| Objective:. Utilizing three-dimensional model analysis to evaluate the gingival width(GW) and gingival recessin(GR) of free gingival margin(FGM),which are affected by the impressions using alginate, polyether and addition silicone and the gingival retraction by presaturated retraction cord(with 8% epinephrine) and diode laser.Materials and methods: Sixty anterior teeth from ten healthy people were selected randomly as test subjects. An intraoral digital impression were gotten by intraoral optical scanning(CEREC? AC Omnicam) prior to the test as baseline data(control group). Then three different impression materials(alginate, polyether and addition silicone) were used to make three different impressions in mouth. Stone casts were obtained respectively after the impressions and were scanned by CEREC? AC Omnicam for experimental group data. The control group data were superimposed with the experimental group data by Geomagic Qualify 2013 soft to measure and compare the GW and GR. Fifty teeth(included 21 anterior teeth and 29 premolars)were selected randomly from 6 patients who ask for fixed dental restorations. Teeth were allocated to two groups(25 teeth each group) by simple randomization in which diode laser and presaturated retraction cords(with 8% epinephrine) were used for gingival retraction respectively. Intraoral optical impressions were performed before and after(immediately, 1 and 6 week) gingival retraction. The 3D models obtained after gingival retraction were superimposed with the 3D models obtained before gingival retraction by Geomagic Qualify 2013 soft and the GW and GR(immediately,1 and 6 week) of the two gingival retraction methods were compared.Results: Different impression materials can affect differently on the FGM. For the GW, the addition silicone(0.185±0.141mm) is the largest, followed by the polyether(0.126±0.124mm), the alginate(0.076±0.103mm) is minimum(P<0.05). For the GR,the addition silicone(0.283±0.102mm)(P<0.05) is maximum while the alginate (0.199±0.066mm) is similar with the polyether(0.205±0.071mm). Different gingival retraction methods can also affect differently on the FGM. The GW of the diode laser group(0.421±0.095mm) is larger than that of presaturated retraction cord group(0.339±0.084mm)(P<0.05). The GW0(0.283±0.097mm) and GR6(0.125±0.075mm)of diode laser are both smaller than the GW0(0.421±0.095mm) and GR6(0.190±0.082mm)(P<0.05) of presaturated retraction cord respectively. The GR1 of diode laser(0.188±0.066mm) is larger than that of retraction cord(0.118±0.088mm)(P<0.05). The GR1 of diode laser(0.125±0.075mm) is larger than presaturated retraction cord. The GR0 > GR1 > GR6 in diode laser, while GR0 > GR6 > GR1 in presaturated retraction cord(P<0.05).Conclusion: The impression process by using alginate, polyether and addition silicone will change the GW and GR of FGM. The GW of addition silicone is the largest, followed by the polyether, and the alginate is minimum. The GR of addition silicone is larger than polyether and alginate. The GR of the polyether is similar with that of alginate. In clinical practice, dentist can choose the impression material reasonably according to the change of FGM affected by different impression materials.The GW of diode laser and presaturated retraction cord both meet the clinical needs,but the diode laser gingival retraction can keep the GW for a longer time. Both of the two gingival retraction ways will cause permanent gingival recession, and more gingival recession are found when presaturated retraction cord is used. The GR of different ways of gingival retraction should be taken into consideration in clinical practice when subgingival finish line is designed for restoration. |
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