The effect of light-cured resin with a glass fiber net as an intermediate material for Hard & Space mouthguard.

BACKGROUND/AIMS: Despite the use of conventional mouthguards, preventable sports-related dental injuries continue to occur. The authors have developed a two-layered ethylene polyvinyl acetate (EVA) mouthguard with a hard polyethylene terephthalate (PET) insert and a buffer space (H&SMG). However, adapting the PET onto the EVA layer requires skill. A light-cured Splint Resin (SRLC) and a glass fiber net (NET) reinforcement appear to resolve this issue. The aim of this study was to investigate whether SRLC with NET could replace PET and find a more practical application for NET. MATERIALS AND METHODS: A pendulum impact testing machine and a dental model with strain gages were used. Six types of mouthguards were made: one with two laminated EVA blanks (LAM-MG), a three-layer type with a PET insert and an intermediate space (PET-H&SMG), a H&SMG with SRLC insert (LC-H&SMG), and three other types with differential NET-SRLC reinforcement; NET on the outer surface of SRLC, NET on the inner surface of SRLC, and NET on both the outer and inner surfaces. Five mouthguards of each type were fabricated and tested ten times with impact distances of 15 and 30 cm. Forty more impacts were applied to all H&SMGs to confirm the durability of the hard inner layer. RESULTS: All H&SMGs showed significant strain reduction compared to the LAM-MG. PET-H&SMG and the four types of LC-H&SMG exhibited an equally slight strain (approximately 95% shock absorbing ability) in all conditions. During the test against the smaller impact, all H&SMGs showed no cracks. When tested against the stronger impact, only the LC-H&SMG with the reinforced inner surface, the double NET-reinforced LC-H&SMG, and the PET-H&SMG remained intact. CONCLUSION: The NET-reinforced SRLC can replace PET as an intermediate mouthguard material. The NET application, at least on the internal surface, is indispensable for the LC-H&SMG reinforcement.

Effects of Line of Vision on Posture, Muscle Activity and Sitting Balance During Tooth Preparation.

OBJECTIVES: Most dentists maintain awkward and restricted postures for prolonged periods that stress the body while providing direct patient care. Information about working posture must be analysed in a more systematic manner to provide a deeper understanding of the relationship between working posture and work-related musculoskeletal disorders (MSD). Therefore, the present study aimed to clarify the effects of different lines of vision during tooth preparation, such as the direct and the mirror view technique, on-body tilt (angle), muscle activity, and sitting balance, which may correlate with the reduction or prevention of MSD. METHODS: A mannequin head with a maxillary right first molar embedded in a model was attached to the dental chair headrest. Two different techniques for tooth preparation were selected: direct view and mirror view. Muscle activity, body tilt (angle), and sitting balance were analysed as independent parameters. RESULTS: Different tooth preparation techniques had a distinct influence on body tilt (angle), muscle activity, and sitting balance. The direct view technique resulted in significantly larger values for all parameters, except for the activity of the spinal column erector muscles than the mirror view technique. CONCLUSION: Based on these results, the direct view technique for tooth preparation, which is used by most dentists in practice, imposes a burden on the lower back, shoulders, and neck of the dentist.