PDF: Associated Dental Anomalies: case report

Tooth agenesis is the most common developmental anomaly of the human dentition, occurring in 25% of the population.

The third molar (M3) represents the tooth most affected with agenesis, having a prevalence rate of 20.7%. In contrast, permanent second molar (M2) agenesis is a rare occurrence, found in only 2 of 6,000 consecutive orthodontic patients (0.03%).

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Excluding the third molars, the prevalence rate of tooth agenesis is reported as 4.3 to 7.8%. The mandibular second premolar (MnP2) is the tooth most often absent, with a relative frequency of 2.2 to 4.1%4. In fact, the MnP2 is highly variable developmentally. Besides the high prevalence of agenesis, the MnP2 often shows significantly retarded development, especially when there is agenesis of other permanent teeth6. 

Despite the fact that the mean initial calcification age for MnP2 is 3 years (varying from 2y3m to 3y7m)7, its development can be suppressed until 6 years8, and some published reports show radiographic appearance of the MnP2 after the age of 9 and even at 13 years old. In addition, the MnP2 accounts for approximately 24% of all impacted teeth, excluding the third molars. 

The most frequent malposition reported for the unerupted MnP2 is distoangular development, with a prevalence rate of 0.2% in dental clinic patients. This malposition was found to be associated with agenesis of the contralateral MnP2.