Accuracy of Different Modalities to Record Natural Head Position in 3 Dimensions: A Systematic Review.

PURPOSE: Three-dimensional (3D) images are taken with positioning devices to ensure a patient's stability, which, however, place the patient's head into a random orientation. Reorientation of images to the natural head position (NHP) is necessary for appropriate assessment of dentofacial deformities before any surgical planning. The aim of this study was to review the literature systematically to identify and evaluate the various modalities available to record the NHP in 3 dimensions and to compare their accuracy. MATERIALS AND METHODS: A systematic literature search of the PubMed, Cochrane Library and Embase databases, with no limitations on publication time or language, was performed in July 2015. The search and evaluations of articles were performed in 4 rounds. The methodologies, accuracies, advantages, and limitations of various modalities to record NHP were examined. RESULTS: Eight articles were included in the final review. Six modalities to record NHP were identified, namely 1) stereophotogrammetry, 2) facial markings along laser lines, 3) clinical photographs and the pose from orthography and scaling with iterations (POSIT) algorithm, 4) digital orientation sensing, 5) handheld 3D camera measuring system, and 6) laser scanning. Digital orientation sensing had good accuracy, with mean angular differences from the reference within 1° (0.07 ± 0.49° and 0.12 ± 0.54°, respectively). Laser scanning was shown to be comparable to digital orientation sensing. The method involving clinical photographs and the POSIT algorithm was reported to have good accuracy, with mean angular differences for pitch, roll, and yaw within 1° (-0.17 ± 0.50°). Stereophotogrammetry was reported to have the highest reliability, with mean angular deviations in pitch, roll, and yaw for active and passive stereophotogrammetric devices within 0.1° (0.004771 ± 0.045645° and 0.007572 ± 0.079088°, respectively). CONCLUSIONS: This systematic review showed that recording the NHP in 3 dimensions with a digital orientation sensor has good accuracy. Laser scanning was found to have comparable accuracy to digital orientation sensing, but routine clinical use was limited by its high cost and low portability. Stereophotogrammetry and the method using a single clinical photograph and the POSIT algorithm were potential alternatives. Nevertheless, clinical trials are needed to verify their applications in patients. Preferably, digital orientation sensor should be used as a reference for comparison with new proposed methods of recording the NHP in future research.

High-Temperature Experimental and Theoretical Study of the Unimolecular Dissociation of 1,3,5-Trioxane.

Unimolecular dissociation of 1,3,5-trioxane was investigated experimentally and theoretically over a wide range of conditions. Experiments were performed behind reflected shock waves over the temperature range of 775-1082 K and pressures near 900 Torr using a high-repetition rate time of flight mass spectrometer (TOF-MS) coupled to a shock tube (ST). Reaction products were identified directly, and it was found that formaldehyde is the sole product of 1,3,5-trioxane dissociation. Reaction rate coefficients were extracted by the best fit to the experimentally measured concentration-time histories. Additionally, high-level quantum chemical and RRKM calculations were employed to study the falloff behavior of 1,3,5-trioxane dissociation. Molecular geometries and frequencies of all species were obtained at the B3LYP/cc-pVTZ, MP2/cc-pVTZ, and MP2/aug-cc-pVDZ levels of theory, whereas the single-point energies of the stationary points were calculated using coupled cluster with single and double excitations including the perturbative treatment of triple excitation (CCSD(T)) level of theory. It was found that the dissociation occurs via a concerted mechanism requiring an energy barrier of 48.3 kcal/mol to be overcome. The new experimental data and theoretical calculations serve as a validation and extension of kinetic data published earlier by other groups. Calculated values for the pressure limiting rate coefficient can be expressed as log10 k∞ (s(-1)) = [15.84 - (49.54 (kcal/mol)/2.3RT)] (500-1400 K).

Theoretical study of the reaction kinetics of atomic bromine with tetrahydropyran.

A detailed theoretical analysis of the reaction of atomic bromine with tetrahydropyran (THP, C5H10O) was performed using several ab initio methods and statistical rate theory calculations. Initial geometries of all species involved in the potential energy surface of the title reaction were obtained at the B3LYP/cc-pVTZ level of theory. These molecular geometries were reoptimized using three different meta-generalized gradient approximation (meta-GGA) functionals. Single-point energies of the stationary points were obtained by employing the coupled-cluster with single and double excitations (CCSD) and fourth-order Møller-Plesset (MP4 SDQ) levels of theory. The computed CCSD and MP4(SDQ) energies for optimized structures at various DFT functionals were found to be consistent within 2 kJ mol(-1). For a more accurate energetic description, single-point calculations at the CCSD(T)/CBS level of theory were performed for the minimum structures and transition states optimized at the B3LYP/cc-pVTZ level of theory. Similar to other ether + Br reactions, it was found that the tetrahydropyran + Br reaction proceeds in an overall endothermic addition-elimination mechanism via a number of intermediates. However, the reactivity of various ethers with atomic bromine was found to vary substantially. In contrast with the 1,4-dioxane + Br reaction, the chair form of the addition complex (c-C5H10O-Br) for THP + Br does not need to undergo ring inversion to form a boat conformer (b-C4H8O2-Br) before the intramolecular H-shift can occur to eventually release HBr. Instead, a direct, yet more favorable route was mapped out on the potential energy surface of the THP + Br reaction. The rate coefficients for all relevant steps involved in the reaction mechanism were computed using the energetics of coupled cluster calculations. On the basis of the results of the CCSD(T)/CBS//B3LYP/cc-pVTZ level of theory, the calculated overall rate coefficients can be expressed as kov.,calc.(T) = 4.60 × 10(-10) exp[-20.4 kJ mol(-1)/(RT)] cm(3) molecule(-1) s(-1) for the temperature range of 273-393 K. The calculated values are found to be in excellent agreement with the experimental data published previously.

Experimental and ab initio investigations of H2S-assisted propane oxidative dehydrogenation reactions.

The oxidative dehydrogenation (ODH) reaction of propane was investigated at temperatures between 923 and 1023 K using either O2 or O2/H2S mixture as oxidant. GC analysis of the product mixtures showed that ethylene was the major olefin product in the conventional ODH reaction whereas propylene became dominant when H2S was included in the feed gas. With an oxygen-rich feed (4:2:2 C3H8:O2:H2S), ∼ 70% propane conversion, and ∼ 50% propylene selectivity could be achieved at 1023 K, a level of performance comparable to that for the ODH reaction employing reducible solid oxide catalysts. Theoretical calculations utilizing CBS-QB3 method were also conducted to explore the causes of the enhanced propylene yield and selectivity of the H2S-assisted ODH reaction. It was found that the increased propane conversion was due to a large enthalpy gain from the in situ formation of S2 that compensated for the high energy cost of hydrogen abstraction by SH and S2H. Also, the promoted propylene selectivity was attributed to the instability of the sulfur-containing products, which made the reaction route to propylene the most thermodynamically favored.

Recording of natural head position using stereophotogrammetry: a new technique and reliability study.

The purpose of this study was to develop a technique to record physical references and orient digital mesh models to a natural head position using stereophotogrammetry (SP). The first step was to record the digital mesh model of a hanging reference board placed at the capturing position of the SP machine. The board was aligned to true vertical using a plumb bob. It also was aligned with a laser plane parallel to a hanging mirror, which was located at the center of the machine. The parameter derived from the digital mesh model of the board was used to adjust the roll, pitch, and yaw of the subsequent captures of patients' facial images. This information was valid until the next machine calibration. The board placement was repeatable, with standard deviations less than 0.1° for pitch and yaw angles and 0.15° for roll angles.

Comparison of computed tomography- and optical image-based assessment of liposome distribution.

The use of multimodal imaging as a tool to assess the in vivo pharmacokinetics and biodistribution of nanocarriers is important in understanding the nature of their in vivo transport. The current study reports the development of a nano-sized liposomal computed tomographic (CT)/optical imaging probe carrying iohexol and Cy5.5 and its use in micro-CT and optical imaging to quantitatively assess the whole-body (macroscopic), intratumoral, and microscopic distribution over a period of 8 days. These multimodal liposomes have a vascular half-life of 30.3 ± 8.9 hours in mice bearing subcutaneous H520 non-small cell lung cancer tumors, with the maximum liposome accumulation in tumor achieved 48 hours postinjection. The in vivo liposome distribution and stability were quantitatively assessed using both micro-CT and fluorescence molecular tomography. The combination of CT and optical imaging enables visualization of the liposomes at the whole-body, tumor, and cellular scales with high sensitivity. Such noninvasive tracking of therapeutic vehicles at the macro- and microscale is important for informed and rational development of novel nanocarrier systems.

Experimental and theoretical investigation of the kinetics of the reaction of atomic chlorine with 1,4-dioxane.

The rate coefficients for the reaction of 1,4-dioxane with atomic chlorine were measured from T = 292-360 K using the relative rate method. The reference reactant was isobutane and the experiments were made in argon with atomic chlorine produced by photolysis of small concentrations of Cl2. The rate coefficients were put on an absolute basis by using the published temperature dependence of the absolute rate coefficients for the reference reaction. The rate coefficients for the reaction of Cl with 1,4-dioxane were found to be independent of total pressure from p = 290 to 782 Torr. The experimentally measured rate coefficients showed a weak temperature dependence, given by k(exp)(T) = (8.4(-2.3)(+3.1)) × 10(-10) exp(-(470 ± 110)/(T/K)) cm3 molecule (-1) s(-1). The experimental results are rationalized in terms of statistical rate theory on the basis of molecular data obtained from quantum-chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, while single-point energies of the stationary points were computed at CCSD(T) level of theory. The calculations indicate that the reaction proceeds by an overall exothermic addition-elimination mechanism via two intermediates, where the rate-determining step is the initial barrier-less association reaction between the chlorine atom and the chair conformer of 1,4-dioxane. This is in contrast to the Br plus 1,4-dioxane reaction studied earlier, where the rate-determining step is a chair-to-boat conformational change of the bromine-dioxane adduct, which is necessary for this reaction to proceed. The remarkable difference in the kinetic behavior of the reactions of 1,4-dioxane with these two halogen atoms can be consistently explained by this change in the reaction mechanism.

Endoscope-assisted rigid fixation for intraoral vertical subsigmoid osteotomy: a preliminary clinical study.

PURPOSE: To illustrate the clinical technique of endoscope-assisted rigid fixation in intraoral vertical subsigmoid osteotomy and to report on early postoperative morbidities. MATERIALS AND METHODS: Six patients presenting with Class III skeletal profile were recruited. The osteotomy was performed through an intraoral route. Rigid fixation was achieved with a 3-mm stab incision located inferior to the ear pinna, allowing access to the transbuccal trocar. A rigid endoscope was introduced intraorally to improve visibility during fixation. Each patient's preoperative and 3-month postoperative radiographs and clinical morbidities (neurosensory status and temporomandibular joint function) were assessed. RESULTS: Most patients (83.3%) fully recovered inferior alveolar nerve function, and 66.6% recovered temporomandibular joint function. The scar from the stab incision was effectively camouflaged by the ear pinna and was not noticeable to the patients. CONCLUSION: This preliminary study confirms that the application of endoscope-assisted rigid fixation in intraoral vertical subsigmoid osteotomy is clinically feasible. All patients presented with minimal clinical morbidities and good stability at the early postoperative period.

Three-dimensional color maps: a novel tool for assessing craniofacial changes.

INTRODUCTION: Three-dimensional (3D) color maps are useful for analyzing data acquired by laser scanning, stereophotography, or computed tomography (CT). The authors aim to illustrate the different applications of color maps in the craniomaxillofacial region. METHODS: The images obtained from the above techniques at 2 different time points are superimposed based on a common area unaffected by the surgical intervention or growth. Using specialized software, the distance differences between the 2 superimposed images are depicted in a graphical format as a 3D color map. A color-coded scale indicating the distances accompanies these maps. RESULTS: 3D color maps can be manipulated and viewed in a variety of angles to extract the maximum diagnostic information. They facilitate the critical evaluation of facial asymmetry, accuracy of fusing CT and 3D photo data sets, and postsurgical changes. CONCLUSION: 3D color maps aid the objective assessment of craniofacial structures while enhancing visual comprehension and communication with patients.

Computer-aided maxillofacial surgery: an update.

INTRODUCTION: Recent developments in technology have revolutionized medicine and surgery. This article aims at providing an update on the current trends in computer-aided maxillofacial surgery and illustrates these advances with clinical cases. METHODS: The PubMed database was searched for articles published during the past 5 years using the keywords "maxillofacial" and "surgery, computer-assisted." Full texts of relevant articles were retrieved, and their study details were extracted. RESULTS: Among the 133 articles, most focused on cone-beam computed tomography (CBCT), stereophotography, surgical panning software, and intraoperative navigation. Stereophotography produces 3D facial photographs with natural color and texture, whereas CBCT generates excellent hard-tissue images with a substantially lower radiation than conventional CT scans. Information gathered from CBCT and stereophotography can be used for accurate diagnosis, virtual planning, and simulation of surgery with the aid of specialized software. The preplanned treatment can be executed accurately via intraoperative surgical navigation. CONCLUSION: Tremendous potential exists for computer-aided maxillofacial surgery as it moves from research to clinical care.

Orbit Segmentation by Surface Reconstruction With Automatic Sliced Vertex Screening.

GOAL: The purpose of this paper is to develop a computational approach to the segmentation of human orbits. METHODS: The first step is to perform Hounsfield units thresholding to segment the bony structure around the orbit. Then, a three-dimensional mesh model is generated. Poisson surface reconstruction is applied to a set of automatically screened vertices, which are facing the inner orbital walls. These procedures effectively close orbital fissures; various nerves foramina; and interpolate the broken surfaces due to thin bone structures around the orbit. We also developed validation models with five dried skulls, where the orbits were filled with dental impression. Validations on the proposed algorithm were performed with the corresponding CT images and verified by experienced radiographer. RESULTS: The mean volume differences are less than 0.3%. Surface differences are within 0.3 mm of root mean square. Both differences are not clinically significant. SIGNIFICANCE: Traditional approaches are slice-by-slice manual editing or shape interpolation with selected slices interactively. It is not only time consuming, but also inefficient, exhibits interoperator variability, and repeatability problems. In the proposed method, most of the manual processes are eliminated with adjustable vertex screening parameters. It makes the proposed method repeatable.

Automatic Detection and Reproduction of Natural Head Position in Stereo-Photogrammetry.

UNLABELLED: The aim of this study was to develop an automatic orientation calibration and reproduction method for recording the natural head position (NHP) in stereo-photogrammetry (SP). A board was used as the physical reference carrier for true verticals and NHP alignment mirror orientation. Orientation axes were detected and saved from the digital mesh model of the board. They were used for correcting the pitch, roll and yaw angles of the subsequent captures of patients' facial surfaces, which were obtained without any markings or sensors attached onto the patient. We tested the proposed method on two commercial active (3dMD) and passive (DI3D) SP devices. The reliability of the pitch, roll and yaw for the board placement were within ±0.039904°, ±0.081623°, and ±0.062320°; where standard deviations were 0.020234°, 0.045645° and 0.027211° respectively. CONCLUSION: Orientation-calibrated stereo-photogrammetry is the most accurate method (angulation deviation within ±0.1°) reported for complete NHP recording with insignificant clinical error.

Frontal facial proportions of 12-year-old southern Chinese: a photogrammetric study.

This study aimed to establish norm values for facial proportion indices among 12-year-old southern Chinese children, to determine lower facial proportion, and to identify gender differences in facial proportions.A random population sample of 514 children was recruited. Fifteen facial landmarks were plotted with ImageJ (V1.45) on standardized photos and 22 Facial proportion index values were obtained. Gender differences were analyzed by 2-sample t-test with 95% confidence interval. Repeated measurements were conducted on approximately 10% of the cases.The rate of adopted subjects was 52.5% (270/514). Intraclass correlation coefficient values (ICC) for intra- examiner reliability were >0.87. Population facial proportion index values were derived. Gender differences in 11 of the facial proportion indices were evident (P < 0.05).Upper face-face height (N- Sto/ N- Gn), vermilion height (Ls-Sto/Sto-Li), upper face height-biocular width (N-Sto/ExR-ExL) and nose -face height (N-Sn/N-Gn) indices were found to be larger among girls (P < 0.01). Males had larger lower face-face height (Sn -Gn/ N-Gn), mandibulo-face height (Sto-Gn/N-Gn), mandibulo-upper face height (Sto-Gn/N-Sto), nasal (AlR-AlL/N-Sn), upper lip height-mouth width (Sn-Sto/ChR-ChL), upper lip-upper face height (Sn-Sto/N-Sto) and upper lip-nose height (Sn-Sto/N-Sn) indices (P < 0.05).Population norm of facial proportion indices for 12-year-old Southern Chinese were derived and mean lower facial proportion were obtained. Sexual dimorphism is apparent.

Angular photogrammetric analysis of the soft tissue profile in 12-year-old southern Chinese.

INTRODUCTION: To quantify average angular measurements that define the soft tissue profiles of 12-year-old southern Chinese and to determine gender differences. MATERIALS AND METHODS: A random population sample of 514 12-year-old children was recruited (about 10% of a Hong Kong Chinese birth cohort). Photographs were taken in natural head posture and 12 soft tissue landmarks were located on the photos to measure 12 angular measurements using ImageJ (V1.45s) for Windows. Approximately 10% of photographs were reanalyzed and method error was calculated. Angular norm values for the 12 parameters were determined and gender differences were assessed using 2 sample T-test with 95% confidence interval. RESULTS: The response rate was 54.1% (278/514). Norm values for the 12 angular measurements were generated. The greatest variability was found for the nasolabial (Cm-Sn-Ls) and labiomental (Li-Sm-Pg) angles. Gender differences were found in 4 angular parameters: vertical nasal angle (N-Prn/TV) (p < 0.05), cervicomental angle (G-Pg/C-Me) (p < 0.001), facial convexity angle (G-Sn-Pg) (p < 0.01) and total facial convexity angle (G-Prn-Pg)(p < 0.01). CONCLUSION: Norm values for 12 angular measurements among 12-year-old southern Chinese children were provided and some variability noted. Gender differences were apparent in several angular measurements. This study has implications in developing norm values for southern Chinese and for comparison with other ethnic groups.

Perioperative antibiotic prophylaxis in orthognathic surgery: a systematic review and meta-analysis of clinical trials.

OBJECTIVE: The aim of this study was to investigate whether the use of antibiotic prophylaxis in orthognathic surgery can effectively reduce the postoperative infection rate. STUDY DESIGN: Electronic databases were searched and reference lists checked. Full articles meeting the inclusion criteria were retrieved. Study details and outcome data of these reports were statistically analyzed. There was no language limitation. RESULTS: Five randomized clinical trials were included in the final review process: 4 articles compared the period of prophylactic antibiotic usage, and 1 compared the infection prevention effect of different types of antibiotics with placebo. Although a significantly higher infection rate was found in the placebo group, no significant difference could be found related to infection prevention between short- and long-term antibiotic regimen. CONCLUSIONS: Prophylactic antibiotic regimen is considered to be useful for infection prevention in orthognathic surgery. A single-dose regimen is recommended; application for extended postoperative period is not advocated.

Three-dimensional cephalometric norms of Chinese adults in Hong Kong with balanced facial profile.

OBJECTIVE: The objectives of this study were (1) to develop a 3D cephalometric analysis scheme applicable to assessing dentofacial deformities; and (2) to create a normative database of 3D cephalometric measurements for adult Chinese in Hong Kong. STUDY DESIGN: A cross-sectional study was conducted on 50 male and 50 female adults with normal balanced facial profile and occlusion. Cone-beam computed tomography and stereo photogrammetry imaging were performed on all subjects. Three-dimensional virtual models were generated from imaging data, and cephalometric analysis was performed using specialized software. A new 3D cephalometric analysis scheme appropriate for orthognathic surgery as well as a new reference plane (supraorbital margin plane) for midfacial assessment was used in this study. RESULTS: The cephalometric norms generated in this study were comparable with those reported in the literature for conventional 2D cephalometric analysis and the unique features of Chinese faces. The results also showed significant differences between males and females in most of the facial height measurements (P < .01). CONCLUSIONS: This is the first database of 3D cephalometric norms based on CBCT and 3D photogrammetry of the Chinese population in Hong Kong. This can be a useful reference for characterizing facial deformities in 3 dimensions. Moreover, 3D cephalometric analysis has the potential of incorporating new measurement methods that are difficult if not impossible in 2D cephalometric analysis.

Three-dimensional photogrammetry for surgical planning of tissue expansion in hemifacial microsomia.

BACKGROUND: We aim to illustrate the applications of 3-dimensional (3-D) photogrammetry for surgical planning and longitudinal assessment of the volumetric changes in hemifacial microsomia. METHODS: A 3-D photogrammetric system was employed for planning soft tissue expansion and transplantation of a vascularized scapular flap for a patient with hemifacial microsomia. The facial deficiency was calculated by superimposing a mirror of the normal side on the preoperative image. Postsurgical volumetric changes were monitored by serial superimposition of 3-D images. RESULTS: A total of 31 cm(3) of tissue expansion was achieved within a period of 4 weeks. A scapular free flap measuring 8 cm × 5 cm was transplanted to augment the facial deficiency. Postsurgical shrinkage of the flap was observed mainly in the first 3 months and it was minimal thereafter. CONCLUSION: 3-D photogrammetry can be used as a noninvasive objective tool for assessing facial deformity, planning, and postoperative follow-up of surgical correction of facial asymmetry.

The long-term effect of transport distraction in the management of temporomandibular joint ankylosis.

BACKGROUND: The purpose of this study was to investigate the long-term effect of condylar reconstruction by transport distraction of the mandibular ramus after the release of temporomandibular joint ankylosis. METHODS: Five patients presenting with unilateral temporomandibular joint ankylosis corrected by gap arthroplasty and transport distraction of the ascending mandibular ramus were recruited for this prospective cohort study. A clinical evaluation of each case was performed longitudinally before and during the operation, during the distraction consolidation period, and 1 to 2 years after removal of the distractor. The assessment criteria included temporomandibular joint mobility and patient satisfaction expressed with reference to a visual analogue scale. RESULTS: The mean preoperative mouth opening of the five patients was 14 mm. Coronoidectomies were performed concurrently to widen the mouth opening in all cases. Maxillomandibular osteotomies were performed in three cases to correct associated dentofacial deformities. The mean mouth opening achieved during the operations was 40.4 mm. At long-term follow-up, the mean mouth opening was 38 mm, and no sign or symptom of temporomandibular joint dysfunction was noted. The mean patient satisfaction score was 8.6 of 10. CONCLUSIONS: Transport distraction of the mandibular ramus is a good treatment modality for temporomandibular joint ankylosis, particularly for adults. It can achieve long-term, symptom-free, stable mouth opening.