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.

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

AIM

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Effects of the mutation R145G in human cardiac troponin I on the kinetics of the contraction-relaxation cycle in isolated cardiac myofibrils

Familial hypertrophic cardiomyopathy (FHC) has been linked to mutations in sarcomeric proteins such as human cardiac troponin I (hcTnI). To elucidate the functional consequences of the mutation hcTnI(R145G) on crossbridge kinetics, force kinetics were analysed in murine cardiac myofibrils carrying either the mutant or the wild-type protein. The mutation was introduced into the myofibrils in two different ways: in the first approach, the endogenous Tn was replaced by incubation of the myofibrils with an excess of reconstituted recombinant hcTn containing either hcTnI(WT) or hcTnI(R145G). Alternatively, myofibrils were isolated either from non-transgenic or transgenic mice expressing the corresponding mcTnI(R146G) mutation. In myofibrils from both models, the mutation leads to a significant upward shift of the passive force-sarcomere length relation determined at pCa 7.5. Addition of 5 mm BDM (2,3-butandione-2-monoxime), an inhibitor of actomyosin ATPase partially reverses this shift, suggesting that the mutation impairs the normal function of cTnI to fully inhibit formation of force-generating crossbridges in the absence of Ca(2)(+). Maximum force development (F(max)) is significantly decreased by the mutation only in myofibrils exchanged with hcTnI(R145G) in vitro. Ca(2)(+) sensitivity of force development was reduced by the mutation in myofibrils from transgenic mice but not in exchanged myofibrils. In both models the rate constant of force development k(ACT) is reduced at maximal [Ca(2)(+)] but not at low [Ca(2)(+)] where it is rather increased. Force relaxation is significantly prolonged due to a reduction of the relaxation rate constant k(REL). We therefore assume that the impairment in the regulatory function of TnI by the mutation leads to modulations in crossbridge kinetics that significantly alter the dynamics of myofibrillar contraction and relaxation.

Mutations in the gamma(2) subunit of AMP-activated protein kinase cause familial hypertrophic cardiomyopathy: evidence for the central role of energy compromise in disease pathogenesis

Familial hypertrophic cardiomyopathy (HCM) has been widely studied as a genetic model of cardiac hypertrophy and sudden cardiac death. HCM has been defined as a disease of the cardiac sarcomere, but mutations in the known contractile protein disease genes are not found in up to one-third of cases. Further, no consistent changes in contractile properties are shared by these mutant proteins, implying that an abnormality of force generation may not be the underlying mechanism of disease. Instead, all of the sarcomeric mutations appear to result in inefficient use of ATP, suggesting that an inability to maintain normal ATP levels may be the central abnormality. To test this hypothesis we have examined candidate genes involved in energy homeostasis in the heart. We now describe mutations in PRKAG2, encoding the gamma(2) subunit of AMP-activated protein kinase (AMPK), in two families with severe HCM and aberrant conduction from atria to ventricles in some affected individuals (pre-excitation or Wolff-Parkinson-White syndrome). The mutations, one missense and one in-frame single codon insertion, occur in highly conserved regions. Because AMPK provides a central sensing mechanism that protects cells from exhaustion of ATP supplies, we propose that these data substantiate energy compromise as a unifying pathogenic mechanism in all forms of HCM. This conclusion should radically redirect thinking about this disorder and also, by establishing energy depletion as a cause of myocardial dysfunction, should be relevant to the acquired forms of heart muscle disease that HCM models.

Effect of hypertrophic cardiomyopathy mutations in human cardiac muscle alpha -tropomyosin (Asp175Asn and Glu180Gly) on the regulatory properties of human cardiac troponin determined by in vitro motility assay

The properties of mutant contractile proteins that cause hypertrophic cardiomyopathy (HCM) have been investigated in expression studies and in mouse models. There is growing evidence that the precise isoforms of both the mutated protein and its interacting partners can qualitatively influence the effects of the mutation. We therefore investigated the functional effects of two HCM mutations in alpha -tropomyosin, Asp175Asn and Glu180Gly, in the in vitro motility assay using recombinant human alpha -tropomyosin, expressed with an N-terminal alanine-serine extension (AStm) to mimic acetylation in vivo, and purified native human cardiac troponin. The expected switching off of reconstituted filament movement at pCa9, and switching on at pCa5, was observed with no difference in fraction of filaments motile or filament velocity, between wild-type and mutant filaments. However, we observed increased Ca(2+)sensitivity of fraction of filaments motile using the mutant tropomyosin compared to wild-type (DeltaEC(50)+0.082+/-0. 019 pCa units for Asp175Asn and +0.115+/-0.021 for Glu180Gly). Indirect measurements using immobilized alpha -actinin to retard filament movement showed that filaments reconstituted with mutant AStm produced the same force as wild-type filaments. The results using human cardiac regulatory proteins reveal different effects of the HCM mutations in tropomyosin compared to studies using heterologous systems. By performing parallel experiments using either human cardiac or rabbit skeletal troponin we show that the cardiac-specific phenotype of HCM mutations in alpha -tropomyosin is not the result of more marked functional changes when interacting with cardiac troponin.

Investigation of a truncated cardiac troponin T that causes familial hypertrophic cardiomyopathy: Ca(2+) regulatory properties of reconstituted thin filaments depend on the ratio of mutant to wild-type protein

Familial hypertrophic cardiomyopathy (HCM) is caused by mutations in at least 8 contractile protein genes, most commonly beta myosin heavy chain, myosin binding protein C, and cardiac troponin T. Affected individuals are heterozygous for a particular mutation, and most evidence suggests that the mutant protein acts in a dominant-negative fashion. To investigate the functional properties of a truncated troponin T shown to cause HCM, both wild-type and mutant human cardiac troponin T were overexpressed in Escherichia coli, purified, and combined with human cardiac troponins I and C to reconstitute human cardiac troponin. Significant differences were found between the regulatory properties of wild-type and mutant troponin in vitro, as follows. (1) In actin-tropomyosin-activated myosin ATPase assays at pCa 9, wild-type troponin caused 80% inhibition of ATPase, whereas the mutant complex gave negligible inhibition. (2) Similarly, in the in vitro motility assay, mutant troponin failed to decrease both the proportion of actin-tropomyosin filaments motile and the velocity of motile filaments at pCa 9. (3) At pCa 5, the addition of mutant complex caused a greater increase (21.7%) in velocity of actin-tropomyosin filaments than wild-type troponin (12.3%). These data suggest that the truncated troponin T prevents switching off of the thin filament at low Ca(2+). However, the study of thin filaments containing varying ratios of wild-type and mutant troponin T at low Ca(2+) indicated an opposite effect of mutant troponin, causing enhancement of the inhibitory effect of wild-type complex, when it is present in a low ratio (10% to 50%). These multiple effects need to be taken into account to explain the physiological consequences of this mutation in HCM. Further, these findings underscore the importance of studying mixed mutant:wild-type preparations to faithfully model this autosomal-dominant disease.

Physiological regulation of eukaryotic topoisomerase II

Topoisomerase II is an essential enzyme in all organisms with several independent roles in DNA metabolism. In this article we review our knowledge on the regulation of the expression and catalytic activity of topoisomerase II in both lower and higher eukaryotes. Current data indicate that the regulation of topoisomerase II gene expression is complex, with positive and negative controls in evidence at the level of both promoter activity and mRNA stability. Similarly, the activity of the mature enzyme can be regulated by the action of several different protein kinases. Of particular interest is the cell cycle-dependent phosphorylation of topoisomerase II, including multiple, mitosis-specific modifications, which are proposed to regulate the essential chromosome decatenation activity of the enzyme.

Casein kinase II stabilizes the activity of human topoisomerase IIalpha in a phosphorylation-independent manner

Previous reports have indicated that topoisomerase II (topo II) co-purifies with and is a substrate for casein kinase II. We have carried out a detailed study of the effect that purified casein kinase II has on the activity of purified recombinant human topo IIalpha. Co-incubation of topo IIalpha and casein kinase II led to an apparent activation of the topo IIalpha; however, in experiments in which topo IIalpha was preincubated at 37 degrees C with or without native casein kinase II prior to assaying for decatenation activity, it emerged that the kinase was exerting its "activating" function via a decrease in the rate of topo IIalpha enzyme inactivation during the incubation period. This stabilization of topo IIalpha by casein kinase II was ATP-independent and was observed in both mutated and truncated derivatives of topo IIalpha lacking the major casein kinase II phospho-acceptor sites, indicating the lack of a requirement for phosphorylation. Consistent with a nonenzymatic role for casein kinase II, stoichiometric quantities of kinase were required for topo IIalpha stabilization. These data indicate that casein kinase II plays a significant role in regulating human topo IIalpha protein action via stabilization against thermal inactivation.