As a method for vertical correction of skeletal long face, orthognathic surgery has been recognized as a general method to control it. There are studies on the stability of long face patients treated with orthognathic surgery. Several studies have revealed that long-face patients with a large mandibular plane angle showed more condylar resorption after surgery than short-face patients.[2–4] Mobarak et al. reported the postoperative response of patients with skeletal class II malocclusion and reported that the frequency and amount of relapse in long-face patients were greater and occurred in a longer-lasting pattern.[5]
The advent of the intraosseous anchor made posterior segmental intrusion possible. It made possible to treat an anterior open bite in adults without excessive extrusion of the anterior teeth, which improved the esthetics of the face. Sassouni[16] and Schudy[17] stated that posterior intrusion is the optimal treatment method as it can obtain stable treatment results and improve the long face with a skeletal anterior open bite.
Subsequently, it also became possible to intrude the total arch. Total arch intrusion can be chosen as a treatment option in hyperdivergent cases displaying severe lip protrusion and/or gummy smile.[18] Following clinical evidences support the idea that monocortical-type miniscrews can displace the whole dentition. Sugawara et al[19, 20] introduced the use of miniplates for respective maxillary or mandibular molar without causing undesired movement of incisors. Related to this, simultaneous incisal and molar movement using interradicular miniscrews placed between the 2nd premolar and the 1st molar was proposed by others, eliminating the need for incisor retraction subsequent to the molar distalization.[21, 22]
Upadhay et al. [23, 24] studied the clinical outcome of en masse retraction of the anterior teeth following premolar extraction using bimaxillary interradicular miniscrews in randomized controlled clinical trial. Interesting finding was the reduction of the mandibular plane angle in the mini-implant group, which was not evident in the conventional retraction group. It was suggesting an intrusive effect.
Furthermore, Bechtold et al. [15] found intrusion of the entire dental arch during distalization of the dental arch using dual interradicular miniscrews in the maxilla. An additional force vector created by interradicular miniscrews positioned between the 1st and the 2nd premolars changed the relationship between the imaginary center of resistance of the entire arch and the lines of force. It caused simultaneous upward and backward displacement of the entire dental arch.
In total arch intrusion, the pattern of displacement is affected by the location of force vector because the distance between the center of resistance and the line of force changes greatly. Even if the center of resistance of the entire arch is localized by experimental methods, it is still difficult to pinpoint the center of resistance in various case. Therefore, it is recommended to use dual miniscrews for predictable total arch intrusion, (Fig. 2) to stabilize the dental arch during intrusion without tilting, and also to have the intrusion force efficiently distributed throughout the dental arch. [18]
By using dual miniscrews between the teeth, the two force vectors cause the direction of force to pass through the center of resistance of the entire maxillary arch, causing intrusion and distalization of the entire dentition without changing the occlusal plane.[15] Therefore, clinicians can control the ratio of intrusion and distalization of the entire dentition by adjusting the force vector direction. When total arch distalization occurs simultaneously with total arch intrusion, it is effective in correcting a protruded lip, gummy smile, and lip incompetency, improving smile esthetics.[11]
Skeletal changes during total arch intrusion include mandibular counterclockwise rotation, which results in a decrease in the mandibular plane angle and anterior facial height (Table 2). Kuroda et al. [12, 25] and Sugawara et al. [26] also reported that posterior intrusion using skeletal anchorage caused counterclockwise rotation of the mandible, reducing the lower facial height and improving the anteroposterior jaw relationship. In our study, Skeletal changes that occurred during the maintenance period of at least one year after the end of treatment showed a statistically significant relapse(Table 2). Intruded maxillary arch was extruded during the retention period, resulting in an increase in the mandibular plane angle and anterior facial height.(Table 2)
After treatment, the maxillary incisors and molars were intruded, and the anterior facial height decreased significantly (Table 2). The anterior facial height was reduced by 2.70 mm(P < 0.001). This had an effect on the improvement of the facial length. It was found that counterclockwise rotation of the mandible caused a reduction in the mandibular plane angle, which improved facial length. This can also be seen from the fact that there was no correlation between the amount of anterior and posterior intrusion and the reduction in anterior facial length (Table 3). In addition, there was no significant difference in the amounts of intrusion of the maxillary anterior and posterior teeth and in the reduction of AFH during treatment between the groups treated with and without premolar extraction.
Statistically significant relapse of facial length and maxillary anterior intrusion occurred during the maintenance phase of at least one year after the end of treatment. (Table 2, Fig. 5).
In this study, miniscrews were placed on the buccal side between the roots of the maxillary first premolar and the second premolar, and between the roots of the second premolar and first molar. After 3–4 weeks, an intrusive force was directly applied on the total arch using elastomeric chains. When a continuous arch wire is used, the target segment is the whole arch, and the center of resistance can be localized around the premolar. (Fig. 2)
Reitan[27] reported that intruded teeth are more stable than extruded teeth because occlusal force is applied continuously. In our study, the stability of the total arch intrusion was evaluated, and the relapse of the posterior intrusion was significantly smaller than that of the anterior region (Table 3). It can be inferred that the posterior region is more stable because it continuously receives greater occlusal force. The stability of the anterior facial height (AFH) was evaluated in our study to determine the stability of non-surgical long-face treatment. The AFH relapse rate was 30.00%. More than half of the reduction amount of AFH during treatment in our study was maintained, so total arch intrusion is effective as a non-surgical treatment method for skeletal long face. It would be more desirable to overcorrect in consideration of the relapse.
This study included patients aged 14 years or older. On average, after the age of 14, there is no dramatic skeletal growth beyond the maximum growth period.[28, 29]
In this study, there was no correlation between the mandibular plane angle and SNPog angle before treatment and the amount of relapse of the anterior facial height after treatment (Table 4).
Regarding the correlation between the amount of change by treatment and the amount of relapse, the change of maxillary incisors and molars during treatment showed a statistically significant correlation with the amount of their relapse.(Table 5) The amount of their relapse was proportional to the maxillary anterior and posterior intrusion achieved during treatment.
Lee et al. [30] reported that the relapse rate of the maxillary posterior intrusion in the maintenance period of one year after the end of treatment was 10.36%. This result showed superior stability compared to the study by Sugawara et al. [26] that reported a 30% relapse rate of mandibular posterior intrusion in the maintenance phase of one year after the end of treatment. In our study, in the maintenance phase of at least one year after the end of treatment, 40.69% of maxillary anterior intrusion and 30.00% of anterior facial height changes relapsed (Table 6). The vertical distance between the maxillary molars and the palatal plane did not significantly relapse. The relapse shown in this study can reduce the need for surgery; therefore, it is considered a good treatment option for patients with mild or moderate skeletal long face. Many literatures about the stability of long face treatment mention the small size of the study subject, short maintenance period, and lack of a control group as limitations of the study. These limitations also apply to this study and it is considered that a larger number of patients will be added in a prospective study with a quantified treatment method in the future. Furthermore, it is important that follow-up studies with longer retention periods should be continued.