Galvano- vs. metal-ceramic crowns: up to 5-year results of a randomised split-mouth study

Mid-term survival and complications of double-crown-retained removable dental prostheses placed in the dental practice - a retrospective study

OBJECTIVES

Clinical data on the performance of double-crown-retained removable dental prostheses (dcRDPs), especially beyond university studies, are rare. The objective of this retrospective clinical study was to evaluate the survival and complication-freeness probabilities of dcRDPs and to identify risk factors for failure and complications in a dental practice setting.

MATERIALS AND METHODS

Anonymized practice data of 174 patients (56.9% female) fitted with a total of 213 dcRDPs (mean of 3.3 abutment teeth per dcRDP) were evaluated up to 11 years after prothesis placement (mean observation time of 3.9 years). Probabilities of survival and complication freeness were calculated on the prosthesis- and abutment level and visualized using the Kaplan-Meier method. Factors influencing failure and complications were computed using Cox regression analyses (R Ver. 7; alpha < 0.05).

RESULTS

During our observation period, 39 (18%) of the dcRDPs failed. The mean (95% CI) overall survival was 94% (90-97%) after 2 years and 86% (80-92%) after 5 years. DcRDP survival correlated with lower patient age and more abutment teeth (P < 0.05), while other analyzed factors did not. The probability of absence of prosthesis-related complications was 92% after 2 years and 80% after 5 years. The probability of no technical complications of abutments (teeth/implants) was 85% after 2 years and 78% after 5 years, and the probability of no biological complications was 87% after 2 years and 72% after 5 years. In total, 141 dcRDPs (66.2%) faced at least one complication during the observation period.

CONCLUSIONS

Double-crown-retained prostheses fitted in a dental practice had acceptable mid-term survival rates and common technical and biological complications that were frequently easily manageable. However, prosthesis performance depended on the quality and number of abutment teeth/implants. Within the limitations of this retrospective analysis, the outcomes we observed in a dental practice are comparable to, albeit slightly worse than, those found in university studies.

CLINICAL RELEVANCE

Evaluation of the clinical performance of dcRDPs fitted in a dental practice is important to estimate durability and complication patterns in order to weigh treatment decisions.

Impact of material combinations and removal and insertion cycles on the retention force of telescopic systems

OBJECTIVES

A variety of dental materials are available for the fabrication of telescopic crowns. The aim was to investigate the impact of material combinations and removal and insertion cycles on their retention forces.

MATERIALS AND METHODS

CAD/CAM-fabricated cobalt-chromium-molybdenum (CoCr) and zirconia (ZrO₂) primary crowns were combined with polyetheretherketone (PEEK), polyetherketoneketone (PEKK), CoCr, and ZrO₂ secondary crowns (four combinations included PEEK/PEKK secondary crowns in a thickness of 0.5 mm bonded to the CoCr tertiary construction), resulting in 12 different material combinations: CoCr-PEEK; CoCr-PEKK; CoCr-ZrO₂; CoCr-CoCr; CoCr-PEEK 0.5; CoCr-PEKK 0.5; ZrO₂-PEEK; ZrO₂-PEKK; ZrO₂-ZrO₂, ZrO₂-CoCr; ZrO₂-PEEK 0.5; and ZrO₂-PEKK 0.5 (n = 15 pairings per material combination). Pull-off tests were performed with a universal testing machine initially and after 500, 5000, and 10,000 removal and insertion cycles in a mastication simulator. Descriptive statistics with the Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests were computed (α = 0.05).

RESULTS

The tested parameters, material combination, and removal and insertion cycles had significant impact on the retention force values (p < 0.001). An increase in removal and insertion cycles was associated with a decrease in retention forces within CoCr and ZrO₂ secondary crowns, regardless of the primary crown material. In contrast, PEEK and PEKK secondary crowns presented higher retention load values after 10,000 cycles than initially.

CONCLUSION

Different material combinations behaved differently after simulated removal and insertion regimens. This difference should be considered during treatment planning.

CLINICAL RELEVANCE

Telescopic crown systems should be made of materials with predictable retention forces that do not deteriorate with time. The implementation of new materials and technologies facilitates reproducibility and time-saving fabrication.

Restoration of 1325 teeth with partial-coverage crowns manufactured from high noble metal alloys: a retrospective case series 18.8 years after prosthetic delivery

OBJECTIVES

To evaluate long-term survival and success rates of conventionally cemented partial-coverage crowns (PCCs) manufactured from high noble metal alloys (hn).

MATERIAL AND METHODS

Restoration-, periodontal- and tooth-related criteria on patients, restored with a single or multiple conventionally cemented hnPCCs in a private dental office were collected from existing patient records. With regard to semi-annual follow-ups, data of the most recent clinical evaluations were considered. Kaplan-Meier and log-rank tests were used for statistical analyses. Level of significance was set at p ≤ .05.

RESULTS

Between 09/1983 and 09/2009, 1325 hnPCCs were conventionally cemented on 1325 teeth in 266 patients (mean age: 44.5 ± 10.7 years). Due to various reasons, 81 hnPCCs showed complications, documenting a success rate of 93.9% after a mean observation period of 18.8 ± 5.7 years. Of these, additional 14 restorations were counted as survival, resulting in a survival rate of 94.9%. Most frequent complications were periodontal issues (n = 29, 35.8%). Significantly higher success rates were documented for hnPCCs of patients aged between 37 and 51 years (p = .012).

CONCLUSION

Partial-coverage crowns from high noble metal alloys showed excellent survival and success rates after a mean observation period of 18.8 ± 5.7 years. Higher patient age was one of the risk factors.

CLINICAL RELEVANCE

According to the results of this study, hnPCCs still represent an excellent therapeutic option-even in modern dentistry.

The effect of simulating porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed gold restorations

Background/purpose

The mechanical properties of pure gold (Au) are modified by thermal treatments. Thus, the aim of this study was to evaluate the effect of porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed Au crowns.

Materials and methods

Twenty electroformed Au specimens were prepared and divided into two groups. The first group did not receive any treatment (ELEC), and the other group was subjected to porcelain firing (PFIR). After metallographic grinding and polishing, all were investigated by scanning electron microscopy, and elemental composition was determined using energy-dispersive X-ray spectroscopy (EDX). Internal porosity was identified by quantitative image processing. Mechanical properties including Martens hardness (HM), indentation modulus (E_IT), elastic index (η_ΙΤ), and Vickers hardness (HV) were determined by instrumented indentation testing. The results were statistically analyzed using unpaired t test (α = 0.05).

Results

A random distribution of tiny pores was identified in cross section, but no significant difference was found between groups [ELEC (%), 0.24 ± 0.13; PFIR (%), 0.31 ± 0.7]. Backscattered electron images revealed no mean atomic number contrast for both groups, indicating that the material was a single-phase alloy, whereas no differences between groups were identified in the composition of C, N, O, and Au after EDX analysis. By contrast, all mechanical properties tested showed statistically significant differences, with the PFIR group showing significantly lower HM, η_ΙΤ, and HV but increased E_IT compared with those of the ELEC group.

Conclusion

Although microstructure and elemental composition of electroformed Au crowns remain unchanged, the mechanical properties are significantly affected by the thermal treatment of porcelain firing.

Evaluation and comparison of the marginal adaptation of two different substructure materials

PURPOSE

In this study, we aimed to evaluate the amount of marginal gap with two different substructure materials using identical margin preparations.

MATERIALS AND METHODS

Twenty stainless steel models with a chamfer were prepared with a CNC device. Marginal gap measurements of the galvano copings on these stainless steel models and Co-Cr copings obtained by a laser-sintering method were made with a stereomicroscope device before and after the cementation process and surface properties were evaluated by scanning electron microscopy (SEM). A dependent t-test was used to compare the mean of the two groups for normally distributed data, and two-way variance analysis was used for more than two data sets. Pearson's correlation analysis was also performed to assess relationships between variables.

RESULTS

According to the results obtained, the marginal gap in the galvano copings before cementation was measured as, on average, 24.47 ± 5.82 µm before and 35.11 ± 6.52 µm after cementation; in the laser-sintered Co-Cr structure, it was, on average, 60.45 ± 8.87 µm before and 69.33 ± 9.03 µm after cementation. A highly significant difference (P<.001) was found in marginal gap measurements of galvano copings and a significant difference (P<.05) was found in marginal gap measurements of the laser-sintered Co-Cr copings. According to the SEM examination, surface properties of laser sintered Co-Cr copings showed rougher structure than galvano copings. The galvano copings showed a very smooth surface.

CONCLUSION

Marginal gaps values of both groups before and after cementation were within the clinically acceptable level. The smallest marginal gaps occurred with the use of galvano copings.

Clinical marginal and internal adaptation of CAD/CAM milling, laser sintering, and cast metal ceramic crowns

STATEMENT OF PROBLEM

Metal ceramic crowns are widely used in clinical practice, but comparisons of the clinical adaptation of restorations made with different processing techniques are lacking.

PURPOSE

The purpose of this study was to compare the clinical marginal and internal adaptation of metal ceramic crowns fabricated with 3 different techniques: computer-aided design and computer-aided manufacturing (CAD/CAM) milling (CCM), direct metal laser sintering (DMLS), and traditional casting (TC).

MATERIAL AND METHODS

Twenty CCM, 20 DMLS, and 20 TC metal ceramic crowns were fabricated for 42 patients. Before luting the crowns, silicone replicas were obtained to measure marginal gap and internal adaptation that was evaluated at 3 regions: axial wall, axio-occlusal angle, and occlusal surface. Measurements were made with a reflected light binocular stereomicroscope at 20× magnification and analyzed with 1-way analysis of variance (ANOVA) and the Bonferroni post hoc test (α=.05).

RESULTS

The mean marginal gap values were 86.64 μm for CCM, 96.23 μm for DMLS, and 75.92 μm for TC. The means at the axial wall region were 117.5 μm for the CCM group, 139.02 μm for the DMLS group, and 121.38 μm for the TC group. One-way ANOVA revealed no statistically significant differences among the groups for measurements at the marginal gap (P=.082) and the axial wall region (P=.114). The means at the axio-occlusal region were 142.1 μm for CCM, 188.12 μm for DMLS, and 140.63 μm for TC, and those at the occlusal surface region were 265.73 μm for CCM, 290.39 μm for DMLS, and 201.09 μm for TC. The mean values of group DMLS were significantly higher at the axio-occlusal region and the occlusal surface region than those of other groups (P<.05).

CONCLUSIONS

CCM, DMLS and TC metal ceramic crowns performed similarly in terms of clinical marginal and axial wall adaptation. The cement film thickness at the occlusal region and axio-occlusal region were higher for DMLS crowns.