DENTO-ALVEOLAR RESORPTION IN PERIODONTAL DISORDERS 



307 



Fig. 6. Drawings of two premolars to demonstrate the reactions after 3 

 (left) and 7 (right) nights' use of an activator. The masticatory stress has 

 mainly been increased in the direction of the arrows. Where the lamina dura 

 is drawn as a double broken line, apposition has occurred. In the areas where 

 the lamina dura is represented bv a solid line, aplasia was found. The zigzag 

 lines indicate resorption areas. 



resorption of the lamina dura could be seen in the pressure zones of 

 the pericementum ( Hiiupl and Psansky, 1938; Andresen et ah, 1957 ) . 



From these and other experiments it is known that circulatory 

 disturbances are the first reaction to an increase in mechanical func- 

 tional stress above the physiological limit. If the stress is not de- 

 creased below this limit in one way or another, the circulatory 

 disturbances are succeeded by atrophy, degeneration, mechanical 

 inflammation, and necrosis (Fig. 7). These alterations which occur 

 in the periodontium and in other organs are due to disturbances in 

 the liying conditions of the cells ( Hiiupl and Lang, 1927; Kronfeld, 

 1931; Coolidge, 1938; Tillotson and Coventry, 1950; Reichborn- 

 Kjennerud, 1956). 



That an exposure of the periodontal tissues to constant mechanical 

 stress above the physiological limit will also break down the alveolar 

 bone is seen in orthodontic treatment. In animal experiments where 

 an uncontrolled, often traumatic effect of the masticatory forces 

 is obtained bv cementing crowns which are too high on single teeth, 

 alveolar bone resorption also occurs (Gottlieb and Orban, 1931; 

 Wentz et al., 1958). In the same type of experiments in monkeys, 

 Glickman and Smulow ( 1962 ) could observe alveolar bone resorp- 



