A retrospective study of micro-implant anchorage in the upper posterior region to improve gummy smiles

Objective To analyze the ability of micro-implant nails placed in different locations in the posterior region to improve the hard and soft tissues of the labiodental region in patients with gummy smiles to provide a reference for clinicians. Methods This study was reviewed and approved by the Ethics Committee, and informed consent was obtained from the patients. Thirty young female patients with anterior tooth protrusions and gummy smiles were included in the retrospective study; 18 patients had micro-implant nails implanted between the premolars (group A), and 12 patients had implant nails placed between the roots of the premolar and the molar and an intraoperatively placed rocking-chair archwire (group B). The preoperative and postoperative distances from the incisal end of the upper mesial incisors to the lower point of the upper lip (U1-Stms), the vertical distance from the incisal end of the upper mesial incisors to the palatal plane (U1-PP), the vertical distance from the point of the alveolar ridge to the palatal plane (Spr-PP), the distance from the incisal end of the upper mesial incisors to the point of the alveolar margin (U1-Spr), and the vertical distance from the point of the proximal middle buccal cusp of the maxillary first molar to the palatal plane of the maxillary first molar (U6-PP) were measured in the cephalometric lateral radiographs of the two groups; additionally, the amount of hard and soft tissues of the upper anterior region exposedduring smiling and the maximum amount of gingiva exposed during smiling were assessed from the smile photograph. Results After correction, the lip-dentition relationship improved significantly in both groups, with an average reduction of 2.6 mm in U1-Stms, 2.4 mm in U1-PP, 1.4 mm in Spr-PP, and 0.9 mm in U1-Spr in Group A. In group B, the U1-Stms was reduced by an average of 2.3 mm, the U1-PPs by an average of 1.6 mm, the Spr-PPs by 1.4 mm, and the U1-Spr by 0.2 mm. The difference between pre- and postoperative U6-PP in both groups was not significant (P>0.05). Group A had greater ∆U1-PP and ∆U1-Spr changes than group B(P<0.05). There was no difference between the two groups in terms of ∆U1-Stms or ∆Spr-PP (P>0.05). The amount of soft and hard tissue exposed and maximum amount of gingiva exposed in the upper anterior region of the smile were reduced in 30 patients postoperatively, with group A having anaverage reduction of 70.19% of the preoperative amount of soft and hard tissue exposed in the upper anterior region and an average reduction of 24.12% of the preoperative maximum amount of gingiva exposed, and group B having an average reduction of 76.12% of the preoperative amount of hard and soft tissue exposed in the upper anterior region and an average reduction of 31.88% of the preoperative maximum gingiva exposed after the operation. The difference in the ratio between the two groups was not statistically significant (P>0.05). Conclusion For patients with proptosis and gummy smiles, placing micro-implant nails between the roots of maxillary premolars can effectively lead to retraction and intrusion of anterior teeth to improve the lip-dentition relationship and improve gummy smile, and placing micro-implant nails between the roots of the maxillary second premolar and the first molar together with the use of rocking chair arches can also achieve a good therapeutic effect