Statement of problem: Although bonding is important for long-term clinical success, studies on the bonding of additively manufactured ceramics are sparse.

Purpose: The purpose of this in vitro study was to determine the influence of manufacturing methods, additive (LCM) versus subtractive (CAM). and ceramic materials, zirconia (ZrO₂) and lithium disilicate (LiSi), on the tensile bond strength (TBS), failure mode, and surface roughness of ceramics.

Material and methods: A total of 240 ceramic specimens (n=60/group; 2×2×10 mm) were prepared. Two additively manufactured (LCM-printed) ceramics, LiSi and ZrO₂ (Lithoz), subtractively manufactured LiSi (IPS e.max CAD), and subtractively manufactured ZrO₂ (KATANA Zirconia HTML PLUS) were evaluated. From each material, 40 specimens were bonded together (n=20 ceramic-ceramic specimens/group), and 20 specimens were bonded to equally sized human dentin specimens (n=20 ceramic-dentin specimens/group). The ZrO₂ specimens were airborne-particle abraded (Al₂O₃, 50 µm, 0.1 MPa), and the LiSi specimens were etched with hydrofluoric acid. Then, a universal primer (Monobond Plus) was applied. After the dentin was coated with an etch-and-rinse adhesive (Syntac Classic), the specimens were bonded with luting composite resin (Variolink Esthetic DC), light polymerized for 40 seconds, thermally aged (10 000 cycles between 5 °C and 55 °C), tested for TBS, and statistically analyzed (1- and 3-way ANOVA and Weibull analysis). The ceramic surface was examined with scanning electron microscopy, and surface roughness was measured with digital microscopy before and after surface pretreatment.

Results: TBS varied between 5.88 ±2.22 MPa and 6.34 ±2.26 MPa in the ceramic-dentin groups and 12.40 ±1.56 MPa and 18.82 ±5.92 MPa in the ceramic-ceramic groups. No significant difference was observed regarding the manufacturing method and material for different bonding conditions (P>.05). Additive and subtractive LiSi showed the highest reliability with m=18.27. The ceramic-ceramic specimens failed cohesively in the luting composite resin, whereas the ceramic-dentin specimens failed adhesively.

Conclusions: The manufacturing method and material used had little effect on bond strength values or surface properties. The recently introduced printed materials performed similarly to conventionally milled materials.

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