THE EFFECT OF UNILATERAL PARTIAL FACIAL PARALYSIS AND MUSCLE ABLATIONON CRANIOFACIAL GROWTH AND DEVELOPMENT - AN EXPERIMENTAL-STUDY IN THERABBIT

The effect of unilateral partial facial nerve ablation anti unilateral partial midface muscle ablation on craniofacial growth and developmen t was investigated. New Zealand White rabbits (12 days old) were rando mly assigned to three experimental groups: control group, to study nor mal craniofacial growth and development (n = 15); nerve ablation group , surgically induced unilateral paralysis of the buccal branches of th e facial nerve (n = 15); and muscle ablation group, surgical unilatera l ablation of the facial muscles innervated by the buccal branches of the facial nerve (n = 12). All animals cere 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 prepu bertal craniofacial growth and development. At the age of 6 months, th e animals are fully grown; therefore, the time period between 2 and 6 months is regarded as the pubertal growth period. Computerized dorsove nural roentgencephalometric (measurement of distances and angles) and computer tomographic (three-dimensional volumetric measurements) inves tigations were per-formed at both ages. Additional dry skull measureme nts were Der formed to determine more precisely the bone segments invo lved in the craniofacial growth alterations studied. The obtained resu lts indicated the following. Unilateral partial facial paralysis invol ving the midface resulted in growth alterations analogous to those see n 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 alterati ons were present in those regions closely related to the facial muscul ature, namely the nasal, maxillary, and premaxillary regions, resultin g in a snout deviation toward the operated side. The growth alteration s occurred during prepuberty and remained rather stable during puberty . Morphologic signs of muscle denervation were related to the craniofa cial growth disturbances. The growth alterations after unilateral part ial facial paralysis were mainly biomechanically induced, as they were analogous to those observed after unilateral midfacial muscle ablatio n. The fact that after unilateral midfacial muscle ablation at the age of 6 months the severity of the alterations had increased was attribu ted to the scar formation inherent to the surgical procedure.