Leonardo Camardella

This PhD thesis is based on six studies that investigate main topics in the use of digital technology in orthodontics: the accuracy of digital model acquisition methods, the accuracy of digital planning tools with software programs and the accuracy of printed models using different 3D printing techniques.

Chapter 1 introduces the application of digital models in orthodontics, their different acquisition methods and their respective accuracy according to the literature. Indirect and direct scanning methods are described including their advantages and disadvantages. The use of digital planning in orthodontics with software programs is reported, emphasizing the virtual setup as an indispensable tool to simulate orthodontic treatments, and to provide more details for proper diagnosis and treatment planning of a malocclusion. The use of 3D printing to print dental models, indirect bonding trays or custom brackets is mentioned and the accuracy, advantages and disadvantages of the available 3D printing techniques are explained.

In chapter 2 and 3 two different indirect acquisition methods for digital models were studied, respectively plaster model scanning and PVS impression scanning. In chapter 2, the accuracy and reliability of measurements performed using two different software programs on digital models acquired from two types of plaster model scanners are compared: a surface laser scanner and a computed tomography (CT) scanner. Two examiners used a sample of 30 pairs of models and performed measurements on plaster models with digital calipers. On digital models the measurements were done with Ortho Analyzer (OA) (3Shape) and Digimodel (DM) (OrthoProof) software programs, creating four different series of digital models: models from the laser scanner measured with OA (Laser OA), models from the laser scanner measured with DM (Laser DM), models from the CT scanner measured with OA (CT OA), and models from the CT scanner measured with DM (CT DM). Forty-two measurements, including tooth diameter, crown height, overjet, overbite, intercanine and intermolar distances and sagittal relationship, were obtained by examiner 1 and 25 selected parameters were measured by examiner 2 to evaluate the reliability of the measurement method. According to the paired t test, examiners 1 and 2 presented excellent interexaminer reliability, with only a few statistically significant differences in the parameters selected, which confirmed the good calibration process between the examiners. Compared with measurements on plaster models, Laser DM models presented three clinically relevant differences: the sum of the 6 upper teeth, the upper intercanine distance, and the right sagittal relationship. For the measurements on Laser OA models, only two parameters presented clinically relevant differences. For the CT OA and CT DM models, only one parameter showed clinically relevant difference. The measurements of dental diameters and dental crown heights on digital models were reliable compared to the measurements on plaster models. The measurements of the upper intercanine distance and the overbite showed the largest differences. These differences could have been caused by misinterpretation of the cuspid landmark due to some attrition on the models and by the subjectivity of the different measurement methods (digital calipers vs. software programs). In the comparisons of only the digital models, the crown height, transversal, and intermaxillary parameters did not show any clinically relevant difference, suggesting that it is easier to mark these points on digital models than on plaster models. Only four parameters in the sum of the mesiodistal diameters presented clinically relevant differences for the four groups of digital models. Finally, it was concluded that digital models generated from plaster models by using laser and CT scanning and measured using two different software programs are accurate and the measurements are reliable. Therefore, both fabrication methods and software programs can be used interchangeably in orthodontics.

Chapter 3 explores another digital model acquisition method: PVS impression scanning. In this study the accuracy and reliability of measurements on digital models obtained by laser scanning impressions 5, 10, and 15 days after they were made, using two different soft putty PVS materials, are evaluated. Thirty volunteers were selected to make impressions of their dention with alginate to create a plaster model and with PVS impression material to create a digital model by laser scanning of the impression. According to the manufacturer’s guidelines, the first PVS impression was made with the heavy putty material and then a soft putty material was used to record the anatomic details. The regular-viscosity soft putty was used for the maxillary arch and the light-viscosity soft putty for the mandibular arch to allow evaluation of possible accuracy differences between the 2 materials. The 30 pairs of digital model were divided into 3 groups of 10 pairs each, according to the time interval between taking the impressions and the scanning of the PVS impressions. T5 represented an interval of 5 days; T10 of 10 days; and T15 of 15 days. Three examiners measured 34 distances (tooth diameter, transverse distances (maxillary and mandibular intercanine and intermolar distances), and 2 interarch relationship measurements (overbite, overjet) on the plaster models with digital calipers and repeated these measurements on the digital models using Ortho Analyzer software. All plaster models of the sample were also scanned with the same laser scanner to acquire the respective digital models and enable comparisons by model superimposition of the digital models made from PVS impression scanning. The intra-examiner errors had low values for the measurements on plaster and digital models. The reproducibility analysis showed high ICC values for both plaster model measurements (r = 0.908) and digital models (r = 0.857). According to the paired t test, statistically significant differences were found for some measurements. From the 34 variables evaluated by each examiner, for examiner one, only 2 clinically significant differences in measurements were found; for examiner two 16; and for examiner three, 2 clinically significant different measurements. Therefore, examiners one and three had similar results, but for examiner two (an undergraduate student with less experience in measuring models) more clinically significant differences were found. On average, measurements on digital models with PVS impression scanning showed lower values compared with measurements on plaster models. The overbite was the only parameter with clinically significant differences for all examiners, with lower values for the digital models. Regarding the time interval between PVS impression taking and scanning, the paired t test showed no significant difference in the results among the 3 time periods (5, 10, and 15 days) compared with the plaster model measurements and by model superimposition. The type of soft putty had no influence on the accuracy of the digital models as the mean differences in maxillary arch superimpositions and mandibular arch superimpositions were not statistically significant. The outcome of this study demonstrates that the acquisition of digital models by laser scanning of PVS impressions scanned within 15 days after impression taking resulted in an accurate digital model, except for the overbite parameter, regardless of the soft putty viscosity type.

The accuracy of digital tools of software programs such as virtual setup and customized digital arch forms are discussed respectively in chapters 4 and 5. A virtual setup is a valuable tool for digital planning in orthodontics due to the possibility to simulate an orthodontic treatment. The evaluation of two different setups can be done by digital model superimposition using specific software programs. Therefore, in chapter 4 the influence of different superimposition methods to compare the accuracy and predictability of diagnostic conventional and virtual setups are evaluated. Ten finished cases were selected to make both a conventional and virtual setup. In these setups second molars were not moved to allow using these molars as a stable reference for surface-based superimposition. The conventional and virtual setups were also compared to the digitized posttreatment models with two superimposition methods: the whole surface best fit (WSBF) method using only the outline of the dentition as a reference, and regional palatal rugae registration best fit (PRBF) method using the medial 2/3 of the third rugae of the palate and a small area dorsal to this rugae as a stable