Background and Aim: The conventional procedure for removal of porcelain laminate veneers (PLVs) is time-consuming and inconvenient. The purpose of this study was to evaluate the efficacy of Er:YAG laser for debonding of PLVs. Materials and Methods: Forty-eight intact extracted human maxillary anterior teeth received discoid PLVs (24 feldspathic and 24 e-max ceramic). The PLVs had 0.7 mm thickness and 4 mm diameter. After cementation of all PLVs with a light-cure cement, samples were stored at 37ºC distilled water for 48 h. Samples of each ceramic were randomly divided into 3 groups of 8 samples. Then, laser was irradiated on the cemented PLVs as follows: (I) feldspathic PLVs without laser irradiation (control group), (II) feldspathic PLVs with laser irradiation (6 s, 10 Hz, 200 mJ, 2 W), (III) feldspathic PLVs with laser irradiation (6 s, 10 Hz, 300 mJ, 3 W), (IV) e-max PLVs without laser irradiation (control group), (V) e-max PLVs with laser radiation (6 s, 10 Hz, 200 mJ, 2 W), (VI) e-max PLVs with laser irradiation (6 s, 10 Hz, 300 mJ, 3 W). The shear bond strength of all samples was measured using a universal testing machine. We used Mann-Whitney and Kruskal-Wallis tests for data analysis (P<0.05). Results: Laser irradiation decreased the shear bond strength of both ceramics. But this decrease was only significant for the e-max group (P<0.05). No significant difference was found between different laser irradiation powers in the two ceramic groups. Conclusion: Er: YAG laser is effective for debonding of e-max PLVs.

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.

Aim: This study investigated the effects of implant angulation and cyclic dislodgment on retention of Locator and Dalbo Plus attachments.Materials and methods: Fifty pairs of acrylic blocks for five implant angulations (0, 10, 20, 30 and 40 degrees) and two attachment systems (locator and Dalbo Plus®; n = 5) were fabricated. In each pair, one block contained two implant analogs connected to their attachments, and the other block contained matrix parts of the attachments. 1440 cycles of insertion and removal were implicated on specimens after mounting the blocks in the universal testing machine. The retention was registered at cycle numbers 1, 120, 360, 720, and 1440. Data were analyzed using one-way analysis of variance (ANOVA) and Duncan's multiple range test (p ≤ 0.05).Results: Data analysis showed that implant angulation had significant effects on retention of both attachments at all different angles (p ≤ 0.05). Dalbo Plus showed no significant differences between 30 and 40 degrees (p ≥ 0.05), but between 0 and 30 degrees, differences were significant (p ≤ 0.05). Moreover, cyclic loading had significant effects on retention of both attachments at all different loading cycles (p ≤ 0.05). On evaluating combined effects of cyclic loading and implant angulation on retention, a significant decrease in retention was noted for both Locator and Dalbo Plus attachments at angulations of 0, 10, 20 degrees after 1440 cycles (1 year of clinical use; p ≤ 0.05). Conclusion:Both angulation and cyclic loading have negative effects on implant-supported overdentures and decrease retention over time. Furthermore, as the angle between implants increases, decrement of retention becomes more significant.

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Purpose : One of the required information in rehabilitating the occlusal plane in dentistry is the radius of Monson’s sphere , which like other anatomical indices varies in different races. The purpose of this study was to determine the radius of the Monson’s  sphere in a group of  Iranian. Materials & Methods  : 45 Iranian subjects (19 males & 26 females ) aged from 18 to 25 were selected for this study . The x,y,z coordinates of cusp tips of all  mandibular teeth except for the third molars obtained  with a 3-dimensional digitizer , were used to  derive a spherical model  of the occlusal surfaces’ curvature . From the best interpolating sphere , the radii of the Monson’s sphere was computed . Results : Although all of the computed variables were greater in men , the occlusal curvature of mandibular arch was not influenced by gender . The mean radius of the Monson’s  sphere was 111.5 mm ( 121 mm in men and 104 mm in women which was closer to the classic value of 4 inch , confirming Monson’s observations ) . Conclusion  : The average radius of the Monson’s sphere in this study was greater than the classic 4 inch value proposed by Monson and this result may suggest racial differences in the normal dental arch form that is important in occlusal rehabilitation. Although more researches are necessary in future to improve treatment results.