Crecimiento compensatorio de la trucha “arco iris” ( Oncorhynchus mykiss )

The biaxial flexural strengths were calculated as follows^^^^’^^^^

S = 3 P ( l + v ) (2.5-5)

where P is the load, v is the Poisson’s ratio, h is the plate thickness, a is the radius of the ring support, R is the radius of the specimen, and b o * = h /3 . The value of Poisson’s ratio specific for RMGICs could not be found in the literature. Since the physico- mechanical characteristics of RMGICs lie between composite resins and conventional GICs(^^^\ it is reasonable to assume that the Poisson's ratio of these materials must lie somewhere between 0.24 for composite resins^^^^) and 0.30 for conventional GICs(^^\ The value of 0.27 which lies between these two values was arbitrarily selected for the RMGICs in this study. Preliminary investigation showed that the difference in the Poisson’s ratio of 0.05 {e.g. from 0.25 to 0.30) resulted in the differences in the calculated bi-axial strength and modulus by 5%.

The bi-axial flexural modulus is obtained from(^^)

(2.5-7)

where Pi and y t are the load and deflection of a point on the straight line portion of the

load-deflection diagram, and = -o.0642 + o.S687^i - - 0J793{^^ + tf.522j(/ -

Statistical analysis of the strengths and moduli among materials, test periods, and storage media were carried out using ANOVA and Tukey’s HSD multiple comparison tests at a 0.05 significance level.

3 .4 .2 R e s u lts (see a\so Appendix C, Tables C. 2 to C. 5)

The results of the statistical analysis are given in Figures 3A-1 to 3.4-4 for each material. The bars connected by horizontal lines are not significantly different at a=0.05.

F o u r-p o in t f le x u re te s t {Figures 3.4-1 and 3.4-2)

The RMGICs in this study showed different patterns of changes in strength. When cured on one side only, Vitremer and Vitrebond had lower strengths at 5 min than at Ih whereas the strengths at these two periods for Fuji II LC and Fuji Lining LC were similar. All specimens, except those prepared from Fuji Lining LC, reached their peak strengths within 7d. After this time the strengths dropped slightly but were then maintained at that level up to 360d. The maximum strength of Fuji Lining LC was between 5 min and Ih after light exposure. Its strength then decreased to minimum values after I80d. The specimens aged in distilled water and artificial saliva had similar strength values; these are in the range 20-28 MPa for the restorative RMGICs and 10- 17 MPa for the liner/bases after Id of storage. The strengths of Vitremer and Fuji II LC were similar whereas Vitrebond was stronger than Fuji Lining LC.

The two-side cured specimens of Vitremer and Vitrebond had greater initial strengths and greater strengths after 90d compared to those cured on top surface only. In contrast, this occurred between Id and 30d for the other two materials.

Figure 3.4-1 Four-point flexural strengths and moduli for Vitremer and Fuji II LC, mean ± sd. 1 = one-side-cured specim ens; 2 = two-side-cured specim ens; DW = distilled w ater; AS = artificial saliva; P = departure from linearity observed from the load-deflection curve. The bars connected by horizontal lines are not significantly different at a = 0 .0 5 .

Flojojral strength (M Pa)

40 --- VITREMER 2IDW) □ l(DW ) 0 1 (AS) 3e0d Tes t penod

Flexjral strength (M Pa)

FUJI II LC 40 □ 1 (DW) 0 1 (AS) ■ 2(D\M 30 20 180d 360d 5 min Id 7d 30d 90d T e s t period

F lexjral m odulus (GPa)

10 _____________________ VITREMER □ 1 (DW) 8 6 4 2 0 Ih Id 7d 30d T e s t period 90d ISOd 380d

Flexural m odulus (GPa)

10 ____________________ 8 □ KDW) 0 1 (AS) ■ 2(D W ) T e s t period 5 min 109

Figure 3.4-2 Four-point flexural strengths and moduli for Vitrebond and Fuji Lining LC, mean ± sd. 1 = one-side-cured specim ens; 2 = two-side-cured specim ens; DW = distilled w ater; AS = artificial saliva; P = departure from linearity observed from the load-deflection curve. The bars connected by horizontal lines are not significantly different at a = 0 .0 5 ._______________________________________

Flexural strength [M Pa]

VITREBOND 40 30 20 - 10 □ 1 (DW) 0 1 (AS) ■ 2(DW) 1 i T 1 i p mtp T e s t period

a

Flejtiral strength (M Pa)

40 ___________________ FUJI LINING LC □ KDW) a H A S ) mZIDW) 30 20 I— i T _ I 10

+

T

F lejcjral m odulus (GPa)

VITREBOND

10

□ 1 (DW) ai (AS) ■ 2(DW)

30d 90d 180d 360d

T e s t period

Flexjral m odulus (GPa)

10 ___________________ 8 FUJI LINING LC □ KDW) 0 1 (AS) h2(DW) 90d IBOd 360d T e s t period 1 1 0

Similarly, the moduli of Vitremer and Vitrebond was initially low. The moduli of these two materials reached their peak at l-7d and was maintained thereafter. The moduli of Fuji II LC and Fuji Lining LC were initially high and remained stable throughout the test periods. After Id of storage, the moduli of Vitremer were similar to those of Fuji II LC (4-5 GPa) and those of Vitrebond were similar to those of Fuji Lining LC (1.5-2 GPa).

B i-axial fle x u re te s t (Figures 3A-3 and 3A-4)

The bi-axial flexural strengths of all RMGICs were significantly greater, by a factor of approximately three, than those obtained from the four-point flexure tests of the same materials. These were in the range 70-80 MPa for the restoratives and 40-50 MPa for the liner/bases after Id of storage. When cured on one side only, all RMGICs, apart from Fuji Lining LC, had the lowest strength at 5 min and reached their maximum strengths between Id and 7d. After 7d, the strengths were maintained at these levels for up to 1 year. The strengths of Fuji Lining LC were similar from 5 min to 360d. The bi­ axial flexural strengths of Vitremer were similar to Fuji II LC and those of Vitrebond were similar to Fuji Lining LC.

The strengths of specimens aged in the two media were similar. Moreover, the methods of cure, i.e. one-side or two-side cure, did not have any effect on the strength values of all materials for all test periods.

Similarly, the moduli of Vitremer and Vitrebond were initially low. The moduli of these two materials reached their peak at Id and were maintained thereafter. The moduli of Fuji II LC and Fuji Lining LC were initially high and remained stable throughout the test periods. After Id of storage, the moduli of Vitremer were similar to Fuji II LC (3 5- 4 GPa) and those of Vitrebond were similar to those of Fuji Lining LC (1-1.8 GPa).

Figure 3.4-3 Bi axial flexural strengths and moduli for Vitremer and Fuji II LC, mean ± sd. 1 = one-side-cured specim ens; 2 = two-side-cured specim ens; DW = distilled w ater; AS = artificial saliva; P = departure from linearity observed from the load-deflection curve. The bars connected by horizontal lines are not s ignificantly different at a = 0 .0 5 .

Fla»jral strength [M Pa)

100 --- VITREMER □ KDW) S l ( A S ) bZIDW) 80 60 40 20 5 min Id Ê i ; 7d 30d T e s t period 90d ISOd 360d

Flexjral strength [M Pa]

100 ---