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Skeletal changes after experimentally displaced condylar process fracture in growing rats
ARTICLE IN PRESS Journal of Cranio-Maxillofacial Surgery (2006) 34, 220–225 r 2006 European Association for Cranio-Maxillofacial Surgery doi:10.1016/j.jcms.2006.01.006, available online at http://www.sciencedirect.com
Skeletal changes after experimentally displaced condylar process fracture in growing rats Vanessa C.B. TEIXEIRA, Antonio C.B. TEIXEIRA, Joa˜o Gualberto C. LUZ Department of Oral and Maxillofacial Surgery (Head: Prof. R.B. Dias), University of Sa˜o Paulo, Sa˜o Paulo, Brazil
SUMMARY. Introduction: Fractures of the mandibular condyle are common. A potential for growth disturbances in young individuals has been reported; however, there are few experiments studying such consequences. Skeletal changes after fracture of the condyle in the growing period were analysed in this study. Material: Fifty young Wistar rats weighing 100 g were used. Under general anaesthesia unilateral fracture dislocations of the condylar process were induced surgically in the experimental group ðn ¼ 25Þ; while only surgical access was performed in the sham-operated group. The animals were sacrificed at 3 months of age. The mandibles were disarticulated, and radiographs were taken (axial skulls and lateral hemimandibles). Cephalometric evaluations were made using a computer system. Statistical tests were applied between groups and contralateral sides in each group. Results: There were atrophy and degenerative change of the fractured condylar process. There was also a significant difference in the height of the mandibular body and in the length of anterior and posterior maxilla. Conclusion: It was concluded that an experimental fracture of the mandibular condyle during the growing period in rats induced degenerative changes of the condyle as well as an asymmetry of the mandible, affecting height of the body, also leading to consequences in the maxilla. r 2006 European Association for Cranio-Maxillofacial Surgery
Keywords: mandibular condyle; lesions – maxilla; growth and development – mandible; growth and development – mandibular fracture
Hovinga et al., 1999; Strobl et al., 1999). In addition, in an experimental study, it has been demonstrated that midface deviation occurred following mandibular fractures (especially of the condylar process), in growing animals (Altonen et al., 1978). The purpose of the present study was to analyse the skeletal changes following dislocated condylar process fractures in growing rats.
INTRODUCTION Condylar process fractures are common, most often unilaterally with medial deviations (Silvennoinen et al., 1992; Joos and Kleinheinz, 1998). Studies have described a favourable prognosis when treated by closed methods in children and adolescents (Feifel et al., 1992; Joos and Kleinheinz, 1998). The ability of the ascending ramus to repair and remodel following trauma has been tested experimentally (Yu¨cel et al., 2002). Also, healing of condylar process fractures has been demonstrated in animal studies (Yasuoka and Oka, 1991; Teixeira et al., 1998). Callus formation, with simultaneous repositioning of the condyle, can lead to normal temporomandibular joints (TMJ; Teixeira et al., 1998). Better results, both in tissue response and time required for repair, were obtained in young animals (Luz and Arau´jo, 2001; Takatsuka et al., 2005). It has been demonstrated that cellular proliferation in fractured condyles is age dependent, being better in the young animals (Sekine et al., 1995). Remodelling of condylar processes following conservative treatment has been radiographically demonstrated (Feifel et al., 1992; Luz and Chilvarquer, 1996). However, concern is reported regarding skeletal changes, represented by mandibular asymmetry, mainly in young individuals (Norholt et al., 1993;
MATERIAL AND METHODS Experimental animals The study animals (50) were 1-month-old Wistar rats, with a mean body weight of 94.3 g. All animals were fed an ordinary diet of rodent feed (Labina, Agribands Purina, Sa˜o Paulo, Brazil), administered in powder form for 2 weeks postoperatively, and in regular form in the remaining period. They were distributed into experimental ðn ¼ 25Þ and shamoperated ðn ¼ 25Þ groups. The study was approved by the local committee on research ethics. Surgical method Under general anaesthesia, induced by intraperitoneal injection of xylazine associated with ketamine, 220
ARTICLE IN PRESS Skeletal changes in growing rats 221
a right sided preauricular incision of 1 cm was made, followed by blunt dissection through the masseter muscle, just below the zygomatic arch, and exposure of the condylar process. Fracture was achieved by using a mosquito (Halstead) forceps, and the condylar fragment was deviated medially. Care was taken so as not to damage the articular surfaces. Sham-operated animals were submitted to the same procedure, but limited to exposure of the condylar process. The procedures were concluded by suturing in layers. The animals were sacrificed 2 months postoperatively, and their body weights were recorded. Their heads and mandibles were carefully macerated and fixed in 10% buffered formalin.
Cephalometric evaluation Following formalin fixation for 1 week, radiographs in axial (dorso-ventral) projection of the skull and lateral projection of hemimandibles were obtained, and care was taken to maintain the horizontal and vertical planes. Radiographs were taken with a standard dental machine at 56 kV and 10 mA, with an exposure time of 0.4 s to skull and 0.3 s to hemimandibles. A constant 40 cm focus-to-film distance was maintained and periapical films were used (Ektaspeed, Eastman Kodak Co, USA). Radiographs were subjected to computerized cephalometric evaluation. The radiographic images were digitized, and measurements obtained with Imagelab software (LIDO, University of Sa˜o Paulo, Brazil). From the axial skull radiographs, the following distances were measured bilaterally: TB–MR – tympanic bulla (the most anterior portion of this round and voluminous structure of the skull base) to the mesial root of the first molar (the apex of this root); TB–IF – tympanic bulla to infraorbital foramen (the vertex of the image of this foramen); and IF–IP – infraorbital foramen to incisal point (the intersection of the lingual face of upper incisors with the midline; Fig. 1). On the lateral radiographs of the hemimandibles, the following distances were measured bilaterally: CP–AP – condylar process (the highest point of this structure) to angular process (the apex of this structure peculiar to the rodent mandible); TM–AN – intersection of the distal face of the third molar with the mandibular ramus to antegonial notch (the latter being located on the mandibular basis anteriorly to the mandibular angle); and II–AP – lower insertion of incisor (the most anterior limit of the lower bone insertion of this tooth) to angular process (Fig. 2). To evaluate the significance of differences between the mean values found in both groups, the Student’s t-test was used, whilst the paired Student’s t-test was used to compare the mean values from right and left sides in each group. The level of significance was set at pp0:05 for all the statistical analyses.
Fig. 1 – Axial radiograph of skull. A discrete asymmetry of the maxilla may be seen. TB, tympanic bulla; MR, mesial root of the first molar; IF, infraorbital foramen; IP, incisal point.
Fig. 2 – Lateral radiograph of hemimandibles. Atrophy of the condylar process of the right side (top) is seen. AN, antegonial notch; TM, distal face of the third molar; II, insertion of incisor; AP, angular process; CP, condylar process.
ARTICLE IN PRESS 222 Journal of Cranio-Maxillofacial Surgery
RESULTS
Tympanic bulla to mesial root of the first molar (TB-MR)
Macroscopic features After the surgical procedure, the animals continued to grow and gain weight. Two months postoperatively, the mean body weights of animals from the experimental group was 269.2736.2 g, and from the sham-operated group was 285.9724.5 g. Student’s t-test of (the arithmetic) means of both groups revealed no significant difference ðp ¼ 0:062Þ: However, macroscopic examination of the specimens revealed facial asymmetry in the experimental group, with deviation of the mandible to the right (side of fracture), and asymmetric wear of the incisors. A smaller volume of the masseter muscle was observed on the right side in the experimental group. There were no such alterations in the shamoperated group. Atrophy and degenerative changes of the condylar process were noted radiographically in the experimental group, whereas the shamoperated group presented normal radiographic findings (Figs. 2 and 3).
Cephalometric evaluation A. The mean values of distances found on axial radiographs of the skulls are listed in Table 1.
There was a statistically significant difference between the means of the experimental and the shamoperated groups on the right side ðp ¼ 0:017Þ; but not on the left side ðp ¼ 0:811Þ: Also, there was a significant difference between the right and left sides in the experimental group ðp ¼ 0:001Þ but not in the sham-operated group ðp ¼ 0:965Þ: Tympanic bulla to infraorbital foramen (TB-IF) There was no significant difference between experimental and sham-operated groups on the right side ðp ¼ 0:071Þ nor on the left side ðp ¼ 0:055Þ; and no significant difference between right and left sides in the experimental group ðp ¼ 0:645Þ nor the shamoperated group ðp ¼ 0:918Þ: Infraorbital foramen to incisal point (IF-IP) There were significant differences between experimental and sham-operated groups on the right ðp ¼ 0:001Þ; and on the left side ðp ¼ 0:004Þ: There was also a significant difference between right and left sides in the experimental group ðp ¼ 0:002Þ; but not in the sham-operated group ðp ¼ 0:104Þ:
Fig. 3 – Radiographic image of right (R) condyle exhibiting atrophy and degenerative changes such as altered form and irregular contour. Compare with normal shape of control (L) condyle.
Table 1 – Data obtained in axial radiographs of the rat skulls (mm) Group
Experimental Sham-operated
TB–MR
TB–IF
IF–IP
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
16.8770.54 17.2270.48
17.1970.64 17.2270.43
21.2871.02 21.7370.71
21.3470.75 21.7370.61
8.4670.75 9.0470.35
8.6370.71 9.1270.35
For definition of distances evaluated see text. sd, standard deviation.
ARTICLE IN PRESS Skeletal changes in growing rats 223 Table 2 – Data obtained in lateral radiographs of rat hemimandibles (mm) Group
Experimental Sham-operated
TM–AN
CP–AP
II–AP
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
6.2570.21 6.1770.17
6.3670.20 6.2270.16
8.8770.61 10.7670.33
10.6670.50 10.9970.37
22.7371.27 23.2671.14
24.2770.94 24.2971.22
For definition of distances evaluated see text. sd, standard deviation.
B. The mean values of distances determined from lateral radiograms of hemimandibles are listed in Table 2. Distal face of the third molar to antegonial notch (TM-AN) There was no significant difference between experimental and sham-operated groups on the right side ðp ¼ 0:163Þ; but there was significance on the left side ðp ¼ 0:009Þ: Also, there was a significant difference between right and left sides in the experimental group ðp ¼ 0:001Þ; but not in the sham-operated group ðp ¼ 0:137Þ: Condylar process to angular process (CP-AP) There were significant differences between experimental and sham-operated groups on the right ðpo0:001Þ; and on the left side ðp ¼ 0:011Þ: Besides, there were also significant differences between right and left sides in both the experimental ðpo0:001Þ as well as in the sham-operated groups ðpo0:001Þ: Lower insertion of incisor to angular process (II-AP) There was no significant difference between experimental and sham-operated groups on the right side ðp ¼ 0:127Þ nor the left side ðp ¼ 0:930Þ: However, there were significant differences between right and left sides in both the experimental ðpo0:001Þ as well as the sham-operated groups ðpo0:001Þ:
DISCUSSION In this model, a unilateral, medially deviated fracture was induced, which is the most frequent form of mandibular condyle fracture (Silvennoinen et al., 1992; Thore´n et al., 1997; Joos and Kleinheinz, 1998; Oji, 1998). The present study has shown that fractures of the mandibular condyle in young rats induced an asymmetry of the mandible affecting both the horizontal and condylar rami with consequences to the maxilla. Thus, the final result was a deviated midline of the mandible associated with an atrophic condylar process. Cephalometric evaluations also identified asymmetric areas in the maxilla. Deviation
of the midline of the mandible towards the side of the fracture occurred in the experimental group. Mandibular asymmetries have been related to condylar fractures in young human patients at variable rates (Proffit et al., 1980; Norholt et al., 1993; Hovinga et al., 1999). Functional results of nonsurgical and surgical treatment of condylar fractures are said to be comparable (Takenoshita et al., 1990; Hidding et al., 1992; Joos and Kleinheinz, 1998), although some degree of deviation can occur in patients treated non-surgically by the closed method (Joos and Kleinheinz, 1998). From an experimental model, only cautious conclusions can be drawn concerning human subjects. It is important to remember that there are differences in the TMJ form and muscular system between rodents and omnivores. While the condyle is elongated in an anteroposterior direction with a narrow, elongated fossa and is performing movements only in one direction in rodents, the condyle is elliptical with a deep and large fossa, performing movements in lateral and anteroposterior directions in humans. Another finding was a smaller volume of masseter muscles on the right side in the experimental group. This is probably associated with the asymmetry following the condylar fracture, with consequently altered mastication. A study by Kuboyama and Moriya (1995) showed that malocclusion induced by extraction of molar teeth and different dietary consistency does influence the development of the masseter muscle. The experimental group suffered a reduced body weight compared with the shamoperated group (not significant). This may indicate some influence of the condylar fracture on the eating ability of the growing animals during healing. Similar findings were reported before (Luz and Arau´jo, 2001). Cephalometric evaluations from radiographs of dissected specimens using a computer system (as in this study) lead to reliable measurements, reducing technical difficulties (Del Campo et al., 1995). Distances found were similar to those noted in other experiments (Del Campo et al., 1995; Yamamoto et al., 1997). Significant alteration in the mandibular body height was the main finding in this study. Compensatory growth of the alveolar bone of the mandible enabling masticatory function has been experimentally demonstrated (Das, 1970). Another significant finding was shortening of the maxilla.
ARTICLE IN PRESS 224 Journal of Cranio-Maxillofacial Surgery
The possibility of maxillary growth influencing mandibular growth and vice versa by occlusal intercuspation has been described by Enlow (1990). Occlusal disturbances were considered the main cause of asymmetry of the midface after condylar fractures in young rabbits (Altonen et al., 1978). Some distances, such as condylar to angular processes, and lower incisor to angular process shared significant differences between sides, but not between groups. This may be attributable to the surgical access, and further studies on this matter are necessary. The possibility of a decrease in growth of the mandible caused by the periosteal lesion should be considered (Koski and Ro¨nning, 1982). However, this study has detected no obvious effects on the mandibular length. Condylar cartilage growth contributes not only to the height of the mandibular ramus but also increases mandibular length (Ayoub and Mostafa, 1992). Hence a lesion of the condylar process could result in facial deformity (Proffit et al., 1980). Apart from the condyle being essential to normal growth of the mandible, dimensions and morphology of the mandibular ramus are also associated with masticatory muscle insertions and activity. Thus, mandibular growth is a product of different forces and of regional functional agents of growth control (Enlow, 1990). Radiographic features of atrophy and degenerative changes of the condylar process were the other important finding. The ability of the TMJ to remodel has been reported following treatment of dislocated condylar fractures (Feifel et al., 1992; Luz and Chilvarquer, 1996), especially in the young individual (Strobl et al., 1999; Gu¨ven and Keskin, 2001). However, the possibility of incomplete restoration of the condyle to a normal form and consequently signs of osteoarthrosis should be considered as a sequel to condylar fractures (Hidding et al., 1992; Hovinga et al., 1999; Strobl et al., 1999). Exactly this was demonstrated in this study of consequences following condylar fracture dislocations in young rats. CONCLUSION In this experimental study the following skeletal changes were noted as a result of fracture dislocations of the condylar process in young animals; atrophy and degenerative changes of the condylar process as well as significant differences in the height of the mandible and in the length of the maxilla. ACKNOWLEDGEMENTS
To Prof. Moacyr D. Novelli (LIDO/FO-USP) for his assistance in computerised cephalometry. References Altonen M, Ranta R, Ylipaavalniemi P: Midface deviation due to mandibular fractures. An experimental study with clinical comparison. J Maxillofac Surg 6: 143–147, 1978
Ayoub AF, Mostafa YA: Aberrant mandibular growth: theoretical implications. Am J Orthod Dentofec Orthop 101: 255–265, 1992 Das AK: Experimental studies on the interrelation of condylectomy and tooth movement. J Indian Dent Assoc 42: 92–97, 1970 Del Campo AI, Elizondo MM, Magnelli LM, Valadez AS, Ontiveros DS: Craniofacial development in rats with early resection of the zygomatic arch. Plast Reconstr Surg 95: 486–495, 1995 Enlow DH: Facial Growth, 3rd edition. W B Saunders, Philadelphia, 1990 Feifel H, Albert-Deumlich J, Riediger D: Long-term follow-up of subcondylar fractures in children by electronic computerassisted recording of condylar movements. Int J Oral Maxillofac Surg 21: 70–76, 1992 Gu¨ven O, Keskin A: Remodelling following condylar fractures in children. J Cranio Maxillofac Surg 29: 232–237, 2001 Hidding J, Wolf R, Pingel D: Surgical versus non-surgical treatment of fractures of the articular process of the mandible. J Cranio Maxillofac Surg 20: 345–347, 1992 Hovinga J, Boering G, Stegenga B: Long term results of nonsurgical management of condylar fractures in children. Int J Oral Maxillofac Surg 28: 429–440, 1999 Joos U, Kleinheinz J: Therapy of condylar neck fractures. Int J Oral Maxillofac Surg 27: 247–254, 1998 Koski K, Ro¨nning O: Condyle neck periostomy and the mitotic activity in the condylar tissues of young rats. Swed Dent J 15 (Suppl.): 109–113, 1982 Kuboyama N, Moriya Y: Influence of diet composition and malocclusion on masticatory organs in rats. J Nihon Univ Sch Dent 37: 91–96, 1995 Luz JGC, Chilvarquer I: Remodelling of bilateral fractures of the mandibular condyle. Acta Stomatol Belg 93: 167–170, 1996 Luz JGC, Arau´jo VC: Rotated subcondylar process fracture in the growing animal: an experimental study in rats. Int J Oral Maxillofac Surg 30: 545–549, 2001 Norholt SE, Krishnan V, Sindet-Petersen S, Jensen I: Pediatric condylar fractures: a long-term follow-up study of 55 patients. J Oral Maxillofac Surg 51: 1302–1310, 1993 Oji C: Fractures of the facial skeleton in children: a survey of patients under the age of 11 years. J Cranio Maxillofac Surg 26: 322–325, 1998 Proffit WR, Vig KWL, Turvey TA: Early fracture of the mandibular condyles: frequently an unsuspected cause of growth disturbances. Am J Orthod 78: 1–24, 1980 Sekine J, Sano K, Inokuchi T: Effect of aging on the rat condylar fracture model evaluated by bromodeoxyuridine immunohistochemistry. J Oral Maxillofac Surg 53: 1317–1323, 1995 Silvennoinen U, Iizuka T, Lindqvist C, Oikarinen K: Different patterns of condylar fractures: an analysis of 382 patients in a 3-year period. J Oral Maxillofac Surg 50: 1032–1037, 1992 Strobl H, Emshoff R, Ro¨thler G: Conservative treatment of unilateral condylar fractures in children: a long-term clinical and radiologic follow-up of 55 patients. Int J Oral Maxillofac Surg 28: 95–98, 1999 Takatsuka S, Terai K, Yoshida K, Narinobou M, Ueki K, Nakagawa K, Yamamoto E: A comparative study of unilateral dislocated mandibular condyle fractures in the rabbit. J Cranio Maxillofac Surg 33: 180–187, 2005 Takenoshita Y, Ishibashi H, Oka M: Comparison of functional recovery after nonsurgical and surgical treatment of condylar fractures. J Oral Maxillofac Sur 48: 1191–1195, 1990 Teixeira ACB, Luz JGC, Arau´jo VC, Arau´jo NS: Healing of the displaced condylar process fracture: an experimental study. J Cranio Maxillofac Surg 26: 326–330, 1998 Thore´n H, Iizuka T, Hallikainen D, Nurminen M, Lindqvist C: An epidemiological study of condylar fractures in children. Br J Oral Maxillofac Surg 35: 306–311, 1997
ARTICLE IN PRESS Skeletal changes in growing rats 225 Yamamoto MK, Novelli MD, Luz JGC: Effects of unilateral upper incisor extraction on facial growth of young rats. J Nihon Univ Sch Dent 39: 191–195, 1997 Yasuoka T, Oka N: Histomorphometric study of trabecular bone remodeling during condylar process fracture healing in the growing period: experimental study. J Oral Maxillofac Surg 49: 981–988, 1991 Yu¨cel E, Bo¨rkan U¨, Mollaoglu N, Erkmen E, Gu¨nhan O¨: Histological evaluation of changes in the temporomandibular joint after direct and indirect trauma: an experimental study. Dent Traumatol 18: 212–216, 2002
Prof. Dr. Joa˜o Gualberto C. LUZ R. Duarte de Azevedo 284, s. 22, 2036-21 Sa˜o Paulo SP Brazil Fax: +55 11 69596266 E-mail: [email protected] Paper received 3 September 2004 Accepted 16 January 2006
Skeletal changes after experimentally displaced condylar process fracture in growing rats Vanessa C.B. TEIXEIRA, Antonio C.B. TEIXEIRA, Joa˜o Gualberto C. LUZ Department of Oral and Maxillofacial Surgery (Head: Prof. R.B. Dias), University of Sa˜o Paulo, Sa˜o Paulo, Brazil
SUMMARY. Introduction: Fractures of the mandibular condyle are common. A potential for growth disturbances in young individuals has been reported; however, there are few experiments studying such consequences. Skeletal changes after fracture of the condyle in the growing period were analysed in this study. Material: Fifty young Wistar rats weighing 100 g were used. Under general anaesthesia unilateral fracture dislocations of the condylar process were induced surgically in the experimental group ðn ¼ 25Þ; while only surgical access was performed in the sham-operated group. The animals were sacrificed at 3 months of age. The mandibles were disarticulated, and radiographs were taken (axial skulls and lateral hemimandibles). Cephalometric evaluations were made using a computer system. Statistical tests were applied between groups and contralateral sides in each group. Results: There were atrophy and degenerative change of the fractured condylar process. There was also a significant difference in the height of the mandibular body and in the length of anterior and posterior maxilla. Conclusion: It was concluded that an experimental fracture of the mandibular condyle during the growing period in rats induced degenerative changes of the condyle as well as an asymmetry of the mandible, affecting height of the body, also leading to consequences in the maxilla. r 2006 European Association for Cranio-Maxillofacial Surgery
Keywords: mandibular condyle; lesions – maxilla; growth and development – mandible; growth and development – mandibular fracture
Hovinga et al., 1999; Strobl et al., 1999). In addition, in an experimental study, it has been demonstrated that midface deviation occurred following mandibular fractures (especially of the condylar process), in growing animals (Altonen et al., 1978). The purpose of the present study was to analyse the skeletal changes following dislocated condylar process fractures in growing rats.
INTRODUCTION Condylar process fractures are common, most often unilaterally with medial deviations (Silvennoinen et al., 1992; Joos and Kleinheinz, 1998). Studies have described a favourable prognosis when treated by closed methods in children and adolescents (Feifel et al., 1992; Joos and Kleinheinz, 1998). The ability of the ascending ramus to repair and remodel following trauma has been tested experimentally (Yu¨cel et al., 2002). Also, healing of condylar process fractures has been demonstrated in animal studies (Yasuoka and Oka, 1991; Teixeira et al., 1998). Callus formation, with simultaneous repositioning of the condyle, can lead to normal temporomandibular joints (TMJ; Teixeira et al., 1998). Better results, both in tissue response and time required for repair, were obtained in young animals (Luz and Arau´jo, 2001; Takatsuka et al., 2005). It has been demonstrated that cellular proliferation in fractured condyles is age dependent, being better in the young animals (Sekine et al., 1995). Remodelling of condylar processes following conservative treatment has been radiographically demonstrated (Feifel et al., 1992; Luz and Chilvarquer, 1996). However, concern is reported regarding skeletal changes, represented by mandibular asymmetry, mainly in young individuals (Norholt et al., 1993;
MATERIAL AND METHODS Experimental animals The study animals (50) were 1-month-old Wistar rats, with a mean body weight of 94.3 g. All animals were fed an ordinary diet of rodent feed (Labina, Agribands Purina, Sa˜o Paulo, Brazil), administered in powder form for 2 weeks postoperatively, and in regular form in the remaining period. They were distributed into experimental ðn ¼ 25Þ and shamoperated ðn ¼ 25Þ groups. The study was approved by the local committee on research ethics. Surgical method Under general anaesthesia, induced by intraperitoneal injection of xylazine associated with ketamine, 220
ARTICLE IN PRESS Skeletal changes in growing rats 221
a right sided preauricular incision of 1 cm was made, followed by blunt dissection through the masseter muscle, just below the zygomatic arch, and exposure of the condylar process. Fracture was achieved by using a mosquito (Halstead) forceps, and the condylar fragment was deviated medially. Care was taken so as not to damage the articular surfaces. Sham-operated animals were submitted to the same procedure, but limited to exposure of the condylar process. The procedures were concluded by suturing in layers. The animals were sacrificed 2 months postoperatively, and their body weights were recorded. Their heads and mandibles were carefully macerated and fixed in 10% buffered formalin.
Cephalometric evaluation Following formalin fixation for 1 week, radiographs in axial (dorso-ventral) projection of the skull and lateral projection of hemimandibles were obtained, and care was taken to maintain the horizontal and vertical planes. Radiographs were taken with a standard dental machine at 56 kV and 10 mA, with an exposure time of 0.4 s to skull and 0.3 s to hemimandibles. A constant 40 cm focus-to-film distance was maintained and periapical films were used (Ektaspeed, Eastman Kodak Co, USA). Radiographs were subjected to computerized cephalometric evaluation. The radiographic images were digitized, and measurements obtained with Imagelab software (LIDO, University of Sa˜o Paulo, Brazil). From the axial skull radiographs, the following distances were measured bilaterally: TB–MR – tympanic bulla (the most anterior portion of this round and voluminous structure of the skull base) to the mesial root of the first molar (the apex of this root); TB–IF – tympanic bulla to infraorbital foramen (the vertex of the image of this foramen); and IF–IP – infraorbital foramen to incisal point (the intersection of the lingual face of upper incisors with the midline; Fig. 1). On the lateral radiographs of the hemimandibles, the following distances were measured bilaterally: CP–AP – condylar process (the highest point of this structure) to angular process (the apex of this structure peculiar to the rodent mandible); TM–AN – intersection of the distal face of the third molar with the mandibular ramus to antegonial notch (the latter being located on the mandibular basis anteriorly to the mandibular angle); and II–AP – lower insertion of incisor (the most anterior limit of the lower bone insertion of this tooth) to angular process (Fig. 2). To evaluate the significance of differences between the mean values found in both groups, the Student’s t-test was used, whilst the paired Student’s t-test was used to compare the mean values from right and left sides in each group. The level of significance was set at pp0:05 for all the statistical analyses.
Fig. 1 – Axial radiograph of skull. A discrete asymmetry of the maxilla may be seen. TB, tympanic bulla; MR, mesial root of the first molar; IF, infraorbital foramen; IP, incisal point.
Fig. 2 – Lateral radiograph of hemimandibles. Atrophy of the condylar process of the right side (top) is seen. AN, antegonial notch; TM, distal face of the third molar; II, insertion of incisor; AP, angular process; CP, condylar process.
ARTICLE IN PRESS 222 Journal of Cranio-Maxillofacial Surgery
RESULTS
Tympanic bulla to mesial root of the first molar (TB-MR)
Macroscopic features After the surgical procedure, the animals continued to grow and gain weight. Two months postoperatively, the mean body weights of animals from the experimental group was 269.2736.2 g, and from the sham-operated group was 285.9724.5 g. Student’s t-test of (the arithmetic) means of both groups revealed no significant difference ðp ¼ 0:062Þ: However, macroscopic examination of the specimens revealed facial asymmetry in the experimental group, with deviation of the mandible to the right (side of fracture), and asymmetric wear of the incisors. A smaller volume of the masseter muscle was observed on the right side in the experimental group. There were no such alterations in the shamoperated group. Atrophy and degenerative changes of the condylar process were noted radiographically in the experimental group, whereas the shamoperated group presented normal radiographic findings (Figs. 2 and 3).
Cephalometric evaluation A. The mean values of distances found on axial radiographs of the skulls are listed in Table 1.
There was a statistically significant difference between the means of the experimental and the shamoperated groups on the right side ðp ¼ 0:017Þ; but not on the left side ðp ¼ 0:811Þ: Also, there was a significant difference between the right and left sides in the experimental group ðp ¼ 0:001Þ but not in the sham-operated group ðp ¼ 0:965Þ: Tympanic bulla to infraorbital foramen (TB-IF) There was no significant difference between experimental and sham-operated groups on the right side ðp ¼ 0:071Þ nor on the left side ðp ¼ 0:055Þ; and no significant difference between right and left sides in the experimental group ðp ¼ 0:645Þ nor the shamoperated group ðp ¼ 0:918Þ: Infraorbital foramen to incisal point (IF-IP) There were significant differences between experimental and sham-operated groups on the right ðp ¼ 0:001Þ; and on the left side ðp ¼ 0:004Þ: There was also a significant difference between right and left sides in the experimental group ðp ¼ 0:002Þ; but not in the sham-operated group ðp ¼ 0:104Þ:
Fig. 3 – Radiographic image of right (R) condyle exhibiting atrophy and degenerative changes such as altered form and irregular contour. Compare with normal shape of control (L) condyle.
Table 1 – Data obtained in axial radiographs of the rat skulls (mm) Group
Experimental Sham-operated
TB–MR
TB–IF
IF–IP
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
16.8770.54 17.2270.48
17.1970.64 17.2270.43
21.2871.02 21.7370.71
21.3470.75 21.7370.61
8.4670.75 9.0470.35
8.6370.71 9.1270.35
For definition of distances evaluated see text. sd, standard deviation.
ARTICLE IN PRESS Skeletal changes in growing rats 223 Table 2 – Data obtained in lateral radiographs of rat hemimandibles (mm) Group
Experimental Sham-operated
TM–AN
CP–AP
II–AP
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
Right side mean7sd
Left side mean7sd
6.2570.21 6.1770.17
6.3670.20 6.2270.16
8.8770.61 10.7670.33
10.6670.50 10.9970.37
22.7371.27 23.2671.14
24.2770.94 24.2971.22
For definition of distances evaluated see text. sd, standard deviation.
B. The mean values of distances determined from lateral radiograms of hemimandibles are listed in Table 2. Distal face of the third molar to antegonial notch (TM-AN) There was no significant difference between experimental and sham-operated groups on the right side ðp ¼ 0:163Þ; but there was significance on the left side ðp ¼ 0:009Þ: Also, there was a significant difference between right and left sides in the experimental group ðp ¼ 0:001Þ; but not in the sham-operated group ðp ¼ 0:137Þ: Condylar process to angular process (CP-AP) There were significant differences between experimental and sham-operated groups on the right ðpo0:001Þ; and on the left side ðp ¼ 0:011Þ: Besides, there were also significant differences between right and left sides in both the experimental ðpo0:001Þ as well as in the sham-operated groups ðpo0:001Þ: Lower insertion of incisor to angular process (II-AP) There was no significant difference between experimental and sham-operated groups on the right side ðp ¼ 0:127Þ nor the left side ðp ¼ 0:930Þ: However, there were significant differences between right and left sides in both the experimental ðpo0:001Þ as well as the sham-operated groups ðpo0:001Þ:
DISCUSSION In this model, a unilateral, medially deviated fracture was induced, which is the most frequent form of mandibular condyle fracture (Silvennoinen et al., 1992; Thore´n et al., 1997; Joos and Kleinheinz, 1998; Oji, 1998). The present study has shown that fractures of the mandibular condyle in young rats induced an asymmetry of the mandible affecting both the horizontal and condylar rami with consequences to the maxilla. Thus, the final result was a deviated midline of the mandible associated with an atrophic condylar process. Cephalometric evaluations also identified asymmetric areas in the maxilla. Deviation
of the midline of the mandible towards the side of the fracture occurred in the experimental group. Mandibular asymmetries have been related to condylar fractures in young human patients at variable rates (Proffit et al., 1980; Norholt et al., 1993; Hovinga et al., 1999). Functional results of nonsurgical and surgical treatment of condylar fractures are said to be comparable (Takenoshita et al., 1990; Hidding et al., 1992; Joos and Kleinheinz, 1998), although some degree of deviation can occur in patients treated non-surgically by the closed method (Joos and Kleinheinz, 1998). From an experimental model, only cautious conclusions can be drawn concerning human subjects. It is important to remember that there are differences in the TMJ form and muscular system between rodents and omnivores. While the condyle is elongated in an anteroposterior direction with a narrow, elongated fossa and is performing movements only in one direction in rodents, the condyle is elliptical with a deep and large fossa, performing movements in lateral and anteroposterior directions in humans. Another finding was a smaller volume of masseter muscles on the right side in the experimental group. This is probably associated with the asymmetry following the condylar fracture, with consequently altered mastication. A study by Kuboyama and Moriya (1995) showed that malocclusion induced by extraction of molar teeth and different dietary consistency does influence the development of the masseter muscle. The experimental group suffered a reduced body weight compared with the shamoperated group (not significant). This may indicate some influence of the condylar fracture on the eating ability of the growing animals during healing. Similar findings were reported before (Luz and Arau´jo, 2001). Cephalometric evaluations from radiographs of dissected specimens using a computer system (as in this study) lead to reliable measurements, reducing technical difficulties (Del Campo et al., 1995). Distances found were similar to those noted in other experiments (Del Campo et al., 1995; Yamamoto et al., 1997). Significant alteration in the mandibular body height was the main finding in this study. Compensatory growth of the alveolar bone of the mandible enabling masticatory function has been experimentally demonstrated (Das, 1970). Another significant finding was shortening of the maxilla.
ARTICLE IN PRESS 224 Journal of Cranio-Maxillofacial Surgery
The possibility of maxillary growth influencing mandibular growth and vice versa by occlusal intercuspation has been described by Enlow (1990). Occlusal disturbances were considered the main cause of asymmetry of the midface after condylar fractures in young rabbits (Altonen et al., 1978). Some distances, such as condylar to angular processes, and lower incisor to angular process shared significant differences between sides, but not between groups. This may be attributable to the surgical access, and further studies on this matter are necessary. The possibility of a decrease in growth of the mandible caused by the periosteal lesion should be considered (Koski and Ro¨nning, 1982). However, this study has detected no obvious effects on the mandibular length. Condylar cartilage growth contributes not only to the height of the mandibular ramus but also increases mandibular length (Ayoub and Mostafa, 1992). Hence a lesion of the condylar process could result in facial deformity (Proffit et al., 1980). Apart from the condyle being essential to normal growth of the mandible, dimensions and morphology of the mandibular ramus are also associated with masticatory muscle insertions and activity. Thus, mandibular growth is a product of different forces and of regional functional agents of growth control (Enlow, 1990). Radiographic features of atrophy and degenerative changes of the condylar process were the other important finding. The ability of the TMJ to remodel has been reported following treatment of dislocated condylar fractures (Feifel et al., 1992; Luz and Chilvarquer, 1996), especially in the young individual (Strobl et al., 1999; Gu¨ven and Keskin, 2001). However, the possibility of incomplete restoration of the condyle to a normal form and consequently signs of osteoarthrosis should be considered as a sequel to condylar fractures (Hidding et al., 1992; Hovinga et al., 1999; Strobl et al., 1999). Exactly this was demonstrated in this study of consequences following condylar fracture dislocations in young rats. CONCLUSION In this experimental study the following skeletal changes were noted as a result of fracture dislocations of the condylar process in young animals; atrophy and degenerative changes of the condylar process as well as significant differences in the height of the mandible and in the length of the maxilla. ACKNOWLEDGEMENTS
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Prof. Dr. Joa˜o Gualberto C. LUZ R. Duarte de Azevedo 284, s. 22, 2036-21 Sa˜o Paulo SP Brazil Fax: +55 11 69596266 E-mail: [email protected] Paper received 3 September 2004 Accepted 16 January 2006