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.

Chewing side preference and laterality in patients treated with unilateral posterior implant-supported fixed partial prostheses.

BACKGROUND: It is not clear to what extent chewing is improved by unilateral oral rehabilitation with implant-supported fixed partial prostheses (ISFPPs). OBJECTIVES: This study aimed to investigate whether patients treated with unilateral ISFPPs in the maxilla use their prostheses during mastication to the same extent as they used their contralateral natural teeth. A further aim was to investigate whether there is a correlation between preferred chewing side and laterality. METHODS: Chewing side preference was assessed in 15 participants treated with unilateral ISFPPs in the maxilla. The first, second, third, fifth and tenth chewing cycles were assessed, and the test was repeated 10 times. All participants also answered a questionnaire about their chewing side preference. RESULTS: Most of the participants presented bilateral chewing, but two (13%) chewed only on the ISFPP. There was no statistically significant association between the objectively assessed chewing side and dental status (natural teeth or ISFPPs) during any of the recorded chewing cycles (p > .1). There were statistically significant correlations between both the subjectively reported usually preferred chewing side and the subjective chewing side preference during the test and the objectively assessed chewing side for the first three chewing cycles (p < .01). No correlation was found between handedness and the objectively assessed chewing side. CONCLUSION: In the present study, most participants chewed bilaterally, and chewing was performed both on the ISFPP and on the natural teeth. No correlation was found between the preferred chewing side, objectively or subjectively determined and laterality.

Inflammatory Response to Cobalt-Chromium Alloys Fabricated With Different Techniques.

OBJECTIVES: To explore the in vitro cytokine expression of human peripheral blood mononuclear cells exposed to cobalt-chromium alloys, manufactured with different techniques, in comparison with commercially pure titanium grade 4 and titanium alloy grade 23. MATERIAL AND METHODS: Peripheral blood mononuclear cells (PBMC) were collected from 10 healthy blood donors and exposed to machine-ground coin-shaped: (a) cobalt-chromium (Co-Cr) specimens (n = 5) manufactured by four techniques, i.e. cast, milled, laser melted and presintered milled; (b) commercially pure titanium grade 4; and (c) titanium alloy grade 23. The cells were cultured for 4, 24 and 72 hours followed by investigations of pro- and anti-inflammatory cytokine release using Bio-Plex Pro™. RESULTS: In general, the PBMC produced significantly more cytokines when exposed to the cast and presintered milled Co-Cr materials compared to laser melted, milled Co-Cr and titanium materials. CONCLUSIONS: Within the limitation of the present study, it may be suggested that cast and presintered milled cobalt-chromium alloys provoke a stronger inflammatory response compared to milled and laser melted cobalt-chromium alloys and titanium materials.

Effect of airborne-particle abrasion and polishing on novel translucent zirconias: Surface morphology, phase transformation and insights into bonding.

PURPOSE: The purpose this study was to investigate the effect of Kern´s air-borne particle abrasion protocol (KAPA) and polishing on two translucent zirconias (4Y, 5Y-zirconias) compared to a traditional zirconia (3Y-zirconia). METHODS: Two different surface treatments were analysed by X-ray diffraction (XRD) and interferometry 1) KAPA (0.1 MPa, 50 µm alumina, 10-12 mm distance, 15 sec and 30 sec and cleaning in ultrasound using isopropyl alcohol 99%) and 2) Clinical-delivery polishing paste (Zircon Brite, Dental Ventures, USA). Shear-bond strength tests (SBS's) were performed with a highly polished and virtually flat surface in combination with a 10-MDP based cement and a surface modified by KAPA in combination with zinc phosphate cement. The SBS was expressed in terms of MPa. RESULTS: The mean values for monoclinic content were 13 wt%, 7 wt% and 2 wt% for 3Y-, 4Y- and 5Y-zirconias respectively, no differences were found between 15 and 30 seconds. Polishing did not result in phase transformation to monoclinic phase in any of the zirconias. The rhombohedral phase was identified in all types of zirconias regardless of surface treatment. Shear-bond strength tests showed 5 MPa for polished/10-MDP based cement and 3 MPa for KAPA/ Zinc phosphate. Statistically significant differences were found between the two different surface treatments but not between the types of zirconias. CONCLUSIONS: KAPA for 15 sec seems to be equal to 30 sec regarding morphology and phase transformation. Sole micro-retention appears not to be fully responsible for the bonding phenomena of 10-MDP and zirconia that underwent KAPA.

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.

A systematic review on the accuracy of manufacturing techniques for cobalt chromium fixed dental prostheses.

Purpose: To compare the fit and assess the accuracy of tooth-supported single and multi-unit FDPs in cobalt chromium fabricated using different manufacturing techniques. Materials and methods: A systematic search was performed in three databases; PubMed, Scopus, and Web of Science, using clearly specified search terms and inclusion criteria. The search yielded 1071 articles and included 18 articles in the analysis. Data regarding the fit analyses and the methods of manufacturing were extracted and the accuracy was defined as the fit result minus the pre-set cement spacer. Internal gap (IntG) was the mean of all the internal measuring points and total gap (TotG) was the mean of all measuring points (marginal, cervical, chamfer, axial, occlusal). Results: The total gap results for fit and accuracy irrespective of manufacturing technique were 96 µm and 54 µm for single crowns, 107 µm and 54 µm for multi-unit FDPs, and 98 µm and 54 µm for both single crowns and multi-unit FDPs combined. For total gap of single crowns soft milling had the highest accuracy, for multi-unit FDPs additive manufactured restorations had the highest accuracy. With the results grouped by impression technique, the accuracy for total gap was highest for digital impressions and lower for conventional impressions. Conclusions: Due to the inherent limitations of this systematic review, it still remains unclear what effect the manufacturing technique has on the fit of FDPs. However, the descriptive results suggest that the marginal fit of cobalt chromium FDPs is not negatively affected by the manufacturing technique.

Chemical Bonding to Novel Translucent Zirconias: A Mechanical and Molecular Investigation.

PURPOSE: To investigate direct bonding of a 10-MDP-based cement to two novel translucent yttria-stabilized tetragonal zirconia polycrystal ceramics (4Y-TZP, 5Y-TZP) and observe the influence of thermocycling on this bonding. MATERIALS AND METHODS: Powders of presintered and isostatically pressed 5Y-TZP, 4Y-TZP and 3Y-TZP were mixed with a 10-MDP-based cement (Panavia F 2.0), then stored in deionized water for 48 h at 37°C or thermocycled 10,000 times. Raman spectroscopy and Fourier-transform infrared spectroscopy were used to assess the presence of a functional group (PO32-) that could indicate bonding before and after thermocycling. X-ray photoelectron spectroscopy was used to identify the presence of the suspected Zr-O-P bond in the same specimens. A shear-bond strength (SBS) test was conducted based on ISO 29022:2013. RESULTS: Marked peaks assigned to the asymmetric vibrations of the PO32- functional group were observed in both zirconias before and after thermocycling. The binding energy corresponding to Zr-O-P interactions (531.5 eV) was masked by the aluminosilicate in the filler of the cement. Shear bond strengths were approximately 20 MPa after water storage and approximately 6 MPa after thermocycling. No differences were found between the control group and the translucent zirconias. CONCLUSION: Direct bonding of the 10-MDP-based cement to both 4Y-TZP and 5Y-TZP was highly plausible. Both 4Y-TZP and 5Y-TZP may be promising alternatives to glass-ceramic restorations.

Limited Effect of Cement Material on Stress Distribution of a Monolithic Translucent Zirconia Crown: A Three-Dimensional Finite Element Analysis.

PURPOSE: The literature shows that the performance of densely sintered zirconia single crowns seems to be unaffected by the cement material. The purpose of this study was to evaluate the effects of various cement materials on the stress distribution in a monolithic translucent zirconia crown. MATERIALS AND METHODS: A crown-cement-dentin complex was modeled. Six cements were evaluated: zinc phosphate, glass-ionomer, resin-modified glass-ionomer, dual-cure resin, calcium aluminate-based, and a theoretical or conceptual cement with mechanical properties close to those of dentin (ie, monoblock cement). RESULTS: While varying stress concentrations were found within the cements, the stress concentrations in the crown and dentin were consistent irrespective of cement material. CONCLUSION: Within the limitations of this study, it can be concluded that cement material had a negligible effect on stress distribution in the monolithic zirconia crown.

Cobalt-chromium alloys in fixed prosthodontics in Sweden.

Aim: The aim of this study was to compile the usage of Co-Cr alloys in fixed prosthodontics (FP) among dental laboratories in Sweden. Methods: From March to October 2015, questionnaires were sent to 542 registered dental laboratories in Sweden. The questionnaires were divided in two parts, one for fixed dental-supported prosthodontics (FDP) and one for fixed implant-supported prosthodontics (FIP). Reminders were sent three times. Results: In total of 542 dental laboratories, 55% answered the questionnaires. Most dental laboratories use Co-Cr in FP, 134 (74%) in FDP and 89(66%) in FIP. The laboratories used Co-Cr alloys of various compositions in the prostheses, 35 for FDP and 30 for FIP. The most commonly used Co-Cr alloys for tooth-supported FDPs were (a) Wirobond® 280, (b) Cara SLM and (c) Wirobond® C. For implant-supported frameworks the frequently used alloys were: (a) Cara SLM, (b) Cara Milled and (c) Wirobond® 280. Except for the difference in composition of these alloys, they were also manufactured with various techniques. In tooth-supported prostheses the dominating technique was the cast technique while newer techniques as laser-sintering and milling were more commonly reported for implant-supported constructions. A fourth technique; the 'pre-state' milling was reported in FDP. Conclusion: More than 30 different Co-Cr alloys were reported as being used in FP. Thus, there is a need for studies exploring the mechanical and physical behavior and the biological response to the most commonly used Co-Cr alloys.

A systematic review of survival of single implants as presented in longitudinal studies with a follow-up of at least 10 years.

BACKGROUND: Placement of single implants is one of the most common applications for implant treatment. Millions of patients have been treated worldwide with osseointegrated implants and many of these patients are treated at a young age with a long expected remaining lifetime. Therefore longterm evidence for such treatment is important. AIM: To report patient treatment, implant and implant-supported single crown survival over at least a 10-year period of follow-up. MATERIAL AND METHODS: After reviewing long-term publications, included by Jung et al (2012), a complementary PubMed search was performed using the same search strategy for the period September 2011 to November 2014. Data on implant and single implant crown treatment survival were compiled from included studies. RESULTS: Four new publications were identified from the 731 new titles. They were added to an earlier list of five manuscripts by Jung et al (2012) , which were already included. Accordingly, nine publications formed the database of available long-term evaluations. The database consisted of 421 patients altogether, provided with 527 implants and 522 single crowns. From the 367 patients that were followed-up for at least 10 years (87%), altogether 502 implants were still in function at the completion of the studies (95.3%), supporting 432 original and 33 remade single implant crowns. Based on patient level and implant level data, implant survival reached 93.8% and 95.0%, respectively. The corresponding survival rate for original crown restorations was 89.5%. CONCLUSIONS: Single implant treatment is a predicable treatment over a 10-year period of time, with no indication of obvious changes in implant failure rate between 5 and 10 years. However, replacement of new single crowns must be considered during the follow-up as part of regular maintenance. Compared to the number of treated patients worldwide, the available numbers with a follow-up of 10 years was low.

A retrospective multicenter study comparing metal-ceramic and composite single crowns performed in public general dentistry: 5-year results.

Objective The aim of this study was to evaluate and compare the 5-year survival and complication rate of metal-ceramic (MC) and composite single crowns performed within Public Dental Service, general dentistry, in three Swedish counties and with patients' gender, tooth position, root canal treatment and the presence of a post-and-core taken into account. Methods Data were collected from dental records of 600 patients who had received either an MC (n = 300) or a composite (n = 300) crown on a premolar or molar tooth in the year 2005 and where 5 years of follow-up data were available. Status at treatment completion and at follow-up was recorded, together with any history of intervention during the follow-up period. Results The 5-year survival rate for MC crowns was higher than for composite crowns (93% versus 70%; p < 0.001). This difference was stable, irrespective of the county, patients' gender or tooth position. No gender difference in survival rate was seen for MC crowns, while the survival of composite crowns was significantly higher among women than among men (75% versus 65%; p < 0.05). For MC crowns, there was a tendency toward a lower survival rate for endodontically treated teeth without a post-and-core (83%) as compared to those provided with a post-and-core (93%) and to vital teeth (94%). Surviving composite crowns had recordings of significantly more complications than MC crowns (p < 0.001). Conclusion On premolars and molars, MC crowns have a better medium-term prognosis and fewer complications than composite crowns.

Positioning errors in panoramic images in general dentistry in Sörmland County, Sweden.

The purpose of this study was to evaluate the frequency and severity of positioning errors in panoramic radiography in general dentistry. A total of 1904 digital panoramic radiographs, taken by the Public Dental Service in the county of Sörmland, Sweden, were analysed retrospectively. The study population consisted of all patients who underwent a panoramic examination during the year 2011. One experienced oral radiologist evaluated all radiographs for 10 common errors. Of the 1904 radiographs examined, 79 per cent had errors. The number of errors varied between 1-4 errors per image. No errors were found in 404 images (21%). Fifty-five images (3%) had severe errors, which made it impossible to make correct diagnostics. The most common error was the tongue not being in contact with the hard palate during exposure. However, this did not greatly affect the diagnostic usefulness of the image due to the ability to enhance the image.The patient's head was tilted too far upwards in 23 per cent of the images and the patient's head was rotated during exposure in 15 per cent. The least common error was due to patient movement during exposure (1%). Panoramic radiographs taken in general dental clinics in a Swedish county show several errors. Proper positioning of the patient is necessary to achieve panoramic images with good image quality. Some of the errors could be adjusted with the digital technique used.This allowed assessment of the images, which reduces radiation dose by avoiding retakes.

In vitro measurements of precision of fit of implant-supported frameworks. A comparison between "virtual" and "physical" assessments of fit using two different techniques of measurements.

BACKGROUND: Comparisons between different techniques measuring fit of implant-supported frameworks are few. PURPOSE: The purpose of this study was to compare data on precision of fit from two highly accurate measuring techniques and, also, to compare results using software programs for fit assessments considering both a "virtual" as well as a "physical" (i.e., more clinical) situation. MATERIALS AND METHODS: Five computer numerical control-milled titanium frameworks (Procera Implant Bridge, Nobel Biocare AB, Göteborg, Sweden) were fabricated from individual model/pattern measurements, simulating a clinical situation. Measurements of fit between frameworks and models were performed by means of a coordinate measuring machine (CMM; Zeiss Prismo Vast, Carl Zeiss Industrielle Messtechnik GmbH, Oberkochen, Germany) linked to a computer and an optical, high-resolution, three-dimensional scanner (Atos 4M SO, GOM International AG, Widen, Switzerland). Collected data on distortions between frameworks and models were analyzed and compared between the two measurement techniques. A comparison between "virtual" and "physical" fit assessments was also performed, based on data from the three-dimensional scanner. RESULTS: When using "virtual" fit assessment programs, overall mean three-dimensional distortion between implant and framework center points in absolute figures was 37 (SD 22) and 14 µm (SD 8) for the CMM and three-dimensional scanning measurements, respectively. Corresponding mean three-dimensional distortion when using a "physical" fit assessment program in the scanner was 43 µm (SD 24) (p < 0.001). Mean horizontal (x-axis) measurements of the distance between the two terminal implants of the models and the frameworks were 33.772 and 33.834 mm for the CMM technique. Corresponding measurements for the three-dimensional scanner was 33.798 and 33.806 mm, respectively. Horizontal distances from the three-dimensional scanner were, for most measurements, greater than for the CMM measurements. CONCLUSION: Measurements of fit between frameworks and models may vary depending on what technique is used and how fit assessments regarding "virtual" or "physical" fit is approached.

Implant-level prostheses in the edentulous maxilla: a comparison with conventional abutment-level prostheses after 5 years of use.

PURPOSE: Long-term comparisons of frameworks at the implant or abutment level are not available, and knowledge of the clinical function of cobalt-chromium (Co-Cr) alloy frameworks is limited. Primarily, the aim of this study was to compare the 5-year clinical performance of frameworks with or without abutment connections to implants. Secondly, the outcomes of prostheses made from Co-Cr alloy with porcelain veneers to those made of commercially pure titanium (CP Ti) with acrylic veneers were compared. MATERIALS AND METHODS: The test groups comprised patients treated with screw-retained fixed prostheses made at the implant level according to the Cresco method in either dental porcelain-veneered Co-Cr alloy (n = 15) or acrylic-veneered CP Ti (n = 25). A control group of 40 randomly selected patients were provided with prostheses made at the standard abutment level in CP Ti with acrylic veneers. For all patients, clinical and radiologic 5-year data were retrospectively collected and evaluated. RESULTS: Five-year implant cumulative survival rates (CSRs) were 98.6% and 97.6% for test and control groups, respectively (P > .05). No major differences in bone level were demonstrated between the groups after 5 years (P > .05). Significantly more complications occurred in the test groups compared to the control group (P < .01), with the most common complications being mucositis and fracture of veneers. CONCLUSIONS: After 5 years, the clinical outcomes of implant-level prostheses made of porcelain-veneered Co-Cr or acrylic-veneered CP Ti seem comparable to acrylic-veneered titanium prostheses made at the standard abutment level regarding implant CSR and bone levels. However, more complications were registered in implant-level prostheses compared to the standard abutment-level prostheses.

Cellular responses to cobalt-chrome and CP titanium--an in vitro comparison of frameworks for implant-retained oral prostheses.

The responses of cell types in peri-implant tissues to cobalt-chrome and titanium were studied in vitro. Cylinders were made from both a cobalt-chrome alloy and commercially pure titanium (length 6 mm, diameter 7.9 mm). Plastic tubes were placed over the cylinders to create cell culture wells, in which human epithelial cells or mouse fibroblasts were cultivated. Cell viability was studied using the Alamar Blue method. The surface structure of two samples of each material was analyzed with optical interferometry. The morphology of cells grown on cylinders of each material was studied with scanning electronic microscopy. Epithelial cells and fibroblasts in the titanium group were more viable than those in the cobalt-chrome group (p = 0.001 and p = 0.000, respectively). The titanium surfaces had a greater height deviation (S(a), p = 0.027) but were less dense (S(ds), p = 0.044) than the cobalt-chrome group. The scanning electronic microscopy revealed no major deviations from normal cell morphology. Within the limitations of the present study, the findings indicate that epithelial cells as well as fibroblasts have a stronger negative response to cobalt-chrome alloy than to titanium. We suggest that these differences can be explained only bythe material per se and not by the minor differences in surface structure. Further and clinical studies are needed to confirm the significance of these findings.

Precision of fit to implants: a comparison of Cresco™ and Procera® implant bridge frameworks.

BACKGROUND: The Cresco™ (Astra Tech AB, Mölndal, Sweden) method aims to reduce the inevitable distortions when cast metal frameworks for implant-supported prostheses are fabricated. However, limited data are available for the precision of fit for this method. PURPOSE: To measure and compare the precision of fit of Cresco- and computer numeric controlled (CNC)-milled metal frameworks for implant-supported fixed complete prostheses. MATERIALS AND METHODS: Two groups of frameworks were fabricated according to the Cresco method, either in titanium (Cresco-Ti, n = 10) or in a cobalt-chrome alloy (Cresco-CoCr, n = 10). A third group comprised CNC-milled titanium frameworks (Procera® Implant Bridge [PIB], Nobel Biocare AB, Göteborg, Sweden), made from individual model/pattern measurements (PIB, n = 5). Measurements of fit were performed by means of a coordinate measuring machine linked to a computer. The collected data on distortions were analyzed. RESULTS: Overall, a maximal three-dimensional range of center point distortion of 279 µm was observed for measured frameworks. The framework width (x-axis) decreased for Cresco-CoCr, but increased in Cresco-Ti and PIB; Cresco-CoCr compared to Cresco-Ti (p = .0002) and Cresco-CoCr compared to PIB (p < .0001). In vertical dimension (z-axis), less distortions were present in PIB compared to Cresco-CoCr (p = .0007) and in PIB compared to Cresco-Ti (p < .0001). CONCLUSIONS: None of the frameworks presented a perfect, completely "passive fit" to the master. Although the direction of distortions varied, the horizontal distortions were of similar magnitudes. However, the PIB frameworks had statistical significant less vertical distortions as compared to the Cresco groups.

On cobalt-chrome frameworks in implant dentistry.

BACKGROUND: Cobalt-chrome (CoCr) alloys have been used in dentistry in decades but very little is known about their behavior and biological impact as framework materials in implant dentistry. Furthermore, few studies have evaluated and compared the clinical and radiological results of abutment and abutment-free implant treatment concepts. AIMS: To investigate in vitro CoCr and commercially pure (CP) titanium frameworks regarding precision of fit, estimated material degradation and possible adverse cellular responses. In addition, to retrospectively evaluate the clinical and radiological five-year outcome of abutment-free porcelain-veneered CoCr prostheses compared to acrylic-veneered CP titanium prostheses, with or without abutments. MATERIALS AND METHODS: Paper I. Two groups of cast, sectioned and laser-welded frameworks were fabricated, either in a CoCr alloy or in CP titanium. A third group comprised computer numeric controlled (CNC) milled CP titanium frameworks. Measurements of fit were performed with a coordinate measuring machine. Paper IL Ion leakage from titanium implants, CoCr and CP titanium framework sections into artificial saliva was observed with mass spectrometry. Surface structures were registered with optical interferometry. Paper III. Viability of epithelial cells and fibroblasts cultured on CoCr and titanium specimens were evaluated with the Alamar Blue method. Specimen surface structures were registered with optical interferometry and cell morphology observed with SEM. Paper IV A test group (n = 40) comprised of patients treated with prostheses made at implant level in dental-porcelain veneered CoCr alloy (n = 15) or acrylic-veneered CP titanium (n = 25). A control group (n = 40) was provided with prostheses made at abutment level, in acrylic-veneered CNC-milled CP titanium. Clinical and radiological data were evaluated after five years. RESULTS: Paper I. The transversal width decreased in CoCr frameworks, but increased in both groups of titanium frameworks. Less vertical distortions were present in the CNC-milled frameworks compared to the two other groups. Paper II. Significantly more cobalt ion leaked than titanium and chrome ions. Both framework sections and implants roughened after saliva exposure. Paper III. Both cell groups were more viable on titanium than on CoCr surfaces. The CoCr surfaces had a lower height deviation but were denser than the CP titanium surfaces. No major deviations from normal cell morphology were present. Paper IV. No significant differences in implant cumulative survival rates were demonstrated between the test and control groups after five years in function (98.6% and 97.6 %, respectively). No major differences in bone levels were demonstrated. Mucositis and veneer fracture were the most common complications in all groups. CONCLUSIONS: None of the frameworks presented a perfect, completely "passive fit". There were indications of active corrosive processes for both implants and framework materials. Epithelial cells and fibroblasts preferred titanium to CoCr surfaces. The clinical outcomes of implant level prostheses made of porcelain-veneered CoCr or acrylic-veneered titanium seem comparable to acrylic-veneered titanium prostheses made at abutment level.

A 3-year retrospective study of Cresco frameworks: preload and complications.

PURPOSE: The aim of this retrospective clinical study was to evaluate the clinical outcome of fixed implant-supported complete prostheses on Astra or Brånemark implants when using either conventional cast frameworks or frameworks produced according to the Cresco Ti Precision method (Cresco Ti Systems Sàrl., Lausanne, Switzerland). MATERIALS AND METHODS: Forty-six patients treated 3 years previously were divided into four groups according to implant system and framework design. Clinical examinations were performed and case records were scrutinized. The stability for each prosthesis retention screw was recorded as the torque profile and was monitored using the Osseocare torque controller (Nobel Biocare AB, Göteborg, Sweden). Complications in association with implants and superstructures were registered. Patient opinions were recorded. The significance level was set to 5%. RESULTS: The Astra-Cresco group demonstrated a lower degree of prosthesis retention screw stability compared with the Astra group. No differences among the four groups were seen regarding plaque, bleeding on probing, or marginal bone resorption. The Brånemark group (Brånemark System, Nobel Biocare AB) demonstrated more mechanical complications than the Brånemark-Cresco group. Mobile prostheses were found in the Brånemark and the Astra-Cresco groups. Fracture of veneer was seen in 20% of the prostheses and was more frequently found in the groups with mobile prostheses. Sixty percent of the prostheses showed reactions in the surrounding soft tissues. The most common reaction was mucosal proliferation. No differences were detected in the patients' opinions. CONCLUSION: Within the limitations of this retrospective study, the following can be concluded: (1) compared with conventional frameworks, the Cresco distortion correction method does not provide a better clinical outcome after prosthesis connection in patients with fixed implant-supported complete prostheses; and (2) the two framework-producing methods behave differently on Astra implants compared with Brånemark implants concerning prosthesis retention screw stability, mechanical and biologic complications, and reactions in patients with fixed implant-supported complete prostheses.