Infraoccluded permanent first molars and their effect on dentoalveolar and root development: a two-center retrospective split-mouth cross-sectional study

Background Infraocclusion of a permanent first molar, frequently due to ankylosis, can disrupt occlusal development and generate asymmetries. This study aimed to evaluate dental developmental differences caused by infraoccluded permanent first molars. Methodology A retrospective, two-center, split-mouth cross-sectional study analyzed panoramic radiographs of 45 patients (9–25 years) with a single, unilateral, infraoccluded permanent first molar. The contralateral molar served as control. Measurements included infraocclusion severity, teeth position within the arch, adjacent-tooth tipping and spacing, root length, presence and degree of root dilaceration. Results Infraoccluded permanent first molars were positioned 5.6(3.3) mm (95% CI, 5 to 7; p < 0.001) lower than controls and were significantly more distal within the arch ( p < 0.001), with adjacent teeth also displaced distally. Adjacent teeth tipped toward the infraoccluded molar: second premolars were 8(12)° more distally angulated (95% CI, 5 to 12; p < 0.001) and second molars 6(19)° more mesially angulated (95% CI, 0.6 to 15; p = 0.003). Posterior spacing was more frequent on the affected side (OR = 15.5; 95% CI 4 to 133; p < 0.001). Infraoccluded molars had roots that were 2.8(5.4) mm shorter than controls (95% CI, 1.2 to 4.4; p < 0.001) and a markedly higher prevalence of root dilaceration (OR = 18.5; 95% CI 5 to 158; p < 0.001). Infraocclusion severity was linearly associated with dilaceration severity ( r = 0.69; p = 0.0001). Adjacent teeth showed a similar trend toward higher prevalence and severity of dilacerations on the affected side. Conclusions Unilateral infraoccluded permanent first molars are strongly associated with shortened roots, increased root dilaceration, and significant distal displacement of the affected and adjacent teeth. Other effects include tipping and spacing of the adjacent teeth.