Journal of Oral Rehabilitation, 1992, Volume 19, pages 385-391

Effect of metal strengthener's surface roughness on fracture resistance of acrylic denture base material P . K . V A L L I T T U an J V . P . L A S S I L A Department of Prosthetics and Stomatognathie Physiology, University of Kuopio, Kuopio Finland

Summary

The aim of this study was to clarify the effect of the surface roughness of various metal wires on the fracture resistance of the acrylic test specimens. The number of test groups compared were 16, and there were 30 test specimens in each group. The investigation showed that the surface roughening of the metal wires used to reinforce acrylic resin denture base material increasead the fracture resistance of the test specimens. The best results were achieved by sandblasting. The differences in resistance were also statistically significant. Introduction

The effect of the strengthening properties of a metal wire on the fracture resistance of polymethylmethacrylate in orthopaedic surgery has been studied by Saha and Kraay (1979). There are also studies on the strengthening properties of metal wires used as strengtheners in denture base material (Siirila & Berg, 1958; Schwickerath, 1966; Jennings & Wuebbenhorst, 1968; Carrol & von Fraunhofer, 1984; Ruffino, 1985; Vallittu & Lassila, 1992). In these investigations metal wires have been shown to increase the fracture resistance of acrylic specimens. Because the strengthening property of braided wire plate was found to be quite good (Carrol & von Fraunhofer, 1984; Ruffino, 1985; Vallittu & Lassila, 1992), it can be assumed that the mechanical retention between the wire and the acrylic has a noticeable effect on the fracture resistance of the acrylic-metal combination. It is not clear yet how the fracture resistance of the acrylic test specimens is influenced by the sandblasting of the metal wires. Sandblasting has also been used when fixed prostheses are made to increase the retention between a cast crown and dentine (O'Connor, Nayyar & Kovarik, 1990). Sandblasting with AI2O3 enhanced the retention significantly. This investigation was carried out to clarify the effect of the surface roughness of metal strengtheners on the fracture resistance of an acrylic resin. Materials and methods

The acrylic resin used for the test specimens was polymethylmethacrylate (Novodon Rapid Denture Base® *, which is an acrylate commonly used. The specimens were prepared in an aluminium mould made for this particular purpose, allowing 24 similar specimens to be done simultaneously (Figs 1, 2). The metal wires were positioned into the mould after the first test pressing of the acrylic resin had been undertaken. * Novodon, Schaan, Austria. Correspondence: Dr Pekka Vallittu. Faculty of Dentistry, University of Kuopio, POB 6, SF-70211, Kuopio, Finland.

385

386

P.K. Vallittu and V.P. Lassila

15

Fig. 1. Aluminium mould in which test specimens were done (dimensions in mm).

4-5

Fig. 2. Shape and dimensions (in mm) of test specimens.

The pressure was 150 bar after the strengtheners were positioned in the mould and the polymerization time was 30min as recommended by the manufacturer. After polymerization the mould was cooled in water, and subsequently the specimens were loosened from the mould. In each polymerization there were specimens from at least three different groups and the specimens were pressed randomly in different parts of the mould. The specimens were stored in water at room temperature for 2 weeks before testing. The metal strengtheners used included semicircle wire ( 0 l-0x2-0mm), braided wire plate ( 0 0-8 x 2-4mm) and clasp wire ( 0 1-0 mm) (Remanium ®)*, (Fig. 3). Five roughness stages of each wire type were used (Table 1, Fig. 4). The sandblasting was done with conventional sandblasting device (Strahlboy M®)t. The sand used was aluminum oxide (AhO^): grain size 50 and 250!.im and the air pressure applied was 5-5 bar. In some groups (B16, B24 and B34) the roughening of wires was done by grinding them with a heatless stoned and in other groups (B17, B25 and B35) with a 0, 6mm separating disc (Fig. 4). After being handled, all of the wires were cleaned in water with an ultrasonic cleaning device (Tec-25®)§ for 5min. * Dentaurum, Pforzheim, Germany. t Dental derate Leceux GmbH. Oberhauscn. Germany. X Busch, Engelskirchen, Germany. §Telsonic, NJ, U.S.A.

Metal strengtheners and fracture resistance

387

Fig. 3. Different types of wires used as strengtheners. From left: B31-3i (clasp wire), B21-25 (braided wire plate), B13-17 (semicircle wire).

Table 1.Classification of specimens according to surface roughness stage of strengtheners A Control group, no strengtheners B13 B14 B15 B16 B17

Semicircle Semicircle Semicircle Semicircle Semicircle

B21 B22 B23 B24 B25

Braided Braided Braided Braided Braided

B31 B32 B33 B34 B35

Clasp Clasp Clasp Clasp Clasp

wire, wire, wire, wire, wire,

plate, plate, plate, plate, plate,

wire, wire, wire, wire, wire.

l-0x2-0mm, 1-0x2 0mm, l-0x2-0mm, 1-0 x 2-Omm, l-0x2-0mm,

glossy 50^m sb. 250|j^m sb. heatless s. separ. disc

0-8x2-4 mm, glossy 0-8 x2-4mm. 50 ^m sb. 0-8x2-4 mm, 250 fim sb. 0-8 X 2-4 mm, heatless s. 0-8x2-4 mm, separ. disc 1-0 mm, 1-0mm, 1-0mm, 1-0mm, 1-0mm,

glossy 50|im sb. 250 |im sb. heatless s. separ. disc

sb. = sandblasting, s. = stone, separ. = separating.

The fracture resistance measurements were carried out with the Schleuniger 2E* testing machine modified for this purpose (Fig. 5), which was also used in the previous studies (Vallittu & Lassila, 1991). As the size of the test specimens and the measurement method were constant, it was possible to use the values of fracture load in kiloponds to indicate unit of fracture resistance. * Schleuniger, Solothurn, Switzerland.

388

P.K. Vallittu and V.P. Lassila

Fig. 4. Different surface roughness stages of strengtheners (semicircle wire). From left: glossy, sandblasted (5()^m), sandblasted (25Oiim), grinded by heatless stone and roughened by separating disc.

T 110

I

-35-0

Fig. 5. Schematic representation of specimen loading, arrow showing direction of load.

Metal strengtheners and fracture resistance

389

The mean values and standard deviations were calculated by statistical analysis. The differences in mean values between groups B13, B21 and B31 were also compared by means of the Student's /-test. Specimens with no strengtheners were used as a control group: group A. Results

All metal wires were found to increase the fracture resistance of the test specimens significantly when compared with the control group A ( P < 0-001). Without special treatment ofthe surface ofthe metal strengtheners, the semicircular wire had the most marked effect on the fracture resistance of the specimens. The braided wire plate did not have as favourable an effect as the semicircle wire. When the different methods of treating the wire surfaces were compared, it was noticed, that the sandblasting was the most effective method with all the metal wires used in this study (Table 2, Fig. 6.). The increase of fracture resistance of the test specimens reinforced with braided wire plate was also statistically significant (P

Effect of metal strengthener's surface roughness on fracture resistance of acrylic denture base material.

The aim of this study was to clarify the effect of the surface roughness of various metal wires on the fracture resistance of the acrylic test specime...
4MB Sizes 0 Downloads 0 Views