Abstract
<title>Abstract</title> <p> Objectives To evaluate the vertical distance (VD) and horizontal distance (HD) between maxillary premolar roots and the maxillary sinus floor (MSF), propose a novel horizontal classification system, and identify associated factors. Materials and Methods This retrospective cross-sectional study included 1076 maxillary premolars [538 first premolars (P1) and 538 second premolars (P2)] from 269 cone-beam computed tomography (CBCT) scans. VD and HD were measured on sagittal, coronal, and axial planes. A novel axial-view horizontal classification of maxillary sinus position relative to root apices was developed. Spearman correlation and multiple linear regression analyses were used to identify independent influencing factors. Results VD was greater in P1 than in P2 ( <italic>P</italic> < 0.001), with the closest proximity observed in single-rooted P2 and palatal roots of P1. Type D was the most prevalent horizontal pattern. Age independently influenced VD in both P1 and P2, whereas gender independently influenced VD in P1 and HD in P2. Laterality showed no significant independent effect. Conclusions The anatomical proximity between maxillary premolars and the MSF is independently influenced by tooth position, age, and gender. Single-rooted P2 and palatal roots of P1 represent the highest-risk configurations. The proposed axial-view horizontal classification complements vertical assessment by characterizing root-sinus relationships in three dimensions. Clinical Relevance: These findings provide an anatomical basis for preoperative risk stratification in the premolar region. The proposed horizontal classification complements vertical parameters in three-dimensional assessment, and routine preoperative CBCT should be considered for single-rooted P2 and palatal roots of P1 because of their closest sinus proximity. </p>