齧歯 is read as げっし (gesshi) and means rodent.
げっし
gesshi
げっしどうぶつ
gnawing animal
げっしもく
Rodentia
げっしるい
rodent
は
support (of a geta)
むしば
cavity
いれば
false tooth
ぜんし
front tooth
ぎし
artificial tooth
よわい
(one's) age
おくば
molars
そういれば
full dentures (e.g. no real teeth left)
ぜんぶしょうぎし
complete denture