Growth and growth pressure of mandibular condylar and some primary cartilages of the rat in vitro

A theoretical analysis of longitudinal temporomandibular joint compressive stresses and mandibular growth

OBJECTIVES

To determine if temporomandibular joint (TMJ) compressive stresses during incisor biting (1) differed between growing children over time, and (2) were correlated with Frankfort Horizontal-mandibular plane angle (FHMPA, °) and ramus length (Condylion-Gonion (Co-Go), mm).

MATERIALS AND METHODS

Three-dimensional anatomical geometries, FHMPA and Co-Go, were measured longitudinally from lateral and posteroanterior cephalographs1 of children aged 6 (T1), 12 (T2), and 18 (T3) years. Geometries were used in numerical models to estimate subject-specific TMJ eminence shape and forces for incisor bite-forces of 3, 5, and 8 Newtons at T1, T2, and T3, respectively. TMJ compressive stresses were estimated via two steps: First, TMJ force divided by age-dependent mandibular condylar dimensions, and second, modified by loading surfaces' congruency. Analysis of variance and Tukey honest significant difference post-hoc tests, plus repeated measures and mixed effects model analyses were used to evaluate differences in variables between facial groups. Regression analyses tested for correlation between age-dependent compressive stresses, FHMPA, and Co-Go.

RESULTS

Sixty-five of 842 potential subjects had T1-T3 cephalographs and were grouped by FHMPA at T3. Dolichofacial (FHMPA ≥ 27°, n = 36) compared to meso-brachyfacial (FHMPA< 27°, n = 29) subjects had significantly larger FHMPA at T1-T3, shorter Co-Go at T2 and T3 (all P < .01), and larger increases in TMJ compressive stresses with age (P < .0001). Higher compressive stresses were correlated with larger FHMPA (all R2 ≥ 0.41) and shorter Co-Go (all R2 ≥ 0.49).

CONCLUSIONS

Estimated TMJ compressive stress increases from ages 6 to 18 years were significantly larger in dolichofacial compared to meso-brachyfacial subjects and correlated to FHMPA and Co-Go.

Mechanobehavior and Ontogenesis of the Temporomandibular Joint

Craniofacial secondary cartilages of the mandibular condyle and temporomandibular joint (TMJ) eminence grow in response to the local mechanical environment. The intervening TMJ disc distributes normal loads over the cartilage surfaces and provides lubrication. A better understanding of the mechanical environment and its effects on growth, development, and degeneration of the TMJ may improve treatments aimed at modifying jaw growth and preventing or reversing degenerative joint disease (DJD). This review highlights data recorded in human subjects and from computer modeling that elucidate the role of mechanics in TMJ ontogeny. Presented data provide an approximation of the age-related changes in jaw-loading behaviors and TMJ contact mechanics. The cells of the mandibular condyle, eminence, and disc respond to the mechanical environment associated with behaviors and ultimately determine the TMJ components' mature morphologies and susceptibility to precocious development of DJD compared to postcranial joints. The TMJ disc may be especially prone to degenerative change due to its avascularity and steep oxygen and glucose gradients consequent to high cell density and rate of nutrient consumption, as well as low solute diffusivities. The combined effects of strain-related hypoxia and limited glucose concentrations dramatically affect synthesis of the extracellular matrix (ECM), which limit repair capabilities. Magnitude and frequency of jaw loading influence this localized in situ environment, including stem and fibrocartilage cell chemistry, as well as the rate of ECM mechanical fatigue. Key in vivo measurements to characterize the mechanical environment include the concentration of work input to articulating tissues, known as energy density, and the percentage of time that muscles are used to load the jaws out of a total recording time, known as duty factor. Combining these measurements into a mechanobehavioral score and linking these to results of computer models of strain-regulated biochemical events may elucidate the mechanisms responsible for growth, maintenance, and deterioration of TMJ tissues.

Mechanobehaviour in dolichofacial and brachyfacial adolescents

OBJECTIVES

To test whether mechanobehaviour (temporomandibular joint (TMJ) loads, jaw muscle use) was different between facial types and correlated with ramus height (Condylion-Gonion, mm).

SETTING AND SAMPLE POPULATION

University of Missouri-Kansas City (UMKC) Orthodontic Clinic. Ten dolichofacial and ten brachyfacial adolescents (Sella-Nasion-Gonion-Gnathion (SN-GoGn) angles ≥37° and ≤27°, respectively) consented to participate.

MATERIALS AND METHODS

Numerical models calculated TMJ loads for a range of static biting based on subjects' three-dimensional anatomy. Subjects were trained to record jaw muscle electromyography (EMG) over 2 days and 2 nights in their natural environments. Laboratory EMG/bite-force calibrations determined subject-specific EMG for 20 N bite-force (T_20Nave ). Jaw muscle use via duty factors (DF=muscle activity duration/total recording time, %) was determined from day and night recordings for muscle-specific thresholds from ≥5% to ≥80%T_20Nave . ANOVA and Tukey's HSD post hoc tests assessed for group differences in mechanobehaviour (TMJ loads, DFs). Regression modelling correlated subjects' normalized TMJ loads, DFs and ramus height.

RESULTS

Dolichofacial compared to brachyfacial subjects produced significantly higher (P<.05) TMJ loads, where ipsilateral loads were ≥20% larger for some biting angles, but had significantly less (all P<.05) masseter (day, night) and temporalis (night) DFs. Regression analysis showed a significant relationship amongst normalized TMJ loads, masseter DF and ramus height (R² =.49).

CONCLUSIONS

Mechanobehaviour showed significant differences between facial types and was correlated with ramus height.

Adolescent internal condylar resorption (AICR) of the temporomandibular joint, part 1: A review for diagnosis and treatment considerations

BACKGROUND

Adolescent internal condylar resorption (AICR) is a temporomandibular joint (TMJ) pathology that develops predominately in teenage females during pubertal growth (onset between ages 11 and 15 years), with a distinct clinical, radiographic, and magnetic resonance imaging (MRI) presentation. Clinical and imaging presentation: The condition usually occurs bilaterally with: (1) Progressive retrusion of the mandible; (2) High occlusal plane angle facial morphology; (3) Worsening Class II occlusion; and (4) TMJ symptoms such as pain, headaches, noises, etc. MRI imaging demonstrates decreased condylar head size and anterior disc displacement. Treatment protocol: AICR can be successfully treated when the condyles and discs are salvageable with the following surgical protocol: (1) Removal of bilaminar tissue surrounding the condyle; (2) Reposition the disc with the Mitek anchor technique; and (3) Orthognathic surgery to advance the maxillo-mandibular complex in a counterclockwise direction.

CONCLUSION

AICR can be successfully treated using the specific protocol presented herein to provide stable and predictable outcomes.

Asporin stably expressed in the surface layer of mandibular condylar cartilage and augmented in the deeper layer with age

Mandibular condylar cartilage (MCC) exhibits dual roles both articular cartilage and growth center. Of many growth factors, TGF-β has been implicated in the growth of articular cartilage including MCC. Recently, Asporin, decoy to TGF-β, was discovered and it blocks TGF-β signaling. Asporin is expressed in a variety of tissues including osteoarthritic articular cartilage, though there was no report of Asporin expression in MCC. In the present study, we investigated the temporal and spatial expression of Asporin in MCC.

Gene expression profile of MCC and epiphyseal cartilage in tibia of 5 weeks old ICR mice were firstly compared with microarray analysis using the laser capture microdissected samples. Variance of gene expression was further confirmed by real-time RT-PCR and immunohistochemical staining at 1,3,10, and 20 weeks old. TGF-β and its signaling molecule, phosphorylated Smad-2/3 (p-Smad2/3), were also examined by immunohistochemical staining.

Microarray analysis revealed that Asporin was highly expressed in MCC. Real-time RT-PCR analysis confirmed that the fibrous layer of MCC exhibited stable higher Asporin expression at any time points as compared to epiphyseal cartilage. This was also observed in immunohistochemical staining. Deeper layer in MCC augmented Asporin expression with age. Whereas, TGF-β was stably highly observed in the layer. The fibrous layer of MCC exhibited weak staining of p-Smad2/3, though the proliferating layer of MCC was strongly stained as compared to epiphyseal cartilage of tibia at early time point. Consistent with the increase of Asporin expression in the deeper layer of MCC, the intensity of p-Smad-2/3 staining was decreased with age.

In conclusion, we discovered that Asporin was stably expressed at the fibrous layer of MCC, which makes it possible to manage both articular cartilage and growth center at the same time.

•

Asporin gene and protein were highly expressed in mandibular condylar cartilage as compared to tibial epiphyseal cartilage.

•

Asporin in mandibular condylar cartilage was augmented with age.

•

TGF-β signaling is suppressed by augmented Asporin and decreased TGF-β production in mandibular condylar cartilage.

Sex hormones receptors play a crucial role in the control of femoral and mandibular growth in newborn mice

Sex hormones are important for bone growth. However, the mechanism by which sex hormone receptors influence bone growth remains unclear. In orthodontic treatment, there is a need to develop an indicator of bone maturity to accurately predict the beginning and end of growth. This indicator might be developed from the screening of sex hormones. The purpose of this study was to investigate the role of each sex hormone receptor on bone growth in newborn mice. Five-day-old C57BL/6J mice were used in this experiment. Forty mice underwent an orchiectomy (ORX), ovariectomy (OVX), or sham surgery. One week after surgery, the femur and the mandible were resected for immunohistochemical staining. Alternatively, 80 mice were daily injected with antagonist against receptors oestrogen alpha (ERα), beta (ERβ), or androgen receptor (AR). One week after the first injection, radiographs of the femur and mandible were taken and then measured. Analysis of variance and pairwise comparisons (Fisher) were performed to examine the differences in values measured among the groups In the sham-operated male and female mice, ERβ was found to be more prominent than ERα and AR during all experimental periods. In the ORX and OVX groups, the expressions of all receptors were significantly reduced in comparison with the sham-operated control group throughout the experiment. Moreover, femur and mandibular growth were significantly affected in the group injected with ERβ antagonist. The deficiency of any sex hormone leads to reduced bone growth. In particular, a disturbance in ERβ produces a greater aberrance in both male and female mice immediately after birth.

Development of the mandibular condylar cartilage in human specimens of 10-15 weeks' gestation

This study analyses some morphological and histological aspects that could have a role in the development of the condylar cartilage (CC). The specimens used were serial sections from 49 human fetuses aged 10-15 weeks. In addition, 3D reconstructions of the mandibular ramus and the CC were made from four specimens. During weeks 10-11 of development, the vascular canals (VC) appear in the CC and the intramembranous ossification process begins. At the same time, in the medial region of the CC, chondroclasts appear adjacent to the vascular invasion and to the cartilage destruction. During weeks 12-13 of development, the deepest portion of the posterolateral vascular canal is completely surrounded by the hypertrophic chondrocytes. The latter emerge with an irregular layout. During week 15 of development, the endochondral ossification of the CC begins. Our results suggest that the situation of the chondroclasts, the posterolateral vascular canal and the irregular arrangement of the hypertrophic chondrocytes may play a notable role in the development of the CC.

Regulation of immature cartilage growth by IGF-I, TGF-beta1, BMP-7, and PDGF-AB: role of metabolic balance between fixed charge and collagen network

Cartilage growth may involve alterations in the balance between the swelling tendency of proteoglycans and the restraining function of the collagen network. Growth factors, including IGF-I, TGF-beta1, BMP-7, and PDGF-AB, regulate chondrocyte metabolism and, consequently, may regulate cartilage growth. Immature bovine articular cartilage explants from the superficial and middle zones were incubated for 13 days in basal medium or medium supplemented with serum, IGF-I, TGF-beta1, BMP-7, or PDGF-AB. Variations in tissue size, accumulation of proteoglycan and collagen, and tensile properties were assessed. The inclusion of serum, IGF-I, or BMP-7 resulted in expansive tissue growth, stimulation of proteoglycan deposition but not of collagen, and a diminution of tensile integrity. The regulation of cartilage metabolism by TGF-beta1 resulted in tissue homeostasis, with maintenance of size, composition, and function. Incubation in basal medium or with PDGF-AB resulted in small volumetric and compositional changes, but a marked decrease in tensile integrity. These results demonstrate that the phenotype of cartilage growth, and the associated balance between proteoglycan content and integrity of the collagen network, is regulated differentially by certain growth factors.

Biomechanical response of condylar cartilage-on-bone to dynamic shear

Shear stress can result in fatigue, damage, and irreversible deformation of the mandibular condylar cartilage. However, little information is available on its dynamic properties in shear. We tested the hypothesis that the dynamic shear properties of the condylar cartilage depend on the frequency and amplitude of shear strain. Ten porcine mandibular condyles were used for dynamic shear tests. Two cartilage-bone plugs were dissected from each condyle and tested in a simple shear sandwich configuration under a compressive strain of 10%. Sinusoidal shear strain was applied with an amplitude of 1.0, 2.0, and 3.0% and a frequency range between 0.01 and 10 Hz. The magnitudes of the shear dynamic moduli were found to be dependent on the frequency and the shear strain amplitude. They increased with shear strain. tan delta ranged from 0.2 to 0.4, which means that the cartilage is primarily elastic in nature and has a small but not negligible viscosity. In conclusion, the present results show that the shear behavior of the mandibular condylar cartilage is dependent on the frequency and amplitude of the applied shear strain. The observed shear characteristics suggest a significant role of shear strain on the interstitial fluid flow within the cartilage.

The effect of mode of breathing on craniofacial growth--revisited

It has been maintained that because of large adenoids, nasal breathing is obstructed leading to mouth breathing and an 'adenoid face', characterized by an incompetent lip seal, a narrow upper dental arch, increased anterior face height, a steep mandibular plane angle, and a retrognathic mandible. This development has been explained as occurring by changes in head and tongue position and muscular balance. After adenoidectomy and change in head and tongue position, accelerated mandibular growth and closure of the mandibular plane angle have been reported. Children with obstructive sleep apnoea (OSA) have similar craniofacial characteristics as those with large adenoids and tonsils, and the first treatment of choice of OSA children is removal of adenoids and tonsils. It is probable that some children with an adenoid face would nowadays be diagnosed as having OSA. These children also have abnormal nocturnal growth hormone (GH) secretion and somatic growth impairment, which is normalized following adenotonsillectomy. It is hypothesized that decreased mandibular growth in adenoid face children is due to abnormal secretion of GH and its mediators. After normalization of hormonal status, ramus growth is enhanced by more intensive endochondral bone formation in the condylar cartilage and/or by appositional bone growth in the lower border of the mandible. This would, in part, explain the noted acceleration in the growth of the mandible and alteration in its growth direction, following the change in the mode of breathing after adenotonsillectomy.

The influence of masseter activity on rat mandibular growth

Many studies have shown that mandibular and condylar growth is affected by compressive forces on mandibular bone and the condyle. It has been reported that chondroblastic differentiation and proliferation in chondrocytes play important roles in condylar growth. However, the influence of reduced compressive force on chondroblastic proliferation and mandibular bone formation is not fully understood. Thirty-six 3-week-old male Wistar rats were used in this study. In the experimental group, the masseter muscles were bilaterally resected to evaluate the influence of masticatory force on mandibular and condylar bone morphology. Six weeks after the operation, while the rats were in the pubertal growth stage, lateral X-rays were taken to analyze the skeletal pattern of the mandible. The form of the condyle and the thickness of the chondroblastic layers were evaluated by toluidine blue staining. Chondroblastic proliferation was identified by insulin-like growth factor-1 receptor (IGF-1r) immunostaining and bone resorption of the condyle was assessed by measuring tartrate-resistant acid phosphatase (TRAP) activity. Lateral X-rays of the mandible showed that rats in the experimental group tended to have large mandibular plane angles. The chondroblastic layer in the condyles of the experimental group rats was thinner than in the control group. The expression of IGF-1r immunopositive cells in the experimental group was significantly lower than in the control chondrocytes, and the number of TRAP-positive cells was significantly higher in the condylar bone of the experimental group. We conclude that masseter muscle activity is closely related to mandibular morphology during growth.

Study on the effects of mechanical pressure to the ultrastructure and secretion ability of mandibular condylar chondrocytes

During mandibular movement, condyle is subjected to repetitive compression and the mandibular condylar chondrocytes (MCCs) can detect and respond to this biomechanical environment by altering their metabolism. The present study was undertaken to investigate the effects of pressure to the ultrastructure, aggrecan synthesis, nitric oxide (NO) and prostaglandin F(1)alpha(PGF(1)alpha) secretion in MCCs. In vitro cultured rabbit MCCs were incubated and pressed under continuous pressure of 90kPa for 60min and 360min by hydraulic pressure controlled cellular strain unit. The ultrastructure, aggrecan mRNA expression, activity of nitric oxide synthase (NOS) and PGF(1)alpha secretion were investigated. Besides, nitric oxide inhibitor was used together with pressure to investigate the role of NO in mechanical effects. The appearance of MCC on TEM showed that after been pressed under 90kPa for 60min, the cellular processes became elongated and voluminous, together with aggrecan mRNA increasing. Under 90kPa for 360min, some of the cells showed distinct sign of apotosis and the aggrecan mRNA decreased. Pressure of 90kPa could cause increase of NOS activity and decrease of PGF(1)alpha composition. Inhibitor experiments indicated that pressure-induced upregulation of aggrecan mRNA and inhibition of PGF(1)alpha synthesis was partly mediated by NO. Continuous pressure could cause changes on the ultrastructure and function of MCC, as well as up-regulation of aggrecan synthesis, increase of NO secretion and decrease of PGF(1)alpha composition. NO was the upstream molecule, which mediated the response of aggrecan and PGF(1)alpha to mechanical pressure.

Genes, forces, and forms: mechanical aspects of prenatal craniofacial development

Current knowledge of molecular signaling during craniofacial development is advancing rapidly. We know that cells can respond to mechanical stimuli by biochemical signaling. Thus, the link between mechanical stimuli and gene expression has become a new and important area of the morphological sciences. This field of research seems to be a revival of the old approach of developmental mechanics, which goes back to the embryologists His (1874), Carey (1920), and Blechschmidt (1948). These researchers argued that forces play a fundamental role in tissue differentiation and morphogenesis. They understood morphogenesis as a closed system with living cells as the active part and biological, chemical, and physical laws as the rules. This review reports on linking mechanical aspects of developmental biology with the contemporary knowledge of tissue differentiation. We focus on the formation of cartilage (in relation to pressure), bone (in relation to shearing forces), and muscles (in relation to dilation forces). The cascade of molecules may be triggered by forces, which arise during physical cell and tissue interaction. Detailed morphological knowledge is mandatory to elucidate the exact location and timing of the regions where forces are exerted. Because this finding also holds true for the exact timing and location of signals, more 3D images of the developmental processes are required. Further research is also required to create methods for measuring forces within a tissue. The molecules whose presence and indispensability we are investigating appear to be mediators rather than creators of form.

Regulatory effects of FGF-2 on the growth of mandibular condyles and femoral heads from newborn rats

The secondary cartilage of the mandibular condyle is considered to be adaptive to functional factors. In the last decades, growth factors have also been shown to be potent regulators of cartilage metabolism. Moreover, it has been suggested that growth factors may differentially regulate the growth of primary and secondary cartilages. However, only a few studies have made a direct comparison of the effects of growth factors on both cartilages. Therefore, the aim here was to compare the effects of FGF-2 on secondary cartilage of the mandibular condyle and primary cartilage of the femoral head from 4-day-old rats in vitro. Cartilages were cultured for 1, 7 and 14 days with 0 and 100 ng/mL FGF-2. We evaluated the effects of FGF-2 on growth, tissue organisation, DNA and glycosaminoglycan (GAG) synthesis and GAG and collagen content. With FGF-2, the morphology of the mandibular condyles changed and the GAG and collagen contents were reduced. However, the growth of the mandibular condyles was not affected. On the contrary, the growth of the femoral heads was strongly reduced due to an inhibition of chondrocyte hypertrophy. In both cartilages, FGF-2 stimulated DNA synthesis in short-term cultures and reduced it in long-term cultures. In conclusion, FGF-2 had a larger effect on the metabolism of the mandibular condyles as compared to the femoral heads. However, the growth of the femoral heads was strongly reduced while that of the mandibular condyles was not affected.

Treatment of TMJ ankylosis in Jordanian children - a comparison of two surgical techniques

INTRODUCTION

The aim of this study was to report Jordanian experience in surgical treatment of TMJ ankylosis in 22 children.

PATIENTS AND METHODS

This retrospective clinical study included children who were diagnosed with TMJ ankylosis and were treated in a dental teaching centre between 1993 and 2001. Patients underwent the release of 24 temporomandibular joint ankyloses and two different surgical techniques were used: either reconstruction of the condyle using costochondral grafts, or using the temporalis muscle as an interpositional material. Patients were followed up for 1-8 years.

RESULTS

Twenty-two children (13 males and 9 females) were included in the study. Costochondral grafts were used as a reconstruction material in 16 TMJs (67%), whilst temporalis muscle was used as an interpositional material in 8 joints (33%). The mean preoperative maximum interincisor distance was 6.6 mm+/-1.3, which was increased to a mean of 30.3 mm+/-2.5 postoperatively. Two female patients (9%) suffered recurrence of the ankylosis within 6-12 months postoperatively. In one of these, a costochondral graft was used and temporalis muscle interposition in the other.

CONCLUSION

Costochondral graft as a reconstruction material and temporalis muscle as an interpositional material showed comparable success rates when treating TMJ ankylosis in 22 children.

Immunolocalization of vascular endothelial growth factor in rat condylar cartilage during postnatal development

It is well known that angiogenesis is essential for the replacement of cartilage by bone during skeletal growth and regeneration. To address angiogenesis of endochondral ossification in the condyle, we examined the appearance of vascular endothelial growth factor (VEGF) and its receptor Flt-1 in condylar cartilage of the growing rat. The early expression of VEGF at various sites during condylar cartilage development indicates that VEGF plays a role in the regulation of angiogenesis at each site of bone formation. From the findings of Flt-1 immunoreactivity, the VEGF produced by the chondrocytes of the hypertrophic zone should contribute to the promotion of endothelial cell proliferation and to stimulate migration and activation of osteoclasts in condylar cartilage, resulting in the invasion of these cells into the mineralized zone.

Growth stimulation of mandibular condyles and femoral heads of newborn rats by IGF-I

Primary and secondary cartilage differ in embryonic origin and are generally considered to have a different mode of growth. However, few experimental studies exist that directly compare the two types of cartilage and their growth regulation. The regulation of cartilage growth is a complex mechanism involving growth factors like insulin-like growth factor-I (IGF-I). The purpose of this study was to compare the growth of mandibular condyles of 4-day-old rats with that of femoral heads in vitro and to analyze the effects of IGF-I. Explants were cultured for up to 2 weeks with 0, 5, and 25 ng/ml IGF-1. Both, 5 and 25 ng/ml IGF-I significantly stimulated growth of the mandibular condyles while only 25 ng/ml IGF-I stimulated growth of the femoral heads. IGF-I increased glycosaminoglycan synthesis of both condylar and femoral cartilage. However, only the DNA synthesis of the mandibular condyles was significantly increased by IGF-I while that of the femoral heads was not affected. It is concluded that IGF-I stimulates growth of both secondary condylar cartilage and primary femoral cartilage. The mandibular condyle appears to be more sensitive to IGF-I than the femoral head, which may partly be due to the different developmental stage.

Growth of the mandible after replacement of the mandibular condyle: an experimental investigation in Macaca mulatta

PURPOSE

The study goal was to investigate growth of the mandible after temporomandibular joint reconstruction in juvenile monkeys.

MATERIALS AND METHODS

Sixteen juvenile monkeys (Macaca mulatta) were used as experiment subjects. Animals were equally divided into 4 experimental groups based on the method of temporomandibular joint reconstruction after bilateral condylar excision via extraoral vertical ramus osteotomies. Group Condyle animals had their condylar segments immediately replaced to serve as surgical controls. Group Bone animals were reconstructed with a bony strut. Group sternoclavicular joint (SCJ) animals were reconstructed with the sternal end of their clavicles. Group costochondral junction (CCJ) animals were reconstructed with costochondral junction of ribs. Standardized lateral cephalometric radiographs with the aid of tantalum bone markers were used to evaluate mandibular growth. Twenty animals were used as controls and were allowed to grow undisturbed for an 18-month period (Group Control).

RESULTS

All animals showed good mandibular function and a Class I molar relationship after an 18-month follow-up period. Statistical and graphic comparisons showed no significant difference in mandibular growth among any of the groups.

CONCLUSIONS

The results of this investigation suggest that, within the limits of this model, the choice of autograft for condyle replacement may be irrelevant.

The effect of a unilateral costochondral graft on the growth of the marmoset mandible

PURPOSE

The purpose of the investigation was to examine growth of the mandible after costochondral grafting with special reference to the amount of cartilage included in the grafts.

MATERIALS AND METHODS

The material consisted of 5 growing and 3 adult marmoset monkeys, Callithrix jacchus, in which the condylar process was removed unilaterally and replaced with a costochondral graft (CCG) containing either a short or long cartilage end. Growing animals were followed for 15 months until they attained maturity; and adult animals were followed for 13 months. Measurements made on frontal radiographs performed bimonthly, and direct measurements made on dry mandibles and crania at the end of the experiment, were used to evaluate the growth of the mandible and glenoid fossa.

RESULTS

Longitudinal cephalometric evaluation revealed a gradual deviation of the lower dental midline to the unoperated side in growing monkeys with a long cartilage transplant. In all other animals, virtually no midline deviation occurred. Measurements on dry mandibles showed that the length and ramus height were longer in growing animals with long cartilage transplants compared with those with short cartilage transplants. In adult animals, the amount of cartilage did not make any difference with regard to the mandibular measurements. Enlargement of the articulating head on the grafted side was recorded in all animals. A morphologic change in the glenoid fossa of growing monkeys with a long cartilage transplant was also noted.

CONCLUSIONS

The findings of this investigation indicate that depending on the amount of cartilage in a unilateral CCG, a tissue-separating force is generated in growing monkeys, capable of propelling the mandible to the unoperated side. This gradual overgrowth occurs during the entire growth period, indicating a strong hormonal and growth factor influence on the growth process. Jaw function may have an effect on the articulating surface of the CCG, seen as enlarged articulating head on the grafted side in all animals.

Chondrocyte proliferation of the cranial base cartilage upon in vivo mechanical stresses

Whereas the growth of the cranial base cartilage is thought to be regulated solely by genes, epiphyseal growth plates are known to respond to mechanical stresses. This disparity has led to our hypothesis that chondrocyte proliferation is accelerated by mechanical stimuli above natural growth. Two-Newton tensile forces with static and cyclic waveforms were delivered in vivo to the premaxillae of actively growing rabbits for 20 min/day over 12 consecutive days. The average number of BrdU-labeled chondrocytes in the proliferating zone treated with cyclic forces was significantly higher than both static forces of matching peak magnitude and sham controls representing natural chondral growth. Cyclic forces also evoked greater area of the proliferating zone than both static forces and sham controls. Thus, chondrocyte proliferation is enhanced by mechanical stresses in vivo, especially those with oscillatory waveform. Analysis of these data suggests that genetically coded chondral growth is up-regulated by mechanical signals.

Accelerated chondrogenesis of the rabbit cranial base growth plate by oscillatory mechanical stimuli

How mechanical stimuli modulate chondral growth is not well understood. To test a hypothesis that chondral growth is accelerated by oscillatory mechanical stimuli rather than the peak magnitude of mechanical force, we delivered 2-N tensile forces with static (frequency = 0 Hz) and cyclic (f = 1 Hz) profiles noninvasively to the maxillae of growing New Zealand white rabbits for 20 minutes/day over 12 days. Computerized histomorphometry revealed significantly greater maximum height of the cranial base growth plate (GP) treated with cyclic forces (870 +/- 130 microm) than static forces (654 +/- 29 microm) and sham controls (566 +/- 47 microm). In addition, the average total GP area treated with cyclic forces (2.63 +/- 0.17 mm2) was significantly greater than static forces (2.12 +/- 0.99 mm2) and sham controls (1.65 +/- 0.13 mm2). The proliferating zone of GPs treated with cyclic forces (158 +/- 38.5 microm) was significantly longer than the corresponding zones of static forces (117 +/- 8.6 microm) and sham controls (54 +/- 14.9 microm). The average number of chondrocytes in the proliferating zone treated with cyclic forces (1045 +/- 127) was significantly greater than static forces (632 +/- 85) and sham controls (632 +/- 60) in standardized grids. Like natural GPs, the cartilage matrix treated with cyclic and static tensile forces consisted of abundant aggrecan-like proteoglycans. These findings indicate that oscillatory components of mechanical force rather than its peak magnitude are potent anabolic stimulus for chondral growth. A cascade of oscillatory mechanical stimuli is likely capable of engineering chondral growth beyond naturally occurring chondrogenesis.

Regulation of cell proliferation in rat mandibular condylar cartilage in explant culture by insulin-like growth factor-1 and fibroblast growth factor-2

Insulin-like growth factor-1 (IGF-1) and fibroblast growth factor-2 (FGF-2) regulate the proliferation and differentiation of growth-plate chondrocytes, but surprisingly little is known of the mechanisms underlying growth regulation in secondary cartilages such as the mandibular condylar. The aims here were to investigate whether IGF-1 and FGF-2 receptors are present in mandibular condylar cartilage in vivo from 28-day-old male Sprague-Dawley rats (by immunohistochemistry), how proliferation in that cartilage responds to increasing concentrations of exogenous IGF-1 or FGF-2 in explant culture (by [3H]thymidine incorporation), and whether the expression of these growth factors and their receptors in the cartilage changes during the transition to puberty (quantitative reverse transcriptase-polymerase chain reaction). Immunoreactivity for receptors (R) for IGF-1 and FGF-2 (IGF-1R, FGFR1, and FGFR3) was most pronounced in chondroblasts and hypertrophic chondrocytes, while FGFR2 immunoreactivity was strongest in the articular and prechondroblastic zones. The proliferative response elicited by exogenous IGF-1 was considerably greater than that induced by FGF-2, although the threshold concentration for a significant response was lower for FGF-2. In the transition from prepuberty (31 days) to the beginning of late puberty (42 days), a pronounced trend of increasing IGF-1 and decreasing FGF-2 gene expression was evident. Of the receptors, only FGFR2 and FGFR3 expression increased. These data provide evidence that proliferation in the mandibular condylar cartilage might be regulated in part by IGF-1 and FGF-2, and that expression of these genes changes considerably at puberty. The data also suggest that mechanisms governing proliferation in mandibular condylar cartilage might have as much in common with those regulating cranial sutures as those regulating growth-plate.

Biomechanical response of retrodiscal tissue in the temporomandibular joint under compression

PURPOSE

The present study was conducted to investigate the biomechanical response of bovine retrodiscal tissue of the temporomandibular joint (TMJ) in compression.

PATIENTS AND METHODS

Using 10 retrodiscal tissues obtained from 10 cattle, the viscoelastic response of the retrodiscal tissue was evaluated by means of stress-strain analyses. These compressive strains were produced at a high strain rate and were kept constant during 5 minutes for stress-relaxation.

RESULTS

Although the stress-strain relationship in the retrodiscal tissue was essentially nonlinear represented by a quadratic or power function of strain, a linear model could reasonably represent its elastic property. In this case, the instantaneous and relaxed moduli were 1.54 and 0.21 MPa, respectively. The stress-relaxation curve showed a marked drop in load during the initial 10 seconds, and the stress reached a steady nonzero level. Furthermore, when using Kelvin's model, a satisfactory agreement can be obtained between the experimental and theoretical stress-relaxation curves.

CONCLUSION

It is concluded that bovine retrodiscal tissue has a great capacity for energy dissipation during stress-relaxation, although it has little or no function to pull the articular disc back.

Compressive force promotes chondrogenic differentiation and hypertrophy in midpalatal suture cartilage in growing rats

Midpalatal suture cartilage (MSC) is secondary cartilage located between the bilateral maxillary bones and has been utilized in the analysis of the biomechanical characteristics of secondary cartilage. The present study was designed to investigate the effects of compressive force on the differentiation of cartilage in midpalatal suture cartilage in rats. Forces of various magnitudes were applied to the midpalatal suture cartilage in 4-week-old male Wistar rats for 1, 2, 4, 7, or 14 days, mediated through the bilateral 1st molars using orthodontic wires. The differentiation pathways in the MSC cells were examined by immunohistochemistry for the differentiation markers type I, type II and type X collagen, and glycosaminoglycans (GAGs), chondroitin-4-sulfate, chondroitin-6-sulfate and keratan sulfate. Histologically and immunohistochemically, the midpalatal suture cartilage in control rats had the characteristic appearance of secondary cartilage. In the experimental groups, the center of the midpalatal suture cartilage that contained osteo-chondro progenitor cells seemed to become mature cartilage and its immuno-reaction to type II and X collagen and GAGs increased as the experiment progressed. This differentiation was dependent upon the magnitude and duration of the force applied to the midpalatal suture cartilage; i.e., cartilaginous differentiation progressed more rapidly as the applied force increased. The present results suggest that the differentiation of osteo-chondro progenitor cells into mature and hypertrophic chondrocytes in the precartilaginous cell layer is promoted by compressive force.

The effect of epidermal growth factor on the fetal rabbit mandibular condyle and isolated condylar fibroblasts

The load-bearing surface of the mandibular condyle presents a unique arrangement of tissues consisting of an avascular layer composed largely of collagen bundles. Fibroblasts are interspersed amongst these bundles and are generally agreed to produce the collagen. The mechanisms controlling development of these tissues have not been determined. This study was conducted to explore the role of epidermal growth factor (EGF), which appears to be important in the development of many oral tissue types as well as in the growth and differentiation of the mandibular condyle. Superficial cells of the fibrous zone of the condyle were isolated from fetal rabbit condyles and [(3)H]thymidine incorporation into DNA measured. The application of EGF produced a significant increase in radiolabel incorporation after 2 days compared to 4 days in the controls, suggesting that EGF induced cells to enter S-phase more rapidly. Fetal condyles were also cultured on gelfoam surgical sponges for up to 21 days. Autoradiography of cultured condyles showed that cells of all three zones may potentially replicate, as indicated by incorporation of [(3)H]thymidine. All three regions displayed greater increases in cell numbers in samples exposed to EGF than in control samples. The measurement of zone thickness in condyles cultured on gelfoam sponges with or without EGF showed that this peptide was able to re-establish thickness, bringing it in line with the relation observed when the condyles were isolated initially, particularly of the intermediate zone over a period of 21 days. As very little autoradiographic labelling occurred at this time-point in any of the zones, the increase in thickness must primarily be due to matrix production. It is concluded that EGF is one factor potentially regulating both replication and differentiation in mandibular condyle and its associated cells.

Morphologic determinants in the etiology of class III malocclusions: a review

Morphospatial disharmony of the craniomaxillary and mandibular complexes may yield apparent mandibular prognathism, but Class III malocclusions can exist with any number of aberrations of the craniofacial complex. Deficient orthocephalization of the cranial base allied with a smaller anterior cranial base component has been implicated in the etiology of Class III malocclusions. Whereas the more acute cranial base angle may affect the articulation of the condyles resulting in their forward displacement, the reduction in anterior cranial size may affect the position of the maxilla. As well, intrinsic skeletal elements of the maxillary complex may be responsible for maxillary hypoplasia that may exacerbate the anterior crossbite seen in the Class III condition. Conversely, with an orthognathic maxilla, condylar hyperplasia and anterior positioning of the condyles at the temporo-mandibular joint may produce an anterior crossbite. Aside from the skeletal components, soft tissue matrices, particularly labial pressure from the circumoral musculature, may influence the final outcome of craniofacial growth of a child skeletally predisposed to Class III conditions. Indeed, as some Asian ethnic groups demonstrate an increased prevalence of Class III malocclusions, it is likely that the skeletal components and soft tissues matrices are genetically determined. Presumably, the co-morphologies of the craniomaxillary and mandibular complexes are likely dependent upon candidate genes that undergo gene-environmental interactions to yield Class III malocclusions. The identification of such genes is a desirable step in unraveling the complexity of Class III malocclusions. With this knowledge, the clinician may elect an early course of dentofacial orthopedic and orthodontic treatments aimed at preventing the development of Class III malocclusions.

Electrical stimulation of masseter muscles maintains condylar cartilage in long-term organ culture

When condylar cartilage is maintained under nonfunctional organ culture conditions, its phenotypic expression is altered to a premature form with less expression of the type II collagen characteristic of mature chondroblasts. The aim of this study was to examine whether, by electrical stimulation of the major masticatory muscle, the masseter muscle, chondrogenic expression could be maintained under organ culture conditions in which the jaws with the craniomandibular joint were cultured in one block. Sixty BALB/c mice of both sexes were divided randomly into three groups of equal size. Two groups were decapitated at the age of 5 days. The cranial base and mandible were dissected out in one block, and the explant was placed on its cut surface on a culture dish. The masseter muscles of the explants in one group were stimulated with an electric pulsing device delivering an AC current of a frequency of 0.7 Hz and an amplitude of 5V with hourly active and silent periods. Five experimental and five control explants were fixed after culture periods of 1, 3, 7, and 14 days. The mice in the third group were used as in vivo controls. By electrical stimulation of the masseter muscle, the phenotypic characteristics of the condylar chondroblasts, such as the deposition of type II collagen and the thickness of the cartilage layers, closely resembled the situation in vivo, while the controls in a non-functional environment gradually lost their characteristic form.

Effects of expansive force on the differentiation of midpalatal suture cartilage in rats

In an attempt to clarify the effects of biomechanical tensional force on chondrogenic and osteogenic differentiation of secondary cartilage, the midpalatal sutures of 4-week-old Wistar male rats were expanded by orthodontic wires which applied 20 g force for 4, 7, 10, and 14 days. The differentiation pathways in the midpalatal suture cartilage were examined by immunohistochemistry for osteocalcin, type I and type II collagen, and von Kossa histochemistry. Although the midpalatal sutures of the control animals consisted mainly of two separate secondary cartilages with mesenchyme-like cells at their midlines, type I collagen-rich fibrous tissue began to appear at day 4 and increased at the midline of the cartilage with days of experiment. At the end of the experiment, type I collagen-rich and calcified bone matrix appeared at the boundary between the precartilaginous and the cartilaginous cell layers. Most of the cartilaginous tissues were separated from each other and the midpalatal suture was replaced by osteocalcin-positive intramembranous bone and fibrous sutural tissue. These results strongly suggest that tensional force changed the phenotypic expression of collagenous components in secondary cartilage, which may reflect the differentiation pathway of osteochondro progenitor cells.

Dimensional growth and extracellular matrix accumulation by neonatal rat mandibular condyles in long-term culture

Mandibular condyles in organ culture commonly have been used as a model system for examination of the factors that influence skeletal growth and development. The work reported here complements previously published histological studies by providing quantitative temporal information on growth and matrix accumulation. Condyles maintained for as long as 5 weeks in serum-free and 1% serum-supplemented culture media were found to remain viable and metabolically active as demonstrated by continued dimensional growth as well as cell and matrix accumulation. Growth occurred by a combination of cell proliferation, matrix synthesis and accumulation, and cell hypertrophy (with the latter two mechanisms dominating). Increases in tissue volume correlated directly with increased glycosaminoglycan content; both increased 7-fold over 5 weeks. In comparison with serum-free culture, after 35 days in medium containing 1% serum, glycosaminoglycan content was 24% lower and collagen content was 36% higher, whereas dry weight, condyle length, and DNA content were not significantly different; in addition, histological observation suggested that, for samples cultured with serum, chondrogenic phenotype had been lost from some regions. The temporal behavior for all growth parameters exhibited a transient phase 1-2 weeks in duration followed by a steady-state period in which dimensions and tissue constituents or content increased at a constant or near constant rate. Comparison of the rates of incorporation of [35S]sulfate with glycosaminoglycan content in serum-free cultures suggests that the loss of glycosaminoglycan occurs only initially or is negligible; therefore, under these baseline conditions, cartilage glycosaminoglycan content reflects the biosynthetic rate. The high degree of reproducibility seen during steady-state growth suggests that these data provide reliable baseline information and further supports the notion that this model system is useful for investigation of the effects of specific physical factors on in vitro growth and development.

Effects of physicochemical factors on the growth of mandibular condyles in vitro

Cartilage growth and remodeling are known to be influenced by the biochemical and mechanical environment of the tissue. Previous investigators have shown that chemical factors that are relevant to mechanical loading, such as osmotic pressure and pH, induce changes in cartilage metabolism in vitro. Using a neonatal rat mandibular condyle culture system, the objectives of the work reported here were to determine (1) how the growth is influenced by osmotically applied mechanical loads; and (2) whether changes in intratissue osmotic pressure or pH cause metabolic changes in the cartilage which are then reflected by altered growth behavior. High molecular weight (MW) uncharged macromolecules polyvinylpyrrolidone (PVP) and Ficoll (presumed unable to penetrate the tissue matrix) were used to examine the effect of osmotic loading on tissue growth; concentrations corresponding to osmotic pressures of up to 100 kPa resulted in a dose-dependent depression in growth and matrix accumulation. Raffinose (which can penetrate the matrix but not the cells) had no significant effect on growth for osmotic pressures of up to 87 kPa, suggesting that compression-induced changes in intratissue osmotic pressure are unlikely to provide a signal by which cells sense and respond to mechanical compression. By contrast, changes in medium pH resulted in dose-dependent changes in growth behavior. Specifically, slight alkalinity (acidity) greatly enhanced (diminished) growth and matrix accumulation; the sensitivity to pH suggests that intratissue pH could provide a mechanism for cells to sense local glycosaminoglycan concentration and mechanical compression.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of costochondral fragments transplanted from mature to young isogeneic rats

Experiments were carried out to determine whether growth of costochondral grafts is associated with age-related humoral factors. Rib fragments containing either short (without germinative zone) or long (with proliferative and germinative zones) cartilaginous ends were excised from adult rats, and the sections transplanted across the interparietal suture in 10-day-old isogeneic rats. The animals with short cartilage transplants were killed 15 or 25 days later; those with long cartilage transplants 25 days postoperatively. Measurements on dry skulls with short transplants showed neurocranial width to be greater in the experimental rats than in the unoperated controls at 25 days, whereas 10 days later the difference was no longer significant. By the latter time, however, the neurocranium was significantly wider in the long cartilage group than in the other groups. It is suggested that the declining growth potential of the costal cartilages from the adult rats was reactivated when transplanted to younger animals, i.e., the growth of costochondral transplants is related to humoral factors.

The role of the condylar cartilage in mandibular growth. A study in thanatophoric dysplasia

A new approach to evaluate the role of the condyle in mandibular growth could be its study in chondrodysplasias. The growth of the condylar cartilage and the mandible has not previously been reported in thanatophoric dysplasia (TD), a lethal osteochondrodysplasia. We have studied the light microscopic, histomorphometric, and radiologic findings in four infants affected by TD and in four control infants. The diagnosis was made on the basis of clinical, radiographic, and pathologic criteria. All the measured radiographic parameters of the patients' mandibles showed a normal longitudinal growth in TD, despite the severe disturbance of the condylar cartilages. The lesions in the chondroblastic cells and the extracellular matrix were similar to those observed in growth plate cartilages in TD. Marked membranous ossification spread from the cartilage canals of the condyles. The articular and prechondroblastic layers were histologically normal. Histomorphometry demonstrated that condylar cartilages were twice as thick as normal in TD, mainly because of the thickening by the chondroblastic layer. Present results support the hypothesis that condylar cartilage is a secondary growth site instead of being a primary growth center.

Comparison of the effects of hydrostatic compressive force on glycosaminoglycan synthesis and proliferation in rabbit chondrocytes from mandibular condylar cartilage, nasal septum, and spheno-occipital synchondrosis in vitro

We have developed a simple in vitro model whereby precise quantities of compressive force can be applied to cultured chondrocytes from craniofacial cartilage: mandibular condylar cartilage (MCC), nasal septal cartilage (NSC), and spheno-occipital synchondrosis (SOS). Using this model, we found that hydrostatic compressive force stimulated glycosaminoglycan (GAG) synthesis, a cartilage phenotype, in MCC and SOS chondrocytes and DNA synthesis in MCC, NSC, and SOS chondrocytes. These stimulations were dependent on force magnitude and duration, reaching maximal GAG synthesis at 27 hours and maximal DNA synthesis at 20 hours after application of force. The maximal increase of GAG synthesis induced by compressive force was about 60% at 100 gm/cm2 for 5 minutes in nonstimulated MCC chondrocytes and 40% at 50 gm/cm2 for 1 minute in nonstimulated SOS chondrocytes. The maximal increase in DNA synthesis, produced by a compressive force of 50 gm/cm2 for 1 minute, was 50% in NSC chondrocytes, 50% in SOS chondrocytes, and 30% in MCC chondrocytes. There was no stimulation of GAG synthesis in NSC chondrocytes. These observations suggest that extrinsic force regulates craniofacial growth by controlling the differentiation and proliferation of chondrocytes in the craniofacial skeleton and that the difference in their responses to compressive force may reflect differences in the characteristics of these cells and their physiologic function in vivo.

Phenotypic changes of rabbit mandibular condylar cartilage cells in culture

The present study describes the behavior of mandibular condylar cartilage (MCC) cells as a function of time in primary culture, since it is not yet clear whether these cells maintain their phenotype in culture. MCC cells from New Zealand white rabbits were seeded at high density and cultured in DMEM containing 50 micrograms/mL ascorbic acid and 10% fetal bovine serum. These cells appeared as a heterogeneous population and changed their shape, size, and refractivity as cultures aged. Cartilage-like cells, which always dominated the culture, were infiltrated with a minority of fibroblast-like cells. Cell number increased progressively, and cultures reached confluence at nine days. Antibody activity for cartilage-specific glycosaminoglycan was determined by ELISA assay. This reaction reached a maximum at six days and decreased thereafter. Cultures stained with Alcian blue (pH 1.0) supported these results. Cytoplasmic mRNA analysis indicated that the transcription of type II collagen gene was present at all time points. Type I collagen and alkaline phosphatase mRNA levels showed progressive increases from 12 h to nine days, with significantly higher values in cells cultured for six, nine, and 12 days than in cells collected from earlier time points. These results suggest that in our present culture system, MCC cells undergo phenotypic changes that resemble their maturation processes in vivo.

Periostomy and growth of the mandibular condyle in the rat

It has been shown that a release of periosteal tension may augment the growth of a long bone; however, similar experiments in the mandible have produced equivocal results. For further definition of the role of periosteal tension in the growth of the mandibular condyle, 80 young female Sprague-Dawley rats were randomly assigned to four equal groups: (1) sham, (2) condylotomy, (3) narrow periostomy, and (4) wide periostomy. All procedures were performed unilaterally. Lateral cephalograms, transcranial condylar radiographs, and metallic implants made possible the measurement of the actual increment of condylar growth over three post-operative periods: 0 to 14 days, 14 to 28 days, and 0 to 28 days. Analysis of covariance was performed (weight gain as the covariate) and, where overall significance was found, Turkey's HSD test was used for determination of individual group differences. Conservative, circumferential periostomy of the condylar neck as well as condylotomy failed to alter the condylar growth rate, whereas removal of a wide band of periosteum led to a small decrease. These findings suggest that, at least in the rat, periosteal tension plays only a minor role-if any-in the control of condylar/mandibular growth. Furthermore, a subsequent increase or decrease in condylar growth, in experiments that use a condylotomy model, cannot be attributed solely to a disturbance in periosteal integrity caused by the condylotomy.