A clinical evaluation of cobalt-chromium metal-ceramic fixed partial dentures and crowns: A three- to seven-year retrospective study

Comparative Analysis of the Structural Weights of Fixed Prostheses of Zirconium Dioxide, Metal Ceramic, PMMA and 3DPP Printing Resin-Mechanical Implications

The aim of this study was to determine the mechanical implications of four-unit fixed dental prostheses (FDPs) made of (1) monolithic zirconium dioxide (ZR O2), (2) polymethylmethacrylate (PMMA), (3) metal ceramic (PFM) and (4) impression resin (3DPP).

METHODS

Four groups were studied with eight samples for each material (n: 32). Each structure was weighed, subjected to compressive tests and analyzed using 3D FEA.

RESULTS

PMMA presented the lowest structural weight (1.33 g), followed by 3DPP (1.98 g), ZR O2 (6.34 g) and PFM (6.44 g). In fracture tests, PMMA presented a compressive strength of 2104.73 N and a tension of 351.752 MPa; followed by PFM, with a strength of 1361.48 N and a tension of 227.521 MPa; ZR O2, with a strength of 1107.63 N and a tension of 185.098 MPa; and 3DPP, with a strength of 1000.88 N and a tension of 143.916 MPa. According to 3D FEA, 3DPP presented the lowest degree of deformation (0.001 mm), followed by PFM (0.011 mm), ZR O2 (0.168 mm) and PMMA (1.035 mm).

CONCLUSIONS

The weights of the materials did not have a direct influence on the mean values obtained for strength, stress or strain. Since the performance was related to the tension and forces supported by the structures in critical zones, the importance of considering design factors is clear. In vitro and 3D FEA assays allowed us to simulate different scenarios for the mechanical properties of certain materials before evaluating them clinically. Thus, they can generate predictions that would allow for the design of a better research methodology in future clinical trials.

Dental Implant Treatment in Bruxers: A Case Report and Literature Review

This case report presents a literature review and a case report of a full-mouth implant rehabilitation for a 65-year-old woman with a history of Bruxism. The patient's oral condition showed dentition with severe occlusal wear, extensive dental work, and missing teeth replaced with bridges and implants. The existing dental work was failing due to recurrent caries and the mechanical failure of long-span bridges. The unique aspect of the treatment presented in this report is the management of existing osseointegrated implants of different systems with different platform designs, which adds to the treatment's complexity. The existing implants were incorporated into the planned treatment, and other implants were added to support maxillary zirconia and mandibular hybrid full-arch prostheses. After 2 years of function, extensive wear was evident on the milled acrylic, even though an occlusal guard was used. New acrylic teeth were processed using the same milled titanium bar of the mandibular hybrid prosthesis, and the occlusal surfaces of the acrylic teeth were protected with gold onlays. The patient is seen regularly for maintenance every 6 months with no further complications. Careful evaluation, planning, and treatment execution are paramount in managing patients with a history of bruxism. Patients should be prepared and informed about possible mechanical failure and seen regularly for maintenance.

The effect of biologically oriented and subgingival horizontal preparation techniques on periodontal health: A double-blind randomized controlled clinical trial

Purpose

The aim of this study was to investigate and compare the influence of subgingival horizontal preparation technique (SHPT) and biological oriented preparation technique (BOPT) on periodontal health at a split-mouth model.

Methods

The sample of 100 patients was divided into two groups using a spilt-mouth study design; each patient had received two crowns with SHPT and BOPT respectively. The teeth were randomly allocated for the preparation techniques. All prepared teeth were restored with fabricated zirconium cores and ceramic layering. Temporary crowns were delivered after taking an impression and patients were recalled for the final cementation of the crowns. After that, follow-up recalls were set at one month, 3 months, 6 months, one year, and two years to record the following clinical parameters; plaque index, probing depth, bleeding on probing, clinical attachment level and patients' satisfaction with treatment.

Results

SHPT had significantly lower plaque and inflammation index at baseline, which increased significantly at 3 months and 2 years' follow-up compared to BOPT. Patients' satisfaction was significantly higher with SHPT at baseline, and it is reduced significantly at 6 months and two years follow- up (P < 0.001). The probing depth was significantly higher in BOPT at baseline and 3 months and decreased significantly at 6 months, 1 year, and 2 years' follow-up.

Conclusion

BOPT is a favorable technique with a full crown or veneer, presenting good marginal stability and periodontal behavior.

Cobalt chromium alloys in fixed prosthodontics: Investigations of mechanical properties and microstructure

STATEMENT OF PROBLEM

Cobalt chromium (Co-Cr) alloys possess beneficial mechanical properties because alloys, even in thin sections, can resist high mastication forces and exhibit an acceptable bond to the surface porcelain layer. Traditional manufacturing techniques of Co-Cr alloys such as casting have been replaced with newer fabrication techniques, such as milling, laser melting, and presintered milling. Despite scarce documentation, these new manufacturing techniques are being used to fabricate dental and implant constructions.

PURPOSE

This in vitro study investigates the hardness, yield strength, elastic modulus, and microstructure of the most commonly used Co-Cr alloys for fixed prosthodontics based on manufacturing technique. In addition, this study investigates the effect of heat treatment on the mechanical properties and microstructure of these materials.

MATERIAL AND METHODS

Five Co-Cr alloys were included (dumbbell and rectangular shaped) based on four manufacturing techniques: cast, milled, laser melted, and presintered milled. Commercially pure titanium grade 4 and titanium-6 aluminum-4 vanadium ELI (extra low interstitial) were included for comparison, and yield strength and elongation after fracture were evaluated. The specimens were tested for hardness using the Vickers test and for elastic modulus using a nondestructive impulse excitation technique. The microstructure of selected specimens was analyzed using focused ion beam-scanning electron microscopy (FIB-SEM) and energy dispersive X-ray spectroscopy (EDS).

RESULTS

The mechanical properties depend on the manufacturing technique used; the laser-melted and presintered Co-Cr specimens demonstrated the highest mechanical properties, followed by the milled and cast groups. Both the laser-melted and the presintered milled Co-Cr specimens showed smaller grain size compared with the cast and milled Co-Cr specimens. The titanium-6 aluminum-4 vanadium ELI demonstrated higher hardness and yield strength compared to commercially pure titanium grade 4. No major differences were observed for the selected materials regarding the mechanical properties and microstructural appearance after heat treatment.

CONCLUSIONS

The laser melting and presintered milling techniques produced higher mechanical properties compared with the cast and milled Co-Cr. These findings were confirmed through microstructural analysis with respect to the grain size, precipitation, and number of pores.

Technical complications with tooth-supported fixed dental prostheses (FDPs) of different span lengths: an up to 15-year retrospective study

BACKGROUNDS

Long-span dental bridges may cause excessive load on abutment teeth and the periodontal area, which may lead to bridge fractures or periodontal problems. However, some reports have revealed that short- and long-span bridges can provide a similar prognosis. This clinical study aimed to investigate the technical complications associated with fixed dental prostheses (FDPs) of different span lengths.

METHODS

All patients with previously cemented FDPs were clinically examined during their follow-up visits. Several data related to FDPs were registered, such as design, material type, location, and type of complication. The main clinical factors analyzed were technical complications. Life table survival analyses were performed to calculate the cumulative survival rate of FDPs when technical complications were detected.

RESULTS

The study examined 229 patients with a total number of 258 prostheses and an average of 98 months of follow-up. Seventy-four prostheses suffered from technical complications, and the most common complication was ceramic fracture or chipping (n = 66), while loss of retention occurred in 11 prostheses. The long-term evaluation of long-span prostheses revealed a significantly higher technical complication rate compared to short-span prostheses (P = ,003). The cumulative survival rate for short-span FDPs was 91% in year 5, 68% in year 10, and 34% in year 15. For long-span FDPs, the cumulative survival rate was 85% in year 5, 50% in year 10, and 18% in year 15.

CONCLUSION

Long-span prostheses (5 units or more) can be associated with a higher technical complication rate compared to short-span prostheses after long-term evaluation.

Metallic Dental Implants Wear Mechanisms, Materials, and Manufacturing Processes: A Literature Review

OBJECTIVES

From the treatment of damaged teeth to replacing missing teeth, dental biomaterials cover the scientific interest of many fields. Dental biomaterials are one of the implants whose effective life depends vastly on their material and manufacturing techniques. The purpose of this review is to summarize the important aspects for metallic dental implants from biomedical, mechanical and materials science perspectives. The review article will focus on five major aspects as mentioned below. Tooth anatomy: Maximizing the implant performance depends on proper understanding of human tooth anatomy and the failure behavior of the implants. Major parts from tooth anatomy including saliva characteristics are explored in this section. Wear mechanisms: The prominent wear mechanisms having a high impact on dental wear are abrasive, adhesive, fatigue and corrosion wear. To imitate the physiological working condition of dental implants, reports on the broad range of mastication force and various composition of artificial saliva have been included in this section, which can affect the tribo-corrosion behavior of dental implants. Dental implants classifications: The review paper includes a dedicated discussion on major dental implants types and their details for better understanding their applicability and characteristics. Implant materials: As of today, the most established dental implant materials are SS316L, cobalt chrome alloy and titanium. Detailed discussion on their material properties, microstructures, phase transformations and chemical compositions have been discussed here. Manufacturing techniques: In terms of different production methods, the lost wax casting method as traditional manufacturing is considered. Selective Laser Melting (SLM) and Directed Energy Deposition (DED) as additive manufacturing techniques (AM) have been discussed. For AM, the relationships between process-property-performance details have been explored briefly. The effectiveness of different manufacturing techniques was compared based on porosity distribution, mechanical and biomechanical properties.

SUMMARY

Despite having substantial research available on dental implants, there is a lack of systematic reviews to present a holistic viewpoint combining state-of-the-art from biomedical, mechanical, materials science and manufacturing perspectives. This review article attempts to combine a wide variety of analyzing approaches from those interdisciplinary fields to deliver deeper insights to researchers both in academia and industry to develop next-generation dental implants.

Up to 10 years clinical performance of zirconia ceramic and metal-ceramic fixed partial dentures: A retrospective study

STATEMENT OF PROBLEM

Completely veneered zirconia ceramic (ZC) fixed partial dentures (FPDs) have been reported to have a higher incidence of ceramic chipping than the standard metal-ceramic FPDs. However, data from comparative long-term studies are sparse.

PURPOSE

The purpose of this retrospective study was to compare the long-term survival, chipping-free survival, and success of ceramic-veneered high noble metal alloy (HN), base metal alloy (cobalt-chromium alloy) (CC), and ZC FPDs and to isolate risk factors for the incidence of failure, veneer chipping, and overall complications.

MATERIAL AND METHODS

Data from 289 study participants (58.7% women; mean age, 57.97 ±11.51 years) provided with a total of 400 FPDs comprising 197 (49.3%) HN FPDs, 121 (30.3%) CC FPDs, and 82 (20.5%) ZC FPDs fabricated from presintered 3 mol% yttria-stabilized zirconia (mean time of service, 6.85 ±3.25 years) were evaluated. Of these, 278 (69.5%) FPDs were provided by dentists and 122 (30.5%) by dental students. Five- and 10-year survival, chipping-free survival, and success rates were calculated using the Kaplan-Meier method and compared with the log-rank test. Risk factors were assessed using Cox regression analysis. The study was exploratory, so all P values were considered exploratory and descriptive.

RESULTS

The 5- and 10-year survival rates were 94.7% and 77.8% for HN, 93.7% and 81.2% for CC, and 92.9% and 53.3% for ZC FPDs, respectively, indicating no clear difference in survival among the framework materials. The 5- and 10-year chipping-free rates were 94.1% and 82.8% for HN, 96.1% and 78.9% for CC, and 82.6% and 62.2% for ZC FPDs, respectively, indicating a difference between HN and ZC, and CC and ZC restorations. The 5- and 10-year success rates were 83.7% and 55.3% for HN, 86.5% and 51.4% for CC, and 68.9% and 30.2% for ZC FPDs, respectively, indicating a difference between HN and ZC, and CC and ZC restorations. The Cox regression model indicated framework material as an influencing risk factor for success, and this influence persisted when chipping was investigated. Compared with zirconia, the use of a metal alloy reduced the risk of chipping or the occurrence of complications by up to one-third.

CONCLUSIONS

All FPDs showed high 5-year survival rates and acceptable 10-year survival rates with no strong differences among the materials. Higher success and chipping-free rates were observed for both HN and CC restorations compared with ZC restorations. Metal frameworks had a lower risk for complications or veneer chipping than zirconia frameworks.

Retrospective Study Comparing Clinical Outcomes of Fixed Dental Prostheses in Matched Groups of Bruxer and Nonbruxer Patients

Background

Tooth-supported fixed dental prosthesis (FDP) is one of the most reliable treatment options to replace missing teeth. The longevity of the treatment could, however, be affected by several general and local factors, especially bruxism.

Objective

To investigate the influence of bruxism on the long-term survival of tooth-supported FDPs in bruxers compared to a matched group of nonbruxers, taking several clinical variables into account.

Materials and Methods

The present retrospective cohort study was based on records of patients treated with 3–7-unit tooth-supported FDPs with a minimum follow-up time of 6 months after prosthesis delivery. The criteria for the diagnosis of “possible” and “probable” sleep or awake bruxism were used. A matched group of nonbruxers was selected on the basis of similarities in four factors, patients' gender and age, number of prosthetic units of the FDPs, and follow-up time. The paired-samples t-test or Wilcoxon signed rank test were used to compared mean values between the two groups. Contingency tables of categorical data were analyzed by McNemar's test.

Results

The cohort group consisted of 62 noncantilevered FDPs in each group, followed up for a mean of 110.1 and 106.5 months (bruxers and nonbruxers, respectively). Tooth-supported FDPs in bruxers presented significantly higher failure rate than in nonbruxers (32.3% vs. 25.8%, respectively; p = 0.001). Loss of retention and tooth loss were the main reasons for failures in both groups. For nonsmokers, the FDP failure rate was higher in nonbruxers. Technical and biological complications were significantly more prevalent in bruxers compared to nonbruxers.

Conclusions

Bruxism is suggested to increase technical and biological complications and FDP failure.

A retrospective clinical study of fixed tooth- and implant-supported prostheses in titanium and cobalt-chromium-ceramic: 5-9-year follow-up

OBJECTIVES

The aim of this retrospective study was to evaluate the clinical outcome of fixed tooth- and implant-supported protheses manufactured in porcelain veneered cobalt-chromium (CoCr) or titanium with a follow-up period of 5-9 years.

MATERIALS AND METHODS

This study included 63 patients with a total of 86 fixed dental protheses (FDPs) (53 implant-supported and 33 tooth-supported). In total, 67 were short-span FDPs (3-5 units) and 19 were long-span FDPs (6-12 units). The FDPs were evaluated using a modified version of the California Dental Association (CDA).

RESULTS

The binary regression analysis indicated that neither CoCr nor titanium had a statistically significant effect on the odds of success or survival of either tooth- or implant-supported FDPs. However, the success of FDPs was negatively affected by greater FDP length and general tooth wear. The survival of FDPs was negatively affected by increased FDP longevity.

CONCLUSIONS

This study found no statistically significant effect on the odds of success and survival outcomes for any combination of tooth-supported, implant-supported, porcelain-veneered CoCr, or porcelain-veneered titanium FDPs. As the number of FDPs was limited, the results should be interpreted with caution.

CLINICAL RELEVANCE

This study shows that the choice between CoCr porcelain and titanium porcelain in fixed protheses did not have a statistically significant effect on the outcome.

Influence of Digital Technologies and Framework Design on the Load to Fracture of Co-Cr Posterior Fixed Partial Denture Frameworks

PURPOSE

To compare the load to fracture of cobalt-chromium (Co-Cr) 3-unit posterior fixed partial denture (FPD) frameworks manufactured by conventional and digital techniques and to evaluate the influence of the framework design on the fracture load.

MATERIAL AND METHODS

Eighty 3-unit Co-Cr posterior FPD frameworks were fabricated with two designs: intermediate pontic (n = 40) and cantilever (n = 40). Each design was randomly divided into four groups (n = 10): casting, direct metal laser sintering, soft metal milling, and hard metal milling. After thermal cycling, all specimens were subjected to a 3-point bending test until fracture. Data were statistically analyzed using one-way ANOVA, Welch and Brown-Forsythe test, Ryan-Einot-Gabriel-Welsch F and Tamhane T2 post hoc test, Student's t test, and Weibull statistics (α = 0.05).

RESULTS

Significant differences (p < 0.001; F = 39.59) were found among intermediate pontic frameworks (except between laser sintering and hard metal milling), and cantilevered frameworks (F = 36.75) (except between laser sintering and hard metal milling, and casting and soft metal milling). The cantilever groups showed load to fracture values significantly lower than those of the intermediate pontic (p < 0.001; F = 28.29). The Weibull statistics corroborated the results.

CONCLUSIONS

Hard metal milling and laser sintered frameworks exhibited the highest load to fracture values. However, all tested frameworks demonstrated clinically acceptable load to fracture values. The framework design directly affected the fracture load, with drastically lower values in cantilevered frameworks.

Efficacy and risks of tooth-supported prostheses in the treatment of partially edentulous patients with stage IV periodontitis. A systematic review and meta-analysis

AIM

The aim was to evaluate the efficacy and effectiveness of tooth-supported fixed prostheses in partially edentulous patients with stage IV periodontitis.

MATERIAL AND METHODS

Randomized and controlled clinical trials (RCTs and CCTs) and prospective/retrospective cohort studies or case series were searched in three databases. Survival rate of abutment teeth was considered the primary outcome. Meta-analyses were performed whenever possible.

RESULTS

Twenty-four publications were included. No RCTs or CCTs compared the efficacy of tooth-supported fixed prostheses between patients with severe periodontitis or non-periodontitis patients. Most of the data retrieved were derived from case series. The incidence of abutment-tooth loss after a follow-up period from 2 to 35.4 years was low (n = 17 studies; weighted mean incidence (WMI) = 4.8%; confidence interval (CI) [3.2, 6.5]). The corresponding figure for prostheses failure was WMI = 6.9% (n = 18; 95% CI [4.1, 9.7]). Technical complications seemed to be more frequent than biological complications (caries, endodontic failure, root fracture, etc.). Periodontal outcomes tended to remain stable over time.

CONCLUSION

Tooth-supported fixed prostheses seemed to be a valid treatment approach to restore masticatory function in patients with stage IV periodontitis once periodontal therapy has been accomplished. However, the comparative efficacy of this treatment among periodontitis and non-periodontitis patients is unclear due to the absence of clinical trials.

Periodontal outcomes of anterior fixed partial dentures on teeth treated with the biologically oriented preparation technique: A 6-year prospective clinical trial

STATEMENT OF PROBLEM

One of the most frequent complications in participants with fixed partial dentures (FPDs) is the apical migration of the gingival margin, which may be associated with factors such as fit, gingival margin location, or tooth preparation type. The prevalence of the complication in participants restored with FPDs prepared by using the biologically oriented preparation technique (BOPT) is unclear.

PURPOSE

The purpose of this prospective clinical trial was to evaluate the clinical and biologic outcomes of FPDs on teeth prepared by using the BOPT, over a 6-year follow-up period.

MATERIAL AND METHODS

Tooth-supported zirconia FPDs in the anterior region prepared by using the BOPT were evaluated. Each participant was monitored annually for 6 years by evaluating plaque index, probing depth, vestibular gingival thickness, and gingival margin stability. Biologic and/or mechanical complications were also recorded. Patient satisfaction was measured by using a visual analog scale (VAS).

RESULTS

A total of 25 FPDs supported by 70 teeth in 24 participants were analyzed. Low plaque index values and stable probing depths were observed, whereas the gingival index was 0 for most of the teeth. Teeth treated by using the BOPT presented significant increase in gingival thickness, and the gingival margin was found to be stable in 100% of the treatments. FPD survival was 100%.

CONCLUSION

Tooth supporting FPDs prepared by using the BOPT presented good periodontal health and gingival margin stability, without recession and with a 100% survival rate during a 6-year follow-up.

Effect of oxidation heat treatment with airborne-particle abrasion on the shear bond strength of ceramic to base metal alloys

STATEMENT OF PROBLEM

Oxidation heat treatment has been studied to increase the metal-ceramic bond strength. However, information about its use with cobalt-chromium (Co-Cr) alloys is lacking.

PURPOSE

The purpose of this study was to evaluate the effect of oxidation heat treatment and oxidation heat treatment with alumina airborne-particle abrasion on the metal-ceramic bond strength of Co-Cr alloys compared with that of nickel-chromium (Ni-Cr) alloys.

MATERIAL AND METHODS

In total, 165 metal cylinders (∅5×8 mm) made of 5 base metal alloys were obtained by casting: 2 Ni-Cr (Fit Cast-SB and Fit Cast-V) and 3 Co-Cr alloys (Keragen, StarLoy C, and Remanium 2001). The specimens were divided into groups (n=11): no treatment, oxidation heat treatment, and oxidation heat treatment with airborne-particle abrasion. Oxidation heat treatment was performed starting at 650 °C and rising to 980 °C. The airborne-particle abrasion was performed with 100-μm alumina (0.2-MPa pressure, 5 seconds). One specimen had the surface topography and composition evaluated by scanning electron microscopy and energy dispersive X-ray spectrometry. The feldspathic ceramic was applied to the base metal alloy specimens (n=10). Shear tests were performed to obtain the metal-ceramic bond strength (MPa). The failure modes were evaluated. Data were evaluated by 2-way ANOVA and the Tukey post hoc test, Pearson correlation, and Fisher exact tests (α=.05).

RESULTS

The group without treatment showed the highest roughness. The treatments increased oxygen and chromium levels and decreased nickel, molybdenum, and tungsten levels. Oxidation heat treatment provided an increase in metal-ceramic bond strength (P<.05) for base metal alloys with over 7% molybdenum (Fit Cast-SB, Fit Cast-V, and Remanium 2001). With oxidation heat treatment with airborne-particle abrasion, there was improvement only in Fit Cast-SB. No treatment was better for StarLoy C. A weak correlation was found between metal-ceramic bond strength and failure mode (ρ=.166; P=.043). The mixed failures were prevalent in Co-Cr alloys (P<.001) and oxidation heat treatment with airborne-particle abrasion (P=.008).

CONCLUSIONS

The oxidation heat treatment was only beneficial for base metal alloy with a molybdenum content of over 7%. Although the oxidation heat treatment with alumina airborne-particle abrasion was a better treatment for Fit Cast-SB, its use is not justified because it showed no difference for oxidation heat treatment and requires another step in the surface treatment.

Evaluating the effect of repeated use of milling burs on surface roughness and adaptation of digitally fabricated ceramic veneers

Objectives

This study aimed to evaluate how repeated use of milling diamond burs with different coarseness affects surface roughness, and marginal and internal adaptation of CAD/CAM veneers.

Methods

Forty leucite-reinforced glass-ceramic veneers were milled in 2 groups based on the milling mode (with fine or extra-fine bur sets). In each group, every 10 veneers were milled with a new bur set. All veneers were cemented to bovine teeth and then polished. Labial surface roughness was measured before cementation, and after polishing. Marginal and internal discrepancies were measured using a field emission scanning electron microscope. Three-way and two-way mixed repeated measures ANOVA were applied to assess changes in surface roughness values of veneers and discrepancy values, respectively. The Bonferroni correction was applied for multiple comparisons.

Results

Repeated use of a milling diamond bur set had a significant effect on surface roughness of the veneers (P < .001). Mean surface roughness of the fine milling mode was significantly higher in comparison to that of extra-fine mode before (P = .002) and after (P = .01) polishing. After polishing a significant decrease in surface roughness occurred in fine (P = .02), but not in extra-fine milling mode (P = .99). Repeated use of milling burs significantly affected marginal and internal adaptation between some repeated uses.

Conclusions

Marginal and internal adaptation were significantly affected by repeated use of milling diamond burs up to 10 times between some repeated uses. However, no specific pattern could be established.

Clinical significance

Repeated use of milling burs could affect surface roughness, surface microcracks, critical defects, and adaptation of CAD/CAM restorations. Therefore, it plays a major role in clinical success of the restorations.

Effect of layer thickness on the flexural strength of multiple-unit laser-sintered metal frameworks

STATEMENT OF PROBLEM

Laser sintering devices have been increasingly used to fabricate the metal frameworks of metal-ceramic restorations. In the fabrication process, the sintering layer thickness is an important parameter; however, information on how it may affect the flexural strength of metal frameworks remains limited.

PURPOSE

The purpose of this in vitro study was to evaluate the flexural strength of 3-unit and 4-unit cobalt-chromium (Co-Cr) metal frameworks laser sintered with 20-μm, 30-μm, and 40-μm layer thicknesses.

MATERIAL AND METHODS

Three-unit and 4-unit master metal die models with premolar and molar abutments were prepared through direct metal laser sintering (DMLS). A total of 40 metal frameworks (n=10 for each metal die model) were fabricated by the lost-wax technique (group C, served as the control group) and through DMLS with 20-μm, 30-μm, and 40-μm layer thickness (experimental groups LS20, LS30, and LS40, respectively). Each metal framework was cemented to a master die with a polyvinyl siloxane impression material and then subjected to a 3-point bend test at a crosshead speed of 1 mm/min. The yield force of each metal framework was used to calculate the flexural strength. Data were statistically analyzed by using 1-way ANOVA followed by a Tukey honestly significant difference (HSD) test and an independent-samples t test (α=.05) The microstructure of the fracture surface was evaluated by scanning electron microscopy.

RESULTS

Group C reported the lowest mean flexural strength (P<.05), whereas group LS20 reported the highest mean flexural strength, although no significant difference (P>.05) in flexural strength was observed among the DMLS groups. The 3-unit metal frameworks exhibited a statistically significant higher mean flexural strength than the 4-unit metal frameworks (P<.05).

CONCLUSIONS

The sintering layer thickness did not significantly affect the flexural strength of the laser-sintered metal frameworks. However, the DMLS groups reported a higher mean flexural strength than the cast group.

Performance of fixed dental prostheses up to 6 years-A massive data analysis

STATEMENT OF PROBLEM

Metal and metal-ceramic fixed dental prostheses (FDPs) have been clinically determined to provide long-term durable restorations. However, data on their performance under practice conditions are sparse.

PURPOSE

The purpose of this clinical study was to evaluate the longevity of FDPs under practice conditions by analyzing a large insurance claims database.

MATERIAL AND METHODS

Data were extracted from the data warehouse of a major German national health insurance company (BARMER). The analysis focused on the FDP types with the lowest deductibles in the insurance system. All metal-based FDPs replacing up to 3 adjacent teeth were included. Ceramic veneering was optional and only approved on the labial surfaces of maxillary teeth mesial to the first molar and mandibular teeth mesial to the second premolar. Fee codes allowed clinical courses to be traced on a day count basis. Three groups with FDPs replacing 1 tooth, 2 teeth, and 3 teeth were formed. Kaplan-Meier survival analyses were conducted for the target events removal or extraction, indicating FDP failure and extraction of an abutment tooth.

RESULTS

The sample comprised 124 660 FDPs that replaced 1 tooth (76.5%), 2 teeth (19.8%), or 3 teeth (3.7%). The cumulative survival rates for removal or extraction at 6 years differed significantly, with 83.0% for 1-pontic FDPs, 78.1% for 2-pontic FDPs, and 74.0% for 3-pontic FDPs. Thus, approximately 1 of 6 one-pontic FDPs, 1 of 5 two-pontic FDPs, and 1 of 4 three-pontic FDPs failed. The cumulative survival rates for extraction of an abutment tooth at 6 years showed no significant difference, with 96.0% for 1-pontic FDPs, 95.6% for 2-pontic FDPs, and 95.1% for 3-pontic FDPs.

CONCLUSIONS

The survival rates of FDPs according to insurance data were lower than those reported by clinical studies, indicating a gap between efficacy and effectiveness.

Cobalt-chromium alloys fabricated with four different techniques: Ion release, toxicity of released elements and surface roughness

OBJECTIVE

To investigate the metal ion release, surface roughness and cytoxicity for Co-Cr alloys produced by different manufacturing techniques before and after heat treatment. In addition, to evaluate if the combination of materials affects the ion release.

METHODS

Five Co-Cr alloys were included, based on four manufacturing techniques. Commercially pure titanium, CpTi grade 4 and a titanium alloy were included for comparison. The ion release tests involved both Inductive Coupled Plasma Optical Emission Spectrometry and Inductive Coupled Plasma Mass Spectrometry analyses. The surface analysis was conducted with optical interferometry. Cells were indirectly exposed to the materials and cell viability was evaluated with the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) method.

RESULTS

All alloys showed a decrease of the total ion release when CpTi grade 4 was present. The total ion release decreased over time for all specimens and the highest ion release was observed from the cast and milled Co-Cr alloy in acidic conditions. The cast and laser-melted Co-Cr alloy and the titanium alloy became rougher after heat treatment. All materials were within the limits of cell viability according to standards.

SIGNIFICANCE

The ion release from Co-Cr alloys is influenced by the combination of materials, pH and time. Surface roughness is influenced by heat treatment. Furthermore, both ion release and surface roughness are influenced by the manufacturing technique and the alloy type. The clinical implication needs to be further investigated.

Analysis of technical complications and risk factors for failure of combined tooth-implant-supported fixed dental prostheses

BACKGROUND

The oral rehabilitation with fixed restorations supported by the combination of teeth and dental implants has been advocated in some cases.

PURPOSE

To assess the clinical outcomes of these prostheses. Fixed restorations supported by the combination of teeth and dental implants.

MATERIALS AND METHODS

This retrospective study included all patients treated with combined tooth-implant-supported fixed dental prostheses (FDPs) at one specialist clinic. Abutment/prosthesis failure and technical complications were the outcomes analyzed.

RESULTS

A total of 85 patients with 96 prostheses were included, with a mean follow-up of 10.5 years. Twenty prostheses failed. The estimated cumulative survival rate was 90.7%, 84.8%, 69.9%, and 66.2% at 5, 10, 15, and 20 years, respectively. The failure of tooth and/or implant abutments in key positions affected the survival of the prostheses. There were seven reasons for prostheses failure, with the loss of abutments exerting a significant influence. Bruxism was possibly associated with failures. Prostheses with cantilevers did not show a statistically significant higher failure rate. No group had a general higher prevalence of technical complications in comparison to the other groups.

CONCLUSIONS

Although combined tooth-implant-supported FDPs are an alternative treatment option, this study has found that across 20 years of service nearly 35% the prostheses may fail.

Evaluation of Marginal and Internal Fit of Presintered Co-Cr and Zirconia Three-Unit Fixed Dental Prosthesis Compared to Cast Co-Cr

PURPOSE

The precision of soft metal processing technologies is poorly documented. This study compared marginal and internal fit of presintered cobalt-chromium (Co-Cr) and zirconia three-unit fixed dental prostheses (FDPs) to cast Co-Cr.

MATERIALS AND METHODS

Three-unit FDPs were prepared on metal dies (N = 60) from typodont preparations of the maxillary right first premolar and molar. A standardized preparation of a metal-ceramic restoration was done on abutment teeth. The dies (N = 60) were scanned and divided into three groups (n = 20/group) to receive the FDP made of presintered Co-Cr (Ceramill Si), presintered zirconia (Ceramill Zi), and cast Co-Cr (Girobond NB). Each framework was seated on its specific cast. A replica technique was used for marginal and internal discrepancies measurements in mesiodistal and buccolingual planes. Data were analyzed using the Levene test, t-test, and analysis of variance (α = 0.05).

RESULTS

When the overall mean discrepancy values were compared in the mesiodistal plane, a significant difference was found between Ceramill Sintron and Ceramill Zi groups (p = 0.026). No significant difference was detected between Girobond NB and Ceramill Sintron groups and between Girobond NB and Ceramill Zi groups (p = 0.537 and p = 0.569, respectively). In the buccolingual plane, there was no significant difference in the overall mean discrepancy between the three groups: CS/CZ (p = 1.000), GI/CS (p = 0.51), and GI/CZ (p = 0.87). Significant differences at several measurement points were found at the inter or intramaterial level. The increase in discrepancy values between marginal and occlusal measurements was evident for the three groups.

CONCLUSIONS

Presintered three-unit FDPs fabricated from zirconia and Co-Cr exhibited internal and marginal discrepancy values similar to cast Co-Cr. A significant difference was reported between CS and CZ in mesiodistal planes. The axial and marginal differences in values for the three tested groups were below or around the 120 µm clinically acceptable threshold except for the occlusal area. When comparing first premolar to first molar, the internal and marginal discrepancies were similar with no apparent distortion of the framework after the sintering process.

A retrospective clinical evaluation of extensive tooth-supported fixed dental prostheses after 10 years

STATEMENT OF PROBLEM

The survival and success of tooth-supported fixed dental prostheses (FDPs) in long-term studies vary greatly, depending on the patient and the size of the FDP. Influencing factors for FDP survival or success may include advanced patient age at the time of FDP treatment, treatment severity, and use of new and cheaper FDP materials. As the patient population ages, prosthodontists will treat tooth wear in a greater number of older adults; however, recent long-term studies on such treatments are lacking.

PURPOSE

The purpose of this retrospective clinical study was to examine extensive, tooth-supported FDPs made at 2 specialist clinics in Sweden after 10 years and to compare the outcomes with those of previous studies.

MATERIAL AND METHODS

Patients rehabilitated by using FDPs of at least 5 units at 2 specialist clinics in Sweden between 2002 and 2006 were recalled after 10 years. Clinical examinations were supplemented by reviewing clinical records and existing radiographs. Statistical analysis was performed by using the Student t test, chi-squared test, Fisher exact test, and Kruskal-Wallis test (α=.05).

RESULTS

A total of 152 patients were recalled for clinical examination. Of these, 78 patients attended and were examined. The mean age of the examined group was 70 years (range 36-94), lower than that of those not attending (80 years; range 46-100; P<.05). The mean number of units of the 78 examined FDPs was 7.3 (range 5-12) and 8.0 (range 5-14) for those not examined. FDP configurations in terms of number of units, abutments, pontics, and post-and-cores did not differ significantly between the 2 groups (P>.05). The survival proportion of the examined 78 FDPs (all units of the original FPD) was 74.4%. The success proportion (FDPs without complications) was 52.6%. The most frequent complications were caries (14.1%), endodontic complications (11.5%), loose retainers (7.7%), root fractures (5.1%), and framework fractures (3.8%). FDPs with post-and-cores (P<.05) and cantilevers (P=.054), especially when in combination (P<.05), showed more complications than FDPs without. Chipping fractures in porcelain were found in 38% of the FDPs (7.7% of the units), with more porcelain fractures on Co-Cr frameworks than on gold and titanium alloy frameworks (P<.05).

CONCLUSIONS

This long-term retrospective study indicated that the prognosis for complicated and extensive FDPs in aging patients does not worsen with increased clinical complexity. New materials, treatment complexity, and older patients did not seem to markedly influence prognosis.

Influence of different surface treatments of nickel chrome metal alloy and types of metal primer monomers on the tensile bond strength of a resin cement

Objective

To evaluate the effect of different surface treatments of nickel chrome (NiCr) with the type of metal primer monomers on the conventional tensile bond strength (CTBS) of resin cement.

Methods

Forty disks of NiCr alloy were prepared for CTBS test and grouped as follows: group (1) no surface treatment (control group), group (2) oxide layer only, group (3) air abrasion, and group (4) air abrasion with an oxide layer. Each main group was subdivided into two subgroups (n = 5) depending upon the type of metal primer used for metal treatment. All specimens were bonded with resin cements. The CTBS was tested using a tensile testing machine. The data were statistically analyzed with One-way ANOVA, Two-way ANOVA, and T-test at 0.05 level of significance.

Results

Significant differences in the mean value of the CTBS between different surface treatments (P ≤ 0.05) were observed. Tukey's test showed that air abrasion surface treatment had the highest mean value followed by the air abrasion with an oxide layer and oxide layer only. The control group showed the lowest value of significant difference compared to all treated groups (P ≤ 0.05).

Conclusions

CTBS of self-adhesive resin cement to NiCr is dependent on surface treatment. Two types of the metal primer of different monomer contents 10-methacryloyloxydecyldihydrogenphosphate (MDP) or Thiophosphoricmethacrylate (MEPS) show similar behavior on the tensile bond strength.

Evaluation of dimensional accuracy of dental bridges manufactured with conventional casting technique and CAD/CAM system with Ceramill Sintron blocks using CMM

Background. Recently, non-presintered chromium-cobalt (Cr-Co) blocks with the commercial name of Ceramill Sintron were introduced to the market. However, comprehensive studies on the dimensional accuracy and fit of multi-unit frameworks made of these blocks using the coordinate measuring machine (CMM) are lacking. This study aimed to assess and compare the dimensional changes and fit of conventional casting and milled frameworks using Ceramill Sintron.

Methods. A metal model was designed and scanned and 5-unit frameworks were fabricated using two techniques: (I) the conventional casting method (n=20): the wax model was designed, milled in the CAD/CAM machine, flasked and invested; (II) the milling method using Ceramill Sintron blocks (n=20): the wax patterns of group 1 were used; Ceramill Sintron blocks were milled and sintered. Measurements were made on the original reference model and the fabricated frameworks using the CMM in all the three spatial dimensions, and dimensional changes were recorded in a checklist. Data were analyzed with descriptive statistics, and the two groups were compared using one-way ANOVA and Tukey test (α=0.05).

Results. The fabricated frameworks in both groups showed significant dimensional changes in all the three dimensions. Comparison of dimensional changes between the two groups revealed no significant differences (P>0.05) except for transverse changes (arch) that were significantly greater in Ceramill Sintron frameworks (P<0.05).

Conclusion. The two manufacturing processes were the same regarding dimensional changes and the magnitude of marginal gaps and both processes resulted in significant dimensional changes in frameworks. Ceramill Sintron frameworks showed significantly greater transverse changes than the conventional frameworks.

Evaluation of the Marginal and Internal Fit of Implant-Supported Metal Copings Fabricated with 3 Different Techniques: An In Vitro Study

PURPOSE

To compare the marginal and internal fit of cobalt-chromium (Co-Cr) alloy copings fabricated by with lost wax technique (LW), computer-aided design and computer-aided manufacturing (CAD/CAM), and direct metal laser sintering (DMLS).

MATERIALS AND METHODS

Thirty-six tissue level, straight titanium abutments were screwed onto implant replicas. All specimens were embedded in acrylic resin and randomly divided into 3 subgroups according to the fabrication of metal coping: LW, CAD/CAM, and DMLS. In total, 36 (n = 12/group) Co-Cr implant-supported metal copings were prepared. Marginal, intermarginal, axial, and occlusal fits of each coping were measured using the silicone replica technique. The data were evaluated statistically using one-way ANOVA and Bonferioni post-hoc test (α = 0.05).

RESULTS

The CAD/CAM group showed significantly lower marginal fit than the LW group and DMLS groups (p < 0.001). The marginal fit of the LW group was not significantly different from the DMLS group (p = 0.721). No significant difference found among the fabrication methods in terms of intermarginal fit (p = 0.913). The CAD/CAM group showed lower axial fit than the LW group (p = 0.026), but there was no statistical difference between the DMLS group and the LW (p = 0.999) and CAD/CAM groups (p = 0.247). No significant differences found among the fabrication methods in terms of occlusal fit (p = 0.158).

CONCLUSIONS

The LW and DMLS groups showed better marginal fit compared to the CAD/CAM group; however, the CAD/CAM group was better than the LW group in terms of axial fit. All fabrication methods demonstrated similar intermarginal and occlusal fit.

A comparison of the marginal and internal fit of porcelain laminate veneers fabricated by pressing and CAD-CAM milling and cemented with 2 different resin cements

STATEMENT OF PROBLEM

The marginal and internal adaptations of porcelain laminate veneers (PLVs) are key elements in their long-term success. However, the marginal and internal fit obtained with a pressable material compared with computer-aided design and computer-aided manufacturing (CAD-CAM) needs further investigation as does the choice of cement used.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal fit of PLVs fabricated using pressing and CAD-CAM milling and cemented using 2 types of composite resin cement.

MATERIAL AND METHODS

Twenty PLVs were fabricated from VITA PM9 pressable material, and 20 veneers were milled using VITA Blocs Mark II. Veneers were cemented to composite resin dies using either RelyX Veneer cement or Variolink-N cement. Specimens were embedded in clear resin and sectioned incisogingivally and mesiodistally. Marginal discrepancy at the incisal and cervical positions and the internal gap at 6 different locations were evaluated by using a scanning electron microscope. Two-way ANOVA followed by Tukey multiple comparisons were used to examine difference among groups (α=.05).

RESULTS

The cement and fabrication methods did not show any significant effect for absolute marginal gap (AMG) at the incisal edge, AMG at the cervical margin or marginal gap at the incisal edge. However, both had a significant effect on marginal gap at the cervical margin (P=.038 for the fabrication method and P=.050 for the cement used). Also, both cement and fabrication methods had a significant effect on internal gap average (P<.001). The lowest gap values were reported for veneers fabricated from VITA PM9 by using the press technique and cemented with RelyX Veneer cement. When the position of gap measurements was taken into consideration, it was the only significant factor (P<.001 for the effect of position on AMG and P<.001 for the effect of position on marginal gap). Gaps at the cervical position were significantly lower than gaps at the incisal position.

CONCLUSIONS

Smaller marginal and internal discrepancies were recorded for PLVs fabricated by using the pressing technique and cemented using RelyX Veneer cement compared with milled veneers and Variolink-N cement. Larger discrepancies were present incisally than cervically.

Assay of Secondary Anisotropy in Additively Manufactured Alloys for Dental Applications

Even though additive manufacturing (AM) techniques have been available since the late 1980s, their application in medicine is still striving to gain full acceptance. For the production of dental implants, the use of AM allows to save time and costs, but also to ensure closer dimensional tolerances and higher repeatability, as compared to traditional manual processes. Among the several AM solutions, Laser Powder Bed Fusion (L-PBF) is the most appropriate for the production of metal prostheses. The target of this paper was to investigate the mechanical and microstructural characteristics of Co⁻Cr⁻Mo and Ti⁻6Al⁻4V alloys processed by L-PBF, with a specific focus on secondary anisotropy that is usually disregarded in the literature. Tensile specimens were built in the EOSINT-M270 machine, along different orientations perpendicular to the growth direction. Density, hardness, and tensile properties were measured and the results combined with microstructural and fractographic examination. For both alloys, the results provided evidence of high strength and hardness, combined with outstanding elongation and full densification. Extremely fine microstructures were observed, sufficient to account for the good mechanical response. Statistical analysis of the mechanical properties allowed to attest the substantial absence of secondary anisotropy. The result was corroborated by the observations of the microstructures and of the failure modes. Overall, the two alloys proved to be high-performing, in very close agreement with the values reported in the datasheets, independently of the build orientation.

Sustained drug release using cobalt oxide nanowires for the preparation of polymer-free drug-eluting stents

Polymer-based drug-eluting stents (DESs) represented attractive application for the treatment of cardiovascular diseases; however, polymer coating has caused serious adverse responses to tissues such as chronic inflammation due to acidic by-products. Therefore, polymer-free DESs have recently emerged as promising candidates for the treatment; however, burst release of drug(s) from the surface limited its applications. In this study, we focused on delivery of therapeutic drug from polymer-free (or -less) DESs through surface modification using cobalt oxide nanowires (Co₃O₄ NWs) to improve and control the drug release. The results demonstrated that Co₃O₄ NWs could be simply fabricated on cobalt-chromium substrate by ammonia-evaporation-induced method. The Co₃O₄ NWs were uniformly arrayed with diameters of 50-100 nm and lengths of 10 µm. It was found that Co₃O₄ NWs were comparatively stable without any delamination or change of the morphology under in vitro long-term stability using circulating system. Sirolimus was used as a model drug for studying in vitro release behavior under physiological conditions. The sirolimus release behavior from flat cobalt-chromium showed an initial burst (over 90%) after one day. On the other hand, Co₃O₄ NWs presented a sustained sirolimus release rate for up to seven days. Similarly, the polymer-less specimens on Co₃O₄ NWs substrates sustained sirolimus release for a longer-period of time when compared to flat Co-Cr substrates. In summary, the current approach of using Co₃O₄ NWs-based substrates might have a great potential to sustain drug release for drug-eluting implants and medical devices including stents.

Complications and survival rates of inlays and onlays vs complete coverage restorations: A systematic review and analysis of studies

OBJECTIVE

The aim of this study was to identify if different types of indirect restorations used for single teeth had different biological and technical complications, as well as survival rates.

METHOD

An electronic search was performed in various electronic databases to identify articles, published between 1980 and 2017. The search terms were categorised into 4 groups: inlay, onlay, inlay/onlay and crown. Manual searches of published full-text articles and related reviews were also performed.

RESULTS

A total number of 2849 papers were retrieved initially. After a detailed assessment for eligibility, 9 studies were selected for inclusion. The heterogeneity of the studies did allow neither a meta-analysis nor any meaningful comparison between types of restorations or materials. Only some pooling was performed for representative reasons. The mean survival rate of inlays was 90.89%, while for onlays and crowns it was 93.50% and 95.38%, respectively. For the fourth study group, consisting of both inlays and onlays, the survival rate was found to be 99.43%. Statistical analysis demonstrated caries to be the main biological complication for all types of restorations, followed by a root and/or tooth fracture incidence (11.34%) and endodontic incidence. Ceramic fractures represented the most common technical complication, followed by loss of retention and porcelain chipping.

CONCLUSION

The 5-year survival rate for crowns and inlays/onlays is very high, exceeding 90%. An association between the kind of complications and different types of restorations could not be established. Nevertheless, a relatively high failure rate due to caries and ceramic fractures was noted.

Mechanical properties of cobalt-chromium 3-unit fixed dental prostheses fabricated by casting, milling, and additive manufacturing

STATEMENT OF PROBLEM

New additive manufacturing techniques for nonprecious alloys have made the fabrication of metal-ceramic fixed partial dentures (FPDs) less expensive and less time-consuming. However, whether the mechanical properties produced by these techniques are comparable is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical properties of cobalt-chromium frameworks for FPDs fabricated by 3 different techniques.

MATERIAL AND METHODS

Thirty frameworks for 3-unit FPDs were fabricated by traditional casting, computer-aided design and computer-aided manufacturing (CAD-CAM) milling, and selective laser melting (SLM), with n=10 in each group. The frameworks were weighed, and distal and mesial connector areas measured. The frameworks were cemented and loaded centrally (0.5 mm/s) until deformation above 1 mm occurred. Stiffness was measured as the slope of the axis between 500 and 2000 N. Microhardness was measured on sectioned specimens by Vickers indentation. The microstructure was also analyzed by scanning electron microscopy. One-way ANOVA with Tukey post hoc analysis was used to compare the groups (α=.05).

RESULTS

The framework design differed among the groups, making a comparison of strength impossible. The milled frameworks appeared bulky, while the cast and SLM frameworks were more slender. Statistically significant differences were found in microhardness, stiffness, wall thickness, weight, and connector size (P<.05), and a significant correlation was found between hardness and stiffness (-0.4, P<.005).

CONCLUSIONS

Fabrication method affects the design, stiffness, microhardness, and microstructure of cobalt-chromium FPD frameworks. The SLM frameworks were stiffer and harder than the cast and milled specimens.

Fracture Resistance of Monolithic High Translucency Zirconia Implant-Supported Crowns

AIM

To evaluate the resistance to axial forces of screw-retained monolithic high translucency zirconia (mHTZr) crowns compared with high translucency zirconia + feldspathic ceramic (HTZrC) crowns, low translucency zirconia + feldspathic ceramic (LTZrC) crowns, and metal-ceramic (MC) crowns, and also to observe the different fracture patterns between all groups.

METHODS

Twenty-four crowns were fabricated (6 of each group) and loaded until failure, using a testing machine with a 5.0-kN load cell.

RESULTS

Mean fracture results varied between 1092.7 N (LTZrC group) and 3439.7 N (mHTZr group). No statistically significant differences were found between the HTZrC, LTZrC, and MC groups. However, statistically significant differences (P < 0.05) were found between mHTZr and the other 3 groups. In the MC group, only chipping of the ceramic veneering occurred. In the mHTZr group, when fracturing occurred, it was of the whole structure. Finally, the LTZrC and HTZrC groups suffered both chipping and core fractures.

CONCLUSION

High translucency monolithic zirconia implant-supported crowns proved to be the toughest group studied when an axial force was applied. Fracture patterns varied between different materials, chipping being the most common occurrence.

Ceramic Fracture in Metal-Ceramic Restorations: The Aetiology

All dental restorations are liable to failure during function. Failure could be biologic, aesthetic, mechanical or a combination. Ceramic restorations in particular, including metal-ceramics, are prone to mechanical fracture, especially the fracture of veneering porcelain. Fracture of a metal-ceramic restoration jeopardizes function as well as aesthetics. It is equally onerous to manage for both patient and dentist. Optimal management of such cases requires a detailed knowledge of the aetiology behind this phenomenon. The current paper aims to highlight possible causative factors involved in the mechanical failures of metal-ceramic restorations. Clinical relevance: Ceramic fracture in metal-ceramic crowns and fixed partial dentures is routinely encountered in dental clinics. Knowledge of the aetiology is required to diagnose and manage such cases accurately as well as to avoid these errors in future.

Evaluation of the fit of metal ceramic restorations fabricated with a pre-sintered soft alloy

STATEMENT OF PROBLEM

Fit is an important factor influencing the success or failure of restorations. Recently, there has been increasing use of a newly developed pre-sintered soft alloy for use in computer-aided design and computer-aided manufacturing (CAD-CAM) of cobalt-chromium alloys for the fabrication of metal ceramic restorations. However, almost no studies are available on the fit of restorations fabricated in this way.

PURPOSE

The purpose of this in vitro study was to evaluate the fit of metal coping fabricated from a newly developed CAD-CAM soft alloy in order to investigate its clinical applicability.

MATERIAL AND METHODS

Metal coping was categorized as casting alloy (CA), fully sintered hard alloy (FHA), or pre-sintered soft alloy (PSA) depending on the material, and 10 specimens of each category were fabricated. Seven measurement locations were selected in both the mesiodistal and labiolingual directions. For measurement of the marginal and internal discrepancies, silicone molds produced using a silicone replica technique were divided into mesiodistal and labiolingual cross-sections, and the width was measured. The Kruskal-Wallis and Mann-Whitney U test were performed (corrected α error level=.05/3).

RESULTS

The mean values of the total discrepancy were smallest in the CA group (52.53 ±33.40 μm) and largest in the FHA group (87.84 ±39.43 μm). The CA group and the PSA group were not significantly different from each other (P>.05) but were statistically significantly different from the FHA group (P<.001). In particular, the absolute marginal discrepancy did not differ significantly between the CA (33.68 ±8.44 μm) and PSA groups (37.01 ±8.04 μm) (P>.05).

CONCLUSIONS

The fit of the PSA restorations determined by this study was similar to that of conventional cast restorations. Both FHA and PSA restorations demonstrated clinically acceptable values (<120 μm).

PEEK Primary Crowns with Cobalt-Chromium, Zirconia and Galvanic Secondary Crowns with Different Tapers-A Comparison of Retention Forces

In prosthetic dentistry, double crown systems have proved their suitability as retainers for removable partial dentures. However, investigations in this context, regarding polyetheretherketone, are scarce. Therefore, the aim of this study was to test the retention force (RF) between polyetheretherketone (PEEK) primary and cobalt-chromium (CoCr), zirconia (ZrO₂) and galvanic (GAL) secondary crowns with three different tapers. Primary PEEK-crowns were milled with the tapers 0°, 1°, and 2° (n = 10/taper, respectively). Afterwards, 90 secondary crowns were fabricated: (i) 30 CoCr-crowns milled from Ceramill Sintron (AmannGirrbach, Koblach, Austria) (n = 10/taper), (ii) 30 ZrO₂-crowns milled from Ceramill ZI (AmannGirrbach, Koblach, Austria) (n = 10/taper), and (iii) 30 GAL-crowns made using electroforming (n = 10/taper). RF was measured in a pull-off test (20 pull-offs/specimen) and data were analyzed using 2-/1-way Analysis of Variance (ANOVA) followed by the Tukey-Honestly Significant Difference (HSD) post hoc test and linear regression analyses (p < 0.05). The measured mean RF values ranged between 9.6 and 38.2 N. With regard to the 0°, 1°, and 2° tapered crowns, no statistically significant differences between CoCr and ZrO₂ were observed (p > 0.141). At 0° taper, no differences in retention forces between GAL, CrCr, and ZrO₂ crowns were found (p = 0.075). However, at 1° and 2° taper, lower RF for GAL-crowns were observed (p < 0.009, p < 0.001, respectively). According to this laboratory study, PEEK might be a suitable material for primary crowns, regardless of the taper and the material of secondary crown. Long-term results, however, are still necessary.

Effect of metal conditioner on bonding of porcelain to cobalt-chromium alloy

PURPOSE

The purpose of this study was to evaluate the efficacy of two different metal conditioners for non-precious metal alloys for the bonding of porcelain to a cobalt-chromium (Co-Cr) alloy.

MATERIALS AND METHODS

Disk-shaped specimens (2.5×10.0 mm) were cast with Co-Cr alloy and used as adherend materials. The bonding surfaces were polished with a 600-grid silicon carbide paper and airborne-particle abraded using 110 µm alumina particles. Bonding specimens were fabricated by applying and firing either of the metal conditioners on the airborne-particle abraded surface, followed by firing porcelain into 5 mm in diameter and 3 mm in height. Specimens without metal conditioner were also fabricated. Shear bond strength for each group (n=8) were measured and compared (α=.05). Sectional view of bonding interface was observed by SEM. EDS analysis was performed to determine the chemical elements of metal conditioners and to determine the failure modes after shear test.

RESULTS

There were significant differences among three groups, and two metal conditioner-applied groups showed significantly higher values compared to the non-metal conditioner group. The SEM observation of the sectional view at bonding interface revealed loose contact at porcelain-alloy surface for non-metal conditioner group, however, close contact at both alloy-metal conditioner and metal conditioner-porcelain interfaces for both metal conditioner-applied groups. All the specimens showed mixed failures. EDS analysis showed that one metal conditioner was Si-based material, and another was Ti-based material. Si-based metal conditioner showed higher bond strengths compared to the Ti-based metal conditioner, but exhibited more porous failure surface failure.

CONCLUSION

Based on the results of this study, it can be stated that the application of metal conditioner is recommended for the bonding of porcelain to cobalt-chromium alloys.

In vitro element release and biological aspects of base-metal alloys for metal-ceramic applications

Objective: The aims of this study were to investigate the release of element from, and the biological response in vitro to, cobalt–chromium alloys and other base–metal alloys used for the fabrication of metal-ceramic restorations.

Material and methods: Eighteen different alloys were investigated. Nine cobalt–chromium alloys, three nickel–chromium alloys, two cobalt–chromium–iron alloys, one palladium–silver alloy, one high-noble gold alloy, titanium grade II and one type III copper–aluminium alloy. Pure copper served as positive control. The specimens were prepared according to the ISO standards for biological and corrosion testing. Passive leaching of elements was measured by using Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) after incubation in cell culture media, MEM, for 3 days. Corrosion testing was carried out in 0.9% sodium chloride (NaCl) and 1% lactic acid for 7 days, and the element release was measured by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES). The biological response from the extract solutions was measured though MTT cytotoxicity testing and the Hen's egg test-chorio-allantoic membrane (HET-CAM) technique for irritationt.

Results: The corrosion test showed similar element release from base-metal alloys compared to noble alloys such as gold. Apart from the high-copper alloy, all alloys expressed low element release in the immersion test, no cytotoxic effect in the MTT test, and were rated non-irritant in the HET-CAM test.

Conclusions: Minimal biological response was observed for all the alloys tested, with the exception of the high-copper alloy.

Effect of oxidation heat treatment on the bond strength between a ceramic and cast and milled cobalt-chromium alloys

There is a dearth of dental scientific literature on the effect of different oxidation heat treatments (OHTs) (as surface pretreatments) on the bonding performance of cast and milled cobalt-chromium (CoCr) alloys. The objective of this study was to evaluate the effect of different OHTs on the bond strength between a ceramic and cast and milled CoCr alloys. Cobalt-chromium metallic specimens were prepared using either a cast or a milled method. Specimens were subjected to four different OHT methods: without OHT; OHT under normal atmospheric pressure; OHT under vacuum; and OHT under vacuum followed by sandblasting. The metal-ceramic bond strength was evaluated using a three-point bending test according to ISO9693. Scanning electron microscopy and energy-dispersive spectroscopy were used to study the specimens' microstructure and elemental composition. The bond strength was not affected by the CoCr manufacturing method. Oxidation heat treatment performed under normal atmospheric pressure resulted in the highest bond strength. The concentration of oxygen on the alloy surfaces varied with the different pretreatment methods in the following order: OHT under normal atmospheric pressure > OHT under vacuum > without OHT ≈ OHT under vacuum followed by sandblasting.

Evaluation of internal and marginal fit of two metal ceramic system - in vitro study

INTRODUCTION

The high strength porcelain fused metal crowns have been extensively used in dentistry. However, the fit is the most encountered problems in porcelain fused metal crowns. This mainly depends on the fabrication technique.

AIM

The purpose was to compare the internal and marginal fit of laser sintered and conventionally casted Cobalt-Chromium copings.

MATERIALS AND METHODS

Twenty stainless steel dies of dimension 15 x 10 mm with 1 mm finish margin were fabricated using CAD-CAM technology. Twenty dies were divided into two groups Group 1 and Group 2 containing 10 samples each. All 20 dies were scanned using LAVA 3M scanner and data were used to fabricate metal copings using Laser sintering technique (Group-1) and Conventional casting technique (Group-2). Copings were cemented onto respective dies and finished and standardized sectioning were made. The sectioned models were scanned under stereomicroscope at 50 x magnification for internal and marginal fit evaluation.

RESULTS

Mean and standard deviation of internal and marginal discrepancy of laser sintered copings/conventional cast metal copings was 107.6 ± 10.9μ and 102.1 ± 17.2μ/187.09 ± 11.47 μ and 176.57 ± 25.82 μ respectively. Statistical analysis showed the laser sintered copings have lesser internal and marginal discrepancy than conventional casted copings with p value < 0.001.

CONCLUSION

The laser sintered Co-Cr copings showed better internal and marginal fit when compared to that of conventional Co-Cr casted copings.

A systematic review of outcome measurements and quality of studies evaluating fixed tooth-supported restorations

PURPOSE

The purpose of this systematic review was to review clinical studies of fixed tooth-supported prostheses, and to assess the quality of evidence with an emphasis on the assessment of the reporting of outcome measurements. Multiple hypotheses were generated to compare the effect of study type on different outcome modifiers and to compare the quality of publications before and after January 2005.

MATERIALS AND METHODS

An electronic search was conducted using specific databases (MEDLINE via Ovid, EMBASE via Ovid, Cochrane Library) through July 2012. This was complemented by hand searching the past 10 years of issues of the Journal of Oral Rehabilitation, Journal of Prosthetic Dentistry, Journal of Prosthodontics, and the International Journal of Prosthodontics. All experimental and observational clinical studies evaluating survival, success, failure, and complications of tooth-supported extracoronal fixed partial dentures, crowns, and onlays were included. No restrictions on age or follow-up time were placed.

RESULTS

The electronic search generated 14,869 papers, of which 206 papers were included for full-text review. Hand-searching added 23 papers. Inclusion criteria were met by 182 papers and were included for the review. The majority were retrospective studies. Only 8 (4.4%) were randomized controlled trials. The majority of the studies measured survival and failure, and few studies recorded data on success; however, more than 60% of the studies failed to define survival, success, and failure. Many studies did not use any standardized criteria for assessment of the quality of the restorations and, when standardized criteria were used, they were modified, thereby not allowing for comparisons with other studies. There was an increase of 21.8% in the number of studies evaluating outcome measurements of all-ceramic restorations in past 8 years.

CONCLUSIONS

Prosthodontic literature presents with a reduced percentage of RCTs compared to other disciplines in dentistry. The overall quality of recording prosthodontic outcome measurements has not improved greatly in the past 8 years.

Common Post-fitting Complications in Tooth-supported Fixed-Fixed Design Metal-Ceramic Fixed Dental Prostheses

Objectives: To report the frequency of common complications and their levels in metal-ceramic fixed dental prostheses (MC-FDPs).

Methods: A Descriptive Cross-sectional study was conducted at the Prosthodontics Department, Khyber College of Dentistry Peshawar from January 2011 to October 2012. Using a structured proforma, data from 139 subjects fulfilling the inclusion and exclusion criteria for the study and reporting complications in their MC- FDPs were collected using the method of interview, clinical & radiographic examination.

Results: Of 139 subjects (Mean age = 34+ 6.4 Years), 81 (58.3%) were males and 58 (41.7%) were females with a male to female ratio of 1.4:1. De-cementation was the most common complication (41.7%). Least common complication was secondary caries (6.5%). Level-1 complications were more prevalent (77.7%) than level-2 complications (22.3%). In 91.4% cases, complications occurred before the FDP completed their fifth-years’ service life with 25.2% of these occurring within the first years’ service life.

Conclusion: Irrespective of the type of complications, level-1 complications were more common with de-cementation being the most common complication. One-quarter of all the complications occurred within the first-year service life of the FDPs highlighting concern over the quality of the provided MC-FDPs. .

Fracture behavior of metal-ceramic fixed dental prostheses with frameworks from cast or a newly developed sintered cobalt-chromium alloy

OBJECTIVES

The aim of this study was to investigate the fracture behavior of metal-ceramic bridges with frameworks from cobalt-chromium-molybdenum (CoCrMo), which are manufactured using conventional casting or a new computer-aided design/computer-aided manufacturing (CAD/CAM) milling and sintering technique.

MATERIALS AND METHODS

A total of 32 metal-ceramic fixed dental prostheses (FDPs), which are based on a nonprecious metal framework, was produced using a conventional casting process (n = 16) or a new CAD/CAM milling and sintering process (n = 16). Eight unveneered frameworks were manufactured using each of the techniques. After thermal and mechanical aging of half of the restorations, all samples were subjected to a static loading test in a universal testing machine, in which acoustic emission monitoring was performed. Three different critical forces were revealed: the fracture force (F max), the force at the first reduction in force (F decr1), and the force at the critical acoustic event (F acoust1).

RESULTS

With the exception of the veneered restorations with cast or sintered metal frameworks without artificial aging, which presented a statistically significant but slightly different F max, no statistically significant differences between cast and CAD/CAM sintered and milled FDPs were detected. Thermal and mechanical loading did not significantly affect the resulting forces.

CONCLUSIONS

Cast and CAD/CAM milled and sintered metal-ceramic bridges were determined to be comparable with respect to the fracture behavior.

CLINICAL SIGNIFICANCE

FDPs based on CAD/CAM milled and sintered frameworks may be an applicable and less technique-sensitive alternative to frameworks that are based on conventionally cast frameworks.

A prospective 10-year study of metal ceramic single crowns and fixed dental prosthesis retainers in private practice settings

STATEMENT OF PROBLEM

Metal ceramic restorations are widely used in prosthodontics, but long-term data on their clinical performance in private practice settings based on prospective trials are sparse.

PURPOSE

This clinical trial was designed to provide realistic long-term survival rates for different outcomes related to tooth loss, crown loss, and metal ceramic defect.

MATERIAL AND METHODS

Ninety-five participants were provided with 190 noble metal ceramic single crowns and 138 participants with 276 fixed dental prosthesis retainer crowns on vital posterior teeth. Follow-up examinations were scheduled 2 weeks after insertion, annually up to 8 years, and after 10 years. Kaplan-Meier survival analyses, Mantel-Cox logrank tests, and Cox regression analyses were conducted.

RESULTS

Because of variations in the time of the last examinations, the maximum observation period was 12.1 years. For the primary outcome 'loss of crown or tooth', the Kaplan-Meier survival rate was 94.3% ±1.8% (standard error) at 8.0 years (last outcome event) for single crowns and 94.4% ±1.5% at 11.0 years for fixed dental prosthesis retainer crowns. The difference between the survival functions was not significant (P>.05). For the secondary outcome 'metal ceramic defect', the survival rate was 88.8% ±3.2% at 11.0 years for single crowns and 81.7% ±3.5% at 11.0 years for fixed dental prosthesis retainer crowns. In Cox regression models, the only significant covariates for the outcome event 'metal ceramic defect' were bruxism in the medical history (single crowns) and signs and symptoms of bruxism (fixed dental prosthesis retainer crowns) with hazard ratios of 3.065 (95% CI 1.063 - 8.832) and 2.554 (95% CI 1.307 - 4.992).

CONCLUSIONS

Metal ceramic crowns provided in private practice settings show good longevity. Bruxism appears to indicate a risk for metal ceramic defects.

Treatment of multiple ceramic alloys before recasting

STATEMENT OF PROBLEM

Dental laboratories often reuse dental casting alloys by recasting them, but the processing methods before recasting require further research.

PURPOSE

The purpose of the study was to determine the treatment methods to remove the surface contamination of the previously melted alloys before recasting.

MATERIAL AND METHODS

Cobalt-chromium (Co-Cr), commercially pure titanium (CP Ti), palladium-copper-gallium (Pd-Cu-Ga), and gold-platinum (Au-Pt) ceramic alloys were investigated in the present study. Field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy (EDAX), and x-ray photoelectron spectroscopy (XPS) were used to evaluate the changes in the surface structures and compositions of Co-Cr, CP Ti, Pd-Cu-Ga, and Au-Pt ceramic alloys after airborne-particle abrasion and immersion in various chemical solutions for different time periods. The data obtained by EDAX and XPS were statistically analyzed by Kruskal-Wallis and Nemenyi tests (α=.05).

RESULTS

By using appropriate mechanical and chemical treatment procedures, the contamination content of previously cast ceramic alloys was found to be below the detection limits of EDAX and XPS. The statistical results showed that, compared to the control group (new alloys after polishing), the impurity element was not detected after being treated with these methods, which was not statistically different to control group.

CONCLUSIONS

The surface contamination of ceramic alloys was effectively removed by using certain mechanical and/or chemical treatment methods. Within the limitations of the present study, the most appropriate ways to treat ceramic alloys before recasting were as follows: (1) for Co-Cr ceramic alloys: Al2O3 airborne-particle abrasion and immersion in aqua regia for 15 min; (2) for CP Ti ceramic alloys: Al2O3 airborne-particle abrasion and immersion in 65% HNO3 and 40% HF 1:7 (V/V) for 60 min; (3) for Pd-Cu-Ga ceramic alloys: glass bead airborne-particle abrasion and immersion in 40% HF solution for 30 min; and (4) for Au-Pt ceramic alloys: glass bead airborne-particle abrasion.