Physical Versus Digital Orthognathic Surgical Planning.

OBJECTIVE: Orthognathic occlusal repositioning wafers could be constructed virtually and 3D printed. This paper assessed the accuracy of a suggested virtual model to the conventionally established Glasgow model surgery. DESIGN: Prospective study of the orthognathic surgery models digitally. PARTICIPANTS: Seven patients who received bi-maxillary orthognathic surgeries for correction of dentofacial deformities. METHODS: The patients were clinically assessed and their cone beam cmputerized tomography (CBCT) studied. Model surgery of each patient was performed conventionally using face-bow and semi-adjustable articulator. Same plan was executed virtually using Mimics (Materialise, Leuven, Belgium) and 3Matic (Materialise, Leuven, Belgium). Conventionally fabricated acrylic wafers as well as 3D printed wafers were CBCT scanned with the casts reflecting the archived repositioning dictated by the wafers. Paired sample t test was performed to compare accuracy between intermediate and final occlusal repositioning wafers within conventional and virtual technique groups. RESULTS: The mean deviation in intermediate wafer group was 0.64 ± 0.33 mm; whereas the mean deviation in final wafer group was 0.53 ± 0.10 mm. Paired sample t test showed that there was no statistically significant difference in mean deviation between both groups ( P = 0.403). CONCLUSIONS: This virtual surgical wafer achieves a similar level of accuracy to the conventional Glasgow model surgery.

Phone-based audience response system as an adjunct in orthodontic teaching of undergraduate dental students: a cross-over randomised controlled trial.

BACKGROUND: The advent of electronic teaching facilities improves tutor-student communication. This study aims to explore the effectiveness of Phone-Based Audience Response System (PB-ARS), as an adjunctive pedagogy tool to enhance the retention of orthodontic information by dental students; and to explore the students' perception of PB-ARS. METHODS: This cross-over clustered randomised control trial included 34 males who were in the final year of their undergraduate dental training. Participants were allocated to one of two event groups (G1 and G2) using computer-generated randomisation. Both groups simultaneously attended two different traditional lectures (L 1 and L2) a week apart. During L1, PB-ARS was used as an adjunct to conventional presentation to teach G1 participants, (PB-ARS group) while G2's participants acted as a control group (CG), and were taught using a traditional presentation. In the second week (L2), the interventions were crossed-over. Participants from both groups completed pre- and post-lecture multiple-choice questionnaires (MCQ) to assess their short-term retention of information. Their performance in the final MCQ exam (10 weeks following L2) was tracked to assess the long-term retention of the information. Participants also completed post-lecture questionnaires to evaluate their perceptions. RESULTS: Twenty-nine and 31 participants from the CG and PB-ARS group completed this trial, respectively. Although 87.5% of students in the PB-ARS group showed an improvement in their immediate post-lecture scores compared with 79.3% for the CG, it was statistically insignificant (p = 0.465). Similarly, the intervention showed an insignificant effect on the long-term retention of the knowledge (p = 0.560). There was a mildly but favourable attitude of students towards the use of PB-ARS. However, the difference in the overall level of satisfaction between both groups was statistically insignificant (p = 0.183). CONCLUSION: PB-ARS has a minimal and insignificant effect on the short- and long-term retention of orthodontic knowledge by male undergraduate dental students. PB-ARS was the preferred adjunct tool to conventional classroom teaching. Due to the limitations of this trial, a long-term randomised controlled trial with a larger sample size is recommended.

3D effects of a bone-anchored intra-oral protraction in treating class III growing patient: a pilot study.

OBJECTIVES: The aim of this prospective case series study is to assess the three-dimensional (3D) skeletal and soft tissue effects of the alternate rapid maxillary expansion and constriction (Alt-RAMEC) protocol in conjunction with a miniscrew-supported class III elastic wear in class III growing patients. MATERIALS AND METHODS: Fourteen consecutive participants (mean age 12.05 ± 1.09 years), who displayed class III malocclusions with retrognathic maxillae, were recruited. A cone beam computed tomography (CBCT) scan was acquired before commencing treatment (T1). All participants were treated with a tooth-bone-borne rapid maxillary expansion (hybrid MARME) appliance that was activated by the Alt-RAMEC protocol for 9 weeks. This was followed by full-time class III elastics, delivering 400 g/side, to protract the maxilla. When a positive overjet was achieved, protraction was ceased and a post-treatment CBCT scan (T2) was taken. The 3D analysis of pre- and post-treatment CBCT scans was blinded. The scans were registered on the anterior cranial base. The Euclidean distance between the two extracted surface models of the pre- and post-treatment scans was displayed as a color surface map. RESULTS: All participants completed the intervention successfully. The majority of the participants showed protraction of the anterior maxillary region (71.4%) and in the zygomatic processes (64.2%). The maxilla significantly protracted (SNA 1.87° ± 1.06°; Vert.T-A 3.29 ± 1.54 mm), while the mandibular base significantly redirected posteriorly (SNB - 2.03° ± 0.85°, Vert.T-B - 3.43 ± 4.47 mm) and that was reflected on the ANB and Wits measurements. No adverse effects were observed. CONCLUSION: Class III elastics combined with the Alt-RAMEC activation protocol of the hybrid MARME appliance is an effective treatment method for mild/moderate class III malocclusions. A long-term follow-up and comparisons with other treatment modalities are required.

Does rapid maxillary expansion affect nasopharyngeal airway? A prospective Cone Beam Computerised Tomography (CBCT) based study.

BACKGROUND AND PURPOSE: There is limited literature discussing the three dimnesional (3D) impact of rapid maxillary expansion (RME) on upper airway. The purpose of this prospective Cone Beam Computerised Tomography (CBCT) based study is to assess the immediate 3D effects and to correlate the volumteric changes in the upper naspharyngeal airway spaces secondary to RME. MATERIALS AND METHODS: Seventeen participants (8 male, 9 female, with a mean age of 12.6 ± 1.8 years), who required RME for the management of narrow maxillary arch, were recruited for this study. The prescribed expansion regimen was quarter turn (0.25 mm), twice a day until over-expansion was achieved. The mean period for the active phase was 14 days with a range of 12-21 days. Pretreatment (T1) and immediate post-expansion (T2) CBCT images were obtained and then processed using ITK snap and OnDemand3D softwar packages. Paired t-test and Interclass Correlation Coefficient (ICC) were used to assess the reproducibility of the measurements, student t-test (P < 0.05) and Pearson Correlation Coefficient (PCC) were applied to evaluate the volumetric changes in the nasopharyngeal airway spaces, linear dentolaveolar changes and correlate these changes. MAIN FINDINGS: Though, the data of one patient was excluded from the study, owing to major differences (>5 degrees) in the head and neck posture between T1 and T2 CBCT scans, the study' findings shows that bonded RME is an effective dentoalveolar expander in growing patients (P= 0.01) with an average expansion of 3.7 mm and 2.8 mm in males and females respectively. Likewise, the upper nasopharynx (UNP) expanded significantly (15.2% in males and 12% in females). In comparison, the upper retropalatal space (URP) was significantly reduced, by almost one sixth of its original volume, more in males than females, 11.2% and 2.8% respectively. A strong direct correlation between the maxillary sinus volumetric changes, and between appliance expansion and dentoalveolar expansion were evident (PCC = 0.86, 0.75, respectively). There was also a moderate correlation between changes in the UNP and URP spaces. CONCLUSIONS: RME was found to be an effective dentoalveolar expander and significantly augment the UNP and minimize the URP space. A similar comparative clinical study with long-term follow-up would be beneficial in accurately deteremining the clinical impact of RME on the airway and breathing as well as the stability of these effects.

The Accuracy of Conformation of a Generic Surface Mesh for the Analysis of Facial Soft Tissue Changes.

PURPOSE: Three dimensional analysis of the face is required for the assessment of complex changes following surgery, pathological conditions and to monitor facial growth. The most suitable method may be "dense surface correspondence". MATERIALS AND METHODS: This method utilizes a generic facial mesh and "conformation process" to establish anatomical correspondences between two facial images. The aim of this study was to validate the use of conformed meshes to measure simulated maxillary and mandibular surgical movements. The "simulation" was performed by deforming the actual soft tissues of the participant during image acquisition. The study was conducted on 20 volunteers and used 77 facial landmarks pre-marked over six anatomical regions; left cheek, right cheek, left upper lip, philtrum, right upper lip and chin region. Each volunteer was imaged at rest and after performing 5 different simulated surgical procedures using 3D stereophotogrammetry. The simulated surgical movement was determined by measuring the Euclidean distances and the mean absolute x, y and z distances of the landmarks making up the six regions following digitization. A generic mesh was then conformed to each of the aligned six facial 3D images. The same six regions were selected on the aligned conformed simulated meshes and the surgical movement determined by determining the Euclidean distances and the mean absolute x, y and z distances of the mesh points making up the six regions were determined. RESULTS: In all cases the mean Euclidian distance between the simulated movement and conformed region was less than 0.7 mm. For the x, y and z directions the majority of differences in the mean absolute distances were less than 1.0mm except in the x-direction for the left and right cheek regions, which was above 2.0 mm. CONCLUSIONS: This concludes that the conformation process has an acceptable level of accuracy and is a valid method of measuring facial change between two images i.e. pre- and post-surgery. The conformation accuracy is higher toward the center of the face than the peripheral regions.

Effects of Le Fort I Osteotomy on the Nasopharyngeal Airway-6-Month Follow-Up.

PURPOSE: The literature discussing the impact of a single Le Fort I osteotomy on nasopharyngeal airways is limited. This study assessed the volumetric changes in the nasopharyngeal airway after a single Le Fort I osteotomy and explored the correlation between these changes and 3-dimensional surgical movements of the upper jaw. MATERIALS AND METHODS: This retrospective study was conducted in 40 patients who had undergone a single Le Fort I (maxillary advancement with or without impaction) to correct Class III malocclusion with maxillary hypoplasia. Preoperative (T1) and 6-month postoperative (T2) cone-beam computed tomographic (CBCT) scans of these patients were used for analysis. Maxillary surgical movements and volumetric changes in the nasopharyngeal airway were measured. The reproducibility of the measurements was evaluated using paired t tests and intraclass correlation coefficients. The Wilcoxon test and Pearson correlation coefficient were applied to evaluate the volumetric changes in the nasopharyngeal airway space and assess the correlations of these changes to the maxillary surgical movements. RESULTS: Six patients were excluded from the study owing to major differences (>5°) in their head and neck posture between the T1 and T2 CBCT scans. The errors of the repeated measurements were insignificant (P > .05), with a high level of agreement (r = 0.99; P < .05) between the repeated digitization of the landmarks. There was a statistically significant impact of a Le Fort I osteotomy on the right maxillary sinus (decreased by 17.8%) and the lower retropalatal space (expanded by 17.3%; P < .05). The correlation between the change in airway volume and the magnitude of surgical maxillary movements was moderate (r = .4). Similarly, there was a moderate correlation between changes in the upper nasopharynx and those in the hypopharynx. CONCLUSION: The single Le Fort I osteotomy was found to increase the retroglossal airway volume. This could be important for the treatment of obstructive sleep apnea in patients with maxillary deficiency. A long-term follow-up assessment of a larger sample with a functional assessment of airway would be beneficial to confirm these findings.

"Direct DICOM Slice Landmarking" A Novel Research Technique to Quantify Skeletal Changes in Orthognathic Surgery.

The limitations of the current methods of quantifying the surgical movements of facial bones inspired this study. The aim of this study was the assessment of the accuracy and reproducibility of directly landmarking of 3D DICOM images (Digital Imaging and Communications in Medicine) to quantify the changes in the jaw bones following surgery. The study was carried out on plastic skull to simulate the surgical movements of the jaw bones. Cone beam CT scans were taken at 3mm, 6mm, and 9mm maxillary advancement; together with a 2mm, 4mm, 6mm and 8mm "down graft" which in total generated 12 different positions of the maxilla for the analysis. The movements of the maxilla were calculated using two methods, the standard approach where distances between surface landmarks on the jaw bones were measured and the novel approach where measurements were taken directly from the internal structures of the corresponding 3D DICOME slices. A one sample t-test showed that there was no statistically significant difference between the two methods of measurements for the y and z directions, however, the x direction showed a significant difference. The mean difference between the two absolute measurements were 0.34±0.20mm, 0.22±0.16mm, 0.18±0.13mm in the y, z and x directions respectively. In conclusion, the direct landmarking of 3D DICOM image slices is a reliable, reproducible and informative method for assessment of the 3D skeletal changes. The method has a clear clinical application which includes the analysis of the jaw movements "orthognathic surgery" for the correction of facial deformities.

Innovation in prediction planning for anterior open bite correction.

This study applies recent advances in 3D virtual imaging for application in the prediction planning of dentofacial deformities. Stereo-photogrammetry has been used to create virtual and physical models, which are creatively combined in planning the surgical correction of anterior open bite. The application of these novel methods is demonstrated through the surgical correction of a case.

Comparison of the accuracy of voxel based registration and surface based registration for 3D assessment of surgical change following orthognathic surgery.

PURPOSE: Superimposition of two dimensional preoperative and postoperative facial images, including radiographs and photographs, are used to evaluate the surgical changes after orthognathic surgery. Recently, three dimensional (3D) imaging has been introduced allowing more accurate analysis of surgical changes. Surface based registration and voxel based registration are commonly used methods for 3D superimposition. The aim of this study was to evaluate and compare the accuracy of the two methods. MATERIALS AND METHODS: Pre-operative and 6 months post-operative cone beam CT scan (CBCT) images of 31 patients were randomly selected from the orthognathic patient database at the Dental Hospital and School, University of Glasgow, UK. Voxel based registration was performed on the DICOM images (Digital Imaging Communication in Medicine) using Maxilim software (Medicim-Medical Image Computing, Belgium). Surface based registration was performed on the soft and hard tissue 3D models using VRMesh (VirtualGrid, Bellevue City, WA). The accuracy of the superimposition was evaluated by measuring the mean value of the absolute distance between the two 3D image surfaces. The results were statistically analysed using a paired Student t-test, ANOVA with post-hoc Duncan test, a one sample t-test and Pearson correlation coefficient test. RESULTS: The results showed no significant statistical difference between the two superimposition methods (p<0.05). However surface based registration showed a high variability in the mean distances between the corresponding surfaces compared to voxel based registration, especially for soft tissue. Within each method there was a significant difference between superimposition of the soft and hard tissue models. CONCLUSIONS: There were no significant statistical differences between the two registration methods and it was unlikely to have any clinical significance. Voxel based registration was associated with less variability. Registering on the soft tissue in isolation from the hard tissue may not be a true reflection of the surgical change.