Objective: Orthodontic aligners have increased popularity due to enhanced esthetics and ease of application by the general practitioner. Studies have demonstrated inclusion of soft internal liners in aligners allows less localized stress to teeth and bone. Question is raised as to optimum aligner thickness required to exert sufficient load for orthodontic movement to minimize the potential risk of unwanted occlusal changes. The purpose of this study was to assess stress distribution as a function 0f laminated aligner thickness.

Methods: “Unaltered” photoelastic model of dentulous adult maxilla was fabricated using different teeth and bone simulants. PVS impression was taken of the unaltered model for CT scan and an “altered” model was fabricated using CAD/CAM technology after making the following lingual movements: Maxillary lateral incisors 0.3mm and maxillary central incisors 0.6mm. Thick laminated aligner (1.0mm) and thin laminated aligner (0.6mm) were fabricated from the digitally altered model. The two aligners were inserted over the photoelastic model to assess stress distribution, observed in the field of a polariscope and photographed.

Results: Both thick and thin laminated aligners demonstrated mild stress to laterals and moderate stress to centrals. However, the number and proximity of fringes associated with the thicker laminated aligner demonstrated greater concentration and intensity of stress. The amount of stress outside of the maxillary laterals and centrals was minimal for both thin and thick aligners tested.

Conclusion: Results indicate potential for greater degree of tooth movement and longer duration of tooth movement by using the thicker laminated aligner. The indicatethat faster orthodontic treatment may be achieved by using the 1mm laminated aligner as compared to the 0.6mm laminated aligner.