Measurement of Electron-Neutrino Charged-Current Cross Sections on ^{127}I with the COHERENT NaIνE Detector

Using an 185-kg NaI[Tl] array, COHERENT has measured the inclusive electron-neutrino charged-current cross section on ^{127}I with pion decay-at-rest neutrinos produced by the Spallation Neutron Source at Oak Ridge National Laboratory. Iodine is one the heaviest targets for which low-energy (≤50  MeV) inelastic neutrino-nucleus processes have been measured, and this is the first measurement of its inclusive cross section. After a five-year detector exposure, COHERENT reports a flux-averaged cross section for electron neutrinos of 9.2_{-1.8}^{+2.1}×10^{-40}  cm^{2}. This corresponds to a value that is ∼41% lower than predicted using the MARLEY event generator with a measured Gamow-Teller strength distribution. In addition, the observed visible spectrum from charged-current scattering on ^{127}I has been measured between 10 and 55 MeV, and the exclusive zero-neutron and one-or-more-neutron emission cross sections are measured to be 5.2_{-3.1}^{+3.4}×10^{-40} and 2.2_{-0.5}^{+0.4}×10^{-40}  cm^{2}, respectively.

First Probe of Sub-GeV Dark Matter beyond the Cosmological Expectation with the COHERENT CsI Detector at the SNS

The COHERENT Collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220  MeV/c^{2} using a CsI[Na] scintillation detector sensitive to nuclear recoils above 9  keV_{nr}. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei. The cross section for this process is orders of magnitude higher than for other processes historically used for accelerator-based direct-detection searches so that our small, 14.6 kg detector significantly improves on past constraints. At peak sensitivity, we reject the flux consistent with the cosmologically observed dark-matter concentration for all coupling constants α_{D}<0.64, assuming a scalar dark-matter particle. We also calculate the sensitivity of future COHERENT detectors to dark-matter signals which will ambitiously test multiple dark-matter spin scenarios.

Measurement of the Coherent Elastic Neutrino-Nucleus Scattering Cross Section on CsI by COHERENT

We measured the cross section of coherent elastic neutrino-nucleus scattering (CEvNS) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source at Oak Ridge National Laboratory. New data collected before detector decommissioning have more than doubled the dataset since the first observation of CEvNS, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision. With these analysis improvements, the COHERENT Collaboration determined the cross section to be (165_{-25}^{+30})×10^{-40}  cm^{2}, consistent with the standard model, giving the most precise measurement of CEvNS yet. The timing structure of the neutrino beam has been exploited to compare the CEvNS cross section from scattering of different neutrino flavors. This result places leading constraints on neutrino nonstandard interactions while testing lepton flavor universality and measures the weak mixing angle as sin^{2}θ_{W}=0.220_{-0.026}^{+0.028} at Q^{2}≈(50  MeV)^{2}.

First Measurement of Coherent Elastic Neutrino-Nucleus Scattering on Argon

We report the first measurement of coherent elastic neutrino-nucleus scattering (CEvNS) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer CEvNS over the background-only null hypothesis with greater than 3σ significance. The measured cross section, averaged over the incident neutrino flux, is (2.2±0.7)×10^{-39}  cm^{2}-consistent with the standard model prediction. The neutron-number dependence of this result, together with that from our previous measurement on CsI, confirms the existence of the CEvNS process and provides improved constraints on nonstandard neutrino interactions.

An assessment of juvenile Atlantic cod Gadus morhua distribution and growth using diver operated stereo-video surveys

Stereo-video scuba transects were conducted during daylight hours from June to September 2013 within a proposed marine protected area (MPA) in the Firth of Clyde, west of Scotland. More juvenile Atlantic cod Gadus morhua of fork length (LF ) range 6-11 cm were observed in substrata containing mixed gravel, including maerl, than in boulder-cobble substrata with high algal cover, or sand with low density seagrass. Community composition was significantly different between substratum types. A decrease in G. morhua abundance was observed over the period of data collection. Over time, mean and variance in G. morhua LF increased, indicating multiple recruitment events. Protecting mixed gravel substrata could be a beneficial management measure to support the survival and recruitment of juvenile G. morhua; other substrata might be important at night given their diel migratory behaviour. Stereo-video cameras provide a useful non-destructive fisheries-independent method to monitor species abundance and length measurements.

Changes in species diversity and size composition in the Firth of Clyde demersal fish community (1927-2009)

Following the repeal in 1962 of a long-standing ban on trawling, yields of demersal fish from the Firth of Clyde, southwest Scotland, increased to a maximum in 1973 and then declined until the directed fishery effectively ceased in the early 2000s. Since then, the only landings of demersal fish from the Firth have been by-catch in the Norway lobster fishery. We analysed changes in biomass density, species diversity and length structure of the demersal fish community between 1927 and 2009 from scientific trawl surveys, and related these to the fishery harvesting rate. As yields collapsed, the community transformed from a state in which biomass was distributed across numerous species (high species evenness) and large maximum length taxa were common, to one in which 90 per cent of the biomass was vested in one species (whiting), and both large individuals and large maximum length species were rare. Species evenness recovered quickly once the directed fishery ceased, but 10 years later, the community was still deficient in large individuals. The changes partly reflected events at a larger regional scale but were more extreme. The lag in response with respect to fishing has implications for attempts at managing a restoration of the ecosystem.

Contribution of the Cheeks to the Intraoral Manipulation of Food

The role of the teeth in chewing has been studied extensively; however, less attention has been paid to soft tissue function. In this study the process of mixing within the bolus and the contribution of the cheeks to this process were investigated using a test food constructed from two differently colored chewing gums. A cheek guard was placed into either the left the or right buccal sulcus. Eighteen dentate subjects were instructed to chew four samples of gum for 30 strokes, two samples with the cheek guard in place and two without. Upon completion, the gum was removed from the mouth and its length was measured. The bolus was then placed into a plastic bag and flattened. Pairs of flattened samples chewed with and without the cheek guard in place were then assessed by five judges who were asked to identify which of each pair was most mixed. Inhibition of the cheek during chewing resulted in significantly longer samples, which were also less mixed.

Validation of communication between elderly denture wearers and dentists: a questionnaire on satisfaction with complete dentures using semi-structured interviews

OBJECTIVES

To validate a semi-structured interview (SSI) for communication between complete denture wearers and dentists.

DESIGN

A SSI using a questionnaire with eight questions on satisfaction with complete dentures (CD): covering function, aesthetics and comfort. The first seven questions used a five-point Likert scale and the last was dichotomous. Two dentists, carefully trained in the use of the structured questionnaire, administered the SSI.

SETTING

A Greek Department of Prosthetic Dentistry.

SUBJECTS

A consecutive sample of 78 CD wearers took part in the study. All subjects presented with complaints from their dentures.

INTERVENTION

All participants and their dentures underwent clinical examination.

RESULTS

The method showed good reliability, verified by the Cronbach alpha (0.86). Both dentists used the questionnaire produced very similar results. (Wilcoxon test 61-99%). Further, the association of the answers with respect to the five-point Likert scale was very high; all gamma coefficients were statistically significant except for pain and discomfort from the upper CD (CDU).

CONCLUSIONS

This method of communication between patients and dentists is reliable and can be used to give good repeatability for qualitatively assessing satisfaction with CD. It can be valuable for clinical use and for extending the study of denture quality to establish outcome measures based on the subjective criteria of satisfaction.

The development of a method for functional assessment of dentures

AIMS

To design and validate a method of assessing complete dentures from a functional standpoint.

SUBJECTS

A random sample of 40 complete denture wearers took part in the study.

SETTING

A university clinical department of prosthetic dentistry.

INTERVENTION

We undertook a pilot study to refine the protocol and criteria. All participants and their dentures were examined by two authors independently, with no prior knowledge of the patients' complaints.

DESIGN

We defined nine clinical factors of functional quality and applied criteria with binary scoring. We analysed the scores for these factors for inter-rater reliability.

RESULTS

The method proved simple to apply and took less than 5 minutes to complete. The inter-examiner agreement for all factors was 86% to 100% giving Kappa scores of 0.64 to 1.00 (all Good or Very Good).

CONCLUSIONS

This study successfully demonstrates that the technique, which we call the Functional Assessment of Dentures (FAD), can give good inter-examiner reliability. It can therefore be used separately as a routine diagnostic tool and to investigate the relationship between denture qualities and functional 'outcome' such as difficulty eating or dietary selection.

Validation of indices for functional assessment of dentures

AIMS

To validate an assessment of qualities of complete dentures that may relate to functional success.

SUBJECTS

A consecutive sample of 131 complete denture wearers took part in the study.

SETTING

a Greek department of prosthetic dentistry.

INTERVENTION

All participants and their dentures underwent clinical examination.

DESIGN

The Functional Assessment of Dentures (FAD) 10-item criteria' describing clinical factors of denture quality was used. The rationale for selecting these particular criteria was to include a range of clinical factors to produce an overall assessment of complete dentures. The 10-item scale was examined for Internal Consistency and Construct Validity providing a summated rating scale whose total score could be used as an index for the quality of dentures.

RESULTS

Both intra- and inter-examiner agreement for all 10 dichotomous scale criteria were all good or very good; the intra-examiner Kappa values were 0.72 to 0.91 and the inter- examiner values were 0.72 to 0.99. Statistical analysis revealed that a 7-item summated rating scale could be constructed which has marginally better internal consistency (reliability) and Construct Validity with fewer questions.

CONCLUSIONS

The FAD criteria' can be used to give good repeatability. The adjustments made to the original summation scale, if confirmed by new studies, would further increase the practical utility of a FAD index for general dentists. In due course with data from future studies, discrimination on weighting of items will be appropriate to relate the impact of denture quality on quality of life.

The development of a simple objective test of mastication suitable for older people, using chewing gums

AIMS

To develop and assess a simple test for evaluating the mastication of visco-elastic foods and prosthodontic success subsequent to treatment of older people.

METHOD

The weight lost from chewing gum during mastication tests and the saliva secreted is weighed. The percentage of the original gum weight that is chewed out in a defined number of strokes is termed the Masticatory Effectiveness (ME) MATERIAL: Five edentate and three dentate volunteers were selected to provide a range of dental states and age. Four commercially available chewing gums of different origins and perceived hardness were tested, one without sweetener acted as a control for salivary stimulation.

INTERVENTION

Pre-weighed samples of each gum were chewed, each for defined numbers of strokes. The saliva secreted was collected and weighed. The chewed gum was desiccated and the total weight loss of sweeteners chewed out provided an objective measure of chewing performance.

RESULTS

Weight loss showed large differences between gums, between subjects and the number of strokes. ME was significantly correlated with salivary secretion rates for two subjects. The interaction between subject and gum was statistically significant, established by an ANOVA model, the value of which is shown for multivariate studies. Differential success between gums of different thickness may provide evaluation of denture stability.

CONCLUSIONS

Measuring the weight lost from gums during chewing provides a simple test of masticatory effectiveness of visco-elastic foods. This has particular value both in functional assessment of older people and in physiological research.

Maximum bite force after the replacement of complete dentures

OBJECTIVE

The aim of the present study was to investigate whether the maximum bite force (MBF) can be improved by the replacement of complete dentures for elderly people.

DESIGN

Nine edentulous volunteers, mean age 74.2 (+/- 5.5) years and average denture experience 19.4 +/- 19.5 years (1 to 50 years) had replacement dentures made. After a rehearsal session, MBF was recorded with the old dentures, and with the new dentures immediately at insertion, at 3, 8 days, 2-3 weeks, 1, 2, 3 and 6-10 months post insertion (p-i.). MBF was recorded with the central bearing point method using a full-bridge strain gauge load cell. Data were analysed off-line using the mean of two peak readings per patient per session.

RESULTS

The results indicate that MBF tended to be impaired when replacement dentures were first fitted (n.s.). However, this trend reversed during the first month p-i. for patients with a "moderate" lower ridge resorption of Atwood grade 3 or 4 (n = 5). Patients with more severe lower ridge resorption Atwood grade 5 or 6 (n = 4) showed a significantly lower MBF over the entire observation period (p < or = 0.05) and took longer to regain bite strength. Only patients with moderate bone resorption exceeded their pre-insertion level of MBF within the observation period of 6-10 months p-i.

CONCLUSION

The present pilot study suggests that, at least for elderly patients with severe bone resorption, delayed improvement of MBF should be expected with replacement complete dentures.

Bolus dimensions in normal chewing

Samples of 17 different types of chewing gum weighing between 0.3 and 22 g were presented to eight subjects. After chewing the samples for between 20 and 100 strokes the boluses of gum were removed from the mouth and their length was measured. Bolus length increased with weight from 0.3 to 4 g, but remained constant between 4 and 18 g at which point it began to increase once more. The range of sizes associated with this plateau is similar to the range of sizes of natural bites with other foods.

Food choice by older people: the use of semi-structured interviews with open and closed questions

OBJECTIVE

To evaluate difficulty chewing, consequent food choice and impacts using both open and closed questions within a semi-structured interview format.

DESIGN

A cross-sectional study using a semi-structured interview (SSI) with open and closed questions.

SETTING

Independently living people in South-West London interviewed in their own homes.

SUBJECTS

A group of 54, edentate people (mean age 82, R = 60-93 years) were studied.

RESULTS

Most subjects (69%) expressed difficulty eating at least one type of food, half were unwilling to eat the foods they found difficult, others were conscious of cooking longer or cutting smaller in order to manage these foods, although no one accepted that they overcooked food. There were dramatic differences in the number of subjects expressing difficulty to chew various foods when responding to open and closed questions. Roast beef proved a good discriminator in this group of predominantly English subjects. The importance of the questioning process was also shown by the discrepancy of responses between variously prepared apples and the inability of any subjects to bite an unpeeled apple.

CONCLUSIONS

For sensitive appraisal of food choice it is obviously essential to assess relevant foods, for the culture of the group being studied. Open questions provide a way of exploring which are the appropriate foods and food preparation as criteria to assess perceived chewing ability and treatment benefit. The semi-structured interview method is particularly valuable for the study of older people. Closed questions provide different information which is also necessary to secure recall by older people.

The teaching of prosthodontic care for older people: a non-rote philosophy

This essay complements that de Baat et al in the last issue with emphasis on the importance of the variability between individual older people. The consequent need for an open minded approach towards planning Prosthodontics is discussed, based on each patient's motivation for aesthetics, function, comfort and self esteem. Both functional expectations and motivation to learn effective health behaviour vary widely, and evaluation of both is essential for realistic planning because further tooth loss and the need for partial dentures occur so frequently. The consequent variation in plans raises the question--which are the strategic teeth to maintain a stable dental occlusion or a future tooth stabilised denture? For undergraduates this demands a non-rote approach to learning.

The effect of variation of the lingual shape of mandibular complete dentures on lingual resistance to lifting forces

Increasing life expectancy, age related reduction in adaptability and progressive severe mandibular resorption all add to the importance of any factor improving the prosthetic success.

OBJECTIVE

To investigate the effect of two different lingual shapes of lower dentures on patients' ability to resist lifting forces.

DESIGN

Tongue pressures on the lingual surface of complete mandibular experimental dentures were recorded from mid-line, premolar and molar transducers. Two experimental prostheses were fabricated for each subject: one conventionally contoured, the other formed by piezography.

SETTING

A clinical research laboratory.

SUBJECTS

Five experienced complete denture wearers between age 64 and 82 years.

INTERVENTION

Lifting forces were applied at the midline, left and right premolar sites in random order.

MAIN OUTCOME MEASURES

Peak resistance to lifting forces and lingual pressures used during these tests.

RESULTS

Lingual pressures exerted anteriorly were dramatically higher than those on premolar and molar surfaces. Significantly higher pressures were used to resist lifting forces applied to piezographically than conventionally formed contours; correspondingly, significantly higher lifting peak forces were, on average, resisted.

CONCLUSIONS

Providing a lower denture with a piezographically produced lingual surface was shown, in this preliminary study, to enhance tongue retentive ability over a conventional design. It seems reasonable to maximise retentive potential with oblique sublingual polished surfaces and minimise the adaptive demand, particularly for older patients, by using a piezographic technique which "customises" the contour and precludes over-extension.

Simplified method of estimating masticatory performance

Methods which measure masticatory performance include gravimetric, volumetric and direct observation which depend on the weight, volume and size, respectively, of a test food once chewing is completed. Almonds, one of the most common test foods used, have a convenient size and texture. However, due to their oily content and mixing with saliva, washing and drying is required to overcome the clumping of chewed particles. A method has been developed using bagged almonds to exclude saliva and preventing loss of almond particles in the mouth. In addition, microwaving the whole almond reduces the oil content of the almond, reducing clumping, and potentially eliminating the need for washing and drying the particles. A dentate volunteer was asked to chew seven blanched almonds and seven microwaved almonds. The chewed particles were separated using two sieves, weighed and optically scanned to measure the number and area of the particles. Results were obtained both before and after washing and drying of the chewed particles. The overall results for the test of masticatory performance is very similar whether or not a washing stage is used for microwaved almonds. For untreated almonds washing has a more noticeable effect and may still be considered necessary.

Chewing performance and occlusal contact area with the shortened dental arch

The aim of this study was to investigate the effect of the loss of posterior teeth on the effectiveness of mastication. To evaluate this, chewing performance and occlusal contact area were investigated in 10 edentate subjects having implants stabilising a mandibular overdenture. A copy of the original lower denture was made for each subject, with removable teeth, which could be separated to convert a complete dental arch to a shortened dental arch, an extremely shortened dental arch, or a broken dental arch. Both post canine occlusal contact area and chewing performance demonstrated significant differences between the different arches. It was concluded that chewing performance is reduced by removing posterior teeth from implant stabilised mandibular complete dentures.

Clinical and microbiological effects of topical minocycline in the treatment of elderly patients with periodontitis

OBJECTIVE

To evaluate a 2% w/w minocycline gel (Dentomycin) in the treatment of older adults with chronic periodontitis.

DESIGN

Vehicle-controlled, split-mouth

SETTING

Dental Institute, St Bartholomew's and the Royal London School of Medicine and Dentistry.

SUBJECTS

22 adults (mean age 60 years).

INTERVENTIONS

At baseline, patients received scaling and root planing. Test and placebo were applied at contralateral disease sites surrounding 22 test and 22 control teeth at baseline, and at weeks 2 and 4.

MAIN OUTCOME MEASURE

Probing pocket depth, bleeding on probing and supragingival plaque measurements, and microbiological sampling, at one pocket site per tooth were undertaken at baseline, and at weeks 2, 4, 6 and 16.

RESULTS

Microbial counts of Porphyromonas gingivalis, Prevotella intermedia and Eikenella corrodens did not change significantly over 16 weeks. No significant reductions in bleeding on probing and supragingival plaque score occurred with either gel. A larger reduction in mean pocket depth, from baseline to week 16, was found at test (6.50 to 4.95 mm; 24% reduction; P < 0.01) than at control sites (6.41 to 5.53 mm; 14% reduction; P < 0.05).

CONCLUSIONS

Minocycline gel administration is a useful adjunct to scaling and root planing in the treatment of older adults with periodontitis.

Prosthodontic treatment, patient response, and the need for maintenance of complete implant-supported overdentures: an appraisal of 5 years of prospective study

The prosthodontic methods and outcomes of treating 127 patients in nine centres over a period of 5 years is described. The benefits perceived by patients and the changes induced in the denture-bearing tissues and temporomandibular joints are reported. To sustain effective treatment outcomes, the levels of maintenance needed by the overdentures are contrasted for restoration of the edentulous mandibles and maxillae.

A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants

This report presents the results of a 5-year prospective multicenter study including nine centers worldwide. A total of 30 patients received 117 Brånemark implants in the maxillae, and 103 patients received 393 implants in the mandibles. According to the protocol, all integrated maxillary implants were to be loaded; however, only two of four mandibular implants were planned for support of the overdentures, leaving the remaining implants covered by mucosa as backup for possible implant failures. Thirty-five patients (26.3%) who were provided with 127 implants (24.9%) were withdrawn from the study. Six patients treated in the maxilla lost all their implants and resumed wearing complete dentures. The cumulative success rates for implants and for overdentures supported by two implants in the edentulous mandible were 94.5% and 100%, respectively. The corresponding cumulative success rates for implants and for overdentures supported by an optimal number of implants in the maxilla were 72.4% and 77.9%, respectively. Significantly better jawbone characteristics at the time of implant surgery were considered to contribute to the better cumulative success rates in the mandibles. Mean marginal bone loss was 0.8 mm (SD 0.8) and 0.5 mm (SD 0.8) for loaded implants during a 5-year period of time in the maxillae and mandibles, respectively. Measurements of the clinical height of the abutment cylinders indicated a mean recession (0.2 mm) of peri-implant mucosa during the follow-up period in the mandibles. Conversely, hyperplasia was observed in the maxillae.

Natural bites, food consistency and feeding behaviour in man

Complete feeding sequences (bite to terminal swallow) were recorded in 11 individuals (Class I occlusions) feeding on apple, banana and biscuit (hard cookie) to establish whether jaw movements characteristic of the stage I transport, chewing, stage II transport and swallowing processes found in non-human mammals could be identified in man. All participants took large natural bites (known weight) of each food, but seven were supplied standard 6-g pieces of apple. Jaw movements (three axes) were recorded using a locally calibrated Sirognathograph. Discrete stage I transport movements (bite moved from incisors to postcanines), were found in most records, but least frequently for banana. The number of chewing cycles before the first in-sequence swallow increased in the order: banana, ( = ) apple without peel, apple with peel, biscuit. Chewing cycles showed subtle changes in gape profile but significant variation in mediolateral movement cycle to cycle. Morphologically distinct stage II transport cycles could not be identified. Swallows occurred intermittently during chewing (79% of all sequences, n = 146) with cycle durations in excess of 1 s in contrast to the range for chewing (0.6-0.7 s). Almost all sequences ended with a period, clearance, of highly irregular jaw movements often including swallows. Clearance has not been described in other mammals. Food consistency affected feeding behaviour. The "chew/swallow' ratio (total number of chews/total number of swallows) increased with food hardness. The number of chewing cycles before the first in-sequence swallow also increased. Food type significantly affected sequence duration. The duration of clearance was also affected by bite weight and food hardness. It is concluded that initial food consistency determines the number of chewing cycles before the first swallow and overall sequence duration. The change in the pattern of jaw movement in both the vertical and mediolateral directions cycle to cycle suggests continuous sensory modulation of the motor output to the mandibular musculature.

Oral health status of a population of community-dwelling older Canadians

A sample of 170 responsive residents of seniors housing centres in Winnipeg, Canada, were studied, (>65 years, mean 82 years), with the objectives of relating their dental state to their perception of need and uptake of service. Only 6% rated their oral health as poor, 46% reported a dental visit within the previous year and 68% felt they needed dental treatment. A lack of perceived need (88%) was the primary reason why dental care was not sought more frequently. Hygiene practices revealed that only 7% brushed < 1 time/day, 60% never flossed, 14% cleaned their dentures <1 time/day, and 42% slept with their dentures. Dental histories showed that examination (94%), prosthodontic treatment (76%), and restorative services (65%) were the most commonly sought treatments. Perceived dental needs included prosthodontic treatment (39%), periodontal/prophylactic treatment (10%), restorative treatment (9%) and pain relief (9%). Study subjects had 2.8 decayed teeth, a DMFT of 25.1, and a Root Caries Index of 38%. CPITN scores of 3 or 4 in at least one sextant were found in 80% of subjects. Of the 41% edentulous, all wore complete dentures but 15% of complete upper dentures and 51% of complete lower dentures fitted poorly. Of the partial dentures, 20% fitted poorly. Soft tissue anomalies were seen in 67% of subjects and 47% had TMJ anomalies. Overall, 77% of edentulous subjects and all dentate subjects required some dental treatment even though 46% had seen a dentist within the preceding year. It is concluded that appropriate management of such people needs further attention.

Automated optical scanning for rapid sizing of chewed food particles in masticatory tests

Analysis of the reduction in sizes of particles after chewing has been a standard method for assessing masticatory efficiency for over 40 years, but the sizing of particles with sieves is very time consuming. A rapid simple method of measuring chewed almond particle sizes by an optical scanning method has been developed and is described. The aim of this study is to validate the accuracy, repeatability and speed of the application of an optical scanning system in measuring chewed particles. To determine the accuracy, paper circles were measured and compared with the travelling microscope measurements. The effect of orientation of the images were assessed by measuring three irregular shaped pieces of paper and three different sized pieces of chewed almonds. Measurements were taken singly at 18 degrees increments from 0-180 degrees orientations with each piece of paper. To assess the repeatability of measuring chewed particles, the particles from a single masticated almond washed with water and absolute alcohol were spread, separated and measured by the optical scanning system. The samples were then remeasured 10 times. The reproducibility of the method was investigated using three repeated masticatory tests for each subject in a group of 13 young dentate subjects. The speed of spreading the particles and of measurement was assessed. The absolute error range for a mean area of 31 mm2 was 2.85% to 7.32% with a mean of 3.86%. The relative accuracy of measurement was higher for larger particles but in no case was the standard deviation > 0.4 mm2.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of prefabricated bar design on the success of overdentures stabilized by implants

Two groups of patients were provided with implant-stabilized mandibular overdentures supported by straight ovoid prefabricated bars with a resilient joint or parallel-sided bars with a rigid joint. Measurements of plaque index, mucosal cuff health and height, marginal bone height, pathology of the denture-bearing mucosa, and patient satisfaction were correlated with the different bar designs. Ovoid bars with a resilient joint between the denture and the bar have been shown to give a slightly increased incidence of problems associated with the denture-bearing mucosa. Furthermore, the only significant mean increase in recession of the mucosal cuff was found on the distal surfaces of the distal abutments in this group of patients.

Factors related to success and failure rates at 3-year follow-up in a multicenter study of overdentures supported by Brånemark implants

An international prospective study of Brånemark implants retaining overdentures was conducted at nine clinical centers. One hundred thirty-three subjects were recruited in a 12-month period and provided with 510 implants, 117 of which were in maxillae and 393 were in mandibles. This study reports the 3-year follow-up status of 120 overdentures and 444 implants. There were 11 overdenture failures (9.2%). Maxillary overdenture failure rates (27.6%) were nearly nine times greater than mandibular overdenture failure rates (3.3%). Maxillary overdenture treatment was less successful than previously reported fixed implant-supported restorations. However, their mandibular counterparts had success rates slightly higher than those reported for fixed implant-supported restorations. At 3 years, 150 implants remained submerged and 66 implants had been withdrawn because the subjects discontinued study participation. Eleven mandibular and 29 maxillary implants had failed and had been removed from 21 subjects. Logistic regression with forward model selection indicated that one two-way interaction was significantly related to implant failure. At highest risk were the subjects who possessed dental arches with bone quantity E and bone quality 4. Subjects with one implant failure were likely to have more than one failure. The Generalized Estimating Equation was used to adjust for the cluster effect in this population because multiple implants (2 to 6) were placed and evaluated in each of the 133 subjects.

Assessment of chewing efficiency: a comparison of particle size distribution determined using optical scanning and sieving of almonds

Particle sizes obtained with progressive chewing cycles were quantified by use of an optical scanning device and compared with the sieving method. The aim of this study was to validate the optical method by comparison with sieving using a natural test food, almond. Masticatory efficiency was assessed in six dentate subjects. The almonds were chewed for 1, 4, 8, 16 and 32 chewing strokes. Each experiment was replicated. The chewed material was sieved through a 1 mm aperture sieve on a Büchner funnel and dried after washing with water and 100% alcohol. The dried particles were weighed and scanned by an optical scanning device for number and size. The same samples were sieved and weighed with a conventional sieve method. The results of both methods were described by particle size distributions based on the volume of particles. The results derived from the optical scanning and sieving showed similarity. It can be concluded that the optical method is simple to use, faster than sieving and needs little skill in the use of equipment. The comparison of the results validates both methods.

The effect of age on the recognition thresholds of three sweeteners: sucrose, saccharin and aspartame

It is believed that people's sensitivity to taste declines with age but the evidence is inconclusive. This study was designed to test the hypothesis that taste recognition thresholds (TRTs) for sweetness are higher in older than in younger individuals, using groups of 16 younger subjects (18-30) and 16 older subjects (60-85). Three test substances were used: sucrose, aspartame and saccharin. A questionnaire recorded variables which might have affected TRTs, but data failed to show any trend that might have biased the principle variate-age. There was a significant alteration with age of recognition thresholds, at least for sucrose and saccharin. The differences between the groups for the three sweeteners were due to the fact that all the very sensitive subjects were young. None of the older subjects had particularly poor discrimination: all but one had TRTs within the range of younger subjects. Although there are age-related taste changes, they are much less dramatic than commonly occurs with other senses, such as sight and hearing. The findings of this study have implications for institutional catering and the dietary management of older people using non-sugar sweeteners.

Recording mandibular movement: technical and clinical limitations of the Sirognathograph

It is essential to know the limitations of any equipment used for research or clinical purposes. Clinical electronic equipment is commonly sold for "black box" use without specification of artifacts. This study tested the technical and clinical limitations of the Sirognathograph, which is a device used for recording mandibular movement. From a technical point of view, the Sirognathograph's slow sampling speed and sample artifacts have been shown to be the system's main limitations; however, it was possible to eliminate sampling artifacts by using a customized pulse generator and software for controlled data acquisition. Clinically, the Sirognathograph appears to have some inherent limitations in its accuracy. The effect of cranial movements during mastication can cause a baseline drift with consequent errors in the recording of mandibular position. This problem was controlled in this study by using a headband to stabilize the cranial movements during mastication. Also, the spatial relationships between the aerial and both the cranial base and the magnet were found to be critical for repeatability of the recordings.

Anterior digastric muscle responses to sudden unloading of the mandibular elevator muscles in younger and older adults

The digastric motor responses in the unloading reflex were investigated in a sample of 10 younger and eight older dentate subjects. The occurrence of the pre-collapse digastric activity (PDA) and the reflex events (burst of activity) following the mandibular unloading (DB) were studied separately. PDA was nearly consistent in half of the subjects of both groups. DB was clearly identified in 60% of the younger subjects, but in 54.2% of the older subjects. The mean latency of DB found in the younger subjects was 32.4 +/- 9.5 ms but 34.5 +/- 8.8 ms in the older subjects. For the latencies found we can infer that they are related to polysynaptic pathways. Also a slight tendency for decreased frequency of occurrence and increased latencies of DB is observed in the older age group.

Contribution of periodontal receptors and food qualities to masseter muscle inhibition in man

Previous studies of human muscle inhibition during chewing have shown that many factors contribute to the incidence and intensity of this reflex but few studies have been in a physiological context. During the first crushing cycle of brittle foods ipsilateral masseter muscle EMG, mandibular movement and vibration were recorded simultaneously in four healthy dentate subjects. Experiments were repeated before and during anaesthesia of the cheek teeth on the chewing side. The results suggest that vibration seems to be the most important factor in muscle inhibition during food crushing; conversely periodontal sensation, mandibular closing movement and the preload by the muscle at the onset of food fracture play a minor role.

A microbiological study of primary root-caries lesions with different treatment needs

Samples of altered or carious dentin for microbiological culture were obtained from 301 primary root-caries lesions in 59 patients by means of a standardized sampling procedure. This involved the cleansing of each root surface of extraneous supragingival plaque by means of a hand-held toothbrush and distilled water and the collection of the sample with a sterile dental excavator passed through the entire vertical dimension of each lesion. The total number of colony-forming units (cfu) in each sample and the numbers of mutans streptococci (primarily Streptococcus mutans), lactobacilli, yeasts, and Gram-positive pleomorphic rods (GPPR) were determined. Individual bacterial counts were expressed as log10 (cfu per sample), as a percentage of the total number of bacteria per sample, and as a frequency of isolation from lesions with different clinical diagnostic criteria. Clinical measurements of each lesion were made for color, texture, position relative to the gingival margin, and treatment need. Lesions classified as soft yielded significantly more bacteria, mutans streptococci, lactobacilli, and GPPR than leathery lesions, which yielded more bacteria than hard lesions. Lesions were classified into 5 treatment categories: soft and restore, leathery and restore, leathery and debride of caries; leathery and treat therapeutically; and hard no treatment. The total numbers of bacteria, mutans streptococci, lactobacilli, GPPR, and yeasts decreased significantly with decreasing treatment need. The frequency of isolation of mutans streptococci, lactobacilli, and yeasts was significantly greater from lesions requiring restoration and from lesions situated within 1 mm of the gingival margin. We suggest that the majority of root caries is initiated adjacent to the gingival margin.

A comparison between data analysis methods concerning particle size distributions obtained by mastication in man

Three mixtures of chewed food particles (coarse, medium and fine) were quantified by measuring the particle sizes with an optical scanning device. The particle sizes were described by three different particle-size distributions: a cumulative volume, a volume and a number distribution. The median particle size was determined from each of the distribution functions. Suitability for characterizing a mixture of chewed food particles was tested, showing that the median particle size as obtained from a cumulative volume (or weight) distribution should be preferred. It was shown to be the most sensitive measure for characterizing mixtures of chewed food.

A comparison between sieving and optical scanning for the determination of particle size distributions obtained by mastication in man

Mixtures of particles of different sizes, as obtained after chewing, were analysed. Coarse, medium and fine mixtures of particles of an artificial (Optosil) test food were used. Mixtures of Optosil particles of known form and size (half-cubes) were used to validate the analytical methods. The results of both methods were described by particle size distributions based on the volume of the particles. Complete agreement between methods was found for the mixtures of half-cubes. In order to determine the median particle size by volume from the results of optical scanning an assumption on the form of the chewed particles had to be made. Using the assumption that, on average, the particles resemble spheres a slight overestimate of the median particle size was obtained for scanning as compared to sieving. It can be concluded that, although different aspects of the fragmented particles are measured, sieving and optical scanning are both adequate methods for quantifying mixtures of chewed food particles and yield similar results for the degree of particle size reduction.

Digastric muscle response as a function of knowledge of the task to be performed

Whether the motor programme executed by the digastric muscles during a forceful bite is modified according to a subject's expectation that the resistance between the teeth will change was investigated. There were two experimental conditions: (1) tracking a ramp (drawn on an oscilloscope screen) by biting (isometrically) on a force transducer and holding it at 120 N, and (2) tracking the same ramp with a sudden unloading at 100 N. There were two groups of experiments: (1) control experiments in which subjects underwent a sudden and unexpected unloading of the jaw, and (2) experiments in which subjects were previously informed whether or not there was to be an unloading. In all experiments the subjects co-contracted their digastric muscles during the bite as compared to the state at rest. The subjects' responses fell into the three different types: (i) those who varied the level of tonic digastric activity only as a function of the experimental condition, (ii) those who co-contracted the digastric muscles at the same time as the masseter muscles, and (iii) those who changed the contraction pattern of the digastric muscles as a function of the experimental condition. If modulation of the digastric muscles occurred this is a 'feedforward' strategy mainly based on immediate past performance.

Assessment of the clinical status of primary root carious lesions using an enzymic assay

The microflora of root carious lesions (n = 151) and sound root surfaces (n = 30) in 22 institutionalized, older patients was investigated using a standardized method of sampling. Material was removed using a sterile excavator and the numbers of bacteria in each sample were determined using conventional culturing techniques and by rapid (2 h) fluorogenic enzyme assay. Correlation between bacterial counts and enzyme assay result was 0.873 (p < 0.001). The numbers of bacteria and fluorogenic enzyme assay values were significantly (p < 0.001) greater from soft lesions than from leathery lesions while hard lesions and sound root surfaces had significantly (p < 0.001) lower values than the other lesion types and were not different from each other. A similar trend was apparent when these values were correlated with treatment needs. The fluorogenic enzyme assay may provide a rapid, objective measure of root caries severity which might be used in the monitoring and comparison of treatment protocols.

Bond strength of fiber-reinforced composite resin restorations

Severe tooth wear is common in older dentate individuals, with one treatment option being composite resin restorations reinforced with a suitable matrix. This study evaluated the use of high modulus polyethylene (Celanese) fibers as a reinforcing matrix for composite resin. Human mandibular incisor teeth were sectioned to simulate severe tooth wear. Sectioned surfaces were measured, the teeth paired and assigned to control or test sample groups, and further assigned to be tested with a labial or lingual shearing force. A phosphorylated dentin bonding adhesive was applied to the abraded dentin surface. Labial and lingual intra-enamel bevel preparations were cut on each specimen. A piece of Celanese fabric was bonded onto the acid-etched labial and lingual bevels of the test specimens using an enamel bonding agent. Class IV composite resin restorations were then placed onto the test and control specimens. Following water storage, the specimens were subjected to shearing forces. Bond strengths for test specimens were significantly greater (p < 0.03) than the controls. Specimens with a labially applied force also had significantly higher bond strengths (p < 0.001). SEM analysis revealed adhesive bond failures over dentin surfaces, with cohesive bond failures within the composite resin. Celanese fibers maintained the restorations on the teeth, although adhesive failures were seen between the fibers and enamel bonding agent.

Salivary levels of mutans streptococci, lactobacilli, yeasts, and root caries prevalence in non-institutionalized elderly dental patients

Root caries prevalence was recorded for a consecutive sample of dental patients (n = 146), aged over 55 yr and with at least 12 natural teeth. The mean root DFS score of the males (n = 49) was 6.34 +/- 4.55 and for the females (n = 97) 3.76 +/- 3.31 (P less than 0.001). The salivary levels of mutans streptococci, lactobacilli, and yeasts were determined in addition to salivary flow rate and buffering capacity. Subjects with greater than 1 root DFS had significantly higher salivary levels of mutans streptococci, lactobacilli, and yeasts. They also had fewer teeth and more exposed root surfaces. In step-wise multivariate analyses the factors significantly related to the root DFS score were the number of exposed root surfaces, number of teeth, sex and salivary yeast levels (R2 = 0.41). In the multivariate analyses salivary levels of mutans streptococci were not significantly related to any clinical measurement of root caries experience due to the greater strength of association between the root DFS score and salivary levels of yeasts. Subjects prescribed medicines with a reported xerostomic effect had significantly fewer active root lesions than those not prescribed such medicines and salivary levels of all microorganisms studied were significantly elevated in subjects prescribed medications containing sucrose.

Swallow thresholds using dentures made on different types of articulator

The purpose of this study was to determine whether edentate subjects achieved different performance when using dentures constructed on different articulators. A cross-over experimental design was employed to evaluate these swallow thresholds using complete dentures constructed on the hinge and free plane articulators. Seven subjects completed the study. Swallow threshold tests were performed 3 months after the insertion of dentures. The overall particle size distribution achieved with the dentures constructed on free plane articulators was significantly better at the end of the 3-month period (P less than 0.01 to P less than 0.0001), but significantly more strokes were used to achieve this success rate (P less than 0.04). A questionnaire revealed that the subjects had a preference for the denture constructed on the free plane articulator. It is concluded that patients performed better with dentures constructed on the free plane articulator.

Case report: the management of severe tooth wear with palatal resin bonded cast restorations combined with removable partial dentures

The restoration of advanced tooth wear can present considerable problems. Conventional fixed prosthodontic treatment can be destructive to the already compromised dental tissues, time consuming and therefore costly. With recent advances in resin bonded technology, this may now be considered an option for definitive treatment in such cases. This case illustrates the use of palatal resin retained cast metal veneers. These veneers restored the worn palatal surfaces of the anterior maxillary teeth, protected them from further wear and controlled thermal sensitivity. They also provided support for a conventional maxillary partial denture.

Root caries in older people attending a general dental practice in East Sussex

With increasing numbers of older people retaining their natural dentitions, dentists are becoming increasingly aware of the problem of dental caries occurring on exposed root surfaces--root caries. This study reports the prevalence of root caries in a selected older population, living in the community and attending a general dental practice in Bexhill, East Sussex. A total of 146 non-institutionalised people, aged at least 55 years with at least 12 teeth, were examined. Most of the subjects (88.4%) had evidence of root caries, males and denture wearers having more lesions than females and non-denture wearers, respectively. Active coronal caries was present in only 11.6% of the subjects, whereas active (soft or leathery) root caries lesions were present in 31.5% of the subjects. The teeth and surfaces most commonly affected by root caries were found to be similar to those seen in previous epidemiological surveys. The majority of active root caries lesions were within 1 mm of the gingival margin, while inactive lesions tended to be greater than or equal to 1 mm from the gingival margin. Colour of root caries lesions was not diagnostic of caries activity. A more detailed method of recording root caries lesions is also described.

Associations between salivary levels of mutans streptococci, lactobacilli, yeasts and black-pigmented Bacteroides spp. and dental variables in elderly dental patients

Multivariate step-wise regression analyses demonstrated that in a population of 146 elderly dental patients (mean age 69.8 yr) the salivary level of mutans streptococci was unrelated to the root DFS score, unlike the levels of lactobacilli and yeasts. Mutans streptococci were related to the wearing of partial dentures and the number of snacks eaten per day, while salivary lactobacillus levels were also related to the number of snacks eaten per day and to denture wearing, and negatively related to saliva buffering. Salivary yeast levels were also related to the wearing of partial dentures and the number of snacks eaten per day, and negatively related to salivary neuraminidase activity. The R2 values ranged from 0.21 to 0.28. Salivary level of black-pigmented Bacteroides spp. were related to maximum CPITN score, mean bleeding index and salivary trypsin-like activity (R2 was 0.08).