Du-Hyeong Lee

A microcomputed tomography evaluation of the marginal fit of cobalt-chromium alloy copings fabricated by new manufacturing techniques and alloy systems

Statement of problem Although new digital manufacturing techniques are attracting interest in dentistry, few studies have comprehensively investigated the marginal fit of fixed dental prostheses fabricated with such techniques. Purpose The purpose of this in vitro microcomputed tomography (&mgr;CT) study was to evaluate the marginal fit of cobalt‐chromium (Co‐Cr) alloy copings fabricated by casting and 3 different computer‐aided design and computer‐aided manufacturing (CAD‐CAM)‐based processing techniques and alloy systems. Material and methods Single Co‐Cr metal crowns were fabricated using 4 different manufacturing techniques: casting (control), milling, selective laser melting, and milling/sintering. Two different commercial alloy systems were used for each fabrication technique (a total of 8 groups; n=10 for each group). The marginal discrepancy and absolute marginal discrepancy of the crowns were determined with &mgr;CT. For each specimen, the values were determined from 4 different regions (sagittal buccal, sagittal lingual, coronal mesial, and coronal distal) by using imaging software and recorded as the average of the 4 readings. For each parameter, the results were statistically compared with 2‐way analysis of variance and appropriate post hoc analysis (using Tukey or Student t test) (&agr;=.05). Results The milling and selective laser melting groups showed significantly larger marginal discrepancies than the control groups (70.4 ±12.0 and 65.3 ±10.1 &mgr;m, respectively; P<.001), whereas the milling/sintering groups exhibited significantly smaller values than the controls (P=.004). The milling groups showed significantly larger absolute marginal discrepancy than the control groups (137.4 ±29.0 and 139.2 ±18.9 &mgr;m, respectively; P<.05). In the selective laser melting and milling/sintering groups, the absolute marginal discrepancy values were material‐specific (P<.05). Nonetheless, the milling/sintering groups yielded statistically comparable (P=.935) or smaller (P<.001) absolute marginal discrepancies to the control groups. Conclusions The findings of this in vitro &mgr;CT study showed that the marginal fit values of the Co‐Cr alloy greatly depended on the fabrication methods and, occasionally, the alloy systems. Fixed dental prostheses produced by using the milling/sintering technique can be considered clinically acceptable in terms of marginal fit.

Shear bond strength of porcelain to a new millable alloy and a conventional castable alloy.

STATEMENT OF PROBLEM A recently introduced presintered cobalt-chromium (Co-Cr) alloy for metal ceramic restorations can be efficiently processed with computer-aided design/computer-aided manufacturing (CAD/CAM) techniques. However, little or no reliable study data are available regarding the bonding ability of porcelain to milled Co-Cr alloys. PURPOSE The purpose of this study was to evaluate the shear bond strength of veneering porcelain to the presintered Co-Cr alloy and to a conventional castable alloy. MATERIAL AND METHODS Ninety-six cylindrical cores (6.8 mm in diameter, 9 mm in height) were made of millable alloy (Ceramill Sintron) and castable alloy (4-all) by means of CAD/CAM or casting, 48 cores for each alloy. Four types of veneering porcelain were fired or pressed to the cores; these specimens had dimensions of 4×4×3 mm. After firing, the specimens were put in resin molds, fixed in a universal testing machine, and subjected to a shear force test. Loading was applied to each specimen through the attached crosshead at a constant drive speed of 0.5 mm/min until fracture occurred. Shear bond strengths (MPa) were calculated by dividing the maximum failure force over the cross-sectional area of each specimen. Failure patterns of the specimens were also investigated and characterized as adhesive, cohesive, or mixed. One-way ANOVA and the Duncan post hoc test were used to analyze statistically significant differences between groups (α=.05). RESULTS The means of the shear bond strengths of (millable) Ceramill Sintron were similar to or higher than those of (castable) 4-all cores. The shear bond strength was significantly lower for Press-To-Metal veneer than for the other fired veneers in the test (P<.001). The pattern of failure in most specimens was mixed, except for Press-To-Metal veneer, where cohesive failure occurred. CONCLUSIONS The bonding ability of the traditional castable alloy was similar to that of the presintered millable Co-Cr alloy.

Fit of interim crowns fabricated using photopolymer-jetting 3D printing

Statement of problem. The fit of interim crowns fabricated using 3‐dimensional (3D) printing is unknown. Purpose. The purpose of this in vitro study was to evaluate the fit of interim crowns fabricated using photopolymer‐jetting 3D printing and to compare it with that of milling and compression molding methods. Material and methods. Twelve study models were fabricated by making an impression of a metal master model of the mandibular first molar. On each study model, interim crowns (N=36) were fabricated using compression molding (molding group, n=12), milling (milling group, n=12), and 3D polymer‐jetting methods. The crowns were prepared as follows: molding group, overimpression technique; milling group, a 5‐axis dental milling machine; and polymer‐jetting group using a 3D printer. The fit of interim crowns was evaluated in the proximal, marginal, internal axial, and internal occlusal regions by using the image‐superimposition and silicone‐replica techniques. The Mann‐Whitney U test and Kruskal‐Wallis tests were used to compare the results among groups (&agr;=.05). Results. Compared with the molding group, the milling and polymer‐jetting groups showed more accurate results in the proximal and marginal regions (P<.001). In the axial regions, even though the mean discrepancy was smallest in the molding group, the data showed large deviations. In the occlusal region, the polymer‐jetting group was the most accurate, and compared with the other groups, the milling group showed larger internal discrepancies (P<.001). Conclusions. Polymer‐jet 3D printing significantly enhanced the fit of interim crowns, particularly in the occlusal region.

Accuracy of a direct drill-guiding system with minimal tolerance of surgical instruments used for implant surgery: a prospective clinical study.

PURPOSE A recently introduced direct drill-guiding implant surgery system features minimal tolerance of surgical instruments in the metal sleeve by using shank-modified drills and a sleeve-incorporated stereolithographic guide template. The purpose of this study was to evaluate the accuracy of this new guided surgery system in partially edentulous patients using geometric analyses. MATERIALS AND METHODS For the study, 21 implants were placed in 11 consecutive patients using the direct drill-guiding implant surgery system. The stereolithographic surgical guide was fabricated using cone-beam computed tomography, digital scanning, computer-aided design and computer-assisted manufacturing, and additive manufacturing processes. After surgery, the positional and angular deviations between planned and placed implants were measured at the abutment level using implant-planning software. The Kruskal-Wallis test and Mann-Whitney U test were used to compare the deviations (α=.05). RESULTS The mean horizontal deviations were 0.593 mm (SD 0.238) mesiodistally and 0.691 mm (SD 0.344) buccolingually. The mean vertical deviation was 0.925 mm (SD 0.376) occlusogingivally. The vertical deviation was significantly larger than the horizontal deviation (P=.018). The mean angular deviation was 2.024 degrees (SD 0.942) mesiodistally and 2.390 degrees (SD 1.142) buccolingually. CONCLUSION The direct drill-guiding implant surgery system demonstrates high accuracy in placing implants. Use of the drill shank as the guiding component is an effective way for reducing tolerance.

Digital approach to assessing the 3-dimensional misfit of fixed dental prostheses

The silicone replica technique has been used for determining the fit accuracy of fixed dental prostheses. Because this technique is performed manually with 2-dimensional evaluations, it is prone to methodological error and yields inadequate information. The application of computer-aided image analysis reduces errors and facilitates 3-dimensional discrepancy measurements. This article describes a method of visualizing and quantifying the fit discrepancy of fixed dental prostheses by digitizing a misfit space replica and using computer-aided spatial analysis.

Estimation of Effective Population Size in the Sapsaree: A Korean Native Dog (Canis familiaris)

Effective population size (Ne) is an important measure to understand population structure and genetic variability in animal species. The objective of this study was to estimate Ne in Sapsaree dogs using the information of rate of inbreeding and genomic data that were obtained from pedigree and the Illumina CanineSNP20 (20K) and CanineHD (170K) beadchips, respectively. Three SNP panels, i.e. Sap134 (20K), Sap60 (170K), and Sap183 (the combined panel from the 20K and 170K), were used to genotype 134, 60, and 183 animal samples, respectively. The Ne estimates based on inbreeding rate ranged from 16 to 51 about five to 13 generations ago. With the use of SNP genotypes, two methods were applied for Ne estimation, i.e. pair-wise r2 values using a simple expectation of distance and r2 values under a non-linear regression with respective distances assuming a finite population size. The average pair-wise Ne estimates across generations using the pairs of SNPs that were located within 5 Mb in the Sap134, Sap60, and Sap183 panels, were 1,486, 1,025 and 1,293, respectively. Under the non-linear regression method, the average Ne estimates were 1,601, 528, and 1,129 for the respective panels. Also, the point estimates of past Ne at 5, 20, and 50 generations ago ranged between 64 to 75, 245 to 286, and 573 to 646, respectively, indicating a significant Ne reduction in the last several generations. These results suggest a strong necessity for minimizing inbreeding through the application of genomic selection or other breeding strategies to increase Ne, so as to maintain genetic variation and to avoid future bottlenecks in the Sapsaree population.

CAD/CAM-fabricated template for locating implant abutment screws in cement-retained anatomic zirconia restorations

Currently, appropriate access to the abutment screw within cement-retained implant restorations is determined using labor-intensive techniques. The introduction of computer-aided design/computer-aided manufacture technology has facilitated a digitized fabrication process to yield a template that can enhance the accuracy of drilling a screw channel. This article describes the method used to create these guide templates by using advanced dental design programs and machining.

Evaluation of internal fit of interim crown fabricated with CAD/CAM milling and 3D printing system

PURPOSE This study is to evaluate the internal fit of the crown manufactured by CAD/CAM milling method and 3D printing method. MATERIALS AND METHODS The master model was fabricated with stainless steel by using CNC machine and the work model was created from the vinyl-polysiloxane impression. After scanning the working model, the design software is used to design the crown. The saved STL file is used on the CAD/CAM milling method and two types of 3D printing method to produce 10 interim crowns per group. Internal discrepancy measurement uses the silicon replica method and the measured data are analyzed with One-way ANOVA to verify the statistic significance. RESULTS The discrepancy means (standard deviation) of the 3 groups are 171.6 (97.4) µm for the crown manufactured by the milling system and 149.1 (65.9) and 91.1 (36.4) µm, respectively, for the crowns manufactured with the two types of 3D printing system. There was a statistically significant difference and the 3D printing system group showed more outstanding value than the milling system group. CONCLUSION The marginal and internal fit of the interim restoration has more outstanding 3D printing method than the CAD/CAM milling method. Therefore, the 3D printing method is considered as applicable for not only the interim restoration production, but also in the dental prosthesis production with a higher level of completion.

Using a guide template with a handpiece sleeve to locate the abutment screw position of a cement-retained implant restoration

The existing techniques for drilling a screw access hole in cement-retained restorations are limited by inaccurate drill guidance and ineffective cooling of the drilling area. An approach for fabricating a guide template to provide screw retrievability using computer-aided design and computer-aided manufacturing (CAD/CAM) is described. A handpiece sleeve was made by 3-dimensional printing and incorporating it into a vacuum-formed template. The handpiece sleeve not only guides the head of the handpiece accurately but also enables the cooling water to reach the area of drilling directly.

Radiopacity for Contemporary Luting Cements Using Digital Radiography under Various Exposure Conditions

PURPOSE This study examined the radiopacity of contemporary luting cements using direct digital radiography under a range of exposure conditions. MATERIALS AND METHODS Disc specimens (N = 80, n = 10 per group, ø5 mm × 1 mm) were prepared from 8 resin-based luting cements (BisCem Clearfil SA Luting, Duolink, Maxcem Elite Multilink Speed, Panavia F 2.0, RelyX Unicem Clicker, V-link). The specimens were radiographed using a charge-coupled device sensor along with an 11-step aluminum step wedge (1.5-mm incremental steps) and 1-mm-thick tooth cut using five tube voltage/exposure time setups (60 kVp, 0.10/0.08 seconds; 70 kVp, 0.10/0.08/0.06 seconds) at 4 mA and 30 cm. The radiopacity of the specimens was compared with that of the aluminum step wedge and human enamel and dentin using NIH ImageJ software (available at http://rsb.info.nih.gov/ij/). A linear regression model for the aluminum step wedge was constructed, and the data were analyzed by ANOVA and Duncan post hoc test. RESULTS Maxcem Elite (5.142 to 5.441) showed the highest radiopacity of all materials, followed in order by Multilink Speed (3.731 to 3.396) and V-link (2.763 to 3.103). The radiopacity of Panavia F 2.0 (2.025 to 2.429), BisCem (1.825 to 2.218), Clearfil SA Luting (1.692 to 2.145), Duolink (1.707 to 1.993), and RelyX Unicem Clicker (1.586 to 1.979) were between enamel (2.117 to 2.330) and dentin (1.302 to 1.685). The radiopacity of 70 kVp conditions was higher than that of the 60 kVp conditions. CONCLUSIONS The radiopacities of the tested luting materials were greater than those of dentin or aluminum, satisfying the criteria of the International Organization for Standardization, and they differed significantly from each other in the exposure setups.