Effect of different surface treatments on surface roughness, phase transformation, and biaxial flexural strength of dental zirconia.

Background. Interfacial failures at the cement‒restoration interface highlights the importance of effective surface treatment with no adverse effect on the zirconia's mechanical properties. This study aimed to determine the effect of different surface treatments on dental graded zirconia's surface roughness and certain mechanical properties. Methods. Forty sintered zirconia specimens were randomly divided into four groups (n=10): control (no surface treatment), sandblasting (SA), grinding with diamond bur (GB), and Er,Cr:YSGG laser (LS). Following surface treatment, the surface roughness and surface topography of the specimens were examined. X-ray diffraction (XRD) was conducted. In addition, the biaxial flexural strengths of specimens were evaluated. The data were analyzed using one-way analysis of variance (ANOVA) and post hoc Tukey tests; the Pearson correlation coefficient was calculated between either volumetric percentage of monoclinic phase or roughness and flexural strength of specimens (α=0.05). Results. The GB group exhibited significantly greater surface roughness compared to the other groups (P < 0.005). The LS and control groups exhibited a significantly lower volumetric percentage of the monoclinic phase (P < 0.001) than the GB and SA treatments. The SA group exhibited significantly higher flexural strength than the control (P = 0.02) and GB groups (P < 0.01). Furthermore, the Weibull analysis for the LS showed higher reliability for the flexural strength than other treatments. Conclusion. Er,Cr:YSGG laser treatment, with the lowest extent of phase transformation and reliable flexural strength, can be a promising choice for surface treatment of zirconia.

Prevalence of Complete Edentulism in Individuals at Least 30 Years Old in Iran since 2000: A Systematic Review.

BACKGROUND: The purpose of this study was to systematically review the literature to investigate the prevalence of complete edentulism in Iran. METHOD: An electronic search was performed using three scientific databases: PubMed, Google Scholar, and Irandoc. Moreover, a hand search was performed on theses in the Dental Faculty of Shahed University. Studies published since 2000 were included if they reported on the prevalence of edentulism in Iran in populations at least 35 years old. Eight articles and seven theses were included in the study. RESULT: The reported prevalence of edentulism in Iran ranges from 3% to 78%. CONCLUSIONS: In this study the reported prevalence has remained stable during the studied period.

Stress distribution of esthetic posts in the restored maxillary central incisor: Three-dimensional finite-element analysis.

BACKGROUND: Glass fiber posts, along with their esthetic properties, may have a better stress distribution than cast posts, Therefore, the aim of the present study was to investigate the effect of glass fiber, casting, titanium, and zirconia posts on stress distribution in maxillary central tooth treated with different amounts of ferrule using finite-element analysis. MATERIALS AND METHODS: In this experimental study, three-dimensional models of maxillary central incisors that have undergone root canal treatment were designed. Then, the models were divided into four groups according to the type of post (Ni-Cr casting, glass fiber, titanium, and zirconia) used. Zirconia monolithic crowns were used in all the four groups. Ferrule heights were repeated at 0 and 2 mm in all models. Models were entered into COMSOL Metaphysics software. Then, the force of 100 N with the angle of 135° on the palatal surface was applied to the longitudinal axis of the tooth, and the stress distribution in the models was investigated. RESULTS: Maximum stress was observed in the middle third of posts. Stress distribution in glass fiber post was better than zirconia and casting posts. Stress accumulation in models with zirconia, titanium, and casting posts was also found in the site between the middle third and coronal third, whereas in models with glass fiber post, stress accumulation was found between the crown and the cemento-enamel junction. In models without ferrule, stress accumulation was observed in one-third of the coronal, especially in glass fiber posts. CONCLUSION: The post material and ferrule height affected stress concentration. The stress in the cervical area of the dentin was more for glass fiber post when compared to other posts. The use of glass fiber post in teeth with no ferrule results in lower stress along the post, but greater stress in the simulated tooth region.

Efficiency of Erbium-Doped Yttrium Aluminum Garnet Laser in Debonding Cemented Glass Fiber Posts: an in vitro Study.

STATEMENT OF THE PROBLEM: The efficacy of erbium-doped yttrium aluminum garnet (Er; YAG) laser on the debonding properties of certain post materials has remained largely unexplored. PURPOSE: This study aimed to investigate the effect of Er; YAG laser irradiation on debonding of cemented glass fiber posts in root canal treated teeth. MATERIALS AND METHOD: In this in vitro study, forty root canal treated mandibular premolar teeth were used in this study. Glass fiber posts were bonded using Panavia F 2.0 cement in the root canal space, and samples were divided into two groups. In the test group, samples were exposed to laser radiation of 7W, 350mJ, frequency of 20Hz and discontinued washing spray. In the control group, samples were left untouched. In each group, samples were sectioned into 1.5mm thick slices from the coronal, middle, and apical thirds of the root (N=120). Tensile bond strengths were evaluated using the push-out test and the failure patterns were evaluated using scanning electron microscopy (SEM). To compare the laser and non-laser groups at each location, independent sample t test was applied, and to compare bond strength between the locations in each group, one-way ANOVA and Tukey's HSD post hoc was applied. RESULTS: A significant difference in tensile strength was observed between the laser-irradiated group and control group; tensile bond strength was much higher in the control group (p<0.001). The highest frequency of fractures was observed at the cement-dentin interface. Given the used parameters, complete debonding was not achieved in the laser-irradiated group. CONCLUSION: Laser radiation reduced the bond strength of glass fiber posts to resin cement without complete debonding.

In vitro evaluation of the accuracy and precision of intraoral and extraoral complete-arch scans.

STATEMENT OF PROBLEM: The accuracy of intraoral and extraoral scanners for different models of edentulousness is unclear. PURPOSE: The purpose of this in vitro evaluation was to determine the accuracy (trueness and precision) of complete-arch scans made by 3 intraoral and 1 extraoral scanners compared with an industrial 3D scanner. MATERIAL AND METHODS: Digital scans were made of a reference cast with 3 intraoral scanners (CEREC Omnicam; Dentsply Sirona, TRIOS 3; 3shape A/S; Carestream CS 3600; Carestream Dental) and an extraoral scanner (Deluxe scanner; Open Technologies). A dental maxilla model was used for tooth preparation for ceramic restorations with a shoulder finishing line. Maxillary right central and lateral incisors and third molar and maxillary left second premolar and first and third molar teeth were removed. One operator scanned the reference cast 10 times with each scanner. All the recorded standard tessellation language (STL) files were imported into an inspection software program and individually overlaid on the STL file for the reference model made by the 3D scanner. The measured distance between the distal point of the maxillary left second molar tooth and the mesial point of the maxillary left first premolar was defined as distance 1; distance 2 was defined as the distance between the mesial point of the maxillary second molar tooth and the distal point of the maxillary right first premolar tooth. The Levene test for homoscedasticity of variances was used to evaluate precision, and a 2-way repeated-measures ANOVA and Bonferroni-corrected Student t tests were used to evaluate trueness (α=.05). RESULTS: A statistically significant difference was found between the Carestream scanner and the other scanners when scanning both mucosa and teeth. The Carestream scanner had the lowest accuracy and highest magnitude mean deviation of all the scanners. CONCLUSIONS: Obtaining an accurate partial-arch impression is still challenging for some intraoral scanners. The Carestream scanner's trueness was outside the acceptable range. However, other scanners tested here appeared to be suitable alternatives to conventional impression techniques.

Comparison of marginal and internal fit of 3-unit zirconia frameworks fabricated with CAD-CAM technology using direct and indirect digital scans.

STATEMENT OF PROBLEM: Accurate marginal and internal fit of dental restorations are essential for their long-term success. The fit of zirconia restorations prepared using digital scan systems has not been fully evaluated. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of 3-unit zirconia frameworks fabricated using direct and indirect digital scans. MATERIAL AND METHODS: In a maxillary model, the left first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses. Conventional impressions were made using stock trays and 2-step putty/wash polyvinyl siloxane material and were scanned using laboratory scanner (Conventional Impression-Laboratory scanner [CIL] group). The impressions were then poured, and the stone casts were scanned (Dental Cast-Laboratory scanner [DCL] group). Digital scans were made using TRIOS (TRIOS Intraoral scanner [TRI] group) and CS3600 (CS3600 Intraoral scanner [CSI] group) scanners (n=10). Zirconia copings were designed and milled from presintered blocks and subsequently sintered. Marginal, mid-axial, axio-occlusal, and mid-occlusal discrepancies were measured using the silicone replica technique with stereomicroscopy at ×50 magnification. The data were analyzed using 1-way ANOVA (α=.01). RESULTS: The ANOVA revealed significant differences among the studied groups in terms of all studied characteristics (P≤.01). Marginal gap was significantly higher in the DCL group (106 ±45 µm) compared with all other groups (P≤.01). However, no significant differences were observed in marginal gap between the TRI (60 ±15 µm) and CSI (55 ±13 µm) groups (P>.01). Internal gap in the mid-occlusal and axio-occlusal regions were significantly higher in the CIL (238 ±92 µm and 227 ±95 µm) and DCL (248 ±71 µm and 216 ±68 µm) groups than those recorded in the TRI (104 ±27 µm and 126 ±31 µm) and CSI (128 ±16 µm and 147 ±28 µm) groups (P≤.01). Internal discrepancies in the mid-axial position were similar between the TRI (70 ±15 µm) and CSI (72 ±23 µm) groups (P>.01), but these values were significantly lower than those recorded in the CIL (88 ±31 µm) and DCL (85 ±30 µm) groups (P≤.01). CONCLUSIONS: Within the limitations of this study, zirconia frameworks in the TRI and CSI groups had lower marginal and internal gaps compared with those in the DCL and CIL groups. Marginal gap in all groups was within a clinically acceptable range.

Effect of Silane Heat Treatment by Laser on the Bond Strength of a Repair Composite to Feldspathic Porcelain.

PURPOSE: Ceramic restoration fracture may occur in the oral cavity. Intraoral repair of fractured porcelain could be advantageous to both patient and dentist. The aim of this study was to evaluate the effect of heat treatment of the silane coupling agent by Er:YAG and CO2 lasers on the microshear bond strength of a repair composite to feldspathic porcelain. MATERIALS AND METHODS: Sixty ceramic blocks were prepared and randomly divided into six groups (n = 10): (i) HF + silane (HS); (ii) silane + CO2 laser (SC); (iii) CO2 laser + silane (CS); (iv) silane + Er:YAG laser (SE); (v) Er:YAG laser + silane (ES); (vi) bur + HF + silane (BuHS). An adhesive resin was applied to the prepared ceramic surfaces and light-cured. Two transparent plastic tubes were placed perpendicularly to each ceramic block. The composite resin was then placed on the treated ceramic surface and light-cured for 40 seconds. The bonded blocks were stored in distilled water at 37°C for 24 hours and subjected to 3000 thermocycles. Microshear bond strength (µSBS) tests were performed using a wire and loop method. Data were analyzed using one-way ANOVA and Duncan's multiple range tests (p ≤ 0.05). RESULTS: The comparison of the mean µSBS values showed no significant differences between the ES and HS groups (p = 0.914). On the other hand, the specimens in these groups exhibited significantly higher bond strengths than those in the other groups (p < 0.01). The mean µSBS of the BuHS group was statistically similar to that of CS and SE groups (p > 0.05). The µSBS for the SC group was significantly lower than that of the other groups (p < 0.01), with the exception of the CS group (p = 0.674). CONCLUSIONS: Treatment with Er:YAG laser prior to silane application can be as effective as HF etching. Heat treatment of silane by CO2 or Er:YAG lasers does not improve the bond strength between feldspathic porcelain and composite resin.

Effects of interimplant distance and cyclic dislodgement on retention of LOCATOR and ball attachments: An in vitro study.

STATEMENT OF PROBLEM: Evaluation of the long-term retentive behavior of overdenture attachments is necessary for successful treatment. Interimplant distance (IID) could affect the retention of these attachments. PURPOSE: The purpose of this in vitro study was to assess the effects of IID and cyclic dislodgement on the retention of LOCATOR and ball attachments. MATERIAL AND METHODS: Ball and LOCATOR attachments were connected to corresponding implant analogs. Metal housings were connected to each attachment. Thirty-six pairs of acrylic resin blocks were fabricated for 3 IIDs (19, 23, and 29 mm) and 2 attachments (n=6). Each pair consisted of 2 attachment assemblies parallel to each other with a specified IID. Overall, 1440 dislodgement cycles were applied by using a universal testing machine, and the maximum dislodging force was recorded after 0, 120, 360, 720, and 1440 cycles. Dislodging force data were analyzed by using repeated-measures 3-way analysis of variance, with the number of cycles as the within-subject factor for each specimen. Bonferroni-corrected Student t tests were used to resolve effects that were statistically significant. Moreover, dislodging force data were fit into an exponential decay model to determine the extent and rate of force decay for each attachment and IID studied. RESULTS: The initial retention of LOCATOR attachments was significantly higher than that of ball attachments with IIDs of 23 and 29 mm, but no significant difference was noted with the 19-mm IID. After 1440 cycles, the retention was statistically similar with that of the 23-mm IID but was significantly higher for ball attachments with IIDs of 19 and 29 mm. CONCLUSIONS: The IID is one of the factors that affect the retention of ball and LOCATOR attachments. The mean retention of both attachments was sufficient for all 3 IIDs at insertion and after 1440 cycles.

The effect of luting agent on the fracture resistance of root canal treated teeth restored with casting post.

INTRODUCTION: The aim of this study was to determine the effect of different luting agents on fracture resistance of endodontically treated teeth restored with casting post. MATERIALS AND METHODS: In this experimental study, forty extracted human maxillary central incisors teeth with the mean length of 23mm were randomly assigned in to four groups. All the studied teeth were caries free without any crack. After root canal treatment, the specimens were stored in 100% relative humidity at 37°C for 72h, and were decoronated 2mm above cementoenamel junction. The teeth in group1, 2, 3, and 4 received casting post and core and they were cemented with Zinc phosphate, Panavia F, Fuji Glass Ionomer, and Rely X, respectively. All teeth received 1.5 mm shoulder finishing line and 0.5mm bevel. Samples were then restored with complete coverage crowns and were loaded with an Instron universal testing machine. The cross-head speed was 0/02 cm/min and specimens were loaded with load values (Newton) computed at a speed of 1000 point/min, until the fracture happened. Loads were applied with 135 degree at middle lingual surfaces of the samples. Fracture loads were recorded. Data were analyzed by the one-way ANOVA test. RESULTS: There was no significant difference between the fracture resistances of four test groups. CONCLUSION: According to the results of this in vitro study, the type of luting cement had no influence on the fracture resistance of teeth.