Trevor Coward

Laser scanning of the ear identifying the shape and position in subjects with normal facial symmetry.

The objective of the present study was to discover if dimensional measurements of the ear could be determined with a laser scanning technique and whether or not the location of landmarks of the ear could be reliably measured with respect to those on the midline of the face. Computer-generated images were created from laser scans of 20 subjects. Dimensional measurements were made between landmarks on the ear and face. Differences between repeated dimensional measurements of the ear were very small, as were those measurements made between landmarks on the ear to the midline of the face. Differences between dimensions of the left and right ears were observed, but were of a small magnitude. The results suggest that the dimensions of the ear and its position with respect to landmarks in the midline of the face can be reliably measured on normal subjects and that laser scanning is a useful technique for planning and monitoring facial reconstruction of the ear.

Computerized Color Formulation for African-Canadian People Requiring Facial Prostheses: A Pilot Study

PURPOSE The aim of this study was to investigate the effectiveness of spectrophotometry and a computerized color formulation system to predict pigment formulas for color mixing silicone elastomer to match the skin color of African-Canadian people. MATERIALS AND METHODS In a prospective study, reflectance spectrophotometery was used to measure the skin color of 19 African-Canadian subjects. The spectral data for each subject was used in a computerized color formulation system to predict colorants required to mix silicone elastomer to match each subjects skin color. Delta-E values were recorded for each silicone sample in comparison to the subjects skin measurement. An analysis of variance was used to determine significance among variables, and a Tukey HSD post hoc test was used to assess paired comparisons. RESULTS Delta-E decreased with iterative mixes of colored silicone for each subject, and pigment loading increased with iterative mixes. Delta-E values for the third iterative mix (fourth and final sample) ranged between 1.49 and 8.82. CONCLUSION Spectrophotometry and computerized color formulation provide a foundation in the color matching procedure for facial prostheses that offers objectivity to an otherwise subjective task. Through further study of spectrophotometry and computerized color formulation, and with the development of pigment databases appropriate for the African-Canadian population, it may be possible to establish a precise and repeatable color matching system that predicts required colorants and controls metamerism.

Comparison of the accuracy of digital stereophotogrammetry and projection moiré profilometry for three-dimensional imaging of the face

The aim of this study was to compare the three-dimensional (3D) imaging accuracy between a digital stereophotogrammetry device and a projection moiré profilometry setup using anatomical models in conjunction with surface matching software. Twenty-two 3D surface models of the middle third of the face derived from computed tomography (CT) scans were used to fabricate photopolymer models by rapid prototyping. These were digitized using digital stereophotogrammetry and projection moiré profilometry. The 3D surface models acquired were compared for shape differences with the original CT models using surface matching software. Global registration between each pair of corresponding models was carried out using an iterative closest point algorithm. The mean surface deviations following registration were used to calculate Bland-Altman limits of agreement between the two methods. The distributions of measured surface differences were used to calculate L-moments. Paired t-tests were carried out for hypothesis testing. Correlation between difference and mean was -0.3, and 95% limits of agreement were -0.084mm and 0.064mm. No statistically significant differences in mean measurement error (L1 moments) were observed (P=0.1882). The experimental moiré profilometry setup employed produced 3D models of facial anatomy of comparable accuracy to a widely used commercialized digital stereophotogrammetry device.

The use of 3D printed external and internal templates for Bonebridge implantation – technical note

The Bonebridge (MedEl, Innsbruck, Austria) is a semiimplantable transcutaneous bone conduction implant (BCI) for rehabilitation of conductive hearing loss, mixed hearing loss and single-sided deafness. The device consists of an internal coil, a demodulator and a bone conduction floating mass transducer (BC-FMT). As it is an active implant, there is no soft tissue attenuation of sound energy, a main limitation of passive transcutaneous bone conduction devices. Its advantages over the conventional percutaneous bone-anchored hearing devices include a potential reduction in soft tissue complications and no external abutment to maintain. Since its launch in 2012, a number of studies have reported promising results to date. Themain surgical challenge in Bonebridge implantation is optimal positioning of the BC-FMTwhichmeasures 8.7 mm in thickness and 15.8 mm in diameter (23.8 mm between anchor holes for screws). It can be placed via either a transmastoid or a retrosigmoid approach, depending on the patient’s anatomical factors. Care needs to be taken not to compromise the dura mater, venous sinus, external auditory canal or mastoid cavity, although some flexibility is afforded by the use of BCI ‘lifts’ which elevate the BC-FMT from the surface of the skull by up to four millimetres. The transition between the demodulator and the BC-FMTmay also be bent 90 degrees in the horizontal plane and 30 degrees in the vertical plane. The current convention is to simulate implant placement preoperatively through 3D planning based on computed tomography (CT). However, there remains the potential difficulty in transferring this information accurately on to an area of the temporal bone with relatively few surface landmarks that can be used as reference points. In this article, we describe the use of 3D printed external soft tissue and internal bone templates in Bonebridge implantation. The patient was a 52-year-old male with a previous history ofmultiple open cavitymastoid surgery and a percutaneous bone-anchored hearing aid (BAHA) with soft tissue reduction, which was complicated by infection, delayed healing, failed osseo-integration and eventually loss of the implant.

Development of a 3D printable maxillofacial silicone. Part II: Optimization of moderator and thixotropic agent

Statement of problem. Conventionally, maxillofacial prostheses are fabricated by hand carving the missing anatomic defect in wax and creating a mold into which pigmented silicone elastomer is placed. Digital technologies such as computer numerical control milling and 3‐dimensional (3D) printing have been used to prepare molds, directly or indirectly, into which a biocompatible pigmented silicone elastomer can be placed. Purpose. The purpose of this in vitro study was to develop a silicone elastomer that could be 3D printed directly without a mold to create facial or body prostheses by varying its composition. Material and methods. The room temperature vulcanizing silicone composition was divided into 2 components which were mixed 1:1 to initiate polymerization in the printer before printing began. Different types of moderators and thixotropic agents were used, and the base composition was varied to obtain 11 formulations. The specimens were printed and polymerized from these formulations and tested for tear and tensile strength and hardness. Ten readings of the specimens were recorded for tear and tensile strength and 6 for hardness. Results were analyzed using ANOVA (&agr;=.05). Visual assessment of uncured printed specimens was undertaken for 5 formulations to assess any differences in their ability to hold their shape after printing. Results. The tear and tensile strength of the 11 formulations with varying moderators, thixotropic agents, and base compositions were statistically similar to each other (P>.05). Five of 11 formulations were chosen for the visual assessment as they had sufficient thixotropic agent to avoid slumping while printing. The specimens showed varied slumping behavior until they polymerized. The filler content was increased in the selected formulation, and the tear and tensile strength of the formulation was increased to 6.138 kNm‐1 and 3.836 MPa; these increases were comparable to those of commercial silicones currently used for the fabrication of facial prostheses. Conclusions. The optimum combination of mechanical properties implies the use of one of the formulations as a suitable material for the 3D printing of facial prostheses.

Evaluation of the effect of ultraviolet stabilizers on the change in color of pigmented silicone elastomer: An in vitro study

Aim and Objective: To compare and evaluate the effect of ultraviolet (UV) stabilizers (Chimassorb 81 and Uvinul 5050) on the color change of pigmented elastomer. Materials and Methods: Two pigments - Red (P112 Brilliant Red) and Yellow (P106 Yellow) and two UV stabilizers Chimassorb 81 and Uvinul 5050 were studied. A total of six groups of 10 samples each were fabricated using a combination of the above colors and stabilizers: Group A1 - Red control, Group A2 - Red + Chimassorb 81, Group A3 - Red + Uvinul 5050. Group B1 - Yellow control, Group B2 - Yellow + Chimassorb 81, Group B3 - Yellow + Uvinul 5050. All samples were subjected to ageing in an accelerated weathering chamber (Weather-Ometer). Color values L, a, and b were measured at 500 and 1000 h for all samples before and after weathering and change in color (Delta E) was calculated. Results: All groups showed a significant color change. At 500 h, Chimassorb 81 showed a statistically significant lesser change in both colors (red - 3.66 and yellow - 2.8) compared to their control groups (red - 5.19 and yellow - 4.9). At 1000 h, both UV stabilizers showed lesser color change (A2 - 5.49, B2 - 4.28, A3 - 7.47 and B3 - 4.09) as compared to their respective control groups (A1 - 9.57 and B1 - 5.91). Overall, the change in the color with Group A was more than Group B. Conclusion: Addition of UV stabilizers helped the reduction of color change. Chimassorb 81 showed a greater reduction in color change in both colors consistently at 500 and 1000 h.

The effect of model inclination during fabrication on mouthguard calliper-measured and CT scan-assessed thickness.

AIM Excessive material thinning has been observed in the production of custom-made mouthguards in a number of studies, due to production anomalies that may lead to such thinning. This study investigated thinning material patterns of custom-made mouthguards when the anterior angulation of dental model was increased during the thermoforming process. MATERIALS AND METHODS A total of 60 samples of mouthguard blanks were thermoformed on identical maxillary models under four anterior inclination conditions (n = 4 × 15): control 0, 15, 30 and 45°. Each mouthguard sample was measured, using an electronic calliper gauge at three anatomical points (anterior labial sulcus, posterior occlusion and posterior lingual). Mouthguards were then CT scanned to give a visual representation of the surface thickness. RESULTS Data showed a significant difference (P < 0.005) in the anterior mouthguard thickness between the four levels of anterior inclination, with the 45° inclination producing the thickest mouthguards, increasing the mean anterior thickness by 75% (2.8 mm, SD: 0.16) from the model on a flat plane (1.6 mm, SD: 0.34). Anterior model inclination of 30 and 45° inclinations increased consistencies between the thickest and thinnest mouthguards in the anterior region of these sample groups. CONCLUSION This study highlights the importance of standardizing the thermoforming process, as this has a significant effect on the quality and material distribution of the resultant product. In particular, greater model inclination is advised as this optimizes the thickness of the anterior sulcus of the mouthguard which may be more prominently at risk from sport-related impact.

Change in color of a maxillofacial prosthetic silicone elastomer, following investment in molds of different materials

Purpose: In the authors′ experience, the color of silicone elastomer following polymerization in molds made of gypsum products is slightly different from the color that was matched in the presence of the patient, before the silicone is packed. It is hypothesized that the investing materials and separating media have an effect on the color during the polymerization process of the silicone. Materials and Methods : This study compares and evaluates the change in color of silicone elastomer packed in three commonly used investing materials - Dental stone (white color), dental stone (green color), and die stone (orange color); coated with three different separating media - Alginate-based medium, soap solution and a resin-based die hardening material. Pigmented silicone samples of dimensions 1.5 cm × 2 cm × 0.5 cm were made from the elastomer in the above-mentioned mold materials using combinations of the mentioned separating media. These served as test group samples. Control group samples were made by packing a mix of the same pigmented elastomer in stainless steel molds. The LFNx01, aFNx01, bFNx01 values of the test and control group samples were determined using a spectrophotometer. The change in color (Delta E) was calculated between the control and test groups. Results: The mean L, a, b values for the control group were, 31.8, 26.2, and 36.3, respectively. Average values of change in color (Delta E) for samples packed utilizing alginate-based medium, die hardener, and soap solution, respectively in white dental stone (2.70, 2.74, and 2.88), green dental stone (2.19, 2.23, 2.42), and orange die stone (3.19, 2.72, 2.80) were tabulated. Conclusion: Among the investing materials studied, die stone showed the most color change (3.19), which was statistically significant. Among the separating media, die hardener showed the least color change (2.23). The best combination of an investing material and separating media as per this investigation is a dental stone (green) and alginate-based separating medium.

The contribution of imaging and digitised data to mandibular reconstruction and implant stabilised occlusal rehabilitation: a case report.

Different methods are recommended for the surgical reconstruction of the resected mandible. The advantages for implant stabilised prostheses in restoring the occlusion are recognised but few papers provide adequate data to identify the successful outcome of treatment. The literature is reviewed and the advantages of imaging together with the use of digitised data is highlighted by a case requiring rehabilitation with enhanced planning methods.

Suitability of a Mobile Phone Colorimeter Application for Use as an Objective Aid when Matching Skin Color during the Fabrication of a Maxillofacial Prosthesis: Mobile App for Color Matching Facial Prosthetics

PURPOSE Color matching a facial prosthesis to human skin is very challenging. Colorimeters aid this process by adding objectivity to what is an otherwise subjective procedure. Mobile phone colorimeter applications offer a less expensive and widely available alternative to dedicated colorimeter devices for color measurement. There is a lack of evidence in the literature regarding the suitability of mobile phone colorimeter applications for the development of silicone shades for facial prosthetics. The purpose of this study is to determine the suitability of a mobile phone colorimeter application for matching natural skin colors during the fabrication of maxillofacial prostheses. MATERIALS AND METHODS Ten pigmented maxillofacial silicone elastomer swatches were fabricated to mimic a range of human skin tones. Color measurements of these swatches were recorded using a test instrument-the mobile phone colorimeter application (RGB Colorimeter) and a reference instrument-the commercially available skin color measurement device e-skin spectrocolorimeter. Comparisons in trueness and precision of the color measurements were made using previously described methods. Data analysis was performed on the recorded results for each of the parameters at three distances (25, 30, and 35 mm) of the test instrument from the target against both a black and a white background. RESULTS The trueness of the mobile phone colorimeter application relative to the colorimeter device varied depending on the distance from the target and the background color. The relative trueness of the color difference measurements fell just within the documented upper threshold of acceptable limits of color difference (∆E 3.0 - 4.4). The calculated precision of the CIE L*a*b* and ∆E measurements of the mobile phone colorimeter application was good, with the latter being well within the documented acceptable limits. CONCLUSIONS A mobile phone colorimeter application would be a suitable aid in objectifying the process of color matching a silicone maxillofacial prosthesis. Further investigation into image calibration to improve trueness and the control of variables such as background noise, uniformity of illumination, and measuring distance is required.