Influence of repeated insertion-removal cycles on the force and magnetic flux leakage of magnetic attachments: an in vitro study.
BACKGROUND
Magnetic attachments are widely used in overdentures and maxillofacial prostheses. Because the patient will routinely have to insert and remove a removable prosthesis, the retentive force and magnetic flux leakage of the magnetic attachments after repeated insertion and removal must be evaluated to assess their clinical performance.


OBJECTIVE
The purpose of this in vitro study was to investigate the retentive force and flux leakage of magnetic attachments after repeated insertion and removal.


METHODS
Magfit EX600W magnet-keeper combinations (n=5) were used in this study. After 5000, 10,000, and 20,000 insertion-removal cycles, the retentive force of the magnetic attachments was measured 5 times at a crosshead speed of 5 mm/min with a universal testing machine. Magnetic flux leakage at 3 positions (P1, the upper surface of the magnet; P2, the lower surface of the keeper; and P3, the lateral side of the magnetic attachment set) was evaluated with a gaussmeter. Data were statistically analyzed by 1-way ANOVA (α=.05). The morphology of the abraded surfaces for both the magnet and the keeper was observed with an optical microscope (5×).


RESULTS
The mean retentive force decreased significantly after 5000, 10,000, and 20,000 insertion-removal movements (P<.05). Significant differences of flux leakage were also observed at P1 after 5000 cycles and 10,000 cycles, at P2 after 5000 cycles, and at P3 after 5000, 10,000, and 20,000 insertion-removal cycles (P < .05). However, no significant differences in flux leakage were evident after 20,000 cycles at P1 and 10,000 cycles and 20,000 cycles at P2.


CONCLUSIONS
Repeated insertion and removal influenced the retentive force and magnetic flux leakage of the magnetic attachments. Retentive force decreased significantly after repeated insertion-removal cycles, whereas the variation of magnetic flux leakage depended on refitting cycles and positions of the magnetic attachments.
Postgraduate student, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
Zhichao
Z
Hao
Professor, Department of Prosthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
Yonglie
Y
Chao
Associate Professor, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China. Electronic address: yukunmeng@hotmail.com.
Yukun
Y
Meng
Postgraduate student, Department of Prosthodontics, The 2nd People's Hospital of Neijiang, Sichuan Province, China.
Hongmin
H
Yin
D000180:Acrylic Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D003781:Denture Retention / Q000295:instrumentation*; D006801:Humans; D060526:Magnetic Fields; D059346:Magnets; D008422:Materials Testing; D013499:Surface Properties
D000180:Acrylic Resins; D003764:Dental Materials