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 restoration''s 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.     

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.     

Marginal fit of anterior 3-unit fixed partial zirconia restorations using different CAD/CAM systems

PURPOSE

Few studies have investigated the marginal accuracy of 3-unit zirconia fixed partial dentures (FPDs) fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) system. The purpose of this study was to compare the marginal fit of zirconia FPDs made using two CAD/CAM systems with that of metal-ceramic FPDs.

MATERIALS AND METHODS

Artificial resin maxillary central and lateral incisors were prepared for 3-unit FPDs and fixed in yellow stone. This model was duplicated to epoxy resin die. On the resin die, 15 three-unit FPDs were fabricated per group (45 in total): Group A, zirconia 3-unit FPDs made with the Everest system; Group B, zirconia 3-unit FPDs made with the Lava system; and Group C, metal-ceramic 3-unit FPDs. They were cemented to resin dies with resin cement. After removal of pontic, each retainer was separated and observed under a microscope (Presize 440C). Marginal gaps of experimental groups were analyzed using one-way ANOVA and Duncan test.

RESULTS

Mean marginal gaps of 3-unit FPDs were 60.46 µm for the Everest group, 78.71 µm for the Lava group, and 81.32 µm for the metal-ceramic group. The Everest group demonstrated significantly smaller marginal gap than the Lava and the metal-ceramic groups (P<.05). The marginal gap did not significantly differ between the Lava and the metal-ceramic groups (P>.05).

CONCLUSION

The marginal gaps of anterior 3-unit zirconia FPD differed according to CAD/CAM systems, but still fell within clinically acceptable ranges compared with conventional metal-ceramic restoration.     

The effect of various veneering techniques on the marginal fit of zirconia copings

PURPOSE

This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques).

MATERIALS AND METHODS

Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (α=.05).

RESULTS

Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 µm) was higher than press-over (50.64 µm) and CAD-on (51.50 µm) veneered groups (P<.001).

CONCLUSION

Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.     

Chipping behaviour of all-ceramic crowns with zirconia framework and CAD/CAM manufactured veneer

Objectives

The aim of this in vitro study was to assess the ultimate load to failure of zirconia based crowns veneered with CAD/CAM manufactured ceramic.

Methods

32 identical, anatoform zirconia (Sirona inCoris ZI, mono L F1) frameworks (thickness 0.6 mm) were constructed (Sirona inLab 3.80). Afterwards, 16 crowns were completed using a CAD/CAM manufactured lithium disilicate ceramic veneer (IPS e.max CAD, Ivoclar Vivadent). The remaining 16 frames were veneered using conventional manual layering technique. For the CAD/CAM manufactured veneers, the connection between framework and veneer was accomplished via a glass fusion ceramics. Before fracture tests, half of the specimens underwent thermocycling and chewing simulation (1.2 million chewing cycles, force magnitude F_max = 108 N). To further investigate the new technique, finite element computations were carried out on the basis of the original geometry.

Results

Nearly all (87.5%) conventionally veneered crowns failed already during chewing simulation, whereas crowns with CAD/CAM manufactured veneers were non-sensitive to artificial ageing. Crowns veneered with lithium disilicate ceramic displayed ultimate loads to failure of about 1600 N.

Conclusion

The CAD/CAM production of veneers for restorations with zirconia framework is a promising way to reduce failures originating from material fatigue.     

Fracture resistance of three porcelain-layered CAD/CAM zirconia frame designs

Objectives

Chipping is the most frequent clinical failure of zirconia crowns. Causes of chipping have not been completely understood and different possible reasons have been considered. The study was aimed at evaluating the fracture resistance of 3 different CAD/CAM zirconia frame designs veneered with porcelain.

Methods

Thirty extracted sound premolars were divided into 3 groups (n = 10). Chamfer preparations were performed, impressions were taken. Three zirconia frame designs (Aadva, GC) were realized: reproduction of the abutment contour (flat design, FD); wax-up as for porcelain-fused-to-metal crowns (PFM); anatomically guided, designed to keep constant the thickness of the overlying porcelain veneering (AG). Porcelain veneering was made with pressure layering technique (Initial Zr, GC). Crowns were cemented utilizing a self-adhesive resin cement (G-Cem, GC). After a 24-h water storage at 37 °C, using a universal testing machine (1 mm crosshead speed), crowned teeth were loaded in the central fossa in a direction parallel to the longitudinal axis of the tooth. Load at fracture was recorded in Newtons (N). Digital photographs of the specimens were taken in order to assess failure patterns. Between-group differences in fracture strength were statistically analyzed (One-Way Analysis of Variance, Tukey test, p < 0.05).

Result

Load at fractures differed significantly among the groups (p = 0.004). AG exhibited significantly higher fracture resistance 1721.6 (488.1) N than PFM 1004.6 (321.3) N and FD 1179.5 (536.2) N, that were comparable. Repairable failures occurred in 80% of AG, 70% of PFM, and 50% of FD specimens.

Significance

Anatomically guided zirconia frames resisted significantly higher loads than flat and PFM-like frame designs.     

Fracture strength testing of crowns made of CAD/CAM composite resins

Purpose

The purpose of this study was to ascertain whether computer aided design/computer aided manufacturing (CAD/CAM) composite resin crowns have sufficient strength to withstand the bite force of the molar teeth. The null hypothesis was that the fracture strength of CAD/CAM composite resin crowns is lower than the average maximum bite force of the molar tooth.

Effects of core characters and veneering technique on biaxial flexural strength in porcelain fused to metal and porcelain veneered zirconia

PURPOSE

The purpose of this study was to assess the impact of the core materials, thickness and fabrication methods of veneering porcelain on prosthesis fracture in the porcelain fused to metal and the porcelain veneered zirconia.

MATERIALS AND METHODS

Forty nickel-chrome alloy cores and 40 zirconia cores were made. Half of each core group was 0.5 mm-in thickness and the other half was 1.0 mm-in thickness. Thus, there were four groups with 20 cores/group. Each group was divided into two subgroups with two different veneering methods (conventional powder/liquid layering technique and the heat-pressing technique). Tensile strength was measured using the biaxial flexural strength test based on the ISO standard 6872:2008 and Weibull analysis was conducted. Factors influencing fracture strength were analyzed through three-way ANOVA (α≤.05) and the influence of core thickness and veneering method in each core materials was assessed using two-way ANOVA (α≤.05).

RESULTS

The biaxial flexural strength test showed that the fabrication method of veneering porcelain has the largest impact on the fracture strength followed by the core thickness and the core material. In the metal groups, both the core thickness and the fabrication method of the veneering porcelain significantly influenced on the fracture strength, while only the fabrication method affected the fracture strength in the zirconia groups.

CONCLUSION

The fabrication method is more influential to the strength of a prosthesis compared to the core character determined by material and thickness of the core.     

The effect of zirconia framework design on the failure of all-ceramic crown under static loading

PURPOSE

This in vitro study aimed to compare the failure load and failure characteristics of two different zirconia framework designs of premolar crowns when subjected to static loading.

MATERIALS AND METHODS

Two types of zirconia frameworks, conventional 0.5 mm even thickness framework design (EV) and 0.8 mm cutback of full contour crown anatomy design (CB), were made for 10 samples each. The veneer porcelain was added on under polycarbonate shell crown made by vacuum of full contour crown to obtain the same total thickness of the experiment crowns. The crowns were cemented onto the Cobalt-Chromium die. The dies were tilted 45 degrees from the vertical plane to obtain the shear force to the cusp when loading. All crowns were loaded at the lingual incline of the buccal cusp until fracture using a universal testing machine with cross-head speed 0.5 mm/min. The load to fracture values (N) was recorded and statistically analyzed by independent sample t-test.

RESULTS

The mean and standard deviations of the failure load were 1,170.1 ± 90.9 N for EV design and 1,450.4 ± 175.7 N for CB design. A significant difference in the compressive failure load was found (P<.05). For the failure characteristic, the EV design was found only cohesive failures within veneering porcelain, while the CB design found more failures through the zirconia framework (8 from 10 samples).

CONCLUSION

There was a significant difference in the failure load between two designs, and the design of the framework influences failure characteristic of zirconia crown.     

Microscopical and chemical surface characterization of CAD/CAM zircona abutments after different cleaning procedures. A qualitative analysis

PURPOSE

To describe and characterize the surface topography and cleanliness of CAD/CAM manufactured zirconia abutments after steaming and ultrasonic cleaning.

MATERIALS AND METHODS

A total of 12 ceramic CAD/CAM implant abutments of various manufacturers were produced and randomly divided into two groups of six samples each (control and test group). Four two-piece hybrid abutments and two one-piece abutments made of zirconium-dioxide were assessed per each group. In the control group, cleaning by steam was performed. The test group underwent an ultrasonic cleaning procedure with acetone, ethyl alcohol and antibacterial solution. Groups were subjected to scanning electron microscope (SEM) analysis and Energy-dispersive X-ray spectroscopy (EDX) to verify and characterize contaminant chemical characterization non-quantitatively.

RESULTS

All zirconia CAD/CAM abutments in the present study displayed production-induced wear particles, debris as well as organic and inorganic contaminants. The abutments of the test group showed reduction of surface contamination after undergoing an ultrasonic cleaning procedure. However, an absolute removal of pollutants could not be achieved.

CONCLUSION

The presence of debris on the transmucosal surface of CAD/CAM zirconia abutments of various manufacturers was confirmed. Within the limits of the study design, the results suggest that a defined ultrasonic cleaning process can be advantageously employed to reduce such debris, thus, supposedly enhancing soft tissue healing. Although the adverse long-term influence of abutment contamination on the biological stability of peri-implant tissues has been evidenced, a standardized and validated polishing and cleaning protocol still has to be implemented.     

Effect of span length on the fit of zirconia framework fabricated using CAD/CAM system

PURPOSE

The purpose of this study was to evaluate the effect of the span length on the fit of zirconia framework fabricated using CAD/CAM system.

MATERIALS AND METHODS

Abutments for single, 4-unit and 6-unit fixed partial prostheses were fabricated. Ten zirconia frameworks were fabricated for each group. The marginal and internal gap were presented by means of replica technique and measured by measuring microscope (AXIO®, Carl Zeiss, Rochester, NY) and software (I-solution®, IMT i-solution Inc., Vancouver, BC, Canada). The results were statistically analyzed by multivariate analysis test and Dunnett T3 test for post hoc test (α=.05).

RESULTS

There were statistically significant differences at 2, 4, 7, 8 points (mesio-distal section) and b, d, e, f, g (labio-lingual section). In some marginal reference points of 6-unit group (P<.05), the marginal gap were larger than 120 µm.

CONCLUSION

Span length of zirconia core may have an influence on marginal and internal fit. Within the limitation of this study, the increase of span length of zirconia framework of 6 or more-unit fixed partial denture may decrease the marginal and internal fit.     

Current status of zirconia restoration

During the past decade, zirconia-based ceramics have been successfully introduced into the clinic to fabricate fixed dental prostheses (FDPs), along with a dental computer-aided/computer-aided manufacturing (CAD/CAM) system. In this article (1) development of dental ceramics, (2) the current status of dental CAD/CAM systems, (3) CAD/CAM and zirconia restoration, (4) bond between zirconia and veneering ceramics, (5) bond of zirconia with resin-based luting agents, (6) surface finish of zirconia restoration and antagonist enamel wear, and (7) clinical evaluation of zirconia restoration are reviewed.Yttria partially stabilized tetragonal zirconia polycrystalline (Y-TZP) showed better mechanical properties and superior resistance to fracture than other conventional dental ceramics. Furthermore, ceria-stabilized tetragonal zirconia polycrystalline and alumina nanocomposites (Ce-TZP/A) had the highest fracture toughness and had resistance to low-temperature aging degradation. Both zirconia-based ceramics have been clinically available as an alternative to the metal framework for fixed dental prostheses (FDPs). Marginal adaptation of zirconia-based FDPs is acceptable for clinical application. The most frequent clinical complication with zirconia-based FDPs was chipping of the veneering porcelain that was affected by many factors. The mechanism for the bonding between zirconia and veneering ceramics remains unknown. There was no clear evidence of chemical bonding and the bond strength between zirconia and porcelain was lower than that between metal and porcelain.There were two alternatives proposed that might avoid chipping of veneering porcelains. One was hybrid-structured FDPs comprising CAD/CAM-fabricated porcelain parts adhering to a CAD/CAM fabricated zirconia framework. Another option was full-contour zirconia FDPs using high translucent zirconia. Combined application of silica coating and/or silane coupler, and 10-methacryloyloxydecyl dihydrogen phosphate is currently one of the most reliable bonding systems for zirconia. Adhesive treatments could be applied to luting the restorations and fabricating hybrid-structured FDPs. Full-contour zirconia FDPs caused concern about the wear of antagonist enamel, because the hardness of Y-TZP was over double that of porcelain. However, this review demonstrates that highly polished zirconia yielded lower antagonist wear compared with porcelains. Polishing of zirconia is possible, but glazing is not recommended for the surface finish of zirconia.Clinical data since 2010 are included in this review. The zirconia frameworks rarely got damaged in many cases and complications often occurred in the veneering ceramic materials. Further clinical studies with larger sample sizes and longer follow-up periods are required to investigate the possible influencing factors of technical failures.     

Effect of different veneering techniques on the fracture strength of metal and zirconia frameworks

PURPOSE

To determine whether the fracture strengths and failure types differed between metal and zirconia frameworks veneered with pressable or layering ceramics.

MATERIALS AND METHODS

A phantom molar tooth was prepared and duplicated in 40 cobalt-chromium abutments. Twenty metal (IPS d.SIGN 15, Ivoclar, Vivadent, Schaan, Liechtenstein) and 20 zirconia (IPS e.max ZirCAD, Ivoclar) frameworks were fabricated on the abutments. Each framework group was randomly divided into 2 subgroups according to the veneering material: pressable and layering ceramics (n=10). Forty molar crowns were fabricated, cemented onto the corresponding abutments and then thermocycled (5-55℃, 10,000 cycles). A load was applied in a universal testing machine until a fracture occurred on the crowns. In addition, failure types were examined using a stereomicroscope. Fracture load data were analyzed using one-way ANOVA and Tukey HSD post-hoc tests at a significance level of 0.05.

RESULTS

The highest strength value was seen in metal-pressable (MP) group, whereas zirconia-pressable (ZP) group exhibited the lowest one. Moreover, group MP showed significantly higher fracture loads than group ZP (P=.015) and zirconia-layering (ZL) (P=.038) group. No significant difference in fracture strength was detected between groups MP and ML, and groups ZP and ZL (P>.05). Predominant fracture types were cohesive for metal groups and adhesive for zirconia groups.

CONCLUSION

Fracture strength of a restoration with a metal or a zirconia framework was independent of the veneering techniques. However, the pressing technique over metal frameworks resisted significantly higher fracture loads than zirconia frameworks.     

97例CAD/CAM氧化锆基底冠桥修复体制作效果评价

目的评价运用CAD/CAM技术制成的氧化锆修复体的制作效果,探讨影响效果的相关因素。方法选择97例CAD/CAM氧化锆冠桥基底修复的临床病例,观察修复体制作的过程,分析其边缘适合性、颜色、固位、折断或破损情况,综合评价制作效果。以70例贵金属烤瓷冠作为对照组进行研究。结果 97例修复体的制作过程中,发现有1例在切削加工时从包埋蜡中脱落,1例上前牙4单位桥在完成烧结后有小幅度翘动,1例上前牙3单位桥体在切削过程中破裂,上述3例修复体通过返工重做解决问题。所有制作的氧化锆支架,通过饰面瓷的堆塑可使修复体获得较好的美观效果。两种修复方式在边缘适合性、固位和破损率上均无统计学差异(P>0.05),而CAD/CAM氧化锆基底冠的颜色良好率要优于贵金属基底冠(P<0.05)。结论高强度氧化锆全瓷修复体的制作效果能符合临床要求,可以考虑用于全瓷修复。     

三维有限元分析在纤维桩力学研究中的应用进展

纤维桩自推出以来以其良好的生物相容性、优良的机械性能、耐疲劳、耐腐蚀以及易拆除、根折发生率低等优点,在残根残冠的修复治疗中逐渐得到广泛的应用。有限元分析能对复杂形态、结构物体在各种载荷下的应力应变进行分析比较,是口腔生物力学研究中的重要手段。其中三维有限元分析因其模型的几何相似性和力学相似性,成为了纤维桩力学研究中的一种高效、精确、直观的方法。     

Clinical gap changes after porcelain firing cycles of zirconia fixed dentures

PURPOSE

The aim of this study was to measure the changes on the marginal and internal adaptation of zirconia based anterior fixed partial dentures after the porcelain firing process.

MATERIALS AND METHODS

A total of 34 anterior fixed partial dentures using LAVA CAD/CAM system (3M ESPE, Germany) were applied. Two silicone replicas were obtained: one is obtained before porcelain firing process (initial) and the other is obtained after porcelain firing process (final), followed by the examination under a binocular stereomicroscope. Kruskal Wallis and Wilcoxon Signed Ranks tests were used for the statistical analysis (P<.05).

RESULTS

No statistically significant difference was found between initial and final marginal gap values (P>.05). At the internal gap measurements, final marginal area values (59.54 µm) were significantly lower than the initial marginal area values (68.68 µm)(P<.05). The highest and the lowest internal gap values were observed at the incisal/occlusal area and at the marginal area, respectively. In addition, lower internal gap values were obtained for canines than for central incisors, lateral incisors and premolars at the incisal area (P<.05).

CONCLUSION

The firing cycles did not affect the marginal gap of Lava CAD/CAM system, but it is controversial for the internal gap.     

Gap comparison between single crown and three-unit bridge zirconia substructures

PURPOSE

To compare marginal and internal gaps of zirconia substructure of single crowns with those of three-unit fixed dental prostheses.

MATERIALS AND METHODS

Standardized Co-Cr alloy simulated second premolar and second molar abutments were fabricated and subsequently duplicated into type-III dental stone for working casts. After that, all zirconia substructures were made using Lava™ system. Marginal and internal gaps were measured in 2 planes (mesial-distal plane and buccal-palatal plane) at 5 locations: marginal opening (MO), chamfer area (CA), axial wall (AW), cusp tip (CT) and mid-occlusal (OA) using Replica technique.

RESULTS

There were significant differences between gaps at all locations. The mean ± SD of marginal gap in premolar was 43.6 ± 0.4 µm and 46.5 ± 0.5 µm for single crown and 3-unit bridge substructure respectively. For molar substructure the mean ± SD of marginal gap was 48.5 ± 0.4 µm and 52.6 ± 0.4 µm for single crown and 3-unit bridge respectively. The largest gaps were found at the occlusal area, which was 150.5 ± 0.5 µm and 154.5 ± 0.4 µm for single and 3-unit bridge premolar substructures respectively and 146.5 ± 0.4 µm and 211.5 ± 0.4 µm for single and 3-unit bridge molar substructure respectively.

CONCLUSION

Independent-samples t-test showed significant differences of gap in zirconia substructure between single crowns and three-unit bridge (P<.001). Therefore, the span length has the effect on the fit of zirconia substructure that is fabricated using CAD/CAM technique especially at the occlusal area.     

Chairside CAD/CAM materials. Part 1: Measurement of elastic constants and microstructural characterization

Objective

A deeper understanding of the mechanical behavior of dental restorative materials requires an insight into the materials elastic constants and microstructure. Here we aim to use complementary methodologies to thoroughly characterize chairside CAD/CAM materials and discuss the benefits and limitations of different analytical strategies.

CAD/CAM氧化锆全瓷在口腔修复领域的应用

回顾全瓷修复的发展历史．其美观逼真的修复效果早已被广大医生和患者所认可。而其强度一直是人们关注的焦点。目前全瓷材料的种类较多，如白榴石、锂基瓷、氧化铝、氧化锆等，制作方法也各有不同，如渗透陶瓷、热压铸造陶瓷、瓷沉积、计算机辅助设计与计算机辅助制作（CAD／CAM）等，其强度也越来越高，修复适应证也越来越广。在所有全瓷修复材料中，以CAD／CAM二氧化锆全瓷的抗弯强度最高㈣。CAD／CAM修复技术是将光电子技术、计算机技术及自控机械加工技术合并用于口腔修复的新技术。该技术起于20世纪70年代。但应用范围有限，效果也不尽人意。随着电子计算机技术与修复材料的迅速发展。有关该技术的研究越来越多㈤．其在口腔修复中的应用也越来越广。我国从2004年开始在临床上应用CAD／CAM氧化锆全瓷修复技术。