Mi-Jung Yun

Sterilization effect of atmospheric pressure non-thermal air plasma on dental instruments.

PURPOSE Autoclaves and UV sterilizers have been commonly used to prevent cross-infections between dental patients and dental instruments or materials contaminated by saliva and blood. To develop a dental sterilizer which can sterilize most materials, such as metals, rubbers, and plastics, the sterilization effect of an atmospheric pressure non-thermal air plasma device was evaluated. MATERIALS AND METHODS After inoculating E. coli and B. subtilis the diamond burs and polyvinyl siloxane materials were sterilized by exposing them to the plasma for different lengths of time (30, 60, 90, 120, 180 and, 240 seconds). The diamond burs and polyvinyl siloxane materials were immersed in PBS solutions, cultured on agar plates and quantified by counting the colony forming units. The data were analyzed using one-way ANOVA and significance was assessed by the LSD post hoc test (α=0.05). RESULTS The device was effective in killing E. coli contained in the plasma device compared with the UV sterilizer. The atmospheric pressure non-thermal air plasma device contributed greatly to the sterilization of diamond burs and polyvinyl siloxane materials inoculated with E. coli and B. subtilis. Diamond burs and polyvinyl siloxane materials inoculated with E. coli was effective after 60 and 90 seconds. The diamond burs and polyvinyl siloxane materials inoculated with B. subtilis was effective after 120 and 180 seconds. CONCLUSION The atmospheric pressure non-thermal air plasma device was effective in killing both E. coli and B. subtilis, and was more effective in killing E. coli than the UV sterilizer.

The Effect of Reduced Graphene Oxide-Coated Biphasic Calcium Phosphate Bone Graft Material on Osteogenesis

This study was conducted to evaluate the effect of biphasic calcium phosphate (BCP) coated with reduced graphene oxide (rGO) as bone graft materials on bone regeneration. The rGO-coated BCP bone graft material was fabricatied by mixing rGO and BCP at various concentrations. The surface charge of rGO-coated BCP was measured to be −14.43 mV, which formed a static electrostatic interaction. Cell viabilities were significantly diminished at higher concentrations of ≥100 μg/mL. The calvarial defects of 48 rats were implanted rGO-coated BCPs at a weight ratio of 2:1000 (rGO2), 4:1000 (rGO4), and 10:1000 (rGO10), repectively. BCP was used as a control group. The micro-CT and histological analysis were performed to evaluate new bone formation at 2 and 8 weeks after surgery. The results showed that the new bone volume (mm3) was significantly higher in the experimental groups than in the control group. Histological analysis showed that new bone areas (%) were significantly higher in the rGO2 and rGO10 than in the control, and significantly higher in rGO4 than in the rGO2 and rGO10. Conclusively, the rGO-coated BCP was found to be effective on osteogenesis and the concentration of the composite was an important factor.

Comparison of the accuracy of digitally fabricated polyurethane model and conventional gypsum model

PURPOSE The accuracy of a gypsum model (GM), which was taken using a conventional silicone impression technique, was compared with that of a polyurethane model (PM), which was taken using an iTero™ digital impression system. MATERIALS AND METHODS The maxillary first molar artificial tooth was selected as the reference tooth. The GMs were fabricated through a silicone impression of a reference tooth, and PMs were fabricated by a digital impression (n=9, in each group). The reference tooth and experimental models were scanned using a 3 shape convince™ scan system. Each GM and PM image was superimposed on the registered reference model (RM) and 2D images were obtained. The discrepancies of the points registered on the superimposed images were measured and defined as GM-RM group and PM-RM group. Statistical analysis was performed using a Students T-test (α=0.05). RESULTS A comparison of the absolute value of the discrepancy revealed a significant difference between the two groups only at the occlusal surface. The GM group showed a smaller mean discrepancy than the PM group. Significant differences in the GM-RM group and PM-RM group were observed in the margins (point a and f), mesial mid-axial wall (point b) and occlusal surfaces (point c and d). CONCLUSION Under the conditions examined, the digitally fabricated polyurethane model showed a tendency for a reduced size in the margin than the reference tooth. The conventional gypsum model showed a smaller discrepancy on the occlusal surface than the polyurethane model.

Effects of anodized titanium implant coated with RGD peptides via chemical fixation on osseointegration and bone regeneration

This study was conducted to investigate the effects of an anodized titanium surface with RGD-peptides. Silane was used to immobilize the RGD peptides to the titanium surfaces. The surfaces were examined by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Crystal violet assay, XTT assay and Alkaline phosphatase (ALP) assay were performed to evaluate response of human mesenchymal stem cell. For in vivo study, twenty-four implants and four beagle dogs were used and made the dehiscence defect model (n=12 in each group). Implant stability quotient (ISQ) value was measured and evaluated by histometric analysis. Histological examination revealed an increase of bone height in the test group. There were significant differences in intra-thread bone density (ITBD) between the groups. The application of RGD peptide to the implant surface may contribute to the improvement of osseointegration quality and bone growth in a small defect area around the implant.

Effect of activation modes on the compressive strength, diametral tensile strength and microhardness of dual-cured self-adhesive resin cements.

The purpose of this study was to compare the compressive strength, diametral tensile strength and microhardnss of several selfadhesive resin cements (Rely-X U200, Clearfill SA Luting, G-CEM LinkAce, Maxcem Elite, PermaCem 2.0, and Zirconite) using different activation modes (self-cured, light-cured) and testing time (immediately, 24 h, thermocycling). Specimens were prepared for the compressive strength (Ø 4×6 mm) and diametral tensile strength and microhardness (Ø 6×3 mm) according to ISO standards. The strength after 24 h was higher than immediately after. In addition, G-CEM showed the highest values. In terms of the activation modes, Rely-X U200, PermaCem 2.0 had higher values in the light-curing than the self-curing. In conclusion, all cements demonstrated clinically available strength values and revealed differences in strength according to their composition, testing time and activation mode. Furthermore, correlation was found between the microhardness (degree of conversion) and mechanical strengths of the cements tested.

Comparison of the fit of cast gold crowns fabricated from the digital and the conventional impression techniques

PURPOSE The purpose of this study was to compare the fit of cast gold crowns fabricated from the conventional and the digital impression technique. MATERIALS AND METHODS Artificial tooth in a master model and abutment teeth in ten patients were restored with cast gold crowns fabricated from the digital and the conventional impression technique. The forty silicone replicas were cut in three sections; each section was evaluated in nine points. The measurement was carried out by using a measuring microscope and I-Soultion. Data from the silicone replica were analyzed and all tests were performed with α-level of 0.05. RESULTS 1. The average gaps of cast gold crowns fabricated from the digital impression technique were larger than those of the conventional impression technique significantly. 2. In marginal and internal axial gap of cast gold crowns, no statistical differences were found between the two impression techniques. 3. The internal occlusal gaps of cast gold crowns fabricated from the digital impression technique were larger than those of the conventional impression technique significantly. CONCLUSION Both prostheses presented clinically acceptable results with comparing the fit. The prostheses fabricated from the digital impression technique showed more gaps, in respect of occlusal surface.

In vitro assessment of cutting efficiency and durability of zirconia removal diamond rotary instruments

Statement of problem Recently, zirconia removal diamond rotary instruments have become commercially available for efficient cutting of zirconia. However, research of cutting efficiency and the cutting characteristics of zirconia removal diamond rotary instruments is limited. Purpose The purpose of this in vitro study was to assess and compare the cutting efficiency, durability, and diamond rotary instrument wear pattern of zirconia diamond removal rotary instruments with those of conventional diamond rotary instruments. In addition, the surface characteristics of the cut zirconia were assessed. Material and methods Block specimens of 3 mol% yttrium cation‐doped tetragonal zirconia polycrystal were machined 10 times for 1 minute each using a high‐speed handpiece with 6 types of diamond rotary instrument from 2 manufacturers at a constant force of 2 N (n=5). An electronic scale was used to measure the lost weight after each cut in order to evaluate the cutting efficiency. Field emission scanning electron microscopy was used to evaluate diamond rotary instrument wear patterns and machined zirconia block surface characteristics. Data were statistically analyzed using the Kruskal‐Wallis test, followed by the Mann‐Whitney U test (&agr;=.05). Results Zirconia removal fine grit diamond rotary instruments showed cutting efficiency that was reduced compared with conventional fine grit diamond rotary instruments. Diamond grit fracture was the most dominant diamond rotary instrument wear pattern in all groups. All machined zirconia surfaces were primarily subjected to plastic deformation, which is evidence of ductile cutting. Zirconia blocks machined with zirconia removal fine grit diamond rotary instruments showed the least incidence of surface flaws. Conclusions Although zirconia removal diamond rotary instruments did not show improved cutting efficiency compared with conventional diamond rotary instruments, the machined zirconia surface showed smoother furrows of plastic deformation and fewer surface flaws.

Clinical evaluation of mandibular implant overdentures via Locator implant attachment and Locator bar attachment

PURPOSE The aim of this study was to evaluate the clinical findings and patient satisfaction on implant overdenture designed with Locator implant attachment or Locator bar attachment in mandibular edentulous patients. MATERIALS AND METHODS Implant survival rate, marginal bone loss, probing depth, peri-implant inflammation, bleeding, plaque, calculus, complications, and satisfaction were evaluated on sixteen patients who were treated with mandibular overdenture and have used it for at least 1 year (Locator implant attachment: n=8, Locator bar attachment: n=8). RESULTS Marginal bone loss, probing depth, plaque index of the Locator bar attachment group were significantly lower than the Locator implant attachment group (P<.05). There was no significant difference on bleeding, peri-implant inflammation, and patient satisfaction between the two denture types (P>.05). The replacement of the attachment components was the most common complication in both groups. Although there was no correlation between marginal bone loss and plaque index, a significant correlation was found between marginal bone loss and probing depth. CONCLUSION The Locator bar attachment group indicates lesser marginal bone loss and need for maintenance, as compared with the Locator implant attachment group. This may be due to the splinting effect among implants rather than the types of Locator attachment.

Effects of Different Implant Osteotomy Preparation Sizes on Implant Stability and Bone Response in the Minipig Mandible.

PURPOSE The purpose of this study was to investigate the influence of implant and drill diameters on the stability of implant and bone response. MATERIALS AND METHODS An implant (GS II, Osstem Implant) with a 3.5-mm diameter and drills with three different diameters, differentiating the volume of bone compacted by the implant, were used in this study. Measurement of the insertion torque and observation of bone compression patterns were done during implant site preparation in minipigs. Also, analysis of resonance frequency, histomorphology, marginal bone resorption, and new bone formation were performed. RESULTS Microstrains and microcracks occurred in cortical bone around the thread when a drill with a smaller diameter than that of the thread was used. Higher implant stability was shown and maintained when a small-diameter drill was used. When using a drill with a smaller diameter than the root diameter of the implant thread, the bone-to-implant contact/bone area (BIC/BA) was higher than the wider drill during the whole test period. However, the use of a wide drill was the most rapid in increasing the BIC/BA value by new bone formation. In the cancellous bone, the speed of new bone formation was not different in each test group. However, the formation of new bone was faster when a large-diameter drill was used in the cortical bone. There was no significant difference in marginal bone loss (MBL) according to drill diameters, but the speed of MBL was fast when using a drill that was smaller than the root diameter of the implant thread. CONCLUSION Implant stability, BIC, and BA were high when using a final drill that was smaller than the root diameter of the implant thread compared with a wide final drill. However, the speed of new bone formation was relatively slow and the speed of MBL was relatively fast if the final drill was excessively smaller.

Effect of solution temperature on the mechanical properties of dual-cure resin cements

PURPOSE This study was to evaluate the effect of the solution temperature on the mechanical properties of dualcure resin cements. MATERIALS AND METHODS For the study, five dual-cure resin cements were chosen and light cured. To evaluate the effect of temperature on the specimens, the light-cured specimens were immersed in deionized water at three different temperatures (4, 37 and 60℃) for 7 days. The control specimens were aged in a 37℃ dry and dark chamber for 24 hours. The mechanical properties of the light-cured specimens were evaluated using the Vickers hardness test, three-point bending test, and compression test, respectively. Both flexural and compressive properties were evaluated using a universal testing machine. The data were analyzed using a two way ANOVA with Tukey test to perform multiple comparisons (α=0.05). RESULTS After immersion, the specimens showed significantly different microhardness, flexural, and compressive properties compared to the control case regardless of solution temperatures. Depending on the resin brand, the microhardness difference between the top and bottom surfaces ranged approximately 3.3-12.2%. Among the specimens, BisCem and Calibra showed the highest and lowest decrease of flexural strength, respectively. Also, Calibra and Multilink Automix showed the highest and lowest decrease of compressive strength, respectively compared to the control case. CONCLUSION The examined dual-cure resin cements had compatible flexural and compressive properties with most methacrylate-based composite resins and the underlying dentin regardless of solution temperature. However, the effect of the solution temperature on the mechanical properties was not consistent and depended more on the resin brand.