The aim of this study was to determine the values of the retentive forces of the telescopic crowns. At the first step of the study, the samples having different heights and angles were compared in relation to retentive force. At the second step, the samples were subjected to removal procedures having a pre-determined speed, force and number. The obtained retention values were compared. Ninety dies were prepared in order to measure the retention of the conus crowns. The removal tests were performed with the insertion/separation device. The speed of the test device was 100 cm min(-1) providing the placement of the pieces with 5 kgf in 100, 200, 300, 500, 1000, 5000 and 10 000 cycles. The mean of the retention values of the changes of the angles were found to be statistically different (P < 0.01). According to the results of the variant analysis, the differences in the changes of the height were statistically significant (P < 0.01). The differences between the changes of the number of procedures of all groups were statistically significant (P < 0.01). The number of procedures, height and angle interactions were statistically insignificant (P = 0.758). According to the results of this study, the effect of the angle and height factors in terms of retention among the groups were not independent of each other. In equal angles, as the height increased, increased retention measurements were obtained. In more acute angles, the increase in retention was more obvious. It was also found that an accessory device was necessary to maintain retention capabilities after a long-term use.

PURPOSE: The aim of this study was to evaluate the influence of different cleaning regimens on the microshear bond strength (SBS) of three different all-ceramic surfaces after saliva contamination. MATERIAL AND METHODS: Cubic ceramic specimens (3 × 3 × 3 mm(3) ) were prepared from three types of ceramics: zirconium dioxide (Z), leucite-reinforced glass ceramic (E), lithium disilicate glass ceramic (EX; n = 12/subgroup). A total of 144 composite resin cylinders (diameter: 1 mm, height: 3 mm) were prepared. Three human-saliva-contaminated surfaces of ceramic specimens were cleaned with either water spray (WS), with 0.5% sodium hypochlorite solution (HC), or with a cleaning paste (CP). Control surface (C) was not contaminated or cleaned. Composite cylinders were bonded to each surface with a resin luting cement. All specimens were stored at 37°C in deionized water until fracture testing. SBS tests were performed in a universal testing machine (0.5 mm/min), and the results (MPa ± SD) were statistically analyzed (two-way ANOVA, Bonferroni a = 0.05). Fractured surfaces were analyzed to identify the failure types using an optical microscope at 50× magnification. Two representative specimens from all groups were examined with scanning electron microscopy. RESULTS: SBS test results were significantly affected by the saliva cleaning regimens (p = 0.01) and the ceramic types (p = 0.03). The interaction terms between the ceramic type and saliva cleaning regimen were also significant (p < 0.05). There were no significant differences among the SBS values (MPa ± SD) for the Z group (C = 17.5 ± 8.8; WS = 16.0 ± 4.9; HC = 17.6 ± 5.8; CP = 16.6 ± 7.5; p > 0.05). In the EX group, C resulted in significantly higher SBS values (32.6 ± 7.4) than CP (17.4 ± 8.9), WS (15.6 ± 7.3), and HC (14.3 ± 4.5) (p < 0.05); however, C (20.4 ± 7.1) and HC (19.2 ± 7.5) showed higher SBS values than CP (13.8 ± 4.8) and WS (10.9 ± 5.7) in the E group. Some cohesive failures within the luting resin were observed in the E and EX groups, whereas only adhesive failures were seen in zirconia groups for all surface treatments. CONCLUSIONS: Different ceramic surface cleaning regimens after saliva contamination of the zirconium dioxide revealed SBS similar to the control group, whereas all surface cleaning regimens tested significantly decreased the bond strength values in the lithium disilicate glass ceramic. The leucitereinforced glass-ceramic group benefited from 0.5% sodium hypochlorite solution cleaning with increased bond strengths. CLINICAL SIGNIFICANCE: Adhesive cementation of zirconia presents a clinically challenging protocol, and the cementation surface contamination of the zirconia restorations and the inadequate removal of the contaminants increase the risk of failure, as for all ceramic types. This study demonstrated that surface cleaning regimens should be applied according to different ceramic properties. Cubic ceramic specimens (3x3x3mm) were prepared from three types of ceramics:Zirconiumdioxide (IPS e.max ZirCAD) (Z), IPSEmpress (...

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The removable partial dentures supported by the telescopic crowns are an alternative for directly retained removable partial dentures. The stress distribution on the retainers and the surrounding tissues created by the telescopic and conus crowns of different sizes (4, 5, 6 mm) and taper (0 degrees, 2 degrees, 4 degrees, 6 degrees ) was investigated with the finite element analysis (FEA) method. The stress values obtained were evaluated either as strain or tensional forces. The loosening force of the secondary crown being determined as 5 N, the increase in tension of the dentine, metal structure, alveolar bone, periodontal ligament and the pulp were determined by the increasing height and taper. The reason for the increase in tensional forces with increasing taper was the result of the constant loosening force of 5 N applied in all experimental models. The strain was more effective than the tension with the highest stress being in the cervical region of the metal structure. The aim of this study was to determine the force exerted on the teeth and surrounding tissues by the loosened secondary crown.

The purpose of this study was to elucidate the origin of initiation of hybrid layer biodegradation. Ninety caries‐free human third molars were divided into three surface groups: enamel, dentin, and NaOCl‐treated dentin. (n = 30/group) Each group was divided into three subgroups (n = 10/group) of luting resin materials with etch‐and‐rinse; self‐etch and self‐adhesive systems. Resin composite blocks and sticks were fabricated and adhered onto dentin and enamel surfaces. The bond strength values were evaluated with micro shear test and statistical analysis were made. On the other hand, teeth were sectioned with a slow‐speed saw into multiple beams. After thermocycling, samples were kept in 50% silver nitrate solution. Samples were analyzed with SEM in back‐scattered mode. According to the micro‐shear bond tests, higher bond strength values were observed in etch‐and‐rinse system. Bond strength values in self‐adhesive and etch‐and‐rinse groups were significantly higher than self‐etch groups in dentin surface and dentin surface treatment with NaOCl. Back‐scattered scanning electron microscope results showed that, different degradation mechanism was observed. The present study indicates that, due to the acid etching in dentin, collagen biodegradation was observed within the hybrid layer. On the enamel surfaces, resin degradation was related with resin monomers in adhesive systems.

Angle of mouth opening provides information concerning temporomandibular joint mobility. The aim of this study was to compare angle of mouth opening of dentate and edentuluous subjects at similar ages. Eighty (80) subjects, 24 women and 16 men (mean age 51.2 yrs.) for the dentate group and 21 women and 19 men (mean age 52.3 yrs.) for the edentuluous group participated in the study. The angle of mouth opening measurements were performed with a mandibular goniometer at four independent sessions of three measurements. The angle of mouth opening values of the dentate group were significantly higher than that of the edentulous group. The results of this study revealed that tooth loss resulted in a decrease in angle of mouth opening values independent of gender and age. The clinical implications of this finding is that oral function might well be preserved with advancing age if dentition is maintained in good condition.

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