Julian M. Yates

The effect of nerve growth factor on functional recovery after injury to the chorda tympani and lingual nerves

Nerve growth factor (NGF) is known to ameliorate central changes and enhance the regeneration of damaged axons in the early stages after peripheral nerve injury. We have assessed the long-term outcome of placing NGF at a nerve repair site by determining the functional characteristics of several groups of sensory afferent and autonomic efferent fibres in the cat lingual nerve. Six months after entubulation repair, with or without the incorporation of NGF, the recovery of secretomotor and vasomotor efferents was determined by recording salivary flow from the submandibular gland and temperature changes on the tongue surface, each evoked by stimulation of the repaired nerve. Electrophysiological recordings from the lingual and chorda tympani nerves proximal to the repair allowed characterisation of mechanosensitive, thermosensitive and gustatory afferents. When compared with data from uninjured control animals, both repair groups showed changes in spontaneous discharge and persistent reductions in conduction velocity, receptor sensitivity, proportion of gustatory units, and rate of salivary secretion. Comparisons between the outcome of repair with or without NGF revealed few differences. In the NGF group the conduction velocity of afferents in the lingual nerve was lower, and the level of spontaneous activity was higher. However, NGF appeared to preferentially enhance the regeneration of thermosensitive afferents, suggesting that it may play a role in determining the phenotypic profile of the regenerating axonal population. This suggests that future therapeutic enhancement of regeneration after peripheral nerve injury may require a combination of factors to encourage regeneration of specific fibre groups.

Color reproduction for advanced manufacture of soft tissue prostheses

OBJECTIVES The objectives of this study were to develop a color reproduction system in advanced manufacture technology for accurate and automatic processing of soft tissue prostheses. METHODS The manufacturing protocol was defined to effectively and consistently produce soft tissue prostheses using a 3D printing system. Within this protocol printer color profiles were developed using a number of mathematical models for the proposed 3D color printing system based on 240 training colors. On this basis, the color reproduction system was established and their system errors including accuracy of color reproduction, performance of color repeatability and color gamut were evaluated using 14 known human skin shades. RESULTS The printer color profile developed using the third-order polynomial regression based on least-square fitting provided the best model performance. The results demonstrated that by using the proposed color reproduction system, 14 different skin colors could be reproduced and excellent color reproduction performance achieved. Evaluation of the systems color repeatability revealed a demonstrable system error and this highlighted the need for regular evaluation. The color gamut for the proposed 3D printing system was simulated and it was demonstrated that the vast majority of skin colors can be reproduced with the exception of extreme dark or light skin color shades. CONCLUSIONS This study demonstrated that the proposed color reproduction system can be effectively used to reproduce a range of human skin colors for application in advanced manufacture of soft tissue prostheses.

Investigation of Elastomer Infiltration into 3D Printed Facial Soft Tissue Prostheses

Objectives: 3D colour printing, a method of additive manufacturing, has been developed and utilised to produce facial soft tissue prostheses. This was achieved by layered fabrication of a biocompatible powder held together by an aqueous binder containing a resin and coloured inks, followed by infiltration with a medical grade silicone polymer. The aim of this study was to investigate the elastomer infiltration depths within the 3D printed models. Methods: Three sets of 30 cubes ? 20x20x20 mm ? were used to investigate the infiltration depth of Sil-25 maxillofacial silicone polymer (an MSP) under atmospheric pressure, 2 bar and 3 bar pressure for 5, 10, 15, 20 and 25 min. The investigation was also repeated with two other MSPs ? Promax-10 and M-3428 ? under 3 bar pressure. Following infiltration, the cubes were bisected, the internal aspects stained with dye, and the infiltration depth measured using a travelling microscope. Infiltration quality was also assessed using scanning electron microscopy (SEM). Results: At standard atmospheric pressure, the maximum infiltration depth of Sil-25 was 1.45 mm after 25 min. However, after 25 min at 2 and 3 bars pressure, the infiltration depth increased to 3.9 mm and 8.7 mm, respectively. At 3 bars the infiltration depth of Promax-10 and M-3428 was 2.4 mm and 7.5 mm, respectively. In all samples SEM revealed a disorganised distribution of starch particles within the MSP infiltrate. Significance: Pressure significantly increased the infiltration rate and depth of the MSPs within 3D printed constructs. The infiltration depth obtained is sufficient for prostheses that are less than 16 mm thick.

Treatment of the edentulous atrophic maxilla using zygomatic implants: evaluation of survival rates over 5–10 years

The aim of this retrospective observational cohort study was to analyse and report the 5-10-year survival rates of endosseous zygomatic implants used in the rehabilitation of the atrophic maxilla. Forty-three consecutive zygomatic implant placements in 25 patients were evaluated over a 5-10-year period. All zygomatic implant surgery was carried out under general anaesthesia. Nobel Biocare zygomatic machined-surface implants were used, and placement was undertaken using the modified sinus slot method. The main outcome measures and determinants for success were survival of the restored implants and the proportion of originally planned prostheses delivered to patients. Of the 25 patients treated, 12 were male and 13 were female; 19 were non-smokers, and the mean age at time of surgery was 64 years. Patients were treatment-planned for implant-retained bridgework, a removable prosthesis retained by fixed cast gold or milled titanium beams, or magnet-retained removable prostheses. A combination of zygomatic and conventional implants was used in all but one patient. In this study it was shown that the overall success rate for zygomatic implants was 86%, with six of the implants either failing to integrate or requiring removal due to persistent infection associated with the maxillary sinus. All patients received their planned prosthesis, although in six cases the method of retention required modification. This study illustrates that zygomatic implants are a successful and important treatment option when trying to restore the atrophic maxilla, with the potential to avoid additional augmentation/grafting procedures and resulting in a high long-term success rate.

The effect of brain-derived neurotrophic factor on sensory and autonomic function after lingual nerve repair.

Brain-derived neurotrophic factor (BDNF) is important in the response to peripheral nerve injury and may enhance regeneration. We have assessed its role in the functional recovery of sensory afferents and autonomic efferents after repair of the chorda tympani and lingual nerves in the cat. Six months after entubulation repair, with or without the incorporation of BDNF at the repair site, the recovery of secretomotor and vasomotor efferents was determined by recording salivary flow from the submandibular gland and temperature changes on the tongue surface, each evoked by stimulation of the repaired nerve. Electrophysiological recordings from the lingual and chorda tympani nerves proximal to the repair were undertaken to characterise mechanosensitive, thermosensitive, and gustatory afferents. When compared with data from uninjured control animals, both repair groups showed changes in receptor sensitivity and spontaneous discharge, and persistent reductions in conduction velocity, proportion of gustatory and thermosensitive units, rate of salivary secretion, and vasomotor responses. Comparisons between the outcome of repair with or without BDNF revealed few differences. In the BDNF group, fewer units in the chorda tympani responded to gustatory or thermal stimuli and the sensitivity of the gustatory units was lower. The conduction velocity of afferents in the lingual nerve was also lower, but the mechanoreceptive field size was higher. Thus, despite its known trophic role in the gustatory system, BDNF had not enhanced recovery of these or other fibre populations. We conclude that the application of BDNF to a site of lingual nerve repair has a negative effect on the long-term outcome.

Improved method for skin reflectance reconstruction from camera images

A improved spectral reflectance reconstruction method is developed to transform camera RGB to spectral reflectance for skin images. Rather than using conventional direct or two-step processes, we transform camera RGB to skin reflectance directly using a principal component analysis (PCA) approach. The novelty in our direct method (RGB to spectra) is the use of a skin-specific colour characterisation chart with spectra closer to human skin spectra, and a new database of skin reflectances to derive the PCA bases. The experimental results using the facial images of 17 subjects demonstrate that our new direct method gives a significantly better performance than conventional, two-step methods and direct methods with traditional characterization charts. This new spectral reconstruction algorithm is sufficiently precise to reconstruct spectral properites relating to chromophores and its performance is within the acceptable range for maxillofacial soft tissue prostheses (error < 3 ΔE*ab units).

Interventions for the prevention of dry socket: an evidence-based update

This paper reviews the latest evidence for local and systemic interventions for the prevention of alveolar osteitis (dry socket). Dry socket is a painful and common post-operative complication following exodontia. Any interventions for the prevention of dry socket could reduce both its incidence and help avoid this painful complication. Prophylactic measures proposed in the literature are discussed. Furthermore, this article discusses both the clinical and histological stages of a normal healing socket.

Can Masticatory Electromyography be Normalised to Submaximal Bite Force

The combination of bite force and jaw muscle electromyography (EMG) provides an insight into the performance of the stomatognathic system, especially in relation to dynamic movement tasks. Literature has extensively investigated possible methods for normalising EMG data encapsulating many different approaches. However, bite force literature trends towards normalising EMG to a maximal voluntary contraction (MVC), which could be difficult for ageing populations or those with poor dental health or limiting conditions such as temporomandibular disorder. The objectives of this study were to (i) determine whether jaw-closing muscle activity is linearly correlated with incremental submaximal and maximal bite force levels and (ii) assess whether normalising maximal and submaximal muscle activity to that produced when performing a low submaximal bite force (20 N) improves repeatability of EMG values. Thirty healthy adults (15 men, 15 women; mean age 21 ± 1·2 years) had bite force measurements obtained using a custom-made button strain gauge load cell. Masseter and anterior temporalis muscle activities were collected bilaterally using surface EMG sensors whilst participants performed maximal biting and three levels of submaximal biting. Furthermore, a small group (n = 4 females) were retested for reliability purposes. Coefficients of variation and intra-class correlation coefficients showed markedly improved reliability when EMG data were normalised compared to non-normalised. This study shows that jaw muscle EMG may be successfully normalised to a very low bite force. This may open possibilities for comparisons between at-risk sample groups that may otherwise find it difficult to produce maximal bite force values.

Correction of a mandibular asymmetry using a custom-made titanium onlay

The diagnosis and treatment of facial deformities, including mandibular asymmetries, can pose a significant clinical problem. The limitations, accuracy and predictability of treatment options available and the expectations of the patient can further compound this. In this article we present a case of facial asymmetry secondary to mandibular angle deficiency corrected by the manufacture and placement of a custom-made titanium onlay. Although alternative methods were potentially available to correct this deformity, patient factors including occlusion, dental/skeletal relationship and chin position limited our options. Furthermore, construction of the custom-made titanium onlay involved the development of a computer-generated 3D virtual model and computer-aided design and computer-aided manufacture (CAD-CAM) of the inlay. This report demonstrates that this technique can be used successfully to address certain cases of facial asymmetry.

Characterising the variations in ethnic skin colours: a new calibrated data base for human skin

Accurate skin colour measurements are important for numerous medical applications including the diagnosis and treatment of cutaneous disorders and the provision of maxillofacial soft tissue prostheses.