Microstructural and mechanical characterization of six Co-Cr alloys made by conventional casting and selective laser melting.

STATEMENT OF PROBLEM: Three Co-Cr alloy types (Co-Cr-Mo, Co-Cr-W, and Co-Cr-Mo-W) have been commonly used in the fabrication of dental prostheses. These alloys can be manufactured using either conventional casting or selective laser melting (SLM) techniques. Nevertheless, research that directly compares these materials and/or manufacturing processes in terms of their microstructural and mechanical characteristics is sparse. PURPOSE: The purpose of this in vitro study was to conduct microstructural and mechanical analysis via X-ray interpretation, optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), image analysis, X-ray diffraction (XRD), instrumented indentation testing (IIT), and 3-point bending testing to characterize Co-Cr-Mo, Co-Cr-W, and Co-Cr-Mo-W alloys produced through conventional casting and SLM. MATERIAL AND METHODS: Six Co-Cr-based alloys were analyzed and divided into 3 types based on their elemental composition (Co-Cr-Mo, Co-Cr-W, and Co-Cr-Mo-W). Additionally, each group was categorized based on the manufacturing process used (casting or SLM). X-ray scans were used to assess porosity. The microstructures of the specimens were assessed through SEM/EDS examination and XRD analysis. IIT was used to determine the Martens hardness (HM) and elastic index (ηIT), while the elastic modulus (E) was estimated through the 3-point bending test. The mechanical properties were statistically analyzed using 2-way analysis of variance (ANOVA) and the Tukey multiple comparison post hoc test, with alloy type and manufacturing process as discriminating variables (α=.05). RESULTS: All cast groups exhibited gross porosity, while no pores or other flaws were found in the SLM groups. Based on the XRD results, the crystalline structure of all Co-Cr specimens consisted of the face-centered cubic γ phase (γ-fcc), along with the hexagonal close-packed ε phase (ε-hcp) and Cr23C6 carbide. Different microstructures were identified between the cast and SLM alloys. Significant differences were identified for the mean standard deviation HM (ranging from 2601 ±94 N/mm2 to 3633 ±61 N/mm2) and mean ±standard deviation ηIT (ranging from 16.8 ±0.3% to 20.9 ±0.3%) among alloys prepared by the same manufacturing process, while all SLM alloys had statistically higher HM and ηIT results than their cast counterparts (P<.05). No statistically significant differences were identified for the mean ±standard deviation Eb (ranging from 170 ±25 GPa to 244 ±36 GPa) among the groups prepared with the same manufacturing process (P>.05), but the SLM alloys had significantly higher results (P<.05) than the cast alloys. CONCLUSIONS: In general, the manufacturing procedure significantly affected the porosity, microstructure, and mechanical properties of the tested Co-Cr alloys. SLM decreased the internal porosity, provided a uniform microstructure, and improved the mechanical properties for all the tested alloy types.

Colour Parameters and Changes of Tea-Stained Resin Composite Exposed to Whitening Pen (In Vitro Study).

BACKGROUND: One of the crucial factors influencing the longevity of anterior aesthetic dental restorations is the colour stability of resin composites. Bleaching and whitening have become popular methods for enhancing dental aesthetics. Home whitening techniques, such as special pens, are widely available commercially. This in vitro study aimed to determine the efficiency of a whitening pen in removing tea stains from resin composite by measuring colour differences (ΔE00). Additionally, the study aimed to evaluate the variations in colour parameters measured by extra-oral and intra-oral spectrophotometers. METHODS: A total of 45 disc-shaped resin composite specimens were randomly divided into three groups; Group 1: stored in artificial saliva (control), Group 2: stored in artificial saliva followed by a whitening pen application, and Group 3: stored in tea followed by a whitening pen application. Colour measurements were taken three times for each specimen using two spectrophotometers (extra-oral and intra-oral devices); T1: before storage (baseline), T2: after storage in artificial saliva or tea for 6 days; and T3: after one week of whitening pen application in groups 2 and 3. The data were statistically analyzed using one-way ANOVA followed by the Tukey post hoc test (p ≤ 0.05). The independent sample t-test was also employed. The equation of CIEDE2000 (ΔE00) was used to calculate the colour difference between the dry, as-prepared specimens (baseline), and those after storage or bleaching. The colour changes exceeding the acceptability threshold (∆E00 = 1.8) were considered unacceptable. RESULTS: After whitening, the colour of the specimens stored in brewed tea (Group 3) remained unacceptable, as indicated by both the extra-oral and intra-oral spectrophotometers (ΔE00 = 4 and 2.9, respectively). Groups 1 and 2 exhibited lower ΔE00 values than Group 3 (p = 0.01 *). No significant difference was observed between Group 1 (stored in artificial saliva) and Group 2 (stored in artificial saliva and then bleached) (p = 0.3). Significant differences were consistently observed between the data obtained from the extra-oral spectrophotometer and the intra-oral one. CONCLUSIONS: The whitening pen proved ineffective in removing tea stains from resin composites. Although significant differences were found between the values obtained by the two spectrophotometers (extra-oral and intra-oral), both devices confirmed the unacceptable colour of the tea-stained resin composites after whitening.

Perception and Knowledge of Oral and Facial Piercings among Dental Students: Web-based Survey.

AIM: The aim of this web-based questionnaire was to survey dental students to obtain their perception and knowledge of oral and facial piercings. MATERIALS AND METHODS: The participants comprised 240 students enrolled in the dental school who were asked to complete 20 close-ended, yes/no, yes/no/do not know, and multiple responses questions. The questionnaire covers general information concerning oral/facial piercing, triggers why youths and early adults get it, probable complications, their appreciation of the possibility of related health conditions, and their knowledge and perception. The survey was distributed to the students by email. The results were tabulated and statistically analyzed. RESULTS: Dental first year (D1) and dental second year (D2) were substantially more likely to indicate that orofacial piercings as unacceptable and are less expected to have an orofacial piercing compared to D3 and D4 (p < 0.01). About 16.8% of the students reported previous orofacial piercings. There was a definite correlation between previous orofacial piercings and thinking that is appropriate in society (p < 0.05). Males were significantly more likely to have an orofacial piercing (p < 0.01). The Internet was reported as the most common source of information. The most popular cause for piercings is to be unique and different. CONCLUSIONS: Orofacial piercings are relatively frequently used by students in dental school and few students intend on getting one in the future. Knowledge of the hazards of orofacial piercing correlated with the requirement for parental approval. The majority of students think piercings are appropriate in society and know their complications and risks. CLINICAL SIGNIFICANCE: Orofacial piercing has been gaining popularity but its risks/complications may not be known by practitioners. There is a need for research to assist dental/medical practitioners in advising, educating, and safeguarding patients by evaluating of the perception and knowledge of students about orofacial piercings.

Different Designs of Deep Marginal Elevation and Its Influence on Fracture Resistance of Teeth with Monolith Zirconia Full-Contour Crowns.

Background and objectives: Even with the demand for high esthetics, the strength of the material for esthetic applications continues to be important. In this study, monolith zirconia (MZi) crowns fabricated using CAD/CAM were tested for fracture resistance (FR) in teeth with class II cavity designs with varying proximal depths, restored through a deep marginal elevation technique (DME). Materials and Methods: Forty premolars were randomly divided into four groups of ten teeth. In Group A, tooth preparation was conducted and MZi crowns were fabricated. In Group B, mesio-occluso-distal (MOD) cavities were prepared and restored with microhybrid composites before tooth preparation and the fabrication of MZi crowns. In Groups C and D, MOD cavities were prepared, differentiated by the depth of the gingival seat, 2 mm and 4 mm below the cemento-enamel junction (CEJ). Microhybrid composite resin was used for DME on the CEJ and for the restoration of the MOD cavities; beforehand, tooth preparations were conducted and MZi crowns were and cemented using resin cement. The maximum load to fracture (in newtons (N)) and FR (in megapascals (MPa)) were measured using the universal testing machine. Results: The average scores indicate a gradual decrease in the load required to fracture the samples from Groups A to D, with mean values of 3415.61 N, 2494.11 N, 2108.25 N and 1891.95 N, respectively. ANOVA revealed highly significant differences between the groups. Multiple group comparisons using the Tukey HSD post hoc test revealed that Group D had greater DME depths and showed significant differences compared with Group B. Conclusions: FR in teeth decreased when more tooth structure was involved, even with MZi crowns. However, DME up to 2 mm below the CEJ did not negatively influence the FR. Strengthening the DME-treated teeth with MZi crowns could be a reasonable clinical option, as the force required to fracture the samples far exceeded the maximum recorded biting force for posterior teeth.

Photodynamic therapy and other pretreatment methods on epoxy-based glass fiber post on the push-out bond strength to radicular dentin.

AIM: To assess the push-out bond strength (PBS) of glass fiber post (GFP) conditioned using different surface treatment regimens bonded to radicular dentin MATERIAL AND METHODS: Sixty central incisors and canine were collected and disinfected. Decoronation following working length was determined using K-file. Rotary file system was used for cleaning and shaping. Canals of all samples were dried with paper points and obturated with gutta percha. Canal space was prepared with peso reamers. Now samples were randomly allocated into six groups based on pretreatment of GFP. Post in group 1 treated with 9% HFA+ Silane, post in group 2 surface treated with silane only, Post in group 3 surface treated with airborne particle (50 µm), group 4 post conditioned with photodynamic therapy (PDT), group 5 post pretreatment was performed with MBP and in group 6 GFP was not treated. Conditioned and non-conditioned posts were positioned in canal space and cemented. Tooth were sectioned coronally, middle and apically. Sections were positioned in universal testing machine (UTM) and debonded surfaces were evaluated for failure modes. The means and standard deviations of PBS were examined using one-way analysis of variance (ANOVA). RESULTS: Coronal third of group 3 in which posts were sandblasted using airborne Al2O3 particle presented the highest PBS (11.21±0.64 MPa). Whereas, an apical section of group 4 in which posts were treated with PDT exhibited the lowest bond integrity. CONCLUSION: Sandblasting using airborne particles (50 µm) and hydrogen peroxide (H3PO4) conditioned with GFP exhibited significantly higher bond strength as compared to the control. However, PDT decreases the PBS of fiber post with the root dentin.