Neuromuscular and skeletal adaptations to altered function in the orofacial region

Activator headgear therapy

A method of treatment is described using an activator and cervical headgear simultaneously to correct malocclusions of the Class II, Division 1 type. The case reports of ten treated patients are used to demonstrate the effects of the application of this technique. Changes in the dentition and facial skeleton were analyzed and the significance of the different responses to the application of the same appliances assessed. The hypothesis proposing that a simultaneous application of both appliances may result in a number of desirable effects greater than that induced by each individual appliance is examined. The hypothetical basis for the application of this technique is partially substantiated by the clinical observations. Within a period of about 1 year, correction of the Class II molar occlusion to a Class I molar occlusion is obtained, with a simultaneous reduction of overbite and overjet. Skeletal changes were found to be variable and related to facial type and the rate of facial growth. Brachyfacial and mesofacial types responded most favorably to treatment. The most favorable effects were observed when there was a large quantitative mandibular growth and brachyfacial or mesofacial growth pattern. In dolichofacial types with a slow mandibular growth rate, mandibular rotation was found to be clockwise; cervical traction appears contraindicated, and a combination of activator with occipital medium to high pull is considered more appropriate.

The effect of Class II elastic forces on craniofacial growth in rats

Full-time Class II elastic forces were applied to eight rats in order to evaluate their effects on the growth of the snout and the mandible. Eight animals served as controls. Lateral cephalograms were taken at the start of the experiment and again at the end, 23 days later. The pre- and post-treatment tracings were superimposed on the cranial base to measure alterations in snout growth, and on metallic implants to measure differences in mandibular growth. As judged by t tests, Class II elastic forces caused a significant antero-posterior growth inhibition both in the snout and in the mandible.

An in-vitro system for studying the effect of variable compressive forces on the mandibular condylar cartilage of the rat

An in-vitro system enabled variable range of continuous and intermittent compressive forces to be applied to the cartilage of 4-day-old rats under serum-free culture conditions. A continuous compressive force below 3 g did not affect the growth of the cartilage; when the force exceeded 3 g, growth ceased. Under an intermittent compressive force up to 8 g, growth continued, but at a lower rate; over 8 g, growth ceased. When growth-restricting compression was removed or reduced, growth was reactivated until a new balance was achieved. The normal architecture of the different zones was altered in the non-compressed in-vitro controls, but not in cultured cartilage during the application of these compressive forces.

Condylar position following mandibular advancement: its relationship to relapse

Forty-one patients who elected to receive a bilateral sagittal osteotomy to advance the mandible were examined clinically and radiographically to assess condylar position preoperatively and at three specific times postoperatively. Parameters designed to measure changes in condylar and distal fragment position were located on tracings and digitized for statistical analysis. Changes in distal fragment position included advancement and clockwise rotation during the surgical interval and significant posterior relapse with continued clockwise rotation during the period of maxillomandibular fixation. A small amount of counterclockwise rotation associated with interocclusal splint removal was seen following fixation release. No significant condylar movement was seen during the surgical interval. During the period of maxillomandibular fixation, both condyles exhibited a significant superior movement, and the left condyle also moved posteriorly. No changes in condylar position were noted following release of fixation. The clinical significance of these condylar movements is not clear. Despite minimal changes, 18 patients, six of whom had had no preoperative symptoms and one of whom had exhibited reciprocal clicking, complained of temporomandibular joint pain or noise postoperatively. This suggests that maintenance of condylar position during surgery may not prevent temporomandibular joint dysfunction. In addition, the observed 37% relapse in surgical advancement in the absence of significant condylar distraction implies the interaction of other factors in the relapse process.

Experimentally induced neuromuscular changes during and after nasal airway obstruction

Neuromuscular changes were studied by electromyography in rhesus monkeys which adapted to nasal obstruction for 2 years and then in the succeeding year recovered to nasal respiration. Obstructing the nasal passage with silicone plugs induced specific behavioral responses which remained for the duration of nasal obstruction and were lost within 8 days after removal of the plugs. Animals demonstrated individual variations, but more than 80% consistently maintained a lower mandibular posture for the entire 2-year period. Rhythmic mandibular, tongue, and upper lip movements were evident in fewer than 60% of the animals. Certain craniofacial and tongue muscles (the genioglossus, dorsal tongue fibers, digastric, geniohyoid, dilator naris, and vertically oriented fibers of the superior orbicularis oris, that is, lip-elevator fibers) were recruited rhythmically and remained rhythmically active throughout the entire 2-year period of nasal obstruction. This rhythmic activity ceased within 1 week after removal of the nose plugs. A tonic or consistent discharge was also induced in the genioglossus, dorsal tongue fibers, the geniohyoid, superior orbicularis oris, and lip-elevator fibers over the entire 2 years of nasal obstruction. Not all muscles lost their tonic discharge after removal of the nasal plugs. The genioglossus, geniohyoid, inferior orbicularis oris, and lip-elevator fibers discharged tonically during the recovery period. These data suggest that nasal obstruction can induce neuromuscular changes which extend beyond the period of obstruction and remain after the original stimulus for neuromuscular change has been removed.

Morphologic response to changes in neuromuscular patterns experimentally induced by altered modes of respiration

The present experiment was designed to test whether specific recordable changes in the neuromuscular system could be associated with specific alterations in soft- and hard-tissue morphology in the craniofacial region. The effect of experimentally induced neuromuscular changes on the craniofacial skeleton and dentition of eight rhesus monkeys was studied. The neuromuscular changes were triggered by complete nasal airway obstruction and the need for an oral airway. Alterations were also triggered 2 years later by removal of the obstruction and the return to nasal breathing. Changes in neuromuscular recruitment patterns resulted in changed function and posture of the mandible, tongue, and upper lip. There was considerable variation among the animals. Statistically significant morphologic effects of the induced changes were documented in several of the measured variables after the 2-year experimental period. The anterior face height increased more in the experimental animals than in the control animals; the occlusal and mandibular plane angles measured to the sella-nasion line increased; and anterior crossbites and malposition of teeth occurred. During the postexperimental period some of these changes were reversed. Alterations in soft-tissue morphology were also observed during both experimental periods. There was considerable variation in morphologic response among the animals. It was concluded that the marked individual variations in skeletal morphology and dentition resulting from the procedures were due to the variation in nature and degree of neuromuscular and soft-tissue adaptations in response to the altered function. The recorded neuromuscular recruitment patterns could not be directly related to specific changes in morphology.

Superimpositional assessment of treatment-associated changes in the temporomandibular joint and the mandibular symphysis

This article analyzes differences in the measured displacement of the condyle and of progonion when different vectors of force are delivered to the maxilla in the course of non-full-banded, Phase 1, mixed-dentition treatment for the correction of Class II malocclusion. The 238-case sample is identical to that for which changes in other parameters of facial form have been reported previously. Relative to superimposition on anterior cranial base and measured in a Frankfort-plane-determined coordinate system, we have attempted to identify and quantitate (1) the displacement of each structure which results from local remodeling and (2) the displacement of each structure which occurs as a secondary consequence of changes in other regions of the skull. We have also attempted to isolate treatment effects from those attributable to spontaneous growth and development. At the condyle, we note that in all three treatment groups and in the control group there is a small but real downward and backward displacement of the glenoid fossa. This change is not treatment induced but, rather, is associated with spontaneous growth and development. (See Fig. 5.) Some interesting differences in pattern of "growth at the condyle" were noted between samples. In the intraoral (modified activator) sample, there were small but statistically significant increases in growth rate as compared to the untreated group of Class II controls. To our surprise, similar statistically significant increases over the growth rate of the control group were noted in the cervical sample. (See Table III, variables 17 and 18.) Small but statistically significant differences between treatments were also noted in the patterns of change at pogonion. As compared to the untreated control group, the rate of total displacement in the modified activator group was significantly greater in the forward direction, while the rate of total displacement in the cervical group was significantly greater in the downward direction. There were no statistically significant differences in the rate of total displacement of pogonion between the high-pull sample and the control sample. (See Table IV, variables 21 and 22.

Orthopedic effects with "conventional" fixed orthodontic appliances: a preliminary report

This retrospective study involved sixty previously treated patients between the ages of 9 and 14 years, all of whom initially had Class II dental malocclusions. The primary purpose of the investigation was to determine whether orthodontic treatment with a specific round-wire edgewise technique (no extraoral forces) was simply producing dentoalveolar manipulations or was actually affecting measurable skeletal or orthopedic alterations in the craniofacial system. The mean linear changes before and after orthodontic treatment in the maxilla (Ar-ANS), mandible (Ar-PGN), and lower facial height (ANS-MN) were statistically compared with an untreated control group (the Burlington Growth Study). The study sample was analyzed selectively according to sex and also according to the angulation of the mandibular base to the anterior cranial base (the SNMP angle). Apparently, from the observations in this study, the particular edgewise technique employed for the orthodontic treatment of the sixty sample patients did statistically affect more than merely dentoalveolar alterations. The normal forward growth of the maxilla appeared to be hindered, the lower facial height was significantly increased (usually without an appreciable increase in the SNMP angle), and the mean increased growth of the mandible was also statistically significant. Admittedly not its primary purpose, this preliminary report appeared to at least indirectly compare, if not the actual treatment modalities, at least the treatment results between a specific fixed orthodontic appliance and certain removable "functional" appliances.

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.

Occlusal variation related to soft diet in a nonhuman primate

Among 43 squirrel monkeys (Saimiri sciureus) raised either on naturally tough or on artificially soft foods, there are significant differences in occlusal features. Animals raised on soft foods show more rotated and displaced teeth, crowded premolars, and absolutely and relatively narrower dental arches. Dietary consistency may be a determinant of occlusal health.

Histologic analysis of temporomandibular joint adaptation to protrusive function in young adult rhesus monkeys (Macaca mulatta)

It is generally believed that the adult temporomandibular joint is incapable of a significant adaptive response to forces produced by functional jaw orthopedics. To evaluate this view, twelve young adult female rhesus monkeys were fitted with functional protrusive appliances for periods ranging from 2 to 24 weeks. Histologic analysis of the temporomandibular joint demonstrated that six of the experimental animals exhibited a tissue response that was qualitatively similar to that noted in juvenile animals. However, the response in young adults was greatly reduced in magnitude from that seen in juveniles and was not related to duration of treatment. It must also be noted that three adult animals developed cross-bites in response to appliance placement, and three animals who functioned anteriorly exhibited little or no detectable condylar response. This study indicates that while some adaptive capability may still be present in the temporomandibular joints of young adults, the potential magnitude of the joint response is limited and highly variable in occurrence.

The mechanism of Class II correction in Herbst appliance treatment. A cephalometric investigation

Sagittal skeletal and dental changes contributing to Class II correction in Herbst appliance treatment were evaluated quantitatively on lateral roentgenograms. The material consisted of forty-two Class II. Division 1 malocclusion cases. Twenty-two of these were treated with the Herbst appliance for 6 months. The other twenty cases served as a control group. The results of the investigation revealed the following: (1) Bite jumping with the Herbst appliance resulted in Class 1 occlusal relationships in all treated cases. (2) The improvement in occlusal relationships was about equally a result of skeletal and dental changes. (3) Class II molar correction averaging 6.7 mm. was mainly a result of a 2.2 mm. increase in mandibular length, a 2.8 mm. distal movement of the maxillary molars, and a 1.0 mm. mesial movement of the mandibular molars. (4) Overjet correction averaging 5.2 mm. was mainly a result of a 2.2 mm. increase in mandibular length and a 1.8 mm. mesial movement of the mandibular incisors. (5) Anterior condylar displacement (0.3 mm.), redirection of maxillary growth (0.4 mm.), and distal movement of the maxillary incisors (0.5 mm.) were of minor importance in the improvement in molar and incisor relationships seen. (6) A direct relationship existed between the amount of bite jumping at the start of treatment and the treatment effects on the occlusion and on mandibular growth. For a maximal treatment response, it is suggested that the Herbst appliance be constructed with the mandible jumped anteriorly as much as possible, namely, to an incisal edge-to-edge position. The clinician should be aware of the dental changes occurring during Herbst appliance treatment and make sure that these changes are not incongruous with his over-all treatment goal.

Postural response of the head to bite opening in adult males

The postural position of the head is a resultant of muscular interactions and reactions, influenced by gravity and functional demands. In order to investigate possible postural adaptation of the head to an altered functional status, a standard degree of jaw opening was produced by mechanical means in the mouths of thirty young males. There was an extension of the head associated with the jaw separation. In the majority of cases, a recovery to approximately the original posture resulted within 1 hour after removal of the bite-opening device.

A technique for the simultaneous measurement of nasal and oral respiration

A technique is developed which for the first time enables the direct and simultaneous measurement of inspired and expired air, both orally and nasally. The apparatus for such measurement consists of a Plexiglas chamber in which the subject's head is enclosed. Attached is a series of valves, flowmeters, differential air pressure transducers, and a physiography for the recording of respiratory activity. The apparatus used in data collection is described. The reliability of the instrument is established. The analysis of the physiographic record is explained and illustrated by data from six trials. The use of this technique to describe respiratory mode is discussed, together with indications for its future use in orthodontics and other research areas.

Morphologic changes in the sagittal dimension using the Fränkel appliance

Interceptive orthodontic treatment of four patients with the Fränkel appliance is presented. The Fränkel appliance is but one of many appliances available using the principle of functional jaw orthopedics. However, the Fränkel appliance seems to offer a broad range of potential corrections and appears worthy of consideration for early treatment by any orthodontist. The cases presented show various combinations of condylar growth, maxillary retraction, and dentoalveolar changes in the correction of Class II, Division I malocclusions with varying degrees of mandibular retrognathia. In all patients facial improvement was noted. Lateral expansion was also noted and offers another possibility in orthodontic treatment. It appears that the Fränkel appliance may be capable of taking advantage of three types of orthopedic correction: condylar growth, maxillary retraction, and lateral expansion. The possibilities of these changes occurring on a routine clinical level are discussed, and further studies of the Fränkel appliance are encouraged. It seems that, regardless of the orthodontist's choice of bands or bonds, the Fränkel appliance could be incorporated into any practice and offer potential orthopedic and/or orthodontic benefits for interceptive orthodontic treatment.

Occlusal dysfunction and stress. An experimental study in macaque monkeys

A dysfunctional occlusal relationship was produced in six macaca irus monkeys by insertion of occlusal splints which raised the vertical dimension of occlusion by 3--4 mm and incorporated interferences into the occlusion. Cortisol levels of plasma and 24 h urine samples were measured by competitive protein-binding analysis. After insertion of the splints there was an immediate, approximately two-fold rise of the mean 24 h urinary cortisol excretion rate and a significant decrease of urinary volume and body weight. The plasma cortisol level did not rise significantly. During the 3 weeks experimental period the teeth showed increasing mobility and occlusal wear facets developed on the splints. Urinary cortisol excretion rates were significantly elevated throughout the experimental period. Urinary cortisol levels declined to basal values when the splints were removed. This animal model produces experimental evidence in support of the hypothesis that a dysfunctional occlusal relationship may result in bruxism associated with emotional stress.

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.

Treatment of class II malocclusions by jumping the bite with the Herbst appliance. A cephalometric investigation

The purpose of this study was to investigate the effect of continuous bite jumping with the Herbst appliance on the occlusion and craniofacial growth. The material consisted of twenty growing boys with Class II, Division 1 malocclusion. Ten of the boys were treated with the Herbst appliance for 6 months. The other ten boys served as a control group. Dental casts, profile roentgenograms, and TMJ radiographs were analyzed before and after 6 months of examination. The following treatment results were found: 1. Normal occlusal conditions occurred in all patients. 2. Maxillary growth may have been inhibited or redirected. The SNA angle was reduced slightly. 3. Mandibular growth was greater than average. The SNB angle increased. 4. Mandibular length increased, probably because of condylar growth stimulation. 5. Lower facial height increased. The mandibular plane angle, however, remained unchanged. 6. The convexity of the soft- and hard-tissue profile was somewhat reduced.

Bioblock therapy

An orthopedic treatment philosophy has been presented. Attention is drawn to the fact that the facial bones of both experimental animals and human beings respond extensively to physiologic and pathologic forces, and it is suggested that these could be mimicked to advantage. A system of appliances designed to achieve this is described. Some case reports which appear to show induced skeletal change are presented, but it will be some time before the real contribution of bioblock therapy can be assessed scientifically. Meanwhile, we should perhaps look more closely at our patients' faces and consider treating them at an earlier age.

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.

Craniofacial adaptations after total maxillary osteotomy in Macaca irus: a cephalometric and histologic study

Five Macaca irus monkeys were used in this study to determine cephalometric and histologic changes after total maxillary impactions. In the three experimental animals, the maxilla was impacted 5 to 7 mm. and lateral cephalograms were taken over a 150-day period. By superimposing on craniofacial implants, osseous and dental changes were measured. Excellent skeletal stability was demonstrated during the postoperative period. Histologically, there was normal osseous healing of the osteotomized maxillas. Accompanying the counterclockwise rotation (overclosure) of the mandible, there was extensive change in the temporomandibular joint. In the experimental monkeys, the fibrous articular covering of the temporal fossa was thin and irregular. The condylar cartilage appeared atrophic and showed considerable aging; also, the articular disc was much thicker in the experimental animals. The study showed the superiorly repositioned total maxillary osteotomy to be a stable procedure after 150 days of postoperative observation. However, further studies are needed to investigate the neuromuscular and adaptive response of temporomandibular articulation and mandibular rest position after maxillary surgical procedures.

Spectral analysis of the electromyogram of the temporal muscle in the rhesus monkey (Macaca mulatta)

Spontaneous EMG activity of one mandibular elevator and postural muscle, the anterior temporalis, was recorded from 20 unanesthetized rhesus monkeys subjected to 4 experimental protocols. The EMG activity was analyzed with a spectral analyzer to determine changes in particular frequency bandwidths after (1) administering a dissociative drug, (2) placing weights on the mandible, (3) detaching the muscle, and (4) adaptation of the muscle to oral respiration. The mean distribution of frequency components indicated that ketamine--HCl increased the power of all frequencies below 400 c/sec, particularly those at 20--40 c/sec. A period of hyperactivity and increased recruitment and discharge of motor units occurred within the first 30 min following administration of the drug. Passive and sustained lowering of the jaw with increased weights indicated that increasing the front incisor distance 2--4 cm significantly decreased the frequency components below 400 c/sec accompanying a decrease in active motor units. Comparison of frequency components of the temporalis EMG before and within 40 days after detachment suggested some subtle variations in the mean distributions predominantly around 200 c/sec but without significant changes. Comparison of the mean spectral distribution between 8 nasal-breathing and 8 oral-breathing monkeys indicated a significant loss of power in the normal dominant frequency range of 20--100 c/sec in the oral respiratory group except for enhancement of the 20 c/sec bandwidth. The results suggest that the anterior temporalis alters its EMG activity during both short (i.e., min, h) and long-term (i.e., months, year) adaptations of the muscle.

Research on control of craniofacial morphogenesis: an NIDR State-of-the-Art Workshop

To assess the wide clinical ramifications of control of craniofacial morphogenesis, a State-of-the-Art Workshop was conducted by the National Institute of Dental Research at the initiative of Richard L. Christiansen, Chief of the Craniofacial Anomalies Program. In conjunction with the authors listed above, the format for the workshop was developed and participants were selected. The workshop was designed to provide an in-depth review of present knowledge and to identify future goals and directions for research on guiding, altering, and thus controlling growth and development of the cranofacial skeleton. The agenda for discussion ranged from molecular biology to clinical arts such as orthopedics and surgery. It was evident during the workshop that the mechanisms and procedures for controlling craniofacial morphogenesis must be derived from many biologic, physical, and clinical fields of knowledge. It is hoped that there will evolve an interdisciplinary clinical art which is aimed at preventing and correcting craniofacial deformities. Substantial biologic information has already been accumulated on the craniofacial skeleton. The clinical art of correcting malocclusion through mechanical forces is now applicable to the entire skull. The outstanding technical accomplishments of radical surgery in the correction of congenital craniofacial anomalies show that the needed surgical skills are now available. When these resources are combined, an area of knowledge and a clinical discipline which might be called "orthocephalics" is already identifiable. The workshop was held at the National Institutes of Health in Bethesda, Maryland, on Feb. 12 and 13, 1974. The ideas exchanged were integrated and summarized by the planning committee to produce this report.

Manibular growth in the rhesus monkey (Macaca mulatta)

Mandibular growth of 42 /1 735) (Macaca mulatta) was analyzed quantitatively and qualitatively. Four groups of animals were defined according to dentitional age (i.e., infant, juvenile, adolescent, young adult). At each age growth was observed fopment, 57 periods of growth were studied. The growth incremental data were collected by superimposing serial cephalograms on mandibular implants. Growth and remodeling of both the skeletal and dento-alveolar components of the rhesus mandible were greatest in the infant monkeys and were less in successive age groups. Posterior relocation of the ramus was noted in all age groups while bone deposition on the anterior and inferior borders of the mandibular body was greatest in the younger animals. The most pronounced dental changes also occurred in the younger animals while the dentitions of the adolescent and adult animals were generally more stable. This study demonstrates that the rate and direction of normal mandibular growth varies with the age of the animal. Furthermore, mandibular growth is quantified at four defined maturational levels to provide a set of values illustrating normal mandibular growth. These values can also be used as control data for experimental studies.