Root canal preparation. Three of us (E.B., A.A., N.T.) established the canal lengths visually by placing a size 15 K-file into each root canal until the tip of the file was visible at the tip of the apical foramen. We also measured the working length radiographically and verified the apical patency. We established working lengths 1.0 millimeter short of the apical foramen.

We instrumented the root canals to the working length with a size 40 K-file by using a step-back technique. The coronal one-third of the roots were flared by using sizes 2, 3 and 4 Gates-Glidden burs and a slow-speed handpiece. We then irrigated the root canals with 10 milliliters of 5.25 percent sodium hypochlorite (NaOCl). We removed the smear layer by washing the roots in 10 mL of 17 percent ethylenediaminetetraacetic acid (Canal+, Septodont, Saint-Maur des Fossés, France) for five minutes, followed by 10 mL of 5.25 percent NaOCl. Finally, we flushed the root canals with 3 mL of saline solution and dried them with paper points.

Root canal obturation. We filled the roots with gutta-percha by using the lateral condensation technique with one of the following sealers (n = 30 per group): MM-Seal, AH 26 and AH Plus. We prepared the sealers according to the manufacturer’s instructions. After the obturation process, we removed excess gutta-percha and filled the coronal access cavities with temporary filling material (Cavit G, 3M ESPE AG, Seefeld, Germany). We stored the specimens for three weeks in 100 percent relative humidity at 37°C to allow the sealers to set.

We randomly divided all 90 roots into two main groups according to the presence or absence of radiotherapy.

Radiotherapy. A radiation therapist in the Department of Radiation Oncology, Faculty of Medicine, Ondokuz Mayis University, delivered radiation to specimens. The therapist placed the roots, which were in resin blocks, in a 25-square-centimeter plastic container during irradiation. To administer a consistent radiation dose, the therapist replaced the saline solution daily to a level up to 0.5 cm above the resin blocks in the plastic container.³ The radiation therapist administered radiation with Co-60 photons (Theratron 780C, Theratronics Int., Carrollton, Texas) by using a single anterior field. The source water surface distance was 80 cm. The therapist delivered a total dose of 60 gray in fractions of 1.8 Gy/day (conventional fractionation schedule) five days a week for seven weeks. After irradiation, we again stored both the irradiated and nonirradiated specimens in saline.

We then coated the roots completely with two layers of nail varnish, except for the apical parts. In addition to the 90 roots, we used six roots as negative controls (filled with gutta-percha and sealant) and six roots as positive controls (filled with gutta-percha only). We removed the apexes of the roots down to the root canal filling or, in the case of the positive controls, to the point at which the canal lumen was visible. We coated the negative controls completely with the nail varnish. We immersed the specimens in 5 percent methylene blue dye and centrifuged them at 30 gauss for four minutes. The final step was to wash the specimens with water.

We grooved the roots longitudinally on both sides by using a diamond disk under water coolant. We then sectioned them carefully and examined each half of each root under a stereomicroscope. We measured the amount of leakage from each half, from the apex to the most coronal section of the root canal to which the dye had penetrated. We then calculated the mean amount of leakage for each of the three sealers.

We used methylene blue as the leakage marker because it has a low molecular weight and penetrates more deeply along the root canal filling.

We used two-way analysis of variance to determine statistically significant differences in apical leakage between the groups. We performed multiple comparisons by using the t test to isolate and compare statistically significant differences. We set the level of significance at = .05.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
The table shows the mean (± standard deviation) apical leakage values for specimens in all of the groups. The positive controls exhibited dye penetration along the entire length of the root canal, while the negative controls exhibited no leakage.

For specimens that did not receive radiotherapy, we found no statistically significant differences between the AH Plus and MM-Seal groups (P > .05). However, the mean leakage values for the AH Plus and MM-Seal groups were significantly different from the mean leakage value for the AH 26 group (P < .05).

For specimens that received radiotherapy, we found no statistically significant differences between the AH Plus and MM-Seal groups (P > .05). However, the mean leakage value for the AH 26 group was statistically different from values for the AH Plus and MM-Seal groups (P < .05).

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Radiotherapy involves the delivery of the correct radiation dose to the tumor mass. Absorbed radiation doses are expressed in gray, the standard unit.⁶ The wide range of side effects of ionizing radiation to the head and neck region are well-known, and they are related to cumulative doses that vary from 50 to 70 Gy delivered across a five- to seven-week period. However, in our study, the specimens were irradiated with 60 Gy delivered incrementally across seven weeks,³ which corresponds to a common clinical procedure for adults receiving radiotherapy.

In this study, we stored the freshly extracted teeth in saline. This is a common procedure, as it does not influence the chemical and physical properties of human tooth structure.

Leakage studies. Leakage studies of the sealing properties of endodontic materials are important and relevant.⁷ Different methods have been used to evaluate the sealing efficacy of endodontic cements. We used methylene blue as the leakage marker because it has a low molecular weight and penetrates more deeply along the root canal filling.^8,9

Air trapped in the root canal filling material or inside the root canal system may inhibit penetration of the dye into the pores and gaps.¹⁰ Oliver and Abbott¹⁰ stated that after centrifugation at 3,000 revolutions per minute for five minutes, dye penetration was 91.7 percent, while dye penetration via passive immersion was 20.7 percent. For this reason, these authors¹⁰ recommended use of active dye penetration tests, whereby trapped air is removed under a vacuum or dye penetration is performed under high pressure. We used centrifugation in this study.

A wide variety of root canal sealers are available commercially. Among the resin-based sealers, the sealing properties of AH Plus and AH 26 are well-known.^11–13 Thus, we compared their leakage values with those of MM-Seal. In addition, the sealing ability of these sealers in patients undergoing radiotherapy had not been assessed before our study.

Zmener and colleagues¹³ and Bodrumlu and Tunga¹⁴ reported that the mean apical leakage value for specimens sealed with AH Plus was lower than that for specimens sealed with AH 26. Although we found similar results in this study, the mean apical leakage values for AH 26 and AH Plus were lower in the previous studies than in this study, because they did not use centrifugation to perform the dye penetration tests (thus, less dye penetrated the roots).

The apical sealing ability of MM-Seal was similar to that of AH Plus. Because no study to date has evaluated the sealing ability of MM-Seal, we could not conduct any comparisons. In addition, regardless of whether the specimens were irradiated or not, MM-Seal and AH Plus were similar with regard to mean leakage values; this might be explained by the sealers’ chemical components.

The failure of sealers may be the result of their physical properties (adhesiveness, dimensional stability, flow, solubility).^13,15 Some authors^16,17 have suggested that the apical seal may be improved by increasing the surface contact between the root canal walls and the sealer (these connections can be affected by radiotherapy).

Bond strength. al-Nawas and colleagues¹⁸ found that the mechanical properties of dentin seem to be much less affected by irradiation than are those of enamel. According to these authors, irradiation has only a minor effect on the mechanical properties of dentin. Gernhardt and colleagues^19,20 found no differences between irradiated and nonirradiated dentin specimens. Changes in hardness, the crystalline structure and the collagen matrix resulting from irradiation do not influence the bond strength of resin-based materials.^19,20 For these reasons, the bonding ability of the sealers in this study was not affected by radiation therapy, and we observed no difference in leakage between specimens in the irradiation and nonirradiation groups.

	CONCLUSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Further studies are needed to assess the sealing ability of the new root canal sealer, MM-Seal, and evaluate its clinical performance. In addition, the results of our study show that the apical sealing ability of the three resin-based root canal sealers was slightly lower in the groups that received radiotherapy than in those that did not, although the differences between the groups were not statistically significant.