graphite fiber reinforced poly(methyl methacrylate) suitable for implant-fixed dental bridges

Development of carbon/ graphite fiber reinforced

I. E. Ruyter 1, K. E k s t r a n d , = N. B j 6 r k 1NIOM - Scandinavian Institute of Dental Materials, Norway, 2Departmentof Prosthetics, Stockholm County Council, Stockholm, Sweden

p01y(methyl methacrylate) suitable for implant-fixed

dental bridges Ruyter IE, Ekstrand K, Bjdrk N. Development of carbon/graphite fiber reinforced poly(methyl methacrylate) suitable for implant-fixed dental bridges. Dent Mater 1986: 2: 6 9 . Abstract - Conventional bridge framework of gold alloys are expensive. After in vitro investigations, materials were selected for preparing bridges from carbon/graphite reinforced poly(methyl methacrylate) on titanium implants. Fracture stress and flexural modulus were higher for the reinforced than for the unreinforced poly(methyl methacrylate) material. Absorption of water decreased the flexural properties of the materials.

Since 1965, dental implants of the Brfinemark type have been used with good clinical results (1). The usual superstructure material for titanium implant-fixed bridge prostheses has been gold alloy (2). The high cost of the gold framework initiated the development of a cheaper system based on a bridge with carbon/graphite (CG) fiber reinforced poly(methyl methacrylate) (PMMA) system. The objective of this study was to investigate the flexural properties in both dry and wet condition of CG fiber-reinforced PMMA systems (CGFP) containing different quantities of fibers. The unreinforced PMMA systems used were also investigated. The longitudinal dimensional changes during polymerization and water uptake were also assessed. On the basi~ of these results a CGFP was selected which was considered suitable for construction of dental prostheses on titanium implants. The clinical and technical procedure have been described (3). Material and m e t h o d s Specimen preparation

The materials listed in Table 1 were used in this study. The powder/liquid

ratios and the quantity of CG fibers are given in Table 2. Test specimens of the control and the CGFP composites for

Key words: flexural properties, polymer, prosthetics, fiber composite.

I. E. Ruyter, NiOM, Forskningsveien 1, 0371 Oslo 3, Norway. Received March 12, 1985; accepted October 28, 1985.

measurements of polymerization contraction and transverse bending tests were produced in a stainless steel mold.

Table 1. Materials used in the investigation. Brand

Code

Batch no.

Manufacturer

Grafil Carbon Fiber XAS 12K uncoated SR 3/60

CG

4CXA 1071/153

Courtauld Ltd. Coventry, UK

SR

SR 3/60 Quick 20

Q20

Palapress

PP

powder 26763 liquid 9109CZ powder 00379598 liquid 9194CZ powder 9050959 liquid 2020650

Ivoclar AG Schaan, Liechtenstein Ivoclar AG Schaan, Liechtenstein Kulzer & Co. GmbH Bad Homburg, FRG

Table 2. Composition of materials of the bend test specimens. Material

Auto-polymerized PP PP PP PP PP Q20 Heat-polymerized SR

CG fiber

Powder/liquid ratio

Curing temperature

20 10 4 0 20 0

1.5:1 1.5:1 1.5:1 2.5:1 1:1 3:1

40 40 40 40 23 23

20 0

1:1 3:1

-" _a

(wt-%)

(v/v)

(~

a The heat-polymerized resin was cured according to ISO R 1567 (1970), i.e. for 90 min at 73 _+ 1~ followed by 30 min in boiling water.

Carbon fiber PMMA bridges: properties Four molds were used for specimen preparation. Each mold was 65 mm long, 10 + 0.05 mm broad, and 3.0 _+ 0.05 m m deep. Two small pits were drilled in the metal mold at a distance of 49.00 + 0.02 mm from each other. After mixing the polymer powder and monomer liquid of the heatpolymerized material SR, the resulting mixture was placed together with the C G fibers in the stainless steel mold and processed. The C G fibers were placed parallel to the long axis of the specimen, i.e. perpendicular to the applied load. The auto-polymerized materials PP and Q20 were processed according to manufacturers' instructions. Test methods

The distances between the 2 pits reproduced on the specimens were measured at 23 + I~ after processing and after storage in water at 37 + 1~ for the periods given in Table 3 using a travelling microscope (Nikon Profile GC-2, Nippon-kogaku, Japan). These distances were c o m p a r e d with the corresponding distances in the respective molds and the percent dimensional change was calculated. The specimens were bent in a threepoint transverse testing rig which was designed and built according to ISO 1567 (4), i.e. similar to the one described by Stafford and Handley (5). The rig was fitted to a mechanical testing machine (Testatron, Z 718, Otto Wolpert Werke G m b H , Ludwigshafen/ Rhein, F R G ) and was surrounded by a temperature-controlled chamber during testing in air. The specimens were also tested during immersion in a water bath connected to a thermocirculator (Thermomix, 1480 THP, B. Braun Melsungen A G , Melsungen, F R G ) . The bending tests were carried out at 37 + 1~ with a crosshead speed of 5 _+ 1 m m / m i n in both dry and wet conditions. Five specimens were used for each testing condition. Before bend testing, the specimens were stored in distilled water at 37 + I ~ for the periods given in Table 3. The dry specimens were stored at 23 _+ I~ for 3 weeks before testing. Results Linear dimensions

The linear changes during the polymerization of the denture base polymers and the CG-fiber reinforced denture base polymers are presented in Table 3.

The results for the auto-polymerized unfilled materials PP and Q20, as well as for the heat-polymerized unfilled material SR, demonstrated a slight linear contraction during polymerization. During storage in water at 37~ the unreinforced denture base polymers showed a slight expansion, expressed as a decreased contraction after storage in water for 90 days (Table 3). The C G fiber reinforced materials showed no significant changes in linear dimension during polymerization or during storage in water at 37~ as indicated in Table 3. Transverse bending test

The data from the transverse bending tests presented as stress-strain diagrams are shown in Figs. 1-6. The superimposed curves in Figs. 1 and 2 illustrate the increased flexural properties, i.e. fracture stress and flexural modulus with increasing content of C G fibers in the auto-polymerized material PP when tested in dry condition at temperatures

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of 23 and 37~ The flexural modulus increased with increasing content of C G fibers (Table 4). Storage in water at 37~ for up to 90 days led to a decrease in flexural strength of the auto-polymerized material PP with 20 wt-% C G fibers (Fig. 3). After immersion in water for 60 days the flexural properties were similar to those after 90 days storage in water. The difference in the observed flexural moduli of the dry material and the various water saturated materials was not statistically significant (Table 4). In spite of the decrease in flexural properties of the auto-polymerized material PP with 20 wt-% C G fibers after storage in water at 37~ for 90 days, these flexural properties remained better than those of the unfilled material PP stored under the same conditions (Fig. 4). The flexural properties of the 3 materials SR, PP and Q20 with 20 wt-% C G fibers differed when tested in dry condition (Fig. 5). H o w e v e r , when the same materials were tested after stor-

Table 3. Linear dimensions. Material, CG fiber (wt-%)

Condition

Dimensional change (mm)

SD

Dimensional change (%)

90 d

+0.003 -0.005 +0.005 -0.005 -0.004 -0.006 -0.190 -0.081

_+0.015 _+0.006 _+0.011 _+0.010 _+0.010 _+0.006 +0.016 _+0.019

+0.01 -0.01 +0.01 -0.01 -0.01 -0.01 -0.39 -0.17

dry, 23_+1~ H20, 37_+1~ 90 d dry, 23_+1~ HzO, 37_+1~ 90 d

-0.001 -0.002 -0.217 -0.078

_+0.014 _+0.012 -0.016 _+0.016

0.00 0.00 -0.44 =0.16

dry, 23_+1~ H20, 37-+1~ 90 d dry, 23_+1~ H20, 37_+1~ 90 d

+0.028 +0.015 -0.208 -0.114

_+0.013 -0.023 _+0.010 _+0.025

+0.06 +0.03 -0.42 -0.23

PP 20 20 20 20 10 4 0 0 Q20 20 20 0 0

dry, 23_+1~ H20, 37_+1~ H20, 37_+1~ H20, 37_+1~ dry, 23_+1~ dry, 23_+1~ dry, 23_+I~ H20, 37_+1~

30 d 60 d 90 d

SR 20 20 0 0

Table 4. Flexural modulus (GPa) in dry and wet condition. Material

CG fiber, wt-%

Dry

Wet, 30 d

Wet, 60 d

Wet, 90 d

37_+1~

37_+1~

37_+1~

37_+1~

3.1_+0.3 2.9_+0.1 6.8_+1.2 5.1_+0.4 9.2_+1.0 8.5+1.5 16.2_+0.6 15.4-+2.0 2.7_+0.1 2.1_+0.4 13.0_+1.8 13.2_+1.5 3.1+0.1 3.1_+0.1 14.6_+1.1 18.0_+4.0

13.6-+0.9 -

15.5-+1.3 -

23+1~ PP PP PP PP Q20 Q20 SR SR

0 4 10 20 0 20 0 20

2.7_+0.2 12.9-+2.1 2.2_+0.1 14.5+1.1 2.5_+0.1 13.3-+0.8

8

R u y t e r et al.

300-

,

4

2

,

0

/

~

400-

wt-% C

SR 10 wt_O4C

300 -

u~ 200-

Q20

4wt-% C

o~

o3 100.

0 wt-% C

1

2 3 STRAIN,%

m 200-

100-

4

Fig. 1. The flexural properties of the autopolymerized material PP with 0, 4, 10 and 20 wt-% CG fibers tested dry at 23~

Fig. 5. The flexural properties of the autopolymerized material PP and Q20 as well as the heat-polymerized SR with 20 wt-% CG fibers tested dry at 37~

300-

20wt-%C

10wt-%C ~6

STRAIN,%

300

200-

100-

Owt-%(;

1

2

3 STRAIN,%

4

100-

5

Fig. 2. The flexural properties of the autopolymerized material PP with 0, 4, 10 and 20 wt-% CG fibers tested dry at 37~

300" DRY 37~ 200-

SR

200'

f

PP

Q20

STRAIN, %

Fig. 6. The flexural properties of the autopolymerized materials PP and Q20 as well as the auto-polymerized SR with 20 wt-% CG fibers stored for 90 days at 37~ in water and tested at the same conditions.

30d H20 37~

~;

~

90d HzO 37~

100"

STRAIN,%

Fig. 3. The flexural properties of the autopolymerized material PP with 20 wt-% CG fibers tested dry at 37~ and after 30 and 90 days at 37~ in water.

Fig. 7. Photo of a CGFP bridge in the lower jaw.

Discussion ~. 2 0 0 -

I ~

20wt-%C

100 Owt % C

1

2 STRAIN,%

3

4.

Fig. 4. The flexural properties of the autopolymerized material PP with 0 and 20 wt-% CG fibers tested after 90 days at 37~ in water.

age in water at 37~ for 90 days, these differences were negligible (Fig. 6).

The minor linear contraction in the longitudinal direction of the specimens for the unfilled polymeric materials is probably due to retention in the mold of the material during polymerization. The contraction was even less when CG fibers were included in the material. In all cases the contraction will be transverse to the long axis of the specimens. During water uptake there was a minor linear expansion of the unfilled materials, whereas CGFP specimens had no longitudinal linear expansion. This was probably due to retention in the longitudinal direction by the fibers.

When tested under dry conditions, the flexural properties increased markedly with increasing content of C G fibers in the denture base polymer. However, with more than 20 wt-% of CG fibers, porosities were seen in the material, and wetting of all fibers with the monomer-polymer system was also difficult. During storage in water, the flexural properties decreased for all the materials investigated. The ultimate strength of the materials was markedly reduced during the first 60 days in water. This reduction in the mechanical properties could be due to the plasticizing effect of absorbed water in the polymer matrix. Absorbed water can also interact with the surface of the C G fibers, resulting in poor adhesion between fiber and matrix. Although the mechanical properties of the C G F P were reduced after water absorption, they were still better than those of an unfilled polymer. The ultimate strength of both the heat-polymerized materials and the auto-polymerized materials with 20 wt-% CG fibers was of the same magnitude when they were water saturated. This may indicate a somewhat poor adhesion between fiber and matrix, as the ultimate properties are equivalent. Water may reduce some properties, i.e. fatigue properties, of the fiber reinforced materials in the mouth. The adhesion between fiber and matrix should, therefore, be improved. There were no differences in flexural properties between the heatpolymerized material SR and the autopolymerized materials PP and Q20, all containing 20 wt-% of GC fibres (Fig. 6). In the dry condition the GC reinforced polymers had better flexural properties with a PP matrix than with a Q20 matrix (Fig. 5). The unreinforced material PP also has higher flexural modulus and flexural strength than Q20 (6). Based on these results and since an auto-polymerized material was easier to process, PP was chosen as matrix for the clinical investigation (3). CG-fiber reinforced implant-fixed bridges in the mandible can be an alternative to conventional cast frameworks, and there is also a potential in CGFP systems to make bridge constructions for conventional, prostheses.

Acknowledgement - This work was partly supported by Praktikertjfinst AB and by the Swedish Dental Society.

Carbon fiber P M M A bridges: properties

References

1. ADELL R, LEKHOLMU, ROCKLERB, BRANEMARKP-I. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981: 10: 387-416.

2. LUNDQUISTS, CARLSSON GE. Maxillary fixed prostheses on osseointegrated dental implants. J Prosthet Dent 1983: 50: 262-270. 3. BJ6RK N, EKSTRANDK, RUYTERIE. Implant-fixed, dental bridges from carbon/ graphite fiber reinforced poly(methyl methacrylate) Biomater (in press). 4. International Organization for Standardization. ISO 1567 1978 (E) Denture base resin, Geneva, Switzerland. 5. STAFFORDGD, HANDLEYRW. Transverse bend testing of denture base polymers. J Dent 1975: 3: 251-255. 6. RUYTER, IE, SVENDSENSA. Flexural properties of denture base polymers. J Prosthet Dent 1980: 43: 95-104.

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