The comparison of bulkfill applied restorative materials and the physical effects of surface coating on these materials

The clinical importance of bulkfill applications has started to attract the attention of clinicians based on the fact that a special care has to be taken for surface preparation of cavity depths in primary teeth due to their anatomical structure and low hard tissue thickness. The aim of this study was to evaluate comparatively the water absorption, the water solubility and the microleakage results of bulkfills made of two different composite resins with low polymerization shrinkage (Tetric EvoCeram®/Ivoclar and SureFilTM/Dentsply); one traditional microhybrid composite resin (Filtek™Z250/3MESPE) and two different glass ionomer cement with high viscosity (ChemFil ®Rock/Dentsply, EQUIA™ Fil /GC) all of which were coated by resin based, low viscosity surface coating material BisCover™LV. To measure the water absorption and water solubility values of each material used in the study, 100 samples with 15 mm. diameter and 1 mm. height were prepared and then each material group was divided into two subcategories of 10 samples. In the subgroup of surface coated positive, the samples were coated and in the subgroup of surface coated negative, the samples were not coated. Water absorption and water solubility measurements were carried out according to the ISO 4049:2000. For microleakage study, 50 units of third permanent molar without dental caries and without restorations were used. In total, 100 units of fifth class cavities on the buccal and lingual/palatal surfaces on 50 teeths. 100 restorations were divided into 5 groups and then each group was divided into 2 subgroups. In one of the subgroup, surface coating was applied on the section with restoration and for the other subgroup surface coating was not applied on the section without restoration. Once the teeth were prepared, they were kept in distilled water for 24 hours then were subjected to 1000 thermocycles between 5º- 55ºC and finally left in %0.5 basic Fuchsine solution for 24 hours. Teeth were cut through the center of restoration area in buccal-lingual direction using dental cutting machine, then paint penetration degree on occlusal and gingival surfaces were examined with stereomicroscope (Leica MZ 16 FA, Swiss) and the findings were scored between 0 to 3. The highest water absorption level was detected with ChemFil®Rock material group. The lowest water absorption level was detected at SureFilTM material group among all materials groups including all surface coating negative and positive subgroups. The water absorption difference compared to the rest of materials was found statically significant (p<0,05). The water absorption values of composite resin SureFilTM and Tetric EvoCeram® bulkfills were lower in comparison to Filtek™Z250 composite resin in statistically significant terms (p<0,05). The surface coating process had no effect in reducing water absorption with any material group in statically significant terms (p<0,05). The difference in water solubility values of material groups including all surface coating negative and also positive subgroups were statistically significant (p= 0,0001). In both subgroups of all materials, the lowest water solubility was found in composite resin Tetric EvoCeram® and the highest one in composite resin SureFilTM. In both subgroups, the water solubility values of glass ionomer cement EQUIA™ was found to be negative. This finding which was separated from the findings of the other materials was related to water absorption of the material instead of solubility. When the relation between the water absorption and water solubility values of materials was evaluated, a statistically significant and a positive relation has been observed in both subgroups of Tetric EvoCeram® (r=0,739 p= 0,015). It was observed that the surface coating application had reduced the microleakage at gingival and occlusal surfaces for all materials. In both subgroups, the highest microleakage was found in ChemFil ®Rock and lowest was found in Tetric EvoCeram® (p=0,0001). ChemFil ®Rock demonstrated very high microleakage score at gingival in negative subgroup compared to positif subgroup with staticialy significant terms (p=0,014). The number of low microleakage score samples obtained in positive subgroup was higher in statically signifant terms compared to negative subgroup with the use of Filtek™Z250. Tetric EvoCeram® applied speciments studied for microleakage characteristics, with and without surface coated, demonstrated lower microleakage on occlusal and gingival surfaces in both negative and positive subgroups compared to SureFilTM applied speciments. Similar diffirences had been finding between glass ionomer speciments. The microleakage scores of ChemFil ®Rock applied speciments were higher on occlusal and gingival surfaces compared to EQUIA™ Fil applied speciments. In result, various physical properties of the composite resin and the glass ionomer materials had been studied. The differences, independent of surface coating, in water absorption, water solubility and microleakage were linked to chemical structure of these materials additionally material properties and chemical properties of study materials demonstrated more effectiveness than surface coating application.