Marginal Fit, Internal Adaptation, and Microleakage of Preformed Metal Crowns: Impact of Three Preparation Techniques and Three Ion-Releasing Cements

Abstract

Highlights What are the main findings? • Preparation technique, not cement, governed the performance of preformed metal crowns (PMCs): the Hall technique showed significantly greater microleakage and a larger angular internal gap than conventional preparation, with the modified Hall technique being intermediate; marginal gap was similar across techniques.• The bioactive (ACTIVA™ BioACTIVE-CEMENT) and bioceramic (Calibra® Bio) cements performed comparably to resin-modified glass ionomer cement. What are the implications of the main findings? • No differences in seal or fit were detected among the three ion-releasing cements.• Tooth preparation improves the crown–tooth seal and angular fit under PMCs compared with no preparation, supporting clinical evaluation of a modified Hall technique with a defined occluso-axial bevel. Abstract Objectives: To compare, in vitro, the marginal and internal fit and marginal microleakage of preformed metal crowns (PMCs) placed with the conventional, Hall, and modified Hall techniques and cemented with three ion-releasing, resin- or glass-ionomer-matrix luting materials: a bioactive resin-matrix cement (ACTIVA™ BioACTIVE-CEMENT), a bioceramic calcium aluminate cement (Calibra® Bio), and a resin-modified glass ionomer cement (RMGIC; Riva Luting Plus). Methods: Forty-five extracted human primary molars were randomly allocated to three preparation groups (n = 15), each subdivided by cement (n = 5). After thermocycling (500 cycles, 5–55 °C, dwell time: 15 s, transfer time: 10 s), specimens were immersed in 1% methylene blue for 24 h, sectioned buccolingually, and examined by image analysis (ImageJ). Microleakage was quantified as the percentage of the crown–tooth interface showing dye penetration; marginal and internal fit were measured at thirteen points across marginal, axial, angular, and occlusal regions. Results: Marginal gap did not differ significantly among techniques or cements (p > 0.05). A significant region × technique interaction (p = 0.025) localised the technique effect to the angular region, where the Hall technique produced a larger gap than conventional preparation (p = 0.004). Microleakage was significantly greater for the Hall than the conventional technique (p = 0.045), with the modified Hall being intermediate. Cement had no significant effect, and fit and microleakage were uncorrelated. Conclusions: Preparation technique, rather than cement, was the principal determinant of seal and angular fit; ACTIVA™ BioACTIVE-CEMENT and Calibra® Bio performed comparably to RMGIC under the conditions tested. Clinical studies of a modified Hall technique incorporating a defined occluso-axial bevel are warranted to confirm these findings.