The mandibular dental arch: Part I, lower incisor position

Area of Science:

• Orthodontics
• Dental Cephalometrics
• Maxillofacial Surgery

Background:

• Understanding lower incisor stability post-orthodontic treatment is crucial for long-term results.
• Previous studies have explored various factors influencing incisor position and relapse.
• Identifying reliable cephalometric predictors for mandibular crowding stability remains a challenge.

Purpose of the Study:

• To evaluate the relationship between lower incisor position and hard tissue references in relation to relapse of mandibular crowding.
• To determine the efficacy of different cephalometric reference planes in predicting lower incisor stability.
• To assess the correlation between incisor position and relapse in patients with normal occlusions and those with post-treatment records.

Main Methods:

• Analysis of cephalometric records from two groups: 78 patients with post-treatment records (≥4 years post-retention) and 82 individuals with normal occlusions.
• Evaluation of lower incisor position relative to hard tissue landmarks and various cephalometric reference lines (APo plane, mandibular plane, facial plane, NB line).
• Statistical comparison of relapse rates based on initial incisor positioning (lingual, labial, or stable) and cephalometric measurements.

Main Results:

• No significant difference in lower incisor crowding relapse was observed regardless of whether the incisor was moved lingually, labially, or maintained its position during treatment.
• The APo plane was identified as a reliable guide for considering maxillary position relative to the lower incisor, unlike the mandibular plane or facial plane.
• Cephalometric reference lines (APo, NB, mandibular plane) did not correlate with the relapse of mandibular crowding, suggesting their limited utility in predicting stability.

Conclusions:

• The final position of the lower incisor relative to hard tissue references is not a significant predictor of relapse in mandibular crowding.
• Maxillary position, assessed using the APo plane, is a more relevant factor for achieving stability than incisor position relative to common cephalometric lines.
• Further research into alternative clinical guides is necessary for accurately determining long-term stability and preventing mandibular crowding relapse.