Evaluation of calcium phosphate as a root canal sealer-filler material

Evaluation of calcium phosphate as a root canal sealer-filler material

0099-2399/87/1308-0384/$02.00/0 JOURNAl. OF ENDOOONTICS Copyright9 1987 by The American Association of Endodontists Printed in U.S.A. VOL. 13, NO. 8...

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0099-2399/87/1308-0384/$02.00/0 JOURNAl. OF ENDOOONTICS Copyright9 1987 by The American Association of Endodontists

Printed in U.S.A.

VOL. 13, NO. 8, AUGUST 1987

Evaluation of Calcium Phosphate as a Root Canal Sealer-Filler Material Aida A. Chohayeb, DDS, MSD, FACD, Larry C. Chow, PhD, and Peter J. Tsaknis, DDS, MS, MA

This study was conducted to evaluate calcium phosphate cement as a root canal sealer-filler material. Fifteen teeth of one adult beagle dog were instrumented to a # 3 0 Hedstrom file and filled with calcium phosphate cement mixed into a creamy paste using glycerin and phosphoric acid in a ratio of 1:1 in group A and a ratio of 3:1 in group B. Four teeth were used as controls and were filled with guttapercha using the lateral condensation technique. Histological evaluation of the periradicular tissues of both experimental and control teeth showed variable degrees of inflammatory response after 62 days. Also, calcium phosphate cement showed a uniform and tight adaptability to the dentinal surfaces of the pulp chamber and root canal walls similar to that of gutta-percha cones.

phosphate cement (CPC) appears to possess these qualities (5-7) as described below. Brown and Chow (5) reported that certain combinations of finely powdered calcium phosphates, when mixed with water, harden into cements which have similar chemical composition and crystal structures to those of tooth and bone mineral. For example, the combination of tetracalcium phosphate and anhydrous dicalcium phosphate react to form hydroxyapatite which is biocompatible (6) and comparable in radiodensity to hard tooth structures. Also, Krell and Wefel (8) showed that CPC when used as a sealer adheres well to the root canal. CPC has the potential of being a better root canal sealer-filler because it has the following advantages over the conventionally used sealers: (a) Its high biocompatibility suggests that inadvertent extrusion beyond the apical foramen should be well tolerated by the periapical tissues. (b) CPC consists of only calcium phosphates, water, and glycerin; thus it would be tolerated by patients who might be allergic to eugenol (7). (c) It appears to be devoid of dimensional changes during setting and provides superior adaptation to the canal surface (9), thus allowing a better hermetic seal of the apical foramen and accessory canals located in the apical third of the root. (d) The setting time of CPC can be controlled easily to provide sufficient working time. Finally, our preliminary in vitro study showed that CPC is injectable into the root canal which would significantly reduce the amount of operating time.

At the present time gutta-percha is the most commonly used root canal filling material (1). Lateral condensation of gutta-percha cones in the root canal is recommended in order to obtain a hermetic seal of the apical foramen (1). Shilder (2) introduced the vertical condensation technique using segments of gutta-percha cones and condensing them vertically into the root canal. McSpadden (3) introduced the compactor, a calibrated stainless steel instrument which, when used with a slow-speed handpiece, warms and then compacts the gutta-percha into the root canal. Yee and Schoeffel (4) introduced a thermoplastic injection molding technique using a special injection syringe which softens the gutta-percha cone and then injects it into the root canal. The injection has to be completed within 10 s to prevent the gutta-percha from hardening and becoming nonamenable for condensation into the canal. Although the currently used techniques are generally satisfactory, the practice of endodontics could benefit significantly from the development of a root canal filling material which is (a) totally biocompatible so that inadvertent overextrusion of the filler would be harmless; (b) highly adaptable so tltat it will adhere to the root canal surface; (c) dimensionally stable and mechanically strong; and (d) more easily introduced into the root canal. Calcium

OBJECTIVE

The objective of this pilot study was to evaluate CPC as a root canal sealer-filler simulating clinical conditions in dog's teeth. CPC was tested in reference to its adaptability to the root canal and pulp chamber. The response of the periradicular tissues to CPC was also histologically evaluated. MATERIALS AND METHODS

One male adult beagle was anesthetized intravenously with sodium pentobarbital. Periapical radio384

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graphs of all teeth determined the tentative length of the roots of the teeth. Incisors and premolars were isolated using 2 x 2-inch gauze cotton rolls. Access cavities were prepared using a #56 carbide bur driven by a high-speed air turbine with water coolant. The pulp tissue was extirpated from each root canal using a sterile broach. The canal length was established using the standard reamer-radiograph method. The working length was 0.5 to 1.0 mm shorter than the radiographic apex. The canals were instrumented with frequent irrigation of 2.6% sodium hypochlorite to a #30 Hedstrom file and were then dried with sterile paper points. By using finger pluggers, the teeth in the experimental group were filled with CPC mixed to a creamy paste with glycerin and 20 mM liquid phosphoric acid in the weight ratio 1:1 or 3:1. The control teeth were filled with gutta-percha cones and Grossman root canal sealer (according to the standard filling techniques) using the lateral condensation technique. The teeth were divided into control and experimental groups of 4 and 15 teeth, respectively. The experimental teeth were further subdivided into two groups; group A and group B. Group A teeth were filled with a mixture of CPC in a glycerin to phosphoric acid ratio of 1:1. Group B teeth were filled with a mixture of CPC in a glycerin to phosphoric acid ratio of 3:1. The access cavities were then restored using a zinc oxide-eugenol temporary filling material. After 62 days, the animal was killed using an overdose of intravenous sodium pentobarbital. The maxilla and mandible were removed posthumously. The teeth and 1 cm of bone beyond the apex of the roots were block dissected using an oscillating surgical saw with water spray and placed into neutral 10% formalin. The crowns and coronal two thirds of the roots were separated from the block and ground to a thickness of approximately 10 #m and mounted on clear glass slides and examined with a light microscope for adaptability of CPC to the canal walls. The apical one third of the teeth and approximately 1 cm of the surrounding tissues were decalcified using 5% formic acid for 2 wk, step-sectioned at a thickness of 6 mm, stained with hematoxylin and eosin, and examined under light microscopy. The histological criteria for evaluating the specimens was based on the presence or absence of (a) a periapical inflammation (acute, chronic, or mixed); (b) foreign body reaction (giant cells); (c) resorption of the root or the surrounding bone, (d) osseous proliferation; (e) mineralization; (f) edema; and (g) necrosis. The type of inflammation and degrees of response were based upon the number and extent of polymorphonuclear leukocytes, eosinophils, plasma cells, multinucleated giant cells, and lymphocytes present in the specimen examined. The degree of inflammation was graded subjectively as none, minimal, moderate, or severe.

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RESULTS Histological Evaluation of Periapical Tissue EXPERIMENTAL TEETH

Five specimens (63%) in group A (CPC with glycerin to phosphoric acid ratio of 1:1) showed no evidence of any inflammatory response to the CPC. Two specimens demonstrated several small foci of chronic inflammatory infiltrate consisting primarily of lymphocytes (Fig. 1). One additional specimen exhibited a chronic inflammatory response composed of lymphocytes and plasma cells (Fig. 2). Four specimens (57%) in group B (glycerin to phosphoric acid ratio 3:1) demonstrated chronic inflammation. One response was minimal, exhibiting a lymphocyte-predominating round cell infiltrate. Another specimen revealed a moderate response with similar types of cells present. However, in the moderate specimen, the inflammatory cells were present in numerically greater numbers. The two specimens that were char-

FIG 1. Photomicrograph of pedapical region of canal obturated with experimental CPC (group A). A small focus of lymphocytes located at the periapex between trabecular bone (hematoxylin-eosin; original magnification x200).

FIG 2. Photomicrograph showing a mixed round cell infiltrate consisting of lymphocyte and plasma cells noted within the periapical tissues (group A) (hematoxylin-eosin; original magnification x200).

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acterized as severe, exhibited abundant lymphocytes and plasma cells (Fig. 3). CONTROL TEETH Three of the four control teeth using gutta-percha and sealer also demonstrated a mild degree of chronic inflammation. The inflammatory response was in the form of several small foci of a chronic round cell infiltrate consisting primarily of plasma cells and lymphocytes.

Adaptability of the Filling Material to Root Canals and Pulp Chamber 1. CPC: The ground sections demonstrated a uniform and tighter adaptation to the dentinal surfaces of both the chamber and root canal walls (Fig. 4). CPC also appeared to infiltrate into the dentinal tubules. 2. Gutta-percha: Adhesion and adaptation to the dentinal walls of the root canals was uniformly tight and equal to that noted with the CPC specimens (Fig. 5).

FIG 3. Intense periapical accumulation of lymphocytes and plasma cells (group B). Necrosis of surrounding tissues was not evident (hematoxylin-eosin; original magnification x320).

FIG 5. Photomicrograph of a ground section demonstrating complete and uniform adaptability of the CPC within the pulpal chamber and root canal walls (original magnification x25, ground section).

DISCUSSION The search for the ideal canal filling material as determined by Grossman's criteria is a continuous one. The results of the present study indicated that CPC can be used as a single/filler material. This combination saves the clinician time by eliminating the gutta-percha condensation step. As previously reported by Gruninger et al. (6), CPC was proven to be biocompatible in laboratory animals. This characteristic of tissue acceptance is beneficial in the event of overextension of the root canal filling material. By contrast, excessive overextension of guttapercha/sealer necessitates either nonsurgical or surgical removal of the excess at the periapex. Recent emphasis has been placed on the advantage of a dentin plug at the apical 1- to 2-mm portion of the root canal (10, 11). CPC, because of its biochemical similarity to dentin, could act as its own apical barrier.

CONCLUSIONS Microscopic evaluation of CPC-filled teeth revealed a spectrum of localized inflammatory response of the periradicular tissues very similar in quality and intensity to that of the control. It could not be determined from the results of this study whether the inflammatory response in some specimens was related to the CPC or the glycerin-phosphoric acid liquid component or both. The results of the ground sections showed that CPC had a uniform and tight adaptability to the dentinal surfaces of the pulp chamber and root canal walls.

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FiG 4. Photomicrograph of a ground section showing extension of the CPC filling materials into the dentinal tubules (arrows) (original magnification x320, ground section).

Dr. Chohayeb is professor, Department of Endodontics, Howard University, College of Dentistry, Washington, DC. Dr. Chow is affiliated with the Health Foundation, Paffenberger Research Center at the National Bureau of Standards, Gaithersburg, MD. Dr. Tsaknis is professor, Department of Histopathology, Howard University, College of Dentistry.

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Evaluation of Calcium Phosphate References

1. Ingle JI. Root canal obturation. J Am Dent Assoc 1956;53:47. 2. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967:723. 3. McSpadden JT. Automated therrnatic gutta-percha condensation. Presentation at the 121st Annual Session of the American Dental Association, October 1980, New Orleans. 4. Yee FS, Schoeffel GJ. A new method of gutta-percha obturation of root canal systems. Presentation at the Greater New York Dental Meeting, November 1983. 5. Brown WE, Chow LC. A new calcium phosphate setting cement. J Dent Res 1983;62:672.

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6. Gruninger SE, Siew C, Chow LC, O'Young A, Tsao NK, Brown WE. Evaluation of the biocompatibility of a new calcium phosphate setting cement. J Dent Res 1984;63:200. 7. Miller RA, Bussell NE, Ricketts SK, Jordi H. Analysis and purification of eugenol. J Dent Res 1979;58:1394-1400. 8. Krell KF, Wefel JS. A calcium phosphate cement root canal sealer-Scanning electron microscopic analysis. J Endodon 1984;10:571-6. 9. Grossman Ll. Endodontic practice. 8th ed. Philadelphia: Lea & Febiger, 1974:284. 10. Brady JE, Himel VT, Weiz JC. Periapical response to an apical plug of dentin fillings intentionally placed after root canal overinstrurnentation. J Endodon 1985;11:323-35. 11. Kuttler Y. A precision and biologic root canal filling technic. J Am Dent Assoc 1958;56:38-50.