A COMPARISON OF THE EFFICACY OF TWO TECHNIQUES FOR REMOVING FRACTURED ABUTMENT SCREWS FROM THE INTERNAL WELL OF TWO DIFFERENT DENTAL IMPLANT SYSTEMS: AN IN-VITRO STUDY

Abstract

Abutment screw fracture is a common mechanical complication that can sometimes lead to dental implant failure. A number of clinical reports have been published, presenting a plethora of different techniques for the management of fractured abutment screws. Despite the abundance of case reports, this complication is still managed by trial and error and no consensus on a standardised management protocol exists. Commercially available screw fragment retrieval kits are either universal or designed to fit only one specific implant system. Most of them include specially designed drills which can create a small hole in the centre of the fractured abutment screw. This notch allows a metal extension to engage and rotate the otherwise-flat headed fragment in an anti-clockwise direction and successfully remove the fragment. Such kits also include a series of drill guides which align the drill in an axial plane with the implant in order to reduce the risk of damaging the implant’s internal threads. The main aim of the study herein was to compare the efficacy of a commercially available abutment screw retrieval kit with a homemade kit. It also attempted to examine possible associations between several independent variables such as operator experience and screw fracture morphology and the ability of the two retrieval techniques to successfully remove the fractured abutment screw fragments. Overall, 64 implants from two different dental implant systems were used. 32 were Osseotite® Certain dental implants and the other 32 were Osseotite® micro mini external hex connection dental implants (n=32). A Certain Gold-Tite™ Screw and a standard Gold-Tite™ screw with a square screw head were used for the abutment connection respectively. The abutment screws were partially sectioned with a diamond disc at the level of the first/second coronal thread and in four different ways in order to mechanically weaken them and to develop different patterns of fracture morphology. The screws were then tightened using a calibrated torque driver until they fractured. The torques at which the screws fractured were recorded. A pair of edentulous maxillary and mandibular typodont models were duplicated with an auto-mixed, autopolymerising silicone material and type IV dental stone was poured over the silicon models. In each cast, four cylindrical cavities were prepared. The cavities were prepared in sites 1.6, 1.2, 2.2, 2.6 for the maxilla, and in 4.6, 4.2, 3.2, and 3.6 for the mandible. The implants were embedded within their respective cylindrical cavities and secured using an autopolymerising resin. After embedding the implants, the specimens were distributed between four operators with varying clinical experience. Each operator was to attempt retrieving 16 fragments. A flow chart was used to rotate operator type, implant system, implant location, and retrieval kit used in an even manner. Two different kits were used for the retrieval of the fractured abutments screws. A conventional or homemade kit consisting of standard and modified standard dental instruments and a universal removal kit which included claws attached to a driver handle and guided by a number of internal, external, or conical connection guides and reverse drills. Success was defined as the retrieval of the screw fragments within 15 minutes without irreversibly damaging the implant's threads. To assess integrity of the implant threads an impression coping from the same system was placed, and the threads were considered not to be damaged when the impression coping could be completely seated. 56 fractured screws were successfully retrieved in less than 15 minutes, representing an (87.5%) success rate. Three screws failed to be retrieved in that time frame (15 minutes) and five could not be retrieved at all. Of the three implants that were retrieved in over 15 minutes, only two were retrieved wi