DENTAL MATERIALS
Figure 3. Flexural Strength. P< 0.05, same letter = same statistical group
Materials and Methods
Nine Dentaurum Grid Strengthener (0.4mm
stainless steel, gold plated with perforations (Ø
2.5mm, Article No. 318-104-00, Dentaurum GmbH
&Co, KG, Ispringen, Germany) were purchased
and pressed in a hydraulic laboratory press (Carver
Lab press, Wabash, IN, USA) at 9800 N for 2 days
until flat. Using wax plates of different thicknesses
(Truwax, USA) (0.5 mm for bottom, 1.6 mm for top)
“sandwiches” of 2.5 mm thickness were produced,
positioning the metal plate at 0.5 mm from the
bottom side.
At 3 peripheral sites the wax was removed, so the
samples could be repositioned into the flask after
boiling out of the wax. Using flasks for the injection
technique (IvoBase, Ivoclar Vivadent, Schaan,
Liechtenstein) and the appropriate spruing (Fig.
2) and yellow microstone, type III (Whip Mix,
Louisville, KY, USA) a two part form was created,
which allowed a defined 3D reposition of the grid
before injecting the resin.
For control purposes wax plates 2.5 mm thick were
embedded as described above.
Three plates per group were conditioned the
following way before being repositioned into the
flask:
Group 1: No grid strengthener (control).
Group 2: No surface treatment of grid strengthener
Group 3: Monobond Plus (Ivoclar Vivadent)16 was
applied to grid strengthener with paint brush, let
react for 30 s and then the solvent was evaporated
for 10 s by blowing with an air syringe.
Group 4: Grid strengthener was grit blasted with
Al2O3 100 µm at 0.25 MPa for 10 s, then Monobond
Plus was applied as described above.
The next step was to injection mold the Ivobase
hybrid material (Ivoclar Vivadent) using the Ivomat
Polymerization unit with program #1 for 45 minutes.
After removing from the flasks the resin/metal
plates and the control plates were sectioned with
102
a diamond saw (IsoMet 1000 Precision Cutter,
Buehler, Lake Bludd, IL USA) under water cooling
into approximately 10mm x 75mm x 2.5 mm
beams.
For testing purposes the thickness and width
of every beam was measured individually using
a caliper (Model 06-664-16, Fisher Scientific,
Pittsburgh, PA, USA). The yield was 4 beams /plate
which produced 12 beams per group. The beams
were stored in water for 7 days prior to perform the
mechanical testing.
The beams were subjected to a 3-point bending
test according to ISO standard 1567 at 5 mm/min.
The fracture strength was calculated using the
following formula:
The Flexural Modulus was calculated as well
according to:
- σ is the flexural strength
- F is the load at fracture or peak load in strength
(specimen embedded with mesh did not break)
- L is the span between the two supports
- w is the width of the specimen
- h is the height (or thickness ) of the specimen
- d is the deflection of the specimen due to the load F
Data were analyzed with an ANOVA (SAS, Cary,
NC, USA) and multiple pairwise comparisons were
performed with the Tukey’s HSD test.
Results
Table 1, Fig. 3 and Fig. 4 show that incorporation
of grid strengthener improves both the flexural
strength and modulus of the denture base resin.
ANOVA shows that there is statistically significant
STOMA.EDUJ (2015) 2 (2)