Development of new hybrid indirect composite resin for crown-TWiNY (Part1) Fundamental properties /Kato T, Hoshikawa T (Yamamoto Precious Metal Co., Ltd.): The purpose of this investigation was to measure and compare thefundamental properties (flexural strength, hardness, polymerization shrinkage, water absorption, solubility, change in transmittance underpolymerization, radiopacity) of the new trial and the four commercially available hybrid resins. The fundamental properties of the trial andthe commercial resins have sufficiently satisfied the values stipulated in ISO 10477. In the trial resin, the change of transmittance wasvery small and the mechanical strength was excellent.

[Abstract]
Among many other demands they face, indirectcomposite resins are required to exhibit sufficientmechanical strength for use on molars, achieve
reproduction of natural tooth aesthetics, and support
x-ray radiopacity.

Table: Evaluation Results of Fundamental Physical Properties

In this investigation, newly-developed aggregatedinorganic filler with an adjusted refractive index wassynthesized using the sol-gel process to develop
highly-functional indirect composite resin, TWiNY1).
This investigation measures and reports the basic
physical properties of the trial resin in comparison withthe four main commercially available indirect composite
resins. The physical properties measured were: flexuralstrength, hardness, polymerization shrinkage, water
absorption, solubility, change in transmittance underpolymerization, and radiopacity.

Test subject

AB

C

D

Inorganic content bypercentage [wt%]

76.5

88.6

70.8

67.8

78.5

Flexural strength
[MPa]

239

218

194

165

186

Hardness [Hv0.2]

107

163

85

71117

Polymerization
shrinkage [vol%]

2.5

1.5

2.9

3.0

2.5

Water absorption[µg/mm3]

14.3

10.7

24.2

25.3

11.0

Solubility [µg/mm3]

0.1

0.2

0.3

0.5

0.3

Transmittance after
polymerization [%]

65.1

75.1

70.0

68.6

61.5

Difference intransmittance values
before and after
polymerization [%]

+2.0

+21.4

+18.0

–2.0+5.3

Inorganic content by percentage showed values from89 wt% (A) to 68 wt% (C); the values achieved
demonstrated close correspondence with hardness andpolymerization shrinkage.

[Materials and Methods]
The experiment was conducted on a newly-developed
DA3 material (Yamamoto Precious Metal Co., Ltd;
hereinafter the “test subject” ) and four commerciallyavailable DA3 materials, A, B, C, and D.

The ISO 10477 standard for hard resins stipulates
flexural strength at 50Mpa and over, hardness at
18HV0.2 and over, water absorption at 32µg/mm3 orless, and solubility at 5µg/mm 3 or less. As the Table
demonstrates, the flexural strength of indirectcomposite resins (168~238Mpa) exceeds the ISO
standard by over three times, while hardness (71~163
HV0.2) does so by a factor of over four. All indirectcomposite resins tested comfortably exceeded
stipulated values for water absorption and solubility,also.

1) Physical properties: Flexural strength, hardness,water absorption and solubility were measured inaccordance with the ISO 10477 standard.
2) Polymerization shrinkage: Density measurement wasperformed before and after polymerization curing, andthe degree of polymerization shrinkage was thencalculated.
3) Change in transmittance under polymerization:
Change in transmittance under polymerization wasmeasured in resin (Trans shade) before and after photopolymerization, using a turbidity meter (Haze MeterHDH2000).

With reference to the four commercially-available
indirect composite resins only, the results recorded in
the Table also indicate that their flexural strength andhardness depend on their level of filler content bypercentage. On the other hand, while the filler content
by percentage of the test subject ranked third after Aand D, its flexural strength displayed the highest value
recorded; the test subject utilizes inorganic coagulant
filler, and it is thought that the flexural strength of theresin which forms its complex is influenced by theshape of the filler particles, apart from its filler content
by percentage.

[Results and Discussion]
The inorganic content by percentage and fundamental
physical properties obtained under firing at 650˚C aregiven in Table.

01

70

After Polymerization

Before Polymerization

After Polymerization

10

Before Polymerization

20

Before Polymerization
After Polymerization30

After Polymerization

40

Before Polymerization50

After Polymerization

60
Before Polymerization

Total Light Transmittance [%] 0.8mm[Reference]
1) Hoshikawa T, Miyazaki A, Kato T, Anraku T,
Yamamoto S: Japanese Patent Number: 4502673

800Test SubjectAB

CDFigure: The influence of resin polymerization on changes intransmittance under total light transmittanceIn terms of its use as a material in the restoration of thedental crown, aesthetics have emerged as a major issue
in addition to the unavoidable question of its durability
under conditions of mastication and digestion. The
Figure shows the change in total light transmittance
before and after polymerization of all the resins tested.
The transmittance levels after polymerization (dentalprosthesis retention) were high at 61-75%, with exterior
appearance pitched at an aesthetic level intended toreproduce the appearance of natural tooth enamel. Also,
the difference in transmittance (here essentiallyequivalent to color tone) after polymerization between
the test subject and C was minor, attesting to astraightforward approach toward color adjustment in
the manufacturing process for these prosthetics. In
other words, the degree of transmittance wasdetermined by the balance between the respective
refractive indexes of the filler of which the resin iscomposed and the matrix (before and afterpolymerization). It is considered that the refractive
indexes of both the test subject and C display values
exactly between those of the filler and matrix before andafter polymerization. Therefore, we have establishedthat radiopacity depends on the refractive index of thematrix (polymer).
From the results obtained above, it is clearly establishedthat the fundamental properties of the test subject,along with those of the four commercially-available
resins tested, comfortably meet the stipulations required
under the relevant ISO standard. The newly developed
resin displayed minor variation in degree oftransmittance (color tone) before and after
polymerization, and is confirmed to be a indirectcomposite resin exhibiting excellent mechanicalstrength.

02