The impact of incorporating fish bone powder (Rainbow trout, Oncorhynchus mykiss) into flowable composite resins on polymerisation shrinkage and mechanical properties

Objective: The aim of this study is to evaluate the effects of the bone obtained from the skeleton of rainbow trout, which is cultivated and exported in our country and then processed into nano-sized hydroxyapatite powder. The powder is then added to commercial dental fluid composite as an inorganic filler at different ratios. This is done to ascertain the effect on the mechanical properties of the composite resin. Materials and methods: This study evaluated the effect of adding inorganic nano-fillers obtained from waste trout bone powder to a flowable composite (Imicryl, Konya) at different ratios on the polymerisation shrinkage, hardness, and flexural strength of the composite resin. The trout waste generated by the Akerko Su Ürünleri processing plant in Trabzon was collected. These wastes were processed at the laboratory of Tarsus University's Chemistry Programme to obtain inorganic nano-hydroxyapatite fillers. The ratio of the organic filler in a commercial fluid composite was kept constant, with different ratios of nano-hydroxyapatite added to the inorganic filler. Five experimental groups including the control group were evaluated. Five experimental groups, including the control group, were evaluated. To evaluate polymerisation shrinkage, 50 samples were prepared as hemispheres (n = 10), and the volumetric shrinkage rate was measured using an Acuvol (Bisco, Schaumburg, IL, USA). For microhardness measurement, 50 disc-shaped samples (n=10) with a diameter of 8 mm and a thickness of 2 mm were prepared and the Vickers hardness value (VHN) (kg/mm2) was determined with a microhardness tester (HWDM-5, TTS Unlimited Inc., Osaka, Japan). For the biaxial bending test, 50 specimens (n = 10) were prepared as 12 mm diameter, 1.2 mm thick discs, and the test was performed using a universal testing machine (Shimadzu, Kyoto, Japan). The surface properties of the composite resin specimens were analysed using scanning electron microscopy (JEOL JSM 7001F, Japan). Statistical analyses of the data were performed using SPSS v.19 package programme (SPSS Inc, IBM Corp, IL, USA). One-way Analysis of Variance (ANOVA) and post-hoc Tukey HSD tests were used in the analyses (p˂0.05). Results: In the microhardness evaluation, the highest value was observed in the 3rd group with 10% nano-hydroxyapatite additive (p<0.05). In the polymerisation shrinkage evaluation, the lowest volumetric shrinkage was observed in the 5th group with 60% nano-hydroxyapatite additive (p<0.05). When the bending strength was evaluated, the highest strength was observed in the control group in which nano-hydroxyapatite was not added (p<0.05). Superficial analysis of the samples by SEM revealed agglomeration in the material containing 10% or more nano-hydroxyapatite additives. Conclusion: Nano-hydroxyapatite can be obtained from waste materials and is economical to produce. Composite resins containing nano-hydroxyapatite exhibited differences in mechanical properties. Keywords: Waste management, hydroxyapatite, microhardness, shrinkage, flexural strength