The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics

Purpose: The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat‐pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite‐reinforced and lithium‐disilicate glass ceramics. In addition, the effect of veneering technique (heat‐pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C‐0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat‐pressed veneering porcelain (subgroup 0.8C‐0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C‐0.7VL, 0.8C‐0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C‐0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C‐0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C‐0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C‐0.7VP subgroup. Conclusions: The present study suggests that veneering porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite‐reinforced glass‐ceramic cores have lower flexural strength than lithium‐disilicate ones, while fabrication techniques (heat‐pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat‐pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia‐veneered ceramics exhibited greater flexural strength than monolithic leucite‐reinforced and lithium‐disilicate ceramics regardless of zirconia veneering techniques (heat‐pressed or powder/liquid technique).     

离子交换强韧化效应对CAD/CAM二硅酸锂玻璃陶瓷机械性能的影响

目的:探究锂-钠离子交换强韧化效应对CAD/CAM二硅酸锂玻璃陶瓷机械性能的影响.方法:制作50个CAD/CAM二硅酸锂玻璃陶瓷圆片状试件,晶化、打磨及抛光后,用4种不同的熔融硝酸钠离子交换工艺进行处理(n=10),分别检测离子交换前后样品的双轴弯曲强度、维氏硬度和断裂韧性.设置未交换组为空白对照.结果:CAD/CAM...     

Can we use the translucency parameter to predict the CAD/CAM ceramic restoration aesthetic?

ObjectivesTo evaluate the effects of background color, ceramic type and coping thickness on masking ability (ΔE) and translucency parameter (TP) of CAD/CAM lithium disilicate glass-ceramic/monolithic zirconia and, to determine the correlations between coping thickness, TP and ΔE.MethodsA total of 120 ceramic specimens (2 mm, 1 mm and 0.5 mm thickness; n = 10) of four CAD/CAM ceramics: IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD, were studied. Specimens were tested over nine fabricated backgrounds: A1, A2, A3.5, ND2 and ND7 shade resin-based composites, cobalt-chromium alloy (CC), medium precious alloy (MPA), black (B) and white (W). CIELab values (L*, a* and b*), color difference (ΔE) and translucency parameter (TP) were measured and calculated using a digital spectrophotometer (color i7, X-Rite, Pantone®). Data were analyzed using the Shapiro-Wilk test, one-way ANOVA, three-way ANOVA, independent t-tests and Tukey post-hoc tests (p < 0.05).Results2 mm CAD/CAM ceramics showed ideal color matching (ΔE<2.6) over different backgrounds, except for CC, B and W backgrounds. Monolithic zirconia had lower ΔE values than lithium disilicate glass-ceramics. ΔE and TP values significantly reduced with the increased coping thickness (p < 0.05). Regardless of ceramic type and thickness, a strong TP-SD of ΔE correlation was observed.SignificanceCAD/CAM ceramic restoration color was significantly affected by background color, ceramic type and coping thickness. TP is a promising predictor for appropriate ceramic selection to receive an acceptable CAD/CAM ceramic restoration aesthetic.     

Flexural properties of three lithium disilicate materials: An in vitro evaluation

ObjectiveThe goal of this study was to investigate the flexural strength, Young’s modulus and Weibull modulus of two heat-pressed and one CAD/CAM processed lithium disilicate (LD) ceramics.Material and methodsA total of 45 specimens with dimensions 16 × 4 × 1.2 ± 0.2 mm were fabricated out of three LD ceramics. For heat-pressed LD specimens, acrylate polymer blocks were cut and divided into two groups (n = 15 per group); a GC LiSi Press LD group (LP) and an IPS e.max Press group (EP). Specimens for each group were pressed corresponding to the manufacturer’s recommendations. For the CAD-CAM Group (EC), IPS e.max CAD blocks were cut to obtain specimens (n = 15) to the desired dimensions. Flexural strength and Young’s modulus tests were executed using a universal testing machine. A one-way ANOVA and post-hoc Tuckey’s tests were applied to analyze the results (p ≤ 0.05).ResultsRegarding flexural strength, the EC group showed higher statistically substantial difference than the EP and LP groups (p = 0.001), while there was no pronounced difference between the EP and LP groups (p = 0.065). For Young’s modulus test, all the three tested groups had no statistically substantial difference (p = 0.798).ConclusionThe IPS e.max CAD group had higher mechanical performance than the IPS e.max Press and GC LiSi Press groups.     

Crack-healing during two-stage crystallization of biomedical lithium (di)silicate glass-ceramics

ObjectiveThe study is aimed to evaluate the two single commercially available two-step lithium-(di)silicate systems by analyzing their parent glass composition and studying the quantitative crystalline and glass phase evolution during the second stage heat-treatment. The mechanical repercussions of the crystallization firing were evaluated using strength and fracture toughness tests.MethodsXRF and ICP-OES were used to determine the oxide composition of the parent glasses in Suprinity PC (Vita Zahnfabrik) and IPS e.max CAD (Ivoclar-Vivadent). The crystalline phase of both materials was determined by quantitative XRD and the G-factor method in the partially and post-crystallization states. The oxide composition of the residual glass phase was derived by subtracting the chemistry of the crystalline phase fractions from the parent glass composition. Mechanical testing of biaxial flexural strength and fracture toughness were used to demonstrate how crack-like defects behave during crystallization.ResultsThe two tested lithium (di)silicate systems showed strong differences in oxide composition of the parent glass. This showed to influence the transformation of lithium metasilicate in lithium disilicate, with the former remaining in high vol.% fraction in the post-crystallization Suprinity PC. In IPS e.max CAD cristobalite precipitated at the surface during the second-heat treatment. Strength and fracture toughness tests revealed that crack in both materials, whether introduced by grinding or indentation, heal during the crystallization firing. Cristobalite seemed to have contributed to a surface strengthening effect in IPS e.max CAD.SignificanceAccurate crystalline phase quantification aids in the determination of the residual glass composition in dental glass-ceramics. For both systems crystallization firing induced healing of cracks generated by CAM grinding.     

Fatigue analysis of computer‐aided design/computer‐aided manufacturing resin‐based composite vs. lithium disilicate glass‐ceramic

Resin‐based composite molar crowns made by computer‐aided design/computer‐aided manufacturing (CAD/CAM) systems have been proposed as an inexpensive alternative to metal‐ceramic or all‐ceramic crowns. However, there is a lack of scientific information regarding fatigue resistance. This study aimed to analyze the fatigue behavior of CAD/CAM resin‐based composite compared with lithium disilicate glass‐ceramic. One‐hundred and sixty bar‐shaped specimens were fabricated using resin‐based composite blocks [Lava Ultimate (LU); 3M/ESPE] and lithium disilicate glass‐ceramic [IPS e.max press (EMP); Ivoclar/Vivadent]. The specimens were divided into four groups: no treatment (NT); thermal cycling (TC); mechanical cycling (MC); and thermal cycling followed by mechanical cycling (TCMC). Thermal cycling was performed by alternate immersion in water baths of 5°C and 55°C for 5 × 10⁴ cycles. Mechanical cycling was performed in a three‐point bending test, with a maximum load of 40 N, for 1.2 × 10⁶ cycles. In addition, LU and EMP molar crowns were fabricated and subjected to fatigue treatments followed by load‐to‐failure testing. The flexural strength of LU was not severely reduced by the fatigue treatments. The fatigue treatments did not significantly affect the fracture resistance of LU molar crowns. The results demonstrate the potential of clinical application of CAD/CAM‐generated resin‐based composite molar crowns in terms of fatigue resistance.     

How adjustment could affect internal and marginal adaptation of CAD/CAM crowns made with different materials

PURPOSERecently introduced hybrid and reinforced glass ceramic computer-aided design/computer-aided manufacturing (CAD/CAM) materials have been used for full-coverage restorations. However; the effect of adjustment and type of materials on internal and marginal adaptation are unknown. This study aimed to evaluate and compare the marginal and internal adaptations of crowns made of three different CAD/CAM materials before and after adjustment.MATERIALS AND METHODSOne acrylic resin maxillary first molar was prepared and served as the master die. Thirty-six restorations were fabricated using CAD/CAM system (CEREC Omnicam, MCXL) with three materials including lithium disilicate (IPS e.max CAD), zirconia-reinforced lithium silicate (Suprinity), and hybrid ceramic (Enamic). Internal and marginal adaptations were evaluated with the reference point matching technique before and after adjustment. The data were analyzed using mixed ANOVA considering α=.05 as the significance level.RESULTSThe effect of adjustment and its interaction with the restoration material were significant for marginal, absolute marginal, and occlusal discrepancies (P<.05). Before adjustment, Suprinity had lower marginal discrepancies than IPS e.max CAD (P=.18) and Enamic (P=.021); though no significant differences existed after adjustment.CONCLUSIONWithin the limitations of this study, crowns fabricated from IPS e.max CAD and Suprinity resulted in slightly better adaptation compared with Enamic crowns before adjustment. However, marginal, axial, and occlusal discrepancies were similar among all materials after the adjustment.     

Properties of hot-pressed lithium silicate glass-ceramics

Objectives

New lithium silicate/disilicate hot-pressed glass-ceramics are introduced into the dental market. It is known that the mechanical properties of this material depend on the microstructure, chemical composition, glass matrix, morphology of crystals, volume ratio crystal/glass, additive, and treatments. This contribution investigates how these factors affect the properties of the new generation of lithium silicate/disilicate hot-pressed glass-ceramics.

Cyclic contact fatigue resistance of ceramics for monolithic and multilayer dental restorations

ObjectiveTo evaluate the cyclic contact fatigue resistance and failure mode of ceramics for monolithic and multilayer restorations.MethodsCeramic structures (10 mm × 1.8 mm) were fabricated as follows (n = 28): (1) CAD-on- trilayer structure composed of Y-TZP (yttria stabilized tetragonal zirconia polycrystal- IPS e.max ZirCAD) infrastructure, fusion glass–ceramic (IPS e.max CAD Crystall/Connect) and lithium disilicate-based glass–ceramic (IPS e.max CAD); (2) ZFC- bilayer structure composed of Y-TZP infrastructure veneered by a fluorapatite glass–ceramic (IPS e.max Ceram); (3) LDC- monolithic lithium-disilicate glass–ceramic (IPS e.max CAD); and (4) YZW- monolithic Y-TZP (Zenostar Zr Translucent). All ceramics structures were bonded to a dentin analog substrate (G10). Specimens were submitted to cyclic contact fatigue test in a pneumatic cycling machine with 80 N load and 2 Hz frequency in distilled water at 37 °C. Test was interrupted after 10⁴, 10⁵, 5 × 10⁵ and 10⁶ cycles and the presence or absence of failure was recorded. Fatigue data were analyzed using Kaplan–Meier (log rank) and Holm–Sidak tests (α = 0.05). The relationship between the type of crack leading to failure and the experimental group was analyzed using chi-square test (α = 0.05).ResultsThere was no statistical difference between CAD-on and YZW groups (p = 0.516), which presented the highest survival rates after cyclic loading, followed by ZFC and LDC groups (p < 0.01). There was a significant relationship between type of crack and experimental group (p < 0.001). LDC specimens showed the greatest frequency of radial cracks, while cone cracks were more prevalent for ZFC and CAD-on specimens.SignificanceMonolithic Y-TZP (YZW) showed similar fatigue resistance to CAD-on multilayer specimens, but different failure mode. Monolithic lithium disilicate glass–ceramic (LDC) and Y-TZP conventionally veneered by glass–ceramic (ZFC) showed lower survival time under fatigue.     

Pressed ceramics onto zirconia. Part 1: Comparison of crystalline phases present, adhesion to a zirconia system and flexural strength

Objectives

To compare the crystalline phases present, quantify the adhesion to zirconia and measure the mechanical properties of four commercially available pressed ceramics suitable for zirconia substructures.Materials and methods This study compares the X-ray diffraction response and the mechanical properties of four different pressed ceramics (Noritake CZR Press, Vita PM9, Wieland PressXzr and IPS e.max ZirPress) to Vita In-Ceram YZ zirconia substrate. The adhesion was determined using the interfacial strain energy release rate fracture mechanics approach; in addition biaxial flexural strength values of each material was determined.

Results

X-ray diffraction analysis revealed that Noritake CZR Press and Vita PM9 contain leucite whereas IPS e.max ZirPress and Wieland PressXzr are non-leucite amorphous materials.The strain energy release rate results revealed that the pressed ceramics with leucite have better adhesion than non-leucite ceramics to zirconia. Differences were observed between biaxial strength results for the pressed ceramics from bilayer compared with monolayer specimens.

Conclusions

Pressed ceramics compatible with zirconia tested in this study were of two types; leucite containing and non-leucite containing essentially glass ceramics. Leucite containing pressable ceramics appears to have better adhesion to zirconia.     

IPS-Empress 2 玻璃陶瓷结构及性能的研究

目的 研究新型IPS-Empress 2牙科高强度陶瓷的显微结构和机械性能。方法采用原子力显微镜、扫描电子显微镜和X射线衍射仪，分析IPS-Empress 2的显微结构和晶相，用三点弯曲实验和压痕法测试其弯曲强度和断裂韧性。结果IPS-Empress 2玻璃陶瓷主要由二硅酸锂晶体和磷酸锂晶体组成，二者形成相互交错的三维网络式结构；这种玻璃陶瓷在热压铸前后晶体相保持不变，其三点弯曲强度和断裂韧性分别为300MPa和3．1MPam^1/2。结论IPS-Empress 2玻璃陶瓷的高强度和韧性与高含量的二硅酸锂晶体、相互锁结的网络结构和裂纹偏转有关。     

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.

Effect of Surface Acid Etching on the Biaxial Flexural Strength of Two Hot-Pressed Glass Ceramics

Purpose: The purpose of this study was to assess the effect of surface acid etching on the biaxial flexural strength of two hot-pressed glass ceramics reinforced by leucite or lithium disilicate crystals.
Materials and Methods: Forty glass ceramic disks (14-mm diameter, 2-mm thick) consisting of 20 leucite-based ceramic disks (IPS Empress®) and 20 lithia disilicate-based ceramic (IPS Empress 2®) were produced by hot-pressing technique. All specimens were polished and then cleaned ultrasonically in distilled water. Ten specimens of each ceramic group were then etched with 9% hydrofluoric (HF) acid gel for 2 minutes and cleaned ultrasonically again. The biaxial flexural strength was measured by the piston-on-three-ball test in a universal testing machine. Data based on ten specimens in each group were analyzed by two-way ANOVA  (α= 0.05)  . Microstructure of ceramic surfaces before and after acid etching was also examined by a scanning electron microscope.
Results: The mean biaxial flexural strength values for each group tested were (in MPa): nonetched IPS Empress = 118.6 ± 25.5; etched IPS Empress = 102.9 ± 15.4; nonetched IPS Empress 2 = 283.0 ± 48.5; and etched IPS Empress 2 = 250.6 ± 34.6. The results showed that the etching process reduced the biaxial flexural strengths significantly for both ceramic types ( p = 0.025). No significant interaction between the ceramic type and etching process was found ( p = 0.407).
Conclusion: From the results, it was concluded that surface HF acid etching could have a weakening effect on hot-pressed leucite or lithia disilicate-based glass ceramic systems.     

Effect of Crystallization Firing on Marginal Gap of CAD/CAM Fabricated Lithium Disilicate Crowns

Purpose

To evaluate the marginal gaps of CAD/CAM (CEREC 3) produced crowns made from leucite‐reinforced glass‐ceramic (IPS Empress CAD) blocks (LG), and lithium‐disilicate (IPS e.max CAD) blocks before (LD‐B), and after (LD‐A) crystallization firing.

Materials and Methods

A human molar tooth (#19) was mounted with adjacent teeth on a typodont and prepared for a full‐coverage ceramic crown. The typodont was assembled in the mannequin head to simulate clinical conditions. After tooth preparation 15 individual optical impressions were taken by the same operator using titanium dioxide powder and a CEREC 3 camera per manufacturer's instructions. One operator designed and machined the crowns in leucite‐reinforced glass‐ceramic blocks (n = 5) and lithium‐disilicate blocks (n = 10) using the CEREC 3 system. The crowns were rigidly seated on the prepared tooth, and marginal gaps (μm) were measured with an optical microscope (500×) at 12 points, 3 on each of the M, B, D, and L surfaces of the leucite‐reinforced glass‐ceramic crowns and the lithium‐disilicate crowns before and after crystallization firing. Results were analyzed by two‐way ANOVA followed by a Tukey's post hoc multiple comparison test (α = 0.05).

Results

The overall mean marginal gaps (μm) for the crowns evaluated were: LG = 49.2 ± 5.5, LD‐B = 42.9 ± 12.2, and LD‐A = 57.2 ± 16.0. The marginal gaps for LG and LD‐B were not significantly different, but both were significantly less than for LD‐A.

Conclusions

The type of ceramic material did not affect the marginal gap of CAD/CAM crowns. The crystallization firing process required for lithium‐disilicate crowns resulted in a significant increase in marginal gap size, likely due to shrinkage of the ceramic during the crystallization process. Clinical Relevance: The marginal gap of CAD/CAM‐fabricated lithium disilicate crowns increases following crystallization firing. The marginal gap still remains within clinically acceptable parameters.     

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.     

Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers

ObjectiveThe fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects.MethodsEighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3 mm IPS Empress CAD and 0.3 and 0.5 mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5 mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50 N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5 mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100 N. Kaplan–Meier survival curves and log-rank tests were used for data analysis.ResultsAll highly standardized and 0.3/0.5 mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks.SignificanceUltrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin–enamel defects.     

Fracture resistance of computer‐aided design/computer‐aided manufacturing‐generated composite resin‐based molar crowns

The aim of this study was to investigate whether different fabrication processes, such as the computer‐aided design/computer‐aided manufacturing (CAD/CAM) system or the manual build‐up technique, affect the fracture resistance of composite resin‐based crowns. Lava Ultimate (LU), Estenia C&B (EC&B), and lithium disilicate glass‐ceramic IPS e.max press (EMP) were used. Four types of molar crowns were fabricated: CAD/CAM‐generated composite resin‐based crowns (LU crowns); manually built‐up monolayer composite resin‐based crowns (EC&B‐monolayer crowns); manually built‐up layered composite resin‐based crowns (EC&B‐layered crowns); and EMP crowns. Each type of crown was cemented to dies and the fracture resistance was tested. EC&B‐layered crowns showed significantly lower fracture resistance compared with LU and EMP crowns, although there was no significant difference in flexural strength or fracture toughness between LU and EC&B materials. Micro‐computed tomography and fractographic analysis showed that decreased strength probably resulted from internal voids in the EC&B‐layered crowns introduced by the layering process. There was no significant difference in fracture resistance among LU, EC&B‐monolayer, and EMP crowns. Both types of composite resin‐based crowns showed fracture loads of >2000 N, which is higher than the molar bite force. Therefore, CAD/CAM‐generated crowns, without internal defects, may be applied to molar regions with sufficient fracture resistance.     

数字化口腔修复（18）--CAD／CAM全瓷冠与个性化基台的适合性

目的：比较不同计算机辅助设计和制造（ computer aided design／manufacture,CAD／CAM）全瓷冠与氧化锆个性化基台的边缘和内部适合性。方法：用CAD／CAM分别设计和加工氧化锆个性化基台和全瓷冠3组（ IPS e． max、Enamic和Suprinity）,每组各5个全瓷冠。通过微机断层扫描（ micro computed tomography,micro?CT）测量全瓷冠与氧化锆个性化基台的绝对边缘差异（ absolute marginal discrepancy,AMD）、轴面间隙（ axial gap,AG）、咬合间隙（ oc?clusal gap,OG）,比较不同材料全瓷冠与氧化锆个性化基台的边缘和内部适合性。结果：Enamic组分别与IPS e． max组和Suprinity组AMD之间的比较差异均具有统计学意义（P＜0．05）;而IPS e． max组与Suprinity组AMD之间的差异则无统计学意义（P＞0．05）。 Suprinity组分别与IPS e． max组和Enamic组AG之间的比较差异均具有统计学意义（P＜0．05）;IPS e． max组与Enamic组AG之间的差异不具有统计学意义（P＞0．05）。 Suprinity组、IPS e． max组和Enamic组3组OG之间的比较差异具有统计学意义（P＜0．05）。结论：不同的CAD／CAM全瓷冠材料影响其边缘和内部适合性。 Suprinity和IPS e． max陶瓷材料的边缘适合性优于Enamic材料,Suprinity材料全瓷冠的轴面间隙和咬合间隙最小。     

数字化口腔修复（6）--应用口内扫描仪精确设计冠边缘位置（附病例报告）

目的：探讨CEREC?椅旁计算机辅助设计（computer aided design,CAD）精确地确定冠边缘位置的方法。方法：报告1例采用CAD／CAM IPS e．max瓷块修复前牙（11、21）牙体缺损的病例,按照改良的美国公共卫生署（United States Public Health Service,USPHS）标准评价临床疗效。牙体预备后,通过CEREC?口内扫描仪测量排龈前后游离龈缘（FGM）的变化。结果：取出排龈线30min后,FGM的变化趋于稳定,11和21的FGM分别根向退缩了0．2 mm。各阶段复查结果表明：患牙无折断、劈裂及继发龋等不良现象。临床指标均达到A级标准。结论：二矽酸锂玻璃陶瓷用于前牙牙体缺损的修复可以取得理想的美学效果,远期疗效有待进一步观察。CEREC?椅旁CAD精确设计冠边缘的位置方法可用于临床。     

Effects of CAD/CAM ceramics and thicknesses on translucency and color masking of substrates

ObjectiveTo compare the translucency and masking of zirconia-reinforced lithium silicate with lithium disilicate glass-ceramic and hybrid composite.Materials and methodsOne hundred and twenty disc-shaped specimens were fabricated using Enamic, Celtra Duo, IPS E.max CAD, and Suprinity. Twelve groups were prepared according to material type and thickness (0.5, 1.0, and 1.5 mm). The specimens were tested over five substrates: composite resin-A3.5 shade (A3.5 control group), zirconia-A1 shade (ZR), nickel–chromium alloy (NC), black (B), and white (W). A spectrophotometer operating at wavelengths from 360 to 750 nm and a view-area size of 9.53 mm was used for color measurement.ResultsMean color difference values (ΔΕ) were found to be lowest in Suprinity and highest in IPS E.max. CAD. Color difference values were significantly related to substrate shade. The A3.5 substrate revealed the significantly lowest ΔΕ values of all the substrates (P = 0.05). Regarding the translucency parameters for ceramics of different thicknesses, a significant difference was observed among all groups except in Suprinity.ConclusionsDifferent ceramic types with different thicknesses and substrate strongly affect translucency and masking.Clinical significanceFabricating durable aesthetic restorations that also meets patients’ expectations is among the most significant challenges in dentistry. With high demand for more natural restorations, ceramics based on computer-aided design (CAD) and computer-aided manufacture (CAM) became popular and exhibited excellent results. However, various factors such as abutment shade, luting cement color, and ceramic type, thickness, and translucency may affect the prosthesis shade. The objective of this study was to evaluate the effects of these factors on the final shades of CAD/CAM-based ceramic restorations.