Yurdanur Ucar

Comparison of the bond strength of laser-sintered and cast base metal dental alloys to porcelain

OBJECTIVE The purpose of this study was to compare shear bond strengths of cast Ni-Cr and Co-Cr alloys and the laser-sintered Co-Cr alloy to dental porcelain. METHODS Dental porcelain was applied on two cast and one laser-sintered base metal alloy. Ten specimens were prepared for each group for bond strength comparison. ANOVA followed by Tukey HSD multiple comparison test (alpha=0.05) was used for statistical analysis. Fractured specimens were observed with a stereomicroscope to classify the type of failure after shear bond testing. RESULTS While the mean shear bond strength was highest for the cast Ni-Cr metal-ceramic specimens (81.6+/-14.6 MPa), the bond strength was not significantly different (P>0.05) from that for the cast Co-Cr metal-ceramic specimens (72.9+/-14.3 MPa) and the laser-sintered Co-Cr metal-ceramic specimens (67.0+/-14.9 MPa). All metal-ceramic specimens prepared from cast Ni-Cr and Co-Cr alloys exhibit a mixed mode of cohesive and adhesive failure, whereas five of the metal-ceramic specimens prepared from the laser-sintered Co-Cr alloy exhibited the mixed failure mode and five specimens exhibited adhesive failure in the porcelain. CONCLUSIONS The new laser-sintering technique for Co-Cr alloy appears promising for dental applications, but additional studies of properties of the laser-sintered alloy and fit of castings prepared by this new technique are needed before its acceptance into dental laboratory practice. SIGNIFICANCE Laser sintering of Co-Cr alloy seems to be an alternative technique to conventional casting of dental alloys for porcelain fused to metal restorations.

Internal fit evaluation of crowns prepared using a new dental crown fabrication technique: Laser-sintered Co-Cr crowns

STATEMENT OF PROBLEM Difficulties encountered during casting of base metal dental alloys limit their use. Application of these alloys might be enhanced if new techniques are used. PURPOSE The purpose of this study was to compare the internal fit of laser-sintered Co-Cr alloy crowns with base metal restorations prepared from another Co-Cr alloy and a Ni-Cr alloy using conventional casting techniques. MATERIAL AND METHODS Internal fit of laser-sintered Co-Cr crowns was compared with the fit of conventionally cast Ni-Cr and Co-Cr alloy crowns. Twelve crown-shaped specimens were prepared on a stainless steel die representing a prepared maxillary right central incisor for each group. Fit of crowns was evaluated using 2 different techniques: (1) weighing the light-body addition silicone that simulated a cement material, and (2) measuring the internal gap width on a die for longitudinally sectioned specimens. One-way ANOVA followed by Tukey multiple comparison test was used for statistical analysis (alpha=.05). RESULTS Significantly higher mean (SD) light-body silicone weights (P<.001) were observed in the laser-sintered Co-Cr alloy group (14.34 (1.67) mg) compared to the conventionally cast Ni-Cr alloy group (9.36 (1.97) mg) and Co-Cr alloy group (7.85 (1.19) mg). Mean internal gap widths (SDs) were 58.21 (19.92) microm, 50.55 (25.1) microm, and 62.57 (21.62) microm, respectively, for the cast Ni-Cr and Co-Cr alloy groups and the laser-sintered Co-Cr alloy group. No significant difference was observed between the 3 groups for internal gap widths (P=.42). CONCLUSIONS Weighing the light-body addition silicone is a convenient method for evaluating the 3-dimensional internal fit of dental crowns. However, no significant difference was found among the 3 alloy groups evaluated for the internal gap width of sectioned crown specimens.

Mechanical Properties of Polyamide Versus Different PMMA Denture Base Materials

PURPOSE Polymethyl methacrylate (PMMA) resins are the most commonly used denture materials; however, they do not have a high flexural strength (FS). This study aimed to compare the mechanical properties of a polyamide-based, injection-molded denture material (Deflex) with another injection-molded PMMA base material (SR-Ivocap) and a conventional compression-molded PMMA (Meliodent). MATERIALS AND METHODS Flexural properties (deflection, bending strength, and bending modulus) of denture base materials were evaluated (n = 10). Specimens meeting International Standards Organization (ISO) specification number 20795-1 requirements were prepared (65 × 10 × 3 mm(3)). A three-point bending test was carried out on an Instron testing machine at a 5 mm/min crosshead speed. The Knoop hardness test was used to compare microhardness values. Data were analyzed using ANOVA, followed by REGWQ. RESULTS The group results, standard deviations, and statistical differences (p < 0.01) for Deflex, SR-Ivocap, and Meliodent were (A) flexural strength (MPa: 78.3 ± 1.0,(a) 69.8 ± 1.4,(b) 81.1 ± 1(a)), (B) flexural modulus (GPa: 0.70 ± 0.13,(a) 0.85 ± 0.27,(a) 1.70 ± 0.23(b)), (C) Knoop Hardness (kg/cm(2) : 7.5 ± 1.0,(a) 13.5 ± 1.4,(b) 16.9 ± 1.0(c)). Different superscript letters indicate significant difference. All Meliodent specimens fractured during flexural testing, but no Deflex specimens did. CONCLUSIONS While polyamide denture material produced good fracture resistance, its modulus is not yet sufficiently high to be equal to standard PMMA materials. Clinical Implications. Polyamide has some attractive advantages, but will require modification to produce consistently better properties than current PMMA materials.

Metal ceramic bond after multiple castings of base metal alloy.

STATEMENT OF PROBLEM Remelting previously cast metal can produce a critical change in metal-oxide composition at the dental alloy surface. PURPOSE The purpose of this study was to evaluate the effect of multiple castings on bonding of a single selected base metal and a dental ceramic, and to compare results from shear bond and 3-point-bending tests. MATERIAL AND METHODS Three groups of dental alloy (Remanium CSe) were prepared by mixing 50% fresh alloy to alloy remnants from previous castings. The specimens in the first casting group used 100% fresh alloy and served as control (C0). The second group consisted of equal amounts of fresh alloy and alloy remnants cast only once (C1). The third and fourth groups contained 50% fresh alloy and alloy cast twice (C2) and 3 times (C3), respectively. The bond load (N) between alloy and dental porcelain (VMK 95 Metal Ceramic) was evaluated, using shear bond and 3-point bending tests. The fracture surfaces of the specimens subjected to testing were analyzed using a stereomicroscope and scanning electron microscope. One-way ANOVA followed by the Tukey multiple comparison test was used for analysis of bond data (alpha=.01). RESULTS The mean shear bond load (SD) of C0 (738.0 (77.1) N) was significantly higher than that of C1 (577.8(139.4) N), C2 (494.8 (77.6) N), and C3 (480.5 (60.9) N). Mean peak load for the 3-point-bending test of specimens cast from C0 (39.8 (1.79) N) was significantly higher than for other groups (P<.01). No significant difference was found between C1 (24.4 (5.60) N), C2 (23.2 (4.03) N), and C3 (22.8 (1.79) N) in terms of the shear bond test and the 3-point bending test. CONCLUSIONS In general, there was agreement between the 2 bond strength tests to indicate that including re cast base alloy with fresh alloy for metal decreases metal-to-ceramic bond strengths. (J Prosthet Dent 2009;102:165-171)

Biocompatibility of dental amalgams.

Objective. The purpose of this review paper is to review the literature regarding the toxicology of mercury from dental amalgam and evaluate current statements on dental amalgam. Materials and Methods. Two key-words “dental amalgam” and “toxicity” were used to search publications on dental amalgam biocompatibility published in peer-reviewed journals written in English. Manual search was also conducted. The most recent declarations and statements were evaluated using information available on the internet. Case reports were excluded from the study. Results. The literature show that mercury released from dental amalgam restorations does not contribute to systemic disease or systemic toxicological effects. No significant effects on the immune system have been demonstrated with the amounts of mercury released from dental amalgam restorations. Only very rarely have there been reported allergic reactions to mercury from amalgam restorations. No evidence supports a relationship between mercury released from dental amalgam and neurological diseases. Almost all of the declarations accessed by the internet stated by official organizations concluded that current data are not sufficient to relate various complaints and mercury release from dental amalgam. Conclusions. Available scientific data do not justify the discontinuation of amalgam use from dental practice or replacement with alternative restorative dental materials.

A clinical prospective study on alveolar bone augmentation and dental implant success in patients with type 2 diabetes

OBJECTIVES The objective of this prospective, controlled clinical study was to determine the outcomes of dental implant therapy with staged guided bone regeneration procedures in patients with type 2 diabetes. PATIENTS AND METHODS Twenty-four patients were included in the study. Half of the patients were diagnosed with type 2 diabetes mellitus (group 1) while the other half (group 2) of the patients consisted of patients without diabetes. The edentulous maxillary anterior/premolar regions with sufficient vertical height but inadequate horizontal width were treated with staged guided bone regeneration technique and with one or two implant-supported fixed restorations. The patients were followed up at least for 12 months. The parameters that were evaluated were radiographic evaluations on CBCT images and periapical radiographs, histomorphometric analysis, resonance frequency analysis (RFA) and wound-healing parameters. The data were analyzed statistically. RESULTS A total of 43 implants were placed in 24 patients (22 implants in group 1 and 21 implants in group 2). The survival rates of implants were 100% for both groups. The success rate of implants was 95% for group 1 and 100% for group 2. None of the parameters including CBCT findings, RFA values, success rates and wound-healing scores showed a significant difference between the two groups. CONCLUSION Staged guided bone regeneration is a feasible augmentation procedure for the treatment of horizontal bone deficiencies of the maxillary anterior/premolar regions in well-controlled type 2 diabetic patients.

Mechanical properties, fracture surface characterization, and microstructural analysis of six noble dental casting alloys

STATEMENT OF PROBLEM Because noble dental casting alloys for metal ceramic restorations have a wide range of mechanical properties, knowledge of these properties is needed for rational alloy selection in different clinical situations where cast metal restorations are indicated. PURPOSE The purpose of this study was to compare the mechanical properties and examine both the fracture and polished surfaces of 6 noble casting alloys that span many currently marketed systems. Five alloys were designed for metal ceramic restorations, and a sixth Type GPT has Type IV alloy for fixed prosthodontics (Maxigold KF) was included for comparison. MATERIAL AND METHODS Specimens (n=6) meeting dimensional requirements for ISO Standards 9693 and 8891 were loaded to failure in tension using a universal testing machine at a crosshead speed of 2 mm/min. Values of 0.1% and 0.2% yield strength, ultimate tensile strength, elastic modulus, and percentage elongation were obtained. Statistical comparisons of the alloy mechanical properties were made using 1-way ANOVA and the REGW multiple-range test (α=.05). Following fracture surface characterization using scanning electron microscopy (SEM), specimens were embedded in epoxy resin, polished, and again, examined with the SEM. RESULTS When the multiple comparisons were considered, there were generally no significant differences in the elastic modulus, 0.1% and 0.2% offset yield strength, and ultimate tensile strength for the d.SIGN 91 (Au-Pd), d.SIGN 59 (Pd-Ag), Capricorn 15 (Pd-Ag-Au) and Maxigold KF (Au-Ag-Pd) alloys, except that the ultimate tensile strength was significantly lower (P<.05) for Maxigold KF than these other 3 alloys. These 4 mechanical properties were generally significantly lower (P<.05) for Aquarius XH (Au-Pt-Pd) and Brite Gold XH (Au-Pt). The d.SIGN 59 (14.6%) and Capricorn 15 (13.8%) alloys had the highest values of mean percentage elongation, which were not significantly different. Aquarius XH (6.0%) and Maxigold KF (4.2%) had the lower mean values of percentage elongation, which were also not significantly different. The polished and etched surfaces for all alloys revealed equiaxed, fine-grain microstructures, and all fracture surfaces contained casting porosity. Incomplete solidification suggestive of dendritic structures was observed for some alloys. Fracture surfaces were complex, with characteristic features of both brittle and ductile fracture. Precipitate particles on the fracture surfaces indicated the multi-phase character of the alloys. CONCLUSIONS For the important mechanical property of yield strength, there were generally no significant differences among the Au-Pd, Pd-Ag, Pd-Ag-Au and Au-Ag-Pd alloys. Wide variation was found in percentage elongation, with the Pd-Ag and Pd-Ag-Au alloys having the highest values and the Au-Pd-Pt and Au-Ag-Pd alloys having the lowest values.

A biomimetic growth factor delivery strategy for enhanced regeneration of iliac crest defects.

The importance of provision of growth factors in the engineering of tissues has long been shown to control the behavior of the cells within the construct and several approaches were applied toward this end. In nature, more than one type of growth factor is known to be effective during the healing of tissue defects and their peak concentrations are not always simultaneous. One of the most recent strategies includes the delivery of a combination of growth factors with the dose and timing to mimic the natural regeneration cascade. The sequential delivery of bone morphogenetic proteins BMP-2 and BMP-7 which are early and late appearing factors during bone regeneration, respectively, was shown in vitro to enhance osteoblastic differentiation of bone marrow derived mesenchymal stem cells. In the present study, the aim was to study the effectiveness of this delivery strategy in a rabbit iliac crest model. 3D plotted poly(ε-caprolactone) scaffolds were loaded with BMP carrying nanoparticles to achieve: (a) single BMP-2 or BMP-7 delivery, and (b) their combined delivery in a simultaneous or (c) sequential (biomimetic) fashion. After eight weeks of implantation, computed tomography and biomechanical tests showed better mineralized matrix formation and bone-implant union strength at the defect site in the case of sequential delivery compared to single or simultaneous delivery modes. Bone mineral density (BMD) and push-out stress were: 33.65±2.25 g cm(-3) and 14.5±2.28 MPa, respectively, and almost 2.5 fold higher in comparison to those without growth factors (BMD: 14.14±1.21 g cm(-3); PS: 6.59±0.65 MPa). This study, therefore, supports those obtained in vitro and emphasizes the importance of mimicking the natural timing of bioavailability of osteogenic factors in improving the regeneration of critical-sized bone defects.

Effect of layered manufacturing techniques, alloy powders, and layer thickness on metal-ceramic bond strength

Statement of problem. Direct metal laser sintering (DMLS) and direct metal laser melting (DMLM) have become popular for fabricating the metal frameworks of metal‐ceramic restorations. How the type of layered manufacturing device, layer thickness, and alloy powder may affect the bond strength of ceramic to metal substructure is unclear. Purpose. The purpose of this in vitro study was to evaluate the bond strength of dental porcelain to metal frameworks fabricated using different layered manufacturing techniques (DMLS and DMLM), Co‐Cr alloy powders, and layer thicknesses and to evaluate whether a correlation exists between the bond strength and the number of ceramic remnants on the metal surface. Material and methods. A total of 75 bar‐shaped metal specimens (n=15) were fabricated using either DMLS or DMLM. The powder alloys used were Keramit NP‐S and EOS‐Cobalt‐Chrome SP‐2 with layer thicknesses of 20 &mgr;m and 30 &mgr;m. After ceramic application, the metal‐ceramic bond strength was evaluated with a 3‐point‐bend test. Three‐way ANOVA followed by the Tukey honest significance difference test were used for statistical analysis (&agr;=.05). De‐bonding surface microstructure was observed with scanning electron microscopy. Energy dispersive spectroscopy analysis was conducted to evaluate the correlation between ceramic remnants on the metal surface and bond strength values. Results. The mean bond strength value of DMLS was significantly higher than that of DMLM. While no statistically significant difference was found between layer thicknesses, alloy powders closely affected bond strength. Statistical comparisons revealed that the highest bond strength could be achieved with DMLS‐Cobalt‐Chrome SP2‐20&mgr;m, and the lowest bond strength was observed in DMLS‐Keramit NP‐S‐20&mgr;m (P≤.05). No correlation was found between porcelain remnants on the metal surface and bond strength values. Conclusions. The layered manufacturing device and the alloy powders evaluated in the current study closely affected the bond strength of dental porcelain to a metal framework. However, layer thickness did not affect the bond strength.

A novel repair method for the treatment of acute Achilles tendon rupture with minimally invasive approach using button implant: A biomechanical study

BACKGROUND Minimally invasive Q3 repair has been proposed for acute Achilles tendon rupture with low rate of complications. However there are still controversies about optimal technique. In this study we aimed to describe Endobutton-assisted modified Bunnell configuration as a new Achilles tendon repair technique and evaluate its biomechanical properties comparing with native tendon and Krackow technique. METHODS 27 ovine Achilles tendons were obtained and randomly placed into 3 groups with 9 specimens ineach. The Achilles tendons were repaired with Endobutton-assisted modified Bunnell technique in group 1, Krackow suture technique in group 2 and group 3 was defined as the control group including native tendons. Unidirectional tensile loading to failure was performed at 25mm/min. Biomechanicalproperties such as peak force to failure (N), stress at peak (MPa), elongation at failure, and Youngsmodulus (GPa) was measured for each group. All groups were compared with each other using one-wayANOVA followed by the Tukey HSD multiple comparison test (a=0.05). RESULTS The average peak force (N) to failure of group 1 and group 2 and control group was 415.6±57.6, 268.1±65.2 and 704.5±85.8, respectively. There was no statistically significant difference between native tendon and group 1 for the amount elongation at failure (p>0.05). CONCLUSIONS Regarding the results, we concluded that Endobutton-assisted modified Bunnell technique provides stronger fixation than conventional techniques. It may allow early range of motion and can be easily applied in minimally invasive and percutaneous methods particularly for cases with poor quality tendon at the distal part of rupture. LEVEL OF EVIDENCE Level II, Biomechanical research study.