Comparison between 2D cephalometric and 3D digital model superimpositions in patients with lateral incisor agenesis treated by canine substitution

Introduction

This study aimed to assess the reliability of measurements obtained after superimposing 3-dimensional (3D) digital models by comparing them with those obtained from lateral cephalometric radiographs in patients with lateral agenesis space closure by mesialization.

Methods

Data were collected from premaxillary and postmaxillary dental casts and lateral cephalometric radiographs of 26 patients presenting lateral incisor agenesis and treated with rapid maxillary expanders and space closure by mesialization of the lateral sectors. Sagittal and vertical movements of the incisors and the maxillary molars were evaluated with lateral cephalometric radiographs and digitized 3D models superimposed on the palatal area. Paired sample t tests were used to determine if any significant difference existed between the 2 measuring techniques and between 2 different localizations of superimpositions.

Results

Cephalograms and 3D digital model measurements were statistically similar in molars and incisor movements according to anteroposterior and vertical planes. Regarding incisor movements in the anteroposterior plane, measurements derived from second ruga 3D models were significantly greater than those derived from third ruga 3D digital models.

Conclusions

The 3D model superimposition method using the palate as a reference area is clinically reliable for assessing anteroposterior and vertical tooth movement as cephalometric superimposition in patients treated with rapid maxillary expanders and space closure by mesialization.

Highlights

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Digital model superimpositions are as valid as cephalometric superimpositions.
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Mesialization of posterior segments did not affect the stability of palatal rugae.
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Posterior palatal rugae are more stable than anterior palatal rugae after orthodontic treatment.

In orthodontics, analyzing the outcome of therapy is crucial. The gold standard for this goal is the superimposition of lateral radiographs. However, there are certain drawbacks to this strategy. These disadvantages have been overcome with digitized laser-scanned dental impressions that provide a 3-dimensional (3D) image of the teeth and dental arches. With the ability to use 3D superimposition techniques and the entire amount of 3D information for a full assessment and visualization of morphologic changes, digital dental models provide significant advantages. For this purpose, 2 serial dental models of the same patient can be placed on a determined anatomically stable reference area. Therefore, changes in nearby structures can be measured precisely in 3 dimensions and shown using color maps.

To superimpose serial 3D intraoral surface representations, several approaches have been explored. There is no credible area for the superimposition of mandibular 3D surface models. In contrast, the maxillary 3D surface model superimpositions have received greater attention and have shown promising results. The palatal rugae area is a superimposition reference in most currently accessible procedures. The medial two thirds of the third rugae is believed to be the most stable part for superimposition purposes. ^, However, there seems to be no consensus on the stability of the palatal rugae as to the effect of growth or treatment.

Multiple studies have evaluated the accuracy of the analysis of tooth movements using superimpositions on 3D digital models. Most of it describes movements of distalization. To our knowledge, no study has evaluated the accuracy of 3D digital model superimpositions in patients with lateral incisor agenesis treated with rapid maxillary expanders (RME) and space closure by mesialization of lateral sectors.

Movements of mesialization are interesting to study because they might cause a contraction in the palate, leading to a diminution of the accuracy of superimpositions on the palatal rugae.

The main goal of this research is to compare the measurements of the anteroposterior and vertical movements of anterior and posterior teeth in the case of space closure by canine substitution during lateral agenesis made on cephalometric superimpositions to those made on 3D digital model superimpositions.

Material and methods

Using the G∗Power software, a power analysis for paired t test was conducted for the sample size calculation. A power of 0.95, an α level of 0.05, and an estimated large size effect of 0.8 were considered, and the minimum sample size required was 23 patients.

The samples were collected from a private practice (E.A.). It first consisted of the records of 30 patients, but 4 of them were lost. The pretreatment and posttreatment maxillary study cast and lateral cephalometric radiographs of 26 patients (10 male and 16 females; mean age, 16.3 ± 4.9 years) were used in this study. The patients presented a skeletal Class I or III tendency or a mild Class III and 2 congenitally missing maxillary incisors or 1 missing maxillary lateral incisor and a riziform contralateral incisor that was further extracted. They were treated with a rapid maxillary expander (RME), followed by a fixed appliance involving the closure of spaces by mesialization using Class III elastics on mandibular miniscrews; the mean effective treatment time lasted 32.0 ± 6.2 months, ranging from 22 to 43 months. The study protocol was reviewed and approved by the Medical Scientific Ethics Committee of Beirut A 16/21 of April 8, 2021, from the Saint-Joseph University of Beirut. To assess the methodological errors of both techniques, 10 sets of randomly selected measurements were repeated by a skilled orthodontist.

Pretreatment and posttreatment lateral cephalograms were calibrated, introduced, and digitally traced into the Dolphin Imaging software (Dolphin Imaging and Management Solutions, Chatsworth, Calif) for analysis. Incisor and molar movements were measured using points and references on each cephalometric radiograph ( Fig 1 ). Details of the reference points and lines are summarized in Tables I and II , and techniques of measurements are summarized in Table III . The final measurement of the movement achieved was obtained by subtracting the posttreatment distance from the pretreatment distance.

Table I

Skeletal and dental reference points

Landmarks	Definition
Nasion (Point N)	The most anterior and superior point of the nasofrontal suture
Anterior nasal spine	Tip of the anterior nasal spine
Posterior nasal spine	Tip of the posterior nasal spine, on the bony palate
Point A	Deepest point on the curvature below anterior nasal spine
U1	Tip of the maxillary central incisor
U6	Point of mesiovestibular cusp of maxillary molar
U6’	Most distal point of the distal contour of the maxillary molar

Table II

Reference planes and lines

Plane/reference line	Definition
Palatin plane	Passing through the anterior and posterior nasal spine
PTV	Perpendicular to the Frankfort plane, tangent to the pterygopalatine fissures
NA plane	Passing through N and A

Table III

Definition of the measurements

Linear measurements	Definition
U6’-PTV	Distance between the most distal point of the distal contour of the maxillary molar and PTV
PP-U6	Distance between the tip of the mesiovestibular cusp of the maxillary molar and PP
U1-NA	Distance between the tip of the maxillary central incisor and NA plane
PP-U1	Distance between the tip of the maxillary central incisor and PP

Note. The units are in millimeters.

For the 3D digital model analysis, dental casts obtained before and after treatment were scanned with the 3Shape Trios intraoral scanner (3Shape, Copenhagen, Denmark) and directly sent to the Orthoanalayzer software (3Shape) for analysis. In the section to compare model sets, there are 3 different options to perform the superimposition (surface 1-point, surface 3-point, and direct 3-point). Once the option is chosen (this study used surface-1 point), the pretreatment and posttreatment maxillary models appear on the screen, and the landmarks are placed on the palate on both models, respectively, at the same place on the specific rugae of each model, as well as the area around it (region of interest). The software then automatically performs the superimposition on the basis of the best-fit method that compensates for the human error. Pretreatment and posttreatment scans of the dental models were superimposed, first on the medial part of the third ruga and an area 5 mm dorsal to it, and second on the second ruga only. In Orthoanalyzer software, there are 2 options for measurements: Three-dimensional and 2-dimensional (2D) measurements. After multiple trials, we decided to use the 2D cross-section measurements tool because it gives more accurate results. To measure the movement of the maxillary molars, we drew a plane that crossed the canines of the posterior segments of both pretreatment and posttreatment models. On the window in the right-down corner, we chose the points representing the mesiobuccal canine of the maxillary molars. On the triangle of measurements, we took the horizontal one for the anteroposterior movement and the vertical one for the vertical movements. The plane we drew was transversal for the incisors, passing by the incisal edges of the maxillary left incisor of both pretreatment and posttreatment models, and the same technique was applied ( Fig 2 ).

Statistical analysis

Data analyses were performed using SPSS software (version 26; IBM, Armonk, NY). All tests were 2-tailed, and a P <0.05 was considered statistically significant. Interrater reliability analysis was assessed using intraclass correlation coefficients for every measurement performed by 2 raters on 11 subjects; an intraclass correlation coefficient of <0.50 indicates poor reliability, 0.50-0.75 moderate reliability, 0.75-0.90 good reliability, and >0.9 excellent reliability. Continuous variables were summarized and presented as mean ± standard deviation. Kolmogorov-Smirnov and Shapiro-Wilk tests were conducted to evaluate the normality of the distribution of continuous variables. Because all continuous variables were normally distributed, paired samples t tests were used to compare means between measurements performed on cephalograms and those done on 3D digital models (third ruga) for incisors and molars movements in anteroposterior and vertical planes and to compare values between 3D digital models using second and third rugae as references.

Results

Results of the interrater reliability are shown in Table IV . Excellent interrater reliability (>90%) was found for all measurements performed using the 3 techniques on movements of incisors and molars in anteroposterior and vertical planes except for the measurements performed on movements of incisors in the vertical plane using cephalograms, which indicated good reliability (85%).

Table IV

Interrater reliability of measurements (n = 11)

Measurements ^†	ICC	95% CI	P value
Cephalograms
Incisors (anteroposterior)	0.996	0.984-0.999	<0.001
Molars (anteroposterior)	0.994	0.978-0.998	<0.001
Incisors (vertical)	0.859	0.561-0.960	<0.001
Molars (vertical)	0.982	0.935-0.985	<0.001
3D digital models (third ruga)
Incisors (anteroposterior)	0.990	0.962-0.997	<0.001
Molars (anteroposterior)	0.987	0.953-0.997	<0.001
Incisors (vertical)	0.912	0.708-0.976	<0.001
Molars (vertical)	0.964	0.873-0.990	<0.001
3D digital models (second ruga)
Incisors (anteroposterior)	0.991	0.969-0.998	<0.001
Molars (anteroposterior)	0.963	0.871-0.990	<0.001
Incisors (vertical)	0.935	0.778-0.982	<0.001
Molars (vertical)	0.975	0.909-0.993	<0.001