J Korean Assoc Oral Maxillofac Surg.  2016 Dec;42(6):352-357. 10.5125/jkaoms.2016.42.6.352.

Stability of the prosthetic screws of three types of craniofacial prostheses retention systems

• Lanata-Flores AG
• Sigua-Rodriguez EA
• Goulart DR
• Bomfim-Azevedo VL
• Olate S
• de Albergaria-Barbosa JR

• KMID: 2364002
• DOI: http://doi.org/10.5125/jkaoms.2016.42.6.352

Abstract

OBJECTIVES
This study aimed to evaluate the stability of prosthetic screws from three types of craniofacial prostheses retention systems (bar-clip, ball/O-ring, and magnet) when submitted to mechanical cycling.
MATERIALS AND METHODS
Twelve models of acrylic resin were used with implants placed 20 mm from each other and separated into three groups: (1) bar-clip (Sistema INP, São Paulo, Brazil), (2) ball/O-ring (Sistema INP), and (3) magnet (Metalmag, São Paulo, Brazil), with four samples in each group. Each sample underwent a mechanical cycling removal and insertion test (f=0.5 Hz) to determine the torque and the detorque values of the retention screws. A servo-hydraulic MTS machine (810-Flextest 40; MTS Systems, Eden Prairie, MN, USA) was used to perform the cycling with 2.5 mm and a displacement of 10 mm/s. The screws of the retention systems received an initial torque of 30 Ncm and the torque values required for loosening the screw values were obtained in three cycles (1,080, 2,160, and 3,240). The screws were retorqued to 30 Ncm before each new cycle.
RESULTS
The sample was composed of 24 screws grouped as follows: bar-clip (n=8), ball/O-ring (n=8), and magnet (n=8). There were significant differences between the groups, with greater detorque values observed in the ball/O-ring group when compared to the bar-clip and magnet groups for the first cycle. However, the detorque value was greater in the bar-clip group for the second cycle.
CONCLUSION
The results of this study indicate that all prosthetic screws will loosen slightly after an initial tightening torque, also the bar-clip retention system demonstrated greater loosening of the screws when compared with ball/O-ring and magnet retention systems.

Keyword

Maxillofacial prosthesis; Prosthesis retention; Prosthesis failure; Torque

MeSH Terms

Grassland
Maxillofacial Prosthesis
Prostheses and Implants*
Prosthesis Failure
Prosthesis Retention
Torque

Figure

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  Fig. 1 Prostheses retention systems. A, B. Bar-clip retention system. C, D. Ball/O-ring retention system. E, F. Magnets retention system.

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  Fig. 2 Detorque reading using a torque meter.

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