The effect of force on craniofacial development

A study in human subjects using a new device designed to mimic the protrusive functional appliances used previously in monkeys

A new appliance is described that mimics in function the protrusive jaw-positioning devices used previously in monkeys. The appliance consists of maxillary and mandibular posterior biteplates separated by a sharp vertical interface perpendicular to the occlusal plane. Function of the appliance was evaluated in 35 consecutively treated patients and compared against matched controls. The patients, who ranged in age from 9 to 14 years, accepted the appliance readily and wore it 24 hours each day, even while eating. Although cephalometrics was the primary assessment tool, tomograms and/or transcranial x-ray films and models were also obtained. The rate of mandibular length increase, measured from articulare, was comparable to or better than that found in monkeys using similar devices. The dentoalveolar effects were also similar to those found in monkeys, including anterior migration of the mandibular dentition and posterior movement of the maxillary dentition. The mandibular molars moved forward 4.8 mm of which 73% was determined to have come from increased anterior movement of the mandible. Subtracting normal growth, the net mandibular length increase was 2.2 mm during the 9.4-month average treatment interval.

The effect of chin cup therapy on the growth and development of the cranial base and midface

The purpose of this study was to determine how the growth rates of certain cranial base and midfacial points and dimensions were affected by force application to the mandible by the chin cup. Control and treated samples consisting of Japanese girls with skeletal Class III relationships were analyzed. Each sample consisted of lateral cephalometric radiographs taken annually (control group) or semiannually (treated group) from early childhood through adolescence. The control sample was composed of seven persons and the treated sample of ten persons. The subjects of the treated sample were required to wear a chin cup a minimum of 12 hours per day. The total force delivered was 500 g, 250 g per side, and the direction of force was, on average, through the condyle. No other appliances were used. The results of this study indicate that the chin cup causes a closing of the cranial flexure angle N-S-Ba, inhibits posterior growth of the point basion, and imposes a vertical growth tendency on the points nasion and sella. The chin cup significantly inhibits anterior and posterior vertical maxillary growth and growth of upper anterior facial height. Because development of vertical posterior facial height is inhibited more than anterior facial height, a clockwise rotation of the maxilla occurs. The chin cup also causes flaring and a decrease in eruption rate of the maxillary incisors. It has no effect on the eruption rate of the maxillary molars, but accelerates their rate of mesial movement as compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

An appraisal of growth and reaction to extraoral anchorage. Simulation of orthodontic-orthopedic results

The purpose of this article was to simulate graphically the probable orthodontic-orthopedic results of different types of extraoral traction applied to the upper dentition. Forces and movements are vectors; apart from individual variation in the amount of reaction to forces, the reactive movement vector at any given site of an influenced hard-tissue unit depends mainly on the position of its center of resistance relative to the force vector and on the amount and time of force application. In growing patients the resulting movement can then be appraised by the addition of reactive movement and average growth-movement vectors. Standardized assumptions have been made to simulate and compare qualitatively the significance and implications of five different types of commonly used extraoral traction on the upper dentition. Biomechanical parameters (such as the system factor describing the reciprocal relation between the lever arm of a force and the corresponding distance between the centers of resistance and rotation) have been arbitrarily assessed. Where cervical gear on the upper dentition is used, the resulting simulations suggest that raising the outer arms of the face-bow means less posterior effect on the upper dentition, less vertical molar control, and an increased tendency to open the bite. Where high-pull traction is applied, graphic simulations using a constant angulation, but different position of the force vector, indicate that moving the force line from a backward to a more forward position would mean a change from posterior to anterior rotation, from pronounced to no vertical molar control, from excessive incisor elongation to complete vertical incisor control, and from considerable distal effects to nearly none on the upper dentition.(ABSTRACT TRUNCATED AT 250 WORDS)

Holographic and cephalometric study of the relationship between craniofacial morphology and the initial reactions to high-pull headgear traction

Eight macerated human child skulls with a dental age of approximately 9.5 years (mixed dentition) were consecutively subjected to an experimental standardized high-pull headgear traction system attached to the maxilla at the first permanent molar area via an immovable acrylic resin splint covering all teeth. This system produced tensile forces from 0.5 to 3.5 N (1 N = 0.10 kg) per side. Laser holography was used to measure displacements in a three-dimensional coordinate system. Displacements varied in direction. In addition, conventional cephalometric analysis of standardized lateral roentgen cephalograms was performed. Displacements and cephalometric data were then compared. Results indicate that the direction of initial displacements of bones of the facial skeleton bears a definite relationship to the morphology of the individual skull. In skulls with high divergency values (large angles, sella-nasion-occlusal plane, sella-nasion-mandibular plane), displacements are in a backward and posterior downward direction; in skulls with a small sella-nasion-occlusal plane angle, backward displacements occur in a direction almost parallel to the occlusal plane.

Treatment of children with ectopic eruption of the maxillary first permanent molar by cervical traction

The sequelae of extraction of the second deciduous molar due to irreversible ectopic eruption of the maxillary first permanent molar are mesial tipping of the permanent molar and subsequent space loss. The purpose of this study was to evaluate the effects of early treatment with the Kloehn type of cervical headgear. Forty-six children with ectopic eruption were treated. The mean age at the start of treatment was 8.3 years (range, 6.5 to 9.9 years) and the mean treatment time was 0.8 year (range, 0.5 to 1.0 year). Nineteen variables from orthopantomograms, lateral head films, and dental casts were analyzed by one-way analysis of variance. The registrations were made at the start of treatment, at the end of treatment, and 1 year posttreatment. The treatment resulted in distal tipping of the first permanent molar to a good occlusion in all children. The s-n-ss angle decreased during treatment in all children, and a mean proclination of the maxillary incisors of 3 degrees was registered. Proclination was independent of the type of occlusion and was unchanged 1 year posttreatment. The ss-n-sm angle was also reduced during treatment and was unchanged 1 year posttreatment. The most favorable time for treatment seems to be when the second premolar is close to eruption or erupting at the end of the treatment period. Because of the risk of inhibited sagittal growth of the maxilla with this type of treatment, careful cephalometric evaluation is considered important before the start of treatment.

A comparison of Class II treatment changes noted with the light wire, edgewise, and Fränkel appliances

The purpose of this study was to determine if selected cephalometric changes noted in groups of growing patients with Class II, Division 1 malocclusions treated with the Fränkel function regulator (FR-2), the edgewise technique, and the light-wire (Begg) mechanism were different and characteristic of a specific technique. To this end, the changes in the SNA, SNB, N-S-Gn, and the SN-GoGn angles, face height (N-M), the anterior movement of pogonion, and the annualized mandibular growth increment (AR-Gn) in a group of patients treated with the FR-2 were compared to the changes noted in similar groups of patients treated by the edgewise technique and the light-wire mechanism. The methods used to compare the groups were an analysis of variance and a discriminant analysis. A reduction in the SNA angle was observed in all groups. It was -0.37 degrees with light wire treatment, -0.60 degrees with Fränkel appliance use, and -1.47 degrees with edgewise therapy. The SNB angle increased in all three groups, ranging from 0.29 degrees in the edgewise group to 0.56 degrees in the Fränkel group. In the light-wire group it was 0.34 degrees. The N-S-Gn angle in the Fränkel group remained essentially the same (0.06 degrees), while in the light-wire and edgewise groups it increased 0.81 degrees and 0.82 degrees. The SN-GoGn angle opened slightly in all groups, ranging from a low of 0.46 degrees with Fränkel therapy to 0.58 degrees with edgewise treatment to 1.25 degrees with the use of the light-wire appliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Intensive treatment of severe Class II malocclusions with a headgear-Herbst appliance in the early mixed dentition

In the correction of large sagittal discrepancies in the relationship between the maxilla and the mandible, the orthopedic effect of treatment is often of small magnitude when compared with the dentoalveolar changes. A group of patients with severe Class II malocclusions were treated to assess the effects of a therapeutic approach which specifically took into consideration important factors such as type of anchorage, amount of force, age at start of treatment, and intensity of treatment to obtain the maximal orthopedic improvement. A special headgear-Herbst appliance was designed and short intensive treatment, lasting 5 months, was performed in the very early mixed dentition. Comparison with an untreated control group revealed the dramatic effects of treatment. The overall average change in the sagittal relationship between the maxillary and mandibular teeth was 7.5 mm after active treatment. The posteriorly directed effect on the maxilla of 3.1 mm was due to a combination of distal movement of the dentoalveolar arch and of posterior translation of the basal portion of the maxilla. The anteriorly directed effect upon the mandible of 4.4 mm was due mostly to anterior movement of the basal part of that bone, with a small part resulting from labial movement of the lower incisors. This appeared to be the result of a stimulation of growth of the mandibular condyles, a change in mandibular morphology, and an anteroinferior change in position of the condyles with a possible anterior translation of the glenoid fossa. After a 10-month posttreatment period during which an activator was used during the initial 6 months, a new comparison between the treated group and the control group was made. Growth continued to the same extent in the treated group as in the control group. However, a tendency toward relapse in overjet of 2.3 mm was observed, leading to some modifications in the treatment approach in recently started cases. A short period of interceptive orthopedic treatment in the very early mixed dentition may be indicated to correct skeletal deviations and establish a normal relationship between the maxilla and the mandible. Treatment could then be followed by a period without appliance wear until final dentoalveolar adjustments, if necessary, are made in the permanent dentition.

Maxillary traction splint: a cephalometric evaluation

Orthodontists are particularly interested in knowing exactly what skeletal and dental changes are produced by headgear. With headgear and fixed appliances, part of the observed change is due to the headgear, part to the fixed appliances, and part to growth. Since the maxillary traction splint moves the teeth en masse, the dentoskeletal changes are due primarily to the headgear force. Selective mandibular dental changes can be produced by adjusting the mandibular occlusal contacts against the splint. In this study forty-seven patients with maxillary dentoalveolar protrusions and Class II, Division 1 malocclusions were treated with orthopedic headgear that attached to a full-coverage maxillary occlusal splint. Fifty-two patients were selected as a control for evaluation of growth changes versus treatment changes. Lateral cephalograms were taken before and after treatment, and the sagittal skeletal and dental changes were evaluated and quantified. The results of the investigation revealed (1) the establishment of a Class I posterior occlusion, (2) a significant overjet reduction, averaging 4.24 mm, (3) inhibition of vertical development of the maxilla and slight intrusion of the maxillary dentition, (4) overbite reduction by leveling of the mandibular dentition, (5) no indication that mandibular growth is accelerated, and (6) no significant increase in the mandibular plane angle. The maxillary traction splint is an effective means of correcting maxillary dentoalveolar protrusion in growing patients prior to fixed appliance therapy. The second phase of treatment with fixed appliances is necessary for individual tooth positioning and for detailing the occlusion.

Orthopedic coordination of dentofacial development in skeletal Class II malocclusion in conjunction with edgewise therapy. Part I

The skeletal Class II malocclusion may be considered to develop as a failure of the coordinating process to maintain harmonious relationships within the developing dentofacial apparatus. If the skeletal elements are too far apart for adaptation to occur and/or if there are functional abnormalities of the orofacial musculature which inhibit coordination from taking place, a malocclusion will result. An orthopedic technique and appliance system has been developed with the intention of improving those factors responsible for the development and perpetuation of the skeletal Class II malocclusion in a primary stage of treatment. This is accomplished by means of restraint and redirection of forward maxillary growth and an increase in the velocity of mandibular growth. Concurrently, adverse soft-tissue influences are eliminated or ameliorated. Edgewise appliance therapy is subsequently carried out for the final correction. The subject is considered in two articles. This first article describes the effects of the restraint of maxillary growth on craniofacial development and the dental changes produced by a maxillary removable splint with extraoral traction and shows how they can be used clinically for correction of the skeletal Class II malocclusion. The experimental and clinical evidence supporting this approach is considered, and case histories show the clinical use of the maxillary splint. This form of maxillary therapy for the skeletal Class II malocclusion has limitations, and it is desirable for it to be incorporated into a comprehensive orthopedic system.

Skeletal changes during the treatment of Class II/I malocclusions

Three groups of Class II/I patients were compared where treatment was carried out using Begg, Andresen and removable appliance techniques. Skeletal growth, as assessed by the dimensions S-Me, N-Me, ALFH and Me-Ar did not show any difference between the groups. All three groups showed an apparent improvement in skeletal pattern during treatment.

The initial effects of orthopedic forces: a study of alterations in the craniofacial complex of a macerated human skull owing to high-pull headgear traction

The initial reaction of components of the craniofacial skeleton of a macerated human skull was studied after high-pull headgear traction. The applied forces were increased step by step from 0.5 N to 3.25 N per side (1N = 100 grams). Laser holography was used for measuring displacements in three dimensions in seventeen indicator points on the skull. These points were located near sutures or on the outer surface of individual bones. The skull was observed from the right frontal and from the left lateral side. Results indicate that displacements range from 0 micrometer to 17.0 micrometers, depending on force magnitude and on the location of the observed point. Individual components of the craniofacial skeleton were mostly displaced in a horizontal backward direction when the skull was viewed from the frontal aspect. Various compression and shearing patterns were observed in the craniofacial sutures, apparently depending on their spatial locations and intersutural surface morphology.

Biomechanical approaches to the study of alterations of facial morphology

An analysis of past experimental and clinical studies on orthopedic changes of craniofacial bones is presented. The theoretical aspects and technical improvements necessary for relating biomechanical principles to attain the desired alterations in craniofacial morphology are discussed. A critical evaluation of the past measurements and histologic techniques is also presented. Suggestions are given for directions to future research methodology which can offer reliable results.

The dentomaxillary complex and overjet correction in Class II, division 1 malocclusion: objectives of skeletal and alveolar remodeling

In recent years it has become apparent that there are limitations to the amount of tooth movement that can be accomplished by alveolar remodeling. Retraction of the maxillary incisor teeth should therefore be avoided during overjet correction if penetration of the palatal alveolar cortex is a probability. Since the Class II, Division 1 phenotype is characterized by abnormalities in both dentoalveolar process and maxillomandibular reactions, trying to compensate for the skeletal discrepancy through alveolar remodeling alone does not have logic on its side. Indeed, treatment philosophies based entirely on a concept of alveolar remodeling cannot be justified on biologic grounds. The most reliable method of avoiding destruction of the palatal alveolar cortex during overjet correction is by means of headgear mechanics designed to produce clinically significant skeletal remodeling. This holds as a general principle, even where extractions are an essential part of the treatment program. Furthermore, because the facial skeleton responds to mechanical deformation more readily in the growing person, the policy adopted by many orthodontists of deferring treatment until the permanent teeth have erupted has little to recommend it.

Distal displacement of the maxilla and the upper first molar

Data from a sample of 198 Class II cases treated with various appliances which deliver distally directed forces to the maxilla were examined to determine the frequency of absolute distal displacement of the upper first molar and of the maxilla. Analysis revealed that such distal displacement is possible and that it is, in fact, a frequent finding following treatment. Long-range stability of distal displacement was not assessed.

The maxillary orthopedic splint

Craniomaxillary orthopedic correction of the skeletal imbalance of Class II malocclusions is often the desired method of treatment in these cases. The ability to apply a "pure" orthopedic force to the maxillary complex has so far eluded research efforts. However, the use of a maxillary splint with a high-pull extraoral traction assembly has been shown to be most effective in reducing Class II skeletal dysplasias through a combination of dentoalveolar and basal bone changes. Force delivery to the maxillary complex in Class II skeletal jaw disharmonies is through the teeth. The philosophy behind the use of the maxillary splint is that if the force delivered to the upper jaw involved the use of all the upper teeth (and hard palate) rather than only the maxillary first molars, as in conventional extraoral orthodontic therapy, the effect on the jaws would be more orthopedic than orthodontic in nature. The advantages of the use of the maxillary splint in the younger patient with a severe Class II malocclusion are that it reduces the vulnerability of the maxillary incisors to accidental fracture, while concomitantly reducing the Class II dysplasia, thereby effectively shortening the later-stage multiband corrective time and procedures. Further advantages of the maxillary splint described are ease of construction and clinical application, which makes it an attractive appliance for use in dental clinics or institutions in which patient volume, infrequent visits, and ecomomic factors are major considerations. This preliminary report on the philosophy of treatment procedure and description of the appliance design is to be followed by a further cephalometric and clinical evaluation of results achieved with its use.

A cephalometric evaluation of high-pull molar headgear and face-bow neck strap therapy

The effects of two different extraoral appliances were evaluated over a 1-year period. Of the thirty-seven cases selected for study, twenty were treated with a face-bow neck strap and seventeen were treated with a high-pull molar headgear. Patients ranged in age from 10.10 to 16.6 years and averaged 13.4 years. The appliances exerted less than 600 Gm. of force per side and were worn for 12 to 16 hours per day. All cases were fully banded, and extraction and nonextraction treatment were included. An analysis of pretreatment data revealed a high degree of selection. Patients selected for high-pull treatment generally exhibited larger anterior face heights, steeper mandibular plane angles, and a greater amount of tooth eruption of the upper first molars than the patients selected for neck strap therapy. A control group of ten untreated subjects was matched to each treatment group to permit assessment of the impact of treatment on growth. Relative to normal growth, treatment with face-bow neck strap traction tended to direct the maxilla and mandible downward and backward. The palatal plane was lowered anteriorly and point A was retracted. The maxillary molars were extruded, and concomitantly an increase in anterior face height and mandibular plane angle was observed. On the other hand, the high-pull molar headgear traction resulted only in increased mandibular molar eruption. However, there was also a nonsignificant tendency for point A to be held back and for lower anterior face height to increase. The comparison of the two treatment samples revealed that the functional occlusal plane was tipped down at the back as the maxillary molars were more extruded in the neck strap sample. In the high-pull sample, the functional occlusal plane was unchanged and the mandibular molars were more extruded than they were in the neck strap group.

The effects of orthodontic treatment on the skeletal pattern

This paper reviews the principal scientific investigations into the effect of orthodontic treatment on the skeletal pattern. Both animal experiments and human studies are considered, covering attempts to move the upper jaw posteriorly by extra-oral forces and to move the mandible anteriorly, by functional appliances, or posteriorly, by use of a chin cap. It is concluded that if such changes occur, they are small in amount and prolong the treatment time unduly.

Innovation in skeletal II treatment including effective incisor root torque in a preliminary removable appliance phase

A new removable appliance design is presented which offers the possibility of significant palatal movement of the maxillary incisor roots and which is capable of producing marked changes in the position of the root apices. Heavy extra-oral forces may be applied through the appliance to the entire maxilla to orthopaedically change the facial growth pattern and ameliorate the Skeletal II problem, with the torquing movements being carried out concurrently.

A second phase of Edgewise treatment, often with directly bonded transparent plastic brackets, is then carried out to complete the correction. This stage is much reduced in complexity and may be confined to alignments and detailing of the occlusion over a relatively short period of time.

The allometric growth of the skull. General mode and prediction of facial growth

Analysis of skull growth in three dimensions indicates that the process is precise and ordered. It can be logarithmically represented as an expansive process taking place in straight lines. This permits prediction of future shape by forward projection of lines derived from at least two records taken at an early age. Although these longitudinal studies have been carried out in animals, the similarity between human and animal cross-sectional material suggests that the mode of growth of the human skull follows the same principles. It should be possible, with the development of more accurate recording techniques suitable for analysis in three dimensions, to project the future shape of the human skull with a substantial degree of accuracy.

Early or late cervical traction therapy of Class II malocclusion in the mixed dentition

It was the purpose of this investigation to evaluate the effect of cervical traction in Class II malocclusions in which treatment was started either early or late in the mixed dentition. Evaluation of the data indicated that the amount and direction of growth were of the greatest importance for effective treatment. Vertical growth appeared to be of particular importance and correlated to the anteroposterior improvement of the relationship between the maxilla and the mandible. Cervical traction, as advocated in this study, was more favorable in the early mixed dentition. A greater amount of growth and a subsequent increased reduction in the ANB angle was recorded during this period. The effect of treatment upon the maxilla, as revealed in posterior movement of the maxillary molar and the pterygomaxillary fissure, was more evident in early treatment. Great individual variability was observed, but in cases in which there was a severe discrepancy in the relationship between the maxilla and the mandible treatment in the early mixed dentition may be essential.