Abstract
BackgroundTo determine the mechanical properties of the NiTi Memoria® Leaf Spring Activated Expander (NiTi MLSAE) in two forms, unaltered (unbent) and altered (bent) to mimic clinical use. Material and MethodsThis in-vitro pilot study was conducted using eight NiTi MLSAE expanders (American Tooth Industries, Oxnard, California) representing four force magnitudes: 10mm 500g, 10mm 900g, 6mm 450g and 6mm 900g models. Two experiments were performed: the first tested the expanders in their unbent form and the second tested them after they were bent by one experienced technician. All expanders were adapted to a standard three dimensional printed maxillary study model. A Dillion Quantrol 500N (110lbf) load cell and a custom-made fixturing apparatus was used to determine the amount of expansive forces delivered. Prior to testing, the ligation compressing the NiTi MLSAE leaves was cut to allow the appliances to expand to their original form. Emperor™ (force) Software was used to measure the expansion forces. ResultsThe average expansion forces generated by the expanders were: unaltered = 897.4g (8.8N) and bent = 877.0g (8.6N) for the 10mm 900g model, unaltered = 489.5g (4.8N) and bent = 479.3g (4.7N) for the 10mm 500g model, unaltered = 458.9g (4.5N) and bent = 438.5g (4.3N) for the 6mm 450g model, and unaltered = 805.6g (7.9N) and bent = 785.2g (7.7N) for the 6mm 900g model. ConclusionsRegardless of whether the expander was straight or bent, the forces generated by the 10mm 900g, 10mm 500g and 6mm 450g Ni-Ti MLSAEs correlated with the benchmark study conducted by the manufacturer. However, the forces generated by the 6mm 900g Ni-Ti MLSAE were less than the data published by the manufacturer. Binding was observed when the expanders were manipulated to mimic clinical use, and this may account for the reported lower expansion force. Key words:Maxillary expansion, NiTi, posterior crossbite, malocclusion, maxillary transverse discrepancy.
Highlights
Maxillary Transverse Discrepancy (MTD) is a common malocclusion in primary, mixed and permanent dentitions [1]
In 2013, Leone SpA (Florence, Italy) introduced a slow maxillary expander which utilizes a new spring-based expansion screw with a leaf-shaped active element, the NiTi Memoria® Leaf Spring Activated Expander (NiTi MLSAE)
The authors found that 1 - 1.5mm per month of expansion is expected in the molar and premolar regions. They concluded that the NiTi MLSAE is capable of obtaining adequate expansion in patients 6 - 16 years without causing significant buccal tipping when compared to untreated controls [7]
Summary
Maxillary Transverse Discrepancy (MTD) is a common malocclusion in primary, mixed and permanent dentitions [1]. After the publication of this article, Leone recanted their statement and published two new forces in their 2018 catalogue – the new reported forces for the Light and Medium models were claimed to be 450g and 900g, respectively[10] This modification in forces, and whether the expanders were bent or not prior to force determination, warranted further research. The aims for this study were to: 1) determine the reactive forces of the NiTi MLSAE by assessing compression and expansion forces under two conditions, unaltered (unbent) and altered (bent), to simulate intra-oral use; and 2) compare data from this study against the benchmark study conducted by Leone. To determine the mechanical properties of the NiTi Memoria® Leaf Spring Activated Expander (NiTi MLSAE) in two forms, unaltered (unbent) and altered (bent) to mimic clinical use. Binding was observed when the expanders were manipulated to mimic clinical use, and this may account for the reported lower expansion force
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