The most influential cephalometric factors affecting variations in the nasolabial angle: A cross-sectional regression study

Background: This study aims to evaluate the most influential cephalometric values affecting variations in the nasolabial angle among a sample of Peruvian individuals. Material and Methods: This retrospective cross-sectional study analyzed 111 lateral head radiographs from individuals aged 15 to 40 years for cephalometric evaluation. Two trained and calibrated researchers measured various cephalometric parameters, including the nasolabial angle, maxillary central incisor inclination (I-NA, UIPP), maxillary position (SNA, SNB, ANB), upper lip thickness (ULT), palatal plane (PP), and occlusal plane (OP) using specialized measurement software. Variables related to affiliation were also assessed. Shapiro-Wilk test and multiple linear regression analyses were performed with significance at p < 0.05. Results: Age has a significant effect on the nasolabial angle (p = 0.017), with the angle increasing by 0.45° for each year of age. The position of the upper incisor (I-NA) also plays a significant role (p = 0.006); specifically, for every millimeter that the upper incisor moves forward, the nasolabial angle decreases by 1.94°. Additionally, the inclination of the upper incisor (UIPP) significantly influences the angle as well (p = 0.040), resulting in a decrease of 0.43° in the angle for every 1° increase in inclination. Furthermore, upper lip thickness (ULT) has a significant impact on the nasolabial angle (p = 0.002); with every millimeter increase in labial thickness, the nasolabial angle decreases by 1.57°. Conclusions: The nasolabial angle is primarily influenced by age, the position and inclination of the upper incisor, and the thickness of the upper lip. Orthodontists should consider this information when planning their treatments.