Fluoride and the Oral Environment

M. A. R. Buzalaf

• Publisher: S. Karger
• Year: 2011
• ISBN:
  9783805596596
• Topic: Medicine
• Subtopic: Dentistry

This volume brings together current concepts relating to the use of fluoride in dentistry. In contributions written by expert authors, data from this large and complex field have been assembled into a clear sequence and presented in a lucid fashion. The first section deals with the sources of fluoride intake and its metabolism, in order to fully understand fluoride toxicity and the importance of monitoring intake. The second section focuses in more detail on modes of fluoride application and the mechanisms by which this ion interacts with the oral environment to cause a remarkable reduction in dental caries. The role of fluoride in the prevention of dental erosion is also elucidated. The complex mechanisms by which fluoride exerts its effects are described with clarity and the entire text is accompanied by particularly useful illustrations.As a clear up-to-date summary of current thinking in the field, this book will be essential reading for research workers and postgraduate students. Established researchers and teachers in both clinical and basic sciences will find it to be a valuable addition to their libraries, and clinicians will be able to better evaluate the current scientific evidence on the advantages as well as the hazards of fluoride in dentistry.

Fluoride Intake, Metabolism and Toxicity

Buzalaf MAR (ed): Fluoride and the Oral Environment.
Monogr Oral Sci. Basel, Karger, 2011, vol 22, pp 1–19

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Fluoride Intake of Children: Considerations for Dental Caries and Dental Fluorosis

Marília Afonso Rabelo Buzalaf^a · Steven Marc Levy^b

^aDepartment of Biological Sciences, Bauru Dental School, University of São Paulo, Bauru, Brazil; ^bDepartments of Preventive and Community Dentistry and Epidemiology, University of Iowa, Iowa City, Iowa, USA

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Abstract

Caries incidence and prevalence have decreased significantly over the last few decades due to the widespread use of fluoride. However, an increase in the prevalence of dental fluorosis has been reported simultaneously in both fluoridated and non-fluoridated communities. Dental fluorosis occurs due to excessive fluoride intake during the critical period of tooth development. For the permanent maxillary central incisors, the window of maximum susceptibility to the occurrence of fluorosis is the first 3 years of life. Thus, during this time, a close monitoring of fluoride intake must be accomplished in order to avoid dental fluorosis. This review describes the main sources of fluoride intake that have been identified: fluoridated drinking water, fluoride toothpaste, dietary fluoride supplements and infant formulas. Recommendations on how to avoid excessive fluoride intake from these sources are also given.

Copyright © 2011 S. Karger AG, Basel

Fluorides play a key role in the prevention and control of dental caries. In the middle of the previous century, it was generally believed that fluoride had to be incorporated into dental enamel during development to exert its maximum protective effect. It was then considered unavoidable to have a certain prevalence and severity of fluorosis in a population to minimize the prevalence and severity of caries among children. In the 1980s, a paradigm shift regarding the cariostatic mechanisms of fluorides was proposed [1]. This considered that the predominant, if not entire, explanation of how fluorides control caries development is their topical effect on the de- and re-mineralization processes that occur at the interface between the tooth surface and the adjacent dental biofilm. This concept became widely accepted [2-6], and made it possible to obtain very substantial caries protection without significant ingestion of fluorides. With this in mind and being aware of the increase in the prevalence of dental fluorosis in both fluoridated and in non-fluoridated areas [7-9], researchers around the world turned their attention toward controlling the amount of fluoride intake.

The most important risk factor for fluorosis is the total amount of fluoride consumed from all sources during the critical period of tooth development. Thus, it is important not only to know the main sources of fluoride intake, but also the critical periods of formation in which the teeth are more susceptible to the effects of fluoride and the levels of fluoride intake above which dental fluorosis is expected to occur. The purpose of this review is to discuss the levels of fluoride intake that have been accepted as ‘optimal’ and the window of maximum susceptibility to the occurrence of dental fluorosis (focusing on the permanent maxillary central incisors), as well as to summarize the recent literature on risk factors for dental fluorosis, and describe the multiple sources of fluoride intake identified thus far and measures that should be adopted to reduce fluoride intake from these sources. All this information is of fundamental interest to clinicians who deal with children, in order that adequate counseling regarding fluoride intake can be provided to their parents.

‘Optimal’ Fluoride Intake

The widely accepted ‘optimal’ intake of fluoride (between 0.05 and 0.07 mg/kg) has been empirically established [10]. Its origin is attributed to McClure [11], who in the 1940s estimated that the ‘average daily diet’ contained 1.0-1.5 mg fluoride, which would provide about 0.05 mg/kg for children aged 1-12 years. Later on this information was interpreted as a recommendation when Farkas and Farkas [12] cited various sources that suggested 0.06 mg/ kg fluoride was ‘generally regarded as optimum’. In the 1980s, this range of estimates started being used as a recommendation for ‘optimal’ fluoride intake [13]. However, it is not clear if this level of intake is ‘optimal’ for caries prevention, for fluorosis prevention or a combination of both. It should also be noted that some authors regard 0.1 mg/kg per day to be the exposure level above which fluorosis occurs [14], although others have found dental fluorosis with a daily fluoride intake of less than 0.03 mg/ kg per day [15]. It is worth mentioning that other factors may increase the susceptibility of individuals to dental fluorosis, including residence at high altitude [16-24], renal insufficiency [25-28], malnutrition [22, 29] and genetics [22, 30, 31]. Some of these factors can produce enamel changes that resemble dental fluorosis in the absence of significant exposure to fluoride (for details, see Buzalaf and Whitford, this vol., pp. 20-36).

Data from a recent cohort study (Iowa Fluoride Study) on longitudinal fluoride intake for children free of fluorosis in the early-erupting permanent dentition and free of dental caries in both the primary and early-erupting permanent teeth were compiled in an attempt to add scientific evidence to the ‘optimal fluoride intake’ [32]. The estimated mean daily fluoride intake for those children with no caries history and no fluorosis at age 9 years was at or below 0.05 mg/kg during different periods of the first 48 months of life, and this level declined thereafter. Children with caries generally had slightly lower intakes, whereas those with fluorosis had slightly higher intakes. Despite this being the only recent outcome-based assessment of ‘optimal’ fluoride intake, the overlap among caries/fluorosis groups in mean fluoride intake and the high variability in individual fluoride intakes for those with no fluoride or caries history discourage the strict recommendation of an ‘optimal’ fluoride intake. When it is necessary to employ parameters of ‘optimal’ fluoride intake, the range of 0.05-0.07 mg/kg should still be used.

Window of Maximum Susceptibility to the Development of Fluorosis

Considering that fluorotic changes in teeth cannot be reversed but may easily be prevented by controlling fluoride intake during the critical period of tooth formation, the identification of periods during which fluoride intake most strongly results in enamel fluorosis assumes great importance.

For the whole permanent dentition (excluding the third molars), the age for possible fluorosis development has been considered to be the first 6-8 years of life [33, 34]. However, most of the studies concerning the window of maximum susceptibility to dental fluorosis development have focused on the permanent maxillary central incisors, which are of the greatest cosmetic importance. While there is general consensus that the early maturation stage of enamel development is more critical for fluorosis than the secretory stage [15, 35-39], the evidence is not completely conclusive regarding the age at which maxillary central incisors are most susceptible to dental fluorosis. The results of studies focused on this topic are summarized in table 1. They can be divided into two categories: studies involving subjects whose exposure to fluoride started at different ages during tooth formation [40-47] and those involving subjects that had been exposed from birth and then had an abrupt reduction in daily fluoride intake [38, 48-51]. Most of these were cross-sectional, retrospective and focused on just one or two sources of fluoride intake. Only one more recent study used longitudinal data on individual fluoride intake [46, 47]. While one study reported that the first year of life was the most critical period for developing fluorosis in the permanent central maxillary incisors [43], three studies found the first 3 years critical [47-49] and another recognized a later period (between 35 and 42 months) [51] - most of the studies agreed that the first 2 years of life are the most important [40-42, 44, 45] which was also the conclusion of a meta-analysis [52]. However, this meta-analysis acknowledged that the duration of fluoride exposure during amelogenesis, rather than specific risk periods, would seem to explain the development of dental fluorosis in the maxillary permanent central incisors, i.e. long periods of fluoride exposure (>2 out of the first 4 years) led to an odds ratio (OR) of 5.8 (95% CI 2.8-11.9) versus shorter periods of exposure (<2 out of the first 4 years of life). This is in line with data from a more recent longitudinal study which concluded that: (1) although the first 2 years of life were generally found to be more important compared with later years, fluoride intake during each individual year (until the fourth year of life) was associated with fluorosis; (2) subjects with higher levels of fluoride intake (estimate...

Table of contents

• Cover Page
• Front Matter
• Fluoride Intake of Children: Considerations for Dental Caries and Dental Fluorosis
• Fluoride Metabolism
• Contemporary Biological Markers of Exposure to Fluoride
• Historical and Recent Biological Markers of Exposure to Fluoride
• Acute Toxicity of Ingested Fluoride
• Chronic Fluoride Toxicity: Dental Fluorosis
• Mechanisms of Action of Fluoride for Caries Control
• Topical Use of Fluorides for Caries Control
• Systemic Fluoride
• Oral Fluoride Reservoirs and the Prevention of Dental Caries
• Fluoride in Dental Erosion
• Author Index
• Subject Index