Acting Wisely: Eliminating Negative Bias in Medical Education-Part 2: How Can We Do Better?

In Part 1 of this 2-article series, the authors reviewed the problem of unmitigated bias in medical education and proposed a wisdom-based framework for a different way of educating medical students. In this article, Part 2, the authors answer a key question: How can medical educators do better? Is a bias-free environment possible? The answer to the latter question likely is "no." In fact, having a zero-bias goal in mind may blind educators and students to the implicit biases that affect physicians' decisions and actions. Biases appear to be a part of how the human brain works. This article explores ways to neutralize their destructive effects by: (1) increasing awareness of personal biases; (2) using mitigation strategies to protect against the undesirable effects of those biases; (3) working to change some negative biases, particularly learned biases; and (4) fostering positive biases toward others. The authors describe the concrete actions-interpersonal, structural, and cultural actions-that can be taken to reduce negative bias and its destructive effects.

Acting Wisely: Eliminating Negative Bias in Medical Education-Part 1: The Fundamentals

Bias is a ubiquitous problem in human functioning. It has plagued medical decision making, making physicians prone to errors of perception and judgment. Racial, gender, ethnic, and religious negative biases infest physicians' perception and cognition, causing errors of judgment and behavior that are damaging. In Part 1 of this series of 2 papers, the authors address the problem of harmful bias, the science of cognition, and what is known about how bias functions in human perception and information processing. They lay the groundwork for an approach to reducing negative bias through awareness, reflection, and bias mitigation, an approach in which negative biases can be transformed-by education, experience, practice, and relationships-into positive biases toward one another. The authors propose wisdom as a conceptual framework for imagining a different way of educating medical students. They discuss fundamental cognitive, affective, and reflective components of wisdom-based education. They also review the skills of awareness, using debiasing strategies, compassion, fostering positive emotion, and reflection that are inherent to a wisdom-based approach to eliminating the negative effects of bias in medical education. In Part 2, the authors answer a key question: How can medical educators do better? They describe the interpersonal, structural, and cultural elements supportive of a wisdom-based learning environment, a culture of respect and inclusion in medical education.

Case Report: Lower Gastrointestinal Bleeding due to Entamoeba histolytica Detected Early by Multiplex PCR: Case Report and Review of the Laboratory Diagnosis of Amebiasis

We report a case of Entamoeba histolytica infection in a young man who presented with cerebral infarction and shortly after admission developed bloody diarrhea with fever. A rapid diagnosis of severe E. histolytica colitis was established through the use of a multiplex polymerase chain reaction enteropathogen stool panel. This result was unexpected in a patient native to the United States without known risk factors for amebiasis and negative stool microscopy examination for ova and parasites. Rapid diagnosis allowed prompt initiation of appropriate anti-amebic therapy and ultimately a good outcome in a condition that otherwise carries high morbidity and fatality.

Management of a Mycobacterium immunogenum infection of a peritoneal dialysis catheter site

Mycobacterium immunogenum is a member of the rapidly growing non-tuberculous mycobacteria and is a relatively new species identified within this group. An 81-year-old immune-competent male was diagnosed with M. immunogenum infection of his peritoneal dialysis catheter exit site and surrounding soft tissue. To our knowledge, this is the first reported case of M. immunogenum infection of a peritoneal catheter. Treatment included catheter removal, local surgical debridement, and combination antimicrobial therapy. Herein, we review literature describing antibiotic management of M. immunogenum, an organism for which optimal therapy is not defined.

Prevalence of infraocclusion of primary molars determined using a new 2D image analysis methodology

BACKGROUND

The reported prevalence of infraocclusion varies widely, reflecting differences in definitions and measurement/scoring approaches. This study aimed to quantify the prevalence and extent of infraocclusion in singletons and twins during the late mixed dentition stage of dental development using a new diagnostic imaging method and objective criteria. The study also aimed to determine any associations between infraocclusion and gender, arch type, arch side and tooth type.

METHODS

Two samples were analysed, 1454 panoramic radiographs of singletons and 270 dental models of twins. Both samples ranged in age from 8 to 11 years. Adobe Photoshop CS5 was used to measure the extent of infraocclusion. Repeatability tests showed systematic and random errors were small.

RESULTS

The prevalence in the maxilla was low (<1%), whereas the prevalence in the mandible was 22% in the singleton sample and 32% in the twin sample. The primary mandibular first molar was affected more often than the second molar. There was no significant difference in the expression between genders or sides.

CONCLUSIONS

A new technique for measuring infraocclusion has been developed with high intra- and interoperator reproducibility. This method should enhance early diagnosis of tooth developmental abnormalities and treatment planning during the late mixed dentition stage of development.

The course and distribution of the buccal nerve: clinical relevance in dentistry

BACKGROUND

The buccal branch of the mandibular division of the trigeminal nerve is commonly anaesthetized for dental procedures and may be damaged during surgery. Descriptions of the distribution of the buccal nerve (BN) in anatomical texts are generally lacking in detail and do not provide information about the extent of its variation between individuals. There are also commonly-held clinical beliefs about the BN that lack support from anatomical dissections.

METHODS

Detailed dissections of the course and distribution of the BN were performed in a sample of 12 hemi-heads from 11 edentulous and partially dentate human adult cadavers.

RESULTS

A broader distribution of the BN was found than described previously, with innervation extending to the lips in all cases. Approximately half of the lateral sides of the lips were innervated by the BN in two cases and approximately one-third of their lateral sides in the other 10 cases. Distribution of the BN to the lower lips was wider than to the upper lips.

CONCLUSIONS

Our findings provide a stronger anatomical basis to underpin clinical procedures involving the BN and indicate that some commonly-held clinical views about this nerve are not supported by anatomical evidence.

Evaluating brain-computer interface performance using color in the P300 checkerboard speller

OBJECTIVE

Current Brain-Computer Interface (BCI) systems typically flash an array of items from grey to white (GW). The objective of this study was to evaluate BCI performance using uniquely colored stimuli.

METHODS

In addition to the GW stimuli, the current study tested two types of color stimuli (grey to color [GC] and color intensification [CI]). The main hypotheses were that in a checkboard paradigm, unique color stimuli will: (1) increase BCI performance over the standard GW paradigm; (2) elicit larger event-related potentials (ERPs); and, (3) improve offline performance with an electrode selection algorithm (i.e., Jumpwise).

RESULTS

Online results (n=36) showed that GC provides higher accuracy and information transfer rate than the CI and GW conditions. Waveform analysis showed that GC produced higher amplitude ERPs than CI and GW. Information transfer rate was improved by the Jumpwise-selected channel locations in all conditions.

CONCLUSIONS

Unique color stimuli (GC) improved BCI performance and enhanced ERPs. Jumpwise-selected electrode locations improved offline performance.

SIGNIFICANCE

These results show that in a checkerboard paradigm, unique color stimuli increase BCI performance, are preferred by participants, and are important to the design of end-user applications; thus, could lead to an increase in end-user performance and acceptance of BCI technology.

An unusual ocular complication following dental anaesthesia: case report

Used routinely by dental practitioners, local anaesthetics are generally a safe and effective means of achieving pain control during invasive dental procedures. Delivery, however, is technique sensitive and the potential for patient complication exists. Although reasonably rare, ocular complications have occurred, often leaving the patient and the clinician in distress. Such reported events have almost always involved tissue responses ipsilateral to the injection site. The current case report presents an unusual event involving involuntary fasciculation or hemifacial spasm and eventual eyelid closure on the contralateral side following a routine inferior alveolar nerve block. Aspects including the patient's history, the observed response, a pathophysiological hypothesis and patient management are discussed.

Suppressing flashes of items surrounding targets during calibration of a P300-based brain-computer interface improves performance

Since the introduction of the P300 brain-computer interface (BCI) speller by Farwell and Donchin in 1988, the speed and accuracy of the system has been significantly improved. Larger electrode montages and various signal processing techniques are responsible for most of the improvement in performance. New presentation paradigms have also led to improvements in bit rate and accuracy (e.g. Townsend et al (2010 Clin. Neurophysiol. 121 1109-20)). In particular, the checkerboard paradigm for online P300 BCI-based spelling performs well, has started to document what makes for a successful paradigm, and is a good platform for further experimentation. The current paper further examines the checkerboard paradigm by suppressing items which surround the target from flashing during calibration (i.e. the suppression condition). In the online feedback mode the standard checkerboard paradigm is used with a stepwise linear discriminant classifier derived from the suppression condition and one classifier derived from the standard checkerboard condition, counter-balanced. The results of this research demonstrate that using suppression during calibration produces significantly more character selections/min ((6.46) time between selections included) than the standard checkerboard condition (5.55), and significantly fewer target flashes are needed per selection in the SUP condition (5.28) as compared to the RCP condition (6.17). Moreover, accuracy in the SUP and RCP conditions remained equivalent (∼90%). Mean theoretical bit rate was 53.62 bits/min in the suppression condition and 46.36 bits/min in the standard checkerboard condition (ns). Waveform morphology also showed significant differences in amplitude and latency.

Predictive spelling with a P300-based brain-computer interface: Increasing the rate of communication

This study compared a conventional P300 speller brain-computer interface (BCI) to one used in conjunction with a predictive spelling program. Performance differences in accuracy, bit rate, selections per minute, and output characters per minute (OCM) were examined. An 8×9 matrix of letters, numbers, and other keyboard commands was used. Participants (n = 24) were required to correctly complete the same 58 character sentence (i.e., correcting for errors) using the predictive speller (PS) and the non-predictive speller (NS), counterbalanced. The PS produced significantly higher OCMs than the NS. Time to complete the task in the PS condition was 12min 43sec as compared to 20min 20sec in the NS condition. Despite the marked improvement in overall output, accuracy was significantly higher in the NS paradigm. P300 amplitudes were significantly larger in the NS than in the PS paradigm; which is attributed to increased workload and task demands. These results demonstrate the potential efficacy of predictive spelling in the context of BCI.

Improving clinical assessment: evaluating students' ability to identify and apply clinical criteria

AIM

There is ongoing concern by health educators over the inability of professionals to accurately self-assess their clinical behaviour and standards, resulting in doubts over a key expectation of effective self-regulation in the health professions. Participation by students in the assessment process has been shown to increase the understanding of assessment criteria in written assessment tasks. How this might transfer to the clinical setting is the focus of this study. This paper is part of an ongoing investigation of the impact on learning of a series of activities that provides students with opportunities to discuss and apply criteria and standards associated with self-assessment in clinical dentistry. Our aim was to evaluate whether participation in these assessment activities improved the ability of first-year dental students to recognise behaviours demonstrated by 'peers' in videos of clinical scenarios and to relate these to the assessment criteria.

MATERIALS AND METHODS

A series of three workshops in conjunction with weekly clinical assessment activities in Semesters 1 and 2 were use to support first-year students' learning of clinical assessment criteria. The design of the workshops was based on the principles of social constructivist theories of learning and the concept of tacit knowledge. Accordingly workshop activities were planned around videos that were specifically constructed to illustrate procedures and behaviours typical of those observed by staff and tutors in the first year of the dental course at The University of Adelaide, Australia. First-year students viewed the videos prior to and after the workshops and recorded observed behaviours that related to the assessment criteria that were used in their clinical practice course. Student learning outcomes were assessed 10-14 weeks after the initial workshop and again up to 42 weeks later. To check whether learning resulted from repeated viewing of the videos without formal discussion, a reference group of third-year students who did not attend the workshops also viewed the videos two times, separated by 12 weeks, and recorded observations in the same way.

RESULTS

There was no consistent evidence that repeat viewing of the videos in isolation resulted in improved recognition of 'peer' behaviours by third-year dental students. Results for the first-year students indicated that the workshops and clinical assessment activities had a significantly positive effect on the ability of students to identify 'peer' behaviours related to the criteria used for clinical assessment. In particular, students' recognition in others of knowledge and professional behaviours improved significantly. This improvement was retained over the year and students were able to recognise these behaviours in other scenarios relevant to their year level.

CONCLUSIONS

This early exposure to the process of clinical assessment, coupled with ongoing self-assessment and tutor feedback throughout first year, improved the ability of first-year students to identify and apply some key assessment criteria to observed 'peer' behaviour, and this ability was retained over time.

A novel P300-based brain-computer interface stimulus presentation paradigm: moving beyond rows and columns

OBJECTIVE

An electroencephalographic brain-computer interface (BCI) can provide a non-muscular means of communication for people with amyotrophic lateral sclerosis (ALS) or other neuromuscular disorders. We present a novel P300-based BCI stimulus presentation - the checkerboard paradigm (CBP). CBP performance is compared to that of the standard row/column paradigm (RCP) introduced by Farwell and Donchin (1988).

METHODS

Using an 8x9 matrix of alphanumeric characters and keyboard commands, 18 participants used the CBP and RCP in counter-balanced fashion. With approximately 9-12 min of calibration data, we used a stepwise linear discriminant analysis for online classification of subsequent data.

RESULTS

Mean online accuracy was significantly higher for the CBP, 92%, than for the RCP, 77%. Correcting for extra selections due to errors, mean bit rate was also significantly higher for the CBP, 23 bits/min, than for the RCP, 17 bits/min. Moreover, the two paradigms produced significantly different waveforms. Initial tests with three advanced ALS participants produced similar results. Furthermore, these individuals preferred the CBP to the RCP.

CONCLUSIONS

These results suggest that the CBP is markedly superior to the RCP in performance and user acceptability.

SIGNIFICANCE

The CBP has the potential to provide a substantially more effective BCI than the RCP. This is especially important for people with severe neuromuscular disabilities.

Leadership, governance and management in dental education - new societal challenges

Dental schools around the world face new challenges that raise issues with regard to how they are governed, led and managed. With rapid societal changes, including globalization and consumerism, the roles of universities and their funding have become intensely debated topics. When financial burdens on universities increase, so does the pressure on dental schools. This is exacerbated by the relative expense of running dental schools and also by the limited understanding of both university managers and the public of the nature and scope of dentistry as a profession. In these circumstances, it is essential for dental schools to have good systems of leadership and management in place so that they can not only survive in difficult times, but flourish in the longer term. This paper discusses the concept of governance and how it relates to leadership, management and administration in dental schools and hospitals. Various approaches to governance and management in dental schools on different continents and regions are summarized and contrasted. A number of general governance and leadership issues are addressed. For example, a basic principle supported by the Working Group is that an effective governance structure must link authority and responsibility to performance and review, i.e. accountability, and that the mechanism for achieving this should be transparent. The paper also addresses issues specific to governing, leading and managing dental schools. Being a dean of a modern dental school is a very demanding role and some issues relating to this role are raised, including: dilemmas facing deans, preparing to be dean and succession planning. The importance of establishing a shared vision and mission, and creating the right culture and climate within a dental school, are emphasized. The Working Group advocates establishing a culture of scholarship in dental schools for both teaching and research. The paper addresses the need for effective staff management, motivation and development, and highlights the salience of good communication. The Working Group suggests establishing an advisory board to the dean and school, including lay persons and other external stakeholders, as one way of separating governance and management to some extent and providing some checks and balances within a dental school. Several other suggestions and recommendations are made about governance, management and leadership issues, including the need for schools to promote an awareness of their roles by good communication and thereby influence perceptions of others about their roles and values.

Factors influencing oral colonization of mutans streptococci in young children

This paper aims to critically review current knowledge about the key factors involved in oral colonization of the cariogenic group of bacteria, mutans streptococci (MS) in young children. MS, consisting mainly of the species Streptococcus mutans and Streptococcus sobrinus, are commonly cultured from the mouths of infants, with prevalence of infection ranging from around 30 per cent in 3 month old predentate children to over 80 per cent in 24 month old children with primary teeth. MS is usually transmitted to children through their mothers, and the risk of transmission increases with high maternal salivary levels of MS and frequent inoculation. Factors that affect the colonization of MS may be divided into bacterial virulence, host-related and environmental factors. Complex interaction among these factors determine the success and timing of MS colonization in the child. As clinical studies have shown that caries risk is correlated with age at which initial MS colonization occurred, strategies for the prevention of dental caries should include timely control of colonization of the cariogenic bacteria in the mouths of young children.

Problem-based learning in dental education: what's the evidence for and against … and is it worth the effort?

All Australian dental schools have introduced problem-based learning (PBL) approaches to their programmes over the past decade, although the nature of the innovations has varied from school to school. Before one can ask whether PBL is better than the conventional style of education, one needs to consider three key issues. Firstly, we need to agree on what is meant by the term PBL; secondly, we need to decide what "better" means when comparing educational approaches; and thirdly, we must look carefully at how PBL is implemented in given situations. It is argued that PBL fulfils, at least in theory, some important principles relating to the development of new knowledge. It also represents a change in focus from teachers and teaching in conventional programmes to learners and learning. Generally, students enjoy PBL programmes more than conventional programmes and feel they are more nurturing. There is also some evidence of an improvement in clinical and diagnostic reasoning ability associated with PBL curricula. The main negative points raised about PBL are the costs involved and mixed reports of insufficient grounding of students in the basic sciences. Financial restraints will probably preclude the introduction of pure or fully integrated PBL programmes in Australian dental schools. However, our research and experience, as well as other published literature, indicate that well-planned hybrid PBL programmes, with matching methods of assessment, can foster development of the types of knowledge, skills and attributes that oral health professionals will need in the future.

15 years of BCI research at Graz University of Technology: current projects

Over the last 15 years, the Graz Brain-Computer Interface (BCI) has been developed and all components such as feature extraction and classification, mode of operation, mental strategy, and type of feedback have been investigated. Recent projects deal with the development of asynchronous BCIs, the presentation of feedback and applications for communication and control.

Molar intercuspal dimensions: genetic input to phenotypic variation

Molecular studies indicate that epigenetic events are important in determining how the internal enamel epithelium folds during odontogenesis. Since this process of folding leads to the subsequent arrangement of cusps on molar teeth, we hypothesized that intercuspal distances of human molar teeth would display greater phenotypic variation but lower heritabilities than overall crown diameters. Intercuspal distances and maximum crown diameters were recorded from digitized images of dental casts in 100 monozygotic and 74 dizygotic twin pairs. Intercuspal distances displayed less sexual dimorphism in mean values but greater relative variability and fluctuating asymmetry than overall crown measures. Correlations between intercuspal distances and overall crown measures were low. Models incorporating only environmental effects accounted for observed variation in several intercuspal measures. For those intercuspal variables displaying significant additive genetic variance, estimates of heritability ranged from 43 to 79%, whereas those for overall crown size were higher generally, ranging from 60 to 82%. Our finding of high phenotypic variation in intercuspal distances with only moderate genetic contribution is consistent with substantial epigenetic influence on the progressive folding of the internal enamel epithelium, following formation of the primary and secondary enamel knots.

Distribution of the mylohyoid nerve: anatomical variability and clinical implications

The mylohyoid nerve is a branch of the mandibular division of the trigeminal nerve that provides motor supply to the mylohyoid and digastric muscles. Accessory innervation to the pulps of both anterior and posterior mandibular teeth by the sensory component of this nerve has been proposed to be one possible anatomical variation leading to failure of an inferior alveolar nerve block. The aim of this study was to trace the path of the mylohyoid nerve, from its origin in the infratemporal region to its terminal branches, in six human cadavers. Dissections of sagittally-sectioned heads were performed using both medial and submandibular approaches. The anatomy of the mylohyoid nerve was variable in terms of its level of branching, course through the mylohyoid groove or canal, branch numbers to the mylohyoid and digastric muscles, and terminal branching in the submental region. In all cases the mylohyoid nerve was seen to pass down the medial surface of the ramus behind the sphenomandibular ligament.

A study of occlusal variation in the primary dentition of Australian twins and singletons

In this study, we quantified the extent of variation in different occlusal features of Australian children of European descent with complete primary dentitions, but no permanent teeth present in the mouth. The study group consisted of 412 individuals, aged between 3 and 7 years, including 70 monozygous (MZ) twin pairs, 68 same-sexed dizygous (DZ) twin pairs, 11 opposite-sexed DZ twin pairs, and 114 singletons. Occlusal traits, including inter-dental spacing, incisal overbite and overjet, arch breadth and arch depth, were obtained directly from dental casts or indirectly from photocopies or impressions of the casts. Descriptive statistics summarised the data and indicated that distributions were similar to those published for other populations. Univariate genetic analysis, using the structural equation modelling package Mx, was carried out on the quantitative data using the normal assumptions of the twin model. Genetic modelling indicated that a model incorporating additive genetic (A) and unique environmental variation (E) was the most parsimonious for interdental spacing, overbite, overjet and arch dimensions. Estimates of heritability for interdental spacing ranged from 0.62 to 0.81. Estimates for overbite and overjet were 0.53 and 0.28, respectively, and estimates for arch dimensions ranged from 0.69 to 0.89. These results indicated a moderate to relatively high genetic contribution to observed variation.

Effect of Down syndrome on the dimensions of dental crowns and tissues

Abnormal growth in Down syndrome (DS) is reflected by variable reduction in size and simplification in form of many physical traits. This study aimed to compare the thickness of enamel and dentine in deciduous and permanent mandibular incisor teeth between DS and non-DS individuals and to clarify how these tissues contribute to altered tooth size in DS. Sample groups comprised 61 mandibular incisors (29 permanent and 32 deciduous) from DS individuals and 55 mandibular incisors (29 permanent and 26 deciduous) from non-DS individuals. Maximum mesiodistal and labiolingual crown dimensions were measured initially, then the crowns were sectioned midsagittally and photographed using a stereomicroscope. Linear measurements of enamel and dentine thickness were obtained on the labial and lingual surfaces of the crowns, together with enamel and dentine-pulp areas and lengths of the dentino-enamel junction. Reduced permanent crown size in DS was associated with a reduction in both enamel and dentine thickness. After adjustments were made for tooth size, DS permanent incisors had significantly thinner enamel than non-DS permanent teeth. The DS permanent teeth also exhibited significant differences in shape and greater variability in dimensions than the non-DS permanent teeth. Crown dimensions of deciduous incisors were similar in size or larger in DS compared with non-DS deciduous teeth. Enamel and dentine thicknesses of the deciduous teeth were similar in DS and non-DS individuals. The findings indicate that growth retardation in DS reduces both enamel and dentine deposition in the permanent incisors but not in the earlier-forming deciduous predecessors. The results are also consistent with the concept of amplified developmental instability for dental traits in DS.

Anatomical variation of the sphenomandibular ligament

The sphenomandibular ligament, which is derived from the sheath of Meckel's cartilage, is a fibrous structure that passes between the spine of the sphenoid bone and the lingula of the mandible. Although anatomical texts provide basic descriptions of this structure, there are few published reports of the extent of its variability or its possible clinical implications. The aim of this study was to provide a detailed description of the nature and extent of anatomical variability in the sphenomandibular ligament of seven human cadavers. Dissections of sagittally sectioned heads were performed using a medial approach that involved displacement of the tongue and mucosal tissues in the oral cavity and oropharynx, then reflection of the medial pterygoid muscle. The ligaments ranged in shape from thin bands that descended for a short distance from the spine of the sphenoid to broad bi-concave ligaments with prominent insertions. The mylohyoid nerve was seen to pass behind the ligament in all specimens, emerging from the postero-inferior border of the mandibular attachment before running into the mylohyoid groove on the medial surface of the ramus. Lying in the pterygomandibular space, the ligament was surrounded by fascia, both structures presenting potential barriers to the diffusion of local anaesthetic solution if injected medially. The appearance of the lingula also varied, and did not seem to reflect the size of attachment of the ligament, suggesting an alternative explanation of lingula morphology, perhaps related to a continuation of the mylohyoid ridge and anterior border of the mylohyoid groove.

Genetic analysis of deciduous tooth size in Australian twins

Investigations of permanent dental crown size in twins and family groups indicate a high degree of transmissible control, but little is known about the relative contributions of genetic and environmental factors to variation in size of the deciduous (primary) teeth. Here, maximum mesiodistal and buccolingual crown dimensions of maxillary and mandibular primary teeth were measured from dental models of 602 individuals, including 99 monozygous (MZ) twin pairs, 81 dizygous (DZ) same-sex pairs, 41 DZ opposite-sex pairs, and 160 singletons. Data were subjected to univariate genetic analysis with the structural-equation-modelling package, Mx using the normal assumptions of the twin model. A model incorporating additive genetic (A) and unique environmental (E) variation was found to be the most parsimonious for all tooth-size variables. Estimates of heritability for deciduous crown size ranged from 0.62 to 0.91. This study shows that variation in deciduous crown size has a strong genetic component, similar to that observed in the permanent dentition. Further studies are required to determine whether the underlying genetic mechanisms are the same for both deciduous and permanent teeth.

A prospective study of Twin-block appliance therapy assessed by magnetic resonance imaging

Forty children displaying Class II Division 1 malocclusion were involved in a prospective magnetic resonance image investigation to evaluate the effects of Twin-block functional appliances on the temporomandibular joints. None of these children had clinical signs or symptoms of temporomandibular disorders. Nineteen children were treated with a Clark Twin-block appliance for 6 months; the other 21 children received no treatment and served as controls. Comparison between control and Clark Twin-block groups suggested that reduction of the condylar axial angle represents a feature of untreated Class II growth patterns, whereas axial angle stability with Clark Twin-block therapy may suggest alteration of condylar growth direction. Condyles that were positioned at the crest of the articular eminence by the Clark Twin-block at the beginning of treatment had reseated back into the glenoid fossa after 6 months. However, 75% of the condyles were more anteriorly positioned in successfully treated Clark Twin-block cases. There was no clear evidence of remodeling of the glenoid fossa at the eminence as a result of Clark Twin-block treatment. The initial prevalence of disk displacements for the combined groups was 7.5% anterior, 5% medial, and 12.5% for lateral disk displacement. Clark Twin-block therapy had neither positive nor negative effects on disk position, and there was no convincing evidence that the disk was recaptured.

Effects of twin-block therapy on protrusive muscle functions

Protrusive mandibular function, including maximum protrusive force and fatigue time, was investigated in 66 children displaying Class II Division 1 malocclusion. Thirty-two children were treated with the Clark Twin-block appliance and the other 34 children served as untreated controls. The observation period was 6 months. Cross-sectional data based on pretreatment records showed that maximum protrusive force ranged from 18.5 N to 160 N, with a mean of 80.3 +/- 30.7 N. Maximum protrusive force was significantly higher in males than in females (P <.001). The correlation between maximum protrusive force and chronologic age was low (r = 0.20) and did not reach significance. Maximum protrusive force in the group of children with disk displacement was not significantly different from that of the group without disk displacement. Comparison of pretreatment and 6-month records in the untreated control group revealed a significant increase in maximum protrusive force (P <.01) as a result of normal growth, while the measured change in the Twin-block-treated children did not reach significance. Fatiguing the protrusive muscles did not alter mandibular position in the Twin-block group after 6 months of treatment. The present study does not support the lateral pterygoid hypothesis, as there was no evidence of an increase in mandibular protrusive function after treatment with the Twin-block functional appliance.

The pterygoideus propius muscle revisited

The pterygoideus proprius muscle is an anomaly in the infratemporal fossa that has immovable attachments to the infratemporal crest and the lateral pterygoid plate of the sphenoid bone. We report the identification of three cases of this anomaly, suggest its embryological origin, and speculate about its function.

Localised enamel hypoplasia of human deciduous canines: genotype or environment?

A discrete area of defective enamel formation that appears on the labial surface of the crowns of deciduous canine teeth has been described in both recent and prehistoric human populations, with reported frequencies varying from 1 to 45 per cent. Suggestions about the aetiology of this localized hypoplasia range from genotypic factors to environmental conditions and systemic effects. The major aims of this study were to describe the frequency of occurrence and pattern of expression of the lesion in Australian Aboriginal and Caucasian ethnic groups, and to clarify the role of genetic factors by examining a sample of twins. The study sample consisted of dental casts of 181 pairs of Australian Caucasian twins, 215 Aborigines and 122 Caucasian singletons, together with 253 extracted deciduous canines. Examination of dental casts and extracted teeth was undertaken under 2x magnification with emphasis being placed upon location and expression of the lesion. The defect was observed in 49 per cent of twins and 44 per cent of Aborigines, but only 36 per cent of singletons. The percentages of affected teeth in each group were: 18 per cent in twins, 17 per cent in Aborigines and 13 per cent in Caucasians. A significant proportion of the defects occurred on the mesial aspect of the labial surface, in the middle area incisocervically, with the majority in the lower jaw. A number of significant differences in frequency were observed between groups, sexes, arches and sides. The results confirm some of the findings of previous studies, but also suggest that none of environmental, genetic or systemic factors can be ruled out as being involved in aetiology of the defect. The higher incidence of the lesion occurring on the mesial aspect of the labial surface is suggestive of physical trauma. Also, the vulnerability of the prominent developing mandibular canine, with its thin or missing labial covering of bone, would be expected to lead to higher prevalence of the lesion in the lower jaw. Although not definitive, the results of concordance analyses in twins were suggestive of a possible genetic predisposition in the formation of the lesion. Further research with a greater clinical orientation and emphasis on determining specific aetiological factors within any given environment in different ethnic groups may provide better insight into the ambiguous aetiology of the hypoplastic enamel defect.

Lamination of the masticatory muscles in the kangaroo according to their innervation

An analysis of the laminations of the masseteric, zygomaticomandibular and temporalis muscles of the Red Kangaroo (Macropus Rufus) and all of the masticatory muscles of the Eastern Gray Kangaroo (Macropus Giganteus) was carried out based on their innervation. The masseteric muscle was divided into superficial and deep layers; the superficial layer was further subdivided into three laminae from the rostro-lateral portion to caudo-internal portion. The deep layer was divided into lateral, caudo-internal and rostro-internal laminae. The zygomaticomandibular muscle which was located between the masseteric and temporal muscles was divided into lateral, internal and rostral laminae, on the basis of its innervation. The lateral and internal laminae were innervated by the nerve which arises between the masseteric nerve and the posterior deep temporal nerve. A small rostral portion of the muscle was innervated by masseteric nerves, which passed through the internal lamina of the deep layer of the masseteric muscle. The temporalis muscle was innervated by an anterior deep temporal nerve and posterior deep temporal nerve. Only the most rostro-internal lamina of the temporalis muscle was innervated by the anterior deep temporal nerve. The anterior deep temporal nerve and lateral pterygoid nerve had a common trunk. We believe that the rostro-internal lamina was closely related to the lateral pterygoid muscle. The lateral pterygoid muscle displayed one lamina, whereas the medial pterygoid muscle was divided into internal and lateral laminae. The lateral lamina was further divided into rostro-internal and caudo-lateral laminae.

Acute myelomonocytic leukemia with histologic features resembling sarcomatoid carcinoma in bone marrow

We report a case of primary acute myelomonocytic leukemia involving the bone marrow that resembled sarcomatoid carcinoma. The neoplastic cells in bone marrow biopsy specimens formed cohesive-appearing clusters and cords separated by an immature fibroblastic proliferation and myxoid stroma. Blasts in the bone marrow aspirate smears formed clusters and sheets, and a subset of blasts exhibited erythrophagocytosis. Dysgranulopoiesis was also present. Lineage was confirmed by immunohistochemical analysis of formalin-fixed, paraffin-embedded tissue. The tumor cells showed strong reactivity for lysozyme, myeloperoxidase, CD45, and CD68 and were negative for keratin, S100, CD20, and CD3. The serum lysozyme concentration (110 microgram/mL) was 13 times greater than the normal value (8 microgram/mL). Cytogenetic studies performed on bone marrow aspirate material revealed a complex karyotype, including trisomy 8 and abnormalities of chromosome 11q. We report this case of acute myelomonocytic leukemia because the neoplastic cells appeared cohesive and spindled, resembling sarcomatoid carcinoma, and therefore caused diagnostic difficulty. Other monocytic neoplasms with similar resemblance to carcinoma or sarcoma have been reported in the literature, suggesting that the tendency to appear cohesive may be an inherent characteristic of neoplastic cells with monocytic differentiation.

Comparison of cervicovertebral dimensions in Australian Aborigines and Caucasians

Cervicovertebral dimensions were compared in a group of 30 male and 30 female young adult Australian Aborigines from the Northern Territory, and a control sample consisting of 60 Caucasian dental students from Adelaide, matched for sex and age. Thirty-six variables, 22 cervical and 14 craniofacial, were derived from standardized lateral roentgenograms with the use of a computerized cephalometric system. Vertebral body height and length were significantly greater in Aboriginal males than females for C3 to C7, while dorsal arch height of C1 and C2 displayed the greatest dimensional variability in both sexes. The antero-posterior length of C1, dens height, and body heights of C3 and C4 were significantly shorter in Aborigines than Caucasians for both males and females. Total length of the column from C2 to C6 was approximately 12 per cent shorter in the Aborigines compared with Caucasians. The height of the posterior arch of C1 was significantly correlated with one or both posterior cranial base lengths in Aborigines and Caucasians. Associations were also noted between mandibular lengths and posterior arch heights of the upper two vertebrae. The results confirm and clarify several previous observations on the relative shortness of the cervical spine in Australian Aboriginals. They also indicate some associations between dimensions of the cervical vertebrae and craniofacial lengths, particularly those representing the posterior cranial base and the mandible.

Introducing Adelaide dental students to a problem-based learning curriculum

A course designed to introduce new students to a problem-based learning (PBL) curriculum in dentistry at the University of Adelaide is described. Australian students are admitted to the Adelaide dental course either directly from school (SL) or after one or more years of tertiary education (TT). The admissions process is designed to select academically able students who will flourish in a problem-based environment. Some international students (INT) are also selected through a modified admissions process. A 9-item questionnaire derived from frequently-asked questions from previous years was administered to the new students at the beginning and at the end of the introductory course, and each individual's responses before and after the course were compared. There was an increased number of positive responses (significant at P < 0.05 to 7 of the 9 items) after the course. Although the course appeared to be effective in familiarising new students with a PBL curriculum, many students were still uncertain about two items which commonly provoke anxiety, namely how to decide when to stop researching a topic, and how to balance group and solo learning.

Comparison of exposed dentinal surfaces resulting from abrasion and erosion

The aim of this study was to compare the shape of exposed dentinal surfaces caused by abrasion and erosion with a view to developing a diagnostic clinical test. The study material consisted of 80 natural teeth and 129 dental models obtained from Australian Aborigines known to display considerable dental abrasion due to their diet, and dental models of 37 Caucasians diagnosed with dental erosion through detailed history and dietary analysis. Polyvinyl siloxane impressions were obtained of all occlusal surfaces with dentinal scooping in both the 'abrasion' and 'erosion' groups. All impressions were sectioned buccolingually through the deepest point of the scooped dentine, and then the profiles were photocopied at x2 magnification. The breadth and depth of dentinal profiles were measured to an accuracy of 0.1 mm, enabling ratios of depth:breadth to be determined, and the position of the deepest part of each scooped surface was recorded. The mean depth:breadth ratio of scooped dentine was significantly greater in the Aboriginal natural teeth (0.19 +/- 0.06, mean +/- SE) than in the Aboriginal dental models (0.15 +/- 0.04). Both Aboriginal natural teeth and models with abrasion showed significantly smaller ratios (p < 0.05) than the Caucasian models showing erosion (0.33 +/- 0.07). Furthermore, in the abrasion samples, the deepest region of the scooped dentine tended to be lingually placed more often in maxillary teeth but buccally placed more often in mandibular teeth (p < 0.05). These results indicate that scooped dentine on abraded occlusal surfaces of teeth displays significant differences in shape compared with that caused mainly by erosion.

Palatal rugae patterns in Australian aborigines and Caucasians

The purpose of this study was to determine whether rugae patterns change with age and to compare the number and pattern of rugae in Australian Aborigines with those of Caucasians. For the longitudinal part of the study, serial dental casts of ten Aborigines, from 6 to 20 years of age, were examined and rugae patterns were recorded. To enable comparisons to be made between different ethnic groups an additional 100 dental casts of Australian Aborigines and 200 casts of caucasians, ranging in age from 13 to 17 years, were examined. Characteristics observed were number, length, shape, direction and unification of rugae. The length of rugae increased significantly with age but the total number of rugae remained constant. Thirty-two per cent of rugae showed changes in shape, while 28 per cent displayed a change in orientation. In contrast to studies suggesting that rugae move forward with age, the majority of Aboriginal rugae that changed direction moved posteriorly. Changes in rugae patterns have been assumed to result from palatal growth but alterations in pattern were observed in the Aboriginal sample even after palatal growth had ceased. The mean number of primary rugae in Aborigines was higher than in Caucasians, although more primary rugae in Caucasians exceeded 10 mm in length than in Aborigines. The most common shapes in both ethnic groups were wavy and curved forms, whereas straight and circular types were least common. There was a statistically significant association between rugae forms and ethnicity, straight forms being more common in Caucasians whereas wavy forms were more common Aborigines.

First-year responses to a new problem-based curriculum in dentistry

The first year of a new Bachelor of Dental Surgery curriculum was introduced at the University of Adelaide in 1993. Four integrated streams replaced the previous large number of separate subjects, with an overall reduction in formal contact hours, more exposure to clinical practise, and an emphasis on problem-based learning and student self-directed learning. This report compares students attitudes to the new programme with their attitudes to the previous course. Evaluation forms were completed by 30 of 53 first-year students in 1992 and 38 of 47 first-year students in 1993. Comparisons between years, made using the Student's that, indicated significant differences for several questions. For example, the workload in the previous course was considered to be significantly heavier, with too much theory and too many topics. It was felt that the aims and objectives of the new course were significantly clearer; there was more time to understand material; more opportunities to choose areas to study; students were encouraged more to think for themselves; and staff were more understanding and supportive. The authors conclude that the new problem-based Adelaide dental curriculum has facilitated a more contextual and better-balanced learning environment for students.

Agenesis of permanent maxillary lateral incisors in South Australian twins

The frequency of agenesis of maxillary lateral incisors (I2) in a sample of South Australian twins was determined, and associations with gender, zygosity, birthweight and dental crown size were investigated. Ten of the 446 twins examined (2.24 per cent) displayed agenesis of one or both I2, a similar frequency to that reported for Australian singletons. Seven of the ten affected individuals were monozygous female twins, including two pairs, while the three affected dizygous twins were each from different male twin pairs. Five pairs of monozygous twins were identified who displayed varying expressions of normal, small, peg-shaped or missing I2. These twin pairs displayed disparate birthweights suggesting they may have been mono-chorionic. These findings are consistent with a multifactorial threshold model linking size and number of I2 with developmental influences modifying phenotypic expression in those monozygous twins whose genetic predisposition places them near to the threshold for agenesis.

Prediction of dental arch development: an assessment of Pont's Index in three human populations

Pont's Index was established by Pont in 1909 to predict maxillary dental arch width from the sum of the mesiodistal diameters of the four maxillary incisors. The usefulness of Pont's Index is controversial and, as there has been a recent resurgence of interest in its clinical use for establishing dental arch development objectives particularly by nonspecialists, reassessment of the Index in different human populations was considered worthwhile. This study aimed to evaluate Pont's Index in untreated, noncrowded samples of Australian Aborigines (n = 80), Indonesians (N = 60), and white subjects (N = 60). Measurements were obtained directly from plaster casts; they included mesiodistal crown diameters of the four maxillary incisors, as well as intercanine, interpremolar and intermolar maxillary arch widths as specified by Pont. A series of double determinations confirmed the reliability of the method. Considerable individual variability was noted in each population with regard to the difference between observed values and Pont's estimates, ranging from -5.9 mm to +6.2 mm (interpremolar width) and -6.1 mm to +12.7 mm (intermolar width). No person displayed the ideal arch dimensions predicted by the Index, but values were within +/- 1.0 mm for 17.5% of the Indonesian sample, 20.6% of the Aboriginal sample, and 30.8% of the white sample. Dental arch width was generally underestimated by the Index in Indonesians who tended to display relatively small tooth size and large arch width. A more even distribution of estimates was noted in Australian Aborigines and white subjects, with the Aborigines showing large tooth size and broad dental arches, and the white subjects displaying smaller tooth size and narrow arches. Correlation coefficients computed between observed and expected values were low in all three populations studied (range r = 0.01 to r = 0.56). Although the concept of a simple index with predictive ability is very appealing to some clinicians, the results of this study have highlighted the marked variation in values of Pont's Index for persons with apparently good occlusions, representing three different human populations. Tooth size variation was poorly correlated with arch width variation, with persons often being over or under Pont's estimation due to variation in tooth dimension, particularly in the size of the maxillary lateral incisor. It is concluded that Pont's Index is unlikely to be a useful clinical predictor of dental arch width and the index should not be used as a guide to dental arch development in contemporary populations.

Upper central incisor and canine tooth crown size in 47,XXY males

Enamel and dentin thicknesses were measured in permanent tooth crowns of 47,XXY (Klinefelter syndrome) males. In 47,XXY males, enamel thickness in maxillary central incisors was significantly greater than that in control males or females, and dentin thickness in incisors and canines was significantly greater than that in control females, but smaller than that in normal males. These findings confirm the concept that human dental growth is affected by sex chromosomes. Amelogenesis is promoted by both X and Y chromosome genes, and sexual dimorphism in average tooth size is evidently determined by a promoting effect of the Y chromosome on dentin growth, probably through cell proliferation. This effect can also explain sex predilection for males in the numbers of supernumerary and ordinary teeth.

Inactivation of thromboxane synthase with hydroperoxy-fatty acids

Bovine lung thromboxane synthase was immobilized on phenyl-Sepharose beads by adsorption. The immobilized enzyme was catalytically active and synthesized both TXA2 and HHT. The structure-activity relationship of several hydroperoxy fatty acids and their ability to inactivate thromboxane synthase was investigated. Millimolar quantities of hydrogen peroxide and tert-butylperoxide were required to inactivate the enzyme: whereas micromolar quantities of C18 and C20 hydroperoxy fatty acids inactivated the enzyme. Pretreatment of the enzyme with long chain hydroperoxy-fatty acids resulted in a decreased synthesis of both TXB2 and HHT.

Measurement of PGH synthase activity using a pan-specific monoclonal antibody

A pan-specific monoclonal antibody that recognizes a variety of prostaglandin moieties and does not recognize arachidonic acid or the hydroxy-eicosatetraenoic acids was used to assess the general ability of a tissue to produce prostaglandins. Although this assay does not give a quantitative measure of PGH synthase activity, it does provide a sensitive and convenient means of screening a large number of samples for prostaglandin production.

Twins and twinning, dentists and dentistry

Comparisons of physical features within identical (monozygous) and non-identical (dizygous) twin pairs have provided valuable insights into the relative contributions of genetic and environmental influences to observed variability. The special nature of the twinning process itself also provides an opportunity to learn more about early human development, including how body symmetry is determined. The mechanisms of twinning, mortality and morbidity in twins, determination of body symmetry including the phenomenon of mirror-imaging, postnatal growth and development of twins, and zygosity determination are discussed. Twin studies with direct relevance to clinical dentistry are reviewed and illustrated by examples from an ongoing investigation of dentofacial morphology in South Australian twins.

Expression of the entoconulid (sixth cusp) on mandibular molar teeth of an Australian aboriginal population

The expression and genetic basis of the entoconulid (sixth cusp) on mandibular molars were examined in a geographically isolated group of aboriginals from Yuendumu in the Northern Territory of Australia. Four grades of trait expression, ranging from trace to small, medium, and large cusps, were defined on dental casts of 399 subjects. Frequencies of occurrence were among the highest reported in human populations. Approximately 80% of dm2s showed the trait, whereas frequencies in the permanent dentition ranged from around 50% on M2 to 70% on M1 and 80% on M3. The degree of expression increased distally along the molar series, with only 3% of dm2s showing large cusps compared with 25% of M3s. Fluctuating asymmetry was highest for M2 and lowest for dm2. No strong evidence for sexual dimorphism in occurrence or degree of expression was found. Based on a quasi-continuous threshold model, a genetic contribution to entoconulid variability was observed that was strongest for M1. Significant associations were noted between entoconulid expression on mandibular molars and metaconule expression on maxillary molars, indicating that similar developmental mechanisms may influence these traits. The entoconulid and the metaconule both provide additional bulk on the distal occlusal surface of molar teeth, an area subjected to early wear during mastication in aboriginals.