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Purpose: To compare the fit of 3D-printed titanium (Ti) and cobalt-chromium (Co-Cr) abutments with implants to computer numerical control (CNC)-milled, ready-made abutment-implant assemblies. Their clinical applicability was also evaluated by measuring removal torque values (RTVs) and percentage torque loss of abutment screws. Materials and Methods: A total of 138 abutments were included in the study: 92 abutments were fabricated with Ti and Co-Cr alloys using computerassisted design (CAD) through selective laser melting, and 46 ready-made abutments were prepared. The fit of interfaces between 90 abutments from the three groups (30 ready-made, 30 3D-printed Ti, and 30 3D-printed Co-Cr abutments) and implant assemblies was demonstrated by scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). After 30-Ncm torque tightening of Ti abutment screws twice within 10 minutes, the RTVs and percentage torque loss of screws of 48 abutments (16 ready-made, 16 3D-printed Ti, and 16 3D-printed Co-Cr) were evaluated after 10 minutes of thermocycling and cyclic loading. Results: The fits of 3D-printed Co-Cr abutments were not statistically different from those of ready-made abutments (P = .383), while the fit of 3D-printed Ti abutments was inadequate (P < .001). The RTVs of 3D-printed abutments after cyclic loading were significantly decreased compared with those of CNC-milled abutments (P < .001). Conclusion: The fit of interfaces between 3D-printed Co-Cr abutments and implants was adequate. The RTVs of 3D-printed Co-Cr abutments were not significantly different from those of CNC-milled abutments after 10 minutes of 30-Ncm torque tightening and thermocycling. [ABSTRACT FROM AUTHOR]

Purpose: To test whether internal accuracy affects the load-bearing capacity of 0.5-mm-thick occlusal veneers made out of milled or heat-pressed lithium disilicate (LS2).Materials and Methods: Extracted human molars (N = 80) were divided into four groups (n = 20 each) depending on the bonding substrate (enamel [E] or dentin [D]) and the fabrication method (milling [CAD] or heat pressing [PRE]) for the occlusal LS2 veneers: (1) E-CAD, (2) D-CAD, (3) E-PRE, or (4) D-PRE. After restoration fabrication, the abutment teeth and the corresponding restorations were scanned and superimposed in order to measure the marginal and internal accuracy. After adhesive cementation, the specimens were thermomechanically aged and thereafter loaded until fracture. The load-bearing capacities (Fmax) were measured. Fmax and the marginal and internal accuracy between the groups were compared using Kruskal-Wallis test (P < .05) and pairwise group comparisons. In addition, the relationship between Fmax and the internal accuracy was analyzed using Spearman rank correlation.Results: Median Fmax values (and first and third quartiles) per group were as follows: 1,495 N (Q1: 932; Q3: 2'318) for E-CAD; 1,575 N (Q1: 1,314; Q3: 1,668) for E-PRE; 1,856 N (Q1: 1,555; Q3: 2,013) for D-CAD; and 1,877 N (Q1: 1,566; Q3: 2,131) for D-PRE. No statistical difference was found between the groups (P = .0981). Overall, the internal accuracy in the areas of the cusp (P < .0007) and fossa (P < .0001) showed significant differences. While no significant differences were detected in the marginal area (P = .3518), a significant correlation with a negative linear relationship was found between the 3D internal accuracy and the Fmax values (P = .0007).Conclusion: An increase in the internal accuracy raised the load-bearing capacity of minimally invasive LS2 occlusal veneers. In general, the restorations bonded to dentin in the occlusal regions showed a better accuracy compared to those bonded to enamel. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to compare the loosening of interchangeable one-piece abutments connected to internal-connection–type implants after cyclic loading. Materials and Methods: Four implant abutment groups (n = 7 in each group) with Straumann tissue-level implants were assessed: Straumann solid abutment (group S), Southern Implants solid abutment (group SI), Implant Direct straight abutment (group ID), and Blue Sky Bio regular platform abutment (group BSB). The implant was firmly held in a special jig to ensure fixation. Abutment screws were tightened to manufacturers’ recommended torque with a digital torque gauge. The hemispherical loading members were fabricated for the load cell of a universal testing machine to evenly distribute the force on the specimens and to fulfill the ISO 14801:2007 standard. A cyclic loading of 25 N at 30 degrees to the implant’s long axis was applied for a duty of a half million cycles. Tightening torques were measured prior to the loading. Removal torques were measured after cyclic loading. The data were analyzed with one-way analysis of variance (ANOVA), and the significance level was set at P < .05. Results: The mean removal torques after cyclic loading were 34.0 ± 1.1 Ncm (group S), 25.0 ± 1.5 Ncm (group SI), 23.9 ± 2.1 Ncm (group ID), and 27.9 ± 1.3 Ncm (group BSB). Removal torques of each group were statistically different in the order of group S > group BSB > groups SI and ID (P < .05). The mean reduction rates were –2.9% ± 3.2% (group S), –21.9% ± 4.8% (group SI), –20.2% ± 7.2% (group ID), and –6.9% ± 4.3% (group BSB) after a half million cycles, respectively. Reduction rates of groups S and BSB were statistically lower than those of groups SI and ID (P < .01). The standard deviation of group S was lower than group BSB. Conclusion: The removal torque of the original Straumann abutment was significantly higher than those of the copy abutments. The reduction rate of the groups S and BSB abutments was lower than those of the other copy abutments. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the clinical usefulness, a customized abutment produced with the Pd-Ag-In alloy was compared with a customized abutment produced with the conventional titanium alloy for discoloration and mechanical accuracy. Materials and Methods: Discoloration and resistance to corrosion of the Pd-Ag-In alloy were evaluated using chemical solutions. Marginal adaptation of internal-type implants and abutments was compared using 10 titanium abutments and 10 Pd-Ag-In abutments using a surface measuring system. A detorque test was performed on 12 implant-abutment complexes of each control and experimental group to investigate screw joint stability. Cyclic loading simulating a human's mastication movement for 1 year was applied after 30 Ncm initial tightening, and the removal torque was measured using a digital torque gauge. The noninferiority test was conducted to compare the Pd-Ag-In alloy with a titanium abutment with a 10% margin. Results: The Pd-Ag-In alloy had a warm yellow color and displayed stable resistance to discoloration and corrosion, resulting in an advantageous esthetic property. When compared to the titanium alloy, it did not show noninferiority with respect to the gap between the implant and the abutment; the gap was approximately 13.3 ym on average, which was not significantly different from those observed in previous studies. After long-term use, it displayed statistically significant noninferiority in the removal torque value compared to the titanium group. Conclusion: The Pd-Ag-In alloy-based customized abutment had good mechanical properties of the implant-abutment complex as well as a superior esthetic property, and can provide favorable outcomes in anterior implant restoration. [ABSTRACT FROM AUTHOR]

Purpose: A biochemical approach to implant surfaces can improve bone growth, resulting in desirable boneimplant interfaces. This study was conducted to identify the effect on osseointegration of direct coating of titanium (Ti) implants with poly(D,L-lactide-co-glycolide)(PLGA)/recombinant human bone morphogenetic 2 (rhBMP-2) submicron particles by electrospray. Materials and Methods: Anodized Ti implants were used as a control group, and implants coated with 80 fjL of PLGA/rhBMP-2 (50 pg/mL rhBMP-2 per implant) submicron particles by electrospray were used as the experimental group in an in vivo rabbit tibia model. After 3 or 7 weeks of healing, specimens were obtained and prepared for histologic and histomorphometric analyses. Results: The implant surface coated with submicron PLGA/rhBMP-2 showed new bone growth in the apical direction earlier than control implants. In the experimental group at 3 weeks, the bone-to-implant contact ratio and bone area of the three best consecutive threads were significantly higher than those in the control group. However, there was no significant difference between groups at 1 weeks. Conclusion: Within the limitations of this study, the PLGA/rhBMP-2-coated implants facilitated osseointegration between bone and the Ti surface during the early healing phase. [ABSTRACT FROM AUTHOR]

Purpose: This study was conducted to examine the effects of coating poly(D,L-lactide-co-glycolide) (PLGA)/ recombinant human bone morphogenetic protein-2 (rhBMP-2) submicron particles by electrospray onto titanium (Ti) implants on the proliferation and differentiation capacity of mesenchymal stem cells. In addition, the duration of rhBMP-2 release was investigated. Materials and Methods: Ti disks were fabricated and divided into four groups as follows. Group C (control) was anodized at 300 V, group P was anodized and then coated with 0.2% PLGA, group B1 was anodized and then coated with PLGA/rhBMP-2 submicron particles at 200 ng per disk, and group B2 was anodized and then coated with PLGA/rhBMP-2 submicron particles at 600 ng per disk. The topography of the PLGA/rhBMP-2-coated Ti surfaces was examined, and proliferation assays, alkaline phosphatase activity tests, and rhBMP-2 releasing tests were conducted in vitro. Results: There was no difference in the roughness of control Ti disks and Ti disks coated with PLGA/rhBMP-2 submicron particles by electrospray. The proliferation of mesenchymal stem cells increased over time; at 7 days, cell proliferation on the Ti disks coated with rhBMP-2 was significantly higher than the other groups. Anodized Ti disks coated with PLGA/rhBMP-2 (groups B1 and B2) released rhBMP-2 for approximately 21 days. In accordance with the amount of rhBMP-2 released from the PLGA/rhBMP-2 construct, the differentiation capacity of mesenchymal stem cells on the PLGA/rhBMP-2-coated disks was increased significantly. Conclusion: Submicron PLGA/rhBMP-2 coating on Ti implants by electrospray facilitated cell proliferation and differentiation, which is important for early healing and integration of implants. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate and compare the strain development at different occlusal heights of an implant prosthesis and adjacent teeth through the use of strain gauges. Materials and Methods: A test model was constructed using autopolymerizing polyurethane resin, artificial composite resin teeth, and an implant gold crown in the mandibular first molar area. The resin block containing the implant and the gold crown was sectioned, and two expansion screws were attached perpendicular to the bottom of the resin block on the buccal and lingual sides. The expansion screws were turned to create a gap. Four groups were created based on the occlusal height of the implant gold crown. Three strain gauges were attached to the buccal surfaces of the mandibular right second premolar, implant gold crown, and second molar. Beef jerky, carrot, and bread were used as test foods. A universal testing machine was used to apply compressive forces of 300 N (beef jerky), 250 N (carrot), and 50 N (bread), and the occlusal force was measured in each group. Results: With 300 N, occlusal forces were concentrated on the adjacent teeth when the occlusal height of the implant prosthesis decreased. With 250 and 50 N, when the occlusal height of the implant prosthesis increased, the occlusal force applied to the implant prosthesis increased, but alterations in the implant crown height had little effect on the adjacent teeth. Conclusion: Different amounts of strain in the implant prosthesis and adjacent teeth were recorded depending on the occlusal height of the prosthesis. With 250 or 50 N of force, an increased prosthesis height affected the implant itself. With 300 N of force, decreased occlusal height of the prosthesis resulted in increased force on the adjacent teeth. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to compare and evaluate the accuracy of surgical templates fabricated using coordinate synchronization processing with five-axis milling and design-related processing with rapid prototyping (RP). Materials and Methods: Master phantoms with 10 embedded gutta-percha cylinders hidden under artificial gingiva were fabricated and imaged using cone beam computed tomography. Vectors of the hidden cylinders were extracted and transferred to those of the planned implants through reverse engineering using virtual planning software. An RP-produced template was fabricated by stereolithography in photopolymer at the RP center according to planned data. Metal sleeves were bonded after holes were bored (group RP). For the milled template, milling coordinates were synchronized using the conversion process for the coordinate synchronization platform located on the model's bottom. Metal bushings were set on holes milled on the five-axis milling machine, on which the model was fixed through the coordinate synchronization plate, and the framework was constructed on the model using orthodontic resin (group CS). A computed tomography image was taken with templates firmly fixed on models using anchor pins (RP) or anchor screws (CS). The accuracy was analyzed via reverse engineering. Differences between the two groups were compared by repeated measures two-factor analysis. Results: From the reverse-engineered image of the template on the experimental model, RP-produced templates showed significantly larger deviations than did milled surgical guides. Maximum deviations of the group RP were 1.58 mm (horizontal), 1.68 mm (vertical), and 8.51 degrees (angular); those of the group CS were 0.68 mm (horizontal), 0.41 mm (vertical), and 3.23 degrees (angular). Conclusions: A comparison of milling and RP template production methods showed that a vector-milled surgical guide had significantly smaller deviations than did an RP-produced template. The accuracy of computer-guided milled surgical templates was within the safety margin of previous studies. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to investigate the effects of abutment screw length on screw loosening after thermocycling. Materials and Methods: Twenty-one grade 5 titanium (Ti) abutments were connected to grade 4 Ti implants with grade 5 Ti abutment screws. These implant/abutment screw/abutment assemblies were divided into seven groups according to the length of the abutment screw; each group included three assemblies. The screws were tightened to 30 Ncm and subjected to 2,000 thermocycles in water baths at 4°C and 60°C, with 60 seconds of immersion at each temperature. Removal torque values (RTVs) were measured before and after thermocycling, and differences in RTVs according to abutment screw length pre- and post-thermocycling were analyzed statistically. Results: Mean RTVs before and after thermocycling were as follows: 23.0 ± 4.4 Ncm and 25.5 ± 0.9 Ncm for 1.4-mm-long abutment screws, 26.7 ± 2.5 and 24.5 ± 2.6 Ncm for 1.8-mm screws, 26.0 ± 1.3 and 25.0 ± 1.8 for 2.2-mm screws, 25.0 ± 2.0 and 25.3 ± 0.8 for 2.6-mm screws, 22.5 ± 4.4 and 22.5 ± 0.5 for 3.0-mm screws, 26.5 ± 2.3 and 25.2 ± 1.3 for 3.4-mm screws, and 25.5 ± 4.8 and 23.2 ± 0.8 for 3.8-mm screws, respectively. As the screw length increased, no statistically significant differences were found in the mean RTVs among the groups before or after thermocycling. Additionally, none of the groups showed significant changes in RTVs after cyclic thermal stress. Conclusion: Abutment screw length had no significant effect on screw loosening under thermal stress. From the results of this study, daily temperature changes in the oral cavity may have no negative influence on the integrity of an implant-abutment joint when a minimum of three and a half threads of an abutment screw are engaged. [ABSTRACT FROM AUTHOR]