Synthesis of ß-tricalcium phosphate by modifying the heating process of a dental casting mold.

This study investigated a novel method for artificial synthesis of ß-tricalcium phosphate (ß-TCP). The binder of the phosphate-bonded investment was replaced with calcium oxide instead of magnesium oxide and sintered in an electric furnace. The water/powder mixing ratio for hardening was determined using preliminary experiments. Thermal analysis was performed to check the thermal behavior of the sample tested. In addition, the fired sample was analyzed using an X-ray diffraction apparatus to identify the compounds after sintering. The hardened sample exhibited multiple compounds, including unreacted components, post which, new compounds were generated by heating. Peaks of calcium pyrophosphate and ß-TCP were confirmed at 800ºC and 1,300ºC, respectively. ß-TCP could be easily synthesized within the limited study by sintering at 1,300ºC both monoammonium phosphate and calcium oxide. Experimental results suggest that ß-TCP can be easily synthesized by simulating the conventional dental casting process.

Fluoride Retention in Root Dentin following Surface Coating Material Application.

This study aimed to use an in-air micro-particle-induced X-ray/gamma emission (in-air µPIXE/PIGE) system to evaluate tooth-bound fluoride (T-F) in dentin following the application of fluoride-containing tooth-coating materials. Three fluoride-containing coating materials (PRG Barrier Coat, Clinpro XT varnish, and Fuji IX EXTRA) and a control were applied to the root dentin surface of human molars (n = 6, total 48 samples). Samples were stored in a remineralizing solution (pH 7.0) for 7 or 28 days and then sectioned into two adjacent slices. One slice of each sample was immersed in 1M potassium hydroxide (KOH) solution for 24 h and rinsed with water for 5 min for the T-F analysis. The other slice did not undergo KOH treatment and was used to analyze the total fluoride content (W-F). The fluoride and calcium distributions were measured in all the slices using an in-air µPIXE/PIGE. Additionally, the amount of fluoride released from each material was measured. Clinpro XT varnish demonstrated the highest fluoride release among all the materials and tended to show high W-F and T-F and lower T-F/W-F ratios. Our study demonstrates that a high fluoride-releasing material shows high fluoride distribution into the tooth structure and low conversion from fluoride uptake by tooth-bound fluoride.

Evaluation of the mechanical properties and biocompatibility of gypsum-containing calcium silicate cements.

Mineral trioxide aggregate (MTA) cement is widely used in the field of endodontic treatment. We herein synthesized calcium silicates from calcium carbonate and silicon dioxide, with the aim of reducing the cost associated with the MTA. Additionally, we prepared gypsum-containing calcium silicate cement to reduce the setting time while enhancing the mechanical strength. We evaluated the physical properties of this cement and investigated the response of human dental pulp stem cells (hDPSCs) grown in culture media containing cement eluate. Our results revealed that calcium silicates could be easily synthesized in lab-scale. Furthermore, we demonstrate that gypsum addition helps shorten the setting time while increasing the compressive strength of dental cements. The synthesized gypsum-containing calcium silicate cement showed minimal cytotoxicity and did not inhibit the proliferation of hDPSCs. These results suggested that the newly developed calcium silicate material could be a promising pulp capping material.

Distribution of elements in teeth and inhibition of demineralization by titanium fluoride: Effects of concentration and pH in a titanium fluoride solution.

The purpose of this study was to assess the effects of titanium fluoride (TiF4) concentration and pH on fluoride distribution and demineralization of root dentin surfaces. Concentrations of 0.1%, 1%, and 2% TiF4 (pH 1), 1% TiF4 solution adjusted to pH 4, 5, 6, and 1.35% sodium fluoride (NaF) solution were applied to root dentin surfaces. Each specimen was subjected to pH cycling (pH: 4.5-7.0) for 4 weeks. Lesion depth and calcium, fluorine, and titanium distribution were then evaluated. Our limited study indicates that lesion depth and fluorine and titanium distribution in dentin depend on the concentration of a TiF4 solution. We also found that a 1% TiF4 solution adjusted to a pH 4-6 can reduce demineralization as effectively as a similar concentration of NaF.

Use of new scratch test and tensile test for evaluation of bond strength of selfadhesive flowable resin composite for repair of artificial tooth erosion.

The purpose of this study was to use a new scratch test and tensile test to evaluate the bond strength between artificial erosive enamel or dentin and self-adhesive resin composites as a coating material. Coronal enamel or dentin surface was exposed to an erosive cycle (artificial saliva [AS], pH:7.0 for 6.5 h and acidic carbonated beverages for 5 min, alternated 3 times per day) for the eroded-surface or stored in AS for the remineralized-surface. Two self-adhesive flowable resin composites, Fusio and LLB-CR6 (prototype), and a conventional flowable resin composite, BEAUTIFIL FLOW with self-etching primer system, Clearfil Mega Bond, were applied to enamel or dentin surfaces; and then the bond strengths were measured. For the eroded-surface, there were no significant differences in bonding strength among all materials, as assessed by the new scratch test. Thus, these self-adhesive flowable resin composites might be useful for coating materials on acid-eroded tooth surfaces.

Efficacy of a new filler-containing root coating material for dentin remineralization.

PURPOSE: To evaluate a new root coating material containing surface pre-reacted glass-ionomer (S-PRG) filler for remineralization of demineralized dentin. METHODS: The dentin was exposed on root surfaces of human third molars and demineralized by immersion in demineralization solution for 4 days. The demineralized dentin surface was divided into three areas. The center area was left untreated. The area on one side of the center area was coated with protective wax. The area on the other side was coated with one of four test materials: fluoride-containing S-PRG filler (PRG Barrier Coat: PR), fluoride-containing bonding agent (Bond Force: BF), fluoride-containing glass-ionomer cement as a positive control (Fuji IX EXTRA: EX), or non-fluoride-containing bonding agent as a negative control (Clearfil MegaBond: MB). The samples were stored in remineralization solution for 7 days, and then cut into two slices. The mineral changes, defined as variation in mineral loss between wax-coated area and the central untreated area, were measured in one slice by transversal microradiography. The fluoride concentration was measured in the other slice by µ-particle-induced gamma/X-ray emission. Seven thin specimens (0.25-mm thickness) of each test material were used to determine fluoride ion release from the materials over 21 days. RESULTS: The mineral changes were greatest for EX, followed by PR, with no difference between BF and MB (P> 0.05). Regarding the fluoride concentrations in dentin, there was no difference between EX and PR (P> 0.05). MB had the lowest value (P< 0.01). Fluoride release from EX was largest, followed by PR, with BF showing low fluoride release (P< 0.05). MB had no fluoride release. CLINICAL SIGNIFICANCE: A new coating material with S-PRG filler can be applied in a thin layer on root dentin, which could be especially useful for hard-to-access lesions. This material remineralized demineralized root dentin and had fluoride diffusion characteristics similar to those of glass-ionomer cement in vitro.

Tri-calcium phosphate (ß-TCP) can be artificially synthesized by recycling dihydrate gypsum hardened.

Calcium phosphate is known as a major component of biological hard tissues. This study aimed to produce calcium phosphate by recycling kneaded surplus gypsum. ß-dihydrate gypsum was derived from commercial dental ß-hemihydrate gypsum, which was mechanically powdered and mixed with the liquid component of a commercial zinc phosphate cement. This mixture was fired at 1,200°C and evaluated by XRD analysis, thermal analysis and scanning electron microscopy (SEM). An acceptable ratio of mixing was 4 g of ß-dihydrate gypsum powder to 1.5 mL of phosphoric acid liquid. XRD peaks were monotonic below 800°C, but new ß-TCP was formed by firing at 900°C or more, although TG-DTA analysis of synthetic ß-TCP suggested that some residual dihydrate gypsum remained in the sample. SEM images indicated a fused-block bone-like structure covered with phosphorus and calcium. These results suggest that production of synthetic ß-TCP is possible through ecological techniques using recycled materials.

Effects of surface roughness and dimorphism on the adhesion of Candida albicans to the surface of resins: scanning electron microscope analyses of mode and number of adhesions.

AIM: Candida albicans is a common oral fungus but can cause serious conditions such as Candida stomatitis. We investigated C. albicans adhesion to the surface of denture-base resins at two growth phases. METHODS: Fungal suspensions of logarithmic (9 h) and stationary phase (24 h) C. albicans (JCM2085) were used. Scanning electron microscopy (SEM) confirmed that yeast and mycelial forms were predominant in 9-h and 24-h cultures, respectively. Resin strips were polished to three surface roughness levels (Ra 3.2 µm, Ra 0.48 µm and Ra 0.06 µm) and were then immersed in C. albicans suspensions for both phases. The SEM images were taken at five sites on each strip. RESULTS: Adhesion of mycelial-form C. albicans on rough surfaces (Ra = 3.2) was 2.2 times higher than on smooth surfaces (Ra = 0.06; 7030 vs 3580 adhesions/mm(2), P < 0.01). The hyphae of these mycelial forms fully penetrated the surface cracks. Fewer adhesions occurred for yeast-form C. albicans, regardless of surface type (440-620 adhesions/mm(2), P = n.s.). CONCLUSION: Adhesion of yeast-form C. albicans was indifferent to surface roughness. In contrast, mycelial adhesion increased with surface roughness of the resin because mycelia infiltrated the minute protuberances on rough surfaces.

Effects of Tooth Coating Material and Finishing Agent on Bleached Enamel Surfaces by KTP Laser.

OBJECTIVE: The purpose of this study was to evaluate the effect of tooth coating material and finishing agent on bleached enamel surfaces after using KTP laser with 27% hydrogen peroxide. BACKGROUND DATA: There have been few reports on the effects of tooth coating materials and finishing agents after bleaching. METHODS: After 40 crowns of human extracted maxillary incisors were bleached by KTP laser, bleached enamels were finished with fluoride only or both of fluoride and nano-hydroxyapatite as a finishing agent. After application(s) of fluoride and/or finishing agent, the enamel surfaces were divided into 2 groups, which were covered with the coating material or without coating material. After application of coating materials, all specimens were kept for 2 weeks at 37°C of 100% humidity. After removing the coating material, color changing was measured and enamel surfaces were examined by scanning electron microscopy (SEM). RESULTS: SEM observation of enamel surfaces treated the fluoride gel, finishing agent and coating material showed the most flattered surface compared to other groups. By measuring the color changing, few color changing was observed on the enamel surfaces treated the fluoride gel, finishing agents and coating material. CONCLUSION: These results suggested that applications of fluoride gel, finishing agent and coating material made the enamel-surfaces flattered and kept effects of bleaching, could prevent the re-coloration. After applications of fluoride gel and finishing agent, covering the bleached-enamel surfaces with the coating material enhanced the keeping whiteness. It would give the patients satisfaction of whiteness.

Compatibility of Ce-TZP/Al2O3 nanocomposite frameworks and veneering porcelains.

The aim of this study was to examine the compatibility of Ce-TZP/Al2O3 nanocomposite (CTA) frameworks and veneering porcelains using the Schwickerath crack initiation test and clarify the effects on debonding/crack initiation strength (DIS) of both surface pretreatment (include heat treatment) of the frameworks, type of veneering porcelain varying the coefficient of thermal expansion (CTE), and surface roughness of the frameworks. The surfaces of Ce-TZP/Al2O3 plates were mechanically treated and followed by post-heat treatment. The liner and body porcelains were built up and fired according to the manufacturer's instructions. Surface analyses of the fractured plates showed compatibility with liner porcelains. Since no statistically difference in the DIS was found amongst the different surface treatments, post-heat treatments don't be mandatory. Whereas, since differences in DIS were found when different porcelains with different CTE were used, we concluded the matching of CTE of the porcelain with that of Ce-TZP/Al2O3 was important for successful all-ceramic restorations using Ce-TZP/Al2O3 frameworks.

Properties of experimental titanium cast investment mixing with water reducing agent solution.

This study aimed to develop a dental investment for titanium casting. ZrO(2) and Al(2)O(3) were selected as refractory materials to prepare three investments (Codes: A-C) according to the quantity of Zr. Al(2)O(3) cement was used as a binder at a ratio of 15%, they were mixed with special mixing liquid. B1 was used as a control mixed with water. Fundamental examinations were statistically evaluated. A casting test was performed with investment B. Fluidities, setting times, and green strengths showed no remarkable differences; however, they were significantly different from those of B1. Expansion values for A, B, C, and B1 at 850°C were 1.03%±0.08%, 1.96%±0.17%, 4.35%±0.23%, and 1.50%±0.28%, respectively. Castings were covered by only small amounts of mold materials. The hardness test showed no significant differences between castings from B and the ones from commercial investments. The experimental special mixing liquid effectively reduced the water/powder ratio and improved the strength and thermal expansion.

Effects of a convenient silica-coating treatment on shear bond strengths of porcelain veneers on zirconia-based ceramics.

Porcelain veneering of zirconia is necessary, but chipping of the veneer may cause clinical problems. We investigated the effects of silica coating to improve the bond strength between porcelain veneers and zirconia-based ceramics. The ceramics tested were zirconia/alumina nanocomposites stabilized with ceria. Three surface treatments, grinding with a carborundum point (CA), sandblasting with alumina (SB), and Silano-Pen treatment (SP), were performed. Untreated specimens (NT) were examined as a control. The surface roughnesses and contact angles after treatment were measured. Shear bond tests were conducted, and the average strengths were calculated. EPMA was used for elemental identifications and surface observations. The bond strengths with SP were 20.00±3.43MPa and were significantly larger than that (15.35±3.12 MPa) of NT (p<0.05). However, differences among treated specimens were not significant. Moreover, SP gave superior wettability, and smoothness as good as NT. These data suggest that SP affects the bond strength between zirconia and a porcelain veneer.

Production of a calcium silicate cement material from alginate impression material.

The purpose of this study was to synthesize biomaterials from daily dental waste. Since alginate impression material contains silica and calcium salts, we aimed to synthesize calcium silicate cement from alginate impression material. Gypsum-based investment material was also investigated as control. X-ray diffraction analyses revealed that although firing the set gypsum-based and modified investment materials at 1,200°C produced calcium silicates, firing the set alginate impression material did not. However, we succeeded when firing the set blend of pre-fired set alginate impression material and gypsum at 1,200°C. SEM observations of the powder revealed that the featured porous structures of diatomite as an alginate impression material component appeared useful for synthesizing calcium silicates. Experimentally fabricated calcium silicate powder was successfully mixed with phosphoric acid solution and set by depositing the brushite. Therefore, we conclude that the production of calcium silicate cement material is possible from waste alginate impression material.

Soda-lime glass as a binder in reusable experimental investment for dental castings.

In this study, different glasses were investigated to improve reusable investments. Borosilicate glass (BSG) powder and soda-lime glass (SLG) powder were prepared by milling broken beakers and microscope slides, respectively, and used in experimental investments (I-BSG, I-SLG) by blending glass powder (10 wt%) with cristobalite (90 wt%). Some properties and casting fits were evaluated with commercial gypsum-bonded investment as the control. Both BSG and SLG were mainly composed of Si, but SLG had a large Ca content. The glass transition temperatures were approximately 800°C (BSG) and 700°C (SLG). Experimental investments with heating showed the significantly (p<0.05) higher expansion than that of the control. The compressive strength of I-SLG was higher than that of I-BSG, and increased with temperature. The MOD inlay obtained from I-SLG had a significantly smaller gap than that from I-BSG, and was comparable to the control. These results suggest SLG could be applied clinically as a reusable dental investment.

Synergistic responses of superficial chemistry and micro topography of titanium created by wire-type electric discharge machining.

Wire-type electric discharge machining has been applied to the manufacture of endosseous titanium implants as this computer associated technique allows extremely accurate complex sample shaping with an optimal micro textured surface during the processing. Since the titanium oxide layer is sensitively altered by each processing, the authors hypothesized that this technique also up-regulates biological responses through the synergistic effects of the superficial chemistry and micro topography. To evaluate the respective in vitro cellular responses on the superficial chemistry and micro topography of titanium surface processed by wire-type electric discharge, we used titanium-coated epoxy resin replica of the surface. An oxide layer on the titanium surface processed by wire-type electric discharge activated the initial responses of osteoblastic cells through an integrin-mediated mechanism. Since the mRNA expression of ALP on those replicas was up-regulated compared to smooth titanium samples, the micro topography of a titanium surface processed by wire-type electric discharge promotes the osteogenic potential of cells. The synergistic response of the superficial chemistry and micro topography of titanium processed by wire-type electric discharge was demonstrated in this study.

A modified porous titanium sheet prepared by plasma-activated sintering for biomedical applications.

This study aimed to develop a contamination-free porous titanium scaffold by a plasma-activated sintering within an originally developed TiN-coated graphite mold. The surface of porous titanium sheet with or without a coated graphite mold was characterized. The cell adhesion property of porous titanium sheet was also evaluated in this study. The peak of TiC was detected on the titanium sheet processed with the graphite mold without a TiN coating. Since the titanium fiber elements were directly in contact with the carbon graphite mold during processing, surface contamination was unavoidable event in this condition. The TiC peak was not detectable on the titanium sheet processed within the TiN-coated carbon graphite mold. This modified plasma-activated sintering with the TiN-coated graphite mold would be useful to fabricate a contamination-free titanium sheet. The number of adherent cells on the modified titanium sheet was greater than that of the bare titanium plate. Stress fiber formation and the extension of the cells were observed on the titanium sheets. This modified titanium sheet is expected to be a new tissue engineering material in orthopedic bone repair.

Effects of investment type and casting system on permeability and castability of CP titanium.

STATEMENT OF PROBLEM: Several factors, such as casting systems and investment properties, are important to obtain a sound titanium casting. Although various casting systems and investments for titanium are commercially available, their effects on CP titanium castability are not clear. PURPOSE: The purpose of this study was to determine permeability of investments and to evaluate the effects of investment type and casting system on titanium castability. MATERIAL AND METHODS: Three investments for titanium (experimental gypsum-bonded investment, Selevest CB, and Speed Titan) and 4 titanium casting systems (Cyclarc, Ti-Cascom, Vulcan T, and Ticast Super R) were used. Permeability was measured using a flow meter and argon gas at 0.1, 0.2, and 0.3 MPa. Castability was calculated as the percentage of reproduced holes compared to a perforated wax pattern. Data for castability and permeability were analyzed separately with 2-way ANOVA and the Tukey HSD test (alpha=.05). RESULTS: The ANOVA for permeability and castability showed significant interaction (P<.001 and P=.004, respectively). Differences in permeability among the 3 investments increased with a higher gas pressure. Permeability of the experimental investment at each pressure level was significantly greater than that of the other investments, except for Speed Titan at 0.1 MPa (P<.05). The permeability of Selevest CB at each pressure level was significantly less than that of the other investments (P<.05). Cyclarc and Ti-Cascom specimens were not significantly different, in terms of castability, using the investments evaluated, but castability of Vulcan T and Ticast specimens varied significantly by the investment used (P<.05). CONCLUSIONS: Within the limitations of this study, investment type, pressure level, and their combinations influenced permeability. Castability of titanium was influenced by investment type, casting system, and their combinations. The investment with the highest permeability did not demonstrate the best result for castability.

Combination treatment of tribochemical treatment and phosphoric acid ester monomer of zirconia ceramics enhances the bonding durability of resin-based luting cements.

The aim of the present study was to evaluate the bonding durability of resin-based luting cement to partially stabilized tetragonal zirconia (Y-TZP) achieved by combination treatment of tribochemical (TBC) treatment and two different phosphate acid ester monomers. Two phosphate acid ester monomers (EP: Epricord opaque primer, AZ: AZ primer) were applied to each surface modification followed by application of resin-based luting cement (Rely-X ARC). Bonding specimens were placed in deionized water at 37 degrees C and stored for 24 h. The other groups were subjected to 30,000 cycles of a thermal stress for the durability test. Shear bond tests were done using a universal testing machine at 1 mm/min. Shear bond strengths of combination treatments using EP and AZ on TBC treatment after thermal stress showed no significant difference (p>0.05) compared with those of storage after 24 h. Combination treatment using phosphoric acid ester monomer could achieve a durable bond.

Properties of a gypsum-bonded magnesia investment using a K2SO4 solution for titanium casting.

The purpose of the study was to investigate the effects of a K2SO4 solution on the improvement of the properties of an experimental magnesia-based gypsum-bonded investment. The characteristics of the experimental investment with different ratios of a K2SO4 solution were as follows: setting time ranged from 34 to 152 minutes, green and fired compressive strengths were approximately 2.15 to 5.81 MPa and 1.63 to 2.45 MPa, respectively; thermal expansion was 0.38 to 0.47% at 700 degrees C, which did not show any significant differences due to the concentration of the K2SO4 solution. Titanium casting could be obtained using the experimental investment mixed with a 1% K2SO4 solution, and the reaction layer thickness of the casting was less than 200 microm. The results suggest that the experimental investment mixed with 1% K2SO4 showed acceptable physical properties and casting characteristics for titanium casting.

A review of dental CAD/CAM: current status and future perspectives from 20 years of experience.

In this article, we review the recent history of the development of dental CAD/CAM systems for the fabrication of crowns and fixed partial dentures (FPDs), based on our 20 years of experience in this field. The current status of commercial dental CAD/CAM systems developed around the world is evaluated, with particular focus on the field of ceramic crowns and FPDs. Finally, we discuss the future perspectives applicable to dental CAD/CAM. The use of dental CAD/CAM systems is promising not only in the field of crowns and FPDs but also in other fields of dentistry, even if the contribution is presently limited. CAD/CAM technology will contribute to patients' health and QOL in the aging society.