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The quality of working impressions for the fabrication of fixed prosthodontics prostheses (crown and bridgework)

Objective: The study was carried out to assess the quality of working impressions sent to commercial laboratories for fabrication of fixed prostheses. Materials and Methods: Impressions (n: 200) received by four dental laboratories were evaluated by two calibrated examiners. The type of work, tray designs, impression materials and techniques were recorded for each impression. Quality data on crucial details of the tooth preparations, voids at tooth preparations, tears along the finished margin line and flow of materials were documented and each criterion scored either with 2 (Good), 1 (Acceptable) or 0 (Unacceptable). The Chi-square test for independence was done for relationship analysis of the impression defects and different type of impression materials. Results: From 200 examined impressions, 53.9% were for crown works, 35.9% bridge works, 1.4% posts and cores and 8.8% for other types of work. The impression materials used were polyether (39.5%) and polyvinyl-siloxane (60.5%). The two main types of trays were metal stock (48.5%) and disposable plastic (37.5%). Impression techniques were monophase one-step technique (50.0%), putty wash two-steps technique (23.5%), putty wash one-step technique (15.5%) and dual phase one-step technique (11.0%). Overall, 64.5% of the impressions sent had unacceptable quality (0 score recorded for at least one criteria). The proportions of impression defects were significant to the type of impression materials (P < 0.05). Conclusion: The percentage of unacceptable impressions (64.5%) sent to the laboratories is a serious concern, as it contributes to the inaccuracy of the crown and bridgeworks provided to patients.