Effect of alcoholic drinks on surface quality and mechanical strength of denture base materials

The effect of pure alcohol as well as several alcoholic drinks on the static and dynamic strength and surface quality of denture base poly(methyl methacrylate) was investigated. Wetting tensile specimens with alcohol led to a reduction of their static strength by 16.1% and their fatigue strength by 14.3%. Polished specimens immersed in various alcoholic drinks with over 40% alcohol exhibited considerable surface corrosion, which was capable of reducing the fatigue strength of the material. The effect of pure alcohol as well as several alcoholic drinks on the static and dynamic strength and surface quality of denture base poly(methyl methacrylate) was investigated. Wetting tensile specimens with alcohol led to a reduction of their static strength by 16.1% and their fatigue strength by 14.3%. Polished specimens immersed in various alcoholic drinks with over 40% alcohol exhibited considerable surface corrosion, which was capable of reducing the fatigue strength of the material

The effect of altering the vertical dimension of occlusion on biting force

The effect of altering the vertical dimension of occlusion (VDO) on the biting force was studied in six men and seven women. The biting force was registered with a newly designed gnathodynamometer that uses two strain gauges cemented on its surfaces and a Wheatstone bridge connected to a chart recorder. Biting force was measured for each subject at the following three positions of vertical dimension: position 1, VD < VDO; position 2, VD = VDO; and position 3, VD > VDO. The recorded force at these positions was statistically different for all of the subjects. All subjects exerted significantly greater biting force when VD > VDO Men exerted greater biting forces than women, but this difference was not statistically significant. © 1994 The Editorial Council of The Journal of Prosthetic Dentistry

Mechanical and interfacial characterization of laser welded Co-Cr alloy with different joint configurations

Purpose: The mechanical and interfacial characterization of laser welded Co-Cr alloy with two different joint designs. Materials and methods: Dumbbell cast specimens (n=30) were divided into 3 groups (R, I, K, n=10). Group R consisted of intact specimens, group I of specimens sectioned with a straight cut, and group K of specimens with a 45° bevel made at the one welding edge. The microstructure and the elemental distributions of alloy and welding regions were examined by an SEM/EDX analysis and then specimens were loaded in tension up to fracture. The tensile strength (TS) and elongation (ε) were determined and statistically compared among groups employing 1-way ANOVA, SNK multiple comparison test (α=05) and Weibull analysis where Weibull modulus m and characteristic strength σ0 were identified. Fractured surfaces were imaged by a SEM. Results: SEM/EDX analysis showed that cast alloy consists of two phases with differences in mean atomic number contrast, while no mean atomic number was identified for welded regions. EDX analysis revealed an increased Cr and Mo content at the alloy-joint interface. All mechanical properties of group I (TS, eopen, m and σ0) were found inferior to R while group K showed intermediated values without significant differences to R and I, apart from elongation with group R. The fractured surfaces of all groups showed extensive dendritic pattern although with a finer structure in the case of welded groups. Conclusion: The K shape joint configuration should be preferred over the I, as it demonstrates improved mechanical strength and survival probability. © 2015 The Korean Academy of Prosthodontics

Preliminary SEM observations on the surface of elastomeric impression materials after immersion or ozone disinfection

Introduction: Surface integrity of dental elastomeric impression materials that are subjected to disinfection is of major importance for the quality of the final prosthetic restorations. Aim: The aim of this qualitative Scanning Electronic Microscopy (SEM) study was to reveal the effects of immersion or ozone disinfection on the surface of four dental elastomeric impression materials. Materials and Methods: Four dental elastomeric impression material brands were used (two vinyl polysiloxane silicones,one polyether,and one vinyl polyether silicone). Total of 32 specimens were fabricated,eight from each impression material. Specimens were immersion (0.525% sodium hypochlorite solution or 0.3% benzalkonium chloride solution) or ozone disinfected or served as controls and examined with SEM. Results: Surface degradation was observed on several speci-mens disinfected with 0.525% sodium hypochlorite solution. Similar wavy-wrinkling surface structures were observed in almost all specimens,when treated either with 0.3% benzalkonium chloride solution or ozone. Conclusion: The SEM images obtained from this study revealed that both immersion disinfectants and ozone show similar impression material surface alterations. Ozone seems to be non-inferior as compared to immersion disinfectants,but superior as to environmental protection. © 2016,Journal of Clinical and Diagnostic Researc. All rights reserved

Effectiveness of low-flow high-ozone concentration disinfection of dental impressions: A comparative study to immersion disinfection

Aims: To examine the effectiveness of low-flow high-ozone concentration disinfection of dental impressions, by means of an automated prototype device. Methodology: Disc shaped dental addition-cured silicone was inoculated with Klebsiella pneumoniae and Staphylococcus aureus, 10 mm discs were removed and ozone disinfected for different time intervals, immersion disinfected or served as controls. Disinfection success was examined by using the viable plate count method, while the statistical analysis was conducted via one way-ANOVA (p < 0.05). Results: Significant eradication was observed for selected Gram (+) and Gram (-) bacteria after 3 minutes of ozone exposure, leading to complete disinfection of the samples. Conclusion: While immersion disinfection of dental impressions is currently the most widely accepted method of disinfecting dental impressions, low-flow high-ozone concentration disinfection provides a quick, efficient, fully automated alternative method, limiting liquid waste generation. Possible alterations of the materials’ physical and chemical properties, like those of immersion disinfection, are not included in the present manuscript. A precise automated method for impression disinfection is established, relieving the dental team of possible cross-contamination

A Functional Stress Analysis in the Maxillary Complete Denture Influenced by the Position of Artificial Teeth and Load Levels: an In-vitro Study

The fracture of complete dentures fabricated using Polymethyl methacrylate resin constitutes a challenge to the clinician and remains an unresolved problem. To determine whether gradual increase in load or different posterior teeth positions in maxillary denture would influence the pattern of stress. Two groups of maxillary dentures were fabricated with different posterior teeth positions (Group I with teeth on the crest of the ridge; Group II with buccal to the crest of the ridge.) using casts prepared from prefabricated edentulous molds, with 5 dentures in each group. Two strain gauges were cemented on to the midline of each denture, one on the anterior palatal area and other on the posterior palatal area. The dentures were loaded from 0 to 110 N in steps of 10 N, and the strains induced were measured. Differences of the stress magnitudes between the 2 groups were statistically analyzed using Mann–Whitney U test. The anterior palatal area of the maxillary denture was dominated by a tensile stress, which was greater in the group II than in group I. The posterior palatal area was dominated by compressive stress but the outer placement of the maxillary teeth caused a significant decrease in the compressive stress. The high anterior tensile stress with compressive stress in the posterior palatal area during loading may be responsible for denture base fractures that initiate from the anterior palatal area. The buccal placement of posterior teeth may play a role in the fatigue fracture of the maxillary denture