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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 9  »  An in vitro evaluation of four materials as barriers to coronal microleakage in root-filled teeth
An in vitro evaluation of four materials as barriers to coronal microleakage in root-filled teeth
Discussion - References.



Discussion.
Previous investigations have pointed out the importance of coronal microleakage in the failure of root-canal treatment. The purpose of this study was to compare four materials used as barriers to coronal microleakage.
There are many factors that can affect coronal leakage. These include the thickness of the sealer cement (Magura et al. 1991), presence of voids within the rootcanal filling (Magura et al. 1991), solubility of sealer (Saunders & Saunders1995), smear layer removal, mastication forces, penetration of bacteria and the effect of saliva (Uranga et al. 1999). In addition, temperature changes in the oral cavity have been shown to adversely affect the marginal seal of a dental material (Uranga et al. 1999) because the linear coefficients of thermal expansion of materials and dentine are different, perhaps representing the leading a etiology of leakage (Noguera & McDonald1990). Thermocycling was therefore incorporated into the protocol of the present study.
Using cleared teeth to assess dye penetration has been employed in other leakage studies (Saunders & Saunders 1990, Torabinejad et al. 1990) and allows specimens to be examined in three dimensions, so that the extent and adaptation of the filling material can be observed and evaluated. Although the limitations of dye studies have been highlighted (Chailertvanitkul et al.1997), they continue to be used.
Taylor et al. (1997) and Saunders & Saunders (1994) have shown that removal of the smear layer decreases coronal leakage, regardless of the obturation technique used. This may occur owing to the increased tubule penetration of filling materials and better sealing ability. Therefore, in the present study we incorporated the use of17% EDTA to remove the smear layer.
Methylene blue dye was not used because it tends to be washed out during the clearing process. India ink, a histological stain, remained stable during this process and was used in this study. Chong et al. (1995) noted that bacterial ingress and India ink penetration provided a similar rank order for the sealing ability of the materials tested.
The results showed that IRM (Fig. 2) material and Coltosol (Fig. 3) allowed significantly less coronal microleakage than the other groups. The mean leakage for IRM was 6% with four of 19 samples displaying dye penetration. Beach et al. (1996) found that one of 18 IRM samples gave positive bacterial growth with a 4-mm layer of material. The present study demonstrated that there was no significant difference between IRM and Coltosol, which showed a mean leakage of 4.85%. Costas & Wong (1991) evaluated the sealing ability of two restorative materials used to retain bleaching agents inside the pulp chamber and reported that IRM provided a satisfactory seal. However, IRM is package das a liquid and powder that must be mixed before placement. This is a disadvantage because it takes considerably longer to place and adjust than Coltosol. However, Coltosol may be affected by occlusal loading and the manufacturer recommends the material not to be left in place for longer than 2 weeks.

Figure 2. IRM group showed mean leakage of 6.38%.

IRM group showed mean leakage

Figure 3. Mean leakage for Coltosol group was 4.85%.

Mean leakage for Coltosol group

Figure 4. Vidrion R group showed mean leakage of 32.2%, which was significantly different from the other groups.

Vidrion R group showed mean leakage of 32.2%, which was significantly different from the other groups

Figure 5. Scotch Bond showed the poor sealing ability. The mean leakage was 54.35%, which did not differ significantly from the positive control group.

Scotch Bond showed the poor sealing ability. The mean leakage was 54.35%, which did not differ significantly from the positive control group

Figure 6. Control group showed mean leakage of 62.07%.

Control group showed mean leakage

The glass ionomer group (Fig. 4), whose setting is an acid-base reaction, showed poor sealing ability, as reported by Beckham et al. (1993). This is probably due to shrinkage of the material upon setting, resulting in a potential avenue for microleakage and its use may be more technique sensitive.
Scotch Bond (Fig. 5) showed the greatest leakage, which did not differ significantly from the positive control group (Fig. 6).The bonding agent has a low viscosity and does not seem to provide an effective seal when used alone. Leonard et al. (1996) have reported that the latest generation of dentine bonding agents has shown increasingly greater bonding strengths, the ability to penetrate dentinal tubules through hydrophilic wetting and a greater tendency to resist microleakage, thereby justifying research efforts to incorporate dentine bonding agents and resin as sealers. Further long-term evaluations are indicated.

References.

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Costas FL, Wong M (1991) Intracoronal isolating barriers: effect of location   on root leakage and effectiveness of bleaching agents. Journal of Endodontics   17, 365-8.
Dow PR, Ingle JI (1955) Isotope determination of root canal failure.   Oral Surgery, Oral Medicine and Oral Pathology 8, 1100-4.
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