Residents’ journal review

Reliability and validity of measurements on digital study and plaster models

Reuschl RP, Heuer W, Stiesch M, Wenzel D, Dittmer MP. Reliability and validity of measurements on digital study models and plaster models. Eur J Orthod 2016;38:22-6

Scientific studies have proven that measurements with OrthoCad models and emodels are as precise and reliable as measurements made on plaster models. Transforming plaster models or impressions into digital format can require offices to send them to companies such as OrthoCad; this increases office costs and reduces efficiency. Fortunately, this extra step can be eliminated when intraoral scanners are used, making it possible to bring the digital model process into the local office. Since this is becoming a more common practice, these authors investigated the reliability and accuracy of the 3Shape system (Orthoanalyzer). Nineteen models were subjected to measurements for tooth width, maxillary intercanine width, mandibular intercanine width, overjet, overbite, midline discrepancy, and duration of time needed to take the measurements. The measurements were made manually on plaster models and digitally with the 3Shape software. Dimensions were measured in millimeters, and time was measured in seconds. Randomization, blinding, calibration of the examiners, and intraexaminer and interexaminer reliability tests were performed. The authors reported no clinically different results between the manual and digital methods. Mandibular intercanine width and overjet were comparatively larger with the digital analysis but not significantly so. The authors deemed the 3Shape software capable of reliable results. They stated that the significant reduction in time of 2 minutes per model to analyze the digital models compared with the plaster models clearly justifies the choice of this technology for a busy orthodontic practice. The authors suggested that digital model software appears to be a dependable, accurate, and time-saving alternative to conventional caliper measurement methods.

Reviewed by Sireesha Veeranki

Changes in mechanical and chemical properties of Invisalign

Bradley TG, Teske L, Eliades G, Zinelis S, Eliades T. Do the mechanical and chemical properties of Invisalign TM appliances change after use? A retrieval analysis. Eur J Orthod 2016;38:27-31

The authors of the study aimed to understand the mechanical and chemical properties of Invisalign appliances used intraorally. Aligners were collected from patients who had good oral hygiene and wore the appliances for a mean period of 44 ± 15 days. Aligners with no history of intraoral exposure were used as the reference for comparison. Both the reference and the intraorally aged aligners were subjected to attenuated total reflectance Fourier transform infrared spectroscopy and instrumented indentation testing. From these tests, the chemical composition of the aligners, indentation modulus, elastic index, Martens hardness, and indentation creep were calculated. No difference in the chemical composition of the aligners was found, but degradation of the mechanical properties was statistically significant for Invisalign. The indentation modulus decreased, suggesting weakening of the force delivery capacity by the appliances. The increased elastic index value of the Invisalign aligners demonstrated that the material becomes more brittle. A decrease in the Martens hardness was found, indicating that the Invisalgn aligners were made of a less wear-resistant material. Indentation creep increased, demonstrating augmented deformation of Invisalign appliances. These results suggested that the orthodontic forces exerted by the Invisalign material were lower than those of the reference aligners. The authors attributed the decrease in mechanical properties to relaxation of the residual stresses developed during the manufacturing procedure and the 2-phase microstructure of the thermoplastic polyurethane material. They stated that, clinically, it is unknown whether the decreases in mechanical properties have a significant effect on treatment or orthodontic tooth movements, and future research is needed to determine any changes in clinical performance.

Reviewed by Brittany Ellis

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Apr 4, 2017 | Posted by in Orthodontics | Comments Off on Residents’ journal review
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