Scientific studies on the dentist's clinical posture and positions are almost nonexistant except for those by H. Fukumoto and O. Yamamoto. Therefore, the determination of the posture and positions of the dentist and his patients, and the layout of the dental equipment in the dental operation room has been merely based on the dentist's personal experience, not on scientific reasons.
Many dentists have been complaining about fatigue and physical pain. The author examined the dentist's operational posture and positions by E. M. G. in this study. According to the reports by H. Fukumoto and O. Yamamoto, the optimum is to keep the patien's mouth at the level of the dentist's nipples from the viewpoint of the dentist's fatigue and his operational efficiency.
In the present study, the author observed muscular movements of the dentist in different conditions-standing and sitting; keeping the patient's mouth in the area between 15 cm higher and 15 cm lower than the level of the optimum.
The findings through the examination of thirty-two (32) muscles are as follows :
1) Seven (7) muscles of the dentist showed active movements when he engaged in his clinical work standing and four (4) muscles, sitting.
2) When the patient's mouth was kept at the level of the dentist's nipples, the number of muscles showing active movements was less than when the patient's mouth was at different levels.
3) This study also revealed which muscles on the right arm and hand of the dentist more often showed active movements when he engaged in cavity preparation, scaling with a hand sealer, removal of slftened dentine with an excavator, and extraction with extracting forceps, and the characteristics of each muscle on various occasions.