Imagine a nine-year-old child sitting in the dental chair, with the upper incisors protruding forward. Clinically, this condition is known as proclination. Psychologically, its impact can run much deeper: eroded self-confidence, teasing from peers, and reluctance to smile. Yet one aspect has received less attention: how protruding teeth, together with the lips covering them, can quietly alter the geometry of the lower face.
A study from the Department of Pediatric Dentistry, Faculty of Dentistry, Universitas Gadjah Mada, addressed this question using concrete data. Published in the August 2025 issue of the Jurnal Kedokteran Gigi Universitas Padjadjaran, the study analyzed the relationship between upper incisor inclination and upper lip thickness and the nasolabial angle in children aged 8–11 years with Angle Class I malocclusion.
A Small Angle That Tells a Bigger Story
The nasolabial angle is the angle formed between the nasal columella and the upper lip, at the subnasale point. Its value reflects the harmony of the lower third of the face. In facial aesthetics, this angle is more than just a number: it reflects the position of the teeth, the thickness of soft tissue, and nasal growth, which continues to change throughout childhood.
The study involved 37 lateral cephalograms from pediatric patients at RSGM UGM Prof. Soedomo, consisting of 21 boys and 16 girls, all aged 8–11 years with Angle Class I malocclusion, Dewey Type 2 modification, in which the maxillary incisors exhibit proclination. The data were collected from the archives of the orthodontic preventive and interceptive clinic from 2018 to 2024, followed by manual cephalometric tracing using CorelDRAW X8.
The research team, consisting of Fadlilah Nur Rohmah, drg. Sri Kuswandari, Sp.KGA, and Prof. Dr. drg. Al. Supartinah, Sp.KGA, measured four main variables: incisor inclination relative to the SN plane, upper lip thickness at the prosthion point, total nasolabial angle, and lower-component nasolabial angle. The selection of the lower-component nasolabial angle as the primary dependent variable was not without reason.
“The lower-component nasolabial angle is not influenced by variations in the basal inclination of the nose among individuals, making the measurement more objective.”
This is important because, in growing children, the nose also develops, and its basal inclination changes from year to year. Using the total nasolabial angle as the sole reference point could result in misleading interpretations.
Two Variables, One Consistent Conclusion
Pearson’s correlation analysis produced clear findings. Upper incisor inclination had a moderate negative correlation with the lower-component nasolabial angle (r = −0.42; p < 0.05). Upper lip thickness showed a stronger negative correlation (r = −0.53; p < 0.05). This means that the greater the tooth proclination and the thicker the lip, the narrower the lower-component nasolabial angle becomes.
Conversely, neither tooth inclination nor lip thickness showed a significant correlation with the total nasolabial angle. This finding is consistent with previous studies showing that facial soft tissues are relatively independent and have their own adaptive capacity in response to changes in the position of the underlying teeth.
Multiple linear regression produced the equation Y = 144 − 0.44X1 − 2.17X2, with a coefficient of determination of R² = 0.345. Lip thickness emerged as the more dominant predictor: every 1 mm increase in lip thickness reduced the lower-component nasolabial angle by 2.17°, while every 1° increase in incisor inclination reduced the angle by only 0.44°. Together, the two variables explained 34.5% of the variation in the lower-component nasolabial angle; the remainder was influenced by other factors not examined in the study, such as lip morphology, orbicularis oris muscle activity, or individual craniofacial growth patterns.
Clinical Implications: Planning Beyond the Teeth
These findings have practical implications that can be directly felt in the treatment chair. In pediatric patients with Angle Class I malocclusion with proclined incisors, pediatric dentists and orthodontists should not focus solely on tooth position. Upper lip thickness should also be measured and considered in cephalometric analysis because its contribution to facial aesthetics appears to be greater than previously assumed.
Furthermore, the study emphasizes the importance of early intervention. The prevalence of Angle Class I malocclusion among Indonesian children aged 9–11 years reaches 57.3%, which is not a small figure. If proclination is left untreated, changes in the nasolabial angle that occur during growth may become permanent and increasingly difficult to correct.
The study also offers a methodological message: when evaluating the aesthetics of the lower third of the face in children, the lower-component nasolabial angle is a more reliable parameter than the total nasolabial angle precisely because it is not “disturbed” by variations in nasal inclination that continue to change during growth and development.
A child’s face is not a static canvas. It moves, grows, and is shaped by many factors simultaneously. Protruding teeth and thick lips are not merely matters of appearance today; they may leave traces that remain visible for years to come in the small angles that are often overlooked.
Source DOI: http://10.24198/jkg.v37i2.60915
Authors: Nanda Ayu, drg. Achmad Zam Zam Aghasy, M.Kes.
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