Ethical approval was obtained from King Abdulaziz University following the Declaration of Helsinki. Forty freshly extracted maxillary premolars with two roots were collected. Informed
consent was obtained from patients for collection of extracted teeth for research purposes. Teeth were cleaned of calculus and remaining tissues using an ultrasonic scaler. Teeth were examined to exclude caries, cracks, and fractures. Samples were stored in a 10% formalin solution at room temperature until used. The labial and palatal surfaces were marked.
40 premolars were accessed and endodontically treated using rotary pro-taper gold files (Dentsply Sirona). Pulp tissue was removed using barbed broach prior using the rotary files (Dentsply Maillefer, Tulsa, OK, USA). After removing pulp tissue, Size 10 K-file was used to establish the working length (Dentsply Maillefer, Tulsa, OK, USA) and to start a glidepath for the rotary files. Furthermore, the root canals were enlarged to size 20 (Dentsply Maillefer, Tulsa, OK, USA) before using the rotary files. Protaper gold Ni-Ti rotary instruments were used according to the manufacture instruction in the following sequence (sizes S1, S2, F1, F2; Dentsply Maillefer, Tulsa, OK, USA). A high torque endodontic motor was used. (X-Smart, Dentsply Maillefer, Tulsa, OK, USA). The canals were irrigated using NaOCl (5.25%) between each file to remove any remaining debris. The canals were then dried using F2 paper points. Subsequently, Obturation was done using Gutta percha size F2 (Kerr Corporation, Brea, CA, USA) and AH sealer (Dentsply Maillefer, Tulsa, OK, USA). The Gutta Percha was removed using gates glidden size 3, leaving approximately 5mm at the apical region.
The teeth were sectioned 2mm coronal to the cemento-enamel junction using a wheel-shaped diamond bur. The teeth were also apically and axially prepared to achieve a 2mm ferrule and a 1.5mm deep chamfer finish margin. A round-end diamond bur was utilized for this step. Next, Post space was created using post space drill RelyX (3M ESPE, Germany) corresponding to the selected post as follows:
A) RelyX™ fiber post size 2 (1.6 mm diameter) for double fiber post group.
B) RelyX™ fiber post size 3 (1.9 mm diameter) for single fiber post group.
In addition, two core build-up strategies were utilized:
A) LuxaCore Z (DMG, Hamburg, Germany), dual-cured core build-up composite as luting cement and core build-up material. LuxaCore Z composed of nanofiller and zirconium dioxide (70%) in a Bis-GMA-based dental resins (28%), additives, pigments, catalysts (2%)
B) RelyX Unicem self-adhesive resin cement (3M ESPE, Germany) as a luting cement, followed by composite 3M ESPE Filtek Z250 XT (3M ESPE, USA) nanohybrid as a core build-up material.
Teeth were divided randomly into 4 groups of 10 teeth each, depending on the number of fiber posts (single or double) and the core build-up material (LuxaCore Z or composite) used.
Group #1. Single fiber post with Luxacore Z as luting cement and core build-up material.
Group #2. Two fiber posts with Luxacore Z as luting cement and core build-up material.
Group #3. Single fiber post with RelyX Unicem as luting cement followed by composite as a core build-up material.
Group #4. Two fiber posts with RelyX Unicem as luting cement followed by composite as a core build-up material. (Table 1).
Table 1
Number of posts, luting material and core build up material used in each group.
Grouping | No. of posts | Luting material | Core build-up material |
Group 1 | Single | Luxacore Z | Luxacore Z |
Group 2 | Double | Luxacore Z | Luxacore Z |
Group 3 | Single | Resin cement | Packable composite |
Group 4 | Double | Resin cement | Packable composite |
An intra-oral periapical radiograph was taken to confirm the position of the post in the canal. The post space and coronal dentin were etched using 37% phosphoric acid (N- etch, Ivoclar Vivadent) for 15s then rinsed and dried using air and paper points.
In group 1 and 2:
Luxacore Z was used as a luting cement for the post and core build up material. The posts were inserted in the root canals and held under digital pressure. Luxacore Z was light cured for 40 s. The core was allowed to set for 5 min for complete polymerization to occur because Luxacore Z is a dual cure composite resin.
In group 3 and 4:
RelyX resin cement was used to cement the posts in the root canals. The posts were inserted in the root canals and held under digital pressure. Excess cement was removed using a microbrush and a sharp instrument. The cement was then light cured for 20s. An adhesive resin (Single Bond, 3M ESPE) was applied following manufacturer’s instructions and cured for 10s. The core build-up composite resin was placed on the post and prepared tooth surfaces and light cured for 40s.
All teeth were finished using fine diamond cylindrical burs. All above procedures were done by a single operator. Subsequently, teeth were mounted perpendicular to the base of customized molds in an autopolymerising acrylic resin (Eco-Cryl cold, Protechno, Spain) 2mm below the cementoenamel junction to simulate bone support.
The specimens were placed in the Universal testing machine (5969L3504, Instron, USA) to test the fracture resistance. Specimens were axially loaded on the center of the occlusal surface. Load was applied using a stainless steel piston with 0.5 mm radius at a cross-head speed of 1mm/min until the specimen fractured. The maximum force required to produce a fracture was recorded in newtons (N). The statistical analysis was performed using One way ANOVA with tukey post hoc.