Catadioptric stereo-vision system using a spherical mirror

Abstract In the computer vision field, the reconstruction of target surfaces is usually achieved by using 3D optical scanners assembled integrating digital cameras and light emitters. However, these solutions are limited by the low field of view, which requires multiple acquisition from different views to reconstruct complex free-form geometries. The combination of mirrors and lenses (catadioptric systems) can be adopted to overcome this issue. In this work, a stereo catadioptric optical scanner has been developed by assembling two digital cameras, a spherical mirror and a multimedia white light projector. The adopted configuration defines a non-single viewpoint system, thus a non-central catadioptric camera model has been developed. An analytical solution to compute the projection of a scene point onto the image plane (forward projection) and vice-versa (backward projection) is presented. The proposed optical setup allows omnidirectional stereo vision thus allowing the reconstruction of target surfaces with a single acquisition. Preliminary results, obtained measuring a hollow specimen, demonstrated the effectiveness of the described approach

La chirurgia guidata di impianti dentali mediante tecniche CAD e sistemi di visione 3D

Il posizionamento di impianti dentali tramite operazioni chirurgiche all’interno dell’osso della mascella o della mandibola può essere pianificato sulla base di dati provenienti da CT o MRI, che consentono una modellazione 3D dell’anatomia dell’osso del paziente. Ciò consente una riduzione delle difficoltà che normalmente incontra il chirurgo durante l’intervento. Il corretto posizionamento degli impianti dentali è un elemento cruciale per ottimizzare gli aspetti funzionali ed estetici. L’utilizzo di guide fisiche rappresenta uno strumento fondamentale per assicurare la loro posizione e angolazione. L’elemento debole della procedura risiede nell’accuratezza con cui vengono trasferite le operazioni pianificate dalle immagini CT in ambiente chirurgico tramite l’utilizzo di guide personalizzate prodotte in stereo-litografia. In questo lavoro si propone una nuova metodologia per il controllo delle possibili cause di perdita di accuratezza durante i vari passi che concorrono al suddetto trasferimento. La metodologia sviluppata è basata sull’integrazione dei dati provenienti da uno scanner ottico a luce strutturata con quelli classici derivanti da scansione CT. L’elevata risoluzione ed accuratezza di tali scanner, consente inoltre di utilizzarli come standard di riferimento per valutare la precisione dei dati derivanti dalla scansione CT e dei processi di fabbricazione delle guide. Si presenta e si discute infine un caso clinico d’applicazione di tale metodologia

Mechanical properties of thermoplastic polymers for aligner manufacturing: In vitro study

The use of metal-free thermoplastic materials plays a key role in the orthodontic digital workflow due to the increasing demand for clear aligner treatments. Three thermoplastic polymers commonly used to fabricate clear aligners, namely Duran\uae, Biolon\uae and Zendura\uae, were investigated to evaluate the effect of thermoforming (T.), storage in artificial saliva (S.A.S.) and their combination on their mechanical properties. Elastic modulus and yield stress of the specimens were characterized. Each material was characterized for each condition through tensile tests (ISO527-1). The results showed that thermoforming does not lead to a significant decrease in yield stress, except for Zendura\uae that showed about a 30% decrease. An increase of the elastic modulus of Duran\uae and Zendura\uae, instead, was observed after thermoforming. The same increase was noticed for the yield stress of Duran\uae. For S.A.S. specimens, the elastic modulus generally decreases compared to supplier condition (A.S.) and simply thermoformed material. A decrease of yield stress, instead, is significant for Zendura\uae. The results demonstrated that the impact of the operating conditions on the mechanical properties can vary according to the specific polymer. To design reliable and effective orthodontic treatments, the materials should be selected after their mechanical properties are characterized in the simulated intraoral environment