Extraction Treatment of an Adult Patient with Severe Bimaxillary Dentoalveolar Protrusion Using Microscrew Anchorage.

Bimaxillary dentoalveolar protrusion is one of the most prevalent malocclusion in Asian population.1 Traditionally, orthodontic treatment often involves the extraction of four first premolars2 and demands the least amount of anchorage loss, therefore headgear used to be an unavoid- able fate of these patients.3 Nowadays, along with the development of implant anchorage,4 more and more patients have benefited from the implant-aided orthodontic treatment,5-7 even escaped from orthognathic surgery. However, for extremely severe cases, orthodontists seem to still have to face the limitation of orthodontic treatment and turn to surgeons for cooperation. In this case, we will see how dramatic changes happened on an adult patient with severe bimaxillary dentoalveolar protrusion malocclusion after the orthodontic treatment with microscrew implants as the temporary skeletal anchorage with the patient's written informed consent, and then we may find with the help of microscrew implants orthodontists even may challenge the work of surgeons. CASE REPORT A 25-year-old woman presented with the chief complaint of having lips protrusion. Facially, the patient had a normal facial form with no asymmetries, but exhibited a severe convex profile and excessive lip strain on closure (Fig. 1). Intraorally, she had Class II molar relationship on the left side and Class I molar relationship on the right side, with severely protruded upper and lower incisors, increased overjet (4 mm), deep anterior overbite (40%), and mild mandibular crowding (Fig. 2). The upper dental midline was deviated to the right by approximate 1 mm supposedly because of the seriously rotated upper left second premolar. Oral hygiene was acceptable, and occlusal fillings were detected on the maxillary and mandibular right first molars. No signs or symptoms of temporomandibular dysfunction were noted at the initial clinical and X-ray examinations. The panoramic radiograph showed the presence of severe decay on the mandibular right first molar, it also revealed the presence of four third molars (Fig. 3). The cephalometric radiograph and analysis (Table) revealed a Class II skeletal relationship with an ANB angle of 7.74° and an average mandibular plane angle (MP-SN) of 35.6°. Both upper and lower incisors displayed severe bimaxillary dentoalveolar protrusion (U1−AP=17.52 mm, L1−AP= 12.56 mm) with small interincisal angle (95.1°). Spontaneous compensation for the severe Class II skeletal relationship was noticed from nearly normal inclination of upper incisors (U1/PP=122.05°) and severely proclined lower incisors (L1/GoGn=113.83°). Therefore she was diagnosed with a skeletal Class II, Angle's Class II, division 1, subdivision malocclusion, and severe bimaxillary dentoalveolar protrusion.Fig. 1.: Pre-treatment extra-oral photographs. A: frontal view; B: frontal view of smile; C: facial profile.Fig. 2.: Pre-treatment intra-oral photographs. A: class I molar relationship on the right side; B: 40% deep overbite in centric occlusion; C: class II molar relationship on the left side; D: increased overjet of 4 mm; E: occlusal view of maxillary arch; F: occlusal view of mandibular arch.Fig. 3.: Pre-treatment lateral cephalometric (A) and panoramic (B) radiographs.Table: Cephalometric analysisTreatment plan Considering the patient's strong desire for great change of facial appearance, the treatment plan we offered to her was orthodonticorthognathic surgery. One of the alternative for presurgical orthodontic treatment involved extraction of four first premolars and four third molars. The other alternative was extraction of the seriously decayed lower right first molar in stead of lower right first premolar, however, the potentially prolonged treatment duration prevented the patient from choosing the second option, then she was suggested to have root canal treatment for the lower right first molar. Anterior teeth would be retracted with microscrew implants as absolute anchorage. Decompensation of the inclination of both upper and lower incisors also should be achieved before the surgery. The orthognathic surgery may involve total horizontal osteotomy of maxilla and sagittal split ramus osteotomy. After close consultation with the surgeons, the patient believed that only the orthognathic surgery could bring her great changes and then accepted this treatment plan. However, we believed that with the help of microscrew implants the orthognathic surgery may finally be avoided, only the genioplasty may be necessary depending on her chin contour after retraction of anterior teeth. Treatment progress Under infiltrative local anesthesia, a titanium alloy microscrew (1.5 mm in diameter, 8 mm in length for upper arch; 7 mm in length for lower arch. MAS, Zhongbang, Xi'an, China) was inserted into the buccal alveolar bone between the second premolar and the first molar in each quadrant (Fig. 4). The insertion surgery was operated by Prof. Zhou, the senior orthodontist who developed the Micro-screw Anchorage System (MAS).Fig. 4.: Microscrew implants were placed in alveolar bone between the second premolars and the first molars. Apical films of upper right (A), upper left (B), lower right (C), lower left (D) posterior teeth. E: Titanium microscrew (MAS).One week after the implantation, MBT Ceramic brackets and molar bands were attached, and 0.016-in heat-activated nickel titanium archwires were placed for initial alignment. Meanwhile, in order to minimize forward movement of the canines, a slight force of approximately 100 g was applied with elastomic ligature between the canine bracket and the microscrew implant in each quadrant. As soon as the canines separated from the lateral incisors the elastomic ligatures ceased. Ten months were spent on alignment, mainly due to the severely rotated left second premolar. Then 0.019×0.025-in heat-activated nickel titanium archwires were placed for further alignment and leveling. Two months later, the archwires were replaced by 0.019×0.025-in stainless steel rocking-chair archwires. Although the arch leveling had not obtained at that moment, retraction of six anterior teeth was started through active tiebacks from hooks on the archwires to heads of the microscrews, the initial force was approximate 200 g in each quadrant. During space-closure process, dental arch leveling was achieved gradually. Along with the proceeding of space-closure, the patient's facial profile experienced a marvelous change (Fig. 5), which made her decide to give up the orthognathic surgery in the 22nd month of the treatment. A lateral cephalometric radiograph was taken for further evaluation, and which revealed that she still presented with slight convex profile despite all the remarkable changes contributed to the dramatic improvement, of her appearance. However, because, the patient was very satisfied with the improvement the orthognathic surgery was finally eliminated from the whole treatment plan.Fig. 5.: Dramatic improvement of facial profile after 22 months of treatment. A: facial profile before treatment; B: facial profile after 22 months' treatment.Meanwhile, normal anterior overjet and overbite had been established, but there was still a Class II tendency of molar relationship on both sides. The results of Bolton Index calculation confirmed anterior tooth size discrepancy. Interproximal enamel reduction for six lower anterior teeth was therefore carried out, active tieback from hooks on the archwires to the first molars by incorporating Class II elastics on the terminal molars brought Class I molar relationships and normal overjet and overbite control eventually. All the four microscrew implants did not show mobility and stayed firmly in place throughout treatment, then they were removed simply by unscrewing them. Total active treatment time was 30 months. The patient was suggested to have full crown restoration for the lower right first molar as soon as possible. Treatment results The change in the patient's facial profile was the most dramatic part of her treatment (Fig. 6). With the extraction of four first premolars and application of microscrew implants as absolute anchorage, significant retraction of her upper and lower lips was achieved, as a result of that, mentails strain was reduced and chin contour was improved. Intraorally, Class I canine and molar relationships with a good interdigitation of the teeth were achieved. And ideal anterior overbite and overjet were established (Fig. 7). The post-treatment panoramic radiograph demonstrated adequate root parallelism in both arches (Fig. 8).Fig. 6.: Post-treatment extra-oral photographs. A: frontal view; B: frontal view of smile; C: facial profile.Fig. 7.: Post-treatment intra-oral photographs. A: class I molar relationship on the right side; B: normal anterior overbite in centric occlusion; C: class I molar relationship on the left side; D: normal anterior overjet; E: occlusal view of maxillary arch; F: occlusal view of mandibular arch.Fig. 8.: Post-treatment lateral cephalometric (A) and panoramic (B) radiographs.Cephalometric superimposition (Fig. 9) and analysis (Table) revealed remarkable retraction of incisors in both arches. The protruded upper incisors were retracted more than 9 mm, which were reflected by a reduction of U1-AP distance from 17.52 mm to 8.17 mm, while the U1-PP distance remained quite stable; the proclined lower incisors were retracted 7.4 mm, uprighted from 113.83° to 101.41° (L1/MP angle), and intruded nearly 5 mm. As a result of compensation for the severe Class II skeletal relationship, inclination of upper incisors was some upright and that of lower incisors was still a little proclined, which ensured the normal anterior overjet after remarkable retraction of both upper and lower incisors. Maxillary molars showed little anchorage loss and slight intrusion, whereas mandibular molars experienced a mesial movement of 1 mm and a little extrusion supposedly due to the short-term application of Class II elastics. Slight reduction of the ANB angle from 7.74° to 6.57° was obtained mainly by a decrease in the SNA angle. And the mandibular plane remainned essentially stable despite the limited use of Class II elastics.Fig. 9.: Superimposition of cephalometric tracings. Registered on the SN plane at S, black solid line for pre-treatment and a red dotted line for post-treatment (A); on the palatal plane at ANS (B); on the mandibular plane at Me (C), blue line for pre-treatment and red line for post-treatment.DISCUSSION Bimaxillary dentoalveolar protrusion is a malocclusion characterized by dentoalveolar flaring of both the maxillary and mandi- bular anterior teeth, with resultant protrusion of the lips and convexity of the face, which is quite commonly seen in Asia population.1 For these patients, in orthodontics field, it is accepted that extraction of the four first premolars is the most viable and effective extraction alternative to reduce their facial convexity,2 meanwhile maximum anchorage is believed to be the most critical part of the treatment plan. It is well known that closure of the extraction sites can occur by retraction of the anterior segments, protraction of the posterior segments or a combination of the two, and when it is indicated to prevent mesial movement of the posterior segments in the anteroposterior dimension, this is termed maximum anchorage.8 Headgear has historically been the standard for maximum anchorage,3 however, it is always complained even rejected by adult patients because of social and esthetic concerns, that certainly will bring anchorage loss and unsatisfactory treatment results. And this requirement for patient compliance and its intermittent also force application have also forced orthodontists to look for substituted techniques. The temporary implants as skeletal anchorage is one of the alternatives that have brought orthodontists more power. So far clinical efficacy and stability of various implant anchorage have been widely described, dental implants,9 miniplates,6 miniscrews,4 and microscrews5,7 all have turned out to be efficient skeletal anchorage devices, which can provide absolute anchorage for tooth movement that can not be achieved by conventional methods. Miniscrew or microscrew implants especially have many benefits such as ease of placement and removal and inexpensiveness. Microscrew implants are particularly small enough to place in the interradicular bone or any area of the alveolar bone depending on the need of tooth movement without discernible damage to tooth roots,7 and orthodontic force application can begin almost immediately after placement.10 With all of these advantages the application of microscrew implants have been expanded in clinical work. The microscrew implants placed in the current case are MAS. En masse retraction of the anterior teeth with sliding mechanics has become quite common with the increased use of preadjusted appliance. However, the tip built into anterior brackets tends to move anterior teeth forward during initial alignment and leveling then jeopardize anchorage.11 Therefore, unless there were powerful anchorage reinforcement devices, it would not be more reasonable to retract the six anterior teeth simultaneously in one rather than two steps. Now, implant anchorage helps clinicians retract six anterior teeth altogether without anchorage loss even with the use of preadjusted appliances and sliding mechanics. This has been confirmed by the treatment result of the current case, according to the cephalometric analysis, the maxillary anterior teeth in this case have been retracted to close all the extraction space through sliding mechanics, and the maxillary posterior teeth showed little mesial movement, even a slight distal movement. This means that microscrew implants can even provide sufficient anchorage to retract the whole dentition distally. And most importantly, patient compliance will not be the determinant factor of ideal treatment result any more. The occlusogingival position of microscrew implants decides the force direction in sliding mechanics, the retraction of anterior teeth therefore can be controlled. Another factor capable of changing the direction of force is the vertical position of anterior hooks on the archwires. For instance, the use of short anterior hooks would increase the vertical component and decrease the horizontal component of the force and vice versa. Theoretically, for patient with normal anterior overbite, the proper position of the maxillary microscrew implants was 8-10 mm apical to the bracket slot with the anterior hooks 6-7 mm gingival to the bracket slot.12 However, for the patient presented here, due to the deep overbite tendency, we chose short hooks, only 3 mm gingival to the bracket slot, and the microscrew implants were placed approximately 8 mm apical to the bracket slot. Then according to the “high-pull en masse retraction machanics”12 the occlusal plane of maxilla and mandible would rotated at counter-clockwise and clockwise direction respectively, accompanied by the rocking-chair archwires, anterior deep overbite therefore could be corrected gradually during the space-closure stage. However, because of the application of Class II elastics, upper incisors in current case showed little intrusion; whereas lower incisors were intruded nearly 5 mm, which mainly contributed to the deep overbite correction. It certainly can not be denied that the change in the patient's facial profile was dramatic, however, according to the value of Z angle and linear distances from upper and lower lips to Rickett's E line after treatment, we have to admit that she still presented with slightly convex profile. While the patient affirmed that she was very satisfied with her current appearance, and therefore rejected the orthognathic surgery. As an orthodontist, we must not simply aim for normal values without considering the patient's personal opinion because society is becoming more tolerant towards increasing esthetical diversity. In fact, it has been found that the general public associates a fuller, more protrusive dentafacial pattern with a youthful appearance.13 Whatever it is, the patient's personal opinion should be always one of the most important things that we need to keep in mind during treatment-planning process. The present treatment may be criticized for an additional implantation surgery of microscrews. However, the surgical procedure has been simplified by elimination of flap raising and suture that are usually required in conventional implant surgery, and can operate just by orthodontists themselves but not surgeons. This patient accepted the surgery without any hesitation, she simply believed that this implantation surgery should not deserve any anxiety compared with orthognathic surgery. Postoperative pain and discomfort symptoms should be negligible because she did not complain anything about it. Additionally, during the whole active retraction of the anterior teeth, we found no mobility of the microscrews, no peri-microscrew soft tissue inflammation, even though they were loaded with 100 g of force just one week after implantation. Nowadays, microscrew implants, because of its particular advantages, have been applied widely in orthodontic field. As an absolute anchorage, it has not only brought great changes in treatment planning, but also set orthodontists free from patients' compliance. Therefore it has enlarged the indication of orthodontic treatment and improved the ability of orthodontists to deal with complicated cases. Most importantly, with the help of microscrew implants teeth can be moved to satisfy a more precise treatment plan and therefore achieve more ideal treatment results.