Attachment direction of the incisors
According to the direction of attachment of the incisors , mammals , especially rodents , distinguish between incisors in the intermaxillary jaw , which form a right angle (orthodontics), an obtuse angle (proodontics) or an acute angle (opisthodontics and hyperopisthodontics) with the skull axis. The assignment is determined by the position of the cutting edge relative to the vertical plane of the tooth, which runs through the front edge of the tooth socket and is perpendicular to the basal plane of the tooth. The difference between the condylobasal length and the condyloincisive length can serve as a measure of the degree of proodontia or opisthodontia.
Orthodontics
Orthodontic incisors (from ancient Greek ὀρθός orthós 'upright, straight' and ὀδόντος odóntos 'teeth') form a right angle with the skull axis . Its cutting edge lies in the vertical plane of the tooth. Condylobasal length and condyloincisive length roughly coincide with one another. Orthodontic incisors are found in wood mice , for example .
Proodontics
Proodonte or Proclivian incisors (from ancient Greek πρό pró 'front, forward' and ὀδόντος odóntos 'teeth' or Latin proclivis 'sloping') form an obtuse angle with the skull axis . Its cutting edge lies in front of the vertical plane of the tooth. The condylobasal length is smaller than the condyloincisive length. Proodontal incisors are found mainly in burrowing rodents that loosen the soil with their incisors, for example in terrestrial forms of the Eastern water vole .
Opisthodontics
Opisthodontic incisors (from ancient Greek ὄπισθεν opisthen 'back, from behind' and ὀδόντος odóntos 'teeth') form an acute angle with the skull axis . Its cutting edge lies behind the vertical plane of the tooth. The condylobasal length is greater than the condyloincisive length. Opisthodontic incisors, for example, are found in many gerbils .
Hyperopisthodontia
Hyperopisthodontic incisors (from ancient Greek ὑπέρ hypér 'over', ὄπισθεν opisthen 'behind, from behind' and ὀδόντος odóntos 'teeth') form an acute angle with the skull axis . In contrast to opisthodontic incisors, however, their cutting edge also lies behind the vertical plane of the tooth running through the rear edge of the tooth socket. Hyperopisthodontic incisors are found in some Sigmodontinae .
literature
- Jochen Niethammer, Franz Krapp (Hrsg.): Handbook of mammals in Europe. Volume 1: Rodents I . Akademische Verlagsgesellschaft, Wiesbaden 1978, ISBN 3-400-00458-8 .
- Scott J. Steppan: Revision of the Tribe Phyllotini (Rodentia: Sigmodontinae), with a Phylogenetic Hypothesis for the Sigmodontinae . In: Fieldiana Zoology . No. 80 , 1995, ISSN 0015-0754 , pp. 1-112 ( BHL : 21401 ).