Frits A. Rangel

Evaluation of reproducibility and reliability of 3D soft tissue analysis using 3D stereophotogrammetry

In 3D photographs the bony structures are neither available nor palpable, therefore, the bone-related landmarks, such as the soft tissue gonion, need to be redefined. The purpose of this study was to determine the reproducibility and reliability of 49 soft tissue landmarks, including newly defined 3D bone-related soft tissue landmarks with the use of 3D stereophotogrammetric images. Two observers carried out soft-tissue analysis on 3D photographs twice for 20 patients. A reference frame and 49 landmarks were identified on each 3D photograph. Paired Students t-test was used to test the reproducibility and Pearsons correlation coefficient to determine the reliability of the landmark identification. Intra- and interobserver reproducibility of the landmarks were high. The study showed a high reliability coefficient for intraobserver (0.97 (0.90 - 0.99)) and interobserver reliability (0.94 (0.69 - 0.99)). Identification of the landmarks in the midline was more precise than identification of the paired landmarks. In conclusion, the redefinition of bone-related soft tissue 3D landmarks in combination with the 3D photograph reference system resulted in an accurate and reliable 3D photograph based soft tissue analysis. This shows that hard tissue data are not needed to perform accurate soft tissue analysis.

The accuracy of matching three-dimensional photographs with skin surfaces derived from cone-beam computed tomography

The state-of-the-art diagnostic tools in oral and maxillofacial surgery and preoperative orthodontic treatment are mainly two-dimensional, and consequently reveal limitations in describing the three-dimensional (3D) structures of a patients face. New 3D imaging techniques, such as 3D stereophotogrammetry (3D photograph) and cone-beam computed tomography (CBCT), have been introduced. Image fusion, i.e. registration of a 3D photograph upon a CBCT, results in an accurate and photorealistic digital 3D data set of a patients face. The purpose of this study was to determine the accuracy of three different matching procedures. For 15 individuals the textured skin surface (3D photograph) and untextured skin surface (CBCT) were matched by two observers using three different methods to determine the accuracy of registration. The registration error was computed as the difference (mm) between all points of both surfaces. The registration errors were relatively large at the lateral neck, mouth and around the eyes. After exclusion of artefact regions from the matching process, 90% of the error was within+/-1.5 mm. The remaining error was probably caused by differences in head positioning, different facial expressions and artefacts during image acquisition. In conclusion, the 3D data set provides an accurate and photorealistic digital 3D representation of a patients face.

Registration of 3-Dimensional Facial Photographs for Clinical Use

PURPOSE To objectively evaluate treatment outcomes in oral and maxillofacial surgery, pre- and post-treatment 3-dimensional (3D) photographs of the patients face can be registered. For clinical use, it is of great importance that this registration process is accurate (< 1 mm). The purpose of this study was to determine the accuracy of different registration procedures. MATERIALS AND METHODS Fifteen volunteers (7 males, 8 females; mean age, 23.6 years; range, 21 to 26 years) were invited to participate in this study. Three-dimensional photographs were captured at 3 different times: baseline (T(0)), after 1 minute (T(1)), and 3 weeks later (T(2)). Furthermore, a 3D photograph of the volunteer laughing (T(L)) was acquired to investigate the effect of facial expression. Two different registration methods were used to register the photographs acquired at all different times: surface-based registration and reference-based registration. Within the surface-based registration, 2 different software packages (Maxilim [Medicim NV, Mechelen, Belgium] and 3dMD Patient [3dMD LLC, Atlanta, GA]) were used to register the 3D photographs acquired at the various times. The surface-based registration process was repeated with the preprocessed photographs. Reference-based registration (Maxilim) was performed twice by 2 observers investigating the inter- and intraobserver error. RESULTS The mean registration errors are small for the 3D photographs at rest (0.39 mm for T(0)-T(1) and 0.52 mm for T(0)-T(2)). The mean registration error increased to 1.2 mm for the registration between the 3D photographs acquired at T(0) and T(L). The mean registration error for the reference-based method was 1.0 mm for T(0)-T(1), 1.1 mm for T(0)-T(2), and 1.5 mm for T(0) and T(L). The mean registration errors for the preprocessed photographs were even smaller (0.30 mm for T(0)-T(1), 0.42 mm for T(0)-T(2), and 1.2 mm for T(0) and T(L)). Furthermore, a strong correlation between the results of both software packages used for surface-based registration was found. The intra- and interobserver error for the reference-based registration method was found to be 1.2 and 1.0 mm, respectively. CONCLUSION Surface-based registration is an accurate method to compare 3D photographs of the same individual at different times. When performing the registration procedure with the preprocessed photographs, the registration error decreases. No significant difference could be found between both software packages that were used to perform surface-based registration.

Integration of digital dental casts in 3-dimensional facial photographs

INTRODUCTION Since 1915, various researchers have tried to make a 3-dimensional (3D) model of the complete face, with the dentition in the anatomically correct position. This was a difficult and time-consuming process. With the introduction of 3D digital imaging of the face and dental casts, researchers have regained interest in this topic. The purpose of this technical report is to present a feasibility study of the integration of a digital dental cast into a 3D facial picture. METHODS For the integration, 3 digital data sets were constructed: a digital dental cast, a digital 3D photograph of the patient with the teeth visible, and a digital 3D photograph of the patient with the teeth in occlusion. By using a special iterated closest point algorithm, these 3 data sets were matched to place them in the correct anatomical position. RESULTS After matching the 3 data sets, we obtained a 3D digital model with the dental cast visible through the transparent picture of the patients face. When the distance between the matched data sets was calculated, an average distance of 0.35 mm (SD, 0.32 mm) was shown. This means that matching the data sets is acceptable. CONCLUSIONS It seems technically possible to make a data set of a patients face with the dentition positioned into this 3D picture. Future research needs to establish the value of this 3D fused data set of the face and the dentition in orthodontic diagnosis and treatment planning.

Dental models made with an intraoral scanner: A validation study.

INTRODUCTION Our objectives were to determine the validity and reproducibility of measurements on stereolithographic models and 3-dimensional digital dental models made with an intraoral scanner. METHODS Ten dry human skulls were scanned; from the scans, stereolithographic models and digital models were made. Two observers measured transversal distances, mesiodistal tooth widths, and arch segments on the skulls and the stereolithographic and digital models. All measurements were repeated 4 times. Arch length discrepancy and tooth size discrepancy were calculated. Statistical analysis was performed by using paired t tests. RESULTS For the measurements on the stereolithographic and digital models, statistically significant differences were found. However, these differences were considered to be clinically insignificant. Digital models had fewer statistically significant differences and generally the smallest duplicate measurement errors compared with the stereolithographic models. CONCLUSIONS Stereolithographic and digital models made with an intraoral scanner are a valid and reproducible method for measuring distances in a dentition.

3D evaluation of the lingual fracture line after a bilateral sagittal split osteotomy of the mandible.

The purpose of this prospective observational study was to evaluate whether cone beam CT (CBCT) is a useful tool for analyzing the fracture line in a bilateral sagittal split osteotomy (BSSO). The patient group consisted of 40 consecutive patients (9 males and 31 females) with a mandibular hypoplasia who underwent a BSSO advancement (Hunsuck modification; n=80 splits) between September 2006 and July 2008. The mean age at the time of surgery was 34 years (range 17-61 years). A newly developed lingual split scale was used to categorize the path of the fracture line on the lingual side of the ramus based on one-day postoperative data sets reconstructed from CBCT data. Although all splits (n=80) were performed according to the standardized protocol, only 51% of the fracture lines run according to the Hunsucks description, whereas 33% ran through the mandibular canal and 16% split otherwise. The split pattern was influenced by the length of the medial osteotomy (p=0.01). In conclusion, 3D imaging is a useful tool for analyzing the surgical outcome of a BSSO and has the potential to provide substantial data on the position of the proximal segments as a result of the lingual fracture line.

Variation of the face in rest using 3D stereophotogrammetry.

To evaluate treatment outcomes following oral and maxillofacial surgery, pre- and post-treatment three-dimensional (3D) photographs of the patients face can assessed, but this procedure is accurate only if the face is captured with the same facial expression every time. The purpose of this prospective study was to determine variations in the face at rest; 100 3D photographs of the same individual were acquired at different times. Initially, 50 3D photographs were obtained; 25 using a wax bite to ensure similar occlusion between subsequent photographs and 25 without wax bite. This procedure was repeated 6 weeks later. Variation of the face at rest was computed. The influence of time and wax bite was investigated. Different anatomical regions were investigated separately. A mean variation of 0.25 mm (0.21-0.27 mm) was found (standard deviation 0.157 mm). No large differences were found between different time points or use of wax bite. Regarding separate anatomical regions, there were small variations in the nose and forehead regions; the largest variations were found in the mouth and eyes. This study showed small overall variation within the face at rest. In conclusion, different 3D photographs can be reproduced accurately and used in a clinical setting for treatment follow-up and evaluation.

Reproducibility of 3 Different Tracing Methods Based on Cone Beam Computed Tomography in Determining the Anatomical Position of the Mandibular Canal

PURPOSE To investigate the reproducibility of 3 different tracing methods to determine a reliable method to define the proper anatomical position of the mandibular canal based on cone beam computed tomography (CBCT) data. MATERIALS AND METHODS Five dentate and 5 edentate patients were selected at random from the CBCT database. Two independent observers traced both the left and the right mandibular canal using 3-dimensional image-based planning software (Procera System NobelGuide; Nobel Biocare, Göteborg, Sweden). All mandibular canals were traced using 3 different methods. Method I was based on coronal views, also known as cross-sections. Panorama-like reconstructions were the starting point for method II. The third method combined methods I and II. RESULTS With respect to interobserver reliability, no significant difference (P = .34) for the various methods was observed. The reproducibility was better in edentate than in dentate jaws (P = .0015). The difference between 2 tracings was the lowest for the combined method: within a range of 1.3 mm in 95% of the course of the canal. The most obvious deviations were mainly seen in the anterior part of the canal. CONCLUSIONS The best reproducible method for mandibular canal tracing is the combined method III. Between observers, still a mean 95th percentile deviation threshold of 1.3 mm (SD 0.384) is noted, indicating that a safety zone of 1.7 mm should be respected. When planning surgery on CBCT-based data, surgeons should be aware of the obvious deviations located in the region of the anterior loop of the canal.

One year postoperative hard and soft tissue volumetric changes after a BSSO mandibular advancement.

In this study, cone beam computed tomography (CBCT) and three dimensional (3D) stereophotogrammetry are used to compare the 3D skeletal and soft tissue changes caused by a bilateral sagittal split osteotomy (BSSO) 1 year after a mandibular advancement. Eighteen consecutive patients with a hypoplastic mandible were treated with a BSSO according to the Hunsuck modification. Preoperatively and 1 year postoperatively, a CBCT scan was acquired and a 3D photograph. The pre- and postoperative CBCT scans were matched using voxel based registration. After registration, the mandible could be segmented in the pre- and postoperative scans. The preoperative scan was subtracted from the postoperative scan, resulting in the hard tissue difference. To investigate the soft tissue changes, the pre- and postoperative 3D photographs were registered using surface based registration. After registration the preoperative surface could be subtracted from the postoperative surface, resulting in the overall volumetric difference. As expected, a correlation between mandibular advancent and volumetric changes of the hard tissues was found. The correlation between advancement and soft tissues was weak. The labial mental fold stretched after surgery. This study proved that using 3D imaging techniques it is possible to document volumetric surgical changes accurately and objectively.

Integration of Digital Dental Casts in Cone-Beam Computed Tomography Scans

Cone-beam computed tomography (CBCT) is widely used in maxillofacial surgery. The CBCT image of the dental arches, however, is of insufficient quality to use in digital planning of orthognathic surgery. Several authors have described methods to integrate digital dental casts into CBCT scans, but all reported methods have drawbacks. The aim of this feasibility study is to present a new simplified method to integrate digital dental casts into CBCT scans. In a patient scheduled for orthognathic surgery, titanium markers were glued to the gingiva. Next, a CBCT scan and dental impressions were made. During the impression-taking procedure, the titanium markers were transferred to the impression. The impressions were scanned, and all CBCT datasets were exported in DICOM format. The two datasets were matched, and the dentition derived from the scanned impressions was transferred to the CBCT of the patient. After matching the two datasets, the average distance between the corresponding markers was 0.1 mm. This novel method allows for the integration of digital dental casts into CBCT scans, overcoming problems such as unwanted extra radiation exposure, distortion of soft tissues due to the use of bite jigs, and time-consuming digital data handling.