PubMed1976
The in vivo effect of formaldehyde on pulp tissue in short-term studies cannot be established by using routine histologic techniques because the tissue is exposed to a fixative in vivo as well as during the histologic preparation. The pulps of permanent premolars were amputated and zinc oxide with 4% formaldehyde or formocresol was used as wound dressing. The observation periods varied from 1 to 16 d. After extraction the teeth were freeze-sectioned, freeze-dried and then incubated for histochemical demonstration of some oxidative and hydrolytic enzymes. A demarcated border between apically stained and cervically nonstained pulp tissue was found in sections incubated for oxidative enzymes. When formocresol, which has a high concentration of formaldehyde, was used, the border was situated closer to the apex. This was also the case when the observation period was increased. The incubation for lactate dehydrogenase gave a high staining intensity. Thus the use of frozen sections in combination with the histochemical method for the demonstration of lactate dehydrogenase appears to be suitable for the study of the penetration of formaldehyde in pulp tissue in short-term studies.