Full-arch accuracy of five intraoral scanners: In vivo analysis of trueness and precision.

OBJECTIVE: To evaluate the trueness and precision of full-arch scans acquired using five intraoral scanners and investigate the factors associated with the dimensional accuracy of the intraoral scan data. METHODS: Nine adult participants (mean age, 34.3 ± 8.3 years) were recruited. Four zirconium spheres (Ø 6 mm) were bonded to the canines and the molars. Following acquisition of reference scans using an industrial-grade scanner, five intraoral scanners, namely i500, CS3600, Trios 3, iTero, and CEREC Omnicam, were used to scan the arches. Linear distances between the four reference spheres were automatically calculated, and linear mixed model analysis was performed to compare the trueness and precision of the intraoral scan data among the different scanners. RESULTS: The absolute mean trueness and precision values for all intraoral scanners were 76.6 ± 79.3 and 56.6 ± 52.4 µm, respectively. The type of scanner and the measured linear distances had significant effects on the accuracy of the intraoral scan data. With regard to trueness, errors in the intermolar dimension and the distance from the canine to the contralateral molar were greater with Omnicam than with the other scanners. With regard to precision, the error in the linear distance from the canine to the molar in the same quadrant was greater with Omnicam and CS3600 than with the other scanners. CONCLUSIONS: The dimensional accuracy of intraoral scan data may differ significantly according to the type of scanner, with the amount of error in terms of trueness being clinically significant.

Evaluation of information in nanomaterial safety data sheets and development of international standard for guidance on preparation of nanomaterial safety data sheets.

Safety data sheets (SDSs) and labelling are the basic hazard communication tools for hazardous chemicals as regards their manufacture, storage, transport and other handling activities. Thus, in the context of the growing use of nanomaterials and nanomaterial-containing materials, this study evaluated the information provided in 97 nanomaterial-related SDSs according to the criteria set by the GHS (Globally Harmonized System of Classification and Labelling of Chemicals) and found that most of the SDSs did not include sufficient information on the safety of nanomaterials, such as their toxicity and physicochemical properties. The reasons for this lack of information in the nanomaterial SDSs can mainly be attributed to (1) a lack of toxicity and physicochemical property information on nanomaterials, (2) unawareness of the effectiveness of conventional exposure controls, such as local exhaust ventilation and encapsulation, and personal protective equipment (PPE), in protecting against nanomaterial exposure, (3) a lack of information on emergency and firefighting measures and (4) a lack of knowledge on how existing regulations apply to nanomaterials. Therefore, to create a consistent standard for the information provided on safety, health and environmental matters for manufactured nanomaterial-containing products, guidance for the preparation of nanomaterial-specific SDSs, including both nanomaterials and mixtures of nanomaterials with conventional non-nanoscale materials, was recently initiated by the ISO TC 229. Their guidance, in the form of a technical report, recommends that nanomaterial-related SDSs should be prepared based on a precautionary approach in terms of the toxicity and other risks associated with the nanomaterial contents within the mixture in question. One of the key recommendations in the technical report is to include additional physicochemical properties, including the particle size (average and range), size distribution aggregation/agglomeration state, shape and aspect ratio, crystallinity, specific surface area, dispersibility and dustiness, which help to distinguish the characteristics of nanomaterials from those of non-nanoscale materials. The technical report also recommends the preparation of SDSs for all nanomaterials and mixtures that meet the GHS criteria for physical, health or environmental hazards, and for all mixtures containing nanomaterials that meet the criteria for carcinogenic, toxic to reproduction or specific target organ toxicity in concentrations exceeding the cut-off limits for an SDS specified by the criteria for mixtures. Finally, the technical report recommends that SDSs be prepared for all nanomaterials, unless there is evidence that they are not hazardous.

Exposure assessment of workplaces manufacturing nanosized TiO2 and silver.

With the increased production and widespread use of nanomaterials, human and environmental exposure to nanomaterials is inevitably increasing. Therefore, this study monitored the possible exposure to nanoparticles at workplaces that manufacture nano-TiO(2) and nano-silver. To estimate the potential exposure of workers, personal sampling, area monitoring, and real-time monitoring using a scanning mobility particle sizer (SMPS) and dust monitor were conducted at workplaces where the workers handle nanomaterials. The gravimetric concentrations of TiO(2) ranged from 0.10 to 4.99 mg/m(3), which were lower than the occupational exposure limit 10 mg/m(3) set by the Korean Ministry of Labor or American Conference of Governmental Industrial Hygienists (ACGIH). Meanwhile, the silver metal concentrations ranged from 0.00002 to 0.00118 mg/m(3), which were also lower than the silver dust 0.1 mg/m(3) and silver soluble compound 0.01 mg/m(3) occupational exposure limits set by the ACGIH. The particle number concentrations at the nano-TiO(2) manufacturing workplaces ranged from 11,418 to 45,889 particles/cm(3) with a size range of 15-710.5 nm during the reaction, although the concentration decreased to 14,000 particles/cm(3) when the reaction was stopped. The particle concentrations at the TiO(2) manufacturing workplaces increased during the reactor and vacuum pump operations, and during the collection of the synthesized TiO(2) particles. Similarly, the particle concentrations at the silver nanoparticle manufacturing workplaces increased when the sodium citrates were weighed or reacted with the silver nitrates, and during the cleaning of the workplace. The number of silver nanoparticles in the samples obtained from the workplace manufacturing silver nanoparticles using induced coupled plasma ranged from 57,789 to 2,373,309 particles/cm(3) inside the reactor with an average size of 20-30 nm and 535-25,022 particles/cm(3) with a wide range of particle sizes due to agglomeration or aggregation after the release of nanoparticles into the workplace air. In contrast, the silver nanoparticles manufactured by the wet method ranged from 393 to 3526 particle/cm(3) with an average size of 50 nm. Thus, when taken together, the TiO(2) and silver nanoparticle concentrations were relatively lower than existing occupational exposure limits.