Full crowns with short posts or deficient ferrules show a high failure incidence. The influence of fatigue loading on the cement layer between the root canal dentin and short glass and fiber posts in resin composite core restorations was investigated.Two adhesive resin composite cements, Panavia 21 and RelyX-ARC, and one resin-modified glass-ionomer cement, RelyX, were used. Posts (6mm length) and core restorations were made on single-rooted premolars from which the coronal sections had been removed at the level of the proximal cementoenamel junction. Following cementing the posts core build-ups were made, using adhesive (Clearfil Photo Bond) and light-cured composite (Clearfil Photo Core). Half of the specimen (n = 8) were exposed to fatigue loading (106 load cycles) almost perpendicular to the axial axis (85°). Three parallel, transverse, root sections of 1.5 mm thickness and 6 mm length were cut from each specimen.The push-out test showed no significantd ifference between the retention strength of the posts in either the fatigue or the control group. For both the push-out strength and SEM evaluation of cement layer integrity the results improved from RelyX to RelyX ARC to Panavia 21, and also from apical to coronal.