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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
Results.



In all postoperative periods the light microscopy analysis showed histological changes in the superficial reaction zone close to the MTA–pulp interface. The underlying pulp tissue was consistently found to be of normal structure without any sign of inflammation or tissue degeneration. Only two 2-week specimens and one 3-week specimen showed haemorrhage in the central pulp core.
The reaction zone was of variable width and composed of pulpal cells, remnants of blood, areas of tissue coagulation, traces of capping material, dentine fragments, and postoperatively formed hard tissue. A few scattered inflammatory cells (predominantly macrophages and lymphocytes) were also seen in most of the examined specimens regardless of the observation period. The analysis was further focused at the reaction zone along the wound surface and the MTA–pulp interface.

TEM micrograph 7 days after application of MTA on mechanically exposed pulp of dog
Figure 1. TEM micrograph 7 days after application of MTA on mechanically exposed pulp of dog.
a) Pulpal cells arrangement along the exposed surface of the MTA and the associated crystalline structures. (x2500);
b) Higher magnification of 1a.
Numerous mitochondria and empty cisternae of the rough endoplasmic reticulum in the cytoplasm of the cell; direct contact between the cell surface and the crystals (arrows) distributed in the extracellular space of the reaction zone (x12000).

TEM micrograph 7 days after application of MTA on mechanically exposed pulp of dog
Figure 2. TEM micrograph 7 days after application of MTA on mechanically exposed pulp of dog. Numerous ribosomes and widened cisternae of the rough endoplasmic reticulum in the cytoplasm of the cell, which is in direct contact with free crystals (arrows) distributed in the extracellular space of the reaction zone (x20000).

TEM micrograph 7 days after application of MTA on mechanically exposed pulp of dog
Figure 3. TEM micrograph 7 days after application of MTA on mechanically exposed pulp of dog. Remnants of pulpal cells in close relation to the pulpal side of MTA ( 20 000).

One-week observation period.
An almost homogeneous front of organized crystalline structures or a thin zone of basophilic matrix was found along the pulpal side of MTA (Figs 1, 2). The TEM study showed elongated pulpal cells arranged at a distance 2–5 m from the crystalline front (Fig. 1a). These cells exhibited increased cytoplasmic/nucleus ratio, an eccentrically located nucleus and well developed cytoplasm with numerous mitochondria, free ribosomes, Golgi elements and rough endoplasmic reticulum (Figs 1b and 2). The apical pole of the elongated pulpal cells was associated with crystalline structures; cytoplasmic processes were also found in direct contact with the crystalline structures (Figs 1b and 2). Degenerated cells in contact with the capping material were also seen (Fig. 3).
The SEM study showed crystalline structures which ranged from intergrown crystal units to complicated oblong forms (Fig. 4a,b). The X-ray microanalysis of the examined surface (MTA and anorganic precipitations) revealed two high peaks corresponding to calcium and silicate and six low peaks corresponding to sodium, magnesium, aluminium, phosphorus, bismuth and iron (Fig. 4c). The oblong forms of crystals showed two peaks corresponding to calcium and phosphorus (Fig. 4d).

SEM micrographs and associated X-ray analyses
Figure 4. SEM micrographs (a and b) and associated X-ray analyses (c and d) 7 days after application of MTA on mechanically exposed pulp of dog. Non-homogenous crystal depositions onto the MTA surface
a) (x1000);
b) (x4000);
c) Two main peaks on MTA surface corresponding to calcium and silicate;
d) Two main peaks on crystalline structures corresponding to calcium and phosphorus.

Two-week observation period.
Production of hard tissue barrier consisting of irregular osteotypic matrix depositions with cellular inclusions was seen along the pulpal side of MTA in all teeth capped for 2 weeks (Fig. 5). The osteodentine barriers were found to be atubular in form and related to cuboidal or columnar cells.

Light microscopy micrograph 2 weeks after application of MTA on mechanically exposed pulp
Figure 5. Light microscopy micrograph 2 weeks after application of MTA on mechanically exposed pulp of dog. Osteodentinal matrix formation (arrows) along the pulpal side of MTA and haemorrhagic infiltration in the underlying pulp. (Hematoxylin-eosin, x40).

The TEM study showed a zone of densely packed collagen fibres elaborated in predentine-like pattern in direct contact with the front of electron dense crystalline-like structures (Fig. 6a). Spindle-shaped or tall columnar cells showing a well developed cytological organization with widened rough endoplasmic reticulum becoming parallel to the long axis of the cells were seen along the collagenous zone (Fig. 6b). Mitochondria, numerous Golgi saccules and dense bodies were distributed throughout the whole cytoplasm.

TEM micrograph 2 weeks after application of MTA on mechanically exposed pulp
Figure 6. TEM micrograph 2 weeks after application of MTA on mechanically exposed pulp of dog.
a) New collagen matrix (NM) formation in direct contact with the zone of crystalline structures (CR) formed along the exposed surface of the MTA (x20000);
b) Numerous mitochondria and parallel cistrernae of the rough endoplasmic reticulum in the cytoplasm of the pulpal cells associated with the new collagenous matrix (NM) zone seen also in 6a (x8000).

The SEM study showed intergrown crystalline structures composed of rod-shaped or spherical units (Fig. 7). The X-ray microanalysis of the examined surface revealed two main peaks corresponding to calcium and phosphorus.

Three-week observation period.
Two-layered hard tissue barriers in contact with vital pulp completely bridging the pulpal wound surfaces were found in six out of seven specimens (Figs 8 and 9a). The barriers consisted of a coronal irregular layer of osteodentine and a pulpally tubular dentine-like matrix lined by elongated cells (Fig. 9b). In one specimen the bridge consisted only of an osteodentine layer lined in a number of serial sections by elongated and polarized cells (Fig. 10).
The pulpal surface of the barriers and the matrix deposited around the exposure site showed in SEM examination the typical surface structure of reparative dentine.