SLJO

Sri Lankan Journal of Orthodontics

GROWTH MODIFICATION OF THE FACE: A REVIEW

V.S.N.Vithanaarachchi

Faculty of Dental Sciences University of Peradeniya Sri Lanka

Multiple theories have been applied in the past to explain the mechanism of growth modification of the craniofacial complex. However from among these various theories, the functional matrix theory is considered to be more acceptable in relation to the growth modification. Most clinicians use growth modification devices for wide variety of skeletal discrepancies.  The use of headgears is mainly considered to control the maxillary growth in class II malocclusions. Furthermore functional appliances are also indicated to correct class II skeletal problems aiming to enhance forward and downward growth of the mandible. Face mask therapy has been more popular among clinicians as it is known to enhance the downward and forward growth of the maxilla. However, clinicians have alternative views regarding the chin cup therapy. Transverse growth modification is practiced by the expansion of mid palatal sutures with narrow maxilla. Vertical growth modification is mainly aimed at the correction of deep bite and for patients with long faces. With all these methods, the ultimate goal of growth modification depends on timing of treatment, length of treatment, working mechanism of appliance, skeletal and dental condition of the patient and compliance of patient towards orthodontic treatment.  This article reviews the literature on growth modification in relation to the class II, class III malocclusions and vertical as well as transverse discrepancies.

Introduction:

Historically the aim of the specialty of orthodontics has been primarily aimed at the correction of malocclusion by means of controlled movement of the developing and mature dentition to a desirable level. However orthodontics is based on the two major considerations which are orthodontic bio- mechanics and craniofacial biology. Proper knowledge on of these areas is essential for successful treatment outcomes for developing malocclusion and dentofacial deformities.

In late 19th and early 20th centuries, growth modification was widely accepted as it was assumed that it was largely controlled by environmental factors. Later, with the evidence of   cephalometric studies, the concept of growth modification was less popular as most of the changes that take place with orthodontic treatment were produced by tooth movement and less due to modified growth (1). The American view was that growth modification was impossible due to genetic control over the growth of the craniofacial structures. However, the concept of the growth modification is still popular among orthodontists especially those in Europe.

In order to understand craniofacial growth a series of competing theories can be used with regard to skeletal growth in general as well as craniofacial growth in particular. Each of these theories attempts to explain the key elements of craniofacial growth focusing the primary mechanism which determined the growth (2). In this article, it is hoped to provide an overview of growth modification with their possibilities and limitations focusing on different malocclusions.

Historical Review:

Studies by Sir John Hunter in eighteen century on the growth of the jaws are widely accepted as first scientific research on craniofacial growth. Further experimental researches on craniofacial growth were continued by Thoma (1848) and Humphrey (1864) in the nineteenth century and Brash and Scott in early twentieth century (3).The first general theory of craniofacial growth was the “remodeling theory” which highlights significance of the distinction between appositional and interstitial bone growth.  Weismann’s concept of the germ plasm was most influential on growth modification in late nineteenth century (4). With the identification of the relationship between genes and chromosomes, genetic correlationship was highlighted in relation to the cranio- facial growth. With advanced studies, it was identified that the remodeling theory was focused on the surface deposition and resorption in bone growth in general. An alternative view highlighted the passive secondary role of the periosteum and bone surfaces in skeletal growth.  In 1940s, the sutural theory was identified with the work done by Weinmanm and Sicher in association with the craniofacial growth (5).

In 1960 Moss published a classic paper on a new theory of craniofacial growth referred to as “functional matrix” hypothesis with regards to the skeletal growth (6).  According to the concept of Moss, the class triad of craniofacial growth which includes sutures, bone surfaces and the cephalic cartilages are the primary growth centers of craniofacial skeleton. According to the functional matrix theory, the craniofacial skeleton develops initially and grows in direct responses to its extrinsic and epigenetic environment.  With further experimental results, the servo system theory was introduced and it attempts to explain the complex number of interrelated factors in the growth of the craniofacial complex (7).

Class II Growth Modification

Skeletal, soft tissue, and dental factors and habits are considered to contribute etiologically to the development of class II malocclusion. Skeletal class II malocclusions are due to protrusion of the maxilla, retrusion of the mandible or combination of both. The modalities available for skeletal correction include growth modification, orthodontic camouflage and orthognathic surgery (8). Many works in the literature have reported the different devices of growth modification for class II skeletal correction. Growth modification of moderate to severe skeletal class II malocclusion can be done with headgears and functional appliances.  Headgear is mainly used to deliver posteriorly directed extra oral forces to the maxilla (9) and it compresses the maxillary sutures altering the growth and apposition of bone at sutures. Therefore, it restricts the normal downward and forward maxillary growth while the mandible grows normally, it “catches up” thereby correcting the maxillary skeletal discrepancy (8).

With the experimental data, it was shown that, an improvement in the antero – posterior position of maxilla relative to the mandible was  greater than 5mm when introduce the maximum growth modification (  10). Further, supportive evidence from randomized controlled clinical trials has shown that the effect of the headgear is not limited to the maxilla and it also enhanced mandibular growth (9). Tulloch et al reported an average reduction of SNA angle by 0.92° per year in a group allocated early correction of class II skeletal problem with headgear therapy (11). In addition to the skeletal effect, the typical response for the headgear wear is to prevent the downward and forward eruption of maxillary first molars. This dento – alveolar effect indirectly enhances the forward direction of mandibular growth.  Intrusive effect of the maxillary molars with headgear treatment is more desirable in class II skeletal problems in maximizing the antero- posterior skeletal correction.  Further inter molar and inter canine widths are increased with headgear treatment and as a result of such increased arch width and length, an appreciable reduction of over jet can be obtained with headgears.

Clinicians have identified different functional appliances such as bionator, activator, twin block, Herbst appliance and Frankel II regulator for growth modification of moderate to severe class II skeletal discrepancies. Functional appliances are indicated to class II skeletal correction with the aim of stimulating downward and forward growth of the mandible. In addition it causes restriction of maxillary growth although the effect is less. However, greater dento- alveolar effects are observed with functional appliances although there is no mechanism to align irregular arches. (8, 9)

With animal studies, McNamara demonstrated 5-6 mm of growth enhancement of mandible with in juvenile rhesus monkeys with protrusive appliances (12). To assess the outcome of the functional appliances, several prospective randomized clinical trials were conducted with human study samples.  Tulloch et al compared the effect of bionator with headgear appliances (13). The outcome comparison was done by Keeling et al with regards to the bionator and headgear and Ghafari et al also compared Frankel appliance with straight pull cervical headgear (14).  All these studies clearly showed that correction of molar relationship was not due to the enhanced mandibular growth alone and mandibular protraction appliance may enhance small magnitude of the mandibular growth.

Successful outcome is also possible in class II correction with functional appliances in combination with headgears. Ozturk and Tankuter conducted comparative study with activator and activator high pull headgear combination appliances and compared with untreated children and showed greater reduction and better control of lower incisors (15).

Class III Growth modification:

Until the 1970s, skeletal class III malocclusions were mainly considered as result of a large and /or protrusive mandible. However currently it is considered to be the   result of various factors such as prognathic mandible, retrognathic maxilla or combination of both.  According to the studies of Ellis and McNamara and Guyer, 40% – 60% of skeletal class III malocclusions are associated with maxillary deficiencies (16). Therefore it is important to recognize maxillary protraction as an appropriate treatment modality for growing patients with class III malocclusion. During the past few decades, many clinicians have practiced protraction face mask therapy as the most popular method of protracting the maxilla. Many primate experiments have shown that dramatic skeletal changes can be obtained with maxillary protraction (17). In human studies Delaire was most interested in maxillary protraction and was the pioneer of the face mask therapy in young children (18). Later, Petit modified the basic concepts of Delaire by increasing the amount of generated force by the face mask, which decreases the overall treatment time. Many clinical studies have revealed that maxillary protraction was enhanced when used in conjunction with a palatal expander (19). De Clerck advanced the method of distraction of the maxillary sutures with rapid palatal expansion or an alternating expansion – constriction of the mid palatal suture before traction (20).  However in   a randomized prospective clinical trial, it was found that the amount of protraction of the mid face was not affected by rapid palatal expansion (21). Therefore application of rapid palatal expansion in face mask is important for patients with severe constriction of the maxilla (20).

A review of the early days of orthodontics reveals that restraining mandibular growth was attempted    with a cup or cap on the chin which was attached to the back of the head.  Much supportive and unsupportive research evidence is found in the literature regarding chin cup therapy. In 1977, Graber conducted a comparative study with class III Caucasian children and showed a posterior rotation of the mandible, a decreased gonial angle, a restriction in vertical condylar growth and a clockwise rotation of the maxilla (22). Mitani and Fukazawa evaluated the effects of chin cup treatment in more  elaborate way in 3 stages of age range and concluded that complete inhibition of mandibular growth is difficult to achieve and individual reactions to the chin cup force varied (23). Ritucci and Nanda focused on the effect of chin cup therapy on the maxilla and cranial base and reported a clockwise rotation of the maxilla with minimal downward vertical growth (24). In 1990 Sugawara also obtained similar results with a group of class III patients and reported that the chin cup had no effect on the antero – posterior growth of the mid face and proclination of upper incisors was common which might be due to occlusal interferences (24).  In 2015 De Clark and Proffit highlighted that chin cup treatment would be more effective for a patient with a large mandible with short face. Therefore, chin cup therapy would be more effective in patients of Asian than European or African descent due to short face height being more common in Asian class III patients (20).

The use of class III elastic to bone plates is relatively new method and has not been thoroughly examined as other treatment procedures in growth modification. However, employment of skeletal anchorage in class III orthopedic has two main benefits such as minimizing dento alveolar changes both downward and backward mandibular rotation and the feasibility of application of continuous light force from class III elastics.  In this process, miniplates are inserted on the infrazygomatic crest and in mandibular canine regions and both these plates are connected with elastics (20). The success rate of the miniplate depends mainly on the surgical procedure and thickness and quality of the bone.   Although it is believed that, higher forces are needed for moving bones than for moving teeth, better clinical results are obtained with light  bone – anchored inter maxillary traction than heavy extra oral forces from protraction headgears. This successful outcome might be due to better compliance of patients with wearing intra oral elastics than an extra oral face mask.

Transverse Growth Modification:

Maxillary arches with less than the average trans palatal width may be crowded and need to indicate orthopedic expansion in growing children. Transverse growth modification is practiced by maxillary expansion opening the mid palatal suture.  Light force is needed to achieve mid palatal expansion of children of 8-9 years and there is a risk of injury to the nose as a result of displacement of the vomer bone with rapid palatal expansion during this age period (20). However, heavier force is needed for sutural expansion of 9-10 years children, due to inter digitation of bone spicules on the edges of the mid palatal suture.  As mid palatal expansion in the late mixed dentition requires a relatively heavy force, it is important to include as many teeth as possible in the unit of anchorage. One disadvantage in late mixed dentition is the reduced resistance from the primary teeth due to the resorption  of their roots. Therefore it is better to resort to sutural expansion after the eruption of 1st premolars (8).

Unfortunately true orthopedic expansion of the lower arch is not possible except by distraction osteogenesis.  Further, excessive transverse growth is a problem in the mandible due to the influence of tongue size and posture.

Vertical Growth Modification:

The ideal over bite in a normal occlusion may vary between 2-4mm or 5%- 20% overlap between upper and lower incisors. When the incisors overlap more than 40%, it is considered as deep bite with deleterious effects on dental health and Temporomandibular Joint ( 9 ). However, deep bite is not considered a disease entity but it is considered as clinical manifestation of an underlying skeletal or dental discrepancy. Usually skeletal deep bite is associated with horizontal growth pattern and characterized by maxillary and mandibular jaw growth discrepancy, convergent rotation of the jaw bones and deficiency in mandibular ramus height, highlighting the reduced lower face height relative to the other facial thirds. The most severe form of the excessive overbite is mainly associated with class II Division 2 malocclusion and it is needed to improve downward growth of the mandible and accepting some downward rotation of the mandible to increase anterior face height. However, while rotating the mandible downwards would improve the face height, it would also move the chin back and worsen the mandibular deficiency (20). Therefore, the most favourable method of growth modification for short face height patients is the use of activator or bionator type appliance which facilitates the eruption of mandibular posterior teeth following trimming of the acrylic.

The primary feature of the long face is a large anterior face height characterized with elongation of the lower third of the face. As a result of the increased face height, maxillary palatal plane and posterior teeth are more inferior and mandible tends to rotate downward and back ward (26). Lip incompetence, tendency for anterior open bite,  mandibular deficiency with  class II malocclusion, lower incisor crowding and narrow maxilla with posterior cross bite are more associated with long face problems(26). There are two traditional methods to address the long face pattern of growth in children namely high pull headgear with maxillary fixed appliance and functional appliances incorporating bite blocks between teeth. The headgear applies a direct external force to oppose vertical maxillary development while functional appliances indirectly involve in that mechanism by stretching the muscular and other facial soft tissue to create a reactive force exerted on the occlusal surfaces of teeth through the bite blocks (8). 

Discussion:

Functional appliances have become part of contemporary orthodontics practice but their mode of action is still controversial.  However, if advantage is not taken of growth modification, dental camouflage or orthognathic surgery are the other treatment options available for the correction. There are many controversies about the optimal time of growth modification treatment. Some clinicians believe that early intervention with growth modification improves facial harmony and simplifies and reduces the time involved in the second phase of orthodontic treatment.   However, others believe that it is a waste of time and resources and all treatment goals could be achieved with one stage comprehensive orthodontic treatment in late mixed dentition (27). Nevertheless, most researchers recommend early intervention with orthodontic treatment for children suffering with psychological and social problems and as a preventive measure for traumatic malocclusion.

There is also much controversy about the most appropriate appliance indicated in a particular case and their efficacy in modifying the growth.  Part of the problem could be due to most research predictions being based on the conventional cephalometric measurements which have some limitations leading to errors. The use of three dimensional cephalometry may help the researchers to identify the effects of growth modification devices with minimum errors (28).

Proffit stated that functional appliances could just accelerate the growth (8). While considering the different devices indicated in growth modification, headgear will restrict the maxilla while functional appliances will enhance the growth of the mandible. Growth modification further can help to manage the open bite and deep bite associated with vertical skeletal discrepancies.

Conclusion:

The ultimate success of growth modification treatment mainly depends on treatment timing, length of treatment, mechanism of the appliance, patient’s skeletal condition and compliance of the patient. Therefore, for any type of orthopedic approach in growing children, there should be defined indications and guidelines with better biomarkers to predict the outcome of treatment.

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