A comparative study of mandibular growth patterns in seven animal models

The effect of low intensity pulsed ultrasound on mandibular condylar growth in young adult rats

There is a need for more effective methods to enhance mandibular growth in young adults with mandibular deficiency. Previous studies suggest that low intensity pulsed ultrasound (LIPUS) can enhance mandibular growth in growing individuals. This study aimed to evaluate the potential growth changes of the mandible following 4-week LIPUS application in young adult rats. Nineteen ≈120-day-old female rats were allocated to experimental (n = 10) and control (n = 9) groups. The animals in the experimental group were treated with LIPUS to their temporomandibular joints (TMJs) bilaterally, 20 min each day for 28 consecutive days. Animals were then euthanized; gross morphological evaluation was performed on 2D photographs and 3D virtual models of hemi-mandibles, and microstructural assessment was done for the mandibular condyle (MC). Evaluation of mineralization and microarchitecture properties of subchondral cancellous bone was performed by micro-computed tomography (μCT) scanning. Qualitative and histomorphometric analysis was done on condylar cartilage and subchondral bone following Alcian Blue/PAS and Goldner's Trichrome staining. Vital flourochrome (calcein green) labeling was also utilized to determine the amount of endochondral bone growth. Gross morphological evaluations showed a slight statistically non-significant increase especially in the main condylar growth direction in the LIPUS group. Moreover, 3D evaluation depicted an enhanced periosteal bone apposition at the site of LIPUS application. Microstructural analysis revealed that LIPUS stimulates both chondrogenesis and osteogenesis and enhances endochondral bone formation in young adult rat MC. Furthermore, the effect of LIPUS on osteogenic cells of subchondral cancellous bone was notable. To conclude, LIPUS can enhance young adult rats' MC residual growth potential.

Longitudinal Radiographic Study of Cranial Bone Growth in Young Cheetah

Focal palatitis (also known as focal palatine erosion) is thought to be a developmental disease, specifically of cheetah in captivity raised on a commercial diet. The lack of chewing is thought to cause the mandibular molar to change angulation, contacting the palate and causing the lesions. We followed the development of five captive cheetah cubs, born within 2 weeks of each other, at the same facility. This longitudinal study followed the cubs cephalometrically from 7-months-old to 25-months-old. Of each cub we made a lateral and dorsoventral radiograph at 7, 13, 20, and 25-months-old. For each radiograph at each age, a predefined series of measurements were made including the angle of the molar. The latter was measured as the angle of the bisecting line running through the apex of the caudal molar root intersecting with a line drawn at the ventral margin of the mandible. The results confirmed that the cheetah skull and neurocranium follows the same neural growth pattern as has been described for other mammalians. Similarly the maxillofacial component follows the same somatic growth as seen in all mammalians excluding humans and non-human primates, where a pubertal growth spurt is present. Finally the angle of the mandibular molar at 7 months differed significantly from the angle at the other ages, however there were no statistical difference in the angulation of the molar after eruption (13 months and older ages). In these five cheetah the lack of chewing (as seen in captivity with a commercial or meat only based diet) did not alter the angulation of the mandibular molar, nor did the mandibular molars super erupt in these patients at 25-months-of-age.

Bilateral TMJ Disk Displacement Induces Mandibular Retrognathia

Unilateral non-reducing TMJ disk displacement has been shown to retard mandibular growth on the ipsilateral side, with facial asymmetry a sequela. We hypothesized that bilateral affliction would impair mandibular growth bilaterally, generating mandibular retrognathia. Non-reducing TMJ disk displacement was surgically created in 10 growing New Zealand White rabbits. Ten additional rabbits served as a sham-operated control group. Facial growth was followed in serial cephalograms, with tantalum implants, during a period corresponding to childhood and adolescence in man. The results verified that bilateral non-reducing TMJ disk displacement retarded mandibular growth bilaterally, the extent corresponding to mandibular retrognathia in man. Maxillary growth was also retarded, but to a lesser degree. Growth impairment fluctuated over time, the most striking retardation occurring during periods of general growth acceleration. This should be taken into consideration when orthodontic treatment, aimed at stimulating mandibular growth, is initiated in adolescent individuals with non-reducing TMJ disk displacement.

Effect of untreated and treated temporomandibular joint arthritis on mandibular volume development in growing rabbits

OBJECTIVES

The goal of this work was to investigate the volume development of the mandible in growing rabbits with bilaterally induced temporomandibular joint (TMJ) arthritis that was either left untreated or treated with the tumor necrosis factor-alpha (TNF-α) antagonist etanercept.

METHODS

A total of 18 New Zealand White rabbits aged 8 weeks were randomized to three groups of 6 animals each. Two of these groups were used as arthritis groups by sensitizing the 12 animals to ovalbumin (OA) at 10 weeks, followed by intraarticular OA injections to induce bilateral TMJ arthritis and repeating these injections every 3 weeks to maintain the inflammation. One of the two arthritis groups was treated by weekly subcutaneous etanercept injections, whereas the other group was left untreated. The remaining 6 animals served as controls. Maxillofacial CT scans were obtained at 3-week intervals (from week 10 of the rabbits' lives to the end of the experiment at 22 weeks) to volumetrically track the development of the mandibles after segmentation.

RESULTS

The mandibles did not grow at a continuous rate, but the rate of development was found to decrease in all groups over the course of the study (weeks 10-22). The most extensive volume increases were noted during weeks 10-13. Severe growth deficiencies, especially of the condylar processes, were observed in the arthritis group not receiving treatment. The arthritis group treated with etanercept showed better rates of growth without, however, reaching the normal range of the control group.

CONCLUSION

Antigen-induced TMJ arthritis was found to involve severe problems of growth similar to those in juvenile idiopathic arthritis. Etanercept can improve the volume development but does not reestablish an entirely normal rate of growth.

Effect of methotrexate on the mandibular development of arthritic rabbits

INTRODUCTION

Juvenile idiopathic arthritis affecting the temporomandibular joint (TMJ) can cause severe disturbances of the mandibular development. Methotrexate (MTX) is often administered as a common used remission-inducing agent to treat this disease. The aim of this study was to investigate the effect of low dose MTX on the mandibular growth in arthritic rabbits.

SUBJECTS AND METHODS

Eighteen 10-week-old female New Zealand white rabbits were randomly assigned to three groups with six animals in each group. After being sensitized to ovalbumin (OA), the first and the second group received intra-articular injections with OA. The first group remained untreated, the second was treated by weekly injections of MTX. Cephalograms were taken from each animal at 10, 13, 16, 19, and 22 weeks of age and six mandibular distances measured.

RESULTS

All distances showed an increase between 10 and 20 per cent, whereas growth was more accentuated in the sagittal dimension. Significant differences in the overall growth could be observed between the arthritic and the control animals and less accentuated between the arthritic and the MTX animals. In contrast, existing differences between the groups were not significant during the intervals, but time had the greatest influence on mandibular growth.

CONCLUSIONS

MTX seems to have a positive impact on growth in rabbits suffering from experimental arthritis of the TMJ.

Cartilage changes link retrognathic mandibular growth to TMJ disc displacement in a rabbit model

Recent experimental research demonstrated that non-reducing temporomandibular joint (TMJ) disc displacement in growing rabbits impaired mandibular growth. TMJ disc displacement is also shown to induce histological changes of the condylar cartilage. The authors hypothesized that the severity of these changes would correlate to the magnitude of mandibular growth. Bilateral non-reducing TMJ disc displacement was surgically created in 10 growing New Zealand White rabbits. Ten additional rabbits constituted a sham operated control group. Aided by tantalum implants, growth was cephalometrically determined for each mandibular side during a period equivalent to childhood and adolescence in man. At the end of the growth period, histologically classified cartilage features were correlated with the assessed ipsilateral mandibular growth. Non-reducing displacement of the TMJ disc during the growth period induced histological reactions of the condylar cartilage in the rabbit model. The severity of cartilage changes was inversely correlated to the magnitude and the direction of mandibular growth, which resulted in a retrognathic growth pattern.

Using a specially designed cephalostat for longitudinal cephalometric studies in rats

To better understand and observe craniofacial growth, researchers carry out longitudinal cephalometric studies on animals. The authors constructed a cephalostat specially designed to study craniofacial growth in rats. They describe and validate a cephalometric technique using this cephalostat. They carried out cephalometric radiography and analysis of 62 Wistar rats. By using this method, the authors were able to take repeated, reproducible intracranial, intramandibular and craniomandibular measurements of the rats. The proposed method is a useful tool for studying the craniofacial growth process.

Animal experimental study on repairing alveolar clefts by using rectilinear distraction osteogenesis

The aim of this study was to evaluate the clinical applicability of rectilinear distraction osteogenesis for repairing alveolar cleft models. Alveolar process distraction surgery to produce bilateral clefts was performed on six adult cats. In our study, the left side with the distraction device was the experimental side, and the other side without a distraction device was the control side. After a 6-day latent period, animals underwent gradual distraction at a rate of 0.6mm per day (distraction was performed twice each day, at a rate of 0.3mm each time), until the tissue on the two sides of the cleft touched, then the distraction strength was maintained for 2 days. Two cats were sacrificed at 2 weeks, 6 weeks and 10 weeks postoperatively. Gross anatomical, histological and radiographical analyses were performed after the animals were sacrificed. In addition, the arch width was measured both before setting the distraction device and after distraction was complete. Two weeks after the distraction was complete, the soft tissue of the two sides of the cleft region on the experimental side touched, and it began to coalesce. The extremities of the two sides of the cleft region on all the experimental sides drew close to each other, but there was no bony conjunction. New bone formation appeared in the distraction region. The arch width at the front of the maxillary bone on the distraction side after distraction was smaller than before distraction. The alveolar cleft could be closed by rectilinear distraction osteogenesis. Two sides of the cleft touched each other and only soft tissue coalesced, but we did not observe bone coalescing. This phenomenon suggested that it might be difficult to achieve complete bony repair by rectilinear distraction osteogenesis. However, rectilinear distraction osteogenesis can minimise the size of the alveolar cleft and make bone grafting advisable for those patients who are not suitable for bone grafting before distraction osteogenesis.

Variation of functional cranial components in six Anthropoidea species

Sixty male crania from three Platyrrhini and three Catarrhini genera were measured by means of the craniofunctional method. The aim was to analyze functional components of the skull and relate their function and the degree of encephalization to life history variables. We recognized two major and eight minor functional components. The objectives were to test (1) if within-taxa (Platyrrhini or Catarrhini) and/or between-taxa (Platyrrhini and Catarrhini) comparisons showed minor-component differentiation; and (2) if encephalization affects both primate groups differently. After standardization by size and scaling, 15 possible within-taxa and between-taxa comparisons were made. We found a strong phylogenetic signal, i.e., cranial differences were not randomly distributed, with the between-taxa variation being greater than within-taxa. Both hypotheses tested were accepted since: (1) There was no random variation between functional cranial components. They followed definite patterns for ancestral and derived traits. (2) Encephalization was present in all scaled comparisons, with Platyrrhini showing a higher degree of encephalization than Catarrhini. We conclude that major and minor craniofunctional components should be considered as correlated traits related to life history, because we found different patterns between platyrrhines and catarrhines, and within species of both taxa.

Efeitos da fratura de corpo da mandíbula no crescimento da maxila e da mandíbula: estudo experimental em ratos jovens

Objetivo: Observar os efeitos da fratura experimental de corpo de mandíbula no crescimento da maxila e mandíbula. Métodos: Utilizando ratos com um mês de idade. Estes foram distribuídos em dois grupos: experimental, onde foi efetuada a fratura de corpo de mandíbula à direita, e controle-operado, no qual foi realizado apenas o acesso cirúrgico. Aos três meses de idade foi realizada a eutanásia e após a maceração, a mandíbula foi desarticulada. O crânio foi submetido à incidência radiográfica axial e as hemi-mandibulas à incidência radiográfica lateral. Com base nestas, foram feitas mensurações cefalométricas por meio de um sistema de computador e os valores submetidos a análises estatísticas. Resultados: O comprimento da maxila, bem como a altura e o comprimento da mandíbula apresentaram diferença significante a menor para o lado direito, no grupo experimental. No grupo controle-operado houve diferença significante a menor para o comprimento da porção posterior da maxila e para a altura e comprimento da mandíbula para o lado direito. O grupo experimental quando comparado ao grupo controle-operado mostrou ser significativamente menor em todas as mensurações da maxila e mandíbula para ambos os lados, com exceção do comprimento da mandíbula. Conclusão: A fratura de corpo da mandíbula, bem como a abordagem cirúrgica, tiveram efeitos negativos no crescimento da maxila e da mandíbula.

Effect of testosterone replacement after neonatal castration on craniofacial growth in rats

Neonatal castration precludes the pubertal increase in serum testosterone and reduces general and craniofacial growth in the male Wistar rat. This study aimed to determine whether exogenous testosterone given at an age beyond the normal pubertal peak restores general and craniofacial growth in male, neonatally castrated rats. The design was a randomized, double-controlled, cross-sectional trial. Male Wistar rats were assigned by weighted randomization to be either castrated early after birth (n = 35) or not (n = 15). On day 57, a 1.5-cm Silastic tube with testosterone was implanted in 18 of the castrated rats. On day 70 and day 110, body length, weight, and craniofacial growth were measured together with the weight of the prostate, and blood samples taken. The exogenous testosterone resulted in a significant increase in serum testosterone and prostate weight. All measures of general and craniofacial growth had higher mean values in the non-castrated control group than in the castrated group, while in the testosterone-implant group the mean values lay between these of the castrated animals and the non-castrated controls. Two-way ANOVA indicated a significant effect of the testosterone administration on lower-incisor growth and the size of the total skull vault.

Maxillary growth following atelocollagen implantation on mucoperiosteal denudation of the palatal process in young rabbits: implications for clinical cleft palate repair

OBJECTIVE

The implantation of atelocollagen matrix on the denuded surface of palatal bone following cleft palate repair has been used because it enhances wound healing. This study was performed to determine whether the beneficial effect of atelocollagen matrix implantation on the prevention of scar tissue contraction also inhibits the scar's interference with the growth of maxillary bone.

METHOD

Fifty New Zealand White rabbits (aged 4 weeks) underwent palatal mucoperiosteal denudation, and etelocollagen matrix was implanted on the left palatal process. The opposite side was left open as a control.

RESULTS

Histopathologically, the implantation side exhibited early infiltration of mononuclear cells and fibroblasts, and better growth of connective tissue strands and epithelium. In addition, the formation of rate ridges were seen that were similar to the normal mucosa. The bone of the atelocollagen-implanted side was covered with regenerated periosteum-like layers, but that of the control side was lined by granulation tissue, suggesting the existence of continuous inflammation on the periosteal region. When the animals reached adulthood (aged 24 weeks), the areas of scars and palatal processes, palatal shelf width, molar teeth incline, and bone mineral contents were measured and compared between sides. The atelocollagen-applied scars showed less contraction, the area and width of atelocollagen-implanted palatal processes showed more satisfactory growth, and the dental arch deformity was suppressed in comparison with the control side.

CONCLUSIONS

Our results suggest that the use of atelocollagen matrix on the denuded bone surface following cleft palate repair decreases the scar's effect on maxillary growth.

Migration of hydroxyapatite onlays into the mandible and nasal bone and local bone turnover in growing rabbits

To determine the effects of local bone turnover on the migration of macroporous hydroxyapatite onlays in the nasal bone and mandibular ramus, we performed histomorphometric analyses of the underlying bone area in 41 New Zealand White rabbits from the age of 4 weeks. The hydroxyapatite implants were placed under the periosteum of the right nasal bone (a depository bone onto its periosteal surface and endosteal resorptive) and the mandibular ramus (resorptive onto its outer surface). The corresponding left sides were sham operated. Following fluorescence bone labeling, composite specimens of the hydroxyapatite block including both sides of the nasal bone and mandible were removed at 0 (n = 1), 3, 6, 9, 12, and 16 weeks postoperatively (n = 8, respectively) and processed to yield undecalcified sections. Bone-bone marrow interfaces in the entire area within 200 microns beneath the base of the hydroxyapatite and in the counter-area on the sham-operated side were measured under a light microscope. In all grafted specimens, the hydroxyapatite matrix was directly united with the underlying tissue by bone ingrowth. However, the sinking of the hydroxyapatite graft in the nasal bone was significant at 3 weeks postoperatively and gradually increased thereafter. In the mandible, the sinking became significant at 6 weeks. In the nasal bone, the bone area density beneath the graft showed a time-dependent decrease during the experimental period, but in the mandibular bone, the value was initially decreased at 3 weeks and then recovered to baseline level. In both bones, parameters of bone resorption, such as osteoclast number and osteoclast surface, were significantly increased from 3 weeks. While the parameters of bone formation, such as osteoblast surface and mineralizing surface, were significantly decreased from 3 weeks in the nasal bone, they were significantly increased in the mandible. Mineral apposition rate showed a significant decrease in both bones. Our data indicate that while the bone area density beneath the hydroxyapatite seemed to depend on bone formation, increased bone resorption would be more critical for the remodeling of underlying bony architecture in the migration of the hydroxyapatite graft.

Onlay silicone and hydroxyapatite-tricalciumphosphate composite (HAP-TCP) blocks interfere with nasal bone growth in rabbits

We investigated how a new type of synthetic porous hydroxyapatite ceramic (HAP-TCP) acts when it is implanted in growing membranous bone. Seventy-six New Zealand White infant male rabbits (4-week-olds) were used. Rabbits received HAP-TCP block or silicone block implantation in their right nasal bone. The left nasal bone was used for a sham. Serial or cross-sectional examinations by morphometry, radiology, blood biochemistry, and histology were carried out. Both the HAP-TCP and silicone groups exhibited no systemic growth disturbance in terms of morphometry and blood biochemistry. Dual energy x-ray absorptiometry (DEXA) revealed, however, a decrease in the bone mineral content (BMC) of the right nasal bone in the silicone group. Histology revealed a superior affinity of HAP-TCP to bone tissue than that of silicone. When a HAP-TCP block was implanted under the periosteum it bonded directly to bone tissue. However, sinking of the implants into the bone tissue were noted both in the HAP-TCP and the silicone groups in longitudinal observation. These results suggest that although HAP-TCP has superior affinity to bone tissue, this by itself is not enough sufficient reason to believe that HAP-TCP can be effectively applied during the growth period.

Comparative cephalometric study of nasal cavity growth patterns in seven animal models

Although primates have been the craniofacial growth models of choice, recent circumstances have stimulated the search for nonprimate models. In a series of studies we have described changes in various regions of the craniofacial complex for seven commonly used animal models. The present study examined the bony nasal cavity. One hundred and forty-four serial and cross-sectional lateral head x-rays were obtained for unoperated controls from previous growth studies. The sample consisted of data from 26 rats, 21 rabbits, 21 domestic cats, 23 domestic dogs, 17 baboons, 16 rhesus monkeys, and 20 chimpanzees. Comparative human data was taken from the Bolton Standards. The samples were divided into three age categories based on dental and somatic development. Midsagittal nasal cavity measurements included length, height, shape index, and area. Analysis was based on the percent increase in measures from the infant condition. Three major shapes were discerned at adulthood (1) vertical quadrangles (humans and cats); (2) triangles (chimpanzees, rhesus monkeys, and baboons), and (3) horizontal quadrangles (rabbits, rats, and dogs). Results showed that overall shape was best modeled by the chimpanzee and, as a nonprimate model, the laboratory cat. Rabbits and rats also showed similar percent changes for length or height dimensions at different ages, suggesting that these animals may be acceptable, inexpensive alternatives to primates in some experimental situations.