Evaluation of marginal and internal fit of occlusal veneer bridges fabricated with different preparation designs and zirconia types: a randomized clinical trial

To evaluate the marginal and internal fit of zirconia occlusal veneer bridges.This was a prospective randomized interventional clinical study with four parallel experimental groups. Forty occlusal veneer bridges (n = 10), replacing maxillary or mandibular first molars were fabricated using two preparation designs and two types of zirconia: second-generation (3Y-TZP) and third-generation (5Y-PSZ) zirconia. Design 1 involved 1 mm occlusal reduction of the abutments, a 1 mm circumferential occlusal shoulder, and axial wall preparation adjacent to the pontic, limited between the buccal and lingual line angles. Design 2 featured an extended adjacent preparation to the lingual midpoint with the addition of an axial groove on each abutment. Following visual evaluation of marginal adaptation on clinical abutments, the replica technique was employed to assess marginal and internal fit using a light microscope at × 100 magnification. Twelve points were evaluated on mesiodistal sections of each bridge: four for marginal fit and eight for internal fit. Data were analyzed statistically, with the significance level set at α = 0.05. Mean marginal fit ranged from 63.5 to 81.3 µm, while mean internal fit ranged from 46.3 µm (axial surface of the molar) to 153.5 µm (occlusal surface of the molar). No statistically significant differences in marginal or internal fit were observed among the groups at any of the evaluated points. Zirconia occlusal veneer bridges fabricated using the investigated zirconia materials and preparation designs demonstrated clinically acceptable marginal and internal fit. Trial Registration Number: ISRCTN13463878.