Impression Accuracy And Precision Of Different Impression Methods Or Impression Materials In Flabby Ridge

Edentulous is a common and frequent disease. Excessive movable tissue or flabby ridge, a special edentulous resulting from excessive resorption of the alveolar ridge followed by fibrous tissue replacement. The common restoration of flabby ridge is complete dentures. During fabricating complete dentures, impression making is the first step to repair edentulous, which is a key step to fabricate complete dentures successfully. Good impressions demand replicating the anatomy morphology of intraoral cavity, thus getting complete dentures with good retention, stability. Flabby ridge area is easily displaced during impression making, which will afterwards affect the retention, stability, and support of complete dentures. Non-surgical methods by optimizing the impression methods or impression materials have been considered to be the favorable choice. According to the custom tray, there are many different impression methods such as normal technique(NT), perforated technique(PT) and window opening technique(WT). In the meanwhile, there are also various impression materials, among which the alginate, light-bodied polyvinylsiloxane and polyether are mostly used in contemporary general dental practice. Despite there are already a lot of literatures concerning improving accuracy of impression by modulating the impression method or impression material appropriately. Which impression method or impression material can decrease the deformation of flabby ridge is still controversial. Consequently, it is worthy to find out a proper impression making method or impression material in flabby ridge condition.With the development of 3D digital scanning technology, it has become the main method to gather the 3D morphology data of oral hard and soft tissue and facial soft tissue. It has been widely used in computer aided design/manufacture(CAD/CAM) system nowadays. The scanning accuracy is high, and the scanning accuracy of a tooth is within 19 um. Theoretically, it can provide the exact 3D morphology data of oral hard and soft tissue, which can be used as a standard model for evaluating the accuracy of impression. The present study was to evaluate the accuracy of impression obtained by different impression methods including CT, BT and WT as well as different impression materials including alginate, light-bodied polyvinylsiloxane and polyether. The CAD/CAM intraoral optical scanner(Sirona CEREC Omnicam, Canada) was applied as a golden standard to compare the differences with flowing analysis of Geomagic software.Purpose. The purpose of the study was to evaluate the impression accuracy and precision of different impression methods as well as different impression materials in flabby ridge.Methods. Five flabby ridge patients during 2014.1 to 2015.3 in our hospital were validated. Different impression methods including normal technique, perforated technique and window opening technique as well as different impression materials including alginate, light-bodied polyvinylsiloxane and polyether were performed to make impressions and then were poured by dental stone. The flabby ridge area was scanned both in patients' mouth and master cast by intraoral optical scanner to get the optical model. The scanning image were exported to STL file format through proprietary conversion. Data handling and computations were made by using 3D inspection and metrology software, regarding standard, mean, and maximum deviations, with subsequent statistical analysis.Results. The edge registration among different impression methods or different impression materials were fitted well with small deviation(-0.05-0.05mm). Impression accuracy and precision of different impression methods in flabby ridge: From general observation of master casts, the morphology of maxilla anterior region in window opening technique was more similar to intraoral than in perforated technique and normal technique. From the analysis of optical model, the fitting precision of window opening technique was better than perforated and normal technique. Statistical significances(SD, Mean+, Mean-) were found between the normal technique and window opening technique, perforated technique(P<0.017). Impression accuracy and precision of different impression materials in flabby ridge: From general observation of master casts, the morphology of flabby in polyether' master casts were more clear than in light-bodied polyvinylsiloxane' and alginate' master cast. From the analysis of optical model, fitting precision of Polyether were better than light-bodied polyvinylsiloxane and alginate. Statistical significances(SD, Mean+, Mean-) were found between alginate and light-bodied polyvinylsiloxane, polyether(P<0.017).Conclusions.1. When make impression of flabby ridge, window opening technique can minimally decrease the deformation of flabby ridge compared with perforated or normal technique.2. Polyether impression material was better in decreasing the deformation of flabby ridge than alginate and light-bodied polyvinylsiloxane.