<prompt>  Fiber-optic trans-illumination FM method of cariesdiagnosis is based on the principle of:When Laser beam falls on carious enamel, it gives a bluish hue.A fluorescent dye is taken up by carious dentine which can be viewed easilyThereisadifferent indexoflighttransmissionfor decayed or sound enamel.The conductance of normal and decayed tooth tissue is different. 