Analysis of vertical deficiency in infraoccluded primary molars: an investigation of dental, gingival, and alveolar parameters

The study aims to evaluate the vertical deficiency associated with infraoccluded primary molars by quantitatively analyzing dental, gingival, and alveolar parameters, and to determine their potential diagnostic and therapeutic relevance in clinical practice. A total of 290 infraoccluded primary molars from 129 patients under 30 years of age were retrospectively analyzed (data collection between 2000 and 2023). Inclusion required at least one infraoccluded primary molar (> 0.5 mm), along with diagnostic dental casts and panoramic radiographs taken within six months. Parameters evaluated included the degree of infraocclusion, gingival margin levels, and alveolar ridge morphology. The presence or absence of the successor tooth was considered. The mean vertical displacement of infraoccluded molars was 1.6 mm (SD 0.87). Atypical gingival margins were observed in 35% (n = 122) of infraoccluded molars, compared to 4% (n = 2) in controls, with higher prevalence in the mandible and second primary molars. The frequency of atypical gingival margins and alveolar ridge morphologies increased with the severity of infraocclusion (P < 0.05, respectively). An infraocclusion of ≥ 2.0 mm predicted atypical alveolar morphology with 70.6% sensitivity and 87.6% specificity. A significant association was also observed between atypical alveolar ridges and atypical gingival margins (P < 0.05). Multiple regression analysis (adjusted R² = 0.42) revealed that infraocclusion severity was significantly associated with age, sex, tooth type, gingival margin, and alveolar ridge morphology, whereas agenesis of the permanent successor showed no significant association. Infraocclusion of primary molars influences not only occlusal relationships but also gingival and alveolar morphology. Atypical gingival and alveolar ridge patterns may offer valuable supplementary diagnostic criteria for the management of dental ankylosis. Further prospective studies are needed to investigate their potential for use in clinical decision-making.