[Effect of different intraoral polishing protocols on the bond interface of three types of resin-matrix ceramic onlays].

Objective: To investigate the effects of nine polishing protocols on the bonding interface of three types of resin-based ceramic onlays, aiming to identify efficient and reasonable polishing procedures for each type of resin-based ceramic. Methods: Forty-six extracted molars were selected and symmetrically sectioned mesiodistally (n=92). Box-shaped cavities of 2 mm depth were prepared on the buccal and lingual surfaces of the molars. Then the samples were randomly divided into four groups (n=23): LU group (Lava Ultimate), VE group (Vita Enamic), H group (Zirconia-Reinforced Resin-Based Ceramic), and Si group (glass ceramic). Each group was further subdivided into nine subgroups (n=5) based on polishing tools (tungsten carbide bur A, silicone polisher polishing paste B, EVE polishing kit C) and time (60、90、120 s). The surface roughness (Sa) of the bonding interface was measured using white light interferometry and statistically analyzed. One sample from each group was randomly selected for surface morphology observation using scanning electron microscopy (SEM), and elemental composition was analyzed using energy-dispersive X-ray spectroscopy (EDS). Results: Different polishing protocols significantly reduced the Sa values (P<0.05), except for LU-B1, LU-C2, Si-A3, and Si-B2, which showed no significant difference before and after polishing (P>0.05). For VE and Si groups, the Sa values were: C1>B1>A1, with no significant difference among them (P>0.05). For the LU group, the Sa values were: B1>C3>A2, with A2 showing the lowest surface roughness, significantly different from B1 and C3 (P<0.05). For the H group, the Sa values were: C1>B2>A1, with C1 showing the highest surface roughness, significantly different from A1 (P<0.05), while A1 and B2 showed similar surface roughness (P>0.05).SEM observations revealed that the yellow bur left deep and long scratches on the molar surface. Different polishing protocols gradually smoothed and homogenized the surface, with the bonding agent interface becoming relatively blurred. Deep pits were more common in the bonding agent area, and some samples (LU-A1, LU-A2, VE-A2) showed adhesive overflow. Conclusions: Vita Enamic is recommended to be polished with a tungsten carbide bur or silicone polisher polishing paste for 60 seconds to achieve clinically acceptable surface roughness and a smooth surface morphology.Lava Ultimate is recommended to be polished with a tungsten carbide bur for 90 seconds to achieve optimal polishing results. Hyramic is recommended to be polished with a tungsten carbide bur for 60 seconds to achieve good polishing results.