The influence of occlusal forces on force delivery properties of aligners during rotation of an upper central incisor

Abstract

Objective: To determine the forces and moments delivered to a maxillary central incisor during rotation with aligners when a simulated occlusal force generated during swallowing acts on the appliance. Materials and Methods: Five identical appliances were manufactured from four different starting materials (Erkodur 0.8 mm and 1.0 mm; Biolon 0.75 mm and 1.0 mm). An upper central incisor fixed in a measuring device was rotated around its central axis in 0.5-degree steps up to 610 degrees with the appliance fixed in place. An occlusal force of 30 N generated during swallowing was simulated with a weight positioned on the appliance. For statistical analysis, the moments Tz (rotation) and forces Fz (intrusion) at a deflection of 60.34 mm to the incisor edge (65 degrees rotation) were tested. Means and standard deviations for Tz and median and 25% and 75% quartiles for Fz were calculated. An analysis of variance was performed.

Forces and moments generated by aligner‐type appliances for orthodontic tooth movement: A systematic review and meta‐analysis

“…As for 0.625 and 0.75 mm PET‐G foils, findings indicate that both presented similar mechanical behaviour with respect to rotational moments during mandibular canine and maxillary central incisor rotation as well as labio‐lingual tipping and bodily movement . Three studies examined the behaviour of 1 mm PET‐G aligners and concluded that forces and moments generated were higher than those recommended. Finally, forces applied by 0.7 mm Invisalign system aligners have been reported to lie within the range of acceptable orthodontic forces …”

“…On the contrary, three studies indicated that bodily movement and torque are the most demanding movements to achieve since plain aligners without modifications cannot establish the force couple required. Upper incisor rotation movement with aligners has been frequently coupled with an intrusive force, which may present an increase in magnitude when combined with simulated occlusal forces . Hahn et al, found that only a slight activation of ±0.17 mm or 0.5° per step during rotation could produce ideal forces which have been estimated to range between 0.35 and 0.6 N .…”

“…All four studies comparing different PET‐G aligner materials of 1 mm thickness reported that aligners vacuum‐formed with Biolon (Dreve Dentamid GmbH, Unna, Germany) delivered the highest forces and moments ranging from 1.15 to 6.19 N during tipping and 35.3‐71.8 Nmm during rotation, depending on the activation magnitude. The only exception was observed during rotation at low rotation range of ±0.17 mm were the Ideal Clear appliance (Dentsply GAC, Gräfelfing, Germany) exerted the highest values (18.3‐20.2 Nmm) .…”

“…Clinical behaviour of thermoplastic aligner‐type appliances is not unaffected by occlusal forces and/or wear‐related properties. The former has been associated with load increases when it comes to rotational moments or intrusive forces . The latter may lead to a considerable force decay and deactivation, which may reach ~50% after a 2‐week period of aligner use …”

A comparative study of two different clear aligner systems

“…Although all clear aligner systems have shown to have evident biomechanical limits [17,18], barely producing bodily movement and expressing torque, both clear aligner systems in this study showed good treatment efficiency. To obtain a good dental alignment and arch coordination, it is mandatory to make a correct diagnosis and to choose treatment objective achievable with the limited biomechanics offered by clear aligners.…”