TEETH, DEVELOPING 



335 



TEETH, DEVELOPING 



used with very large teeth or large 

 blocks of tissue containing bone and 

 teeth, objectionable precipitates may- 

 be formed in the depth of the block. 



Celloidin imbedding before decal- 

 cification helps preserve tissue relation- 

 ships (See Teeth, celloidin technique). 

 Arnim has perfected a technique of 

 double imbedding for rat jaws ana teeth 

 which, though tedious, yields beautiful 

 results. Enamel matrix is frequently 

 preserved. (Anat. Rec, 62, pp. 321- 

 330, 1935.) This method has been 

 modified by Burket for larger teeth 

 (McClung, p. 366). 



Tooth buds may be decalcified after 

 paraffin imbedding by the following 

 method given by Dr. L. R. Doling in a 

 personal communication. Carefully re- 

 move from the tooth bud all surround- 

 ing bone. Fix, dehydrate, clear and 

 imbed in paraffin in the usual way. 

 Shave away paraffin and soft tissue from 

 one surface of the specimen so that 

 enamel is exposed. Immerse block in 5 

 per cent aq. nitric acid until decalci- 

 fication is complete. Place in 5 per cent 

 aq. sodium sulphate for a few hours. 

 Wash over night in running water and 

 reimbed, handling the tissue as gently 

 as possible in order not to disturb rela- 

 tionship of hard and soft tissues. This 

 method permits demonstration of Golgi 

 apparatus and mitochondria in amelo- 

 blasts and odontoblasts in situ. It 

 works best with teeth of small animals 

 easily penetrated by fi.xative. The 

 paraffin protects the soft tissues but does 

 not interfere with action of acid on 

 enamel and dentin. (See also Teeth, 

 Developing.) 



Successful preparation of decalcified 

 tooth sections depends as much or more 

 on the care of the tissues before and 

 after decalcification than on the actual 

 process. Good fixation of the pulp 

 tissue is difficult but essential to pre- 

 vent shrinkage. Ten per cent formalin 

 in physiological salt solution may be 

 used for several days or weeks without 

 injury to the soft tissue and allow 

 thorough penetration. Better results 

 are obtained in a short time if the fixa- 

 tive can be perfused through the blood 

 vessels. In the preparation of human 

 or other large teeth, fixation artifacts 

 are minimized if the tooth is ground 

 longitudinally on a flat stone until the 

 pulp is just exposed. Two opposite 

 surfaces may be ground. Grinding 

 should be done on a sharp stone under 

 running water to prevent heating. 

 Cutting of holes through the dentin to 

 the pulp or the amputation of the tips 

 of teeth is often resorted to in order to 

 get better penetration but these meth- 



ods are apt to disturb the position of 

 the pulp and should be avoided if pos- 

 sible. After decalcification the teeth 

 should be carefully handled and the de- 

 hydration process should be slow to 

 prevent separation of tissues of different 

 densities. The substitution of n-butyl 

 alcohol for ethyl alcohol and xylol in 

 dehydration and clearing processes has 

 proven advantageous (Morse, loc. cit.). 

 By this method dehydration may be 

 prolonged with less hardening. 



Over decalcification should be care- 

 fully avoided because it will partially 

 destroy the dentin matrix, cause sepa- 

 ration of tissues of differing consistency 

 and disturb staining reactions. Testing 

 for completion of decalcification by prob- 

 ing with needles or bending and saueez- 

 ing in the fingers should be avoided at 

 all costs if tissue relationships are de- 

 sired. The progress of decalcification 

 can be followed radiographically but the 

 end point can not be accurately deter- 

 mined. The best method of testing is 

 that described by Arnim (loc. cit.). 

 Five cc. of the acid used in decalcifica- 

 tion is placed in a clean test tube and 

 neutralized with ammonium hydroxide, 

 and .1 cc. of a saturated solution of 

 ammonium oxalate added. If no pre- 

 cipitate forms additional .1 cc. portions 

 of oxalate are added at 15 minute inter- 

 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 paraflfin block, cut 

 surface down, on acid if the dentin is 

 exposed. 

 Teeth, Developing. L 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 CultiTation 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 

 etal. (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 



