Abstract: Objective： To investigate the changes of collagen secondary structure in collagen fibers of human periodontal ligament(PDL) treated with collagenase I by Raman spectroscopy. Methods: The human premolars were divided into three 2 mm slices from the neck to the apex; experimental samples were selected from the PDL in the middle of the root. The mesial and distal samples of the same tooth were divided into the control group and the enzyme treatment group. Samples in the treatment group were soaked in 10 mg/ml type I collagenase solution for 2 hours at room temperature. The samples in the two groups were detected by Raman spectroscopy, and the Raman spectra were obtained and the peak value was analyzed. Results: Raman spectra of human PDL showed characteristic peaks in amide I, amide III, CH2, tyrosine, and phenylalanine. The main chain conformation of the secondary structure of collagen was mainly characterized by the amide I band (1600-1700 cm-1) and the amide III band (1200-1350 cm-1). Furthermore, the characteristic peak deviated after collagenase treatment. Comparatively, in the untreated group, the percentages of the secondary structure of collagen in the amide III band were random curl 45%, α - helix 25%, β - fold 22%, and β - fold 8%. After collagenase treatment, the contents of α - helix and β - fold decreased, while the contents of random coil and β - fold increased. Conclusion: Collagenase type I can degrade the collagen of the PDL and change the secondary structure of the protein, which may be related to the decrease of the biomechanical properties of PDL.

Key words: Collagen, Periodontal ligament, Collagenase type I, Raman spectroscopy