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The purpose of the study was to measure the cement thickness obtained when ceramic rods were luted to dentin and to analyze the relation between cement thickness and the previously published tensile bond strength of similar test specimens. In addition,
the ISO standard 4049:2019 method was used to determine the film thickness of the used cements. Zirconia (n = 100) and lithium disilicate (n = 50) rods were cemented to bovine dentin using one of five different resin-based cements. The ceramic-dentin test specimens were cut into two slices and the cement thickness was measured using a scanning electron microscope and compared to the bond strength values of similar specimens already published. The mean cement thickness recorded for ceramic rods cemented to dentin was in the range 20–40 µm, which was larger than the cement film thickness found by the ISO method. The cement film thickness determined according to ISO standard methods did not concur with the results obtained when cementing ceramic rods to dentin. For cementing ceramic restorations, a cement thickness in the range 25–35 µm seems to be favorable for the bond strength.

Reference
The influence of the resin- based cement layer on ceramic-dentin bond strength
Sagen MA, Dahl JE, Matinlinna JP, Tibballs JE, Rønold HJ
Eur J Oral Sci. 2021;00:e12791.
https://doi.org/10.1111/eos.12791