Polymerization shrinkage, degree of conversion of zirconia reinforced rice husk nanohybrid composite and its fracture strength on the endodontically treated maxillary incisors

• Main Author: Lin, Galvin Sim Siang
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: R Medicine
• Online Access: http://eprints.usm.my/48866/1/GALVIN%20SIM%20SIANG%20LIN%20-FINAL%20THESIS%20P-SGM001419%28R%29%20PWD_-24%20pages.pdf; http://eprints.usm.my/48866/
• Institution: Universiti Sains Malaysia

The present study aimed to compare the polymerization shrinkage, degree of conversion and fracture strength of endodontically treated maxillary lateral incisors restored using novel zirconia reinforced rice husk nanohybrid composite with commercialized microhybrid and nanofilled composites. 180 samples were used for polymerization shrinkage and degree of conversion tests, divided into Group 1 – nanofilled composite (Filtek-Z350-XT), Group 2 – microhybrid composite (Zmack- Comp) and Group 3 – experimental nanohybrid composite (Zr-Hybrid). The test for polymerization shrinkage was performed using buoyancy and optical methods. For the buoyancy method, samples were weighed in air and water to calculate the shrinkage value, while for the optical method, images of samples before and after light-curing were captured using a microscope to calculate the shrinkage value. The conversion degree was tested using the FTIR spectrometer. Eighty mature permanent lateral maxillary incisors were selected for the fracture strength test and divided into: Group 1 – ET + Filtek-Z350- XT, Group 2 – ET + Zmack-Comp, Group 3 – ET + Zr-Hybrid and Group 4 – Intact teeth (control). Standardised MPD cavity was prepared, and endodontic treatment was performed using crown-down technique up to size 30. Obturation was completed using single cone technique with gutta-percha and AH Plus sealer. Cavity access was restored with respective composite resins. Next, the teeth were stored in the incubator for 24 hours and subdivided into aged and non-aged subgroups. Teeth in aged subgroups underwent 2,500 thermal cycles. Subsequently, all teeth were tested under the Universal Testing Machine until fractures occurred. They were then examined under a microscope to determine the fracture pattern and type of fracture. Data were analysed using One-way ANOVA for polymerization shrinkage, conversion degree and fracture strength. The fracture pattern and fracture type were analysed using the Chi-square test. Zr-Hybrid showed comparable shrinkage (p>0.05) to Filtek-Z350-XT, but lower shrinkage (p<0.05) than Zmack-Comp. Zr-Hybrid showed a higher conversion degree (p<0.05) than Filtek- Z350-XT and a comparable conversion value with Zmack-Comp. Besides, ET + Zr- Hybrid demonstrated the highest fracture strength in both aged and unaged subgroups. The fracture strength decreased significantly in ET + Filtek-Z350-XT and ET + Zmack- Comp (p<0.05) as the thermocycles increased but no significant differences were noted in ET + Zr-Hybrid and control Group 4. Moreover, ET + Zr-Hybrid and control Group 4 showed more favourable fracture pattern. In conclusion, Zr-Hybrid exhibited excellent shrinkage and conversion values. Endodontically treated teeth restored with Zr-Hybrid demonstrated superior fracture strength and favourable fracture pattern.