Comparing the color match of monolithic CAD-CAM dental ceramics with the VITA Classical shade guide.

STATEMENT OF PROBLEM: Matching the shade selected and the final color of a ceramic restoration is challenging, and studies on matching monolithic ceramics to the shade selected are lacking. PURPOSE: The purpose of this in vitro study was to compare the color match of monolithic lithium disilicate (LDS), zirconia-reinforced lithium silicate (ZLS), presintered zirconia-reinforced lithium silicate (PS-ZLS), polymer-infiltrated ceramic network (PICN), and multilayer zirconia with the 3 modes of the VITA Classical shade guide. MATERIAL AND METHODS: This study was performed on 50 rectangular plates (14×12×1 mm) of 5 types of ceramics with A2 shade (n=10). Zirconia specimens were evaluated in 3 locations: incisal, medial, and cervical thirds. The color coordinates of the specimens of all 7 groups were measured on #3 and #8 Ivoclar Natural Die Color material by using a reflective spectrophotometer. The color coordinates of A2 VITA shade were measured in 5 modes: without backing placed in specimen holder, shade tab on the backgrounds #3 and #8, and 1-mm-thick shade tab on the backgrounds #3 and #8. The color difference of each specimen with 3 modes of A2 shade (without backing and on similar backgrounds) was calculated by using the ΔE00 formula, and comparison among groups was performed by using 2-way ANOVA and Tamhane post hoc tests. The comparison of ΔE00 between the values obtained from backgrounds #3 and #8 was performed by using the independent t test (α=.05). RESULTS: In both backgrounds, statistically significant differences were found between the studied groups and VITA shade (P<.001). In most situations, the amount of color difference was lowest for the "shade tab on the backgrounds" mode. On background #3, the highest color difference was related to ZLS (6.48 ±0.23), and the lowest values were observed in the PICN group (1.02 ±0.31). On background #8, the highest color difference was related to ZLS compared with the "without backing" mode (8.62 ±0.27), and the lowest values were reported for ZLS compared with the "shade tab on the backgrounds" mode (1.27 ±0.44). The independent t test showed a statistically significant color difference on the 2 different backgrounds for all situations (P<.001). CONCLUSIONS: Color selection of monolithic ceramics with the VITA Classical shade guide is improved by placing the VITA tabs on a similar background. Background color has a significant effect on the final shade of the monolithic ceramics. Choosing the correct color for LDS, ZLS, and PS-ZLS requires more care than for PICN and zirconia.

Marginal Accuracy of Lithium Disilicate Full-Coverage Single Crowns Made by Direct and Indirect Digital or Conventional Workflows: A Systematic Review and Meta-Analysis.

PURPOSE: Several studies have compared digital intraoral scanners and conventional impressions. The accuracy of these two methods in terms of marginal accuracy of lithium disilicate crowns is not well-established, yet. The purpose of this study was to systematically review available publications on marginal fit of single-unit, full-coverage, tooth-supported lithium disilicate restorations. METHODS: Pubmed, Web of Science, Cochrane, EMBASE, and Scopus were electronically searched along with a manual search. After critical appraisal, data from selected studies were extracted and mean marginal difference with a 95% confidence interval was calculated. Meta-analysis of the collected data was conducted using STATA software. RESULTS: The meta-analysis revealed similar marginal gap values in intraoral scanners with conventional groups (p>0.05) and in intraoral scanners with extraoral canners (p>0.05). CONCLUSION: No significant difference was seen between digital and conventional impressions or intra- and extraoral scanners for marginal accuracy of lithium disilicate crowns.

Marginal adaptation of zirconia complete-coverage fixed dental restorations made from digital scans or conventional impressions: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Intraoral scanners have been increasingly used in recent years. However, the accuracy of digital scans as it affects marginal adaptation is unclear. PURPOSE: The purpose of this systematic review and meta-analysis was to compare the marginal adaptation of single-unit zirconia crowns fabricated with digital scans or with conventional impressions. MATERIAL AND METHODS: The electronic databases PubMed (MEDLINE), Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science (ISI), Scopus, and EMBASE were searched and complemented by a manual search. Risks of bias were assessed by using a modified methodological index for nonrandomized studies (MINORS). Mean ±standard deviation (SD) values of marginal accuracy of studies were extracted for both methods. Mean marginal difference and 95% confidence interval (CI) were calculated to evaluate the marginal accuracy of each method. Pooled data were statistically analyzed by using a random-effect model. RESULTS: Seventeen studies were used to perform the meta-analysis. Subgroup analysis was performed based on intraoral scanners. Standardized mean marginal difference and 95% CI of each subgroup were as follows: Lava: -0.85 µm (95% CI: -1.67, -0.03) (P=.043); CEREC: -1.32 µm (95% CI: -2.06, -0.59) (P<.001); iTero: -0.44 µm (95% CI: -1.35, 0.47) (P=.338); TRIOS: -1.26 µm (95% CI: -2.02, -0.51) (P=.001); unknown scanner: -0.21 µm (95% CI: -1.14, 0.72); all studies: -0.89 µm (95% CI: -1.24, -0.54) (P<.001). CONCLUSIONS: Digital scanning of prepared teeth for single-unit zirconia restorations resulted in better marginal accuracy than conventional techniques using elastomeric impression materials.

Comparison of translucency and opalescence among different dental monolithic ceramics.

STATEMENT OF PROBLEM: Monolithic ceramic restorations designed by computer-aided design and computer-aided manufacturing are increasingly being used by clinicians. With the introduction of new materials, their optical characteristics also need to be investigated. PURPOSE: The purpose of this in vitro study was to compare the translucency and opalescence of lithium disilicate, zirconia-reinforced lithium silicate, presintered zirconia-reinforced lithium silicate, polymer-infiltrated ceramic-network material, and multilayer zirconia. MATERIAL AND METHODS: A total of 50 rectangular plates (14×12×1 mm) of 5 monolithic ceramics were prepared in this in vitro study (n=10). Each zirconia specimen was divided into 3 groups of incisal, middle, and gingival thirds. Each group was then evaluated separately. The color parameters of specimens were measured on 3 backgrounds, white, black, and #3 Ivoclar Natural Die Color material, by using a spectrophotometer. The translucency and opalescence of the specimens were determined by the relevant equations, and between-group comparisons were made. One-way ANOVA and Tamhane post hoc tests were used to compare groups (α=.05). RESULTS: The difference among the groups was significant in translucency (F=137.346, df=6, P<.001), contrast ratio (F=134.148, df=6, P<.001), and opalescence parameters (F=128.028, df=6, P<.001). The 3 zirconia groups (10.87 ±0.54 to 11.88 ±0.26) had a significantly lower translucency than the other groups, and the zirconia-reinforced lithium silicate group (18.14 ±0.74) showed the highest translucency. Zirconia-reinforced lithium silicate (12.36 ±0.42) had the highest opalescence, and the lowest opalescence was found for polymer-infiltrated ceramic-network (5.43 ±0.28) and the incisal third of zirconia (5.45 ±1.06). CONCLUSIONS: The zirconia-reinforced lithium silicate and presintered zirconia-reinforced lithium silicate specimens had the highest translucency and opalescence. The studied multilayer zirconia, which had different cubic phase values from incisal to gingival blank, showed similar translucency over the entire range, and differences among different regions were related to chromatic variables.

Effect of repeated firing on the translucency of CAD-CAM monolithic glass-ceramics.

STATEMENT OF PROBLEM: The effects of multiple firings on the translucency of newly introduced computer-aided design and computer-aided manufacturing (CAD-CAM) glass-ceramics have not been well evaluated. PURPOSE: The purpose of this in vitro study was to assess the changes in the translucency of high-translucency (HT) and low-translucency (LT) lithium disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS) glass-ceramics of 0.6 and 1 mm thickness during crystallization, correction, and glaze firing cycles. MATERIAL AND METHODS: Eighty specimens in 8 groups (n=10) were sectioned and polished to obtain thicknesses of 0.6 and 1 mm. The specimens were then fired in 3 cycles, and the color coordinates were measured by using a spectrophotometer after each cycle. The translucency parameter (TP) and the contrast ratio (CR) were calculated to determine the translucency level. The data were analyzed by using a statistical software program. The TP and CR data after each firing cycle were compared within each group by using repeated-measures ANOVA. Pair-wise comparisons were made by using a multiple paired t test. Comparisons between the 2 thicknesses of different materials were made by using the independent t test (α=.05). RESULTS: Repeated firings significantly increased the translucency of 0.6-mm LT-LDS and decreased the translucency of 0.6-mm HT-ZLS (P<.017). No significant changes were noted in the translucency of specimens of 1-mm thickness after repeated firings. Also, 0.6-mm-thick specimens of all materials had significantly higher translucency than 1-mm-thick specimens (P≤.001). The highest translucency was noted in HT-LDS, followed by HT-ZLS. CONCLUSIONS: Repeated firings significantly affected the translucency of LDS and ZLS CAD-CAM glass-ceramics. The translucency increased with decreasing thickness.

Effect of cleaning methods on retentive values of saliva-contaminated implant-supported zirconia copings.

OBJECTIVE: The aim of this study was to evaluate the effect of different cleaning regimens on retentive strength of saliva-contaminated implant-supported zirconia copings. MATERIAL AND METHODS: Seventy solid titanium abutments with 5.5 mm height (Straumann) were attached to the regular neck implant analogs (Straumann). The abutment-analog complex was mounted vertically in an autopolymerized T-shaped acrylic resin block. Seventy zirconia copings with an occlusal loop were made. The copings were contaminated with fresh human saliva for 1 min (except the control group). Afterward, the specimens were washed with water spray for 15 s and dried for 15 s. The copings were divided into seven groups according to cleaning methods (n = 10). Group 1: no contamination (control group); Group 2: water spray rinsing; Group 3: airborne particle abrasion; Group 4: immersion in 96% isopropanol; Group 5: applying Ivoclean (Ivoclar Vivadent); Group 6: applying 1% sodium hypochlorite; and Group 7: applying Monobond Plus (Ivoclar Vivadent). The copings were luted with a resin luting agent (RelyX Unicem; 3M ESPE). After 5,000 thermal cycles, the retentive values of the restorations were tested using universal testing machine. The dislodging forces were analyzed using one-way analysis of variance and the Tukey's HSD tests (α = 0.05). RESULTS: The copings, which were cleaned with Ivoclean and 96% isopropanol, showed the highest retentive values (204.79 ± 44.49 and 232.65 ± 71.36, respectively). There was a significant difference between the studied groups (F = 2.735; p = .02). Tukey's HSD showed that there was no significant difference between the different cleaning procedures and control group except water rinsing group (p = .14). The lowest retentive value was related to the saliva-contaminated group, which were only cleaned with water rinsing method. CONCLUSION: The retentive values of zirconia-based restorations were adversely affected by saliva contaminations. These restorations can be cleaned by Ivoclean, 96% isopropanol, airborne particle abrasion, 1% sodium hypochlorite, or applying Monobond Plus before luting procedures.

Improvement of in vitro behavior of an Mg alloy using a nanostructured composite bioceramic coating.

Magnesium (Mg) alloys as a new group of biodegradable metal implants are being extensively investigated as a promising selection for biomaterials applications due to their apt mechanical and biological performance. However, as a foremost drawback of Mg alloys, the high degradation in body fluid prevents its clinical applications. In this work, a bioceramic composite coating is developed composed of diopside, bredigite, and fluoridated hydroxyapatite on the AZ91 Mg alloy in order to moderate the degradation rate, while improving its bioactivity, cell compatibility, and mechanical integrity. Microstructural studies were performed using a transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, and energy dispersive spectroscopy (EDS). The degradation properties of samples were carried out under two steps, including electrochemical corrosion test and immersion test in simulated body fluid (SBF). Additionally, compression test was performed to evaluate the mechanical integrity of the specimens. L-929 fibroblast cells were cultured on the samples to determine the cell compatibility of the samples, including the cell viability and attachment. The degradation results suggest that the composite coating decreases the degradation and improves the bioactivity of AZ91 Mg alloy substrate. No considerable deterioration in the compression strength was observed for the coated samples compared to the uncoated sample after 4 weeks immersion. Cytotoxicity test indicated that the coatings improve the cell compatibility of AZ91 alloy for L-929 cells.

The evaluation of prepared microgroove pattern by femtosecond laser on alumina-zirconia nano-composite for endosseous dental implant application.

Ceramic dental materials, especially alumina (20 %vol)-yttrium stabilized tetragonal zirconia poly crystal (A-Y-TZP20), have been considered as alternatives to metals for endosseous dental implant application. For increasing the bone-to-implant contact as well as the speed of bone formation, a new surface modification can be effective. The aim of this study was to design microgroove patterns by femtosecond laser on A-Y-TZP20 nano-composite disks for endosseous dental implant application. The phase composition and the morphology of the A-Y-TZP20 nano-composite samples were characterized using X-ray diffraction and Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy techniques. Statistical analysis was submitted to Kolmogorov-Smirnov test and Student's t test for independent variables, with a 5 % significance level. EDAX analysis revealed a significant decrease in the relative content of contaminants like carbon (p < 0.05) in laser surface-treated group as compared to non surface-treated group. X-ray diffraction did not show any change in the crystalline structure induced by laser processing. It was concluded that the femtosecond laser is a clean and safe method for surface modification of A-Y-TZP20.

Clinical outcomes of zirconia-based implant- and tooth-supported single crowns.

OBJECTIVES: Zirconia-based restorations have been increasingly used on implant and teeth abutments, but the evidence about clinical outcomes of these restorations is limited. The aim of this study was to assess up to 7-year clinical outcomes of implant- and tooth-supported zirconia-based single crowns. MATERIALS AND METHODS: In this retrospective study, 261 patients with 556 single crowns supported by either teeth (324) or implants (232) were examined during 3- to 7-year follow-up (mean observation of 60.70 months for tooth and 59.20 months for implant-supported crowns). California Dental Association (CDA) quality evaluation system was used to evaluate the restorations. Soft tissue status was assessed using plaque and gingival index scores, bleeding on probing, and pocket depth. Patient and professional satisfaction were evaluated by visual analog scale (VAS). RESULTS: The 5-year Kaplan-Meier survival probability was 98.3 and 97.3 for implant- and tooth-supported crowns, respectively. In regard to CDA rating, most of the crowns were ranked as either excellent or acceptable (99.5 %). The recorded failures were replacement of the crown due to porcelain chipping (3), implant failure (1), and teeth extraction (5). Soft tissue parameters were not affected by the restorations compare to control teeth. The VAS was high for both patients and clinicians. CONCLUSIONS: Zirconia-based single crowns on both tooth and implant abutments showed promising clinical performance in this up to 7-year follow-up. CLINICAL RELEVANCE: The zirconia-based single crowns can be used clinically for tooth- and implant-supported restorations.

Comparison of Marginal and Internal Adaptation of CAD/CAM and Conventional Cement Retained Implant-Supported Single Crowns.

PURPOSE: To evaluate the accuracy of marginal and internal adaptation of 2 computer-aided design/computer-aided manufacturing (CAD/CAM) and 2 conventionally made cement retained implant-supported restorations. MATERIALS AND METHODS: An abutment and its corresponding fixture analog (Astra Tech) were inserted in left central incisor area of a maxillary cast. Four types of implant-supported single restorations were fabricated on the abutment (n = 10): e.max CAD (Cerec AC system), zirconia-based (Cercon system), IPS e.max Press, and metal-ceramic restorations. The internal and marginal gaps of the studied groups were measured by replica method and stereomicroscope. Data were subjected to 1-way ANOVA and Scheffe post hoc tests (α = 0.05). RESULTS: Mean internal gaps of Cercon (59.48 ± 16.49 µm) and e.max Press (75.62 ± 26.92 µm) groups were significantly different from e.max CAD (120.29 ± 16.74 µm) group, but there was no significant difference between metal-ceramic restorations (89.65 ± 47.84 µm) and e.max CAD. The marginal gaps of e.max CAD (32.02 ± 10.38 µm) and Cercon restorations (34.26 ± 11.41 µm) were significantly superior from metal ceramics (59.19 ± 17.81 µm) and e.max press (74.99 ± 24.51 µm). CONCLUSION: Within the limitations of this study, it can be concluded that although the marginal and internal gaps of the studied implant-supported restorations were in the clinically acceptable range, single crowns made with CAD/CAM technology provide better marginal fit.

In vivo biocompatibility of Mg implants surface modified by nanostructured merwinite/PEO.

Magnesium (Mg) alloys have been suggested as biodegradable bone implant materials due to their good intrinsic biocompatibility and great mechanical properties. Although magnesium has attractive properties as an orthopedic implant material, its quick degradation and low bioactivity may lead to the loss of mechanical integrity of the implant during the bone healing process. In this paper, we endeavor to surmount the abovementioned defects using the surface coating technique. We have recently coated AZ91 magnesium implants with merwinite (Ca3MgSi2O8) through the coupling of plasma electrolytic oxidation (PEO) and electrophoretic deposition method. In this work, we are specifically focused on the in vivo examinations of the coated implants in comparison with the uncoated one. For the in vivo experiment, the rod samples, including the uncoated and merwinite/PEO coated implants, were imbedded into the greater trochanter of rabbits. The results of the in vivo animal test indicated an improvement in biodegradability including slower implant weight loss, reduction in Mg ion released from the coated implants in the blood plasma, lesser release of hydrogen bubbles and an improvement in biocompatibility including an increase in the amount of bone formation and ultimately a mild bone inflammation after the surgery according to the histological images. In summary, proper surface treatment of magnesium implants such as silicate bioactive ceramics may improve their biocompatibility under physiological conditions to making them suitable and applicable for future clinical applications.

Relationship between subjective halitosis and psychological factors.

OBJECTIVES: Subjective halitosis is a growing concern in the fields of dentistry and psychology. This study was designed to determine the association between subjective halitosis and contributing psychological factors. METHODS: Data for this cross-sectional study were gathered from 4,763 participants who had answered questions on subjective halitosis and psychological factors (depression, anxiety, stress and personality traits) in the study on the epidemiology of psychological, alimentary health and nutrition (SEPAHAN). Binary logistic regression was used for data analysis. RESULT: The mean age of all subjects was 36.58 years; and the majority of subjects were female (55.8%), married (81.2%) and graduates (57.2%). The prevalence of subjective halitosis was 52.8%. The majority of subjects with the complaint of subjective halitosis were married (P<0.001) and young (P=0.07). Participants with subjective halitosis were significantly more anxious [odds ratio (OR)=1.76, 95% confidence interval (95% CI): 1.38-2.24], stressed (OR=1.41, 95% CI: 1.17-1.71) and depressed (OR=1.31, 95% CI: 1.09-1.57). Among personality traits, neuroticism was a risk factor (tertile 1 vs. tertile 2: OR=1.29, 95% CI: 1.09-1.51; and tertile 1 vs. tertile 3: OR=1.74, 95% CI: 1.43-2.13) and conscientiousness was revealed to be a protective factor (tertile 1 vs. tertile 2: OR=0.82, 95% CI: 0.70-0.98; and tertile 1 vs. tertile 3: OR=0.65, 95% CI: 0.53-0.80). CONCLUSION: It seems that psychological factors, such as anxiety, depression and stress, as well as some personality traits, can be considered as risk factors for subjective halitosis. Multidisciplinary efforts by dental and psychological professionals must be considered to address this problem.

Retentive strength of implant-supported base metal copings over short metal abutments using different luting agents and surface treatments.

PURPOSE: To evaluate the effect of surface treatments on retention of implant-supported restorations over short abutments. MATERIALS AND METHODS: One hundred twenty metal copings were made on Straumann solid abutments (3 mm length). The copings were divided into 2 groups: control and air abraded (50 µm Al2O3). The copings were luted using Fleck's, Poly F, Panavia F, and Fuji Plus. In resin cements groups, 2 subgroups were studied base on the application of Alloy Primer (n = 10). After conditioning in saliva and 5000 thermal cycles, retentive strengths of specimens were measured. Data were analyzed by 1-way ANOVA and Tukey honestly significant difference tests (α = 0.05). RESULTS: Panavia F 2.0 combined with Alloy Primer showed the most retentive values. In control and air abraded groups, there was no significant difference between the studied luting agents. Alloy Primer significantly increased the retention of copings luted with Panavia F 2.0. CONCLUSION: Within the limitations of this study, the retentive strength of metal copings over short implant abutments was not improved by airborne-particle abrasion. However, Alloy primer enhanced the retention of metal copings that were luted using Panavia F 2.0.

Effect of surface treatment on the retention of implant-supported zirconia restorations over short abutments.

STATEMENT OF PROBLEM: The retention of cement-retained implant-supported restorations can be affected by the height of the abutments. PURPOSE: The purpose of this study was to evaluate the effects of the surface treatment on the retention of implant-supported zirconia restorations over short abutments. MATERIAL AND METHODS: Eighty solid abutments reduced to 3 mm in height and their corresponding fixture replicas were embedded vertically in autopolymerizing acrylic resin blocks. Eighty zirconia copings (Cercon) with an occlusal loop were fabricated and divided into 2 groups (n=40). One group was airborne-particle abraded with 110 µm aluminium oxide and the other group was treated with silica coating (Rocatec System). Each group was then divided into 4 subgroups (n=10). The subgroups received either no treatment (control) or were treated with silane (Clearfil Porcelain Bond Activator+SE Primer), acid etching followed by silane, or ceramic primer (Clearfil). All copings were luted with a self-adhesive luting agent (Clearfil SA). After 1 week of conditioning in artificial saliva and thermal cycling (5000 cycles, 5°C-55°C), the removal force of the copings were tested with a universal testing machine at a 5 mm/min crosshead speed. The dislodgment force and failure mode were recorded. Two-way ANOVA and the Tukey honestly significant difference and the Fisher exact tests were used for data analysis (α=.05). RESULTS: The highest retentive values were obtained for airborne-particle abrasion--ceramic primer (228.84 N) and silica coating--ceramic primer (230.37 N), which were not significantly different from silica coating alone (216.26 N; P=.95) or a combination of airborne-particle abrasion followed by silanation (211.67 N; P=.87). The failure mode was primarily adhesive and cement principally remained on the copings. CONCLUSIONS: Within the limitations of this study, ceramic primer that contains adhesive phosphate monomer significantly improved the retention of zirconia ceramic restorations. Silicoating as a mechanical treatment provided greater retention for zirconia copings than airborne-particle abrasion when a resin-luting agent was used.

Use of Pindex system in fabrication of the sectional custom tray.

This article describes a new, precise, and simple method for making an impression with an individual tray for a patient with microstomia. In this method, a Pindex system on the handle of the tray was used for attaching two parts of the sectional tray.

Evaluation of interleukin-1α, interleukin-10, tumor necrosis factor-α and transforming growth factor-ß in the serum of patients with pemphigus vulgaris.

UNLABELLED: Pemphigus is an autoimmune blistering disease characterized by a loss of cell adhesion result in acantholysis. Genetic factors and immunologic factors such as cytokines particularly IL-1α, IL-10, TNF-α, and TGF-ß may counterpart to developing of Pemphigus. The aim of this study was to evaluate. The concentration of IL-1α, IL-10, TNF-α, TGF-ß in serum of pemphigus vulgaris (PV) patients and normal individuals. MATERIAL AND METHODS: In this analytic and descriptive study 25 patients with pemphigus vulgaris (in active phase) and 25 healthy per sons were examined. Serum samples of two groups were obtained and the level of IL-1α, IL-10, TNF-α and TGF-ß were measured by ELISA technique. The data were analyzed statistically by independent T test (α = 0/05). RESULTS: All cytokines tested, showed higher concentration in patient's sera comparing to healthy control individuals. The level of IL-1α (p = 0.004), TNF-α (p = 0.008) and TGF-ß (p = 0.009) were statistically different in two experimental groups, There was no significant difference in IL-10 level (p = 0.605). CONCLUSION: Cytokines such as IL-1α, IL-10, TNF-α and TGF-ß probably have a role in pathogenesis of PV. Further comprehensive studies are suggested to confirm these findings.

Retention of implant-supported zirconium oxide ceramic restorations using different luting agents.

OBJECTIVE: The aim of this study was to evaluate the retention value of implant-supported zirconium oxide ceramic copings using different luting agents. METHOD AND MATERIALS: Twenty ITI solid abutments of 5.5 mm height and ITI implant analogs were mounted vertically into autopolymerizing acrylic resin blocks. Ninety zirconium oxide copings (Cercon, Degudent) with a loop on the occlusal portion were made. All samples were airborne particle abraded with 110 µm Al2O3 and luted using different types of luting agents: resin cements (Clearfil SA, Panavia F2.0, Fuji Plus), conventional cements (Fleck's, Poly F, Fuji I), and temporary cements (Temp Bond, GC free eugenol, TempSpan) with a load of 5 Kg. (N = 10) All copings were incubated at 37°C for 24 h and conditioned in artificial saliva for 1 week, and thermal cycled for 5000 cycles 5-55°C with a 30-s dwell time. The dislodging force of the copings along the long axis of the implant-abutment complex was recorded using universal testing machine with 5 mm/min crosshead speed. Data were subjected to Kruskal-Wallis (α = 0.05) and Mann-Whitney tests with Bonferroni step down correction (α = 0.001). RESULTS: There was significant difference between the mean rank retention values of different luting agents (P < 0.001). The resin cements showed the highest retention (Clearfil SA, 203.49 ± 52.86; Fuji Plus, 190.61 ± 48.00; Panavia F 2.0, 172.16 ± 70.76 N). The conventional cements had more retention than the temporary cements and glass ionomer cement (P < 0.001). CONCLUSION: The retention of zircona ceramic restorations, over ITI solid abutments may be influenced by the type of cement. The application of an MDP-containing resin and resin-modified glass ionomer luting agents increase the retentive value of implant-supported zirconium oxide restorations.

Retention of implant-supported overdenture with bar/clip and stud attachment designs.

The degree of retention for overdenture attachments depends on design, location, and alignment of supporting dental implants and the type of attachments. The aim of this study was to evaluate the retention of an implant-supported overdenture with different attachment designs. An overdenture was made on an edentulous mandibular model with 2 ITI implants (4.1 × 10 mm) in the symphyseal region. Five specimens of 8 attachment designs with corresponding abutments and superstructures were used: ITI regular Dolder bar with 1 metal clip, ITI regular Dolder bar with cantilever and 3 metal clips, Hader bar with 1 plastic clip, Hader bar with cantilever and 3 plastic clips, Sphero block abutment with Rhein plastic caps (green, white, and pink), and retentive anchor with ITI elliptical matrix. The attachments' housings were interchangeable and fixed into the overdenture through nut and screw. The overdenture attachments were subjected to 8 consecutive pulls on a universal testing machine with a crosshead speed of 50.8 mm/min in the vertical and posteroanterior directions. Analysis of variance and Duncan tests were used to determine differences between mean retention values (α = .05). The highest average value retention was recorded for the ITI Dolder bar with cantilever and 3 metal clips in both the vertical and posteroanterior directions, respectively (P < .05). The Rhein pink caps had the lowest retention in the posteroanterior direction (P < .05). Retention decreased over the course of consecutive pulls for all attachments in both directions. The type, number, and placement of attachments affect the retention of implant-supported mandibular overdentures.

Lithium metasilicate glass-ceramic fabrication using spark plasma sintering.

Background: The digital dentistry, requires materials with wo opposite properties of machining ability and also enough hardness. The main objective of this experimental study was to investigate the fabrication feasibility of the lithium metasilicate glass-ceramic in partially crystalized stated using the spark plasma sintering (SPS) method. Materials and Methods: In this study, SPS for the first time was used to fabricate primary lithium metasilicate glass-ceramic (LMGC) blocks. The raw materials were mixed and melted and then quenched in water and the resulted frits were grinded. The resulting powder was sintered by SPS at 660, 680, and 700°C. Results: Scanning Electron Microscope (SEM), X-ray diffraction (XRD), and Vicker's microhardness assay were used to evaluate the properties of samples. Statistical comparison of the obtained data was performed by ANOVA, followed by the post hoc test of Duncan. Microstructural studies by SEM and XRD showed that all samples were composed of lithium metasilicate phase in a glassy matrix. With increasing the sintering temperature, the number and size of lithium metasilicate particles increased and higher mechanical properties have been achieved. However, the sintered sample at 700°C has less processing ability than the samples sintered at 660 and 680°C. Conclusion: The optimum sintering temperature for glass frit consolidation was determined by SPS at 680°C.

Effect of a novel rotation coordinating device on registered horizontal condylar guidance of nonarcon semi-adjustable articulators.

Background: Horizontal condylar guidance (HCG) is registered by protrusive interocclusal records but in nonarcon articulators, these records can affect the accuracy. The present study aimed to evaluate the effect of a novel rotation coordinating device (RCD) on condylar guidance setting with protrusive interocclusal records. Materials and Methods: The study was designed as a comparative in-vitro investigation. Stone maxillary and mandibular casts were mounted on a fully adjustable instrument as the patient. Duplicate casts were mounted on an arcon and a nonarcon articulator with corresponding face bow records and in maximum intercuspation relation. Five different condylar guidance inclinations for both sides (20°, 30°, 40°, 50°, and 60°) were set on the fully adjustable instrument and 16 protrusive interocclusal records were established at each setting. HCG was set for arcon, nonarcon articulators, and nonarcon articulators with RCD. Data were analyzed using one-sample t-test to compare with actual HCG and one-way analysis of variance (α =0.05). Results: Mean HCG for studied articulators was 35.40 for arcon, 30.31 for nonarcon without RCD, and 35.61 for nonarcon with RCD which were significantly different from actual HCG (P < 0.05). HCG of the nonarcon with RCD showed no significant difference with arcon articulator (P = 0.71) while both were significantly different from nonarcon without RCD (P < 0.001). Conclusion: "The RCD" compensates the condylar guidance inclination difference between arcon and nonarcon articulators. The device precisely transfers the hinge movement of the upper member of the articulator to the condylar track.