Comment on 'Modeling the conductance and DNA blockade of solid-state nanopores'.

Recently, Kowalczyk et al (2011 Nanotechnology 22 315101) introduced a model for calculating the conductance of an hourglass-shaped nanopore, and the conductance change when DNA is introduced into such a pore. Here, we comment on their model in the context of other literature addressing the same general problem. Existing work includes widespread use of an alternative model, contradicts the authors' claim that the conductance change should be expected not to vary with pore size, and has frequently utilised access resistance.

A globally applicable location-specific screening model for assessing the relative risk of pesticide leaching.

A screening model of pesticide leaching loss is described which forms part of a multi-criteria risk-based indicator system called PRoMPT (Pesticide Risk Management and Profiling Tool). The leaching model evaluates pesticide fate in soil for any application rate and time of application (including multiple applications), for any land-based location in the world. It considers a generic evaluative environment with fixed dimensions and soil properties. The soil profile is conceptualised as a number of discrete layers. Equilibrium partitioning between adsorbed and dissolved chemical (based on the organic carbon-water partition coefficient [K(OC)]) is assumed in each time step, in each layer. Non-leaching losses are described using first order kinetics. Drainage is assumed to be uniform throughout the soil profile but varies temporally. The drainage rate, which can be augmented by evapotranspiration-adjusted irrigation, is derived from long-term mean monthly water balance model calculations performed for 30 arc-minute grid cells across the entire ice-free land surface of the earth. Although, such predictions are approximate, they do capture the seasonality and relative magnitude of drainage and allow the model to be applied anywhere, without the need for extensive data compilation. PRoMPT predictions are shown to be consistent with those made by more sophisticated models (PRZM, PELMO and PEARL) for the FOCUS groundwater scenarios.

A New Mechanism for the Regulation of Stomatal Aperture Size in Intact Leaves (Accumulation of Mesophyll-Derived Sucrose in the Guard-Cell Wall of Vicia faba).

At various times after pulse-labeling broad bean (Vicia faba L.) leaflets with 14CO2, whole-leaf pieces and rinsed epidermal peels were harvested and subsequently processed for histochemical analysis. Cells dissected from whole leaf retained apoplastic contents, whereas those from rinsed peels contained only symplastic contents. Sucrose (Suc)-specific radioactivity peaked (111 GBq mol-1) in palisade cells at 20 min. In contrast, the 14C content and Sucspecific radioactivity were very low in guard cells for 20 min, implying little CO2 incorporation; both then peaked at 40 min. The guard-cell apoplast had a high maximum Suc-specific radioactivity (204 GBq mol-1) and a high Suc influx rate (0.05 pmol stoma-1 min-1). These and other comparisons implied the presence of (a) multiple Suc pools in mesophyll cells, (b) a localized mesophyll-apoplast region that exchanges with phloem and stomata, and (c) mesophyll-derived Suc in guard-cell walls sufficient to diminish stomatal opening by approximately 3 [mu]m. Factors expected to enhance Suc accumulation in guard-cell walls are (a) high transpiration rate, which closes stomata, and (b) high apoplastic Suc concentration, which is elevated when mesophyll Suc efflux exceeds translocation. Therefore, multiple physiological factors are integrated in the attenuation of stomatal aperture size by this previously unrecognized mechanism.

Dielectric resonator-based side-access probe for muscle fiber EPR study.

We present a novel dielectric resonator (DR)-based resonant structure that accommodates aqueous sample capillaries in orientations that are either parallel (i.e., side-access) or perpendicular to the direction of an external (Zeeman) magnetic field, B(0). The resonant structure consists of two commercially available X-band DRs that are separated by a Rexolite spacer and resonate in the fundamental TE(01delta) mode. The separator between the DRs is used to tune the resonator to the desired frequency and, by appropriately drilled sample holes, to provide access for longitudinal samples, notably capillaries containing oriented, spin-labeled muscle fibers. In contrast to the topologically similar cylindrical TE(011) cavity, the DR-based structure has distinct microwave properties that favor its use for parallel orientation of lossy aqueous samples. For perpendicular orientation of a dilute (6.25 microM) aqueous solution of IASL spin label, the S/N ratio was at least one order of magnitude better for the side-access DR-based structure than for a standard TE(102) cavity. EPR spectra acquired for maleimide spin-labeled myosin filaments also revealed ca. 10 times better S/N ratio than those obtained with a standard TE(102) cavity. For the side-access DR with sample capillaries oriented either parallel or perpendicular to the external magnetic field, the Q- and filling factors are in good agreement with the theoretical estimates derived from the distribution of magnetic (H(1)) and electric (E(1)) components.

Ferulic acid is esterified to glucuronoarabinoxylans in pineapple cell walls.

The ester-linkage of ferulic acid (mainly E) to polysaccharides in primary cell walls of pineapple fruit (Ananas comosus) (Bromeliaceae) was investigated by treating a cell-wall preparation with 'Driselase' which contains a mixture of endo- and exo-glycanases, but no hydroxycinnamoyl esterase activity. The most abundant feruloyl oligosaccharide released was O-[5-O-(E-feruloyl)-alpha-L-arabinofuranosyl](1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose (FAXX). This indicated that the ferulic acid is ester-linked to glucuronoarabinoxylans in the same way as in the primary walls of grasses and cereals (Poaceae). Glucuronoarabinoxylans are the major non-cellulosic polysaccharides in the pineapple cell walls.

Effectiveness of the boston brace in treatment of large curves in adolescent idiopathic scoliosis.

STUDY DESIGN: This is a retrospective study of 50 patients with adolescent idiopathic scoliosis with curves measuring 35 degrees to 45 degrees who were treated with a Boston brace. OBJECTIVES: The purpose of this study was to determine whether the Boston brace could effectively halt long-term progression in skeletally immature adolescents with idiopathic scoliosis who had a curve between 35 degrees and 45 degrees. SUMMARY OF BACKGROUND DATA: The Boston brace has been shown to be effective in preventing curve progression in adolescent idiopathic scoliosis, but its efficacy in large curves has not been fully studied. METHODS: Fifty adolescents were treated with a Boston brace for idiopathic scoliosis curves of 35-45 degrees (mean, 38.55 degrees ). All were judged to be skeletally immature based on menarcheal status (mean, 2.6 months before menarche), Risser sign (mean, 0.90; range, 0-2), and chronologic age (mean, 13 +/- 1 years). Patients were recalled for long-term follow-up at a mean of 9.7 years (range, 6.23-13.22 years) after brace discontinuation. Three well-matched patient subsets were then identified based on compliance. Group 1 (n = 24) consisted of patients who were compliant with the brace program and wore the brace 18 or more hours per day, Group 2 (n = 14) contained patients who wore the brace 12-18 hours per day, and Group 3 (n = 12) contained patients who wore the brace 0-12 hours per day. RESULTS: There was a significant difference in the amount of initial correction seen in the brace between the groups: 49%, 45%, and 33% curve correction in the brace for Groups 1, 2, and 3, respectively (P < 0.05). At long-term follow-up there was a statistically significant difference between Groups 1, 2, and 3 in the percentage of patients in whom the curve had progressed to more than 45 degrees (P < 0.001), who had more than 5 degrees of curve progression (P < 0. 05), or who had undergone posterior spinal fusion (P < 0.001). CONCLUSIONS: These long-term data confirm that the Boston brace when used 18 or more hours per day is effective in preventing progression of large curves at a mean of 9.8 years after bracing is discontinued.

Results and morbidity in a consecutive series of patients undergoing spinal fusion for neuromuscular scoliosis.

STUDY DESIGN: A retrospective clinical and radiographic review. OBJECTIVES: To provide current data on the results and complications of patients who have undergone spinal fusion for neuromuscular scoliosis at a center with physicians experienced in these types of cases. SUMMARY OF BACKGROUND DATA: The reported complication rate in the management of neuromuscular scoliosis ranges from 44% to 62% in the recent literature. This literature is that of 1991 or earlier reflecting operative techniques of the mid-1980s, and it has been used to argue against the efficacy of neuromuscular spinal fusions. METHODS: A retrospective chart and radiographic review of 50 consecutive spinal fusions for neuromuscular scoliosis was performed at Connecticut Children's Medical Center between January 1990 and January 1994. The three most common diagnoses were spastic quadriplegic cerebral palsy (20 patients), myelomeningocele (13 patients), and muscle disease (8 patients). There were 38 posterior spinal fusions including two kyphectomies and 12 anteroposterior spinal fusions. The Luque-Galveston technique was used in 39 of 50 patients. The average age at surgery was 13 years and 6 months, with an average follow-up of 40 months (minimum, 24 months). RESULTS: Before surgery, the mean major scoliosis measured 72 degrees, with mean best bend or traction view of 35 degrees. At most recent follow-up, the mean scoliosis magnitude was 25 degrees (mean correction, 65%). There were 17 minor complications in 14 patients and three major complications (deep wound infections) in three myelomeningocele patients. Rod breakage was noted in two patients, one of whom had an asymptomatic pseudarthrosis. There were no neurologic complications or deaths, and none of the complications affected the final results. CONCLUSIONS: The data in the current study support the authors' belief that with current surgical techniques and perioperative management in an experienced center, the results for patients undergoing spinal fusion for neuromuscular scoliosis have been improved, and major complications have been minimized.

Regurgitation erosion as a possible cause of tooth wear in ancient British populations.

Clinically, in modern populations, tooth wear can be differentiated into three main types--attrition, abrasion and erosion, acting either separately or together. Anthropologists generally have not recognized erosion as a factor affecting the teeth of past populations. This study compares the patterns of wear known to be associated with erosion in present-day dental patients with those found in some British, pre-Conquest, skeletons. It is concluded that erosion may have been a major factor causing the extensive tooth wear in some 20 of 151 individuals.

Replacement of missing cusps: an in vitro study.

One of the commonest methods of replacing a missing cusp, a pinned amalgam restoration, was compared with three adhesive restorative techniques, two of them with additional pin retention. All the teeth were subjected to occlusal/lateral forces and loaded to fracture in an Instron testing machine. A layered restoration of glass ionomer cement replacing the dentine, and resin composite replacing the enamel, without pins required more force to fracture than any of the other techniques including the pinned amalgam restoration. A composite restoration with dentine bonding agent and additional pin retention was second best and significantly better than the pinned amalgam restoration. A cermet restoration with additional pin retention required slightly less force to fracture than pin-retained amalgam restorations, but not significantly so.

Dental erosion in patients with chronic alcoholism.

Tooth wear attributed to the physical wear of teeth by clenching and grinding (attrition) has been described previously in alcoholic patients. However, the pattern of wear seen in the series of cases reported here is more consistent with chemical damage (erosion) than attrition. A possible mechanism for this process is suggested, and it is further suggested that erosion is likely to play a more important role in the wear of the teeth in chronic alcoholic patients than attrition.

Chronic alcoholism: an important condition in the dentist-patient relationship.

OBJECTIVES: This paper aims to give the dental practitioner an insight into the impact of chronic alcoholism on sufferers. METHODS: A review of the psychiatric and dental literature covering the aetiology, prevalence and complications is presented. CONCLUSIONS: Chronic alcoholism has a number of serious medical and social problems which may affect the provision of dental treatment. It is important for the dental practitioner to be aware of the impact of this condition on patients as he or she may be in an ideal position to stop the alcoholic before a medical consultation has been sought.

Anorexia and bulimia nervosa (the eating disorders): conditions of interest to the dental practitioner.

OBJECTIVES: This paper aims to give the dental practitioner an insight into the impact of the eating disorders on sufferers. METHODS: A review of the psychiatric literature on the diagnosis, aetiology and treatment of these conditions is given. CONCLUSIONS: The dental practitioner is in an ideal position to identify the warning signs of these conditions before they have attracted medical attention.

Oral pH and drinking habit during ingestion of a carbonated drink in a group of adolescents with dental erosion.

OBJECTIVES: To investigate the relationship between dental erosion, oral pH and drinking habit in a group of adolescents. METHODS: Oral pH was measured simultaneously at the surface of four teeth in 11 patients, aged 10-16 years, with erosion and in 10 controls subjects without erosion using antimony electrodes. Measurements were made before, during and after drinking 330 ml of a carbonated drink. The method and timing of drinking the beverage, reported dietary intake of acidic foods and flow rate and buffering capacity of saliva were recorded. RESULTS: The erosion patients reported drinking more carbonated drinks (p<0.01) and drinking directly from a can more frequently than the controls (p<0.05). They also drank twice as quickly (p<0.05). The pH at the buccal surface of a molar remained lower for longer in the erosion patients than in the patients without erosion (p<0.01), whilst the labial surface of the upper central incisor had a longer exposure to low pH in the controls subjects (p<0.05). CONCLUSION: The pattern of oral pH differed between subjects with and without erosion after drinking an acidic beverage. This may be related to observed differences in drinking habit, which could have influenced the pattern of erosion in these subjects.

The role of the esophagus in dental erosion.

OBJECTIVE: The aim of this study was to measure lower esophageal sphincter pressure, sphincter length, and esophageal motility in patients with dental erosion and compare the results with measurements made in patients without gastroesophageal reflux or dental erosion. STUDY DESIGN: Lower esophageal sphincter length and esophageal motility were measured in 39 patients (age range, 15-74 years) with dental erosion through use of static esophageal pressure monitoring; the data were compared with those from 10 control subjects (age range, 26-46 years) with nonparametric statistical tests. RESULTS: Median lower esophageal sphincter pressure was 9 mmHg (range, 0-26 mmHg) in the patients with erosion and 9.5 mmHg (range, 0 -14 mmHg) in the controls; there was no statistically significant difference between the two subject groups. Similarly, there was no statistically significant difference in esophageal length between the subject groups. There was a statistically significant difference between the groups (P =.01) in the measurement of esophageal motility; the median value was 8% (range, 0% to 100%) in the patients with erosion and 0% (range, 0% to 18%) in the controls. CONCLUSIONS: It appears that esophageal motility in patients with dental erosion is more likely to be associated with low amplitude changes than with sphincter pressure alone. Poor esophageal motility may therefore be a risk factor in regurgitation erosion.

Audit in restorative dentistry.

Auditing activity requires patient data to be collected and analysed to allow comparisons to be made and conclusions drawn. Within the General Dental Services the Dental Practice Board regularly collects practitioner specific clinical data and distributes this to allow dentists to compare their own clinical activity with local and national means. In hospital dentistry, a software package has been developed to enable orthodontic audit to be performed in hospital practice. The package is now being piloted in several centres. A similar software package is required for auditing restorative dentistry activity in units where consultant services are provided. Hospital patient administration systems provide demographic data and appointment systems predominantly with little opportunity for patient specific clinical analysis. Carefully designed software will allow appropriate clinical data and analysis. To ensure compliance and accurate recording both by clinical and support staff it is essential that any software system should be easy to use.

A personal, historical view of the management of tooth wear.

The management of caries, periodontal disease and tooth wear has followed similar patterns over the last 30 years but at different rates. The reduced emphasis on surgery in the treatment of periodontal disease has now caught up with minimum interventive treatment of caries. Tooth wear is still, in my opinion, often over-treated and it is time that the management of tooth wear followed the same pattern.

A longitudinal study of the value of a spatial relations test in selecting dental students.

Potential academic ability, practical skill and personality characteristics should all be assessed in selecting dental students. Of these, practical skill commonly receives the least attention, largely because valid and reliable predictive tests are not available. The Spatial Relations Test, which might be used for this purpose, was administered to 1391 applicants to a dental school. There was little correlation between the results of the test and GCE 'A' level grades, showing that the test measured different abilities. However, there was a strong relationship between poor scores on the test and the number of students resigning from the course or failing to graduate on time.

Prevalence of pathological tooth wear in patients with chronic alcoholism.

Although chronic alcoholism is a very common condition, with potentially harmful consequences for the sufferer, there has been little emphasis in the literature on its effects on the teeth. This study of 37 alcoholic patients showed that their teeth had significantly more wear than age and sex matched controls. The tooth wear was most marked in males, and those whose alcohol consumption was continuous rather than in the form of episodic binges. The wear appeared to be erosive in nature, and in 40% of the sample it affected the palatal surfaces of the upper anterior teeth. It is therefore suggested that general dental practitioners should bear in mind the possibility of chronic alcoholism in cases of unexplained dental erosion.

Reinforcement of weakened cusps by adhesive restorative materials: an in-vitro study.

Pairs of extracted premolar teeth were prepared with MOD cavities reducing the lingual cusp at its base to one of five widths: 1.25-2.25 mm. One of each pair was then restored with one of five adhesive restorative techniques and the weakened cusp of both teeth fractured by a force applied to the cusp at an angle of 30 degrees to the long axis of the tooth. At all cusp widths a layered restorative technique in which the cavities were filled to the enamel-dentine junction with glass-ionomer cement and the enamel replaced by composite, reinforced the weakened cusp more than the other restorative materials tested. This combination of materials to reinforce weakened cusps is worth considering as a cost effective alternative to removing the cusp entirely and making a crown or protecting the cusp with a cuspal coverage gold inlay.

Measurement of tooth wear in patients with palatal erosion.

AIM: To develop a reproducible method for the assessment of tooth wear in vivo using a laser profilometer. DESIGN: A controlled study to measure tooth wear. SUBJECTS AND METHODS: Wear was measured over a 6-month period in 13 patients with unexplained palatal dental erosion and compared with a group of 7 controls without any evidence of abnormal wear. MAIN OUTCOME MEASURES: Metal disks were cemented to the tooth surface and impressions taken at 6-month intervals. Wear was estimated by scanning the impressions with a contacting laser profilometer and measuring a change in depth around the disk over a 6-month period using fixed reference points on the metal disks. RESULTS: A statistically significant difference was observed between patients with palatal erosion and the controls. Patients with erosion had a median of 36.5 microns of wear over 6 months (range 17.6-108.2) and the controls had a median of 3.7 microns (range 0.5-15.8). CONCLUSIONS: This paper presents a novel method for measuring erosion using fixed reference points cemented to the palatal surfaces of upper incisor teeth.