New Methods to Evaluate Craniofacial Deformity and to Plan Surgical Correction

Computer-Aided Freehand Maxillary Repositioning

The authors aimed to test the hypothesis that in orthognathic surgery the maxilla could be repositioned using spatial distances from Glabella to 3 maxillary dental landmarks as references. An asymmetric skeletal Class 3 malocclusion patient was involved and bimaxillary orthognathic surgery was planned. Virtual surgery was simulated and spatial distances from Glabella to midpoint of the upper dentition (U0) and bilateral medial-buccal cusp of the first molar (6L and 6R) were measured. These distances were used as the repositioning references and were imported intraoperatively into a digital caliper after the maxilla was mobilized, the repositioning of maxilla was manipulated till all the true spatial distances reached the references. Postoperative computed tomography head model were superimposed onto the planned head model, the maxillary repositioning error was assessed using spatial distances between the pre- and postoperative dental landmarks. The asymmetric skeletal Class 3 malocclusion was corrected through bimaxillary surgery and the errors at U0, 6R and 6L was 1.37, 1.79, and 1.45 mm. The maxilla could be repositioned using spatial distances from Glabella to 3 maxillary dental landmarks as references.

A new approach of splint-less orthognathic surgery using a personalized orthognathic surgical guide system: A preliminary study

The purpose of this study was to evaluate a personalized orthognathic surgical guide (POSG) system for bimaxillary surgery without the use of surgical splint. Ten patients with dentofacial deformities were enrolled. Surgeries were planned with the computer-aided surgical simulation method. The POSG system was designed for both maxillary and mandibular surgery. Each consisted of cutting guides and three-dimensionally (3D) printed custom titanium plates to guide the osteotomy and repositioning the bony segments without the use of the surgical splints. Finally, the outcome evaluation was completed by comparing planned outcomes with postoperative outcomes. All operations were successfully completed using the POSG system. The largest root-mean-square deviations were 0.74mm and 1.93° for the maxillary dental arch, 1.10mm and 2.82° for the mandibular arch, 0.83mm and 2.59° for the mandibular body, and 0.98mm and 2.45° for the proximal segments. The results of the study indicated that our POSG system is capable of accurately and effectively transferring the surgical plan without the use of surgical splint. A significant advantage is that the repositioning of the bony segments is independent to the mandibular autorotation, thus eliminates the potential problems associated with the surgical splint.

A new design of CAD/CAM surgical template system for two-piece narrowing genioplasty

The purpose of this study was to develop and validate a new chin template system for a two-piece narrowing genioplasty. Nine patients with wide chin deformities were enrolled. Surgeries were planned with the computer-aided surgical simulation (CASS) planning method. Surgical splints and chin templates were designed in a computer and fabricated using a three-dimensional printing technique. The chin template system included a cutting guide and a repositioning guide for a two-piece narrowing genioplasty. These guides were also designed to avoid the mental foramen area and inferior alveolar nerve loops during the osteotomy, for nerve protection. After surgery, the outcome evaluation was completed by first superimposing the postoperative computed tomography model onto the planned model, and then measuring the differences between the planned and actual outcomes. All surgeries were completed successfully using the chin template system. No inferior alveolar nerve damage was seen in this study. With the use of the chin templates, the largest linear root mean square deviation (RMSD) between the planned and the postoperative chin segments was 0.7mm and the largest angular RMSD was 4.5°. The results showed that the chin template system provides a reliable method of transfer for two-piece osseous narrowing genioplasty planning.

Comparative validity and reproducibility study of various landmark-oriented reference planes in 3-dimensional computed tomographic analysis for patients receiving orthognathic surgery

Background

Three-dimensional computed tomographic imaging has become popular in clinical evaluation, treatment planning, surgical simulation, and outcome assessment for maxillofacial intervention. The purposes of this study were to investigate whether there is any correlation among landmark-based horizontal reference planes and to validate the reproducibility and reliability of landmark identification.

Materials and Methods

Preoperative and postoperative cone-beam computed tomographic images of patients who had undergone orthognathic surgery were collected. Landmark-oriented reference planes including the Frankfort horizontal plane (FHP) and the lateral semicircular canal plane (LSP) were established. Four FHPs were defined by selecting 3 points from the orbitale, porion, or midpoint of paired points. The LSP passed through both the lateral semicircular canal points and nasion. The distances between the maxillary or mandibular teeth and the reference planes were measured, and the differences between the 2 sides were calculated and compared. The precision in locating the landmarks was evaluated by performing repeated tests, and the intraobserver reproducibility and interobserver reliability were assessed.

Results

A total of 30 patients with facial deformity and malocclusion—10 patients with facial symmetry, 10 patients with facial asymmetry, and 10 patients with cleft lip and palate—were recruited. Comparing the differences among the 5 reference planes showed no statistically significant difference among all patient groups. Regarding intraobserver reproducibility, the mean differences in the 3 coordinates varied from 0 to 0.35 mm, with correlation coefficients between 0.96 and 1.0, showing high correlation between repeated tests. Regarding interobserver reliability, the mean differences among the 3 coordinates varied from 0 to 0.47 mm, with correlation coefficients between 0.88 and 1.0, exhibiting high correlation between the different examiners.

Conclusions

The 5 horizontal reference planes were reliable and comparable for 3D craniomaxillofacial analysis. These reference planes were useful in standardizing the orientation of 3D skull models.

Measuring mandibular asymmetry in Class I normal subjects using 3D novel coordinate system

Introduction:

Orthodontic treatment plays a major role in cosmetic dentistry. A harmonious facial balance is normally the end point in comprehensive orthodontic outcomes. In order to achieve this goal, correct diagnosis of asymmetry should be done starting from the outer facial morphology forms and progressively moving to the dental occlusion. The prime importance of measuring mandibular asymmetry is its tremendous effect on the occlusion.

Objective:

The aim of this study was to measure mandibular asymmetry in a cohort Class I molar relationship comparing right and left sides using new three-dimensions (3D) imaging technique with the aid of 3D software (in vivo 5.2.3 [San Jose, CA]).

Materials and Methods:

35 DICOM files were initially collected retrospectively and seven were excluded due to (1) condylar resorption, (2) history of trauma and (3) unclear DICOM file. A new coordinate system was set for the mid-sagittal plane (MSP), Frankfort horizontal plane and frontal plane (FP). Each cone beam computed tomography (CBCT) was appraised using 16 evaluation criteria bilaterally. Five mandibular landmarks were selected: Condylion_R, Gonion_R, Menton, Gonion_L and Condylion_L. Using these points, the mandible was further divided into four parts: (1) Ramus length right side, body of the mandible right side, body of the Ramus left side and Ramus length left side. The angles between each line and the three different planes were acquired in order to compare each line from a 3D aspect. Mean and standard deviation were calculated for the 28 CBCTs.

Results:

Significant bilateral differences were reported in the angle between the ramus length and MSP and the ramus length and the FP (P < 0.05). Significant lateroanterior shift of the mandibular ramus on the left side in comparison with the right side.

Conclusion:

Viewing an object using three different angles between the four parts of the mandible and each plane is a valid method to replicate the actual object.

Interdisciplinary treatment of a patient with bilateral cleft lip and palate and congenitally missing and transposed teeth

The comprehensive treatment of a patient with cleft lip and palate requires an interdisciplinary approach for functional and esthetic outcomes. A 20-year-old woman with bilateral cleft lip and palate had a chief complaint of unesthetic appearance of her teeth and the presence of oronasal fistulae. Her clinical and radiographic evaluation showed a dolichofacial growth pattern, a Class II skeletal relationship with retroclined maxillary central incisors, 5 mm of negative overjet, maxillary constriction, maxillary and mandibular crowding, congenitally missing maxillary right incisors and left lateral incisor, and a transposed maxillary left canine. Her treatment plan included the extraction of 3 premolars, maxillary expansion, segmental maxillary osteotomy, repair of the oronasal fistulae, rhinoplasty, periodontal surgery, and prosthodontic rehabilitation. To obtain a better occlusion and reduce the dimensions of the fistulae, orthognathic surgery comprising linear and rotational movements of the maxillary segments (premaxilla, right and left maxillary alveolar segments) in all 3 axes was planned by performing 3-dimensional virtual surgery on 3-dimensional computerized tomography. At the end of the interdisciplinary treatment, a functional occlusion, a harmonious profile, and patient satisfaction were achieved. Posttreatment records after 1 year showed stable results.