Longitudinal study of craniofacial growth in Macaca fascicularis

Mandibular Vertical Growth Deficiency After Botulinum-Induced Hypotrophy of Masticatory Closing Muscles in Juvenile Nonhuman Primates

The purpose of this study was to investigate the relationship between masticatory muscular hypotrophy and mandibular growth in juvenile nonhuman primates (cynolmolgus monkeys, Macaca fasicularis). We hypothesized that botulinum toxin (BTX)-induced neuro-muscular junctional block and its resultant hypotrophy of masticatory muscles would produce mandibular growth disturbances in size and shape. Ten male cynomolgus monkeys were divided into three groups: group I (control; n = 3), group II (unilateral BTX; n = 4), and group III (bilateral BTX; n = 3). The unilateral or bilateral muscular hypotrophy of major masticatory closing muscles was induced by synchronous BTX application to masseter, medial pterygoid, and temporal muscle. Mandibular growth was tracked by linear, angular, area and volume measurements using three-dimensional (3D) computed tomography imaging before BTX treatment and after 3 and 6 months. After unilateral hypotrophy of masticatory muscles in group II, vertical growth deficiency was prominent on the BTX side, with compensatory overgrowth on the control side. The bilateral muscular hypotrophy in group III also showed smaller ramal height and width than that of control (group I) and control side (group II). Moreover, ramal sagittal angles (posterior tilt) increased on the BTX side of both groups II and III, but coronal angles (lateral tilt) did so on the BTX side of group II, resulting in asymmetry. The results confirmed our hypothesis that functional activity of masticatory closing muscles is closely related to mandibular growth in size and shape of juvenile nonhuman primates. In addition, the focused growth disturbances on the ramal height and posterior-lateral tilt suggested the possible role of masticatory closing muscles for ramal vertical and angular growth vector of the mandible.

Cranial growth in normal and low-protein-fed Saimiri. An environmental heterochrony

Protein malnutrition has a significant and measurable effect on the rate and timing of growth. Heterochrony is generally viewed as the study of evolutionary changes in the relative rates and timing of growth and development. Although changes in growth commonly result from experimental manipulations of diet, nobody has previously attempted to explain such changes from a heterochronic perspective. We use a heterochronic perspective to compare a group of squirrel monkeys fed a low-protein diet to individuals on a high-protein diet, but, in contrast to previous works, we focus particularly on the effects of environmental and not genetic factors. In the present study, Gould's (1977) and Godfrey and Sutherland's (1996) methodologies for studying heterochrony, as well as geometric morphometrics, are used to compare two groups of Saimiri sciureus boliviensis. Two groups of Saimiri were constructed on the basis of the protein content in their diets: a high-protein group (HP) (N=12) and a low-protein group (LP) (N=12). All individuals are males born in captivity. Two major functional components of the skull, the neurocranium and the face, were analysed. Four minor components were studied in each major component. Comparison of craniofacial ontogeny patterns based on major and minor components suggests that changes in the skull of LP animals can be explained by heterochrony. The skull of LP animals exhibits isomorphism produced by proportioned dwarfism. Our results suggest that heterochrony can be environmentally, rather than exclusively genetically, induced. The study of genetic assimilation (Waddington, 1953, 1956; see Scharloo, 1991; Hallgrimsson et al., 2002) has demonstrated that environmentally induced phenotypes often have a genetic basis, and thus parallel changes can be easily induced genetically. It is possible that proportioned dwarfism is far more common than currently appreciated.

Field methodology for lateral cranial radiography of nonhuman primates

The historical lack of field-based radiographic studies of nonhuman primates within the field of anthropology is likely due to the perceived difficulty of transporting and operating X-ray equipment. Here we present a method for taking lateral cranial radiographs of nonhuman primates in the field that is simple to employ, and that produces exposed films suitable for collection of measurement data useful for growth and development studies, as well as for investigating bone and soft-tissue pathology. Several different X-ray units, film types, and portable power sources were used, all producing suitable images of similar quality, indicating that this methodology is likely not overly sensitive to these important parameters.

Influences of nasal respiratory obstruction on craniofacial growth in young Macaca fuscata monkeys

This study was conducted to investigate the influences of artificial nasal respiratory obstruction on craniofacial growth in young Macaca fuscata monkeys. Eleven monkeys were used; seven monkeys served as the experimental animals and the remaining four as the control animals. Further, the experimental animals were divided into light and heavy obstruction groups. Nasal respiratory obstruction was created by injecting dental impression material into the nasopharyngeal region. Nasal respiratory function was evaluated in terms of nasal airway resistance. Craniofacial structure in the experimental monkeys was compared with the control animals by means of cephalometric analysis. Nasopharyngeal respiratory obstruction was associated with downward and backward rotation of the mandible, upward and backward growth of the condyle, divergent gonial angle, anterior open bite, and spaced dental arch in the lower anterior region. These changes were significantly greater in the experimental monkeys with heavy respiratory obstruction. The current findings support the hypothesis that nasal obstruction existing before and during pubertal growth may result in permanent craniofacial deformities pertinent to skeletal open bite.

The role of interdigitation in sagittal growth of the maxillomandibular complex in Macaca fascicularis

The role of the interdigitation of posterior teeth in maxillomandibular growth and development was studied longitudinally in Macaca fascicularis monkeys. Fourteen monkeys were divided into a control group (n = 7) and an experimental group (n = 7). At the start of the study, the mean age of the animals was 29 weeks. At that stage the interdigitation in the experimental group was eliminated by grinding the cusps of the molars and canines. The animals were followed until 143 weeks of age and studied with the aid of tantalum implants and lateral radiographs. The findings indicated that elimination of the interdigitation resulted in a deviating anteroposterior relationship between the jaws and a significant inhibition of the vertical growth of the maxilla in the second half of the experimental period, while total face height was not noticeably affected. As a result, a more prognathic mandible and a more mesial occlusion developed. It can be concluded that the interdigitation plays a role in the regulation of vertical and anteroposterior facial growth and constitutes an important factor in the jaw relation in Macaca fascicularis monkeys.

Changes in skull components of the squirrel monkey evoked by growth and nutrition: an experimental study

Twenty weanling 6-month-old male squirrel monkeys were allotted to the following treatments: 1) first control animals were killed at weaning; 2) second control animals were killed when 24 months old; and 3) malnourished animals were fed on a low-protein diet and killed at age 24 months. Lateral and vertical teleradiographies were taken. Growth of the neurocranial and splanchnocranial components were measured by volumetric (size estimators) and morphometric (shape estimators) indices. All facial components grew. The neurocranial components showed a heterogeneous behavior: The anteroneural component remained stable, and the increase of the midneural component was compensated by a decrease in the posteroneural component. Malnutrition affected the growths of 1) the craniofacial complex, 2) the splanchnocranium, and 3) the respiratory and midneural components. Growth influenced skull shape through 1) increases of the splanchnocranium and the midneural component relative to the neurocranium; 2) decreases of the masticatory and optic components relative to the splanchnocranium, and 3) decreases of the anteroneural and posteroneural components relative to the neurocranium. Malnutrition influenced skull shape through the relationship between the anteroneural component and the neurocranium. These results confirmed the existence of functional interrelationships among the cranial components. A new approach to craniological studies is suggested.