Coronal microleakage of endodontic access restorations in zirconia crowns

Inadequate marginal sealing in endodontically treated teeth can lead to microleakage and treatment failure. The purpose of this in vitro study was to quantify and compare the quality of the marginal seal when different materials and bonding techniques were used to restore endodontic access cavities in zirconia cylinders. Fifty custom zirconia cylinders (10.0 mm in diameter × 14.0 mm in height; wall thickness of 1.5 mm) were prepared with simulated endodontic access cavities (5.0 mm in diameter). The cylindrical specimens were divided into 5 groups, each assigned a different method of access cavity restoration (n = 10 per group): direct glass ionomer cement restorations; direct composite resin restorations adhesively bonded without prior aluminum oxide (Al₂O₃) particle abrasion of the zirconia surface; direct composite resin restorations adhesively bonded after Al₂O₃ particle abrasion of the zirconia surface; custom zirconia inlays adhesively bonded without Al₂O₃ particle abrasion of the zirconia surface or inlay; and custom zirconia inlays adhesively bonded after Al₂O₃ particle abrasion of the zirconia surface and inlay. Specimens were immersed in 2% methylene blue solution and stored in a humidified incubator at 37°C, and dye penetration was quantified with a spectrophotometer (at 450 nm) every 7 days for 28 days. Statistical analysis was conducted using 2-way analysis of variance with the Tukey test and chi-square analysis. Statistically significant differences in dye penetration were observed, with microleakage influenced by the restoration material and bonding protocol. Zirconia inlays placed after Al₂O₃ abrasion exhibited the least leakage, showcasing significantly superior sealing compared with direct composite resin restorations without Al₂O₃ abrasion. The results indicated that Al₂O₃ particle abrasion is essential for secure bonding of restorations to zirconia. The results of the study confirm that glass ionomer cement should be avoided for long-term restoration of access cavities in zirconia restorations due to its inferior microleakage prevention. Instead, composite resins and zirconia are favored, with Al₂O₃ air abrasion showing the potential to enhance marginal seal in endodontically treated teeth.