A novel method of photogrammetry measurements of study models in orthodontics

Abstract

Introduction/Objective Rapid developments in information technologies lead to the wider use of digital representations of dental study models in orthodontics. Most popular way of digitizing the models is to use a 3D scanner and then perform measurements on 3D models, which requires additional and expensive hardware and software resources. In this paper we present an alternative approach based on the use of photogrammetry in the newly developed OrthoPhoto4D software that calculates and corrects perspective distortion errors. Methods We measured individual tooth width for 24 teeth, 12 two-teeth segments as well as inter-molar and inter-canine distances on 50 models. Measurements are performed in OrthoPhoto4D software that uses four photographs of each model for measurements, uses QR codes for automation, calculates the camera position and corrects perspective distortion-caused errors in measurements. Obtained measurements are compared to ones obtained from models generated by structured light 3D scanner. Results Statistical analysis strongly indicates that there is no significant difference between the two methods. The recorded differences also have no clinical impact as they have mean values of 0.2 mm for individual tooth widths, approximately 0.2 mm for two teeth segments, and under 0.3 mm for both inter-canine and inter-molar distances. All recorded differences fall within the expected measurement error. Conclusion We concluded that the described photogrammetry measurements performed in OrthoPhoto4D can be used in diagnosis and therapy planning.

Uvod/Cilj Brzi razvoj informacionih tehnologija doveo je do široke upotrebe digitalnih studijskih modela u ortodonciji. Najpopularniji način digitalizacije modela je korišćenje 3D skenera, a zatim i merenja na 3D modelima, što zahteva dodatne i skupe hardverske i softverske resurse. U ovom radu predstavljamo alternativni pristup zasnovan na korišćenju fotogrametrije u novorazvijenom softveru OrthoPhoto4D, koji izračunava i ispravlja greške nastale kao posledica perspektivne distorzije. Metod Na 50 studijskih modela merena je meziodistalna širina za 24 zuba, širina 12 segmenata dvostrukih zuba, kao i interkanina i intermolarna širina. Merenja su vršena u programu OrthoPhoto4D, koji koristi četiri fotografije svakog merenog modela, QR kodove za automatizaciju, računa udaljenost kamere i koriguje greške merenja izazvane perspektivom. Merenja su poređena sa rezultatima dobijenim na modelima generisanim 3D skenerom. Rezultati Analiza rezultata snažno ukazuje na to da ne postoji statistički značajna razlika između dva metoda. Zabeležene razlike takođe nemaju klinički značaj, jer su srednje vrednosti do 0,2 mm za pojedinačne širine zuba, do približno 0,2 mm za segmente od dva zuba i ispod 0,3 mm za interkaninu i intermolarnu širinu. Sve zabeležene razlike su unutar očekivane greške merenja. Zaključak Opisani metod fotogrametrijskih merenja u programu OrthoPhoto4D se može koristiti u dijagnozi i planiranju ortodontske terapije.