Dental Fluorosis

Etiology

Dental fluorosis is caused by the excessive ingestion of fluoride during tooth development. The severity of dental fluorosis is dose-dependent and influenced by the extent of time an individual is exposed to excessive fluoride within the critical window of development and genetic factors.[8] Excessive plasma fluoride is believed to interfere with the removal of amelogenins during enamel maturation leading to the formation of hypomineralized enamel.[9]

The critical window for dental fluorosis to develop in response to excessive fluoride intake ranges from birth to eight years of age.[6] Thus, excessive consumption of fluoride outside of amelogenesis will not result in dental fluorosis. The visually detectable enamel changes characteristic of dental fluorosis are associated with water fluoride levels in excess of 1.5 ppm.[10] 

Artificially fluoridated water has a target fluoride concentration of 1 ppm, which is thought to optimize the anti-cariogenic properties of fluoride while minimizing the risk of adverse effects, including dental fluorosis.[11]

Epidemiology

The worldwide prevalence of dental fluorosis is increasing.[12] In the US, 23% of the total population is affected. In adolescents, this increases to 41%, a figure which has almost doubled since 1987.[13] As a result of the significant increase in the prevalence of mild to moderate cases of dental fluorosis, the US Department of Health has reduced the target concentration in fluoridated water from 1ppm to 0.7 ppm.

 It is important to note that although mild-moderate dental fluorosis is relatively common, clinically severe forms are rare in the US and Europe.[13][14] Dental fluorosis occurs equally in both genders and can occur in both primary and permanent dentition.[15][16]

Pathophysiology

Ameloblasts are responsible for enamel synthesis during amelogenesis, a tightly regulated process involving multiple phases in which hydroxyapatite crystals are produced.[17] The definitive pathophysiology of dental fluorosis is not fully understood.[18] 

Exposure to high plasma fluoride levels during amelogenesis results in the formation of porous hypomineralized enamel.[10] In severe cases, the porosity can extend toward the dentino-enamel junction. The early maturation phase is the most vulnerable stage of amelogenesis to chronically elevated plasma fluoride levels.[17] 

During the maturation phase, enamel matrix proteins, including amelogenin, are hydrolyzed by proteinases. This process is delayed in fluorosed enamel. Fluoride has also been shown to induce apoptosis in ameloblasts during enamel maturation which is thought to contribute to the enamel pitting found in severe cases of dental fluorosis.

History and Physical

Patients with dental fluorosis will have a history of chronic excessive fluoride ingestion within the critical window of amelogenesis. This is between birth and eight years of age.[6] Clinically the severity of dental fluorosis ranges from virtually undetectable surface-level enamel changes comprising of minute white opaque flecks, which the patient may be unaware of, to pitted enamel which becomes stained dark yellow-brown. Most patients will have aesthetic concerns bringing attention to the discoloration of their teeth.[19] 

In mild and moderate cases, this is in the form of light enamel opacities.[20] In severe cases of dental fluorosis, they may also be concerned about structurally compromised enamel which becomes hypoplastic, a yellow-brown discoloration of the teeth, and occasionally dentine hypersensitivity.[19] Dental fluorosis has a symmetrical distribution, and the severity to which individual teeth are affected within the dentition can vary.[6]

Evaluation

A diagnosis of dental fluorosis is contingent on a positive fluoride history within the critical window of tooth development and a visual intraoral examination.[21] The utilization of effective lighting and a dental mirror is essential. Magnification can be a useful adjunct, especially in subtle cases of dental fluorosis. In cases where the surface enamel is pitted, a dental probe can be used carefully so as not to damage the already compromised tooth structure further. Radiographs and other dental investigations, such as sensibility testing, are of limited use where dental fluorosis is concerned.[22] 

There is active research into tools to supplement the diagnosis of fluorosis, such as the use of short-wavelength infrared light. Under this spectrum, dental fluorosis appears in high contrast, which can help identify more subtle cases of fluorosis.[23] This also enables dental professionals to stage the grade of fluorosis more accurately. However, the use of these tools is not yet commonplace in clinical practice.

Treatment / Management

Where mild cases of dental fluorosis are concerned, involving subtle enamel changes, patients may be unaware or unconcerned with the appearance of their teeth. As such, no treatment may be necessary. Thus, treatment is patient-led where dental fluorosis is concerned, and patient concerns are cosmetic in most cases.[24] (A1)

Vital dental bleaching can be a highly effective treatment modality in mild cases of dental fluorosis. The concentration of hydrogen peroxide utilized varies between countries depending on legislation pertaining to the maximum permitted concentrations of hydrogen peroxide permissible for dental whitening.[25] 

Generally, dental bleaching completed in a dental clinic will use a higher concentration than that provided to patients for at-home bleaching using bleaching trays. Lightening the healthy, unaffected tooth structure allows it to camouflage with lighter fluorosed hypomineralized enamel, providing a more aesthetic appearance.[24](A1)

Other minimally invasive techniques suitable for treating mild to moderate cases of dental fluorosis include enamel microabrasion and resin infiltration. Microabrasion involves mechanically removing the superficial layers of flurosed enamel, thus reducing the visibility of enamel discoloration.[24] This method can have limited effectiveness when treating deeper and more severely discolored lesions.(A1)

The use of dental whitening and microabrasion together has been shown to provide a more aesthetic result and help overcome this limitation. Resin infiltration involves applying hydrochloric acid to etch the enamel, followed by low-viscosity resin, which infiltrates the enamel.[26] Isolation using a rubber dam is recommended.[27] This method has been shown to effectively reduce the visibility of white patches and thus improve cosmesis.[24]   (A1)

In cases where these methods are ineffective in improving the appearance of fluorosed teeth, the next minimally invasive step includes using resin-based dental composite bonding to mask the discoloration. This can be in the form of localized fillings or composite veneers. Composite veneers require less, if any, mechanical preparation of the natural tooth and are, therefore, more conservative of tooth structure than traditional veneers.[24] (A1)

In cases with severe discoloration, veneers or conventional crowns may become necessary to achieve a cosmetically acceptable result for the patient. Crowns may be the only viable long-term restorative option in cases with insufficient or poor-quality enamel, as composite and veneer restorations rely on effective enamel-resin bonding for retention.[28](B3)

More invasive indirect restorative options such as veneers and crowns start patients on the restorative cycle leading to the need for lifelong maintenance, patients must be fully informed, and a judgment must be made based on the risks and benefits. Occasionally a combination of the techniques available is required to achieve an optimal aesthetic result.[24](A1)

Differential Diagnosis

The differential diagnoses of dental fluorosis are extensive. They include and are not limited to early carious lesions, molar-incisor hypomineralisation, developmental disorders of enamel and dentine, including amelogenesis imperfecta, Turner hypoplasia, tetracycline staining, and dental manifestations of celiac disease.[29][30][31] 

The key to recognizing dental fluorosis is a positive fluoride history within the critical window of amelogenesis, a symmetrical chronological distribution in the pattern of affected teeth, and an increased caries resistance.[22] Clinicians must be able to differentiate dental fluorosis from conditions such as dental caries as the management required varies substantially.[29]

Treatment Planning

Treatment planning is an individualized patient-centered process focusing on prevention and minimally invasive treatment modalities where possible.[26] Once the signs of dental fluorosis are evident in dentition clinically, it is too late for prevention strategies to be effective.[6] 

Prevention must be instigated from birth and lies primarily in the education of caregivers and government strategy and policy. These strategies include the control of fluoride levels in drinking water and educating caregivers about the etiology of fluorosis and the importance of receiving the optimum amount of fluoride.[3] This may include avoiding fluoride supplements, especially in areas with fluoridated water, and focusing on the use of topical fluorides such as those in fluoridated toothpaste and mouthwashes.[3] 

The primary concern for most patients affected by dental fluorosis is aesthetics.[24] Once patients start on the restorative cycle, they will require lifelong maintenance of their restorations.[32] For this reason, especially where there are minimal symptoms and functional deficits, treatment plans must be centered around the principles of minimally invasive dentistry when possible.[20] Severe cases of dental fluorosis may warrant more destructive therapeutic options, but patients must be fully aware of the risks.[24]

Staging

Multiple indices have been formulated to facilitate the reliable and consistent staging of dental fluorosis.[33] These systems are primarily used in epidemiological studies using clinicians that have been calibrated to increase inter-rater reliability. Indices include the Thylstrup Fejerskov Index, Dean Modified Fluorosis Index, the Tooth Surface Index of Fluorosis, and the Fluorosis Risk Index.[33] 

All of these systems are currently in use and are associated with their own strengths and weaknesses.[34] The Dean Modified Index consists of six distinct categories allocating teeth scores ranging from 0 to 5.[34] Its simplicity and ease of use have made it a popular choice amongst epidemiologists and researchers alike.[34][35] However, it has been criticized for its lack of detail where the staging of severe dental fluorosis is concerned.[34]

Table 1. The Dean Modified Fluorosis Index[36]

The Thylstrup Fejerskov index is an alternative staging system comprised of 10 categories with scores ranging from 0 to 9.[34] It has been described as having biological validity as codes correspond to observable histological enamel changes.[33] The Thylstrup Fejerskov index has significantly more categories relating to severe dental fluorosis.

Table 2.The Thylstrup Fejerskov index[37]

Prognosis

In mild and moderate cases of dental fluorosis, the prognosis is very good, with concerns and treatment being patient-led with a focus on improving aesthetics and patients being otherwise asymptomatic.[24] Minimally invasive restorative techniques have been shown to be very effective in treating these cases with high levels of patient satisfaction.[26] 

In the rarer severe cases of dental fluorosis, the structure of the dentine and enamel becomes compromised.[19] As a result, patients may suffer from dentine hypersensitivity, excessive tooth wear, and enamel fractures. In these cases, minimally invasive techniques produce improvements in appearance.[19] 

To produce satisfactory results in more destructive techniques such as full coverage, conventional crowns may need to be considered. If this course is taken, patients must be informed of the lifelong maintenance such restorative work requires, including the need for repair, replacement, and even the eventual loss of teeth.[32]

Complications

In mild and moderate cases of dental fluorosis, the affected dentition is caries resistant.[22] This is unsurprising given the well-documented role of fluoride in caries prevention.[24] In severe cases of dental fluorosis, where the structural integrity of the enamel and dentine are compromised, patients are at a higher risk of dental caries, dentin hypersensitivity, dark discoloration, and tooth wear.[19] 

This will impact the aesthetics, function, and longevity of an individual's dentition.[24] Furthermore, it is essential to consider whether patients affected by severe dental fluorosis may also suffer from skeletal fluorosis.[38]