Volume Assessment of the Effect of Obturators on Facial Form Following Surgery for Head and Neck Cancer Using Stereophotogrammetry.

PURPOSE: To determine if stereophotogrammetry could be used to determine the effects of obturators on facial contour in relation to the measurement of facial volumes. MATERIALS AND METHODS: Stereophotogrammetry images were recorded from 20 subjects with and without their obturators in place. These were converted into a stereolithographic format and overlaid. Registrations were made using the tissues on the normal areas of the face. Difference images were created, enabling surface areas and volumes to be calculated. To assess repeatability of measurement, 2 readings were recorded on each of 2 separate registrations. Data analysis between the sets of readings used correlation coefficients and paired t-tests. Coefficients of repeatability were also calculated. RESULTS: A comparison of readings for the surface areas showed the method of measurement was repeatable with no significant differences between the 2 repeated readings for registration 1 (p = 0.977, coefficient of repeatability = 101 mm2 ), registration 2 (p = 0.085, coefficient of repeatability = 106 mm2 ), and the mean of the two readings for registration 1 compared with registration 2 (p = 0.355, coefficient of repeatability = 103 mm2 ). Similar results were found for the volume measurements with no significant differences between the repeated readings for registration 1 (p = 0.862, coefficient of repeatability = 229 mm3 ), registration 2 (p = 0.200, coefficient of repeatability = 209 mm3 ), and the mean of the 2 readings for registration 1 compared with those for registration 2 (p = 0.131, coefficient of repeatability 339 mm3 ). There was a statistically significant range of volumes that appeared to have been restored by the obturators (p < 0.0005). CONCLUSIONS: Stereophotogrammetry is reliable in assessing the effects of obturators on facial form. In the sample of subjects, obturators generally appeared to be effective in supporting facial tissues following surgical resections of the maxilla and therefore contribute in some degree to the restoration of facial appearance.

Development of a morphing technique for predicting the position and size of an artificial ear in hemifacial microsomia patients.

PURPOSE: People with hemifacial microsomia may be missing an ear on the affected side of the face. The principal aim of the study was to develop a morphing technique and to determine whether it could be used to appropriately position an artificial ear, as well as to give an indication of prosthesis size in comparison with the natural ear. Comparisons also were made between the artificial ears being worn by the patients with their natural ears. MATERIALS AND METHODS: Data from stereophotogrammetry images of the faces of 10 people were converted into stereolithographic format. Anthropometric points on the face and ear of the unaffected side were plotted. By a process of scaling, the distance between facial landmarks on the unaffected side was estimated for the affected side so as to identify where the morphed ear would be positioned once generated. RESULTS: Generally, the morphed ears appeared to be in acceptable positions. There was a statistically significant difference between the position of the morphed and natural ears (P = .011), as well as the artificial and natural ears (P = .001), but this was unlikely to have any clinical implications. There were no significant differences among the sizes of the natural, morphed, and artificial ears (P = .072). CONCLUSIONS: Morphing appears to offer a more precise way of planning the positioning and construction of an artificial ear on patients with hemifacial microsomia than traditional methods. Differences in facial shape on either side of the face may impact on the process. This requires further study.

Forces, movements and reflexes produced by pushing human teeth.

Pushing a tooth results in movement of the tooth and reflex inhibition of activity in jaw-closing muscles. The aims of this study were to determine how much tooth movement is required to elicit such reflexes and whether this is dependent on the point of force application to the tooth. Eight experiments were performed on six volunteer subjects. Electromyograms (EMGs) were recorded from a masseter muscle while the subjects produced approximately 12.5 % of the EMG associated with maximal clenching. Reflexes were evoked by pushing at two positions (incisal and cervical) on an upper central incisor. The forces applied and the resulting movements of the tooth were recorded. There was a linear relationship between force and movement regardless of whether the force was incisal or cervical (Pearson's r = 0.91 and r = 0.93 respectively). There were no differences between the slopes or intercepts for these relationships (ANCOVA p = 0.42, p = 0.46 respectively). There were linear relationships between the logarithms of force or movement and the resulting inhibitory reflexes (r = 0.81, 0.79, 0.81 and 0.74 for incisal and cervical forces and incisal and cervical movements, respectively). Again, there were no significant differences between the slopes for these relationships (ANCOVA p = 0.75, p = 0.46 for force and movement, respectively). There were no significant differences between the reflex thresholds for incisal and cervical stimuli in terms of force (0.23 and 0.25 N, ANCOVA p = 0.1) or movement (9.7 and 8.5 µm, ANCOVA p = 0.22). Thus, it appears that neither tooth movements nor jaw reflexes are dependent on the point of force application to a tooth.

A comparison of three methods to evaluate the position of an artificial ear on the deficient side of the face from a three-dimensional surface scan of patients with hemifacial microsomia.

PURPOSE: Patients with hemifacial microsomia may have a missing ear on the deficient side of the face. The fabrication of an ear for such individuals usually has been accomplished by directly measuring the ear on the normal side to construct a prosthesis based on these dimensions, and the positioning has been, to a large extent, primarily operator-dependent. The aim of the present study was to compare three methods, developed from the identification of landmarks plotted on three-dimensional surface scans, to evaluate the position of an artificial ear on the deficient side of the face compared with the position of the natural ear on the normally developed side. MATERIALS AND METHODS: Laser scans were undertaken of the faces of 14 subjects with hemifacial microsomia. Landmarks on the ear and face on the normal side were identified. Three methods of mirroring the normal ear on the deficient side of the face were investigated, which used either facial landmarks from the orbital area or a zero reference point generated from the intersection of three orthogonal planes on a frame of reference. To assess the methods, landmarks were identified on the ear situated on the normal side as well as on the face. These landmarks yielded paired dimensional measurements that could be compared between the normal and deficient sides. Mean differences and 95% confidence intervals were calculated. RESULTS: It was possible to mirror the normal ear image on to the deficient side of the face using all three methods. Generally only small differences between the dimensional measurements on the normal and deficient sides were observed. However, two-way analysis of variance revealed statistically significant differences between the three methods (P = .005). CONCLUSIONS: The method of mirroring using the outer canthi was found to result in the smallest dimensional differences between the anthropometric points on the ear and face between the normally developed and deficient sides. However, the effects of the deformity can result in limitations in relation to achieving a precise alignment of the ear to the facial tissues. This requires further study.

Development of a stereophotogrammetry technique to assess facial change following surgery for head and neck cancer.

A stereophotogrammetry technique is described that can be used to map the face following surgery for head and neck cancer. It enables the effects of obturators on facial form to be assessed and may have a wide variety of applications. Int J Prosthodont 2011;24:342-344.

Creating complete dentures that are stable in function.

UNLABELLED: Many edentulous people can experience difficulty in carrying out functional activities when wearing complete dentures. This may be due to a number of factors, one of which is the ability to control the dentures effectively during mastication and speech. For this reason, it is critical when constructing complete dentures to incorporate features in their design which will aid stability in function. Usually, the challenges are greater in constructing a prosthesis to replace the missing mandibular teeth. It is recognized that the use of osseointegrated implants offers considerable advantages for people who have to wear complete dentures, and the contribution of implantology to the provision of stable complete dentures will be explored. However, many people will not have the opportunity to experience the benefits of this approach. Furthermore, for people who need to wear conventional dentures, age and other factors may impact on their ability to control the prostheses effectively during oral function. In this paper, the ways in which design features may impact on the stability of complete dentures will be discussed. CLINICAL RELEVANCE: This paper considers how complete dentures can be designed and constructed so that they are stable in oral function, and can be worn comfortably without causing damage to the intra-oral tissues.

A comparison of prosthetic ear models created from data captured by computerized tomography, magnetic resonance imaging, and laser scanning.

PURPOSE: To compare the dimensional measurements and surface topography of stereolithographic models generated from computerized tomography (CT), magnetic resonance imaging (MRI), and laser scanning (LS) data with the same subjects' natural ears and ear casts. MATERIALS AND METHODS: Stereolithographic models were manufactured from images of the subjects' ears and ear casts recorded by CT, MRI, and LS, and dimensional measurements were compared. In the second part of the study, all stereolithographic models were CT scanned and reconstructed in an STL file format. A comparison of the surface topography of the CT, MRI, and LS model ears was made. RESULTS: Intraclass correlation coefficients indicated that dimensions could be reliably measured on the CT, MRI, and LS stereolithographic models. A 2-way analysis of variance revealed no statistical differences between the various sources of data (P = .991). The smallest differences of surface topography were observed on the MRI/CT superimpositions. CONCLUSION: The dimensional measurements on the stereolithographic models were similar to those from the original source. Only small differences were apparent between the surface topography of the CT, MRI, and LS models. MRI may be particularly appropriate to fabricate a prosthesis because it involves no radiation for the patient and internal form can be reproduced. The use of this technique in clinical practice requires further study.

Dissociation of nociceptive modulation of a human jaw reflex from the influence of stress.

In human beings, inhibitory jaw reflexes can be depressed by painful stimulation of remote parts of the body. Since similar effects can be produced by the stress of anticipating pain, we wished to investigate whether the effects of remote painful stimuli are dependent on stress. EMG recordings were made from a masseter muscle while subjects maintained activity in the muscle at approximately 12.5% of maximum using visual feedback. The protocols involved three sequences: (1) "standard controls" in which reflexes were evoked by electrical test stimuli applied to the upper lip; (2) "standard conditioning" in which painful electrical conditioning stimuli were applied over the sural nerve 100 ms before the test stimuli; (3) "random sequences" in which test-only and conditioning-test combinations were employed in a double-blind, random, order. Data are presented as means +/- SEMs. In the standard controls, the stimuli evoked clear inhibitory reflexes (latency 37 +/- 1.3 ms, duration 62 +/- 5.6 ms; n = 10) in all the subjects. During standard conditioning, the reflex magnitude was reduced significantly (by 50.0 +/- 8.5%, P = 0.0002, one-sample t-test). When the test-only and conditioning-test responses were extracted from the random sequences, there was also a significant reduction in the reflex magnitude following conditioning (by 34.6 +/- 5.5%, P = 0.0002, one-sample t-test) albeit less so than between the standard sequences (P = 0.03, paired t-test). A second series of experiments suggested that these lesser effects during the random sequences were not substantially due to any loss of temporal summation of the conditioning mechanisms. The evidence for this was that application of pairs of conditioning stimuli did not produce a significantly greater effect than single conditioning stimuli within a random sequence (39.9 +/- 9.6% as opposed to 32.7 +/- 9.1% reductions in the reflex, P = 0.117, paired t-test). Therefore since any stress in the random sequences would not have been "tied" to the conditioned responses alone, the effects of remote painful stimuli on this inhibitory jaw reflex cannot be entirely secondary to stress.

A comparison between computerized tomography, magnetic resonance imaging, and laser scanning for capturing 3-dimensional data from a natural ear to aid rehabilitation.

PURPOSE: To compare dimensional measurements on computer images generated from data captured digitally by 3 different methods to those obtained directly from natural ears and ear casts, so as to determine the optimal method of creating a computer-generated ear image. MATERIALS AND METHODS: Magnetic resonance imaging (MRI) was used to obtain 3-dimensional (3D) data images of the normal ears of 14 subjects. Computerized tomography (CT) and laser scanning (LS) were used to obtain 3D data images from stone casts of the same ears. Dimensional measurements were recorded on 2 occasions between anthropometric landmarks on the subjects' natural ears, casts of the ears, and reconstructed ear images obtained by CT, MRI, and LS. The intraclass correlation coefficients and coefficients of repeatability were calculated. The means of the 2 measurements for each of the dimensions were analyzed using 2-way analysis of variance to determine whether there were differences between the methods of data collection. RESULTS: The intraclass correlation coefficients indicated that dimensions could be reliably measured on the natural ears, casts, and CT, MRI, and LS images. The coefficients of repeatability were all of a small magnitude in relation to the overall dimensions studied. No statistical differences existed between the various sources of data (P = .866) (i.e., direct, cast, CT, MRI, and LS). CONCLUSION: The 3 methods of imaging have generally resulted in dimensional measurements on the reconstructed images that are similar to those of the original source. These are considered appropriate for manufacturing 3D models that can be used to fabricate a prosthesis. However, other factors may also be important, such as shape, contour, and internal form, and these require further investigation.

A comparison between computerized tomography, magnetic resonance imaging, and laser scanning for capturing 3-dimensional data from an object of standard form.

PURPOSE: The study's aim was to compare dimensional measurements on computer images generated from data captured digitally by 3 different methods of the surfaces of a plastic cube of known form to those obtained directly from the cube itself. MATERIALS AND METHODS: Three-dimensional images were reconstructed of a plastic cube obtained by computerized tomography (CT), magnetic resonance imaging (MRI), and laser scanning. Digital calipers were used to record dimensional measurements between the opposing faces of the plastic cube. Similar dimensional measurements were recorded between the cube faces on each of the reconstructed images. The data were analyzed using a 2-way ANOVA to determine whether there were differences between dimensional measurements on the computer images generated from the digitization of the cube surfaces by the different techniques, and the direct measurement of the cube itself. RESULTS: A significant effect of how the measurements were taken (ie, direct, CT, MRI, and laser scanning) on the overall variation of dimensional measurement (P < .0005) was observed. Post hoc tests (Bonferroni) revealed that these differences were due principally to differences between the laser-scanned images compared to other sources (ie, direct, CT, and MRI). The magnitude of these differences was very small, up to a maximum mean difference of 0.71 mm (Cl +/- 0.037 mm). CONCLUSION: All 3 methods of imaging would be of value in further studies, not only for the fabrication of complex shapes such as prosthetic ears, but also for other facial prostheses.

A study to compare the oral health impact profile and satisfaction before and after having replacement complete dentures in England and Scotland.

OBJECTIVE: To assess the oral health impact profile (OHIP) on edentulous subjects in Scotland and England who needed to have their dentures replaced, and to determine whether any change in the subjects' assessment of their original and replacement dentures impacted on oral health related quality of life parameters. BACKGROUND: The loss of all teeth may impact on functional activities. The OHIP is an instrument used to measure subjects' perception of the social impact of oral disorders on their well being. METHODS: A total of 58 edentulous subjects were studied. Subjects completed the OHIP-14 questionnaires before and after being provided with a set of replacement complete dentures. They also assessed specific features of the upper and lower dentures. Responses were recorded on a Likert scale. RESULTS: For many subjects, the responses in the before treatment questionnaires were at the lower end of the Likert scale, indicating that there were no major impacts on oral health related quality of life parameters. There were significant improvements in four of the 14 OHIP parameters assessed after treatment. With the new dentures, subjects expressed improved satisfaction, particularly for the lower prosthesis. There were no major differences between the responses of the subjects in Scotland and England. CONCLUSION: For this group of edentulous subjects, although they may need dentures to be replaced after a period of wear, this does not necessarily have significant social impacts. For this reason the provision of new dentures did not result in major changes to the OHIP.

So you want to be an academic?

Academic dentistry offers a rewarding and varied career in which the practice of dentistry can be combined with teaching and research. This article outlines the activities that academic staff undertake, discusses the routes by which entry into an academic post can be made, and the ways in which progression and development can take place.

The distal extension base denture.

The distal extension base denture may be indicated in situations in which the edentulous area to be restored is without a terminal abutment tooth. There may be significant challenges in providing a prosthesis with sufficient support and retention to make it comfortable without damaging the intra-oral tissues. This can be a greater problem in the mandible as the denture-bearing area is usually much smaller than in the maxilla. This paper considers how distal extension removable prostheses can be designed to restore edentulous spaces.

Remote noxious stimuli modulate jaw reflexes evoked by activation of periodontal ligament mechanoreceptors in man.

The purpose of the study was to investigate whether jaw reflexes evoked by selective stimulation of periodontal ligament me canoreceptors are susceptible to modulation by remote noxious stimulation. Experiments were performed on 10 volunteer subjects. Skin surface recordings were made from the jaw-closing masseter muscle. The subjects activated the muscle to approximately 10% of maximum by biting on a rubber impression of their molar teeth while they received visual feedback of the electromyogram (EMG) of the muscle. Reflexes were produced by the application of gentle mechanical stimuli to an upper central incisor tooth. The stimuli were in the form of 'ramp and hold' forces with a 5 ms rise-time and a 1.5 N plateau which lasted 350 ma. The resulting reflexes were recorded both under control conditions and while the subjects received a remote noxious stimulus (immersion of a hand in water at 3 degrees C). In all 10 subjects, the stimuli produced a single period of inhibition of masseteric activity (latency, 12.8 t 04 ms; duration, 18.1+/-1.3 ms; means +/- S.E.M.), which was usually followed by a period of increased masseteric activity. The period of inhibition constituted a downward wave in full-wave rectified, averaged signals. The integrals of such waves were significantly smaller (by 17+/- 6.5 %; P = 0.027; Student's t test) when the reflex was evoked during remote noxious stimulation rather than under control conditions. As such reflexes are beLieved to play a modulatory role during normal oral function this finding maybe relevant to disorders of mastication associated with pain.