Seung-Geun Ahn

Evaluation of in vitro and in vivo tests for surface-modified titanium by H2SO4 and H2O2 treatment

Titanium is widely used as an implant material for artificial teeth. Furthermore, various studies have examined surface treatment with respect to the formation of a fine passive film on the surface of commercial titanium and its alloys and to improve the bioactivity with bone. However, there is insufficient data about the biocompatibility of implant materials in the body. The purpose of this study was to examine whether surface modification affects the precipitation of apatite on titanium metal. Specimens were chemically washed for 2 min in a 1∶1∶1.5 (vol.%) mixture of 48 %HF, 60%HNO3 and distilled water. The specimens were then chemically treated with a solution containing 97%H2SO4 and 30%H2O2 at the ratio of 1∶1 (vol.%) at 40°C for 1h, and subsequently heat-treated at 400°C for 1h. All the specimens were immersed in HBSS with pH 7.4 at 36.5°C for 15d, and the surface was examined with TF-XRD, SEM, EDX and XPS. In addition, specimens of commercial pure Ti, with and without surface treatment, were implanted in the abdominal connective tissue of mice for 28 d. Conventional aluminum and stainless steel 316L were also implanted for comparison. An amorphous titania gel layer was formed on the titanium surface after the titanium specimen was treated with a solution of H2SO4 and H2O2. The average roughness was 2.175 μm after chemical surface treatment. The amorphous titania was subsequently transformed into anatase by heat treatment at 400°C for 1h. The average thickness of the fibrous capsule surrounding the specimens implanted in the connective tissue was 47.1μm in the chemically treated Ti, and 52.2, 168.7 and 101.9μm, respectively, in the untreated commercial pure Ti, aluminum and stainless steel 316L.

Analysis of proximal contact loss between implant-supported fixed dental prostheses and adjacent teeth in relation to influential factors and effects. A cross-sectional study

OBJECTIVES The aim was to analyze influential factors and effects of proximal contact loss between implant-supported fixed dental prostheses (FDP) and adjacent teeth. MATERIAL AND METHODS Ninety-four subjects treated with 135 FDPs supported by 188 implants were included. Degree of proximal contact tightness, food impaction, and periodontal/peri-implant tissue conditions were assessed in 191 proximal embrasures between implant-supported FDPs and adjacent teeth. Potential factors influencing proximal contact loss were estimated with the generalized estimation equation (GEE) procedure. RESULTS Thirty-four percent of the proximal embrasures between implant-supported FDPs and teeth lost a proximal contact. The proximal contact loss rate continuously increased over the follow-up periods. A longer follow-up period, splinted implants, and mesial aspect of proximal contact were significant factors influencing the proximal contact loss in the univariate GEE analysis, whereas a longer follow-up period was the only significant factor in the multivariate GEE analysis. Food impaction was more frequently reported in the proximal contact loss group than the proximal contact group (odds ratio: 2.2). However, the proximal contact loss did not appear to affect the periodontal/peri-implant tissue conditions. CONCLUSIONS Proximal contact loss between implant-supported FDPs and teeth occurred frequently and increased continuously over the follow-up period. The proximal contact loss significantly affected food impaction, but not the periodontal/peri-implant tissue conditions. Proximal contact loss should be carefully monitored during follow-up examinations in relation to food impaction.

Evaluation of effect of galvanic corrosion between nickel-chromium metal and titanium on ion release and cell toxicity

PURPOSE The purpose of this study was to evaluate cell toxicity due to ion release caused by galvanic corrosion as a result of contact between base metal and titanium. MATERIALS AND METHODS It was hypothesized that Nickel (Ni)-Chromium (Cr) alloys with different compositions possess different corrosion resistances when contacted with titanium abutment, and therefore in this study, specimens (10×10×1.5 mm) were fabricated using commercial pure titanium and 3 different types of Ni-Cr alloys (T3, Tilite, Bella bond plus) commonly used for metal ceramic restorations. The specimens were divided into 6 groups according to the composition of Ni-Cr alloy and contact with titanium. The experimental groups were in direct contact with titanium and the control groups were not. After the samples were immersed in the culture medium - Dulbeccos modified Eagles medium[DMEM] for 48 hours, the released metal ions were detected using inductively coupled plasma mass spectrometer (ICP-MS) and analyzed by the Kruskal-Wallis and Mann-Whitney test (P<.05). Mouse L-929 fibroblast cells were used for cell toxicity evaluation. The cell toxicity of specimens was measured by the 3-{4,5-dimethylthiazol-2yl}-2,5-diphenyltetrazolium bromide (MTT) test. Results of MTT assay were statistically analyzed by the two-way ANOVA test (P<.05). Post-hoc multiple comparisons were conducted using Tukeys tests. RESULTS The amount of metal ions released by galvanic corrosion due to contact between the base metal alloy and titanium was increased in all of the specimens. In the cytotoxicity test, the two-way ANOVA showed a significant effect of the alloy type and galvanic corrosion for cytotoxicity (P<.001). The relative cell growth rate (RGR) was decreased further on the groups in contact with titanium (P<.05). CONCLUSION The release of metal ions was increased by galvanic corrosion due to contact between base metal and titanium, and it can cause adverse effects on the tissue around the implant by inducing cytotoxicity.

Effects of core characters and veneering technique on biaxial flexural strength in porcelain fused to metal and porcelain veneered zirconia

PURPOSE The purpose of this study was to assess the impact of the core materials, thickness and fabrication methods of veneering porcelain on prosthesis fracture in the porcelain fused to metal and the porcelain veneered zirconia. MATERIALS AND METHODS Forty nickel-chrome alloy cores and 40 zirconia cores were made. Half of each core group was 0.5 mm-in thickness and the other half was 1.0 mm-in thickness. Thus, there were four groups with 20 cores/group. Each group was divided into two subgroups with two different veneering methods (conventional powder/liquid layering technique and the heat-pressing technique). Tensile strength was measured using the biaxial flexural strength test based on the ISO standard 6872:2008 and Weibull analysis was conducted. Factors influencing fracture strength were analyzed through three-way ANOVA (α≤.05) and the influence of core thickness and veneering method in each core materials was assessed using two-way ANOVA (α≤.05). RESULTS The biaxial flexural strength test showed that the fabrication method of veneering porcelain has the largest impact on the fracture strength followed by the core thickness and the core material. In the metal groups, both the core thickness and the fabrication method of the veneering porcelain significantly influenced on the fracture strength, while only the fabrication method affected the fracture strength in the zirconia groups. CONCLUSION The fabrication method is more influential to the strength of a prosthesis compared to the core character determined by material and thickness of the core.

Fabrication of a metal-ceramic crown to fit an existing partial removable dental prosthesis using ceramic pressed to metal technique: a clinical report

Fabricating a crown to retrofit an existing abutment tooth for a partial removable dental prosthesis (PRDP) is one of the most time-consuming and labor-intensive clinical procedures. In particular, when the patient is concerned with esthetic aspects of restoration, the task of fabricating becomes more daunting. Many techniques for the fabrication of all-metallic or metal-ceramic crowns have been discussed in the literature. This article was aimed to describe a simple fabrication method in which a retrofitting crown was fabricated for a precise fit using a ceramic-pressed-to-metal system.

Immediate placement and functional loading of implants on canine with fixed partial denture for a patient having canine protected occlusion: a case report

Conventional implant protocols required a load-free healing period of three to six months between placement and functional loading of the implants. Many efforts have been made to minimize the duration of treatment time. Several literatures have documented immediate function with provisional or definitive prosthesis within a week of the placement in response to these demands. In addition, immediate implant placement has advantages such as shortened treatment time and preservation of soft tissue architectures. This article presents immediate implant placement into fresh extraction sockets followed by functional immediate loading with provisional prosthesis on canine and premolars for a patient having canine protected occlusion.