Dental Development in the Cotton Ear Marmoset (Callithrix jacchus) ' GARY W. JOHNSTON, SAMUEL DREIZEN AND BARNET M. LEVY University of Texas Dental Science Institute at Houston, Houston, Texas 77025 The dental development of the cotton ear marmoset (Callithrix jacchus) was determined from gross and radiographic examinations of 40 colony born specimens to provide a biological yardstick for estimating the age of wild caught young animals. In this species 4 deciduous teeth (Idl) erupt during the first week; 4 (Ida) during the second week; 12 (Cd, Mdl, Mds) during the third week and 4 (Mdr) during the fourth week of age. Four permanent teeth ( M I ) are visible on oral Mz, 11, 12, examination at 3 to 4 months: 8 (MI, M2) at 4 to 6 months; 12 to 20 (MI, Pm3) at 7 to 8 months; 24 to 28 (MI, Mz,11, IP, P m , Pmz, Pml) at 8 to 11 months and the full complement of 32 at 11 to 12 months of age. The stage of mixed dentition extends from age 112 to 340 days. There is a close correspondence in the age related eruption pattern in each quadrant with no significant difference between males and females. ABSTRACT Marmosets are South American primates of the suborder Anthropoidea, family Callithricidae, native to the Amazon basin and Eastern Brazil. Small size (200 to 500 gm) and comparatively low purchase, care and housing costs have favored their use in many areas of biomedical research. They breed well in captivity following acclimatization, have a gestation period of approximately 140 days and usually give birth to biovular twins. Weaning is complete by three months of age and physical maturity is attained in 12 to 18 months. Their estimated life span is 15 years. In the wild, marmosets are highly arboreal, diurnal and omnivorous subsisting on a diet of fruits, tender vegetation, seeds, seed pods, insects, bird eggs and nestlings. They live in family groups of three to seven with the father and older offspring participating actively in the care of the young. The husbandry requirements for the successful breeding and maintenance of marmosets in a laboratory environment have been detailed by Levy and Artecona ('64) and by Hampton, Hampton and Landwehr ('66). Criteria for definitively identifying the age of wild caught marmosets are lacking. Immature animals are conventionally classified as infant, juvenile and subadult on the basis of appearance, size and weight. AM. J. PHYs. ANTHROP.,33: 41-48. The purpose of this study was to develop a method for more accurately ageing young cotton ear marmosets (Callithrix jacchus) by ( a ) delineating the pattern of dental development from animals of known birth date and by (b) collating the readily detectable dental maturity indicators with chronological age. MATERIALS AND METHODS Postmortem dental radiographs of 40 (21 male and 19 female) cotton ear marmosets were available for study. The age at death ranged from 2 to 390 days. All animals had been delivered at term by mothers in the breeding colony of the University of Texas Dental Science Institute. They had been born in hanging wire cages in a room maintained at 80°F and a relative humidity of 6 0 % . The parents had received a diet containing adequate amounts of all of the presently known nutritional requirements of the species (Diet 82-7. Theracon, Inc., Topeka, Kansas). Only animals which had been sacrificed or died within 24 hours following an acute illness or accident were included in the investigational series. 1 This study was supported by grants from the National Institute of Dental Research, National Institutes of Health (DE-02232)and from the Medical Research Foundation of Texas.' 41 42 G. W. JOHNSTON, S. DREIZEN AND B. M. LEVY The radiographs were prepared from heads removed at necropsy, fixed in 10% neutral formalin and sawed midsagittally following fixation. Grenz ray roentgenograms of each side were made on three and one-quarter by four inches Kodak projector slide plates of medium contrast emulsion. The target film distance was 16 cm, exposure time five minutes, and the machine settings 4 ma and 10 KV (Model VI. X-Ray Mfg. Corp. of America, Great Neck, New York). After processing, the radiographs were examined at X 3 magnification with a Bausch and Lomb Model BVB 73 stereomicroscope fitted with a fluorescent illuminator for the stage of crown and root formation and the eruption status of the deciduous and permanent teeth. Gingival eruption was distinguished from alveolar eruption by inspection of the gross specimens using the stereomicroscope and a metallic probe. A tooth was considered erupted when part of the crown had pierced the gingiva. Crown formation was rated as cusp or incisal tip present, cusp fully formed and crown completed; root formation as initial, partial or entire; eruption as impending, partial or complete. Both gross and radiographic examinations were used to establish the sequence and time of eruption of the deciduous and permanent dentition. Ink line drawings and photographs of representative radiographs were made to depict the most noteworthy age related sequential changes in the dental developmental pattern. at the contact points, a feature repeated in all deciduous molars and all permanent teeth. Each of the upper deciduous molars is morphologically distinct. Md, is shaped like the canine, Md, like a two cusped premolar and Md, like a three cusped molar. All buccal cusps are sharply exaggerated. There is a progressive increase in crown circumference from Md, through Md,. The lower deciduous teeth form a V shaped arch. In each quadrant the six crowns are paired into three distinct configurations. Idi and Id, are chisel shaped, rectangular in labial view, narrow and of approximately equal height and width. Cd and Md, are cone shzped and Md, and Md, are molariform with two large buccal and two small lingual cusps. Md, is the largest tooth in the lower deciduous arch. All deciduous anterior teeth have one root, upper molars three roots and lower molars two roots. There are no distinguishable sex differences in the deciduous dentition. The permanent upper incisors have short crowns and project slightly forward and outward. I, is broader mesiodistally and more spatulate than I,. The upper canines are tusk-like and extend well below the occlusal plane of the other teeth. They are separated from I, by a large diastema and their size and height are much greater in males than in females. The three upper premolars are unequal in size, widened buccolingually and bicuspid contoured with a well formed buccal and diminutive lingual cusp. The upper M, is a large tricuspid tooth with two high buccal and a single low lingual cusp. M, has a similar configuraOBSERVATIONS tion but is smaller and rounder. Thirteen of the specimens had a decidThe crowns of the permanent lower inuous, 23 a mixed and 3 a permanent den- cisors slant forward and are almost as long tition. The deciduous dental formula was as the adjoining canines. They are narrow I 2 / 2 , C 1/1, M 3/3; the permanent for- mesiodistally and broad labiolingually. The mula I 2 / 2 , C 1/1, Pm 3/3, M 2/2. One incisal edge of I, is slightly convex. Each animal also had a lower permanent third lower canine is fusiform in shape and has molar. a prominent cingulum on the lingual surAnatomically, the deciduous upper in- face. The lower Pml has a very high pointed cisors are centrally placed in front of the buccal cusp and a rudimentary lingual maxilla. Idl and Id, are spade shaped with equivalent resembling the adjacent canine sloping concave lingual surfaces. Id, is in appearance. Pm2 and Pm, are obliquely distinguished by a small midcrown tuber- oval with a prominent buccal and a miniacle on the distal surface. The upper decid- ture lingual cusp. Buccal cusp height diuous canines are conical and come to a minishes progressively from Pm, through point at the occlusal line. Both proximal Pm,. The permanent lower molars are surfaces are expanded into small tubercles quadrangular in outline and have two well 43 DENTAL DEVELOPMENT IN CALLITHRIX JACCHUS formed buccal and two lesser lingual cusps separated by a cruciate sulcus. As in the upper arch M, is smaller and more rounded than M,. All permanent anterior and premolar teeth have one root; lower molars two roots and upper molars three roots. For each of the parameters measured in the deciduous and permanent dentition the mean age values in each sex for each quadrant were essentially identical. The deciduous eruption sequence was Idl > Id, > (Cd = Md, = Md,) > Md,. Average ages of eruption ranged from 2.5 days (Id,) through 9.3 days (Id$), 21.0 days (Cd, Mdl, Md,) to 27.5 days (Md,). The minimum ages of appearance of radiographic evidence of crown formation, root formation, crown eruption and root completion for each of the permanent teeth are shown in figure 1. Calcification of the permanent crown began at 12 days in MI, 22 days in I,, 37 days in I,, C and Pmt, 44 days in Pm, and M, and 52 days in Pma. Crown completion and initiation of root 400 a- formation were first seen at 37 days in MI, 112 days in I, and M2,116 days in Iz, 136 days in Pms, 138 days in Pm, and Pmz and 244 days in C. The age and eruption sequence of the permanent teeth were 112 days for M1, 138 days for M2, 160 days for 11,244 days for Iz and Pms, 288 days for Pm, and 340 days for C and Pml. Root formation was complete at 152 days in M,, 244 days in M2,348 days in 11,370 days in Pm, and Pms, 377 days in Iz and 390 days in C and Pm,. The time required for complete development of the permanent teeth ranged from 140 days for MI to 353 days for C and Pml. Some minor variations in eruption sequence of the permanent teeth were found in five (13.1 % ) of the specimens. They consisted of delays in the eruption of upper Pm, and lower Pma in a 244 day old female; lower Pm, in a 298 day old male; and I, in a 348 day old male. In two females (age 158 and 180 days) I1 erupted before M*. *- d300 a- c-- c/) > d v Lu 200 c3 *- *- Q IOC 0- 0C ~ TEETH c3 I, I2 C Pm I Pmz Pm, MI M 2 M I N I M U M AGE SHOWING CUSP T I P F O R M I N G M I N I M U M A G E SHOWING ROOT F O R M A T I O N B E G I N N I N G c* M I N I M U M AGE SHOWING PERMANENT TOOTH ERUPTING 4 M I N I M U M AGE SHOWING ROOT F O R M A T I O N C O M P L E T E D A- G USED T O I L L U S T R A T E DEVELOPMENTAL PROGRESSION Fig. 1 Minimum age of radiographic appearance of dental developmental indicators i n the marmoset (Callithrir iacchus). The letters A through G identify the age of the animals used in the preparation of the dental patterns shown in figure 3. 44 G . W. JOHNSTON, S . DREIZEN AND B. M. LEVY (MI, M,, I,, Iz, Pma, Pme, Pml) at age 8 to 11 months and the full complement of 32 at age 11 to 12 months. The stage of mixed dentition lasted from 112 to 340 days of age (fig. 2). Table 1 contains the distribution of erupted deciduous and permanent teeth in each marmoset arranged according to sex and increasing chronological age. In each sex four deciduous teeth (Idl) erupted during the first postnatal week; four (Idz) during the second week; 12 (Cd, Mdl, Mdz) during the third week and four (Ma:,) during the fourth week. Four permanent teeth (MI) emerged during the third to fourth month and four (M,) during the fourth to sixth month of age. The animals had 12 to 20 erupted permanent teeth (MI, Mz,11, I,, Pm,) at age 7 to 8 months; 24 to 28 The salient features of postnatal odontogenesis in the cotton ear marmoset are depicted in figure 3. At birth the jaws contain the calcified crowns of the 20 deciduous teeth and the crypts of MI and Mz. The age related stages in the formation and migration of the succedaneous teeth are representative of the group. The migration pathways of the permanent teeth follow a TABLE 1 Distribution of erupted teeth in 40 marmosets Age Id1 Idt Cd Mdl Mdz Mdt 11 12 C Pml Pmz Pms MI Ma days Males (21) 2 2 11 15 22 30 44 52 72 112 142 148 153 160 164 245 298 298 348 1 370 390 X X x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x X x x X X X x x X X x x x x x x x x x x X x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Females (19) 9 20 36 113 134 136 136 138 146 157 158 180 198 204 244 244 287 288 377 1 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Animals with disturbances in eruption sequence. X X x x X X X x x X X X x x x x x x x x x x X x x x x x x x x x x x x x x x x x x 45 DENTAL DEVELOPMENT IN CALLITHRIX JACCHUS AGE R A N G E S F R A D I O G R A P H I C EVIDENCE OF E R U P T I O N OF M A R M O S E T TEETH d ' l P o 1 11 I2 C I MI DECIDUOUS M 2 I M3 TEETH 1, 12 C Pm, Prn, Pm, MI MZ PERMANENT TEETH Fig. 2 Age schedule and sequence of eruption of deciduous and permanent dentition in the marmoset (Callitkrix j a c c h u s ) . forward, downward and lateral course in the upper jaw and a forward, upward and lateral course in the lower jaw as the face grows and expands. DISCUSSION The dental development of the cotton ear marmoset resembles that of the insectivorous primates as the permanent molars are added to the dental arch before any of the deciduous teeth are replaced by pennanent successors (Garn and Lewis, '63). A distinguishing feature of the marmoset permanent dentition is the presence of three premolars and two molars in each jaw quadrant in contrast to three premolars and three molars in the other new world monkeys and two premolars and three molars in the old world monkeys (James, '60). The anomalous third molar found in one specimen was the first encountered in over 200 representatives of this species examined in this laboratory. There have been only two reports of the order of eruption of the deciduous teeth in primates of the family Callithricidae. In the white lipped tamarin, Saguinus nigri- collis, the incisors and canines are present at birth and are followed postnatally by Mdl > Md, > Md, (Chase and Cooper, '69). Serra ('52) listed the sequence in the genus Callithrix as Id, > Id, > Mdl > Md, > Md, > C without making any distinction as to species. In the colony born members of the Callithrix jacchus included in this study the deciduous canines emerged before the deciduous molars, eruption proceeding from Id, through Md, in a consecutive manner. The eruption sequence of the permanent teeth of the genus Callithrix has been variously reported as MI > 1, > I, > Pm, > Pm, > M, > C Pm, (Bennejeant, '36), M, > M2 > I, > 1, > Pm? > Pmi > Pm2 > C for uppers and Ml > I, > M, > I, > Pml > Pml > Pm, > C for lowers (Steliscka, '47) and either Mi > I1> M, > Pmj > I, > Pma > Pm, > C, or MI > M2 > II > Pms > I, > Pmz > Pml > C, or Mi > II > Mz > Pmj > Pm2> It > Pml > C (Serra, '52). Each of these sequences was derived from gross and/or radiographic studies of defleshed skulls of unknown age. In the present series in which gingival penetration 46 G . W. JOHNSTON, S . DREIZEN AND B. M. LEVY Fig. 3 Chronology of dental development in the marmoset ( C a l l i t h ~ i jxa c c h u s ) . A, 112 days; B, 160 days; C, 204 days; D, 244 days. DENTAL DEVEI>OPMENT IN CALLlTHRlX JACCHUS Figs. 3E-G 47 E, 288 days; F, 298 days; G , 370 days rather than alveolar breakthrough was used as the criterion of eruption in cotton ear marmosets of known age the order was M j > M I , > 1, > I, = Pm? > Pm2 > PmL = C. The analysis of the age-related roentgenograpically detectable dental developmental indicators was limited by the sample size and the availability of only a single radiogram for each animal. Methods of x-raying the dentition of live young animals are presently being developed to permit a longitudinal study of dental development in the cotton ear marmoset. These involve the use of a dental x-ray machine operating a t 10 m a and 70 KV and intraoral non-radiatizcd periapical dental films with a n exposure time of 0.5 second trimmed to fit the siLe of the mouth. The time staggered emergence of 24 deciduous and 32 permanent teeth in the cotton ear marmoset during the first year of life provides a large and informative spectrum of useful age indicators. There is sufficient consistency in the age and order of eruption of the dentition in this species to permit a fairly accurate assessment of the relative chronological age of immature 48 G. W. JOHNSTON, S. DREIZEN AND B. M. LEVY animals. The lack of a demonstrable sex difference and the near proximity in the eruption patterns of each quadrant permits the use of a single general standard for this purpose. LITERATURE CITED Bennejeant, C. 1936 Anomalies et Variations Dentaires chez les Primates. P. Vallier, Clermont-Ferrand (Tese). Chase, J. E., and R. W. Cooper 1969 Sangzcinus nigricollis - physical growth and dental eruption in a small population of captive-born individuals. Am. J. Phys. Anthrop., 30: 111-116. Garn, S. M., and A. B. Lewis 1963 Phylogenetic and intra-specific variations i n tooth sequence polymorphism In: Dental Anthropology. D. R. Brothwell, ed. The Macmillan Company, New York. Hampton, J. K., Jr., S. H. Hanipton and B. T. Landwehr 1966 Observations on a successful breeding colony of the marmoset, Oedipomfdas oedipus. Folia Primat., 4: 265-287. James, W. W. 1960 The Jaws and Teeth oE Primates. Pitman Medical Publishing Co. Ltd., London. Levy, B. M., and J. Artecona 1964 The marmoset as an experimental animal i n biological research: care and maintenance. Laboratory Animal Care, 14: 2 C ~ 2 7 . Serra, 0. D. 1952 A sequencia eruptiva dos dentes definitivos nos simios platyrrhina e sua interpretacao filogenetica. Anais da Faculdade de Farmacia e Odontologia da Universidade de Sao Paulo, 10: 215-296. Steliscka, W’. 1947 Uzebienie naczelmych (The dentition of primates). An. Universitatis MariaeCurie-Sklodowska, 8: 183-276.