Jai-Bong Lee

Effect of sandblasting and various metal primers on the shear bond strength of resin cement to Y-TZP ceramic

OBJECTIVES This study was designed to evaluate the effect of sandblasting and metal primers on the shear bond strength of three commercial resin cements to Yttria-Tetragonl Zirconia Polycrystal (Y-TZP) ceramics. METHODS One hundred and twenty Y-TZP ceramic cylinders (Ø7 mm x 12 mm) were embedded in polytetrafluoroethylene (PTFE) molds using PMMA. The specimens were divided randomly into 12 groups (n=10), according to the surface treatments (control; sandblast-only; metal primer-only; sandblast+metal primer) and metal primer-resin cements (Alloy primer - Panavia F 2.0, V-primer - Superbond C&B, Metaltite - M bond) rendered. The mixed resin cements were placed onto the treated zirconia surfaces in cylindrical shape (Ø3 mm x 3 mm) using PTFE molds. All specimens were thermocycled (5 and 55 degrees C, 5000 cycles) and subjected to shear bond strength test by a universal testing machine with a crosshead speed of 0.5 mm/min. All data were statistically analyzed using two-way ANOVA and multiple comparison Scheffé test (alpha=0.05), and SEM images of the fractured areas were used to evaluate the fracture mode. RESULTS In Panavia F 2.0, the bond strength of the specimens treated with sandblasting and metal primer (Alloy primer) was significantly higher than those of the other subgroups. In Superbond C&B and M bond, sandblasting significantly increased the shear bond strength, but the effect of metal primers (V-primer and Metaltite) was not significant and there was disordinal interaction. SIGNIFICANCE Metal primers are not always effective for bonding between Y-TZP ceramics and resin cements. Even though a metal primer is not enough to be used alone, combined application with sandblasting seems to be an appropriate pretreatment for improving the bond strength of resin cement to Y-TZP ceramics, especially in Panavia F 2.0.

The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

STATEMENT OF PROBLEM Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported. PURPOSE The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM). MATERIAL AND METHODS Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05). RESULTS The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION The monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns

PURPOSE Marginal fit is a very important factor considering the restorations long-term success. However, adding porcelain to copings can cause distortion and lead to an inadequate fit which exposes more luting material to the oral environment and causes secondary caries. The purpose of this study was to compare the marginal fit of 2 different all-ceramic crown systems before and after porcelain veneering. This study was also intended to verify the marginal fit of crowns originated from green machining of partially sintered blocks of zirconia (Lava CAD/CAM system) and that of crowns obtained through machining of fully sintered blocks of zirconia (Digident CAD/CAM system). MATERIALS AND METHODS 20 crowns were made per each system and the marginal fit was evaluated through a light microscope with image processing (Accura 2000) at 50 points that were randomly selected. Each crown was measured twice: the first measurement was done after obtaining a 0.5 mm coping and the second measurement was done after porcelain veneering. The means and standard deviations were calculated and statistical inferences among the 2 groups were made using independent t-test and within the same group through paired t-test. RESULTS The means and standard deviations of the marginal fit were 61.52 ± 2.88 µm for the Digident CAD/CAM zirconia ceramic crowns before porcelain veneering and 83.15 ± 3.51 µm after porcelain veneering. Lava CAD/CAM zirconia ceramic crowns showed means and standard deviations of 62.22 ± 1.78 µm before porcelain veneering and 82.03 ± 1.85 µm after porcelain veneering. Both groups showed significant differences when analyzing the marginal gaps before and after porcelain veneering within each group. However, no significant differences were found when comparing the marginal gaps of each group before porcelain veneering and after porcelain veneering as well. CONCLUSION The 2 all-ceramic crown systems showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.

The effect of preparation order on the crystal structure of yttria-stabilized tetragonal zirconia polycrystal and the shear bond strength of dental resin cements

OBJECTIVES The purpose of this study was to evaluate the effect of preparation order on the crystal structure of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and the shear bond strength of dental resin cements. METHODS One-hundred fifty pre-sintered Y-TZP cylinders (Ø 9mm×13.5mm) were prepared and divided into three groups (control group, SBS group and SAS group). Specimens in control group were not treated. Specimens in SBS group were sandblasted and then densely sintered, and specimens in SAS group were sintered in advance, and then sandblasted. The specimens were analyzed by X-ray diffractometry, confocal laser scanning microscopy and Energy dispersive X-ray spectroscopy before and after sandblasting. All specimens were embedded in polytetrafluoroethylene (PTFE) molds using PMMA and each group was divided into five subgroups. The mixed resin cements (Clearfil SA luting cement, Zirconite, Superbond C&B, Rely-X Unicem, and Multilink) were placed onto the Y-TZP surfaces using PTFE molds with Ø 3mm×3mm, followed by storage in distilled water at 37°C for 24h, and thermocycling (5000 cycles at 5°C and 55°C with a 30s dwelling time). All specimens were tested for the shear bond strengths with a universal testing machine, and fractured surfaces were evaluated by SEM. Statistical analysis was performed using one-way ANOVA and Scheffé comparison with α=.05. RESULTS Sandblasting of the zirconia significantly increased shear bond strength of resin cements, but the preparation order had no significant influence on the shear bond strength in both test groups. In SEM observation, the natures of the surface faceting of the zirconia grains were totally different between SBS and SAS groups. SBS group exhibited less monoclinic structures than SAS group. SIGNIFICANCE Sandblasting of pre-sintered Y-TZP and then sintering may induce favorable proportion of tetragonal structures. This might have positive effect on the clinical performance of zirconia restorations.

In vitro evaluation of fracture strength of zirconia restoration veneered with various ceramic materials

PURPOSE Fracture of the veneering material of zirconia restorations frequently occurs in clinical situations. The purpose of this in vitro study was to compare the fracture strengths of zirconia crowns veneered with various ceramic materials by various techniques. MATERIALS AND METHODS A 1.2 mm, 360° chamfer preparation and occlusal reduction of 2 mm were performed on a first mandibular molar, and 45 model dies were fabricated in a titanium alloy by CAD/CAM system. Forty-five zirconia copings were fabricated and divided into three groups. In the first group (LT) zirconia copings were veneered with feldspathic porcelain by the layering technique. In the second group (HT) the glass ceramic was heat-pressed on the zirconia coping, and for the third group (ST) a CAD/CAM-fabricated high-strength anatomically shaped veneering cap was sintered onto the zirconia coping. All crowns were cemented onto their titanium dies with Rely X™ Unicem (3M ESPE) and loaded with a universal testing machine (Instron 5583) until failure. The mean fracture values were compared by an one-way ANOVA and a multiple comparison post-hoc test (α=0.05). Scanning electron microscope was used to investigate the fractured interface. RESULTS Mean fracture load and standard deviation was 4263.8±1110.8 N for Group LT, 5070.8±1016.4 for Group HT and 6242.0±1759.5 N for Group ST. The values of Group ST were significantly higher than those of the other groups. CONCLUSION Zirconia crowns veneered with CAD/CAM generated glass ceramics by the sintering technique are superior to those veneered with feldspathic porcelain by the layering technique or veneered with glass ceramics by the heat-pressing technique in terms of fracture strength.

Variation in the total lengths of abutment/implant assemblies generated with a function of applied tightening torque in external and internal implant–abutment connection

AIM Settling (embedment relaxation), which is the main cause for screw loosening, is developed by microroughness between implant and abutment metal surface. The objective of this study was to evaluate and compare the relationship between the level of applied torque and the settling of abutments into implants in external and internal implant-abutment connection. MATERIAL AND METHODS Five different implant-abutment connections were used (Ext, External butt joint + two-piece abutment; Int-H2, Internal hexagon + two-piece abutment; Int-H1, Internal hexagon + one-piece abutment; Int-O2, Internal octagon + two-piece abutment; Int-O1, Internal octagon + one-piece abutment). All abutments of each group were assembled and tightened with corresponding implants by a digital torque gauge. The total lengths of implant-abutment samples were measured at each torque (5, 10, 30 N cm and repeated 30 N cm with 10-min interval) by an electronic digital micrometer. The settling values were calculated by changes between the total lengths of implant-abutment samples. RESULTS All groups developed settling with repeated tightening. The Int-H2 group showed markedly higher settling for all instances of tightening torque and the Ext group was the lowest. Statistically significant differences were found in settling values between the groups and statistically significant increases were observed within each group at different tightening torques (P<0.05). After the second tightening of 30 N cm, repeated tightening showed almost constant settling values. CONCLUSIONS Results from the present study suggested that to minimize the settling effect, abutment screws should be retightened at least twice at 30 N cm torque at a 10-min interval in all laboratory and clinical procedures.

Calorimetric investigations of liquid Cu-Sb, Cu-Sn and Cu-Sn-Sb alloys

Abstract The integral enthalpies of mixing ( ΔH ) of liquid binary Cu-Sb and Cu-Sn as well as liquid ternary Cu-Sn-Sb alloys were determined calorimetrically. The peculiar S-shaped concentration dependence of ΔH could be successfully described with the help of the associate model. By the calculation of ΔH for the ternary Cu-Sn-Sb alloy the model parameters are fixed using the data of the three binary bordering systems.

Effect of polishing and glazing on the color and spectral distribution of monolithic zirconia.

PURPOSE The aim of this study was to evaluate the effect of polishing and glazing on the color and spectral distribution of monolithic zirconia. MATERIALS AND METHODS Forty-five monolithic zirconia specimens (16.3 mm × 16.4 mm × 2.0 mm) were fabricated and divided into 5 groups according to the number of A2-coloring liquid applications (Group I to V). Each group was divided into 3 subgroups according to the method of surface treatments (n=3): N: no treatment; P: polishing; G: glazing. Color and spectral distribution of five different areas of each specimen were measured according to CIELAB color space in the reflectance mode relative to the standard illuminant D65 on a reflection spectrophotometer. Data were analyzed using one-way ANOVA followed by Tukeys HSD test, Pearson correlation and regression analysis (α=.05). RESULTS There was a significant difference in CIE L* between Subgroup N and P, and in CIE b* between Subgroup P and G in each group. Spectral reflectance generally decreased in Subgroup P and G in comparison with Subgroup N. Color differences between Subgroup P and G were within the perceptibility threshold (ΔE*ab< 3.7) in most groups. Highly significant correlation was found between CIE b*and each subgroups as the number of coloring liquid applications increased (R2>0.88, P<.001). CONCLUSION A perceptible color difference can be detected after polishing of monolithic zirconia. Polishing decreases the lightness, and glazing also decreases the lightness, but increases the yellowness of monolithic zirconia.

Biomechanical evaluation of dental implants with different surfaces: Removal torque and resonance frequency analysis in rabbits

STATEMENT OF PROBLEM Macroscopic and especially microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. Dental implants with modified surfaces have shown stronger osseointegration than implants which are only turned (machined). Advanced surface modification techniques such as anodic oxidation and Ca-P application have been developed to achieve faster and stronger bonding between the host bone and the implant. PURPOSE The purpose of this study was to investigate the effect of surface treatment of titanium dental implant on implant stability after insertion using the rabbit tibia model. MATERIAL AND METHODS Three test groups were prepared: sandblasted, large-grit and acid-etched (SLA) implants, anodic oxidized implants, and anodized implants with Ca-P immersion. The turned implants served as control. Twenty rabbits received 80 implants in the tibia. Resonance frequencies were measured at the time of implant insertion, 2 weeks and 4 weeks of healing. Removal torque values (RTV) were measured 2 and 4 weeks after insertion. RESULTS The implant stability quotient (ISQ) values of implants for resonance frequency analysis (RFA) increased significantly (P < .05) during 2 weeks of healing period although there were no significant differences among the test and control groups (P > .05). The test and control implants also showed significantly higher ISQ values during 4 weeks of healing period (P < .05). No significant differences, however, were found among all the groups. All the groups showed no significant differences in ISQ values between 2 and 4 weeks after implant insertion (P > .05). The SLA, anodized and Ca-P immersed implants showed higher RTVs at 2 and 4 weeks of healing than the machined one (P < .05). However, there was no significant difference among the experimental groups. CONCLUSION The surface-modified implants appear to provide superior implant stability to the turned one. Under the limitation of this study, however, we suggest that neither anodic oxidation nor Ca-P immersion techniques have any advantage over the conventional SLA technique with respect to implant stability.

Effect of the amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics

PURPOSE This study investigated the effect of amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics. MATERIALS AND METHODS One-hundred sixty-five monolithic zirconia specimens (16.3 mm × 16.3 mm × 2.0 mm) were divided into 5 groups (Group I to V) according to the number of A2-coloring liquid applications. Each group was then divided into 11 subgroups by reducing the thickness up to 1.0 mm in 0.1-mm increments (Subgroup 0 to 10, n=3). Colors and spectral distributions were measured according to CIELAB on a reflection spectrophotometer. All measurements were performed on five different areas of each specimen. Color difference (ΔE*ab) and translucency parameter (TP) were calculated. Data were analyzed using one-way ANOVA and multiple comparison Scheffé test (α=.05). RESULTS There were significant differences in CIE L* between Subgroup 0 and other subgroups in all groups. CIE a* increased (0.523.7) were obtained between Subgroup 0 and other subgroups. TP values generally increased as the thickness reduction increased in all groups (R2>0.89, P<.001). CONCLUSION Increasing thickness reduction reduces lightness and increases a reddish, bluish appearance, and translucency of monolithic zirconia ceramics.