Introduction:
Many authors are interested in the results of research on composites, in which artificial fibers are now often used in their reinforcing phase. Often, in specific clinical situations, they become an alternative to conventional permanent prosthetic restorations.

Aim of the study:
Comparison of changes in composite strength parameters depending on the reinforcement with one or two bands of glass fibers.

Material and methods:
Light-cured Gradia Direct Posterior composite and G Bond bonding agent were used in the study. The composite was reinforced with long glass fibers. A total of 30 samples were tested, including 10 control ones. The study group consisted of two series of 10 composite samples with one or two bands of glass fibers used as reinforcement. The samples were made and the tests were carried out in accordance with the PN-EN ISO 4049: 2019-07 standard. The three-point bending strength test was used for the mechanical strength tests. Four strength parameters were assessed.

Results:
In terms of all strength parameters the differences between the control group (KONT) and the composite samples with the presence of one glass fibers band (SKL 1) were statistically highly significant. Also the comparison between KONT and the composite samples with two single bands of glass fibers (SKL 2) showed highly significant statistical differences in all strength parameters. The differences between SKL 1 and SKL 2 were statistically significant in the distribution of two parameters: deflection and Young’s modulus.

Conclusions:
One or two bands of glass fibers used as reinforcement significantly improve the mechanical properties of the dental composite.