1. Introduction
One of the goals of orthodontic treatment is to achieve aesthetic harmony between maxillofacial morphology and facial features, whilst also establishing occlusion. Obtaining a beautiful smile line is important [
1,
2]. In general, gingival exposure of less than 2 mm with a full smile is considered aesthetically pleasing and youthful [
3]. On the other hand, a gummy smile is a condition in which excess gingiva is visible during a full smile. Gummy smiles are thought to be caused by soft tissue odontogenic causes due to the overeruption of maxillary anterior teeth, altered passive eruption, short upper lip, and skeletal causes due to excessive vertical growth of the maxilla [
2,
4,
5,
6]. Moreover, gummy smiles are considered an instigation factor for gingivitis in the anterior maxillary region [
7,
8], and improvement of the gummy smile from a young age is considered beneficial.
Conventional methods for improving a gummy smile include the intrusion of incisors, extrusion of posterior teeth using activator, bite ramps, gingivectomy of the maxillary anterior teeth, injection of Botox into the upper lip, retraction of the maxillary anterior teeth, and surgical orthodontic treatment by a combination of LeFort 1 and maxillary horseshoe osteotomy [
4,
5,
6]. Treatments are chosen in accordance with the cause. In recent years, a method for improving gummy smiles in adults using an orthodontic anchor screw has been reported [
9,
10]. However, the improvement of a gummy smile by surgical orthodontic treatment is usually achieved by combined LeFort 1 and maxillary horseshoe osteotomy, a type of orthognathic surgery, to shorten the facial height [
11,
12], which is very invasive. Furthermore, ways to improve a gummy smile using an orthodontic anchor screw are also slightly invasive. In addition, these approaches are used after growth is complete.
Several treatment methods using orthodontic anchor screws have been reported for gummy smiles during the growth period [
13,
14]. Kim et al. treated two Angle Class II division patients with gummy smiles, in the growth period, using orthodontic anchor screws, and reported the correction of excessive vertical growth of the maxillary anterior teeth and the subsequent alleviation of gummy smiles [
13,
14]. This suggests that gummy smiles may be improved if the vertical growth of the maxillary anterior teeth is suppressed. However, gummy smile patients, especially those of school age, and their parents, may exhibit resistance to surgical invasion or treatment using orthodontic anchor screws. In addition, patients in the growth period require special attention because permanent tooth germs may be present in the bone, or the roots may be immature. We therefore considered whether it would be possible to suppress the eruption of maxillary anterior teeth with a removable orthodontic appliance without surgical intervention in patients with gummy smiles in their growth period.
Here, we used SBJA [
15] in combination with the high-pull J-hook headgear to suppress the vertical excessive growth of the upper jaw in three class II patients with vertical excessive growth of the upper jaw during the growth period.
Consent was obtained from patients and their guardians for their inclusion in this report according to Ethical Guidelines for Medical and Health Research Involving Human Subjects in Japan.
3. Discussion
All three cases in this study were in their growth period, and gummy smiles caused by the overeruption of maxillary anterior teeth were observed. There have been various reports on the causes and ways of improving gummy smiles [
2,
4,
5,
6,
9,
10]. However, there have been no reports on the spontaneous disappearance of gummy smiles observed during growth. Rather, it has been reported that the amount of exposure of the maxillary anterior teeth does not change during the growth process [
19]. We thought, therefore, that it was unlikely that overeruption of the anterior teeth would improve spontaneously during the growth process. In addition, even if orthodontic treatment was started in childhood, it was not desirable to postpone improvement of the gummy smile complaint until the use of multi-bracket appliances. Therefore, in order to improve gummy smiles, we decided to develop a treatment plan that would lead to improvement by means of the application of orthodontic force in the direction of suppressing the eruption of maxillary anterior teeth from the growth stage.
The high-pull J-hook headgear is a device that is connected to hooks attached to the anterior teeth of the arch wire of a multi-bracket device, pulling the maxillary anterior teeth upward. By pulling the maxillary anterior teeth upward, the maxillary anterior teeth are pushed down, and the overbite is reduced, thereby facilitating improvement of a deep overbite [
20,
21,
22]. Furthermore, since it is often used in combination with a multi-bracket device, there have been no reports of the use of the high-pull J-hook headgear during the growth period.
Since the three cases examined here had skeletal maxillary prognathism in the growth period, we decided to improve their skeletal characteristics in the first stage of treatment. In addition, although we considered that pressing down the maxillary anterior teeth using a multi-bracket device after the end of growth would improve the gummy smiles, we thought that the combined use of high-pull J-hook headgear with a removable applianc, would render it possible to actively improve gummy smiles at an early stage by suppressing the eruption of maxillary anterior teeth before the end of the growth period.
As patients were in the mixed dentition stage, rather than using the headgear in combination with a multi-bracket device, we devised a plan to attach a loop to a part that is equivalent to the maxillary anterior teeth of a SBJA. This was then used to improve maxillary prognathism, and to use the high-pull J-hook headgear to draw the part corresponding to the maxillary anterior teeth upwards to suppress their eruption and improve the gummy smiles.
In general, the effects of BJA include a decrease in the ANB angle due to maxillary growth suppression and mandibular growth promotion, as well as a change in the anteversion of the occlusal plane, clockwise rotation of the mandible, and lingual inclination of the anterior maxillary teeth [
23,
24]. The common BJA effect seen in these three cases was the decrease in the ANB angle due to mandibular growth promotion.
It has been reported that normally, the SNA angle increases slightly with growth [
25]. The general maxillary growth suppression effect of BJA is the reduction in the SNA angle by around 0.5°, but without a significant difference [
23,
24]. Here, the SNA angle remained almost unchanged in all three cases. This may be the result of the suppression of the SNA angle, which should increase with normal growth, due to the general effect of BJA, but this is difficult to ascertain.
In addition, the combined use of SBJA and high-pull J-hook headgear caused a change in the anterior elevation of the occlusal plane, which is generally not an observed effect of BJA. It is an opposite consequence of the general BJA effect, which is the anteversion of the occlusal plane. We found, however, that when an upward force was applied to the anterior part of the SBJA by the high-pull J-hook headgear, the entire maxillary dentition being covered with a plate, which is a feature of the SBJA, led to the application of an anti-clockwise force being applied to the entire maxillary dentition. This suppressed the eruption of maxillary anterior teeth and caused anterior elevation changes to the occlusal plane due to the normal growth of the maxillary molars. In addition, we conceived that the suppression of eruption of maxillary anterior teeth improved the gummy smile.
Furthermore, although BJA is generally associated with the clockwise rotation of the mandible [
23], this was not observed in any of the three cases. Sakai et al. [
24] reported that BJA generally involves a large amount of protrusion of the mandibular molars. In this study, the amount of protrusion of the mandibular molars was smaller than that of the maxillary molars in all the three cases observed, so it is possible that the clockwise rotation of the mandible was not noted. This mechanism will, however, need to be investigated in the future. Additionally, the treatment duration was long in all three cases. It took time for the effect of the appliance to appear. It is considered that long treatment duration is a demerit of the method of improving gummy smiles using SBJA and high-pull J-hook headgear.
In these cases, as a result of using SBJA in combination with high-pull J-hook headgear with the aim of improving the overeruption of maxillary anterior teeth, the eruption of maxillary anterior teeth was suppressed, and led to a result similar to those reported on treatments that improved gummy smiles using orthodontic anchor screws in patients in the growth stage [
13,
14]. It was thought that the method of improving gummy smiles using SBJA and high-pull J-hook headgear, as examined in this study, may be an option for school-age patients and their parents, who may be resistant to surgically invasive treatments. When an orthodontic anchor screw is used to improve a gummy smile during the growth period, the anchor screw may be lost, and it has been reported that the dropout rate from treatment after implanting orthodontic anchor screws is high in young patients [
26]. We suspect that the improvement of gummy smiles using SBJA and high-pull J-hook headgears are an alternative treatment in such situations. However, the lengthening of the treatment period must be considered.
In conclusion, the combined use of SBJA with a loop attached to the labial side of maxillary anterior teeth and high-pull J-hook headgear may suppress the eruption of maxillary anterior teeth and improve gummy smiles in growth period patients with maxillary prognathism. However, this study was a case series, and therefore future studies are needed to assess the ideal treatment for specific subgroups of patients, the ideal timing and so on.