Marginal and internal fit of pre-sintered Co-Cr and zirconia 3-unit fixed dental prostheses as measured using microcomputed tomography

STATEMENT OF PROBLEM Limited information is available on the precision of new metal processing technologies. PURPOSE The purpose of this in vitro study was to evaluate the marginal and internal fit of pre-sintered cobalt-chromium (Co-Cr) and zirconia 3-unit fixed dental prostheses using x-ray microcomputed tomography. MATERIAL AND METHODS Three-unit fixed dental prostheses were prepared on metal dies (N=12) using a typodont model from the maxillary first premolar to the first molar. A standardized preparation with a 1.2-mm chamfer (360 degrees) and a 2-mm occlusal reduction was prepared on abutment teeth. The dies were scanned and divided into 2 groups to receive the fixed dental prostheses (n=6) made of pre-sintered Co-Cr and pre-sintered zirconia. Each framework was seated on its cast, and marginal and internal discrepancies were measured at 9 points, starting from the most distal point from the pontic for the maxillary first premolar and the first molar (points 1-4, mesial; point 5, occlusal; points 6-9, distal) of each abutment tooth using microcomputed tomography. The data were analyzed using the Levene test, t test, and ANOVA (α=.05). RESULTS When overall mean discrepancy values were compared, no significant difference was observed between pre-sintered Co-Cr and pre-sintered zirconia (P=.085). Discrepancy values for points 1, 2, and 3 were significantly different for pre-sintered Co-Cr and pre-sintered zirconia, with the lowest mean values for point 1 and the highest for point 5. On the abutment tooth basis, for the maxillary first premolar and the first molar, a significant difference was found only in points 6 (P<.001) and 8 (P<.003) for both materials. When the discrepancies for the maxillary first premolar were considered for pre-sintered Co-Cr and pre-sintered zirconia, the mean values were significantly different only at points 1 (P<.001), 2 (P=.007), and 3 (P=.003) and were smaller for pre-sintered zirconia. For the tooth the first molar, a significant difference was observed at point 2 (P=.002) and point 3 (P=.008) for both materials, where the mean values were higher for pre-sintered Co-Cr than for pre-sintered zirconia. The pairwise comparison between points showed a significant difference between measurement points within each material (P<.05). The increase in values between points 1 and 5 was evident for both pre-sintered Co-Cr and pre-sintered zirconia materials. CONCLUSIONS Three-unit fixed dental prostheses made of pre-sintered Co-Cr or zirconia showed similar marginal and internal discrepancy values, with the highest discrepancy values at the occlusal region in both the first premolar and first molar

Evaluation of ceramic adherence to cobalt-chromium alloys fabricated by different manufacturing techniques

STATEMENT OF PROBLEM: Selective laser melting has been increasingly used in the fabrication of metal-ceramic prostheses. The longevity of the prostheses depends on the strength of the metal-ceramic bond, which may differ with the framework manufacturing technique. PURPOSE: The purpose of this in vitro study was to compare the bond strength of ceramic to cobalt-chromium (Co-Cr) alloys fabricated by different manufacturing methods. MATERIAL AND METHODS: Sixty Ø15×2-mm disk-shaped specimens were prepared and assigned to 3 groups (n=20) with different manufacturing methods: milled Co-Cr (M), selective laser melted Co-Cr (SLM), and cast Co-Cr (C). The disks were ceramic layered with a 2-mm thickness. Half of the specimens from each group were thermocycled. The shear bond strength (SBS) test was applied to all specimens. The microstructure changes after ceramic layering were evaluated by X-ray diffraction (XRD). The specimens' surface morphology was analyzed by using scanning electron microscopy (SEM). RESULTS: Thermocycling had a significant effect on SBS values in the SLM group (P=.017). Considering the registered F$_{max}$ (force inducing bonding failure), a significant difference was found between SLM and both M and C groups (P<.001). No significant difference was found between milled and cast Co-Cr (P=.885). The failure types were mostly mixed failures. Ceramic layering induced a crystallization increase in groups C and SLM. CONCLUSIONS: The adhesion strength of ceramic to Co-Cr differed with alloy composition and manufacturing technique. The aging process influenced the results in the SLM group

The incidence of prosthetic materials on wear mechanism of antagonist dentition: a review

Wear is a process that includes both natural teeth and restoration materials. Wear mechanism remains unclear and conflicting results are still found. It is normally a slow multifactorial process. Various influencing factors have been cited through the literature.This paper presents an overview of the prosthetic materials commonly used and their implication in the wear process of antagonist teeth or prostheses. A search was conducted on PubMed and Elsevier using the following key-words: wear, wear resistance, abrasiveness, prostheses wear, prostheses resistance, restorations wear, prostheses material, abrasion etiology and abrasion physiopathology. Patient and material–related factors were reported. Comparison of the protocols remains difficult due to the differences in the methodology

Comparison of Adhesion of a Novel Pre-sintered Cobalt-Chromium to Pre-sintered Zirconia and Cast Nickel-Chromium

AIM This study compared the bond strength of pre-sintered Ceramill Sintron to pre-sintered zirconia and cast nickel-chromium (NiCr). MATERIALS AND METHODS Specimens (n = 60) (diameter: 15 mm; thickness: 2 mm) were prepared (n = 20/group) (Ceramill Sintron, Ceramill Zi, and Wirobond 99). Disks were layered with vita VM ceramic (4 mm). Specimens were randomly divided into two subgroups. Only one subgroup was thermocycled. Specimens were tested under shear strength. Energy-dispersive X-ray (EDX) mapping was done on one disk of each material before and after ceramic layering. RESULTS Failure types were mostly mixed failures. Significant difference was found between the three materials for Y and Z failure types (p-values: 0.032 and 0.010 respectively). Thermocycling had no major effect on the results reported. Considering Fmax (force-inducing bonding failure) registered, significant difference was found between the control group and milled alloys groups. No significant difference was found between Ceramill Sintron and Zi. The EDX mapping showed a net increase in the control group oxide layer, whereas only slight increase and decrease were reported for Zi and Sintron respectively. CONCLUSION When compared with cast NiCr, novel Ceramill Sintron has higher bond strength, comparable to Ceramill Zi. Thermocycling had no major effects on the results. CLINICAL SIGNIFICANCE Ceramic-alloy bonding is a primary factor in the prosthesis' longevity

Comparison of Adhesion of a Novel Pre-sintered Cobalt-Chromium to Pre-sintered Zirconia and Cast Nickel-Chromium.

AIM This study compared the bond strength of pre-sintered Ceramill Sintron to pre-sintered zirconia and cast nickel-chromium (NiCr). MATERIALS AND METHODS Specimens (n = 60) (diameter: 15 mm; thickness: 2 mm) were prepared (n = 20/group) (Ceramill Sintron, Ceramill Zi, and Wirobond 99). Disks were layered with vita VM ceramic (4 mm). Specimens were randomly divided into two subgroups. Only one subgroup was thermocycled. Specimens were tested under shear strength. Energy-dispersive X-ray (EDX) mapping was done on one disk of each material before and after ceramic layering. RESULTS Failure types were mostly mixed failures. Significant difference was found between the three materials for Y and Z failure types (p-values: 0.032 and 0.010 respectively). Thermocycling had no major effect on the results reported. Considering Fmax (force-inducing bonding failure) registered, significant difference was found between the control group and milled alloys groups. No significant difference was found between Ceramill Sintron and Zi. The EDX mapping showed a net increase in the control group oxide layer, whereas only slight increase and decrease were reported for Zi and Sintron respectively. CONCLUSION When compared with cast NiCr, novel Ceramill Sintron has higher bond strength, comparable to Ceramill Zi. Thermocycling had no major effects on the results. CLINICAL SIGNIFICANCE Ceramic-alloy bonding is a primary factor in the prosthesis' longevity