Submicrometer Superconducting YBa2Cu3O6+x Particles Made by a Low-Temperature Synthetic Route.

Evidence suggests that superconducting, orthorhombic YBa(2)Cu(3)O(6+x)+ (x greater, similar 0.5) is always produced by oxidation of the oxygen-deficient, tetragonal form (x less, similar 0.5) of this phase (commonly referred to as 123). A synthetic route whereby solution-derived, carbon-free precursors are decomposed at 650 degrees to 700 degrees C in inert atmosphere to yield tetragonal 123 is now available. Appropriate precursors include hydrated oxides derived from the hydrolysis of organometallic solutions and aqueous solution-derived hyponitrites. Subsequent oxidation of the tetragonal phase at 400 degrees C results in submicrometer particles of orthorhombic 123. Superconductivity (T(c) onset approximately 87 K) has been confirmed in these materials by both Meissner effect and specific-heat measurements.

Amounts of fluoride in self-administered dental products: safety considerations for children.

With the increased use of various fluoride preparations for caries prevention, all dental personnel should know their potential toxicity and the margins of safety associated with their use. An understanding of the body's mechanisms for handling fluoride provides a rational basis for assessing the possible risks of excessive fluoride ingestion. Five to 10 g of sodium fluoride is considered a certainly lethal dose for a 70-kg adult. One quarter of the certainly lethal dose can be ingested without producing serious acute toxicity and is known as the safely tolerated dose. Comparisons of certainly lethal and safely tolerated doses for commonly used fluoride agents and procedures show that they can be applied with little or no risk of adverse acute effects, as long as they are used judiciously. If their use is abused, there is a risk of illness or even death. If amounts of fluoride close to the certainly lethal dose are ingested, the speed of initiating proper treatment is critical for survival. Vomiting should be induced, if it is not spontaneous; fluoride-binding liquids, such as milk or liquid or gel antacids, administered; and the patient taken to the nearest hospital for emergency care. Frequent ingestion of low but excessive quantities of fluoride during the period of tooth formation can lead to dental fluorosis. Particular concern is warranted for the ingestion of fluoride-containing toothpastes by young children and the inappropriate use of dietary fluoride supplements in communities with sufficient fluoride already present in drinking water.(ABSTRACT TRUNCATED AT 250 WORDS)

The future of water fluoridation and other systemic fluorides.

School and community water fluoridation, salt fluoridation, and use of dietary fluoride supplements have abundant scientific support as effective caries-preventive methods. Because caries has declined greatly in many developed countries from use of topical fluorides, the absolute caries reduction will be considerably smaller when systemic fluoride methods are implemented now than it was 20 to 40 years ago. For countries with most of the population living in cities with communal water supplies, community fluoridation is the most logical approach from the standpoints of cost-effectiveness and total caries-preventive impact. In countries with a mostly rural population without central water supplies, salt fluoridation is more practical. Dietary fluoride supplements can be recommended only for regions where neither water fluoridation nor salt fluoridation is possible, or as a temporary measure. Although divergent views exist concerning the relative caries-preventive effects of pre-eruptive and post-eruptive fluoride administration, the effectiveness of systemic fluoride methods for preventing dental caries remains unchallenged. Persuasive scientific and public health arguments exist to justify implementing and sustaining their use. The future of these methods will be influenced by the findings of new clinical and epidemiological research. Social, political, economic, and educational factors will be of equal, if not greater, importance. Perceptions of the current severity of dental caries as a health problem and of risks associated with preventing the problem may affect the future uses of systemic fluorides more than will recommendations of scientists.

Decision-making for national programs of community fluoride use.

Every community, region or country with a high or rising prevalence of dental caries should implement a caries-preventive program that automatically brings the benefits of systemic and topically applied fluoride to the entire population. The fluoridation of community water supplies or salt fulfills the requirements of providing safe, effective protection from dental caries at reasonable cost. The use of dietary fluoride supplements or fluoridated milk does not meet the requirements of a comprehensive national or community program because compliance is poor or only selected age groups are targeted. Water fluoridation is ideal for countries, regions or communities with many central water supplies or where salt production or distribution is not centralized or easy to control. Water fluoridation also has advantages where many areas exist with natural water fluoride concentrations at optimal or greater than optimal concentrations. Salt fluoridation is ideal for countries or regions with few, potable central water supplies in which salt production and distribution are centralized and easily controlled. Concentrations of fluoride for water fluoridation range from 0.5 to 1.2 parts per million (ppm) parts of water depending on climate and dietary practices. The concentration for fluoridation of salt is approximately 200 to 250 mg fluoride per kg of salt, also depending on dietary practices. Properly fluoridated salt should produce levels of urinary fluoride excretion similar to those found in communities with fluoridated water. Benefits of the two methods are similar. Salt fluoridation may be done more cheaply.

Research issues in early childhood caries.

Research is needed to establish what nomenclature and case definition for early childhood caries (ECC) are most relevant to health care professionals and to the public. Profiles or indexes for predicting the prevalence of ECC in communities should be developed on the basis of the socioeconomic factors, immigrant status and ethnic/racial backgrounds of populations. Future research should target risk factors of ECC, particularly prenatal and perinatal histories, nutritional status and microbiologic factors. Determining the relation of malnutrition of infants and young children, low birthweight, complicated pregnancies and traumatic births with the development of enamel linear hypoplasia deserves research attention. Factors that affect how and when infants and young children are colonized by mutans streptococci also need further study. The evaluation of chemotherapeutic preventive agents will likely yield more fruitful interventions for prevention than trying to change behaviors. Research in young children to prevent ECC, however, has particular ethical considerations. Withholding treatments or administering placebos to vulnerable subjects is not acceptable. Consequently, future clinical research likely will determine the relative rather than the absolute effectiveness of preventive regimens; the former requires large sample sizes and may necessitate multi-center studies. Human studies may be hampered by problems of recruitment, compliance and transiency of subjects. Because federal support for research on dental caries has declined in recent years, a special initiative that focuses specifically on ECC may be necessary to obtain adequate funding for research on the disease.

Overview of ethical aspects of clinical studies.

Research in human subjects should be conducted only if the rights and welfare of the participants are protected. Prospective study subjects must be given adequate information about all aspects of a study so that they can make a rationally exercised decision about participation; coercive techniques to solicit participants should not be used. Research in humans may be classified in one of three categories: (1) research on treatment of existing conditions; (2) research on preventive measures; and (3) research other than for treatment or prevention. Different concerns and aspects of informed consent assume particular importance in each category. In research on the treatment of existing conditions, untreated or placebo-treated control groups are rarely justified if the condition is irreversible. In research on preventive methods prospective subjects should be informed of the likelihood of receiving an ineffective treatment, if one or more placebo groups are included. A randomized clinical trial is usually the best design for studies of preventive methods. Non-randomized designs, which are feasible and statistically valid, may be employed in order to avoid depriving some subjects from receiving effective preventive methods. In social or behavioral research, confidentiality of collected information and privacy of the subject are essential considerations.

Evaluation of the effect of interexaminer reliability in clinical trials of dental caries prevention.

Data from a 3-yr clinical trial were used to assess reliability of two dentists who, without standardizing techniques, independently examined 286 continuous participants. Only 13.1 of 128 tooth surfaces (third molars excluded) showed a change in caries status during the trial by one or both examiners' findings. Although there was poor agreement between the examiners (46.5%) on these changes, they agreed very closely on measuring the cariostatic effects in the various treatment groups because the disagreements were random and were similar among groups.

Ethical considerations of study participants in dental caries clinical trials.

During the past 30 years there has been increasing concern for ethical considerations that pertain to the conduct of human biomedical research. Consequently, many national and international medical and dental organizations and agencies have developed regulations, policies or ethical guidelines for the protection of human subjects who take part in clinical investigations. In the United States, more than 500 research institutions have established permanent committees to review research in humans conducted by their institutions. Members of these committees must represent a broad range of backgrounds, interests, and concerns. Prospective study subjects must be able to make an informed decision on whether to participate in any study, without any element of force, deceit, duress, or other form of constraint or coercion. Obtaining informed consent for studies of children, the mentally infirm, and persons with restricted civil freedom presents special problems. Ethical considerations also raise questions on appropriate designs for clinical studies, e.g. use of untreated controls. Dental studies, particularly those testing caries-preventive agents, raise special questions of design, informed consent, ethical procedures and the use of diagnostic radiographs. The director of a clinical study is responsible for the conduct of all personnel connected with the investigation.

Comparison of blind and non-blind assessments of occlusal sealant retention.

A comparison was made of scoring the retention status of BIS-GMA occlusal sealants 5 years after they had been placed, according to a non-blind and blind method of identification of teeth that had been sealed. Subjects were 175 children ages 15--18. One examiner made all the assessments. Retention of sealant was classified as all present, partly missing or all missing. There was 90.5% complete agreement between non-blind and blind examinations in scoring the retention status of 893 occlusal sites. Essentially no difference in agreement was found between sites on maxillary and mandibular teeth nor according to sites in specific teeth. There was only a slight tendency to classify more sites as having sealant present at the non-blind examinations than at the blind examinations, 56.7% and 55.1%, respectively. These findings would seem to indicate that whether examinations are done blindly or non-blindly is of minor importance in making an accurate assessment of sealant retention.

A program self-administered fluorides in a rural school system.

In 1972, a self-administered fluoride program was initiated in Nelson County, VA, a fluoride-deficient area. Children in elementary school (grades K-6) ingest daily a 1-mg fluoride tablet, rinse weekly with 0.2% NaF solution and receive fluoride dentifrice for home use. In 1978, dental examinations of elementary schoolchildren (ages 6-12) who had continuously participated in the program for 1 to 6 years showed a prevalence of 2.70 DMFS, 45% lower than the score of 4.89 DMFS for their cohorts at the baseline. The preventive program inhibited dental caries effectively in all types of surfaces, but the reduction in proximal surfaces of 85% is particularly striking. Findings of high school children (ages 13-17) in 1978, who had not participated in the elementary school program for 1-5 years, showed evidence of strong post-treatment effects. At each succeeding follow-up survey, benefits have continued to improve. For elementary school participants, benefits were 17.7% after 2 years, 35.3% after 4 years and 44.8% after 6 years. Weekly fluoride mouthrinsing and daily ingestion of a fluoride tablet are feasible school-based procedures for the prevention of dental caries. Combined with the use of a fluoride dentifrice at home, these procedures have a pronounced cariostatic effect.

Examiner consistency and group balance at baseline of a caries clinical trial.

Two experienced investigators (G.L. & H.H.) independently examined 629 children in grades 6-9 (ages 10-17 yr) for baseline DMFS data in a clinical trial of a caries preventive. The examiners used the same written and visual (slides) criteria for dental caries diagnosis, but did not standardize or calibrate their methods before or during the survey. Results showed overall mean DMFS scores for Examiners 1 and 2 that were remarkably similar, 8.35 and 8.16, respectively; coefficients of variation were identical, C.V. = 87%. The reliability coefficient for the two sets of data showed that only 4% of the variability in DMFS scores was due to examiner inconsistency and other measurement errors. The findings indicate that, without undergoing clinical calibration, the two experienced examiners attained a high level of agreement in scoring dental caries merely by adhering to clearly defined written and visual criteria. Only the 308 children in the 6th grade (ages 10-14 yr) participated in the study (children in grades 7-9 were a reference population). Participants were randomly assigned to one of two treatment groups. The allocation procedure produced mean DMFS scores for Groups I and II of 7.87 and 6.17 (Examiner 1) and 8.07 and 6.41 (Examiner 2), respectively. The mean scores differed by about 21% (II compared with I) for each examiner. Both differences were clinically and statistically significant (P less than 0.05). Randomized assignment had generated an imbalance of baseline DMF scores by group.

Overview of ethical issues in clinical studies.

Research in human subjects should be conducted only if the rights and welfare of the participants are protected. Prospective study subjects must be given adequate information about all aspects of a study so that they can make a rationally exercised decision about participation; coercive techniques to solicit participants should not be used. Research in humans may be classified in one of three categories: A. Research on treatment of existing conditions; B. Research on preventive measures; and C. Research other than for treatment or prevention. Different concerns and aspects of informed consent assume particular importance in each category. In research on the treatment of existing conditions, untreated or placebo-treated control groups are rarely justified if the condition is irreversible. In research on preventive methods prospective subjects should be informed of the likelihood of receiving an ineffective treatment, if one or more placebo groups are included. A randomized clinical trial is usually the best design for studies of preventive methods. Nonrandomized designs, that are feasible and statistically valid, may be employed in order to avoid depriving some subjects from receiving effective preventive methods. In social or behavioral research, confidentiality of collected information and privacy of the subject are essential considerations.

Indexes for measuring dental fluorosis.

Dental fluorosis, a hypoplasia or hypomineralization of tooth enamel or dentin, ranges in intensity from barely noticeable whitish striations to confluent pitting and staining. Various indexes or classification systems have been used in surveys to measure the presence and severity of enamel fluorosis. Other systems and indexes record all defects in enamel, based on a premise that an etiology for the condition should not be presumed. If all defects are recorded, a retrospective attempt to reconstruct which of them are fluorosis is inappropriate. Dean's classification system has been used most frequently over the years for assessing fluorosis. Therefore, its continued use is sometimes important for historical comparisons. Dean's system, however, has several shortcomings, principally its inability to measure fluorosis in different tooth surfaces. As it has been traditionally used, it also does not permit specifying the cosmetic importance of the most severe fluorosis detected in a dentition. The Tooth Surface Index of Fluorosis (TSIF) eliminates or reduces some of the shortcomings of Dean's method. Use of the TSIF in a survey in Illinois was able to discriminate between the prevalence and severity of fluorosis in four groups of communities with different concentrations of fluoride in their drinking water.

Commentary on and recommendations for the proper uses of fluoride.

Fluorosis has been associated with the fluoride concentration of drinking water, use of dietary fluoride supplements, early use of dentifrices, and prolonged use of infant formula. The literature, however, does not show associations between fluorosis and use of fluoride mouthrinses, professionally applied fluorides, bottled waters, carbonated beverages, and juices. It is unwise to issue laundry lists of items that may be implicated as problem-causing when, in fact, they may not be. Although usually classified without fluorosis, children in Dean's "questionable" category would be classified with the condition if the TFI or TSIF were used. Accordingly, Dean, in 1942, really reported only 52.8 percent of children without fluorosis in Kewanee, a community with 0.9 ppm fluoride in drinking water. Because the morbidity and sequelae of dental caries have declined, undue emphasis has been placed recently on the risks of using fluoride rather than on its profound beneficial effects. Although of paramount importance, conclusions cannot be drawn on whether fluoride protects against, contributes to, or has no effect on bone fractures or is valuable in treating osteoporosis. Careful thought is required before making recommendations that may reduce health benefits because of unfounded concerns about perceived risks. There should be greater regulation of extraneous fluoride sources, rather than reliance on educational efforts or recommendations to eliminate use of highly effective preventive regimens.

The effectiveness of community water fluoridation in the United States.

Grand Rapids, the first city in the world to implement controlled water fluoridation, has served as a model for thousands of other communities. Fluoridation is one of the greatest public health and disease-preventive measures of all time. Its advantages include effectiveness for all, ease of delivery, safety, equity, and low cost. Today, nearly 56 percent of the US population lives in fluoridated communities (62% of those on central water supplies). Previously observed caries reductions of one-half to two-thirds are no longer attainable in the United States because other fluoride methods and products have reduced the caries prevalence in all areas, thus diluting the measurement of effectiveness, and because benefits of fluoridation are dispersed in many ways to persons in nonfluoridated areas. Water fluoridation itself, however, remains as effective as it ever was among groups at high risk to dental caries. Contrary to early beliefs that stressed the importance of preeruptive fluoride exposure, fluoridation also provides an important source of topical fluoride and facilitates remineralization. Although data on effectiveness and safety are compelling, future progress of water fluoridation will be affected by economic, political, and public perception factors.

Effectiveness of school water fluoridation and dietary fluoride supplements in school-aged children.

School water fluoridation and school-based fluoride tablet programs both have been shown in many studies to be effective in preventing dental caries. These studies indicate that school water fluoridation reduces dental decay by approximately 40 percent and school-based fluoride tablet programs by about 30 percent. However, nearly all the studies were done when the prevalence of caries among US schoolchildren was greater than it is today, which makes it difficult to assess their current effectiveness. Data from dental surveys of school-aged children conducted during the past 30 years indicate that overall caries prevalence has declined by more than 75 percent and that of approximal tooth surfaces by more than 90 percent. Recent national data indicate the difference in caries prevalence between children with lifetime residence in either fluoridated or nonfluoridated areas has also diminished, which raises questions about the cost effectiveness of initiating school-based fluoride programs for all areas. There are still groups of children, however, seriously affected by dental caries. It is safe to assume that implementation of school water fluoridation or fluoride tablet programs will result in traditionally reported benefits among these children. Ongoing school-based fluoride programs should not be discontinued until it is known what impact their cessation will have on dental disease.

The role of dietary fluoride supplements in caries prevention.

Nearly all dental researchers and public health authorities agree that fluoride supplements are highly effective in reducing dental caries in primary and permanent teeth, that benefits to all teeth are greater when administration begins at 2 years of age or younger, that both preeruptive and posteruptive exposure is important in imparting cariostatic benefits, that effectiveness is neither enhanced nor reduced by their being combined with vitamins, and that benefits to the offspring of pregnant women who take supplements are uncertain. Several studies show that fluoride supplements delivered in school-based programs effectively reduce dental caries, and benefits are greater to teeth that receive preeruptive exposure in addition to posteruptive exposure. Many parents who, for a variety of reasons, did not administer fluoride supplements at home will enroll their children in school-based fluoride tablet programs. Effectiveness of fluoride supplements today is undoubtedly smaller than observed previously because of dilution and diffusion effects from other fluoride sources; nevertheless, they still have the same potential efficacy. It is apparent that the current ADA dosage schedule is too high and requires modification; however, the availability of this known-to-be-effective regimen should not be eliminated or restricted.

The need for toothpastes with lower than conventional fluoride concentrations for preschool-aged children.

Since 1945, when community water fluoridation was first implemented in the United States, not only has the procedure grown to cover more than half of the US population, but the development and use of other fluoride methods have expanded greatly. A concomitant, dramatic decrease has occurred in the caries prevalence of US school-aged children. Recent studies indicate, however, that the prevalence and, to a lesser extent, the intensity of dental fluorosis have increased in schoolchildren in both fluoridated and fluoride-deficient areas. Several studies show that young children inadvertently ingest sizable proportions of toothpaste during toothbrushing. Although ingestion of fluoride toothpastes by preschool-aged children may not be the major contributor to the increase in fluorosis, the findings of at least four studies suggest that the use of fluoride toothpastes by young children is a risk factor. The direct dose-response relation between effectiveness and fluoride concentration of toothpastes is far from clear-cut and, at best, is weak. Thus, considering today's reduced risk of caries, it is timely to market fluoride toothpastes in the US with 400-500 ppm fluoride for preschool-aged children, who are still at risk for developing fluorosis, as has been done in several other countries. Dental public health authorities must work with toothpaste manufacturers, professional organizations, and regulatory agencies to facilitate the approval and marketing of such pediatric fluoride toothpastes.

A researcher's view.

The Food and Drug Administration (FDA), by ensuring that the health care products used by Americans are both safe and effective, provides an essential regulatory function. With respect to the regulation of dental drug products, this researcher perceives that the FDA has not changed or modified its position on a number of issues to reflect new scientific information. Reasons for this inflexibility include the size and ponderousness of the agency, inadequate staff with dental expertise, and a failure to keep current with new dental research findings. The FDA must solve these problems if it wishes to regulate intelligently. The acceptance and certification programs of the American Dental Association ensure that products offered to the profession and the public that bear its seal of acceptance are safe and effective. The ADA's Council on Dental Therapeutics has a long history of staying current on issues in dental research and public health and regularly seeks consultation from eminently qualified experts. Overall, it has done an excellent job over the years in conducting an important voluntary regulatory program. Both the FDA and the ADA benefit and help protect the oral health of the public.

Prevalence of dental caries in white and black children in Nelson County, Virginia, a rural southern community.

Until a few years ago, the results of most surveys of the prevalence of dental caries among school-age children in the United States, particularly those done in the south, showed that black children had a lower prevalence of dental caries than did white children who lived in the same community.4-6,11,16,19,20-23,25 However, in several recent surveys, the formerly observed race-caries relation has not been detected.2,8,17,18,26 In connection with a study initiated in 1972 in Nelson County, Virginia to determine the effectiveness of a combination of self-applied procedures for the administration of fluoride, baseline data on dental caries experience were collected for 1,374 white and 761 black children attending the County's public schools. The availability of data for large numbers of white and black children prompted a cross-racial comparison of prevalence of dental caries. Findings of the comparative analysis are contained in this report.