Research for Endo

1. The Effects of Surgical Exposures
in Germ-Free and Conventional
Laboratory Rats
Kakehashi, S., Stanley, H.R., Fitzgerald,
R.J. (1965)

2. ● Following a clinical exposure of dental pulp,
maintaining vitality by various conservative
measures (i.e. pulp-capping), encourages the
development of dentinal bridging. However, the
clinical results are unpredictable.
● Successful management of pulpal exposures has
been attributed to an extraordinary degree of pulpal
tissue resistance and subsequent dentinal bridge
formation.
● Therefore, the microorganisms present in acute and
chronically inflamed pulpal exposures have been
attributed as the major cause of failures in an
attempt to dentinal bridge.
Introduction
2

3. ● Dentinal Bridging: Thin layer of secondary dentin that forms over
an exposed pulp, creating a protective pulpal barrier. Formation
stimulated by the presence of calcium hydroxide.
● Reasons for dentinal bridging failure include:
○ Patient’s age
○ Degree of surgical trauma
○ Excessive sealing pressures
○ Improper choice of medication
○ Bacterial infection
○ Low threshold of host resistance
Matrix Formation & Dentinal Bridging

4. ● The study was undertaken to observe the pathologic changes
resulting from untreated pulp exposures in Germ-free and
conventional rats, with a normally complex microflora.
Aim of Study

5. ● 36, 7-week old inbred Fisher rats, divided equally by sex (18 male,
18 female) used in the experiment.
○ 21 germ-free rats (experimental)
○ 15 conventional rats (control)
● Rats maintained in Reynier germ-free system unit, both fed ad
libitum, identical diets of pellet-form autoclaved Purina 5010
laboratory chow & distilled water.
Materials & Methods

6. ● Animals anesthetized with intraperitoneal injection of pentobarbital
sodium, carbide round bur (size ½) used to create access through the
occlusal of maxillary right first molars.
● No attempt was made to restore or seal the exposures.
● Animals were killed at intervals ranging from 1 to 42 days.
● A jaw block of maxillary right quadrant was cut, removed, and
placed in formalin.
● Tissues were cut in the mesiodistal plane (thickness = 6µm), stained
with hematoxylin, eosin, Masson’s trichrome, Giemsa, and Brown
and Brenn stains.
Materials & Methods

7. Conventional (Control) Animals:
● All access cavities were packed with food and
debris.
● Specimens taken on the 8th day demonstrated vital
pulp tissue remaining only in the apical half;
remaining coronal portions of the pulp were
necrotic and purulent.
● All specimens obtained after the 8th day
demonstrated complete pulpal necrosis with
chronic inflammatory tissue and abscess formation
at periapical and accessory foramina.
● None of the pulpal tissues demonstrated evidence
of repair (matrix formation nor dentinal bridging).
Results

8. Germ-Free (Experimental) Animals:
● Started with 21 germ-free rats, 18 survived the procedure.
● Minimal pulpal inflammation and no apical abscesses were
noted.
● No completely devitalized pulp in any specimen.
● Matrix formation began immediately with dentinal bridging
evident at 14 days, partially or completely covering the
exposure.
● Pulp tissue under the dentinal bridge remained vital in all 18
rats.
● As postoperative time intervals increased, there was a
gradual constrictive obliteration of the pulp canal by new
matrix formation.
● In cases of pulpal exposure which resulted in root severance,
the pulp of the severed root maintained its vitality.
Results

9. ● Major significance in the role of microorganisms being present or not
in the pulp chamber and subsequently acting upon the repair of
exposed and damaged pulp tissues.
● Key point: present techniques for clinical management of exposed
pulps should include maximal measures for the eradication of all
bacteria from the site.
● Success of treatment attributed to an abundant pulpal blood supply
due to incomplete root formation; only applicable to adolescent
dentition.
Discussion

10. Goldberg M, Six N, Chaussain C, DenBesten P, Veis A, Poliard A. Dentin Extracellular Matrix
Molecules Implanted into Exposed Pulps Generate Reparative Dentin: a Novel Strategy in
Regenerative Dentistry. Journal of Dental Research. 2009;88(5):396-399.
KAKEHASHI, S., STANLEY, H. R., & FITZGERALD, R. J. (1965). THE EFFECTS OF
SURGICAL EXPOSURES OF DENTAL PULPS IN GERM-FREE AND CONVENTIONAL
LABORATORY RATS. Oral surgery, oral medicine, and oral pathology, 20, 340–349.
https://doi.org/10.1016/0030-4220(65)90166-0
Sources

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