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.     

In vitro fracture strength of teeth restored with different all-ceramic crown systems

STATEMENT OF PROBLEM: There is insufficient knowledge of the strength of all-ceramic crowns bonded to natural teeth to warrant the use of all-ceramic crowns in place of metal-ceramic crowns. PURPOSE: The purpose of this study was to evaluate and compare fracture resistance of crowns made of 3 different types of 2 all-ceramic crown systems-0.4-mm and 0.6-mm aluminum oxide coping crowns and zirconia ceramic coping crowns-and metal-ceramic crowns. MATERIAL AND METHODS: Forty intact, noncarious human maxillary central incisors were divided into 4 groups (n=10): Group MCC (control), metal-ceramic crown (JRVT High Noble Alloy); Group AC4, crown with 0.4-mm aluminum oxide coping (Procera AllCeram); Group AC6, crown with 0.6-mm aluminum oxide coping (Procera AllCeram); and Group ZC6, crown with 0.6-mm zirconia ceramic coping (Procera AllZirkon). Teeth were prepared for complete-coverage all-ceramic crowns so that a final dimension of 5.5 +/- 0.5 mm was achieved incisocervically, mesiodistally, and faciolingually. A 1.0-mm deep shoulder finish line was used with a rounded internal line angle. All restorations were treated with bonding agent (Clearfil SE Bond) and luted with phosphate-monomer-modified adhesive cement (Panavia 21). Fracture strength was tested with a universal testing machine at a crosshead speed of 2 mm per minute with an angle of 30 degrees to the long axis of the tooth after restorations were stored in 100% relative humidity of a normal saline solution for 7 days. The mode of fracture was examined visually. Means were calculated and analyzed with 1-way ANOVA and Tukey's HSD (alpha=.05). RESULTS: The means of fracture strength were: Group MCC, 405 +/- 130 N; Group AC4, 447 +/- 123 N; Group AC6, 476 +/- 174 N; and Group ZC6, 381 +/- 166 N. There was no significant difference between groups ( P =.501). The mode of failure for all specimens was fracture of the natural tooth. CONCLUSIONS: There was no significant difference in the fracture strength of the teeth restored with all-ceramic crowns with 0.4- and 0.6-mm aluminum oxide copings, 0.6-mm zirconia ceramic copings, and metal ceramic crowns.     

In vitro marginal fit of three all-ceramic crown systems

STATEMENT OF PROBLEM: Studies on marginal discrepancies of single restorations using various systems and materials have resulted in statistical inferences that are ambiguous because of small sample sizes and limited numbers of measurements per specimen. PURPOSE: The purpose of this study was to compare the marginal adaptation of single anterior restorations made using different systems. MATERIAL AND METHODS: The in vitro marginal discrepancies of 3 different all-ceramic crown systems (Celay In-Ceram, conventional In-Ceram, and IPS Empress 2 layering technique), and a control group of metal ceramic restorations were evaluated and compared by measuring the gap dimension between the crowns and the prepared tooth at the marginal opening. The crowns were made for 1 extracted maxillary central incisor prepared with a 1-mm shoulder margin and 6-degree tapered walls by milling. Thirty crowns per system were fabricated. Crown measurements were recorded with an optical microscope, with an accuracy of +/-0.1 microm, at 50 points spaced approximately 400 microm along the circumferential margin. The criterion of 120 microm was used as the maximum clinically acceptable marginal gap. Mean gap dimensions and standard deviations were calculated for marginal opening. The data were analyzed with a 1-way analysis of variance (alpha=.05). RESULTS: Mean gap dimensions and standard deviations at the marginal opening for the incisor crowns were 87 +/- 34 microm for control, 83 +/- 33 microm for Celay In-Ceram, 112 +/- 55 microm for conventional In-Ceram, and 46 +/- 16 microm for the IPS Empress 2 layering technique. Significant differences were found among the crown groups (P<.05). Compared with the control group, the IPS Empress 2 group had significantly smaller marginal discrepancies (P<.05), and the conventional In-Ceram group exhibited significantly greater marginal discrepancies (P<.05). There was no significant difference between the Celay In-Ceram and the control group. CONCLUSION: Within the limitations of this study, the marginal discrepancies were all within the clinically acceptable standard set at 120 microm. However, the IPS Empress 2 system showed the smallest and most homogeneous gap dimension, whereas the conventional In-Ceram system presented the largest and more variable gap dimension compared with the metal ceramic (control) restoration.     

Integration of all-ceramic restorations in reconstructive prosthetic dentistry: a case report.

A male patient presented for maxillary and mandibular complete-arch prostheses. A total of eight all-ceramic restorations, eight metal-ceramic crowns, and four metal-ceramic fixed partial dentures were placed. The restorations were examined for marginal integrity, anatomic form, surface, and color for a period of 12 months. All restorations were in function at the end of the evaluation period. There was no adverse event. No substantial difference between the all-ceramic onlays and the metal-ceramic crowns was apparent. The all-ceramic restorations exhibited the least plaque growth. Bleeding on probing was minimal at both restoration types. The marginal integrity of the all-ceramic restorations was considered to be nearly as precise as that of the metal-ceramic crowns.     

Fracture resistance of all-ceramic and metal-ceramic inlays

PURPOSE: Metal-ceramic inlay designs were developed to determine if the esthetic qualities of all-ceramic inlays could be duplicated and at the same time improve their strength and stability. The objectives of this study were to: (1) compare the fracture resistance of metal-ceramic inlays with that of all-ceramic inlays; (2) determine the correlation between the degree of preparation taper and fracture resistance; and (3) determine the correlation between marginal gap width and fracture resistance. MATERIALS AND METHODS: Inlay preparations were made on 60 Dentoform teeth, with 30 teeth allocated for metal-ceramic inlays and 30 teeth for all-ceramic inlays. Each group was further subdivided into 5-, 10-, and 20-degree taper preparations. Metal-ceramic inlays were fabricated using Goldtech Bio 2000 metal and Ceramco porcelain extending to the margin, while all-ceramic inlays were made from Empress II ceramic. Marginal gap widths were measured at six critical areas after fabrication. The load at failure was measured using an Instron Universal Testing Machine. RESULTS: The mean fracture load for all-ceramic inlays and metal-ceramic inlays at 5, 10, and 20 degrees was 70+/-40 N, 48+/-37 N, 33+/-7 N, and 40+/-23 N, 29+/-22 N, and 14+/-4 N, respectively. The mean gap width was 105 microm and 126 microm for all-ceramic and metal-ceramic inlays, respectively. CONCLUSION: The mean fracture load for Empress inlays was significantly higher than that for metal-ceramic inlays. Inlays with a 5-degree taper were significantly more fracture resistant than those with a 20-degree taper. There was no relation between marginal gap width and fracture resistance.     

Vertical marginal discrepancy of ceramic copings with different ceramic materials, finish lines, and luting agents: an in vitro evaluation

STATEMENT OF PROBLEM: Prosthetic restorations that fit poorly may affect periodontal health and occlusion. Studies that have evaluated the accuracy of fit of ceramic restorations before and after cementation assessed primarily intracoronal restorations. PURPOSE: This in vitro study evaluated the effect of different finish lines, ceramic manufacturing techniques, and luting agents on the vertical discrepancy of ceramic copings. MATERIAL AND METHODS: Two stainless steel molars were prepared for complete crowns with 2 different finish lines (heavy chamfer and rounded shoulder); each molar was duplicated to fabricate 90 copings. A total of 180 copings generated 18 groups (n=10 for each finish line-coping material-luting agent combination). Luting agents tested included zinc phosphate, resin-modified glass ionomer (Fuji Plus), and resin composite cements (Panavia F). A metal frame was developed on which to screw the stainless steel model and a ceramic coping; the distance (microm) between 2 predetermined points was measured before and after cementation by a profile projector under a torquing force. A 4-way ANOVA with repeated measurements was performed to assess the influence of each factor in the vertical marginal discrepancy: 3 between-coping factors (finish line-coping material-luting agent) and 1 within-coping factor (before and after cementation) (alpha=.05). RESULTS: Procera copings presented the lowest mean values ( P <.05) of vertical marginal discrepancy before and after cementation (25/44 microm) when compared to Empress 2 (68/110 microm) and InCeram Alumina copings (57/117 microm), regardless of any combinations among all finish lines and luting agents tested. CONCLUSION: Considering each factor separately, the ceramic manufacturing technique appeared to be the most important factor tested for the definitive vertical discrepancy of all-ceramic copings, with lower mean values for Procera copings.     

Precision of Fit of Two Margin Designs for Metal-Ceramic Crowns

STATEMENT OF PROBLEM: Although metal-ceramic restorations are widely used, there is a lack of information about how the fit is affected by margin designs. PURPOSE: This study measured and compared the precision of fit of metal-ceramic crowns with two margin designs. MATERIAL AND METHODS: Thirty-two extracted human premolar teeth were prepared for complete-coverage restorations with an internally rounded shoulder preparation. Impressions were made from all teeth, and master dies were poured with improved stone type V. MC crowns were fabricated with a porcelain-butt margin on the buccal aspect (n = 32) and a feather-edge metal margin on the lingual aspect (n = 32), which served as a control group. Precision of fit was measured three times at the mid-buccal and mid-lingual margins of each crown with a profilometer. The data were statistically analyzed with the paired t-test (alpha < .05). RESULTS: Mean marginal gap size of porcelain-butt margins was 27.93 microm (+/-15.84) and of feather-edge metal margins 42.43 microm (+/-24.12). The marginal gap size of feather-edge metal margins was statistically significantly greater than that of porcelain-butt margins (p = 0.0045). CONCLUSION: The marginal fit of porcelain-butt margins was significantly better than that of feather-edge metal margins. CLINICAL IMPLICATIONS: Porcelain-butt margins in this study had a better marginal fit than feather-edge metal margins, and thus have given clinicians evidence to prefer the use of porcelain-butt margins.     

In vitro fracture strength and thermal shock resistance of metal-ceramic crowns with cast and machined AuTi frameworks

STATEMENT OF PROBLEM: AuTi alloys with 1.6% to 1.7% (wt%) Ti provide sufficient bond strength to veneering ceramics, but the strength of entire metal-ceramic restorations fabricated from these alloys is not known. However, this information is important to assess the clinical performance of such materials. PURPOSE: This in vitro study evaluated the fracture strength and thermal shock resistance of metal-ceramic crowns with AuTi frameworks produced by milling or casting. MATERIAL AND METHODS: Frameworks of the alloy Au-1.7Ti-0.1Ir (wt%) (Esteticor Vision) were produced by milling or casting (test groups). A high-gold alloy (Esteticor Special) was used as the control. The frameworks were veneered with ceramic (VMK 95). Specimens (n=7) were loaded until fracture. Loads at failure (N) were recorded and the mean values statistically evaluated using 1-way analysis of variance and a post hoc Dunnett test (alpha=.05). To assess the crazing resistance of the veneering ceramic, 6 additional crowns of each group were subjected to a thermal shock test. Fractured surfaces were documented by scanning electron microscopy. Coefficients of thermal expansion of the materials used were measured (n=2) to assess the thermal compatibility between alloys and ceramic. RESULTS: The mean fracture strength of the crowns with machined AuTi frameworks (1294 +/- 236 N) was significantly lower (P=.012) than that of the cast AuTi frameworks (1680 +/- 150 N), but statistically not different than the high-gold alloy (1449 +/- 159 N). Bonding failure to the AuTi alloy predominantly occurred at the alloy-oxide interface. For the high-gold alloy, more ceramic residues were observed. In the thermal shock test, crowns with milled AuTi frameworks showed significantly higher thermal shock resistance compared to the other groups. The coefficients of thermal expansion (Esteticor Vision cast: 14.5 microm/m.K; Esteticor Vision milled: 14.3 microm/m.K; Esteticor Special cast: 13.7 microm/m.K) did not correlate with the results of the thermal shock test. CONCLUSION: The in vitro fracture strength of crowns with milled AuTi frameworks is lower than that obtained with cast AuTi frameworks, but comparable to those crowns produced with a high-gold alloy.     

In vitro fracture resistance of posterior metal-ceramic and all-ceramic inlay-retained resin-bonded fixed partial dentures

STATEMENT OF PROBLEM: Inlay-retained resin-bonded fixed partial dentures (RBFPDs) are conservative prosthetic restorations; however, their resistance to fracture is not clear. PURPOSE: The purpose of this study was to compare fracture loads of posterior complete coverage metal-ceramic restorations with all-ceramic inlay-retained RBFPDs. MATERIAL AND METHODS: Thirty-two posterior ceramic RBFPD restorations were divided into 4 groups (n=8): (1) Complete metal-ceramic fixed partial dentures (MC-FPDs) fabricated of Ni-Cr-based alloy (Wirolloy) and veneered with a ceramic (IPS d.SIGN) as the control group; (2) inlay-retained metal-ceramic (MC RBFPDs) with the same materials as the control; (3) inlay-retained lithium disilicate (LD) glass-ceramic (IPS Empress 2) RBFPDs; and (4) inlay-retained zirconia-based (Z) ceramic (Cercon) RBFPDs. Control specimens were prepared to receive conventional complete MC-FPDs designed to include a 1.3-mm-circumferential, 90-degree flat shoulder with rounded angles. Inlay-retained RBFPD specimens were prepared with 2-mm occlusal reduction but without bevels at the occlusal or gingival margins. Specimens were loaded and fracture loads (N) measured at fracture with a universal testing machine at a crosshead speed of 1.0 mm/min and 250 kgf load cell. Data were analyzed with 1-way ANOVA and Duncan test (alpha=.001). RESULTS: Fracture loads (mean +/- SD) were greatest for control specimens (1318.43 +/- 211.00 N) and Z-RBFPD (1247.70 +/- 262.51 N) specimens as compared to MC-RBFPD or LD-RBFPD (P < .001). MC-RBFPD exhibited the next highest fracture loads (958.01 +/- 194.29 N), and LD-RBFPD exhibited the significantly lowest values (303.23 +/- 92.54 N) of the materials tested (P < .001). CONCLUSION: Inlay-retained zirconia-based ceramic RBFPDs demonstrated the greatest fracture resistance among all inlay-retained restorations tested.     

全瓷修复与烤瓷修复临床效果比较的Meta分析

目的：：通过Meta分析系统评价全瓷修复与烤瓷修复的临床效果。方法：计算机检索PubMed、Cochrane Library、EMbase、SinoMed、中国知网和万方、维普数据库,按标准纳入比较全瓷与烤瓷修复临床效果的随机对照研究,进行资料提取及偏倚评价,采用RevMan 5.3软件进行Meta 分析。结果：最终纳入15篇文献,其中全瓷修复体768例,烤瓷修复体1386例。 Meta分析结果显示：相比于烤瓷修复,全瓷修复能显著降低牙龈炎症(RR=0.30,95%CI=0.10-0.90,P=0.03)的发生风险。还能减少基牙继发龋、改善修复体的龈缘着色及边缘适合性,但无统计学差异。二者颜色匹配及修复体崩瓷状况相当。全瓷修复易导致牙髓炎症及牙髓失活,且固定桥修复时全瓷桥支架断裂(RR=6.24,95%CI=1.20-32.41,P=0.03)的危险性显著增高。结论：现有的有限证据表明,全瓷修复的临床效果要优于烤瓷修复,在临床应用中占有一定优势,但全瓷桥的强度有待提高。     

Spectrophotometric evaluation of the optical influence of different metal alloys and porcelains in the metal-ceramic complex

STATEMENT OF THE PROBLEM: Color matching between natural teeth, shade guides, and metal-ceramic restorations is a common clinical problem. Difficulties related to color matching arise from structural differences that exist between metal-ceramic crowns and natural teeth, the limited range of available ceramic shades, inadequate shade guides, different types of metal alloys, and varying compositions of ceramic materials. PURPOSE: The aim of this study was to investigate the influence of various metal alloys and 2 porcelains on the final color of metal-ceramic complex. Material and methods Four commercial alloys for metal-ceramic restorations, a Ni-Cr (Thermobond), a Co-Cr (Wirobond), a Pd-rich noble (Cerapal-2), and a high noble Au-alloy (V-Delta) were combined with 2 porcelains (Vita Omega and Ceramco Silver) in metal-ceramic specimens with a standardized thickness of layers. Five disc-shaped (10 x 1 mm) specimens were prepared for each alloy/porcelain combination. Only opaque and dentin layers were applied (shade A3). The specimens were analyzed with a spectrophotometer, and data were obtained in the CIE Lab color system. The recorded data were analyzed with a 2-way multiple analysis of variance , a pair-wise comparison of group means (Student's t test), and finally, a categorical regression analysis of variance (CATREG) (alpha=.01). RESULTS: The types of alloy substrate and overlying porcelain significantly affected the color (P < .01). Au and Co-Cr alloys were found to be brighter (higher L* values) than the Ni-Cr and the Pd alloys ( P <.01, SE 0.239). Ceramco porcelain was found to be most red (higher a* values) of all tested alloys ( P <.01). Gold and Pd alloys caused a yellow shift to the metal-ceramic color compared to the Ni-Cr and the Co-Cr alloys with both porcelains ( P < .01, SE 0.165). The detected color differences were visually perceptible for some alloy-porcelain combinations. CONCLUSIONS: The final color of metal ceramic specimens was influenced both from the type of alloy substructure and from the type of overlying porcelain.     

In vivo fracture resistance of implant-supported all-ceramic restorations

STATEMENT OF PROBLEM: Because of their specific mechanical properties, all-ceramic restorations demonstrate a lower fracture resistance than ceramic restorations supported by metal substructures. However, advances have been made in the fabrication of high-strength all-ceramic abutments for anterior implants. No previous study has compared the fracture loads between 2 different all-ceramic abutments restored by glass-ceramic crowns. PURPOSE: The purpose of this in vitro investigation was to quantify the fracture load of implanted-supported Al(2)O(3) and ZrO(2) abutments restored with glass-ceramic crowns. MATERIALS AND METHODS: Two ceramic abutments were tested: an Al(2)O(3) abutment (CerAdapt) and a ZrO(2) abutment (Wohlwend Innovative). The abutments (n = 10) were placed on Br?nemark dental implants and prepared for restoration with glass-ceramic crowns (IPS Empress). After fabrication, in accordance with the manufacturer's guidelines, the crowns were bonded to the all-ceramic abutments with a dual-polymerizing resin luting agent. The fracture loads (N) were determined by force application at an angle of 30 degrees by use of a computer-controlled universal testing device. The data were analyzed with the unpaired t test (alpha=.05). RESULTS: Statistical analysis showed significant differences between both groups (P=.001) of all-ceramic abutments, with mean fracture load values of 280.1 N (+/- 103.1) for the Al(2)O(3) abutments and 737.6 N (+/- 245.0) for the ZrO(2) abutments. CONCLUSION: Within the limitations of this study, both all-ceramic abutments exceeded the established values for maximum incisal forces reported in the literature (90 to 370 N). The ZrO(2) abutments were more than twice as resistant to fracture as the Al(2)O(3)-abutments.     

在模型上应用Cerec III制作全瓷冠

目的:应用间接法制作cerecIII全瓷冠,避免了直接法的缺点,使完成的修复体更为精确。方法:从2002年1月至2003年7月采用间接法制备cerecIII全瓷冠35个单位,对后牙采用功能法进行设计;对前牙采用数据库法进行设计。戴牙后1个月随访检测颈缘密贴性、牙周状况和与邻牙的邻接状况。结果:后牙采用功能法制备,在模型上调改较少,而前牙采用数据库法制备,在模型上调改较多。戴入患者口内1个月有一后牙病例破损。其它病例全瓷冠颈缘与基牙肩台密贴,与邻牙的邻接状况良好,牙周状况未见异常。结论:对于大多数CerecIII的初学者来说,应用间接法可利用较长的时间来反复制取光学印模,光学印模较直接法更准确。还可更为精细地进行修复体的设计并在模型上调改精修修复体。完成修复体后也会有较长时间来总结经验。     

The effect of all-ceramic and porcelain-fused-to-metal restorations on marginal peri-implant soft tissue color: a randomized controlled clinical trial

The aim of this study was to test the color-change effect of all-ceramic restorations compared with porcelain-fused-to-metal (PFM) restorations on marginal peri-implant soft tissue. Thirty patients were randomly divided into 2 groups of 15 subjects each. The all-ceramic group received all-ceramic crowns on aluminum oxide-based abutments, while the PFM group received crowns on titanium or gold abutments. A reflectance spectrophotometer was used to measure the color difference (deltaE(Implant)) between the midfacial peri-implant mucosa before and after restoration insertion. The color difference (deltaE(Tooth-implant)) between the midfacial peri-implant mucosa and the gingival margin of the corresponding neighboring tooth was tested. The mucosal thickness was measured midfacially around the implant (MT(Implant)) and neighboring tooth (MT(Tooth)). deltaE(Implant) values were similar for the all-ceramic (7.4 +/- 2.7) and PFM groups (7.6 +/- 2.8). The all-ceramic group induced significantly less visible mucosal color change (3.4 +/- 1.4) compared to the PFM group (5.2 +/- 2.3). The MT(Implant) value of the all-ceramic group was 3.4 +/- 0.8 mm, while that of the PFM group was 2.9 +/- 0.9 mm, which was not significantly different. Significant differences were found when comparing MT(Implant) (3.1 +/- 0.9) and MT(Tooth) (1.2 +/- 0.3) values for test and control groups. All-ceramic restorations revealed a better color match to the neighboring teeth than PFM restorations.     

Marginal adaptation of different types of all-ceramic partial coverage restorations after exposure to an artificial mouth

OBJECTIVES: To determine the influence of the preparation design and the dimensions of all-ceramic partial coverage restorations (PCR) on the marginal accuracy before and after masticatory simulation. METHODS: In this in vitro study 80 extracted human maxillary molars were restored with MOD inlay restorations and four different modified PCR restorations using a new press ceramic IPS e.max Press (IPS e.max Press VP 1989). The teeth were divided into five groups of 16 specimens each and prepared as follows: Group A received an MOD inlay preparation and Group B, C, D and E received modified PCR. The restorations were adhesively luted and exposed to a mastication simulator. The discrepancies of the marginal fit were examined on epoxy replicas before and after luting as well as after masticatory simulation at 200x magnification. RESULTS: The mean (geometrical) [95% confidence limits] marginal gap decreased from Group A to E before cementation (A-83[77-90]microm, B-68[65-70]microm, C-59[55-64]microm, D-56[52-61]microm, E-50[45-55]microm). Group A had significantly higher marginal gap values than group B (p = 0.017) and the other groups (p<0.0001). After cementation the marginal accuracy was recorded as following: A-103[93-114]microm, B-101[94-108]microm, C-93[89-98]microm, D-102[98-105]microm and E-99[96-102]microm. Cementation increased the marginal gap in groups B-E significantly (p<0.00001), not significantly in group A (p = 0.059). Artificial ageing (A-116[106-127]microm, B-114[109-120]microm, C-106[103-110]microm, D-109[100-118]microm and E-109[105-112]microm) led to further significant decrease of marginal accuracy in Group B (p = 0.029) and C (p = 0.026) only. After cementation and masticatory simulation of the ceramic restorations, the marginal gap values of Groups A, B, C, D and E did not significantly differ from each other (p = 1.00). CONCLUSIONS: The result of this in vitro study showed that IPS e.max Press can be used to fabricate all-ceramic inlays and PCR which meet the requirements in terms of a clinically acceptable marginal gap, irrespective of the preparation design used. However, the preparation design and dimensions of the restorations appeared to affect the initial marginal fit and flowing off of luting material during the cementation process. The factors responsible for these findings require further substantiation.     

Influence of finish line design on marginal adaptation of electroformed metal-ceramic crowns

STATEMENT OF PROBLEM: Gold electroformed metal-ceramic restorations have been promoted as alternatives to conventional metal-ceramic restorations. However, little is known about the relationship between tooth preparation design and marginal adaptation for this type of crown. PURPOSE: This study evaluated the influence of 3 different finish line designs on the marginal adaptation of electroformed metal copings and metal-ceramic crowns. MATERIAL AND METHODS: Three steel dies were prepared for maxillary central incisor crowns with 3 finish line designs: shoulder, rounded shoulder, and deep chamfer preparations. Eight standardized electroformed metal-ceramic crowns were fabricated for each group. Marginal discrepancies were measured at 60 points for each specimen along the circumferential margin at 4 sites (labial, mesial, lingual, and distal surfaces, with 15 points for each site) before and after firing procedures using a laser microscope. Data among the 3 different groups were statistically analyzed using the Kruskal-Wallis test and the Mann-Whitney U test with the Bonferroni correction. Marginal discrepancies between prefiring and postfiring procedures were evaluated using the Wilcoxon signed-ranks test (alpha = .05). RESULTS: Significant differences in the marginal discrepancies of electroformed metal copings without porcelain and metal-ceramic crowns were found among all groups. The lowest range of median marginal discrepancy values (P < .05) at 4 sites, both before and after firing, occurred with the deep chamfer preparation (17.64-21.78 microm and 23.96-25.72 microm, respectively). The highest range values were observed in the shoulder preparation (38.13-49.89 microm and 73.87-89.44 microm, respectively). In all situations, the marginal discrepancies of the postfiring procedures were significantly greater (P = .02 or less) than those of the prefiring procedures. CONCLUSION: Within the limitations of this study, the marginal adaptation of electroformed metal copings or metal-ceramic crowns is affected by finish line design and sequentially diminished by porcelain firing procedures.     

不同颈缘弯曲度和肩台形态的泽康全瓷冠的精度

目的调查不同颈缘弯曲度和肩台形态的泽康CAD／CAM全瓷冠的边缘精度。方法准备6种不同形态的基牙（弯曲度：1mm,3mm,5ram;肩台外形：圆弧肩台,直角肩台）。制作30个泽康CAD／CAM全瓷冠（每种肩台各5个）,测定陶瓷基底冠和全瓷冠的边缘缝隙。采用双因子ANOVA分析后用T检验测定有无统计学差异。结果弯曲度1mm,3mm,5mm圆弧肩台的泽康全瓷冠的边缘缝隙分别为51（21）μm,53（22）μm,54（20）μm。弯曲度1mm,3mm,5mm直角肩台的泽康全瓷冠的边缘缝隙分别为49（18）μm,51（19）μm,50（22）μm。统计结果显示6种基牙之间没有显著性差异。结论泽康全瓷冠有良好的边缘精度,颈缘弯曲度和肩台形态对泽康全瓷冠的边缘精度没有显著影响。     

A study on the fracture strength of implant-supported restorations using milled ceramic abutments and all-ceramic crowns

PURPOSE: The purpose of this study was to compare five different abutment-crown combinations for single implant-supported restorations regarding their capabilities to withstand loads. MATERIALS AND METHODS: Fifty implants were placed into resin blocks, and the restorations were connected to the implants. The five tested restorations were: (1) metal-ceramic crowns cemented to titanium abutments, (2) In-Ceram crowns cemented to titanium abutments, (3) Celay feldspathic crowns cemented to titanium abutments, (4) In-Ceram crowns cemented to milled ceramic abutments, and (5) Celay feldspathic crowns cemented to milled ceramic abutments. The specimens were loaded at 0- and 45-degree angles to the long axis, and the load values at the moment of failure were recorded using a universal testing machine. RESULTS: The fracture strengths under vertical loading were greater than those under oblique loading. The fracture strengths of metal-ceramic crowns cemented to the titanium abutments were higher than those of all-ceramic crowns cemented on the milled ceramic abutments, regardless of loading direction. There were no differences in the fracture strengths of the ceramic crowns between the two different abutment types under oblique loading. CONCLUSION: All-ceramic crowns on the milled ceramic abutments were weaker than the metal-ceramic crowns on the titanium abutments under oblique loading.     

Fracture strength of all-ceramic crowns luted using two bonding methods

STATEMENT OF THE PROBLEM: Excellent esthetic quality is one of the major advantages of all-ceramic restorations; however, catastrophic fracture of such restorations is still a disadvantage. Ceramic bonding systems using ceramic primers without the use of hydrofluoric acid have been introduced, but data about the efficiency of these systems are lacking. PURPOSE: This study investigated the influence of 2 bonding procedures on the fracture resistance of low-fusing ceramic and computer aided design-computer aided manufacturing (CAD-CAM) all-ceramic crowns. MATERIAL AND METHODS: Forty-two standardized all-ceramic crowns were fabricated on human maxillary premolars. Seven unprepared maxillary premolars were used as control. Three all-ceramic crown systems were used: 1 low-fusing ceramic (Duceram) and 2 machineable ceramics (Vita Mark II and ProCAD) using the Cerec 3 CAD-CAM system. The intaglio surfaces of fabricated crowns (n=7) were subjected to 2 different conditioning techniques: etching, using 4.9% hydrofluoric acid followed by application of Mirage ABC silane, or cleaning, using 65% phosphoric acid and application of primer (Porcelain Liner-M). The crowns were luted to the teeth using Superbond C&B luting agent. After 24 hours storage in water, specimens were loaded in a universal testing machine with the compressive load applied along the long axis of the specimen at a crosshead speed 1 mm/min until fracture. Fracture loads (N) were recorded. One-way analysis of variance (ANOVA) and the Tukey HSD test (alpha=.05) were used for statistical analysis of the data. RESULTS: The mean fracture load of control specimens (738.3+/-195.3 N) was not significantly different from that of the 2 CAD-CAM crowns (667.7+/-72.3 N, 715.9+/-105.2 N). However, fracture load of natural teeth and the 2 CAD-CAM crowns was significantly higher than the fracture load of the low-fusing ceramic crowns treated with HF acid and silane (465.5+/-101.1 N) and, when cleaned, using phosphoric acid and an application of primer (447.5+/-63.4 N) (P<.05). There was no significant difference in the mean fracture load of each ceramic material when bonded using the 2 different procedures, either treated with HF acid and silane or cleaned using phosphoric acid and application of primer (P>.05). CONCLUSION: The application of a primer (Procelain Liner-M) was an effective method for treating the intaglio surface of all-ceramic crowns before cementation.     

Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM

OBJECTIVES: To examine the marginal fit of resin composite crowns manufactured with the CEREC 3 system employing three different margin designs; bevel, chamfer and shoulder, by means of a replica technique and a luting agent. METHODS: Three master casts were fabricated from an impression of a typodont molar tooth and a full-coverage crown prepared with a marginal finish of a bevel, a chamfer and a shoulder. Each cast was replicated 10 times (n=10). Scanning of the replicas and crown designing was performed using the CEREC Scan system. The crowns were milled from Paradigm MZ100 composite resin blocks. The marginal fit of the crowns was evaluated with a replica technique (Aquasil LV, Dentsply), and with a resin composite cement (RelyX Unicem, Aplicap) and measured with a travelling microscope. Statistical analysis was performed using two-way ANOVA. RESULTS: For the replica technique the average marginal gaps recorded were: Bevel Group 105+/-34 microm, Chamfer Group 94+/-27 microm and Shoulder Group 91+/-22 microm. For the resin composite cement the average marginal gaps were: Bevel Group 102+/-28 microm, Chamfer Group 91+/-11 microm and Shoulder Group 77+/-8 microm. Two-way ANOVA analysis showed that there was no statistically significant difference between the three groups of finishing lines regardless of the cementation technique used. CONCLUSIONS: The marginal gap of resin composite crowns manufactured with the CEREC 3 system is within the range of clinical acceptance, regardless of the finishing line prepared or the cementation technique used.