| Objective The purpose of the study was to reveal the stretched force when 3 kinds of orthodontic rubber elastics were stretched to a intended length, and to investigate tensile properties of 3 kinds of orthodontic rubber elastics, and to evaluate the influence patterns of such factors as temperature,stretched length,internal diameter,time on the force degradation of 3 kinds of orthodontic rubber elastics in vitro. Thus this may give the clinicians a guideline in selecting the proper rubber elastics for treatment of orthodontic diseases.Methods 3 kinds of orthodontic rubber elastics: 3/16(4.6mm),1/4(6.4mm),5/16(7.9mm) with the same elastic parameters 3.5OZ, which were commonly used in clinics, were tested in this study. The specimens were tested on an Instron testing machine. The relationship between force and extension with a stretched length range of 15～55mm was explored. The remaining forces of specimens with the four elongation distances (20mm,30mm,40mm,50mm) were tested in 25℃,37℃,60℃saliva; respectively for 4hours,12hours,24hours and 72hours. Then calculated the percentage of remaining force and analysed the results.Results1. When the stretched length of 3/16 group was between 15～35mm,the stretched force was between 135.76～249.9g. When the stretched length of 1/4 group was between 15～45mm, the stretched force was between 114.24～256.02g. When the stretched length of 5/16 group was between 20～55mm, the stretched force was between 104.04～222.36g. When the stretched length was between 15～35mm, each group'load-deformation curve was similar to the parallel. When the stretched length was between 35～50mm, the slope of 3/16'Load-deformation curve, the ratio of force and displacement, increased significantly.2. There were significant differences on initial forces among the 3 kinds of orthodontic rubber elastics(P<0.05).3. All orthodontic rubber elastics degraded the most force at the initial 4hours, and at 4hours, the mean percentage of remaining force were 61%. Then the force degraded slowly, the increase of time was not accompanied by the decrease of mean percentage of remaining force. At 72hours, the mean percentage of remaining force were 56.29%.4. The mean percentage of remaining force of all orthodontic rubber elastics emerged the characteristics: 25℃>37℃>60℃. The mean percentage of remaining force under 60℃were lower than those under 25℃or 37℃, and there were statistically different(P<0.05). However, there were no significant difference between 25℃and 37℃( P>0.05).5. The mean percentage of remaining force of all orthodontic rubber elastics emerged the characteristics: 20mm>30mm>40mm>50mm. The mean percentage of remaining force at the extension of 20mm were higher than those at the extension of 40mm or 50mm, and there were statistically different(P<0.05). The mean percentage of remaining force at the extension of 30mm or 40mm were higher than those at the extension of 50mm, and there were statistically different(P<0.05). However, there were no significant difference between the extension of 30mm and the extension of 20mm or 40mm(P>0.05).6. The mean percentage of remaining force of all orthodontic rubber elastics emerged the characteristics: 5/16>1/4>3/16. The influence of internal diameter on the force degradation ratio of all orthodontic rubber elastics was statistically significant(P<0.05).Conclusion1. When the stretched length was between 15～35mm, all orthodontic rubber elastics'tensile properties were similar, and the stretched force were commonly used for clinics.2. Significant drop of force happened at the initial 4 hours on the observation and the degradation tended to stable after 4 hours. The larger internal diameter, the lower force degradation ratio was.3. High temperature has profound effect on the resilience of elastics. When orthodontic rubber elastics were used, the patients should try to avoid eating hot food.4. With the increase in the stretched length, the force degradation ratio was increased insequence. But in the range of 0～10mm, its increased length did not significantly affect the force degradation ratio of all orthodontic rubber elastics.5. Most of orthodontic rubber elastics did not match the specified index. It is suggested that the clinician do not completely use the rubber elastics according to the specification. So while elastics applied to clinical treatments, it is important to use the dynameter for the precise force. |
PDF Full Text Request