Growth: Is it a friend or foe to orthodontic treatment?

The understanding of facial growth and occlusal development plays an important role in orthodontic diagnosis and treatment planning of problems encountered in dental and skeletal malocclusions. This article reviews the growth of the craniofacial complex, how we can modify growth in the maxilla and mandible, and suggests possible ways to enhance orthopedic changes in our every day orthodontic practice. # 2008 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved. avai lab le at www.sc iencedi rec t .com journal homepage: www.elsevier.com/locate/odw 1. Where is orthodontics going in the next 50 years? Technological advances such as reduced friction (self-ligation) brackets, temporary anchorage (TAD) devices and clear aligners have provided additional options for treatment of orthodontic patients [1–4]. However, none of these can replace the impact of applying growth and development to the treatment of skeletal malocclusions [5,6]. Orthopedic appliances such as removable functional appliances, Herbst and protraction facemask have been used to modify growth in an attempt to normalize skeletal * Tel.: +1 304 293 3222; fax: +1 304 293 2327. E-mail address: [email protected]. 1344-0241/$ – see front matter # 2008 Elsevier Ltd and the Japanese doi:10.1016/j.odw.2008.10.003 discrepancies [7–10]. The immediate results are quite promising, but the long-term benefits of these appliances are still awaiting results from clinical trials. 2. What do we know about growth of our young patients that are applicable to orthodontic and orthopedic treatment? The sagittal intermaxillary relationships in Class II [11] and Class III [12] malocclusions were established before 8 years Orthodontic Society. All rights reserved. o r t h o d o n t i c w a v e s 6 8 ( 2 0 0 9 ) 1 – 5 2 of age and did not change significantly through puberty. The craniofacial skeleton is derived from mainly endochondral bone formation, which is the process of converting cartilage into bone; and intramembranous bone formation, which is the process of bone formation from undifferentiated mesenchymal tissue. Bone can form directly from osteoblasts, a process called intramembranous ossification, or have a cartilaginous precursor called endochondral ossification [13]. 2.1. Growth of the cranial base The growth of the cranial base affects the position of the maxilla and mandible. Growth of the cranial base occurs through a system of synchondroses. A synchondrosis is a cartilaginous joint where the hyaline cartilage divided and subsequently is converted into bone. Most of the synchondroses close before birth. The spheno-ethmoidal synchondrosis closes around 6 years of age, and the spheno-occipital synchondrosis closed by 13–15 years of age. Studies have shown that the flexure of the cranial base increased in Class II patients compared to normal skeletal pattern and decreased in Class III patients [11,14]. Fig. 1 – (A) Circummaxillary sutures connecting the maxilla to th Median palatal suture. (B) Circummaxillary sutures connecting zygomaticotemporal suture; b: pterygomaxillary suture; c: zygo Fig. 2 – (A and B) Patient with a hypodivergent g 2.2. Growth of the nasomaxillary complex The maxillary bones are connected to the surrounding bones by circummaxillary sutures that include the zygomaticomaxillary, frontomaxillary, pterygomaxillary, and the median palatal sutures (Fig. 1A and B). These sutures allow the displacement as well as growth of the maxilla. Theoretically, they are patent until the third or fourth decade. However, the sutures start to interlock after the pubertal growth spurt and are difficult to separate using orthopedic forces [15]. Treatment directed at the maxilla should be attempted before the pubertal growth period. 2.3. Growth of the mandible Growth of the mandible is both endochondral and intramembranous. Growth at the head of the condyle occurs in an upward and backward direction. Mandibular growth is expressed as a downward and forward displacement. Bjork examined the growth rotation of the mandible [16]. Patients with forward and upward growth rotation, when taken to extreme, can result in a severe overbite and short lower face (Fig. 2). Similarly, patients with downward and backward e adjacent bones (frontal view), a: frontomaxillary suture; b: the maxilla to the adjacent bones (lateral view), a: maticomaxillary suture. rowth pattern (forward and upward rotator). Fig. 3 – (A and B) Patient with a hyperdivergent growth pattern (downward and backward rotator). o r t h o d o n t i c w a v e s 6 8 ( 2 0 0 9 ) 1 – 5 3 rotation of the mandible can results in an anterior open bite and long lower face (Fig. 3). In order for the teeth to fit together, the jaws have to be lined up. In patients with anteroposterior jaw discrepancies, one can modify growth with orthopedic devices. Growth modification on the maxilla using appliances such as headgears and protraction facemask has been shown to be quite successful [17,18]. The suture, in most instances, responds to orthopedic force resulting in displacement of the maxilla. Growth modification on the mandible, on the other hand, is not as stable because it is genetically controlled. Treatment with appliances such as activators, Herbst and chin cups often result in relapse after treatment [19,8]. Sugawara et al. [20] evaluated the results of chin cup therapy on skeletal profile concluded that the skeletal profile was greatly improved during the initial stage of therapy, but such was not maintained in most cases. Chin cup force seldom alters the inherited prognathic characteristics of skeletal Class III profiles after growth. Mitani [21] hypothesized that compressive force on the condyle, if released before growth completion, will lead to recovery or rebound growth after chin cup use. Several investigators attempted to predict mandibular growth potential using skeletal maturation [12,22–24]. The error between the predicted and actual increments was 1.45– 2.91 mm. Using serial radiographs such as the Growth Treatment Response Vector (GTRV) analysis may help to improve the accuracy of prediction [10]. 3. How do we modify growth in the maxilla? Patients with protrusive and deficient maxilla can be treated by headgears and protraction facemask, respectively. Orthopedic force from the headgear restrains the forward and downward growth of the maxilla and allows the mandible to catch up if the mandible has forward and upward growth potential. The maxilla is connected to multiple pieces of bones by sutural joints. Orthopedic forces or tension on the maxilla can pull the maxilla away from the other connected bones such as in the case of a facemask. Similarly, compression forces on the maxilla can restrain forward and downward growth of the maxilla. Results seem to be stable long-term [25]. 4. How do we modify growth in the mandible? Patients with deficient and protrusive mandible can be treated by functional appliance and chin cup appliance, respectively. Protrusion of the mandible with functional appliances increases the proliferation of the condylar cartilage leading to bone formation [26]. On the other hand, compressive forces on the condyle with chin cup slow down condylar growth and may even modify the growth direction of the mandible [27]. The draw back of removable functional appliances is the need for patient cooperation. In order to obtain good skeletal and dental changes, patients have to wear the appliance for a significant period of time. In addition, condylar growth is genetically control. If patient does not have a forward and upward growth potential, the correction of mandibular deficiency will not be forthcoming. Similarly, if patient has a Class III growth tendency or excessive mandibular growth, relapse after chin cup therapy will most likely occur. 5. What do we need to do to increase orthopedic changes in the future? For treatment of mandibular deficiency greater orthopedic changes can be obtained with fixed instead of removable appliances. Studies have shown that greater skeletal Class II corrections can be obtained with fixed appliances such as the Herbst appliance instead of removable functional appliances because of better patient cooperation (Figs. 4 and 5). Greater skeletal changes can be reported with step-wise advancement Fig. 4 – (A–C) Edgewise Herbst appliance for treatment of patients with mandibular deficiency. The mandible was advanced stepwise to an end-to-end incisal relationship for overcorrection. Fig. 5 – (A and B) Preand post-treatment radiographs of patient treated with the edgewise Herbst appliance showing the improvement in overjet and molar relationship. (C) Superimposition of radiographs before treatment and after 8 months of treatment with the Herbst appliance showing a restraint in forward maxillary growth and stimulation of mandibular growth. o r t h o d o n t i c w a v e s 6 8 ( 2 0 0 9 ) 1 – 5 4 of the mandible during fixed or removable functional therapy [28,29]. Overcorrection of the mandible during functional appliance therapy seems to provide stability for mandibular advancement [8]. In vitro studies have shown that continuous orthopedic forces can stimulate remodeling in the glenoid fossa [6]. Normally, remodeling in the glenoid fossa is downward and backward. Treatment with the Herbst appliance stimulates remodeling in a forward and downward manner bring the mandible in a more forward position. Table 1 – Repeated expansion and constriction protocol for maxillary distraction [32,33]. Week 1 Expand 4 turns/day 7 days (total 7 mm) Week 2 Constrict 4 turns/day 7 days Week 3 Expand 4 turns/day 7 days Week 4 Constrict 4 turns/day 7 days Week 5 Expand 4 turns/day 7 days Week 6 Constrict 4 turns/day 7 days Week 7 Expand 4 turns/day 7 days, protract with facemask on protraction spring 14 h/day 6 months For treatment of maxillary deficiency, greater orthopedic changes can be obtained with distraction of the skeletal units and increase the stability of the anchorage units for maxillary distraction. In the case of Class III patients with maxillary deficiency, literature have shown that protraction of the maxilla can be more effective if the maxillary sutures are Fig. 6 – A double-hinge maxillary expansion appliance. o r t h o d o n t i c w a v e s 6 8 ( 2 0 0 9 ) 1 – 5 5 ‘‘disarticulated’’ or loosen up’’ with an expansion appliance [30]. Liou presented a protocol of repeated expansion and constriction of the maxilla for sutural distraction (Table 1) [31,32]. He also advocated the use of a double-hinge expansion appliance and a protraction spring for greater orthopedic changes (Fig. 6). Maxillary protraction in conjunction with one time expansion resulted in an average of 1.0–3.0 mm of forward movement of the maxilla [9,25,30,33]. Liou reported an average of 5.5 mm of forward movement of the maxilla with his technique [31,32]. Finally, with the help of temporary anchorage device such as mini-implants or miniplates, the stability of the maxillary distraction unit can be improved with fewer side effects [34].