Search

Materials have been developed to reduce the chipping of ceramic veneer and improve the esthetics of anterior ceramic veneered restorations. However, studies of the effects of material and substructure design on fracture resistance are sparse.The purpose of this in vitro study was to investigate the fracture resistance of metal-ceramic (MC), zirconia-feldspathic porcelain (ZC), and zirconia-lithium disilicate (ZL) anterior restorations and evaluate the effect of material and substructure design.After preparing and scanning artificial maxillary central incisor teeth, titanium abutments and restoration specimens (n=90) were fabricated. MC, ZC, and ZL materials were prepared with substructure designs A (two-third coverage of the palatal surface) and B (one-third coverage of the palatal surface). After cementation, the specimens were thermocycled (10 000 cycles, 5 and 55 °C). Fracture load measurements, failure mode analysis, energy dispersive X-ray spectroscopy (EDS), line scan analysis, fractography, finite element analysis (FEA), and Weibull analysis were performed. Two-way ANOVA was used to identify the effects of material and substructure design on fracture load. One-way ANOVA was used to identify significant differences of fracture load (α=.05).MC and ZL showed significantly higher fracture load than ZC (P.05). MC_A showed a significantly higher fracture load than MC_B (P.05). ZC_A exhibited the lowest Weibull modulus. FEA revealed that the maximum principal stress occurred near the loading area of the veneer. ZL displayed the lowest maximum principal stress among all the materials.ZL and MC_A exhibited more favorable fracture resistance. The substructure design of MC, with increased metal coverage of the palatal surface, improved fracture resistance significantly.

Statement of problem How axial displacement may be affected by the mechanical properties and internal discrepancy of a cement-retained implant-supported prosthesis is unclear. Purpose The purpose of this in vitro study was to assess the difference in internal discrepancy and axial displacement according to the prosthesis material in cement-retained prostheses splinting nonparallel implants. Material and methods Computer-aided design and computer-aided manufacture (CAD-CAM) titanium abutments were fabricated for a vertically placed implant and a 15-degree tilted implant. Three types of prostheses, in zirconia, cobalt-chromium (Co-Cr) alloy, and polymethylmethacrylate resin (PMMA), were fabricated (n=10). The internal discrepancy between the CAD-CAM titanium abutment and the prosthesis was measured by using the replica technique. After luting with an interim cement, they were mounted in Type IV gypsum. The specimens were cyclic loaded, and axial displacement of the prosthesis was measured after 3, 10, 100, and 106 cycles. The internal discrepancy and cumulative axial displacement were assessed by using a 3-way analysis of variance and repeated measures analysis of variance (α=.05). Results The internal discrepancy of the prosthesis did not differ based on the prosthesis material (P=.869); however, it was significantly different based on the measurement location, with the occlusal discrepancy (224 ±29 μm) being greater than the axial discrepancy (21 ±10 μm) (P Conclusions Prostheses made with high-elastic moduli materials exhibited less axial displacement than PMMA prostheses, even though the internal discrepancy was not different. Moreover, vertically placed implants presented a greater axial displacement of the prosthesis than implants with angled placement.

The mechanical and physical properties of implant screw access opening deteriorate if composite resin is not polymerized properly. Therefore, this study aimed to analyze the effect of using composite resin in implant access opening on the degree of conversion (DC).Two prosthetic materials (Co-Cr and zirconia), two types of composite resin (low and high viscosity), two light-cured resin depths (2 and 3 mm), and two polymerization methods (max-mode 10 s and mid-mode 20 s: 16 and 22 J/cm2, respectively) were considered (n = 192). The DC of the polymerized composite resin was measured through Fourier-transform infrared (FTIR) spectroscopy. The top and bottom surfaces of the polymerized composite resin body were observed through scanning electron microscopy. Multiple linear regression analysis and analysis of variance (ANOVA) were used to identify significant differences in DC (α = .05).The DC was lower when the low-viscosity composite resin (β = -0.431), light-polymerized resin depth of 2 mm (β = -0.430), zirconia prosthesis (β = -0.191), and mid-mode polymerization method (β = -0.164) were used. The resin type, depth of resin to be light-cured, prosthesis material, and polymerization method had an effect on the DC.Low-viscosity composite resin should be polymerized at a low irradiance and long polymerization time (such that the light-cured resin depth does not exceed 2 mm) to ensure proper composite resin polymerization in implant screw access opening. This article is protected by copyright. All rights reserved.

PURPOSE The aim of this study is to compare the hardness according to the conditions of metal alloys. Moreover, the correlation between the cast crown hardness before and after wear testing and the degree of wear for each dental alloy was assessed. MATERIALS AND METHODS Cast crowns of three metal alloys (Co-Cr, gold, and Ni-Cr alloys) opposing smooth-surface monolithic zirconia were used. The Vickers microhardness of the ingot (which did not undergo wear testing) and the cast crown before and after wear testing were measured for each alloy. Two-way ANOVA and Scheffé tests were used to compare the measured hardness values. Moreover, the Pearson correlation coefficient was used to evaluate the relationship between the surface hardness and the wear of the cast crown (α=.05). RESULTS There was no significant difference in the hardness before and after wear testing for the gold alloy (P>.05); however, the hardness of the worn surface of the cast crown increased compared to that of the cast crown before the wear tests of Ni-Cr and Co-Cr alloys (P.05). CONCLUSION There was a significant difference in hardness between dental alloys under the same conditions. No correlation existed between the surface hardness of the cast crown before and after wear testing and the wear of the cast crown.

The purpose of this study was to investigate the effect of barium silicate filler contents on mechanical properties of resin nanoceramics (RNCs) for additive manufacturing (AM).Additively manufactured RNC specimens were divided into 4 groups depending on the content of ceramic fillers and polymers: 0% barium silicate and 100% polymer (B0/P10, control group); 50% barium silicate and 50% polymer (B5/P5); 60% barium silicate and 40% polymer (B6/P4); 67% barium silicate and 33% polymer (B6.7/P3.3). The compressive strength (n = 15) and fracture toughness (n = 12) of the specimens were measured, and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) analyses were performed. Independent sample Kruskal-Wallis tests were performed on the compressive strength and fracture toughness test results, and the significance of each group was analyzed at the 95% confidence interval through post-tests using the Bonferroni's method.B6/P4 and B6.7/P3.3 exhibited much higher yield strength than B0/P10 and B5/P5 (Increasing the ceramic filler content improves the mechanical properties, but it can be accompanied by a decrease in the flowability and the homogeneity of the slurry.

PURPOSE The effect of core design on the fracture resistance of zirconia-lithium disilicate (LS2) bilayered crowns for anterior teeth is evaluated by comparing with that of metal-ceramic crowns. MATERIALS AND METHODS Forty customized titanium abutments for maxillary central incisor were prepared. Each group of 10 units was constructed using the same veneer form of designs A and B, which covered labial surface to approximately one third of the incisal and cervical palatal surface, respectively. LS2 pressed-on-zirconia (POZ) and porcelain-fused-to-metal (PFM) crowns were divided into “POZ_A,” “POZ_B,” “PFM_A,” and “PFM_B” groups, and 6000 thermal cycles (5/55℃) were performed after 24 h storage in distilled water at 37℃. All specimens were prepared using a single type of self-adhesive resin cement. The fracture resistance was measured using a universal testing machine. Failure mode and elemental analyses of the bonding interface were performed. The data were analyzed using Welch's t-test and the Games-Howell exact test. RESULTS The PFM_B (1376. 8 ± 93.3 N) group demonstrated significantly higher fracture strength than the PFM_A (915.8 ± 206.3 N) and POZ_B (963.8 ± 316.2 N) groups (P.05). Regardless of the design differences of the zirconia cores, fractures involving cores occurred in all specimens of the POZ groups. CONCLUSION The bilayered anterior POZ crowns showed different fracture resistance and fracture pattern according to the core design compared to PFM.

Materials used for dental restorations should cause wear similar to that of natural teeth. Studies on the wear of dental alloys against monolithic zirconia are lacking.The purpose of this in vitro study was to compare the wear of Co-Cr, gold, and Ni-Cr alloys against monolithic zirconia of different surface roughness.Cylindrical monolithic zirconia specimens were prepared by a sintering process. Sintered zirconia was then polished to prepare 30 zirconia substrate specimens with a smooth surface (Ra0.1 μm) and 30 with a rough surface (3.5 μmRa4.5 μm). As antagonist specimens, 3 types of metal alloys (Co-Cr, gold, and Ni-Cr alloys) were used. Twenty cast crowns were prepared from each metal alloy in the shape of a maxillary premolar. For each alloy, 10 cast crowns were randomly selected to oppose the smooth-surface zirconia specimens and 10 to oppose the rough-surface zirconia specimens. A total of 6 wear test groups were formed. Wear tests were performed by using a mastication simulator at 240 000 mastication cycles. Wear on the antagonist specimens was measured by using a laser 3D scanner. After wear testing, antagonist and substrate specimens were inspected by using a scanning electron microscope (SEM). For statistical analysis of the data, the 2-way ANOVA and the Scheffé multiple comparison tests were used (α=.05).Of the 6 test groups, the gold alloy specimens opposed to rough-surface zirconia exhibited the most wear, while the Co-Cr alloy specimens opposed to smooth-surface zirconia exhibited the least wear (P.05). Rough-surface monolithic zirconia caused significantly more wear of the metal alloy specimens than did smooth-surface monolithic zirconia (P.01).Increased surface roughness of monolithic zirconia was associated with increased wear of the opposing dental alloy. When monolithic zirconia surface roughness was increased, wear of dental alloys increased most for gold alloys, followed by Ni-Cr, and then Co-Cr alloys.

Studies that compared the fracture strength of monolithic lithium disilicate and 5-mol% yttria partially stabilized zirconia multiunit fixed dental prostheses are sparse.As the connector is the weakest part of a fixed dental prosthesis, the purpose of this in vitro study was to investigate the effect of connector designs and material on the fracture strength of 3-unit monolithic fixed dental prostheses.Resin-ceramic canine and premolar teeth (N=144) were prepared for fixed dental prosthesis abutments. Prostheses with 3 connector designs (width=height, widthheight, and widthheight) were made from 2 types of lithium disilicate (IPS e.max CAD and Amber Mill) and 5-mol% yttria partially stabilized zirconia (3M Lava Esthetic and Katana Zirconia UTML). Fracture strengths were measured after 200 000 cycles of dynamic loading of 50 N and thermocycling at 5 °C and 55 °C, and the fracture patterns were analyzed. Two-way analysis of variance and the Fisher exact test were used for statistical analysis (α=.05).The material and connector design affected the fracture strength of fixed dental prostheses (P.05), and a significant interaction was found between the material and connector design (P.05). The IPS e.max CAD material had significantly lower fracture strength than Amber Mill, 3M Lava Esthetic, or Katana Zirconia UTML (P.05). Connector designs with a greater width versus height showed significantly lower fracture strengths than other designs (P.05).The connector design of 3-unit fixed dental prostheses, particularly the connector height, may affect fracture strength depending on the prosthesis material.

This study aimed to determine the correlation between occlusal contact area and masticatory performance using BiteEyeTo calculate the occlusal contact area at various levels of interocclusal thicknesses and to measure masticatory performance with peanuts as the test material.Fifty-two adults (30 men and 22 women) were enrolled according to specific exclusion/inclusion criteria. The occlusal contact area was measured by obtaining the interocclusal record of the maximum intercuspal position (MIP) using silicone impression material. Occlusal contact area measurements were performed in the ranges of 0-149, 0-89, 0-59, 0-29 and 0-9 μm. Masticatory performance was measured by obtaining the median particle size (XInterocclusal thickness comparison revealed the highest correlation with XThe larger the occlusal contact area, the higher the masticatory performance; this correlation was statistically significant. Regarding interocclusal thickness, the highest correlation between the occlusal contact area and masticatory performance was observed in the 0-149 μm range.GWNUDH IRB 2020-A001.

PURPOSE To compare the effect of 3 tray designs and 3 commonly used impression materials on the displacement of flabby tissue during maxillary edentulous impression by superimposition of 3D digital models. MATERIALS AND METHODS Fifteen maxillary edentulous casts with simulated flabby tissue were fabricated by modifying a standard maxillary edentulous acrylic resin cast. Three types of impression trays were fabricated: trays with conventional relief, trays with additional relief, and trays with an open window. Three impression materials were tested: light-body polysulfide, light-body vinylpolysiloxane, and zinc oxide eugenol paste. For the analysis of tissue displacement during impression making, the test and control stone casts were scanned using a 3D laser scanner, and the 3D digital models were superimposed using metrology software. Statistical analyses were performed with an α = 0.05. RESULTS Negative deviations were recorded at the areas of the alveolar crest, posterior part of flabby tissue, and middle of the palate. On the other hand, a positive deviation was recorded at the area of the anterior part of flabby tissue. A significant difference in the displacement of flabby tissue was found when using different tray designs (p < 0.0001). The tray with the open window showed significantly low tissue displacement at the flabby tissue region. Depending on sites, the amount of flabby tissue displacement showed different significances by the different impression materials used (anterior part: p < 0.0001; alveolar crest: p = 0.097; posterior part: p < 0.0001). Conventionally relieved trays showed significantly higher values of displacement at the anterior part of flabby tissue (p < 0.0001), while trays with open windows showed similar values of displacement at all measuring points, and no significant differences among different impression materials were found (p = 0.104). CONCLUSIONS There were significant differences in the displacement of flabby tissue with different tray designs, especially with displacement occurring at the anterior and posterior parts of flabby tissue. Tray designs should be considered in order to make proper impressions when flabby tissue is present.

The mechanical properties and residual stress of dental Co-Cr-Mo (CCM) alloy depend on the manufacturing and post-processing methods, which affect the prognosis of dental prostheses. Two CCM alloys manufactured by casting and selective laser melting (SLM) were compared, and the effect of heat treatment temperature for CCM alloys manufactured by SLM method was evaluated. Specimens were fabricated by casting (Cast Co-Cr) and SLM (SLM Co-Cr). SLM Co-Cr specimens were heat treated at 750, 950, and 1150 °C to compare their properties. Microstructures were analyzed via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscattered diffraction (EBSD), and the residual stress was measured via x-ray diffraction (XRD). Mechanical properties were evaluated by a Vickers hardness test and a tensile test; fractography was performed after this. The SLM Co-Cr group exhibited a decrease in porosity, grain size, increase in solid solution limit, and high residual stress compared to Cast Co-Cr; the ultimate tensile strength, yield strength, and hardness were also higher. The microstructures, residual stresses, and mechanical properties differed significantly depending on the heat treatment, and the strength and hardness showed a tendency inverse to that of the elongation. Type I residual stresses mostly decreased after 750 °C heat treatment, however type II and III residual stresses remained even after 1150 °C heat treatment. SLM presented superior mechanical properties to casting. Considering the reduction of tensile residual stress and increased ductility, CCM alloys should be heat treated at a temperature of 950 °C or higher.

Lithium disilicate and 5 mol% yttria partially stabilized zirconia (5Y-PSZ) are commonly used for anterior restorations. However, studies comparing the durability of 5Y-PSZ and lithium disilicates are sparse.The purpose of this in vitro study was to investigate the fracture load of anterior monolithic crowns made of 2 lithium disilicates and a 5Y-PSZ under dynamic loading.Titanium abutments of the maxillary incisors were prepared (N=48, 8 for each group). Monolithic anterior crowns were made from the lithium disilicates (e.max CAD, Rosetta SM) and 5Y-PSZ (Katana UTML). After cementation, the specimens were stored in water for 24 hours and then thermocycled 10 000 times. Dynamic loading (70 N, 200 000 cycles, 1 Hz) was applied to half the specimens. The fracture load was measured by using a universal testing machine. The fracture patterns were analyzed and fractography applied. Two-way ANOVA and the Fisher exact test were used for statistical analysis (α=.05).The material and dynamic loading affected the fracture load of the anterior monolithic crowns (P.05). However, there was no interaction between the material and the dynamic loading (P=.079). Both lithium disilicates had higher fracture loads than 5Y-PSZ (P.05). The fracture load of each specimen was reduced after dynamic loading (P.05). Lithium disilicate showed marginal and bulk fractures, and 5Y-PSZ presented catastrophic fractures (P.001).5Y-PSZ materials with large grains and low flexural strength may be less resistant to fractures under dynamic loading than lithium disilicates.

Zirconia prostheses show a high rate of retention loss, and more information is needed regarding the treatment of the intaglios of zirconia prostheses to improve the bond strength between zirconia and resin cement.The purpose of this in vitro study was to evaluate the retention of titanium abutments and zirconia prostheses treated with silica-containing glass-ceramic liners. The effect of the abutment convergence angle on retention force was also examined.Titanium abutments and zirconia copings (n=90) were fabricated with 3 different convergence angles (6, 12, and 24 degrees). Specimens were divided into 2 groups according to surface treatment: an airborne-particle-abraded control group and a group that was coated with a silica-containing glass-ceramic liner after airborne-particle abrasion (liner group). The thickness of the liner was measured, and the inner spacing of the zirconia coping was modified in the liner group. The coping was cemented, and the retention was evaluated with a tensile bond strength test by using a universal testing machine. Retention was analyzed by using a 2-way analysis of variance. Modes of failure were evaluated by examining the fracture surface. Elemental analysis of the interface was also performed.The liner group showed a significantly higher retention force for the zirconia prosthesis (P.05). Regardless of surface treatment, the retention force at a convergence angle of 6 degrees was higher than that at 24 degrees (P.05). The control group showed mostly adhesive type failures, whereas the liner group exhibited mostly mixed type failures.Silica-containing glass-ceramic liner treatment increased the retention compared with airborne-particle abrasion treatment alone. Tensile bond strength increased with decreasing abutment convergence angle.

PURPOSE To determine the effects of the total thickness and core/veneer thickness ratio of bilayered ceramics on their three-point flexural strength and translucency. MATERIALS AND METHODS Two groups of specimens were prepared with two different total thicknesses, 1.0 mm and 0.6 mm. These groups were divided into five and three subgroups with ten specimens each, respectively, having different core/veneer thickness ratios. Lithium disilicate was pressed on the zirconia surface using the "lost-wax technique." The translucency and three-point flexural strength were measured, and a one-way analysis of variance test (p < 0.05) was performed to determine whether the translucency and three-point flexural strength were affected by the total thickness and core/veneer thickness ratio of the specimens. RESULTS For the same total thickness, translucency decreased with a increase in the zirconia core proportion (p < 0.001). For the same core/veneer ratio, the translucency decreased with an increase in the total thickness (p < 0.001). If the zirconia thickness was less than half of the total thickness, the bilayered ceramic specimens containing zirconia cores and monolithic lithium disilicate specimens exhibited a similar translucency. The three-point flexural strength increased with the increasing proportion of zirconia; however, it did not change significantly with the total thickness. However, for the same total thickness, the flexural strengths of the bilayered ceramics were higher than those of the monolithic specimens. CONCLUSIONS At the same total thickness, increasing the zirconia core thickness decreased the translucency and increased the three-point flexural strength. Bilayered ceramic specimens with low zirconia ratios exhibited translucency similar to that of monolithic lithium disilicate ceramic but a higher flexural strength.

Statement of problem Little information is available for the strength of bonding between zirconia and lithium disilicate as affected by surface pretreatment methods. Purpose The purpose of this in vitro study was to investigate the shear bond strength (SBS) between zirconia core and lithium disilicate (LS 2 ) veneered ceramic after surface pretreatments. Material and methods Fully sintered yttrium oxide partially stabilized tetragonal zirconia (Y-TZP) disk specimens were fabricated from zirconia ceramic materials. Specimens were divided into 4 groups with surface pretreatments applied (the as-received group, the liner group, the airborne-particle abrasion group, and the airborne-particle abrasion-plus-liner group). After pressing LS 2 on a zirconia disk, shear force was applied perpendicular to the zirconia-LS 2 interface. Data were analyzed using 2-way ANOVA and Tukey test ( α =.05). For each group, the failure modes were measured by using optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. Results Airborne-particle abrasion induced significantly lower interfacial strength between zirconia and lithium disilicate ( P 2 . The liner treatment significantly improved the adhesion between zirconia core and veneering LS 2 ( P airborne-particle abrasion-plus-liner group > airborne-particle abrasion group. The interfacial image of zirconia and LS 2 showed a fusion of crystal structure between the 2 materials. Some components of the silica-containing glass-ceramic liner led to an increase in SBS as diffusion occurred on the zirconia surface. Conclusions The bond strength between zirconia and veneering LS 2 was significantly increased by application of silica-containing glass-ceramic liner but was decreased with airborne-particle abrasion.

Purpose To evaluate the axial displacement of the implant-abutment assembly of different implant diameter after static and cyclic loading of overload condition. Materials and Methods An internal conical connection system with three diameters (O 4.0, 4.5, and 5.0) applying identical abutment dimension and the same abutment screw was evaluated. Axial displacement of abutment and reverse torque loss of abutment screw were evaluated under static and cyclic loading conditions. Static loading test groups were subjected to vertical static loading of 250, 400, 500, 600, 700, and 800 N consecutively. Cyclic loading test groups were subjected to 500 N cyclic loading to evaluate the effect of excessive masticatory loading. After abutment screw tightening for 30 Ncm, axial displacement was measured upon 1, 3, 10, and 1,000,000 cyclic loadings of 500 N. Repeated-measure ANOVA and 2-way ANOVA were used for statistical analysis (α = 0.05). Results The increasing magnitude of vertical load and thinner wall thickness of implant increased axial displacement of abutment and reverse torque loss of abutment screw (p < 0.05). Implants in the O 5.0 diameter group demonstrated significantly low axial displacement, and reverse torque loss after static loading than O 4.0 and O 4.5 diameter groups (p < 0.05). In the cyclic loading test, all diameter groups of implant showed significant axial displacement after 1 cycle of loading of 500 N (p < 0.05). There was no significant axial displacement after 3, 10, or 1,000,000 cycles of loading (p = 0.603). Conclusions Implants with O 5.0 diameter demonstrated significantly low axial displacement and reverse torque loss after the cyclic and static loading of overload condition.

Purpose The purpose of this study was to evaluate axial displacement in cement-retained prostheses using computer-aided design/computer-aided manufacturing (CAD/CAM) abutments with three different types of implant-abutment connections. Materials and methods CAD/CAM abutments made with two types of titanium blocks (made by the same manufacturer as the implant manufacturer and by a manufacturer with a patent for CAD/CAM abutment fabrication) were connected with three types of implant connections: external, internal butt, and internal conical connection. Titanium custom abutments and zirconia prostheses were fabricated using the CAD/CAM system for each specimen. The geometries and surface morphologies of CAD/CAM abutments and ready-made abutments were comparatively evaluated using scanning electron microscopy. Cemented prostheses on abutments were mounted on a universal testing machine and subjected to 250-N sine wave cyclic loads. Cumulative axial displacement was measured at loading cycles of 3, 10, 100, and 106 and analyzed by repeated measures analysis of variance (ANOVA). Results Surface geometries and morphologies of CAD/CAM abutments varied according to the implant-abutment connection and manufacturers of the titanium block. The internal conical connection exhibited the greatest axial displacement, while the external connection showed the lowest axial displacement. The CAD/CAM abutment made with a compatible titanium block exhibited a greater axial displacement than that exhibited by the abutment fabricated using a titanium block made by the implant manufacturer. Conclusion In implant connections with a vertical stop, axial displacement occurred primarily in the early loading period and was self-limited. However, long-term axial displacement can occur with internal conical connection implants. Therefore, in internal conical connection implants, axial displacement should be managed more carefully using a provisional restoration, with consideration of the abutment fabrication method.

Purpose: To evaluate the effect of implant coronal wall thickness on load-bearing capacity and screw joint stability. Materials and Methods: Experimental implants were customized after investigation of the thinnest coronal wall thickness of commercially available implant systems with a regular platform diameter. Implants with four coronal wall thicknesses (0.2, 0.3, 0.4, and 0.5 mm) were fabricated. Three sets of tests were performed. The first set was a failure test to evaluate load-bearing capacity and elastic limit. The second and third sets were cyclic and static loading tests. After abutment screw tightening of each implant, vertical cyclic loading of 250 N or static loading from 250 to 800 N was applied. Coronal diameter expansion, axial displacement, and removal torque values of the implants were compared. Repeated measures analysis of variance (ANOVA) was used for statistical analysis (α = .05). Results: Implants with 0.2-mm coronal wall thickness demonstrated significantly low load-bearing capacity and elastic limit (both P < .05). These implants also showed significantly large coronal diameter expansion and axial displacement after screw tightening (both P < .05). Greater vertical load and thinner coronal wall thickness significantly increased coronal diameter expansion of the implant, axial displacement of the abutment, and removal torque loss of the abutment screw (all P < .05). Conclusion: Implant coronal wall thickness of 0.2 mm produces significantly inferior load-bearing capacity and screw joint stability.

Purpose: The aim of this study was to evaluate correlations between denture satisfaction and various factors related to patients` and wearing dentures. Materials and Methods: Total 43 edentulous patients were recalled and they were wearing complete dentures fabricated more than one year ago. For patients` subjective assessment, the questionnaire based on the various literatures was developed and applied to patients for data acquisition. In addition, correlations were evaluated between subjective assessment and denture satisfaction score. For statistical analysis, Spearman correlation coefficient, multiple regression analysis, Mann-whitney U test and Kruskal-Wallis test were used to found out what the most considerable factors to denture satisfaction score (P

Purpose: When the edentulous area is restored by implant prostheses, the opposing hypofunctioned teeth will receive physiologic mechanical stimuli. This study evaluated the bone changes around the maxillary teeth opposing an implant restoration installed in the mandibular posterior area. Materials and Methods: Radiographs of the opposing teeth were taken at prostheses delivery (baseline), 3 and 6 months later. A customized film holding device was fabricated to standardize the projection geometry for the serial radiographs of the opposing teeth. The gray values of the region of interest of each digital image were compared according to time. Repeated measured analysis of variance was performed at the 95% significance level. Results: The gray values of the alveolar bone around the antagonist teeth of implants increased with time. The changes in gray values of the middle area were greater than those of the crestal area. However, the gray values of the mesial and distal areas were not different. The changes in gray values were different according to the unloaded time. Conclusion: A change in bone tissue will occur if a proper physiologic load is again applied to the bone tissues around a hypofunctioned tooth. (J Dent Rehabil Appl Sci 2015;31(4):301-9)

PURPOSE To compare the bone responses of chemically modified implants using the plasma immersion ion implantation and deposition method with those of blasted implants. MATERIALS AND METHODS The titanium implants were blasted with resorbable blasting media (RBM) and designated as controls. The ion-implanted implants were divided into two test groups, namely, calcium (Ca) and magnesium (Mg) implants. Six implants (two implants per group) were placed into the proximal tibias of 11 New Zealand white rabbits. Fluorochrome labeling was administered at 2 and 4 weeks after surgery. Resonance frequency analysis (RFA) was conducted immediately after surgery and at 6 weeks of healing. The removal torque was measured in half of the tibiae. The implants in another tibia were subjected to fluorescence analysis and histologic and histomorphometric evaluations. RESULTS The fluorescence analysis suggested that osteoconductivity was improved in the early osseointegration stages in the Ca and Mg implants. In the cortical region, the bone-to-implant contact in the Mg implants and the bone area % in the Ca and Mg implants were higher than those in the RBM implants (P < .05). All groups demonstrated similar biomechanical strengths with respect to the RFA and the removal torque measurements. CONCLUSION The osseointegration speed and the bone contact were positively affected by the Ca and Mg ion implantation, especially in the Mg implants, because of the synergistic effect. However, no remarkable differences were found in biomechanical strength in the later osseointegration stages.

Purpose To investigate the stress distribution in an implant-abutment complex with a preloaded abutment screw by comparing implant-abutment engagement features using three-dimensional finite element analysis (FEA). Materials and methods For FEA modeling, two implants-one with a single (S) engagement system and the other with a double (D) engagement system-were placed in the human mandibular molar region. Two types of abutments (hexagonal, conical) were connected to the implants. Different implant models (a single implant, two parallel implants, and mesial and tilted distal implants with 1-mm bone loss) were assumed. A static axial force and a 45-degree oblique force of 200 N were applied as the sum of vectors to the top of the prosthetic occlusal surface with a preload of 30 Ncm in the abutment screw. The von Mises stresses at the implant-abutment and abutment-screw interfaces were measured. Results In the single implant model, the S-conical abutment type exhibited broader stress distribution than the S-hexagonal abutment. In the double engagement system, the stress concentration was high in the lower contact area of the implant-abutment engagement. In the tilted implant model, the stress concentration point was different from that in the parallel implant model because of the difference in the bone level. Conclusion The double engagement system demonstrated a high stress concentration at the lower contact area of the implant-abutment interface. To decrease the stress concentration, the type of engagement features of the implant-abutment connection should be carefully considered.