Primary Stability of Temporary Screws after Dentary and Orthopedic Forces under Static and Dynamic Load Cycles

Daniel Fernandes,Carlos Elias,Flavia Barbosa,Ligia Ferreira

doi:10.3390/met7030080

Abstract

The objective was to analyze the influence of dentary and orthopedic forces under static and dynamic loads in temporary screw stability. Self-drilling titanium (Ti6Al4V) screws (6 × 1.5 mm) were inserted and removed from pig ribs. Screws were loaded by static loads of 2 N and 5 N for 5 weeks. Dynamic force was applied during 56,000 cycles for simulations of a patient’s opening–closing mouth movements. Dynamic applied loads ranged from 2 to 5 N and from 5 to 7 N under a frequency of 1 Hz. Torque peak values at placement and removal were measured before and after static and dynamic cycles. Similarities in torque peaks (p = 0.3139) were identified at placement (12.54 Ncm) and removal (11.2 Ncm) of screws after a static load of 2 N. Statistical comparisons showed significant stability loss after dynamic cycles under loads of 2 N (64.82% at p = 0.0005) and 5 N (64.63% at p = 0.0026). Limited stability loss occurred in temporary screws submitted to 2 N static forces (p = 0.3139). The detrimental effects of dynamic cycles in temporary screws stability was attested after the simulation of dentary and skeletal forces, being intermittent forces more relevant in the loss of mechanical stability.

Highlights

Temporary screws are multi-purpose devices used in different specialities of medical sciencesand dentistry [1,2,3]
The primary stability of temporary screw is a reference of the mechanical interlocking attained between screw surface and bone architecture
This torsional moment is analyzed in terms of the placement torque, mainly in situations where a non-osseointegration device response is planned for temporary purposes [4,5,15,16,17,18,22,23,24,25]

Summary

Introduction

Temporary screws are multi-purpose devices used in different specialities of medical sciencesand dentistry [1,2,3]. Titanium alloys have excellent corrosion resistance and adequate mechanical properties, for applications as permanent devices in orthopedic spine surgeries or for temporary use in the biomechanics involving the dental movements. The selection of the adequate alloy is based on its application, including a commercially pure titanium choice when osseointegration is desired or another types of titanium alloys when just a temporary implantation period is planned. Because these devices are outlined for a limited period, the primary stability is prioritized instead of the osseointegration potential. Satisfactory mechanical interlocking can be attained if a suitable balance is accomplished among screws design, host architecture and technical factors, which include surgeons expertise.

Methods

Discussion

Conclusion