Mandibular forces during simulated tooth clenching

Differential, functional loading of the mandibular condyles has been suggested by several human morphologic studies and by animal strain experiments. To describe articular loading and the simultaneous forces on the dental arch, static bites on a three-dimensional finite element model of the human mandible were simulated. Five clenching tasks were modeled: in the intercuspal position; during left lateral group effort; during left lateral group effort with balancing contact; during incisal clenching; and during right molar clenching. The model's predictions confirmed that the human mandibular condyles are load-bearing, with greater force magnitudes being transmitted bilaterally during intercuspal and incisal clenching, as well as through the balancing-side articulation during unilateral biting. Differential condylar loading depended on the clenching task. Whereas higher forces were found on the lateral and lateroposterior regions of the condyles during intercuspal clenching, the model predicted higher loads on the medial condylar regions during incisal clenching. The inclusion of a balancing-side occlusal contact seemed to decrease the forces on the balancing-side condyle. Whereas the predicted occlusal reaction forces confirmed the lever action of the mandible, the simulated force gradients along the tooth row suggest a complex bending behavior of the jaw.     

Biodegradation of poly(ethylene adipate) microcapsules in physiological media

Spherical reservoir-type microcapsules fabricated using a water/oil/water (W/O/W) double emulsion technique with solvent evaporation and composed of poly(ethylene adipate) (PEAD) blended with 20% poly-epsilon-caprolactone (PCL II) containing a range of bovine serum albumin (BSA) loadings were incubated in Hank's buffer, pH 7.4, newborn calf serum, 1.5% pancreatin and synthetic gastric juice containing 10% pepsin A over 30 days and their percentage weight loss (PWL) and changes in ultrastructural morphology monitored by gravimetry and stereoscan electron microscopy (SEM) respectively. The greatest PWL from microcapsules was observed after incubation in newborn calf serum (NCS) and pancreatin and decreased in the order NCS > pancreatin > synthetic gastric juice > Hank's buffer. Only microcapsules theoretically loaded with 5-20% BSA and incubated in synthetic gastric juice showed a significant increase in PWL with increasing percentage BSA loading. The structural biodegradation of PEAD microcapsules in both Hank's buffer and synthetic gastric juice was minimal whilst the morphological changes observed during incubation in NCS involved pitting of the membrane, some surface erosion and reduction in diameter, followed by microcapsule membrane disruption and loss of reservoir contents. Biodegradation in pancreatin was associated with surface flaking and loss of large fragments of the microcapsule membrane. Only in NCS and pancreatin, where one would expect to see the effects of enzyme activity in addition to simple ester hydrolysis, did biodegradation proceed to the stage where there was a loss of spherical shape and almost total disruption of the microcapsule structure within 30 days.     

Plasma sprayed hydroxyapatite coatings on titanium substrates. Part 1: Mechanical properties and residual stress levels

Heat treatment and the introduction of a Ti bond coat have been applied to hydroxyapatite (HA) coatings sprayed using different plasma powers and gas mixtures. Attempts were made in this way to achieve optimal coating properties for orthopaedic implants. In particular, the effects on the degree of crystallinity, the adhesion, the OH ion content and the purity were evaluated. Heat treatment at 700 C for 1 h in air proved to be effective in increasing the crystallinity, regaining the OH- ion and removing other non-HA compounds, although it caused a significant decrease in the degree of adhesion (interfacial fracture toughness) for those specimens sprayed at high powers. This heat treatment was found to induce significant transformation of amorphous HA to the crystalline form, while not detrimentally changing the properties of the underlying Ti-6Al-4V substrates. Precoating with a 100 microm Ti layer increased the adhesion of the HA coatings on Ti-6Al-4V substrates, primarily by providing a rougher surface and promoting better mechanical interlocking. Changes in coating properties during immersion in biological fluids were also studied and were found to depend critically on the chemical composition of the fluids. Small precipitates formed on the coating surfaces when immersed in Ringers solution. These might account for the apparent drop in the degree of crystallinity when measured using X-ray diffraction. A significant drop in the interfacial adhesion was found for those coatings sprayed at high powers. This could be offset by prior precoating with a titanium bond coat and suitable heat treatment. In summary, the following processing sequence is suggested in order to achieve optimum coating properties: precoating the substrate with a layer of Ti (approximately 100 microm), spraying HA at a sufficiently high-power level (depending on particle size and gas mixture) and heat treatment at 700 degrees C for 1 h in air.     

Mapping protein-protein interactions by affinity-directed mass spectrometry

A precise and rapid method for identifying sites of interaction between proteins was demonstrated; the basis of the method is direct mass spectrometric readout from the complex to determine the specific components of the proteins that interact--a method termed affinity-directed mass spectrometry. The strategy was used to define the region of interaction of a protein growth factor with a monoclonal antibody. A combination of proteolytic digestion and affinity-directed mass spectrometry was used to rapidly determine the approximate location of a continuous binding epitope within the growth factor. The precise boundaries of the binding epitope were determined by affinity-directed mass spectrometric analysis of sets of synthetic peptide ladders that span the approximate binding region. In addition to the mapping of such linear epitopes, affinity-directed mass spectrometry can be applied to the mapping of other types of molecule-molecule contacts, including ligand-receptor and protein-oligonucleotide interactions.     

To be lean or not to be lean. Is leptin the answer?

Coronary heart disease (CHD) has been considered as a multifactorial disorder with the involvement of both environmental and genetic factors. The advent of tools to investigate individual variability of DNA has allowed us to perform the association studies of candidate genes. However, an association between genetic trait and phenotypic variations is not easy to demonstrate and several reported association between genetic markers and risk factors or overt CHD have gone unconfirmed. It should not be assumed that for a given genetic trait, the impact on risk will be similar in all populations. In particular, most studies of the molecular bases of CHD have involved Caucasian subjects, so much more work with the Korean population is needed before genetic testing for susceptibility to CHD can be offered to Koreans as a clinical service. In this review, we discuss two aspects of the molecular bases of CHD: i) Molecular bases of the candidate gene related to lipoprotein metabolism including apolipoprotein AI-CIII-AIV gene duster, apolipoprotein B, apolipoprotein E-CI-CII gene cluster, apolipoprotein(a), LDL receptors, lipoprotein lipase, cholesteryl ester transfer protein, and apo B editing protein; ii) Molecular bases of the candidate gene related to thrombotic and other factors including fibrinogen, factor VII, plasminogen activator inhibitor 1, homocysteine, stromelysin, paraoxonase, and angiotensin converting enzyme. Studies involving the Korean population, especially those performed by our teams, are also summarized.     

Oligomerization of epidermal growth factor receptors on A431 cells studied by time-resolved fluorescence imaging microscopy. A stereochemical model for tyrosine kinase receptor activation

The aggregation states of the epidermal growth factor receptor (EGFR) on single A431 human epidermoid carcinoma cells were assessed with two new techniques for determining fluorescence resonance energy transfer: donor photobleaching fluorescence resonance energy transfer (pbFRET) microscopy and fluorescence lifetime imaging microscopy (FLIM). Fluorescein-(donor) and rhodamine-(acceptor) labeled EGF were bound to the cells and the extent of oligomerization was monitored by the spatially resolved FRET efficiency as a function of the donor/acceptor ratio and treatment conditions. An average FRET efficiency of 5% was determined after a low temperature (4 degrees C) incubation with the fluorescent EGF analogs for 40 min. A subsequent elevation of the temperature for 5 min caused a substantial increase of the average FRET efficiency to 14% at 20 degrees C and 31% at 37 degrees C. In the context of a two-state (monomer/dimer) model for the EGFR, these FRET efficiencies were consistent with minimal average receptor dimerizations of 13, 36, and 69% at 4, 20, and 37 degrees C, respectively. A431 cells were pretreated with the monoclonal antibody mAb 2E9 that specifically blocks EGF binding to the predominant population of low affinity EGFR (15). The average FRET efficiency increased dramatically to 28% at 4 degrees C, indicative of a minimal receptor dimerization of 65% for the subpopulation of high affinity receptors. These results are in accordance with prior studies indicating that binding of EGF leads to a fast and temperature-dependent microclustering of EGFR, but suggest in addition that the high affinity functional subclass of receptors on quiescent A431 cells are present in a predimerized or oligomerized state. We propose that the transmission of the external ligand-binding signal to the cytoplasmic domain is effected by a concerted relative rotational rearrangement of the monomeric units comprising the dimeric receptor, thereby potentiating a mutual activation of the tyrosine kinase domains.     

Adenosine monophosphate as a mediator of ATP effects at P1 purinoceptors

1. When perfused with a medium containing no added magnesium and 4-aminopyridine (4AP) (50 microM) hippocampal slices generated epileptiform bursts of an interictal nature. We have shown in a previous study that adenosine 5'-triphosphate (ATP) depressed epileptiform activity and that this effect was blocked by the adenosine A1 receptor antagonist cyclopentyltheophylline but was not affected by adenosine deaminase. This implied that ATP might act indirectly at P1 receptors or at a xanthine-sensitive P2 receptor. The aim of the present study was to investigate further the action of ATP on epileptiform activity. 2. ATP can be metabolized by ecto-nucleotidases to adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate (AMP) and adenosine, respectively. Each of these metabolites can activate receptors in its own right: P2 receptors for ADP and P1 receptors for AMP and adenosine. 3. We now show that both AMP and ATP (50 microM) significantly decrease epileptiform discharge rate in a rapid and reversible manner. 5'Adenylic acid deaminase (AMP deaminase, AMPase) (0.2 u ml(-1)), when perfused alone did not significantly alter the discharge rate over the 10 min superfusion period used for drug application. When perfused concurrently with AMP (50 microM), AMP deaminase prevented the depressant effect of AMP on discharge rate. 4. AMP deaminase, at a concentration of 0.2 u ml(-1) which annulled the effect of AMP (50 microM), prevented the inhibitory activity of ATP (50 microM). A higher concentration of ATP (200 microM) depressed the frequency of spontaneous bursts to approximately 30% control and this response was also prevented by AMP deaminase. 5. Superfusion of the slices with 5'-nucleotidase also prevented the inhibitory activity of ATP on epileptiform discharges. 6. The results suggest that AMP mediates the inhibitory effects of ATP on epileptiform activity, a conclusion which can explain the earlier finding that cyclopentyltheophylline but not adenosine deaminase inhibited the effect of ATP. A corollary to this is that, when examining the pharmacology of ATP, care must be taken to inactivate AMP with AMP deaminase, as well as adenosine with adenosine deaminase, before a direct action of ATP on P1 receptors can be postulated. Failure to do so may have led to erroneous conclusions in some previous studies of nucleotide activity on nucleotide receptors.     

Functional defects of Cx26 resulting from a heterozygous missense mutation in a family with dominant deaf-mutism and palmoplantar keratoderma

BACKGROUND: There is controversy about the impact on morbidity from delayed diagnoses of blunt hollow viscus injuries. A recent study suggested that the increased morbidity was primarily from delayed diagnosis of blunt duodenal injury (BDI). STUDY DESIGN: We studied the medical records from a 10-year period from June 1987 to June 1997 examining the data on 22,163 cases of blunt trauma. We assessed the incidence and consequences of delayed diagnoses of BDI, and identified preoperative factors associated with these delayed diagnoses. RESULTS: Thirty-five patients (0.2%) were identified in the retrospective study of the records from 22,163 blunt trauma patients to have sustained BDI. Of these, 25 patients (71%) were male. Ages ranged from 1 to 58 years (mean 18.8 years), and the predominant mechanism was motor vehicle accident in 18 patients (51%). Seven patients (20%) (group I) had a diagnostic delay of > 6 hours; 28 patients (80%) (group II) were diagnosed in < 6 hours. Six of the seven group I patients (86%) were evaluated initially with CT scans, and five (83%) showed findings suggestive of BDI. Among the 28 group II patients, 14 (50%) underwent initial diagnostic peritoneal lavage (DPL), and 14 (50%) had a CT scan. In seven of the group II patients (50%) who were initially evaluated by CT scan, there were findings suggestive of BDI. Diagnostic peritoneal lavage was initially equivocal (red blood cell count=5,000 to 100,000) in the remaining one group I patient compared with three of the group II patients who had DPL. Deterioration found on physical examinations prompted followup CT scans in 6 group I patients (86%), and the scans were diagnostic for BDI in all cases. CONCLUSIONS: Blunt duodenal injury is an uncommon entity. Despite the presence of suggestive CT and DPL findings, the diagnosis was delayed in 20% of the 35 patients whose records were examined in the study; this delayed diagnosis was associated with increased abdominal complications. Patients with persistent abdominal complaints and equivocal CT or DPL findings should undergo laparotomy or repeat CT scan evaluations.