Comparison of the suitability of intra-oral scanning with conventional impression of edentulous maxilla in vivo. A preliminary study

Aim According to recent literature, the accuracy of digital impression can be compared with traditional impressions for most indications. However, little is known about their suitability in digitizing edentulous jaws in view of mobile prosthetic rehabilitation. The aim of this study was to compare in vivo an intra-oral scanner with conventional impression in case of maxillary edentulous jaws. Material and methods Four (1 male, 3 female) subjects who had no previous experience with either conventional or digital impression participated in this study. Digital impression were taken using an intra-oral scanner. After that conventional impressions of maxillary edentulous jaws were taken with an irreversible hydrocolloid impression material. Then all IOSs datasets were loaded in a three-dimensional evaluation software (3DReshaper 2017, Hexagon), where they were superimposed on the model obtained using conventional impression and compared. Results The mean value of difference between the two impression techniques ranged from 219 to 347 μm. The comparison of models obtained with the two techniques showed that the compression given by the impression material on the peripheral areas, such as oral vestibule and soft palate, determined the most important differences recorded. Conclusion Digitizing edentulous jaws with the use of IOS appeared to be feasible in vivo, although peripheral tissue were not effectively reproduced. On the basis of the results of this study, the authors could not recommend the use of IOS for digitization of edentulous jaws in vivo in view of mobile prosthetic rehabilitation, until it will be found a way to give a selective pressure in peripheral areas as occurs during edging of impression tray

Digital workflow in complete dentures: A narrative review

Aim The aim of the present study is to review the literature evaluating the main steps required in complete denture rehabilitation in case of edentulous jaws in the digital workflow. Methods This review was conducted using PubMed and Scopus databases. It focuses on the following clinical and laboratory steps: the impression, the registration of the centric relation, the try-in and the finalization. Results According to the reported data in literature, impression, try-in and finalization are feasible with a complete digital approach. Registration of the centric is possible only combining the digital with the traditional one. Digital impression is accurate, but shows some limitations in the peripheral areas. The printing process, because of accuracy and its cost, can be used for the try-in of the prototype. Milling machine is more accurate than 3D printing and offers a good level of retention and of satisfaction for the patient. Conclusions In relation to optical scanning, there are still some limitations because of the impossibility to perform selective pressure in the areas of the peripheral seal. Fully digital methods to register the centric are not described. More evidence based evidence on qualitative and quantitative results is required to validate digital denture protocols

Effect of storage time on the accuracy of casts made from different irreversible hydrocolloids.

AIM: Several new irreversible hydrocolloid formulations have recently become available with claims of an improved dimensional stability by the manufacturers. The aim of this study was to evaluate the accuracy of casts made from alginate impression materials poured immediately and after specific storage periods. METHODS AND MATERIALS: Five alginates were tested: CA 37 (Cavex); Jeltrate (Dentsply Caulk); Jeltrate Plus (Dentsply Latin America); Hydrogum 5 (Zhermack); and Alginoplast (Heraeus Kulzer). A master model was mounted on a special device and used to obtain the impressions. These impressions were stored at 23 degrees C and 100% relative humidity, then poured with gypsum immediately, and again after 24, 72 and 120 hours. The casts were measured and the data were analyzed by one way analysis of variance (ANOVA) and Tukey test at p<0.05. RESULTS: The dimensional stability of the alginate impressions was both material and time dependent (p0.05). After 72 and 120 hours, only Hydrogum 5 was dimensionally stable (p>0.05). CONCLUSION: The dimensional stability of the alginate impressions is influenced by the selected material and the storage time. CLINICAL SIGNIFICANCE: Alginate impressions should generally be poured immediately. However, some new types of alginate may have the pouring delayed

Influence of polymerization cycle on the flexural strength of four different PMMA-based heat-polymerized denture base RESIN

Purpose: PMMA-based heat-polymerized acrylic resins used in the fabrication of denture bases may be cured in different ways. As the polymerization cycle length affects fabrication costs and time, a fast cycle is more advantageous. However, polymerization cycles may influence mechanical properties. Objective: The purpose of this study was to evaluate the influence of the polymerization cycle on the flexural strength of four types of PMMA-based heat-polymerized resins used as denture base materials. Materials and methods: The ISO Standard 1567:1999 (Dentistry - Denture base material) was followed in specimen preparation and flexural strength testing of four types of PMMA-based heat-curing resins: Characterized Lucitone (Dentsply-DeTrey); Paladon 65 (Heraeus Kulzer); ProBase Hot (Ivoclar-Vivadent); Prothyl Hot (Zhermack). Resin specimens were obtained following different curing cycles: Standard and Slow for Lucitone; Fast, Standard, and Slow for Paladon 65; the five variants defined by the manufacturer for ProBase Hot; the Standard cycle for Prothyl Hot. For each polymerization cycle six specimens (64 ± 1) mm in length, (10 ± 0,2) mm in width, and (3,3 ± 0,2) mm in height, were prepared. For flexural strength measurements each specimen was loaded until failure with a new testing device (Flexural Test Rig), developed following the indications of ISO 1567:1999. The flexural strength was calculated in MPa and the values were compared with ANOVA and Tukey’s test for post-hoc (p = 0.05). Results: The polymerization cycle has no or minimal influence on the flexural strength of the tested resins. Lucitone exhibited relatively low resistance to flexural loads as when compared with the other resins (Group 7: 78,467 ± 5,623 MPa; Group 8: 71,198 ± 3,775 MPa). Conclusion: With regard to flexural strength, a slow curing cycle does not appear to be justified for the either Lucitone or ProBase Hot, whereas slow polymerization may be advisable for Paladon 65 tested resins, whereas the fast curing cycle V3 was the most favourable to achieve the optimal flexural strength for ProBase Hot

Valutazione della resistenza alla fatica di alcuni tipi di perni in fibra mediante esecuzione del test “three-point bending”.

PREMIO PER LA RICERCA IN ITALI