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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 3  »  The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments
The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments
Introduction - Materials and methods.



D. Tziafas, O. Pantelidou, A. Alvanou, G. Belibasakis  & S. Papadimitriou
Departments of  Endodontology, School of Dentistry,  Histology and Embryology, Faculty of Medicine,
Clinical Sciences/Surgery Clinic, School of Veterinary Sciences, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Introduction.
Direct pulp capping/pulpotomy is a well established method of treatment, in which the exposed dental pulp is covered with a suitable material that protects the pulp from additional injury and permits healing and repair (American Association of Endodontists 1981). Pulp capping is mainly indicated for reversible pulp tissue injury after physical or mechanical trauma on developing or mature teeth. Pulpotomy is also indicated for pulp exposures in carious developing teeth. The removal of the injurious challenge, the control of infection and the cytotoxic and biological properties of the capping material are critical factors influencing the treatment prognosis (Seltzer & Bender 1985). It is widely accepted that the ultimate goal of the application of a capping material is to induce the dentinogenic potential of pulpal cells (Schröder 1985, Stanley 1989, Mjör et al. 1991). The dentinogenic potential can be induced directly as a specific biological effect of the capping material on pulpal cells, or indirectly as a part of the stereotypic wound healing mechanism in the traumatized pulp (Baume 1980, Lesot et al. 1994).
Calcium hydroxide-based materials have found widespread use in traditional vital pulp therapy over a number of decades (Nyborg 1955, Tronstad 1974). The antibacterial effects of calcium hydroxide on infected pulp tissue are of considerable importance (Cox et al. 1982). Clinical and experimental observations in animal and human teeth have repeatedly demonstrated that reparative dentine formation is physiologically induced after pulp capping with calcium hydroxide (Nyborg 1955, Schröder & Granath 1971, Schröder & Sundström 1974, Fitzgerald 1979, Heys et al. 1990). The beneficial effect of Ca(OH) 2 -based materials is mainly attributed to the initial low-grade irritation of the traumatized pulp tissue, due to release of hydroxyl ions (Schröder 1985, Cvek et al. 1987). Calcium ions released from these materials and the subsequently formed anorganic precipitations (Holland et al. 1982, Hanks et al. 1983, Tziafas & Economides 1999) have recently been associated with the mechanism controlling cytological and functional changes in the interacting pulpal cells (Seux et al. 1991, Tziafas et al. 1995). The molecular interactions between pulpal extracellular matrix molecules and growth factors and their role as critical morphogenetic influences for initiation of reparative dentinogenesis after pulp capping with calcium hydroxide have been studied also (Lesot et al. 1993, Lesot et al. 1994, Yoshiba et al. 1996, Tziafas et al. 2000).
Pulp capping with calcium hydroxide remains an unpredictable method of treatment for mature teeth. A number of new agents have been tested during the last two decades as potential materials of choice (e.g. calcium phosphate ceramics, collagens, biologically active matrices and molecules, mineral trioxide aggregate (MTA). MTA has recently been introduced to clinical dentistry (Torabinejad & Chivian 1999). By culturing human osteosarcoma cells (Mitchell et al. 1999), or osteoblasts (Koh et al. 1997, Koh et al. 1998) in the presence of MTA, good cell growth was found. MTA further offered a biologically active substrate for cell attachment, whilst increased levels of alkaline phosphatase, osteocalcin, and interleukin-6 and -8 were measured. In vitro studies have demonstrated that the antibacterial effects of MTA are comparable to those of Ca(OH) 2 but it is more effective in preventing bacterial microleakage (Torabinejad et al. 1995). Pitt Ford et al. (1996) have documented that MTA placed in mechanically exposed pulps of monkeys stimulated pulp healing with minimal inflammatory reactions and dentinal bridge formation. The early pulpal cell response to MTA and the mechanism by which extracellular matrix is deposited after its application at pulp capping situations remains to be determined. The aim of the present study was to evaluate the early dentinogenic activity of MTA on mature dog teeth.

Materials and methods.
Three healthy dogs 12–18 months of age were used. All experimental procedures were carried out in accordance with European Communities Directive (86/609/EEC). The animals were anaesthetized with pentothal and intubated with a cuffed endotracheal tube at the beginning of the experimental procedures. Intact teeth (first molars, canines and third incisors from both jaws) with healthy periodontium were used. The teeth were isolated with cotton rolls, polished and washed with 0.5% chlorhexidine.
Buccal class V cavities were prepared by means of a size 31 inverted cone carbide bur in an air turbine with sterile saline spray. The pulps were exposed with a size 00 round bur in an air turbine, producing a wound the size of the cutting edge of the bur. The cavities were washed with sterile saline and dried with sterile cotton pellets. Light pressure with cotton pellets was applied to control haemorrhage.
The exposed pulps were capped with ProRoot MTA (Dentsply), which was mixed with sterile water to provide a grainy, sandy mixture. The material was placed at the exposure site and light pressure was applied with a wet cotton pellet according to the manufacturer’s instructions, resulting in cramming of material into the pulp space. The cavities were immediately restored with amalgam. Light pressure was applied to the amalgam during condensation. The teeth were treated sequentially so that three observation periods (1, 2 and 3 weeks) distributed amongst the three dogs were available. The animals were killed by an overdose of pentothal, the jaws were immediately dissected and the teeth were fixed and processed for light and electron microscopy analyses.
Twenty-one teeth distributed equally in the three observation periods were fixed in 10% buffered formalin (pH 7.2) and processed for light microscopic analysis. The teeth were demineralized for 40–50 days in 5% trichloroacetic acid and embedded in paraffin. Serial sections 6 m thick were cut labio-lingually through the exposure site and stained with Mayer’s haematoxylin-eosin and Gomori’s trichrome. The amalgam (with a part of the capping material) was gently removed before sectioning.
Six teeth, distributed equally in the 1- and 2-week observation periods, were processed for Transmission Electron Microscopic (TEM) analysis. Teeth were extracted and cut labio-lingually immediately after jaw’s dissection and fixed for 1 h in 3% glutaraldeyde buffered with 0.1 mol L –1 cacodylate (pH 7.3). The pulp tissue with the capping material was removed and small specimens of the capping area were fixed in the same fixative for 2 h. After rinsing in 0.1 mol L –1 cacodylate buffer, the samples were postfixed in 1% osmium-tetroxide in the same buffer and embedded in Epon 812. Semi-thin sections were stained with toluidine blue and ultrathin sections were stained with uranyl acetate and lead citrate.
Six teeth, distributed equally in the three observation periods, were processed for scanning electron microscopic (SEM) analysis. After fixation of the specimens in 10% buffered formalin, the pulp cavity of the teeth were cut and soft tissues were mechanically removed. The specimens were immersed in 5% sodium hypochlorite for 4 h and dehydrated in alcohol. The pulpal surface of the MTA were examined in a JEOL JSM-840 A SEM. In association with the SEM, X-ray microprobe analysis was performed for qualitative examination of the chemical composition of the MTA surface and the associated crystal deposits.