Maxillary anterior segmental distraction osteogenesis to correct maxillary hypoplasia and dental crowding in cleft palate patients: a preliminary study

Six patients with CLP (5 females and 1 male; mean age, 15.2 years; age range, 14–16 years) who underwent MASDO using a miniscrew assisted tooth-borne device from January 2012 to July 2021 at the Department of Orthodontics, were enrolled and analyzed. The choice of MASDO was determined by a team including oral and maxillofacial surgeons, orthodontists, speech pathologists and periodontists irrespective of patient gender and age. Inclusion criteria: maxillary skeletal hypoplasia secondary to CLP without an alveolar cleft (submucous cleft palate, cleft of the soft palate and incomplete cleft palate); a sella-nasion-A point (SNA) angle less than 78°; a reverse overjet greater than 3 mm; age from 14 to 16 years; cervical vertebral maturation Stage (CVMS) IV and V [16]; and a collapsed dental arch and crowding in maxilla.

Before distraction (T1), after the consolidation period (T2) and after orthodontic treatment or before orthognathic surgery (T3), extra- and intraoral photographs, lateral cephalograms and panoramic images were obtained for all cases.

The miniscrew assisted tooth-borne distraction device was custom fabricated and consisted of a Hyrax expansion screw, four orthodontic metal bands (Tomy, Tokyo, Japan) and five metallic arms (Fig. 1). Appropriate bands were selected for maxillary first molars, maxillary premolars or canines (according to the position of incision and the space assignment). With bands well positioned in the mouth, an alginate impression was obtained, and the bands were seated in the impression material. Separating elastics were placed to prevent space closure while the appliance was being constructed. A Hyrax expansion screw was placed parallel to the occlusal plane and positioned at the center of the palate. The screw was oriented in an anteroposterior direction to move the anterior maxillary segment in the sagittal plane. The expansion screw was soldered with 1.0-mm metallic arms (connective arms) close to the bands. Another arm (anchorage arm) was soldered transversely between the two anterior connective arms, the middle of which was shaped like a pocket. A mini-screw would be implanted exactly in the “pocket” against the distractor in the surgery. After implantation, the mini-screw was attached to the anchorage arm so that more expanding force was transferred to the mini-screw through the anchorage arm, which was finally applied to the premaxilla, reducing the force applied to the anterior teeth, thus enhancing the distraction effect. These positions of the “pocket” should be determined by means of three-dimensional computed tomography so that the surgeon can confirm the palatal bone shape and thickness, the location of the incisive foramen and the position of the incisor’s root. The number of “pockets” can be two to avoid the mini-screw being implanted into the incisive foramen.

All operations were carried out under general anesthesia by the same surgeon. Osteotomy was conducted in accordance with the planned lines. First, a complete horizontal osteotomy was performed at least 4 mm away from the dental root apex toward the edge of the piriform. Nasal septum was then separated from the nasal base was conducted. Next, the vertical osteotomy lines were marked using a small round burr and completed with a surgical saw. Buccal maxillary, lateral nasal bone, interdental, and palatal osteotomies were performed and joined with each other with the guidance of vertical osteotomies. The mucoperiosteal flap was closed after osteotomies, and the distractor was cemented to the teeth with glass-ionomer cement [12, 17]. Finally, the miniscrew (Bioray, Taiwan) was inserted in accordance with the distractor as planned.

After a 7-day latency period, the distraction period began by turning the hyrax screw twice a day (0.5 mm/d). After a total of 14 days of distraction, the consolidation period was started and lasted for three months. The distraction protocol was referred to the study of Block et al. and Dolanmaz et al. [5, 11]. At the end of this period, the distractor was removed, and postoperative orthodontic treatment began at the same time. Notably, removal of the distractor can be performed easily without anesthesia, and the patients experienced little pain.

After consolidation, orthodontic treatment began with a self-ligating bracket (0.022-inch slots, Damon Q, Ormco). Leveling and alignment initiated by 0.014 copper-nickel-titanium (CuNiTi, Ormco) was followed by 0.014*0.025 CuNiTi, 0.018*0.025 titanium molybdenum, and stainless-steel in arch wires. A power chain was delivered to close the residual space by MASDO. After preoperative orthodontic treatment was completed, orthognathic surgery was performed as planned.

Lateral cephalometric tracings of T1, T2, and T3 were superimposed on the SN plane at sella. The measuring coordinate system was established on the superimposition of cephalometric tracings. The horizontal reference line, the x-axis, was constructed with the Frankfurt Horizontal (CFH). This line was drawn with an angle of 7 degrees to the SN line at the sella point. A perpendicular line passing through the sella to the x-axis served as the y-axis (Vertical Reference Line, VRL) [17]. Table 1 shows landmarks and reference lines traced on the radiograph. Thirty-one cephalometric variables (12 skeletal, 9 dental, and 10 soft tissue variables) were used to evaluate changes in the dentofacial structures and the soft tissue profile (Fig. 2). All cephalometric tracings and measurements were completed by one author.

Since the data did not show a normal distribution, Friedman (p < 0.05) and Wilcoxon (p < 0.05) tests were applied to identify significant differences in hard and soft tissue changes during the T1–T2, T2–T3, and T1–T3 periods. Six weeks after the first measurements, tracings and calculations were repeated by the same author.

All 6 patients successfully underwent MASDO with customized tooth-borne distractors (two patients with 2 miniscrews and four patients with 1 miniscrew) to correct the maxillary deficiency. During both the surgical and distraction periods, no serious complications, such as severe hemorrhage, infection, tooth and nerve injury or bone necrosis, were observed. No obvious pulpitis, gingival recession or abnormal dental mobility was observed among any anchorage teeth. Loosening of the mini-screw occurred in only one patient during the consolidation period. All patients received routine orthodontic treatment after MASDO and orthognathic surgery was performed in four patients. The follow-up period from T2 to T3 ranged from 22 to 26 months (mean 23.8 months) (Table 2). Two representative cases with improved facial profiles and dental alignment are shown in Figs. 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.

All the tracings and calculations were repeated by the same author six weeks after the first measurements. The intraclass correlation coefficients between the first and second measurements indicated high reliability (> 0.90). The mean values of hard tissue (skeletal and dental) and soft tissue angular and linear measurements at T1, T2, and T3 are given in Table 3. The mean changes during distraction (T1–T2), fixed orthodontic treatment (T2–T3) and the entire treatment period (T1–T3) and the significance of these mean changes are presented in Table 4.

From T1 to T2, we found that MASDO caused significant advancement in the anterior segment of the maxilla, with changes of 3.94 ± 0.94 mm (p < 0.05), 3.98 ± 0.71 mm (p < 0.05) and 4.66 ± 0.73 mm (p < 0.01) for FH ⊥ N–A, VRL–ANS and VRL–A, respectively. Statistical analyses also revealed increases in SNA and ANB. At the same time, significant upward movements of points ANS (CFH–ANS) and A (CFH–A) by 0.93 ± 0.40 mm (p < 0.05) and 1.03 ± 0.52 mm (p < 0.05) were observed, respectively. The maxillary plane angle (SN/ANS–PNS) decreased significantly by 1.13 ± 0.63° (p < 0.05).

After distraction, a significant decrease in overjet and an increase in overbite were obtained (p < 0.05). Anterior movements of the upper incisors (VRL–U1) were significant (p < 0.05). Anterior tipping of the upper incisors (U1/ANS–PNS and U1/SN) were observed (p < 0.05). In addition, the skeletal movement (VRL–A) was 86% (4.66 mm/5.45 mm) of the incisor movement (VRL–U1) during distraction.

Comparative evaluation between T1 and T2 showed that anterior movement of the point pro-nasale (VRL–Pn) and upper lip (Ls–E line, VRL–Sn, VRL–Ss, and VRL–Ls) was significant (p < 0.05). In addition, a significant increase in the nasolabial angle was measured (p < 0.05). However, none of the above data showed statistically significant changes between T2 and T3.