Please activate JavaScript!
Please install Adobe Flash Player, click here for download

implants - the journal of oral implantology UK Edition

10 I I case report_ Er:YAG lasers implants1_2012 The abutment screw fracture presents a rare, but quite unpleasant failure and can be a serious prob- lem13,14 , as the fragment remaining inside the implant may prevent the implant from functioning efficiently asananchor.15 Theprimaryreasonforscrewfractureis undetectedscrewloosingwhichcanbeduetobruxism, an unfavourable superstructure, overloading16,17 or malfunction.10,11,18,19 Fractures of the implant abut- ment or of the abutment screw have been observed as a consequence of screw loosening and undetected micro-movements of the abutment under functional loading20 and consequently, it is advised that the repeated loosening of an abutment screw should alert thecliniciantopossiblesignificantcontributingcauses. However, the behavior of the implant/abutment jointcomponentswithrespecttocriticalbendingforce is still unclear.20,21 Studies show that implant abutment failure occurs when lateral forces exceed 370 Newtons for abutment with a joint depth of at least 2.1mm and 530Newtons with a joint depth of at least 5.5mm.7 _Preventive recommendations The number, position, dimension and design of implants, as well as the design of the prosthesis are critical factors to be considered during the treatment planning phase.11,12,13,22,23 To withstand high bending stresses, implants should be as long and as wide as possible, used in adequate numbers, and be positioned such as to allow axial loading.13,20,24,27 Implant compo- nents are known to fracture more frequently in the posterior region and in partially dentate patients com- pared to completely edentulous patients.5,6,9,11,12,19,23,25 Retightening an abutment screw ten minutes af- ter the initial torque applications should be routinely performed, and increasing the torque value for abut- ment screws above 30Newtons can be beneficial for the abutment, implant stability and to decrease the possibility of the screw becoming loose.25 Proper case selection, excellent surgical technique, placing an adequate restoration on the implant, educating the implant patient as to the importance of maintaining meticulous oral hygiene, and evalu- ating the implant both clinically and radio-graphi- cally at frequent recall visits26 ; reinforcing periodic maintenance. A procedure for using dimples inside the abutment screw cylinder above the screw, and filling the holes with elastomeric impression material will prevent the screw-retained prosthesis from loosening.27 • Using the correct fixation screw • Replacing loose screws instead of retightening them • Immediate investigation; looseness of the prosthesis is detected by the clinician or patient.28,29 _Fragment retrieval methodology The methods employed to grasp the broken frag- ments or screw are determined according to the lo- cation of the fracture abutment—above or below the head of the implant. If an abutment screw fractures Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9