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 Table of Contents  
REVIEW ARTICLE
Year : 2014  |  Volume : 1  |  Issue : 1  |  Page : 3-13

Therapeutic management of dental fluorosis: A critical review of literature


Department of Restorative Sciences, Faculty of Dentistry, Kuwait University, Kuwait Department of Restorative Dentistry, Lagos State University College of Medicine, Lagos, Nigeria

Date of Web Publication2-Jan-2014

Correspondence Address:
Enosakhare S Akpata
Department of Restorative Dentistry, Lagos State University College of Medicine, Lagos
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/WKMP-0056.124179

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  Abstract 

Dental fluorosis is a specific condition due to chronic ingestion of excessive fluoride during enamel formation. The cleavage and removal of enamel proteins are disturbed. Retention of the proteins and water results in varying degrees of subsurface porosities related to the severity of fluorosis. The porosities may attract extrinsic stains, causing enamel discoloration. Posteruptively, occlusal trauma may cause detachment of surface enamel weakened by the subsurface porosities. The therapeutic management options include bleaching, microabrasion, veneering and crowning. The bleaching agents break down the chromogens into smaller molecules, resulting in teeth with lighter and brighter shades. The microabrasion is aimed at removing the superficial microporous zone together with the entrapped extrinsic stains, while laminate veneers and crowns provide esthetic masking of the discolored fluorosed enamel. It is suggested that mild-to-moderate fluorosis be treated by microabrasion and bleaching, while severe fluorosis, with loss of some surface enamel, is managed by veneering and crowning, depending on the extent of surface enamel loss. Long-term clinical trials are needed to evaluate the appropriateness of the various management options for fluorosis of varying severity.

Keywords: Bleaching, bonding, fluorosis, management, microabrasion


How to cite this article:
Akpata ES. Therapeutic management of dental fluorosis: A critical review of literature. Saudi J Oral Sci 2014;1:3-13

How to cite this URL:
Akpata ES. Therapeutic management of dental fluorosis: A critical review of literature. Saudi J Oral Sci [serial online] 2014 [cited 2019 Jul 23];1:3-13. Available from: http://www.saudijos.org/text.asp?2014/1/1/3/124179


  Introduction Top


Dental fluorosis is a specific disturbance due to chronic ingestion of excessive fluoride during the formative period of the dentition. [1] As far back as 1888, [2] it was described as a condition that appeared to be endemic dental fluorosis in certain areas of Mexico. It was not until 1931 that Churchill discovered the correlation between fluoride from drinking water and dental fluorosis, a condition that is still endemic in many parts of the world, including certain areas of Africa, China, India, Middle East and South America. [3]

The use of fluoride in preventive dentistry has been the most effective anti-caries measure, but is also associated with the increasing prevalence of dental fluorosis in many countries. The level of fluoride exposure at which dental fluorosis is minimal, and anti-caries effect maximal is said to be appropriate, [4] being influenced by ambient temperature: Appropriate fluoride level is lower in tropical than in temperate climates. Exposure to 1 ppm of fluoride in drinking water in temperate countries has been reported to reduce caries experience by up to 50-60%. [5],[6] When fluoride in drinking water exceeds 1.5 ppm, esthetically objectionable dental fluorosis becomes highly prevalent. [7] However, at 4-8 ppm, bone may be dense (slight osteosclerosis), and above 8 ppm handicapping osteosclerosis may develop in persons exposed for more than 10 years. [8] Water is the most common source of fluoride ingestion. Other sources of fluoride ingestion include sea foods, [9] beverages, [10] toothpastes, [11] infant formula and fluoride supplements. [12] In particular, ingestion of fluoride from toothpastes by young children (e.g., those aged 0-3 years) has been associated with increased prevalence of dental fluorosis in several communities. [13]

Excessive fluoride ingestion during enamel maturation adversely affects cleavage and removal of enamel proteins, such as amelogenins. [14],[15] Retention of the proteins and water interferes with enamel crystal growth, resulting in varying degrees of subsurface porosities. [16] The pore volume and depth of the subsurface porosities increase with the severity of fluorosis. [17] The more severe the fluorosis, the more deep-seated the enamel subsurface microporous zone. [17] In fluorosed dentin of permanent teeth, there is increased interglobular dentin formation and accentuation of  Incremental lines of von Ebner More Details. [18] It was observed that interglobular dentin as well as regular bands of hypo- and hypermineralized dentin in cheek teeth of the deer chronically exposed to high fluoride levels. [19] Furthermore, a study of hydraulic conductance in primary teeth showed a decrease in the permeability of dentin as severity of fluorosis increased. [20]

In its mildest form, fluorosed enamel is characterized by white lines due to accentuated perikymata or rod ends. In some cases, the white lines may be confluent while in others, there may be discrete white opaque areas with white lines in between. In more severe cases, the entire enamel surface may be opaque and chalky white. Posteruptively, sub-surface porosity in fluorosed enamel may attract extrinsic stains, resulting in tooth discoloration. In cases with extensive sub-surface porosity, post-eruptive trauma causes detachment and pitting of surface enamel. In the most severe cases only the opaque cervical rim of enamel may be retained. [17]

The later in life the mineralization of a tooth, the more severe the effect of dental fluorosis. [21] Thus, dental fluorosis is more severe in premolars and second permanent molars and least in permanent mandibular incisors and first permanent molars. The thicker the enamel, the more severe the effect of dental fluorosis; hence, the snow capped appearance of cusp tips and incisal edges off luorosed teeth. [22] This may also explain the greater severity of dental fluorosis in maxillary than mandibular teeth.

Discolored and pitted enamel of fluorosed teeth may be esthetically objectionable and a cause of psychological ill health. Although it has been suggested that soft tissue changes due to excessive fluoride ingestion may be reversed in children by withdrawal of fluoride intake as well as dietary supplementation with calcium, vitamin D 3 , ascorbic acid and antioxidants, [23],[24] there is no evidence that fluorotic changes in hard dental tissues are reversible. Hence, therapeutic intervention, albeit minimally invasive, is often needed to correct cosmetic defects due to dental fluorosis. In fact, dental fluorosis has become such a common clinical problem that clinicians are increasingly seeking information on bonding to fluorosed teeth. [25] Several management strategies have been proposed for teeth with fluorosis of varying severity. However, many of the published papers have been short-term case reports and the suggested management strategies anecdotal, with little attempt to explain the underlying principles. The aims of this paper were to: (i) review the literature on the therapeutic management of dental fluorosis, (ii) suggest the management options for fluorosis of varying severity, (iii) describe the basic research on bonding to fluorosed teeth, and (iv) suggest areas for future research.

Epidemiological indices

Several indices have been used to describe the clinical appearance of dental fluorosis. There are three most widely used. [17],[18],[26],[27] More recently, the Fluorosis Risk Index (FRI) [28] has been in use. In addition, there are the descriptive indices that attempt to differentiate dental fluorosis from other causes of enamel opacities.

Dean's index

The Dean's index is of historical interest because most of the older studies have used this index. [26] Dean's index assigns a score to the two most affected teeth. Thus, depending on the severity of fluorosis, the two teeth are scored normal (0), questionable (0.5), very mild (1), mild (2), moderate (3) and severe (4). The index presupposes the diagnosis of the condition and the diagnostic criteria are unclear, imprecise and not sensitive enough to measure dental fluorosis in persons exposed to very high or very low fluoride levels. [29] Consequently, the index may not be suitable for the determination of appropriate treatment option for a fluorosed tooth.

Thylstrup and Fejerskov index

Of the epidemiological indices, the Thylstrup and Fejerskov (T-F) index is, perhaps, the most suitable for use in the clinical management of dental fluorosis. [17] This classification was modified in 1988 and is based on the observed clinical and pathological changes in fluorosed teeth. [22] Score of 0 through 9 are assigned, depending on the severity of the condition [Table 1]. Tooth surfaces are dried before diagnosis.

The T-F index has several advantages. It is compatible with histopathological changes in fluorosed enamel. It is highly reproducible [30] and sensitive, [31] being suitable for measuring the severity of dental fluorosis in areas with high or low fluoride levels in drinking water. Furthermore, it can measure severity of dental fluorosis in an individual tooth, making it useful in the determination of the clinical management option for a fluorosed tooth.
Table 1: Classification of dental fluorosis according to Thylstrup and Fejerskov Index*, TFI (7)


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Tooth surface index of fluorosis

In the Tooth Surface Index of Fluorosis (TSIF), an 8-point scale is used for the classification. [27] Scores 1-3 are based on the areas of the different tooth surfaces affected by fluorosis and score 4 given when there is staining which is so heavily weighted that it supersedes all lower scores. Because esthetics is the primary concern of this classification, it should theoretically be most useful in making a decision on the restorative management of dental fluorosis. Unlike the T-F index, the scoring is unrelated to biological changes in fluorosed teeth. Thus, a tooth with mild superficial enamel porosities may receive a high score, if stained while a tooth with severe deep-seated enamel porosities may receive a low score, if unstained. This is the weakest aspect of the classification.

Nevertheless, higher scores are assigned, depending on whether pitting of the enamel surface is discrete or confluent. This makes the index more sensitive than Dean's index.

Fluorosis risk index

The FRI, proposed by Pendrys in 1990, is aimed at differentiating between different areas of tooth surfaces at risk during the various ages of development. The tooth surfaces are divided into zones that depend on the age when they start to develop. Thus, the tooth surfaces can be related to narrow age bands that facilitate identification of the age at which fluoride exposure gave rise to fluorosis. This index is rather complicated to use, and is unrelated to biological changes in fluorosed teeth. Hence, its application is not useful in the therapeutic management of dental fluorosis.

Descriptive indices

There are a few notable among the descriptive indices that have been suggested for measuring dental fluorosis. [32],[33],[34]

According to these descriptive indices, no diagnosis of enamel defect should be made on the basis of presumed etiology. [32],[33],[34] Accordingly, the classification of all defects should be based on descriptive criteria. In an attempt to do this, however, there is a cumbersome differentiation between dental fluorosis and non-fluoride-induced enamel opacities. But it is reported that the clinical changes in fluorosed teeth are quite distinct, making definitive diagnosis possible. [17]


  Management Options Top


Discoloration of teeth is the most common reason why patients seek treatment of fluorosed teeth. The discoloration may be due to white opacity resulting from enamel hypomineralization. Uptake of extrinsic stains into the porous subsurface enamel may give rise to discoloration which may be yellowish, light brown, dark brown or black [Figure 1] and [Figure 2]. To restore the natural white creamy enamel appearance, the tooth may be bleached or the subsurface porosities abraded together with the entrapped extrinsic stains, by microabrasion or macroabrasion. If the subsurface porosities [Figure 3] are so deep-seated that they cannot be easily removed by microabrasion without causing hypersensitivity or resulting in unaesthetic tooth morphology, the enamel surface is veneered with porcelain or resin composite. Where more than 50% of surface enamel has been lost as a result of fluorosis, the remaining enamel may be insufficient for adhesive bonding; in which case, the fluorosed tooth may have to be crowned.
Figure 1: Opaque white anterior teeth with staining (TFI = 4)

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Figure 2: Fluorosed teeth with yellow stains and loss of surface enamel (TFI = 5-8)

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Figure 3: Schematic representation of enamel subsurface porosities

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It has been reported that the more severe the enamel fluorosis, the more deep-seated the subsurface porosities. [17] Thus, Akpata suggested that mild fluorosis with T-F score of 1-2 should be managed by bleaching, as the subsurface porosities may be sufficiently superficial for the entrapped extrinsic stains to be removed by the bleaching agent. [35] To make it easier for the bleaching agent to penetrate to the area of enamel subsurface porosities, the hypermineralized surface enamel may be etched with phosphoric acid.

At T-F scores of 3-4, Akpata in 2001 suggested microabrasion because the subsurface porosities may be so deep-seated that entrapped extrinsic stains may not be accessible to the bleaching alone. Rather, it is felt that microabrasion may remove the subsurface porosities together with the entrapped extrinsic stains. As loss of surface enamel of a fluorosed tooth is due to post-eruptive occlusal trauma, a tooth with TFI = 4 may have the potential to transform to T-F score of 5 when it has been subjected to sufficiently high occlusal trauma. [17] Therefore, in order to be as conservative as possible in the management of dental fluorosis, it has been suggested that microabrasion should first be tried on teeth with TFI = 4, and if ineffective, the tooth should then be treated by laminate veneer. [35] For teeth with TFI = 5-7 veneering is suggested, but if more than 50% of enamel surface has been lost, as in teeth with TFI = 8-9, the fluorosed tooth should be crowned.

The management options suggested for discolored fluorosed teeth are, therefore, bleaching, microabrasion (or macroabrasion), veneering and crowning. The literature shows variations in the application of these management options.

Bleaching

Discolored, mildly fluorosed teeth have been treated by in-office or at-home bleaching or a combination of both. Hydrogen peroxide (35%) and carbamide peroxide (10%) are the commonly used bleaching agents. High concentrations (e.g. 35% hydrogen peroxide) of the bleaching gel are used for in-office bleaching. The teeth are isolated and cleaned before applying the gel directly to the teeth. Action of the gel may be accelerated by halogen or light-emitting diode (LED) curing light. It may require several sessions of in-office bleaching to achieve the desired result. To facilitate penetration of the bleaching agent to the subsurface porosities of the fluorosed tooth, the hypermineralized surface layer may be conditioned with 37% phosphoric acid. [36] The in-office bleaching may be followed by at-home bleaching until the desired shade is attained.

Sometimes, white enamel opacities of fluorosed teeth may be the cause of the patient's concern. In cases with focal areas of opacities, as may be found in teeth with TFI = 3, the unaffected portion of the enamel surface may be bleached until it matches the opaque part of the tooth surface. This was the approach followed by Bussadori et al. [36] in 2004, in the esthetic management of fluorosis blemishes on the maxillary incisors of an 8-year-old boy. Furthermore, it has been suggested that application of calcium sucrose phosphate gel could improve the appearance of areas of the fluorosed tooth affected by white opacities. [37] The tooth is cleaned and etched with 37% phosphoric acid for 2 minutes, followed by application of 2% sodium fluoride for 4 minutes. Finally, 40% calcium sucrose phosphate is applied. The best results were obtained in children than adults, while results were poor in teeth with very dark stains and those with chalky fluorosis.

Enamel blemishes due to dental fluorosis may also be removed by making use of the Wright's protocol. [38] The fluorosed tooth is cleaned, using prophylaxis paste. The enamel surface is then etched with 35% phosphoric acid to facilitate penetration of sodium hypochlorite that acts as the bleaching agent. The bleaching session may be repeated until the desired shade is attained. After bleaching, the enamel pores are sealed with low viscosity resin composite to prevent further uptake of stains into the subsurface porosities. The Wright's protocol was applied to fluorosis stains on the teeth of 33 young children, and found significant improvement in color of the teeth, assessed by Minolta Chroma Meter CR300 (Chromameter, Minolta, Osaka, Japan) [39] The fluorosed teeth selected for the bleaching technique were within grades 1-4 of the TSIF. [27]

The technique suggested by Belkir et al. [40] in 1991 is not much different from the Wright's protocol. In this technique, enamel is etched with 12% hydrochloric acid to remove the post-eruptive calcified surface enamel and denude microcavities containing the stains. This is followed by the application of pure sodium hypochlorite to remove the stain. Finally, the chemically opened micro-cavities are filled with resin composite.

The effectiveness of night guard vital bleaching technique (NGVBT) in the removal of dental fluorosis stain was studied in 2003. Different concentrations of carbamide peroxide and hydrogen peroxide were used: 20% carbamide peroxide (Opalescence/Ultradent, USA), 10% carbamide peroxide (NuProgold/Dentsply, USA) and 7.5% hydrogen peroxide (Day White/Discus Dental, USA). [41] The teeth of the subjects in the double blind clinical trial, had TSIF of 1-3, while patients with TSIF of 4-5 were excluded. The three bleaching products were effective in bleaching the discolored teeth, the 20% carbamide peroxide being most effective after 1 week of bleaching.

Microabrasion

Microabrasion is the controlled removal of superficial stain from enamel. The technique is used for removing stains due to mild-to-moderate fluorosis. [42] Microabrasion is often combined with bleaching to effectively remove fluorosis stains. It was suggested that this is a treatment of choice when fluorosis is mild (TFI = 1-3) [Figure 4], but it may also be tried in cases with moderate fluorosis (TFI = 4). [35] The technique is conservative and if unsuccessful, more invasive treatment options can still be followed.
Figure 4: Microabrasion of maxillary anterior teeth with mild fluorosis (TFI = 3): (a) - Preoperative, (b) - Postoperative.[35]

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The discolored tooth may be etched with phosphoric acid, after which a thick mix of pumice and 18% hydrochloric acid is used to abrade the tooth surface. Microabrasion removes the enamel porosities together with the entrapped extrinsic stains. Lower concentrations of hydrochloric acid have been used in commercially produced pastes. For example, Premamicroabrasion kit (Premier Dental) contains 15% hydrochloric acid with silicon carbide in water soluble slurry, while Opalustre (Ultradent) is made up of 6.6% hydrochloric acid combined with silicon carbide abrasive, and silica gel as a binding agent. The slurry may be applied with a rubber cup at slow speed (about 100 revolutions per minute) [42] or with gentle pressure from a wooden tongue spatula. [43] Generally, microabrasion is recommended when the enamel discoloration is not more than 0.2-0.3 mm deep. [44] To reduce tooth hypersensitivity after microabrasion, amorphous calcium phosphate (ACP) was applied. [42] It should also be noted that a complex comprising casein phosphopeptide (CPP) and ACP has the potential to reduce the opaque white discoloration of enamel fluorosis by encouraging remineralization.

A combination of microabrasion and at-home bleaching was recommended, followed by chair-side recreation of superficial enamel microstructure. [45] In this technique, microabrasion is aimed at removing the hypermineralized, white-colored superficial enamel layer, while at-home bleaching is to remove the extrinsic stains entrapped in the subsurface porosities. The clinicians reported only one case. They made use of Opalustre (Ultradent) for microabrasion, then sodium fluoride to minimize hypersensitivity, followed by at-home bleaching with 10% carbamide peroxide for 2 weeks. Finally, the enamel surface was reshaped with fine-grit diamond to recreate natural enamel appearance.

The effectiveness of two commercial microabrasion products was compared, and it was found that Opalustre (Ultradent, USA) more effective than Prema (Premier Dental, USA) although both products were effective in removing dental fluorosis stains. [46] It should, nevertheless, be realized that the effectiveness of an abrasion product is influenced by the type of acid content, grit and hardness of the abrasive as well as the pressure of application of the abrasive to the tooth surface.

The enamel surface was roughened with fine grit diamond at low speed, and used rubber cup and brush to apply 1 mm thick 6.6% hydrochloric acid microabrasion slurry to fluorosed enamel surface for 60 seconds. [47] No bleaching agent was used. Scanning electron microscopic study showed that enamel etching patterns were not different from those of non-fluorosed control teeth.

Abrasion of enamel prisms combined with enamel erosion by acid from the abrasion slurry results in compacted prism-free enamel surface, with altered optical properties. This is sometimes referred to as the 'abrasion effect' or 'enamel glaze'. [48],[49] The amount of surface enamel removed by microabrasion is negligible, being less than 100 μm in most cases. [50] Esthetic improvement and surface alterations have been evaluated when fluorosis stain was removed, using the commercial microabrasion product, Prema; the paste was applied with 10:1 gear reduction hand piece. [51] It was found that ten, 30 second (total 5 minutes), applications were sufficient to remove stains from most cases of mild fluorosis, classified according to Dean's index. [26] The results were not as good when cases of moderate-to-severe fluorosis were treated by this technique. Surface irregularities (due to exposure of extensive deep-seated porosities) were apparent after treatment of severe fluorosis. It was concluded that microabrasion could only be recommended for treatment of mild fluorosis.

Faster methods for removing fluorosis stains, sometimes referred to as macroabrasion, have been advocated, and these include the use of fine-grit diamond points at high speed, or sandpaper discs at slow speed. [44],[52] These methods may be used to remove deep-seated fluorosis stains, but they may also result in excessive tooth tissue removal.

Laminate veneers

Laminate veneers are used to manage severe dental fluorosis, especially where there has been surface enamel loss. It has been suggested that teeth with TFI = 5-7 should be restored with laminate veneers. [35] Likewise cases with TFI = 4 in which microabrasion or macroabrasion have not been successful. The veneer may be made of porcelain [Figure 5] and [Figure 6] or resin composite.
Figure 5: Moderate-to-severely fluorosed teeth. Note that the premolars and right maxillary incisors are pitted (TFI = 5), and the entire labial surfaces of the remaining teeth are opaque (TFI = 4)

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Figure 6: Fluorosed teeth in Figure 5 prepared for laminate veneers (a), and after cementation of the veneers (b)[35]

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As adhesive bonding to enamel produces more predictable outcome than bonding to dentin, laminate veneer is not recommended when more than 30% of the labial enamel has been lost. [53] Moreover, considerable enamel loss makes it difficult to avoid placing margins of the veneer preparation in dentin and thus reduce the possibility of postoperative sensitivity. Hence, it has been suggested that teeth with TFI = 8-9 be crowned, as more than 50% of enamel has been lost in such fluorosed teeth. [35]

Porcelain laminate veneers have very good track records. Not only do they have excellent appearance and predictability, they are biocompatible. In a prospective longitudinal study of 323 porcelain laminate veneers, [54] survival rate, after 3-11 years, was very good, there being de-bonding in 9% of the restorations. Marginal integrity was excellent in 98% of the cases, and about the same percentage of the patients rated the treatment outcome to be excellent. There were very few fractures (4%), but gingival recession occurred in 7.7% of cases, while gingival bleeding was observed in 21.6% of cases. Hypersensitivity and change in sensibility of the restored teeth were uncommon (about 3%), and recurrent caries in 3% of the patients.

In contrast, resin composite laminate veneers suffer from a number of disadvantages: Marginal staining, material loss, and gingival irritation. In a 2-year clinical evaluation of resin composite laminate veneers, marginal staining occurred in 75% of the treated teeth, while chipping was recorded in 52% of lateral incisors, and 79% of central incisors and canines. [55] Gingival irritation was highly prevalent. Thus, prognosis of resin composite appears not to be good. However, the introduction of the modern bonding systems and fiber-reinforced resin composites may result in resin composite veneers with better prognosis.

Tooth preparation

Preparation of severely fluorosed teeth for laminate veneers follows the usual general principles. [56] Nevertheless, certain special considerations need to be borne in mind. Display of incisal enamel would be unaesthetic. Therefore, the window type [57],[58] of labial enamel preparation, should be avoided. Rather, the incisal bevel preparation is preferable. [59]

After removing 0.3-0.5 mm of labial enamel during preparation of a severely fluorosed tooth for a laminate veneer, there may be residual enamel discoloration. The enamel stain should be removed by in-office bleaching, using 25-38% hydrogen peroxide or 35-40% carbamide peroxide. [35] Teeth that mineralize later in life are more severely affected by fluorosis. [21] Therefore, fluorosis blemishes tend to be darker on premolars. If only the anterior teeth are being prepared for veneer, and the premolars are very dark, the posterior teeth should be bleached before shade selection for the veneers. Alternatively, the shade should be made progressively lighter from the posterior to the anterior teeth.

Etching of fluorosed enamel

Management of severely fluorosed teeth by means of veneers or crowns requires adhesive cementation of the restorations to enamel and dentin. To achieve this, the hard dental tissues need to be etched. As part of the hydroxyapatite in the hypermineralized surface layer of enamel has been replaced by the acid-resistant fluoroapatite, fluorosis will be expected to make etching of enamel more difficult. Hence, it has been suggested that etching time for fluorosed teeth should be doubled. [60]

Moreover, the fluoride content of fluorosed enamel depends on the severity of fluorosis. [54],[60] Consequently, the effect of varying severity of fluorosis on the pattern and depth of etch (depth of demineralization) of human enamel was investigated, using 37% phosphoric acid, an etchant commonly used in restorative dentistry. [61] It was observed that the depth of etching teeth with mild fluorosis (TFI = 1-3) was similar to that in non-fluorosed teeth (TFI = 0), suggesting that etching of teeth with mild or no fluorosis should be similar. A similar observation was seen in East Africa. [62] This is not surprising because fluoride concentration of surface enamel of mildly fluorosed (TFI = 1-3) teeth is not significantly different from that in non-fluorosed teeth (TFI = 0). [60],[63]

In contrast, etching time had to be doubled in teeth with moderate fluorosis (TFI = 4) to obtain the depth of etch as with non-fluorosed teeth. This indicates that etching time of teeth with TFI = 4 should be, at least, twice that for non-fluorosed teeth. In teeth with surface enamel loss (TFI = 5+), depth of etch depended on whether the surface enamel was intact or detached. [61]


  Bonding to Fluorosed teeth Top


Enamel

Resin cements are used for bonding laminate veneers and crowns in the esthetic management of severe fluorosis. Several laboratory studies have, therefore, been carried out to investigate the effect of fluorosis on bond strength of resin composite to enamel. Some of the studies were done with the hypermineralized surface enamel intact, while in other investigations, the outer 2-3 mm of enamel was removed to flatten the tooth surface for shear bond strength testing. In studies in which the hypermineralized surface enamel was left intact, bond strength was adversely affected by fluorosis. [64] On the other hand, bond strength was unaffected by severity of fluorosis when surface enamel was removed prior to bond strength testing. [65],[66] Furthermore, microtensile bond strength of porcelain laminate veneer, bonded to enamel after removal of the hypermineralized surface layer, was unaffected by severity of fluorosis. [66] Also, it was reported that shear bond strength was significantly lower with self-etching and etch-and-rinse bonding systems when enamel was ground. [67] It should be remembered that high fluoride concentration is usually in the outer 200 μm. [60] This hypermineralized surface layer is more resistant to acid dissolution. Removal of the outer 2-3 mm exposes the subsurface enamel with lower fluoride concentration. This possibly explains why bond strength may be unaffected by severity of fluorosis when the hypermineralized surface enamel is removed.

It has been reported that the mode of bond failure is influenced by age and severity of fluorosis. For example, it was reported that shear bond strength of resin composite to fluorosed enamel was significantly higher in teeth extracted from patients aged below 40 years than those aged 40 years and above [65] At T-F score of 1-3, bond failure was predominantly mixed at all ages and etching times, but at TFI = 4-6, bond failure was mostly cohesive in enamel, especially in teeth of patients aged 40 years and above. [65] This may be due to extensive subsurface porosity and protracted post-eruptive occlusal trauma in teeth with moderate-to-severe fluorosis.

Bond strength of different types of bonding systems on fluorosed enamel has been studied by a number of investigators. Just as in non-fluorosed teeth, bond strength was significantly higher with etch-and-rinse bonding systems than self-etch adhesives. [25],[64],[68] Pre-etching with 37% phosphoric acid improved bonding to moderately and severely fluorosed enamel when self-etching primer was used. [68] The bond strength of 2 mm × 3 mm ceramic discs was investigated (IPS Empress 2) to fluorosed and non-fluorosed tooth surfaces, using etch-and-rinse or self-etch luting resin cements. [69] Shear bond strength was significantly higher with the etch-and-rinse resin cement.

The micro-shear bond strength (MSBS) of two all-in-one dentin bonding systems to unground enamel surfaces of fluorosed and non-fluorosed teeth was studied. [70] It was observed that fluorosis had no significant effect on MSBS. This may be due to the shallow hybrid layer produced by both adhesives. Moreover, bond failure was mostly adhesive. The purported advantage of using all-in-one adhesive for cementation of an esthetic restoration on unprepared fluorosed teeth is that the treatment would be non-invasive: If the restoration fails, enamel surface would not have been damaged. By measuring MSBS, there was no need to flatten the enamel surface for shear bond strength testing. [70],[71]

Dentin

As dentin may sometimes be exposed in teeth prepared for laminate veneers or crowns, cementation of the restorations with resin cement may involve dentin. Thus, information on bond strength of resin composite to fluorosed dentin is of interest. No statistically significant difference was observed when Scotchbond Multipurpose (3M) (an etch-and-rinse bonding system) was used for bonding resin composite to dentin of teeth with mild, moderate and severe fluorosis. [72] Similarly, it was also observed that fluorosis had no significant effect on shear bond strength when Clearfil SE Bond(Kuraray ESPE) was used as an adhesive. [73] These two studies suggest that fluorosis may not adversely affect adhesive cementation of veneers and crowns to dentin of fluorosed teeth.

The micro-tensile bond strength of resin composite to teeth with either mild, moderate or severe fluorosis was compared. [77] It was observed that the two-step self-etching adhesive (Clearfiil SE Bond/Kuraray Medical) generally had higher bond strength than the all-in-one bonding system (Clearfil Tri S Bond/Kuraray Medical) and the etch-and-rinse bonding system (Single Bond/3M-ESPE). Although the bond strength of Clearfil SE Bond was higher than that of Single Bond for moderately fluorosed dentin, the difference was not statistically significant. The high bond strength with Clear filSE Bond may be due to the fact that its primer is only mildly acidic, enabling its adhesive monomer (10-methacryloyloxydecyl dihydrogen phosphate, 10-MDP) to chemically bond with residual hydroxyapatite crystals in the hybrid layer. This may be a result of altered mineralization of interglobular dentin of fluorosed teeth. It is possibly analogous to decrease in bond strength of glass-ionomer-based materials to dentin with increasing severity of fluorosis; calcium ions for bonding to carboxyl group of glass-ionomers are depleted in interglobular dentin of severely fluorosed teeth. [75] Further research, particularly clinical trials, are needed to clarify the effect of fluorosis on dentin bond strengths of different types of adhesive systems.


  Discussion Top


The cosmetic defect from tooth discoloration of severe fluorosis in endemic countries may affect the quality of life. [76] In most other countries, however, dental fluorosis tends to be mild or very mild, in spite of the increasing prevalence of the condition due to the use of fluoride in preventive dentistry. Mild fluorosis may require no therapeutic intervention. In fact, Do and Spencer reported that teeth with mild fluorosis (TFI = 1-2) in Australia were considered more esthetically pleasing than non-fluorosed teeth. [77] In a study carried out among children and their mothers in three Ethiopian Rift Valley villages known for endemic fluorosis, the children considered teeth with TFI = 2 and 3 esthetically acceptable, but found TFI = 5 and 7 unacceptable. [78] Their mothers were more critical of the appearance of fluorosed teeth than the children. Moreover, parents in Iceland, Ireland and England considered only teeth with TFI = 3+ to be of esthetic concern [80] ). In all the studies, esthetic concern of fluorosed teeth increased with T-F scores, and mild fluorosis (TFI = 1-2) were not of esthetic concern and therefore do not usually require the rapeutic intervention.

In line with the current trend toward minimally invasive dentistry, many clinicians advocate that teeth with cosmetically objectionable mild-to-moderate fluorosis be treated by bleaching. [38],[39],[40] In some cases, bleaching was preceded by etching with 35-37% phosphoric acid. [39] While Loyola-Rodriguez et al. in 2003 applied this non-invasive form of treatment to teeth with TSIF = 1-3, Flores et al. in 2009 advocated it for teeth with TSIF = 1-4. It is possible that the biological changes in the teeth treated by these two groups of clinicians were similar, but that the weighting given to staining in Horowitz's index made the difference between TSIF = 1-3 and TSIF = 1-4. [27]

Clinicians appreciate the fact that a bleaching agent may not easily penetrate the hypermineralized surface enamel to remove stains entrapped in the subsurface porosities of fluorosed teeth. Hence, bleaching is often preceded by etching or microabrasion. [39],[42],[45] Because the slurry used for microabrasion contains acid, there may be no need for etching as a separate step. Thus, there seems to be a consensus that esthetically objectionable fluorosed teeth, without surface enamel loss, should be treated by a combination of microabrasion and bleaching. It should be noted that microabrasion results in the loss of about 100 μm of surface enamel. As the porous enamel zone in teeth with TFI = 1-3 is located about 80-100 μm into surface enamel, it is possible that the porosities together with the entrapped extrinsic stains are removed by microabrasion of mildly fluorosed teeth. [17]

Train et al. reported marked enamel surface irregularities following treatment of severe fluorosis by microabrasion. [51] Such surface irregularities, due to exposed subsurface enamel porosities, predispose to recurrent staining. It has been suggested that the porosities be sealed with low viscosity resin, but the longevity of such a seal has not been evaluated by randomized clinical trials. The alternative is to place laminate veneers, preferably porcelain laminate veneers. If 0.3-0.5 mm of surface enamel is removed during tooth preparation, bond strength of the restoration, luted by resin cement, would not be expected to be compromised by the severity of fluorosis. If the veneer is bonded to unprepared fluorosed tooth, however, bond strength would be expected to be relatively low. To maximize bond strength under this situation, etch-and-rinse bonding system should be used. In addition etching time with 35-37% phosphoric acid may be at least doubled. [61],[79]

When up to half of the surface enamel has been lost as a result of fluorosis, the remaining enamel may be inadequate for bonding laminate veneers. In which case the severely fluorosed tooth should be crowned. Judging by the results of laboratory studies, bond strength of the luting resin cement to dentin of the prepared tooth would be expected to be similar to that of non-fluorosed tooth. [72],[73] If fluorosis is severe, the clinician may take advantage of the relatively high bond strength obtainable with two-step self-etch bonding system to severely fluorosed dentin. [74]

Future Research

Most reports of the management options for fluorosed teeth have been anecdotal. There appears to be no reports of long-term follow-up of treated cases. There is, therefore, a need for prospective randomized clinical trials of various management options for cases with varying severity of fluorosis. Most clinicians have used hydrogen peroxide or carbamide peroxide for bleaching fluorosed teeth, while others have used sodium hypochlorite. Studies are needed to compare sodium hypochlorite with hydrogen peroxide/carbamide peroxide as bleaching agent for fluorosed teeth. The visual analog scale (VAS) for assessing the effectiveness of microabrasion in the removal of fluorosis stains may be a useful tool for the long-term studies. [44] It should be realized, however, that the VAS does not take into consideration the severity of biological changes in the fluorosed enamel, factors that may influence the treatment outcome.

The poor prognosis of microabrasion in the treatment of severe fluorosis may be due to at least two factors. Firstly, the microporous zone may be too deep-seated to be completely removed by the treatment. The residual porosities may therefore attract extrinsic stains responsible for recurrence. Secondly, the pore volume of the residual microporous zone may exceed the critical level of about 10-15% above which surface enamel may be prone to damage by occlusal forces, thereby creating a rough surface. [17] To overcome these problems, some clinicians apply low viscosity resin to seal the irregularities on the enamel surface, after microabrasion. Clinical studies are needed to evaluate, on the long term, the ability of the resin to prevent recurrent staining in teeth with severe fluorosis. The research should also investigate the most appropriate type of resin that should be used, from the point of view of viscosity and filler particle size. The results of these clinical studies could well make it possible to manage all fluorosed teeth by microabrasion and bleaching, irrespective of the severity of fluorosis.

In parts of severely fluorosed teeth with surface enamel loss, Thylstrup and Fejerskov observed a tendency toward various degrees of reduced pore volume. [17] This may be due to remineralization of the microporous zone. Prolonged stimulation of remineralization after the removal of the entrapped extrinsic stains may, therefore, result in sclerosis of the hypomineralized enamel. Sclerosis of the enamel would prevent recurrence of staining. Hence, future research should investigate the effect of application of compounds with potential to encourage enamel remineralization, such as fluoride, calcium sucrose phosphate or a complex comprising amorphous calcium phosphate and casein phosphate.


  Conclusions Top


  1. As a result of the use of fluoride in preventive dentistry, the prevalence of mild to moderate dental fluorosis is on the increase in most countries. Because mild fluorosis may not necessarily be of esthetic concern in many communities, therapeutic intervention may not be required in many of such cases.
  2. The Thylstrup and Fejerskov classification provides an index that is most useful in the selection of the appropriate treatment option for esthetically objectionable fluorosed teeth.
  3. Teeth with TFI = 3+ are of esthetic concern in most communities and as the effects on the hard dental tissues are irreversible, therapeutic intervention is needed to improve appearance.
  4. Esthetically objectionable fluorosed teeth with no loss of surface enamel (TFI = 1-4) may be treated by a combination of microabrasion and bleaching.
  5. Where there has been loss of surface enamel, esthetically objectionable fluorosed teeth may be managed by porcelain laminate veneers, provided not more than 30-50% of labial enamel has been lost, and the margins of the restoration can be placed on intact enamel.
  6. Cases of fluorosed teeth in which more than 50% of surface enamel has been lost (TFI = 8-9) should be treated by crowning.
  7. If porcelain laminate veneer is bonded to a fluorosed tooth after removal of the hypermineralized enamel surface layer, bond strength may not be adversely affected by severity of fluorosis. However, if the ceramic veneer is bonded to unprepared tooth surface, fluorosis may compromise bond strength; and, in such a circumstance, etch-and rinse bonding system should be preferred.
  8. Long-term clinical studies are required to evaluate the various management options for teeth with varying severity of fluorosis, measured by TFI.



  cknowledgement Top


Author is grateful to Professor Tonie V.I. Akpata for proof reading the manuscript and Mohammed Said for the secretarial support.

 
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