Key Engineering Materials Vols. 330-332

Abstract: This in vitro study compared the abrasivity of commercial desensitizing dentifrices with a sodium metasilicate (Na2SiO3) dentifrice using a Surface Profile Method. Dentin specimens were made from the root of extracted human molars. The cervical part of the teeth was sectioned with a diamond wheel disk. The teeth were embedded into an epoxy resin mold and the surface was gradually polished by silicone carbide paper. After grinding, the degree of surface roughness was tested within the range of 2 mm with tapping. The British Standard Institution reference dentifrice (BSI: CaCO3 40%) and experimental dentifrices (group 1: Na2SiO3 25%, CaCO3 10% and SiO2 10%, group 2: CaCO3 10% and SiO2 10%, group 3: CaCO3 10% and SrCl2 10%, group 4: Colloidal Silica 2-3% and Hydroxyapatite 10-20%) were evaluated. The dentifrice slurries were prepared by mixing 24 grams of the dentifrice in 12 ml distilled water. Each tooth specimen was brushed with the dentifrice slurries 1,000 times. The relative abrasivity of each dentifrice was evaluated from the ratio of the BSI standard dentifrice to each experiment. The results were analyzed by one-way ANOVA and Tukey’s multiple comparisons using Window SPSS (Statistical analysis system) 12.0. Groups 1 (71), 2 (74.2), 3 (38) and 4 (7.8) showed a lower abrasivity than the BSI dentifrice (100) (p<0.05). The relative abrasivity of groups 3 (38) and 4 (7.8) was the lowest compared with the BSI dentifrice (100). However, group 1 (71) containing Na2SiO3 showed a similar abrasivity to group 2 (74.2), which did not contain Na2SiO3 (p>0.05). Therefore, Na2SiO3 had no influence on the abrasivity of the dentifrice. In conclusion, the dentifrice containing Na2SiO3 had a lower abrasivity than the BSI reference dentifrice, but showed a significantly higher abrasivity than the existing commercial desensitizing dentifrices. Overall, the relatively high abrasivity of Na2SiO3 dentifrice is believed to be the result of other components in the abrasive system.

Abstract: Dental ceramic materials do not always show linear expansion behavior. In general, thermal contraction behavior of dental porcelain can be described with the polynomial function: L/L= C+α1 T+α2 T2. In addition, a new method for taking into consideration of nonlinear contraction behavior of dental ceramics is proposed for calculating thermal mismatch value (α) between substrate and veneering materials. Discs of eight substrate/veneer combinations (n=10) were fabricated for thermal shock testing. In this study, a stepwise multiple regression analysis was performed to determine the relationship between thermal shock test results and thermal mismatch value (α) on these combinations. A high degree of correlation was found between αs-b and T. The new method proves to be a reliable one to predict thermal compatibility of multi-layer dental ceramic composites.

Abstract: The effect of two bleaching materials on dental enamel was studied by vibrational spectroscopy. Human molar enamel sections parallel to the dentin-enamel junction were one-side polished and treated with bleaching agents containing 38% hydrogen peroxide (Opalescence Xtra Boost) or 20% carbamide peroxide (Opalescence PF 20%). Then the crystalline structure and molecular inclusions of the bleached samples were analyzed by Raman scattering and attenuated total reflectance infrared spectroscopy. No spectral difference was observed between the unbleached enamel and that bleached with the two different agents, which indicates no significant occurrence of structural or chemical changes in enamel apatite due to bleaching.

Abstract: This study evaluated the marginal fit of CAD-CAM Zirconia cores with different proximal height. Thirty Zirconia cores and ten metal ceramics crowns were used to evaluate the marginal gap. The marginal fit was determined to be perpendicular to the tooth axis between the most apical point on the coping margin (core) and the reference marks on the mesial, distal, labial, and palatal surfaces of the die at several key stages of crown fabrication; before porcelain built-up, after body porcelain built-up, and after glazing. Additionally, an opaque stage for the metal ceramic copings was compared as well. Each measurement was carried out with a microscope. The means of gaps among the groups were 58±27 -m, 69±23 -m, 89±29 -m and 80±28 -m, groups I, II, III and IV, respectively. In relation to the proximal and labiopalatal surfaces there were no statistical difference among the groups, except group I. No significant differences were observed in firing stages of all groups. The findings of this study showed that the mean marginal gap of Zirconia cores with different proximal heights fell well within the acceptable clinical ranges.

Abstract: To evaluate the effects of progressive loading on implants placed into extraction sockets. 4 beagle dogs were extracted bilateral 3rd, 4th and 2nd premolar and immediately inserted the implant at first surgery (0d), 14d and 21d. Using the newly developed vertical occlusion loading system, progressive loading procedures were taken 24h after insertion. The vertical bone loss (VBL) and bone-to-implant contact ratio (BIC) was measured by image analysis software and analyzed using the paired student t test. After 28d period of healing, each animal was sacrificed and the samples were evaluated by scanning electron microscopy (SEM). The mean vertical bone loss in control groups was larger than that of the experimental groups at 14, 21 and 28 day (P<0.05). SEM showed that the mineralization rate of experimental groups was faster than the control groups. The bone-implant contact ratios in experimental groups were more than that in the control groups. The differences were statistically significant (P<0.05). Compared with non-loading implant, progressive loading can promote osseointegration and decrease vertical bone loss. Progressive loading of implants placed into extraction sockets can be performed without interfering with the osseointegration process.

Abstract: The aim of this study is to evaluate treatment effects of novel GBR membranes (PDLLA membranes) applied to bony defects around dental implants on new bone regeneration alone or in combination with bioceramic bone graft (BIO-OSS®) on the mongrel dog model in comparison with collagen membrane (BIO-GIDE®) and therefore to assess the clinical values of the novel GBR membranes and bioceramic bone graft material in dental implantology. 6 implants were placed in bilateral mandibular of each mongrel dog after preparation of mid- crestal defects. The defects on one side were covered with PDLLA membranes alone or with bone graft, while the contra-lateral sides received collagen membranes alone or with bone graft. These animals were sacrificed at 2, 4, 8,12 weeks post the GBR-operation. And gross sample examination, standardized radiographs, 99mTc-MDP SPECT and histomorphometric analysis were taken. All examinations showed similar amounts of newly formed bone beneath both types of barriers. The PDLLA or collagen membrane with bone graft groups showed better results than the membrane used alone groups. The results indicated that PDLLA membranes especially with bioceramic bone graft presented an improved response in dealing with bony defects around implants.

Abstract: Yttria and iron co-doped tetragonal zirconia polycrystals ((Y, Fe)-TZPs) were investigated to evaluate the feasibility for the ceramic bracket application. Presintered the (Y,Fe)-TZPs brackets were machined, abraded and coated with granule spray containing 10~50 wt% of flux. Finally, the base-coated brackets were sintered. Roughness of the coated surface was decreased to 13 um and 10 um when the flux content was 30 wt% and 50 wt%, respectively. It may be due to the fusion and the collapse of the granules as a result of the high amount of flux. Better adhesion to the base surface of the brackets and irregular shape were observed by raising the amount of flux in the slurries. Wetting angle of ethylene glycol droplet on the (Y,Fe)-TZP bare surface was determined to be 41.85°, however, the angle became 0° after the granule spraying treatments. The (Y,Fe)-TZP brackets exhibited uniform embossed base and good wetting. The newly developed base-coated bracket could be highly applicable to enhance retention and to reduce adhesive resin remnant during the bracket debonding.

Abstract: Recasting of economic alloys can change several properties. The number of recasting was found to have negligible effect on surface texture and on the amount of corrosion products released. The methods and equipments utilized in the casting of an alloy are important on the quality of casting. Carbon incorporated in a noble or economic alloy during casting is known to affect the mechanical values of the metal. In the present study we aimed to investigate the change in structure and metal hardness due to recasting. Materials and method: The effect of recasting, up to four times of a non precious “Finalloy” commercial dental alloy on their Rocwell C hardness behavior and their microstructures was inspected. Using “Kerr casting waxes” patterns were prepared similar to the samples from “Finalloy”. The investments were pre-heated to phase at temperatures between 900°C and 1000°C. The alloy was melted by an acetylene-oxygen flame in a silicate crucible and four groups were compared: New alloy and alloys casted two, three, and four times (n = 7). After casting, Brinell harnesses were recorded. Values of Rocwell C strength, for each specimen group were analyzed by one-way analysis of variance, followed by the Student- Newman-Keuls multiple range test. A metal microscope was used to evaluate the surface morphology of the samples before hardness tests. 1st Casting :30.65 ± 0.3 kgf, 2nd Casting: 31.33 ± 0.4 kgf, 3rd Casting:34.80 ± 0.3 kgf, 4th Casting: 35.5 ± 28 kgf represents the Rocwell hardness of the castings. The results showed that hardness, increased with repeated castings. The experimental data indicates that increasing the number of successive recasting of “Finalloy” enhances the Rocwell C hardness, thus, after remelting and recasting, the biological properties decreases. Microscope study: Increase of the carbon content on the gren bounders of a cobalt-chromium alloy causes a considerable change in its microstructure. The hardness and yield point for 0.05 %, 0.1 % and 0.2 % tensile strength and elongation were determined for these test-pieces. The results showed that hardness, yield points and tensile strength increased with increased carbon content, whereas the elongation lessened. We determined that carbon concentrated at gren bounders. The clinical importance of the study is that recasting affected the properties of the metal, for best biological results with dental alloys always new metals must be used.

Abstract: Exposed dentine with patent tubules allows the movement of tubule fluid leading to dentine sensitivity. Occlusion of patent dentinal tubules effectively reduces the state of dentine hypersensitivity. Strontium chloride (SrCl2) has been well known as a component of desensitizing dentifrice. Recently, new dentifrice containing sodium metasilicate was on the market for desensitizing dentifrice. The aim of this in vitro study was to compare the occlusion effect of dentinal tubule between the sodium metasilicate and the existing desensitizing dentifrices. Sixtyfour human dentine specimens were embedded into a Teflon mold and were grinded with the use of silicone carbide papers to expose the surface of dentin. The dentin surface was etched with 37% phosphoric acid for 60 seconds and was treated with ultrasonic washing for 1 hour. The dentifrices used in the study are classified into four groups: G1-dentifrice containing Sodium metasilicate, G2- dentifrice containing Strontium chloride, G3-dentifrice containing Hydroxyapatite and G4-BSI reference dentifrice (control group). Toothpaste slurries were prepared as 20 gram of toothpaste in 80 ml of distilled water. Thirty-two specimens were brushed with the toothpaste slurries using V8 Cross Brushing Machine. Tooth-brushing was performed 5,000 times using a back-and–forth stroke. The pictures of the sizes of dentinal tubules were taken by scanning electron microscopy (×3000) and changes of tubule sizes were analyzed by digital analysis. The results showed that the difference of tubule size in descending order: G1-3.30±1.80, G2-2.82±1.73, G3-1.49±1.14, G4- 1.04±0.94. The dentifrice containing Sodium metasilicate (22.5%) showed the highest dentinal tubule occlusion. Moreover, the dentifrice containing Sodium metasilicate statistically significantly increased occlusion of dentinal tubule as compared to BSI reference dentifrice (p<0.05). Thus, new desensitizing dentifrice containing sodium metasilicate was more effective than existing desensitizing dentifrice on occlusion of dentin tubules.