IS Case 440: Agenesis second left premolar, retained second deciduous molar

Gunvir Gill, MD

University of Rochester

Imaging Sciences URMC 2010
Publication Date: 2010-08-30


Patient is a 21-year-old male with trauma to face and neck.


Panorex and coronal CT views demonstrated agenesis of the second left mandibular premolar and retained second deciduous mandibular molar. This patient also had a right-sided mandibular subcondylar fracture, seen on the panorex view.


Agenesis second left premolar, retained second deciduous molar


Process of tooth formation has been termed odontogenesis. Humans have 2 sets of teeth, the primary dentition which consists of 20 teeth and has been termed deciduous, and the secondary dentition which consists of 32 teeth and has been termed permanent.

The primary dental lamina is a thickening of the oral epithelium overlying the jaws, this lamina invaginates into the primitive jaws in about the sixth week of human development. The lamina cells then begin to multiply and condense to form the tooth buds for the deciduous teeth. The tooth buds for the permanent teeth arise lingual to the deciduous teeth, from the so called secondary lamina. Specifically, the (permanent) premolars arise from the secondary lamina associated with the deciduous molars. So agenesis of the second left mandibular premolar will often lead to a retained deciduous molar. These are typically asymptomatic, as in this patient.

In a study out of Denmark a group of patients was re-imaged approximately 16 years following initial diagnosis of agenesis of premolars with retained deciduous molars. The retained deciduous molars were evaluated for interval root absorption, and abnormalities in tooth morphology and alveolar bony contour. The majority of the 26 molars examined showed no abnormalities, leading the authors to conclude that retained deciduous molars in patients with premolar agenesis can be an acceptable at least semi-permanent solution for the patient.


  1. Ith-Hansen K, Kjaer I. Persistence of deciduous molars in subjects with agenesis of the second premolars. Eur J Orthod. 2000 Jun;22(3):239-43. PMID: 10920556
  2. Som PM, Curtin HD. Head and Neck Imaging. 4th ed. Mosby 2003.

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