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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 1  »  Occlusal loading of EBA and MTA root-end fillings in a computer-controlled masticator: a scanning electron microscopic study
Occlusal loading of EBA and MTA root-end fillings in a computer-controlled masticator: a scanning electron microscopic study
Discussion - References

Little has been published on how root-end filling materials are affected by loading during chewing action (Blum et al . 1997). A computer-controlled masticator (Krejci et al . 1990b) allows occlusal loading of tooth restorations in vitro in a manner that resembles clinical conditions and therefore delivers clinically relevant results (Krejci et al . 1999). Natural human enamel cusps are used as antagonists in a chewing simulator which is able to simulate physical forces, wear mechanisms and temperature changes that can occur in the oral environment (Krejci et al . 1990b).
For evaluation of the wear of restorative materials, it is important to gain not only short-term data but also long-term results concerning durability and marginal continuity. Thus, the time frame that is aimed at is an observation period of 5 years or a five-year equivalent (Krejci et al . 1990a). It has been repeatedly demonstrated that this method is valid and is not compromised by artefacts. For instance, the amount of margin obscured by bubbles or other artefacts is typically small and not included in the calculation.
The results obtained in the current study show that the root-end filling materials EBA and MTA both yielded excellent pre-loading results with less that 1% gap formation between the surrounding dentine wall of the root-end cavity and the root-end filling. The amount of continuous margin after loading for both root-end filling materials decreased slightly but still displayed highly satisfactory findings. After the specimens were stressed by 1.2 million chewing cycles or a five-year equivalent, EBA still showed 93.1 1.3% and MTA demonstrated 98.9 0.7% continuous margin. These findings confirm that under in vitro conditions both materials were reliable and stable over time. MTA requires a 3–4 h setting time (Torabinejad & Chivian 1999) in comparison to the shorter setting time of EBA (0.75–6 min). This, added to the fact that MTA contains 5% calcium sulphate dihydrate (gypsum, Dentsply-Tulsa 1999) that expands during setting may contribute to the superior marginal adaptation of MTA filling material after loading.

Palatal root with MTA root-end filling displaying through and through microcrack (arrows) after occlusal loading
Figure 7.
Palatal root with MTA root-end filling displaying through and through microcrack (arrows) after occlusal loading. Original magnification x100.

Mesio-buccal root revealing intradentine microcrack (arrows) after occlusal loading of a specimen with an EBA rootend filling
Figure 8. Mesio-buccal root revealing intradentine microcrack (arrows) after occlusal loading of a specimen with an EBA rootend filling. Original magnification x100.

The majority of EBA root-end fillings were overfilled initially, even though these fillings had been carefully finished using a fine diamond-coated bur under the operating microscope. The amount of surplus filling material decreased significantly during occlusal loading and was probably washed away in the test chamber by surrounding fluid.
In contrast, a substantial number of the MTA root-end fillings were underfilled before loading, the amount of underfilled margin increased significantly after occlusal loading. Other authors have discovered that the outer layer of MTA dissolves in a solution of phosphate-buffered saline, resulting in a loss of half a millimetre of the surface of root-end fillings (Yatsushiro et al . 1998). This finding corresponds with the results of the present study, with 36.3 5.2% of the MTA filling margins being underfilled (Fig. 6) before the loading procedure had taken place. After occlusal loading, the amount of underfilling had increased significantly, but there was no apparent influence on the marginal integrity of the MTA root-end fillings.
Under in vivo conditions, this surface disintegration of the root-end filling material might not take place to such an extent or might be self-limiting. Studies have shown an inductive effect of MTA on cementoblasts, resulting in growth of a complete layer of cementum-like material over the surface of MTA root-end fillings in monkeys as early as 5 months (Torabinejad et al . 1997). Investigations have also shown cell growth of osteoblasts on MTA (Mitchell et al . 1999). This creation of an intimate connection between the filling material MTA and the periodontium may prevent or limit possible loss of material.
The second topic of investigation in the current study was crack formation before and after occlusal loading of the specimens. Other authors have divided microcracks into incomplete or complete canal cracks, intradentine cracks and cemental cracks (Layton et al . 1996). In the current study, only one cemental crack was observed. The distribution of microcracks into complete canal cracks (through and through cracks, Fig. 7), incomplete canal cracks and intradentine cracks (Fig. 8) did not differ significantly.
Mesio-buccal roots were shown to be significantly more susceptible to crack formation than the other root types. A possible explanation is the cross-sectional shape of this root with a deeply fluted indent between the two main canals. As a result, the biconcave middle portion of a mesio-buccal root is potentially overprepared or weakened during root-end preparation and is predisposed to microcracking (Abedi et al . 1995, Frank et al . 1996). With respect to different types of cracks, only four cracks were complete. However, it is not known whether or not the other types of microcracks could eventually become complete cracks or root fractures.


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