There are a number of effective strategies available to prevent dental caries, which include the use of fluorides including community fluoridation schemes (water, salt and milk), fluoridated toothpastes, and other fluoride delivery systems, such as tablets, drops, and varnishes. The US Surgeon General has reported that community water fluoridation is an effective, safe, and ideal public health activity that benefits individuals of all ages across all socioeconomic strata [1
] Indeed, the Centers for Disease Control and Prevention has listed community water fluoridation as one of the top ten public health achievements in the past century [2
Changes in the appearance of tooth enamel can occur if ingestion of excessive
amounts of fluoride occurs during critical time periods during tooth development [3
]. These changes can result in dental fluorosis, which in its mildest forms presents as areas of white striations following the developmental lines of enamel [5
]. The severity of fluorosis observed is multifactorial but is strongly linked with both the amount and timing of fluoride exposure [3
]. Figure provides an example of mild fluorosis. High fluoride exposure, such as seen in areas with naturally occurring water fluoridation in excess of 1
ppm, may result in more severe presentations of fluorosis that include enamel pitting, brown discoloration and ultimately enamel loss [5
] (Figure ).
Example of mild fluorosis of the type seen in lifetime residents of optimally fluoridated drinking water communities.
More severe dental fluorosis of the type seen in individuals living in areas with naturally high fluoride content in their drinking water.
There is a need to measure the prevalence and severity of fluorosis within populations for surveillance purposes. For example in England there is a legislative obligation on those health authorities who have added fluoride to water systems to measure and report dental fluorosis prevalence. Other countries, such as the United States, have included assessments of dental fluorosis within population surveys, e.g. the National Health and Nutrition Examination Survey (NHANES) [6
] and the National Survey of Oral Health in U.S. School Children (1986-1987) [8
]. These assessments have been traditionally undertaken by clinical examiners who assign scores based upon a clinical index. Examples of indices used include Dean’s Index [9
], the Fluorosis Risk Index (FR) [10
], Thylstrup and Fejerskov Index (TF) [5
] and the Tooth Surface Index of Fluorosis (TSIF) [11
]. In the US, the Dean’s Index is predominant and has been used in NHANES for national population surveillance efforts while in Europe the TF Index is well accepted.
While these indices have been used extensively their deployment is not without criticism. Like many clinical indices, they are highly subjective and prone to bias [12
], for example knowledge of water fluoridation status by the examiner, especially in countries where such activities are uncommon. In England, the York Centre for Reviews and Dissemination (CRD) report on the evidence supporting water fluoridation cited lack of examiner blinding as a particular weakness and potential source of significant examiner bias that could potentially lead to over estimation of dental fluorosis [13
]. While it may be possible to reduce this effect by moving subjects from one location to a central examining centre, this does have obvious logistical, safety and consent issues [16
The most common means of mitigating examiner bias is via the use of photographs. These can be taken during examinations and graded remotely, thus enabling the examiners to be blinded [17
]. However, there is a lack of research looking at how such images can be standardized, their quality optimized (especially with regard to specular reflections caused by ring flashes) and their analysis recorded [18
]. Collecting images as part of epidemiological studies has additional benefits including archiving, the ability to assess longitudinal changes, scoring by multiple examiners, remote examiner scoring and producing training sets for examiner calibration. A visual record of the study can also be of help for research governance reasons.
However, while photographic methods serve to address the blinding issue there are numerous other sources of potential bias in relation to the use of such indices. These include the assessment of dental fluorosis against other enamel defects, especially in populations with low dental fluorosis prevalence or severity, and the application of personal thresholds and examiner drift [17
]. Additionally, training examiners is a complex and costly procedure and there is an acute lack of appropriately trained individuals. Therefore, there is also a need to consider if the assessment of dental fluorosis could be undertaken using an automated grading system [18
The use of quantitative light induced fluorescence (QLF) in such a system was described by Pretty et al. in 2006 [18
] when a camera based system was employed on 26 subjects to determine if both the hardware and software would enable automated quantification. Early results were encouraging. The principles of QLF are described elsewhere in detail. Briefly, there is a loss of fluorescence intensity in areas of enamel hypomineralisation, which can be measured compared to sound areas and expressed as ΔF (% fluorescence loss), the area of the effected enamel measured in mm2
and a composite value Δ Q reported [20
The system was then deployed in a large-scale epidemiological study of some 600 children in Thailand, followed by 2000 children in the UK. Data from these studies suggested that the system was able to detect a dose–response relationship between dental fluorosis and fluoride exposure and, in the UK study, between communities with and without optimally fluoridated drinking water. In these studies a single QLF camera was employed and white light images were taken with a standard 35
mm digital SLR (Single Lens Reflex).
Such photographs are difficult to standardize in an epidemiological setting and are also prone to the effects of specular reflection. This is often a confounding factor in the assessment of such images. Polarized white light (PWL) images have no specular reflection and have been employed in dental research to examine the impact of tooth bleaching therapies [25
]. It was therefore proposed to produce a new imaging system that combined fluorescent imaging with PWL images. This new system should be able to take the images simultaneously, or at least within seconds of each other, record them in a lossless format and be simple and rapid to employ within an epidemiological survey. The resultant white light images should be simple to score and the fluorescent images should provide sufficient discrimination between sound and fluorotic areas for an automated software system. The software should produce metrics that are strongly correlated with the clinical scores.
The aim of this current study is to report on the effectiveness of this new dual imaging system (QLF
PWL) and the reliability of the remotely graded dental fluorosis images versus the dental fluorosis scores obtained from clinical examination.