ABSTRACT
BACKGROUND: Fixed orthodontic retainers must be well retained on the tooth surfaces, allow physiologic movement of teeth and exert minimal forces on the teeth to be retained. Previous studies analyzed the bond strength and amount of deflection caused due to the debonding force but not the magnitude of force needed for unit deformation. AIMS: This study aims to evaluate and compare the bond strength and load deflection rate (LDR) of three different fixed retainer wires. MATERIALS AND METHODS: The wires were divided into three Groups: A - three-stranded twisted ligature wire, B - Bond-A-Braid (Reliance Orthodontics), and C - three-stranded twisted lingual retainer wire (3M Unitek). Twenty models were prepared for each group with a passive 15 mm long lingual retainer wire bonded to two lower incisors. An occlusogingival force was applied to the wire until it debonded. For LDR, three-point bending test was done at 0.5 mm deflection. These forces were measured using a Universal Instron Testing Machine. STATISTICAL ANALYSIS: Mean bond strength/LDR and pairwise comparisons were analyzed with one-way ANOVA and Tukey's honest significant difference post hoc test, respectively. RESULTS: Group C exhibited the highest mean bond strength and LDR of 101.17N and 1.84N, respectively. The intergroup comparisons were all statistically significant. CONCLUSION: Compared to the other two wire types, Group C might be better retained on the teeth due to its higher bond strength. With its relatively higher LDR value, it may resist deformation from occlusal forces, thereby reducing inadvertent tooth movement and yet remain flexible enough to allow physiologic tooth movements.
ABSTRACT
Objective:To compare the regional load deflection rate(LDR) of multiloop edgewise arch wire(MEAW) in the individual interbracket span,to understand the mechanical properties of MEAW.Methods:The stainless steel wire of 0.41 mm?0.64 mm was bent with single L-loop of 5 different sizes as described by Kim.The LDR of each L-loop at the individual interbracket span when loading and unloading was measured by using the Instron at a crosshead speed of 1 mm/min and maximum deflection of 1.0 mm at room temperature.Five specimens were tested under each experimental condition to eliminate the possibility of changes in the physical properties of the wires as a result of the stress from repeated measurements.The date were analysed by SPSS 11.0.Results:L-loops of MEAW had different LDRs regionally,except the regional LDRs between the canine and the first premolar and that between the first and second premolar were identical and moderate,a high value for the anterior segments and a low value for the posterior segments,the difference was statistically significant(P
ABSTRACT
This study was conducted in order to analyze the mechanical characteristics of multiloop edgewise archwire(MEAW). The purposes were 1) to compare load deflection rate(LDR) of MEAW with that of various other archwires in the individual interbracket span, 2)to compare the wire stiffness in the interbracket span with that in the multi-L-loop region (the span from distal border of the bracket of the lateral incisor to the mesial border of the buccal tube of second molar), and 3) to verify the experimental results with theoretically derived formula. The single L-loops five different horizontal lengths and multi-L-loops for the upper and lower arches were made out of .016 X .022 permachrome stainless steel wire. Straight segment of plain stainless steel, TMA and NiTi wire of the same dimension were prepared. The LDR was measured using Instron model 4466 with the load cell of 50N capacity at cross head speed of 1.0mm/min, and maximum deflection of 1.0mm. Five specimens were tested under each experimental condition. The wire stiffness number for each interbracket region and multi-L-loop region was calculated from the LDR and the interbracket spans. By dividing the theoretical model of multi-L-loop into 35 linear segments, the energy stored in each segment was obtained. Then the LDR and wire stiffness of single L-loop and multi-L-loop were calculated and compared. The findings were as follows : 1) The average LDR of MEAW in the individual interbracket region was 1/1.53 of that of the NiTi, 1/247 of TMA and 1/5.16 of the plain stainless steel wire. 2) The wire stiffness of MEAW in the multi-L-loop region was 1.53 times larger than that in the interbracket region, and the LDR was almost twice as large as that of NiTi in that region. 3) According to the theoretically derived equation, the wire stiffness of the single L-loop was lower than that of multi-L-loop. The results of this study suggest that MEAW has the unique mechanical property which could allow individual tooth movement and transmit elastic force effectively through the entire arch wire.
