Development of new hybrid indirect composite resin for crown-TWiNY (Part 5) Durability / Kato T, Yamada B,Nagai M, Yamamoto S (Yamamoto Precious Metal Co., Ltd.): This study deals with the impact resistance and toothbrush abrasion
properties of a newly developed indirect composite resin (TWiNY) and of four commercially available indirect composite resins, in order toevaluate their durability. TWiNY showed the highest impact resistance among the resins examined and the equivalent abrasion property.
These results indicate that TWiNY, which exhibits higher or equivalent durability in comparison to the commercially available indirectcomposite resins, is suitable for use on the molar.

[Abstract]
Among the many demands indirect composite resins
face, achieving sufficient durability to withstandpotential problems (such as abrasion and chipping)
within the oral cavity is particularly vital. Chipping is
considered to be caused by factors such as mastication
impact and impact forces from opposing teeth acting on
the molar inlay and jacket crown1). Toothbrush abrasion
and tooth attrition from opposing teeth have also been
identified as contributory factors2). In this investigation,
the newly developed indirect composite trial resin3) iscompared with four major commercially available
indirect composite resins. Through repeated impact andabrasion tests, the impact and abrasion resistance ofeach of the resins is ascertained and compared.

[Results and Discussion]
Figure 1 shows the number of times the impact force
was applied until cracks appeared on the test
specimen. The order in which cracks appeared on theresins under impact was A ＜ D ＜ C ＜ B ＜ TW.
TW therefore displayed the most outstanding
durability among the test samples compared in thisinvestigation. It is therefore apparent that TW is theleast likely of the resins tested to display crack
formation under impact, and is the resin most suitablefor use in contexts subject to repetitive compressive
load, such as the molar. It is thought that the impact
resistance values of TW and the other commerciallyavailable tested resins is influenced by their respective
flexural strengths and fracture energy limits, whichhave already been compared and analyzed.
Impact Resistance (No. of impacts before cracking)[Materials and Methods]
1. Test specimens
In this investigation, the newly developed indirectcomposite resin DA3 (TWiNY (TW)) and fourcommercially available indirect composite resins DA3(A, B, C and D) were used. Samples of each resin wereloaded into a metal mold 15 mm in diameter and 1 mm
thick. Each sample underwent polymerization curingaccording to the manufacturer’ s stipulated instructions.
The sample surfaces were polished using water-resistantsandpaper (#2000) and then polished to a mirror finish
using diamond paste, achieving a disk-shaped test
specimen.

2000
1600
1200
800
4000TWA

BCDFigure 1: Number of Times Repetitive Compressive Load wasApplied until Crack Formation

2. Measurement Method
For repeated impact tests, a collision abrasion testing
apparatus (K655, manufactured by Tokyo Giken Co.,
Ltd.) was used. A stainless steel rod (diameter 4 mm)with a hemispherical tip was repeatedly dropped onto
each test specimen affixed to the metal mold, applying
an impact force of 6kg at the hemispherical tip to thetest specimen. The number of times the impact force
was applied until cracks appeared on the test specimen
was confirmed visually. The toothbrush abrasion test
was carried out in conformance with the ISO 14569-1
standard; surface abrasion was measured in Ra, using asurface abrasion measurement apparatus (SV-600,manufactured by Mitutoyo). Surface abrasion wasapplied at a loading weight of 2.0 N for a set number ofbrush strokes.

0.140

D

0.120

Ra (µm)

0.100

B

0.080
0.060

TWCA

0.040
0.020
0.000

05000

10000 15000 20000 30000

Toothbrush abrasion cycles

Figure 2: Surface Roughness by Toothbrush Abrasion Cycles

01Figure 2 shows surface roughness by toothbrushabrasion cycles. No differences are apparent up to
10,000 cycles, but after 20,000 cycles, surface roughness
was apparent in the order A ＜ C ＜ TW ＜ B ＜ D.
The abrasion resistance displayed by TW was similar tothat of A and C, and surface roughness increased only
moderately as the number of abrasion cycles wasincreased, thus demonstrating adequate anti-abrasion
characteristics. Differences by resin in toothbrushabrasion are thought to be influenced by differences in
the resin hardness and filler particle diameter.
[Conclusion]
The newly developed indirect composite resin(TWiNY) displayed high impact resistance ascompared with the other four commercially availableproducts, while the comparison results for toothbrushabrasion for TWiNY were in line with most of thecommercially available products. This demonstrates thatTWiNY displays durability equivalent to or higher thanthat of the commercially available products, and that it
is suitable for use on the molar.
[Reference]
1) A Hthag et al.: Journal of the Japanese Society for
Dental Materials and Devices, 14(25), 90-91, 1995．
2) Kawahara et al.: Journal of the Japanese Society for
Dental Materials and Devices, 6(6), 88-794, 1987．
3) Hoshikawa , Miyazaki, Kato, Anraku, Yamamoto:Japanese Patent Number: 4502673

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