A Study on Root Canal Obturation after Apical Closing by Apexification

Apexification was performed on an immature tooth with the apex spreading in a blunderbuss-like shape, and standardized root canal models were prepared under the assumption that the apex opening was closed. On each of these models, root canal obturation was carried out by applying 8 different obturation methods: lateral compaction method, Obtura II, Ultrafil, Thermafil, System B, combination of System B and Obtura II, sectional method, and obturation only with ZOE sealer. Based on the images taken from the surface of the root canal wall and on three dimensional CT images taken by a micro focus X-ray CT device, and by calculating the ratio of obturation material in the root canal (obturation ratio), the following conclusions were obtained: among the root canal obturation methods thus applied, the whole of the obturation ratio was the highest in Obtura II, being 98.1%, followed in order by Ultrafil (98.0%), sectional method (97.8%), lateral compaction method (97.7%), combination of System B and Obtura II (97.1%), System B (95.8%), and ZOE sealer obturation (93.3%). It was the lowest when Thermafil was applied, being 87.1%. The obturation ratio of the sliced plane 1mm from the apex was at the highest in Ultrafil being 93.4%, followed in order by System B (90.2%), sectional method (90.0%), Obtura II (88.8%), ZOE sealer obturation (87.9%), combination of System B and Obtura II (86.5%), and lateral compaction method (72.1%). It was the lowest when Thermafil was applied, being 17.8%. In the results of one-way ANOVA, the influence of the type of obturation method on the ratio of obturation was found to be significantly high (p<0.01). When Obtura II, Ultrafil, System B and combination of System B and Obtura II were used, the end of the root canal, which was spread in a blunderbuss-like shape, could be filled with gutta-percha, while obturation was slightly insufficient when the sectional method was applied. When the lateral compaction method and Thermafil were applied, obturation was extremely insufficient. When ZOE sealer obturation was applied, air bubbles of various sizes were widely disperses in the hardened material. In the obturation method where gutta-percha softened by heating or by using a solvent was filled into the root canal, the sealer had to be simultaneously used because gutta-percha tended to peel off from the canal wall. Because air bubbles in the sealer might cause the formation of dead space, precaution had to be taken to prevent the intermingling of air bubbles at the time of mixing or when coating it on the canal wall. These results suggest that, in the root canal with apex spreading in a blunderbuss-like shape and closed by apexification, root canal obturation should be performed by one of the following methods: Obtura II simultaneously using sealer, Ultrafil, System B, or combination of System B and Obtura II.