Relationships between growth at the sutures of the rabbit calvarium

The effect of unilateral partial facial paralysis and muscle ablation on craniofacial growth and development: an experimental study in the rabbit

The effect of unilateral partial facial nerve ablation and unilateral partial midface muscle ablation on craniofacial growth and development was investigated. New Zealand White rabbits (12 days old) were randomly assigned to three experimental groups: control group, to study normal craniofacial growth and development (n = 15); nerve ablation group, surgically induced unilateral paralysis of the buccal branches of the facial nerve (n = 15); and muscle ablation group, surgical unilateral ablation of the facial muscles innervated by the buccal branches of the facial nerve (n = 12). All animals were operated on at the age of 12 days; follow-up evaluations were performed at the ages of 2 months and 6 months. The age of 2 months represents the endpoint of the prepubertal craniofacial growth and development. At the age of 6 months, the animals are fully grown; therefore, the time period between 2 and 6 months is regarded as the pubertal growth period. Computerized dorsoventral roentgencephalometric (measurement of distances and angles) and computer tomographic (three-dimensional volumetric measurements) investigations were performed at both ages. Additional dry skull measurements were performed to determine more precisely the bone segments involved in the craniofacial growth alterations studied. The obtained results indicated the following. Unilateral partial facial paralysis involving the midface resulted in growth alterations analogous to those seen after unilateral total facial paralysis. The growth alterations were not to be seen as a growth restriction (reduction in bony volume) but as growth misdirections (alterations in shape). Major growth alterations were present in those regions closely related to the facial musculature, namely the nasal, maxillary, and premaxillary regions, resulting in a snout deviation toward the operated side. The growth alterations occurred during prepuberty and remained rather stable during puberty. Morphologic signs of muscle denervation were related to the craniofacial growth disturbances. The growth alterations after unilateral partial facial paralysis were mainly biomechanically induced, as they were analogous to those observed after unilateral midfacial muscle ablation. The fact that after unilateral midfacial muscle ablation at the age of 6 months the severity of the alterations had increased was attributed to the scar formation inherent to the surgical procedure.

Body weight gain as related to craniofacial and calvarial volumetric changes in growing rabbits

This investigation was conducted to evaluate the relationship between calvarial and craniofacial volumetric growth relative to body weight gain. Ten male New Zealand white rabbits received spherical tantalum bone markers in the nasal, frontal, parietal, and temporal bones: a minimum of two in each bone segment. The animals were followed from age 32 to 144 days using a roentgen stereophotogrammetric system and an accurate scale. Implant stability was checked at each stereometric examination. Sutural growth and volumetric changes were computed and correlated to weight increase. Successive calvarial and craniofacial polyhedron expansion, as well as weight, showed considerable variability and interindividual variation throughout the observation period. Calculated coefficients of determination, linear regressions, and the correlation coefficients for each age interval demonstrated weak correlations, especially for calvarial to weight data. Consequently, this study suggests a low dependence of calvarial volumetric growth, reflecting the neural mass expansion on body weight development. Thereby, further indications of the low reliability of weight as a parameter of general health evaluation was provided.