Cumhur Sipahi

Annealing of Co-Cr dental alloy: effects on nanostructure and Rockwell hardness.

PURPOSE The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring 4 × 2 × 2 mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukeys HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant. RESULTS The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness (48.16 ± 3.02 HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness (27.40 ± 3.98 HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 Å). CONCLUSION After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

Effects of six surface treatment methods on the surface roughness of a low-fusing and an ultra low-fusing feldspathic ceramic material.

PURPOSE The purpose of this in vitro study was to determine the effects of six surface treatment methods on the surface roughness of two feldspathic ceramic materials. MATERIALS AND METHODS One hundred twenty metal discs were cast (Remanium CS). A low-fusing feldspathic ceramic (Vita Omega 900) was fired onto 60 metal discs, and an ultra low-fusing feldspathic ceramic (Finesse) was fired onto the other 60 metal discs. Six surface treatment methods were selected: (1) autoglazing (AUG), (2) overglazing (OVG), (3) polishing (POL), (4) fine diamond disc grinding + polishing + autoglazing (FDPA), (5) coarse diamond disc grinding + polishing + autoglazing (CDPA), (6) polishing + autoglazing (PA). Omega specimens were assigned to six experimental groups representing six surface treatment methods (Om-AUG, Om-OVG, Om-POL, Om-FDPA, Om-CDPA, Om-PA) (n = 10). Finesse specimens were also assigned to six experimental groups (Fn-AUG, Fn-OVG, Fn-POL, Fn-FDPA, Fn-CDPA, Fn-PA) (n = 10). Treated ceramic surfaces were examined by means of profilometry and transmission electron microscopy. RESULTS In Omega groups mean roughness values ranged as follows: group Om-AUG = Om-POL > Om-OVG > Om-CDPA = Om-FDPA > Om-PA (p < 0.001). No significant difference was found between groups Om-AUG/Om-POL and Om-CDPA/Om-FDPA (p > 0.05). In Finesse groups mean roughness values ranged as follows: Fn-CDPA > Fn-FDPA = Fn-AUG = Fn-POL = Fn-OVG > Fn-PA (p < 0.001). No significant difference was found between Fn-FDPA, Fn-AUG, Fn- POL and Fn-OVG (p > 0.05). CONCLUSIONS For both ceramic types, the smoothest surfaces were obtained with polishing prior to autoglazing. Diamond disc grinding prior to polishing and autoglazing (Fn-FDPA, Fn-CDPA) displayed the roughest surfaces in ultra low-fusing ceramic (Finesse). Autoglazing alone and polishing displayed the roughest surfaces in low-fusing ceramic material (Om-AUG, Om-POL).

Adhesion between glass fiber posts and resin cement: evaluation of bond strength after various pre-treatments

Abstract Purpose. To evaluate surface roughness and bond strength of glass fiber posts to a resin cement after various surface treatments. Materials and methods. Sixty individually formed glass fiber posts with a diameter of 1.5 mm and a length of 20 mm were used for this study. They were randomly assigned to six groups of pre-treatment (n = 10/group): Group C, untreated (control); Group SB, sandblasted; Group SC, silica coated; Group HF, hydrofluoric acid-etched; Group N, Nd:YAG laser irradiated; Group E, Er:YAG laser irradiated. Surface roughness of the posts was measured before and after pre-treatment. The posts were then bonded to resin cement and tensile bond strengths were determined in a universal testing machine. For statistical analysis, two-way ANOVA and post-hoc comparison tests (α = 0.05) were performed. Results. The highest bond strength value was observed in group HF, followed by group SC. There was a statistically significant difference in bond strength between group C and groups HF, SC and E (p < 0.001, p = 0.002 and p = 0.041, respectively). Posts of group SB and group N showed the highest surface roughness. Conclusions. The findings of the present study reveal that hydrofluoric acid-etching, silica coating and Er:YAG laser irradiation provided a significant increase in bond strength between glass fiber posts and resin cement.

Radiofrequency heating and magnetic field interactions of fixed partial dentures during 3-tesla magnetic resonance imaging

OBJECTIVE This study evaluated the heating and magnetic field interactions of fixed partial dentures in a 3-Tesla (3T) magnetic resonance imaging (MRI) environment. STUDY DESIGN Three substructure materials (Co-Cr, Ni-Cr, ZrO₂) were used to fabricate twelve 4-retained bridges and 12 crowns. Specimens were evaluated at 3T for radiofrequency heating and magnetic field interactions. One-way analysis of variance (ANOVA) test was used to compare continuous variables of temperature change. Significance was set at P < .05. Translational attraction and torque values of specimens were also evaluated. RESULTS None of the groups exhibited excessive heating (mean temperature change, < 1.4 °C), with maximum increase at the end of the T-1. Moreover, in all groups, only relatively minor magnetic field interactions that would not cause movement in situ were observed. CONCLUSION The study findings indicated that patients with fixed partial dentures (single crown or bridge) fabricated from Co-Cr, Ni-Cr, and zirconia substructures may safely undergo MRI at up to 3T.

Effect of dental technician disparities on the 3-dimensional accuracy of definitive casts

Statement of problem Studies that evaluated the effect of dental technician disparities on the accuracy of presectioned and postsectioned definitive casts are lacking. Purpose The purpose of this in vitro study was to evaluate the accuracy of presectioned and postsectioned definitive casts fabricated by different dental technicians by using a 3‐dimensional computer‐aided measurement method. Material and methods An arch‐shaped metal master model consisting of 5 abutments resembling prepared mandibular incisors, canines, and first molars and with a 6‐degree total angle of convergence was designed and fabricated by computer‐aided design and computer‐aided manufacturing (CAD‐CAM) technology. Complete arch impressions were made (N=110) from the master model, using polyvinyl siloxane (PVS) and delivered to 11 dental technicians. Each technician fabricated 10 definitive casts with dental stone, and the obtained casts were numbered. All casts were sectioned, and removable dies were obtained. The master model and the presectioned and postsectioned definitive casts were digitized with an extraoral scanner, and the virtual master model and virtual presectioned and postsectioned definitive casts were obtained. All definitive casts were compared with the master model by using computer‐aided measurements, and the 3‐dimensional accuracy of the definitive casts was determined with best fit alignment and represented in color‐coded maps. Differences were analyzed using univariate analyses of variance, and the Tukey honest significant differences post hoc tests were used for multiple comparisons (&agr;=.05). Results The accuracy of presectioned and postsectioned definitive casts was significantly affected by dental technician disparities (P<.001). The largest dimensional changes were detected in the anterior abutments of both of the definitive casts. The changes mostly occurred in the mesiodistal dimension (P<.001). Conclusions Within the limitations of this in vitro study, the accuracy of presectioned and postsectioned definitive casts is susceptible to dental technician differences.

Evaluation of surface roughness and bond strength of quartz fiber posts after various pre-treatments

Abstract Purpose. Debonding at the post-adhesive interface is a major problem for quartz fiber posts. The objective of this study was to evaluate surface roughness and bond strength of quartz fiber posts after various surface treatments. Materials and methods. Sixty-six quartz fiber posts were randomly divided into six experimental groups (n = 11) including group C, untreated (control); group SB, sandblasted; group SC, silica coated; group HF, hydrofluoric acid-etched; group N, Nd:YAG laser irradiated; group E, Er:YAG laser irradiated. Surface roughness of the posts was measured before and after pre-treatment. They were then bonded to resin cement and tensile bond strength was determined in a universal testing machine. Furthermore, two-way ANOVA and post hoc comparison tests (α = 0.05) were performed on all data. Results. The highest mean force value was observed in group SB and followed by group E. Tukey’s HSD test showed that there was no statistical difference between group SB and group E (p = 0.673). The highest mean roughness value was observed in group SB and a significant difference was found between group SB and all other groups (p < 0.001). This study reveals that sandblasting and Er:YAG laser irradiation provided a significant increase in bond strength between quartz fiber posts and resin cement. Conclusions. Sandblasting or Er:YAG laser-irradiation of the surface of the quartz fiber post before cementation is recommended for increasing retention.

Can Impression Procedures Affect Certain Vital Functions of Edentulous Patients? A Clinical Study

PURPOSE The most suitable treatment conditions and timing for medically unstable patients with severe systemic diseases about to undergo invasive dental treatment are well documented in the literature; however, no medical guides or recommendations identify these conditions for noninvasive dental treatments in such patients. The aim of this clinical study was to determine the effect of impression procedures on arterial oxygen saturation (AOS) and pulse rates (PRs) of edentulous subjects. MATERIALS AND METHODS A total of 28 Caucasian edentulous participants (15 females, 13 males) were included in the study. Pulse oximetry recordings (150 seconds) were performed for each participant at three stages; recording at rest (CON), during mandibular impressions (MANIs), and maxillary impressions (MAXIs). The mean values of PR, AOS, and event scores (ESs) indicating desaturation were obtained from the records. The comparisons of mean PR and AOS values were performed with the Bonferroni-corrected Wilcoxon-signed ranks test. The ESs were analyzed with the McNemar Test. RESULTS The mean AOS values of MANI and MAXI did not display significant changes when compared with CON; however, the ESs obtained in both MANI and MAXI were significantly higher than those of CON (p = 0.008, p = 0.004). In addition, mean PR values obtained in MAXI were significantly higher than CON (p = 0.009). CONCLUSIONS According to the results of this clinical study, the impression procedures may affect the PR values and lead to desaturation events in edentulous patients; however, further studies evaluating blood gas levels, which indicate precise AOS values, are necessary to support the results of this study.

Use of an individual mandibular advancement device for an?obstructive sleep apnoea patient with facial paralysis: a short-term follow-up case report

This case report aimed to describe the fabrication procedure and treatment efficacy of an individual, one-piece, non-adjustable mandibular advancement device (MAD) for a moderate obstructive sleep apnoea patient with facial paralysis (FP). Mandibular advancement device was fabricated with autopolymerising acrylic resin. The intermaxillary relations were recorded such as to fix the mandible at a protruded position with increased vertical dimension. Initial evaluation of the MAD was made with axial magnetic resonance imaging and polysomnography on the first day of usage. Following evaluations were made on the third and sixth month. After a follow-up period of 6 months, Apnoea/Hypopnea Index (AHI) significantly decreased from 26·7 to 3·0. However, the average oxygen saturation did not improve as expected initially. The MAD therapy decreased the AHI scores of a patient with FP. At the end of a follow-up period of 6 months, the patient did not report any serious complaint except temporary tooth pains.

Influence of core thickness and artificial aging on the biaxial flexural strength of different all-ceramic materials: An in-vitro study

The purpose of this study was to investigate the flexural strength of all-ceramics with varying core thicknesses submitted to aging. In-Ceram Alumina (IC), IPS e.max Press (EM) and Katana (K) (n=40), were selected. Each group contained two core groups based on the core thickness as follows: IC/0.5, IC/0.8, EM/0.5, EM/0.8, K/0.5 and K/0.8 mm in thickness (n=20 each). Ten specimens from each group were subjected to aging and all specimens were tested for strength in a testing machine either with or without being subjected aging. The mean strength of the K were higher (873.05 MPa) than that of the IC (548.28 MPa) and EM (374.32 MPa) regardless of core thickness. Strength values increased with increasing core thickness for all IC, EM and K regardless of aging. Results of this study concluded that strength was not significantly affected by aging. Different core thicknesses affected strength of the all-ceramic materials tested (p<0.05).

Comparison of Physicochemical Surface Conditioning Methods for Adhesion of bis-GMA Resin Cement to Particulate Filler Composite and Surface Characterization

This study compared the effect of physicochemical surface conditioning methods on the adhesion of bis-GMA-based resin cement to particulate filler composite (PFC) used for indirect dental restorations. PFC blocks (N block = 54, n block = 9 per group) were polymerized and randomly subjected to one of the following surface conditioning methods: a) No conditioning (Control-C), b) Hydrofluoric acid (HF)etching for 60 s (AE60), c) HF for 90 s (AE90), d) HF for 120 s (AE120), e) HF for 180 s (AE180), and f) air-abrasion with 30 µm silica-coated alumina particles (AB). The conditioned surfaces were silanized with an MPS silane, and an adhesive resin was applied. Resin composite blocks were bonded to PFC using resin cement and photo-polymerized. PFC–cement–resin composite blocks were cut under coolant water to obtain bar specimens (1 mm × 0.8 mm). Microtensile bond strength test (μTBS)was performed in a universal testing machine (1 mm/min). After debonding, failure modes were classified using stereomicroscopy. Surface characterization was performed on a set of separate specimen surfaces using Scanning Electron Microscopy (SEM), X-Ray Dispersive Spectroscopy (XDS), X-Ray Photoelectron Spectroscopy (XPS), and Fourier Transform-Raman Spectroscopy (FT-RS). Mean μTBS (MPa) of C (35.6 ± 4.9) was significantly lower than those of other groups (40.2 ± 5.6–47.4 ± 6.1) (p < 0.05). The highest μTBS was obtained in Group AB (47.4 ± 6.1). Prolonged duration of HF etching increased the results (AE180: 41.9 ± 7), but was not significantly different than that of AB (p > 0.05). Failure types were predominantly cohesive in PFC (34 out of 54) followed by cohesive failure in the cement (16 out of 54). Degree of conversion (DC) of the PFC was 63 ± 10%. SEM analysis showed increased irregularities on PFC surfaces with the increased etching time. Chemical surface analyses with XPS and FT-RS indicated 11–70% silane on the PFC surfaces that contributed to improved bond strength compared to Group C that presented 5% silane, which seemed to be a threshold. Group AB displayed 83% SiO2 and 17% silane on the surfaces.