An innovative analysis of nasolabial dynamics of surgically managed adult patients with unilateral cleft lip and palate using 3D facial motion capture.

AIM: To compare dynamic nasolabial movement between end-of-treatment cleft and a matched non-cleft group in adult patients. MATERIALS AND METHODS: Thirteen treated adult participants with unilateral cleft lip and palate had images taken using a facial motion capture system performing a maximum smile. Seventeen landmarks were automatically tracked. For each landmark pair, on either side of the midline, changes in the x, y, and z directions were used to analyze the magnitude of displacement and path of motion. An asymmetry score was developed at rest, mid-smile, and maximum smile to assess the shape of the mouth and/or nose. RESULTS: At maximum smile, displacement of right and left cheilion was clinically and statistically (p < 0.05) less in the cleft group. The lip asymmetry score was greater (p < 0.05) at each time point in the cleft group using the clinical midline. Using Procrustes superimposition, the differences were significant (p < 0.05) only at rest and mid-smile. The alar bases were displaced significantly less (p < 0.05) in the z direction in the cleft group. The asymmetry score of the alar base was significantly higher using the clinical midline than using Procrustes superimposition in patients with cleft conditions (p < 0.001). In the cleft group, at maximum smile, the right and left cristae philter moved significantly less (p < 0.05) in the x and z directions. CONCLUSIONS: There was an increase in asymmetry score of the corners of the mouth and alar bases from rest to maximum smile. The lips were similar in shape but oriented differently in the faces of patients with cleft conditions than in individuals without those conditions.

Fluctuating asymmetry of dynamic smiles in normal individuals.

The aim of this study was to quantify the fluctuating dynamic facial asymmetry during smiling in a group of 'normal' adults, using three-dimensional (3D) motion facial capture technology. Fifty-four male and 54 female volunteers were recruited. Each subject was imaged using a passive markerless 3D motion capture system (DI4D). Eighteen landmarks were tracked through the 3D capture sequence. A facial asymmetry score was calculated based on either a clinically derived midline or Procrustes alignment; scores were based on the Euclidean distance between landmark pairs. Facial asymmetry scores were determined at three time points: rest, median, and maximum frame. Based on the clinically derived midline and on Procrustes alignment, the differences between male and female volunteers, as well as those at the three different time points, were not clinically significant. However, throughout a smile, facial and lip asymmetry scores increased over the duration of the smile. Fluctuating facial asymmetry exists within individuals, as well as between individuals. Procrustes superimposition and the clinically derived midline produced similar asymmetry scores and both are valid for symmetrical faces. However, with facial asymmetry, Procrustes superimposition may not be a valid measure, and the use of the clinically derived midline may be more appropriate, although this requires further investigation.

Quantitative dynamic analysis of the nasolabial complex using 3D motion capture: A normative data set.

INTRODUCTION: Smile reanimation should be considered from a dynamic perspective. Any intervention should restore normality. To date no such normative dynamic data has been published. AIM: To quantitatively analyse maximal smiles between a healthy group of Caucasian male and female adults using 3D motion capture (4D stereophotogrammetry). METHOD: Using a 3D facial motion capture system 54 males and 54 female volunteers were imaged whilst performing a maximal smile. Eight nasolabial landmarks were digitised and tracked. Differences in displacement and speed of bilateral landmarks between males and females were analysed in each direction (x, y, z and Euclidian), from rest (T0), to median smile (T1) and maximal smile (T2), using paired t-tests and Wilcoxon-Signed Rank tests. RESULTS: In males and females the displacement and speed of the left and right alar base landmarks were similar in the x and y directions but less in the z direction. For the philtrum, the displacement and speed of the bilateral landmarks were similar in the y and z directions, but less in the x direction. The left alar base and left philtrum moved significantly more in males. Left and right cheilion moved a similar amount in the x and y directions but more in the z direction. Labiale superius moved significantly more in the z direction, and labiale inferius moved significantly more in the y direction in males. In conclusion, this study has presented a novel normative data set of dynamic nasolabial complex movement for males and females during maximum smile. The data, as well as providing magnitudes of displacements of the nasolabial complex, also provides the speeds of movement.

Immediate effects of rapid maxillary expansion on the naso-maxillary facial soft tissue using 3D stereophotogrammetry.

BACKGROUND: Rapid maxillary expansion (RME) is used to expand the narrow maxilla. Dental and skeletal affects have previously been reported but few studies have reported on the overlying soft tissue changes. This study reports on the immediate effects of RME on the naso-maxillary facial soft tissue using 3D stereophotogrammetry. METHODS: Fourteen patients requiring upper arch expansion using RME as part of their full comprehensive orthodontic plan were recruited. Cone beam CT scans and stereophotogrammetry images were taken for each patient; pre-RME activation (T0) and immediately post-RME expansion (T1). Based on twenty-three landmarks, 13 linear and 3 angular measurements were made from each of the stereophotogrammetry images. A linear measurement at ANS was taken from each CBCT image. Using a Wilcoxon signed rank test, the pre-RME and post-RME measurements were compared. RESULTS: The mean separation of the anterior nasal spine was 3.8 mm ± 1.2 mm. The largest median increase was in nasal base width (1.6 mm), which was statistically significant (p = 0.001). Changes in the nasal dorsum height, nasal tip protrusion, philtrum width, and upper lip length were not statistically significant (p < 0.05). No significant differences were observed in the nostril linear measurements, expect for columella width (p = 0.009). Naso-labial angle decreased but was not statistically significant (p = 0.276). The only statically significant angular change was an increase in the nasal tip displacement angle (p = 0.001). CONCLUSION: Rapid maxillary expansion produces subtle changes in the naso-maxillary soft tissue complex. There is an increase in nasal base width, retraction and flattening of the nasal tip. These changes are small, less than 2 mm and variable between patients.

The validity of using surface meshes for evaluation of three-dimensional maxillary and mandibular surgical changes.

The three-dimensional (3D) changes in hard tissue position following orthognathic surgery have been reported using 3D cephalometry, changes in volume, principal component analysis, and changes based on the surface model of the hard tissue. The aim of this study was to determine the validity of using surface models as a method of assessing positional changes of the maxilla and mandible. The actual unidirectional movement of the maxilla (advancement or downgraft) and the mandible (advancement), together with bidirectional movement of the maxilla (simultaneous advancement and downgraft) were simulated on a plastic skull. Following cone beam computed tomography scanning of each surgical simulation, the actual surgical movement was compared to the analysis based on surface model movement using the mean absolute distance of all points, the 90th percentile, and the root mean square (RMS) distance. All three methods of assessment of analysis consistently underestimated the actual amount of surgical movement. The movement was approximately one-third to one-half of the actual surgical movement. The use of surface meshes and point-to-point measurements grossly underestimates the 3D changes in the maxilla and mandible in simulated surgical procedures. Currently there are limitations in fully describing the true positional changes of the maxilla or the mandible in three dimensions.

Accuracy of three-dimensional soft tissue predictions in orthognathic surgery after Le Fort I advancement osteotomies.

Prediction of postoperative facial appearance after orthognathic surgery can be used for communication, managing patients' expectations,avoiding postoperative dissatisfaction and exploring different treatment options. We have assessed the accuracy of 3dMD Vultus in predicting the final 3-dimensional soft tissue facial morphology after Le Fort I advancement osteotomy. We retrospectively studied 13 patients who were treated with a Le Fort I advancement osteotomy alone. We used routine cone-beam computed tomographic (CT) images taken immediately before and a minimum of 6 months after operation, and 3dMD Vultus to virtually reposition the preoperative maxilla and mandible in their post operative positions to generate a prediction of what the soft tissue would look like. Segmented anatomical areas of the predicted mesh were then compared with the actual soft tissue. The means of the absolute distance between the 90th percentile of the mesh points for each region were calculated, and a one-sample Student's t test was used to calculate if the difference differed significantly from 3 mm.The differences in the mean absolute distances between the actual soft tissue and the prediction were significantly below 3 mm for all segmented anatomical areas (p < 0.001), and ranged from 0.65 mm (chin) to 1.17 mm (upper lip). 3dMD Vultus produces clinically satisfactory 3-dimensional facial soft tissue predictions after Le Fort I advancement osteotomy. The mass-spring model for prediction seems to be able to predict the position of the lip and chin, but its ability to predict nasal and paranasal areas could be improved.

The novel use of three-dimensional surface models to quantify and visualise the immediate changes of the mid-facial skeleton following rapid maxillary expansion.

BACKGROUND: The transverse skeletal effects of rapid maxillary expansion (RME) have previously been assessed using cone-beam CT (CBCT). However, to date the majority of studies assess the changes based on two-dimensional slice images, which under utilises the three-dimensional (3D) data captured. This study optimizes the volumetric CBCT data by generating 3D rendered surface models to quantity and visualize the immediate 3D changes of the mid-facial bone surfaces following RME. METHODS: The sample consisted of 14 patients who required RME prior to fixed appliances. Pre-treatment (T0) and immediate post expansion (T1) CBCT images were taken. Following superimposition the mid face was divided into six anatomical regions. A one-sample t-test was used to determine if the differences between the two surfaces were significantly ≥0.5 mm. FINDINGS: All regions showed a change following RME ≥ 0.5 mm. The maxillary and nasal bones showed 2.3 mm and 2.4 mm expansion respectively, followed by the zygomatic bones (1.4 mm), 2 cases showing asymmetric expansion. CONCLUSIONS: The use of 3D surface rendered models allows quantification and visualisation of 3D changes in the mid-facial skeleton at anatomical sites distant of RME activation. Following activation there can be a pan mid-facial expansion, including not only the maxilla but also the nasal lateral bones and zygomas. The response was highly variable and asymmetric expansion can occur.

The clinical application of three-dimensional motion capture (4D): a novel approach to quantify the dynamics of facial animations.

The aim of this pilot study was to evaluate the feasibility of measuring the change in magnitude, speed, and motion similarity of facial animations in head and neck oncology patients, before and after lip split mandibulotomy. Seven subjects (four males, three females) aged 42-80 years were recruited. The subjects were asked to perform four facial animations (maximal smile, lip purse, cheek puff, and grimace) from rest to maximal position. The animations were captured using a Di4D motion capture system, which recorded 60 frames/s. Nine facial soft tissue landmarks were manually digitized on the first frame of the three-dimensional image of each animation by the same operator and were tracked automatically for the sequential frames. The intra-operator digitization error was within 0.4mm. Lip purse and maximal smile animations showed the least amount of change in magnitude (0.2mm) following surgery; speed difference was least for smile animation (-0.1mm/s). Motion similarity was found to be highest for lip purse animation (0.78). This pilot study confirmed that surgery did influence the dynamics of facial animations, and the Di4D capture system can be regarded as a feasible objective tool for assessing the impact of surgical interventions on facial soft tissue movements.

Digital replacement of the distorted dentition acquired by cone beam computed tomography (CBCT): a pilot study.

During cone beam computed tomography (CBCT) scanning, intra-oral metallic objects may produce streak artefacts, which impair the occlusal surface of the teeth. This study aimed to determine the accuracy of replacement of the CBCT dentition with a more accurate dentition and to determine the clinical feasibility of the method. Impressions of the teeth of six cadaveric skulls with unrestored dentitions were taken and acrylic base plates constructed incorporating radiopaque registration markers. Each appliance was fitted to the skull and a CBCT performed. Impressions were taken of the dentition with the devices in situ and dental models were produced. These were CBCT-scanned and the images of the skulls and models imported into computer-aided design/computer-aided manufacturing (CAD/CAM) software and aligned on the registration markers. The occlusal surfaces of each dentition were then replaced with the occlusal image of the corresponding model. The absolute mean distance between the registration markers in the skulls and the dental models was 0.09±0.02mm, and for the dentition was 0.24±0.09mm. When the method was applied to patients, the distance between markers was 0.12±0.04mm for the maxilla and 0.16±0.02mm for the mandible. It is possible to replace the inaccurate dentition on a CBCT scan using this method and to create a composite skull which is clinically acceptable.

Evaluation of an improved orthognathic articulator system. 2. Accuracy of occlusal wafers.

The errors produced by occlusal wafers constructed on casts of the teeth mounted on a standard articulator and an improved orthognathic articulator were investigated by carrying out simulated orthognathic surgery on plastic skulls. The wafers were used to relocate the position of the maxillae of the skulls. The vertical and horizontal displacements of the maxillae were determined from measurements of the positions of markers on the skull and teeth. Comparison of the magnitudes of the actual and intended movements showed that wafers constructed on the standard articulator had systematic prediction errors of up to 5mm, but the improved orthognathic articulator showed much smaller random errors. There was a statistically significant improvement in overall accuracy in predicting maxillary Le Fort I position with the use of the improved orthognathic articulator which the authors recommend for clinical use.

Evaluation of an improved orthognathic articulator system: 1. Accuracy of cast orientation.

A systematic study was carried out using plastic model skulls to quantify the accuracy of the transfer of face bow registration to the articulator. A standard Dentatus semi-adjustable articulator system was compared to a purpose built orthognathic articulator system by measuring the maxillary occlusal plane angles of plastic model skulls and of dental casts mounted on the two different types of articulators. There was a statistically significant difference between the two systems; the orthognathic system showed small random errors, but the standard system showed systematic errors of up to 28°.

Errors in orthognathic surgery planning: the effect of inaccurate study model orientation.

The results of orthognathic surgery may differ significantly from the planned outcome using dental models. The orientation of dental models mounted on articulators using conventional face bows does not accurately replicate the orientation of the patients' teeth and jaws, but introduces a systematic error. A mathematical analysis showed that the misalignment of the maxillary model introduces errors in the perioperative wafers, which may lead to the incorrect surgical positioning of the maxilla reported in the literature. The results of the mathematical analysis were validated by image analysis of photographs of mounted maxillary models, used to simulate five orthognathic procedures. No significant difference between the experimental results and the theoretical predictions from the mathematical equations was noted. Planning for maxillary forward and upward movement produced more advancement and only 50% of maxillary impaction. Planning for maxillary forward and downward movement produced less advancement and more inferior displacement in relation to horizontal and vertical reference planes.

The validity of a computer-assisted simulation system for orthognathic surgery (CASSOS) for planning the surgical correction of class III skeletal deformities: single-jaw versus bimaxillary surgery.

The aim of this study was to assess the accuracy of the two-dimensional profile prediction produced by the computer-assisted simulation system for orthognathic surgery (CASSOS), for the correction of class III facial deformities. Correction was by maxillary advancement (n=17) or bimaxillary surgery (n=16). The mean age was 24 years (range 18-42). The surgical and dental movements obtained from the postoperative cephalogram were used to produce a CASSOS profile prediction, which was compared with the soft-tissue profile. The prediction was superimposed onto the postoperative radiograph, and a coordinate system was used to measure linear differences. For the maxillary advancement group there were statistical differences for three horizontal landmarks: superior labial sulcus (p=0.017), labrale superious (p=0.038) and labiomental fold (p=0.014). In the bimaxillary group only the landmark vertical labrale superious (p=0.002) showed a statistical difference. Generally, CASSOS produced useful profile predictions for maxillary advancement surgery or bimaxillary surgery for Class III patients, although there was considerable individual variation. The main areas of inaccuracy were the lips. The major difference between the two types of surgery was that most of the errors in the maxillary surgery group were in the horizontal direction, whilst for the bimaxillary surgery the errors were mainly in the vertical direction.

Magnitude and reproducibility of forces generated by clinicians during laceback placement.

OBJECTIVE: To determine the magnitude and reproducibility of forces generated by clinicians during laceback placement using a force-measuring typodont. SETTING: An in vitro investigation. MATERIALS AND METHODS: An in vitro typodont model was developed, which incorporated strain gauges attached to a personal computer to allow measurement of the force generated on application of lacebacks. Ten operators were instructed to place lacebacks five times, on two separate occasions (T1 and T2). Inter-operator and intra-operator forces produced at T1 and T2 were compared. MAIN OUTCOME MEASURES: Forces generated by laceback placement. RESULTS: The forces generated by clinicians ranged from 0 to 11.1 N. There were significant differences in the mean forces generated by the different operators (P < 0.001), with differences between time points not being consistent across all operators (P < 0.001). Some operators were more consistent than others in the forces generated. CONCLUSION: In vitro, there was a large inter-operator variation in the forces produced during laceback placement. With the in vitro model used in this study, few operators applied similar forces when placing lacebacks on two separate occasions.

Skeletal stability after correction of maxillary hypoplasia by the Glasgow extra-oral distraction (GED) device.

Maxillary distraction osteogenesis delivers excellent results, particularly in patients with clefts. In the past, devices such as the conventional facemask and the rigid external distraction device have been used to correct maxillary hypoplasia after a Le Fort I osteotomy. We describe a new device, the Glasgow extra-oral distraction device. The extent of skeletal and dental stability of corrections achieved in 10 patients with maxillary hypoplasia associated with clefts was satisfactory. This device costs little, can be produced in developing countries, and provides effective treatment for severe secondary deformity associated with clefts.

Preliminary assessment of skeletal stability after sagittal split mandibular advancement using a bioresorbable fixation system.

We studied skeletal stability during the first year after mandibular advancement and fixation with bioresorbable self-reinforced poly-L-lactide (SR-PLLA) screws in 11 patients by cephalometric measurements. We compared these with a cohort of 11 patients, in whom titanium screws were used for fixation. We found no significant difference between the two groups in the median preoperative cephalometric values and the median changes after operation. There was also no significant difference between the two groups regarding the median extent of relapse 1-year after operation. We conclude that bioresorbable SR-PLLA screws are comparable to metallic screws for fixation of bone after sagittal split mandibular advancement.

Investigations into the use of an ultrasonic chisel to cut bone. Part 1: Forces applied by clinicians.

OBJECTIVES: To measure in vitro the direction and force of applied loads applied by clinicians when using both a conventional slow surgical handpiece (CH) and an ultrasonic chisel (USC) for cutting bone. STUDY DESIGN: Five clinicians were asked to cut bovine bone using either an USC or a CH. The bone was placed on a force measurement system that could measure both longitudinal and downward loads. The rate of cut was calculated over a fixed time-period and the depth of cut measured using a penetratometer. RESULTS: The magnitude of the longitudinal forces generated varied between 1.48 and 3.22 N (USC) and 0.04 and 4.56 N (CH). The CH had a pulling force directed towards the operator. Both instruments produced a similar range of downward forces although there was intra- and inter-operator variability. The rate of cut varied in a similar manner, however, the CH produced a significantly greater depth of cut (p < 0.05). CONCLUSIONS: The force measurement system demonstrated differences in the way clinicians used the USC and CH instruments to cut bone. Of the two cutting methods investigated, the rotary bur is more efficient than the ultrasonic chisel. An ultrasonic chisel does cut bone in a different manner from a conventional bur and clinicians may require training before using it clinically.

Investigations into the use of an ultrasonic chisel to cut bone. Part 2: Cutting ability.

OBJECTIVES: Ultrasound may offer a possible alternative to rotary instruments for removing bone. This study was undertaken to analyse in vitro the various factors that influence the cutting of bone by an ultrasonic chisel. STUDY DESIGN: A block of bovine femur was moved in a longitudinal direction under a stationary ultrasonic chisel. The force and depth of the cut was recorded for cutting rates of 28-112 mm/min and with increasing rake angles of 0 to +20 degrees. The pressure exerted by the chisel was recorded for different cutting rates. RESULTS: When the cutting rate increases there is a corresponding increase in the downward force which is followed by a decrease in the force at rates greater than 56 mm/min. The depth of the cut increases up to a rate of 56 mm/min after which it decreases. Both the longitudinal and downward forces do not change when the rake angle changes from 0 to +10 degrees. The downward force decreases when the rake angle increases from +10 to +20 degrees. CONCLUSIONS: The bone is cut slowly with the ultrasonic chisel, but this would assist in precision. Where such an instrument is used for cutting bone the clinicians should be aware that both low forces and cutting rates are required, and the instrument should be held at a low rake angle.

Acoustic microstreaming: detection and measurement around ultrasonic scalers.

BACKGROUND: Acoustic microstreaming (AMS) may be useful to the clinician when using the ultrasonic scaler to remove particulate matter from the teeth. The aim of this study was to detect and measure the effects of AMS produced by ultrasonic scalers. METHODS: For the study, an ultrasonic generator was selected with 4 differently shaped scaling tip inserts (TFI-3, TFI-9, TFI-1, and P-12). A plaque substitute (0.2 mm thick soft cream cheese) was coated onto a microscope slide and immersed in water. The ultrasonic scaler tip was placed in the water and orientated either perpendicular or parallel to the slide. The instrument was operated both contacting the slide under a load of 0.3 N and non-contacting at various distances from the slide surface. This was repeated with the tip parallel to the slide. The area of medium removed was quantified by digital image analysis. RESULTS: It was found that AMS removed the plaque substitute from around the tip. The TFI-9 insert significantly removed more material with increasing displacement amplitude (P <0.05). Significantly larger areas of plaque substitute were removed when the tips of the TFI-3, TFI-9, and P-12 inserts were orientated perpendicularly to the slide compared to the parallel orientation (P <0.05). Of the 4 inserts used, the TFI-9 insert removed the most material while the straight tip produced no apparent removal. Removal by AMS required the presence of a water medium and such forces were found to decrease with distance from the scaling tip. No plaque substitute removal was seen at a distance of 7 mm for the TFI-9 insert at 37.5 microm displacement with the tip orientation parallel to the slide. CONCLUSIONS: It is concluded that AMS occurs around ultrasonic scalers and this depends on the displacement amplitude, tip orientation, and presence of a water medium. AMS may play a role in disruption of subgingival biofilms associated with periodontal disease.

An in vitro evaluation of electric toothbrushes.

Four commercially available electric toothbrushes (Sonicare, Braun Electric Toothbrush, Interplak, and Blend-a-Dent) were assessed both for their operating characteristics and their ability to remove a "food debris" medium. The Sonicare and Blend-a-Dent have a lateral vibratory action, while the Interplak and Braun produce a rotary movement of the brush head. The vibratory action of the Sonicare was susceptible to loading. All devices produced both stable-pulsating cavitation and acoustic microstreaming that was demonstrated in vitro using a suspension of particles in water. Their effectiveness in removing a food debris medium was assessed with and without water. Three of the brushes (Sonicare, Braun, and Blend-a-Dent) were similar in their ability to remove the plaque, and all were superior to the Interplak; its streaming forces removed no food debris. The results indicated that the Blend-a-Dent was the most effective brush design in vitro, although the differences between Blend-a-Dent and Sonicare were not statistically significant.