Emerging Dental Applications of Raman Spectroscopy - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 268

Fig. 11.5. Representative parallel-polarized ( black lines) and cross-polarized ( grey
lines) Raman spectra of ( A) sound and ( B ) carious enamel

ρ 959 = I 959( ⊥ ) /I 959( )

or (11.1)

A 959 = I 959( ) − I 959( ⊥ ) / I 959( ) +2 I 959( ⊥ )

(11.2)

where I 959( ⊥ ) and I 959( ) are the integrated peak intensities of the 959 cm − 1
peak detected with the polarization analyzer oriented perpendicular to ( ⊥ )

and parallel to ( ) the polarization direction of the incident linearly polar-

ized laser light, respectively. Using this approach, the depolarization ratio
is a parameter that can discriminate sound enamel from incipient caries
with the depolarization ratio being higher for carious enamel compared
to sound enamel (Fig. 11.6). In a study comparing the Raman depolar-
ization ratio from sound ( n =47 measurements) and carious ( n =27 mea-
surements) sites from 23 extracted human teeth, the mean depolarization
ratio was statistically significantly different at p< 0 . 001 (Student's t -test)
[48, 49].
The spectral change demonstrated using polarized Raman spectroscopy
indicates that biochemical and structural changes in the enamel occur due
to demineralization. The structural changes could arise from changes in the
orientation or scrambling of the previously ordered enamel rods from acid
dissolution. Furthermore, as caries present with a more porous structure,
there is also increased light scattering within the lesion that scrambles the
polarization state of the Raman-scattered photons leading to increased depo-
larization of the Raman signal in caries. Thus a combination of increased scat-
tering, structural/orientational changes and/or biochemical alterations of the

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