throughout the surrounding bone and the bone crest, in particular, by distributing the stress deeper towards the apical region. The stress distribution at the crown was unaffected by variations in the PDL elastic modulus. CONCLUSIONS PDL with a lower elastic modulus can help protect the alveolar bone crest from stress concentration.