A randomized controlled clinical trial on press and block lithium disilicate partial crowns: A 4-year recall.

PURPOSE: To evaluate clinical performances of two lithium disilicate systems (Initial LiSi press vs Initial LiSi Block, GC Co.) using modified United States Public Health Service (USPHS) evaluation criteria and survival rates after 4 years of clinical service. METHODS: Partial adhesive crowns on natural abutment posterior teeth were made on 60 subjects who were randomly divided into two groups: Group 1: Initial LiSi press and Group 2: Initial LiSi Block. Fabrication of partial crowns was made with full analog and digital procedure in Groups 1 and 2 respectively. The restorations were followed-up for 1 and 4 years, and the modified USPHS evaluation was performed at baseline and each recall together with periodontal evaluation. Contingency tables to assess for significant differences of success over time in each group and time-dependent Cox regression to test for differences between the two groups were used and the level of significance was set at P< 0.05. RESULTS: Regarding modified USPHS scores, all evaluated parameters showed Alpha or Bravo and no Charlie was recorded. No statistically significant difference emerged between the two groups in any of the assessed variables (P> 0.05). No statistically significant difference between scores recorded at the baseline and each recall. All modified USPHS scores were compatible with the outcome of clinical success and no one restoration was replaced or repaired, and the survival rate was 100% after 4 years of clinical service. No difference was found between traditional and digital procedure to fabricate the crowns. The two lithium disilicate materials showed similar results after 4 years of clinical service. CLINICAL SIGNIFICANCE: The crowns made with the two tested lithium disilicate materials with analog and digital procedures showed 100% survival after 4 years of clinical service with no statistically significant difference using the modified USPHS scores.

Comparison of trueness and repeatability of facial prosthesis design using a 3D morphable model approach, traditional computer-aided design methods, and conventional manual sculpting techniques.

STATEMENT OF PROBLEM: Manually sculpting a wax pattern of a facial prosthesis is a time-, skill-, and resource-intensive process. Computer-aided design (CAD) methods have been proposed as a substitute for manual sculpting, but these techniques can still require high technical or artistic abilities. Three-dimensional morphable models (3DMMs) could semi-automate facial prosthesis CAD. Systematic comparisons of different design approaches are needed. PURPOSE: The purpose of this study was to compare the trueness and repeatability of replacing facial features with 3 methods of facial prosthesis design involving 3DMM, traditional CAD, and conventional manual sculpting techniques. MATERIAL AND METHODS: Fifteen participants without facial defects were scanned with a structured light scanner. The facial meshes were manipulated to generate artificial orbital, nasal, or combined defects. Three methods of facial prosthesis design were compared for the 15 participants and repeated to produce 5 of each design for 2 participants. For the 3DMM approach, the Leeds face model informed the designs in a statistically meaningful way. For the traditional CAD methods, designs were created by using mirroring techniques or from a nose model database. For the conventional manual sculpting techniques, wax patterns were manually created on 3D printed full face baseplates. For analysis, the unedited facial feature was the standard. The unsigned distance was calculated from each of the several thousand vertices on the unedited facial feature to the closest point on the external surface of the prosthesis prototype. The mean absolute error was calculated, and a Friedman test was performed (α=.05). RESULTS: The median mean absolute error was 1.13 mm for the 3DMM group, 1.54 mm for the traditional CAD group, and 1.49 mm for the manual sculpting group, with no statistically significant differences among groups (P=.549). Boxplots showed substantial differences in the distribution of mean absolute error among groups, with the 3DMM group showing the greatest consistency. The 3DMM approach produced repeat designs with the lowest coefficient of variation. CONCLUSIONS: The 3DMM approach shows potential as a semi-automated method of CAD. Further clinical research is planned to explore the 3DMM approach in a feasibility trial.

Current challenges for 3D printing complete dentures: experiences from a multi-centre clinical trial.

Aims To develop an optimal clinical and laboratory protocol for the fabrication of 3D printing dentures.Design A prospective feasibility study across three UK dental schools.Material and methods Each patient received one conventional and one 3D-printed denture. Both dentures were constructed using the same impression, jaw registration and wax trial denture. Variables investigated included methods of digitisation of the impression and optional use of a 3D-printed baseplate for jaw registration.Results Clinicians strongly preferred 3D-printed baseplates. Patients felt that conventional and printed dentures were similar in retention and stability. More patients favoured conventional dentures over 3D-printed dentures in terms of comfort.Discussion It is feasible to combine conventional clinical work with digital techniques to produce 3D-printed dentures. 3D-printed baseplates offer a cost-effective alternative to conventional bases at the jaw registration stage. Challenges were faced in tooth positioning and managing occlusion, particularly where roots required adjustment.Conclusion 3D printing is suitable for producing baseplates for jaw registration blocks and wax trial insertions. It is feasible to produce 3D-printed dentures using conventional clinical techniques for impressions, jaw registration and wax trial insertion. The workflow used in this study for 3D-printed dentures is not superior to conventional dentures. Further work is required.

IMproving facial PRosthesis construction with contactlESs Scanning and Digital workflow (IMPRESSeD): study protocol for a feasibility crossover randomised controlled trial of digital versus conventional manufacture of facial prostheses in patients with orbital or nasal facial defects.

BACKGROUND: Facial prostheses can have a profound impact on patients' appearance, function and quality of life. There has been increasing interest in the digital manufacturing of facial prostheses which may offer many benefits to patients and healthcare services compared with conventional manufacturing processes. Most facial prosthesis research has adopted observational study designs with very few randomised controlled trials (RCTs) documented. There is a clear need for a well-designed RCT to compare the clinical and cost-effectiveness of digitally manufactured facial prostheses versus conventionally manufactured facial prostheses. This study protocol describes the planned conduct of a feasibility RCT which aims to address this knowledge gap and determine whether it is feasible to conduct a future definitive RCT. METHODS: The IMPRESSeD study is a multi-centre, 2-arm, crossover, feasibility RCT with early health technology assessment and qualitative research. Up to 30 participants with acquired orbital or nasal defects will be recruited from the Maxillofacial Prosthetic Departments of participating NHS hospitals. All trial participants will receive 2 new facial prostheses manufactured using digital and conventional manufacturing methods. The order of receiving the facial prostheses will be allocated centrally using minimisation. The 2 prostheses will be made in tandem and marked with a colour label to mask the manufacturing method to the participants. Participants will be reviewed 4 weeks following the delivery of the first prosthesis and 4 weeks following the delivery of the second prosthesis. Primary feasibility outcomes include eligibility, recruitment, conversion, and attrition rates. Data will also be collected on patient preference, quality of life and resource use from the healthcare perspective. A qualitative sub-study will evaluate patients' perception, lived experience and preference of the different manufacturing methods. DISCUSSION: There is uncertainty regarding the best method of manufacturing facial prostheses in terms of clinical effectiveness, cost-effectiveness and patient acceptability. There is a need for a well-designed RCT to compare digital and conventional manufacturing of facial prostheses to better inform clinical practice. The feasibility study will evaluate key parameters needed to design a definitive trial and will incorporate early health technology assessment and a qualitative sub-study to identify the potential benefits of further research. TRIAL REGISTRATION: ISRCTN ISRCTN10516986). Prospectively registered on 08 June 2021,  https://www.isrctn.com/ISRCTN10516986 .

Digital database for nasal prosthesis design with a 3D morphable face model approach.

Designing nasal prostheses can be challenging because of the unpaired nature of the facial feature, especially in patients lacking preoperative information. Various nose model databases have been developed as a helpful starting point for the computer-aided design of nasal prostheses, but these do not appear to be readily accessible. Therefore, an open-access digital database of nose models has been generated based on a 3-dimensional (3D) morphable face model approach. This article describes the generation of the database, highlights steps for designing a nasal prosthesis, and points readers to the database for future clinical application and research.

Quantifying composite restoration removal and cavity re-preparation using novel region-specific volumetric analysis.

OBJECTIVES: This in-vitro study investigated the effect of 400-405 nm light used during removal of a composite restorations on volume of tooth tissue removed iatrogenically (IATR) and the volume of residual composite. METHODS: Thirty unrestored premolar teeth obtained via a university tissue bank were evenly allocated to test and control groups; material removal with and without violet light. Three clinicians (blinded to the protocol) prepared class V buccal cavities in the teeth. The teeth were scanned using CEREC Omnicam and reallocated to another clinician prior to restoration and rescanning. The teeth were reallocated, and the restorations were removed prior to rescanning. Volumetric scan data was obtained on: changes in cavity volume; the volume of IATR; the volume of residual composite. Data were analysed using Shapiro-Wilk and Kruskal-Wallis tests to a significance of p<0.05. RESULTS: Data showed that there is more IATR when the light was used with mean volume CAV2-over cut of (3.4 mm3, SD 4.22) whereas less IATR was seen when the light was not used (1.2 mm3, SD 1.00), (p<0.05). Data also showed that there is no significant difference in the overall volume of resin composite left when the light was used or not (p> 0.05). However when the light was used, less resin composite material was left around the margins of the cavities when compared to the no light group. SIGNIFICANCE: This novel region-specific cavity analysis method reveals patterns of iatrogenic damage and retained composite which may hold clinical relevance. The use of violet light may result in more complete removal of composite at margins, but also increase IATR. Further research using the novel method is required to ascertain the repeatability and clinical significance of findings.

Pilot study assessing 3D-printed teeth as a caries removal teaching tool.

INTRODUCTION: In UK universities, caries removal teaching utilises plastic teeth. This format does not enable students to learn how to distinguish between tooth layers and caries via tactile feedback. The aim of this study was to assess the applicability of a novel, 3D-printed carious tooth within caries removal teaching. MATERIALS AND METHODS: Single-material 3D-printed teeth containing simulated tactile caries were developed and 14 final-year undergraduates were briefed to remove caries and minimise damage to healthy tissue within the tooth. Students completed evaluation questionnaires for their opinion of 3D-printed teeth in comparison to plastic teeth and perceived confidence to subsequently treat patients. Cavity preparation perimeters were measured, using photographs with a standard protocol. Heat map analysis illustrated variation in location and extent of cavity preparations produced by the cohort. RESULTS: Student feedback indicated the 3D-printed caries exercise was positively received, 71.4% agreed 3D-printed teeth would have better prepared students for patient treatment; 78.6% rated their preclinical stress/anxiety as 'very high' or 'high' and 57.1% agreed that if preclinical teaching incorporated 3D-printed teeth, their stress/anxiety when treating their first caries patient would have been reduced. The average perimeter of cavity preparation indicated relative variation, with a maximum perimeter of 19.6 mm and a minimum of 10.7 mm, and a range of 8.9 mm. DISCUSSION: Introducing 3D-printed teeth into preclinical teaching would allow students to gain confidence in clinically relevant experience in tactile aspects of caries treatment earlier in their training than currently possible. CONCLUSION: This study demonstrates student acceptance of an alternative caries removal teaching method, with potential to increase aptitude in caries removal in a clinically relevant manner.

Sources of error in maximum intercuspation from complete dentate full-arch intraoral scans in vitro.

AIM: Recording maximum intercuspal position (ICP) is critical for many dental procedures. Digital ICP from intraoral scanners (IOSs) produces variable results. This study investigated the sources of error in recording ICP using an IOS and a recently reported method. MATERIALS AND METHODS: A set of dentate models was scanned three times in a Rexcan DS2 scanner. The models were then scanned six times with a Cerec Omnicam IOS. For each scan, 10 bilateral 'bite' scans were performed (n = 6 x 10 bite registrations). Three key points were identified on the first intraoral scan and automatically transplanted onto all subsequent scans. The key point method was validated by using a 'secondary' key point transplantation from each scan back to the three laboratory scans, where the location of each point was compared using one-way analysis of variance. Full-arch errors on the intraoral scans were identified by comparing the intermolar key point distances on all intraoral scans against the 'gold standard' model scans. Precision of the virtual occlusion was identified by comparing the distance between all upper-lower key point pairs for all intraoral scans using intraclass correlation. RESULTS: Automatic key points were transplanted to model scans with standard deviations (SDs) in location of ≤ 0.003 mm (upper [maxillary]) and ≤ 0.004 mm (lower [mandibular]) arch. The intermolar width of the intraoral scans had a mean error of 0.183 (± 0.061) mm (upper) and 0.017 (± 0.092) mm (lower) arch. Interocclusal key point separation showed poor reliability across groups, but good precision (SD < 0.022 mm) within groups. CONCLUSION: Automatic key points allowed valid linear distance comparisons across repeated scans. Poor trueness and precision in the full-arch intraoral scans adversely affected interocclusal registrations. Bite scan precision had a less detrimental effect on interocclusal registration.

Outcome measures in facial prosthesis research: A systematic review.

STATEMENT OF PROBLEM: Facial prosthesis research uses a wide variety of outcome measures, which results in challenges when comparing the effectiveness of interventions among studies. Consensus is lacking regarding the most appropriate and meaningful outcome measures to use in facial prosthesis research to capture important perspectives. PURPOSE: The purpose of the systematic review was to identify and synthesize outcome measures used in facial prosthesis research. MATERIAL AND METHODS: Electronic searches were performed in 11 databases (including nonpeer-reviewed literature). The citations were searched, and expert societies were contacted to identify additional studies. Inclusion criteria comprised studies of participants with facial defects who required or had received prosthetic rehabilitation with an external facial prosthesis. Exclusion criteria comprised participants with ocular prostheses, case reports, case series with fewer than 5 participants, laboratory-based studies, and studies published before 1980. Study selection was performed independently by 2 reviewers. Discrepancies were resolved through discussion or by a third reviewer. Outcome measures were synthesized with a categorization approach based on the perspective, theme, and subtheme of the outcome measures. Quality assessment was performed with an appraisal tool that enabled evaluation of studies with diverse designs. RESULTS: Database searching identified 13 058 records, and 7406 remained after duplications were removed. After initial screening, 189 potentially relevant records remained, and 186 full texts were located (98% retrieval rate). After full-text screening, 124 records were excluded. Citation searches and contact with expert societies identified 4 further records. In total, 69 articles (grouped into 65 studies) were included. Studies were categorized as per the perspective of their outcome measures, with the following findings: patient-reported (74% of studies), clinical indicators (34%), clinician-reported (8%), multiple viewpoints (6%), and independent observer-reported (3%). Patient-reported outcome measures included tools to assess satisfaction, quality of life, and psychologic health. Variability in the choice of outcome measures was evident among the studies, with many self-designed, unvalidated, condition-specific questionnaires reported. A greater number of outcome measure themes emerged over time; themes such as service delivery and health state utility have recently been evaluated. CONCLUSIONS: Over the past 40 years, facial prosthesis research has focused on patient-reported outcome measures. Outcome measures relating to other perspectives have been used less frequently, although new themes appear to be emerging in the literature. Future research should use outcome measures with appropriate measurement properties for use with facial prosthetics.

Investigating the construct validity of a haptic virtual caries simulation for dental education.

Introduction: Teaching dental caries removal is limited by the material and methods available in the preclinical teaching space. Plastic teeth do not simulate the tactile feel of a lesion and natural teeth do not allow for standardised training and assessment. A novel method for simulating caries has been reported. Here, to investigate the construct validity of a caries simulation, whether haptic simulation could contribute to the understanding of caries removal, the performance of first-year dental students on the haptic simulation exercise is compared with that of experienced dentists. Method: A virtual block comprising healthy dentine, pulp, enamel and a carious lesion with significant spread along the amelodentinal junction (ADJ) was developed for the Simodont dental trainer. The case was presented to 112 first-year students and 17 clinicians following a 15 min training period on a block which contained green caries and displayed live progress throughout the exercise. All participants were given the same verbal instructions: to remove all unsupported enamel and caries along the ADJ while retaining as much healthy tissue as possible. Results: Clinicians performed better than the dental novices in precision and overall performance. Clinicians removed more material on average, except for healthy dentine, of which similar amounts were removed by both groups. Discussion: We presented a novel haptic caries exercise and investigated the construct validity of the task. The simulation may bridge the gap between preclinical and clinical dental education in caries removal. Conclusion: Clinically experienced dentists outperformed novices on a haptic caries simulation exercise. The exercise may be a useful tool for assessing conceptual understanding of caries removal.

Influence of Scanner Precision and Analysis Software in Quantifying Three-Dimensional Intraoral Changes: Two-Factor Factorial Experimental Design.

BACKGROUND: Three-dimensional scans are increasingly used to quantify biological topographical changes and clinical health outcomes. Traditionally, the use of 3D scans has been limited to specialized centers owing to the high cost of the scanning equipment and the necessity for complex analysis software. Technological advances have made cheaper, more accessible methods of data capture and analysis available in the field of dentistry, potentially facilitating a primary care system to quantify disease progression. However, this system has yet to be compared with previous high-precision methods in university hospital settings. OBJECTIVE: The aim of this study was to compare a dental primary care method of data capture (intraoral scanner) with a precision hospital-based method (laser profilometer) in addition to comparing open source and commercial software available for data analysis. METHODS: Longitudinal dental wear data from 30 patients were analyzed using a two-factor factorial experimental design. Bimaxillary intraoral digital scans (TrueDefinition, 3M, UK) and conventional silicone impressions, poured in type-4 dental stone, were made at both baseline and follow-up appointments (mean 36 months, SD 10.9). Stone models were scanned using precision laser profilometry (Taicaan, Southampton, UK). Three-dimensional changes in both forms of digital scans of the first molars (n=76) were quantitatively analyzed using the engineering software Geomagic Control (3D Systems, Germany) and freeware WearCompare (Leeds Digital Dentistry, UK). Volume change (mm3) was the primary measurement outcome. The maximum point loss (µm) and the average profile loss (µm) were also recorded. Data were paired and skewed, and were therefore compared using Wilcoxon signed-rank tests with Bonferroni correction. RESULTS: The median (IQR) volume change for Geomagic using profilometry and using the intraoral scan was -0.37 mm3 (-3.75-2.30) and +0.51 mm3 (-2.17-4.26), respectively (P<.001). Using WearCompare, the median (IQR) volume change for profilometry and intraoral scanning was -1.21 mm3 (-3.48-0.56) and -0.39 mm3 (-3.96-2.76), respectively (P=.04). WearCompare detected significantly greater volume loss than Geomagic regardless of scanner type. No differences were observed between groups with respect to the maximum point loss or average profile loss. CONCLUSIONS: As expected, the method of data capture, software used, and measurement metric all significantly influenced the measurement outcome. However, when appropriate analysis was used, the primary care system was able to quantify the degree of change and can be recommended depending on the accuracy needed to diagnose a condition. Lower-resolution scanners may underestimate complex changes when measuring at the micron level.

Quantifying increased rates of erosive tooth wear progression in the early permanent dentition.

OBJECTIVES: To investigate if quantitative analysis of intraoral scans of study models can identify erosive tooth wear progression. METHODS: Data were collected from a retrospective longitudinal study, using pre-and post-orthodontic treatment casts of 11-13 year olds, recorded at two consecutive appointments 29 months apart. Casts were digitised with intra-oral scanner TRIOS™ (3Shape, Copenhagen, Denmark) and first molar scan pairs used for analysis. Occlusal surfaces of each molar pair were visually assessed using the BEWE index as having no BEWE progression (n = 42) or BEWE progression (n = 54). Scan pairs were aligned and analysed for volume loss, maximum profile loss and mean profile loss in WearCompare (Leedsdigitaldentistry.com/wearcompare) using previously published protocols. Data were analysed in SPSS and not normal. Mann-Whitney U test with a Bonferroni correction assessed differences between progression groups. Receiver-operating-characteristic (ROC) curves were used to identify the sensitivity and specificity of quantified wear progression rates at determining visual wear progression. RESULTS: Surfaces with visible progression demonstrated a median volume loss of -2.19 mm3 (IQR-3.65, -0.91) compared to a median volume loss of -0.37 mm3 (IQR -1.02, 0.16) in the no visible progression group (p < 0.001). Mean profile loss was -75.2 µm (IQR-93.9, -61.0) and 63.2 µm (IQR -82.5, -49.7) for the progression and no-progression groups respectively (p = 0.018). Volume loss of -1.22mm3 represented a 79 % sensitivity and 61 % specificity. The estimated area under the curve for volume loss was 0.80 (95 %CI 0.71-0.89, p < 0.001). CONCLUSIONS: This is the first study to propose rates of high wear progression in adolescents. Limited sensitivity and specificity confirms that quantitative analysis is an adjunct tool to be used alongside history taking and clinical judgement. CLINICAL SIGNIFICANCE: The rapid advancement of digital technologies may result in improved diagnosis in erosive tooth wear (ETW). Intra-oral scans and registration software are a promising adjunct for monitoring ETW progression in clinical practice.

Early assessment with a virtual reality haptic simulator predicts performance in clinical practice.

Background: Prediction of clinical training aptitude in medicine and dentistry is largely driven by measures of a student's intellectual capabilities. The measurement of sensorimotor ability has lagged behind, despite being a key constraint for safe and efficient practice in procedure-based medical specialties. Virtual reality (VR) haptic simulators, systems able to provide objective measures of sensorimotor performance, are beginning to establish their utility in facilitating sensorimotor skill acquisition, and it is possible that they may also inform the prediction of clinical performance. Methods: A retrospective cohort study examined the relationship between student performance on a haptic VR simulator in the second year of undergraduate dental study with subsequent clinic performance involving patients 2 years later. The predictive ability was tested against a phantom-head crown test (a traditional preclinical dental assessment, in the third year of study). Results: VR scores averaged across the year explained 14% of variance in clinic performance, while the traditional test explained 5%. Students who scored highly on this averaged measure were ~10 times more likely to be high performers in the clinical crown test. Exploratory analysis indicated that single-trial VR scores did not correlate with real-world performance, but the relationship was statistically significant and strongest in the first half of the year and weakened over time. Conclusions: The data demonstrate the potential of a VR haptic simulator to predict clinical performance and open up the possibility of taking a data-driven approach to identifying individuals who could benefit from support in the early stages of training.

CAD/CAM techniques for the conservative and efficient management of tooth wear.

The prevalence of tooth wear has increased significantly in recent decades. Whilst many treatment approaches are available, there is no consensus on the best materials or techniques. Advances in digital workflows have the potential to reduce the biological cost of treatment, improve treatment outcomes and reduce costs. This article describes modern CAD/CAM techniques which preserve tooth tissue and improve efficiency.

Investigation into the validity of WearCompare, a purpose-built software to quantify erosive tooth wear progression.

OBJECTIVES: The use of surface matching software with intraoral scanners is developing rapidly which increases the need for accessible, accurate and validated measurement software. This investigation compared the current gold-standard Geomagic Control software to a purpose-built software "WearCompare". METHODS: Artificially created occlusal defects of a known size were created on 10 natural molar teeth scanned with a structured-light model-scanner (Rexcan DS2, Europac 3D, Crewe). The volume change, maximum profilometric loss and mean profilometric loss were obtained from both Geomagic Control (3D Systems, Darmstadt, Germany) and WearCompare (leedsdigitaldentistry.com). Duplicated datasets were randomly repositioned and re-alignment performed. The effect of the re-alignment was calculated by analysing differences between the known defect size and defect size after re-alignment using the same measurement metrics. Lastly, clinical wear measurements were compared on natural molar surfaces (n=60) over 6 months using study models collected from a previous longitudinal trial. Data analysis was performed in SPSS v25 (paired t-tests, Pearson correlations, p<0.05). RESULTS: Measurement correlation between the softwares was greater than 0.97 (p<0.001) for all measurement metrics. The volume change error (SD) after alignment was -0.67mm3(1.14) for Geomagic and -0.06mm3(0.93) for WearCompare (p=0.140 and r=0.065, p=0.86). Measurement errors were observed after alignment in both softwares and no statistical differences were observed between softwares. The volume change on the clinical dataset over 6 months was +0.29 mm3(3.97) in Geomagic and -0.30mm3(1.82) for WearCompare (p=0.19 and r=0.61, p<0.001). The mean profile gain was 42.86µm(40.19) for Geomagic and 32.17µm(23.72) for WearCompare (p=0.048). Correlations between the softwares were greater than 0.6 for all measurement metrics except for mean profile gain. SIGNIFICANCE: WearCompare is a comparable tool to Geomagic for quantifying erosive tooth wear. WearCompare reported statistically less profile gain indicating less error but further research is needed to reduce the human errors in both softwares.

Accuracy of capturing oncology facial defects with multimodal image fusion versus laser scanning.

STATEMENT OF PROBLEM: Fabrication of conventional facial prostheses is a labor-intensive process which traditionally requires an impression of the facial defect and surrounding tissues. Inaccuracies occur during the facial moulage because of soft-tissue compression, the patient's reflex movements, or the lack of support for the impression material. A variety of 3D imaging techniques have been introduced during the production of facial prostheses. However, the accuracy of the different imaging techniques has not been evaluated sufficiently in this clinical context. PURPOSE: The purpose of this in vitro study was to compare the difference in accuracy of capturing oncology facial defects with multimodal image fusion and laser scanning against a cone beam computed tomography (CBCT) reference scan. MATERIAL AND METHODS: Ten gypsum casts of oncology facial defects were acquired. To produce reference models, a 3D volumetric scan was obtained using a CBCT scanner and converted into surface data using open-source medical segmentation software. This model was cropped to produce a CBCT mask using an open-source system for editing meshes. The multimodal image fusion model was created using stereophotogrammetry to capture the external facial features and a custom optical structured light scanner to record the defect. The gypsum casts were also scanned using a commercial 3D laser scanner to create the laser-scanned model. Analysis of the best fit of each experimental model to the CBCT mask was performed in MeshLab. The unsigned mean distance was used to measure the absolute deviation of each model from the CBCT mask. A paired-samples t test was conducted to compare the mean global deviation of the 2 imaging modalities from the CBCT masks (α=.05). RESULTS: A statistically significant difference was found in the mean global deviation between the multimodal imaging model (220 ±50 µm) and the laser-scanned model (170 ±70 µm); (t(9)=2.56, P=.031). The color error maps illustrated that the greatest error was located at sites distant to the prosthesis margins. CONCLUSIONS: The laser-scanned models were more accurate; however, the mean difference of 50 µm is unlikely to be clinically significant. The laser scanner had limited viewing angles and a longer scan time which may limit its transferability to maxillofacial practice.

Deformation and retentive force following in vitro cyclic fatigue of cobalt-chrome and aryl ketone polymer (AKP) clasps.

OBJECTIVE: To compare the retention force of individual clasps made from cobalt chromium (CoCr) or new aryl ketone polymer (AKP) material, Ultaire™ AKP, following prolonged fatigue testing along ideal and non-ideal paths of removal and to assess 3D deformation of the active and passive clasp tips. METHODS: CoCr and AKP clasps were manufactured in their standard, respective processes, digitally scanned prior to testing, then cycled 15,000 times over an e.max analogue crown in artificial saliva. Retentive load was measured in situ, as a function of cycles. Clasps were rescanned to assess deformation and along with their antagonists subjected to SEM to assess localised wear. RESULTS: Distortion of the CoCr clasps was consistently larger than Ultaire™ AKP clasps, irrespective of removal path. CoCr clasps had significantly higher retentive forces than AKP clasps, for both removal paths. Ultaire™ AKP clasps showed a lower but relatively constant retentive force. The non-ideal path of removal affected retentive forces for both clasp materials. SEM showed localised removal of glaze for e.max crowns used with CoCr clasps. SIGNIFICANCE: Ultaire™ AKP clasps showed significantly less permanent deformation and lower retentive force than CoCr clasps. Unlike CoCr, the Ultaire™ AKP clasps did not work harden, nor had as large a reduction in retentive force and accompanying permanent deformation; the retentive force for the Ultaire™ AKP clasps was consistent over 15,000 cycles of fatigue mimicking prolonged clinical use. The AKP material was more robust; showing minimal deformation even in non-ideal paths of removal, as many patients would routinely use.

The factors that count in selecting future dentists: sensorimotor and soft skills.

Introduction Dental schools across the world are increasingly adopting 'multiple mini interview' (MMI) approaches to evaluate prospective students. But what skills and abilities are being assessed within these short, structured 'interview' stations and do they map on to the requirements of dental practice? Understanding the fundamental processes being measured is important if these assessments are to serve the purpose of identifying the students with the greatest potential to succeed in dental practice.Materials and methods To this end, we performed factor analysis on data from 239 participants on ten MMI stations used for undergraduate selection at a UK dental school.Results The analysis revealed that this assessment approach captured two fundamental underlying traits. The first factor captured scores on six stations that could be labelled usefully as a 'soft skill' factor. The second captured scores on four stations that could be described usefully as a 'sensorimotor' factor.Conclusion The present study demonstrates that the structure of at least one MMI used within the UK for dental school entry can be parsed into two distinct factors relating to soft skills and sensorimotor abilities. This finding has implications for the efficiency of the interview process, the refinement of MMI assessment in dental schools across the world and understanding of the critical skills that a successful dental practitioner must possess.

Investigation into the accuracy and measurement methods of sequential 3D dental scan alignment.

OBJECTIVES: Alignment procedures have yet to be standardised and may influence the measurement outcome. This investigation assessed the accuracy of commonly used alignment techniques and their impact on measurement metrics. METHODS: Datasets of 10 natural molar teeth were created with a structured-light model-scanner (Rexcan DS2, Europac 3D, Crewe). A 300µm depth layer was then digitally removed from the occlusal surface creating a defect of known size. The datasets were duplicated, randomly repositioned and re-alignment attempted using a "best-fit" alignment, landmark-based alignment or reference alignment in Geomagic Control (3D Systems, Darmstadt, Germany). The re-alignment accuracy was mathematically assessed using the mean angular and translation differences between the original alignment and the re-aligned datasets. The effect of the re-alignment on conventional measurement metrics was calculated by analysing differences between the known defect size and defect size after re-alignment. Data were analysed in SPSS v24(ANOVA, post hoc Games Howell test, p<0.05). RESULTS: The mean translation error (SD) was 139µm (42) using landmark alignment, 130µm (26) for best-fit and 22µm (9) for reference alignment (p<0.001). The mean angular error (SD) between the datasets was 2.52 (1.18) degrees for landmark alignment, 0.56 (0.38) degrees for best-fit alignment and 0.26 (0.12) degrees for reference alignment (p<0.001). Using a reference alignment statistically reduced the mean profilometric change, volume change and percentage of surface change errors (p<0.001). SIGNIFICANCE: Reference alignment produced significantly lower alignment errors and truer measurements. Best-fit and landmark-based alignment algorithms significantly underestimated the size of the defect. Challenges remain in identifying reference surfaces in a robust, clinically relevant method.