Does surface priming increase the bond strength of orthodontic brackets? An experimental study.

OBJECTIVE: To evaluate the effects of metal primer II (MP II) on the shear bond strength (SBS) of orthodontic brackets bonded to teeth and bis-acryl composite provisional material (Bis-Acryl). MATERIAL AND METHODS: Twenty extracted human premolars specimens and 20 premolar shaped Bis-Acryl specimens were obtained and randomly divided into two surface groups. The first group consisted of human premolars (T) bonded to brackets in the conventional way while in the second (T-MP) MP II was applied on the bracket base before bonding. Similarly, one group of provisional material (PM) was prepared according to conventional treatment and another with the application of MP-II metal bonder (PM-MP). In all cases Ortho-brackets (Victory Series, 3 M) were bonded employing Transbond XT resin cement. Then the brackets were debonded under shear and the results were statistically analyzed by two-way analysis of variance and Holm Sidak at α = .05. The debonded surfaces of all specimens were examined by light microscopy and the Adhesive Remnant Index (ARI) was recorded. RESULTS: The SBS results exhibited significant differences er (p < .001). For both the T and TM the application of MP-II increased the SBS compared to respective control groups (p < .001). The T-C group was found inferior compared to PM-C (p < .001) and the same is true for the comparison between T-MP and PM-MP (p < .001). ARI indexes demonstrated that the tooth groups were characterized by a predominantly adhesive failure at the resin-dentin interface. In contrast, the control group for provisional crowns (PM-C) showed a predominantly cohesive failure mode, which moved to predominantly adhesive after the application of MP II. CONCLUSION: The application of MP II enhances the SBS on both, human enamel and provisional crown materials.

Failure analysis of eleven Gates Glidden drills that fractured intraorally during post space preparation. A retrieval analysis study.

The purpose of this study was to determine the failure mechanism of clinically failed Gates Glidden (GG) drills. Eleven retrieved GG drills (sizes #1 to #3) which fractured during root canal preparation were collected and the fracture location was recorded based on macroscopic observation. All fracture surfaces were investigated by a SEM. Then the fractured parts were embedded in acrylic resin and after metallographic preparation, the microstructure and elemental composition was evaluated by SEM and EDS. The Vickers hardness (HV) of all specimens was also determined. Macroscopic examination and SEM analysis showed that the drills failed near the hand piece end by torsional fatigue with fatigue cracks initiating at several locations around the circumference and propagating toward the center. Final fracture followed by a tensile overloading at the central region of cross section. Microstructural analysis, hardness measurements and EDS show that the drills are made of a martensitic stainless steel like AISI 440C. Based on the findings of this study, clinicians should expect fatigue fracture of GG drills that have small size during root canal preparation. Selection of a more fatigue resistant stainless steel alloy and enhancing the instrument design might reduce the incidence of quasi-cleavage fracture on GG drills.

A global probe into dental student perceptions about philanthropy, global dentistry and international student exchanges.

BACKGROUND: Training culturally competent graduates who can practice effectively in a multicultural environment is a goal of contemporary dental education. The Global Oral Health Initiative is a network of dental schools seeking to promote global dentistry as a component of cultural competency training. OBJECTIVE: Before initiating international student exchanges, a survey was conducted to assess students' awareness of global dentistry and interest in cross-national clerkships. METHODS: A 22-question, YES/NO survey was distributed to 3,487 dental students at eight schools in seven countries. The questions probed students about their school's commitment to enhance their education by promoting global dentistry, volunteerism and philanthropy. The data were analysed using Vassarstats statistical software. RESULTS: In total, 2,371 students (67.9%) completed the survey. Cultural diversity was seen as an important component of dental education by 72.8% of the students, with two-thirds (66.9%) acknowledging that their training provided preparation for understanding the oral health care needs of disparate peoples. A high proportion (87.9%) agreed that volunteerism and philanthropy are important qualities of a well-rounded dentist, but only about one-third felt that their school supported these behaviours (36.2%) or demonstrated a commitment to promote global dentistry (35.5%). In addition, 87.4% felt that dental schools are morally bound to improve oral health care in marginalised global communities and should provide students with international exchange missions (91%), which would enhance their cultural competency (88.9%) and encourage their participation in charitable missions after graduation (67.6%). CONCLUSION: The study suggests that dental students would value international exchanges, which may enhance students' knowledge and self-awareness related to cultural competence.

The Effect of Artificial Aging on The Bond Strength of Heat-activated Acrylic Resin to Surface-treated Nickel-chromium-beryllium Alloy.

PURPOSE: The debonding load of heat-activated polymethylmethacrylate (PMMA) denture base resin material to a nickel-chromium-beryllium (Ni-Cr-Be) alloy conditioned by three different surface treatments and utilizing two different commercial bonding systems was investigated. MATERIALS AND METHODS: Denture resin (Lucitone-199) was bonded to Ni-Cr-Be alloy specimens treated with Metal Primer II, the Rocatec system with opaquer and the Rocatec system without opaquer. Denture base resin specimens bonded to non-treated sandblasted Ni-Cr-Be alloy were used as controls. Twenty samples for each treatment condition (80 specimens) were tested. The 80 specimens were divided into two categories, thermocycled and non-thermocycled, containing four groups of ten specimens each. The non-thermocycled specimens were tested after 48 hours' storage in room temperature water. The thermocycled specimens were tested after 2,000 cycles in 4°C and 55°C water baths. The debonding load was calculated in Newtons (N), and collected data were subjected by non parametric test Kruskal-Wallis One Way Analysis of Variance on Ranks and Dunn's post hoc test at the α = 0.05. RESULTS: The Metal Primer II and Rocatec system without opaquer groups produced significantly higher bond strengths (119.9 and 67.6 N), respectively, than did the sandblasted and Rocatec system with opaquer groups, where the bond strengths were 2.6 N and 0 N, respectively. The Metal Primer II was significantly different from all other groups (P<0.05). The bond strengths of all groups were significantly decreased (P<0.05) after thermocycling. CONCLUSIONS: Although thermocycling had a detrimental effect on the debonding load of all surface treatments tested, the Metal Primer II system provided higher values among all bonding systems tested, before and after thermocycling.

Perceptions of Saudi dental students on cultural competency.

OBJECTIVES: To probe dental students' perceptions on their cultural competency and international student exchange programs as a way of improving cultural competency training. METHODS: A cross-sectional survey (n=460) was distributed to predoctoral students at the College of Dentistry, King Saud University, Riyadh, Kingdom of Saudi Arabia in May 2014 at the male and female university campuses. Descriptive statistics were carried out using Statistical Package for Social Sciences (p=0.05).  RESULTS: It was found that 79.6% of students think that teaching them regarding cultural diversity is important. Only 41% of students thought their dental education teaches them on the importance of volunteerism and philanthropy. Most students (89.8%) think that international student exchanges can enhance their cultural competence. CONCLUSION: In this study, it was found that students believe that cultural competence is important and participation in international student exchange programs can enhance their training.

The effect of simulating porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed gold restorations.

BACKGROUND/PURPOSE: The mechanical properties of pure gold (Au) are modified by thermal treatments. Thus, the aim of this study was to evaluate the effect of porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed Au crowns. MATERIALS AND METHODS: Twenty electroformed Au specimens were prepared and divided into two groups. The first group did not receive any treatment (ELEC), and the other group was subjected to porcelain firing (PFIR). After metallographic grinding and polishing, all were investigated by scanning electron microscopy, and elemental composition was determined using energy-dispersive X-ray spectroscopy (EDX). Internal porosity was identified by quantitative image processing. Mechanical properties including Martens hardness (HM), indentation modulus (E IT), elastic index (η ΙΤ), and Vickers hardness (HV) were determined by instrumented indentation testing. The results were statistically analyzed using unpaired t test (α = 0.05). RESULTS: A random distribution of tiny pores was identified in cross section, but no significant difference was found between groups [ELEC (%), 0.24 ± 0.13; PFIR (%), 0.31 ± 0.7]. Backscattered electron images revealed no mean atomic number contrast for both groups, indicating that the material was a single-phase alloy, whereas no differences between groups were identified in the composition of C, N, O, and Au after EDX analysis. By contrast, all mechanical properties tested showed statistically significant differences, with the PFIR group showing significantly lower HM, η ΙΤ, and HV but increased E IT compared with those of the ELEC group. CONCLUSION: Although microstructure and elemental composition of electroformed Au crowns remain unchanged, the mechanical properties are significantly affected by the thermal treatment of porcelain firing.

Metallurgical characterization of experimental Ag-based soldering alloys.

AIM: To characterize microstructure, hardness and thermal properties of experimental Ag-based soldering alloys for dental applications. MATERIALS AND METHODS: Ag12Ga (AgGa) and Ag10Ga5Sn (AgGaSn) were fabricated by induction melting. Six samples were prepared for each alloy and microstructure, hardness and their melting range were determined by, scanning electron microscopy, energy dispersive X-ray (EDX) microanalysis, X-ray diffraction (XRD), Vickers hardness testing and differential scanning calorimetry (DSC). RESULTS: Both alloys demonstrated a gross dendritic microstructure while according to XRD results both materials consisted predominately of a Ag-rich face centered cubic phase The hardness of AgGa (61 ± 2) was statistically lower than that of AgGaSn (84 ± 2) while the alloys tested showed similar melting range of 627-762 °C for AgGa and 631-756 °C for AgGaSn. CONCLUSION: The experimental alloys tested demonstrated similar microstructures and melting ranges. Ga and Sn might be used as alternative to Cu and Zn to modify the selected properties of Ag based soldering alloys.

Effects of surface treatment and artificial aging on the shear bond strength of orthodontic brackets bonded to four different provisional restorations.

OBJECTIVE: To evaluate the combined effects of material type, surface treatment, and thermocycling on the bond strength of orthodontic brackets to materials used for the fabrication of provisional crowns. MATERIALS AND METHODS: Four materials were included in this study (ProTemp, Trim Plus, Trim II, and Superpont C+B). Sixty cylindrical specimens (1 × 3 cm) were prepared from each material and equally divided into three groups. The first group was ground with silica carbide paper, the second was polished with pumice, and the last group was sandblasted with 50-µm aluminum oxide particles. Stainless-steel maxillary central incisor brackets (Victory Series, 3M) were bonded to the provisional material specimens with Transbond XT light-cured composite resin, and half of the specimens from each group were thermocycled 500 times in 5°C and 55°C water baths. Then the brackets were debonded with shear testing, and the results were statistically analyzed by three-way analysis of variance and Tukey's multiple-comparison tests at α  =  0.05. Adhesive Remnant Index (ARI) was also identified. RESULTS: Before and after thermocycling, ProTemp materials showed the highest shear bond strength with orthodontic brackets (10.3 and 13.1 MPa, respectively). The statistical analysis indicated an interaction among the three independent variables (P < .05) and statistically significant differences in bond strength among provisional materials (P < .001), surface treatments (P < .001), and thermocycling (P < .05). According to the ARI, most groups demonstrated adhesive failure. CONCLUSIONS: The provisional material type, surface treatment, and artificial aging have a significant effect on bond strength. Sandblasting treatment exerts a beneficial effect on shear bond strength.