bubble_chart Overview

Dental fluorosis, also known as mottled enamel, is a regional condition and the most common and prominent early symptom of chronic fluorosis. Cases of dental fluorosis have been reported worldwide. In China, many areas are affected by dental fluorosis, including Northeast China, Inner Mongolia, Ningxia, Shaanxi, Shanxi, Gansu, Hebei, Shandong, Guizhou, and Fujian, where chronic fluorosis is prevalent. Fluorosis poses a significant threat to public health, and severe cases may also involve skeletal fluorosis, warranting serious attention.

bubble_chart Etiology

In 1931, Churchill was the first to confirm that excessive fluoride levels in water were the disease cause of this condition. In the same year, Smith conducted experiments on rats using fluoride, proving that high fluoride levels could induce this condition. It is generally believed that a fluoride concentration of 1 ppm (1 mg/L) in water is optimal, as this level effectively prevents dental caries without causing dental fluorosis. However, individual factors and other living conditions also contribute to variations in fluoride sensitivity. Drinking water is the primary source of fluoride intake, which is determined by: ① age; ② climatic conditions; and ③ dietary habits. The optimal fluoride concentration in water primarily depends on the local annual average maximum temperature. In the U.S., it ranges from 0.7 to 1.2 ppm, while in Guangzhou, it is approximately 0.7 ppm. Given China's vast territory and significant temperature differences between the north and south, a single optimal concentration is impractical. Therefore, the current national water quality standard for fluoride concentration of 0.5–1 ppm is considered appropriate.

The absorption of fluoride from food depends on the solubility of inorganic fluoride in the food and its calcium content. If calcium compounds are added, fluoride absorption is significantly reduced. Animal experiments have confirmed that sufficient vitamins A and D, along with appropriate amounts of calcium and phosphorus, can mitigate the damage caused by fluoride. This indicates that excessive fluoride is not the sole cause of dental fluorosis, as not everyone in areas with slightly higher fluoride levels in water develops the condition.

Additionally, the occurrence of dental fluorosis depends on the timing of excessive fluoride intake. Fluoride primarily damages the ameloblasts in tooth enamel during its developmental stage. Thus, excessive fluoride must enter the body during tooth development and mineralization to cause dental fluorosis. If a person resides in an endemic area with high fluoride levels in drinking water before the age of 6 or 7, even if they later move elsewhere, the permanent teeth that erupt subsequently will still be affected. Conversely, those who move to high-fluoride areas after the age of 7 will not develop dental fluorosis.

bubble_chart Pathogenesis

Alkaline phosphatase can hydrolyze various phosphoric esters, providing sufficient inorganic phosphorus for bone and tooth metabolism as raw material for bone salt formation. When fluoride concentration increases, it can inhibit the activity of alkaline phosphatase, leading to skeletal disorders such as enamel hypoplasia, incomplete mineralization, and brittle bones. The result is poor mineralization of the interprismatic substance and excessive mineralization of enamel rods. This condition is more pronounced in the superficial enamel, where the fluoride content is about 10 times higher than in the deep enamel. Consequently, the superficial enamel in dental fluorosis becomes porous and prone to adsorbing external pigments, such as manganese and iron compounds, resulting in fluorosis stains. In severe cases of dental fluorosis, the microporosity can reach 10-25%, located between enamel rods and distributed along the striae. If the volume of this porosity is large, the enamel surface may collapse, forming pitted enamel hypoplasia.

bubble_chart Clinical Manifestations

1. The clinical manifestation of dental fluorosis is characterized by chalky white to brown patches on the enamel of teeth that erupt during the same period. In severe cases, it may also be accompanied by substantial enamel defects. Clinically, it is often classified into three types based on mild, moderate, and severe grades: chalky type (grade I), pigmented type (grade II), and defective type (grade III).

2. It is more common in permanent teeth and rarely occurs in deciduous teeth, with milder severity. This is because deciduous teeth develop during the embryonic and infant stages, and the placenta has a certain barrier effect against fluoride. Therefore, dental fluorosis is generally observed in permanent teeth. However, if fluoride intake is excessive and exceeds the placental filtration limit, it may also irregularly manifest in deciduous teeth.

3. The enamel has poor resistance to friction but strong resistance to acid etching.

4. Patients with severe chronic fluorosis may exhibit proliferative changes in bones, calcification of bone membranes and ligaments, and consequently develop symptoms such as lower back pain, leg pain, and systemic joint discomfort. Acute poisoning symptoms include nausea, vomiting, and diarrhea. Since fluoride binds with blood calcium to form insoluble calcium fluoride, it can lead to muscle spasms, collapse, respiratory distress, and even death.

Dean classified dental fluorosis into six categories based on the severity of fluorosis, as shown in Table 1.2-1.

Table 1.2-1 Classification of Dental Fluorosis

^* DFI: Dental Fluorosis Index

According to Dean's classification, the severity of lesions in individuals from a specific region is assigned a corresponding grade, represented numerically. Based on this, the dental fluorosis index for the population in that region is calculated. The formula is as follows:

Example: The results of dental fluorosis examination for 110 cases in a certain area are shown in Table 1.2-2.

Table 1.2-2 Survey results of dental fluorosis in 110 cases

DFI = 82.5 / 110 = 0.75

Dean pointed out: As a guideline for public health management, when the dental fluorosis index is 0.4 or less, there is no fluorosis problem; but when the index exceeds 0.6, it constitutes a noteworthy public health issue.

bubble_chart Treatment Measures

For already formed dental fluorosis, the following treatment methods can be used:

1. **Bleaching Method** Also known as the grinding and acid etching method. Suitable for dental fluorosis without substantial defects. The specific steps are as follows:

(1) Clean the affected tooth.

(2) Select a fine, pointed diamond bur. While grinding, continuously drip water to maintain a moist environment and evenly remove the stained layer by about 0.1–0.2 mm. Pay attention to the tooth's shape, avoiding deepening the stained patch area to prevent leaving indentations. A turbine handpiece can be used if available. The finer the diamond bur, the better, to reduce surface roughness.

(3) Isolate the affected tooth and apply petroleum jelly to the gingival margin.

(4) Prepare the bleaching solution in a small cup-shaped dish with the following composition:

Stir well with a stainless steel needle and set aside.

(5) Apply the bleaching solution to the stained area using a small cotton ball or swab for 5–10 minutes, then rinse thoroughly with water.

(6) Polish the tooth with pumice powder.

Since the pigmentation in dental fluorosis is superficial and exogenous—composed of manganese or iron compounds—the combination of grinding, acid etching, and bleaching yields good results. Although approximately 50–150 μm of the surface layer is lost, the exposed demineralized surface can naturally remineralize.

2. **Visible Light-Cured Composite Resin Restoration** Suitable for dental fluorosis with substantial defects. The specific steps are as follows:

(1) Grind away the stained or porous enamel on the labial surface, typically removing 0.3–0.5 mm in thickness.

(2) Acid etching: Under isolation, evenly apply 35–50% phosphoric acid to the tooth surface for 1 minute using a small brush. Avoid prolonged etching, as it may form insoluble byproducts and severely damage the enamel structure without improving retention. Ensure the etching agent does not flow into the gingival sulcus. After etching, rinse repeatedly with distilled water or water to remove acid and calcium salt debris. The patient should not rinse during this process. Finally, dry the tooth surface with oil-free compressed air until it appears chalky white or grayish-white.

(3) Apply bonding agent: Use a small white brush to apply the bonding agent evenly onto the etched surface. Avoid applying too thickly, as excessive thickness can lead to shrinkage, high thermal expansion, and poor mechanical properties, resulting in bonding failure. Cure the bonding agent for 20 seconds with visible light for initial polymerization.

(4) Restoration: Select the appropriate composite resin based on the patient's age, complexion, and adjacent tooth color under natural light. Apply the composite resin to the desired area using a white plastic sculpting tool, ensuring no air bubbles. Adjust the proximal contacts, gingival margins, and labial anatomy. Once satisfied with the shape, cure the material for 40–60 seconds with visible light, depending on its thickness and shade. Keep the light guide tip as close as possible to the material, ideally no more than 2 mm away.

(5) Trimming and polishing: Pay attention to the morphology of the labial surface and the occlusal relationship. Eliminate premature contacts and remove excess material at the gingival margin. A tapered diamond bur or a flexible diamond disc can be used for trimming. Diamond burs and polishing discs come in coarse and fine varieties. The general sequence for trimming and polishing is: coarse trimming → fine trimming → precision trimming → fine polishing → precision polishing.

There are many types of composite resins on the market, and their properties and methods also vary. Practitioners should carefully read the product instructions from each manufacturer before use, and then follow the specified procedures to achieve optimal results.

bubble_chart Prevention

The most ideal preventive method is to select a new water source with an appropriate fluoride content, or to use activated alumina (Al₂O₃) or activated bone charcoal separately to remove excessive fluoride from the water source. However, the latter is expensive and difficult to promote.

bubble_chart Differentiation

This condition should primarily be differentiated from enamel hypoplasia.

1. The chalky white patches of enamel hypoplasia have relatively clear boundaries, and their lines are parallel and consistent with the growth lines of enamel; dental fluorosis is a chronic injury, so its patches appear as scattered cloudy areas with unclear boundaries that do not align with the growth lines.

2. Enamel hypoplasia can occur in a single tooth or a group of teeth, whereas dental fluorosis affects multiple teeth, especially the maxillary anterior teeth.

3. Patients with dental fluorosis may have a history of living in high-fluoride areas.