Accuracy and mechanical performance of passivated and conventional fabricated 3-unit fixed dental prosthesis on multi-unit abutments.

PURPOSE: The aim of this study was to evaluate the fit and mechanical stability of conventional versus passive fitting 3-unit fixed dental prosthesis (FDP) screw-retained on implants. METHODS: Twenty acrylic models, each with two embedded implants, were fabricated and functioned as patient-models. Impressions were taken and 20 all-ceramic FDPs were pre-fabricated on the plaster casts. Respectively 10 FDPs were fixed on the plaster casts (group 1) and on the patient-models for passive fitting (group 2). The fit of each FDP was checked on the patient-model by means of visual control (grades 1-10) and microscopic examination. Furthermore, specimens were artificially aged for possible prosthodontic failures, followed by a fracture strength test. RESULTS: Group 2 [1.4 (±0.3)] showed significantly (p<0.001) better results in the visual examination of the marginal fit compared to group 1 [6.3 (±2.4)]. The microscopic marginal misfit was 160µm (±80µm) at the abutment margin and 150µm (±80µm) at the axial wall of the abutment for group 1, respectively, 0µm and 0µm up to 17µm for group 2 (p<0.001). No failure of the FDPs could be observed during artificial aging in both groups. The fracture load showed no significant difference (p=0.60) between group 1 [2583N (±664N)] and group 2 [2465N (±238N)]. CONCLUSIONS: Visual and microscopic examination detected huge differences in marginal fit between groups 1 and 2. However, no statistically verifiable differences could be detected in long-term stability of implant-supported FDPs irrespective of the fit.

Tooth-implant-supported posterior fixed dental prostheses with zirconia frameworks: 3-year clinical result.

OBJECTIVES: This case series compared the clinical survival of tooth-implant-supported (TI-S) and tooth-supported (T-S) three-unit fixed dental prostheses (FDPs) with zirconia frameworks and described the incidence of biological and technical complications. MATERIALS AND METHODS: Forty-four patients received 27 TI-S FDPs and 22 T-S FDPs. Twenty-seven titanium screw implants were inserted at the dislodged position of two missing posterior teeth. All implants were provided with customized zirconia abutments. Zirconia frameworks were fabricated by a CAD/CAM system and veneered in powder build-up technique. All restorations were cemented with glass ionomer. Baseline evaluation was performed 2 weeks after cementation with recall examinations performed at 6, 12, 24 and 36 months by calibrated investigators. Survival probabilities according to Kaplan-Meier were calculated. Gingival parameters and bone loss were assessed and statistically evaluated. RESULTS: The mean service time of the FDPs was 35 months (±6). Two technical complications (fracture of veneering porcelain) were observed. One biological complication was recorded. The Kaplan-Meier survival probability was 93.9 % for all types of complications and 100 % related to restorations in service. The type of abutment support (TI-S vs. T-S) had no significant influence on the survival probability (p = 0.412, log rank test). No difference of the gingival parameters was detected between implants and natural teeth. CONCLUSIONS: Tooth-implant-supported zirconia-based FDPs showed similar clinical performance compared to tooth-supported zirconia-based FDPs. CLINICAL RELEVANCE: Within the limitations of this case series, tooth-implant-supported FDPs with zirconia frameworks seem to be a reliable treatment option.

Full-arch prostheses from translucent zirconia: accuracy of fit.

OBJECTIVES: The aim of this study was to evaluate the marginal and internal fit of single crowns, compared to 14-unit frameworks made of translucent yttria-stabilized zirconia. We hypothesized that there is an influence of the type of restoration on the marginal and internal fit. METHODS: Eight teeth (FDI locations 17, 15, 13, 11, 21, 23, 25 and 27) of a typodont maxillary model were provided with a chamfer preparation to accommodate a 14-unit prosthesis or four single crowns (SCs). Ten 14-unit fixed dental prostheses (FDPs) and 40 single crowns were fabricated using a computer aided design (CAD)/computer aided manufacturing (CAM) system with pre-sintered translucent yttria-stabilized zirconia blanks. The restorations were cemented onto twenty master dies, which were sectioned into four pieces each. Then, the marginal and internal fits were examined using a binocular microscope. In order to detect the differences between the two types of restorations a non-parameteric test (Mann-Whitney-U) was carried out; to detect differences between the abutment teeth and the abutment surfaces non-parametric tests (Kruskal-Wallis) and pairwise post hoc analyses (Mann-Whitney-U) were performed after testing data for normal distribution (method according to Shapiro-Wilk). Level of significance was set at 5%. RESULTS: The mean (SD) marginal opening gap dimensions were 18 µm (14) for the single crowns and 29 µm (27) for the 14-unit FDPs (p<0.001). Abutment 21 of the FDPs showed statistical differences concerning the location of the teeth in both marginal and internal fit (p<0.001). The measured gaps (types I-IV) revealed statistical differences between all types, when comparing SCs to the FDPs (p<0.001). SIGNIFICANCE: Single crowns showed significantly better accuracy of fit, compared to the 14-unit FDPs. However, both restorations showed clinically acceptable marginal and internal fit.

Retention forces of 14-unit zirconia telescopic prostheses with six double crowns made from zirconia--an in vitro study.

OBJECTIVES: The aim of this study was to evaluate the retention forces (RFs) of zirconia double-crown systems, with primary and secondary crowns made from zirconia in vitro. MATERIALS AND METHODS: Ten maxillary models with six abutment teeth were prepared. Sixty inner crowns were fabricated from pre-sintered zirconia with a taper of 0°. Ten 14-unit telescopic prostheses (removable partial dentures, RDPs) were fabricated, using the same computer-aided design/computer-aided manufacturing system as that used for the inner crowns. The removal test was performed in a standardized setup using a universal testing device at a crosshead speed of 10 mm/min. Ten separation cycles were carried out for each single primary crown as well as for each 14-unit RDP in the presence of artificial saliva. The results were imported into a statistic program and analysed by a one-way ANOVA and post hoc tests. The level of significance was set at 5 %. RESULTS: The mean RFs of the single double-crown systems were in the range of 0.611-2.895 N, whereas the RFs for the whole RDP varied between 8.1 and 13.6 N. RF was dependent on the abutment tooth (p < 0.001) and on the model (p < 0.001). CONCLUSIONS: The results of this study indicate that the manufacturing of full-zirconia double-crown systems is possible as well as reproducible. The RFs are comparable to those reported from casted and electroformed double-crown systems. CLINICAL RELEVANCE: It has been shown that the RFs of the presented telescopic system are comparable to existing double-crown systems.

Computer-aided fabrication of a zirconia 14-unit removable dental prosthesis: a technical report.

Double crown systems with primary crowns made from zirconia are used to support removable dental prostheses (RDPs). However, the fabrication of RDPs is labor-intensive and costly. Manufacturing primary and secondary crowns from zirconia with a CAD/CAM system might simplify the fabrication protocol and reduce costs. Furthermore, only ceramic materials are used in this method, providing an RDP with the highest possible biocompatibility and greatest possible esthetics. This article describes the fabrication protocol step by step.

The zebrafish dystrophic mutant softy maintains muscle fibre viability despite basement membrane rupture and muscle detachment.

The skeletal muscle basement membrane fulfils several crucial functions during development and in the mature myotome and defects in its composition underlie certain forms of muscular dystrophy. A major component of this extracellular structure is the laminin polymer, which assembles into a resilient meshwork that protects the sarcolemma during contraction. Here we describe a zebrafish mutant, softy, which displays severe embryonic muscle degeneration as a result of initial basement membrane failure. The softy phenotype is caused by a mutation in the lamb2 gene, identifying laminin beta2 as an essential component of this basement membrane. Uniquely, softy homozygotes are able to recover and survive to adulthood despite the loss of myofibre adhesion. We identify the formation of ectopic, stable basement membrane attachments as a novel means by which detached fibres are able to maintain viability. This demonstration of a muscular dystrophy model possessing innate fibre viability following muscle detachment suggests basement membrane augmentation as a therapeutic strategy to inhibit myofibre loss.