This study evaluated the shear bond strength of zirconia bonded to dentin specimens using a self etch dual cure resin cement after various surface treatments of zirconia. Twenty zirconia rods (3 × 2.5 mm) were prepared from zirconia blocks and assigned into 5 groups for the following surface treatments. (1) Group I: Control (C) no treatment (2) Group II: airborne-particle abrasion (APA), (3) Group III: hydrofluoric acid etching (HF), (4) Group IV: hydrofluoric acid etching followed by silanation (HF/S), and (5) Group V: application of zirconia primer (Z). Dentin Specimens were prepared from extracted molars stored in 0.5% chloramine-T. Zirconia rods were bonded to dentin using resin cement (Multilink Speed), then light polymerized. The specimens tested for failure were tested using the notched shear bond test method in a universal loading apparatus. One way ANOVA followed by Tukey HSD for cell means were used to analyze the data (=0.05). The highest values were obtained with group V (Z) (8.66 MPa) followed by group II (APA) (6.71 MPa), and group IV (HF/S) (4.41 MPa). The least values were obtained for group III (HF) (3.88 MPa) with no significant difference (P value 0.53) between group III (HF) (3.88 MPa) and group I (C) (3.70 MPa). Among the surface treatments employed in this study zirconia primer application is a practical procedure to improved bond strength of zirconia to resin cement followed by Airborne Particle Abrasion with 50 μm Al2O3 particles.

Background:One method used to disinfect a dental cast is immersion in a disinfecting solution. Repeated immersion of a cast in disinfectant may affect its physical properties.Purpose:The purpose of this study was to evaluate the changes in dimensional accuracy and hardness of the dental casts as a result of repeated disinfection in 0.525% sodium hypochlorite and 2% glutaraldehyde solutions.Materials and Methods:Sixty specimens were made of type III dental stone. Twenty specimens were immersed in slurry, a supernatant solution of calcium sulfate in distilled water (control casts), 20 specimens in 0.525% sodium hypochlorite, and 20 specimens in 2% glutaraldehyde solutions for 30 min and air dried for 24 h. This process was repeated for 7 times for testing. Linear dimensional change and hardness were determined according to American National Standards Institute/American Dental Association (ANSI/ADA) standards. The data were analyzed using two-way analysis of variance.Results:For specimens prepared with type III stones, treatment was by immersion in slurry (group I – control casts), and by immersion in 0.525% sodium hypochlorite (group II – test group 1) and in 2% glutaraldehyde solution (group III – test group 2). The specimens treated with sodium hypochlorite and glutaraldehyde showed more linear dimensional change compared to the specimens treated in slurry. However, the difference between test casts and control casts was significant. But the difference between the two test groups was not significant. Both the test groups showed decrease in hardness of the specimens compared to that specimens in control group. But the difference between two test groups was not significant in hardness. However,the values remained close to ANSI/ADA standards.Conclusion:The results demonstrated that repeated immersion of type III dental stone specimens in slurry with distilled water, 0.525% sodium hypochlorite and 2% glutaraldehyde, along with drying in air, caused a significant increase in linear dimension and a significant decrease in hardness.

Increased ridge resorption may occur due to inappropriate pressure applied during final impression making phase of complete denture fabrication. This study was done to evaluate the pressure applied on the residual ridge while making impressions with two tray designs (with and without spacer) using, zinc oxide eugenol and light body polyvinyl siloxane impression material. Five edentulous subjects were randomly selected. For each of the five subjects four maxillary final impressions were made and were labelled as, Group A-Impression made with tray without spacer using zinc oxide eugenol impression, Group B-Impression made with tray with spacer using zinc oxide eugenol impression material, Group C-Impression made with tray without spacer using light body polyvinyl siloxane impression material, Group D-Impression made with tray with spacer using light body polyvinyl siloxane impression material. During the impression procedure a closed hydraulic system was used to remotely measure the pressures produced in three areas. The pressure produced were calibrated according to the micro strain record. Statistical comparisons of readings were done using t test and ANOVA. The acquired data revealed that ZOE produced an average pressures value of 26.534 and 72.05 microstrain, while light body PVS produced 11.430 and 37.584 microstrain value with and without spacer respectively. Significantly high values were recorded on the vault of the palate when using trays without spacer. The use of light body polyvinyl siloxane and zinc oxide eugenol impression material showed insignificant difference. Within the limitations of this study, tray design has a significantly effected on the pressures produced, while the impression materials does not have any significant difference.

Dimensionally stable autoclavable impressions will be effective in controlling the cross-infection and contamination caused by patient's saliva and other oral secretions. The accuracy of newly introduced autoclavable polyvinyl siloxane impression material was assessed for its dimensional stability and accuracy. A standard metal model (Dentoform, U-501, Columbia) was customised for impression making. The impressions were made using the newly introduced polyvinyl siloxane impression materials (AFFINIS, Coltene/Whaledent AG, 9450 Alstalten, Switzerland). Fifty impressions were made and were divided into two groups A and B of 25 each. Group A was the control sample (non-autoclaved impressions) and group B was the test sample (autoclaved impressions), which was subjected to the steam autoclave procedure at 134 °C for 18 min, casts were poured in type IV gypsum products. The customised metal model, casts obtained from control and test group were subjected to laboratory evaluation with help of a travelling microscope (×10 magnification), and digital vernier calliper (0.01 mm/10 μm accuracy). Data analysis was done using one-way ANOVA and One-Sample t test to evaluate the overall accuracy (P < 0.005). As a result, there was an average reduction of 0.016 μm in overall dimension between the test and the control group when compared with the master model, which is not statistically or clinically significant. The newly introduced polyvinyl siloxane impression material is accurate and dimensional stable for clinical use when steam autoclaved at 134 °C for 18 min.

On the basis of the results of this study, the use of both the impression materials i.e., polyether and polyvinyl siloxane impression is recommended for impression making in parallel as well as angulated implants.