A cross-sectional ecological analysis of international and sub-national health inequalities in commercial geospatial resource availability.

BACKGROUND: Commercial geospatial data resources are frequently used to understand healthcare utilisation. Although there is widespread evidence of a digital divide for other digital resources and infra-structure, it is unclear how commercial geospatial data resources are distributed relative to health need. METHODS: To examine the distribution of commercial geospatial data resources relative to health needs, we assembled coverage and quality metrics for commercial geocoding, neighbourhood characterisation, and travel time calculation resources for 183 countries. We developed a country-level, composite index of commercial geospatial data quality/availability and examined its distribution relative to age-standardised all-cause and cause specific (for three main causes of death) mortality using two inequality metrics, the slope index of inequality and relative concentration index. In two sub-national case studies, we also examined geocoding success rates versus area deprivation by district in Eastern Region, Ghana and Lagos State, Nigeria. RESULTS: Internationally, commercial geospatial data resources were inversely related to all-cause mortality. This relationship was more pronounced when examining mortality due to communicable diseases. Commercial geospatial data resources for calculating patient travel times were more equitably distributed relative to health need than resources for characterising neighbourhoods or geocoding patient addresses. Countries such as South Africa have comparatively high commercial geospatial data availability despite high mortality, whilst countries such as South Korea have comparatively low data availability and low mortality. Sub-nationally, evidence was mixed as to whether geocoding success was lowest in more deprived districts. CONCLUSIONS: To our knowledge, this is the first global analysis of commercial geospatial data resources in relation to health outcomes. In countries such as South Africa where there is high mortality but also comparatively rich commercial geospatial data, these data resources are a potential resource for examining healthcare utilisation that requires further evaluation. In countries such as Sierra Leone where there is high mortality but minimal commercial geospatial data, alternative approaches such as open data use are needed in quantifying patient travel times, geocoding patient addresses, and characterising patients' neighbourhoods.

The nexus between improved water supply and water-borne diseases in urban areas in Africa: a scoping review.

Background: The sub-Saharan Africa has the fastest rate of urbanisation in the world. However, infrastructure growth in the region is slower than urbanisation rates, leading to inadequate provision and access to basic services such as piped safe drinking water. Lack of sufficient access to safe water has the potential to increase the burden of waterborne diseases among these urbanising populations. This scoping review assesses how the relationship between waterborne diseases and water sufficiency in Africa has been studied. Methods: In April 2020, we searched the Web of Science, PubMed, Embase and Google Scholar databases for studies of African cities that examined the effect of insufficient piped water supply on selected waterborne disease and syndromes (cholera, typhoid, diarrhea, amoebiasis, dysentery, gastroneteritis, cryptosporidium, cyclosporiasis, giardiasis, rotavirus). Only studies conducted in cities that had more than half a million residents in 2014 were included. Results: A total of 32 studies in 24 cities from 17 countries were included in the study. Most studies used case-control, cross-sectional individual or ecological level study designs. Proportion of the study population with access to piped water was the common water availability metrics measured while amounts consumed per capita or water interruptions were seldom used in assessing sufficient water supply. Diarrhea, cholera and typhoid were the major diseases or syndromes used to understand the association between health and water sufficiency in urban areas. There was weak correlation between the study designs used and the association with health outcomes and water sufficiency metrics. Very few studies looked at change in health outcomes and water sufficiency over time. Conclusion: Surveillance of health outcomes and the trends in piped water quantity and mode of access should be prioritised in urban areas in Africa in order to implement interventions towards reducing the burden associated with waterborne diseases and syndromes.

The use of objective digital matching to achieve an esthetic composite restoration.

OBJECTIVE: To investigate the ability to match composite restorations to teeth using digital imaging and CIE L*a*b* color differences. METHODS: Ten extracted human central incisors were used. Eleven discs of composite of differing shades were produced and mounted on white cardboard to create a customized shade guide (CSG). The CSG was photographed next to each of the ten teeth in a phantom head using a digital SLR camera. The images were analyzed, and color differences (deltaE) between the teeth and the shade discs were calculated using CIE L*a*b* values. Three cavities were then drilled into the labial surface of each tooth. Composite shades with the lowest three deltaE values were then used to restore the cavities. Ten observers evaluated the teeth under a standard D65 light source and recorded the best match. RESULTS: The majority of the observers selected the lowest deltaE in six out of the 10 teeth, and in a further two out of 10 teeth the second lowest deltaE was chosen. CONCLUSION: The lowest deltaE selected by objective color matching was agreed as the best match by observers. The high correlation between digital and visual color matching confirms the ability of digital camera and image analysis software to detect color differences.

Staining of in vivo subsurface degradation in dental composites with silver nitrate.

A previously reported technique for staining areas of degradation in dental composite restorations was evaluated in 51 removed restorations. The staining reagent was silver nitrate, which penetrated the degraded subsurface as ionic silver and was subsequently developed into colored deposits of metallic silver. Several artefacts were recognized that resulted in an apparent image of subsurface stain. Most importantly, the presence of a layer of adsorbed silver on the edge of the specimen exaggerated the extent of staining. In order for the true depth of stain to be determined, thin sections of the materials should first be examined with a stereomicroscope to distinguish any contribution from adsorbed silver on the specimen edge. With this regimen, no stain was present in 41% of the restorations, and in a further 30%, the depth of stain was less than 50 microns. In two composites, the depth of stain was greater than 900 microns, and in a number of specimens, localized stain was found in association with attrition scars. Energy-dispersive x-ray analysis indicated that the amount of silver present in the degraded layers was very small. Overall, the results indicated that the staining technique is useful in the study of composite degradation.

An association between the regular use of 3,4 methylenedioxy-methamphetamine (ecstasy) and excessive wear of the teeth.

AIMS: This study was established to determine if users of ecstasy had greater tooth wear than a comparison group of non-users. DESIGN: The study involved a direct comparison between two groups of young people gathered by a peer information network and divided by the response to the question "Do you take ecstasy?" SETTING: The information network was established at the Maryland Centre in Liverpool (UK). Besides offering advice on drug and sex-related problems this centre distributes free condoms and is therefore visited by many young people who would not consider themselves to have these problems. PARTICIPANTS: There were 30 users and 28 non-users with no significant difference in the gender ratio. Age was not recorded to maintain absolute confidentiality, but all the participants appeared to be of student age. MEASUREMENTS: Tooth wear was measured using the index of Smith & Knight. The social and drug-taking profile of the two groups was ascertained by questionnaire. FINDINGS: It was found that the mean (+/- STD) tooth wear score for the back teeth was 0.96 +/- 0.16 in the users compared with 0.12 +/- 0.08 for the comparison group. These values were significantly different (p < 0.001). The values for the front teeth were not significantly different. Many users were aware of clenching their teeth 12 or even 24 hours after taking the drug. CONCLUSION: Taking ecstasy results in an increased likelihood of tooth wear on the back teeth. This is likely to result from clenching the teeth in the acidic environment caused by carbonated (fizzy) drinks.

Subsurface compression fatigue in seven dental composites.

OBJECTIVES: The purpose of this study was to evaluate subsurface fatigue in seven dental composites. METHODS: Cylindrical test pieces were subjected to 2000 compression cycles with a load of 120 N. The area of stained subsurface was measured, and subsequently, the specimens were examined by scanning electron microscopy. RESULTS: The greatest staining occurred in the composites with large quartz fillers, whereas there was little staining in the microfilled materials. Electron microscopy demonstrated very little evidence of cracks, suggesting that silver nitrate stained a network of crazes and microcracks in the subsurface. The pattern of staining indicated that the microcracks formed within the depth of the subsurface rather than by direct nucleation from the indenter. SIGNIFICANCE: The different patterns of subsurface damage occurring as a result of compression should be considered when studying the wear and degradation of these materials.

The colors of silver with silver nitrate staining in dental materials.

Silver nitrate has been used as a stain to study the permeability, degradation, and marginal integrity of dental composite restorations. The reagent results in various colors in the composite or marginal interface. So that the cause of these colors could be investigated, this study compared the appearances of the stained layers by light and electron microscopy. The results indicated that the colors could be explained by the distribution of silver particles ranging from minute colloidal particles (20 nm) in the composite or dentin, to clusters of large particles (0.1-1 micron) in marginal interfaces. The colors can be explained by the absorption and scattering of light by these particles. At elevated temperatures, fused concretions of silver formed in the composite subsurface, resulting in direct reflection of incident light. The colors which appear with silver nitrate staining may indicate the size and distribution of microporosity in the material.

An investigation into the permeability of composite materials using silver nitrate.

A new effect of silver-nitrate staining on dental composites and unfilled polymers has been observed which may be useful in the study of polymer permeability. After extended storage in silver nitrate, the materials developed a layer of brown stain in the subsurface. The color was thought to be caused by the presence of finely divided silver precipitated in microcavities within the composite. Energy Dispersive Analysis by x-ray confirmed the presence of silver in the stained zone. The width and shade of staining varied in different materials. After 90 days, layers of different shades could be seen within the stained zone. The exact shade of the stain is thought to depend upon the size of the precipitated silver particles, which is directly related to the sizes of the microcavities.

Surface permeability and degradation of dental composites resulting from oral temperature changes.

The surface changes in dental composites caused by thermal cycling and different temperatures were evaluated by use of silver nitrate to stain the surface layers. Rapid temperature change resulted in the formation of layers within the surface which may have resulted from microcracking. Slow rates of change increased the depth and rate of diffusion of silver nitrate. Determination of the temperature changes at the surface of a restoration in the mouth indicated that in vivo temperature change is more likely to increase the depth of diffusion of oral fluids than to cause microcracking of the surface.

The silver sorption layer in dental composites: three year results.

OBJECTIVES: The purpose of this investigation was to observe the behaviour of a recently discovered silver sorption layer in seven dental composites for three years. METHODS: Rectangular block testpieces (3.0 x 2.5 x 2.5 mm) of seven resin composites were fabricated and the resin rich layer removed from one surface by grinding on silica carbide paper. The testpieces were immersed in aqueous AgNO3 (3 mol/l). After 26, 42, 90, 180, 360, 540, 720 and 1085 days, respectively, nine specimens of each material were removed to measure the depth of silver stain in the different composites. RESULTS: The depth of silver stain continued to increase at a rate proportional to (time)0.5. After three years, five homogeneous subsets [HS] were distinguished for the resin rich surface [HS1] Occlusin (stain depth = 45.6 microns); [HS2] Clearfil (117.8 microns), [HS3] Heliomolar (145.6 microns), Concise (148.8 microns), P-30 (168.9 microns); [HS4] Silux (243.3 microns); [HS5] Profile-TLC (446.7 microns). For the ground surface, the materials were in similar subsets but the depth of stain was less. Different coloured layers were seen within the sorption layer in some materials. SIGNIFICANCE: The linear relationship between the depth of stain and (time)0.5 indicate that the mechanism controlling the sorption is Case 1 (Fickian) diffusion. The different depths in the individual materials may indicate differences in the segmental mobility of the polymer chains and free space within the resin phase of the composites. If the silver sorption layer marks the extent of water penetration, then the results show different depth distributions for individual composites.

Measurement and analysis of clinical abrasion--a modified approach.

The abrasion of three posterior composites, after three years' clinical service, was measured by use of a calibrated stone step-wedge. The enamel exposure by each cusp was measured, so that the maximum and overall abrasion could be calculated. The results indicated uneven abrasion around the margin, signifying that local factors, acting by each cusp, had a significant effect on abrasion. This differs from the behavior of the earlier composites, where there was uniform abrasion around the margins. The overall abrasion had a nonparametric distribution, and frequency distribution diagrams proved to be the best way of comparing the performances of the individual materials.

The effect of thermal cycling on the fracture toughness of seven composite restorative materials.

Short-red chevron-notch samples of seven composite materials were thermal-cycled between 0 degrees C and 60 degrees C. The stress intensification factor, KIC, was found for four sample groups subjected to 10(1)-10(4) cycles, respectively. One group of uncycled samples was tested at the commencement of the investigation and another group after exposure to water for the equivalent time taken by 10(4) cycles (42 days). The KIC decreased for all materials, but the decrease after 10(4) cycles was not significantly different from that after storage in water for an equivalent period of time. These results indicate that, in the determination of KIC, the filler/matrix bond is of secondary importance to the presence of fillers. The effects of cyclic temperature changes likely to be encountered in the mouth are not a significant factor in reduction of the fracture strength of composite filling materials.

Effect of surface conditioning on the abrasion rate of dental composites.

Seven dental composites were conditioned prior to wear testing in a three body abrasion machine. The physical conditioning comprised thermal cycling or storage in water for equivalent times. Chemical conditioning was with 75 per cent ethanol or n-heptane. The results indicated that specimens conditioned by 50,000 thermal cycles had an increased surface abrasion rate. With chemical conditioning, 75 per cent ethanol increased the abrasion rate in a number of materials. Both of the latter treatments are clinically unrealistic. As the specimens in other groups were not statistically separable, the results do not support the concept that surface degradation in the mouth is a major variable for three body abrasion.

Wear patterns in two amalgams and three posterior composites after 5 years' clinical service.

OBJECTIVES: The purpose of this research was to evaluate the wear patterns of three posterior composites (Clearfil Posterior. Occlusin and P-30) and two amalgams (New True Dentalloy, Solila Nova) after 5 years' clinical service. METHODS: Marginal wear was measured using the stepwedge technique which determines the maximal marginal wear by any one cusp together with the mean marginal value. The overall maximum depth of wear, occurring at any site on the occlusal surface, was determined using an impression technique with epoxy models. RESULTS: The mean values (+/- standard deviations) for the overall maximum wear were: New True Dentalloy, 203 +/- 98 microns; Solila Nova, 200 +/- 96 microns; Clearfil Posterior, 252 +/- 141 microns; Occlusin, 324 +/- 189 microns; P-30, 380 +/- 273 microns. These values were significantly different (ANOVA F = 2.86 P = 0.05). There was no correlation between the marginal scores and the overall maximum depth of wear (P > 0.05). There was no correlation between the marginal scores and the overall maximum depth of wear (P > 0.05). With some restorations the maximum wear occurred at the margins, marginal ridges or cavity extensions rather than sites of occlusal contact. CONCLUSIONS: After 5 years' service the overall wear of three posterior composites exceeded that of two amalgams; however, for a number of restorations the difference was not significant. Marginal wear values cannot be used to predict the overall maximal depth of wear.

Wear in dentistry--current terminology.

There is some confusion in the dental literature concerning the phenomenon of wear which is usually considered in terms of its clinical manifestations rather than its underlying processes. The parent discipline for the study of these processes is tribology. The terms attrition, abrasion and erosion are common to both dentistry and tribology; however their meanings are different. Even within the various disciplines of dentistry there are differences in the understanding of the same terms. This article relates the dental appreciation of wear to the underlying processes.

Wear: mechanisms, manifestations and measurement. Report of a workshop.

OBJECTIVE: The purpose of this workshop was to bring together a tribologist (T.A.S.), a clinician (L.H.M) and a dental materials scientist (R.W.V) to discuss the fundamental mechanisms of wear and how these relate to the manifestations and measurement of wear in dentistry. Eighty delegates contributed to a valuable discussion led by the workshop chairman (C.H.L.). KEY POINTS: Wear is the net result of a number of fundamental processes: abrasion, adhesive effects, fatigue and corrosive effects which act in different combinations on the various classes of materials. In ceramics, sliding compression and surface corrosion greatly increase wear, whereas the ability to deform either plastically or elastically influences the wear of polymers. The filler particle distribution is a major variable influencing the wear of composites. In the mouth, wear can be considered in terms of its site, timing and mechanism. The latter may involve direct contact between surfaces or result from the action of slurries; both of which are affected by surface corrosion (erosion). Although wear can be categorized at the chairside, its precise measurement involves the use of replica models and surface contouring. Laboratory simulation is useful to study fundamental wear mechanisms; but it is not able to predict clinical wear. CONCLUSIONS: The management of clinical wear requires a proper understanding of the underlying mechanisms. This can only be achieved through close co-operation between all the disciplines which seek to understand and manage wear. The attendance of so many delegates at this workshop indicates the willingness to participate in this process.

Science, myths and lies in dentistry.

Over the past 20 years there has been an explosion in the number of techniques, materials and concepts advocated for clinical dentistry. Unfortunately, this explosion is mild compared with the number of myths, falsehoods and downright lies which have accompanied these ideas. Practitioners are misinformed, and many are justifiably cynical about dental research. This article gives my opinion as to the cause of these myths together with some important ideas to constrain the problem.

Clinical evaluation of three posterior composite and two amalgam restorative materials: 3-year results.

The clinical performance of three posterior composites and two amalgams was evaluated over 3 years. Three hundred and nine composites and 200 amalgams were reviewed at the 3-year recall. The following parameters were assessed: fractures, gingival condition, interproximal contacts, marginal adaptation, staining and colour match. Although there was no significant difference in the overall failure rate between the two types of material, there was a significantly higher incidence of fracture in the amalgam restorations. The amalgam failures were exclusively mechanical, whereas those affecting composites also included failures that were more biological in nature. A significantly higher proportion of the Class II composites failed to achieve an adequate approximal contact, but this was not reflected in a more adverse gingival response. Colour match, surface and marginal stain varied significantly within the composite group and appeared to be material-related. Overall, the materials Occlusion and P-30 were considered to be performing adequately. The clinical handling, colour match and radiopacity of Clearfil Posterior were considered to be unsatisfactory.

The clinical wear of three posterior composites.

The wear of three posterior composites and two amalgams was assessed clinically and measured on replica models. For the composite restorations abrasion was measured as the depth of enamel exposed at the cavity margin. Attrition was measured for all materials as the depth of surface wear determined by laser interfereometry. For the posterior composites the mean abrasion was: Clearfil 79.2 microns, Occlusin 175.9 microns and P-30 96.1 microns. The corresponding values for attrition were: 153.4 microns, 205.9 microns and 255.5 microns, respectively. The attrition of the two amalgams was: New True Dentalloy 120.8 microns, Solila Nova 115.3 microns. Therefore, attrition was greater than abrasion and the attrition of the three composites was greater than that of the two amalgams. Abrasion was affected by local factors, including the marginal contour of the restoration, whereas attrition was largely a function of the properties of the material itself. These findings indicate that composites should not be considered as a direct alternative to amalgam, especially in patients with high occlusal stress.

Three body wear studies of five dental composites preconditioned in food simulating media.

Progressive three body wear up to 30 min for five dental composites (Concise, Heliomolar, Occlusin, P-30, Profile, TPH) stored for 9 months at 37 degrees C in citrate, lactate and PBS buffers, 25 and 75% ethanol media, has been measured using a wear tester. Particle size of the filler and the storage media are found to play dominant roles in determining the extent of wear. Heliomolar, which is a microfilled composite, shows maximum wear whereas wear is least in composites containing filler particles of conventional and hybrid size such as P-30 (> 1 micron). The storage media is found to attack and degrade glass filler particles compared to composites having quartz fillers.