Dentofacial remodelling produced by intermaxillary forces in Macaca mulatta

Revolutionizing Class II Division 1 Malocclusion Treatment With Forsus Appliance: A Clinical Case

Angle's Class II Division 1 malocclusion is illustrated as a prominent maxilla along with protrusive maxillary anteriors, mandibular retrognathism, or both, often leading to functional and aesthetic concerns. Effective management of this condition in growing patients typically involves a combination of functional and orthodontic appliances to correct dental and skeletal discrepancies. Treating this malocclusion in the deceleration stages of growth is often challenging for orthodontists. This case report exemplifies the potency of Forsus appliance in addressing Class II Division 1 malocclusion in growing patients, underscoring its role in achieving favorable orthodontic outcomes.

Dental and Skeletal Effects of Herbst Appliance, Forsus Fatigue Resistance Device, and Class II Elastics-A Systematic Review and Meta-Analysis

Background: Our study aimed to systematically summarize the dentoskeletal effects of Herbst appliance; Forsus fatigue resistance device; and Class II elastics in adolescent Class II malocclusion. Methods: Five databases; unpublished literature; and reference lists were last searched in August 2022. Randomized clinical trials and observational studies of at least 10 Class II growing patients that assessed dentoskeletal effects through cephalometric/CBCT superimpositions were eligible. The included studies quality was assessed with the RoB 2 and ROBINS-I tools. A random-effects model meta-analysis was performed. Heterogeneity was explored with subgroup and sensitivity analyses. Results: Among nine studies (298 patients); two-to-three studies were included in each meta-analysis. Less post-treatment upper incisor retroclination (<2) and no overbite; overjet; SNA; SNB; and lower incisor inclination differences were found between Herbst/Forsus and Class II elastics. No differences in maxilla; condyle; glenoid fossa; and most mandibular changes were found between Herbst and Class II elastics; except for a greater 1.5 mm increase in mandibular length and right mandibular ramus height (1.6 mm) with Herbst. Conclusions: Herbst and Class II elastics corrected the molar relationship; but Herbst moved the lower molars more mesially. Apart from an additional mandibular length increase; no other dental and anteroposterior skeletal difference was found. Forsus was more effective in molar correction; overjet reduction; and upper incisor control than Class II elastics. Trial registration number OSF: 10.17605/OSF.IO/8TK3R.

Evaluation of anteroposterior and vertical stability 25 years after Angle class II division 1 treatment with cervical headgear

PURPOSE

The goal was to investigate long-term (minimum 20 years) skeletal and dental changes in Angle class II division 1 patients treated with full-fixed orthodontic appliances and cervical pull headgear.

METHODS

A longitudinal retrospective study was performed with 20 orthodontic patients, who were treated exclusively by one experienced clinician and whose treatment had been completed a minimum of 20 years ago. Former patients who had been treated from the mid-1970s to the early 1990s were actively sought. After the recall, 20 patients agreed to participate in the study. Lateral cephalometric radiographs at pretreatment (T1), posttreatment (T2), and long-term follow-up (T3) were digitized and measurements were performed. Angular variables used were SNA, SNB, ANB, OcclPl-FH, PalPl-FH, GoMe-FH, 1‑NA, and Y axis. Linear measures were A‑NPerp, Pg-NPerp, 1‑NAmm, Wits, and LAFH.

RESULTS

From T1 to T2, a significant reduction (p < 0.01) in ANB angle from 4.70 to 2.48° and in Wits value from 3.42 to 0.98 mm were observed. It was also noticed a significant increase (p < 0.01) in LAFH from 62.02 to 67.39 mm, probably due to normal facial growth. From T2 to T3, these variables remained stable. No significant changes were observed for any other measure in any of the periods studied.

CONCLUSIONS

In the assessed sample, Angle class II division 1 patients treated with cervical pull headgear presented cephalometric outcome stability of treatment, even after a long-term follow-up of a mean of 25 years postretention.

A Custom Made Skeletal Class II Corrector Appliance in Late Adolescent Phase

Skeletal Class II correction in deceleration phase of growth is both a challenge and dilemma with choice between extraction and myofunctional therapy. With marginal growth remaining the convenient choice is extraction for camouflage of the skeletal discrepancy. On the other hand, the treatment with Fixed Functional Appliances (FFAs) helps in resolution of the problem without sacrificing the dentition. However, the conventional FFAs requires a phase of alignment which results in further loss of time to utilize any remaining growth. The present report proposes the use of a novel custom made functional appliance for Class II skeletal correction which is simple to fabricate and convenient to use.

Class II Non-Extraction Patients Treated with the Forsus Fatigue Resistant Device Versus Intermaxillary Elastics

Objective: To evaluate the Forsus Fatigue Resistant Device (FRD) as a compliance-free alternative to Class II elastics.

Materials and Methods: A sample of 34 (14 female, 20 male) consecutively treated nonextraction FRD patients (12.6 years of age) were matched with a sample of 34 (14 female, 20 male) consecutively treated nonextraction Class II elastics patients (12.2 years of age) based on four pretreatment variables (ANB, L1-GoMe, SN-GoMe, and treatment duration). Pretreatment and posttreatment cephalometric radiographs were traced and analyzed using the pitchfork analysis and a vertical cephalometric analysis. t-Tests were used to evaluate group differences. Group differences were evaluated using t-tests.

Results: No statistically significant differences were found in the treatment changes between the groups. There was a general trend for mesial movement of the maxilla, mandible, and dentition during treatment for both groups. The mandibular skeletal advancement and dental movements were greater than those in the maxilla, which accounted for the Class II correction. Lower incisor proclination was evident in both groups. Vertically, the maxillary and mandibular molars erupted during treatment in both groups, while lower incisors proclined. With the exception of lower molar mesial movements and total molar correction, which were significantly (P &lt; .05) greater in the Forsus group, there were no statistically significant group differences in the treatment changes.

Conclusions: The Forsus FRD is an acceptable substitute for Class II elastics for noncompliant patients.

Remodeling the dentofacial skeleton: the biological basis of orthodontics and dentofacial orthopedics

Orthodontic tooth movement is dependent upon the remodeling of the periodontal ligament and alveolar bone by mechanical means. Facial sutures are also fibrous articulations, and by remodeling these joints, one can alter the positional relationships of the bones of the facial skeleton. As might be expected from the structure and mobility of the temporomandibular joint (TMJ), this articulation is more resistant to mechanical deformation, and whether functional mandibular displacement can alter the growth of the condyle remains controversial. Clinical investigations of the effects of the Andresen activator and its variants on dentofacial growth suggest that the changes are essentially dento-alveolar. However, with the popularity of active functional appliances, such as the Herbst and twin-block based on 'jumping the bite', attention has focused on how they achieve dentofacial change. Animal experimentation enables informed decisions to be made regarding the effects of orthodontic treatment on the facial skeleton at the tissue, cellular, and molecular levels. Both rat and monkey models have been widely used, and the following conclusions can be drawn from such experimentation: (1) Facial sutures readily respond to changes in their mechanical environment; (2) anterior mandibular displacement in rat models does not increase the mitotic activity of cells within the condyle to be of clinical significance, and (3) mandibular displacement in non-human primates initiates remodeling activity within the TMJ and can alter condylar growth direction. This last conclusion may have clinical utility, particularly in an actively growing child.

Passive repositioning of maxillary fractures: An occasional impossibility without osteotomy

PURPOSE

To present cases where passive repositioning of maxillary fractures was not achievable during surgery, and a method to provide passive occlusal positioning in those cases.

PATIENTS AND METHODS

Over a 10-year period, the maxillae of 24 patients with fractures of the maxilla could not be passively repositioned during surgery. In these cases, a Le Fort I osteotomy was performed in addition to reduction and fixation of the other midfacial fractures.

RESULTS

All patients had passive restoration of their pretrauma occlusion during surgery. All patients except 1 had maintenance of their pretrauma occlusion at the last follow-up visit (6 weeks or more) following surgery.

CONCLUSION

When passive positioning of the maxilla is not possible, a concomitant Le Fort I osteotomy can provide passive positioning of the occlusion.

Condyle-fossa modifications and muscle interactions during herbst treatment, part 1. New technological methods

Changes in the condyle, the glenoid fossa, and the muscles of mastication were investigated in subjects undergoing continuous orthopedic advancement of the mandible with a Herbst-block appliance. The total sample consisted of 56 subjects and included 15 nonhuman primates (in the middle mixed, early permanent, and permanent dentitions), 17 human Herbst patients in the early permanent dentition, and 24 human controls from the Burlington Growth Center. The 8 nonhuman primates in the middle mixed dentition were the focus of this study. Mandibular advancement was obtained progressively in 5 animals by adding stops to the telescopic arms of fixed functional Herbst appliances with occlusal coverage; activations of 5.0 mm, 7.0 mm, and 8.0 mm were achieved. Two primates served as controls, and the third was a sham control. Two experimental animals and the 2 controls also wore surgically implanted electromyographic electrodes in the superior and inferior heads of the lateral pterygoid muscles and in the superficial masseter and anterior digastric muscles. Changes in condylar growth direction and amount were assessed with the Björk method from measurements made on serial cephalometric tracings superimposed on metallic implants. Undecalcified sections, treated with intravenous tetracycline vital staining, were viewed with fluorescence microscopy to examine histologic changes in the condyle and the glenoid fossa. New bone formation in the fossa associated with continuous mandibular protrusion was quantified by using computerized histomorphometric analysis of decalcified histological sections and polarized light. The unique combination of permanently implanted electromyographic electrodes, tetracycline vital staining, and histomorphometry represents a significant technological advancement in methods and materials. Together, they demonstrated different muscle-bone interaction results for functional appliances than those reported in previous studies. In Part 1 of this study, we describe and discuss the techniques used in this research and give a brief overview of the findings; in Part 2 (to be published next month), we offer a more in-depth discussion of the results and the implications of our findings.

Osteogenesis in the glenoid fossa in response to mandibular advancement

The purpose of this study was to identify the temporal sequence of cellular changes in the glenoid fossa and to quantify the amount of bone formation in response to mandibular advancement. One hundred 35-day-old female Sprague-Dawley rats were randomly divided into 5 experimental groups (15 rats each) and 5 control groups (5 rats each). In the experimental groups, functional appliances were used to create continuous forward mandibular advancement. The rats were killed after 3, 7, 14, 21, and 30 days. Sections were cut through the glenoid fossa in the parasagittal plane and stained with periodic acid and Schiff's reagent for evaluation of bone formation and with hematoxylin and eosin for observation of cellular response. The results showed that, in the control rats, bone formation was initially higher in the posterior and middle regions than in the anterior region then decreased over time in all regions. In the experimental group, bone formation significantly increased from day 7 to day 30 compared with control rats. Day 21 marked the highest levels of bone formation in the middle (+184%) and posterior regions (+300%). Mandibular protrusion resulted in the osteoprogenitor cells being oriented in the direction of the pull of the posterior fibers of the disc and also resulted in a considerable increase in bone formation in the glenoid fossa.

Improved clinical use of Twin-block and Herbst as a result of radiating viscoelastic tissue forces on the condyle and fossa in treatment and long-term retention: growth relativity

Understanding mechanisms of action for orthopedic appliances is critical for orthodontists who hope to treat and retain the achieved corrections in patients with initial Class II mandibular retrognathism. That knowledge can help orthodontists produce clinically significant bone formation and avoid compression at the condyle-glenoid fossa region. It also assists us to understand the differences between short-term and long-term treatment results. It was previously thought that increased activity in the postural masticatory muscles was the key to promoting condyle-glenoid fossa growth. By analyzing results from several studies, we postulate that growth modification is associated with decreased activity, which leads to our nonmuscular hypothesis. This premise has its foundation on 3 key specific findings: significant glenoid fossa bone formation occurs during treatment that includes mandibular displacement; glenoid fossa modification is a result of the stretch forces of the retrodiskal tissues, capsule, and altered flow of viscous synovium; observations that glenoid fossa bone formation takes place a distance from the soft tissue attachment. The latter observation is explained by transduction or referral of forces. Evidence is presented, therefore, that the 3 trigger switches for glenoid fossa growth can similarly initiate short-term condylar growth modifications because the 2 structures are contiguous. These are displacement, several direct viscoelastic connections, and transduction of forces. Histologic evidence further shows that stretched retrodiskal tissues also insert directly into the condylar head's fibrocartilaginous layer. The impact of the viscoelastic tissues may be highly significant and should be considered along with the standard skeletal, dental, neuromuscular, and age factors that influence condyle-glenoid fossa growth with orthopedic advancement. These biodynamic factors are also capable of reversing effects of treatment on mandibular growth direction, size, and morphology. Relapse occurs as a result of release of the condyle and ensuing compression against the newly proliferated retrodiskal tissues together with the reactivation of muscle activity. To describe condyle-glenoid fossa growth modification, an analogy is made to a light bulb on a dimmer switch. The condyle illuminates in treatment, dims down in the retention period, to near base levels over the long-term.

Temporomandibular joint condyle changes after surgically induced non-reducing disk displacement in rabbits: a macroscopic and microscopic study

Experimentally induced displacement of the temporomandibular joint (TMJ) disk has previously been shown to induce shortening of the mandibular ramus on the ipsilateral side. The aim of this investigation was to reveal whether this shortening develops due to primary influence on condyle growth or by secondary loss of condyle mass due to degenerative tissue breakdown. Disk displacement was created in the right TMJ in seven 3-month-old rabbits, the posterior disk attachment kept intact. Seven rabbits underwent surgical opening of the TMJ without disk intervention. Seven additional animals served as references. After a 3-month experimental period, the animals were sacrificed. Previous analysis revealed shortening of mandibular height and length caused by ipsilateral TMJ disk displacement. The condyles were examined macroscopically and by histologic sectioning or scanning electron microscopy. All condyles were covered with smooth articulating soft tissue and without visible signs of degenerative changes. Four condyles from joints with disk displacement demonstrated substantial regressive remodeling resulting in a change of condyle shape with forward/downward rotation of an enlarged articulating surface. It was concluded that TMJ disk displacement in a growing individual can induce reduction of mandibular height and length before a stage where visible osteoarthrotic changes develop. It implies a primary adverse effect on condyle growth.

Temporomandibular joint remodeling in adolescents and young adults during Herbst treatment: A prospective longitudinal magnetic resonance imaging and cephalometric radiographic investigation

The aim of this prospective study was to analyze and compare the temporomandibular joint adaptive mechanisms in 25 adolescent and 14 young adult Class II malocclusions treated with the Herbst appliance. Temporomandibular joint remodeling was analyzed by magnetic resonance imaging. In each subject, 4 magnetic resonance images of both temporomandibular joints were available: before treatment, at the start of treatment (when the Herbst appliance was placed), during treatment (6 to 12 weeks after appliance placement), and after treatment (when the appliance was removed). Furthermore, effective temporomandibular joint changes (the sum of condylar remodeling, fossa remodeling, and condyle-fossa relationship changes) were analyzed with the aid of lateral cephalometric radiographs from before and after treatment. All subjects were treated to Class I or overcorrected Class I dental arch relationships, and their mandibles became significantly (P <.001) more prognathic. After 6 to 12 weeks of Herbst treatment, signs of condylar remodeling were seen at the posterosuperior border in 48 of the 50 adolescent condyles and in 26 of the 28 young adult condyles. Bilateral remodeling of the mandibular ramus could be detected in 1 adolescent and 2 young adult patients. Signs of glenoid fossa remodeling at the anterior surface of the postglenoid spine were noted in 36 adolescent and 22 young adult temporomandibular joints. Effective temporomandibular joint changes during treatment were more horizontally directed and larger in both adolescents and young adult patients treated with the Herbst appliance than in an untreated group of subjects with ideal occlusion (Bolton standards). The increase in mandibular prognathism accomplished by Herbst therapy in both adolescents and young adults seems, in particular, to be a result of condylar and glenoid fossa remodeling. Because the Herbst appliance is most successful in Class II patients also at the end of the growth period, the treatment method could be an alternative to orthognathic surgery in borderline skeletal Class II cases. Magnetic resonance imaging renders an excellent opportunity to visualize the temporomandibular joint remodeling growth processes.

Differences in biologic response of the mandibular condyle to forward traction or opening of the mandible. An experimental study in the rat

The effect of different mandibular postures on the growth of the mandible was studied. A total of 60 female Wistar rats were divided into 3 groups, and all the animals were anesthetized for 6 h daily from the age of 30 days onwards. The first group served as controls. The second had the mandible maintained in a protracted position, and the third had the mandible in an open position during the anesthesia. Macroscopic measurements showed the growth of the mandibular condyle to be increased in a posteroinferior direction and also in a superior direction in the animals with the mandible in an open position. The cartilage layer containing collagen type II was significantly thinned, whereas cell proliferation had significantly increased in the posterosuperior region. In association with mandibular protrusion the thickness of the cell layer containing collagen type II had increased, and cell proliferation in the posterosuperior region had significantly decreased. Significant differences in the growth of the condylar process were observed histologically and histochemically between the experimental animals, implying that the most rewarding aspect of the regulation of condylar growth seems to be the possibility to regulate the maturation rate of the cartilage cells.

Molecular biology of temporomandibular joint disorders: proposed mechanisms of disease

PURPOSE

The biologic processes of temporomandibular joint adaptation and disease are poorly understood. However, recent technologic advances have provided methods that allow sophisticated studies of the molecular mechanisms that are relevant to the pathophysiology of degenerative temporomandibular joint diseases. This review examines current models of the molecular events that may underlie both adaptive and pathologic responses of the articular tissues of the temporomandibular joint to mechanical stress. It is hoped that an increased understanding of these complex biologic processes will lead to improved diagnostic and therapeutic approaches directed to the management of temporomandibular disorders.

Long-term stability of Angle Class II, division 1 malocclusions with successful occlusal results at end of active treatment

The purpose of this study was to examine long-term stability of Angle Class II, Division 1 malocclusions with successful occlusal results at the end of active appliance therapy, search for predictors of relapse, and look for characteristics associated with successful treatment. Records taken before and after treatment and a mean of 14.0 years postretention of adolescent patients treated for a significant Angle Class II, Division 1 malocclusion both with and without tooth extraction were evaluated. The sample was limited to successfully treated cases as judged by subjective evaluation of intercuspation and incisor occlusion of posttreatment study models and included 78 patients. Cephalometric characteristics or postretention occlusion was not considered in sample selection. The mode response was no change postretention for molar, premolar, and canine relationships and relapse of 0.5 mm for overjet and overbite. Maximum relapse was 3.5 mm for molar, premolar, and canine relationship, 3 mm for overjet, and 4.5 mm for overbite. Stepwise backward multiple regression analyses revealed no associations between either pretreatment characteristics or skeletal and dental treatment changes and relapse of overjet. However, relapse of overjet was associated with relapse of molar, premolar, and canine relationships, postretention increase in overbite, postretention proclination of maxillary incisors, and postretention retroclination of mandibular incisors. Active treatment changes included redirection or inhibition of maxillary growth and retraction of maxillary incisors. Mandibular incremental growth was favorable both during and after treatment. It was concluded that successful correction of Angle Class II, Division 1 malocclusions through differential growth adaptation and tooth movement appears to be very stable.

Connective tissue forces from mandibular advancement

PURPOSE

To quantify the connective tissue forces generated during surgical lengthening of the mandible.

PATIENTS AND METHODS

Sixty-three patients who had mandibular advancements by sagittal ramus osteotomy were used in this study. Prior to sectioning the rami, the overjet was recorded. After sectioning the rami, a spring-gauge was attached to the mandibular orthodontic wire and pulled anteriorly to determine how much force was necessary to bring the mandibular incisors into a Class I relationship with the maxillary incisors. Aggressive stripping of the perimandibular periosteum and connective tissues on the distal segment was then performed. The amount of force was again recorded.

RESULTS

The mean preoperative overjet in the 63 patients was 6 mm (range, 3 to 11 mm). The mean amount of force required to advance the mandible prior to stripping the tissues was 1,498 g compared with a mean of 787 g after stripping (P < .001). There were statistically significant correlations between the preoperative overjet and the prestripping and poststripping force levels (P < .001). There was also a significant relationship between prestripping and poststripping values (P < .001).

CONCLUSION

The results of this study indicate that orthopedic forces are generated by the perimandibular connective tissues following advancement by the mandible. The effect of these forces on the temporomandibular joint should be evaluated in future studies.

Reaction of the pterygomaxillary fissure and the condylar cartilage to intermaxillary Class III magnetic mechanics

The skeletal reaction to Class III intermaxillary magnetic mechanics was previously found to affect two target areas, the pterygomaxillary fissure (PMF) and the condylar cartilage. The objectives of this study were to analyze, radiographically and histologically, the response of these tissues to Class III intermaxillary functional orthopedic magnetic appliance (FOMA III), and to postulate possible models of their dichotomous biomechanism. Nine Macaca fascicularis monkeys received periodic administration of vital bone procion dye and were treated for 4 months with FOMA III (6 subjects) and sham appliance (3 subjects). The PMF (the target area of the midfacial complex) demonstrated a decreased skeletal reaction in inferosuperior and lateromedial directions. Cephalometrically, the lowermost PMF point was displaced inferiorly 1.98 +/- 1.74 mm and 0.42 +/- 0.38 mm and anteriorly 1.42 +/- 0.96 mm and 0.58 +/- 0.38 mm in the treated and control groups, respectively. The displacement of the uppermost PMF point, compared with the lowermost point, was three to five times lower. Histologically, two modes of response were found; first, a sutural response (disarticulation and osteogenesis) of the palatomaxillary and pterygopalatine sutures, which was distinctive of the lateral PMF aspect, and second, a dentosutural response, which was characteristic of the medial PMF aspect (bony microfractures between the third molar germ and the maxillary tuberosity in conjunction with mild sutural response). In the mandible, a discrepancy was found between the histologic and the cephalometric findings. Radiographically, mandibular length was unaffected after 4 months of treatment, and the distance condylion-pogonion was equally increased in the treated (0.75 +/- 0.78 mm) and the control animals (0.77 +/- 0.32 mm). Histologically, however, the condylar cartilage demonstrated increased osteoclastic activity at the zone of endochondral ossification and a decreased apposition rate at the adjacent bony trabeculae. Conceivably, the two target areas (PMF sutures versus condylar cartilage) demonstrate two diverse time-related responses that are either unrelated or interrelated to each other. An unrelated tissue response suggests that tissue stimulation (sutural) is always superior to tissue suppression (condylar). Another possible unrelated tissue reaction implies diverse response velocity (high sutural, low condylar). An interrelated mechanism suggests that an applied force will dissipate initially at the less resistant target area (sutures), and will subsequently affect the more resistant target area (condyle) once the sutural resistance exceeds a certain threshold. The fact that no pathologic change was found in the condylar cartilage encourages a long-term use of the FOMA III appliance, initiating treatment at an early skeletal age.

The effects of induced dental malocclusion on the fibrocartilage disc of the adult rabbit temporomandibular joint

Unilateral cast occlusal splints were fitted to the mandibular posterior teeth of adult rabbits, for periods of 1-28 days. The reactivity of the mandibular disc was examined by the effect on cell proliferation across the anterior, intermediate and posterior discal bands, as measured by metaphase arrest using vincristine sulphate. The effect on the disc was to activate cell proliferation on the splinted side. Intensity of response varied according to the length of time after fitting the splint, and the site involved. The findings suggested that the adult mandibular disc may participate in compensatory change at a cellular level and thus respond to changing functional loads placed upon the adult temporomandibular joints.

Temporomandibular joint adaptation following inferior repositioning of the maxilla in adult monkeys

Treatment of adults with vertical maxillary deficiency (short faces) has continually been an intriguing challenge for surgeons and orthodontists. For this category of patients, the introduction of simultaneous bone grafting and Le Fort I osteotomy has opened the door for improved treatment. However, despite the improved surgical techniques, surgeons have been reluctant to increase the vertical dimension of the maxilla by Le Fort I osteotomy with interpositional bone grafts because of inconsistent and variable stability after surgery. This study examines structural and functional adaptation of the adult temporomandibular joint and stability in a primate model following surgical lengthening of the maxilla in the vertical dimension. Results suggest that maxillary surgery and autorotation can alter condylar stress within physiologic ranges. However, further studies are indicated to clarify the surgery's long-term effect.

Histologic examination of the temporomandibular joint after mandibular advancement with and without rigid fixation: an experimental investigation in adult Macaca mulatta

This study evaluated the histologic response of the temporomandibular joint (TMJ) following mandibular advancement using rigid and nonrigid fixation in monkeys. Twelve adult female rhesus monkeys underwent sagittal ramus osteotomies with advancement. Six of them were placed into maxillomandibular fixation (MMF); six underwent bicortical bone-screw fixation without MMF. Changes in condylar position were quantified using lateral cephalograms with the aid of bone markers. The animals were killed at 6 weeks and the TMJs were prepared for histologic analysis. Three measures of condylar cartilage thickness were obtained for each animal and were correlated to changes in position of the condyle. Animals who underwent MMF showed a tendency for anterior movement of the condyles; animals who underwent rigid fixation showed a tendency for posterior condylar position. Thicker cartilage layers were found in the MMF animals. Animals who had posterior displacement of the condyles showed evidence of resorption of the posterior surface of the condyle and anterior surface of the postglenoid spine. There was a significant correlation between a change in the horizontal position of the condyle and the thickness of the posterior aspect of the condylar cartilage. The results of this study indicate that alterations in condylar position may induce remodeling changes within the TMJ.

Functional orthopedic magnetic appliance (FOMA) III--modus operandi

An intraoral intermaxillary appliance has been developed for the treatment of Class III malocclusions that exhibit midface sagittal deficiency with or without mandibular excess. The functional orthopedic magnetic appliance (FOMA) III consists of upper and lower acrylic plates with a permanent magnet incorporated into each plate. The upper magnet is linked to a retraction screw. The upper magnet is retracted periodically (e.g., monthly) to stimulate maxillary advancement and mandibular retardation. The attractive mode neodymium magnets used in this study produced a horizontal force of 98 gm and a vertical force of 371 gm. Six female Macaca fascicularis monkeys were treated with FOMA IIIs. An additional three animals were treated with sham appliances. After 4 months of treatment, the following results were found: the growth pattern of the cranial base (saddle angle) was not altered; midfacial protraction did occur along a recumbent hyperbolic curve with a horizontal maxillary displacement and an anterosuperior premaxillary rotation; the cumulative protraction of the maxillary complex was initiated at the pterygomaxillary fissure with an additional contribution provided by other circummaxillary sutures (zygomaticomaxillary s., transverse s., premaxillary s.); and inhibition of mandibular length was minimal, but a tendency toward a vertical condylar growth pattern was observed. The interaction between sutural and condylar growth sites appeared biphasic, characterized by an immediate and rapid excitation of the circummaxillary sutures followed by a delayed and slow suppression of the condylar cartilage. Long-term animal and clinical FOMA III studies are recommended.

Biochemical and autoradiographical evidence that anterior mandibular displacement in the young growing rat does not stimulate cell proliferation or matrix formation at the mandibular condyle

A removable bite plate was used to induce forward mandibular displacement in four-week-old rats for 10 h/day for 1, 3, 7, 11 and 14 days. The animals were killed and the condylar explants pulsed in vitro for 6 h with either [3H]-thymidine or [3H]-proline or 35SO(2-)4. The specific activity of radio-isotope incorporation was expressed as dis/min per microgram DNA, dis/min per mg protein and dis/min per microgram sulphated glycosaminoglycans (GAG). [3H]-thymidine autoradiography was also used in a 14-day experiment to establish a radioactive index (labelled cells per 1000 cells counted) for the anterior, middle and posterior regions of the condyle. There was no significant alteration in either cell proliferation (dis/min per microgram DNA and radioactive index) or matrix formation (dis/min per mg protein and dis/min per microgram GAG) at any point in the time scale.

The influence of functional appliance therapy on glenoid fossa remodeling

This study investigates the remodeling changes in the condyle and glenoid fossa following a period of progressively activated and continuously maintained mandibular advancement using the Herbst appliance. Progressive mandibular advancement was achieved by adding stops to the telescopic arms of the appliance, with the total activation reaching 7.0 to 10.0 mm, dependent upon the length of the treatment phase. This mandibular advancement produced extensive remodeling and anterior relocation of the glenoid fossa, which contributed to anterior mandibular positioning and altered jaw relationships.

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 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.

The use of in vitro models for investigating the response of fibrous joints to tensile mechanical stress

To clarify the role of mechanical deformation in the remodeling of fibrous joints, organ culture systems have been developed to apply mechanical stress to cranial sutures under controlled experimental conditions. Tensile mechanical stress applied to cranial sutures from newborn rabbits produces a two- to threefold increase in protein synthesis and a twofold increase in collagen synthesis that can be detected within 6 hours. There is also a threefold increase in the DNA content of the sutures after 48 hours. Under normal conditions sutural fibroblasts synthesize type I collagen but respond to tensile deformation by synthesizing significant amounts of type III collagen. This suggests that the biomechanical environment of a connective tissue cell is an important determinant of the collagen type synthesized. However, the effect is likely to be an indirect one by virtue of its influence on the metabolic activity of the cells. Mechanically activated cells do not preferentially synthesize structural proteins, since mechanical stress stimulates the synthesis not only of structural macromolecules but also of the enzymes responsible for their specific hydrolysis. This is not accompanied by increased degradation, however, perhaps because the metalloproteinase inhibitor TIMP synthesized by the tissues is also increased. Confluent rabbit and mouse periosteal fibroblasts synthesize and release into the culture medium factors that can inhibit bone cell proliferation and stimulate bone resorption in vitro. It seems likely that further investigation of the interaction between fibroblasts and osteoblasts at the bone--fibrous tissue interface will require a reassessment of current thinking concerning the mechanisms regulating sutural osteogenesis.

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.

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 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.

Experimental and postexperimental response to anteriorly directed extraoral force in young Macaca nemestrina

An anteriorly directed extraoral force was applied to the maxillas of four healthy young M. nemestrina monkeys. Experimental, retention, and postretention alterations were evaluated through a combination of cephalometric, histologic, and gross techniques. In view of the results of the present study, the following conclusions can be made: 1. Skeletal remodeling occurs in all circummaxillary sutures following the application of an anteriorly directed extraoral force to the maxilla. The amount of remodeling appears to be proportional to a suture's distance from and orientation to the applied force system. 2. The maxillary complex exhibited a marked anterior positioning with a small amount of counterclockwise rotation during the experimental period. 3. The application of an extraoral force to the maxilia produces compensatory deposition and resorption of bone, not only at the sutural margins but also at the external surface of the bones themselves. 4. It is possible that the experimental appliance transmits its effect to the facial bones adjacent to the maxilla through an alteration in the skull's periosteal envelope. 5. A substantial reorientation of the maxillary complex occurs following the termination of active force, and the degree of relapse or reorientation is directly proportional to the length of stabilization. 6. The dentition, through the periodontal ligament, undergoes approximately four times as much relapse as do the facial bones through their sutural articulations, following a minimal period of stabilization. 7. Extraoral forces applied to the craniofacial complex are transmitted through the maxilla and related midfacial bones, resulting in changes in such deep cranial structures as the cartilaginous synchondroses of the sphenoid bone. 8. Anterior displacement of the maxilla by extraoral traction appears to have a minimal effect on the mandible and the temporomandibular joint. 9. The number of sinusoidal vessels in the sutural ligament tends to increase in those sutures subjected to a tensional force.

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.

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.

Late results of activator-treatment: a cephalometric study

The purpose of this study was to analyse cephalometrically the long-term effect of Activator treatment on the dentofacial skeleton in 50 consecutively treated cases of postnormal and prenormal occlusion. Comparisons of dentofacial form between successful and unsuccessful cases were performed. The results of the study showed that the sagittal relationship between the jaws became normal in postnormal and prenormal cases during Activator treatment. The effect was achieved mainly by reciprocal dentoalveolar changes of the maxilla and mandible supported by a retardation of the forward growth of the maxilla in Class II cases and a stimulation of the forward growth of the maxilla in Class III cases. The normal downward-forward growth of the mandible appeared unaffected. The effect of Activator treatment on the vertical growth of the jaws was a significant increase in lower face height (bite-raising). No tendency to induce a harmful posterior growth rotation of the mandible was noted. Before treatment there was no highly significant difference in the morphology of the dentofacial skeleton between successfully and unsuccessfully treated Activator cases, except for the basal relationship between the jaws (ss-n-sm) which was larger in the successful cases. It would rather appear that good cooperation, high growth intensity and a favourable growth pattern of the patient together with a well constructed appliance is of decisive importance for a successful result of treatment.