เอกสารการประชุมวิชาการและเสนอผลงานวิจัย มหาวิทยาลัยทักษิณ ครั้งที่ 19 2552 - page 953

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perimeter curing light that might interfere with the subsequent bonding processes. The coronal portion of each
tooth was removed at 3 mm above the cement-enamel junction (CEJ) under copious water cooling. Each root
canal was endodontically instrumented with a NiTi instrument (ProTaper; Dentsply Maillefer, Ballaigues,
Switzerland) from no.10 to no.25 at a working length of 0.5 mm from the apex using an endodontic micromotor
(X-smart; Dentsply Maillefer, Ballaigues, Switzerland). Finally, the canal was flushed with 2 ml of 2.5% sodium
hypochlorite (NaOCl), dried with adsorbent paper points, and obturated with a gutta percha main cone no.25
(ProTaper Universal Gutta Percha; Dentsply Maillefer, Ballaigues, Switzerland) and a eugenol free sealer (AH 26;
Dentsply DeTrey, Konstanz, Germany). The access was then filled with temporary filling (Cavit; 3M ESPE AG,
Seefeld, Germany), and all specimens were stored in distilled water at 37 °C for 24 hrs. After storage, post spaces
were prepared with Peeso drills (Dentsply Maillefer, Ballaigues, Switzerland) in the handpiece attached to a
vertical spindle of a surveyor from no.1 to no.3, then expanded with low speed dowel drills (Parapost drills;
Coltène/Whaledent, Altstätten, Switzerland) to achieve 9-mm deep and 1.5-mm diameter post spaces. The canals
were rinsed with 2.5% NaOCl for one minute followed by distilled water and dried with paper points.
All 15 prepared roots were randomly divided into three groups of 5 specimens each according to the
resin-based luting agents used: the etch-and-rinse system (Variolink II®; Ivoclar Vivadent, Schaan, Liechstein), the
self-etch system (Panavia F 2.0 ®; Kuraray Medical Inc., Osaka, Japan), and the self-adhesive system (RelyX
Unicem® ; 3M ESPE, MN, USA). Prefabricated glass fiber-reinforced composite posts (Parapost Tenax Fiber
White; Coltène/Whaledent, Altstätten, Switzerland) were used after removing the taper part, wiping the post
surfaces with alcohol for cleaning, and treating surfaces with a silane coupling agent (Monobond-S®; Ivoclar
Vivadent, Schaan, Liechstein). Finally, the post was cemented into the root canal with the assigned resin-based
luting agent in accordance with the manufacturer’s instruction. After storage in water at 37 °C for 24 hrs, each root
was cut perpendicularly to the bonding interface using a low speed diamond saw to harvest six 1-mm-thick slabs
from CEJ towards the apex.
Push-out test was performed by applying compressive load to the center of each slice using a universal
testing machine (LRX-Plus, Lloyd Instrument Limited., Hants, UK) equipped with a 1.3 mm diameter cylindrical
plunger. Loading was performed at a crosshead speed of 0.5 mm/min until failure occured. The bond strength in
MPa was computed by dividing the load at the time of debonding by the area (A) of the bonded interface. The
latter was calculated by the formula A=2¶rh, where r represented the post space radius and h represented the
thickness of the slice in mm. The data of each two-slabs from the coronal end were considered respectively to be
the bond strength of the coronal, middle and apical portion of the post-space. Therefore, each sub-experimental
group contained 10 specimens. Bond strength data were statistically analyzed using a two-way ANOVA followed
by post-hoc multiple comparisons, Tukey’s HSD in case of homogeneity of variance, and Dunnett’s T3 in case of
non homogeneity of variance, (Į = 0.05). Failure mode of the fractured specimen was observed under a
stereoscopic microscope (SMZ1500, Nikon, Tokyo, Japan) and classified as one of the following: (a) Cohesive
fracture of root dentin; (b) Adhesive fracture at root dentin–cement interface; (c) Cohesive fracture of cement; (d)