External surface topography
The mental trigone (trigonum mentale) is located in the region of the symphysis as a triangular bony support that strengthens the symphysis and safeguards against transverse stresses. The inferior corners of the mental trigone lying on one side are formed by the mental tubercles (tubercu-lum mentale).
The mental foramen (foramen mentale), despite its name, is not directly in the chin but rather at the apices of the premolar roots. It is an exit point for blood vessels and nerves from the mandibular canal, some of which supply the chin area. The mental foramen generally lies at the level of the vestibular fornix and, when the alveolar part is resorbed following tooth loss, may lie on the alveolar ridge; as this can be associated with a risk of pressure points, it should be covered during prosthetic treatment.
The oblique line (linea obliqua) forms the anterior projection of the mandibular ramus into the body of the mandible (corpus mandibulae). This thickened ridge of bone is the attachment site for the buccinator muscle (musculus buccinator).The border of a mandibular denture must be shortened in keeping with the oblique line because, if not, pressure points may arise during muscle movements or the denture may be levered off. In this case, denture reduction is a necessity.
The alveolar juga (juga alveolaria) are the prominences in the alveolar part caused by the roots. They are particularly pronounced in the region of the anterior teeth and ought to be reproduced on an anterior denture body for esthetic reasons. However, they should be omitted in the posterior region because, if this is not done, deposits may form on the denture. This usually means calcu-
lus deposits in the region of the posterior teeth because this is where exit points for the salivary glands are located.
The free alveolar border (limbus alveolaris), as an arcuate free border of the alveolar part, marks the superior boundary of the mandibular body.
The external surface topography of the mandible is shown in Fig 6-24.