Comparative Clinical Efficacy Evaluation Of Different Gingival Retraction Methods

In fixed prosthodontics,subgingival soft tissue treatment of the tooth preparation is the key to obtain the accurate oral impression,and the impression quality will ultimately determine the success of the restoration's edge suitability and long-term results of dental restoration.As a treatment method for gingival soft tissue,gingival retraction technique used in oral fixation and repair can not only reduce the damage for the periodontal tissue during the tooth preparation,but more importantly,it has become the core steps to obtain the high-quality accurate impressions that have a clear hard-soft tissue demarcation line so far.Research contents: After history taking and clinical examination of healthy periodontal volunteers who met the inclusion criteria,the first and second maxillary premolars were selected.The volunteers were randomly divided into two groups: cord technique of gingival retraction in one group and cordless technique of gingival retraction for gingival retraction treatment in another group.The clinical comparative study was conducted by comparing effective gingival width before and after gingival retraction,the volume of gingival crevicular fluid,alkaline phosphatase and activity changes of aspartase in the subjects.Objective: To provide important clinical experimental evidence for the popularization and application of cordless gingival retraction by conducting a comparative study in the clinical gingival effect and the periodontal tissue damage with different gingival retraction methods(cord and cordless gingival retraction).Research Methods: A total of 4 premolars of maxillary periodontal tissues of healthy periodontal volunteers were selected.We randomly chose one of cord techniques in Ultrapak E(UL group)or three cordless techniques in Expasyl group(EX group),astringent retraction paste group(AS group)and Racegel group(RA group).(1)Silicone rubber impression before and after gingival retraction,die stone model of conventional infusion and the scanning plaster model with 3shape scanner were made,respectively.The digital model was established with Geomagic Studio 2013 software to measure the horizontal distance from the gingival top surface to facing of the mesial 1/3,center 1/3,and distal 1/3 of the subjects' buccal side of the tooth.The distance difference(?W)was statistically analyzed and the actual clinical gingival retraction effect with different drainage methods was evaluated.(2)The gingival crevicular fluid was extracted in tooth position 10 minutes before gingival retraction and 30 minutes,1 day,3 days,5 days,7 days,14 days,and 28 days after gingival retraction.The change of gingival crevicular fluid volume was analyzed by weighing method.The changes in the level and content of the activity of aspartase and alkaline phosphatase in the gingival crevicular fluid were analyzed by the fully automatic biochemical analyzer,and the effect of different drainage methods on the periodontal tissue was analyzed.Results:(1)Effective gingival sulcus width(W)was obtained for all four types of gingival retraction,among which the UL group had the most significant gingival retraction effect,followed by the AS group,the EX group,and the RA group,and there were significant differences between the groups(F=1114.4,P<0.0001).(2)Four different types of gingival retraction could cause changes in GCF volume and activity levels of GCF-AST and GCF-ALP,all of which first increased and then decreased,and the parameters returned to pre-discharge levels 14 days after gingival retraction.There was a significant difference in GCF volume and GCF-AST activity levels before and after gingival retraction(P<0.05).GCF volume and activity levels of GCF-AST and GCF-ALP reached a peak after 1 day of cord technique of gingival retraction,and the parameters reached a peak 3 days after the cordless technique of gingival retraction in 3 groups.There was a statistical difference in the GCF volume and GCF-AST activity level at different time points after gingival retraction between the cord technique of gingival retraction and the cordless technique of gingival retraction(P<0.05).Conclusion:(1)Radioactive gingival retraction effect can be achieved with the cordless technique of gingival retraction.(2)Four different gingival retraction methods can cause changes in gingival crevicular fluid volume,GCF-AST and GCF-ALP activity levels,reflecting that the four groups of different gingival retraction methods lead to varying degrees of damage to the periodontal tissues.(3)Acute mechanical injury in periodontium was caused by cord technique of gingival retraction,chemical injury with the 3 methods of the cordless technique of gingival retraction.Compared with cord technique of gingival retraction,it has a slighter injury for periodontal tissue with the cordless technique of gingival retraction.(4)The injury in periodontal tissue with 4 different methods of gingival retraction can return to normal condition 14 days after gingival retraction.