The human medial pterygoid muscle: Attachments and distribution of muscle spindles.

Published descriptions about the sites of origin of the human medial pterygoid muscle vary and there are few reports on the distribution and density of muscle spindles in this muscle. We aimed to: (1) determine the extent of anatomical variability in the origins and insertions of the superficial and deep heads of the human medial pterygoid muscle and (2) determine the extent of variation in the distribution of spindles in the two heads of the muscle. Thirty-nine human cadaver hemi-heads were dissected and the attachments of the medial pterygoid muscle examined. The whole muscle was removed, weighed, cut into segments and embedded in wax for light microscopy. Sections were stained with Weigert-Van Gieson stain and scanned into digital images. Spindles were manually counted. In seven specimens, the deep head of the muscle arose from the medial surface of the lateral pterygoid plate and the pterygoid fossa. In 28 specimens, the origin extended onto the lateral surface of the medial pterygoid plate. There were abundant muscle spindles in the middle of the muscle, slightly fewer 1 cm toward the insertion, significantly fewer 1 cm toward the origin, and few or no spindles near the origins of the superficial and deep heads or near their insertion. In conclusion, firstly, this study shows that in 72% of the specimens examined, the origin of the medial pterygoid is wider than conventionally described in anatomical textbooks. Secondly, the segmental distribution of muscle spindles is described for the first time. Clin. Anat. 30:1064-1071, 2017. © 2017 Wiley Periodicals, Inc.

Alterations in mandibular morphology associated with glypican 1 and glypican 3 gene mutations.

OBJECTIVES: Glypican 1 (GPC1) and glypican 3 (GPC3) are bone co-regulators that act downstream in many of the signalling pathways associated with craniosynostosis. Morphometric data from GPC-knockout mice were analysed to determine whether elimination of GPC1 and GPC3 genes would alter mandibular morphology. SETTING AND SAMPLE POPULATION: The murine model included five male and five female mandibles in each of GPC1-knockout, GPC1/GPC3-knockout and wild-type (control) groups. Female GPC3-knockout mice had a very high rate of perinatal lethality, and therefore, only five males were included in this group. METHODS: The mandibular morphology of GPC1-knockout (n=10), GPC3-knockout (n=5), GPC1/GPC3-knockout (n=10) and wild-type (n=10) mice was compared by analysing five landmark-based linear dimensions: anterior and posterior lengths, as well as ascending, descending and posterior heights. Measurements were recorded on three-dimensional micro-CT reconstructions. RESULTS: GPC3-knockout mandibles were larger than wild-type mandibles for all dimensions (P<.05). Mandibular heights were more affected than lengths. A decreasing trend of mandibular dimensions across the mouse groups (GPC3-knockout>GPC1/GPC3-knockout>GPC1-knockout=wild-type) (P<.05) indicated that an increase in mandibular size was associated with increased GPC3 expression, but not GPC1. CONCLUSIONS: Alterations in GPC3 expression are likely to mediate changes to mandibular size in craniosynostosis. These findings have potential future applications in the prevention and treatment of craniosynostosis and associated craniofacial dysmorphology.

Surface-Sensitive Microwear Texture Analysis of Attrition and Erosion.

Scale-sensitive fractal analysis of high-resolution 3-dimensional surface reconstructions of wear patterns has advanced our knowledge in evolutionary biology, and has opened up opportunities for translatory applications in clinical practice. To elucidate the microwear characteristics of attrition and erosion in worn natural teeth, we scanned 50 extracted human teeth using a confocal profiler at a high optical resolution (X-Y, 0.17 µm; Z < 3 nm). Our hypothesis was that microwear complexity would be greater in erosion and that anisotropy would be greater in attrition. The teeth were divided into 4 groups, including 2 wear types (attrition and erosion) and 2 locations (anterior and posterior teeth; n = 12 for each anterior group, n = 13 for each posterior group) for 2 tissue types (enamel and dentine). The raw 3-dimensional data cloud was subjected to a newly developed rigorous standardization technique to reduce interscanner variability as well as to filter anomalous scanning data. Linear mixed effects (regression) analyses conducted separately for the dependent variables, complexity and anisotropy, showed the following effects of the independent variables: significant interactions between wear type and tissue type ( P = 0.0157 and P = 0.0003, respectively) and significant effects of location ( P < 0.0001 and P = 0.0035, respectively). There were significant associations between complexity and anisotropy when the dependent variable was either complexity ( P = 0.0003) or anisotropy ( P = 0.0014). Our findings of greater complexity in erosion and greater anisotropy in attrition confirm our hypothesis. The greatest geometric means were noted in dentine erosion for complexity and dentine attrition for anisotropy. Dentine also exhibited microwear characteristics that were more consistent with wear types than enamel. Overall, our findings could complement macrowear assessment in dental clinical practice and research and could assist in the early detection and management of pathologic tooth wear.

Effects of non-carious cervical lesion size, occlusal loading and restoration on biomechanical behaviour of premolar teeth.

BACKGROUND: Information on fracture biomechanics has implications in materials research and clinical practice. The aim of this study was to analyse the influence of non-carious cervical lesion (NCCL) size, restorative status and direction of occlusal loading on the biomechanical behaviour of mandibular premolars, using finite element analysis (FEA), strain gauge tests and fracture resistance tests. METHODS: Ten buccal cusps were loaded on the outer and inner slopes to calculate the strain generated cervically. Data were collected for healthy teeth at baseline and progressively at three lesion depths (0.5 mm, 1.0 mm and 1.5 mm), followed by restoration with resin composite. The magnitude and distribution of von Mises stress and maximum principal stress were simulated at all stages using FEA, and fracture strength was also determined (n = 7 per group). RESULTS: There were significant effects of the lesion size and loading directions on stress, strain and fracture resistance (p < 0.05). Fracture resistance values decreased with increase in lesion size, but returned to baseline with restorations. CONCLUSIONS: Combined assessment of computer-based and experimental techniques provide an holistic approach to characterize the biomechanical behaviour of teeth with both unrestored and restored NCCLs.

Nanoscratch testing for the assessment of enamel demineralization under conditions simulating wine erosion.

BACKGROUND: Erosive tooth wear and dentinal hypersensitivity are common problems affecting professional wine tasters. By using nanoscratch testing, the aim of this in vitro study was to assess enamel softening under conditions simulating 10 one-minute episodes of wine erosion. METHODS: Ten enamel specimens were bathed in artificial saliva for 2 hours before being eroded for 10 episodes, with each episode comprising one minute of wine erosion followed by one minute of remineralization in artificial saliva. Nanoscratches were placed with a spherical tip (20 µm radius) in a nanoindenter under a load of 100 mN at baseline (stage 1), after a one-erosion episode (stage 2) and after 10-erosion episodes (stage 3). RESULTS: There were significant effects of erosion stages on both scratch depth (p<0.001) and surface roughness (p<0.001). Post hoc tests showed significant differences in both scratch depths and surface roughness between stages 1 and 3 (p<0.001), and between stages 2 and 3 (p<0.01). CONCLUSIONS: Enamel softening occurs at an early stage of wine tasting, emphasizing the need to implement early preventive strategies in professional wine tasters. Further research elucidating the fundamental mechanisms involved in early stages of erosion has the potential to lead to development of more effective preventive strategies.

Features of an effective operative dentistry learning environment: students' perceptions and relationship with performance.

OBJECTIVE: Students' perceptions of their learning environment influence the quality of outcomes they achieve. Learning dental operative techniques in a simulated clinic environment is characterised by reciprocal interactions between skills training, staff- and student-related factors. However, few studies have examined how students perceive their operative learning environments and whether there is a relationship between their perceptions and subsequent performance. Therefore, this study aimed to clarify which learning activities and interactions students perceived as supporting their operative skills learning and to examine relationships with their outcomes. METHODS: Longitudinal data about examples of operative laboratory sessions that were perceived as effective or ineffective for learning were collected twice a semester, using written critical incidents and interviews. Emergent themes from these data were identified using thematic analysis. Associations between perceptions of learning effectiveness and performance were analysed using chi-square tests. RESULTS: Students indicated that an effective learning environment involved interactions with tutors and peers. This included tutors arranging group discussions to clarify processes and outcomes, providing demonstrations and constructive feedback. Feedback focused on mistakes, and not improvement, was reported as being ineffective for learning. However, there was no significant association between students' perceptions of the effectiveness of their learning experiences and subsequent performance. CONCLUSIONS: It was clear that learning in an operative technique setting involved various factors related not only to social interactions and observational aspects of learning but also to cognitive, motivational and affective processes. Consistent with studies that have demonstrated complex interactions between students, their learning environment and outcomes, other factors need investigation.

Under your nose: a rare finding during dissection provides insights into maxillary supernumerary teeth.

BACKGROUND: A supernumerary tooth was found during anatomical dissection. The position of this tooth, still impacted in the maxilla, and the associated pathology make this a rare case. METHODS: During dissection by dental students of the sagittally-sectioned head of a cadaver, a supernumerary tooth was identified in the mid-palatal area. Further dissection revealed a swelling with a thin bony covering related to the crown of the tooth. The maxilla was removed en bloc and radiographic examination, CT scanning, electron microscopy and histology were undertaken. RESULTS: The tooth had a crenulated occlusal surface and a single root. It was 25 mm posterior to the root apex of the permanent upper central incisor. The swelling, confirmed by radiographs and CT imaging to be associated with the crown, occupied approximately one-third of the maxillary sinus. The 3D shape of the cystic lesion was visualized by a composite digital movie. CONCLUSIONS: The crown form, position of the tooth and the associated dentigerous cyst suggested it was a palatally developing supernumerary premolar which had been displaced to the palatal midline by the expanding cyst. This rare case highlights the learning and teaching opportunities available during dissection, showing important variations in both development and clinical anatomy.

Variation in natural head position and establishing corrected head position.

Corrected head position (CHP) has been simulated by using the Frankfurt horizontal (FH) for over 100 years but FH varies between individuals. Because CHP is biologically relevant for orthodontic diagnosis and treatment planning, orthognathic surgical planning, and art, this study examined relationships between head position and selected cephalometric planes. Natural head position cephalograms of Aboriginal Australians and two contemporary samples from private orthodontic practices were analysed. Each sample comprised 40 individuals (20 males and 20 females). The Aboriginal Australian sample comprised longitudinal data (T1 early adolescent, T2 late adolescent, and T3 adult), enabling examination of natural head position (NHP) reproducibility over a period of approximately 8 years. Results of reproducibility differences revealed an absolute mean=2.9°, range=-7.9° to 8.2°, and standard deviation=3.6°. Stable basicranial line (SBL), neutral horizontal axis (NHA), FH, palatal plane (P plane), and Krogman-Walker plane (KW plane) demonstrated near parallelism and their mean angulations from the true horizontal (HOR) ranged between -4.6° and 2.4°. While NHP is not consistently reproducible at the individual level, the combined use of multiple planes such as SBL, P plane, and KW plane enables a more consistent CHP to be achieved.

General and craniofacial development are complex adaptive processes influenced by diversity.

Complex systems are present in such diverse areas as social systems, economies, ecosystems and biology and, therefore, are highly relevant to dental research, education and practice. A Complex Adaptive System in biological development is a dynamic process in which, from interacting components at a lower level, higher level phenomena and structures emerge. Diversity makes substantial contributions to the performance of complex adaptive systems. It enhances the robustness of the process, allowing multiple responses to external stimuli as well as internal changes. From diversity comes variation in outcome and the possibility of major change; outliers in the distribution enhance the tipping points. The development of the dentition is a valuable, accessible model with extensive and reliable databases for investigating the role of complex adaptive systems in craniofacial and general development. The general characteristics of such systems are seen during tooth development: self-organization; bottom-up emergence; multitasking; self-adaptation; variation; tipping points; critical phases; and robustness. Dental findings are compatible with the Random Network Model, the Threshold Model and also with the Scale Free Network Model which has a Power Law distribution. In addition, dental development shows the characteristics of Modularity and Clustering to form Hierarchical Networks. The interactions between the genes (nodes) demonstrate Small World phenomena, Subgraph Motifs and Gene Regulatory Networks. Genetic mechanisms are involved in the creation and evolution of variation during development. The genetic factors interact with epigenetic and environmental factors at the molecular level and form complex networks within the cells. From these interactions emerge the higher level tissues, tooth germs and mineralized teeth. Approaching development in this way allows investigation of why there can be variations in phenotypes from identical genotypes; the phenotype is the outcome of perturbations in the cellular systems and networks, as well as of the genotype. Understanding and applying complexity theory will bring about substantial advances not only in dental research and education but also in the organization and delivery of oral health care.

Epigenetics: a new frontier in dentistry.

In 2007, only four years after the completion of the Human Genome Project, the journal Science announced that epigenetics was the 'breakthrough of the year'. Time magazine placed it second in the top 10 discoveries of 2009. While our genetic code (i.e. our DNA) contains all of the information to produce the elements we require to function, our epigenetic code determines when and where genes in the genetic code are expressed. Without the epigenetic code, the genetic code is like an orchestra without a conductor. Although there is now a substantial amount of published research on epigenetics in medicine and biology, epigenetics in dental research is in its infancy. However, epigenetics promises to become increasingly relevant to dentistry because of the role it plays in gene expression during development and subsequently potentially influencing oral disease susceptibility. This paper provides a review of the field of epigenetics aimed specifically at oral health professionals. It defines epigenetics, addresses the underlying concepts and provides details about specific epigenetic molecular mechanisms. Further, we discuss some of the key areas where epigenetics is implicated, and review the literature on epigenetics research in dentistry, including its relevance to clinical disciplines. This review considers some implications of epigenetics for the future of dental practice, including a 'personalized medicine' approach to the management of common oral diseases.

Dental phenomics: advancing genotype to phenotype correlations in craniofacial research.

The field of dental phenomics provides many opportunities to elucidate the roles of genetic, epigenetic and environmental factors in craniofacial development. To date, research findings have helped to clarify the pathogenesis of many conditions, aiding diagnosis and clinical management. This paper provides an overview of dental phenomics research in some commonly encountered oral diseases in everyday clinical practice, as well as research relating to craniofacial growth and development. Clinically, advances in cariology and periodontology have led to better diagnostic capabilities and treatment provision. In the study of growth and development, important information regarding the varying clinical presentation and pathogenesis of many disorders is now apparent through the accurate quantification of phenotypes. Improvements in two-dimensional (2D) and three-dimensional (3D) imaging and analytical techniques have allowed for accurate dental phenotyping, and efforts are ongoing to apply these in vitro techniques to the in vivo setting. The field of dental phenomics represents an exciting avenue that links research findings to practical application, and collaboration between researcher and clinicians will help advance the field further.

The face, the future, and dental practice: how research in craniofacial biology will influence patient care.

It has been a privilege to assemble a group of Australian and international researchers to produce a special issue of the Australian Dental Journal that reflects the cutting edge of research in different aspects of craniofacial biology, and also considers how these advances will influence future education and practice within dentistry. The aim of this special issue is to provide a collection of concept papers and critical reviews on key topics that cover both fundamental and applied research in craniofacial biology and to consider the clinical implications. To do this, four questions have been addressed that lead to the four sections of this issue. These are: How have we come to the present exciting position in craniofacial biology with breakthroughs over the past 50 years? What are current fundamental research topics that are helping us to understand more about craniofacial and general development, possibly leading to future clinical developments? What are the current applied research topics that will influence future clinical practice? Looking forward, what new developments in craniofacial biology may come about that will change the face of dental education and practice? The refereed papers in this special issue are grouped into the four sections that seek to respond to these demanding questions.

The dentition: the outcomes of morphogenesis leading to variations of tooth number, size and shape.

The clinical importance of variations of tooth number, size and shape is seen in many dental disciplines. Early diagnosis allows optimal patient management and treatment planning, with intervention at an appropriate time to prevent complications in development and so reduce later treatment need. Understanding the process of dental morphogenesis and the variations in outcomes is an important contribution to the multidisciplinary clinical team approach to treatment. Tooth number, size and shape are determined during the initiation and morphogenetic stages of odontogenesis. The molecular evidence of repetitive signalling throughout initiation and morphogenesis is reflected clinically in the association of anomalies of number, size and shape. This association has been statistically modelled from epidemiological evidence and confirmed by 2D and 3D measurement of human dental study casts. In individuals with hypodontia, the teeth that are formed are smaller than the population mean and often show reduced and simplified shape. In contrast, in individuals with supernumerary teeth, the other teeth are larger than average and may show an enhanced shape. Clinical observations in humans and studies of laboratory animals gave rise to the concept of morphogenetic fields within the dentition. The findings, which can also be considered as reflecting gene expression territories, have been developed to incorporate field, clone and homeobox theories. The clinical distribution of developmental anomalies tends to follow the pattern of these fields or territories. Improved care for patients with these anomalies will come not only from utilizing a multidisciplinary clinical team but also by expanding the approach to include other relevant scientific disciplines.

Functional dental occlusion: an anthropological perspective and implications for practice.

Physiologic changes occur in dental occlusion throughout life, resulting from the interplay between functional demands and reciprocating adaptive responses. These changes have been reported in the anthropological literature and they reflect evolutionary changes in the human stomatognathic system during the Paleolithic, hunter-gatherer period. Specific occlusal changes occur in response to different environments, leading to extensive variation within and between extinct and extant human populations. For example, functional demands can cause occlusal and interproximal tooth wear, resulting in shortening of the dental arch, continual tooth eruption and changes in masticatory patterns. Since the advent of farming through to our current industrialized culture, functional demands on the human masticatory system, and its adaptive responses to these demands, have been reduced considerably. Indeed, it is only occasionally that functional demands are severe enough to lead to obvious pathology in the modern human dentition. In contrast to normal masticatory activity, 'modern-day conditions' such as dental caries, periodontal disease and erosion, can lead to significant changes in dental occlusion that are pathological and need to be treated. The masticatory system is a dynamic, functional unit that displays considerable change over a lifetime. In this concept paper, it is proposed that modern human populations living in industrialized environments display dental occlusions that can be considered to be 'neotenous'; that is, our dentitions tend to reflect an unworn stage of our ancestors that was only seen in infants, juveniles and young adults. Clinicians can draw on both phylogenetic and ontogenetic perspectives of 'functional dental occlusion' to differentiate continual physiological changes occurring over time that require ongoing review, from pathological responses that require intervention.

The teeth and faces of twins: providing insights into dentofacial development and oral health for practising oral health professionals.

The continuing studies of the teeth and faces of Australian twins and their families in the Craniofacial Biology Research Group in the School of Dentistry at the University of Adelaide began 30 years ago. Three main cohorts of twins have been recruited, enabling various objectives and specific hypotheses to be addressed about the roles of genetic, epigenetic and environmental influences on human dentofacial growth and development, as well as oral health. This paper highlights some key findings arising from these studies, emphasizing those of direct relevance to practising oral health professionals. We also draw on published literature to review the significant developments in relation to the use of precision 2D and 3D imaging equipment, the application of modern molecular techniques, and the development of sophisticated computer software for analysing genetic relationships and comparing complex shapes. Such developments are valuable for current and future work. Apart from the classical or traditional twin model, there are several other twin models that can be used in research to clarify the relative contributions of genetic, epigenetic and environmental contributions to phenotypic variation. The monozygotic (MZ) co-twin model is one particularly valuable method, given that examination of only one pair of MZ twins can provide considerable insights into underlying causes of observed variation. This model can be used in a dental practice environment, with oral health professionals having the opportunity to explore differences in orofacial structures between MZ co-twins who are attending as patients. As researchers have become more aware of the complexities of the interactions between the genome, the epigenome and the environment during development, there is the need to collect more phenotypic data and define new phenotypes that will better characterize variations in growth processes and health status. When coupled with powerful new genetic approaches, including genome-wide association studies and linkage analyses, exciting opportunities are opening up to unravel the causes of problems in craniofacial growth and common oral diseases in human populations.

Non-carious cervical lesions: influence of morphology and load type on biomechanical behaviour of maxillary incisors.

BACKGROUND: The aim of this study was to measure the effect of simulating two different loads on maxillary incisors displaying eight morphological types of non-carious cervical lesions, unrestored and restored with an adhesive restoration, by quantifying the stress distributions generated using finite element analysis. METHODS: Virtual models of maxillary incisors were generated using the CAD software (RhinoCeros). After composing virtual dental and supporting structures with and without non-carious cervical lesions, each model was meshed using a control mesh device (ANSYS Finite Element Analysis Software). All of the virtual models were subjected to two load types, oblique load and vertical load, to simulate occlusal forces of 100 N each. Comparisons were made between simulated teeth with non-carious cervical lesions, with and without composite resin restorations, and a simulated sound tooth. Data summarizing the stress distributions were obtained in MPa using von Mises criteria. RESULTS: Oblique loading on simulated non-carious cervical lesions resulted in greater stress concentration compared with vertical loading, and non-carious cervical lesions with acute angles displayed higher stress concentrations at the depth of the lesion. Restoring the lesions with an adhesive restoration, such as composite resin, appeared to overcome this stress concentration. CONCLUSIONS: Restoring NCCLs with adhesive restorative materials, such as a nanohybrid composite resin, appears to recover the biomechanical behaviour similar to sound teeth.

Reorientating dental curricula to reflect a minimally invasive dentistry approach for patient-centred management.

Minimally invasive dentistry (MID), together with patient-centred care (PCC), can be considered central to patient management. These approaches have been incorporated in the structure of various dental curricula and indeed formally assessed. However, there is limited evidence that students have an integrated skill-set and are able to apply these skills when providing direct patient care within the clinical setting. Assessment of students' application of core clinical skills has identified numerous deficiencies that need to be addressed. The revised Bachelor of Dental Surgery curriculum at the School of Dentistry, The University of Adelaide, provides an example of how MID, underpinned by PCC, can be presented throughout a dental curriculum. Essentially, MID and PCC are not considered as separate subjects but as a patient management approach that is 'woven into the whole fabric' of the curriculum. The programme relies on the development of empathic communication skills that enable students to obtain key patient information, including their patients' values, beliefs, needs, preferences and expectations, thereby allowing management to be tailor-made. As a result, patients are empowered to be a part of the oral health care team. The Adelaide undergraduate dental curriculum consists of one clinical stream called Dental Science and Practice (DSP), that promotes the application of student knowledge, skills and behaviours in the clinical setting. Vertical and horizontal integration, aligned with an integrated approach to assessment, drives the learning throughout the programme. Clearly-defined outcomes are introduced by Integrated Learning Activities (ILAs) that provide a focus for associated learning activities (e.g. class meetings, tutorials, simulation laboratories, etc). The aim of this approach to learning and teaching is to ensure the required learning outcomes are achieved. It also requires coordinated teaching teams including trained external tutors who clearly understand all aspects of MID and PCC within the curriculum structure.

Intrauterine hormone effects on tooth dimensions.

The human dentition is a complex adaptive system that is influenced by genetic, epigenetic, and environmental factors. Within this system, is sexual dimorphism related to the growth promotion of the Y chromosome, or to hormonal influences, or both? This study is the first to investigate both primary and permanent tooth sizes in females from opposite-sex dizygotic (DZOS) twin pairs compared with females from dizygotic same-sex (DZSS) and monozygotic (MZ) twin pairs to indicate the influence of intrauterine male hormone, including the initial testosterone surge, on dental development. Serial dental models of the primary, mixed, and permanent dentitions of 134 females from DZOS, DZSS, and MZ twins were examined. Mesiodistal, buccolingual, crown height, and intercuspal dimensions of all primary teeth and selected permanent teeth were determined by image analysis. Univariate and multivariate analyses showed statistically significantly larger crown size in DZOS females in both dentitions, with the crown height dimensions displaying the greatest increase in size. These findings strongly support the Twin Testosterone Transfer (TTT) hypothesis. We propose that the growth-promoting effects of the Y chromosome and intrauterine male hormone levels influence different tooth dimensions and contribute differentially to the sexual dimorphism of human teeth.

Determining the direction of tooth grinding: an in vitro study.

The analysis of microwear patterns, including scratch types and widths, has enabled reconstruction of the dietary habits and lifestyles of prehistoric and modern humans. The aim of this in vitro study was to determine whether an assessment of microwear features of experimental scratches placed on enamel, perpendicularly to the direction of grinding, could predict the grinding direction. Experimental scratches were placed using a scalpel blade on standardised wear facets that had been prepared by wearing opposing enamel surfaces in an electromechanical tooth wear machine. These control 'baseline' facets (with unworn experimental scratches) were subjected to 50 wear cycles, so that differential microwear could be observed on the leading and trailing edges of the 'final' facets. In Group 1 (n=28), the 'footprint' microwear patterns corresponding to the known grinding direction of specimens in the tooth wear machine were identified. Then, they were used to predict the direction of tooth grinding blindly in the same sample after a 2-week intermission period. To avoid overfitting the predictive model, its sensitivity was also cross-validated in a new sample (Group 2, n=14). A crescent-shaped characteristic observed in most experimental scratches matched the grinding direction on all occasions. The best predictor of the direction of grinding was a combined assessment of the leading edge microwear pattern and the crescent characteristic (82.1% in Group 1 and 92.9% in Group 2). In conclusion, a simple scratch test can determine the direction of tooth grinding with high reliability, although further improvement in sensitivity is desirable.

Dynamic Systems (Complexity) theory as a new conceptual model for researching PBL in dental education.

Although problem-based learning (PBL) was introduced into dental education some 20 years ago, there have been relatively few well-designed studies carried out to clarify whether, how or why it works in a dental context. This paper introduces the Dynamic Systems (Complexity) theory as a new and potentially productive theoretical framework for researching PBL in dental education. This framework emphasises the importance of emergent self-organisation, perception and brain plasticity in learning. In this paper, a brief overview of the history of PBL in dentistry is presented and then the fundamentals of a Dynamic Systems Approach (DSA) are explained, drawing on two recently published papers advocating the DSA in medical education and teacher education. We focus on three key points related to this new approach: emergent self-organisation rather than simple construction of knowledge; the notion that perception drives the learning process; and the brain as the substrate of all learning. The paper also suggests how the DSA can help us move forward, both in terms of the future application of PBL in dental education and also in relation to posing new types of research questions.