Asymmetrical Eruption of Permanent Teeth in Australian Aborigines

A better understanding of the factorsinfluencing tooth eruption is important given theassociation between altered eruption patterns andcrowded or decayed teeth. Hence, the aims of this studywere to quantify the extent of asymmetry in tooth eruptionand to determine whether eruption asymmetry wassignificantly influenced by sex, tooth position or timingof emergence. Additionally, directionality of asymmetryand variation between ethnic groups were also explored.Data collection was based on the examination of serialdental casts from a sample of 90 Aborigines (50 male, 40female) aged 6 to 18 years from the Yuendumu settlementin the Northern Territory of Australia. These casts wereobtained at yearly intervals from the 1950s to the early1970s. Tooth antimeres on each cast were compared usinga 4-grade eruption score. Relatively high (> 70%) interandintra-observer concordances confirmed reliabilityof the recording system. Asymmetry frequencies werecalculated and associations between variables assessedusing chi-square analyses, with statistical significanceset at alpha = 0.05. Evidence of patterned asymmetry forpermanent tooth eruption was noted among the sample ofAustralian Aborigines, with the distally positioned, laterformingteeth showing the highest levels of asymmetry.

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.

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.

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.

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.

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.

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.

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.

Acquiring psychomotor skills in operative dentistry: do innate ability and motivation matter?

OBJECTIVE

The acquisition of psychomotor skills is a key competence in the practice of dentistry, and innate abilities and motivation have been shown to influence motor performance. However, the explicit integration of these factors into the design of research projects about skill acquisition in dentistry has been limited. Therefore, the purpose of this study was to provide a comprehensive analysis of how dental students' abilities and motivation affected their performance in an operative task.

METHODS

A longitudinal study with two cohorts of dental students was conducted in laboratory classes forming part of an operative technique course. A range of standardised psychometric tests was used to assess different abilities before completing a cavity preparation on Frasaco teeth. This was followed immediately by completion of an Intrinsic Motivation Inventory.

RESULTS

Low but statistically significant correlations (P<0.05) were found between dental performance and psychomotor ability (r=0.22), and also dental performance and motivation (r=0.19). A significant difference (P<0.05) was found in the grades obtained for the cavity preparation exercise in one cohort between students with higher levels of psychomotor ability compared with those with lower levels (Tracing scores) (P<0.05). No significant differences in grades obtained for the cavity preparation exercise were found between students with higher and lower levels of motivation.

CONCLUSION

Both innate psychomotor ability and motivation showed only weak positive associations with dental performance on cavity preparation exercises. Our study suggests that student-related factors only provide limited information to explain differences in performance or to be useful as specific predictors of future performance by individuals.

Non-carious cervical lesions on permanent anterior teeth: a new morphological classification

BACKGROUND

Various cross-sectional forms of non-carious cervical lesions have been described but no formal morphological classification system has been developed. The aims of this study were to describe the spectrum of common morphological forms of non-carious cervical lesions observed within a large sample of extracted human permanent anterior teeth and to develop a system for classification based on morphological features.

METHODS

Over 15,000 extracted permanent anterior teeth were examined macroscopically under illumination at 2x magnification. Well-defined, descriptive categories were formed, based on observable non-carious cervical lesion features and using terminology currently reported in the literature. The lesions were then sorted into these categories.

RESULTS

Five hundred and forty-two non-carious cervical lesions were identified on 15 289 teeth extracted in the early to mid 20th century, representing a frequency of 3.5%. The main categories developed were "shallow", "concave", "wedge-shaped", "notched", and "irregular".

CONCLUSIONS

The new morphological classification system provides an alternative to presently used systems based on aetiology, and should facilitate future research on non-carious cervical lesions.

Non-carious cervical lesions: a scanning electron microscopic study

BACKGROUND

Examining non-carious cervical lesions using scanning electron microscopy (SEM) provides an opportunity to clarify their complex aetiology. This study aimed to examine the morphological forms of non-carious cervical lesions found within a sample of extracted human permanent anterior teeth using scanning electron microscopy.

METHODS

Five examples of non-carious cervical lesions from each of eight different morphologic categories were replicated and examined using scanning electron microscopy.

RESULTS

In total, 40 non-carious cervical lesions were examined at magnifications ranging from 10x to 2605x magnification. Qualitative ultrastructural features evident in the lesions were described and classified according to their appearance. A total of 13 different qualitative features were observed throughout the sample of NCCLs.

CONCLUSIONS

SEM highlighted a broad range of microscopic features of NCCLs, providing valuable insights into their complex, multifactorial aetiology.

Van der Woude syndrome: dentofacial features and implications for clinical practice

BACKGROUND

Van der Woude syndrome (VWS) is the most common clefting syndrome in humans. It is characterized by the association of congenital lower lip fistulae with cleft lip and/or cleft palate. VWS individuals have a high prevalence of hypodontia. Although caused by a single gene mutation, VWS has variable phenotypic expression. This study aimed to describe the range of clinical presentations in 22 individuals with VWS to facilitate its diagnosis.

METHODS

A retrospective study of 22 patients with a diagnosis of VWS was undertaken at the Australian Craniofacial Unit (ACFU) in Adelaide. Three extended families with affected members were included in the study cohort.

RESULTS

The overall prevalence of lip pits in this study cohort was 86%. Cleft phenotypes included bilateral cleft lip and palate (32%); unilateral cleft lip and palate (32%); submucous cleft palate (23%); and isolated cleft hard and soft palate (9%). Missing permanent teeth were reported in 86% of affected individuals.

CONCLUSIONS

Submucous cleft palate in VWS may go undiagnosed if the lower lip pits are not detected. Associated hypodontia and resultant malocclusions will also require management by a dental team.

Tooth size patterns in patients with hypodontia and supernumerary teeth

AIMS

Anomalies of tooth number may not be isolated conditions but may have wider associations in the development of the dentition including tooth size. This study aimed to examine links between hypodontia, supernumerary teeth and crown size, considering the effect on the development of the whole dentition and so increase understanding of the aetiology of these conditions.

METHODS AND RESULTS

The patients, who were all of European ancestry, were 60 young adults (30 males and 30 females) with hypodontia and 60 age and sex matched controls together with 60 young adults (39 males and 21 females) with supernumerary teeth and 60 age and sex matched controls. Hand measurements of mesiodistal and buccolingual dimensions were made of the teeth on dental study models using Mitutoyo electric callipers. The mean value of two measurements was used and intra-operator and inter-operator reliability determined. Patients with hypodontia had smaller teeth than the control group and this difference was statistically significant (p<0.05) for all teeth except the MD dimensions of 13, 23, 24 and 44. The difference in size was greatest for the BL dimensions in hypodontia patients. Further, the greater the number of missing teeth the smaller the tooth size. The hypodontia patients also showed higher variability in tooth dimensions than the control group. Patients with supernumerary teeth had larger teeth than the controls, with the greatest differences in the MD dimensions. In both hypodontia and supernumerary patients the differences in tooth size were generalised throughout the dentition.

CONCLUSIONS

In anomalies of tooth number the size of teeth is also involved. In patients with hypodontia and supernumerary teeth the crown size of the whole dentition is affected. These findings are compatible with a multifactorial aetiology of these conditions.

A qualitative assessment of non-carious cervical lesions in extracted human teeth

BACKGROUND

Opinions vary about the causes of non-carious cervical lesions (NCCLs). They have been attributed to toothbrush abrasion, acid corrosion (commonly termed dental erosion), and abfraction. The purpose of this study was to examine the microwear details of NCCLs in a collection of extracted human teeth using scanning election microscopy (SEM).

METHODS

Negative replicas of large NCCLs in 24 extracted human teeth were obtained in polyvinylsiloxane impression material (Light Body Imprint II, 3M ESPE) and viewed under SEM.

RESULTS

All NCCLs extended from the cemento-enamel junction to the root surface and they displayed a variety of wedge-shaped appearances. There was evidence of both abrasion and corrosion in 18 of the 24 teeth (75.0 per cent), abrasion only in one tooth (4.2 per cent) and corrosion only in five teeth (20.8 per cent). Horizontal furrows with smooth edges and minor scratch marks, characteristic of abrasion and corrosion, were noted in 13 teeth (54.2 per cent).

CONCLUSIONS

Based on microscopic assessment of a sample of extracted teeth, it appears that abrasion and corrosion are common associated aetiological factors in the formation of NCCLs.

Prevalence and side preference for tooth grinding in twins

BACKGROUND

Estimates of the prevalence of tooth grinding in children range considerably, reflecting different methods of recording. The main aims of this study were to determine the prevalence of tooth grinding in monozygotic (MZ) and dizygotic (DZ) twin pairs by assessing wear faceting on the primary canines, and to compare the faceting on the right and left to determine whether children have a side preference for grinding.

METHODS

The sample consisted of 116 MZ twin pairs and 124 dizygous DZ twin pairs, all participants in an ongoing study of dento-facial development at the dental schools in Adelaide and Melbourne. Evidence of wear faceting on primary maxillary and mandibular canine tips was recorded from dental casts, and the side with the larger wear facet recorded. Types of occlusal relationship, handedness, zygosity and gender were also recorded, and associations between variables analysed statistically.

RESULTS

Canine tip wear facets were found in 100 per cent of the sample, and grinding was lateralized in 59 per cent of children. MZ twin pairs showed a higher discordance for grinding side preference than DZ twin pairs (33.8 per cent compared with 16.8 per cent), providing evidence of a mirror-imaging effect for grinding side preference. There was no strong evidence that individuals had the same preference for grinding side and handedness, although right-handers (RH) showed a preference for a grinding side more often than non-right-handers (NRH) (63.6 per cent compared with 51.2 per cent), consistent with previous findings that RHs display more cerebral lateralization than NRHs.

CONCLUSIONS

Tooth grinding appears to be a universal phenomenon in children and is commonly expressed more on one side than the other. The significantly higher discordance for grinding side preference in MZ twin pairs compared with DZ twin pairs may reflect a mirror-imaging effect in the former. However, at present we have no evidence to suggest that handedness and preferred tooth grinding side are associated.

A model for the prediction of tooth wear in individuals

BACKGROUND

Easily applied, age-specific standards are useful in assisting clinicians to decide whether the extent of tooth wear observed in a given patient at a specific age is acceptable or whether intervention is indicated.

METHOD

A simple method of scoring tooth wear and previously established mathematical relationships between tooth wear scores and age, provide the basis of a method for predicting tooth wear scores. In its most specific form, the method can be used to predict tooth wear scores for individual patients at subsequent ages. Alternatively, tables or graphs can be consulted to provide a less precise prediction of tooth wear that can assist clinicians to decide whether the amount of wear reflects high, moderate or low rates of wear at the specified age.

CONCLUSION

In cases where there is no reason to believe that aetiological factors have changed significantly over time, data obtained from the methods described can assist clinicians to plan appropriate management for patients presenting with unacceptable levels of tooth wear.

Strong genetic control of emergence of human primary incisors

Our understanding of tooth eruption in humans remains incomplete. We hypothesized that genetic factors contribute significantly to phenotypic variation in the emergence of primary incisors. We applied model-fitting to data from Australian twins to quantify contributions of genetic and environmental factors to variation in timing of the emergence of human primary incisors. There were no significant differences in incisor emergence times between zygosity groups or sexes. Emergence times of maxillary central incisors and mandibular lateral incisors were less variable than those of maxillary lateral incisors and mandibular central incisors. Maxillary lateral incisors displayed significant directional asymmetry, the left side emerging earlier than the right. Variation in timing of the emergence of the primary incisors was under strong genetic control, with a small but significant contribution from the external environment. Estimates of narrow-sense heritability ranged from 82 to 94% in males and 71 to 96% in females.

Three-dimensional computed tomography cephalometry of plagiocephaly: asymmetry and shape analysis

OBJECTIVE

To investigate facial asymmetry associated with both deformational and synostotic plagiocephaly and to identify variables based on skeletal landmarks that distinguish the conditions and quantify severity.

DESIGN

Retrospective, cross sectional.

SETTING

Australian Craniofacial Unit, Adelaide.

MAIN OUTCOME MEASURES

Proportional differences between bilateral distances and principal component (PC) analysis of the skeletal landmarks.

PATIENTS

The three-dimensional positions of 78 osseous landmarks were determined from computed tomography (CT) scans of 21 patients with deformational plagiocephaly (DP), 20 patients with unilateral coronal synostosis (UCS), and 2 patients with unilateral lambdoid synostosis (ULS).

RESULTS

For both DP and UCS, significant asymmetry was found for the orbital depths, mandibular lengths, maxillary depths, zygomatic arch lengths, lateral base of the parietal bone, and the angle between the anterior and the posterior cranial base projected onto the axial plane. The small sample size for ULS precluded definitive statistical statements but allowed some useful comparisons with the other conditions. The first three PC scores were able to distinguish among the three conditions and which side was affected.

CONCLUSIONS

The asymmetry of the cranial base and facial structures, arising from localized abnormality or deformational forces in either the frontal or the occipital regions, can be quantified by a plethora of bilateral features or summarized by PC analysis.

Discal attachments of the human temporomandibular joint

BACKGROUND

Despite its clinical significance, the anatomy of the human temporomandibular joint (TMJ) and its relationship to the lateral pterygoid muscle remains poorly described and often misrepresented in standard texts. The aim of this study was to describe how the anterior and posterior attachments of the TMJ disc vary between lateral, central and medial regions of the joint.

METHODS

Ten left TMJs were removed en bloc from cadavers and serial sections were made at 3-4mm intervals. Observations were made to ascertain the anterior and posterior attachments of the disc and the joint structures were traced from standardized photographs.

RESULTS

Laterally, the capsule and lateral discal ligament merged prior to their attachment at the condylar pole. Medially, muscle fibres, capsule and the disc converged on the medial pole of the condyle. There was no evidence that fibres of the upper head of the lateral pterygoid muscle inserted directly into the disc. The upper head inserted into the condyle either directly at the pterygoid fovea or via a central tendon or indirectly via the capsule. Posteriorly, the superior part of the posterior attachment of the disc attached to the cartilaginous meatus and tympanic part of the temporal bone. The inferior part of the posterior attachment of the disc attached to the posterior surface of the condyle. In four joints, this attachment was folded beneath the posterior band of the disc, creating a wedge-shaped flap that ran medio-laterally.

CONCLUSION

This study is in broad agreement with other anatomical TMJ studies but there are two main points of difference. Firstly, a true muscle insertion of the superior head of the lateral pterygoid muscle to the disc was not observed. Secondly, a wedge-shaped flap of retrodiscal tissue was identified between the condyle and the disc.

Linear enamel hypoplasia and historical change in a central Australian community

BACKGROUND

The current study extends the use of linear enamel hypoplasia (LEH) to examine the historical changes in living conditions encountered by Aboriginal people at Yuendumu who were born between 1890 and 1960. LEH provides health information beyond written records and gives information beyond written records and gives insight into the relationship between individual health and living conditions during initial and ongoing contact with Europeans.

MATERIALS AND METHODS

The dental casts of 446 people, collected as part of the University of Adelaide longitudinal study of growth and development, were recorded for the presence of hypoplastic defects. Defects were recorded according to the Development Defects of the Enamel (DDE) standards and assigned to developmental units based on their crown position.

RESULTS

The frequency of LEH on the permanent dentitions increased five-fold from the 1890-1929 birth cohort to the 1955-1960 cohort. LEH also affected earlier developing enamel units. Deciduous defects did not show a strong temporal trend but overall prevalence was comparable to other disadvantaged groups.

CONCLUSION

The changes in permanent LEH frequency and age distribution correspond to altered living conditions with the worst hypoplasia recorded after settlement of Aboriginal people at Yuendumu. Prior to that period LEH was comparable to precontact Australian populations indicating that resettlement had a dramatic impact on childhood morbidity.

Epigenetic influences may explain dental differences in monozygotic twin pairs

BACKGROUND

Comparisons between monozygotic (MZ) co-twins have tended to focus on the similarities between their dentitions rather than differences. The aim of this study was to determine the prevalence of discordant expression for simple hypodontia and supernumerary teeth in MZ twin pairs and to explain how phenotypic differences might occur despite their similar genotypes.

METHODS

Records of 278 pairs of MZ twins, including dental casts and radiographs, were examined and the prevalences of discordant expression for missing upper lateral incisors (ULI) or second premolars (PM2), and of mesiodentes, were determined. Zygosities were confirmed by comparisons of blood markers and DNA.

RESULTS

There was evidence of at least one missing ULI or PM2 in 24 of the 278 MZ pairs (8.6 per cent), with 21 of these 24 pairs (87.5 per cent) showing discordant expression. Nine of the 278 MZ pairs (3.2 per cent) displayed evidence of mesiodentes, with eight of these nine pairs (88.9 per cent) being discordant.

CONCLUSION

Our findings show that differences in the expression of missing or extra teeth occur often between MZ co-twins whose genetic make-up predisposes them to simple hypodontia or mesiodentes. We postulate that minor variations in epigenetic events during odontogenesis may account for these distinct differences.

Association of frontal sinus development with somatic and skeletal maturation in Aboriginal Australians: a longitudinal study

There have been very few studies of frontal sinus development and its association with other growth parameters in humans. The aim of this study was to investigate the relationship of frontal sinus development with somatic and skeletal maturation in a sample of Aboriginal Australians. The sample comprised 31 individuals, of whom 17 were males and 14 females. For the selected subjects the following records were available: lateral head radiographs, hand-wrist radiographs and stature recordings, generally covering the age range from 7 to 18 years. Descriptive statistics for frontal sinus size, skeletal ossification and body height were calculated at yearly intervals and comparisons made between the sexes. Growth velocities in frontal sinus height, frontal sinus depth and stature were also calculated for both sexes. The frontal sinus was found to display a well-defined adolescent growth spurt, with its peak velocity occurring after the peak velocity in body height. Females were found to attain peak velocity in sinus height earlier, on average, than males but they attained peak velocity in sinus depth at a similar age to males. The sequence of hand-wrist ossification events followed a similar pattern in both sexes, with events in females occurring approximately one year earlier than those in males. These results indicate that an adolescent spurt is present in frontal sinus growth and that the spurt tends to occur after statural velocity has peaked. Hand-wrist ossification events also tend to have a close relationship to peak statural and frontal sinus velocity and these relationships may be useful in clinical situations for predictive purposes.

Sexual dimorphism in crown units of mandibular deciduous and permanent molars in Australian Aborigines

Sexual differences in the crown units of mandibular molars were investigated in Australian Aborigines. The first and second deciduous molars (dm1 and dm2), and first to third permanent molars (M1, M2 and M3) were measured on dental casts using a sliding caliper. Measurements of tooth crowns included overall mesiodistal and buccolingual diameters, as well as the mesiodistal and buccolingual diameters of the trigonid and talonid. Percentage dimorphism values were greater in the talonid dimensions than the trigonid, indicating that sex differences tend to be larger in the later-developing crown units. Sex differences in mesiodistal diameters increased from dm1 to M2 but decreased for M3, the tooth that showed the least dimorphism of all the molars. This result seems to be due to the marked variability in size of the M3 between individuals.

The value of twins in dental research

Due to recent advances in molecular genetics, studies of twins will continue to provide important insights into how genetic and environmental factors contribute to variation in human physical and behavioural traits and disorders. This review emphasizes that biometrical genetic studies of twins are particularly valuable in complementing and directing molecular approaches to facilitate the detection of quantitative trait loci. It also describes several other research models involving twins, apart from the traditional comparison of similarities in monozygotic (identical) and dizygotic (non-identical) pairs, that have the potential to provide new information in the future. Current knowledge about the genetic bases of common dental problems is summarized and future directions in dental research involving twins are outlined.

Decline in enamel hypoplasia in relation to fluoridation in Australians

Enamel hypoplasias are thought to represent calcification disruption indicative of metabolic stress during development. Hypoplasias of permanent maxillary central incisors and mandibular canines have undergone a notable reduction in frequency between Euro-Australian twins born around 1965 and those born ca. 1990. Even when scored very liberally these linear defects are 3.1-4.6 times as prevalent in the earlier Australians, and the discrepancy is proportionately greater among strictly scored defects. Likely correlates of this secular trend logically include reduced childhood fevers and clinical intervention to reduce circum-natal stresses acting on cotwins. However, fluoridation of metropolitan water has emerged as the statistically strongest hypoplasia-preventing factor.

Tooth wear prevention: A quantitative and qualitative in vitro study

BACKGROUND

Management of tooth wear from grinding presents a significant clinical challenge. Acrylic nightguards are often used to protect the teeth, but many patients still grind with these appliances. This study aimed to test the effectiveness of three lubricants in reducing enamel wear by using an electro-mechanical machine under controlled conditions, with a view to undertaking a subsequent longitudinal clinical study.

METHODS

Sectioned tooth specimens were worn against each other under different loads and with the addition of three different lubricants: calcium fluoride (CaF) powder, olive-oil, and a combination of calcium fluoride with olive-oil in the form of a slurry. Wear rates of enamel only were quantified by weighing the specimens, and resin replicas of the worn tooth surfaces were made for examination under a scanning electron microscope.

RESULTS

All three lubricants reduced the amount of enamel wear significantly compared with wearing specimens without adding lubricants. Wear rate was influenced by the type of lubricant and the load applied. Wear rates were significantly less for olive-oil and the olive-oil/CaF slurry compared with CaF alone. The microwear detail differed between the three lubricants.

CONCLUSIONS

This study has shown that enamel wear can be reduced using dry or wet lubricants between opposing teeth that are worn under controlled conditions. Further research is required to clarify their possible clinical applications.

New standards for permanent tooth emergence in Australian children

BACKGROUND

Published standards for permanent tooth emergence in Australian children are 40 years old. The aim of this study was to present new data on the timing and sequence of permanent tooth emergence in a large sample of Australian children and to compare the findings with those of earlier studies.

METHODS

Records of a randomly selected sample of 8676 children, aged between 4 to 16 years, who had attended the clinics of the South Australian Dental Service were scanned optically and coded to provide the data for this study. A logistic regression analysis enabled median times of emergence, together with percentile ranges, to be calculated for each tooth, except third molars, in boys and girls. Comparisons were made between the sexes and with previously published values. The frequencies of occurrence of emergence polymorphisms for different tooth pairs were also computed.

RESULTS

The earliest teeth to emerge in both boys and girls were the central incisors and first molars, whereas the second premolars and molars and maxillary canines tended to be last to emerge. The mandibular teeth tended to precede the corresponding maxillary teeth in emergence in both sexes. Tooth emergence was advanced in girls compared with boys, averaging 4.5 months in the maxilla and 5.3 months in the mandible. In general, emergence times of children in the present sample were later than those reported previously for Australian children. The most common emergence polymorphism in the maxilla involved the canine and second premolar, whereas common polymorphisms in the mandible were noted for the central incisor and first molar, canine and first premolar, and the second premolar and second molar.

CONCLUSIONS

Given that they have been collected relatively recently from a large sample of children, the new data reported in this paper can now be used as standards when assessing permanent tooth emergence of Australian children.

Dental characteristics of patients with Duchenne muscular dystrophy

A comprehensive assessment of the dental characteristics of 23 patients with Duchenne muscular dystrophy (DMD) was carried out, based on dental records, oral examinations and dental models. Decreasing muscle function was associated with increased plaque and calculus accumulation, leading to gingival inflammation, but caries experience was low. Disturbances in tooth form, number and eruption of the second premolars were observed in 39% of patients. Anterior and posterior open bites were common, associated with lip incompetence, mouth breathing, macroglossia and tongue thrusting. Maxillary and mandibular arch breadths were significantly larger, on average, in the DMD group than in controls. Rather than a normal parabolic arch form, the dental arches in DMD patients tended to be hyperbolic, with the posterior teeth being displaced buccally, consistent with an imbalance between the lingual and facial musculature.

Tooth development standards for South Australia

BACKGROUND

Chronological age, as recorded by registration of birth date, is referred to throughout an individual's life. This information is relevant in medical and dental practice for evaluating developmental progress, for educational purposes, and in legal matters, particularly in the application of criminal law. The absence of birth date information raises particular concerns, and estimates of chronological age are often required. Standards of dental maturation may be used to estimate age, but they have been shown to be gender and population sensitive.

METHODS

The revised Demirjian' system of dental age estimation was applied to a sample of 615 South Australian children in order to assess its accuracy.

RESULTS

The results of our study have shown that the Demirjian system is of limited accuracy when used to estimate the age of South Australian children.

CONCLUSIONS

Generation of new standard curves, specific to the Australian population, is indicated.

A radiographic assessment of the prevalence of pulp stones in Australians

BACKGROUND

Pulp stones are discrete calcified bodies found in the dental pulp. The aims of this study were to calculate the prevalence of pulp stones in young Australian adults using radiographs, and to report any associations between occurrence of pulp stones and sex, tooth type, dental arch, side and dental status.

METHODS

From 217 undergraduate dental students, comprising 123 males and 94 females aged between 17-35 years, 3296 teeth were examined under 2x magnification on bitewing radiographs. Pulp stones were scored as present or absent, and associations with sex, tooth type, dental arch, side and dental status noted.

RESULTS

Pulp stones were found in 100 (46.1 per cent) of the subjects and 333 (10.1 per cent) of the teeth examined. Occurrences were rare in premolars (0.4 per cent) but significantly higher in molars (19.7 per cent). Pulp stones were significantly more common in first molars than in second molars, and in maxillary first molars than in mandibular first molars. Carious and/or restored maxillary right first molars and maxillary left second molars displayed higher prevalences of pulp stones than unrestored and intact molars.

CONCLUSION

Pulp stones may provide useful forensic information when examining dental records to identify deceased persons.

Tooth wear in children with Down syndrome

BACKGROUND

Several studies have described the impact that dental caries and periodontitis may have on the dentitions of individuals with Down syndrome, but there are few reports about the effects of tooth wear. This investigation aimed to compare the aetiology, prevalence and severity of tooth wear in 49 cytogenetically confirmed Down syndrome children with 49 non-Down syndrome controls.

METHODS

This study involved three aspects: an oral examination, including obtaining dental impressions; a dietary analysis spanning three days; and a questionnaire seeking information about habits, medical problems and medications. Tooth wear severity was scored on a 4-grade scale (none-to-little; moderate; severe; very severe), while aetiology was classified as being due to attrition mainly, erosion mainly, or a combination of both. Double determinations established scoring method reliability and chi-square tests assessed associations between samples.

RESULTS

Tooth wear was significantly more frequent (p<0.01) in the Down syndrome than the non-Down syndrome sample (67.4 per cent cf 34.7 per cent), with more of the Down syndrome children showing severe to very severe wear (59.2 per cent cf 8.2 per cent). Significantly more Down syndrome children (p<0.05) displayed a multifactorial aetiology of tooth wear, i.e., both attrition and erosion (46.7 per cent cf 28.6 per cent), although no particular dietary link was established. Gastric reflux and vomiting were reported in over 20 per cent of the Down syndrome sample.

CONCLUSIONS

Given the potential consequences of high levels of tooth wear, associated with tooth grinding and an acidic oral environment in Down syndrome children, educational programmes aimed at increasing awareness of carers and health professionals are needed urgently.