Materials and methods
This study was approved by the institutional ethics committee. A CAD-CAM (MTAB XL MILL, MTAB Engineers Private Limited, Chennai, India) die was made to simulate the partially edentulous condition of a three-unit maxillary, posterior FPD (Nejatidanesh et al., 2006). Nonanatomic patterns of 7.5mm in height and 5mm in diameter as well as 6mm in height and 8mm in diameter were made to replicate prepared teeth of the maxillary second premolar and maxillary molar, respectively. The prepared teeth simulation had a two-degree taper and supragingival chamfer finish line. A gap of 8mm in height and 10mm in width placed between the two teeth simulated the pontic space for the maxillary first molar. The precision of the anatomical form of the clinical tooth preparation could not be simulated in this study due to limitations in the use of the sample in the universal testing machine (UTM). The designed die had a rectangular platform (50cm×25cm×14cm) to facilitate holding of the aluminum dies in the UTM (Fig. 1).
A wax pattern (Krohenwachs® – Bego) of a definite size, shape, and lesser anatomic details of a three-unit resin-bonded FPD consisting of the second premolar (8mm in length×7.5mm in mesio-distal width×7mm in bucco-lingual width), first molar (7.5mm×11mm×9mm), and second molar (7mm×10.5mm×10mm) was made on the aluminum die. An impression of the wax pattern was made with polyvinyl siloxane (putty consistency; Virtual Refill®, Ivoclar Vivadent). Type 4 stone nicotinic receptor agonist (Ultrarock®, Kalabhai, India) was made from the impression. The cast obtained was used to make a vacuum-formed template using a pressure molding machine (Biostar®, SCHEU-DENTAL GmbH) (Fig. 2). The vacuum-formed template was used to standardize the specimen size and shape (Fig. 3). The materials were manipulated in accordance with the manufacturer’s instructions.
Heat-cured polymerized PMMA specimens A and B were processed by an indirect technique. Impression of the CAD CAM die was made with polyvinyl siloxane (putty consistency; Virtual Refill®, Ivoclar Vivadent). Type 4 stone cast (Ultrarock®, Kalabhai, India) was made from the impression. The cast obtained was used to make the wax patterns. The wax patterns were made over the cast using the template. The fabricated wax patterns were processed by a compression molding technique, according to the manufacturer’s instructions for the materials.
The specimens were evaluated for defects. The defective specimens were discarded. The chosen specimens of all groups were trimmed and finished with abrasive stones and 300-grit sandpaper. The specimens were polished with a pumice/water mixture and finished with diamond polishing paste. The entire procedure was performed by the same person for standardization (Figs. 4 and 5).
Specimens B, D, and F were made with polyester fiber reinforcement (particle size of 100μm, Industrial use, Indian Institute of Technology, Chennai). The fibers were presilanated with methacryloxypropyltrimethoxysilane by the manufacturer to enhance adhesion with resin materials. The polyester fibers were added to the polymer or base paste of the provisional materials in a ratio of 1:10 (2% of the specimen by weight) (Kamble and Parkhedkar, 2012). The weight of the fibers was measured using an electronic machine and transferred to the polymer or base paste of the provisional FPD materials to prepare specimens B, D, and F. These specimens were then prepared in a similar manner as specimens A, C, and E. In total, 30 specimens (5 samples per group) were fabricated for this study (Fig. 6). The materials, code, and lot numbers of the materials used in this study are summarized in Table 1.
Before analysis, the specimens were stored at 37°C for 24h and air dried for 1day at room temperature. The fabricated specimens were tested in the UTM (LR 100K, Lloyd; U.K., CIPET, Guindy, India) with a cell load of 5kN. The specimens were positioned and stabilized on the testing platform with a span length of 5mm, and they were loaded compressively at the mid-pontic region with a cross head speed of 0.5mm/min (Fig. 7). Failure was marked by a perceptible crack and reconfirmed by the abrupt decrease in the recorded load–deflection curve. Fracture load and deflection were documented for all specimens (Fig. 8). The other mechanical properties were derived using formulae. The load–deflection curves were recorded using computer software (NEXYGEN™ MT).where, P=compressive load; L=length in mm; b=width in mm; d=specimen thickness (diameter); FS=flexural strength; P=(FS×bd2)/(3/2×L); compressive strength (CS)=compressive load/cross-sectional area; cross-sectional area=π·D2/4; π=22/7; and D=diameter of the sample analyzed.
Materials and methods