Effects of the development changes in dentition on the retention of mouthguards

Summary The use of mouthguards is one of the main strategies that are considered effective in preventing sports–related trauma.Although mouthguards are recommended for use in children during sports activities,little is known as to how growth and developmental changes in the oral cavity, jaw, and dentition affect the retention of mouthguards. In the present study, we designed mouthguards for primary,mixed(4 types),and permanent detention stages and performed tensile testing to determine the effects of dental growth and development on their retention.We also designed mouthguards for the left maxillary second milk molar,left maxillary second premolar, and left maxillary first molar to determine how the shape of the teeth affects their retention.Data was analyzed statistically,and the following results were obtained:1.Mouthguards for permanent detention stage had a significantly higher level of retention than those for primary and mixed detention stages.2.Mouthguards for primary detention stage had a significantly lower level of retention than those for mixed and permanent detention stages. 3.The retention of mixed detention stage mouthguards became poorer with the number of teeth requiring relief.4.Differences in the shape of the teeth(left maxillary second milk molar, left maxillary second premolar, left maxillary first molar)had no significant effect on the retention of mouthguards.These findings indicate that the level of mouthguard retention is lower in children at primary and mixed detention stages than in adults and children with complete eruption of central incisor to second molar.This difference may be attributed to the differences in the coverage areas of mouthguard

Single-Step Synthesis of W₂C Nanoparticle-Dispersed Carbon Electrocatalysts for Hydrogen Evolution Reactions Utilizing Phosphate Groups on Carbon Edge Sites

A novel, one-step protocol for the selective synthesis of W₂C nanoparticles from phosphotungstic acid (H₃PW₁₂O₄₀), a low-cost and commercially available tungsten compound, was developed. The nanoparticles had diameters of 1–50 nm and were dispersed on a carbon substrate. The W₂C nanoparticles were prepared by a simple operation sequence, involving impregnation of carbon black with H₃PW₁₂O₄₀ followed by calcination at 1000 °C. X-ray diffraction study revealed the selective formation of the W₂C phase in the samples prepared, whereas the tungsten carbide (WC) phase was present in the control prepared from H₂WO₄. Stable W₂C nanoparticles were obtained using this method owing to the presence of phosphate at the interfaces between the W₂C nanoparticles and the carbon substrates, which inhibited the diffusion of carbon atoms from the carbon substrates to the W₂C nanoparticles, leading to the formation of WC. The W₂C nanoparticles prepared showed an excellent catalytic activity for the hydrogen evolution reaction (HER), with low Tafel slopes of ∼50 mV/decade. The HER catalytic activity was notably high, being comparable to that of MoS₂, which is a promising alternative to Pt. The present method can potentially be applied to produce highly effective, low-cost, Pt-free electrocatalysts for the HER