| Gingival retraction technique is widely used in prosthetics to reduce the damages of periodontal soft tissue during the preparation of abutment and have an accurate impression that record the location of the finish line of the prepared tooth and a portion of apical uncut tooth structure, which is important for restoration having a well-adapt margin to reach the long-term success. However, gingival retraction procedure itself may cause some damages to periodontal tissue. In this study, we attempt to evaluate the periodontal tissue damages caused by three most commonly used gingival retraction techniques to choose the one with minimal injury.This study can be divided into two parts:(1) Clinical research: to evaluate the change of quantity of gingival crevicular fluid(GCF), two kinds of enzyme and two cytokines before and after gingival retraction in human. (2) Animal research: to observe the histopathological changes of periodontal tissue after gingival retraction in dogs.Methods:(1) 10 students with healthy gingival conditions were selected and three premolars of each subject were treated with pure cord (Ultrapak), cord with HCl- epinephrine (Ultrapak) and a paste-like material (Expasyl) respectively on the buccal aspects. The quantity of GCF fluid and the active of aspartate aminotrans- ferase (AST) and alkaline phosphatase (ALP) in GCF were assessed at baseline, and 30 min, 1 d, 3 d, 7 d, 14 d and 28 d after application.(2) To evaluate the amount of interleukin-1β(IL-1β) and tumor necrosis factor-α(TNF-α) in GCF by enzyme-linked immunosorbent test (ELISA) at baseline, and 30 min, 1 d, 3 d, 7 d, 14 d and 28 d after application.(3) 3 adult dogs with healthy gingival conditions were selected, and 18 teeth of each subject were treated with pure cord, cord with HCl-epinephrine and Expasyl at 30 min, 1 d, 3 d, 7 d, 14 d and 28 d on the buccal aspects. Then killed the animals and evaluated histologically the effect of each kind of retraction on gingival tissue.Result:(1) The quantity of GCF and the active of GCF-AST and GCF-ALP increas- ed after all the retractions (P<0.05), then decreased and finally reached the baseline (P>0.05). But all the parameters were not statistically significant among the 3 groups if consider time as a whole factor (P>0.05).(2) The quantity of IL-1βand TNF-αin GCF increased immediately after all kinds of gingival retraction procedures and reached their peak at 1 d, and then decreased slowly. All the parameters were statistically significant among the 3 groups if consider time as a whole factor (P<0.05). The quantity of TNF-αdropped to baseline in all the groups (P>0.05). The amount of IL-1βof pure cord declined to baseline at 28 d (P>0.05) whereas the other two groups were still higher than baseline (P<0.05).(3) All the gingival retraction methods induced some degree of destruction of sulcular epithelium and part of junctional epithelium, including necrosis and hydropic degeneration of epithelium cells and looseness of cell junctions. The cord with HCl-epinephrine also caused the presence of a few inflammatory cells in connective tissue below sulcular epithelium and Expasyl caused more inflamma- tory cells in this area.Conclusion:(1) All the gingival retraction procedures could induce some degree destru- ction to periodontal tissues, which could repaired in a period of time.(2) The destruction resulted from cord was acute and most serious but could recover in a short time.(3) Expasyl induced milder mechanical injuries than cord but more serious inflammation in the connective tissue which needed more time to recover.
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