The quality of impressions for crowns and bridges: an assessment of the work received at three commercial dental laboratories. assessing qualities of impressions that may lead to occlusal discrepancies with indirect restorations.

There are few published studies that directly assess the quality of impressions for crowns and bridges in the UK. This paper considers aspects of impression quality with particular attention to factors causing potential occlusal discrepancies in the final restoration. To this end three dental laboratories were visited over a 3-month period. All impressions for conventional crown and bridgework that arrived on the days of the visits were examined and assessed against criteria defined on a custom-designed assessment form. A total of 206 impression cases were considered in this study. Flexible impression trays were used for 65% of working impressions. Their use was more common for NHS work than for private work. 31.9% of all alginate impressions examined were not adequately fixed to the tray. Visible contamination of impressions was not uncommon.

The quality of impressions for crowns and bridges: an assessment of the work received at three commercial dental laboratories. assessing the quality of the impressions of prepared teeth.

The literature is limited in studies directly assessing the quality of impressions for crowns and bridges in the UK. The aim of the study was to assess the quality of impressions for conventional crown and bridgework received by commercial dental laboratories. Three dental laboratories were visited over a 3-month period. All impressions for conventional crowns and bridges that arrived on the days of the visits were examined prior to any laboratory processing. A total of 206 impression cases were examined and assessed against criteria laid out in a custom-designed assessment form. Defects were commonly found in the recording of prepared teeth. Overall, 44.2% of impression cases were unsatisfactory. NHS impressions were more than twice as likely to be unsatisfactory compared to private impressions. If the results of this survey are typical then the general quality of impressions for fixed crown and bridgework is unacceptable. This is particularly true for work completed under the NHS contract.

Effect of obturators on facial form following surgery for head and neck cancer and impact on the perception of appearance.

OBJECTIVES: To describe the correlation between changes in the surface area and depth of the face in individuals wearing an obturator compared with it not being in place, and self-reported Quality of Life in relation to appearance. METHODS: Difference images were created from stereophotogrammetry images recorded from research participants with and without their obturators in place. On the difference images of the face, surface areas and mean depths were calculated. Oral health impact profile questionnaires (OHIP-49) were completed. RESULTS: Data from 19 research participants were recorded. The mean size of the outlined area of the face when the obturators were present compared to when they were not was 1411 mm2 (SD ± 848). Similarly the mean depth differences ranged up to 6.14 mm. Although a proportion of the individuals reported effects in relation to their quality of life, there were no statistically significant relations between the surface areas and mean depths with the participants' responses to the quality of life questions. CONCLUSIONS: There are clear changes in facial tissues, both in relation to surface area and depths when obturators are worn compared to when they are not. There is no simple relationship between the extent of facial change with and without an obturator and quality of life around appearance. The determinants of changed quality of life in this group of patients require greater exploration.

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 subject's skin color. Delta-E values were recorded for each silicone sample in comparison to the subject's 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.

Locating angulated abutments: a technical note.

A simple laboratory-made acrylic resin guide offers rapid location of angulated abutments after the healing abutments are removed. An impression recording the relation of the implants to the dental arch enables the choice of abutments to be made in the laboratory. The precise position and angulation of each abutment can be transferred to the mouth.

Results of treatment of 20 patients with implant-retained auricular prostheses.

A prospective study of 20 patients receiving rehabilitation for a missing external ear revealed the failure of three flanged implants in a total of 60 placed for the support of a prosthesis and 10 for retention of a bone-anchored hearing aid. Factors limiting an optimal outcome were health of the cutaneous cuff around the abutments, bonding of the silicone ear to the acrylic-resin substructure, and the ability to minimize disfigurement of a congenitally deformed face.

Considerations in treatment planning for implant-supported auricular prostheses.

Improvements in planning for the provision of silicone auricular prostheses have been achieved with CT scanning. The analysis of information using a computer workstation has enabled preoperative determination of skull thickness and position of implants in relation to the proposed location of the prosthesis. The technique is of particular value in cases of craniofacial microsomia.

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.

Identifying the position of an ear from a laser scan: the significance for planning rehabilitation.

Laser scanning techniques are used to plan the construction of prosthetic ears as dimensional measurements between anthropometric points can be accurately measured on a screen image. The aim of this study was to determine if these techniques could be used to assess the position of ears on the face. Computer-generated images were created from laser scans of 20 subjects. Frames of reference were constructed by locating a series of anthropometric points on the face from which three orthogonal planes were constructed. A central reference point was identified at the intersection of the three orthogonal planes. Dimensional measurements were made between anthropometric points on the ear and the reference planes. The differences between anthropometric points and the reference planes on the left and right sides of the face were small. It was possible to describe the location of points three-dimensionally with respect to a central reference point. The development of frames of reference and a central reference point would appear to offer many advantages in the assessment and description of ear position for patients requiring reconstruction with prostheses.

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.

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.

Laser scanning for the identification of repeatable landmarks of the ears and face.

OBJECTIVE: To determine whether or not landmarks of the ears and face could be reliably identified using a laser scaning system. DESIGN: A single centre study with two assessors jointly agreeing the siting of the landmarks on the ear on two separate occasions from an original laser scanned image. SETTING: University based research study in London, UK. SUBJECTS: 20 subjects, 11 males, 9 females, aged 16-24 years with normal facial development. MAIN OUTCOME MEASURES: Differences were determined between the locations of landmarks on the two occasions studied. Differences were assessed for the x, y and z co-ordinates of each point. RESULTS: The mean difference between the two sitings of 21 landmarks ranged between 0 and 0.85 mm in the x, y and z axes. With a small number of exceptions, the differences were not statistically significant. The three-dimensional mean differences between the two sitings of each landmark ranged between 1 and 2.5 mm. Coefficients of repeatability ranged between 1.6 and 7.0 mm. CONCLUSIONS: Landmarks of the ears and face from a laser scanned image can be sited consistently by two assessors. Since the landmarks can be located it should be possible to evaluate dimensional measurements of the ear and its position on the face.

Fabrication of a wax ear by rapid-process modeling using stereolithography.

PURPOSE: The purpose of this article is to describe an automated technique that creates a mirror-image wax model of the contralateral ear using a rapid prototyping technique, which allows precise positioning and adaptation to the deficient side of the face. MATERIALS AND METHODS: Magnetic resonance images (MRI) are taken of the face and then digitized and reformatted into a 3-dimensional image. The image of the normal ear is extracted, mirrored, and positioned onto the image of the deformed side of the face. The digitized data, when used in conjunction with stereolithography, produces a photopolymerized resin model ear. A model wax ear is created by pouring molten wax into a silicone mold of the resin model ear. RESULTS: A model wax ear of identical dimensions, shape, and internal contouring as the contralateral normal ear is created. The technique allows the undersurface of the model wax ear to be precisely positioned against the surface contours of the deformed side of the face in 1 patient. CONCLUSION: The use of stereolithography from MRI scan data is a suitable technique for producing a model wax ear that fits the deformed side of the face. The 3-dimensional computer image of the face may also be used to plan the position (level and protrusion) of the ear.

A comparison between videotaped and live demonstrations, for the teaching of removable partial denture procedures.

AIM: This study was devised to test the effectiveness of videotaped demonstrations as opposed to live demonstrations, to small groups of undergraduate dental students. The outcome was assessed by comparing the students' understanding of the clinical and laboratory technical stages of the altered cast impression technique, which is used in the construction of removable partial dentures. METHOD: 31 students watched a series of videotaped demonstrations and 30 received a similar series of live demonstrations. The altered cast procedure was divided into 5 distinct stages, each of which was assessed with the aid of agreed criteria, initially by the students and then by 2 staff assessors and these results were compared. The students were subsequently asked to rate how helpful the videotaped or live demonstration had been on a 5-point scale. RESULTS: The live demonstration group showed better agreement between the students' assessment and the assessors' assessment of the quality of the work for the first part of the clinical stage. There was no difference in the groups' assessment of the final outcome of this clinical stage and the subsequent laboratory technical stages. Students who observed the live demonstrations indicated higher scores for its helpfulness in performance of all the stages of the technique, when compared to those who had observed a videotaped demonstration. CONCLUSION: Both teaching methods developed a similar level of understanding of the principles behind the exercise, although the students preferred the live demonstrations. A carefully produced videotaped demonstration can be a useful alternative to a live demonstration in teaching the short and clear cut technique selected for this study.