Influence of flow rate and different size of suction cannulas on splatter contamination in dentistry: results of an exploratory study with a high-volume evacuation system.

OBJECTIVES: SOPs recommend high-volume evacuation (HVE) for aerosol-generating procedures (AGPs) in dentistry. Therefore, in the exploratory study, the area of splatter contamination (SCON in %) generated by high-speed tooth preparation (HSP) and air-polishing (APD) was measured when different suction cannulas of 6 mm diameter (saliva ejector (SAE)), 11 mm (HC11), or 16 mm (HC16) were utilized versus no-suction (NS). MATERIALS AND METHODS: Eighty tests were performed in a closed darkened room to measure SCON (1m circular around the manikin head (3.14 m2) via plan metrically assessment through fluorescence technique. HSP (handpiece, turbine (Kavo, Germany)) or APD (LM-ProPowerTM (Finland), Airflow®-Prophylaxis-Master (Switzerland)) for 6 min plus 5 s post-treatment were performed either without suction or with low-flow (150 l/min for SAE) or high-flow rate (250 l/min/350 l/min for HC11/HC16) suction. All tests were two-tailed (p≤0.05, Bonferroni corrected for multi-testing). RESULTS: Irrespective the AGP, SCON was higher for NS (median [25th; 75th percentiles]: 3.4% [2.6; 5.4]) versus high-flow suction (1.9% [1.5; 2.5]) (p=0.002). Low-flow suction (3.5% [2.6; 4.3]) versus NS resulted in slightly lower but not statistically significantly lower SCON (p=1.000) and was less effective than high-flow suction (p=0.003). Lowest contamination values were found with HC16 (1.9% [1.5; 2.5]; p≤0.002), whereat no significant differences were found for HC11 (2.4% [1.7; 3.1]) compared to SAE (p=0.385) or NS (p=0.316). CONCLUSIONS: Within study's limitations, the lowest splatter contamination values resulted when HC16 were utilized by a high-flow rate of ≥250 l/min. CLINICAL RELEVANCE: It is strongly recommended to utilize an HVE with suction cannulas of 16mm diameter for a high-flow rate during all AGPs and afterwards also to disinfect all surface of patients or operators contacted.

Comparative evaluation of torque prescription of commercially available 018Roth and 022MBT PEA brands in maxillary anterior teeth.

BACKGROUND: Torque is an important component of preadjusted edgewise prescriptions to achieve ideal/optimum tooth position and more so in aesthetics sensitive maxillary anterior teeth. Thus, the need to audit available commercial brands of 018Roth and 022MBT was felt and in vitro analysis of eight brands namely 3M Unitek, Dentaurum, d-tech, IMD Medical, Libral Leone, Modern Orthodontics, Ormco and Ortho Organizer, was carried out. METHODS: The method involved perfect superimposition of two standardized images: one delineating facial axis of the tooth with stainless steel straight wire and other with full dimension arch wire engagement in bracket. The two images were superimposed and opacity of one of the images altered using Adobe Photoshop software to reveal the position of two wires. The angle obtained between two wires gave a direct read-out of torque expression. The comparison was statistically done with one-way ANOVA and Tukey's HSD test. RESULTS: In 018Roth group, IMD Medical did not show any significant difference from the standard while comparison independent of standard showed that IMD, Modern Orthodontics and Ormco were not significantly different from each other. In 022MBT group, IMD Medical, d-tech, 3M Unitek and Modern Orthodontics did not have statistically significant difference from and independent of standard. CONCLUSION: Significant variations from the standard values of both 018 Roth and 022 MBT exist in the market products and thus selection of product must be based on proper guidance in addition to clinical acumen/experience. Also the methodology provides easy to use, inexpensive set-up in the clinical settings.

In vitro comparison of the mechanical behaviour of archwires after computer-assisted and conventional bracket positioning protocols.

INTRODUCTION: The mechanical properties of orthodontic archwires can be defined using experimental setups incorporating brackets that provide conditions closer to those encountered in vivo. We aimed to compare a methodology based on computer-aided design with the gold standard protocol, performed when brackets are engaged to a full-size archwire to test the behaviour of wires in this condition. METHODS: Three models simulating a dental arch with an orthodontic fixed appliance (0.018-inch aesthetic conventional brackets) were designed. The brackets were positioned with a stainless-steel full-size wire on the first two models, with different interbracket distances. The setup 3, based on a computer-assisted design, allowed individualized placement of each bracket. Mean forces recorded and standard deviation were compared for a 0.016×0.022-inch copper-nickel-titanium wire deflected until 2mm. RESULTS: The inter-bracelet distances do not cause a statistical difference in the average maximum force recorded (12.6N and 11.4N; P=0.081) whereas the behaviour of the wires is affected. With setup 3, the recorded efforts (mean value: 8N) are statistically lower than with setup 1 and 2 respectively (P=0.018; P=0.012). CONCLUSION: An individualization of the housings by CAD-CAM dedicated to each bracket optimizes their placement. In our test conditions, the mechanical behaviour of the wires is more influenced by the positioning methods of the brackets than by the value of the interbracket distance. In perspective, our innovative methodology can be extended to other types of brackets.

On the mechanical characterization and modeling of polymer gel brain substitute under dynamic rotational loading.

The use of highly sensitive soft materials has become increasingly apparent in the last few years in numerous industrial fields, due to their viscous and damping nature. Unfortunately these materials remain difficult to characterize using conventional techniques, mainly because of the very low internal forces supported by these materials especially under high strain-rates of deformation. The aim of this work is to investigate the dynamic response of a polymer gel brain analog material under specific rotational-impact experiments. The selected polymer gel commercially known as Sylgard 527 has been studied using a specific procedure for its experimental characterization and numerical modeling. At first an indentation experiment was conducted at several loading rates to study the strain rate sensitivity of the Sylgard 527 gel. During the unloading several relaxation tests were performed after indentation, to assess the viscous behavior of the material. A specific numerical procedure based on moving least square approximation and response surface method was then performed to determine adequate robust material parameters of the Sylgard 527 gel. A sensitivity analysis was assessed to confirm the robustness of the obtained material parameters. For the validation of the obtained material model, a second experiment was conducted using a dynamic rotational loading apparatus. It consists of a metallic cylindrical cup filled with the polymer gel and subjected to an eccentric transient rotational impact. Complete kinematics of the cup and the large strains induced in the Sylgard 527 gel, have been recorded at several patterns by means of optical measurement. The whole apparatus was modeled by the Finite Element Method using explicit dynamic time integration available within Ls-dyna(®) software. Comparison between the physical and the numerical models of the Sylgard 527 gel behavior under rotational choc shows excellent agreements.