Crowns revisited

This paper overviews recent changes to making crowns. For the most part it presents clinically relevant information using examples where necessary. The paper will act as a useful reminder for the techniques involved with crown preparations and the choices of materials available.     

Game of Crowns der MHH-Fachschaft

Der Freie Zahnarzt - FVDZ-Landesverband Sachsen Es ist inzwischen eine liebgewonnene Tradition, wenn der FVDZ-Landesverband in Sachsen Zahnmedizinstudenten vor Weihnachten zum stimmungsvollen...     

Short-Term Results of IPS-Empress Full-Porcelain Crowns

Purpose A leucite-reinforced, glass-ceramic material was recently introduced for clinical use. In this clinical trial, IPS-Empress material was tested in the form of full-porcelain crowns. Materials and Methods Thirty-four patients were restored with 78 full-porcelain crowns. After etching the crowns with hydrofluoric acid, they were silanized and luted using dentin bonding agents and resin composite cement, which was primarily a dual-cured type. The 41 anterior and 37 posterior crowns were evaluated clinically with a mirror and probe, radiographically, and using clinical photographs, according to the modified United States Public Health Service criteria. Restorations having neither charlie nor delta criteria were defined as successful, and their survival rate was calculated according to Kaplan-Meier analysis. Results The mean observation period for the 78 restorations was 19.7 ± 8.5 months. Seventy-four crowns were defined as successful. Four restorations failed because of fractures. Three of the four failures occurred in the first 2 months after cementation. The survival rate was estimated to be 95% successful after 2 years in service. Eighty percent of the crowns demonstrated an excellent esthetic result. Conclusions The initial clinical results of this esthetic full-porcelain crown system are encouraging. However, because of fatigue phenomena for all ceramic materials, a longer observation period is needed to provide a definitive prognosis about the long-term clinical behavior.     

纯钛烤瓷冠与镍铬烤瓷冠抗折力的对比研究

目的:对比研究两种方式(铸造及CAD/CAM)制作的纯钛烤瓷冠及镍铬烤瓷冠的抗折力。方法:制作3组前磨牙形态金属烤瓷冠每组各10个:镍铬合金烤瓷冠(Ni组)、CAD/CAM纯钛烤瓷冠(T1组)、铸造纯钛烤瓷冠(T2组)。制作过程中对金属底层冠的厚度进行测量、校正,对烤瓷冠进行扫描、图像测量及校正,所获得的数据进行统计分析排除组间差异。所有烤瓷冠粘结于统一切削制作的纯钛代型上,然后在万能材料测试机上接受静态加载至崩瓷,获得崩瓷时的载荷力值(F),采用单因素方差分析法对比3组F值的差异。折裂面置于体式显微镜下观察折裂范围及破坏形式。结果:3组试件的F值分别为:Ni组(2348 ± 441)N、T1组(2144 ± 501)N、T2组(1823 ± 576)N,差异无统计学意义。折裂主要发生在冠的舌1/3;Ni组、T1组的主要破坏形式为混合破坏,而T2组主要为界面破坏。结论:两种方式制作的纯钛烤瓷冠的抗折力与传统镍铬合金烤瓷冠的相近,且都超过正常咬合力值。     

All-Porcelain Labial Margin for Ceramometal Crowns

The elimination of the labiogingival metal collar of a porcelain-fused-to-metal (PFM) restoration is an attempt to achieve an improved esthetic result. In their expectation of a more cosmetic tooth restoration, patients may influence dentists to use the all-porcelain labial margin to avoid metal showing in the final restoration. Success of this type of restoration depends upon proper tooth preparation. The all-porcelain margin requires a 1.2-mm wide labiogingival shoulder of approximately 70 or 90 degrees wrapping into the interproximal area. Much of the effectiveness of the restoration depends upon the design of the metal substructure. The following change is made in the design of this substructure for this modified PFM crown: the labiogingival portion of the metal is finished back to the gingival-pulpal line angle with the metal against the axial wall being from 0.3 mm to 0.5 mm thick. This allows for 0.2 to 0.3 mm of opaque and 0.7 to 1.0 mm of shoulder porcelain. The direct liftoff technique is a useful method of achieving clinically acceptable all-porcelain margins. Such restorations may give excellent results.     

Comparison of Repair Methods for Ceramic-Fused-to-Metal Crowns

PURPOSE: The objective of this study was to evaluate the effect of four repair methods on the fracture load of repaired ceramic-fused-to-metal crowns. MATERIALS AND METHODS: Metal-ceramic crowns were fractured, and the failure load was measured. The fractured metal-ceramic crowns (n = 9) were assigned randomly to the following treatment groups: (1) hydrofluoric acid (9.5%) etching, (2) air-particle abrasion (50 microm Al(2)O(3)), (3) silica coating (30 microm SiO(x)), and (4) the application of a layer of glass fiber-reinforced composite (FRC) (thickness: 0.12 mm) on the repair surface. The crowns were repaired with a highly filled resin composite and subjected to 3 repair cycles (n = 27). All specimens were stored in water at 37 degrees C for 24 hours and then thermocycled (6000 cycles, 5 degrees C to 55 degrees C). The fracture load values for final failure of intact and repaired crowns were measured with a universal testing machine, and failure types were recorded. RESULTS: No significant differences (p > 0.05) were found between the final failure values for the groups treated with 9.5% hydrofluoric acid (376 N) and airborne particle abrasion with either Al(2)O(3) (432 N) or SiO(x) (582 N) followed by silanization, respectively. Significantly, higher (p < 0.0001) final failure values (885 N) were obtained with the use of the FRC layer when compared with the other repaired groups. There was no significant difference (p > 0.05) between the final fracture load of intact crowns (872 N) and those repaired with FRC (885 N) (One-way ANOVA with repeated measures, Bonferroni test). No significant difference in fracture loads was found between the 1st, 2nd, and 3rd repair cycles (558 N, 433 N, 485 N, respectively). Failure sites were predominantly at the alloy/veneering resin interface in Group 1; Groups 2 and 3 both showed more cohesive failures than Group 1. In the case of FRC, the failure pattern was exclusively cohesive between the two laminates of FRC layer. CONCLUSIONS: The conditioning methods (Groups 1 to 3) of the repair surfaces did not show differences between each other; each resulted in mean fracture loads at lower levels than that of the intact crowns. Addition of an FRC layer increased the fracture load to the level of intact crowns. This suggests that the use of FRC in repairs of metal-ceramic crowns might be a viable option.     

Facilitated Cement Removal Technique Between Splinted Crowns

A technique for facilitating cement removal between splinted crowns is described. The technique involves tying dental floss with the large-diameter yarn portion around the embrasure of the splinted crown before cementing, and pulling it through before the cement has reached a final set. This simple, quick technique achieves removal of cement without damage to the interproximal crown surface.