Abstract
Objective
To explore a new method of repair of alveolar cleft by trans-sutural distraction osteogenesis.
Design
Nine 8-week-old mongrel dogs were assigned randomly to two groups with three in the control group and six in the experimental group.
Setting
First, an alveolar cleft model was created surgically in all animals. After 2 weeks, a U-shaped distractor, made of nickel-titanium (NiTi) shape memory alloy wire with 200 g tensile force, was inserted into the premaxilla of the experimental dogs to distract the mid-premaxillary suture for 3 weeks. Periosteoplasty of the alveolar cleft was performed when the premaxilla at the side of cleft approached the maxilla at the same side. The distractor was removed 2 weeks post periosteoplasty.
Outcome Measures
The results were evaluated clinically, radiographically, and morphologically.
Results
The cleft model was stable and similar to the human alveolar cleft. No spontaneous bone union occurred in the control. In experimental dogs, the premaxilla was moved slowly toward the maxilla, and the cleft became gradually narrower and closed in the third week. Radiographically, the distracted mid-premaxillary suture showed a gradually widened triangle, with the tip of the triangle pointed posteriorly. The density of the distracted triangle suture was increased gradually. The alveolar cleft was completely bony 3 months post periosteoplasty. The morphology of the mid-premaxillary suture was also restored.
Conclusion
The alveolar cleft could be repaired by the technique of mid-premaxillary suture distraction using the elastic device of NiTi shape memory alloy.
There are a few techniques for alveolar cleft repair, including secondary bone grafting, gingivoperiosteoplasty (Skoog, 1965), maxillary orthopedics plus gingivoperiosteoplasty (Millard and Latham, 1990), and premaxilla osteotomy shifting to the side of cleft. Skoog's technique of gingivoperiosteoplasty usually resulted in a slim bony bridge across the cleft. Millard and Latham's presurgical orthopedics and gingivoperiosteoplasty might shorten the length of the alveolar crest and result in crowding of teeth. Alveolar bone grafting, prevalent in the last 20 years, often produces complications including bone resorption, infection and donor site trauma, and defect (Cohen et al., 1993; Long et al., 1995).
Craniofacial sutures were first studied by stomatoorthopedics. Recently, trans-sutural distraction osteogenesis has appeared in craniomaxillofacial surgery. Tung et al. (1999) achieved successful distraction osteogenesis across a growing cranial suture without osteotomy in an experimental study in rabbits. Liu et al. (2000, 2005) reported on the study of sutural expansion osteogenesis for bony repair of the cleft palate in dogs in 2000, and on the clinical experience of trans-sutural distraction for midfacial advancement in children in 2005.
In this study, trans-mid-premaxillary suture distraction was designed for artificial alveolar cleft repair in young dogs.
Materials and Methods
Experimental Design
Nine 8-week-old mongrel dogs were used in this study. They were divided randomly into two groups: the control group (n = 3) and the experimental group (n = 6). This experiment complied with the guidelines for use of laboratory animals (www.apa.org/science/anguide.html).
Trans-sutural Distraction Device
The distractor was a ring-shaped wire made of nickel-titanium (NiTi) shape memory alloy. It had two arms perpendicular to the plane of the ring. The ends of the arms curved in opposite directions for fixation in the bone. While the arms were inserted into the bone holes drilled by a dental burr across the mid-premaxillary suture, the distractor would exert persistent forces vectored laterally to expand the mid-premaxillary suture and friction between the laterally curved arm, and the lateral wall of the bone hole would hold the distractor in place. The diameter of the wire was 0.8 mm, with about 200 g of traction force, the distance of distraction between the two arms was 12 mm.
Cleft Creation
An alveolar cleft was created surgically in both the experimental and control group. Under general anesthesia with ketamine, 5 mg/kg intramuscularly, and endotracheal intubation, the palatal and alveolar mucosa was infiltrated with lidocaine (HCl 0.5% mixed with epinephrine 1:200,000). The second deciduous lateral incisor was removed. Mucoperiosteal flaps were designed in such a way that the raw bone surface left by segmental removal of alveolar bone could just be covered by the mucoperiosteal flaps. A 7-mm wide alveolar bone extending from the first deciduous lateral incisor to the cuspid was excised with a fissure bur, extending medially to the nasopalatine foramen and superiorly to the nasal floor. The raw bone surface was closed by mucoperiosteal flaps. A strip of iodoform gauze was packed in the new alveolar cleft (Fig. 1).
Creation of artificial alveolar cleft. Two gingivoperiosteal flaps were elevated for covering the raw bone surface.
Mid-premaxillary Suture Distraction
Two weeks after artificial alveolar cleft creation, holes were drilled at the midpoint of the mid-premaxillary suture through bone and mucosa. Two arms of the distractor were inserted into the bone holes to expand the mid-premaxillary suture gradually. The ring part of the distractor was fixed by silk thread oversew (Fig. 2).
Trans-sutural distractor. A: Sketch showing placement and force vector. B: Distractor in place.
Alveolus Cleft Repair
Two to three weeks after distraction, the premaxillary bone moved laterally and approached the distal cleft edge (Fig. 3). Under general anesthesia, the cleft was repaired. The gingivoperiosteum was incised at the labial cleft margin medially and the palatine cleft margin distally, respectively. The gingivoperiosteal flaps were elevated and closed to cover the bony cleft (Fig. 4). The distractor had not been removed until 2 weeks postoperatively.
After trans-mid-premaxillary sutural distraction, the premaxilla gradually moved laterally (A, B) and the cleft was closed (C).
A: Closure with mucoperiosteal flaps. B: Three months after alveolar cleft repair.
Animal Management
Postoperatively, all dogs were fed gruel food and examined physically daily. The experimental group dogs were sacrificed 3 months after their alveolar cleft repair.
The control group dogs were sacrificed 3 months after their alveolar cleft creation.
X-ray Examination
The results were evaluated radiographically. Maxillary occlusal films of the experimental group were obtained instantly after suture distraction, and on days 3, 9, 18, 30, 40, and 90. In the control group, x-ray film was taken instantly after artificial alveolar cleft formation and at 3 months.
Dry Skull Preparation
The skulls of both the control and the experimental animals were cleaned of all soft tissues and air dried.
Results
Clinical Observations
All experimental and control animals tolerated the procedure and grew well. Two weeks after artificial cleft creation and cleft repair, the wound recovered uneventfully. After the procedure of artificial cleft creation, the weight gain of both the control and experimental dogs was slow, but the dogs recovered gradually 1 week postoperatively. Compared with the control dogs, after twice as much anesthesia and procedures of distraction and cleft alveolar repair, the body weight of the experimental dogs was lower but caught up to the control dogs in 2 to 3 weeks after the last operation.
In the control group, no autonomous healing of the artificial cleft was found. The morphologic characteristics of the artificial cleft were similar to a natural cleft. The lower deciduous canine was overerupted without the antagonist tooth.
In the experimental group, no postoperative infections, hematomas, or other complications secondary to the surgery occurred. The distraction device was well fixed in the premaxillary bone during the experimental process. The premaxillary bone gradually moved laterally under persistent elastic force and eventually met the distal cleft edge on days 16 to 20 of distraction. In the distraction process, the two deciduous central incisors separated gradually, and the premaxilla became obviously widened (Fig. 3).
Two weeks after the alveolar cleft repair, the wound healed very well. There was no relapse after the distraction device was removed (Fig. 4A and 4B).
Radiologic Investigations
In the control animal, a trapeziform transparent area was observed at the site of the artificial cleft. The mid-premaxillary suture showed a slender straight line. Bone density of the cleft margin increased slightly. No new bone formation was found in the cleft (Fig. 5A).
Radiographic images of the alveolar cleft. A: Artificial alveolar cleft. B: Day 9 after suture distraction, the mid-premaxillary suture was expanded. C: Day 18, new bone formation was seen at the expanded suture. D: Day 30, new bone formation at the mid-premaxillary suture. E: Day 40, bony healing of the cleft and the mid-premaxillary suture was in reform. F: Three months after repair of alveolar cleft, the cleft was bony and repaired completely, and the mid-premaxillary suture was restored.
On the third day of distraction in experimental dogs, the mid-premaxillary suture showed a triangle-shaped transparent image with the tip pointed posteriorly. On day 9, the triangle-shaped transparent zone enlarged along with movement of the premaxilla. On day 12, the arms of the distractor opened in distances of 6.5 to 9 mm, with an average span of 7 mm. Meanwhile, the triangle-shaped zone at the premaxillary suture became larger, and the density increased slightly. On day 18, the premaxillary bone approached the distal margin of the cleft, and new bone formation could be seen in the distracted zone of the premaxillary suture. The two central incisors were seen separated and sloped dramatically. Two weeks after the alveolar cleft repair, bone density increased dramatically at the distraction zone and a new premaxillary suture clearly appeared. Bony healing could be seen at the site of the artificial cleft. Three months after cleft repair, the distracted mid-premaxillary suture and the cleft restored normal configuration, although the local teeth were somewhat irregular (Fig. 5B through F).
Findings of the Dry Skull
The dry skull in the control dogs showed a bone defect at the alveolar ridge from the first lateral incisor distally to the canine. The cleft width was approximately equivalent to the width of segmental bone removal (Fig. 6A).
A: Artificial alveolar cleft on dry skull. B: Dry skull showed repaired alveolar cleft.
In the experimental animal, the artificial cleft restored bony succession of alveolus. The premaxilla on the cleft side was similar to its counterpart in three dimensions. The configuration of the mid-premaxillary suture in the experimental dogs was similar to that in the control. There were irregular teeth on the affected side of the premaxilla (Fig. 6B). The dry skulls of both the control and experimental dogs were in early permanent dentition. After dry skull treatment, some canines split into two halves and sunk into the socket, and one or two deciduous teeth could be seen stagnated on the dry skull of experimental dogs (Fig. 6B). Stagnated deciduous canines could also be observed on the dry skulls of the controls (Fig. 6A).
Discussion
The alveolar cleft is a common deformity accompanied by tissue defect and shift of surrounding structures. Associated with this deformity is anterior-superior displacement of the premaxilla in unrepaired cleft lip, relapse of the lateral maxillary segment, and deviation of the nasal septum. The ideal treatment of this deformity should be to repair the defect and move the deviated structures into normal position at the same time. These goals are included in various protocols of orthopedics and cleft repair (Millard et al., 1999; Liou et al., 2000; Cho, 2006; Power and Matic, 2009).
In our study of trans-mid-premaxillary suture distraction, the premaxilla on the cleft side was pushed toward the cleft, and the gap of the cleft was narrowed. New bone formation was found at the mid-premaxillary suture and at the cleft after gingivoperiosteoplasty. Thus, changing the premaxillary position and repairing the cleft by increased new bone were achieved simultaneously.
Compared to the popular osteotomy distraction osteogenesis (ODO), trans-sutural distraction osteogenesis (TSDO) might provide a more minimally invasive method for correction of nonsynostosis craniofacial anomalies. Many orthopedic techniques in dentistry deal with maxillary sutures. These techniques have been referred to as “maxillary expansion,” “palatal expansion,” and “maxillary protraction” (Nelson, 1968; Hicks, 1978; Nanda, 1978; Wagemans et al., 1988), to name a few. In recent reports of craniofacial surgery, the terms “distraction without osteotomy,” “suture expansion osteogenesis,” and “sutural distraction osteogenesis” have been used (Liu et al., 2000, 2005; Pellerin et al., 2001; Graewe et al., 2008). However, a discussion between Drs. Liu, Barlett (University of Pennsylvania Health System), and McCarthy (New York University Medical Center) led to the term “trans-sutural distraction osteogenesis” as more suitable for this new technique.
Compared to ODO, the technique of TSDO possesses the following characteristics: (1) the connection of the bone segments bordering the distraction site is the natural suture, as opposed to newly formed fibrous callus in ODO; (2) there is no need for osteotomy, fixation of bone segments, and a latent phase, as in the technique of ODO. It is much simpler and easier to manipulate and much less invasive; (3) the suture is in a growth zone of the craniofacial skeleton, and thus possesses stronger potential for bone regeneration during the developmental ages; and (4) TSDO is suitable only for young patients before the suture maturity (Liu et al., 2005).
Nguyen et al. (2009) reported a study of critical-sized alveolar defect in the rat. A 7 X 4 X 3-mm complete alveolar defect was created surgically, and micro computed tomography demonstrated that new bone filled 43% of the alveolar defect at 4 weeks, 53% at 8 weeks, and 48% at 12 weeks. In the current study, two gingivoperiosteal flaps were designed to cover the raw bone surface left by segmental removal of the alveolar. We think that this maneuver is more important in preventing autonomous healing of the cleft.
It is difficult to know how much force is most appropriate to distract a certain suture or sutures. Almost all chosen forces in previous studies have been empirical. On the basis of correlated research experience (Liu et al., 2000, 2005), 200 g of initial elastic force was chosen in the present study, and it seemed suitable. The premaxilla was distracted successfully with an appropriate rate. New bone formation was perfect at the mid-premaxillary suture, and the mid-premaxillary suture recovered to its original configuration after dramatic change induced by distraction.
Dry skull specimens showed that the premaxilla on the cleft side was smaller than its counterpart. This might be due to interference of gingivoperiosteum caused by artificial cleft creation and gingivoperiosteoplasty afterwards. In the experimental studies of Herfert (1958) and Kremenak (1984), the same change was observed. This interference should be less in naturally occurring alveolar clefts than in experimental alveolar clefts.
There is certainly a long way to go from this method to clinical application. With this simple distractor, the mid-premaxillary suture was distracted apart and new bone formation induced; but at the same time, the teeth were disturbed. The surgically created cleft model is quite different from the clinical alveolar cleft. It is not possible to investigate the effect of trans-sutural distraction osteogenesis on canine eruption as in a real alveolar cleft case.
There are three main features associated with trans-mid-premaxillary sutural distraction osteogenesis for repair of alveolar cleft: (1) bone regeneration at the mid-premaxillary suture induced by distraction force compensates for the missing tissue at the alveolar cleft, and the configuration and structure of new bone are similar to original alveolar bone; (2) alveolar cleft healing after gingivoperiosteoplasty was just like the union of a bone fracture; (3) the premaxillary was moved laterally gradually by distraction to return to the normal position, which might correct deviated structures connected to the moved structures. Of course, the distractor used in this study is only a rough one, and further study is required prior to clinical application.