جستجوی مقالات مرتبط با کلیدواژه « orthodontic appliance design » در نشریات گروه « پزشکی »

Ectopic eruption of molars occurs more frequently in developing permanent dentition, and requires immediate intervention. Herein, two cases are discussed with ectopic eruption of permanent maxillary first molars which were diagnosed and managed conservatively using a modified Humphrey's appliance, named the NR’s appliance. The appliance was fabricated by band adaptation and using wire components of a 21-gauge stainless-steel wire. Also, the Nance palatal arch was used as the anchorage unit. The molars were uprighted and distalized within 3 months. Early diagnosis and prompt treatment could result in prevention of malocclusion in the early mixed dentition period.

The aim of this study was to compare two nickel-titanium (NiTi) closed coil springs (CCSs) from two different manufacturers regarding their force degradation over 4- and 8-week periods.   

In this in vitro experimental study, 20 NiTi CCSs from 3M® and GAC® were compared. The springs were extended until a tensile strength of 250 g was achieved, and the length of springs was recorded. They were then mounted on customized jigs according to the registered length, so as to keep them extended constantly. Springs from each manufacturer (n=10) were randomly divided into two subgroups (n=5): one subgroup was stored in artificial saliva and the other was stored in a dry environment. The forces were assessed 4 and 8 weeks later. Data were analyzed by repeated measures ANOVA and the Tukey post-hoc test (alpha=0.05).

The mean force of 3M® CCSs significantly decreased by 56% after 4 weeks and 14% after 8 weeks in dry condition, and by 46% after 4 weeks in wet environment; however, after 8 weeks in wet environment, the force decay was insignificant. The changes in force of GAC® CCSs in dry environment after 4 weeks and 8 weeks were not significant, indicating a constant force property. However, in artificial saliva, a statistically significant yet mild increase in force level was recorded.

The results showed a force decay for the 3M® CCSs after 4 weeks while for the GAC® CCSs, an almost constant force level was observed even after 8 weeks.

The design of an orthodontic mini-implant is a significant factor in determining its primary stability and therefore its clinical success. The purpose of this study was to measure the relative influence of mini-implant design factors including diameter, length, degree and length of taper both in the threaded and non-threaded area, pitch and thread depth/diameter on the primary stability. Thirty two 3-dimensional assemblies of mini-implant models with their surrounding bone were generated using finite element analysis software. The maximum displacement of each mini-implant model was measured as they were loaded with a 2 N horizontal force. Employing Taguchi’s design of experiments as a statistical method, the contribution of each design factor to primary stability was calculated. As the effect of the upper diameter and length was abundant, to better detect the impact of the remaining design factors, another set of twenty five models with a fixed amount of length and diameter was generated and evaluated. The diameter and length showed a great impact on the primary stability in the first set of experiments (p<0.05). The effect of the remaining factors was not statistically significant. According to the second set of experiments, threaded taper angle, non-threaded taper angle and non-threaded taper length were the main factors influencing the primary stability, respectively. An approximate proportion of 20% of threaded taper length to MI length, with minimum taper angle, would be desirable for an average-sized MI.

An ideal orthodontic force system should exert continuous light force. Thus, many efforts have been made to improve the memory characteristics of elasto-meric chains. The aim of this study was to compare elastomeric chains (ECs) claimed by their manufacturers to offer high memory with traditional ones according to their force-extension diagrams. In this in-vitro study, ECs were divided into six groups, each containing 40 pieces of chain, from three brands (American Orthodontics, GAC and Ortho-Technology). Each brand was divided into two groups with respect to their claimed characteristics (with or without memory). Each sample was stretched to twice its original length and kept constant in 37°C distilled water. Force-extension diagrams were drawn by universal testing machine at 0,1,8,24,72 hours and 1, 2, 4-week inter-vals. Additionally, the amounts of elongation required to deliver 200 g force were calculated. To compare the results, ANOVA and Tukey tests were performed. Force-decay rate was significantly different between traditional and memory chains (p<0.05). For traditional chains, there was a substantial decay in force in the first hour and 30-40% of the force was retained at 4 weeeks. The memory chains demonstrated more constant force and retained 60% of the force. The maximum amount of elongation required to deliver 200 g force belonged to American Ortho-dontics memory chains (61.9% after 24hr) and the minimum to Ortho-Technology ECs (23.4% initially). Memory chains exhibited superior mechanical properties compared to traditional ones. For delivering the same force, memory chains required more elonga-tion. Memory chains of GAC and American Orthodontics showed better characteris-tics among all chains.