In vitro comparison of the efficacy of two fractured implant-prosthesis screw extraction methods: Conventional versus mechanical

Abstract

Statement of problem: Implant-supported prostheses may be subject to esthetic, biological, or mechanical complications. Protocols for dealing with these mechanical problems are sparse.

Purpose: The purpose of this in vitro study was to compare the efficacy of a mechanical system for extracting fractured implant-prosthesis screws with the conventional method.

Material and methods: A total of 60 screws were divided into 2 groups according to their morphology (flat screws with a smooth shaft and threaded apical area and screws with a completely threaded body) and subjected to fatiguing and static load testing until fracture. The specimens were assigned to 3 operators with varying levels of clinical experience (high, medium, low) in extracting fractured screws by using the conventional method (explorer and ultrasound device) and a mechanical method (extractor kit). The extraction event (whether the screw fragment was extracted or not within 10 minutes) was recorded, and the time taken to perform the extraction was measured for each method in relation to screw type, operator experience, and damage to the threads. The influence of screw morphology, extraction method, operator experience, and fracture type on the time needed to extract a screw fragment was assessed with the Mann-Whitney and Kruskal-Wallis tests. Thread damage was compared by using the Fisher's exact test and the Kruskal-Wallis test (α=.05).

Results: The mechanical method was more effective for screw extraction than the conventional method (P=.032). Screw morphology also had a significant influence on extraction, whereby the screw design with apical thread took less time to extract (P=.022). Coronal fractures had a higher probability of extraction than apical fractures (P=.05).

Conclusions: Mechanical extraction is more effective for extracting fractured implant-prosthetic screws, showing a higher probability of extraction than the conventional method. Prosthetic fixing screws with a smooth shaft and threaded apical area are the easiest to extract.