Prevalence and patterns of permanent tooth agenesis in patients with nonsyndromic Pierre Robin sequence Gregory S. Antonarakis a and Sunjay Suri b Toronto, Ontario, Canada Introduction: Individuals with Pierre Robin sequence (PRS) frequently have tooth agenesis, especially in the mandible. The aims of this study were to characterize permanent tooth agenesis patterns and to determine their prevalence in patients with nonsyndromic PRS. Methods: Radiographs and clinic charts of 146 children with nonsyndromic PRS were examined for permanent tooth agenesis, excluding third molars, and the tooth agen- esis patterns were identified with the tooth agenesis code. Results: The overall prevalence of permanent tooth agenesis was 32.9% (48 of 146 patients), with about two thirds having bilateral tooth agenesis. No sex or racial predilection was found for tooth agenesis. The most common tooth agenesis pattern was the absence of both mandibular second premolars. Among the children with tooth agenesis, almost half had agenesis patterns involving both mandibular second premolars. Other common patterns of permanent tooth agenesis involved the maxillary lateral incisors and the maxillary premolars. Conclusions: Symmetric agenesis of individual tooth types occurs much more frequently in the mandible than in the maxilla in patients with nonsyndromic PRS. Bilat- eral absence of the mandibular second premolars is the predominant pattern of dental agenesis. (Am J Orthod Dentofacial Orthop 2014;145:452-60) R obin 1 described what is known today as Pierre Robin sequence (PRS) as the triad of microgna- thia, glossoptosis, and resultant airway obstruc- tion. The prevalence of PRS has been reported to be between 1 in 8500 and 1 in 20,000 births. 2,3 A universal consensus on the exact definition of PRS is lacking; however, in current practice, this congenital anomaly is commonly recognized by the triad of micrognathia, cleft palate, and severe respiratory distress caused by airway obstruction in the neonatal period. 4 Tooth agenesis (or hypodontia) is also found commonly in those with PRS. 5 The prevalence of agenesis of permanent teeth in the general population, excluding third molars, according to a recent meta-analysis, ranges from 3.2% to 7.6%. 6 This prevalence varies according to the tooth type; the mandibular second premolar is most commonly affected (3.1%), followed by the maxillary lateral incisor (1.7%) and the maxillary second premolar (1.5%). Among peo- ple with tooth agenesis, 1 tooth is missing in 48%, 2 teeth are missing in 35%, and more than 2 teeth are missing in 17%. Bilateral agenesis of the maxillary lateral incisors occurs more frequently than unilateral agenesis. On the contrary, bilateral agenesis of the mandibular second premolars occurs less frequently than unilateral agenesis. Racial and regional differences in the preva- lence of tooth agenesis have been observed; these range from a mean prevalence of 2.5% for a Saudi Arabian population to 3.9% for both North American white and African American populations, 5.5% for a European white population, 6.3% for an Australian white popula- tion, and 6.9% for a Chinese population. 6 In patients with PRS, a much higher prevalence of permanent tooth agenesis has been reported by several authors, with an approximate range of 30% to 50%. 7-11 In a group of 56 Finnish children with PRS, the prevalence of hypodontia, excluding third molars, was shown to be 50%. 7,8 In this sample, the mandible was more frequently affected than the maxilla. In a group of 36 patients with PRS in their deciduous dentition, Amaratunga 12 reported that 27.7% had agen- esis of a maxillary deciduous lateral incisor. In a group of a Clinical orthodontic fellow, Hospital for Sick Children, Toronto, Ontario, Can- ada. b Associate professor, Discipline of Orthodontics, Faculty of Dentistry, University of Toronto; staff orthodontist, Hospital for Sick Children, Toronto, Ontario, Canada. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Sunjay Suri, 124 Edward St, Rm 519-B, Discipline of Orthodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Can- ada M5G 1G6; e-mail, sunjaysuri@hotmail.com. Submitted, August 2013; revised and accepted, November 2013. 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.11.021 452 ORIGINAL ARTICLE