Stability of the anterior arm of three different Hyrax hybrid expanders: an in vitro study

ABSTRACT Introduction: The force applied to the teeth by fixed orthopaedic expanders has previously been studied, but not the force applied to the orthodontic mini-implant (OMI) used to expand the maxilla with Hyrax hybrid expanders (HHE). Objective: The aim of this article was to evaluate the clinical safety of the components (OMI, abutment and double wire arms) of three different force-transmitting systems (FTS) for conducting orthopaedic maxillary expansion: Jeil Medical & Tiger Dental™, Microdent™ and Ortholox™. Methods: For the realization of this in vitro study of the resistance to mechanical load, three different abutment types (bonded, screwed on, and coupling) and three different OMIs’ diameters (Jeil™ 2.5 mm, Microdent™ 1.6 mm and Ortholox™ 2.2 mm) were used. Ten tests for each of these three FTS were carried out in a static lateral load in artificial bone blocks (Sawbones™) by a Galdabini universal testing machine, then comparing its performance. Comparisons of loads, deformations and fractures were carried out by means of radiographs of FTS components in each case. Results: At 1- mm load and within the elastic deformation, FTS values ranged from 67 ± 13 N to 183 ± 48 N. Under great deformations, Jeil & Tiger™ was the one who withstood the greatest loads, with an average 378 ± 22 N; followed by Microdent™, with 201 ± 18 N, and Ortholox™, with 103 ± 10 N. At 3 mm load, the OMIs shaft bends and deforms when the diameter is smaller than 2.5 mm. The abutment fixation is crucial to transmit forces and moments. Conclusions: The present study shows the importance of a rigid design of the different components of HHEs, and also that HHEs would be suitable for maxillary expansion in adolescents and young adults, since its mean expansion forces exceed 120N. Furthermore, early abutment detachment or smaller mini-implants diameter would only be appropriate for children.

摘要 引言：此前已有研究针对固定正畸扩弓器施加于牙齿的力展开探讨，但尚未有研究关注采用Hyrax混合型扩弓器（Hyrax hybrid expanders, HHE）进行上颌扩弓时，其所使用的正畸微种植体（orthodontic mini-implant, OMI）所承受的作用力。
目的：本文旨在评估三种不同力传递系统（force-transmitting systems, FTS）的各组件（OMI、基台及双丝臂）用于正畸上颌扩弓治疗的临床安全性，该三类力传递系统分别为Jeil Medical & Tiger Dental™、Microdent™及Ortholox™。
方法：本体外力学载荷抗性研究采用了三种不同类型的基台（粘结型、螺固型及耦合型）以及三种不同直径的OMI：Jeil™ 2.5 mm、Microdent™ 1.6 mm及Ortholox™ 2.2 mm。通过Galdabini品牌万能试验机在人工骨块（Sawbones™）中对上述三类力传递系统分别开展十次静态侧向载荷测试，随后对其性能进行对比分析。同时通过各力传递系统组件的放射影像，对载荷、变形及断裂情况进行比对。
结果：在加载至1 mm位移且处于弹性变形范围内时，三类力传递系统的载荷值介于67 ± 13 N至183 ± 48 N之间。当发生较大变形时，Jeil & Tiger™系统所能承受的最大载荷最高，平均为378 ± 22 N；其次为Microdent™系统，平均载荷为201 ± 18 N；Ortholox™系统最低，为103 ± 10 N。当加载位移达到3 mm时，直径小于2.5 mm的OMI杆部会发生弯曲变形。基台固定方式对于力与力矩的传递至关重要。
结论：本研究证实了HHE各组件采用刚性设计的重要性，同时表明HHE适用于青少年及年轻成年人的上颌扩弓治疗，因其平均扩弓载荷超过120 N。此外，若出现早期基台脱落或使用直径更小的微种植体，仅适用于儿童群体。