Efficient Sectioning of Incisors for Estimating Ages of Mule Deer

Cementum annuli in transverse, 95-micron, demineralized, Harris hematoxylin-stained sections of first-incisor roots provide a largely objective means of reliably estimating ages. From 20 to 25 teeth per hour can be prepared for age estimation by embedding 5 at a time in blocks of plastic and sawing 3 sections of each with a thin-sectioning machine. Ages estimated from counts of cementum annuli agreed with the known ages of 16 mule deer (Odocoileus hemionus). Laws (1952), studying the canine teeth of the southern elephant seal (Mirounga leonina), first showed that internal dentinal and cemental annulations were definitely correlated with age. Sergeant and Pimlott (1959) found cementum annulations in longitudinal, ground sections (method of Fisher and Mackenzie 1954) of incisors of moose (Alces alces). Mitchell (1963) bisected red deer (Cervus elaphus) molars, polished the cut surface, and counted the exposed cementum annuli. Low and Cowan (1963), using a standard microtome blade, cut 10micron sagittal sections of mule deer incisors, stained them with Ehrlich's hematoxylin, and estimated deer ages from counts of cementum annuli; estimated ages agreed completely with all 23 known ages. Mundy and Fuller (1964) cut teeth into 150-micron sections with a Niclas brand bone saw. Armstrong (1965), using the teeth of Bovidae, experimented further with sawing techniques, using the Niclas saw. Many other workers have applied published techniques to other species but few new procedures have been described. The technique of Low and Cowan (1963) is reliable and accurate, but also slow. Our objective was to find a faster and simpler 1 Contribution from Colorado Federal Aid Project W-105-R and National Institute of Health Grants 5-RO1-DE-02308-03 and 1-K3-DE-1857701, and based, in part, on J. A. Erickson's M.S. thesis, Colorado State University, Fort Collins. 384 technique for mule deer, as reliable and accurate as that of Low and Cowan (1963), which would make large-sample age estimations practical. We thank R. W. Davis and T. Hakonson, Colorado State University, and W. T. McK an, A. E. Anderson and D. E. Medin, Colorado Division of Game, Fish, and Parks for supplying teeth from mule deer of known age. MATERIALS AND METHODS Incisors from mule deer of unknown age from north-central Colorado were used in the development of the technique. Six wild, and 10 pen-reared mule deer of known age were used to verify the reliability of the technique. Five of the wild deer were from Little Hills Research Station, Meeker, Colorado, and one was from Cache la Poudre River drainage, north-central Colorado. All pen-reared animals were from Larimer County, Colorado and raised at Colorado State University. In the experimental phase of this study, both a rotary microtome and a thin-sectioning saw were used. The saw proved much faster and simpler than the microtome, and was used throughout the study. Sources and cost of equipment used in the method are listed in Table 1. The saw destroys a 305-micron section of tooth between each section. Thus, about six This content downloaded from 157.55.39.59 on Sat, 15 Oct 2016 04:14:54 UTC All use subject to http://about.jstor.org/terms AGING MULE DEER BY INCISOR SECTIONING Erickson and Seliger 385 longitudinal sections could be sawed from each tooth. However, only one or two sections were usable because not all were from an area of well-defined annuli. Because longitudinal sectioning was not entirely satisfactory, transverse sectioning was tried. Twenty or more usable 95-micron transverse sections can be sawed from an incisor root, and a transverse section always includes the area of most distinct cementum annuli at that level on the longitudinal axis. Longitudinal sagittal sections often miss the area of most distinct cementum annuli. Sagittal sections pass through most first incisors perpendicular to the incisal edge. But the best longitudinal sections of most first incisors pass through the lingual-lateral quarter of the root, about 10? to 45? from the sagittal plane. Incisors from 116 freshly killed mule deer were removed with straight-beaked, upper anterior tooth-extracting forceps, labeled, and placed in 10-percent formalin. Slitting the gingiva and periodontal membrane in several places around the tooth prior to extraction eliminated occasional root fracture. After 3 days in the formalin solution, the incisors were removed and dried. Another 110 incisors were taken from mandibles which had dried at least 1 year. Dry teeth were soaked overnight in uncatalyzed resin, drained, blotted nearly free of the resin, and embedded in catalyzed resin, 6-8 mm deep, in the mold. Five incisors were placed in one layer on the bottom of a 22x 30-mm Peel-a-way disposable plastic mold. Removal of the crowns with pliers made positioning the teeth in the mold easier. A permanent label was embedded in each block and the resin hardened overnight. Final hardening in an oven at 60 C took from 34 hours. After cooling slowly, the blocks were ready to be sawed. Thicker blocks containing two rows of five teeth were not Table 1. Names and addresses of the sources, and the prices, of some equipment and supplies used in this study. ITEM PRICE IN U.S.A. SOURCE Gillings-Bronwill Thin-Sectioning Machine Model No. 60 No. 60-A 4 Diamond Wheel Microtome Block Vise Object Clamp 286-11-A Tooth-Extracting Forceps No. 1 Standard Casting Resin Bioplastic Peel-A-Way Molds Plastic, Disposable Tissue Capsules Plastic, Disposable Zeiss Standard RA(GFL) Microscope with Fluorescence Illuminator lla Neofluar Lens 16/0.40 (46 05 20) $1,595.00 Bronwill Scientific Inc., P. 0. Box 277, Rochester, New York