REINFORCEMENT OF POLYMETHYLMETHACRYLATE (PMMA) RESIN WITH PERFORATED METAL PLATES
Figure 4. Flexural Modulus p< 0.05, same letter = same statistical group
Table 1 Results for Flexural Strength and Flexural Modulus
Groups
Fracture Strength (MPa)
SD
Fracture Modulus (MPa)
SD
Group 1 C.
78.8A
5.9
2261.7C
261.4
Group 2: GS
97.2B
14.1
3477.9D
770.6
Group 3: GS, MP
95.4B
19.3
3952.4D
268.5
Group 4: GS, GB , MP
91.7AB
15.5
3239.1D
366.6
p-value (ANOVA)
0.03
<0.0001
C= control, GS = grid strengthener, MP = Monobond Plus, GB = grit blasted
difference among the four group of specimens in
flexural strength (p=0.0137) and flexural modulus
(p<0.0001). Tukey’s HSD test shows that there
is no statistical difference among the three grid
strengthener containing groups, and there is no
statistical difference between the control and the
group reinforced with gritblasted strengthener
and bonding agent.
For flexural modulus, all three groups with grid
strengthener are significantly higher than that
of the control, and additional surface treatment
of the strengthener did not result in additive
strengthening of the denture base.
Thus the first null hypothesis can be rejected, which
is not the case for the second null hypothesis,
which must be partially accepted.
Discussion
The purpose of the study was to investigate
if the grid strengthener had a strengthening
effect on the flexural strength and modulus of
a PMMA based denture base resin and should
additional surface treatment, such as roughening
and bonding, enhance these properties. Three
point bending test was chosen, because its test
geometry represents the closest the load situation
in a denture in a patients mouth.
The grids were positioned close to the bottom of
the bars (~ 0.5 mm), where the bar is under tension
during testing and fractures of the denture resin
were expected.
Thus it could be expected to have the best
possible strengthening of a metal plate to a PMMA
structure.
The injection molding technique was chosen,
because it allowed better precision in positioning
the metal grids within the PMMA plate and the
resin injection does not subject strengthener to
vertical forces during processing keeping the grid
to stay in place.
Traditional compressive molding technique,
which requires multiple trial flasking, would
103