Marginal Fit, Internal Adaptation, and Microleakage of Preformed Metal Crowns: Impact of Three Preparation Techniques...

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).

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.

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.

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.