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Condylectomy in the rat
Arch. oral Bid.
Vol.10, pp.lOl-106,
1965. Pergamon Press Ltd. Printed in Ct. Britain.
CONDYLECTOMY
IN THE RAT
A. A. GIANELLYand C. F. A. MOORREES Forsyth Dental Center and Harvard School of Dental Medicine, Boston, Massachusetts Summary-To asses?the contribution of the conayle to the growth of the mandible, forty-two Holtzman albino lats weighing between 40-50 g, were bilaterally condylectomized and at maturity compared anatomically and radiographically with 10 shamoperated and 27 control animals. From standardized lateral radiographs, the incisor overjet and molar overjet were determined. Comparisons were also made of the anteroposterior length of the mandibles, utilizing as landmarks infradentale and the most posterior point of the distal angular proces?. Findings showed that the mandibles of the condylectomized group were 2 mm shorter than those of controls. However, the relation of the mandibular to maxillary dentition as seen radiographically was unaffected Histologically, a scar tissue type response was noted in the condylectomized area. INTRODUCTION
THE CONTRIBUTION of the condyle to the growth of the mandible has been debated for a considerable length of time, and at present, there are two schools of thought as to its function. According to conventional concepts, the condyle is a primary and essential growth center for development of the mandible, which also must maintain its normal relation to the maxilla. More recently, an opposing hypothesis has been advanced which views growth of the condyle merely as a response to functional requirements of the oral viscera or to stimuli conditioned by the oro-facial musculature. Growth of the mandible therefore requires adaptive changes in the condylar area. Since neither thesis can be accepted in the absence of satisfactory evidence, the present project was undertaken to furnish experimental data on the effect of condylectomy in an attempt to clarify some aspects of this issue. MATERIALS
AND
METHODS
From a total of seventy-nine Holtzman albino rats, weighing between 40 and 50 g, forty-two animals were bilaterally condylectomized, ten animals were sham operated and twenty-seven others served as controls. The surgery was performed under ether anesthesia following an approach designed by JOLLY (1961). This method entailed a vertical incision through the skin, subcutaneous tissue, and platysma, approximately 3-4 mm anterior to the ear. The extra-orbital lacrimal gland, branches of the facial nerve, and parotid duct were exposed and the gland was reflected posteriorly (Fig. 1). By blunt dissection, the vital tissues were carefully retracted, and the fibers of the masseter overlying the joint were separated. The condyle was grasped with forceps and it was snipped off with scissors just below the level of the instrument. The excised part, still in the forceps, was 101
102
A. A. GIANELLY AND C. F. A. MOORREES
removed. Haemorrhage was controlled by applying local pressure, and sutures were used to close the area. The animals were allowed to grow to maturity. Food and water were provided ad libitum, but the condylectomized and sham operated animals were given ground rat chow, while the control group received pellets. The differences in diet required more vigorous chewing of the rats in the control group. Since these animals received additional functional stimuli, the effect of the diet on growth, if significant, would therefore contribute to magnify differences in the dimensions of the mandible’in the experimental and control group. For the development of the operated animals, ground chow was a necessity, because their chewing was impaired after the condylectomy. At maturity, standardized lateral head radiographs were obtained with the aid of a specially-constructed rat cephalostat. Fixation of the head was achieved by means of a rod with a small loop at its end in which the maxillary incisors were inserted. In this manner, the midsagittal plane was at a constant distance to the X-ray beam on one side and to the film, placed in an appropriate receptacle, on the other side. All animals were sacrificed, when their mature weight (330-370 g) was attained. Four of the forty-two condylectomized animals were processed for histologic sections of the condylar area. The specimens were fixed in formalin, embedded in paraffin and stained with haematoxylin and eosin. The mandibles of the remaining thirty-eight rats were removed and cleaned. Their antero-posterior length was measured with a vernier caliper to 0.1 mm. The most ventral aspect of the mandible (infradentale), and the most dorsal aspect of the distal angular process served as landmarks for obtaining mandibular length. Owing to slight movement of the animals during ether anaesthesia, the head radiographs were not all satisfactory. Inspection revealed that twenty-two radiographs of condylectomized animals and seven head radiographs of controls were of optimal quality for studying the relation of maxillary and mandibular incisors as well as molar occlusion in the sagittal plane. Incisor overjet was obtained as the distance between the palatal aspects of the maxillary incisors to the most labial aspects of the mandibular incisors. The relation of the molars was determined as the distance from the most mesial aspect of the maxillary first molar to that of the mandibular first molar. Methods of measuring the radiographs are shown graphically in Fig. 3. The sources contributing to errors inherent in cephalometry of the rat, as performed in the present study, are concerned with the reproducibility of tracing technique, identification of landmarks and positioning of animals in the cephalostat. The total effect of these factors was assessed by obtaining radiographs of twenty animals on two separate occasions. Measurements were taken on tracings of the molar relation in the sagittal plane. The standard deviations of the differences in molar relation for both tests were calculated according to the formula:
SD. error
=
Sum of difference9 + 2 x Number of animals >
103
CONDYLECTOMYINTHERAT
Although discrepancies in the findings resulting from positioning the rats in the cephalostat were unavoidable, the tracing and measurements were done with the utmost care, averaging repeated observations on both incisor and molar relationships. FINDlNGS
Gross examination of the mandibles of the forty-two condylectomized and the twenty-seven control animals revealed that the coronoid process appeared larger, while the antegonial notch was definitely more pronounced in the condylectomized group (Fig. 2).
B
FIG.
3. Method of measuring incisor and molar overjet.
The histologic sections of the condylectomized animals indicated that a reparative process occurred, similar to a scar tissue response, after the removal of the condyle. The presence of fibroblastic like cells and collagenous tissue were noted (Fig. 4, A-D). Mandibular length of the condylectomized animals differed slightly (2.0 mm) but at a statistically significant level (p
MANDIBULAK
.~
LENGTH
(mm)
___~
_____
Number of animals
Mean
Standard deviation ______
Condylectomy
38
22.0
0.53
Control
21
24.0
0.30
Sham operated
10
23.9
0.25
Group .~
_~~
Significance ____ ~ pco.01
104
A. A. GIANELLYAND C. F. A. MO~RREES
The incisor overjet was apparently not affected by condylectomy if judged by the mean findings, but the relation of the maxillary and mandibular molars averaged slightly larger (O-38 mm) in the group subjected to condylectomy (Table 2). This difference just lacked statistical significance (O.O5
RELATIONS
Group
DENTALARCHESIN THE SAGITTALPLANE ACCORDING MOLARAND INCISOROCCLUSION(II1ITI)
OF
Number of animals
Mean
22
2.0
0.42
7
1.62
0.42
22
2.38
0.46
7
2.41
0.39
Molar Condylectomy
Standard deviation
TO
Significance
0.05
N.S. Control
____~_ DISCUSSION
The surgical technique used was also tried on 7-day-old animals (20 g) as part of an earlier protocol to assess the contribution of condylar growth. Fragility of the barely calcified tissue, poor tolerance to ether anaesthesia permitting sufficient time (&-1 hr) for the operation and the uncontrollable nature of the haemorrhage when extricating the condyle, made the procedure unfeasible. Thus, the earliest state of maturation for conducting the experimentation was established at the immediate post-weaning phase (40 g). Quantitation of the early growth was, nevertheless, undertaken by gross crosssectional analysis of twenty-seven animals. The results show that the mean increment in mandibular length was 3.6 mm (Table 3). Thus, at birth the mandible had acquired approximately 50 per cent of its mature length and at weaning, 66 per cent had been attained. TABLET.
MANDIBULAR
LENGTH
(mm) SHORTLY WEANING
AFTER
BIRTH
AND
AT
~____
Group
-__ 1 week old (20 g) 3 weeks old (40 g)
Number of animals 14 13 ___~__
Mean 12.6 16.2
Standard deviation 0.27 0.20
The 2 mm difference in over-all mandibular length of controls and the operated animals studied after weaning, which retained the normal incisor and molar relation, suggests that condylar growth is of an adaptive nature in the rat. This conclusion
CONDYLECTOMY IN THE RAT
105
must be interpreted with caution, inasmuch as the earlier contribution of condylar growth has not been adequately assessed. In fact, one may even go so far as to argue that the 2 mm post-weaning difference in the two groups represents an anatomically significant finding, since it constitutes 25 per cent of the remaining growth potential of the mandible. The agreement of mandibular lengths in control and sham operated animals, confirm that differences in dietary consistency do not affect certain parameters of mandibular growth (WATTS and WILLIAMS,1951; BARBER,GREEN and cox, 1963). The literature contains few comparable data. SARNAT and ENGLE (1951) condylectomized three Rhesus monkeys and studied gross changes as well as the position of the mandible. These authors found both antegonial notching and larger coronoid processes characteristic of mandibles in the condylectomized animals. In the present experiment, similar remodelling phenomena were noted. Interestingly, SARNATand ENGLE’S(1951) findings confirmed the maintenance of anatomically correct jaw relationships as judged by the occlusion. As proponents of VANDER KLAUW’S(1948-52) functional hypothesis of cranial growth, Moss and YOUNG(1960) have been most articulate in describing the condyle as a secondary growth centre. They implicate the oral viscera as the primary growth factor which necessitates downward and forward movement of the mandible within the facial capsule. To keep the T-M joint intact, the condylar cartilage profilerates as the mandible maintains its spatial position in relation to the maxilla. KAZANJIAN(1956) stated that there was little, if any, impairment in the relationship of the maxilla and mandible in the case of a woman with bilateral congenital absence of the mandibular rami. This report together with the findings of SARNAT and ENGLE(1951), as well as those of the present study, tend to support the hypothesis of MOSS (1962). However, the lack of experimental evidence precludes further discussion of the functional hypothesis. More recently, KOSKI (1963) has shown that transplanted condylar cartilage behaves differently from transplanted epiphyseal cartilage. Similarly, the condyle is virtually insensitive to papain administration while growth cartilages, such as the tibia1 epiphyseal cartilage and the :spheno-occipital synchondrosis, are severely affected (IRVING and R~~NNING,1962). Finally, the scorbutic changes in the tibia1 epiphysis are quite different from those in the mandibular condyle (IRVING and DURKIN,Private Communication, 1964). Actually, there is no experimental evidence to indicate that the condyle is a growth centre. The resemblance of condylar cartilage and epiphyseal plate in their cellular morphology and its location at the end of a bony shaft probably explain the inference that the condyle is an active growth centre. The regeneration of cartilage noted by JOLLY(1961) in adult rats (250 g) after removal of the condyle was not observed in the histologic sections of this study. In contrast, healing response with apparently a fibro-granulation tissue was clearly defined. In final analysis, considerable investigation is necessary for clarification of the role of the condyle, in its relation to the growth of the mandible also considering possible species differences.
A. A. GIANELLYANDC. F. A. M~~RREES
106
R&sum&--Pour definir le role de condyle sur la croissance mandibulaire, 42 rats albinos Holtzman, pesant entre 40 et 50 grs., subissent une resection bilaterale des condyles. Un fois arrives a maturite, ces animaux sont compares anatomiquement et radiographiquement avec 10 rats, ayant subi une operation-temoin, et 27 animaux de contrble. Les supraclusies incisive et molaire sont determinees sur des radiographies laterales standardis&. Une etude comparative de la longueur ant&o-posterieure des mandibules est egalement reali&, en utilisant comme reperes l’infradental et le point le plus posterieur de Tangle mandibulaire. 11 apparait ainsi que les mandibles de rats a condyles reseques sont plus courtes de 2 mm. que celles des temoins. Cependant, le rapport des dents des maxillaires suptrieur et inferieur, apprecie sur les radiographies, ne parait pas affect& Un tissu de cicatrisation est visible histologiquement au niveau des condyles resCquCs. Zusannnenfassung-Urn den Beitrag des Kondylus fiir das Unterkieferwachstum zu ermessen, wurden 42 Holtzmann-Albinoratten mit 40-50 g Gewicht bilateral kondylektomiert und nach Ausreifung anatomisch und radiographisch mit 10 scheinoperierten und 27 Kontrolltieren verglichen. Nach standardisierten seitlichen Rontgenaufnahmen wurde der Schneidezahn- und der Molarentiberbiss bestimmt. Vergleiche wurden such beziiglich der anterior-posterioren Lange der Mandibula angestellt, wobei als Bezugspunkte das lnfradentale und der rtickwiirtigste Punkt des distalen Prozesses des Unterkieferwinkels verwendet wurden. Die Befunde zeigen, dass die Mandibula der kondylektomierten Gruppe 2 mm kiirzer waren als jene der Kontrolle. Wie aus den Rontgenaufnahmen ersichtlich war jedoch die Beziehung zwischen den Zahnreihen der Unter- und Oberkiefer unbeeinflusst. Histologisch wurde in dem kondylektomierten Bereich eine Art Narbengewebe als Antwort beobachtet. REFERENCES BARBER,C. G., GREEN,L. J. and Cox, G. J. 1963. Effects of the physical consistency of diet on the condylar growth of the rat mandible. J. dent. Rex 42, 848. IRVING,J. T. and R&NMG, 0. V. 1962. The selective action of papain on calcification sites. Arch. oral Not. 7, 357-363. JARABAK,J. R. 1951. Regeneration of the mandibular condyle following bilateral resection. J. dent. Res. 30,491. (Abstract) JOLLY, M. 1961. Condylectomy in the rat. An investigation of the ensuing repair process in the region of the temporomandibular articulation. Austral. dent. J. 6, 243-256. KAZANJIAN,V. H. 1956. Bilateral absence of the ascending rami of the mandible. Brit. J. Plast. Surg. 9, 77-82. KLAIJ~, C. J. VAN DER. 1948-1952. Size and position of the functional components of the skull. Arch. nPer1.Zool. 9, l-559. KOSKI, K. and MAKINEN,L. 1963. Growth potential of transplanted components of the mandibular ramus of the rat. I. Finska Tandliik-SZillsk. F&h. 59,296-308. Moss, M. L. and YOUNG,R. W. 1960. A functional approach to craniology. Amer. J. Phys. Anthrop. l&291-292.
Moss, M. L. 1962. The Functional Matrix in: Vistas in Orthodontics. (Ed. KRAUS, B. S. and RIEDEL, R. A.) pp. 85-98. Lea and Febiger, Philadelphia. SARNAT,B. F. and ENGLE, M. B. 1951. A serial study of mandibular growth after the removal of the condyle of the Rhesus monkey. Plast. Reconstrl. Surg. 7, 364-380. SCHWARTZ,L. 1959. Disorders of the Temporomandibular Joint. Saunders, Philadelphia. WATIS, D. G. and WILLIAMS,C. H. M. 1951. The effect of the physical consistency of food on the growth of the mandible and maxilla of the rat. Amer. J. Orthodont. 37, 895-928. PLATE 1 FIG. 1. The approach to the condylar area entailed a vertical incision anterior to the ear, exposing the extra-orbital lacrimal gland (reflected posteriorly) and the facial complex of nerves, vessels and parotid duct. FIG. 2. Left buccal and right lingual view of a mature normal rat mandible (top row) and a left buccal and right lingual view of a rat mandible subjected to bilateral condylectomy at weaning (bottom row). Notice the more pronounced antegonial notching and the larger coronoid processes of the mandibles of the operated animals.
CONDYLECTOMY
f.p.106
IN THE
RAT
A. A.
GIANELLY
AND
C. F. A.
MOORREES
FIG. 4. A. Frontal section of the condylar area in a normal rat depicting the ascending ramus and the condyle. The encapsulated well organized condylar cartilage is delineated at the end of the ramus. PLATE
2
CONDYLE(‘lOMY
F1c.4. B. HighermagnificationofA,showingin and chondrocytes in the cartilaginous matrix, cancellous bone of the ascending ramus.
IN THE
RAT
more detail thecapsule,fibrouslayer as well a’; the “primary sponqiosum”
and
A. .4.
C;IANELI.Y
AND
C.
F. A. M~ORREES
CONDYLECTOMY
f.p. 106
IN THE RAT
PLATE
5
Vol.10, pp.lOl-106,
1965. Pergamon Press Ltd. Printed in Ct. Britain.
CONDYLECTOMY
IN THE RAT
A. A. GIANELLYand C. F. A. MOORREES Forsyth Dental Center and Harvard School of Dental Medicine, Boston, Massachusetts Summary-To asses?the contribution of the conayle to the growth of the mandible, forty-two Holtzman albino lats weighing between 40-50 g, were bilaterally condylectomized and at maturity compared anatomically and radiographically with 10 shamoperated and 27 control animals. From standardized lateral radiographs, the incisor overjet and molar overjet were determined. Comparisons were also made of the anteroposterior length of the mandibles, utilizing as landmarks infradentale and the most posterior point of the distal angular proces?. Findings showed that the mandibles of the condylectomized group were 2 mm shorter than those of controls. However, the relation of the mandibular to maxillary dentition as seen radiographically was unaffected Histologically, a scar tissue type response was noted in the condylectomized area. INTRODUCTION
THE CONTRIBUTION of the condyle to the growth of the mandible has been debated for a considerable length of time, and at present, there are two schools of thought as to its function. According to conventional concepts, the condyle is a primary and essential growth center for development of the mandible, which also must maintain its normal relation to the maxilla. More recently, an opposing hypothesis has been advanced which views growth of the condyle merely as a response to functional requirements of the oral viscera or to stimuli conditioned by the oro-facial musculature. Growth of the mandible therefore requires adaptive changes in the condylar area. Since neither thesis can be accepted in the absence of satisfactory evidence, the present project was undertaken to furnish experimental data on the effect of condylectomy in an attempt to clarify some aspects of this issue. MATERIALS
AND
METHODS
From a total of seventy-nine Holtzman albino rats, weighing between 40 and 50 g, forty-two animals were bilaterally condylectomized, ten animals were sham operated and twenty-seven others served as controls. The surgery was performed under ether anesthesia following an approach designed by JOLLY (1961). This method entailed a vertical incision through the skin, subcutaneous tissue, and platysma, approximately 3-4 mm anterior to the ear. The extra-orbital lacrimal gland, branches of the facial nerve, and parotid duct were exposed and the gland was reflected posteriorly (Fig. 1). By blunt dissection, the vital tissues were carefully retracted, and the fibers of the masseter overlying the joint were separated. The condyle was grasped with forceps and it was snipped off with scissors just below the level of the instrument. The excised part, still in the forceps, was 101
102
A. A. GIANELLY AND C. F. A. MOORREES
removed. Haemorrhage was controlled by applying local pressure, and sutures were used to close the area. The animals were allowed to grow to maturity. Food and water were provided ad libitum, but the condylectomized and sham operated animals were given ground rat chow, while the control group received pellets. The differences in diet required more vigorous chewing of the rats in the control group. Since these animals received additional functional stimuli, the effect of the diet on growth, if significant, would therefore contribute to magnify differences in the dimensions of the mandible’in the experimental and control group. For the development of the operated animals, ground chow was a necessity, because their chewing was impaired after the condylectomy. At maturity, standardized lateral head radiographs were obtained with the aid of a specially-constructed rat cephalostat. Fixation of the head was achieved by means of a rod with a small loop at its end in which the maxillary incisors were inserted. In this manner, the midsagittal plane was at a constant distance to the X-ray beam on one side and to the film, placed in an appropriate receptacle, on the other side. All animals were sacrificed, when their mature weight (330-370 g) was attained. Four of the forty-two condylectomized animals were processed for histologic sections of the condylar area. The specimens were fixed in formalin, embedded in paraffin and stained with haematoxylin and eosin. The mandibles of the remaining thirty-eight rats were removed and cleaned. Their antero-posterior length was measured with a vernier caliper to 0.1 mm. The most ventral aspect of the mandible (infradentale), and the most dorsal aspect of the distal angular process served as landmarks for obtaining mandibular length. Owing to slight movement of the animals during ether anaesthesia, the head radiographs were not all satisfactory. Inspection revealed that twenty-two radiographs of condylectomized animals and seven head radiographs of controls were of optimal quality for studying the relation of maxillary and mandibular incisors as well as molar occlusion in the sagittal plane. Incisor overjet was obtained as the distance between the palatal aspects of the maxillary incisors to the most labial aspects of the mandibular incisors. The relation of the molars was determined as the distance from the most mesial aspect of the maxillary first molar to that of the mandibular first molar. Methods of measuring the radiographs are shown graphically in Fig. 3. The sources contributing to errors inherent in cephalometry of the rat, as performed in the present study, are concerned with the reproducibility of tracing technique, identification of landmarks and positioning of animals in the cephalostat. The total effect of these factors was assessed by obtaining radiographs of twenty animals on two separate occasions. Measurements were taken on tracings of the molar relation in the sagittal plane. The standard deviations of the differences in molar relation for both tests were calculated according to the formula:
SD. error
=
Sum of difference9 + 2 x Number of animals >
103
CONDYLECTOMYINTHERAT
Although discrepancies in the findings resulting from positioning the rats in the cephalostat were unavoidable, the tracing and measurements were done with the utmost care, averaging repeated observations on both incisor and molar relationships. FINDlNGS
Gross examination of the mandibles of the forty-two condylectomized and the twenty-seven control animals revealed that the coronoid process appeared larger, while the antegonial notch was definitely more pronounced in the condylectomized group (Fig. 2).
B
FIG.
3. Method of measuring incisor and molar overjet.
The histologic sections of the condylectomized animals indicated that a reparative process occurred, similar to a scar tissue response, after the removal of the condyle. The presence of fibroblastic like cells and collagenous tissue were noted (Fig. 4, A-D). Mandibular length of the condylectomized animals differed slightly (2.0 mm) but at a statistically significant level (p
MANDIBULAK
.~
LENGTH
(mm)
___~
_____
Number of animals
Mean
Standard deviation ______
Condylectomy
38
22.0
0.53
Control
21
24.0
0.30
Sham operated
10
23.9
0.25
Group .~
_~~
Significance ____ ~ pco.01
104
A. A. GIANELLYAND C. F. A. MO~RREES
The incisor overjet was apparently not affected by condylectomy if judged by the mean findings, but the relation of the maxillary and mandibular molars averaged slightly larger (O-38 mm) in the group subjected to condylectomy (Table 2). This difference just lacked statistical significance (O.O5
RELATIONS
Group
DENTALARCHESIN THE SAGITTALPLANE ACCORDING MOLARAND INCISOROCCLUSION(II1ITI)
OF
Number of animals
Mean
22
2.0
0.42
7
1.62
0.42
22
2.38
0.46
7
2.41
0.39
Molar Condylectomy
Standard deviation
TO
Significance
0.05
N.S. Control
____~_ DISCUSSION
The surgical technique used was also tried on 7-day-old animals (20 g) as part of an earlier protocol to assess the contribution of condylar growth. Fragility of the barely calcified tissue, poor tolerance to ether anaesthesia permitting sufficient time (&-1 hr) for the operation and the uncontrollable nature of the haemorrhage when extricating the condyle, made the procedure unfeasible. Thus, the earliest state of maturation for conducting the experimentation was established at the immediate post-weaning phase (40 g). Quantitation of the early growth was, nevertheless, undertaken by gross crosssectional analysis of twenty-seven animals. The results show that the mean increment in mandibular length was 3.6 mm (Table 3). Thus, at birth the mandible had acquired approximately 50 per cent of its mature length and at weaning, 66 per cent had been attained. TABLET.
MANDIBULAR
LENGTH
(mm) SHORTLY WEANING
AFTER
BIRTH
AND
AT
~____
Group
-__ 1 week old (20 g) 3 weeks old (40 g)
Number of animals 14 13 ___~__
Mean 12.6 16.2
Standard deviation 0.27 0.20
The 2 mm difference in over-all mandibular length of controls and the operated animals studied after weaning, which retained the normal incisor and molar relation, suggests that condylar growth is of an adaptive nature in the rat. This conclusion
CONDYLECTOMY IN THE RAT
105
must be interpreted with caution, inasmuch as the earlier contribution of condylar growth has not been adequately assessed. In fact, one may even go so far as to argue that the 2 mm post-weaning difference in the two groups represents an anatomically significant finding, since it constitutes 25 per cent of the remaining growth potential of the mandible. The agreement of mandibular lengths in control and sham operated animals, confirm that differences in dietary consistency do not affect certain parameters of mandibular growth (WATTS and WILLIAMS,1951; BARBER,GREEN and cox, 1963). The literature contains few comparable data. SARNAT and ENGLE (1951) condylectomized three Rhesus monkeys and studied gross changes as well as the position of the mandible. These authors found both antegonial notching and larger coronoid processes characteristic of mandibles in the condylectomized animals. In the present experiment, similar remodelling phenomena were noted. Interestingly, SARNATand ENGLE’S(1951) findings confirmed the maintenance of anatomically correct jaw relationships as judged by the occlusion. As proponents of VANDER KLAUW’S(1948-52) functional hypothesis of cranial growth, Moss and YOUNG(1960) have been most articulate in describing the condyle as a secondary growth centre. They implicate the oral viscera as the primary growth factor which necessitates downward and forward movement of the mandible within the facial capsule. To keep the T-M joint intact, the condylar cartilage profilerates as the mandible maintains its spatial position in relation to the maxilla. KAZANJIAN(1956) stated that there was little, if any, impairment in the relationship of the maxilla and mandible in the case of a woman with bilateral congenital absence of the mandibular rami. This report together with the findings of SARNAT and ENGLE(1951), as well as those of the present study, tend to support the hypothesis of MOSS (1962). However, the lack of experimental evidence precludes further discussion of the functional hypothesis. More recently, KOSKI (1963) has shown that transplanted condylar cartilage behaves differently from transplanted epiphyseal cartilage. Similarly, the condyle is virtually insensitive to papain administration while growth cartilages, such as the tibia1 epiphyseal cartilage and the :spheno-occipital synchondrosis, are severely affected (IRVING and R~~NNING,1962). Finally, the scorbutic changes in the tibia1 epiphysis are quite different from those in the mandibular condyle (IRVING and DURKIN,Private Communication, 1964). Actually, there is no experimental evidence to indicate that the condyle is a growth centre. The resemblance of condylar cartilage and epiphyseal plate in their cellular morphology and its location at the end of a bony shaft probably explain the inference that the condyle is an active growth centre. The regeneration of cartilage noted by JOLLY(1961) in adult rats (250 g) after removal of the condyle was not observed in the histologic sections of this study. In contrast, healing response with apparently a fibro-granulation tissue was clearly defined. In final analysis, considerable investigation is necessary for clarification of the role of the condyle, in its relation to the growth of the mandible also considering possible species differences.
A. A. GIANELLYANDC. F. A. M~~RREES
106
R&sum&--Pour definir le role de condyle sur la croissance mandibulaire, 42 rats albinos Holtzman, pesant entre 40 et 50 grs., subissent une resection bilaterale des condyles. Un fois arrives a maturite, ces animaux sont compares anatomiquement et radiographiquement avec 10 rats, ayant subi une operation-temoin, et 27 animaux de contrble. Les supraclusies incisive et molaire sont determinees sur des radiographies laterales standardis&. Une etude comparative de la longueur ant&o-posterieure des mandibules est egalement reali&, en utilisant comme reperes l’infradental et le point le plus posterieur de Tangle mandibulaire. 11 apparait ainsi que les mandibles de rats a condyles reseques sont plus courtes de 2 mm. que celles des temoins. Cependant, le rapport des dents des maxillaires suptrieur et inferieur, apprecie sur les radiographies, ne parait pas affect& Un tissu de cicatrisation est visible histologiquement au niveau des condyles resCquCs. Zusannnenfassung-Urn den Beitrag des Kondylus fiir das Unterkieferwachstum zu ermessen, wurden 42 Holtzmann-Albinoratten mit 40-50 g Gewicht bilateral kondylektomiert und nach Ausreifung anatomisch und radiographisch mit 10 scheinoperierten und 27 Kontrolltieren verglichen. Nach standardisierten seitlichen Rontgenaufnahmen wurde der Schneidezahn- und der Molarentiberbiss bestimmt. Vergleiche wurden such beziiglich der anterior-posterioren Lange der Mandibula angestellt, wobei als Bezugspunkte das lnfradentale und der rtickwiirtigste Punkt des distalen Prozesses des Unterkieferwinkels verwendet wurden. Die Befunde zeigen, dass die Mandibula der kondylektomierten Gruppe 2 mm kiirzer waren als jene der Kontrolle. Wie aus den Rontgenaufnahmen ersichtlich war jedoch die Beziehung zwischen den Zahnreihen der Unter- und Oberkiefer unbeeinflusst. Histologisch wurde in dem kondylektomierten Bereich eine Art Narbengewebe als Antwort beobachtet. REFERENCES BARBER,C. G., GREEN,L. J. and Cox, G. J. 1963. Effects of the physical consistency of diet on the condylar growth of the rat mandible. J. dent. Rex 42, 848. IRVING,J. T. and R&NMG, 0. V. 1962. The selective action of papain on calcification sites. Arch. oral Not. 7, 357-363. JARABAK,J. R. 1951. Regeneration of the mandibular condyle following bilateral resection. J. dent. Res. 30,491. (Abstract) JOLLY, M. 1961. Condylectomy in the rat. An investigation of the ensuing repair process in the region of the temporomandibular articulation. Austral. dent. J. 6, 243-256. KAZANJIAN,V. H. 1956. Bilateral absence of the ascending rami of the mandible. Brit. J. Plast. Surg. 9, 77-82. KLAIJ~, C. J. VAN DER. 1948-1952. Size and position of the functional components of the skull. Arch. nPer1.Zool. 9, l-559. KOSKI, K. and MAKINEN,L. 1963. Growth potential of transplanted components of the mandibular ramus of the rat. I. Finska Tandliik-SZillsk. F&h. 59,296-308. Moss, M. L. and YOUNG,R. W. 1960. A functional approach to craniology. Amer. J. Phys. Anthrop. l&291-292.
Moss, M. L. 1962. The Functional Matrix in: Vistas in Orthodontics. (Ed. KRAUS, B. S. and RIEDEL, R. A.) pp. 85-98. Lea and Febiger, Philadelphia. SARNAT,B. F. and ENGLE, M. B. 1951. A serial study of mandibular growth after the removal of the condyle of the Rhesus monkey. Plast. Reconstrl. Surg. 7, 364-380. SCHWARTZ,L. 1959. Disorders of the Temporomandibular Joint. Saunders, Philadelphia. WATIS, D. G. and WILLIAMS,C. H. M. 1951. The effect of the physical consistency of food on the growth of the mandible and maxilla of the rat. Amer. J. Orthodont. 37, 895-928. PLATE 1 FIG. 1. The approach to the condylar area entailed a vertical incision anterior to the ear, exposing the extra-orbital lacrimal gland (reflected posteriorly) and the facial complex of nerves, vessels and parotid duct. FIG. 2. Left buccal and right lingual view of a mature normal rat mandible (top row) and a left buccal and right lingual view of a rat mandible subjected to bilateral condylectomy at weaning (bottom row). Notice the more pronounced antegonial notching and the larger coronoid processes of the mandibles of the operated animals.
CONDYLECTOMY
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FIG. 4. A. Frontal section of the condylar area in a normal rat depicting the ascending ramus and the condyle. The encapsulated well organized condylar cartilage is delineated at the end of the ramus. PLATE
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more detail thecapsule,fibrouslayer as well a’; the “primary sponqiosum”
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