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
は
support (of a geta)
むしば
cavity
いれば
false tooth
まえば
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
じゅうもんじしだ
Polystichum tripteron (species of the wood fern family)
ぶぶんいれば
partial denture