Comparison of the marginal adaptation of zirconium dioxide crowns in preparations with two different finish lines

Purpose: The purpose of this study was to evaluate the marginal adaptation of zirconium dioxide crowns in preparations with two different finish line configurations before and after porcelain firing cycles, after a glaze cycle, and after cementation. Materials and Methods: Twenty human molar teeth were prepared to receive full crowns; ten were prepared with a 90° round shoulder and another ten with a 45° chamfer finish line. Zirconium dioxide copings were fabricated using CAD/CAM technology (Lava? system). They were then veneered with a low‐fusing glass‐ceramic (IPS e.max® Ceram). Finally, they were glazed and cemented with a resin‐composite cement (RelyX? Unicem, Aplicap?). Measurements for marginal adaptation using stereomicroscopy (40×) were performed at four stages: copings (S1), after porcelain firing cycles (S2), after glazing (S3), and after cementation (S4). One‐way ANOVA was used to assess the influence of the finish line design on the marginal adaptation in each stage. Two‐way ANOVA with repeated measurements was performed to assess the influence on the marginal adaptation of the porcelain firing cycles, glaze firing cycle, and cementation. Results: The measured marginal gap mean values for the shoulder group (μm) were: 50.13 (S1), 54.32 (S2), 55.12 (S3), and 59.83 (S4). The values for the chamfer group were: 63.56 (S1), 71.85 (S2), 74.12 (S3), and 76.97 (S4). When comparing marginal gaps between specimens with two different finish lines, differences were noticed at the four studied stages (p= 0.0165, p= 0.0027, p= 0.0009, and p= 0.0009, respectively). No differences were manifested in the marginal gap measurements of the shoulder group at the different stages of fabrication (p= 0.4335); however, in the chamfer group, differences were noticed between S1 and S3 (p= 0.0042). Conclusions: Marginal adaptation was influenced by the finish line design. The firing cycles significantly affected the chamfer group; nevertheless, the marginal gap was within the range of clinical acceptability.     

A comparison of marginal fit of glass infiltrated alumina copings fabricated using two different techniques and the effect of firing cycles over them

PURPOSE

This study evaluated marginal fit of glass infiltrated alumina cores fabricated using two techniques and their marginal stability after firing cycles of veneering porcelain.

MATERIALS AND METHODS

Fifteen standardized all-ceramic crowns were fabricated on a metal die using each technique: slip cast technique of VITA In-Ceram sprint Alumina (Group A as control) and plastic foil matrix technique of Turkom-Cera fused alumina core system (Group B). Copings were compared between groups and within groups at coping stage and after firing each layer of veneering porcelain. A device was used to standardize seating of copings on the metal die and positioning of the specimens under the microscope after each stage of fabrication. The specimens were not cemented and marginal gap was measured using an image analyzing software (Imagepro Express) on the photographs captured under an optical microscope. Two tailed unpaired ''t test'' was used to compare marginal gaps in two groups and one way ANOVA was used to analyze marginal distortion within each group at 95% confidence interval.

RESULTS

The marginal gap was smaller at the coping stage in group B (60 + 30 µm) than group A (81 + 21 µm) with statistical significance. After firing of veneering porcelain the difference was insignificant. At the final stage, both groups exhibited lower mean marginal gaps than at the initial coping stage with the difference of 11.75 µm for group A and 11.94 µm for group B, but it was statistically insignificant due to high value of standard deviation.

CONCLUSION

Within the limitations of this study, it was concluded that both techniques produced copings with comparable and acceptable marginal fit and marginal stability on firing veneering porcelain.     

不同设计和饰/釉瓷烧结对氧化锆种植全瓷冠内部和边缘适合性的影响

目的 研究氧化锆不同设计和饰/釉瓷烧结对种植全瓷冠内部和边缘适合性的影响。方法 采用Cercon计算机辅助设计及制作（CAD/CAM）系统制作3组黏结固位氧化锆种植全瓷冠,每组8颗（n=8）。A组（常规氧化锆烤瓷全冠组）：常规边缘氧化锆基底冠+饰瓷,B组（360°氧化锆颈环烤瓷全冠组）：360°氧化锆颈环冠边缘基底冠+饰瓷,C组（全解剖式氧化锆全冠组）：解剖形态氧化锆全冠+釉瓷。饰/釉瓷烧结前和烧结后采用硅橡胶分别复制氧化锆基底冠、氧化锆全瓷冠在基台就位后的内部及边缘间隙,Micro-CT扫描硅橡胶获得内部及边缘间隙图像,测量基底冠、氧化锆全瓷冠边缘垂直间隙（MG）、冠边缘水平间隙（ HMD）、肩台区间隙（CA）、轴面中点间隙（AW）、轴面和面交界处间隙（AOT）。采用SPSS 17.0软件对测量结果进行统计学分析。结果 不论饰/釉瓷烧结前还是烧结后,A组HMD均大于B组和C组（P<0.05）,B、C组HMD差异无统计学意义（P>0.05）,A、B、C三组间MG、CA、AW、AOT均无统计学差异（P>0.05）。饰/釉瓷烧结后,A组MG较烧结前明显减小（P<0.05）,A组HMD、CA、AW、AOT及B、C两组各部位间隙与烧结前相比均无统计学差异（P>0.05）。结论 360°氧化锆颈环烤瓷全冠和全解剖式氧化锆全冠的边缘适合性优于常规氧化锆烤瓷全冠,饰瓷烧结对常规氧化锆烤瓷全冠垂直间隙的影响最明显。     

The effect of different fabrication steps on the marginal adaptation of two types of glass-infiltrated ceramic crown copings fabricated by CAD/CAM technology

Purpose: Marginal adaptation is an important factor affecting the longevity of all‐ceramic restorations, although the effects of different fabrication steps on marginal adaptation at various stages of fabrication are not fully understood. The purpose of this study was to assess with an in vitro model whether In‐Ceram alumina (IA) or In‐Ceram zirconia (IZ) copings produced by the CAD/CAM method would be clinically acceptable, and to evaluate the effect of each fabrication step (post‐milling, post‐trimming, and post‐glass infiltration) on the marginal discrepancy of the coping. Materials and Methods: A melamine tooth was prepared, duplicated, poured with inlay wax, and then cast with metal to fabricate a master die. An InLab 3D system was used to scan the master die and to design and mill the copings. Thirty IA and IZ copings each were developed with thicknesses of 0.6 mm and a 30‐μm thick computer luting space. Epoxy resin replicas of the master die were fabricated, and the vertical and horizontal marginal discrepancies were measured using a Micro‐Vu optical microscope at three stages of the fabrication (post‐milling, post‐trimming, post‐infiltration). One‐way ANOVA was used to analyze the data between the three stages of fabrication for each marginal discrepancy, and a t‐test was used to compare vertical and horizontal marginal discrepancies (after glass infiltration) between IZ and IA copings Results: There were no significant differences (p > 0.05) in the vertical marginal discrepancies (μm) between IA (36 ± 14) and IZ (40 ± 14) copings after glass infiltration. ANOVA (comparing three stages within horizontal marginal discrepancy for IZ copings) showed that post‐milling (40 ± 26) > post‐trimming (23 ± 11) = post‐infiltration (19 ± 13). ANOVA (comparing three stages within vertical marginal discrepancy for IZ copings) showed that post‐milling (53 ± 12) = post‐trimming (47 ± 13) > post‐infiltration (36 ± 14). ANOVA (comparing three stages within horizontal marginal discrepancy for IA copings) showed that post‐milling (52 ± 28) > post‐trimming (30 ± 16) > post‐infiltration (30 ± 16). ANOVA (comparing three stages within vertical marginal discrepancy for IA copings) showed that post‐milling (54 ± 13) = post‐trimming (56 ± 26) > post‐infiltration (40 ± 14). Conclusion: There was no significant difference in the marginal adaptation of both material copings. After the trimming process, the glass infiltration firing cycle improved the vertical marginal discrepancy for both IZ and IA copings. Clinical implications. IA and IZ copings fabricated by CAD/CAM technology have an acceptable marginal fit as documented in the literature, and the glass infiltration process improves the marginal fit after machining.     

The Effect of Multiple Firings on Microtensile Bond Strength of Core‐Veneer Zirconia‐Based All‐Ceramic Restorations

Purpose: Differences in core and veneer coefficients of thermal expansion, firing shrinkage, and speed of increasing and decreasing the temperature may generate stress in veneered all‐ceramic restorations. Given the necessity of performing multiple firing cycles to achieve improved contour, color, and esthetics, the purpose of this study was to determine the effect of multiple firing cycles on the microtensile bond strength (MTBS) of zirconia core to the porcelain veneer in zirconia‐based all‐ceramic restorations. Materials and Methods: Thirty blocks (12 × 12 × 4 mm³) of semi‐sintered zirconia were machined and sintered according to manufacturer's instruction. Specimens were placed in three groups based on the number of firing cycles (4, 6, 8) for the veneering process. After veneering, the specimens were sectioned into microbars with 8 mm length and 1 mm cross‐section. Twenty sound microbars in each group were stressed to failure in a microtensile tester machine at 1 mm/min. Fractured specimens were surveyed under a scanning electron microscope and classified as cohesive in core, cohesive in veneer, and mixed. MTBS data were analyzed using one‐way ANOVA and Tukey test (p < 0.05). Results: The mean MTBS (MPa) after 4, 6, and 8 firing cycles were 30.33 ± 2.13, 27.43 ± 1.79, and 25.06 ± 1.76, respectively. There was a statistically significant difference between the bond strengths of each of the three groups (p < 0.001). Conclusion: Increase in firing cycles decreased MTBS. Most of the failures (90–95%) in all three groups were cohesive in the veneering porcelain and did not change as the number of firing cycles increased.     

Effect of repeated firings on the marginal and internal adaptation of implant-supported metal-ceramic restorations fabricated with different thicknesses and fabrication methods

Statement of problemThe effect of repeated firing on the marginal and internal adaptation of copings fabricated with different techniques, thicknesses, and alloy types is unclear.PurposeThe purpose of this in vitro study was to compare the effects of repeated firing cycles on the marginal and internal adaptation of metal copings with different thicknesses fabricated by using casting, selective laser sintering (SLS), presintered soft metal milling (PSMM), postsintered hard metal milling (PHMM), and titanium milling methods.Material and methodsSingle-unit implant-supported copings (N=120) were fabricated with 0.5-mm and 1.5-mm thicknesses, and porcelain was applied in accordance with the manufacturer's instructions (n=12). The marginal and internal adaptation of the metal copings were examined before the firing cycles and after the fourth and seventh firing cycles by using a silicone replica technique with a stereomicroscope at ×80 magnification. The results were analyzed by using 3-way analysis of variance for repeated measurements on a single factor, 2-way analysis of variance, and an independent samples t test (α=.05).ResultsAs a result of the repeated firing cycles, the changes in the marginal discrepancy and internal discrepancy values in the PSMM, PHMM, and titanium milling groups and the change in the internal discrepancy value in the casting group were statistically significantly different (P<.05). The effect of the interaction of the firing, method, and thickness difference on the marginal discrepancy and internal discrepancy values was not statistically significantly different (P>.05).ConclusionsAfter the firing cycles, the PSMM, SLS, and titanium milling groups were found to have better marginal and internal adaptation for both thicknesses than the casting and PHMM groups.     

An In Vitro Evaluation of Fit of Zirconium‐Oxide‐Based Ceramic Four‐Unit Fixed Partial Dentures,Generated with Three Different CAD/CAM Systems,before and after Porcelain Firing Cycles and after Glaze Cycles

Purpose: The purpose of this study was to assess in vitro the marginal fit of four‐unit fixed partial dentures (FPDs) produced using three different computer aided design/computer aided manufacturing (CAD/CAM) all‐ceramic systems before and after porcelain firing cycles and after glaze cycles. Materials and Methods: An acrylic resin model of a maxillary arch was fabricated. Teeth #6 and 9 were prepared; teeth #7 and 8 were absent. Forty‐five four‐unit zirconium‐oxide‐based ceramic FPDs were made following conventional impression and master cast techniques: 15 were made with the Everest system, 15 with the Procera system, and 15 with the Lava system. Marginal gaps along vertical planes were measured for each bridge before (Time 0) and after (Time 1) porcelain firing cycles and after glaze cycles (Time 2) using a total of 8 landmarks (4 for tooth #6 and 4 for tooth #9) by means of a microscope at a magnification of ×50. MANOVA was performed to determine whether the 8 landmarks, jointly considered, differed between CAD/CAM systems and time phases. Two‐way ANOVA was performed to investigate in detail, for each landmark, how gap measurements were related to CAD/CAM systems and time phases. Differences were considered to be significant at p < 0.05. Results: The mean values of the Everest system (μm) were: 63.37 (Time 0), 65.34 (Time 1), and 65.49 (Time 2); the mean values of the Lava system (μm) were: 46.30 (Time 0), 46.79 (Time 1), and 47.28 (Time 2); the mean values of the Procera system (μm) were: 61.08 (Time 0), 62.46 (Time 1), and 63.46 (Time 2). MANOVA revealed quantitative differences of the 8 landmarks, jointly considered, between the three CAD/CAM systems (p < 0.0001), but it did not reveal any quantitative differences among the three time phases (p > 0.4). Two‐way ANOVA revealed that the Lava system produced gap measurements statistically smaller than the Everest and Procera systems (p < 0.0001 for each landmark). Conclusions: Within the limitations of this study, it was concluded that the three zirconium‐oxide‐based ceramic CAD/CAM systems demonstrated a comparable and acceptable marginal fit; however, the Lava system produced gap measurements statistically smaller than the Everest and Procera systems. The porcelain firing cycles and the glaze cycles did not affect the marginal fit of the zirconium‐oxide‐based ceramic CAD/CAM systems.     

Influence of firing cycles on the margin distortion of 3 all-ceramic crown systems

STATEMENT OF PROBLEM: Although all-ceramic restorations are widely used, there is a lack of information about how the fit is affected by fabrication procedures. The adequacy of the fit of all-ceramic restorations has been questioned. PURPOSE: This study examined the effect of porcelain and glaze firing cycles on the fit of 3 types of all-ceramic crowns. MATERIAL AND METHODS: Ten standardized all-ceramic crowns were fabricated on a metal die from each of 3 systems: conventional In-Ceram, copy-milled In-Ceram, and copy-milled feldspathic crowns. Copings of the conventional and copy-milled In-Ceram crowns and nonglazed copy-milled feldspathic crowns served as the control. A device was used to apply a uniform load on specimens during measurement and to reposition the specimens on the measurement device after each manufacturing process. The specimens were not cemented and were measured on the metal die using a profile projector. Measurements were recorded at 18 points selected along horizontal and vertical planes. The crown systems were compared by use of the Student t test and 1-way analysis of variance (ANOVA). Data of measurements repeated at identical locations were analyzed with a multivariate repeated-measures ANOVA. The Bonferroni post hoc test was used for multiple comparisons (alpha=.05). RESULTS: The conventional In-Ceram (57 +/- 24 microm) and copy-milled In-Ceram (57 +/- 32 microm) crowns demonstrated nearly identical marginal discrepancy values, followed by the copy-milled feldspathic crowns with a mean of 17 +/- 12 microm in the vertical plane. The copy-milled In-Ceram crowns had a mean horizontal discrepancy value of -12 +/- 4 microm, followed by the copy-milled feldspathic crowns with a mean of -4 +/- 5 microm and the conventional In-Ceram crowns with a mean of -6 +/- 4 microm. Statistical analyses demonstrated no significant differences in the marginal discrepancy values among the 3 all-ceramic crown systems, except for the horizontal discrepancy values between the conventional and copy-milled In-Ceram crowns after the porcelain firing cycle. Results indicated that the addition of porcelain to the copings caused a significant change ( P <.05) in the marginal fit of the crowns, except for the fit in the horizontal plane of the conventional In-Ceram crowns. However, no significant changes occurred in the fit of the 3 all-ceramic crowns after the glaze firing cycle. There were significant differences in the marginal discrepancy values among the measurement locations ( P <.05), and the discrepancy value at each location was independent of the mean of the entire crown. CONCLUSIONS: Within the limitations of this study, it was concluded that the 3 all-ceramic crown systems demonstrated a comparable and acceptable marginal fit. The porcelain firing cycle affected the marginal fit of the all-ceramic crowns. However, the glaze firing cycle had no significant effect on fit. The conventional and copy-milled In-Ceram crowns demonstrated medial deformations at the labial and palatal surfaces that might result in occlusal displacement of the crown.     

Stress-relieving and porcelain firing cycle influence on marginal fit of commercially pure titanium and titanium-aluminum-vanadium copings.

OBJECTIVES: This study evaluated: (1) the marginal fit of copings fabricated from commercially pure titanium (cp Ti) and titanium-aluminum-vanadium alloy (Ti-6Al-4V) after each firing cycle for a recommended porcelain; and (2) the effectiveness of a stress-relieving treatment on the fit. The results were compared with copings made with Pd-Ag alloy submitted to the recommended porcelain firing protocol. METHODS: Bovine teeth were machined for metal-ceramic crowns and die casts were obtained for waxing patterns. The firing cycle of titanium porcelain was performed on cp Ti and Ti-6Al-4V copings obtained using the Rematitan System. A stress-relieving treatment (cp Ti treated and Ti-6Al-4V treated groups) was performed on original invested castings at the first porcelain firing temperature (800 degrees C). Fit (microm) was measured in the 'as cast' condition and after each porcelain firing cycle with a traveling microscope. The values were compared using the analysis of variance and Tukey's test (P<0.05), the Pd-Ag group was compared to titanium groups using Dunnett's test (P<0.05). RESULTS: The marginal fit values in the as-cast condition (initial) were 84.43 microm for Ti-6Al-4V not treated, 76.35 microm for Ti-6Al-4V treated, 86.09 microm for cp Ti not treated, 97.66 microm for cp Ti treated and 58.11 microm for Pd-Ag group. The Ti-6Al-4V, cp Ti, and Pd-Ag groups exhibit significant differences in marginal fit values when the as-cast condition (initial) was compared with those after the recommended porcelain firing protocol (by Tukey's test at 5% probability level). No significant differences were observed between stress-relieving treated and not treated groups.Significance. The firing cycles used for porcelain build-up may worsen the fit of titanium copings to values that suggest no inferences to the detriment of clinical applications.     

Evaluation of some properties of an opaque porcelain fired simultaneously with the body porcelain

Recently, a porcelain-fused-to-metal opaque porcelain was introduced that does not require a separate firing before application of the body porcelain. The objective of this study was to determine the properties of this new opaque porcelain and its ability to bond to metal. The properties studied included flexural strength, linear firing shrinkage, coefficient of thermal expansion, powder particle size, and ability to bond to body porcelain and dental alloys. Sintering of this opaque porcelain was complete when fired at 1760 ° F (960 ° C) with a linear firing shrinkage of 13.1% ± 0.2%. No boundary between the opaque and body porcelains could be found with a scanning electron microscope after firing at 1760 ° F (960 ° C). The mean flexural strengths were 99 ± 7 and 101 ± 8 MPa respectively, for this opaque porcelain and a conventional opaque porcelain, and were not significantly different as assessed with Student's t-test (p = 0.548). The coefficient of thermal expansion for this opaque porcelain was 13.3 ± 0.2 × 10⁻⁶/ ° C. Particle size analysis showed a 63% increase in the particles below 5 μm for this opaque porcelain and bonding to two alloys was adequate as indicated by its cohesive failure. Simultaneous firing of this special opaque porcelain and body porcelain produced satisfactory sintering, strength, and bonding to metal.     

An in vitro assessment of a ceramic-pressed-to-metal system as an alternative to conventional metal ceramic systems

Purpose: This article reviews a press‐on metal (POM) ceramic versus a conventional veneering system regarding marginal gaps, fracture resistance, microhardness, and surface roughness. This was done to provide clinical recommendations for its use. Materials and Methods: Forty crowns were constructed and divided into two main groups according to the metal coping design. Group 1: Twenty metal copings with metal margin extending to the axiogingival line angle. Group 2: Twenty metal copings with metal margin 1 mm occlusal to the axiogingival line angle. The specimens of each group were further subdivided into two subgroups (A and B) according to the veneering porcelain used. The vertical marginal gaps of the crowns were measured after veneering placement. For fracture resistance testing, the crowns were subjected to compressive load to failure. Representative samples of the two main groups were selected to measure surface roughness and microhardness. Results: No statistically significant difference was evident regarding the vertical marginal gap distance in relation to the margin design of both tested groups (p= 0.249, p= 0.815); however, the POM veneer group with metal porcelain margin showed statistically lower marginal gaps than the conventional ceramic veneer group (p= 0.043). Fracture resistance values did not show statistically significant difference regarding the margin design (p= 0.858, p= 0.659) or type of the ceramic veneer material (p= 0.592, p= 0.165). Both groups showed no significant difference in their mean roughness values (p= 0.235). Conventional ceramics showed statistically significantly higher mean microhardness values than POM did (p= 0.008). Conclusion: This study showed superior marginal adaptation, decreased microhardness, and similar load to failure and roughness values of the POM ceramic system. Moreover, considerable ease and speed of fabrication of this system were evident. The high variation in range values of some tested groups is among the limitations of this study, along with the lack of clinical trials to test the system in vivo.     

Thermal cycling distortion of porcelain fused to metal fixed partial dentures

Statement of problem. The initial fit of porcelain fused to metal restorations deteriorates during the firing cycle of porcelain. Purpose. This study evaluated thermal cycling distortion of 3-unit porcelain fused to metal frameworks at different firing stages. Material and methods. A master model was designed to represent the 2 abutments of a 3-unit fixed partial denture replacing a missing mandibular molar. Standard techniques were used to fabricate 10 castings. Half of the copings were cast in a Ni-Cr alloy and the other half in a Pd-Cu alloy. Framework distortion was measured by means of inner fit changes, horizontal linear measurements of the framework length, and vertical fit changes of each retainer. Measurements were made (1) initially, (2) after degassing firing, and (3) after glaze firing. Differences between the firing cycles created distortion values of the retainers in 3 dimensions. Repeated measures ANOVA was used to analyze data statistically. Results. Measured differences between the 2 firing stages ranged from –47 to 81.7 μm. For both alloy groups, retainers showed increase in vertical gap that implied poorer vertical fit after porcelain application. Mean values of inner fit change recorded for porcelain application firing were higher in magnitude than the values of metal-conditioning firing. In addition, no statistically significant differences were found among alloy types. Conclusions. A 3-dimensional distortion was observed both in Pd-Cu and Ni-Cr frameworks during porcelain firing cycle. The distortion seen after porcelain application firing was significantly greater than that seen after metal-conditioning firing. This result can be attributed to these factors, contamination of porcelain to the inner surface of metal coping and reduction in resilience of metal. (J Prosthet Dent 1998;80:654-60.)     

Effect of Veneering Techniques on Color and Translucency of Y‐TZP

Purpose: This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria‐stabilized tetragonal zirconia polycrystalline (Y‐TZP) all‐ceramic restorations. Materials and Methods: Thirty disc specimens (10‐mm diameter, 0.50 ± 0.01 mm thick) were fabricated of IPS e.max ZirCAD core material, and ZL1 IPS e.max ZirLiner (0.10‐mm thick) was layered. The specimens were randomly divided into three groups (n = 10/group). Group ZP (fully anatomical technique) was veneered 0.60 mm by heat‐pressing IPS e.max ZirPress fluorapatite glass‐ceramic ingots; Group ZC (traditional layering technique) was veneered 0.60 mm by condensing and sintering IPS e.max Ceram low‐fusing nano‐fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 0.30 mm with veneering porcelain. Color parameters (L*, a*, b*) and total luminous transmittance (τ) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively. Color saturation (C*ab) and color difference (ΔE) were calculated using color difference formula. One‐way analysis of variance (ANOVA) combined with a Tukey multiple‐range test were used to analyze the data (α= 0.05). Results: As to ZP, ZPC, and ZC groups, the value of a* increased (?1.35 ± 0.07, ?0.64 ± 0.06, ?0.36 ± 0.05, respectively) (p < 0.05); b* decreased (27.01 ± 0.07, 25.48 ± 0.11, 23.28 ± 0.25, respectively) (p < 0.05); and C*ab decreased (27.04 ± 0.08, 25.49 ± 0.11, 23.28 ± 0.25, respectively) (p < 0.05). L* value and total luminous transmittance were highest in ZP group (87.53 ± 0.48, 1.64 ± 0.03, respectively), and lowest in ZPC group (82.14 ± 0.18, 1.47 ± 0.01, respectively) (p < 0.05). Conclusions: Y‐TZP all‐ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest.     

Marginal fit and microleakage of cast and metal laser sintered copings—An in vitro study

PurposeThis study aimed to compare the marginal fit and microleakage of metal laser sintered Co–Cr alloy copings and conventional cast Ni–Cr alloy copings using a stereomicroscope.MethodsForty extracted maxillary premolars were randomly divided into two groups. One group was subjected to coping fabrication using conventional lost wax (LW) technique while the other group was subjected to coping fabrication using metal laser sintering (MLS) technology. The marginal fit of these copings were compared before and after ceramic addition using images obtained with a steromicroscope and an ImageJ analysis software. All the specimens were cemented using Type 1 glass ionomer cement and were subjected to thermocycling. The specimens were evaluated for microleakage using stereomicroscope and 2% methylene blue die used as a tracer. The data were subjected to statistical analysis using paired t-test, Mann–Whitney test and Chi-Square test.ResultsThe mean marginal fit of copings before and after ceramic addition in Group B (MLS) was better than the copings in Group A (LW) and was statistically significant (P < 0.05). The influence of ceramic firing had a significant (P < 0.05) increase in mean marginal gap in Group A (LW) but not in Group B (MLS). And the difference in mean microleakage between the groups was not statistically significant (P ≥ 0.05).ConclusionThe copings fabricated using MLS technique had a better marginal fit and an observable decrease in microleakage when compared to the copings fabricated using the conventional lost wax (LW) technique.     

Porcelain Fracture Resistance of Screw‐Retained,Cement‐Retained,and Screw‐Cement‐Retained Implant‐Supported Metal Ceramic Posterior Crowns

Purpose: The purpose of this in vitro study was to compare the porcelain fracture resistance between screw‐retained, cement‐retained, and combined screw‐ and cement‐retained metal–ceramic (MC) implant‐supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw‐access opening on porcelain fracture resistance of screw‐retained and cement‐retained MC implant‐supported posterior single crowns. Materials and Methods: Forty standardized MC molar‐shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw‐retained, screw‐access hole placed in the center of the occlusal surface; Group SRO: screw‐retained, screw access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement‐retained, zinc phosphate cement was used; Group CSC: cement‐retained with a screw‐access hole in the center of the occlusal surface. The screw‐retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one‐way ANOVA and Tukey's Studentized test (α= 0.05). Results: Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 ± 593; Group SRO: 1885 ± 491; Group CRP: 3707 ± 1086; Group CSC: 1700 ± 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05). Conclusion: The cement‐retained restorations showed significantly higher mean fracture loads than the restorations having screw‐access openings in their occlusal surface. The position of the screw‐access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.     

Fracture strength of porcelain fused to metal crowns made of cast,milled or laser-sintered cobalt-chromium

Abstract

Aims. The aim was to compare the fracture strength of porcelain fused to metal crowns with copings fabricated in Co-Cr using different manufacturing techniques (casting, milling and laser-sintering) with crowns manufactured in a high-gold alloy. Methods. A total of 50 identical crowns were fabricated and sub-divided into five groups; cast Co-Cr, milled Co-Cr, two groups of laser-sintered Co-Cr and a control group cast in a high-gold alloy. After thermocycling (5000 cycles, 5–55°C) and pre-load (30–300 N, 10,000 cycles) the crowns were loaded until fracture. Load (N) and fracture mode were recorded. Results. There was a significant difference (p < 0.05) in fracture strength between the control group and one of the laser-sintered groups. The mean values (N) for the groups were as follows: cast Co-Cr, 1560 ± 274; milled Co-Cr, 1643 ± 153; laser-sintered Co-Cr 1, 1448 ± 168; laser-sintered Co-Cr 2, 1562 ± 72; control group, 1725 ± 220. Conclusion. There is no difference in strength between Co-Cr crowns produced using the different production technologies: casting, milling or laser-sintering. Metal ceramic crowns made with copings fabricated in a high-gold alloy present numerically higher fracture strength than crowns made with copings fabricated in Co-Cr alloys. The difference is confirmed when analyzing the fracture surfaces, but the difference in fracture strength value is limited and is only significant with regard to one of the two laser-sintered groups.     

氧化锆和纯钛基底冠材料及饰瓷烧结对种植全冠适合性的影响

目的 研究氧化锆和纯钛基底冠材料及饰瓷烧结对种植全冠内部和边缘适合性的影响。方法 制作计算机辅助设计/计算机辅助制作（CAD/CAM）氧化锆烤瓷种植全冠（A组）和纯钛烤瓷种植全冠（B组）各8个（n=8）。分别用硅橡胶轻体复制饰瓷烧结前基底冠和饰瓷烧结后全冠的内部和边缘间隙,采用Micro-CT扫描硅橡胶,建立三维图像,测量冠边缘垂直间隙（MG）、冠边缘水平间隙（HMD）和冠内部轴面中点间隙（AW）。采用SPSS 17.0软件对测量结果进行统计学分析。结果 饰瓷烧结前,A组基底冠MG、HMD和AW均大于B组（P<0.05）。饰瓷烧结后,A组全冠MG小于B组（P<0.05）,两组的HMD和AW均无统计学差异（P>0.05）。饰瓷烧结使A组MG减小（P<0.05）,使B组MG、HMD和AW均增大（P<0.05）,而A组HMD和AW烧结前和烧结后的差异无统计学意义（P>0.05）。结论 氧化锆烤瓷种植全冠边缘适合性优于纯钛烤瓷种植全冠;饰瓷烧结对氧化锆和纯钛烤瓷种植全冠适合性均会产生影响。     

Effect of sandblasting on fracture load of titanium ceramic crowns

Purpose of the Study:

It is difficult to achieve a reliable bond between the titanium and veneering porcelain. The aim of this study was to evaluate the bond strength between titanium ceramic crowns.

Materials and Methods:

The surfaces of titanium copings were divided in two groups. Group A sandblasted with 250 um (n = 10) and Group B without sandblasting (n = 10). Low-fusing porcelain was bonded over copings. A universal testing machine was used to determine the fracture load (N) of the crowns. All data were compared using Student''s t-test.

Results:

There was a significant difference in fracture toughness between two groups (P = 0.05). The mean value of fracture strength for Group A was 721.66 N and for Group B was 396.39 N.

Conclusions:

Sandblasting improves the bond strength between titanium, and ceramic, mechanical bonding plays a crucial role in the bonding between titanium and ceramic.Key Words: Bonding, fracture load, sandblasting, titanium     

Comparison of the Marginal Fit of Pressable Ceramic to Metal Ceramic Restorations

Purpose: The aim of this in vitro study was to compare the marginal adaptation of a pressed ceramic material, when used with and without a metal substructure, to a traditional feldspathic porcelain‐fused‐to‐metal restoration with a porcelain butt margin. Materials and Methods: A maxillary central incisor typodont tooth was prepared with a 1.5 mm 360° shoulder with rounded internal line angle, and 30 polyether impressions were made. Dies were poured in type IV dental stone, and 30 restorations were fabricated: 10 metal ceramic restorations (MCR) with porcelain butt joints, 10 pressed to metal restorations (PTM), and 10 all‐ceramic restorations (PCR). All restorations were evaluated on their respective dies at 45× magnification using an Olympus SZX‐12, measurements of the marginal openings were made, and ANOVA and Scheffé post hoc tests were used to evaluate the data. Results: The mean marginal opening was 72.2 ± 5.9 μm for MCR, 49.0 ± 5.9 μm for PTM, and 55.8 ± 5.9 μm for PCR. The post hoc tests showed that there was a statistical difference between the marginal adaptation of the PTM and MCR groups (p < 0.05). There was no significant difference in marginal adaptation between the PTM and the PCR groups, or the PCR and the MCR groups. Conclusions: The PTM group demonstrated a smaller mean marginal opening than the MCR group. The mean marginal openings of all three groups were within a clinically acceptable range.     

The effect of endodontic access cavity preparation and subsequent restorative procedures on molar crown retention

Preparation of an endodontic access cavity through a full crown may affect its retention. This study was undertaken to investigate the effects on molar crown retention of endodontic access cavities and their subsequent restoration. Thirty human molars were mounted in resin, crown preparations were cut and their surface areas were determined. Vented metal copings were cemented with zinc phosphate and the forces required to displace each coping were measured using a tensile-testing machine. The copings were recemented, access cavities were cut and their surface areas determined prior to the displacement forces being re-measured. The copings were recemented, assigned to two groups, and the access cavities were restored - Group 1 with amalgam; Group 2 with glass ionomer (GIC). Displacement forces were re-measured and the copings were recemented. The occlusal margins of the access cavities were ***bevelled and restored again prior to displacement forces being re-measured. Mean displacement forces were -Group 1: Original (kg force), 37.86 ± 3.97; After access cavity, 29.28 ± 3.22; Amalgam, 50.21 ± 4.71; Amalgam + bevel, 46.45 ± 6.21. Group 2: Original, 42.77 ± 4.49; After access cavity, 39.25 ± 5.91; GIC, 48.11 ± 3.55; GIC + bevel, 39.63 ± 5.31. Statistical analyses with paired t tests showed that retentive values with access cavities were significantly lower than with intact crowns. Amalgam or GIC restorations increased retention beyond original values, significantly with amalgam. Bevelled occlusal margins decreased retention of crowns with restored access cavities but this was not significantly different from the original values. A significant relationship existed between total surface areas of the crown preparations, areas of the occlusal tables, and retentive values for crowns without access cavities. The access cavity area, as a proportion of the total area of the preparation, was related to the decrease in retention.