Browsing by Author "Johnston, William M."

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Citation Count: 25
Effect of different resin cements and surface treatments on the shear bond strength of ceramic-glass polymer materials
(Mosby-elsevier, 2018) Alp, Gulce; Subasi, Meryem Gulce; Johnston, William M.; Yilmaz, Burak
Statement of problem. The effect of different surface treatment techniques on the bond strength of different types of ceramic-glass polymer computer-assisted design and computer-assisted manufacturing (CAD-CAM) materials and resin cements after aging is unknown. Purpose. The purpose of this in vitro study was to evaluate the surface roughness of different ceramic-glass polymer CAD-CAM materials after 2 different surface treatments and the effect of material, surface treatment, resin cement, and aging on bond strength. Additionally, it was to determine any correlation between the surface roughness and bond strength. Material and methods. CAD-CAM ceramic-glass polymer materials, a polymer-infiltrated ceramic network (PICN) (VITA ENAMIC), a resin nanoceramic (Lava Ultimate), and a nanoparticle-filled resin (Cerasmart) (1.5 mm in thickness; n=144) were divided into 2 subgroups in terms of surface treatments: airborne-particle abraded or silica-coated. The surface roughness values of specimens were measured. Composite resin cylinders were prepared and bonded to the restorative specimens using 2 different types of resin cements (dual-polymerizing [DP] and light-polymerizing [LP]). Half of the specimens were stored in distilled water for 24 hours, while the other half were submitted to 5000 thermocycles. The shear bond strength was measured, and the failure modes of the specimens were evaluated. The data were analyzed with ANOVA and Tukey HSD tests (alpha=.05). The correlation between roughness and bond strength values was analyzed using Pearson correlation analysis. Results. Material (P=.012) and surface treatment type (P=.031) significantly affected the surface roughness. For bond strength, significant interactions were found among the material type, surface treatment, resin cement, and aging factors (P=.009). No significant correlation was found between roughness and bond strength (P=.943). Conclusions. The surface treatment and resin cement type affected the bond strength and surface roughness of tested restorative materials. DP resin cement provided higher bond strength for airborne-particle abraded nanohybrid composite resin materials. LP resin cement achieved a higher bond strength when used with silica-coated, nanoparticle-filled resin and PICN materials.
Citation Count: 3
Effect of framework material on the color of implant-supported complete-arch fixed dental prostheses
(Mosby-elsevier, 2019) Yilmaz, Burak; Alp, Gulce; Johnston, William M.
Statement of problem. The effect of framework material on the color of implant-supported complete-arch fixed dental prostheses is unclear. Purpose. The purpose of this in vitro study was to investigate the effect of different framework materials on the final color of implant-supported complete-arch fixed dental prostheses. Material and methods. A master model was used to simulate an edentulous maxilla with 4 implants. A screw-retained complete-arch resin prototype with a 1.5-mm cut back on the facial surfaces of the teeth was fabricated. The master model and resin prototype were scanned and digitized with a laser scanner. A computer-aided design (CAD) model was constructed using software and used for milling titanium (Ti) and zirconia (Zir) frameworks. Four Zir frameworks were milled from solid presintered Zir blocks, and 4 Ti frameworks were milled from solid Ti blocks. The Zir frameworks were then sintered. To simulate gingiva on the Zir and Ti frameworks, feldspathic porcelain was layered on the facial aspects of the teeth (except for the molars) and glazed. Color coordinates (L*, a*, b*) of anterior teeth and gingiva on both Zir and Ti frameworks were measured with a spectroradiometer, and color differences (CIEDE2000) were calculated between Zir and Ti frameworks using the CIEDE2000 formula. The color coordinates of the teeth and gingival porcelain on the frameworks were analyzed using an ANOVA (alpha=.05). Results. For the teeth, the 3-way ANOVA revealed a significant interaction for material, tooth, and coordinate (P=.014), material and coordinate (P<.001), and tooth and coordinate (P<.001). For the gingival porcelain, the 2-way ANOVA revealed a significant interaction between material and coordinate (P<.001). The L* values of the teeth and gingival porcelain on Zir frameworks were statistically different from those on the teeth and gingival porcelain on the Ti frameworks (P<.001). The maxillary right central incisor on the Ti frameworks had a significantly higher a* (P=.013) and b* value (P<.001) than those on the Zir framework. The color differences (CIEDE2000) of teeth and gingival porcelain between Ti and Zir frameworks were 6.6 and 8.6, respectively. Conclusions. Feldspathic porcelain layered for teeth and gingiva was lighter on Zir frameworks than on Ti frameworks. Porcelain on the facial aspects of teeth was redder and yellower on Ti compared with Zir. Gingival porcelain on Zir was yellower than that on Ti. The color of layering porcelain on the teeth and gingival areas was significantly different when different frameworks (Ti or Zir) were used.
Citation Count: 37
Effect of shading technique and thickness on color stability and translucency of new generation translucent zirconia
(Elsevier Sci Ltd, 2018) Alp, Gulce; Subasi, Meryem Gulce; Seghi, Robert R.; Johnston, William M.; Yilmaz, Burak
Objective: To evaluate the effect of shading technique and thickness on the color stability and translucency of translucent zirconia after coffee thermocycling. Methods: Specimens in different thicknesses (1; 1.5; 2 mm) (n = 4 for each thickness) were sectioned from translucent preshaded zirconia (Pre) and externally shaded zirconia (Ext). After sintering, specimens were glazed and subjected to 10,000 thermocycling in coffee solution. The color coordinates of specimens were measured with a spectroradiometer before and after coffee thermocyling. Color differences and relative translucency parameter (RTP) values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze the CIEDE2000 color difference and RTP values (alpha = 0.05). Results: According to 2-way ANOVA, no significant effect of shading technique and thickness on the color difference values was found (P > .05). According to 3-way ANOVA, a significant interaction between the shading technique and thickness (P < .0001) was found for RTP. The RTP parameter decreased with the increase in the thickness. Ext specimens presented significantly higher RTP than Pre specimens (P < .0001), except for between Ext 1 mm and Pre 1 mm (P = .179). Conclusions: Neither shading technique nor tested thicknesses affected the color of translucent zirconia. Shading technique and thickness affected the RTP of translucent zirconia. The RTP was inversely affected with the thickness of the material. Externally shaded zirconia presented higher RTP than preshaded zirconia for specimens thicker than 1 mm. Clinical significance: Discoloration with coffee was insignificant for the tested translucent zirconia in tested thicknesses (1, 1.5, 2mm). When a translucent restoration is intended, thinner externally shaded translucent zirconia restorations should be preferred instead of preshaded translucent zirconia.
Citation Count: 64
Effect of surface treatments and coffee thermocycling on the color and translucency of CAD-CAM monolithic glass-ceramic
(Mosby-elsevier, 2018) Alp, Gulce; Subasi, Meryem Gulce; Johnston, William M.; Yilmaz, Burak
Statement of problem. The effects of surface treatments and coffee thermocycling on the color and relative translucency of a recently introduced computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic glass-ceramic are unknown. Purpose. The purpose of this in vitro study was to evaluate the effect of coffee thermocycling on the color and relative translucency parameter (RTP) of CAD-CAM monolithic glass-ceramics after different surface treatments. Material and methods. Specimens (1.5-mm-thick) were sectioned from zirconia-reinforced lithium silicate glass-ceramic (ZLS) (n=18) and lithium disilicate glass-ceramic (LDS) blocks (n=18). Two different types of surface treatments (glazing or polishing) were applied to the specimens. The specimens were subjected to 5000 thermocycles in a coffee solution. The color coordinates of specimens were measured before and after coffee thermocycling by using a spectroradiometer, and color differences and relative translucency values were calculated by using CIEDE2000 color difference and RTP formulas. ANOVA was used to analyze the color difference and relative translucency values by using maximum likelihood estimation and the Satterthwaite degrees of freedom methods. Any significant interaction between surface subgroups was further analyzed by using the Tukey-Kramer adjustment (alpha(=).05). Results. Material type had a significant effect on color difference (P=.018). All color difference values of all materials were smaller than the clinical acceptability threshold (<1.8 units). For relative translucency, material (P<.001) and coffee thermocycling had a significant effect (P=.014), and an interaction was found between the surface treatments and materials (P<.001). The Tukey-Kramer test revealed significant differences between glazed and polished subgroups of LDS material, except for ZLS-glazed and ZLS-polished subgroups. Conclusions. Different surface treatments of CAD-CAM monolithic zirconia-reinforced lithium silicate and lithium disilicate glass-ceramics resulted in clinically acceptable color changes after coffee thermocycling. The color changes in all groups, except for LDS-polished, were not perceivable. Lithium disilicate was more translucent than zirconia-reinforced lithium silicate before and after coffee thermocycling. Coffee thermocycling decreased the translucency of both of the materials. Different surface treatments affected the translucency of only lithium disilicate for tested thickness.
Citation Count: 53
Effect of thickness on optical properties of monolithic CAD-CAM ceramics
(Elsevier Sci Ltd, 2018) Subasi, Meryem Gulce; Alp, Gulce; Johnston, William M.; Yilmaz, Burak
Objective: To compare the effect of material and thickness on the color stability and relative translucency parameters (RTP) for monolithic ceramics subjected to coffee thermocycling. Methods: Four specimens each at thicknesses of 0.5, 0,7 and 1mm were sectioned from monolithic ceramics [preshaded monolithic zirconia (MonZr), lithium disilicate (LDS) and zirconia reinforced lithium silicate (ZLS)]. The specimens were glazed and subjected to 5000 coffee thermocycling. The color coordinates of specimens were determined with a spectroradiometer and color differences and RTP values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze CIEDE2000 color difference and RTP values (alpha = .05). Results: For the color difference data, the 2-way ANOVA revealed a significant interaction between material and different thickness (P = .002). Except for 0.5mm thick ZLS material, all materials in all thicknesses studied presented color changes within the clinically acceptable limits after coffee thermocycling. For the RTP data, the 3-way ANOVA revealed a highly significant interaction between material and different thicknesses (P < .001). Conclusions: Material type and thickness can be expected to affect color change and relative translucency of the restorations made with preshaded MonZr, LDS and ZLS materials. Except for 0.5mm thick ZLS material, color changes of all studied materials were within the clinically acceptable limits. Except ZLS material, color changes of other materials were not significantly affected by thickness. Staining in coffee was not found to affect translucency, and the materials' translucency parameters were ranked from high to low as LDS, ZLS and MonZr at each thickness studied.
Citation Count: 29
Effects of fabrication and shading technique on the color and translucency of new-generation translucent zirconia after coffee thermocycling
(Mosby-elsevier, 2018) Subasi, Meryem Gulce; Alp, Gulce; Johnston, William M.; Yilmaz, Burak
Statement of problem. The color stability and translucency of preshaded and externally shaded monolithic and veneered new generation translucent zirconia are not well known. Purpose. The purpose of this in vitro study was to investigate the effect of fabrication (veneered or monolithic) and shading (preshaded or externally shaded) techniques on the color and relative translucency of translucent zirconia after coffee thermocycling. Material and methods. Specimens of different thicknesses (0.5 mm for veneered and 1.5 mm for monolithic) were sectioned from preshaded and externally shaded translucent zirconia. Externally shaded specimens were colored by using the dipping technique. Externally shaded (Ext Mono) and preshaded (Pre Mono) monolithic zirconia specimens were sintered and glazed. Externally shaded (Ext Vene) and preshaded (Pre Vene) 0.5-mm-thick specimens were sintered, veneered with feldspathic porcelain (1 mm), and glazed. The color coordinates of specimens were measured with a spectroradiometer before and after 10 000 thermocycles in coffee solution. Color differences were calculated using CIEDE2000, and relative translucency parameter (RTP) values were calculated using the RTPCIEDE2000 formula. Analysis of variance (ANOVA) was used to analyze the CIEDE2000 color differences and RTP values (alpha=.05). Results. Shading technique had a significant effect on the color difference values (P=.018). For the translucency data, the 3-way ANOVA revealed a significant interaction between the fabrication technique and shading technique (P=.002). Each pair of material subgroups within each combination of fabrication technique and shading technique was found to have a significantly different RTP, except between Ext Vene and Pre Vene (P=.115). Conclusions. Externally shaded translucent zirconia had a greater color change in coffee than the preshaded translucent zirconia, either in monolithic or veneered form. Fabrication technique significantly affected the RTP, and the monolithic zirconia was more translucent than the veneered zirconia.
Citation Count: 15
Fracture analysis of CAD-CAM high-density polymers used for interim implant-supported fixed, cantilevered prostheses
(Mosby-elsevier, 2018) Yilmaz, Burak; Alp, Gulce; Seidt, Jeremy; Johnston, William M.; Vitter, Roger; McGlumphy, Edwin A.
Statement of problem. The load-to-fracture performance of computer-assisted design and computer-assisted manufacturing (CAD-CAM) high-density polymer (HDP) materials in cantilevers is unknown. Purpose. The purposes of this in vitro study were to evaluate the load-to-fracture performance of CAD-CAM fabricated HDPs and to compare that with performance of autopolymerized and injection-molded acrylic resins. Material and methods. Specimens from 8 different brands of CAD-CAM HDPs, including Brylic Solid (BS); Brylic Gradient (BG); AnaxCAD Temp EZ (AE); AnaxCAD Temp Plus (AP); Zirkonzahn Temp Basic (Z); GDS Tempo-CAD (GD); Polident (Po); Merz M-PM -Disc (MAT); an autopolymerized acrylic resin, Imident (Cony) and an injection-molded acrylic resin, SR-IvoBase High Impact (Inj) were evaluated for load to-fracture analysis (n=5). CAD-CAM specimens were milled from poly(methyl methacrylate) (PMMA) blocks measuring 7 mm in buccolingual width, 8 mm in occlusocervical thickness, and 30 mm in length. A wax pattern was prepared in the same dimensions used for CAD-CAM specimens, flasked, and boiled out. Autopolymerizing acrylic resin was packed and polymerized in a pressure container for 30 minutes. An identical wax pattern was flasked and boiled out, and premeasured capsules were injected (SR-IvoBase) and polymerized under hydraulic pressure for 35 minutes for the injection-molded PMMA. Specimens were thermocycled 5000 times (5 degrees C to 55 degrees C) and fixed to a universal testing machine to receive static loads on the 10-mm cantilever, vertically at a 1 mm/min crosshead speed until fracture occurred. Maximum load-to-fracture values were recorded. ANOVA was used to analyze the maximum force values. Significant differences among materials were analyzed by using the Ryan-Einot-Gabriel-Welsch multiple range test (alpha=.05). Results. Statistically significant differences were found among load-to-fracture values of different HDPs (P<.001). GD and Po materials had significantly higher load-to-fracture values than other materials (P<.001), and no statistically significant differences were found between GD and Po. The lowest load-to-fracture values were observed for autopolymerized and BG materials, which were significantly lower than those of GD, Po, AE, AP, Z, MAT, Inj, and BS. The load-to-fracture value of autopolymerized acrylic resin was not significantly different from that of BG CAD-CAM polymer. Conclusions. GD and Po CAD-CAM materials had the highest load-to-fracture values. AE, AP, Z, MAT, and BS CAD-CAM polymers and injection-molded acrylic resin had similar load-to-fracture values, which were higher than those of BG and autopolymerized acrylic resin. Autopolymerized acrylic resin load-to-fracture value was similar to that of BG CAD-CAM polymer, which is colored in a gradient pattern.
Citation Count: 94
Optical properties and surface roughness of prepolymerized poly(methyl methacrylate) denture base materials
(Mosby-elsevier, 2019) Alp, Gulce; Johnston, William M.; Yilmaz, Burak
Statement of problem. Studies of the color stability, relative translucency, and surface roughness of newly introduced computer-assisted design and computer-assisted manufacturing (CAD-CAM) prepolymerized poly(methyl methacrylate) (PMMA) denture base materials are lacking. Purpose. The purpose of this in vitro study was to evaluate the color stability, relative translucency, and surface roughness of conventional and different prepolymerized CAD-CAM PMMA denture base materials after coffee thermocycling (CTC). Material and methods. Six disk-shaped specimens (10x2 mm) were prepared from 3 different brands of prepolymerized CAD-CAM PMMA and a conventional heat-polymerized PMMA denture base material (N=24). Specimens were polished conventionally in 2 stages. The specimens were subjected to 5000 coffee thermocycles. The surface roughness (R-a) of each specimen was measured 3 times before and after CTC, using a contact profilometer, and the mean roughness (R-a) values were calculated. The color coordinates of the specimens were determined by using a noncontact spectroradiometer, and color differences and relative translucency parameter (RTP) values were calculated by using CIEDE2000 color difference and RTPCIEDE2000 formulas. ANOVA was used to analyze surface roughness values, CIEDE2000 color differences, and RTP values (alpha=.05). Result. CTC did not change the color of the tested materials. However, with regard to relative translucency, 2-way ANOVA revealed a significant interaction between the material and CTC (P=.011). Also, although CTC increased the surface roughness of all tested materials (P=.031), R-a values were lower than the plaque accumulation threshold of R-a =0.2 mu m. Conclusion. Mean color changes in all materials were clinically imperceptible after 5000 coffee thermocycles. One tested material had significantly lower relative translucency than other materials before and after CTC. The surface roughness values of all tested denture base materials were below the plaque accumulation threshold.
Citation Count: 4
Screw stability of CAD-CAM titanium and zirconia abutments on different implants: An in vitro study
(Wiley, 2021) Yilmaz, Burak; Cakmak, Gulce; Batak, Burcu; Johnston, William M.
Background Limited information is available regarding the removal torque values (RTVs) of screws of different abutment materials when used with different implants. Purpose To evaluate the effect of implant type and abutment material (zirconia; Zir and titanium; Ti) on the RTVs of abutment screws after cyclic loading. Materials and methods Internal conical connection implants (CC, OsseoSpeed TX) and modified internal conical connection implants (MCC, OsseoSpeed EV) (n = 10) were clamped in resin dies. Zir and Ti (N = 20) custom abutments were tightened to implants (20 Ncm for CC and 25 Ncm for MCC) as specified by their manufacturers. The abutments were cyclically loaded by using a sequentially increased loading protocol; 2-million cycles under 100 N, 3-million cycles under 200 N, and 2-million cycles under 300 N loads with 2 Hz. After 7 million cycles, RTVs (Ncm) were measured by using a torque gauge. The data were analyzed with ANOVA by using the restricted maximum likelihood estimation method. Tukey-Kramer adjustment was used for any significant interaction of implant-abutment pairs (alpha = 0.05). Results Two CC implants, 1 with Ti and 1 with Zir abutment, fractured during cyclic loading (under 300 N loads within the 6th and 7th million cycles) and discarded for statistical analysis. Only implant type had a significant effect on RTVs (p <0.001). Screws of Ti abutments on MCC implants had significantly higher RTVs than the screws of Ti (p = 0.003) and Zir (p = 0.005) abutments on CC implants. Conclusions Implant type affected the RTVs, however, the RTVs were higher than the initial torque values for all groups. Screws of Ti abutments on implant, which required greater initial torque values had higher RTVs than the screws of Ti and Zir abutments on the implant that required smaller initial torque values. RTVs were similar for Zir and Ti abutment screws within each implant type.
Citation Count: 12
Surface roughness of high-performance polymers used for fixed implant-supported prostheses
(Mosby-elsevier, 2021) Batak, Burcu; Cakmak, Gulce; Johnston, William M.; Yilmaz, Burak
Statement of problem. High-performance polymers have been recommended by their manufacturers as a framework material for implant-supported fixed prostheses. However, little is known about the surface roughness of high-performance polymers in different compositions and whether they require layering with a composite resin or acrylic resin on the tissue surface. Purpose: The purpose of this in vitro study was to evaluate the surface roughness of different computer-aided design and computer-aided manufacture (CAD-CAM) high-performance polymers and the effect of polishing on their surface roughness. Material and methods: Seventy high-performance polymer specimens (n=10) for 4 different polyetheretherketone (PEEK) brands (BRE, CP, ZZ, J), 1 polyetherketoneketone (PEKK) (PK), and 2 different fiber-reinforced composite resin (FRC) materials (T, TR) were milled from 7x8x30-mm CAD-CAM blocks. The surface roughness (Ra) of each specimen was measured on the same surfaces after milling (baseline) and after polishing by using a contact profilometer. Two-way repeated measures ANOVA (MIXED procedure) and the Bonferroni corrected t test (alpha=.05) were used to analyze the surface roughness data. Results: No significant differences were found among high-performance polymers when the baseline surface roughness measurements of the materials were compared (P>.05). All materials (BRE, PK, CP, T, TR, ZZ), except for a PEEK material (J) (P<.05), had no significant differences in their surface roughness before and after polishing. After polishing, the surface roughness of the J PEEK material was higher than that of CP, PK, T, and ZZ (P<.05). Conclusions: The surface roughness of high-performance polymers in different compositions after milling was similar. Polishing increased the surface roughness of only one PEEK (J) material. All surface roughness values were above the clinical acceptability threshold of 0.2 mu m.