Table 1.

Mean and standard deviation of fracture toughness values (MPa)

Group	Mean ± S.D.	P value	Significance at 5% level
I	0.102 ± 0.002	< 0.05	I Vs II, III, IV
II	0.112 ± 0.002	< 0.05	II Vs I, III, IV
III	0.080 ± 0.001	< 0.05	III Vs I, II, IV
IV	0.064 ± 0.002	< 0.05	IV Vs I, II, III