Characteristics of anatomical landmarks in the mandibular interforaminal region : a cone-beam computed tomography study

Objectives: This study was conducted to assess appearance, visibility, location and course of anatomical landmarks in mandibular interforaminal region using cone-beam computed tomography (CBCT). Study design: A total of 96 CBCT examinations was re-evaluated to exploit anatomical landmarks. The examinations used the Promax 3D CBCT unit. A sole examiner carried out all the measurements. Visibilities of the anatomical landmarks were scored using a four-point rating scale. Results: The mandibular foramen, anterior loop, incisive canal and lingual foramen were observed in 100,84,83,49 % of the images, respectively. The mean size, diameter and width of anterior loop, incisive canal and lingual foramen were obtained 3.54± 1.41, 1.47±0.50 and 0.8 ± 0.09mm, respectively. Conclusion: It is not safe to recommend any definite distance mesially from the mental foramen. The diameter of the canals and foramens should be determined on a case-by-case basis to exploit the appropriate location for each individual

Single Tooth Replacement Using InCeram Resin Bonded Fixed Partial Denture: A Clinical Report.

This clinical report describes a treatment option for replacement of a missing mandibular anterior tooth using InCeram resin bonded fixed partial denture (RBFPD). The conventional approach for replacing mandibular incisors dictates the placement of either a conventional porcelain-fused-to-metal (PFM) bridge, Maryland bridge, or fiber-reinforced composite veneer bridge and several appearance-related disadvantages have been reported in the use of a prosthesis that incorporates a metal substructure. The InCeram bridge is a minimally invasive restoration and eliminates undesirable incisal graying frequently observed in metal RBFPDs. This method was successfully clinically applied to overcome shortcomings of other approaches that may require a minimal invasive technique to preserve lasting sound tooth structure

Corrosion Behavior of a Nickel-Base Dental Casting Alloy in Artificial Saliva Studied by Weight Loss and Polarization Techniques

Objectives:Corrosion of Ni-Cr base dental alloys in saliva influences their application in prostheses. Material and methods: Corrosion behaviour of the NiCr alloy was studied using two techniques including weight lossdescribed by corrosion rate (CR) per mil per year (mpy)and potentiodynamic polarizationdescribed by corrosion potential (CP) in mV and current density (CD) in mA/cm2in artificial saliva with different pH.Surface morphology was studied using scanning electron microscopy (SEM). Statistical difference was assessed using one-way ANOVA and post-HOC Tukey-HSD tests with a difference significance of 95%. Results:In weight loss method,CRwas 71.95±3.40, 17.26±1.03, 8.92±0.35 and 6.93±0.54mpy in pH values of 2.5, 5, 7 and 9, respectively. CR obtained in pH of 2.5 was significantly different with that in other groups, but those obtained in pH of 5, 7 and 9 were not significantly different. In polarization method, CPwere significantly different. CD measured in pH of 2.5 and 5 was significantly different with the rest of pH values. Corrosion rates in pH of 7 and 9 were not significantly different. Conclusion:The results obtained by both techniques are consistent. Corrosion resistance decreases as pH increases. In more acidic saliva, corrosion rate is greater likely due to the higher dissolution rate of Ni through weak passivation. However, the less acidic saliva leads to formation of more stable passive film on Ni and therefore the dissolution of Ni decreases leading to lower corrosion rates

Effect of TiO2 Nanoparticles on Tensile Strength of Dental Acrylic Resins

Background and aims. Adding further fillers to dental resins may enhance their physical characteristics. The aim of this study was to evaluate the tensile strength of heat-curing acrylic resin reinforced by TiO2nanoparticles added into the resin matrix. Materials and methods. Commercially available TiO2 nanoparticles were obtained and characterized using X-ray diffrac-tion (XRD) and scanning electron microscopy (SEM) to determine their crystalline structure, particle size and morphology. TiO2-acrylic resin nanocomposite was prepared by mixing 0.5, 1 and 2 (wt%) of surface modified TiO2 nanoparticles in an amalgamator providing three groups of samples. Before curing, the obtained paste was packed into steel molds. After cur-ing, the specimens were removed from the molds. The tensile strength test samples were prepared according to ISO 1567. Results. Two crystalline phases were found in TiO2 nanoparticles including: (i) anatase as the major one, and (ii) rutile. The average particle size calculated according to the Scherrer equation was 20.4 nm, showing a normal size distribution. Ac-cording to SEM images, the nanocomposite with 1wt% TiO2 nanoparticles had a better distribution compared to other groups. In addition, the group by 1wt% TiO2 exhibited higher tensile strength with a significant difference compared to other groups. ANOVA showed significant differences between the contents of TiO2 particles in acrylic resin (F = 22.19; P < 0.001). Conclusion. A considerable increase in tensile strength was observed with titania NPs reinforcement agents in 1wt% by weight. Further increase of TiO2 nanoparticles decreased the tensile strength

Attitude of Dental Prostheses Residents of Faculty of Dentistry of Tabriz University of Medical Sciences to Objective Structured Clinical Examination(OSCE)

Introduction: Objective Structured Clinical Examination (OSCE) is one of the most authentic ways to evaluate clinical skills. The present study aimed at evaluating the attitude of dental prostheses residents of the faculty of dentistry of Tabriz University of Medical Sciences toward this kind of examination. Methods: In this cross sectional-descriptive study, two questionnaires were designed. One questionnaire dealt with nature of OSCE and the other dealt with the attitude of residents about OSCE. After holding the OSCE in July 2012, 2013, and 2014, the questionnaires were delivered to all dental prostheses residents of the Tabriz dental faculty. In total, 40 questionnaires were filled out within three years. Questions included five-choice items based on a Likert scale. Furthermore, the students’ scores in each exam were recorded to evaluate any possible relationship between the acquired grade and the student’s attitude toward the exam. The collected data were analyzed using SPSS17 software (α=5%). Results: Most residents (62.5%) referred to the large number of questions as a positive factor. In addition, a majority of residents (90%) suffered from high levels of stress during OSCE. There was a close relation between the grade acquired by the residents in the examination and their attitude to OSCE as well as their evaluation about the examination. The students with better grades had more positive attitudes toward OSCE. Conclusion: Considering the satisfaction level of the students in this study, OSCE was held efficiently and may be considered as part of the training program of the residents

Effect of Disinfectants on the Hardness of Dental Stones

Background and Aim : Considering the risk of cross contamination, disinfection of dental stones is essential provided that their mechanical and structural properties remain unchanged. The aim of this study was to evaluate the effect of disinfection on the hardness of dental stones .   Materials and Methods : In this experimental study, 40 discs were fabricated of type III and IV dental stones and divided into three groups. The three understudy chemical disinfectants namely 1% Virkon, 0.525% hypochlorite and slurry water were sprayed on samples in each group. The hardness of sprayed samples was evaluated by measuring the width of scratch according to the Mohs scale of mineral hardness. Surfaces of sprayed samples were also inspected by optical microscopy. Data were analyzed using Kruskal-Wallis and Mann-Whitney tests (P<0.05 ).   Results : Mohs scale of mineral hardness revealed that the width of scratches was narrower in samples sprayed with Virkon than in those sprayed with hypochlorite and slurry water. In type III dental stone specimens, the maximum width was observed in samples sprayed with slurry water (1.35±0.02) and the minimum width was observed in Virkon group samples (0.97±0.01). For type IV, the maximum and minimum widths were observed in samples sprayed with slurry water (1.20±0.01) and Virkon (0.61±0.01), respectively . In both types of stones, no significant differences were noted between the sprayed groups, while the differences between each sprayed group and the control stones (no spraying) were significant .   Conclusion : Surface hardness of dental stones decreased after spraying them with the three understudy disinfectants. Dental stones sprayed with Virkon exhibited the lowest reduction in hardness

Comparison of the Effect of Nd:YAG Laser and Sandblasting on Shear Bond Strength of a Commercial Ni-Cr Alloy to Porcelain

Introduction: Failures might occur at metal‒porcelain interfaces as a problem with metal‒ceramic restorations even with the application of airborne-particle abrasion technique. This study was undertaken to evaluate the effect of Nd:YAG laser treatment on the bond strength of porcelain fused to metal. Methods:  Twenty-four cylindrical specimens (4 mm in diameter and 4 mm in height) were made of a commercially available nickel‒chromium alloy by lost-wax technique. Half of the specimens were surface-treated by air-borne particles and the other half was irradiated with Nd:YAG laser beams (wavelength of 1064 nm, energy and frequency of 120 mJ and 10 Hz, respectively, and a power setting of 6 kW). All the specimens (air-abraded and laser-treated) were covered with a 4-mm layer of opaque porcelain in two-stage baking and subjected to shear bond strength test (a 10-kgf at 1 mm/min) until fracture occurred. A fractured specimen from each group was evaluated using scanning electron microscopy. T-test was used for statistical analysis and statistical significance was set at

Evaluation of Surface Roughness of a Ni-Cr Alloy Treated With the Nd/YAG Laser and the Sandblast Technique: Surface Roughness of Laser Treated Ni-Cr Alloy

Introduction: This study was to assess the effect of various output parameters of laser treatment on roughening the surface of a commercial nickel-chromium (Ni-Cr) alloy as compared to the sandblasting technique.Materials and Methods: Ninety-six disk-shaped (5 mm diameter and 2 mm thickness) specimens in the total were made of a nickel-chromium alloy by using the lost-wax technique. Air-abrasion surface treatment was used for sixteen specimens. Specimens were divided into six groups; one of them was sandblasted and the rest were irradiated by different Nd: YAG laser output parameters as follows: Group A: energy: 122 mJ, frequency: 20 Hz, irradiation duration: 20 seconds, spot size: 1.5 mm; Group B: energy: 122 mJ, frequency: 20 Hz, irradiation duration: 20 seconds, spot size: 3.5 mm; Group C: energy: 122 mJ, frequency: 10 Hz, irradiation duration: 20 seconds, spot size: 3.5 mm; Group D: energy: 102 mJ, frequency: 10 Hz, irradiation duration: 20 seconds, spot size: 3 mm; Group E: energy: 102 mJ, frequency: 20 Hz, irradiation duration: 20 seconds, spot size: 3 mm. Thesurface roughness of all surface-treated specimens was evaluated by using a profilometer, and their average roughness (Ra) was calculated. The average value of each group was analyzed by t-test and one-way ANOVA (SPSS 17).Results: Significant differences (P&lt;0.05) were observed between the study groups. The highest Ra was achieved for the sandblasted group. The Ra value in group C was the highest value among the laser-etched groups.Conclusion: Based on the results, Nd: YAG laser irradiation increases surface roughness, but it is not as efficient as the sandblasting method as a gold standard. DOI:10.34172/jlms.2021.69

Efficacy of Disinfection of Dental Stone Casts: Virkon versus Sodium Hypochlorite

Objectives: The purpose of this experimental study was to compare the disinfection efficacy of sodium hypochlorite and peroxygenic acid (Virkon) solutions for dental stone casts contaminated with microbial strains. Materials and Methods: A total of 960 spherical stone beads with a diameter of 10 mm were prepared and used as carriers of bacterial inoculums. They were individually inoculated by soaking in broth culture media containing each of the four understudy microorganisms. Different concentrations of Virkon and hypochlorite solutions were prepared using distilled water and then were sprayed on the surfaces of dental casts contaminated with Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis and Candida albicans. The pour plate technique was used to evaluate the antimicrobi- al efficacy of each solution. Microbicidal effect (ME) was calculated according to the log10 of control colony counts minus the log10 of the remaining colony counts after the antimicrobial procedure. Statistical difference was assessed using the Kruskal Wallis and the Man Whitney U tests with a significance of 95%. Results: We observed different bactericidal effects of Virkon at various concentra- tions; 1% Virkon killed S. aureus, P aeruginosa, and Candida albicans, while 3% Virkon solution was required to kill B. subtilis. For S. aureus, P. aeruginosa, and C. albicans, no significant difference was observed between1% Virkon and 0.525% so- dium hypochlorite (P >0.05). For B. subtilis, the efficacy of 3% Virkon and 0.525%sodium hypochlorite was not significantly different (P >0.999). Conclusion: According to the obtained results for Virkon and based on its low toxici- ty and good environmental compatibility, it may be recommended as an antimicrobial disinfectant for dental stone casts as non-critical items