On Clinical and Mechanical Aspects in Implant Supported Screw Retained Multi-unit CAD-CAM Metal Framework

Abstract: Conventionally casted frameworks have been considered the preferredsolutions for complete and partial restorations since the beginningof implantology. However, following technological development, thecomputer aided design/computer aided manufacturing (CAD-CAM)with milling the frameworks has been introduced as an alternativeoption with the potential of minimising inaccuracies, reducing theoperator dependence and offering a homogeneous structure with highmechanical properties. The CAD-CAM multi-unit reconstructionvaries with fixation type, implant framework connection, andprostheses material. However, the materials developed for theuse of CAD-CAM, may have different technical and biologicalcomplications with time.The present thesis aims to provide insights into the risk ofcomplications in screw-retained multi-unit frameworks manufacturedusing the CAD-CAM technique. An in vitro test (Study I) was performed to assess the effectsof misfit at implant-level FPDs and supporting bone levels on thegeneration of implant cracks. Three clinical studies were conducted:in Study II, partially edentulous patients were rehabilitated with eitheran abutment or implant level multi-unit Cobalt-Chromium metalceramicframework; in Study III, patients, edentulous in the maxilla,were treated with either four or six implants and rehabilitated witha fixed titanium metal-acrylic framework; in Study IV edentulouspatients were treated with removable overdentures retained bytitanium milled bars. In Study III and IV, Oral Health Related Qualityof Life was evaluated.The marginal bone level change was clinically not significantregardless of fixation type (Study II), retention (Study III-IV), andmaterial used (Study II-III-IV). No framework complications wereregistered. Patients reported a high level of satisfaction after thetreatment (Study III-IV).Based on the studies included in this thesis, the followingconclusions can be made: (i) the risk of implant cracks in screwretainedImplant Level (IL) Fixed Partial Denture (FPD) is low, evenwith a misfit; (ii) according to the 1-year data presented in Study II,abutment level (AL) retention is recommended for FPDs; (iii) the costeffectivefor a maxillary Fixed Complete Denture (FCD) supported byfour implants can be considered predictable and comparable to siximplants; (iv) implant-supported FCDs and Implant supported Over-Dentures (IOD) are associated with high rates of patient satisfaction,related to aesthetics and mastication function mainly resulting fromthe high stability of the prostheses; (v) the technical and biologicalcomplications reported in FPDs, FCDs and IODs were limited.However, a considerable percentage of prosthetic fractures andchippings were reported for FCDs at 1-year and 3-year follow-ups.Clinicians have to be aware that additional visits may be required formaintaining the prostheses.