Evaluation of the optical and surface properties of monolithic CAD-CAM ceramics after simulated tooth-brushing.

STATEMENT OF PROBLEM: Monolithic computer-aided design and computer-aided manufacturing (CAD-CAM) ceramics have various microstructures, but studies on their optical and surface properties after tooth-brushing are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the changes in the color, gloss, surface roughness, and surface topography of different monolithic CAD-CAM ceramics after simulated tooth-brushing and compare the tested parameters of the different ceramics. MATERIAL AND METHODS: Ninety specimens were prepared with a 1.5-mm thickness from 9 different materials: monolithic zirconia (ZR), lithium disilicate ceramics (precrystallized and crystallized), zirconia reinforced lithium silicate ceramics (precrystallized and crystallized), interpenetrating network ceramic, leucite reinforced ceramic, feldspathic ceramic, and interpenetrating network nanoceramics (n=10). After mechanical polishing, the color parameters, gloss, and surface roughness values of each specimen were measured. Then, the specimens were subjected to 50 000 tooth-brushing cycles. After the brushing simulation, the color change (ΔE00) values were calculated, and the gloss and surface roughness values of the specimens were measured. Data were statistically analyzed with 2-way repeated measures of ANOVA and Bonferroni multiple comparison tests (α=.05). RESULTS: The brushing simulation and ceramic type affected the gloss and surface roughness values of the tested ceramics (P<.001). The surface roughness values of the ceramics increased after 50 000 cycles of simulated brushing. The surface gloss of the ZR group significantly increased after 50 000 cycles of simulated brushing (P<.001). Only the ceramic type affected the color change values (P<.001). The color change value (ΔE00) of ZR was the highest among the tested materials, exceeding the perceptibility threshold after 50 000 cycles, while the ΔE00 of the other materials was lower. CONCLUSIONS: Simulated tooth-brushing affected the surface gloss and surface roughness of the tested materials. The ceramic type affected the surface gloss, surface roughness, and color change values. Except for the monolithic zirconia, the color change values were below the perceptibility threshold (0.8) in the experimental groups.

Comparison between direct and indirect "digital image" dental visual shade matching considering the effect of clinical experience and gender.

INTRODUCTION: Shade matching is an essential procedure to obtain an esthetic prosthesis. The Direct Visual Shade Matching (DSM) method using shade guides is the most used method by dentists. However, The Indirect Visual Digital Shade Matching (ISM) method based on digital imaging is concerned to be reliable and useful in determining shade matching in dental practice. Several factors such as method, clinical experience, and gender can affect the success of shade matching. AIM OF THE STUDY: This study aimed to compare these two methods and evaluate the effect of experience and gender on the results. MATERIALS AND METHODS: Three volunteers' maxillary central incisor teeth were evaluated using (DSM) and (ISM) methods by 87 examiners (42 males, 45 females). These examiners were further divided into three groups based on their clinical experience: Undergraduate Preclinical Dental Students (UPDS) with 31 examiners, Undergraduate Clinical Dental Students (UCDS) with 34 examiners, and Postgraduate Dental Students from the Department of Prosthodontics (PDS) with 22 examiners. The spectrophotometer device results of three teeth were considered as a reference for shade matching. Statistical analyses of the data were performed using Kruskal-Wallis, Mann-Whitney U, and Chi-square tests. RESULTS: No significant difference was found between indirect and direct methods according to Perfect Matches (p > 0.05). However, according to Shade Matching Deviation Score (SMDS) values a statistically significant difference was found between the two methods where the best result was obtained with the ISM method (p < 0.05). There was a significant difference between the PDS group and the other two groups in terms of clinical experience (p < 0.05). There was no significant difference between gender groups (p > 0.05). CONCLUSION: Digital images, captured under standardized lighting conditions, may serve as a reliable alternative method for direct shade matching. The (ISM) method requires a camera, related accessories, and computer skills. However, as these tools are commonly available nowadays, the focus for practitioners should be on effectively learning and applying these tools to achieve the best results. While clinical experience plays a significant role in the shade matching process, gender does not appear to have a substantial influence. CLINICAL SIGNIFICANCE: This study found no significant differences between the (DSM) and (ISM) methods, leaving the clinical relevance of this method open to debate. However, the ISM method yielded superior responses. Despite requiring specialized tools, conditions, and training, the widespread use of cameras and computers in modern clinics makes the necessary equipment and software readily available. This method enhances clinician-technician communication, potentially improving prosthesis esthetics and patient satisfaction, especially for less experienced clinicians or those with color deficiencies. Further research is crucial to determine its clinical significance.

Effect of 2-ethylhexyl salicylate incorporation on the color stability of different maxillofacial silicone elastomers after outdoor weathering.

STATEMENT OF PROBLEM: Silicone elastomers are considered the most favorable materials for the prosthetic rehabilitation of facial defects. However, color change, because of the ultraviolet (UV) light, limits the life of facial prostheses. The addition of 2-ethylhexyl salicylate as a UV-protective may improve the color stability of different maxillofacial silicone elastomers. PURPOSE: The purpose of this in vitro study was to evaluate the effect of 2-ethylhexyl salicylate on the color stability of 3 different maxillofacial silicone elastomers after outdoor weathering. MATERIAL AND METHODS: Three different ratios of UV-protective 2-ethylhexyl salicylate (UV-ES) were incorporated into 3 different types of maxillofacial silicones (M511, TechSil S25, and A-2000) in 1%, 2%, and 5% ratios, and a control group for each silicone was generated. A total of 120 Ø15×2-mm disk-shaped specimens were prepared from 3 different silicone elastomers according to the 4 different UV-ES ratio groups (n=10). The specimens were subjected to outdoor weathering in Ankara, Türkiye, from June 2021 to June 2022. Color differences in the specimens were measured at 3 months and 1 year of weathering. The color change values (ΔE) were statistically analyzed by using repeated measures of 3-way ANOVA. The differences were compared by using the Tukey honest significant difference test (α=.05). RESULTS: No interaction was found among the factors (silicone type, UV-ES ratio, and aging) (P=.29). The highest ΔE values were found in TechSil S-25 (P<.001), while the results were not significantly different between the M511 and A2000 groups (P=.324) The higher ΔE values were found in the control group when compared with those of the UV-ES added group of each material, while the results were not significantly different among the 1%, 2%, and 5% groups (P>.05). CONCLUSIONS: Incorporating 2-ethylhexyl salicylate into the tested maxillofacial silicones reduced color change.

The effects of cement thickness and cement shade on the final color of lithium disilicate crowns.

PURPOSE: The aim of this study is to evaluate the effect of resin cement color, cement thickness, and thermocycling on the final color of monolithic lithium disilicate crowns. MATERIALS AND METHODS: A total of ninety prepared central incisors of typodont teeth were restored with lithium disilicate crowns which have different cement thicknesses (40 µm, 80 µm, and 120 µm) and cement shades (clear, yellow, and white). Color parameters of restorations were measured with a spectrophotometer in three different steps 1) before cementing 2) after cementing and 3) after thermocycling with 10000 cycles. Color differences (ΔE00) were calculated with the CIEDE2000 formula and evaluated according to perceptibility (0.8) and acceptability (1.8) thresholds. The ΔE00 data were analyzed by using two-way ANOVA before and after thermocycling (α = .05). RESULTS: There was no interaction between the cement shade and the cement thickness factors. After cementation, the mean ΔE00 was under the perceptibility threshold in the group of 40 µm cement thickness and clear cement while it was between the perceptibility and acceptability thresholds (0.8 < ΔE00 < 1.8) for all other groups. After thermocycling, the ΔE00 values were between the perceptibility and acceptability thresholds for all experimental groups. Although there were no significant differences among the groups, thermocycling increased the color difference values. CONCLUSION: The cementation of restorations with clear, yellow, and white resin cements resulted in color differences with uncemented restorations except for the group cemented with clear cement in 40 µm cement thickness. All study groups revealed perceptible color change after thermocycling.

Effect of ultraviolet-protective 2-ethylhexyl salicylate incorporation on the mechanical properties of different maxillofacial silicone elastomers.

STATEMENT OF PROBLEM: Whether the incorporation of ultraviolet-protective 2-ethylhexyl salicylate (UV-ES) affects the mechanical properties of different maxillofacial silicone elastomers, limiting the service life of facial prostheses, is unclear. PURPOSE: The purpose of this in vitro study was to examine the mechanical properties of different maxillofacial silicone elastomers incorporating different ratios of UV-ES. MATERIAL AND METHODS: Three different ratios of UV-ES were incorporated into 3 different types of maxillofacial silicones (M511, TechSil-25, and A-2000), and the mechanical properties of the silicones were investigated. Silicone pigments were added to each silicone type to mimic skin color. Dumbbell-shaped specimens were fabricated for tensile strength, percentage elongation, and hardness measurements, and trouser-shaped specimens for tear strength measurement. A total of 240 specimens were prepared. UV-ES in 3 different ratios (1%, 2%, and 5%) and a control group of each silicone type were generated (n=10). The effects of maxillofacial silicone type and ultraviolet protective ratios on hardness, tensile strength, percentage elongation, and tear strength were examined by factorial ANOVA (α=.05). RESULTS: The Shore-A hardness in the control and UV-ES added groups was not significantly different in M511 material (P>.05), and a statistically significant decrease was observed in all ratios in TechSil S-25 and A-2000 silicones (P<.05). After adding 1%, 2%, and 5% UV protective into the silicones, the tensile strength and elongation of TechSil S-25 silicone material decreased significantly (P<.05), while these mechanical properties of M511 and A-2000 were not affected by UV-ES addition (P>.05). Tensile and tear strength values of the silicone elastomers were highest for TechSil S-25. CONCLUSIONS: The mechanical properties of M511 and A-2000 silicone elastomers were not adversely affected by the addition of 1%, 2%, or 5% UV-ES.

Effect of ultraviolet protective agents on maxillofacial silicone elastomer, part 2: Mechanical properties after artificial aging.

STATEMENT OF PROBLEM: The addition of ultraviolet (UV) protectives may affect the materials' mechanical properties, which can limit the service life of facial prostheses. PURPOSE: The purpose of this in vitro study was to investigate the effect of UV protectives on the mechanical properties of maxillofacial silicones after artificial aging. MATERIAL AND METHODS: Six color groups (unpigmented, white, yellow, red, blue, and mixed) of addition-type maxillofacial silicone were prepared. Four UV protectives, benzophenone-3 (UV-BP), ethylhexyl methoxycinnamate (UV-EM), titanium dioxide (UV-TD), and ethylhexyl salicylate (UV-ES), at 0.5% and 1% concentrations by weight were incorporated into the silicone before polymerization. The specimens were subjected to accelerated aging in a weathering chamber for 300 and 600 hours and to thermocycling. The tensile strength and percentage elongation, tear strength, and hardness of maxillofacial silicones were evaluated. Data were analyzed by using 4-way ANOVA. The differences were compared by the Tukey honestly significant difference test (α=.05). RESULTS: Tensile strength decreased after 300 and 600 hours of UV aging in 0.5% and 1% UV-BP protective-added groups and increased in thermocycled groups (P<.05). Aging conditions generally showed no effect on the tensile strength of UV-EM, UV-TD, and UV-ES added groups (P>.05). Aging generated a decrease in percentage elongation values compared with nonaged specimens of groups (P<.05). The addition of UV protectives generally did not significantly affect the tear strength of specimens compared with control in the aged groups (P>.05). The hardness of UV protective-added groups increased when compared with that of nonaged groups after 300 and 600 hours of UV aging (P<.05). Also, thermally aged groups showed increased hardness than nonaged groups (P<.05). CONCLUSIONS: The protective UV-BP addition caused decreased tensile strength, percentage elongation, and tear strength in both concentrations. The UV-EM and UV-ES provided increases in tensile strength and percentage elongation of the silicone in the 0.5% concentration. The addition of UV-BP, UV-EM, and UV-ES did not make significant differences; however, UV-TD significantly decreased the hardness values of the silicone.

Effect of ultraviolet protective agents on maxillofacial silicone elastomer, part 1: Color stability after artificial aging.

STATEMENT OF PROBLEM: Silicone elastomers have been widely used for rehabilitation of facial defects for more than 50 years. However, color change is the most common problem limiting the service life of facial prostheses. Whether the addition of ultraviolet protectives may enhance color stability of these materials is unclear. PURPOSE: The purpose of this in vitro study was to investigate the effect of ultraviolet protectives on the color stability of maxillofacial silicones after artificial aging. MATERIAL AND METHODS: Six color groups (unpigmented, white, yellow, red, blue, and mixed) of addition-type maxillofacial silicone were prepared. Four ultraviolet protectives benzophenone-3, ethylhexyl methoxycinnamate, titanium dioxide, and ethylhexyl salicylate at 0.5% and 1% concentrations by weight were incorporated into the silicone before polymerization. The specimens were artificially aged in an accelerated weathering chamber for 300 and 600 hours and in a thermocycling device. The color change values (E) of the maxillofacial silicones were evaluated. Data were statistically analyzed by using 4-way ANOVA. The differences were compared by the Tukey honestly significant difference test (α=.05). RESULTS: Benzophenone-3 and ethylhexyl methoxycinnamate protectives did not reduce the ΔE values, and the 1% titanium dioxide groups exhibited lower ΔE values than the 0.5% titanium dioxide groups. Ethylhexyl salicylate protective generally reduced the ΔE values significantly in all color and aging groups when compared with the control groups (P<.05). In all control and ultraviolet protective groups, the highest ΔE values were seen with the red color in 300 and 600 hours of aging. Generally, no significant difference (P>.05) was seen in the ΔE values, which were clinically acceptable among the thermocycled color groups. After 600 hours of accelerated aging, the ΔE values were found to be higher than the values of 300-hour aging. CONCLUSIONS: Ethylhexyl salicylate protective incorporated into maxillofacial silicones may improve color stability.

Visual and instrumental color evaluation of computerized color matching system for color reproduction of maxillofacial prostheses.

STATEMENT OF PROBLEM: A commercially available computerized color matching system (e-Skin) has been introduced for maxillofacial prostheses. However, studies that have tested its ability to produce an acceptable color match for skin color are lacking. PURPOSE: The purpose of this clinical study was to determine the color match acceptability of light and dark skin silicone replicas fabricated with the use of the computerized color matching system. MATERIAL AND METHODS: Fifteen participants with light skin and 15 participants with dark skin were recruited through personal invitation. These 30 participants (aged around 20 years) voluntarily consented to forearm skin color measurements with a spectrophotometer and a spectrocolorimeter integrated in a computerized color matching system. Silicone skin replicas for each participant were produced from the color formulations provided by the online calculator tool of the system according to the manufacturers' recommendations. The color difference between initial skin color measurements with the spectrophotometer and skin replica color measurements with the spectrophotometer for all participants was calculated by using both the CIELab (ΔE∗ab) and CIEDE2000 (ΔE00) color difference formulas. To compare the instrumental and visual evaluation of color match, 3 observers (a maxillofacial prosthodontist, a prosthodontist, and a postgraduate student) visually evaluated and rated the color match of each silicone replica on a 5-point scale. Statistical analyses were performed by using the Student t, Mann Whitney U, and chi-square tests (α=.05). RESULTS: No significant differences were detected between the light and dark skin groups in terms of the ΔE∗ab and ΔE00 values obtained between the first skin color measurements and their silicone replica color measurements (P=.573, P=.338, respectively). However, a significant difference was found between light and dark skin groups for the ΔL and Δa values obtained from the same measurements (P=.031, P=.017, respectively). L∗, a∗, and b∗ values of light skin were significantly higher than those of their silicone replications (P=.008, P=.033, P=.046, respectively). Color match ratings of observers did not significantly differ when comparing the ratings of light skin replicas to ratings of dark skin replicas. CONCLUSIONS: The e-Skin system provided skin replicas that matched the skin color within clinically acceptable thresholds and with ratings of at least "good" by experienced dental clinicians.

The stability of implants and microbiological effects following photobiomodulation therapy with one-stage placement: A randomized, controlled, single-blinded, and split-mouth clinical study.

BACKGROUND: Studies have reported a positive effect on bone healing and the elimination of microorganisms placed on the titanium implants, while others have not confirmed the positive photobiomodulation therapy (PBMT) effects on bone regeneration and bone structure around the implants. PURPOSE: The aim of the present study was to address the following questions: Does PBMT improve implant stability and affect microbiota around dental implants in the early stage of osseointegration? MATERIALS AND METHODS: This study was designed as randomized-controlled prospective, split mouth, single-blinded clinical trial. Implants were randomly divided into two groups and implants placed in the test group were treated with Gallium-aluminum-arsenide (GaAlAs) diode laser with PBMT immediately after surgery and for 15 days (n = 47). In the control group, implants were not irradiated(n = 46). The primary stability of the implants was measured by the Resonance frequency analysis (RFA) after insertion and the secondary stability values were recorded at 30th, 60th, and 90th days after surgery as implant stability quotient (ISQ). The hand-held RFA was held perpendicular to the jaw line as indicated by the manufacturer for buccal-lingual (BL), mesial-distal (MD), and lingual-buccal (LB) measurement and different measurements were analyzed as separately. RESULTS: Significantly higher magnetic RFA values were achieved on the 90th day in all measurement sides for both groups. ISQ levels in groups at baseline and the day-30, 60, and 90. ISQ readings were not statistically significant between test and control groups for each time point. A statistically significant increase in ISQ reading for BL, MD, and LB dimensions in both groups was noted from baseline to the day-90 (P < .05). CONCLUSION: It was concluded that PBMT did not have a clinically significant effect on implant stabilization, especially in terms of ISQ values at early alveolar bone healing term. Clinical trial number is NCT04495335.

Effects of glazing methods on the optical and surface properties of silicate ceramics.

PURPOSE: This study aims to evaluate the effect of different glazing methods on translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), surface roughness (Ra) and topography of the silicate ceramics. METHODS: Seventy specimens (10×10×1mm) were fabricated from lithium disilicate (IPS e.max CAD, abbreviated as E) and zirconia-reinforced lithium silicate (Vita Suprinity, abbreviated as VS) ceramics and divided into 7 subgroups (n=10) according to the polishing and glazing procedures: (1) mechanical polishing before-crystallization (m-BC), (2) mechanical polishing after-crystallization (m-AC), (3) glaze powder/liquid after-crystallization (pl-AC), (4) glaze-paste before-crystallization (gp-BC), (5) glaze-paste after-crystallization (gp-AC), (6) glaze-spray before-crystallization (gs-BC), (7) glaze-spray after-crystallization (gs-AC). Color and Ra measurements were performed. CIEL*a*b* and CIEXYZ parameters were recorded and TP, CR, and OP values were calculated. Data were analyzed using two-way ANOVA and Tukey HSD tests (α=0.05). RESULTS: In E groups, the highest Ra value was found in gs-AC (1.66±0.14µm) while the lowest value was found in pl-AC (0.68±0.08µm). In VS groups, the highest Ra value was found in gp-BC (1.64±0.25µm) while the lowest value was found in m-AC (0.77±0.06µm) (p<0.05). The mean TP value of E (17.62±0.73) was found to be higher than VS (15.37±1.16). The CR (0.72±0.030) and OP (12.06±0.74) values of VS were found higher than CR (0.57±0.02) and OP (6.72±0.40) values of E. CONCLUSIONS: Zirconia-reinforced silicate ceramics have higher opalescence and lower translucency values than lithium disilicate ceramics. Increase in surface roughness reduces translucency. Glaze powder/liquid after-crystallization is the most effective way to reduce surface roughness of lithium disilicate ceramics while that is mechanical polishing after-crystallization for zirconia-reinforced silicate ceramics.

Effects of accelerated artificial aging on the translucency and color stability of monolithic ceramics with different surface treatments.

STATEMENT OF PROBLEM: Different surface finishing procedures can be applied to monolithic restorations. However, information is limited regarding the long-term performance of these procedures. PURPOSE: The purpose of this in vitro study was to evaluate the effect of aging on the translucency and color stability of monolithic ceramics with different surface finishing procedures. MATERIAL AND METHODS: Disk-shaped (14×1.5 mm) specimens of monolithic zirconia (Zirkonzahn Prettau [ZZ]) and lithium disilicate glass-ceramic (IPS e.max Press [IPS]) were fabricated. The specimens were divided into 3 subgroups according to the surface treatments (n=9, G: glazing, R: rubber polishing system, and P: rubber polishing system followed by polishing paste). Color measurements were made by using a spectrophotometer before and after an ultraviolet aging process. L*, a*, and b* parameters were recorded. ΔE and translucency parameter (TP) values were calculated. One specimen from each subgroup was examined by scanning electron microscopy (×30 000). The data were statistically analyzed using the Mann-Whitney U, Kruskal-Wallis, and post hoc tests (α=.05). RESULTS: ΔE values of group ZZ (5.03) exceeded the clinically acceptable level (3.5); however, the color change was not clinically perceptible for IPS (0.41). The ΔE value of the subgroup P was found to be higher than that of the others for ZZ (P<.001). The ΔE value was not affected by the surface treatment for IPS. Group IPS showed significantly higher translucency than the ZZ group (P<.001). TP values were not affected by the surface treatment in either material and decreased after aging. However, changes in the TP values were too slight to be clinically perceptible. CONCLUSIONS: Lithium disilicate ceramic was found to be more esthetic than monolithic zirconia ceramic in terms of color stability and translucency.

In vitro evaluation of color and translucency reproduction of maxillofacial prostheses using a computerized system.

PURPOSE: Accurate color matching of maxillofacial prostheses to skin is important for esthetics. A computerized color matching system specific to human skin has recently been developed. The purpose of this study was to evaluate the accuracy in color and translucency matching of the computerized color matching system across different skin colors. MATERIALS AND METHODS: The silicone was colored to simulate 28 different skin colors (n=5) to serve as "target skin colors". Using a spectrocolorometer (e-skin), color codes were determined for "replicate skin color" fabrication. CIELAB Delta-E between target skin color-replicate skin color pairs and translucency parameter were calculated. CIELAB Delta-E values were compared with one-way ANOVA and Tukey multiple-comparison. The agreement between L*, a*, b* and translucency parameter of target skin colors and replicate skin color were calculated by a two-way mixed average measures intraclass correlation coefficient. Translucency parameter of target skin color-replicate skin color pairs were compared with Paired t-test (α=.05). RESULTS: The mean CIELAB Delta-E value was 3.83 and significant differences were found among colors. The intraclass correlation coefficient showed excellent reliability for L*, a*, b* and good reliability for translucency parameter (P<.001). The mean translucency parameter of replicate skin colors was significantly higher than that of translucency parameter. CONCLUSION: The computerized color matching system specific to human skin was found to be reliable in terms of color and translucency between target skin colors and replicate skin color.

Fracture strength of CAD/CAM fabricated lithium disilicate and resin nano ceramic restorations used for endodontically treated teeth.

The purpose of the present study was to evaluate and compare the fracture strength and failure modes of endocrowns, zirconia post, and fiber post supported restorations and predict the clinical outcomes of six different prostheses used for endodontically treated teeth. Sixty (n=10) maxillary central incisors were restored with zirconia post/resin-nano-ceramic crown (ZrRNC), fiber post/resinnano-ceramic crown (FbRNC), zirconia post/lithium disilicate ceramic crown (ZrLDS), fiber post/lithium disilicate ceramic crown (FbLDS), resin-nano-ceramic endocrown (EndoRNC), and lithium disilicate ceramic endocrown (EndoLDS). Fracture strength test was performed. Fracture loads and modes were determined. The EndoLDS group had the highest fracture strength, followed by ZrRNC and EndoRNC group. However the results were not significantly different among groups (p>0.05). The failure modes of the restorations changed according to the restorative materials. Endodontically treated anterior teeth might be restored with endocrowns as well as other post-core restorations, however tooth fracture failures should be considered that affect reliability of endocrowns.

Effect of surface treatments on the biaxial flexural strength, phase transformation, and surface roughness of bilayered porcelain/zirconia dental ceramics.

STATEMENT OF PROBLEM: Veneered zirconia restorations are widely used in prosthetic applications. However, these restorations often fail because of chipping of the veneer porcelain. Surface treatments of zirconia core materials may affect the connection between the 2 layers. PURPOSE: The purpose of this study was to evaluate the effect of surface treatments on the biaxial flexural strength, phase transformation, and mean surface roughness of different bilayered porcelain/zirconia ceramics. MATERIAL AND METHODS: Forty disk-shaped specimens were obtained for each material (Kavo and Noritake) and divided into 4 (n=10) groups (control, airborne-particle abraded, ground, and ground and airborne-particle abraded). Airborne-particle abrasion was performed with 110-µm Al2O3 particles for 15 seconds and at 400 kPa. Diamond rotary instruments with 100-µm grain size were used for grinding. The monoclinic phase transformation and surface roughness of the specimens were measured. Then, the specimens were veneered and subjected to a biaxial flexural strength test to calculate the Weibull moduli (m values) and the stresses occurring at the layers, outer surfaces of the bilayer, and interfaces of the layers. RESULTS: The Kavo airborne-particle abraded group showed higher strength values in both layers (P<.05) than those of all experimental groups. The Kavo airborne-particle abraded group showed the lowest m values at the core and veneer layers. According to the phase analysis, significantly higher Xm values were found in the ground and airborne-particle abraded groups for both materials (P<.05). In both materials, except in the airborne-particle abraded groups, the relative monoclinic phases showed no difference (P<.05). CONCLUSION: Surface treatments affected the phase transformation, surface roughness, and biaxial flexural strength of Kavo and Noritake zirconia ceramics differently. Surface treatments increased the relative monoclinic phase content and average surface roughness.

Biaxial flexural strength and phase transformation of Ce-TZP/Al2O3 and Y-TZP core materials after thermocycling and mechanical loading.

PURPOSE: The purpose of the present study was to evaluate the effect of thermocycling and mechanical loading on the biaxial flexural strength and the phase transformation of one Ce-TZP/Al2O3 and two Y-TZP core materials. MATERIALS AND METHODS: Thirty disc-shaped specimens were obtained from each material. The specimens were randomly divided into three groups (control, thermocycled, and mechanically loaded). Thermocycling was subjected in distilled water for 10000 cycles. Mechanical loading was subjected with 200 N loads at a frequency of 2 Hz for 100000 times. The mean biaxial flexural strength and phase transformation of the specimens were tested. The Weibull modulus, characteristic strength, 10%, 5% and 1% probabilities of failure were calculated using the biaxial flexural strength data. RESULTS: The characteristic strengths of Ce-TZP/Al2O3 specimens were significantly higher in all groups compared with the other tested materials (P<.001). Statistical results of X-ray diffraction showed that thermocycling and mechanical loading did not affect the monoclinic phase content of the materials. According to Raman spectroscopy results, at the same point and the same material, mechanical loading significantly affected the phase fraction of all materials (P<.05). CONCLUSION: It was concluded that thermocycling and mechanical loading did not show negative effect on the mean biaxial strength of the tested materials.

Efficacy of various disinfecting agents on the reduction of bacteria from the surface of silicone and polyether impression materials.

The aim of the present study was to evaluate the effectiveness of different disinfectants on the reduction of two resistant bacteria from the surface of impression materials. Impressions were made of a sterile metal model of the edentulous maxillary arch which had been contaminated with Staphylococcus aureus and Enterecoccus faecalis. The impressions were cultured before and after disinfection with 0.525% sodium hypochlorite, Gludex and Mikrozid spray disinfectant. For each of the three impression materials and the two microorganisms, spray disinfectant was found to be less effective than either sodium hypochlorite or Gludex.