Baseline data
Fifty-one (5.1%) patient of the 993 assessed treated by 2 orthodontists during 12 years had at least one vestibular GR before OT. Of those, 37 (72.5%) patients, 8 males (21.6%) and 29 females (78.4%), were included in the final analysis according to the inclusion criteria. The mean age of the included patients was 28.7 (95% CI: 26.01, 31.40) years. Orthodontic treatment lasted for a mean of 21.4 (95% CI: 18.99, 23.82) months. The characteristics of the included patients are presented in Table 2. Number of teeth with GR in 37 patients before OT is shown in Figure 1.
Significant improvement of GR was found between T0-T1 at patient level (0.41 mm, 95% CI: 0.24, 0.57), p<0.001. Number of improved GR in 37 patients is shown in Figure 2.
At tooth level, 718 teeth mesial to molars in 37 patients were evaluated before and after OT; of these, 114 (15.9%) teeth had GR on the vestibular surfaces. The prevalence of gingival recessions before orthodontic treatment in different groups of teeth is presented in Figure 3. The mean GR improvement was 0.51 (95% CI: 0.40, 0.63) mm (p<0.001), with 42 (36.9%) gingival recessions improving by ≥1mm. GR improved in 62.3% (n=71), did not change in 32.4% (n=37), and worsened in 5.3% (n=6) teeth. GR changes in different groups of teeth are presented in Table 3. Of the 71 gingival recessions, which improved, full healing was observed in 21.1% (n=15) teeth (Figure 4).
Mean gingival recession change in the different groups of teeth is presented in Figure 5. The percentage of improved GR was highest on maxillary canines (84.6%); however, the highest amount of GR improvement in millimetres was observed on maxillary incisors and maxillary premolars. Healing of GR was mostly observed on maxillary incisors (43.8%). No recession was completely healed on mandibular incisors.
As significant changes in GR were found, the influence of specific factors was analysed.
Patient-related factors
Univariate binary logistic regression analysis revealed a statistically significant association between gingival recession improvement and:
- Gingival biotype: GR had a greater chance for improvement in cases with a thick/normal gingival biotype compared with the thin biotype (OR 2.4; 95% CI: 1.07, 5.28; p=0.03).
- Overbite (OB): A significant change in the amount of GR (median 1.0 mm; Q1, Q3: 0, 1.0), as well as percentage of recession improvement (83.3%) was found in cases with normal or deep bite (OB >1mm), in comparison with overbite <1mm (median 0 mm; Q1, Q3: 0, 0.5) (p<0.001). Odds ratio for the GR improvement was 4.69 (95% CI: 63, 13.55; p=0.004) greater if the pre-treatment overbite was >1mm in comparison to OB ≤1mm.
- Overjet (OJ): A greater improvement of GR (median 1.0 mm; Q1, Q3: 0, 1.0) was observed in cases with large pre-treatment overjet (OJ ≥4mm), in comparison with an OJ <4mm (median 0.5 mm; Q1, Q3: 0, 1.0) (p=0.017). The odds ratio for the GR improvement was also greater (OR 1.81; 95% CI: 0.75, 4.40; p=0.19) in the presence of a larger pre-treatment overjet (OJ ≥4mm).
- Sagittal dental discrepancy: GR showed less tendency for healing in dental Angle Class III patients on one or both sides (p=0.006). Also odds ratio for the GR improvement was 3.2 times less (95% CI: 37, 7.54, p=0.007) in cases with dental Class III.
Multilevel regression analysis showed a lower chance for GR improvement in cases with pre-treatment OB≤1 (OR 3.29; 95% CI: 1.10, 9.81; p=0.03) and dental Class III patients (OR 2.79; 95% CI: 1.14, 6.83; p=0.03).
Changes in gingival recessions during orthodontic treatment were not influenced by: gender and/or age, (p=0.42, p=0.88).
Treatment-related factors
The results showed that the duration of orthodontic treatment (p=0.08) and tooth extraction (p=0.77) did not influence changes in GR.
Since 62.3% (n=71) of gingival recessions improved and 21.1% (n=15) were completely healed, the null hypothesis was accepted.