Nasolabial Soft Tissue Changes Following Maxillary Expansion: Influence of Baseline Morphology

Objectives: To determine whether intraoral and nasolabial changes after maxillary expansion (ME) can be predicted based on pretreatment morphology. Methods: The treatment group included 10-16-year-old adolescents who received treatment with RPE or MARPE. The RPE group comprised 13 females and nine males with a median age of 13 (interquartile range [IQR]: 11.1-13.8) years, and the MARPE group comprised 13 females and eight males with a median age of 14.4 (IQR: 13.2-15.2) years. Pre-treatment and post-expansion facial and intraoral scans were analysed. Linear regression was performed to assess whether pretreatment parameters were associated with differences in the change in parameters, adjusting for age, sex, and type of ME appliance. Results: The initially increased nostril widths were associated with a greater increase in the anatomical nose width, compared to the patients with decreased nostril widths, by 1.8 mm (p = 0.014) and 1.5 mm (p = 0.039) for the right and left nostrils, respectively. Individuals with reduced nose height (n-sn) experienced greater expansion in the medial rugae width (Tm3), by 0.9 mm (p = 0.001) and 1.3 mm (p = 0.002), compared to the medium- and increased-nose-height groups, respectively. Initially increased medial rugae width was associated with greater increase after ME. On the contrary, the increased maxillary base and intermolar widths were associated with less increase in those parameters. Conclusions: Initially larger distance between the third rugae was associated with a greater increase in the distance after ME, and a smaller distance in the maxillary width was associated with a greater increase after expansion. Larger initial nostril size was associated with a greater increase in the anatomical nose width after ME.