Taek-Ka Kwon

Marginal fit of anterior 3-unit fixed partial zirconia restorations using different CAD/CAM systems

PURPOSE Few studies have investigated the marginal accuracy of 3-unit zirconia fixed partial dentures (FPDs) fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) system. The purpose of this study was to compare the marginal fit of zirconia FPDs made using two CAD/CAM systems with that of metal-ceramic FPDs. MATERIALS AND METHODS Artificial resin maxillary central and lateral incisors were prepared for 3-unit FPDs and fixed in yellow stone. This model was duplicated to epoxy resin die. On the resin die, 15 three-unit FPDs were fabricated per group (45 in total): Group A, zirconia 3-unit FPDs made with the Everest system; Group B, zirconia 3-unit FPDs made with the Lava system; and Group C, metal-ceramic 3-unit FPDs. They were cemented to resin dies with resin cement. After removal of pontic, each retainer was separated and observed under a microscope (Presize 440C). Marginal gaps of experimental groups were analyzed using one-way ANOVA and Duncan test. RESULTS Mean marginal gaps of 3-unit FPDs were 60.46 µm for the Everest group, 78.71 µm for the Lava group, and 81.32 µm for the metal-ceramic group. The Everest group demonstrated significantly smaller marginal gap than the Lava and the metal-ceramic groups (P<.05). The marginal gap did not significantly differ between the Lava and the metal-ceramic groups (P>.05). CONCLUSION The marginal gaps of anterior 3-unit zirconia FPD differed according to CAD/CAM systems, but still fell within clinically acceptable ranges compared with conventional metal-ceramic restoration.

In vivo comparison between the effects of chemically modified hydrophilic and anodically oxidized titanium surfaces on initial bone healing.

Purpose The aim of this study was to investigate the combined effects of physical and chemical surface factors on in vivo bone responses by comparing chemically modified hydrophilic sandblasted, large-grit, acid-etched (modSLA) and anodically oxidized hydrophobic implant surfaces. Methods Five modSLA implants and five anodized implants were inserted into the tibiae of five New Zealand white rabbits (one implant for each tibia). The characteristics of each surface were determined using field emission scanning electron microscopy, energy dispersive spectroscopy, and confocal laser scanning microscopy before the installation. The experimental animals were sacrificed after 1 week of healing and histologic slides were prepared from the implant-tibial bone blocks removed from the animals. Histomorphometric analyses were performed on the light microscopic images, and bone-to-implant contact (BIC) and bone area (BA) ratios were measured. Nonparametric comparison tests were applied to find any significant differences (P<0.05) between the modSLA and anodized surfaces. Results The roughness of the anodized surface was 1.22 ± 0.17 µm in Sa, which was within the optimal range of 1.0-2.0 µm for a bone response. The modSLA surface was significantly rougher at 2.53 ± 0.07 µm in Sa. However, the modSLA implant had significantly higher BIC than the anodized implant (P=0.02). Furthermore, BA ratios did not significantly differ between the two implants, although the anodized implant had a higher mean value of BA (P>0.05). Conclusions Within the limitations of this study, the hydrophilicity of the modSLA surface may have a stronger effect on in vivo bone healing than optimal surface roughness and surface chemistry of the anodized surface. Graphical Abstract

Identification of a bioactive core sequence from human laminin and its applicability to tissue engineering.

Finding bioactive short peptides derived from proteins is a critical step to the advancement of tissue engineering and regenerative medicine, because the former maintains the functions of the latter without immunogenicity in biological systems. Here, we discovered a bioactive core nonapeptide sequence, PPFEGCIWN (residues 2678-2686; Ln2-LG3-P2-DN3), from the human laminin α2 chain, and investigated the role of this peptide in binding to transmembrane proteins to promote intracellular events leading to cell functions. This minimum bioactive sequence had neither secondary nor tertiary structures in a computational structure prediction. Nonetheless, Ln2-LG3-P2-DN3 bound to various cell types as actively as laminin in cell adhesion assays. The in vivo healing tests using rats revealed that Ln2-LG3-P2-DN3 promoted bone formation without any recognizable antigenic activity. Ln2-LG3-P2-DN3-treated titanium (Ti) discs and Ti implant surfaces caused the enhancement of bone cell functions in vitro and induced faster osseointegration in vivo, respectively. These findings established a minimum bioactive sequence within human laminin, and its potential application value for regenerative medicine, especially for bone tissue engineering.

Comparative fracture strength analysis of Lava and Digident CAD/CAM zirconia ceramic crowns

PURPOSE All-ceramic crowns are subject to fracture during function. To minimize this common clinical complication, zirconium oxide has been used as the framework for all-ceramic crowns. The aim of this study was to compare the fracture strengths of two computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia crown systems: Lava and Digident. MATERIALS AND METHODS Twenty Lava CAD/CAM zirconia crowns and twenty Digident CAD/CAM zirconia crowns were fabricated. A metal die was also duplicated from the original prepared tooth for fracture testing. A universal testing machine was used to determine the fracture strength of the crowns. RESULTS The mean fracture strengths were as follows: 54.9 ± 15.6 N for the Lava CAD/CAM zirconia crowns and 87.0 ± 16.0 N for the Digident CAD/CAM zirconia crowns. The difference between the mean fracture strengths of the Lava and Digident crowns was statistically significant (P<.001). Lava CAD/CAM zirconia crowns showed a complete fracture of both the veneering porcelain and the core whereas the Digident CAD/CAM zirconia crowns showed fracture only of the veneering porcelain. CONCLUSION The fracture strengths of CAD/CAM zirconia crowns differ depending on the compatibility of the core material and the veneering porcelain.

Effects of Computer-Aided Manufacturing Technology on Precision of Clinical Metal-Free Restorations

Purpose. The purpose of this study was to investigate the marginal fit of metal-free crowns made by three different computer-aided design/computer-aided manufacturing (CAD/CAM) systems. Materials and Methods. The maxillary left first premolar of a dentiform was prepared for all-ceramic crown restoration. Thirty all-ceramic premolar crowns were made, ten each manufactured by the Lava system, Cercon, and Cerec. Ten metal ceramic gold (MCG) crowns served as control. The marginal gap of each sample was measured under a stereoscopic microscope at 75x magnification after cementation. One-way ANOVA and the Duncans post hoc test were used for data analysis at the significance level of 0.05. Results. The mean (standard deviation) marginal gaps were 70.5 (34.4) μm for the MCG crowns, 87.2 (22.8) μm for Lava, 58.5 (17.6) μm for Cercon, and 72.3 (30.8) μm for Cerec. There were no significant differences in the marginal fit among the groups except that the Cercon crowns had significantly smaller marginal gaps than the Lava crowns (P < 0.001).  Conclusions. Within the limitation of this study, all the metal-free restorations made by the digital CAD/CAM systems had clinically acceptable marginal accuracy.

A Comparative Study On The Marginal Fit Of Zirconia Cores Manufactured By CAD/CAM And Copy Milling Methods

Purpose: The marginal fit of zirconia cores that were produced by CAD/CAM and by copy milling systems was compared and analyzed to confirm the significance of the variation in dental technicians’ skill between the two systems. Materials and Methods: Using dental resin teeth and individual trays, 30 plaster casts were produced. Fifteen casts were assigned to be used with five different zirconia core manufacturing dental laboratories using the same CAD/ CAM system, which were designated as the CC group. The remaining 15 were assigned to be used with five different zirconia core manufacturing dental laboratories using also the same copy milling system and were designated as the CM group. The zirconia cores were fabricated and were cemented onto the casts. The vertical marginal opening was measured under an optical microscope at 75x magnification. The measured vertical marginal discrepancies were analyzed using an independent sample t-test, and the significance of the vertical marginal gap value for each dental laboratory was analyzed by performing the Kruskal-Wallis test. Results: The means and standard deviations for the marginal discrepancies of the CC and CM groups were found to be 102.73 ± 29.73 µm and 82.25 ± 22.37 µm, respectively. The independent sample t-test showed a significant difference between the two systems; the CAD/CAM system showed a larger vertical marginal gap than the copy milling system. The Kruskal-Wallis test indicated that no significant distributional differences were found between the dental laboratories in either the CAD/CAM or the copy milling systems. Conclusions: The copy milling system may produce more accurate zirconia restorations than the CAD/CAM system. The technician’s skill of a copy milling system may not be a determining factor influencing the accuracy of a single zirconia core.

Patterns of vertical facial growth in Korean adolescents analyzed with mixed-effects regression analysis

INTRODUCTION To understand the growth patterns of skeletal open bite and deepbite, we present observations from 9 years of pure longitudinal data based on lateral cephalometric radiographs using mixed-effects regression model analysis. METHODS In total, 51 children (14 years old) with extreme values for the ratio of lower anterior facial height to total anterior facial height were assigned to 1 of 2 groups: a skeletal open-bite group (11 boys, 14 girls) or a skeletal deepbite group (14 boys, 12 girls). Measurements of total anterior facial height, upper anterior facial height, lower anterior facial height, total posterior facial height, ramus height, and ratio of lower anterior facial height to total anterior facial height were obtained for all subjects. All data were analyzed and interpreted using a mixed-effects regression model analysis with random effects. RESULTS From these 4 groups at 14 years old, statistically significant differences were observed between the groups when subjects of the same sex were compared; however, statistical significance was not reached between subjects of opposite sexes in each group. Morphologic differences were clearly evident from the start and became more pronounced with age. There were statistical significances in the initial values and increases with age in all 6 variables except for increases with age in the ratio of lower anterior facial height to total anterior facial height. Statistical significance was also reached for morphologic differences between the annual increases in the ratio of lower anterior facial height to total anterior facial height and lower anterior facial height. In general, individual random variability was high in all variables when compared with the annual changes over time. CONCLUSIONS Divergent patterns were established early and became more pronounced with age, with anterior facial height dimensions primarily contributing to these differences. Individual variations were so pronounced that caution is recommended for all clinical decisions.

Removal torque analysis of chemically modified hydrophilic and anodically oxidized titanium implants with constant angular velocity for early bone response in rabbit tibia

Implant geometry and surface properties are important factors for successful osseointegration. The purpose of this study was to compare hydrophilic and hydrophobic implants with different geometries via the continuous measurement of removal torque (RT) and calculation of angular momentum for each implant. Five New Zealand white rabbits were used in the study. Each rabbit received 2 implants. A chemically modified hydrophilic implant with buttress thread was inserted into one tibia, and an anodically oxidized hydrophobic implant with V-shape threads was inserted into the other. After 1 week of healing, RT values were measured continuously in real-time. Using the time-torque curve resulting from the measurements, the maximum values were determined and angular momentums were calculated. The chemically modified hydrophilic implant exhibited significantly higher peak RT and mean torque values before the peak torque (MTBP) than the anodically oxidized hydrophobic implant (p < 0.05). The chemically modified hydrophilic implants exhibited superior early bone response compared to the anodically oxidized implants.

Evaluation of early bone response to fluoride-modified and anodically oxidized titanium implants through continuous removal torque analysis.

Purpose:To compare between a bioactive and a bioinert implant with different geometries by continuous measurement of the removal torque and calculation of the angular momentum of each surfaced implant. Materials and Methods:Six New Zealand white rabbits were used in the study. Each rabbit received 2 implants. A bioactive fluoride-modified implant with a conical connection and microthread design was inserted into one tibia, and a bioinert anodically oxidized implant with an external connection design was inserted into the other. After 2 weeks of implant insertion, the removal torque values were continuously measured according to time. Using the time-torque curve resulting from the measurements, the maximum values were determined, and the angular momenta were calculated. Results:The anodically oxidized implant had significantly higher peak removal torque and angular momentum values than the fluoride-modified implant (P < 0.05). Conclusions:The impact of the fluoride-modified bioactive implant on early bone response remains unclear. Considering the angular momentum of dental implants may assist in the elucidation of the effect of implant geometry on bone response.

Adhesion and spreading of osteoblast-like cells on surfaces coated with laminin-derived bioactive core peptides

Functional peptides are attractive as novel therapeutic reagents because their amino acid sequences are flexible in adopting and mimicking the local functional features of proteins. These peptides are of low molecular weight, synthetically versatile and inexpensive to produce, suggesting that they can be used as drug targeting, potent, stable and bioavailable agents. A short bioactive peptide is expected to be more beneficial in regenerative medicine than an entire protein because of the lower antigenicity of short amino acid sequences. We detected core peptides from human laminin that are involved in adhesion and spreading, which are the first steps of various cells including osteogenic cells, in becoming functional. In this experiment, we detected adhesion and spreading of osteoblast-like cells seeded on the core peptide-coated surface. These in vitro data are related to the research article, entitled “Identification of a bioactive core sequence from human laminin and its applicability to tissue engineering” (Yeo et al., 2015) [1].