Mechanical properties and antibacterial effects of glass ionomer cement containing gallium phosphate glass (GPG) / 대한치과재료학회지

This study investigated the mechanical properties and antibacterial activity of glass ionomer cement (GIC) containing 1 mol% or 5 mol% gallium phosphate glass (GPG) powder. GPG were added to conventional GIC powder in a range of 0~20 wt%. The specimens for compressive strength (4 mmØ×6 mm) and diametral tensile strength (6 mmØ×4 mm) were prepared by mixing with the cement liquid and kept in an water of 37±1℃. Mechanical properties were evaluated at an interval of 1 h, 24 h, and 7 days. Antibacterial activity of specimens against to S. mutans and S. sobrinus was evaluated using agar diffusion methods. Data were statistically analyzed by one-way ANOVA and Tukey HSD post-hoc test (p<0.05). Diametral tensile strength of GIC containing GPG were significantly higher than control GIC while compressive strength showed no statistical difference. There was an increasing tendency of antibacterial activity for GPG-GICs. Results indicated that GPG can be considered as potential reinforcing agent for increasing antibacterial and mechanical properties for conventional GIC.

Investigation of the cytotoxicity of thermoplastic denture base resins

PURPOSE: The purpose of this study was to investigate the in vitro cytotoxicity of thermoplastic denture base resins and to identify the possible adverse effects of these resins on oral keratinocytes in response to hot water/food intake. MATERIALS AND METHODS: Six dental thermoplastic resin materials were evaluated: three polyamide materials (Smile tone, ST; Valplast, VP; and Luciton FRS, LF), two acrylic materials (Acrytone, AT; and Acryshot, AS), and one polypropylene resin material (Unigum, UG). One heat-polymerized acrylic resin (Vertex RS, RS) was chosen for comparison. After obtaining extracts from specimens of the denture resin materials (Φ=10 mm and d=2 mm) under different extraction conditions (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour), the extracts (50%) or serial dilutions (25%, 12.5%, and 6.25%) in distilled water were co-cultured for 24 hours with immortalized human oral keratinocytes (IHOKs) or mouse fibroblasts (L929s) for the cytotoxicity assay described in ISO 10993. RESULTS: Greater than 70% viability was detected under all test conditions. Significantly lower IHOK and L929 viability was detected in the 50% extract from the VP (70℃) and AT (121℃) samples (P < .05), but only L929 showed reduced viability in the 50% and 25% extract from LF (37℃) (P < .05). CONCLUSION: Extracts obtained from six materials under different extraction conditions (37℃, 70℃, and 121℃) did not exhibit severe cytotoxicity (less than 70% viability), although their potential risk to oral mucosa at high temperatures should not be ignored.

A study on the stress distribution of posterior fixed partial denture with various all-ceramic systems / 대한치과보철학회지

PURPOSE: The purpose of this study was to analyze stress distribution of all ceramic posterior fixed partial denture using a three dimensional finite element method. MATERIAL AND METHOD: A three dimensional finite element model was created to demonstrate all-ceramic posterior fixed partial denture and then this computer model measured the stress distribution of the all ceramic bridges which has a ceramic core materials such as Zirconia, IPS Empress 2, In-Ceram zirconia, Metal-Ceramic. Also the stress distribution was examined according to loading sites when force was applied to sites such as the central area of second premolar, the mesial connector of pontic, the central fossa of pontic, the distal connector of pontic, and the central fossa of second molar. RESULTS: 1. In all the materials of the core in this study, von Mises stress indicated that the stress increased as force was applied to loaded sites, just at those points, on the connector, and the margin in the area adjacent to the connectors. 2. The maximum principal stress was much higher in the lower part of the connectors than in any other region. 3. As the load was applied to the different locations, the research showed a consistent increase of stress in the lower connectors. The maximum value of the von Mises stress was two or three times greater when the load was applied directly to the connectors rather than indirectly through another stressed region. 4. In the case of In-Ceram zirconia, the stress in lower connectors was the highest of all the reference points, the stress showed 75% of all the maximum stress. Ziconia showed 72%, Metal-Ceramic 67% and IPS Empress 2 50%. 5. In the case of Ziconia, the stress was well dispersed in each reference point that the stress differences were smaller when compared to In-Cream ziconia.

A study of contraction shrinkage of composite resins and ormocers with various curing times / 대한치과보존학회지

Ormocer has organic-inorganic compound polymers. One of advantages of ormocer is reduced polymerization shrinkage. The purpose of this study was to compare the amount of contraction shrinkage of composite resins and ormocers. Additionally, the time of each material when there is no further change of contraction shrinkage was analysed. Four brands of composite resins (P-60, Surefil, Z-250 and Denfil) and two brands of ormocers (Definite and Admira) were used. 20 seconds, 40 seconds and 60 seconds of curing times were given. Contraction shrinkage of them were measured using a linometer for 80 seconds. The effect of material and curing time to contraction shrinkage at the time of 80 seconds was analysed by two-way ANOVA. The effect of time to contraction shrinkage was analysed by one-way ANOVA, and the time when there was no further change of the contraction shrinkage was analysed. The results are as follows : 1. P-60, Definite, Z-250 and Denfil had no further change of contraction shrinkage from the time of 20 seconds, and Surefil and Admira had no further change of contraction shrinkage from the time of 10 seconds. 2. Statistical analysis revealed volumetric shrinkage varied among material (p<0.05). No significant difference of contraction shrinkage among different curing times was found, and there was no effect of interaction between materials and curing times to contraction shrinkage. 3. Definite and Admira showed the statistically same contraction shrinkage with those of Z-250 and P-60, which is higher than that of Surefil and lower than that of Denfil (p<0.05).

Fracture Strength Of The Ips Empress Crown: The Effect Of Occlusal Depth And Axial Inclination On Lower Second Premolar / 대한치과보철학회지

The purpose of this study was to compare the fracture strength of the IPS Empress ceramic crown according to the occlusal depth(1.5mm, 2.0mm, 2.5mm) and axial inclination(4 degrees, 8 degrees, 12 degrees) of the lower second premolar. After 10 metal dies were made for each group, the IPS Empress ceramic crowns were fabricated and cemented with resin cement. The cemented crowns were mounted on the testing jig with inclination of 30 degrees and the universal testing machine was used to measure the fracture strength. The results of this study were as follows: 1. The fracture strength of the ceramic crown with 2.5mm depth and 12 degrees inclination was the highest (1284 N).Crowns of 1.5mm depth and 8 degrees inclination had the lowest strength (951N). 2. There were no significant differences in the fracture strength by axial inclination of the same occlusal depth group. 3. Most fracture lines began at the loading area and extended through proximal surface perpendicular to the margin, irrespective of occlusal depth.