Lin, Galvin Sim Siang
(2020)
Polymerization shrinkage, degree of conversion of zirconia reinforced rice husk nanohybrid composite and its fracture strength on the endodontically treated maxillary incisors.
Masters thesis, Universiti Sains Malaysia.
Abstract
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.
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