Neanderthal behaviour, diet, and disease inferred from ancient DNA in dental calculus.

Recent genomic data have revealed multiple interactions between Neanderthals and modern humans, but there is currently little genetic evidence regarding Neanderthal behaviour, diet, or disease. Here we describe the shotgun-sequencing of ancient DNA from five specimens of Neanderthal calcified dental plaque (calculus) and the characterization of regional differences in Neanderthal ecology. At Spy cave, Belgium, Neanderthal diet was heavily meat based and included woolly rhinoceros and wild sheep (mouflon), characteristic of a steppe environment. In contrast, no meat was detected in the diet of Neanderthals from El Sidrón cave, Spain, and dietary components of mushrooms, pine nuts, and moss reflected forest gathering. Differences in diet were also linked to an overall shift in the oral bacterial community (microbiota) and suggested that meat consumption contributed to substantial variation within Neanderthal microbiota. Evidence for self-medication was detected in an El Sidrón Neanderthal with a dental abscess and a chronic gastrointestinal pathogen (Enterocytozoon bieneusi). Metagenomic data from this individual also contained a nearly complete genome of the archaeal commensal Methanobrevibacter oralis (10.2× depth of coverage)-the oldest draft microbial genome generated to date, at around 48,000 years old. DNA preserved within dental calculus represents a notable source of information about the behaviour and health of ancient hominin specimens, as well as a unique system that is useful for the study of long-term microbial evolution.

A simple rule governs the evolution and development of hominin tooth size.

The variation in molar tooth size in humans and our closest relatives (hominins) has strongly influenced our view of human evolution. The reduction in overall size and disproportionate decrease in third molar size have been noted for over a century, and have been attributed to reduced selection for large dentitions owing to changes in diet or the acquisition of cooking. The systematic pattern of size variation along the tooth row has been described as a 'morphogenetic gradient' in mammal, and more specifically hominin, teeth since Butler and Dahlberg. However, the underlying controls of tooth size have not been well understood, with hypotheses ranging from morphogenetic fields to the clone theory. In this study we address the following question: are there rules that govern how hominin tooth size evolves? Here we propose that the inhibitory cascade, an activator-inhibitor mechanism that affects relative tooth size in mammals, produces the default pattern of tooth sizes for all lower primary postcanine teeth (deciduous premolars and permanent molars) in hominins. This configuration is also equivalent to a morphogenetic gradient, finally pointing to a mechanism that can generate this gradient. The pattern of tooth size remains constant with absolute size in australopiths (including Ardipithecus, Australopithecus and Paranthropus). However, in species of Homo, including modern humans, there is a tight link between tooth proportions and absolute size such that a single developmental parameter can explain both the relative and absolute sizes of primary postcanine teeth. On the basis of the relationship of inhibitory cascade patterning with size, we can use the size at one tooth position to predict the sizes of the remaining four primary postcanine teeth in the row for hominins. Our study provides a development-based expectation to examine the evolution of the unique proportions of human teeth.

The functional role of the Carabelli trait in early and late hominins.

The Carabelli trait is a dental feature that forms along the lingual margin of the protocone of deciduous and permanent maxillary molars. It is variably expressed, ranging from a small pit or furrow to a large cusp, and its development seems to be associated with crown size and molar cusp spatial configuration. The degree of expression of the Carabelli trait differs systematically between hominin taxa, and for this reason, it has been used extensively in the reconstruction of their phylogeny. However, the functional implications of having a large Carabelli trait remain unclear. In this study, we analyze the macrowear pattern of maxillary molars of early and late hominins using the occlusal fingerprint analysis method, an approach based on digital models of teeth that helps in reconstructing occlusal dynamics occurring during mastication. Tooth crowns with a small Carabelli cusp generally exhibit larger wear contact areas that extended cervically, while two additional new occlusal contact areas are common in teeth characterized by a large Carabelli cusp. These wear areas are created at the beginning of the chewing cycle, when occluding with the slopes of the lingual groove of the lower molars, between the metaconid and entoconid cusps. Advancing tooth wear leads to a slight enlargement of Carabelli occlusal contacts increasing their functional area. A steep inclination could be mechanically important in food reduction and in balancing the functional load distribution during mastication contacts. Steep wear areas are particularly developed in primates that process foods characterized by tough and fibrous textural properties. Future biomechanical and microwear texture analyses could provide additional information on the mechanical adaptation of this dental trait.

Patterns of heritability across the human diphyodont dental complex: Crown morphology of Australian twins and families.

OBJECTIVES: This study generates a series of narrow-sense heritability estimates for crown morphology of the deciduous and permanent dentition with two overarching aims. The first is to test the hypothesis that deciduous teeth provide a more faithful reflection of genetic information than their permanent successors. The second is to use quantitative genetic methods to evaluate assumptions underlying common data collection and analysis practices in biodistance research. MATERIALS AND METHODS: Dental morphology data were collected from longitudinal dental casts representing Australian twins and families using Arizona State Dental Anthropology System standards. Polygenic models and estimates of narrow-sense heritability were generated using SOLAR v.8.1.1. Each model considered age, sex, and age/sex interaction as covariates. RESULTS: Heritability estimates significantly differed from zero for the majority of morphological crown characters. Most estimates fell within the 0.4-0.8 range typically observed for crown morphology. Mean heritability was stable across the dental complex, but for paired homologues, permanent traits often yielded higher estimates than their deciduous counterparts. Results indicate directional asymmetry in environmental influence for crown morphology and inform biodistance "best practices" related to data collection and treatment. CONCLUSIONS: Overall, results for this sample support the use of crown morphology as a proxy for genetic variation in evolutionary research. This includes the deciduous dentition, which justifies the expansion of efforts to incorporate subadults into reconstructions of past microevolutionary processes. Results do not indicate that deciduous phenotypes more closely approximate underlying genotype, at least for deciduous/permanent homologues.

The lingual nerve: overview and new insights into anatomical variability based on fine dissection using human cadavers.

This article, for both researchers and clinicians, presents an overview of the lingual nerve and highlights how new insights into human anatomical variability can be gained by integrating fine dissection of cadavers with neuroanatomical approaches, microscopic studies, and morphometric techniques. Textbooks mainly provide descriptions of the typical or common gross anatomical appearance of structures in the human body with little reference to the nature and extent of variation that may be encountered within and between populations. Furthermore, few texts attempt to integrate descriptions of the regional distribution and branching of neural structures with their central connections or their microscopic anatomy. Using the lingual nerve as an example from the head and neck region, we show that there is still an important place for detailed fine dissections of human cadavers when they are also integrated with morphometric techniques applied to data representing observed variation at both macro- and micro-levels. It is essential that health professionals have a sound understanding of the nature and extent of anatomical variation displayed normally by their patients so that they can perform procedures, such as local anaesthesia and surgery, safely and also be able to correctly diagnose pathology when it is present.

Three-dimensional (3D) geometric morphometric analysis of human premolars to assess sexual dimorphism and biological ancestry in Australian populations.

OBJECTIVES: This study aimed to investigate size and shape variation of human premolars between Indigenous Australians and Australians of European ancestry, and to assess whether sex and ancestry could be differentiated between these groups using 3D geometric morphometrics. MATERIALS AND METHODS: Seventy dental casts from each group, equally subdivided by sex, were scanned using a structured-light scanner. The 3D meshes of upper and lower premolars were processed using geometric morphometric methods. Seventy-two landmarks were recorded for upper premolars and 50 landmarks for lower premolars. For each tooth type, two-way ANOVA was used to assess group differences in centroid size. Shape variations were explored using principal component analysis and visualized using 3D morphing. Two-way Procrustes ANOVA was applied to test group differences for ancestry and sex, and a "leave-one-out" discriminant function was applied to assess group assignment. RESULTS: Centroid size and shape did not display significant difference between the sexes. Centroid size was larger in Indigenous Australians for upper premolars and lower second premolars compared to the Australians of European ancestry. Significant shape variation was noted between the two ancestral groups for upper premolars and the lower first premolar. Correct group assignment of individual teeth to their ancestral groups ranged between 80.0 and 92.8% for upper premolars and 60.0 and 75.7% for lower premolars. DISCUSSION: Our findings provide evidence of significant size and shape variation in human premolars between the two ancestral groups. High classification rates based on shape analysis of upper premolars highlight potential application of geometric morphometrics in anthropological, bioarcheological and forensic contexts.

Technical note: The use of 3D printing in dental anthropology collections.

OBJECTIVES: Rapid prototyping (RP) technology is becoming more affordable, faster, and is now capable of building models with a high resolution and accuracy. Due to technological limitations, 3D printing in biological anthropology has been mostly limited to museum displays and forensic reconstructions. In this study, we compared the accuracy of different 3D printers to establish whether RP can be used effectively to reproduce anthropological dental collections, potentially replacing access to oftentimes fragile and irreplaceable original material. METHODS: We digitized specimens from the Yuendumu collection of Australian Aboriginal dental casts using a high-resolution white-light scanning system and reproduced them using four different 3D printing technologies: stereolithography (SLA); fused deposition modeling (FDM); binder-jetting; and material-jetting. We compared the deviations between the original 3D surface models with 3D print scans using color maps generated from a 3D metric deviation analysis. RESULTS: The 3D printed models reproduced both the detail and discrete morphology of the scanned dental casts. The results of the metric deviation analysis demonstrate that all 3D print models were accurate, with only a few small areas of high deviations. The material-jetting and SLA printers were found to perform better than the other two printing machines. CONCLUSIONS: The quality of current commercial 3D printers has reached a good level of accuracy and detail reproduction. However, the costs and printing times limit its application to produce large sample numbers for use in most anthropological studies. Nonetheless, RP offers a viable option to preserve numerically constraint fragile skeletal and dental material in paleoanthropological collections.

The physiological linkage between molar inclination and dental macrowear pattern.

OBJECTIVES: Exact symmetry and perfect balance between opposite jaw halves, as well as between antagonistic teeth, is not frequently observed in natural masticatory systems. Research results show that asymmetry in our body, skull, and jaws is often related to genetic, epigenetic, environmental and individual ontogenetic factors. Our study aims to provide evidence for a significant link between masticatory asymmetry and occlusal contact between antagonist teeth by testing the hypothesis that tooth inclination is one of the mechanisms driving distribution of wear in masticatory phases in addition to dietary and cultural habits. MATERIALS AND METHODS: The present work investigates the relationship between dental macrowear patterns and tooth inclinations on a sample of complete maxillary and mandibular 3D models of dental arches from 19 young and adult Yuendumu Aboriginal individuals. The analysis was carried out on first molars (M1) from all quadrants. Occlusal Fingerprint Analysis was used for the quantification of macrowear patterns, and 2D cross-sectional geometric analysis was carried out to investigate asymmetry in dental arches. RESULTS: The asymmetry is highly variable on both arches, and it is associated with differences in the inclination of upper M1 crowns. Each molar has variable inclination (buccal/lingual) which influence tooth to tooth contact, producing greater or lesser variation in wear pattern. Interindividual variability of morphological variation of the occlusal relationship has to be considered in macrowear analysis. DISCUSSION: Our results suggest that overall asymmetry in the masticatory apparatus in modern humans affects occlusal contact areas between antagonist teeth influencing macrowear and chewing efficiency during ontogeny.

The facial nerve: anatomy and associated disorders for oral health professionals.

The facial nerve, the seventh cranial nerve, is of great clinical significance to oral health professionals. Most published literature either addresses the central connections of the nerve or its peripheral distribution but few integrate both of these components and also highlight the main disorders affecting the nerve that have clinical implications in dentistry. The aim of the current study is to provide a comprehensive description of the facial nerve. Multiple aspects of the facial nerve are discussed and integrated, including its neuroanatomy, functional anatomy, gross anatomy, clinical problems that may involve the nerve, and the use of detailed anatomical knowledge in the diagnosis of the site of facial nerve lesion in clinical neurology. Examples are provided of disorders that can affect the facial nerve during its intra-cranial, intra-temporal and extra-cranial pathways, and key aspects of clinical management are discussed. The current study is complemented by original detailed dissections and sketches that highlight key anatomical features and emphasise the extent and nature of anatomical variations displayed by the facial nerve.

The Influence of Chorion Type on Health Measures at Birth and Dental Development in Australian and Dutch Twins: A Comparative Study.

Chorion type may significantly influence the prenatal environment of twins. This study explored the associations between chorion type and gestational age, birth weight, birth length, and the timing of emergence of the first primary tooth in two populations of twins, Australian and Dutch. Additionally, we investigated the relationship between chorion type and birth weight discordance (BWD) in order to determine whether a significant relationship existed between discordance in birth weight and discordance in the timing of emergence of the first primary tooth. The two study samples consisted of 409 Australian twin pairs and 301 Dutch twin pairs, all of European ancestry. Data were collected through a combination of questionnaires and recording charts administered to the parents and through linkage with biological databases. In the Australian sample, monozygotic monochorionic (MZMC) twins experienced the shortest mean gestation time (35 weeks), the lowest mean birth length (46 cm) and the lowest mean birth weight (2.3 kg) compared with other twin groups. For the same variables in the Dutch sample, these trends with MZMC twinning were not observed. Chorion type did not significantly affect the mean timing of emergence of the first primary tooth in either sample. Monochorionicity was found to be significantly associated with BWD in both samples, but there was a significant association between BWD in MZMC twin pairs and timing of emergence of the first primary tooth only in the Australian sample. Results from this study support previous findings that the timing of emergence of the first primary tooth is influenced strongly by genetic factors and is well protected from environmental disturbances.

Bacterial colonization, enamel defects and dental caries in 4-6-year-old mono- and dizygotic twins.

BACKGROUND: Knowledge of the genetic and environmental influences in caries aetiology has relevance for preventive dentistry. AIMS: This classical twin study compared concordance of mutans streptococci (MS) and lactobacilli (LB) colonization, enamel defects, and caries in a cohort of 4-6-year-old mono- (MZ) and dizygotic (DZ) twin pairs. DESIGN: The twins were examined for prevalence and concordance of enamel opacities and hypoplasia, oral counts of MS and LB, and dental caries. Bacterial counts were assessed using a commercial microbiological kit. RESULTS: Thirty-four MZ and 50 DZ twins (mean gestational age 35.0 ± 2.4 weeks, and birthweight 2.4 ± 0.6 kg) were examined. There were no statistically significant differences between MZ and DZ twins in the prevalence of MS, LB, and enamel hypoplasia. Concordance rates for MS and LB presence and prevalence of enamel defects within MZ and DZ twin pairs were not significantly different. There were more children with caries in DZ compared with MZ twins (18% vs 3%, P = 0.0029), most likely due to increased daily frequency of sugar consumption and less toothbrushing. CONCLUSIONS: Concordance data from MZ and DZ twins did not demonstrate any statistically significant difference in susceptibility for enamel defects and colonization of MS and LB.

Evaluation of carrier RNA and low volume demineralization for recovery of nuclear DNA from human teeth.

PURPOSE: Teeth and bones are frequently used in the genetic analysis of degraded and ancient human and animal remains. Standard extraction methods, including most commercially available systems, may not yield sufficient DNA to enable successful genetic analysis. Addition of a carrier molecule and demineralization (via EDTA) can increase yields from samples containing limited amounts of DNA. However the benefits of carrier molecules have not been demonstrated for bones and teeth and demineralization introduces large reagent volumes that are difficult to integrate into commercial DNA extraction systems. METHODS: We compared nuclear DNA yields recovered from small samples of partially decomposed human teeth using a commercial silica-based DNA extraction system with and without the addition of carrier RNA and/or a low-volume demineralization step. RESULTS: DNA yield was significantly improved with demineralization, but there was no significant effect of carrier RNA. The DNA content of a sample did not influence the significance of the effect of demineralization. CONCLUSION: Using a simple low-volume (1 mL) demineralization step, prior to DNA extraction with the QIAmp DNA Investigator kit (Qiagen), as little as 50 mg of tooth powder can yield more than 500 ng of nuclear DNA.

Prevalence and patterning of maxillary premolar accessory ridges (MxPARs) in several human populations.

We present new data on the prevalence and patterning of the maxillary premolar accessory ridge (MxPAR), a common but understudied morphological dental trait that is expressed as a linear elevation extending from the buccal cusp ridge to the medial sulcus of maxillary premolar teeth. A total of 579 sets of dental casts, representing six ethnic groups, were scored using the five-grade system proposed by Burnett et al. (2010). The frequency and distribution of the MxPAR were determined by tooth type, sex, side, locus and ethnicity, and the applicability of the scoring system was assessed. The MxPAR was found in approximately two-thirds of premolar teeth, more often on second than first premolars, and more often on the distal aspect of the occlusal surface than the mesial. There was some evidence that more pronounced forms of the feature occurred more often in males than females, and that there may be some directionality in its expression between sides. Variation was also noted in the frequency of occurrence and degree of expression of the MxPAR between ethnic groups. Intra- and inter-observer concordance rates for scoring the MxPAR were low, confirming that it was difficult to score the trait identically on two different occasions. Our findings have clarified the distribution of the MxPAR within the dentition and between ethnic groups, and highlighted the need for researchers to carry out thorough replicability studies and to decide on an appropriate breakpoint for determining presence or absence of this feature before embarking on genetic studies or bio-distance analyses.

Genetic, epigenetic, and environmental influences on dentofacial structures and oral health: ongoing studies of Australian twins and their families.

The Craniofacial Biology Research Group in the School of Dentistry at The University of Adelaide is entering an exciting new phase of its studies of dental development and oral health in twins and their families. Studies of the teeth and faces of Australian twins have been continuing for nearly 30 years, with three major cohorts of twins recruited over that time, and currently we are working with twins aged 2 years old to adults. Cross-sectional data and records relating to teeth and faces of twins are available for around 300 pairs of teenage twins, as well as longitudinal data for 300 pairs of twins examined at three different stages of development, once with primary teeth, once at the mixed dentition stage, and then again when the permanent teeth had emerged. The third cohort of twins comprises over 600 pairs of twins recruited at around birth, together with other family members. The emphasis in this third group of twins has been to record the timing of emergence of the primary teeth and also to sample saliva and dental plaque to establish the timing of colonization of decay-forming bacteria in the mouth. Analyses have confirmed that genetic factors strongly influence variation in timing of primary tooth emergence. The research team is now beginning to carry out clinical examinations of the twins to see whether those who become colonized earlier with decay-forming bacteria develop dental decay at an earlier age. By making comparisons within and between monozygotic (MZ) and dizygotic (DZ) twin pairs and applying modern molecular approaches, we are now teasing out how genetic, epigenetic, and environmental factors interact to influence dental development and also oral health.

Genetic, environmental and epigenetic influences on variation in human tooth number, size and shape.

The aim of this review is to highlight some key recent developments in studies of tooth number, size and shape that are providing better insights into the roles of genetic, environmental and epigenetic factors in the process of dental development. Advances in molecular genetics are helping to clarify how epigenetic factors influence the spatial and temporal regulation of the complex processes involved in odontogenesis. At the phenotypic level, the development of sophisticated systems for image analysis is enabling new dental phenotypes to be defined. The 2D and 3D data that are generated by these imaging systems can then be analysed with mathematical approaches, such as geometric morphometric analysis. By gathering phenotypic data and DNA from twins, it is now possible to use 'genome-wide' association studies and the monozygotic co-twin design to identify important genes in odontogenesis and also to clarify how epigenetic and environmental factors can affect this process. Given that many of the common dental anomalies affecting the human dentition are interrelated, apparently reflecting pleiotropic genetic effects, the discoveries and new directions described in this paper should have important implications for clinical dental practice in the future.

Stereophotogrammetric analysis of nasolabial morphology among Asian Malays: influence of age and sex.

OBJECTIVE: It is clear that population-specific norms should be used when planning plastic and reconstructive surgery for selected patients. In this study, we aimed to generate nasal and labial reference values by applying a stereophotogrammetric technique. A further aim was to investigate the effect of sexual dimorphism, age-related changes, and the interrelation between nasal and labial morphology. DESIGN: Cross-sectional study. SETTING: The data were collected from different locations on the Malaysian peninsula. PARTICIPANTS: A total of 276 Asian Malays (138 males and 138 females) were included in this study, and a three-dimensional system was used for capturing data. The sample was divided into three age groups: 13 to 14, 15 to 17, and 18 to 36 years. MAIN OUTCOME MEASURE(S): Twenty-five dimensions of the nose and lips were measured and analyzed separately in males and females. RESULTS: Significant differences between males and females were identified in 11 distances, and significant effects of age were found in most of the dimensions (p < .05). Significant correlations between the nasal and labial dimensions were recorded, particularly between lateral lip height and width of the ala insertion. A principal component analysis showed interrelationships between the nasal width distances and upper lip height. CONCLUSION: This study has provided a new three-dimensional database for nose and lip morphology in Malays and demonstrated patterns of variation that can be used by surgeons to make comparisons within and between different human populations and also to develop treatment plans for their patients.

Validity and reliability of tooth size and dental arch measurements: a stereo photogrammetric study.

BACKGROUND: The development of three-dimensional computer imaging has many applications in dentistry, including the analysis of dental casts. AIMS: To assess the validity and reliability of a dental stereophotogrammetric imaging system. METHODS: The sample consisted of 35 sets of dental costs. Maxillary and mandibular dental crown widths and selected dental arch dimensions were measured directly using digital calipers. Cast images were also captured by a stereophotogrammetric system and analysed using Australis software. Dahlberg's formula, paired t-tests and intra-class correlations were used to assess the random error, validity and reliability of the measurements, respectively. RESULTS: Most values demonstrated no significant difference between the direct and three-dimensional measurements with mean differences ranging from 0.05-0.21 mm. Moreover, values of intra-class correlation coefficients ranged between 0.80-0.99 for intra-examiner reliability. CONCLUSIONS: Mesiodistal crown widths and dental arch dimensions may be measured accurately with relatively small error by the specially-designed 3D system and confirms its suitability for clinical and research purposes.

Genetic Correlation, Pleiotropy, and Molar Morphology in a Longitudinal Sample of Australian Twins and Families.

This study aims to expand our understanding of the genetic architecture of crown morphology in the human diphyodont dentition. Here, we present bivariate genetic correlation estimates for deciduous and permanent molar traits and evaluate the patterns of pleiotropy within (e.g., m1-m2) and between (e.g., m2-M1) dentitions. Morphology was observed and scored from dental models representing participants of an Australian twin and family study (deciduous n = 290, permanent n = 339). Data collection followed Arizona State University Dental Anthropology System standards. Genetic correlation estimates were generated using maximum likelihood variance components analysis in SOLAR v.8.1.1. Approximately 23% of deciduous variance components models and 30% of permanent variance components models yielded significant genetic correlation estimates. By comparison, over half (56%) of deciduous-permanent homologues (e.g., m2 hypocone-M1 hypocone) were significantly genetically correlated. It is generally assumed that the deciduous and permanent molars represent members of a meristic molar field emerging from the primary dental lamina. However, stronger genetic integration among m2-M1/M2 homologues than among paired deciduous traits suggests the m2 represents the anterior-most member of a "true" molar field. The results indicate genetic factors act at distinct points throughout development to generate homologous molar form, starting with the m2, which is later replaced by a permanent premolariform crown.

Enamel hypoplasia in the primary dentition of monozygotic and dizygotic twins compared with singleton controls.

BACKGROUND: The study of enamel hypoplasia (EH) and opacity in twins provides insights into the contribution of genetic and environmental factors in the expression of enamel defects. AIM: This study examined prevalence and site concordance of EH and opacity in the primary dentition of 2- to 4-year-old twins and singleton controls to assess the relative contribution of genetics and the environment to the aetiology of these defects. DESIGN: The study sample consisted of 88 twin children and 40 singletons aged 2-4 years of age. Medical histories were obtained and the children examined for enamel defects. RESULTS: The prevalence of EH by teeth was 21% in monozygotic twins (MZ), 22% in dizygotic twins (DZ), and 15% in singleton controls. Twins showed a higher prevalence of EH compared with singletons (P < 0.05). Factors contributing to increase EH in twins were neonatal complications including intubation. There were no significant differences in site concordance of EH within the MZ twin pairs compared with DZ twin pairs when only presence of EH was considered, whereas a greater concordance was noted between MZ twin pairs compared with DZ twin pairs when both presence and absence of EH were considered. CONCLUSIONS: The results suggest that both genetic and environmental factors contribute to observed variation of EH, although it is likely that environmental factors exert a greater influence.

Problem-based learning interventions in a traditional curriculum are an effective learning tool.

DATA SOURCES: PubMed, ERIC and PsycLIT. The database search was supplemented with manual search of the electronic archives of the following journals: Academic Medicine, Medical Education, Teaching and Learning in Medicine, Journal of Dental Education and European Journal of Dental Education. Further articles were retrieved from the reference lists of selected papers. The review covered the period 1976-2008. STUDY SELECTION: Studies were eligible if they presented original research using PBL in research settings compared with another educational method (at a whole curriculum level or as a single intervention). This review included both randomised controlled trials (RCTs) and comparative studies. Qualitative and quantitative designs were eligible. DATA EXTRACTION AND SYNTHESIS: Three dental educators selected studies. It is not clear that there were predefined criteria. The studies showed considerable heterogeneity in their study designs, characteristics, outcome variables and results. A descriptive review of the data was presented. RESULTS: Sixty-nine studies were initially identified. The authors excluded 17 of these because they could not obtain full texts. Thirteen studies were excluded because they used purely qualitative data. Of the remaining 39 studies six were RCTs and 33 comparative studies. The RCTs gave little information about the curriculum design and used markedly different outcome measurements including test scores, personal characteristics and subjective approaches to learning and experiences. There was no overall difference in student performances between the integrated and the PBL curriculum but a significant difference in favour of these two when compared with a conventional curriculum. A modest advantage of PBL was noted in relational skills, humanistic attitudes and diagnostic accuracy. Test scores did not appear to be influenced by the use of PBL. Though PBL seems to have a good effect on several competencies after graduation no significant effects were observed in lifelong learning attitudes. Comparative studies on the whole showed a benefit from using PBL, for example in critical reasoning, problem solving abilities and creativity. CONCLUSIONS: Some evidence exists that single PBL intervention in a traditional curriculum is an effective learning tool, though test results appear not to be affected.