Retentive force and magnetic flux leakage of magnetic attachment in various keeper and magnetic assembly combinations.

STATEMENT OF PROBLEM: Magnetic attachments are commonly used for overdentures. However, it can be difficult to identify and provide the same type and size of magnetic assembly and keeper if a repair becomes necessary. Therefore, the size and type may not match. PURPOSE: This study evaluated the retentive force and magnetic flux strength and leakage of magnetic attachments in different combinations of keepers and magnetic assemblies. MATERIAL AND METHODS: For 6 magnet-keeper combinations using 4 sizes of magnets (GIGAUSS D400, D600, D800, and D1000) (n=5), retentive force was measured 5 times at a crosshead speed of 5 mm/min in a universal testing machine. Magnetic flux strength was measured using a Hall Effect Gaussmeter. Data were statistically analyzed using a 1-way ANOVA, and between-group differences were analyzed with Tukey's HSD post hoc test (α=.05). RESULTS: The mean retentive force of the same-size magnet-keeper combinations was 3.2 N for GIGAUSS D400 and 5.1 N for GIGAUSS D600, but was significantly reduced when using larger magnets (P<.05). Magnetic flux leakage was significantly lower for corresponding size combinations. CONCLUSIONS: Size differences influence the retentive force and magnetic flux strength of magnetic attachments. Retentive force decreased due to the closed field structure becoming incomplete and due to magnetic field leakage.

[Shock absorption of mouthguard materials--influence of temperature conditions and shore hardness on shock absorption].

PURPOSE: To consider changes in the physical properties of mouthguard materials with the change of temperature, shock-absorbing examination and Shore hardness measurement of existing MG materials and other elastic materials were carried out. METHODS: Both examinations were done under two temperature conditions: at room temperature (25 degrees C) and simulated intraoral temperature (37 degrees C). In addition, a comparative study of the relation between Shore hardness and shock absorption of the materials was made. A self-made drop impact machine was used for the shock-absorbing examination. The thickness of a sample was assumed to be 3 mm. The loading was applied by dropping 3 kinds of steel ball, phi 10 mm (4.0 g), phi 15 mm (13.7 g), and phi 20 mm (32.6 g) from a height of 60 cm. The shock absorption of all materials was compared by the maximum impact force. Shore hardness was measured based on the JIS standard. RESULTS: The shock absorption of each material showed a different tendency depending on the loading condition. Furthermore, the shock absorption of the same material showed different results depending on the temperature condition. Shore hardness measurements tended to show low values with the condition of 37 degrees C for all materials. CONCLUSION: From the relation between shock absorption and Shore hardness, it was confirmed that there is a correlation between hardness and the maximum impact force in the materials that showed shock absorption by elastic deformation. Some materials showed high shock absorption compared with existing MG materials.