Authors: Kakehashi S, Stanley HR, Fitzgerald RJ.
Title: The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats.
Journal: Oral Surg Oral Med Oral Pathol
Date: Sep 1965
Citation: 20(3):340-49
Category: Endodontic Microbiology
Evidence-based Ranking: 5
Purpose/Objectives: To observe the pathologic changes resulting from untreated experimental pulp exposures in germ-free rats as compared with conventional rats with a normally complex microflora. Materials & Methods: Thirty-six 7-week-old Fisher rats were divided into 21 germ-free animals and 15 conventional control animals. A ½ -round carbide bur was used to drill a hole through the occlusal enamel and dentin of the maxillary right first molar to expose the pulp. No attempt was made to restore or seal the exposure which allowed food, debris and microorganisms (in the conventional rats) to become impacted into the pulpal tissues. The animals were then sacrificed at intervals from 1 to 42 days post-op. The tissues were serially cut in a mesiodistal plane, stained and studied microscopically. Results: Conventional (control) rats: All occlusal cavities were packed with food and debris. Specimens taken on the eighth day showed vital pulp tissue remaining in the apical half of the roots only. Remaining coronal portions of the pulp were necrotic and purulent. Colonies of microorganisms were usually seen. All specimens taken after eight days showed complete pulpal necrosis with chronic inflammatory tissue and abscess formation in the apical areas. Abscesses were also seen at accessory foramina. There was no evidence of pulpal repair in any of the cases. Germ-free rats: No completely devitalized pulp was observed in any of the test animals. Pulpal inflammation resulting from the exposure was minimal in every specimen. Not a single apical abscess was found. Dentinal bridging was evident at 14 days. Older specimens showed matrix formation completely bridging or sealing the exposure. In every animal, the pulp tissue remained vital beneath the newly formed reparative dentinal bridge. Periodontal responses in cases of perforation were similar in both groups – periodontal lesions and pockets were seen. In the germ-free rats, cases of perforation that permitted embedding of food and debris into the periodontal tissues resulted in root resorption while the pulpal tissues remained vital. As the root resorbed, new bone was deposited to compensate for the reduction in root size. Author’s Conclusions: The presence or absence of a microbial flora is the major determinant in the healing of exposed rodent pulps.

Validity of Conclusions: Conclusions are valid.

Reviewer’s Comments: Good basic study. Of great importance in explaining etiology of pulp disease. Small sample size, not blinded, no mention of specific criteria used for comparing the two groups.