Predictability of overbite control with the Invisalign appliance comparing SmartTrack with precision bite ramps to EX30

Introduction: Although the Invisalign appliance has reported difficulty in achieving the overbite outcomes predicted by ClinCheck software (Align Technology, Santa Clara, Calif), the effect of modifications to the material and components of the appliance are largely unquantified. This study aimed to investigate and determine the accuracy of Invisalign in correcting a deep overbite by comparing the predicted outcome from ClinCheck to the achieved posttreatment outcome for treatment groups that use different components of the appliance system.

Methods: A retrospective study was conducted using pretreatment and posttreatment intraoral scans and predicted outcomes (ClinCheck) stereolithography files of 2 groups of consecutively treated adult patients from private specialist orthodontic practices, 1 group treated with EX30 material with no bite ramps (n = 29) and 1 treated with the newer SmartTrack material and precision bite ramps (n = 39). Inclusion criteria comprised nonextraction treatment, with a minimum of 14 dual arch Invisalign aligners using a 2-weekly aligner change protocol. Geomagic Control X software (3D Systems, Rock Hill, SC) was used to measure overbite in the pretreatment, posttreatment, and predicted outcome stereolithography files for each patient. Results were compared with a previously published treatment group that used SmartTrack material and no precision bite ramps.

Results: The regression coefficient analysis indicated that for both groups, the deeper the pretreatment overbite and the greater overbite reduction projected according to ClinCheck, there is a linear increase in the discrepancy of overbite expression posttreatment. ClinCheck overpredicted overbite reduction in 96.6% of patients with precision bite ramp in which, on average, 43.4% of the prescribed overbite reduction was expressed. For EX30 patients, ClinCheck overpredicted overbite reduction in 87.2% of patients in which, on average, 55.1% of the prescribed overbite reduction was expressed.

Conclusions: The use of precision bite ramps does not appear to significantly improve the ability of SmartTrack material to predictably open the bite. SmartTrack material with or without bite ramps does not appear to produce better bite opening predictability than that seen with EX30 material.