SummaryA light‐cured glass ionomer cement was investigated as a retrograde root seal, without a retrograde cavity. This was compared with the material used in a retrograde cavity, and with a conventional glass ionomer cement, as a seal. The adaptation and sealing ability of the test materials were assessed using a confocal optical microscope with a fluorescent dye.The root canals of 40 extracted human single‐rooted teeth were prepared and filled with gutta‐percha and sealer. All the teeth were subsequently apicected, then divided into four equal groups. In one group, a retrograde cavity was prepared, and the light‐cured glass ionomer cement was placed as a retrograde root filling. No retrograde cavities were prepared in the three remaining groups. The light‐cured glass ionomer cement was applied directly onto the apicected root face. Two different thicknesses of light‐cured glass ionomer cement were tested, a thin layer (≈1 mm) in one group, and a thicker layer (0.001). The greatest extent of dye penetration was found with the thick (<1 mm) light‐cured and conventional glass ionomer cement (≈1 mm) root seals; the differences between these were not significant. The light‐cured glass ionomer cement was only suitable as a retrograde root seal whe
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