Color match of ultra-translucency multilayer zirconia restorations with different designs and backgrounds.

PURPOSE: The purpose of this in vitro study was to assess the color match of ultra-translucency multilayer zirconia restorations with different designs and backgrounds. MATERIALS AND METHODS: Thirty ultra-translucency multilayer zirconia crown specimens were made in VITA classical shade B2 for a prepared maxillary central incisor. The specimens were divided into three groups based on the restoration design: veneered zirconia with a trestle design (VZT), veneered zirconia with a dentin core design (VZD), and full-contour zirconia (FCZ). In the groups VZT and VZD, the zirconia specimens were layered with a feldspathic veneering ceramic. The specimens were seated on five different backgrounds: shade B2 composite resin, shade B2 zirconia, copper-colored metal alloy, silver-colored metal alloy, and the prepared central incisor. CIELab values of the labial middle sections of the crown specimens were measured with a spectrophotometer. Color differences between the specimens and a shade B2 VITA classical tab (as a control) were calculated from the ΔE* ab formula and compared with an acceptability threshold (ΔE* ab = 3.7) to be clinically explicated. RESULTS: Mean ΔE* ab values ranged between 1.17 and 8.48. The restoration design, the background type, and their interaction affected the ΔE* ab (p < 0.001). The mean ΔE* ab values for VZT with all backgrounds and for VZD with the silver-colored metal background were greater than the threshold (p < 0.001), whereas the mean ΔE* ab values for VZD with the other backgrounds and FCZ with all backgrounds were less than the threshold (p = 1). CONCLUSIONS: Restoration design and background type affected the color match of ultra-translucency multilayer zirconia restorations. VZT restorations on all backgrounds and VZD restorations on a silver-colored metal background showed color mismatches. However, VZD restorations on the other backgrounds and FCZ restorations on all backgrounds demonstrated color matches.

Fracture Resistance of Zirconia Restorations with Four Different Framework Designs.

Objectives: This study assessed the fracture resistance of zirconia crowns with four framework designs, fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) technology. Materials and Methods: In this experimental study, a maxillary central incisor was prepared and scanned with a CAD/CAM scanner, and 40 frameworks with 4 designs (N=10) were fabricated as follows: simple core, dentine core with a design similar to dentine, 3mm trestle design collar in the lingual aspect with proximal buttresses, and monolithic or full-contour. After porcelain applying and 20h immersion in distilled water (37°C), crowns were cemented on metal dies using zinc phosphate cement. Fracture resistance was measured by a universal testing machine. Data were analyzed with one-way ANOVA (alpha=0.05). Results: Fracture resistance was maximum in the monolithic group, followed by the dentine core, trestle design, and simple core groups, respectively. The mean fracture resistance of the monolithic group was significantly higher than that of the simple core group (P<0.005). Conclusion: Zirconia restorations with frameworks that provided higher and more support for porcelain, showed increased fracture resistance.

Effect of Different Nd:YAG Laser Power Outputs on Bond Strength of Resin Cement to Zirconia in Comparison to Sandblasting.

Introduction: This study investigated the effect of various laser powers on the shear bond strength (SBS) of resin cement to the zirconia surface. Methods: Seventy-five zirconia disks were prepared and assigned to five groups including no surface treatment (control group), sandblasting with 50 µ Al2 O3 particles (second group), and Nd:YAG laser treatments with 2 W, 2.5 W and 3 W powers respectively (third, fourth and fifth groups). Afterwards, composite resin cylinders were cemented on zirconia disks using dual-curing resin cement. Before thermocycling (2000 cycles, 5-55°C), all samples were placed in distilled water at 37°C for 24 hours. Using a universal testing machine at the crosshead speed of 0.5 mm/min, the SBS was examined. Also, using a stereomicroscope, the failure type was determined. Data analyses were performed using Welch and Games-Howell tests (P < 0.05). Results: The mean bond strength difference between the control group and the other groups was significant. The respective bond strength from the highest to the lowest was observed in the sandblast group, the laser group with 2.5 W power, the laser group with 3 W power, the laser group with 2 W power, and finally the control group. However, no significant difference was observed between different laser groups (P < 0.05). Also, there was no significant difference between the sandblast and laser groups with 2.5 W and 3 W power (P < 0.05). Most of the failures in the sandblasting and laser groups with powers of 2.5 W and 3 W were mixed, but in the control and 2 W laser groups, most of the failures were of adhesive nature. Conclusion: The highest bond strength was achieved by sandblasting with Al2 O3 particles and then using an Nd: YAG laser with a power of 2.5 W.

Shear Bond Strength of Zirconia Ceramic to Four Different Core Materials, An in vitro Study.

STATEMENT OF THE PROBLEM: Different materials can be used to reconstruct the core foundation in all-ceramic restorations. Bond strength of the core material to zirconia is an important factor in long-term restoration success. PURPOSE: The aim of this study was to assess shear bond strength (SBS) of zirconia to four different core materials. MATERIALS AND METHOD: In this experimental in vitro study, 40 zirconia ceramic disks (10×3 mm) were prepared and divided to four groups based on core material. Cylinder shaped core specimens (3×4 mm) of non-precious gold alloy (NPG), zirconia ceramic, natural dentin, and composite resin were prepared and bonded perpendicularly to the zirconia disks using Gillmore Needle Apparatus and dual cure resin cement. All samples were thermocycled for 2000 cycles. To evaluate SBS, the specimens were tested by universal testing machine. Data were analyzed using Kruskal-Wallis test followed by Dunn's test with Bonferroni correction. Statistical significance was set at p< 0.05. RESULTS: The highest values for SBS were achieved in composite resin group (11.58±1.74 MPa) followed by NPG (10.32±0.94 MPa), zirconia (7.3±1.11 MPa) and dentin group (6.53±0.56 MPa). SBS in composite resin and NPG core materials were significantly higher than other core materials (p< 0.05). CONCLUSION: Composite resin and NPG cores showed significant higher bond strength to zirconia in comparison to dentine and zirconia core materials.

Effect of multiple pouring on the accuracy of casts made using 3D-printed custom trays with different spacer thicknesses: A research study.

Background. This study aimed to evaluate the effect of different pouring times and spacer thicknesses on the three-dimensional accuracy of casts made of 3D-printed custom trays. Methods. A partial edentulous maxillary model was scanned for fabricating custom acrylic trays. Twenty custom trays were created using a CAD/CAM system and divided into two groups in terms of their spacer thicknesses (2 mm and 4 mm). All the trays were designed with 2-mm thickness, multiple retentive holes measuring 2 mm in diameter, and three interior seating stops (two on the edentulous ridge and one on the incisal edge of the central incisors). Impressions were made using monophasic polyvinyl siloxane and poured in two different times (one hour and 24 hours after removal) with type IV dental stone. All the casts were scanned to measure three distances (inter-buccal cusps, inter-palatal cusps, and inter-fossa distances) between the two first premolars. The data were analyzed with two-way ANOVA and Bonferroni test at a significance level of 0.05. Results. There was no significant difference between the 3D accuracy of casts made using two different spacer thicknesses poured at 1-hour and 24-hour intervals. However, there was a difference between casts made after 1 hour and 24 hours when using custom trays with 2 mm of spacer thickness in terms of inter-buccal distance. Conclusion. There was no significant difference between the accuracy of casts made using custom trays with either 2 or 4 mm of spacer thickness, which were poured 1 hour or 24 hours after tray removal.

Influence of Different Surface Treatments on the Shear Bond Strength of Resin Cement to Base Metal Alloys.

Introduction: This study aimed to investigate the effect of different surface treatments on the bond strength of resin cement to nickel-chrome (Ni-Cr) alloy. Methods: Forty disk-shaped specimens of Ni-Cr alloy were prepared and divided into 4 groups. In the first group, the specimens' surface was sandblasted with 50 µ Al2 O3 particles. In the second group, the specimens were prepared with the Er:YAG laser. In the third group, the specimens were prepared using the Er:YAG laser after sandblasting. In the fourth group, the specimens' surface was covered with a thin layer of MKZ metal primer after sandblasting. Then the cylinders of composite resin were bonded to the treated metal surfaces using Panavia F2.0 resin cement. All of the samples were subjected to 2000 thermal cycles. The shear bond strength was tested using a universal testing machine at the crosshead speed of 0.5 mm/min. The failure mode was also observed by a stereomicroscope. Data were analyzed using the one-way ANOVA and the Tukey HSD test at a significance level of 0.05. Results: The shear bond strength from the highest to the lowest were as follows: the Er:YAG laser group, the sandblast and MKZ primer combination group, the sandblast group, and the sandblast and Er:YAG laser combination group. The mean differences of shear bond strength between the Er:YAG laser group and the sandblast group (P=0.047) and also between the Er:YAG laser group and the sandblast and Er:YAG laser combination group (P=0.015) were statistically significant. Conclusion: Among the different surface treatments employed in this study, Er:YAG laser treatment increased the shear bond strength between the metal alloy and the resin cement (Pavnavia F2).

A radiographic comparison of progressive and conventional loading on crestal bone loss and density in single dental implants: a randomized controlled trial study.

OBJECTIVE: Crestal bone loss is a biological complication in implant dentistry. The aim of this study was to compare the effect of progressive and conventional loading on crestal bone height and bone density around single osseointegrated implants in the posterior maxilla by a longitudinal radiographic assessment technique. MATERIALS AND METHODS: Twenty micro thread implants were placed in 10 patients (two implants per patient). One of the two implants in each patient was assigned to progressive and the other to conventional loading groups. Eight weeks after surgery, conventional implants were restored with a metal ceramic crown and the progressive group underwent a progressive loading protocol. The progressive loading group took different temporary acrylic crowns at 2, 4 and 6 months. After eight months, acrylic crowns were replaced with a metal ceramic crown. Computer radiography of both progressive and conventional implants was taken at 2, 4, 6, and 12 months. Image analysis was performed to measure the height of crestal bone loss and bone density. RESULTS: The mean values of crestal bone loss at month 12 were 0.11 (0.19) mm for progressively and 0.36 (0.36) mm for conventionally loaded implants, with a statistically significant difference (P < 0.05) using Wilcoxon sign rank. Progressively loaded group showed a trend for higher bone density gain compared to the conventionally loaded group, but when tested with repeated measure ANOVA, the differences were not statistically significant (P > 0.05). CONCLUSION: The progressive group showed less crestal bone loss in single osseointegrated implant than the conventional group. Bone density around progressively loaded implants showed increase in crestal, middle and apical areas.

Full mouth rehabilitation of an ectodermal dysplasia patient with implant-supported prostheses: a clinical report.

Full mouth rehabilitation in patients with ectodermal dysplasia (ED) is difficult to manage, especially because the afflicted individuals are quite young when they are evaluated for treatment; therefore, esthetics is an important concern. This clinical report describes the rehabilitation of a 19-year-old girl diagnosed with ectodermal dysplasia. Eleven implants were placed in the maxilla and mandible along with bone grafting to the upper jaw and both arches were constructed by metal-ceramic implant-supported fixed prostheses. This treatment plan seems to be favorable for ED patients.