Specificity of meal pattern analysis as an animal model of determining temporomandibular joint inflammation/pain

Analyzing feeding behavior, and in particular meal duration, can be used as a biological marker for temporomandibular joint (TMJ) inflammation/pain. The present study determined the specificity of meal duration as a measure of TMJ inflammation/pain in a rodent model. The model was also used to test the efficacy of dexamethasone (DEX) as a treatment for TMJ inflammation/pain that was induced by TMJ injection of complete Freund's adjuvant (CFA). In the first study, anesthetized male Sprague-Dawley rats housed in computerized feeding modules received bilateral intra-articular knee injections of CFA or saline. The next day, CFA-injected rats had significant knee swelling and impaired mobility. Food intake in the CFA-injected group was reduced over the next two days and this was due to reduced meal number with no change in meal size. Notably, meal duration was normal in both the CFA and saline knee-injected groups. In the second study, male rats were assigned to one of four groups: Group 1, no CFA and no DEX treatment; Group 2, no CFA and treatment with DEX (0.4 mg/kg i.m. once daily); Group 3, bilateral TMJ CFA injection and no DEX treatment; and Group 4, bilateral TMJ CFA injection and treatment with DEX. CFA significantly increased TMJ swelling and stress-induced chromodacryorrhea in Group 3, but treatment with DEX attenuated these effects in Group 4. Compared to the controls, meal duration was significantly lengthened 24 and 48 h post-CFA injection in Group 3, whereas DEX treatment attenuated TMJ swelling, chromodacryorrhea and normalized meal duration. The data demonstrate that meal pattern analysis, and in particular meal duration, can be used as a non-invasive specific measure of TMJ inflammation/pain and can be used as a marker of DEX treatment efficacy.

Meal pattern changes associated with temporomandibular joint inflammation/pain in rats; analgesic effects

Establishing a valid animal model to study temporomandibular joint (TMJ) pain has proven extremely difficult. Using complete Freund's adjuvant (CFA) to induce TMJ inflammation, we recently showed that meal pattern analysis could be used as a noninvasive biological marker to study TMJ pain in an animal model. The purpose of this study was to further validate our animal model by determining whether aspects of CFA-induced TMJ inflammation/pain are reversed with ibuprofen (IBU) treatment. In the first trial, 48 male rats were used and in the second trial, 32 female ovariectomized rats, given 17beta-estradiol replacement, were used. The rats were assigned to one of four groups: control (CON-CON); control+IBU (CON+IBU); CFA-CON; and CFA+IBU. In the male trial, CFA injection (P<.01) caused TMJ swelling and chromodacryorrhea (CFA-CON); IBU eliminated these changes in the CFA+IBU group. Meal pattern analysis showed the pertinent CFA-induced change and the IBU effect was that meal duration was increased in the CFA-CON group (P<.01), but normal in the CFA+IBU-treated group on the first, but not second, day postinjection. In the female trial, CFA increased TMJ swelling, but did not cause significant chromodacryorrhea (CFA-CON); IBU eliminated swelling in the CFA+IBU group. Meal duration was increased (P<.01) in the CFA-CON group, but was normal in the CFA+IBU-treated group on both the first and second days postinjection. In both trials, interleukin-1beta (IL-1beta) levels were increased similarly in CFA-CON and CFA+IBU groups (P<.01). This study shows that CFA-induced TMJ inflammation/pain can cause changes in meal patterns (i.e., meal duration), which may be used as a behavioral marker for TMJ inflammation/pain.

Tgf-beta1, Tgf-beta2, Tgf-beta3 and Msx2 expression is elevated during frontonasal suture morphogenesis and during active postnatal facial growth

OBJECTIVES

It is hypothesized that regulation of facial suture morphogenesis is similar to that of cranial sutures, with expression of similar regulatory molecules, governing suture formation and patency. The present study was designed to characterize the morphology of the frontonasal (FN) suture of the rat at different developmental stages and to investigate the presence and temporal-spatial expression of transforming growth factor-beta 1 (Tgf-beta1), Tgf-beta2, Tgf-beta3 and Msx2 mRNA within these structures.

SETTING AND SAMPLE POPULATION

The Department of Biomedical Sciences at Texas A&M University System Health Science Center, Baylor College of Dentistry, Dallas, TX USA. Histological sections and RNA isolated from FN suture tissues of Sprague-Dawley rats, aged embryonic day 16 through postnatal day 20.

METHOD

Sections were examined after immunohistochemical staining. Gene expression was determined by densitometric analysis of RT-PCR products run on agarose gels.

RESULTS

FN sutures develop slightly later than cranial sutures and show increased complexity over time when compared to cranial sutures. FN sutures were closely associated with the nasal capsular cartilage, with intervening layers of perichondrium and periosteum. The pattern of expression of Tgf-betas within the FN suture tissues was similar to that seen in the cranial sutures. However, mRNA and protein of the Tgf-betas were differentially expressed over time compared to cranial sutures. In FN sutures, Tgf-beta mRNA levels were elevated both during the period of suture morphogenesis and during active bone growth from the suture in the early postnatal period. Msx2 mRNA expression was elevated in both the prenatal and postnatal periods, similar to Tgf-beta mRNA expression.

CONCLUSION

Tgf-beta and Msx2 are present in facial sutures similar to cranial sutures, but are differentially expressed over time, perhaps reflecting different bone growth rates from these sutures.

Maximum shortening velocity and myosin heavy-chain isoform expression in human masseter muscle fibers

While human masseter muscle is known to have unusual co-expression of myosin heavy-chain proteins, cellular kinetics of individual fibers has not yet been tested. Here we examine if myosin heavy-chain protein content is closely correlated to fiber-shortening speed, as previously reported in other human muscles, or if these proteins do not correlate well to shortening speeds, as has been demonstrated previously in rat muscle. Slack-test recordings of single, skinned human masseter fibers at 15 degrees C revealed maximum shortening velocities generally slower and much more variable than those recorded in human limb muscle. The slowest fiber recorded had a maximum shortening velocity (V0) value of 0.027 muscle lengths x s(-1), several times slower than the slowest type I fibers previously measured in humans. By contrast, human limb muscle controls produced V0 measurements comparable with previously published results. Analysis by gel electrophoresis found 63% of masseter fibers to contain pure type I MyHC and the remainder to co-express mostly type I in various combinations with IIA and IIX isoforms. V0 in masseter fibers forms a continuum in which no clear relationship to MyHC isoform content is apparent.

Meal pattern analysis in response to temporomandibular joint inflammation in the rat

Inflammation of the temporomandibular joint (TMJ) can alter behavioral responses such as food intake and mobilize stress hormones. The hypothesis of this study was that food intake and diurnal corticosterone analysis can be used as indicators of adjuvant-induced TMJ inflammation. Groups of rats received adjuvant or no injections at the beginning of the resting (AM) or activity (PM) phase. Forty-eight hours (early) or 6 weeks (late) after adjuvant injection, plasma corticosterone was assayed and food intake was recorded. Food intake was suppressed up to 4 days post-injection. As expected, the non-injected group showed low AM and high PM corticosterone. AM corticosterone was elevated, but PM corticosterone was attenuated in both early- and late-stage-injected rats. A computerized pair-fed experiment showed that adjuvant-induced hypophagia did not alter corticosterone levels. Meal pattern analysis revealed decreased food intake due to a decrease in the number of meals taken. Notably, meal size remained the same but meal duration increased. This model demonstrated that food intake and stress hormone analysis could be used as indicators for sequelae of adjuvant-induced TMJ inflammation.

Implications of temporomandibular disorders for facial growth and orthodontic treatment

The purpose of this article is to review the literature concerning the possible associations between temporomandibular disorders (TMD), orthodontic therapy, mandibular growth, and facial form. Consideration of the association between TMD and orthodontic treatment leads to one conclusion: there is no evidence that orthodontic treatment generally increases or decreases the chances of developing TMD later in life. Still, our understanding of TMD is not final, and the expanding diagnostic knowledge continues to call for new longitudinal studies focusing on the developmental basis of temporomandibular disorders. Little is known about the potential effect of TMD on facial development. However, information relating to the normal development, growth, and adaptation of the temporomandibular joint all tend to emphasize the significant ontogenetic plasticity of the growth-related secondary cartilage associated with the TMJ, within the bounds of normal function and histophysiology. With the exception of such diseases as juvenile rheumatoid arthritis and osteoarthritis, little is known about the influence of TM pathology or myofascial disorders on facial growth. Also, little is known about the possible influence of disc interferences on facial growth. However, the condyle is known to play a prominent role in normal mandibular growth and, consequently, facial development. Thus, categories of TMD that involve dysplasia of the condylar cartilage could be associated with aberrant facial growth and form.

Histomorphologic analysis of the soft palate musculature in prenatal cleft and noncleft A/Jax mice

The two specific aims of this study were as follows: to evaluate the appropriateness of the A/Jax mouse model in the investigation of the key cellular stages in prenatal soft palate morphogenesis and myogenesis; and to describe structural differences in the histomorphology of the soft palate anatomy from cleft and noncleft mice prior to, during, and after palatogenesis. Cleft-induced and control groups of A/Jax mouse embryos from timed pregnancies were harvested sequentially on gestational days 15 to 19. Embryos were weighed and staged for external body morphology. The heads were removed and fixed for light microscopy, sectioned serially in the frontal plane at 10 microns and stained with hematoxylin-eosin to characterize and compare the soft palate musculature. All observations were made at the head depth of the trigeminal ganglion in both age- and stage-matched embryos. The following findings were made: (1) the A/Jax mouse is a suitable animal model for the study of soft palate myogenesis; (2) there were no discernible morphologic differences between the soft palate muscles in cleft and noncleft A/Jax mice when viewed under light microscopy; (3) the soft palate and related muscles were identifiable as muscle fields, in both the cleft and noncleft fetuses, as early as gestational day 15 and as specific muscles at gestational day 18; (4) in both the cleft and noncleft A/Jax fetuses, the soft palate muscles appeared in a sequential anatomic fashion (the palatine aponeurosis appeared first, next the tensor palatini, and then the levator palatini muscles); and (5) in the cleft palate fetuses, both pterygoid plates were angulated and displaced laterally.

Condylar adaptation after alteration of vertical dimension in adult rhesus monkeys, Macaca mulatta

Remodeling in the cartilage of the mandibular condyle was investigated in young adult monkeys after an increase in vertical dimension of the midface through the use of a tooth-borne intraoral appliance. Six young adult male rhesus monkeys had bite-splints of 5 mm, 10 mm or 15 mm cemented to their maxillary dentition for 48 weeks. Five age- and sex-matched monkeys were used as controls. The thickness of the articular tissue and of the prechondroblastic and chondroblastic layers of the condylar cartilage in the superior, posterosuperior and posterior regions was measured from parasagittal sections of the temporomandibular joint (TMJ). It was found that articular tissue thickness was reduced in the superior region; the prechondroblastic layer, absent in control animals, was very distinctive (30-75 microns) in experimental animals; and there was a 62% increase in the thickness of the chondroblastic layer in the experimental animals. These findings indicate that chronic alteration of mandibular posture via increase in vertical dimension stimulates progressive remodeling of the mandibular condyle in young adult monkeys.

Myosin expression in the jaw-closing muscles of the domestic cat and American opossum

Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), glycerol SDS-PAGE, two-dimensional electrophoresis, and protein immunoblotting techniques were used to identify myosin heavy chain (MHC) and light chain (MLC) isoforms in limb and masticatory muscles of the cat and American opossum. The fibre types in which these isoforms are expressed were identified by histochemistry and immunohistochemistry. Antibodies specific for the type IIM MHC isoform characteristic of cat jaw-closing muscles and the type I MHC isoform were produced and characterized. The IIM antibody stained the majority of fibres found in the jaw-closing muscles of both species. These IIM-containing fibres characteristically had a histochemical ATPase that remained active after both acid and alkali pre-incubations. A minority of type I fibres was also present in cat jaw-closing muscles, and these reacted positively with antibody specific for type I MHC. It was confirmed that the vast majority of fibres in the cat jaw-closing muscles contained only the characteristic masticatory MHC (IIM) and masticatory MLCs (LC1m and LC2m). These muscles did not contain either the type II fibre isoforms of limb muscles or the atrial cardiac (alpha-cardiac) MHC. The type IIM MHC could also be identified in jaw-closing muscles of the opossum. Two-dimensional gel electrophoresis was used to identify the MLC composition of single, histochemically defined, type I fibres in the cat soleus and deep masseter. The type I fibres of limb muscle contained the usual slow MLCs, but type I fibres from the jaw-closing muscles contained only the masticatory light chains.

Evaluation of the beta energy spectrum from a distributed uranium mill tailings source

The beta energy spectra from uranium mill tailings, 90Sr with different absorber thicknesses, and a uranium metal slab were measured and compared to select an appropriate beta source for calibrating a personal dosimeter to measure shallow dose equivalent when exposed to uranium mill tailings. The measured beta energy spectrum from the 90Sr source, with a 111 mg cm-2 cover thickness, was selected as a possible calibration source for a personnel dosimeter. The dose equivalent rate to the skin at 1 cm from a distributed tailings source of infinite thickness, with a 226Ra activity of 56 Bq g-1 (1.5 x 10(3) pCi g-1), was measured to be 0.024 mSv h-1 (2.4 mrem h-1).

Effect of maxillomandibular fixation on condylar growth in juvenile Macaca mulatta: a cephalometric and histologic study

The effect of maxillomandibular fixation on the growth of the mandibular condyle was studied in eight control and eight experimental male juvenile monkeys. All animals had metallic implants placed throughout the craniofacial complex in order to facilitate cephalometric analysis of growth-related changes in the maxillomandibular complex during jaw immobilization. Every 3, 6, 12, and 24 wk after insertion of the appliance two experimental animals were killed for histologic analysis. Cephalometric analysis indicated no major deviation from normal maxillary or mandibular growth in the experimental animals. The condylar growth in the experimental animals was comparable with that of the controls. Histologic analysis indicated that the articular connective tissue in experimental joints remained the same thickness as in the controls. On the postero-superior aspect of the condyle, the thickness of the prechondroblastic-chondroblastic cell layer was reduced by 70-80% in the experimental animals. On the posterior aspect this cell layer was not visible after 12 wk of fixation, but was replaced by a periosteum-like, cell-rich tissue which appeared to be active in appositional formation of cancellous bone. These results indicate that long-term maxillomandibular fixation does not cause major alterations in the growth of condyle or the entire mandible despite a profound decrease of the prechondroblastic-chondroblastic cell layer in the postero-superior and posterior regions of the condyle. The growth is probably due to a compensatory appositional bone formation along the surface of the condyle. It is also concluded that jaw mobility is not a prerequisite for normal maxillary or mandibular growth.

Autoradiographic study of the effects of pulsed electromagnetic fields on bone and cartilage growth in juvenile rats

Application of pulsed electromagnetic fields (PEMF) has been used in growth and repair of non-union bone fractures. The similarities between the fibrocartilage callus in non-union bone fractures and the secondary cartilage in the mandibular condyle, both histologically and functionally, lead naturally to study the effects of PEMFs on growth in the condyle. The purposes of this study were: (1) to describe the effects of PEMFs on the growth of the condyle using autoradiography, [3H]-proline and [3H]-thymidine, and (2) to differentiate between the effects of the magnetic and electrical components of the field. Male pre-adolescent Sprague-Dawley rats (28 days old) were divided into three experimental groups of five animals each: (1) PEMF-magnetic (M), (2) PEMF-electrical (E) and (3) control, and were examined at three different times-3, 7 and 14 days of exposure. Each animal was exposed to the field for 8 h per day. Histological coronal sections were processed for quantitative autoradiography to determine the mitotic activity of the condylar cartilage and the amount of bone deposition. The PEMF (magnetic or electrical) had statistically significant effects only on the thickness of the articular zone, with the thickness in the PEMF-M group being the most reduced. Length of treatment was associated with predictable significant changes in the thickness of the condylar cartilage zones and the amount of bone deposition.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of the mandible following replacement of the mandibular condyle with the sternal end of the clavicle: an experimental investigation in Macaca mulatta

This study was designed to investigate the long-term effects of transplanted clavicles to the temporomandibular joint (TMJ) in juvenile monkeys. Sixteen juvenile female monkeys (Macaca mulatta) were used in this experiment. Eight animals were used as controls and were allowed to grow undisturbed for an 18-month period (group control). Eight animals were divided into two groups and underwent bilateral condylar excision via extraoral vertical ramus osteotomies. Four of these animals had their condylar segments removed and immediately replaced to serve as surgical controls (group condyle). The other four underwent condylar replacement with the sternal end of their clavicles (group SCJ). Standardized lateral cephalometric radiographs with the aid of tantalum bone markers were used to evaluate maxillary and mandibular growth. One-way analysis of variance (ANOVA) was used to determine the significance of differences between groups. All animals showed good mandibular function and a class I molar relationship following an 18-month evaluation period. Statistical analysis showed there was no significant difference in maxillary or mandibular growth between any of the three groups. The results of this investigation show that the sternal end of the clavicle may be a viable option in mandibular condylar transplant surgery.

Proteinase, phosphatase and glucuronidase activities in the growing mandible and temporomandibular joint of the guinea pig

This study investigated the effect of muscle function and occlusal form on the activity levels of several enzymes present in the mandible or temporomandibular joint of the guinea pig. Restriction of maxillary width and asymmetric function of the mandible was caused in 12 animals at the age of 10 days, as described in the accompanying paper (Isotupa et al. 1992). Tissue samples from six anatomical sites were obtained from the animals sacrificed 4, 8, or 12 weeks after manipulation (4 animals in each group). Six age-matched animals acted as controls. Five samples were from the following sites of the mandible: the condylar cartilage, the lower and upper parts of processus angularis, and the anterior and posterior halves of the condyle neck. A sample was also obtained from fossa mandibularis of the temporal bone. Buffer extracts of powderized samples were studied for acid and alkaline phosphatase, glucuronidase and two types of proteolytic activity. Although the asymmetric manipulation of occlusion caused observable, localized asymmetric growth, the enzyme findings were not consistently asymmetric. Manipulation generally increased all enzyme activities regardless of whether apposition or resorption was involved. The activities of alkaline phosphatase more consistently showed this pattern, and changes in enzyme activities seemed to be sensitive, reflecting cellular or molecular level of growth. The enzyme activities may also reflect a certain type of after-effect of irritation, or a healing period. The inclusion of several types of enzyme determinations is recommended to complete macroscopic measurements. Subsequent chromatographic and electrophoretic studies are also useful.

Influence of asymmetric occlusal relationships and decreased maxillary width on the growth of the facial skeleton in the guinea pig

The purpose of this study was to evaluate the effect of muscle function and occlusal form on mandibular growth in guinea pigs. We hypothesized that restriction of maxillary width and asymmetric function of the mandible would lead to mandibular asymmetry. The hard palate of 12 animals was exposed at the age of ten days, and cyanocrylate was used to close the midpalatal suture in order to restrict transverse maxillary growth. The right incisors and right molars were ground obliquely at the time of surgery and every two weeks thereafter until the animals were sacrificed 4, 8 and 12 weeks later (four animals in each time group). Six age-matched animals served as controls. Dorsoversal x-rays were taken at sacrifice, followed by the removal of small biopsies from six different sites of the maxillomandibular skeleton for biochemical studies, which will be reported separately. Relative to controls, the treated animals exhibited a narrow maxilla and asymmetry in the height of the ramus and in the length of the mandible from the mental foramen to the angular process. The maximum width between the angular processes of the mandible was extremely narrow, as was the condylar neck especially on the right side. It was concluded that abnormal masticatory muscle function caused by occlusal deviation led to a narrowing and a slight asymmetry of the mandible in the growing guinea pig.

Osseous healing of the sagittal ramus osteotomy: a histologic comparison of rigid and nonrigid fixation in Macaca mulatta

Twenty-three adult female rhesus monkeys underwent advancement of the mandible by the sagittal split ramus osteotomy. Twelve had the proximal and distal segments wired together and underwent 6 weeks of maxillomandibular fixation (MMF). Eleven animals had bicortical bone screws placed between the segments and no postsurgical MMF. The animals were killed at 6 and 12 weeks and the osteotomy sites were prepared for histologic examination. Overall, the results showed that the two groups of animals underwent markedly different patterns of osseous healing. The osteotomy sites in the MMF animals were filled with callus, which then formed bone. In contrast, no callus was found in the majority of the rigid fixation osteotomy sites; direct bony deposition was found instead. The results of this investigation show that, like long bones, the sagittal osteotomy can heal by direct or indirect means depending on the rigidity of the fixation.

Making a challenge out of an NLN visit: any more questions?

Any educator, regardless of experience, feels apprehension as the final preparations are made for a National League for Nursing (NLN) review. Recognizing that 70% of our faculty had never experienced the review process, school administrators decided to take a novel approach to prepare faculty for the NLN visit. The authors discuss program development for a faculty workshop that modeled a popular television game show.

Coronoid process elongation in rhesus monkeys (Macaca mulatta) after experimentally induced mandibular hypomobility. A cephalometric and histologic study

The present study provided an experimental model that allowed a cephalometric and histologic analysis of craniofacial growth in monkeys with induced translatory impairment of the mandibular condyle. Cauterization was performed anterior to the joint in nine experimental rhesus monkeys, while eight animals served as control subjects. The experimental procedure produced mandibular hypomobility in six animals, in three by means of temporomandibular joint ankylosis and in three by means of dense scar tissue formation anterior to the joint. In the remaining three experimental animals no restriction of mandibular mobility was created. Mandibular hypomobility was found to induce elongation of the coronoid process and was also associated with bone deposition in the gonial region. In contrast, normal remodeling of the gonial region was found in the experimental animals with normal range of movements and in the control animals.

The effect of bite-opening appliances on mandibular rotational growth and remodeling in the rhesus monkey (Macaca mulatta)

Previous experimental studies that have used a bite-block cemented to the maxillary dental arch have shown that the direction of growth of the maxillary complex is redirected in a superior and anterior direction for approximately 12 weeks but reassumes a normal inferior and anterior direction after that time. The purposes of this study were (1) to examine the effect of increased vertical dimension and altered mandibular posture on growth of the mandible and (2) to determine whether or not an alteration in chronic mandibular position alters mandibular intramatrix rotation. Eleven Macaca mulatta monkeys wore 15 mm vertical bite-opening appliances for 24 or 48 weeks. Nine untreated animals were used as controls. All animals received tantalum bone implants to facilitate cephalometric analysis. Serial lateral radiographs of the mandible were traced and superimposed on bone implants for each animal to determine overall changes in mandibular shape (gonial angle) and the location of bone remodeling. During normal growth, the gonial angle closed an average of 0.1 degrees over a 48-week period. In the experimental animals, the gonial angle opened 6.4 degrees (p less than 0.005) as a result of remodeling during the period that mandibular posture was altered. Once normal mandibular posture was restored, this process was reversed; the gonial angle once again became more acute over time, and remodeling along the body and ramus of the mandible was similar to that observed in control animals. These results suggest that mandibular growth and remodeling can be influenced by altered mandibular vertical posture.

Occlusal force and craniofacial biomechanics during growth in rhesus monkeys

The masticatory muscles in 132 anesthetized male and female rhesus monkeys ranging in age from juvenile to adult were unilaterally stimulated. Muscle forces and speeds were measured with a bite force transducer positioned at the incisors, premolars, and molars during twitch and tetanic contractions. Lateral cephalographs of all animals were used to estimate the orientation and mechanical advantage of the masticatory muscles. Results showed that maximal occlusal forces increased at a greater rate than body weight during growth. However, maximal occlusal forces increased isometrically relative to mandibular length. Mean forces at the incisors ranged from 70.3 newtons (n) in juveniles up to 139.9 n in adult males. Forces at the molars were 2-2.5 times greater than at the incisors. Time-to-peak tension decreased with increasing body size from 44.1 msec in juveniles to 37.4 msec in adult females to 31.0 msec in adult males. Regression analysis showed that adult males have faster muscles than adult females or juveniles even when corrected for body size. Temporalis and masseter orientation was found to change little throughout growth. The mechanical advantage of the masseter and temporalis muscles for producing occlusal forces on the distal molars improved between juveniles and adults, which is contrary to findings of Oyen et al. (Growth 43:174-187, 1979). Among adults, females had a greater mechanical advantage of the masseter muscles than males.

Histochemical analysis of the masseter and temporalis muscles in macaca mulatta after mandibular advancement using rigid or nonrigid fixation

This study compared the histochemical characteristics of the temporalis and masseter muscles in monkeys who underwent mandibular advancement with and without immobilization of the mandible. The results showed, when compared with controls, that the animals who underwent maxillomandibular fixation (MMF) following advancement of the mandible had significant atrophy in both temporalis and masseter muscles. In contrast, much less myoatrophy was noted in the animals who underwent rigid internal fixation and no MMF following advancement of the mandible.

Adaptation of the lateral pterygoid and superficial masseter muscles to mandibular protrusion in the rat

It has been suggested that protrusion of the mandible results in an alteration of the functional activity of the lateral pterygoid muscle. If this is true, however, it is unclear whether this altered muscle function is a transient phenomenon with no long-term effect or whether it results in structural and functional adaptation of the involved musculature. The purpose of this study was to determine whether or not physiologic and metabolic changes take place within two jaw-protruder muscles--the lateral pterygoid muscle and the superficial masseter muscle--in rats after treatment with a protrusive appliance. Thirty 45-day-old male Sprague-Dawley rats were divided equally into experimental and control groups. The experimental animals wore bonded protrusive-type appliances for 2 weeks. Histochemical analysis of muscle fiber types and in vivo whole-muscle contractile-property analysis were used to evaluate structural and functional muscle adaptations. Mandibular length was slightly but significantly greater in the experimental group, indicating that the protrusive appliance had the expected positive effect on mandibular growth. Histochemically, the lateral pterygoid muscle in the experimental group exhibited a significantly greater area occupied by type I fibers at the expense of type IIb fibers. The superficial masseter muscle exhibited a significantly greater percentage of areas for both type IIa and type IIb fibers in the experimental group. Contraction time (TPT) increased in both muscles; that is, the muscles became slower. The histochemical and contractile-properties data indicate that the protrusive appliance caused the lateral pterygoid muscle to become more active with respect to tonic (postural) activity, whereas the superficial masseter muscle became more active phasically.

Electromyography of the suprahyoid musculature following mandibular advancement with and without rigid fixation

The purpose of this investigation was to determine if the activity of the suprahyoid musculature changes following advancement of the mandible and the use of rigid or nonrigid fixation. Ten monkeys underwent mandibular advancement; six underwent 6 weeks of maxillomandibular fixation (MMF), and four had rigid fixation without MMF. Electromyography (EMG) of the suprahyoid musculature was performed preoperatively, and at 3, 7, and 10 weeks postoperatively. The results of this study fail to demonstrate an increase in suprahyoid EMG activity following mandibular advancement. Furthermore, there were no differences between the groups with different types of fixation.

Aggregation of proteoglycans in cephalic, epiphyseal and articular cartilages in growing sheep

The purpose of this study was to determine whether there are age and site related differences in proteoglycan aggregation in craniofacial and epiphyseal cartilages from neonatal and two-month-old lambs. Proteoglycans were extracted using a dissociative extraction method, and aggregates and monomers separated with molecular sieving. Only a small proportion of the proteoglycans were isolated as aggregates in the articular and mandibular condylar cartilage of the neonatal animals, while in the nasal septal, epiphyseal and synchondrosal cartilages of the same animals the portion of proteoglycans isolated as aggregates, was 3 to 6 times as high. During the first 2 months of postnatal development the proportion of proteoglycans isolated as aggregates tripled in the articular and mandibular condylar cartilages, it decreased substantially in the anterior and posterior nasal septum, while it decreased slightly in the other cartilages. These observations indicate that there are age and site related differences in the extent of proteoglycans isolated as aggregates in cephalic, epiphyseal and articular cartilages.

Stability of midface augmentation: an experimental study of musculoskeletal interaction and fixation methods

This study examined stability of vertical midface augmentation when different methods to alleviate potentially distracting muscles were used. Eighteen adult monkeys underwent Le Fort I osteotomy with interpositional bone grafts. One group had wire fixation of the maxilla and bone graft. A second group underwent a similar procedure with the addition of myotomies of the masseter and temporalis muscles. A third group wore a bite-opening appliance before downgrafting. A fourth group underwent downgrafting with rigid internal fixation. Serial cephalograms with the aid of bone markers were used to assess postsurgical change. The results showed that the animals who underwent rigid fixation had the most stable results, followed by the myotomy and bite-opening appliance groups. The animals who underwent wire fixation with no supplemental procedures had gross relapse, resulting in an average retention of only 15% of the surgical change by 12 weeks.

Short-term stability and muscle adaptation after mandibular advancement surgery with and without suprahyoid myotomy in juvenile Macaca mulatta

The purpose of this study was to examine the short-term adaptations that occur within the mandible and anterior digastric muscle complex after mandibular advancement with and without suprahyoid myotomy in 20 juvenile rhesus monkeys. The results showed that the animals that did not undergo myotomy experienced relapse equivalent to 13% of the surgical advancement. Those animals that underwent a myotomy of the digastric muscle complex showed complete stability of the surgical lengthening of the mandible. Both groups of animals grew normally after the fixation period when compared to age-matched control animals. Analysis of adaptations within the digastric muscle complex was performed with the use of radiopaque muscle and tendon markers. The results showed an immediate lengthening of the entire digastric muscle complex with mandibular advancement surgery in the group that underwent advancement without myotomy. Further analysis showed that most lengthening in these animals occurred at the connective tissue interfaces of the complex--at the muscle-bone and muscle-tendon interfaces. No significant changes in sarcomere or fiber length were found in the group that did not undergo myotomy, although there was a significant shortening of muscle fibres resulting from loss of serial sarcomeres in the myotomy group. Comparison of histochemical characteristics of the anterior digastric muscle before and after surgery revealed the following findings: (1) there were no significant differences in percentage of composition between control and experimental muscles; (2) despite fixation of the jaws and myotomy, there was no evidence of atrophy of the anterior digastric muscle at any experimental interval; and (3) the type I fibers of the anterior digastric muscle underwent significant stretch-induced hypertrophy after lengthening. The results of this study support the hypothesis that tension produced by stretching of the connective tissues associated with the digastric muscle complex can contribute to postsurgical relapse of the surgically advanced mandible. However, no adverse effect on future growth of the mandible was observed from stretching the digastric muscle complex by mandibular advancement surgery in juvenile subjects.

Collagenolytic and phosphatase activity in the rat mandible after functional protrusion

The effect of chronic mandibular protrusion on the collagenolytic and phosphatase activity of several mandibular bone sites and the condylar cartilage was evaluated. Ninety-three male Sprague-Dawley rats were equally divided into two experimental and one control group. One experimental group wore a protrusive appliance for 2 weeks, the other for 4 weeks. All animals were killed at 59 days of age. Collagenolytic, alkaline and cid phosphatase activities were determined in the condylar cartilage, the subchondral bone and condylar neck, and in the gonial angle and coronoid process. In the cartilage and subchondral bone, the protrusive appliance caused a reduction in collagenolytic and alkaline phosphatase activity. In the condylar neck, it caused a large increase in collagenolytic activity and a decrease in alkaline phosphatase activity in both experimental groups. In the gonial angle and coronoid process, the appliance increased the collagenolytic activity only in the 2-week group. In the 4-week group, the alkaline phosphatase and collagenolytic activities were not different from the activities in those tissues in the control animals. Thus a protrusive appliance induced quantitative changes in enzyme activities in condylar cartilage and mandibular bone. The increase in collagenolytic activity (representing increased bone resorption) occurred typically in areas of muscle attachment and might have been the result of the neuromuscular changes induced by the protrusive appliance. The recovery to normal values of collagenolytic activity in the coronoid process and gonial angle of the 4-week group suggests that at these sites the muscles (and subperiosteal bone) might have adapted to their new biomechanical environment after the longer period of appliance wear.

The effects of mandibular immobilization on the masticatory system. A review

It is clear from this review that mandibular immobilization is not as benign a procedure as once thought. Detrimental effects on several tissues within the masticatory apparatus have been observed following mandibular immobilization. Atrophy of the muscles of mastication, degenerative changes within the mandibular condyle, and decreases in range of passive bite opening are all consistent findings following several weeks of mandibular immobilization. The use of fixation procedures which avoid the use of mandibular immobilization (i.e., rigid internal fixation) has been shown to minimize these problems. As with any procedure, however, the risks and benefits of rigid internal fixation must be weighed against the time-honored standard (i.e., maxillomandibular fixation). It is hoped that future research and clinical experience will direct the surgeon to select whichever technique is in the best interest of the patient.

Maxillomandibular growth 2 years after mandibular advancement surgery with and without suprahyoid myotomy in juvenile Macaca mulatta

There is conflict in the literature on whether continued and harmonious growth occurs after mandibular advancement in growing persons. The studies available are difficult to interpret because of the differing age ranges and the questionable growth potential inherent within the mandibular deficient patient. This study was performed to isolate the major question of interest to clinicians: Does the mandibular advancement surgical procedure inhibit future growth in a normally growing person? Six juvenile male Macaca mulatta monkeys were divided equally into two experimental groups. Group MAA had mandibular advancement surgery of approximately 4 mm. Group MAD had a similar surgical procedure with detachment of the suprahyoid musculature. All underwent 4 to 5 weeks of maxillomandibular fixation. Serial computerized cephalograms with the aid of bone markers were used to analyze the changes during a 2-year follow-up period. The postsurgical changes of the two experimental groups were compared statistically with control growth data on a large sample of normal Macaca mulatta animals available in our laboratory. The results showed the following. (1) There were significant short-term differences in the stability of the mandibular advancement between experimental groups. Group MAA (suprahyoid musculature attached) experienced significant relapse during the period of maxillomandibular fixation. Group MAD (suprahyoid musculature detached) experienced no relapse. (2) During the 2-year follow-up period after fixation, the rate and amount of mandibular growth in both experimental groups were not significantly different from age-matched controls or from each other. (3) At the end of the 2-year experimental period, the advanced mandibles were longer than the mandibles in age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation of the suprahyoid muscle complex to large mandibular advancements

The purpose of this study was to provide quantitative data concerning the changes and adaptations that take place within the suprahyoid complex to larger mandibular advancements. Mandibular advancement of 6.5 mm was performed on 12 adult rhesus monkeys. Six underwent maxillomandibular fixation (MMF) using the dentition, six underwent MMF using the dentition plus skeletal suspension wires. Mandibular position and changes in the length of the various anatomic regions of the suprahyoid complex were evaluated cephalometrically with the aid of radiopaque bone, muscle, and tendon markers implanted preoperatively. Relapse of the mandible in the dental MMF animals was 27% of the advancement, whereas there was none in the dental plus skeletal MMF group. Results of adaptations within the suprahyoid complex showed that 1) the suprahyoid complex was elongated slightly less than the mandible, and 2) the major adaptations (lengthening) occurred at the muscle-bone interface, the muscle-tendon interface, and within the belly of the anterior digastric muscle. On the basis of these results, it was concluded that adaptations within the suprahyoid complex to mandibular lengthening occur first at the connective tissue attachments of the muscle, and then within the muscle belly itself. The methods of dealing with the potentially distracting forces from the stretch within the suprahyoid complex are discussed.

Histochemical characteristics of masseter and temporalis muscles after 5 weeks of maxillomandibular fixation--an investigation in Macaca mulatta

This study describes the histochemical characteristics and cross-sectional areas of the superficial masseter and temporalis muscles in juvenile rhesus monkeys after 5 weeks of maxillomandibular fixation. Four juvenile male Macaca mulatta underwent mandibular surgery and 5 weeks of maxillomandibular fixation as part of a study of temporomandibular joint (TMJ) adaptations after condylar replacement. Immediately before the time the animals were killed (5 weeks postsurgically), biopsies of the masseter and temporalis muscles were obtained and submitted to histochemical analysis and calculation of muscle-fiber areas. The data were compared to histochemistry from 12 juvenile control Macaca mulatta. Significant decreases in mean cross-sectional area were exhibited in both type I (p less than 0.05) and type II (p less than 0.01) fibers in all muscles when compared to controls (n = 12). The ratio of type I to type II fibers, however, remained constant during maxillomandibular fixation in masseter and temporalis muscle samples, indicating no change in relative types of fibers. We conclude from this experimental investigation that (1) significant atrophy occurs in the temporalis and masseter muscles after 5 weeks of maxillomandibular fixation, and (2) this atrophy occurs in both type I and type II fibers, indicating that overall recruitment of the muscle (and not just of one fiber type of motor unit) was affected during fixation.

Increased masticatory muscle stiffness during limb muscle flaccidity associated with succinylcholine administration

The resistance of mouth opening to a constant force of 1.7 N was measured in 44 pediatric subjects anesthetized with enflurane and paralyzed with succinylcholine or vecuronium. Measurements were made during a deep level of anesthesia before relaxant administration, immediately after the loss of the adductor pollicis muscle twitch and 45 s later. In 22 patients receiving succinylcholine, there was a significant reduction in mean mouth opening (from 16.9 +/- 2.8 to 12.6 +/- 4.3 to 13.0 +/- 4.3 mm; P less than 0.0005) and an increase in jaw stiffness (from 102.3 +/- 21.9 to 154.5 +/- 77.4 to 150.5 +/- 77.0 Nm/degree; P less than 0.02) immediately after disappearance of the evoked thenar muscle twitch, as well as 45 s later. In six patients receiving succinylcholine, measurements were continued at 1 min intervals; mouth opening reduction and jaw stiffness increase lasted up to 10 min and extended beyond the return of visible twitch. One patient had a reduction of mouth opening from 20 to less than 1 mm; his corresponding jaw stiffness changed from 83.4 to 3335.4 Nm/degree. This patient, considered by us to have masseter spasm, required several attempts at tracheal intubation due to an increased resistance to mouth opening, as did one other patient. Patients receiving vecuronium showed a significant (P less than 0.02) increase of mouth opening 45 s following loss of twitch (from 19.8 +/- 3.6 to 20.9 +/- 4.1 mm; jaw stiffness changed from 87.0 +/- 15.3 to 83.0 +/- 17.2 Nm/degree). Anesthesia and surgery proceeded normally; in most patients, in excess of 1 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Stability of the mandible following advancement: a comparison of three postsurgical fixation techniques

This study examines short-term stability of the mandible following mandibular advancement surgery by means of three standard techniques of postsurgical fixation. Twenty-two adult female rhesus monkeys (Macaca mulatta) underwent sagittal ramus advancement osteotomy of approximately 4 to 6 mm. Six animals had dental maxillomandibular fixation alone. Six animals had dental plus skeletal maxillomandibular fixation with circummandibular wires connected to pyriform aperture wires. Ten animals had rigid internal fixation with bicortical bone screws between the proximal and distal segments without maxillomandibular fixation. Radiographic cephalograms with the aid of tantalum bone markers and dental amalgams were analyzed during the first 6 postoperative weeks to evaluate skeletal and dental stability. Rigid internal fixation and the use of dental plus skeletal maxillomandibular fixation were both equally effective in the prevention of postsurgical relapse. However, in the animals in which only dental maxillomandibular fixation was used, statistically significant changes (relapse) occurred when compared with either of the other groups.

A comparison of stimulated bite force after mandibular advancement using rigid and nonrigid fixation

This study evaluated maximum stimulated molar bite force following advancement of the mandible in 17 adult Macaca mulatta using rigid and nonrigid fixation techniques. Cephalometric analysis was also performed to determine the amount of proximal segment rotation. Analysis of the bite force showed the animals whose mandibles were advanced using rigid fixation to have significantly greater bite force at six weeks postsurgery when compared to those animals who underwent mandibular advancement and six weeks of maxillomandibular fixation. By the ninth postoperative week, there was no longer any significant difference between the two groups, indicating a rapid recovery of muscle function in the animals whose mandibles were immobilized following advancement. Both groups, however, had significant decreases in bite force at 12 weeks postsurgery when compared to preoperative values. Neither group had a significant amount of proximal segment rotation from the surgery.

The effects of pain from the mandibular joint and muscles on masticatory motor behaviour in man

Habitual chewing of a coherent bolus was studied in 12 dentate subjects with painful mandibular-joint disorders and 12 healthy, dentate controls. Bilateral electromyograms of jaw elevators, and jaw movement, were recorded for three complete masticatory sequences. Computer analysis was used to classify chewing movements as continuous or discontinuous. Root-mean-square (r.m.s.), myoelectric signal amplitudes were computed for each of four jaw elevators. Although discontinuous chewing cycles were significantly more frequent in painful function (p = 0.001), they also occurred in pain-free function, a finding which reduces their diagnostic significance. During painless and painful function, r.m.s. activities did not differ statistically when elevators acted as agonists on both the dominant and non-dominant chewing side (p greater than 0.1). When used as antagonists, such as during jaw opening, the elevators had greater mean peak activities during painful than painless function (p = 0.0001). Variability in maximum gape was greater during painful than painless function (p = 0.001), but peak maximum gapes in complete masticatory sequences were not affected by pain, and neither were minimum interocclusal gapes. More frequent reshaping and repositioning of the bolus in the presence of pain could explain these differences between painful and pain-free function.

The effects of succinylcholine on mouth opening

Mouth opening and the resistance to opening developed by the muscles of mastication were measured in 63 children anesthetized with halothane and relaxed with succinylcholine, pancuronium, or vecuronium. Measurement of mouth opening, induced by a constant test force, was made when each patient was deeply anesthetized, as judged by clinical parameters. Succinylcholine, vecuronium, or pancuronium was then administered. The mouth opening measurement was repeated immediately after the loss of limb muscle twitch response and 45 s following the loss of twitch response. For the 24 patients receiving succinylcholine, there was a significant reduction in mean mouth opening (P less than 0.0001) and a significant increase in jaw stiffness (P less than 0.0001) immediately after limb relaxation. Forty-five seconds after full limb relaxation was attained, the mean mouth opening was still reduced (P less than 0.0001) and the mean jaw stiffness was still increased (P less than 0.0003) in the succinylcholine group. Patients receiving either vecuronium or pancuronium did not show a significant change of mouth opening or jaw stiffness following limb relaxation. Three patients, who received succinylcholine, required several attempts at tracheal intubation due to increased resistance to mouth opening. Anesthesia and surgery proceeded in all patients. None of the patients developed malignant hyperthermia. In view of the fact that a reduction in mouth opening was a constant finding when succinylcholine was administered during halothane anesthesia, the assumption that isolated "masseter spasm" or jaw stiffness heralds malignant hyperthermia should be reconsidered.

Histologic analysis of costochondral and sternoclavicular grafts in the TMJ of the juvenile monkey

Variability in growth response of the mandible after replacement of the mandibular condyle with the costochondral junction of a rib (CCJ) is common. Other donor graft sites that are more similar to the mandibular condyle might be more suitable for mandibular condylar replacement. Previous studies have shown the histomorphologic and developmental similarities between the sternoclavicular joint (SCJ) and temporomandibular joint (TMJ). The purpose of this study was to evaluate histologically short-term adaptations within the TMJ after replacement of the mandibular condyle with the autogenous sternal head of the clavicle, and to compare these adaptations with autogenous CCJ and mandibular condyle (surgical control) transplants. Bilateral vertical ramus osteotomies were performed in 12 juvenile Macaca mulatta with the left condyle being immediately replaced and the right condyle removed and replaced with either the sternal head of the clavicle or costochondral junction of a rib. All grafts were stabilized with maxillomandibular fixation for five weeks. Two animals in each group were killed at five, 11, and 17 weeks postsurgery and prepared for histologic analysis. The results indicate that: 1) incorporation of all grafts into the recipient site occurred and all animals had good mandibular function and occlusion throughout the follow-up period; 2) the clavicular and mandibular condylar grafts were incorporated sooner than the CCJ grafts; 3) clavicular graft changes resembled those of the condylar grafts histologically while the costal grafts remained inert and unchanged; and 4) a new condylar process with cartilage similar to that of a normal mandibular condyle regenerated in the costal graft animals from cells presumably contributed by the periosteum of the mandibular ramus and TMJ capsule.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation of the suprahyoid muscle complex to mandibular advancement surgery

The suprahyoid musculature has been implicated as one of the major factors responsible for relapse after mandibular advancement surgery. Previous studies have also indicated that the muscle and connective tissues comprising the suprahyoid complex must adapt to increased length brought about by mandibular advancement for skeletal stability to be achieved. The purpose of this study was to provide quantitative data concerning the immediate changes and long-term adaptations that take place within the suprahyoid complex over a 2-year period after mandibular advancement. Mandibular advancement was performed on ten adult Macaca mulatta monkeys with and without suprahyoid myotomy (n = 5/group). Six animals were used as controls. Mandibular length and changes in the length of the various anatomic regions of the suprahyoid complex were evaluated radiographically with the aid of radiopaque bone, muscle, and tendon markers implanted preoperatively. The results for the nonmyotomy group showed that the suprahyoid complex was elongated approximately two thirds the amount of mandibular lengthening, the major immediate adaptations within the suprahyoid complex after the surgical procedure occurred at the muscle-bone interface and the muscle-tendon interface, the change in length at the muscle-tendon junction was maintained throughout the 2-year follow-up period, indicating that significant long-term adaptations took place primarily at that location, and no significant short-term changes or long-term adaptations were seen within the anterior digastric muscle or the intermediate digastric tendon. Within the myotomy group, it was found that the suprahyoid complex recoiled immediately after myotomy such that the anterior belly of the digastric muscle became separated from the advanced distal mandibular segment by more than twice the amount of mandibular lengthening, the anterior digastric muscle remained essentially at this posterior position throughout the 2-year follow-up period, and though not significant, there was a trend for a decrease in the length of the anterior digastric muscle belly. On the basis of these results, it was concluded that both short-term changes and long-term adaptations to lengthening of the suprahyoid complex as a result of mandibular lengthening occur primarily within the connective tissues comprising the muscle-tendon and muscle-bone interfaces, not within the muscle fibers themselves.

Communicating Leveled Clinical Expectations to Nursing Students

Nurse educators agree on the need for objectives in the classroom situation and frequently communicate them in a written form. Written expectations for clinical, however, are rarely given to student nurses prior to their clinical experience. Clinical expectations are understood by instructors, but communicating them to students result in mixed interpretations. The article describes the development of a written method of communicating clinical expectations to solve this problem. This method correlates clinical expectations with classroom content and course objectives and levels the expectations in increasing complexity by using the nursing process as a framework. The written leveled expectations are distributed to student nurses on a weekly basis. Clinical experiences are enhanced for students and faculty who use this method.

Occlusal force after mandibular advancement in adult rhesus monkeys

Maxillofacial surgery not only alters facial appearance and occlusion but also affects the morphology, physiology, and biomechanics of the craniofacial skeleton and the muscles of mastication. This study was performed to evaluate one aspect of craniofacial function--maximum stimulated bite force (BF)--after mandibular advancement. BF in the molar region was measured with a transducer during muscle stimulation in 63 rhesus monkeys that had been divided into two groups: a control group of various ages and sexes (n = 50); and an experimental sample of 13 monkeys that had undergone mandibular advancement via C-osteotomy at least one year prior to BF measurement. Biomechanical analysis of lateral cephalograms was performed to estimate the amount of the change in BF in the experimental group that could be attributed to alteration of craniofacial form. Regression analysis demonstrated a significant relation between molar bite force and weight in control animals (r = 0.94). In the monkeys that underwent surgery, BF values were an average of 16.7% less than those found for the control animals relative to body weight. However, the biomechanical analyses suggested a smaller and less variable BF loss in the operated monkeys (11.6%). These results indicate a greater and more variable change in BF following mandibular advancement than would be predicted on the basis of biomechanical considerations.

Adaptations in the temporalis muscles of rabbits after masseter muscle removal

Masseter muscles were surgically removed in six young female rabbits so that we could study adaptations of the superficial temporalis muscles (ST) to increased functional requirements. Eight weeks following surgery, we used morphological measurements, histochemistry, contractile properties in situ, and occlusal force in vivo to compare the muscles in the experimental animals and six control rabbits. Analysis of the results demonstrated a decrease in fatigability of ST after masseter myectomy. Incisal occlusal force decreased by 65% during the first two weeks, and no recovery was observed during the following six weeks. At eight weeks post-surgery, the mass, twitch tensions, and tetanic tensions of ST were not significantly different from those of the controls. An increase in the percent of the cross-sectional area composed of fast fatigue-resistant fibers, a slower time-to-peak twitch tension, and a decrease in fatigability suggest an increase in oxidative metabolism. Analysis of these results suggests that muscles used for highly repetitious activities with submaximal loadings adapt to increased functional requirements by increasing fatigue-resistant properties.

Histologic comparison of the costochondral, sternoclavicular, and temporomandibular joints during growth in Macaca mulatta

The costochondral joint (CCJ) is commonly used to replace defective mandibular condyles in children for the restoration of normal temporomandibular (TMJ) growth and function. However, continued and harmonious growth following rib grafting is the exception rather than the rule. This may be due to the differences in the growth characteristics of the costal cartilage and the condyle. A joint that is similar both developmentally and structurally to the TMJ is the sternoclavicular joint (SCJ). The purpose f this study was to describe histologically the SCJ and CCJ during growth in Macaca mulatta and to compare the histomorphologic features with those of the TMJ. Costochondral and sternoclavicular joints were obtained from infant, juvenile, adolescent, and adult Macaca mulatta. The histologic sections were compared with mandibular condyles of the same ages available in our laboratory. The results indicate that the TMJ and SCJ are very similar morphologically throughout the growth period. The clavicular head contained layers of cartilage typical of the mandibular condyle, i.e., articular, prechondroblastic, chondroblastic, hypertrophic, and endochondral ossification layers, at each age during growth. Like those in the condyle, the hypertrophic cartilage cells were arranged in an apparently random, noncolumnar fashion. The CCJ, however, did not resemble the condyle but appeared to be more similar to the growth plate in a long bone epiphysis during growth. The results of this investigation indicate that the SCJ may be more suitable for mandibular condylar replacement than the CCJ.

Response of the mandibular joint to loss of incisal function in the rat

In a study of the rat mandibular joint (MJ), Simon [Acta anat. 97: 351-360 (1977)] suggested that reduction in condylar cartilage thickness noted in animals subjected to removal or trimming of incisors resulted from the lessening of joint reaction forces produced during incision. In order to explore this question further, the microanatomy of the MJ in 47-day-old rats whose incisors had been trimmed every other day was compared to that in control animals and in a third group fed a soft diet as a control for reduced joint reaction forces. Both the incisor-clipped and soft-diet groups exhibited reduced size and density of bony trabeculae underlying the condylar cartilage and diminished staining for alcian blue. The thickness of the prechondroblastic layer of the condylar cartilage was significantly (p less than or equal to 0.01) reduced relative to controls in both experimental groups on the superior aspect of the cartilage, but was reduced in the more posterior parts of the cartilage only in the incisor-clipped group. While not denying that joint reaction forces may affect MJ response, the reduced proliferative response noted in the posterior region of the condylar cartilage in incisor-clipped animals is perhaps best explained by a decrease in the frequency and extent of protrusion of the lower jaw due to a lack of incisal preparation of food items.