Purpose To assess the effect of tooth preparation design on fracture resistance of zirconia‐reinforced lithium silicate overlays. Materials and Methods This study evaluated 50 human maxillary first molars with no caries, restorations or anatomical defects. The teeth were randomly divided into five groups (n = 10/group) based on preparation design for the fabrication of overlay restorations: (O) anatomical occlusal reduction, (OS) anatomical occlusal reduction with round shoulder preparation, (OG) anatomical occlusal reduction with a central groove, (OSG) anatomical occlusal reduction with round shoulder preparation and central groove, and (C) no preparation of tooth (control group). All restorations were fabricated using zirconia‐reinforced lithium silicate (Vita Suprinity). The specimens underwent thermomechanical fatigue loading in a masticatory simulator (1.2 million cycles at 98 N). Fracture resistance was measured using a universal testing machine. The mode of failure was determined as well. Data were analyzed using one‐way ANOVA followed by Tukey's post‐hoc test, paired t‐test and Fisher's exact test (α = 0.05). Results Group O showed significantly higher fracture resistance than groups OG and OSG (p = 0.002 and p = 0.001, respectively). The fracture resistance of group OS was significantly higher than that of group OSG (p = 0.008). The fracture resistance of the control group was significantly higher than that of OG and OSG (p = 0.001) and had no significant difference with other groups. Conclusions Group O (anatomical occlusal reduction alone), which had the most conservative preparation design, yielded the highest fracture resistance.

PurposeAnalyzing different patterns of maxillary sinus septa in cone-beam computed tomography (CBCT) images and predicting maxillary sinus membrane perforations.Materials and MethodsIn this cross-sectional study, CBCT images of 222 patients ranging from 20 to 81 years old were evaluated. One hundred fifty-two patients (93 females and 59 males) who had maxillary sinus septa in axial views were included in this study. Cross-sectional images were used to determine classifications of sinus septa and the risk of membrane perforation using a method modified from Al-Faraje et al. Variables of sex, age, and dental status were considered. Chi-squared and Kruskal-Wallis tests were used for data analysis (P<.05).ResultsIn this study, 265 maxillary sinus septal patterns were found. The mean age of the patients was 44.1±14.7 years old. The Class I and VII-div II patterns had the greatest and least prevalence, respectively. Furthermore, there was a significant relationship between the location of septa and the frequency of membrane perforation risk (P<.05). In this study, the relationship of different patterns of septa with dental status did not differ significantly (P>0.05).ConclusionA higher prevalence of moderate risk of membrane perforation in the molar region relative to the premolar region was observed. Furthermore, maxillary sinus septa occur most frequently in the molar region, demonstrating the importance of paying attention to this region during sinus lift surgery. This study did not show any relationship between tooth loss and the presence of septa.

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Background: Detorquing value is an important factor in the amount of preload stresses during abutment screw fastening. This study evaluated the percentage of detorque values in two‐piece machined titanium and premachined cast abutments in small diameter implants. Materials and Methods: Three groups of five samples were evaluated. Group 1 (G1), machined titanium abutments, group 2 (G2), premachined cast straight abutments that cast with gold‐palladium, and group 3 (G3), premachined angled cast abutments that cast with the same alloy, were angled before casting. Each abutment was torque to 24 Ncm according to the manufacturer's instructions and detorqued five times. The means of detorquing and torquing values in all groups were recorded. The mean of detorque in each group as a percentage of the toque value was calculated. The data for all groups were compared and calculated using analysis of variance (ANOVA) and t‐test. Results: Mean detorque values in G1, G2, and G3 were 88.1 ± 1.69, 93.1 ± 2.68, and 80.9 ± 4.95%, respectively. The ANOVA showed significant differences in mean of applied detorque (p < .001) and torque (p = .06) tightening among different groups. G2 had significantly greater detorque values (p < .05). No significant differences were found between G1 and G2. Surprisingly, abutment screw fracture occurred in three samples of G3. Conclusions: G3 showed significant percentage torque reduction (p < .05) and exhibited abutment screw fracture during evaluation. G2 presented the lowest torque reduction. Screw fracture occurred only in G3.

Objective: Following the advent of strong adhesive bonding, the conservative tooth preparation designs without a retentive form gained increasing popularity. This study aimed to evaluate the marginal adaptation of zirconia-reinforced lithium silicate (ZLS) overlays with different preparation designs. Materials and methods: Forty sound human maxillary first molars were collected and divided into four groups (n = 10) according to their preparation design for the fabrication of ZLS overlays: (O) anatomical occlusal reduction, (OS) anatomical occlusal reduction with rounded shoulder, (OG) anatomical occlusal reduction with a central groove, and (OSG) anatomical occlusal reduction with rounded shoulder and central groove. A video measuring machine (VMM) was used to measure the marginal gap. Statistical analysis was carried out using one-way ANOVA followed by paired t test and Tukey's test (α = .05). Results: The gap size was significantly different between the groups both before (P = .004) and after (P = .008) cementation, and it was significantly smaller in group O than group OSG (P = .002 before and P = .004 after cementation). Marginal gap increased in all groups following cementation (P < .001). Conclusions: Group O showed comparable marginal adaptation with groups OS and OG while group OSG with the most complex design showed the lowest marginal adaptation for ZLS overlays. Clinical Significance: According to the results of this in vitro study, it may be stated that for defect-free teeth requiring occlusal restoration, the occlusal surface preparation alone would suffice to achieve optimal marginal adaptation, and retentive and more invasive preparation designs are not required.

Aim:The purpose of this study was to evaluate the effect of grinding, over-glazing, regrinding, and polishing on flexural strength of monolithic zirconia. Materials and methods:In this in vitro study, 50 bar-shaped zirconia specimens were fabricated and divided into 5 groups (n = 10) of no-treatment control group (C), grinding (G), grinding + glazing (GGl), grinding + glazing + grinding (GGlG), and grinding + glazing + grinding + polishing (GGlGP). A universal testing machine was used to measure the flexural strength. Data were analyzed using the Tukey's HSD test and ANOVA (p < 0.05). Results: There were significant differences between group C and other groups (p < 0.001). Group C showed the highest mean flexural strength among all groups. There was also a significant difference between groups GGlG and GGlGP (p = 0.031), and the latter group showed higher mean flexural strength. There was no significant difference between other groups (p > 0.001). Conclusion:Regrinding does not have a significant effect on flexural strength of monolithic zirconia compared with grinding. Glazing slightly decreased the flexural strength of ground zirconia surfaces, which was not statistically significant. Polishing improved the flexural strength of ground zirconia surfaces; however, their mean flexural strength was significantly lower than that of the control group. Clinical significance: Grinding may lead to significant strength reduction and decrease the durability of zirconia restorations. Therefore, polishing of ground surfaces is suggested while glazing has an adverse effect on the strength.

Objective. Considering the increasing number of adults seeking orthodontic treatment, and the possible need for bracket bonding to monolithic zirconia restorations, knowledge about the preferred type of bracket (metal/ceramic) and the most efficient surface treatment is imperative to achieve acceptable shear bond strength (SBS). This study aimed to assess the effect of different surface treatments and orthodontic bracket types on SBS of high-translucent zirconia. Materials and Methods. Totally, 248 disc-shaped zirconia specimens were assigned to two groups for bonding to metal and ceramic brackets. Each group was divided into four subgroups (n = 31) for the following surface treatments: no surface treatment (control group), airborne-particle abrasion (APA), tribochemical silica coating with CoJet, and CO2 laser irradiation. The mean surface roughness (Ra value) was measured. The SBS was measured after bracket bonding and thermocycling. Data were analyzed by two-way ANOVA, Tukey, Kruskal–Wallis, Mann–Whitney, and Fisher exact tests, and Bonferroni correction ( α = 0. 05 ). Results. The mean Ra value was significantly different among the surface treatment subgroups ( P < 0.001 ). The APA and CoJet subgroups were not significantly different regarding Ra ( P = 0.754 ). All other pairwise comparisons yielded significant differences ( P < 0.001 ). Bracket type, surface treatment, and their interaction significantly affected the SBS ( P < 0.001 ). Ceramic brackets bonded to zirconia surfaces treated with CoJet yielded the maximum SBS while ceramic brackets bonded to control and lased surfaces resulted in minimum SBS. No significant difference was noted in the SBS of different surface treatment groups when metal brackets were used ( P > 0.05 ). Conclusions. The use of ceramic brackets and CoJet surface treatment would be the most appropriate combination to achieve optimal bonding to high-translucent zirconia restorations.