TEETH, DECALCIFICATION 



240 



TEETH, INNERVATION 



vals until .4 cc. have been added. If a 

 precipitate is formed the tissue is placed 

 in fresh acid and retested in 24 hours. 

 Formation of no precipitate with .4 cc. 

 oxalate solution after 24 hours in fresh 

 acid is indicative of complete decalcifica- 

 tion. 



When tissues are found to be not suffi- 

 ciently decalcified after imbedding the 

 process can be completed by immersing 

 the celloidin block in acid 70 per cent 

 alcohol or floating the paraffin block, cut 

 surface down, on acid if the dentin is 

 exposed. 

 Teeth, Developing. 1. Tooth germs. (Glas- 

 stone S., J. Anat., 1935-36, 70, 260- 

 266) has described a method for the 

 excision of tooth germs from 18-21 day 

 rat embryos and their Cultivation in 

 fowl plasma and embryo extract. The 

 technique of Transplantation of tooth 

 germs of young pups into the abdominal 

 wall has been reported by C. H. Huggins 

 et al. (J. Med., 1934, 60, 199). Bevelan- 

 der, G., Anat. Rec, 1941, 31, 79-97 ob- 

 tained fine preparations of Korff's fibers 

 in pig's tooth beginning with 110 mm. 

 stage by fixation in Formalin-Zenker 

 and silver impregnation by Foot's 

 Method. 



2. Young teeth. Beams, H. W. and 

 King, R. L., Anat. Rec, 1933, 57, 29-40 

 fixed the developing molar teeth of white 

 rats 1-5 days old in a variety of fluids. 

 They employed the Nassonov technique 

 for the Golgi apparatus and Regaud's 

 for mitochondria without any special 

 provision for decalcification. In some 

 cases Boling's Decalcification (Teeth, 

 Decalcification) method after paraffin 

 imbedding may prove useful. Dr. Bol- 

 ing states in a personal communication 

 that a modification of Bouin's picro- 

 formol fixative may be used for fixing 

 and decalcifying very young tooth buds 

 or teeth and jaws of rats. A mixture 

 of 75 parts saturated aqueous solution 

 of picric acid, 25 parts formalin and 10 

 to 20 parts glacial acetic acid will de- 

 calcify a mature rat jaw and teeth in 

 less than a week. Ordinary Bouin's 

 picro-formol is sufficiently acid to de- 

 calcify very young tooth buds in a few 

 days. After decalcification the tissues 

 are handled in the same manner as soft 

 tissues after Bouin fixation except that 

 a longer period is allowed for removal of 

 picric acid. This procedure allows 

 better than average staining of decal- 

 cified tissues. Nuclear structure is 

 especially well preserved and little 

 separation of hard and soft tissues is 

 found. The method of microincinera- 

 tion has been adjusted to developing 

 teeth by Hampp, E. G., Anat. Rec, 

 1940, 77, 273-286. 



Teeth, Innervation. Methods described 

 under Nerve Endings require consider- 

 able adaptation before they can be em- 

 ployed for the teeth. For obvious 

 reasons methylene blue is particularly 

 difficult to use. From a great many 

 techniques 2 are selected. 



1. Van der Sprenkel, H. B., J. 

 Anat., 1935-36, 70, 233-241. Grind den- 

 tinal wall of normal human canine tooth 

 down to a thickness of 300-500 microns 

 leaving the cavity closed and the pulp 

 untouched. Saw remainder of tooth 

 into rings (not decalcified). From them 

 cut on freezing microtome cross sections 

 about 40 n thick and impregnate accord- 

 ing to the Gros method. Van der Spren- 

 kel does not give a reference to this 

 method. Perhaps the Gros method, as 



fiven by Lee (p. 494) will serve. Treat 

 rozen sections with pyridine. Wash 

 with aq. dest. to remove odor of pyri- 

 dine. 20% aq. silver nitrate, in dark, 1 

 hr. Transfer without washing to 20% 

 formalin neutralized with magnesium 

 carbonate. Change twice until no more 

 white ppt. is formed. Reduce under 

 microscope in following solution : Add 

 ammonia to 15 cc. 20% silver nitrate 

 until ppt. formed just disappears. 

 Then add 1 drop ammonia per each cc. 

 silver nitrate solution. After this 20% 

 aq. ammonia 1 min. or more. 1% acetic 

 acid, same. Tone in 0.2% aq. gold 

 chloride treat with sodium hyposul- 

 phite, wash, dehydrate, clear and 

 mount. Counterstain with Van Gieson 

 or toluidin blue, if desired before dehy- 

 dration. See Van der Sprenkel's illus- 

 trations. 



2. Christensen, K., J. Dent. Res., 

 1940, 19, 227-242 was concerned pri- 

 marily with determination of the source 

 of the large proportion of unmyelinated 

 and small myelinated fibers in the pulp. 

 His technique is a combination of dis- 

 section and the making of histological 

 preparations of cats. First inject ar- 

 teries with a yellow corn starch mass 

 (composition not specified) and harden 

 tissues in formalin. Expose cervical 

 sympathetic, common carotid and its 

 chief branches, mandibular canal and 

 floor of orbit. Wash dissected areas 

 with aq. dest., and brown nerves with 

 dilute aq. silver nitrate so that they can 

 be easily followed along the walls of the 

 yellow colored vessels. To trace their 

 final path to lower teeth serial sections 

 of inferior alveolar nerve and artery are 

 required and to upper teeth similar ones 

 of internal maxillary plexus and superior 

 alveolar nerves. Wrap canine teeth in 

 cotton, carefully crack with vise and 

 remove pulps. Slightly stretch each 

 pulp along surface of short glass tube 



