Effect of sintering speed, aging processes, and different surface treatments on the optical and surface properties of monolithic zirconia restorations.

STATEMENT OF PROBLEM: Advances in dentistry have led to more esthetic and biocompatible restorative materials such as translucent zirconia and to faster and more accurate manufacturing methods. How changes in the surface and optical properties of translucent zirconia affect the esthetics and durability of these restorations under different conditions and manufacturing processes is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the sintering speed, aging process, and different surface treatments on the translucency and surface structure of monolithic zirconia restorations. MATERIAL AND METHODS: Prepared typodont teeth were scanned, and 40 three-unit fixed partial dentures (FPDs) and 40 disk specimens were designed and prepared from monolithic zirconia blanks. The specimens were divided into traditional or speed sintering groups (20 FPDs and 20 disks each); half of each group (10 FPDs and 10 disks) was polished with a handpiece at 10 000 rpm, and the other half was glazed. Half of the specimens were thermocycled with 3500 cycles in 5 °C and 55 °C water baths, and the remaining half were not thermocycled. Translucency was measured with a spectrophotometer. Surface free energy was calculated in mNm with a contact angle device; surface roughness was measured in nm with an atomic force microscope. Translucency data were analyzed by the Kruskal-Wallis and Mann-Whitney tests, while surface free energy and surface roughness data were analyzed by 3-way ANOVA (α=.05). RESULTS: The highest transmittance was in the speed sintered, polished, nonthermocycled group, and the lowest transmittance was in the speed sintered, polished, thermocycled group (P=.029). The transmittance of the traditionally sintered, polished, nonthermocycled group was significantly higher than that in all the speed sintered, glazed groups; the traditionally sintered, glazed groups; and the traditionally sintered, polished, thermocycled group (P=.029). The transmittance of the traditionally sintered, polished, thermocycled group was significantly higher than that of all traditionally sintered, glazed groups (P=.029). The mean surface free energy in the traditionally sintered groups was higher than that in the speed sintered groups (P=.002); also, it was higher in the glazed groups than in the polished groups (P<.001). The aging process decreased surface free energy (P=.023). The mean surface roughness in the speed sintered groups was significantly lower than that in the traditionally sintered groups (P=.004). No significant difference in surface roughness was found between the polished and glazed groups and between the 2 variables of the aging process (P>.05). CONCLUSIONS: Speed sintering and polishing may decrease the surface free energy and increase the translucency of the monolithic zirconia restoration. Also, speed sintering creates a smoother surface. Aging had a more significant effect on decreasing the surface free energy of the specimens and could make the least translucent restorations.

Effect of Sintering Speed and Polishing or Glazing on the Failure Load of Monolithic Zirconia Fixed Partial Dentures.

PURPOSE: To evaluate the effect of sintering speed and polishing or glazing on the failure load (FL) of monolithic zirconia fixed partial dentures (FPDs). MATERIALS AND METHODS: A total of 40 three-unit FPDs extending from the mandibular first premolar to the first molar were evaluated. The prepared typodont teeth were scanned, and the prostheses were designed. Afterwards, the prostheses were milled from monolithic zirconia blanks. The samples were divided into classic and speed sintering groups (n = 20 each). Half of the samples in each group (n = 10) were polished with an electric handpiece according to the manufacturer's instructions, and the other half (n = 10) were glazed. All of the samples were thermocycled for 3,500 cycles between 5ºC and 55ºC in water baths. The FL was calculated in Newtons with the three-point bending test. RESULTS: The mean ± SD FL values were as follows: classic sintering/polished group = 2,026.5 ± 172.8 N; classic sintering/glazed group = 1,917.58 ± 174.45 N; speed sintering/polished group = 1,787.58 ± 145.81 N; and speed sintering/glazed group = 1,719.6 ± 143.9 N. There was a significant difference in the mean FL between the two sintering methods (P < .001), with the classic sintering group exhibiting the highest FL. CONCLUSION: Classic sintering of the monolithic zirconia FPDs led to the maximum amount of FL and strength.

Determination of strain around distal implants as abutments for partial and fixed implant-supported prostheses with posterior cantilever.

This study aimed to compare strain around implants used as abutments for removable partial dentures with wrought wires and fixed partial dentures with ball attachments and fixed dentures with posterior cantilever. An edentulous mandibular model was constructed using epoxy resin with four parallel implants in the area between the two mental foramina. Four strain gauges were attached to the buccal, lingual, mesial, and distal aspects of each implant. One fixed prosthesis with cantilever and two removable partial dentures were considered as prosthetic treatments. A vertical 500-N force was applied with 10-N intervals. The maximum strain in the fixed prosthesis was higher than that of the partial removable denture; in the removable denture with a wrought wire arm, it was higher than that in the denture with a ball attachment (P < 0.001). The lowest rate of strain was recorded on the mesial aspect (P < 0.05). However, the highest rate of strain was recorded on the lingual and distal aspects of the removable denture with a wrought wire in the buccal aspect and the removable prosthesis with the ball attachment on the buccal and lingual aspects (P < 0.05). Finally, despite minor differences in the maximum strain rate in each implant position, the differences were not statistically significant (P > 0.05). Partial removable denture with a ball attachment decreased strain more than that by the removable portal denture with a wrought wire arm. The worst type of prosthesis in terms of the overall strain rate was the fixed prosthesis with cantilever.

Comparing the Dimensional Accuracy of Casts Obtained from Two Types of Silicone Impression Materials in Different Impression Techniques and Frequent Times of Cast Preparation.

INTRODUCTION: The dimensional accuracy of casts is essential in the quality of fixed prosthesis treatment, whereby the impression method is a very crucial factor affecting it. The aim of this in vitro study is to compare the dimensional accuracy of casts resulting from two types of silicone impression materials in different impression techniques and frequent times of cast preparation. MATERIALS AND METHODS: A metal model was made from two prepared abutments, and 10 casts were prepared from each material technique (n = 40). The impressions were made by condensation and addition silicone (one-stage and two-stage impressions). The casts were made from same impressions 1 h, 24 h, and 14 days. The diameter, height, and the distance between two dies were recorded. Data were analyzed by repeated measure ANOVA (P value <0.05). RESULTS: The dimensional accuracy of all four materials techniques of impression (diameter, height, and the distance between dies) was the same in different times of impression. Dimensional accuracy of the die diameter and distance between dies in one-stage (Speedex) condensation silicon and one-stage (Panasil) addition silicone did not differ significantly, and their one-stage method developed more accurate casts compared to the two-stage method of the same impression material. The height of the casts prepared from the one-stage method through Speedex and Panasil did not differ significantly from the two-stage method of the same impression material. CONCLUSION: One-stage condensation silicone and one-stage addition silicone material techniques offered the maximum dimensional accuracy in the obtained casts. The time of impression did not have any significant effect in the accuracy of any of the four impression material techniques.

Effect of laser-microtexturing on bone and soft tissue attachments to dental implants: A systematic review and meta-analysis.

Background. It is critical to understand laser-microtextured implant collars' influence on peri-implant pocket depths and marginal bone levels, especially in crucial areas. The present review investigated the peri-implant marginal bone loss (MBL) and pocket depths and failure rates of dental implants with laser-microtextured collars. Methods. An electronic search was run in the PubMed and Embase databases until September 15, 2019. Randomized and prospective clinical studies comparing peri-implant MBL and pocket depths and failure rates between implants with laser-microtextured and machined collar surfaces were included. Five studies (two cohort studies and three RCTs) were included in the meta-analysis after the inclusion and exclusion criteria and qualitative assessments were applied. The risk ratio of osseointegrated implant failure and mean differences in peri-implant MBL and pocket depths were calculated using the Comprehensive Meta-Analysis (CMA) software. Results. Implants with laser-microtextured collars exhibited significantly better marginal bone level scores (P < 0.001; MD: 0.54; 95% CI: 0.489‒0.592) and a significant reduction in peri-implant probing depths than implants with machined collars (P < 0.001; MD: 1.01; 95% CI: 0.90‒1.13). The assessed studies showed that 17 out of 516 implants failed (3.29%), comprising nine implants with machined (3.62%) and eight implants with laser-microtextured collars (2.98%). However, no significant differences were detected in the implant neck surface characterization (P = 0.695; RR: 1.205; 95% CI: 0.472‒3.076). Conclusion. This study suggests that laser-microtexturing of implant collar significantly affected the peri-implant MBL and probing depths. Although no significant differences were noted in implant failure rates between implants with laser-microtextured and machined collar surfaces, the peri-implant MBL and probing depths with laser-microtextured collars were significantly lower than the machined collars.

Effect of connector size and design on the fracture resistance of monolithic zirconia fixed dental prosthesis.

Background. Designing a high strength all-ceramic fixed partial denture with favorable esthetics can be challenging for clinicians; this study aimed to evaluate the effect of connector size and design on the fracture resistance of monolithic zirconia fixed dental prostheses. Methods. Two groups of twenty 3-unit monolithic zirconia (Sirona inCoris TZI, Sirona Dental Systems GmbH) bridges, extending from the mandibular first premolar to the first molar with different connector sizes (9 mm2 and 12 mm2), were divided into two subgroups with different connector designs (round and sharp). The specimens were subjected to the three-point bending test to obtain the fracture-bearing load. The results were reported using descriptive statistics (mean ± standard deviation). Mann-Whitney U test was used to compare the fracture load in two types of designs for each connector size and two connector size types for each connector design. The significance level was considered at P<0.05. Results. The minimum failure load was related to the group with a 9-mm2 connector size and a sharp embrasure design (1054.4±133.89 N), and the highest mean value belonged to the group with 12-mm2 connector size and rounded embrasure design (1599.8±167.09 N). Mann-Whitney U test indicated a significant difference between the mean failure load of the rounded and sharp embrasure designs in the 9-mm2 connector size (P =0.007). However, the difference was insignificant in the 12-mm2 connector size (P =0.075). Conclusion. Sharp embrasure design is not recommended for high-stress areas with restricted occlusogingival height. A 9-mm2 connector size for 3-unit monolithic zirconia fixed dental prosthesis (FDP), which is recommended by the manufacturer, should be used more cautiously.

Double-Layer Surface Modification of Polyamide Denture Base Material by Functionalized Sol-Gel Based Silica for Adhesion Improvement.

PURPOSE: Limited surface treatments have been proposed to improve the bond strength between autopolymerizing resin and polyamide denture base materials. Still, the bond strength of autopolymerizing resins to nylon polymer is not strong enough to repair the fractured denture effectively. This study aimed to introduce a novel method to improve the adhesion of autopolymerizing resin to polyamide polymer by a double layer deposition of sol-gel silica and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (AE-APTMS). MATERIALS AND METHODS: The silica sol was synthesized by acid-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) as silica precursors. Polyamide specimens were dipped in TEOS-derived sol (TS group, n = 28), and exposed to ultraviolet (UV) light under O2 flow for 30 minutes. UV-treated specimens were immersed in AE-APTMS solution and left for 24 hours at room temperature. The other specimens were either immersed in AE-APTMS solution (AP group, n = 28) or left untreated (NT group, n = 28). Surface characterization was investigated by fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Two autopolymerizing resins (subgroups G and T, n = 14) were bonded to the specimens, thermocycled, and then tested for shear bond strength with a universal testing machine. Data were analyzed with one-way ANOVA followed by Tukey's HSD (α = 0.05). RESULTS: FTIR spectra of treated surfaces confirmed the chemical modification and appearance of functional groups on the polymer. One-way ANOVA revealed significant differences in shear bond strength among the study groups. Tukey's HSD showed that TST and TSG groups had significantly higher shear bond strength than control groups (p = 0.001 and p < 0.001, respectively). Moreover, bond strength values of APT were statistically significant compared to controls (p = 0.017). CONCLUSION: Amino functionalized TEOS-derived silica coating is a simple and cost-effective method for improving the bond strength between the autopolymerizing resin and polyamide denture base. CLINICAL IMPLICATIONS: Amino-functionalized silica coating could represent a more applicable and convenient option for improving the repair strength of autopolymerizing resin to polyamide polymer.

Evaluation of strain in mandibular denture-supporting area in three different occlusal schemes during jaw movements.

Background. Various occlusal schemes have been introduced over the years to enhance the stability, comfort, beauty and function of complete denture, of which lingualized, bilateral balanced and monoplane occlusions are the most recommended. The aim of this study was to compare the strain in mandibular denture-supporting structures in three different occlusal schemes. Methods. Two mandibular and maxillary models were simulated using epoxy resin, and strain gauges were embedded on each side of the mandible in mental foramen, buccal shelf and distolingual area. Strain values were measured in three occlusal schemes at centric occlusion protrusive and lateral movements. Data were analyzed with one-way and three-way ANOVA, followed by post-hoc Tukey tests. The significant level was set at 0.05. Results. The mean strain in denture-supporting area was lower in monoplane occlusion than the two other occlusal schemes, and the mean of values in the buccal shelf was higher than that of mental foramen and distolingual area. In all the three occlusal schemes, the mean strain values on the working side were higher than those on the non-working side during eccentric movements. Conclusion. Monoplane occlusal scheme imposed lower strain on denture-supporting area, with the buccal shelf being the primary strain-bearing area to tolerate more pressure than the rest of the denture-supporting areas. In terms of strain distribu-tion scheme, in all the three occlusal schemes, the working side received more strain than the non-working side during eccen-tric movements.

The effect of resin cement type and cleaning method on the shear bond strength of resin cements for recementing restorations.

PURPOSE: This laboratory study assessed the effect of different dentin cleaning procedures on shear bond strength of resin cements for recementing prosthesis. MATERIALS AND METHODS: 4 × 4 flat surface was prepared on the labial surface of 52 maxillary central incisors. Metal frames (4 × 4 × 1.5 mm) were cast with nickel-chromium alloy. All specimens were randomly divided into 2 groups to be cemented with either Panavia F2.0 (P) or RelyX Ultimate (U) cement. The initial shear bond strength was recorded by Universal Testing Machine at a crosshead speed of 0.5 mm/min. Debonded specimens were randomly allocated into 2 subgroups (n = 13) according to the dentin cleaning procedures for recementation. The residual cement on bonded dentin surfaces was eliminated with either pumice slurry (p) or tungsten carbide bur (c). The restorations were rebonded with the same cement and were subjected to shear test. Data failed the normality test (P < .05), thus were analyzed with Mann Whitney U-test, Wilcoxon signed rank test, and two-way ANOVA after logarithmic transformation (α = .05). RESULTS: The initial shear bond strength of group P was significantly higher than group U (P = .001). Pc and Uc groups presented higher bond strength after recementation compared to the initial bond strength. However, it was significant only in Pc group (P = .034). CONCLUSION: The specimens recemented with Panavia F2.0 provided higher bond strength than RelyX Ultimate cement. Moreover, a tungsten carbide bur was a more efficient method in removing the residual resin cement and increased the bond strength of Panavia F2.0 cement after recementation.

Effect of Zirconia Dental Implant Surfaces on Bone Integration: A Systematic Review and Meta-Analysis.

Background. The information available about osseointegration and the bone to implant interaction of zirconia implants with various surface modifications is still far from sufficient. Objective. The purpose of this systematic review and meta-analysis was to evaluate and compare zirconia dental implants with different surface topographies, with a focus on bone to implant contact and removal torque. Methods. The systematic review of the extracted publications was performed to compare the bone to implant contact (BIC) with removal torque (RT) values of titanium dental implants and machined and surfaced modified zirconia implants. Results. A total of fifteen articles on BIC and RT values were included in the quantitative analysis. No significant difference in the BIC values was observed between titanium and machined zirconia implants (p = 0.373; 95% CI: -0.166 to 0.443). However, a significantly better BIC values were observed for acid etched zirconia implants compared with those of titanium implants (p = 0.032; 95% CI: 0.068 to 1.461). Unmodified zirconia implants showed favorable BIC values compared to modified-surface zirconia implants (p = 0.021; 95% CI: -0.973 to -0.080). Conclusion. Acid etched zirconia implants may serve as a possible substitute for successful osseointegration.

Effect of surface treatment methods on the shear bond strength of auto-polymerized resin to thermoplastic denture base polymer.

PURPOSE: Polyamide polymers do not provide sufficient bond strength to auto-polymerized resins for repairing fractured denture or replacing dislodged denture teeth. Limited treatment methods have been developed to improve the bond strength between auto-polymerized reline resins and polyamide denture base materials. The objective of the present study was to evaluate the effect of surface modification by acetic acid on surface characteristics and bond strength of reline resin to polyamide denture base. MATERIALS AND METHODS: 84 polyamide specimens were divided into three surface treatment groups (n=28): control (N), silica-coated (S), and acid-treated (A). Two different auto-polymerized reline resins GC and Triplex resins were bonded to the samples (subgroups T and G, respectively, n=14). The specimens were subjected to shear bond strength test after they were stored in distilled water for 1 week and thermo-cycled for 5000 cycles. Data were analyzed with independent t-test, two-way analysis of variance (ANOVA), and Tukey's post hoc multiple comparison test (α=.05). RESULTS: The bond strength values of A and S were significantly higher than those of N (P<.001 for both). However, statistically significant difference was not observed between group A and group S. According to the independent Student's t-test, the shear bond strength values of AT were significantly higher than those of AG (P<.001). CONCLUSION: The surface treatment of polyamide denture base materials with acetic acid may be an efficient and cost-effective method for increasing the shear bond strength to auto-polymerized reline resin.

Evaluation of Implant Collar Surfaces for Marginal Bone Loss: A Systematic Review and Meta-Analysis.

Background. It is important to understand the influence of different collar designs on peri-implant marginal bone loss, especially in the critical area. Objectives. The purpose of the present systematic review and meta-analysis was to compare dental implants with different collar surfaces, evaluating marginal bone loss and survival rates of implants. Methods. Eligibility criteria included clinical human studies, randomized controlled trials, and prospective and retrospective studies, which evaluated dental implants with different collar surface in the same study. Results. Twelve articles were included, with a total of 492 machined, 319 rough-surfaced, and 352 rough-surfaced microthreaded neck implants. There was less marginal bone loss at implants with rough-surfaced and rough-surfaced microthreaded neck than at machined-neck implants (difference in means: 0.321, 95% CI: 0.149 to 0.493; p < 0.01). Conclusion. Rough and rough-surfaced microthreaded implants are considered a predictable treatment for preserving early marginal bone loss.

Effect of dentin surface roughness on the shear bond strength of resin bonded restorations.

PURPOSE: This study aimed to investigate whether dentin surface preparation with diamond rotary instruments of different grit sizes affects the shear bond strength of resin-bonded restorations. MATERIALS AND METHODS: The buccal enamel of 60 maxillary central incisors was removed with a low speed diamond saw and wet ground with silicon carbide papers. The polished surfaces of the teeth were prepared with four groups of rotary diamond burs with super-coarse (SC), coarse (C), medium (M), and fine (F) grit sizes. Following surface preparation, 60 restorations were casted with nickel-chromium alloy and bonded with Panavia cement. To assess the shear bond strength, the samples were mounted on a universal testing machine and an axial load was applied along the cement-restoration interface at the crosshead speed of 0.5 mm/min. The acquired data was analyzed with one way ANOVA and Tukey post hoc test (α=.05). RESULTS: The mean ± SD shear bond strengths (in MPa) of the study groups were 17.75 ± 1.41 for SC, 13.82 ± 1.13 for C, 10.40 ± 1.45 for M, and 7.13 ± 1.18 for F. Statistical analysis revealed the significant difference among the study groups such that the value for group SC was significantly higher than that for group F (P<.001). CONCLUSION: Dentin surface roughness created by diamond burs of different grit sizes considerably influences the shear bond strength of resin bonded restorations.

Components of Adult Class III Malocclusion in an Iranian Population.

BACKGROUND AND AIMS: Class III malocclusions are considered complex and difficult orthodontic problems to diagnose and treat. The purpose of this study was to investigate the morphologic characteristics of the craniofacial complex of adults with Class III malocclusion in an Iranian population. MATERIALS AND METHODS: Lateral cephalometric radiographs of 50 patients with Class III malocclusion (20 males and 30 females; age range of 18-27 years) were selected on the basis of molar relationship, concave profile and an overjet of ≤ 0 mm. The standard values of 19 soft tissue measurements were determined using McNamara, Burstone and Viazis methods. RESULTS: Adults with Class III malocclusion exhibited distinct craniofacial morphologic characteristics manifested by a com-bination of retrusion of maxilla and protrusion of mandible. CONCLUSION: The most prevalent component was mandibular prognathism, normal maxilla and LAFH on the basis of the component analysis.