Mastication in springhares,Pedetes capensis: A cineradiographic study

Analysis of lateral and dorsoventral radiographic films shows that ingestion, transport, and mastication in Pedetes capensis (Rodentia) are cyclic and their movement patterns are essentially similar for the three food types offered. During the ingestion cycle, closing of the mouth is accompanied by a backward translation of the condyles, so that movement is predominantly orthal. During the opening stage, the extent of the anterior condylar translation is smaller. As a result the mandibular incisors move ventrally and posteriorly. During the ingestion cycles, food is transported to the back of the tongue, with the transverse rugae and the folds of the upper lip playing important roles. Springhares show a bilateral masticatory pattern; food is chewed on both sides simultaneously. During chewing, the condyles lie in their most forward position at maximum opening of the mouth. The mouth is closed by rotation of the lower jaw around the temporomandibular joint coupled with posterior condylar translation. At the beginning of the slow-closing stage, the upward rotation of the mandible slows and the jaw slowly shifts forward. During the grinding stage, the mandible is shifted forward with both toothrows in occlusion. During the opening stage, the jaw returns to its starting position. Comparison of kinematic and anatomical data on rodent mastication suggests that some dental characteristics form the most important factors regulating the masticatory pattern and consequently allow reasonably reliable prediction of rodent masticatory patterns.     

Biomechanical scaling of mandibular dimensions in New World Monkeys

Previous studies show that folivorous Old World monkeys have shorter, deeper mandibles and shorter, wider condyles than frugivorous ones. These morphologies have been related to leaf mastication in colobines and ingestion of large, tough fruits in cercopithecines. This study examines New World monkeys in order to determine whether they exhibit similar adaptations to diet. New World monkeys have relatively long, transversely thin mandibles and somewhat deep mandibles and narrow condyles. Except for their deep mandibles, folivorous New World monkeys (i.e., Alouatta) do not exhibit the mandibular and condylar specializations typical of cercopithecid folivores. Reliance on comparatively nonfibrous foods plus alterations in masticatory muscle ratios among New World monkeys partially accounts for observed differences between folivorous New and Old World monkeys. In addition, adaptations for howling in Alouatta appear to have a significant effect on mandibular morphology. A biomechanical interpretation of craniofacial scaling patterns suggests that the mandibles of New World monkeys are subjected to lower condylar loads and considerably less twisting of the mandibular corpus than those of comparable Old World monkeys.     

The significance of a differential distribution of alkaline phosphatase in the perichondrium of the mandibular condylar cartilage in the wistar albino rat

Summary The aim of the present investigation has been to further study an incidentally observed rare distribution of alkaline phosphatase in the covering of the mandibular condyle. It was felt that this phenomenon might be related to the necessary interaction between the bony and the cartilaginous condylar head during the transformative growth movements of the condylar process.The study has been based on histomorphological and histochemical observations on frontal and sagittal sections of mandibular condyles from rats between 10 and 21 days of age. As regards the bony condylar head which is oval with its long axis in the antero-posterior direction the observations showed that this structure during growth is transformed in a superior, posterior and medial direction. This involves differential resorption on the surfaces in the anterior part and differential apposition on the surfaces in the posterior part.As regards the cartilaginous condylar head, the observations showed that its shape in the frontal plane changes from triangular in the anterior part to rectangular in the posterior part. Alkaline phosphatase reaction in its perichondrium always reaches a higher level medially than laterally.General observations of perichondrial alkaline phosphatase reaction were applied to the distribution of the enzyme in the perichondrium of the mandibular condyle. These data suggest that as the condylar cartilage grows medially, it becomes narrower anteriorly and broader posteriorly.     

Effects of mechanical loads on surface morphology of the condylar cartilage of the mandible in rats

Mechanical loads on the condylar cartilage were varied by feeding either a hard diet, a soft diet, or a sequential combination of a soft diet followed by a hard diet to young male and female rats for a total period of 4 weeks, and to mature male rats for 12 weeks. Gross condylar dimensions were greatest in the hard-diet groups, intermediate in the combination soft/hard-diet groups, and smallest in the soft-diet groups. Scanning electron microscopy of the condyle revealed a smooth, nonporous articular surface in the soft-diet groups. Hard-diet condyles had a rougher, more porous articular surface while soft/hard-diet condyles were intermediate between nonporous and slightly roughened condyles. None of the condyles showed ridges or elevations on the articular surface. Sex, age and time of the diets did not significantly affect these results.     

Comparative myology of the hominoid cranial base. I. The muscular relationships and bony attachments of the digastric muscle

This paper aims to document accurately the soft tissue anatomy and bony attachments of the posterior belly of the digastric muscle and other closely related muscles in the mastoid region of extant hominoids and fossil hominids. Five wet specimens including individuals of Pan, Gorilla and Pongo were dissected and described. Eight casts of fossil hominid cranial bases were also studied along with measurements and notes made from the same original fossil hominid specimens to assess their soft tissue markings in the light of the findings for the three great apes. The results indicate that whereas the attachment of the posterior belly of the digastric muscle in Homo sapiens is associated with a deep groove or fossa, it originates from a widened area and leaves no bony markings on the cranial base of the three great apes. Following a change in the position of the foramen magnum and the occipital condyles in hominids and H. sapiens the insertion of the posterior belly of the digastric has remained posteriorly positioned but has become compressed into a deep groove. It is likely that this has come about by the displacement of the more medial soft tissue structures which have been moved laterally away from the occipital condyles.     

Variations of femoral condyle shape

The aim of this study is to mathematically approximate the shape of the femoral articulating line and compare radiuses of condylar curves within and between males and females. Ten male and ten female participants were included in the study. Radiuses of medial and lateral condylar curves were calculated from the side view knee X-ray by original mathematical equation. Average radiuses of condylar curves were between 4.5 and 1.7 cm medially, and between 3.2 and 1.8 cm laterally, for 0 degrees and 90 degrees flexion contact point respectively. Males had longer curve radiuses of both condyles (p < 0.05). Differences turned out to be statistically insignificant after adjusting to body height. Even small changes in the joint geometry during lifetime could make a joint susceptible to osteoarthritis or injuries. Approximation of the radiuses of femoral condyle curves is a useful method in anthropometric, radiological and virtual calculations of the knee geometry, and other ellipsoidal structures in human body, like wrist, scull segments, dental arches, etc.     

The false and the true bifid condyles

The bifid mandibular condyle has been described as a condition of unknown ætiology and uncertain pathogenesis. Many see it as the product of accidental trauma or forceps delivery, with the two heads occurring one behind the other in the sagittal plane.

In bioanthropological literature, “bifid condyle” often describes pitting in the sagittal plane, dividing the condyle mediolaterally.

We examined 38 male and 16 female pre-European-contact Pacific islanders’ adult mandibles, and 24 male and 29 female modern Indian mandibles, recording frequency, prominence and position of any condylar groove in both coronal and sagittal planes.

We report the tenth known case of a bilaterally-bifid condyle. A groove was found almost twice as likely to occur on the left condyle of the Indians than of the Pacific Islanders, but equally likely to occur on the right side of both groups. That same finding applied to males and females.

In order to avoid terminological ambiguity, we suggest that the term “bifid condyle” should be reserved for describing multiple condyles in the sagittal plane only – the true bifid condyle.

An hypothesis is offered for the occurrence of the groove in the sagittal plane.     

New aspects of the histology of the mandibular condyle in the rat

The function of the multipotential mesenchymal cells in the mandibular condyle was studied histochemically and histologically in 27 Long Evans/Turku rats. Sagittal sections from the temporomandibular joint were stained with haematoxylin and eosin, toluidine blue, or van Gieson's stain. A weakly orthochromatically stained fibrous layer was followed in the upper region by a weakly metachromatically stained mesenchymal cell layer. Deep within this was a strongly metachromatically stained layer of immature chondroblasts. The metachromasia of the matrix of these layers disappeared abruptly in an anterior direction and gradually in a posterior direction. The changes in the staining reactions are explained by the fact that mesenchymal cells can differentiate into chondrogenic or osteogenic cells depending on the environmental conditions. A new hypothesis is presented according to which regulation of the direction of condylar growth is achieved by choosing the cells for chondrogenesis more posteriorly or anteriorly from among the mesenchymal cells covering the whole condylar cartilage.     

Quantitative method for the classification of human mandibular condyles

This study is concerned with the classification of mandibular condyles on the basis of the shape of their frontal section. In a previous work, Yale et al. [Oral Surg. 16: 572-577, 1963] had divided mandibular condyles into 4 groups: flat, convex, angled, and round. The distinction between them had been found upon simple inspection. In this paper a quantitative method is proposed, in which mandibular condyles may be classified into the same 4 groups according to inequalities concerning measurable parameters of their frontal section. The process is greatly facilitated by the use of a programmable computer. The proposed method has been applied to a sample of 254 human mandibles (hence 508 condyles); the percentage of each group has been the following; flat 11%; convex 38%; angled 41%, and round 10%. It is plausible to surmise that the quantitative character of the proposed method may be of significant use in oral radiology as well as in anthropological research.     

Mandibular condylar growth alterations after unilateral partial facial paralysis: an experimental study in the rabbit.

In a previous study in the rabbit, the authors defined the macroscopic growth alterations after unilateral partial facial paralysis. Dry skull measurements revealed a reduced premaxillary, maxillary, mandibular, and anterior corpus length with a simultaneous increase in mandibular ramal height on the paralyzed side. The authors hypothesize that these mandibular growth alterations are, among others, caused by alterations in condylar growth activity and that an altered occlusal relationship may be involved in the adaptive condylar growth response after facial paralysis.A total of 84 New Zealand White rabbits were used for this study. The animals were randomly assigned to either a control group that was not operated on (n = 28), a group that underwent a sham-operation (n = 28), or an experimental group (n = 28). In the sham-operation group, the facial nerve was dissected as in the experimental group but was left intact. In the experimental group, a left-side partial facial paralysis involving the midfacial muscles was induced by an operation at the age of 12 days. After different follow-up time intervals of 3.5, 7, 14, 21, 28, 42, and 56 days, four control, four sham-operation, and four experimental animals (all randomly selected) were killed for histomorphometric measurements of the left control and sham condyles and the left-side and right-side experimental condyles.No significant differences between the control and sham-operation groups were found. The other results revealed that shortly after the paralysis in the experimental group, as compared with the controls, a decrease in condylar growth activity was seen before a catch-up increase in activity, as expressed by the time-sequenced decrease and increase in the height of the functional and hypertrophic chondroblast layer. The response on the right side was analogous, though less intense.It is suggested that the mandibular ramal growth alterations might be the result of a chain of adaptations involving the lateral pterygoid muscle and the condylar growth activity. The unilaterally restricted length increment of the maxillary snout, as a result of the loss of tensile forces caused by paralysis of the midfacial musculature, necessitated an adaptation in the position of the mandible to maintain a normal occlusal relationship. Subsequently, the function of muscles involved or influenced by an altered mandibular position, such as the lateral pterygoid muscle, were changed. These altered muscle activities induced condylar growth adaptations, which in turn explained the alterations in mandibular ramal growth.     

The morphological basis of hallucal orientation in extant birds

The perching foot of living birds is commonly characterized by a reversed or opposable digit I (hallux). Primitively, the hallux of nonavian theropod dinosaurs was unreversed and lay parallel to digits II-IV. Among basal birds, a unique digital innovation evolved in which the hallux opposes digits II-IV. This digital configuration is critical for grasping and perching. I studied skeletons of modern birds with a range of hallucal designs, from unreversed (anteromedially directed) to fully reversed (posteriorly directed). Two primary correlates of hallucal orientation were revealed. First, the fossa into which metatarsal I articulates is oriented slightly more posteriorly on the tarsometatarsus, rotating the digit as a unit. Second, metatarsal I exhibits a distinctive torsion of its distal shaft relative to its proximal articulation with the tarsometatarsus, reorienting the distal condyles and phalanges of digit I. Herein, I present a method that facilitates the re-evaluation of hallucal orientation in fossil avians based on morphology alone. This method also avoids potential misinterpretations of hallucal orientation in fossil birds that could result from preserved appearance alone.     

Relationship between the mandibular condyle and the occlusal plane during hominid evolution: Some of its effects on jaw mechanics

A selection of mandibles from recent higher primates, fossil hominids, and hominoids has been studied from photographs of skulls, reproductions, and material published by others, all viewed in the sagittal plane. Tracings of each mandible were constructed so that the dentitions were all scaled to the same length (d) and superimposed. The (scaled) positions of the articular surfaces of the condyles (J = joint point) were compared. The height of each J point above the scaled dentition (h = effective condyle height) and its distance behind the dentition (r = effective ramus width) were compared. With very few exceptions d r > d/2. There was a poor correlation between r and the amount of prognathism. The position of the J point with respect to the occlusal plane was different for different groups within the material analysed and could prove to be a useful tool to help improve the reconstruction of fragmented fossil material. Some examples are given. A. afarensis and Homo habilis shared a low and anterior J point (r ～ d/2). The later australopithecines evolved a high and anterior J point, whereas that of Homo erectus was raised and displaced posteriorly (r ～ 3d/4). The value of r was increased to d in the Neanderthals, and recent man has moved the J point forward again. The effect of the position of the J point, the slope of the preglenoid plane, and the curve of Spee on the relationship between upper and lower postcanines when the jaw is opened and then closed to process food have been analysed. The results show that the position of the J point affects the way in which the mandible moves, and this may be related to changes in diet during evolution.     

Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using 'interventional' MRI

The aim of this study was to image tibio-femoral movement during flexion in the living knee. Ten loaded male Caucasian knees were initially studied using MRI, and the relative tibio-femoral motions, through the full flexion arc in neutral tibial rotation, were measured. On knee flexion from hyperextension to 120 degrees , the lateral femoral condyle moved posteriorly 22 mm. From 120 degrees to full squatting there was another 10 mm of posterior translation, with the lateral femoral condyle appearing almost to sublux posteriorly. The medial femoral condyle demonstrated minimal posterior translation until 120 degrees . Thereafter, it moved 9 mm posteriorly to lie on the superior surface of the medial meniscal posterior horn. Thus, during flexion of the knee to 120 degrees , the femur rotated externally through an angle of 20 degrees . However, on flexion beyond 120 degrees , both femoral condyles moved posteriorly to a similar degree. The second part of this study investigated the effect of gender, side, load and longitudinal rotation. The pattern of relative tibio-femoral movement during knee flexion appears to be independent of gender and side. Femoral external rotation (or tibial internal rotation) occurs with knee flexion under loaded and unloaded conditions, but the magnitude of rotation is greater and occurs earlier on weight bearing. With flexion plus tibial internal rotation, the pattern of movement follows that in neutral. With flexion in tibial external rotation, the lateral femoral condyle adopts a more anterior position relative to the tibia and, particularly in the non-weight bearing knee, much of the femoral external rotation that occurs with flexion is reversed.     

Light- and electron-microscopic observations on the mandibular condylar cartilages in growing rats on a low-calcium diet.

In order to obtain more insight into the physiologic mechanism of endochondral ossification, histological changes occurring in the mandibular condylar cartilage of growing rats fed on a low-calcium diet were investigated by light and electron microscopy. Twenty-three-day-old rats were fed on a normal diet or a low-calcium diet for 8 weeks. For the histological observations the mandibular condyles were dissected from each animal at 1, 2, 4, 5 and 8 weeks after the initiation of the experiment. Histological changes occurring in the mandibular condylar cartilages of the rats fed on a low-calcium diet were as follows: (1) narrow proliferative and mature cell zones and a wide hypertrophic cell zone, (2) inhibition of development of cell organelles in the mature chondrocytes, (3) decrease in dead cells in the proliferative zone, (4) decrease in glycogen accumulation in the chondrocytes and (5) inhibition of calcification in the extracellular matrix of the hypertrophic cell zone. Additionally at the end of the experimental period, the following findings were observed: (1) appearance of small light cells in the mature cell zone and the hypertrophic cell zone and (2) decrease in proteoglycan granules and appearance of large collagen fibrils in the pericellular region of the hypertrophic cell zone.     

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.     

The effect of dietary consistency on gross and histologic morphology in the craniofacial region of young rats

Three groups of weanling rats and three groups of juvenile rats were fed diets which differed in physical consistency for periods of 5 and 8 weeks, respectively. In both the weanling and juvenile rats, one group was fed a soft diet, a second group was fed a hard diet, and a third group was initially fed the soft diet and then was switched to the hard diet for the remainder of the experimental period. The effects of these differences in dietary consistency on gross and histologic morphology of the craniofacial region were examined. Significant differences were found in the dimensions and morphology of the condyle and condylar cartilage as a result of the differences in dietary consistency in both the weanling and juvenile groups. Soft-diet rats generally had smaller condyles and a thinner layer of condylar cartilage than either hard-diet or soft/hard-diet rats. Little change, however, was found in the overall dimensions of the mandible and maxilla in any of the groups of rats.     

A dynamic model of jaw and hyoid biomechanics during chewing

Our understanding of human jaw biomechanics has been enhanced by computational modelling, but comparatively few studies have addressed the dynamics of chewing. Consequently, ambiguities remain regarding predicted jaw-gapes and forces on the mandibular condyles. Here, we used a new platform to simulate unilateral chewing. The model, based on a previous study, included curvilinear articular guidance, a mobile hyoid apparatus, and a compressible food bolus. Muscles were represented by Hill-type actuators with drive profiles tuned to produce target jaw and hyoid movements. The cycle duration was 732 ms. At maximum gape, the lower incisor-point was 20.1mm down, 5.8mm posterior, and 2.3mm lateral to its initial, tooth-contact position. Its maximum laterodeviation to the working-side during closing was 6.1mm, at which time the bolus was struck. The hyoid's movement, completed by the end of jaw-opening, was 3.4mm upward and 1.6mm forward. The mandibular condyles moved asymmetrically. Their compressive loads were low during opening, slightly higher on the working-side at bolus-collapse, and highest bilaterally when the teeth contacted. The model's movements and the directions of its condylar forces were consistent with experimental observations, resolving seeming discordances in previous simulations. Its inclusion of hyoid dynamics is a step towards modelling mastication.     

A kinematic and anthropometric study of the upper cervical spine and the occipital condyles

The center of rotation (COR) of the upper cervical spine (UCS) is an important biomechanical landmark that is used to determine upper neck moment, particularly when evaluating injury risk in the automotive environment. However, neither the location of the UCS CORs nor the occipital condyles (OCs), which are frequently the referenced landmark for UCS CORs, have been measured with respect to known cranial landmarks. This study determines the CORs using pure bending (+/-3.5 N m), 3D digitization, and image analysis. Landmarks digitized included the OCs, external auditory meatus (EAM), infraorbital foramen, zygion, nasion, and the foramen magnum. The centroid of each occipital condylar surface (area 301+/-29.8 mm(2); length 25.4+/-3.2 mm) was located 18.4 mm posterior, 54.4 mm medial, and 31.0 mm inferior of the EAM. The UCS CORs were distinct: On average, OC-C1 CORs (22.5 mm posterior and 22.6 mm inferior to the left EAM) were superior and more posterior of OCs; C1-C2 CORs (7.4 mm posterior and 46.7 mm inferior to the left EAM) were inferior and more anterior of OC; and OC-C2 CORs (17.0 mm posterior and 33.1 mm inferior to the left EAM) were aligned with OC. There was a statistically significant difference between the percentage of UCS rotation in C1-C2 and OC-C1; 45% of the flexion and 71% of the extension occurred in OC-C1. Details of an anatomical variant with two pairs of distinct condylar surfaces are also presented.     

Geometry and motion of the knee for implant and orthotic design

By analysing sections of distal femurs in the computer, and by making direct measurements, the posterior femoral condyles were shown to closely fit spherical surfaces. The center of the spheres were then used as reference points and used to define reference axes in a motion study. In flexing from 0 to 120 degrees the medial femoral condyle moved little, the lateral moved posteriorly by 17 mm, and there was an axial rotation of 20 degrees. The data were applied to implant and orthotic design and evaluation.