Relationship between thickness and strength of resin base on top of rootcaps-Examination of using high impact resistance denture base resinK.Sakurai, K.Ohtani, E.Nagai, S.Nakabayashi, A.Tateno,T.Ishigami
Department of Partial Denture Prosthodontics, Nihon University School of Dentistry

Abstract
Fracture of overdenture was greatly involved in thickness of resin base on top of root caps. However,it was often difficult to have thickness on top of root caps. Therefore, it was evaluate denture basestrength influence of thickness of resin base on top of root caps. It was compare in two kinds ofdenture base resin which were high impact resistance and conventional it.
Specimens made of heat curing resin which were two kinds of denture base resin. Then each of thedenture base resin was institute its thickness to 2.5, 3.0 and 3.5 mm. The bending strength of three andfour point bending of the specimens were measured at a crosshead speed of 5 mm/min in a universal
testing machine.
There were significant difference in thickness of specimens and in two kinds of resin. This result
indicated that high impact resistance denture base resin may be useful as a material used for theoverdenture.

Introduction
Fracture of overdenture was greatly involved in thickness of resin base on top of root caps. However, it
was often difficult to have the thickness on top of root caps. Therefore, it was evaluate denture basestrength influence of thickness of resin base on top of root caps.it was compare in two kinds of denture baseresin which are high impact resistance and conventional denture base resin.

Objective
Experiments were performed using two types of bending test (modified 3-point bending test and modified
4-point bending test) to simplified overdenture models.

Materials and Methods
1. Materials
a. Coping models
Fig1 showed the coping model made of the stainless steel (TOKYO GIKEN, Inc). The coping
model which shape was trapezoidal. Trapezoidal was 6.0mm in the diameter of bottom, 4.5mm indiameter of surface, and 2.0mm in height.

4.5 mm
2.0 mm

6.0 mm	  	  	  	  	  	  	  	  	  	  	  	  	  	  Trapezoidal shape coping
Fig1
b. Bending specimens
Heat-curing resin were high impact resistance (PRO IMPACT, GC) and conventional (ACRON,GC). Rectangular solid bending specimens were fabricated by heat-curing resin. The shape ofspecimens was 64.0mm in width, 10.0mm in length, and 2.5, 3.0 and 3.5mm in thickness (Fig 2,3).
1)

Polymerized resin blocks were shaped by using semi-automatic polishing machine (Doctor Lap

ML 180, NARUTO) and silicon carbide paper.
According the number of concave portion, two specimen groups were fabricated and named TypeA and B. Two specimens were randomly assigned to each groups.
Type A had one concave part in center. Type B had two concave surfaces in the position of
9.5mm and 39.5mm from the left end of the major axis

4.5mmSp e cim en p ro to type12.0mm66.0mmEm bedd in g
fl askp lasterp araffi n w ax
fl ask
Se tti ng

T yp e A

T yp e B

10 .5 mm

30 .0

P o lym eri zatio n and
M od i ng

10 .0 mm

10 .0 mm
64 .0 mm

64 .0mm
2.5 mm

0.5 mm

3.0 mm

1.03.5 mm

1.5 mm

2.5 mm

0.5 mm

3.0 mm1.0

3.5 mmmm
1.5 mm

9.5 mm30 .064 .0 mm

Fig264 .0 mm

Fig3

2. MethodsEach specimen used for the experiments was soaked in the water of 37℃ for 48 hours. The bending
test utilized a universal testing machine (EZ-test, SHIMADZU). The loading plunger according to JIS
T6501 was used for the experiments. 2) The experiments were conducted on two kinds (modified
three-point bending test and modified four-point bending test). The modified three-point bending test(3PB) was assumed for experiment 1, and the modified four-point bending test (4PB) was assumed toexperiment 2.
a. Modified three-point bending test (3PB)Type A was loading until fracture from both sides on a coping model. (Fig4)Coping model attached tounder part in EZ-test. Type A was on top of trapezoidal model. Loading plunger attached the crossing
head part in EZ-test by the distance 30.0mm between fulcrums. Bending test was done a crossheadspeed of 5.0 mm/min. Bending strength of the specimen measured in the maximum loading point andenergy of rupture of the specimen measured in the amount of energy until fracture. And it wascalculated the average value.
Acquire data did statistical analysis by critical region 5%. It was used to one-way ANOVA andTukey’s Test for statistical analysis.
b.

Modified four-point bending test (4PB)

Type B was loaded until fracture on same kind of two coping models. (Fig5)On the right coping
model it loaded from both sides. On the left coping model it loaded from one side only. It wasassuming unilateral free-end in this state. The bending test did at the distance between fulcrums 30.0mm and a crosshead speed of 5.0 mm/min. The statistical analysis was similar experiment 1.

5.0 mm/min

5.0 mm/min
30.0 mm30.0 mm	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 30.0 mmFig5	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 Fig4Results3)

Fig6 and Fig7 showed the result of experiment1. Bending strength and Energy of rupture increased

intentionally in both models of ACRON and PRO IMPACT whenever the thickness of the specimen
increased. As a result of Tukey’s test, PRO IMPACT indicated the small value significantly more thanACRON in each thickness of 2.5 millimeters, 3 millimeters and 3.5 millimeters for bending strength. PROIMPACT indicated the big value significantly more than ACRON in each thickness of 2.5 millimeters, 3millimeters and 3.5 millimeters for energy of rupture.

*

300200*ACRON

100PRO IMPACT
n=502.5

33.5*: p<0.05

Thickness of resin on the coping (mm)Fig6

Energy of rupture (J)	 

Bending Strength (N)	 

*

400

*

32.5

*

21.5
10.5

ACRON

*PRO IMPACT
n=502.5

33.5*: p<0.05

Thickness of resin on the coping (mm)	 

Fig7

Fig7 and Fig8 showed the result of experiment 2. It’s not fractured in 3.5mm (ACRON and PROIMPACT) in the loading areas of EZ-test. Therefore, the value was not able to calculate. Bending strength
increased intentionally in both models of ACRON and PRO IMPACT whenever the thickness of thespecimen increased. The significant difference wasn't admitted by bending strength of PRO IMPACT andACRON in 2.5 millimeters and 3 millimeters and each thickness for bending strength. As a result of
Tukey’s test, PRO IMPACT indicated the big value significantly more than ACRON in each thickness of
2.5 millimeters, 3 millimeters for energy of rupture. Energy of rupture in ACRON increased intentionallywhenever the thickness of the specimen increased, but PRO IMPACT significant difference was notobserved by the thickness.

400300200ACRON100PRO IMPACT
n=502.5

3*: p<0.05

Energy of rupture (J)Bending Strength (N)	 

500

1.4
1.2
1
0.8
0.6
0.4
0.20*

*

ACRONPRO IMPACT
n=52.5Thickness of resin on the coping (mm)

3*: p<0.05

Thickness of resin on the coping (mm)	 

Fig6

Fig7Discussion
Bending strength was significantly smaller PRO IMPACT than ACRON for the 3PB, there was no
significant difference for the ACRON and PRO IMPACT for the 4PB. For the 3PB, PRO IMPACT had thelargest elastic modulus in denture base resin, so bending strength is smaller.

Conclusion
Bending strength increased intentionally in both models of ACRON and PRO IMPACT whenever thethickness of the specimen increased. Bending strength was significantly smaller PRO IMPACT than
ACRON for the 3PB, there was no significant difference for the ACRON and PRO IMPACT for the 4PB.
When energy of rupture compared ACRON with PRO IMPACT, the one of PRO IMPACT was big
intentionally. Therefore, when compared at the same thickness, PRO IMPACT was suggested to be adifficult material fracture.

References
1. E. Kishimoto, K. Ogata, K. kawahara: The Effect of the Overdenture Abutment Teeth onToothbrushing : Evaluation with a Simulator, J Dent Hlth, 47, 132-138, 1997.
2. JIS T6501: Acrylic denture base resins, 2012.

3. T.Kanazawa, Y.Umekawa, T.Ishii et al: Denture base strength influence of its thickness surrounding
magnetic assembly –Examination by the model experiments- ,2015