Matthias Rödiger

New insights in prism orientation within human enamel.

The knowledge about the orientation of the prisms in human dental enamel is mainly based on morphological observations (light optical, SEM, etc.). Hence there are many schematic drawings, showing the orientation as seen in the microscope. Locally resolved direct measurements of the orientations, proofing the observations, have not been done in detail up to now. X-ray diffraction methods adapted from material science are used in this study, providing directly the orientation of the crystallites in the examined positions. Hereby new and better detailed information was obtained, showing the orientation of the prisms and giving information about their intrinsic structure. Based on the measurements, existing prism orientation models can be enhanced and two structural suggestions can be made, showing possible inner building principles for the prisms. Future planned measurements will even allow deciding which of the two models is more likely.

Organic anion transporter 3 (OAT3) and renal transport of the metal chelator 2,3-dimercapto-1-propanesulfonic acid (DMPS).

Recent investigations involving intact rabbit renal proximal tubules indicated that organic anion transporter 3 (OAT3) may be involved in the transport of 2,3-dimercapto-1-propanesulfonic acid (DMPS). Therefore, we evaluated the interaction of OAT3 with DMPS to determine the effect of OAT3 on basolateral DMPS uptake. We used stably transfected HEK293 cells expressing human and rabbit orthologs of the exchanger OAT1 and OAT3. Using 6-carboxyfluorescein (6-CF) as a substrate, the IC50 determinations for reduced DMPS (DMPSH) revealed a stronger interaction with OAT1 than with OAT3 (rbOAT1, 123.3 +/- 13.7; hOAT1, 85.1 +/- 8.8; rbOAT3, 171.7 +/- 22.3; and hOAT3, 172.2 +/- 36.4 micromol/L). However, inhibition of 6-CF uptake by the oxidized form of DMPS (DMPSS), the main form of DMPS in the blood, showed a greater affinity for OAT3 (rbOAT1, 237.4 +/- 23; hOAT1, 104.6 +/- 13.1; rbOAT3, 52.4 +/- 7.6; and hOAT3, 31.6 +/- 6.6 micromol/L). To determine whether DMPSH and DMPSS are substrates for OAT3, we performed efflux studies with [14C]glutarate and inwardly directed gradients of glutarate. The inhibitors trans-stimulated the efflux of [14C]glutarate, suggesting that OAT3 may be able to transport both forms of DMPS. On the basis of the substantial interaction of OAT3 with DMPSS, we conclude that OAT3 represents the dominant basolateral player in renal detoxification processes resulting from use of DMPS.

Fabrication of Zirconia-Reinforced Lithium Silicate Ceramic Restorations Using a Complete Digital Workflow

This case report describes the fabrication of monolithic all-ceramic restorations using zirconia-reinforced lithium silicate (ZLS) ceramics. The use of powder-free intraoral scanner, generative fabrication technology of the working model, and CAD/CAM of the restorations in the dental laboratory allows a completely digitized workflow. The newly introduced ZLS ceramics offer a unique combination of fracture strength (>420 MPa), excellent optical properties, and optimum polishing characteristics, thus making them an interesting material option for monolithic restorations in the digital workflow.

Evaluation of removal forces of implant-supported zirconia copings depending on abutment geometry, luting agent and cleaning method during re-cementation

PURPOSE To evaluate the effects of different abutment geometries in combination with varying luting agents and the effectiveness of different cleaning methods (prior to re-cementation) regarding the retentiveness of zirconia copings on implants. MATERIALS AND METHODS Implants were embedded in resin blocks. Three groups of titanium abutments (pre-fabricated, height: 7.5 mm, taper: 5.7°; customized-long, height: 6.79 mm, taper: 4.8°; customized-short, height: 4.31 mm, taper: 4.8°) were used for luting of CAD/CAM-fabricated zirconia copings with a semi-permanent (Telio CS) and a provisional cement (TempBond NE). Retention forces were evaluated using a universal testing machine. Furthermore, the influence of cleaning methods (manually, manually in combination with ultrasonic bath or sandblasting) prior to re-cementation with a provisional cement (TempBond NE) was investigated with the pre-fabricated titanium abutments (height: 7.5 mm, taper: 5.7°) and SEM-analysis of inner surfaces of the copings was performed. Significant differences were determined via two-way ANOVA. RESULTS Significant interactions between abutment geometry and luting agent were observed. TempBond NE showed the highest level of retentiveness on customized-long abutments, but was negatively affected by other abutment geometries. In contrast, luting with Telio CS demonstrated consistent results irrespective of the varying abutment geometries. Manual cleaning in combination with an ultrasonic bath was the only cleaning method tested prior to re-cementation that revealed retentiveness levels not inferior to primary cementation. CONCLUSION No superiority for one of the two cements could be demonstrated because their influences on retentive strength are also depending on abutment geometry. Only manual cleaning in combination with an ultrasonic bath offers retentiveness levels after re-cementation comparable to those of primary luting.

Chairside Fabrication of an All-Ceramic Partial Crown Using a Zirconia-Reinforced Lithium Silicate Ceramic.

The chairside fabrication of a monolithic partial crown using a zirconia-reinforced lithium silicate (ZLS) ceramic is described. The fully digitized model-free workflow in a dental practice is possible due to the use of a powder-free intraoral scanner and the computer-aided design/computer-assisted manufacturing (CAD/CAM) of the restorations. The innovative ZLS material offers a singular combination of fracture strength (>370 Mpa), optimum polishing characteristics, and excellent optical properties. Therefore, this ceramic is an interesting alternative material for monolithic restorations produced in a digital workflow.

Retrospective evaluation of extended heat-pressed ceramic veneers after a mean observational period of 7 years

OBJECTIVES Retrospective evaluation of extended anterior glass-ceramic veneers 7 years after placement in a private practice. MATERIALS AND METHODS A total of 31 patients (20 females/11 males) underwent restoration with adhesively luted extended veneers that were fabricated using heat-pressed glass-ceramic (Cergo, Dentsply Sirona). A single dentist restored 101 teeth (maxilla, n = 65; mandible, n = 36). Adhesive cementation was performed using an etch-and-rinse adhesive (OptibondFL, Kerr Corporation), and two different dual-curing composite cements (Variolink, Ivoclar Vivadent/Calibra, Dentsply Sirona). RESULTS After 7 years, the Kaplan-Meier survival rate (in situ criteria) was 93.6% (95% CI: 0.89; 0.98). The observed failures were caused by ceramic fractures for seven restorations and biological failure for one restoration. In total 80 of the 101 restorations were still in service and did not require any clinical intervention (7-year success rate: 84.3% [95% CI]: 0.76; 0.93). Interventions were necessary in 13 cases (8 recementations, 2 endodontic treatments, 2 composite fillings (caries), and 1 polishing of minor fractures). The clinical performance was not influenced by the veneer position (maxilla/mandible, survival P = .56/success P = .30). The veneers that covered large areas of exposed dentin (>50%) exhibited a significantly increased risk (hazard ratio 3.71, P = .0041) for requiring a clinical intervention; however, no effect on the survival rate was observed for these veneers (P = .35). CONCLUSIONS Following 7 years of clinical service, extended anterior ceramic veneer restorations exhibited comparable survival and success rates for the upper and lower jaw. Large areas of exposed dentin (>50%) were associated with significantly lower success rates. CLINICAL SIGNIFICANCE Dentin exposure (more than 50% of the preparation surface) during preparation significantly affects the clinical performance of extended heat-pressed glass-ceramic veneers.

Prospective Evaluation of Posterior Fixed Zirconia Dental Prostheses: 10-Year Clinical Results

PURPOSE To investigate the clinical survival and success rates of conventionally luted three- and four-unit fixed dental prostheses (FDPs) with zirconia frameworks (Cercon Smart Ceramics, DeguDent) after a mean observation period of 119 ± 36 months. MATERIALS AND METHODS A total of 75 patients were treated in the Department of Prosthodontics at the University of Goettingen, Germany, and a total of 99 posterior FDPs were inserted and luted with zinc phosphate cement. Time-dependent survival and success rates were calculated using Kaplan-Meier curves, and their relationships with the type of veneer (ceramic), location (maxilla vs mandible), and span length (three-unit vs four-unit) were analyzed with a Cox regression model (P < .05). RESULTS Of the 99 inserted FDPs, 24 were lost to follow-up, 51 remained functional and passed the 10-year examination (overall survival rate: 75.0%; 95% confidence interval [CI]: 0.64, 0.85), and 13 were absolute failures caused by technical events (technical survival rate: 84%; 95% CI: 0.64, 0.85). In 50 FDPs, relative failure required a clinical intervention to maintain function (overall success rate: 40%; 95% CI: 0.29, 0.52). For 35 of these FDPs, the relative failure was caused by technical events (technical success rate: 61%; 95% CI: 0.49, 0.73). None of the evaluated factors showed an association with overall or technical survival or success. CONCLUSION Zirconia-based posterior FDPs produced with a first-generation computer-assisted manufacturing (CAM) system revealed high rates of absolute and relative failure, mainly due to technical events, after a mean observational period of 10 years. Further clinical studies with updated computer-assisted design (CAD)/CAM systems are needed to determine the long-term performance of zirconia-based FDPs.

Influence of Material Selection on the Marginal Accuracy of CAD/CAM-Fabricated Metal- and All-Ceramic Single Crown Copings

This study evaluated the marginal accuracy of CAD/CAM-fabricated crown copings from four different materials within the same processing route. Twenty stone replicas of a metallic master die (prepared upper premolar) were scanned and divided into two groups. Group 1 (n = 10) was used for a pilot test to determine the design parameters for best marginal accuracy. Group 2 (n = 10) was used to fabricate 10 specimens from the following materials with one identical CAD/CAM system (GAMMA 202, Wissner GmbH, Goettingen, Germany): A = commercially pure (cp) titanium, B = cobalt-chromium alloy, C = yttria-stabilized zirconia (YSZ), and D = leucite-reinforced glass-ceramics. Copings from group 2 were evaluated for the mean marginal gap size (MeanMG) and average maximum marginal gap size (AMaxMG) with a light microscope in the “as-machined” state. The effect of the material on the marginal accuracy was analyzed by multiple pairwise comparisons (Mann–Whitney, U-test, α = 0.05, adjusted by Bonferroni-Holmes method). MeanMG values were as follows: A: 46.92 ± 23.12 μm, B: 48.37 ± 29.72 μm, C: 68.25 ± 28.54 μm, and D: 58.73 ± 21.15 μm. The differences in the MeanMG values proved to be significant for groups A/C (p = 0.0024), A/D (p = 0.008), and B/C (p = 0.0332). AMaxMG values (A: 91.54 ± 23.39 μm, B: 96.86 ± 24.19 μm, C: 120.66 ± 32.75 μm, and D: 100.22 ± 10.83 μm) revealed no significant differences. The material had a significant impact on the marginal accuracy of CAD/CAM-fabricated copings.