Effect of surface treatment with commercial primers on tensile bond strength of auto-polymerizing resin to magnetic stainless steel

Jian-rong Chen, DDS,(a,b) Kenji Oka, DDS, PhD,(c) Wei Hua, DDS,(a) and Tetsuo Ichikawa, DDS, PhD(c)

(a)The University of Tokushima Graduate School of Oral Science, Tokushima, Japan, (b)Tonji University, School of Oral Stomatology, Shanghai, P. R. China, and (c)Department of Oral & Maxillofacial Prosthodontics and Oral Implantology, The University of Tokushima Graduate School, Institute of Health Biosciences, Tokushima, Japan

Purpose: It often happens that magnets clinically detach from denture bases. To establish the appropriate laboratory procedure to fix the magnet in the denture base, the tensile bond strength of magnetic steel in auto-polymerizing resin was measured under several conditions.
Materials and Methods: Magnetic stainless steel cylinders (AUM 20) of 4 mm diameter were prepared as specimens. The cross section of the specimens was ground with silicon-carbide abrasive paper (#800) to create a bondable surface. After grinding, half of the specimens were treated by air abrasion with 50 _m alumina. Both surfaces were treated with one of the three commercial primers: Metal Primer II (MPII), Metal Link Primer (MLP), and Meta Fast Bonding Liner (MFL). Auto-polymerizing resin was poured on the bonded surfaces of the metal. The tensile bond strength between the metal and resin was measured after the specimens were stored in water at 37℃ for 24 hours. Thermal cycle examinations, with immersion alternately in water baths at 4℃ and 60℃ for 1 minute up to 2,000 times were conducted.
Results: The bond strength of sanded surfaces with primer treatment varied from 21.6 to 32.2 MPa and the value increased significantly when primer treatments other than MPII were used. The bond strength of air-abraded surfaces with primer treatment varied from 31.1 to 38.3 MPa and the value increased significantly with all primer treatments. Bond strengths of all groups were significantly reduced by the application of thermal cycling (p<0.05). The bond strength of air-abraded surfaces with primer treatment varied from 3.6 to 4.2 MPa and the bond strength was significantly (p<0.05) larger than those in other groups.
Conclusion: The combination of air abrasion and primer application is the most effective procedure to fix the magnet. (Int Chin J Dent 2005; 5: 7-11.)
Clinical Significance: To solve the clinical problem of magnetic detachment, enhancement of bond strength is necessary.
Key Words: air abrasion, magnetic attachment, magnetic stainless steel, primer, tensile bond strength.