Biological mechanisms of fluorosis and level and timing of systemic exposure to fluoride with respect to fluorosis

Orthodontic bonding in special circumstances

This clinical paper provides an in-depth exploration of advanced techniques for bonding orthodontic attachments under special circumstances. Challenges arise when bonding brackets to non-enamel surfaces, such as dental restorations, and in conditions such as amelogenesis imperfecta, which affect enamel integrity. Distinct approaches required for bonding to different restorative materials, including glassy ceramics, zirconia, resin composites and metals, are outlined. Moreover, we describe strategies to manage bonding in conditions including amelogenesis imperfecta, hypodontia and microdontia in a multidisciplinary context.

Bonding to Fluorosed Teeth: A Review of the Literature

Excessive fluoride availability during tooth formation can cause structural alterations in enamel and dentin. These alterations may negatively impact the adhesion of various dental materials to teeth with dental fluorosis. The aim of this review of literature is to identify updates in bonding to fluorosed teeth and summarize relevant recommendations. Findings from the available literature suggest that bonding procedures may be carried out reliably on most fluorosed teeth with consideration to the severity of fluorosis and the employment of additional bond-enhancing measures for the severely involved teeth.

Effects of fluorosed enamel on orthodontic bracket bonding : An in vitro study

OBJECTIVE

To investigate the effect of enamel deproteinization and air abrasion on shear bond strength (SBS), adhesive remnant index (ARI) scores, and surface topography when bonding orthodontic brackets to fluorosed enamel.

MATERIALS AND METHODS

The sample included 90 fluorosed and 30 normal premolars divided into four groups: group I (fluorosed premolars subjected to air abrasion before acid etching), group II (fluorosed premolars subjected to deproteinization before acid etching), group III (fluorosed premolars; control for groups I and II), and group IV (normal premolars; control for group III). Bonding procedures included etching with 37% phosphoric acid, priming with TransbondTM XT primer (3M Unitek, Monrovia, CA, USA), and application of TransbondTM XT adhesive paste (composite; 3M Unitek, Monrovia, CA, USA). Air abrasion was done using 50 µm aluminum oxide particles under 0.28 MPa pressure for 5 s with the micro-etcher held at a distance of 10 mm. Deproteinization was done for 60 s with 5% sodium hypochlorite (NaOCl).

RESULTS

Fluorosed premolars subjected to deproteinization showed the lowest (median = 6.57 MPa) SBS among the four groups, followed by 8.14, 8.90, 8.14 MPa for groups I, III, and IV respectively. ARI scores were significantly different between the four groups (p = 0.006). Fluorosed enamel etched after air abrasion or deproteinization with NaOCl showed a predominance of type 4 etching pattern with some areas appearing unetched.

CONCLUSIONS

Shear bond strength of all groups was within the 6-8 MPa acceptable range for orthodontic purposes. Fluorosed premolars subjected to deproteinization showed the lowest values. Further studies are recommended to scrutinize the deproteinization technique.

Effects of SNPs in SOD2 and SOD3 interacted with fluoride exposure on the susceptibility of dental fluorosis

A total of 649 children aged 7-13 years of age were recruited in a cross-sectional study in Tongxu County, China (2017) to assess the effects of interaction between single nucleotide polymorphisms (SNPs) in SOD2 and SOD3 gene and fluoride exposure on dental fluorosis (DF) status. Associations between biomarkers and DF status were evaluated. Logistic regression suggested that the risk of DF in children with rs10370 GG genotype and rs5746136 TT genotype was 1.89-fold and 1.72-fold than that in children with TT/CC genotype, respectively. Increased T-SOD activity was associated with a lower risk of DF (OR = 0.99). The rs2855262*rs10370*UF model was regarded as the optimal interaction model in generalized multifactor dimensionality reduction analyses. Our findings suggested that rs4880 and rs10370 might be useful genetic markers for DF, and there might be interactions among rs10370 in SOD2, rs2855262 in SOD3, and fluoride exposure on DF status.

Calcium Transport in Specialized Dental Epithelia and Its Modulation by Fluoride

Most cells use calcium (Ca2+) as a second messenger to convey signals that affect a multitude of biological processes. The ability of Ca2+ to bind to proteins to alter their charge and conformation is essential to achieve its signaling role. Cytosolic Ca2+ (cCa2+) concentration is maintained low at ~100 nM so that the impact of elevations in cCa2+ is readily sensed and transduced by cells. However, such elevations in cCa2+ must be transient to prevent detrimental effects. Cells have developed a variety of systems to rapidly clear the excess of cCa2+ including Ca2+ pumps, exchangers and sequestering Ca2+ within intracellular organelles. This Ca2+ signaling toolkit is evolutionarily adapted so that each cell, tissue, and organ can fulfill its biological function optimally. One of the most specialized cells in mammals are the enamel forming cells, the ameloblasts, which also handle large quantities of Ca2+. The end goal of ameloblasts is to synthesize, secrete and mineralize a unique proteinaceous matrix without the benefit of remodeling or repair mechanisms. Ca2+ uptake into ameloblasts is mainly regulated by the store operated Ca2+ entry (SOCE) before it is transported across the polarized ameloblasts to reach the insulated enamel space. Here we review the ameloblasts Ca2+ signaling toolkit and address how the common electronegative non-metal fluoride can alter its function, potentially addressing the biology of dental fluorosis.

Comprehensive Management of Severe Dental Fluorosis with Adhesively Bonded All-Ceramic Restorations

Dental fluorosis is a common disorder caused by excessive fluoride intake during tooth development. The esthetic consequences of dental fluorosis can negatively affect oral health-related quality of life and have lasting psychosocial effects. In severe cases, where the fluorosed enamel is prone to chipping, flaking, and developing caries, minimally invasive procedures are ineffectual and a more substantial restorative approach is required to restore optimal function and esthetics. However, no definitive guidelines exist for the management and treatment of severe dental fluorosis due to the limited evidence available in the literature. This case report describes the full-mouth rehabilitation of a patient with severe dental fluorosis utilizing adhesively bonded all-ceramic crowns, veneers, and overlays. The successful follow-up on this case indicates that adhesively bonded restorations may provide a viable option in the functional and esthetic management of severely fluorosed dentition.

JNK Signaling Pathway Mediates Fluoride-Induced Upregulation of CK1α during Enamel Formation

Fluorosis is a defect in the enamel mineral content caused by excessive fluoride intake during amelogenesis; the interaction of various factors in the development and progression of fluorosis has not been defined. Casein kinase 1α (CK1α) is constitutively active in cells and is involved in diverse cellular processes; however, its expression in fluorosis has not been measured. This study aimed to investigate the effects of fluoride on CK1α expression and to assess the regulation of molecular signaling involving fluoride and CK1α during enamel development. Kunming mice were randomly divided into the control and F groups with induced clinical features of fluorosis. The F group mice, including mothers and newborns, were treated with 50 ppm fluoridated water. Immunohistochemical staining of the sections of the embryonic mandible regions was performed at the bell stage. Protein expression and signaling pathways in a mouse-derived ameloblast-like cell line (LS8) exposed to fluoride or a Jun N-terminal kinase (JNK) inhibitor were compared to those in control cells without exposure. CK1α and proteins of the JNK signaling pathways were assayed by quantitative real-time PCR and Western blotting. Mice of the F group developed dental fluorosis. Scanning electron microscopy showed a significant reduction in the degree of mineralization in the F group mice, which manifested as thin, loosely arranged, and disorganized enamel rods. Additional analysis revealed that the expression of CK1α in the F group was significantly elevated compared with that in the control group; LS8 cells responded to fluoride by upregulation of CK1α expression through the JNK pathway. Our findings identified the potential effects of CK1α on fluorosis using a mouse model and revealed that a high fluoride level increases the expression of CK1α and that JNK can be a key regulatory factor in CK1α expression.

Shear Bond Strength of Three Composite Resins to Fluorosed and Sound Dentine: In Vitro Study

Introduction

This in vitro study compared the shear strength of three composite resin systems to fluorosed and normal dentin.

Methods

Silorane FiltekTM P90, FiltekTMZ250 XT in combination with the adhesive system AdperTM Single bond 2, and Amelogen® Plus in association with Peak Universal Bond® were tested. Fifteen normal and 15 fluorosed dentine disks were prepared per material. The shear bond strength test was performed using a universal machine.

Results

One-way ANOVA revealed significant differences in bond strength between the tested composite resins. All tested materials had significantly different adhesion at the fluorosed and the nonfluorosed interface. FiltekTM Z250 XT and Silorane had lower adhesion values to fluorosed than to normal dentin. In contrast, Amelogen® Plus presented a better average resistance at the fluorosed interface.

Conclusion

Amelogen® Plus presented a better average shear bond strength on the fluorosed dentine. FiltekTMZ250 XT showed the best adhesion forces and shear bond strength with sound dentine. Further studies are needed to better understand the sealing of these systems.

Underlying Resin Infiltration and Direct Composite Veneers for the Treatment of Severe White Color Alterations of the Enamel: Case Report and 13-Month Follow-Up

Pronounced white color alterations due to structural anomalies of the enamel are often insufficiently masked by bleaching techniques or resin infiltration procedures alone. This frequently leads to the choice of more invasive prosthetic restorations in order to correct tooth color and form. This article describes a minimally invasive treatment option for esthetic and functional rehabilitation in the case of a 13-year-old female patient with suspected severe fluorosis and misalignment of the anterior teeth. The restorations were performed using underlying resin infiltration to homogenize the tooth shade. In a second step, direct composite veneers were applied on top to attain a natural tooth color and adjust tooth alignment and form. By joining the two minimally and noninvasive techniques, this treatment option combines the directive for preservation of hard tooth structure while treating adolescents with the benefits of easy adaptation and repair when the occlusion is still in adjustment.

Effects of at-home bleaching and resin infiltration treatments on the aesthetic and psychological status of patients with dental fluorosis: A prospective study

OBJECTIVE

This study aims to evaluate the effect of the combination approach of at-home bleaching (HB) and resin infiltration (RI) techniques on different severity degrees of dental fluorosis (DF) and further analyze the psychological changes caused by HB and RI in patients.

METHOD

Twenty-two patients (4 males, 18 females, 27.8 ± 1.6 yrs) with 186 fluorotic teeth were included in this study and classified into mild (N = 56), moderate (N = 100) and severe (N = 30) DF groups according to the Dean's index. The treatment effects on patients with DF were assessed by questionnaires including the changes in patients' subjective evaluation of their teeth and psychological status before and after treatments. Standardized digital photographs were taken at each time point of the treatment process, including baseline (T1), after bleaching (T2), immediately after RI treatment (T3) and more than six months after RI treatment (T4). The color alterations (ΔE) between the fluorotic (F2) and the surrounding relatively sound areas (F1) were analyzed.

RESULTS

Bad tooth appearance caused 13.64% of patients often depressed, frustrated, or disappointed, whereas 72.72% occasionally had these feelings. After treatment, the satisfaction of DF patients regarding tooth appearance increased from 0% (satisfied) to 58.82% (satisfied) and 23.53% (very satisfied). Moreover, these treatments improved all patients' confidence in smiling, laughing and showing their teeth. The percentage of fluorotic teeth with ΔE values more than 3.0 and 3.7 units decreased gradually from T1 stage to T3 stage in mild and moderate DF groups (p < 0.05), whereas the ΔE value in T3 stage was significantly lower than that of T2 stage in severe DF group (p < 0.05). In T4 stage, no significant difference was observed in the ΔE values between T4 and T3 stages (p > 0.05).

CONCLUSION

This study shows the obvious positive aesthetic effect of HB and RI treatment on different severity degrees of DF and the great improvements in psychological discomforts.

CLINICAL SIGNIFICANCE

The combination treatment of RI and low concentration HB gel improves the aesthetics of DF and may have a stable effect after 6-months follow-up, suggesting that this approach is a valuable clinical choice for dentists to treat DF.

Fast Capture of Fluoride by Anion-Exchange Zirconium-Graphene Hybrid Adsorbent

Fluoride contamination is a severe problem affecting the safety of drinking water around the world. High-rate adsorbent materials are particularly desirable for potable water defluoridation. Current research on fluoride adsorbent materials is primarily focused on metal-based adsorbents with high capacities. However, they generally suffer from slow adsorption kinetics due to the adsorption mechanism of a sluggish exchange between coordinated hydroxyl groups and fluoride ions. Designing metal-based adsorbents to mimic the rapid ion-exchange behavior of anion-exchange resins is a promising approach to integrate fast adsorption and high capacity for fluoride removal. Herein, a ZrO(OH)_1.33Cl_0.66-reduced graphene oxide (rGO) hybrid adsorbent containing exchangeable chloride ions was synthesized with the assistance of cation-π interactions. Unlike most adsorbents requiring a high surface area, this composite has a negligible surface area (1.45 m² g^-1), but can deliver a fast fluoride capture performance (reaching equilibrium in 5 min) with high adsorption rate constants of 1.05 min^-1 and 0.171 mg g^-1 min^-1, around 10 times faster than the best result reported in the literature. Besides, ZrO(OH)_1.33Cl_0.66-rGO can also demonstrate a high fluoride uptake (44.14 mg g^-1) and high removal efficiency (94.4%) in 35 mg L^-1 fluoride solution, both among the highest performances for fluoride adsorption.

Enamel Microabrasion and Dental Bleaching on Teeth Presenting Severe-pitted Enamel Fluorosis: A Case Report

The present clinical case report describes the clinical steps of enamel microabrasion associated with dental bleaching to restore severely-pitted fluorosed teeth. The process of removing the fluorotic superficial stains started by using macroabrasion with a water-cooled fine tapered 3195 FF diamond bur. Rubber dam isolation of the operative field was used to remove the remaining enamel stains and superficial irregularities with the Opalustre microabrasive compound (6.6% hydrochloric acid associated with silicon carbide particles) followed by polishing using fluoridated paste and subsequent 2% neutral fluoride gel topical application. After one month, dental bleaching was performed using 10% carbamide peroxide in custom-formed acetate trays for two hours/day for 42 days. The association of enamel microabrasion with dental bleaching was effective for reestablishing the dental esthetics of a patient with severe dental fluorosis.

The relationships between fluoride intake levels and fluorosis of late-erupting permanent teeth

OBJECTIVES

To examine the relationships between fluoride intake levels and fluorosis of late-erupting permanent teeth.

METHODS

The current study used information collected from 437 children in the longitudinal Iowa Fluoride Study. Participants' fluoride intake information was collected using questionnaires from birth to age 10 years. Estimated mean daily fluoride intake was categorized into low, moderate, and high intake tertiles for each age interval (2-5, 5-8, and 2-8 years). Bivariate analyses were performed to study the relationships between self-reported fluoride intake levels during three age intervals and dental fluorosis.

RESULTS

For canines and second molars, the prevalence of mostly mild fluorosis was less than 10% in the lowest fluoride intake tertile and more than 25% in the highest intake tertile. For both first and second premolars, the prevalence in the low and high intake tertiles was approximately 10-15% and 25-40%, respectively. When estimated total daily fluoride intake was 0.04 mg/kg BW during ages 2-8 years, the predicted probability of fluorosis was 16.0%, 20.5%, 21.8%, and 15.4% for canines, 1st and 2nd and premolars and 2nd molars, respectively. We found that an incremental increase in fluoride intake during the age 5- to 8-year interval led to greater odds for development of mostly mild dental fluorosis in late-erupting teeth compared to increases in fluoride intake during other age intervals.

CONCLUSIONS

Our results clearly show that dental fluorosis prevalence is closely related to fluoride intake levels and that teeth have greater susceptibility to fluoride intake during certain age intervals.

Fluoride Alters Klk4 Expression in Maturation Ameloblasts through Androgen and Progesterone Receptor Signaling

Fluorosed maturation stage enamel is hypomineralized in part due to a delay in the removal of matrix proteins to inhibit final crystal growth. The delay in protein removal is likely related to reduced expression of kallikrein-related peptidase 4 (KLK4), resulting in a reduced matrix proteinase activity that found in fluorosed enamel. Klk4 transcription is known to be regulated in other cell types by androgen receptor (AR) and progesterone receptors (PR). In this study, we determined the possible role of fluoride in down-regulation of KLK4 expression through changes in AR and PR. Immunohistochemical localization showed that both AR and PR nuclear translocation was suppressed in fluoride exposed mice. However, when AR signaling was silenced in mouse ameloblast-lineage cells (ALCs), expression of both Pgr and Klk4 were increased. Similar to the effect from AR silencing, fluoride also upregulated Pgr in ALCs, but downregulated Klk4. This finding suggests that though suppression of AR transactivation by fluoride increases Prg expression, inhibition of PR transactivation by fluoride has a much greater effect, ultimately resulting in downregulation of Klk4 expression. These findings indicate that in ameloblasts, PR has a dominant role in regulating Klk4 expression. We found that when AR was retained in the cytoplasm in the presence of fluoride, that co-localized with heat shock protein 90 (HSP90), a well-known chaperone for steroid hormone receptors. HSP90 also known to regulate TGF-β signaling. Consistent with the effect of fluoride on AR and HSP90, we found evidence of reduced TGF-β signaling activity in fluorosed ameloblasts as reduced immunolocalization of TGFB1 and TGFBR-2 and a significant increase in Cyclin D1 mRNA expression, which also possibly contributes to the reduced AR signaling activity. In vitro, when serum was removed from the media, aluminum was required for fluoride to inhibit the dissociation of HSP90 from AR. In conclusion, fluoride related downregulation of Klk4 is associated with reduced nuclear translocation of AR and PR, and also reduced TGF-β signaling activity, all of which are regulated by HSP90. We suggest that a common mechanism by which fluoride affects AR, PR, and TGF-β signaling is through inhibiting ATP-dependent conformational cycling of HSP90.

Timing of fluoride intake and dental fluorosis on late-erupting permanent teeth

OBJECTIVE

Very few studies have examined the relationship between timing of fluoride intake and development of dental fluorosis on late-erupting permanent teeth using period-specific fluoride intake information. This study examined this relationship using longitudinal fluoride intake information from the Iowa Fluoride Study.

METHODS

Participants' fluoride exposure and intake (birth to 10 years of age) from water, beverages, selected food products, dietary fluoride supplements, and fluoride toothpaste was collected using questionnaires sent to parents at 3- and 4- month intervals from birth to 48 months of age and every 6 months thereafter. Three trained and calibrated examiners used the Fluorosis Risk Index (FRI) categories to assess 16 late-erupting teeth among 465 study participants. A tooth was defined as having definitive fluorosis if any of the zones on that tooth had an FRI score of 2 or 3. Participants with questionable fluorosis were excluded from analyses. Descriptive and logistic regression analyses were performed to assess the importance of fluoride intake during different time periods.

RESULTS

Most dental fluorosis in the study population was mild, with only four subjects (1%) having severe fluorosis (FRI Score 3). The overall prevalence of dental fluorosis was 27.8%. Logistic regression analyses showed that fluoride intake from each of the individual years from age 2 to 8 plays an important role in determining the risk of dental fluorosis for most late-erupting permanent teeth. The strongest association for fluorosis on the late-erupting permanent teeth was with fluoride intake during the sixth year of life.

CONCLUSION

Late-erupting teeth may be susceptible to fluorosis for an extended period from about age 2 to 8. Although not as visually prominent as the maxillary central incisors, some of the late-erupting teeth are esthetically important and this should be taken into consideration when making recommendations about dosing of fluoride intake.

Effects of long-term repeated topical fluoride applications and adhesion promoter on shear bond strengths of orthodontic brackets

Objective:

The purpose of this study was to assess the effects of long-term repeated topical application of fluoride before bonding and an adhesion promoter on the bond strength of orthodontic brackets.

Materials and Methods:

A total of 76 bovine incisors were collected and divided equally into four groups. In group 1, the brackets were bonded without topical fluoride application or adhesion promoter. In group 2, before bonding, the adhesion promoter was applied to nonfluoridated enamel. In group 3, the brackets were bonded without the application of the adhesion promoter to enamel, which had undergone long-term repeated topical fluoride treatments. Teeth in group 4 received the long-term repeated topical applications of fluoride, and the brackets were bonded using the adhesion promoter. All the brackets were bonded using BeautyOrtho Bond self-etching adhesive. The shear bond strength was measured and the bond failure modes were evaluated with the use of the adhesive remnant index (ARI) after debonding.

Results:

The mean shear bond strength was significantly lower in group 3 than in groups 1, 2, and 4, and there were no significant differences between the groups except for group 3. There were significant differences in the distribution of ARI scores between groups 2 and 3, and between groups 3 and 4.

Conclusions:

The adhesion promoter can recover the bond strength reduced by the long-term repeated topical applications of fluoride to the prefluoridation level and had a significantly great amount of adhesives left on either fluoridated or nonfluoridated enamel.

Micromorphology analysis and bond strength of two adhesives to Er,Cr:YSGG laser-prepared vs. bur-prepared fluorosed enamel

Preservation of enamel during composite veneer restorations of fluorosed teeth could be achieved by conservative preparation with Erbium lasers. This study evaluated the effect of fluorosed enamel preparation with Er,Cr:YSGG vs. conventional diamond bur on the micromorphology and bond strength of a self-etch and an etch-and-rinse adhesives. Er,Cr:YSGG laser or diamond bur preparation was performed on the flattened midbuccal surfaces of 70 extracted human premolars with moderate fluorosis (according to Thylstrup and Fejerskov index, TFI = 4-6). Adper Single Bond (SB) with acid etching for 20 or 40 s and Clearfil SE Bond (SEB) alone or with additional etching was applied in four laser groups. The same adhesive procedures were used in three bur groups except for 40 s of etching along with SB. After restoration, microshear bond strength was measured (MPa). Data were analyzed using ANOVA and Tamhane tests (α = 0.05). Six additional specimens were differently prepared and conditioned for scanning electron microscopy evaluation. The highest and lowest bond strengths were obtained for bur-prepared/SB (39.5) and laser-prepared/SEB (16.9), respectively, with a significant difference (P = 0.001). The different adhesive procedures used associated to two adhesives exhibited insignificantly lower bonding in laser-prepared groups compared to bur-prepared ones (P > 0.05), with the exception of additional etching/SEB, which bonded significantly higher to bur-prepared (36.4) than to laser-prepared enamel (18.7, P = 0.04). Morphological analyses revealed a delicate etch pattern with exposed enamel prisms on laser-prepared fluorosed enamel after acid etching and less microretentive pattern after self-etching primer. The etch-and-rinse adhesive was preferred in the laser-prepared fluorosed enamel in terms of bonding performance.

Fluoridated toothpaste: usage and ingestion of fluoride by 4- to 6-yr-old children in England

Fluoridated toothpaste is effective for dental caries control, yet may be a risk factor for dental fluorosis. This study aimed to quantify fluoride ingestion from toothpaste by children and to investigate the effects of age, gender, and social class on the amount of fluoride ingested per toothbrushing session. Sixty-one children, 4-6 yr of age, were recruited: 38 were from low socio-economic (LSE) areas of Newcastle, UK, and 23 were from high socio-economic (HSE) areas of Newcastle, UK. All expectorated saliva, rinse water (if used), and residual toothpaste were collected after brushing at home and were analysed for fluoride. Of the children, 74% and 69% from HSE and LSE areas, respectively, claimed that they brushed twice per day. The mean (SD) weight of toothpaste dispensed was 0.67 (0.36) g. The mean (SD) amount of fluoride ingested per toothbrushing session and per day was 17.0 (14.7) and 29.3 (32.8) μg kg(-1) of body weight, respectively. Daily fluoride intake per kilogram of body weight did not differ significantly between children from LSE and HSE areas. Fluoride intake per toothbrushing session was significantly influenced by weight of toothpaste, its fluoride concentration, and the child's age. Whilst the average amount of toothpaste used per toothbrushing session was more than twice the recommended amount (of 0.25 g), only one child had a daily fluoride intake that exceeded the tolerable upper intake level of 0.1 mg kg(-1) of body weight for this age group.

Evidence-based clinical recommendations regarding fluoride intake from reconstituted infant formula and enamel fluorosis: a report of the American Dental Association Council on Scientific Affairs

BACKGROUND

This article presents evidence-based clinical recommendations regarding the intake of fluoride from reconstituted infant formula and its potential association with enamel fluorosis. The recommendations were developed by an expert panel convened by the American Dental Association (ADA) Council on Scientific Affairs (CSA). The panel addressed the following question: Is consumption of infant formula reconstituted with water that contains various concentrations of fluoride by infants from birth to age 12 months associated with an increased risk of developing enamel fluorosis in the permanent dentition?

TYPES OF STUDIES REVIEWED

A panel of experts convened by the ADA CSA, in collaboration with staff of the ADA Center for Evidence-based Dentistry (CEBD), conducted a MEDLINE search to identify systematic reviews and clinical studies published since the systematic reviews were conducted that addressed the review question.

RESULTS

CEBD staff identified one systematic review and two clinical studies. The panel reviewed this evidence to develop recommendations.

CLINICAL IMPLICATIONS

The panel suggested that when dentists advise parents and caregivers of infants who consume powdered or liquid concentrate infant formula as the main source of nutrition, they can suggest the continued use of powdered or liquid concentrate infant formulas reconstituted with optimally fluoridated drinking water while being cognizant of the potential risks of enamel fluorosis development. These recommendations are presented as a resource to be considered in the clinical decision-making process. As part of the evidence-based approach to care, these clinical recommendations should be integrated with the practitioner's professional judgment and the patient's needs and preferences.

Oral-health-related quality of life in schoolchildren in an endemic fluorosis area of Mexico

OBJECTIVE

To evaluate the oral-health-related quality of life (OHRQoL) of children living in an endemic hydrofluorosis area.

METHODS

Schoolchildren aged 8-10 years living in an area with 3.38 ppm F water concentration completed a validated Spanish version of the Child Perceptions Questionnaire (CPQ(8-10ESP)). World Health Organization (WHO) criteria were applied for the diagnosis of dental caries and malocclusion. Additionally, the Thylstrup and Fejerskov Index (TFI) was used for fluorosis diagnosis. CPQ(8-10ESP) scores and oral health status were analyzed using non-parametric tests and logistic regression models.

RESULTS

Two hundred and twelve schoolchildren participated in this study. The mean CPQ(8-10ESP) score was 12.98 (SD 11.4). General oral health was rated as "poor" in 14.6%, "fair" in 41.5%, "good" in 25.9%, and "very good" in 17.9% of the children. Regarding overall well-being, half (51.6%) of the children perceived that the condition of their mouths disturbs their quality of life (QoL). Children with dental fluorosis (TF >4) had a high CPQ(8-10ESP) score in all domains (P < 0.005). Additionally, children with DMFS + dmfs >5 had higher scores in the oral symptoms, functional limitation, and emotional well-being CPQ(8-10ESP) domains (P < 0.05). Applying a CPQ(8-10ESP) cutoff point of 32, the OR values for severe malocclusion, caries, and fluorosis were 5.2 (P = 0.034), 4.6 (P = 0.006), and 5.1 (P = 0.007), respectively.

CONCLUSIONS

Malocclusion, caries, and fluorosis were associated with a negative impact on children's QoL.

Fluoride's effects on the formation of teeth and bones, and the influence of genetics

Fluorides are present in the environment. Excessive systemic exposure to fluorides can lead to disturbances of bone homeostasis (skeletal fluorosis) and enamel development (dental/enamel fluorosis). The severity of dental fluorosis is also dependent upon fluoride dose and the timing and duration of fluoride exposure. Fluoride's actions on bone cells predominate as anabolic effects both in vitro and in vivo. More recently, fluoride has been shown to induce osteoclastogenesis in mice. Fluorides appear to mediate their actions through the MAPK signaling pathway and can lead to changes in gene expression, cell stress, and cell death. Different strains of inbred mice demonstrate differential physiological responses to ingested fluoride. Genetic studies in mice are capable of identifying and characterizing fluoride-responsive genetic variations. Ultimately, this can lead to the identification of at-risk human populations who are susceptible to the unwanted or potentially adverse effects of fluoride action and to the elucidation of fundamental mechanisms by which fluoride affects biomineralization.

The acid test of fluoride: how pH modulates toxicity

Background

It is not known why the ameloblasts responsible for dental enamel formation are uniquely sensitive to fluoride (F⁻). Herein, we present a novel theory with supporting data to show that the low pH environment of maturating stage ameloblasts enhances their sensitivity to a given dose of F⁻. Enamel formation is initiated in a neutral pH environment (secretory stage); however, the pH can fall to below 6.0 as most of the mineral precipitates (maturation stage). Low pH can facilitate entry of F⁻ into cells. Here, we asked if F⁻ was more toxic at low pH, as measured by increased cell stress and decreased cell function.

Methodology/Principal Findings

Treatment of ameloblast-derived LS8 cells with F⁻ at low pH reduced the threshold dose of F⁻ required to phosphorylate stress-related proteins, PERK, eIF2α, JNK and c-jun. To assess protein secretion, LS8 cells were stably transduced with a secreted reporter, Gaussia luciferase, and secretion was quantified as a function of F⁻ dose and pH. Luciferase secretion significantly decreased within 2 hr of F⁻ treatment at low pH versus neutral pH, indicating increased functional toxicity. Rats given 100 ppm F⁻ in their drinking water exhibited increased stress-mediated phosphorylation of eIF2α in maturation stage ameloblasts (pH<6.0) as compared to secretory stage ameloblasts (pH∼7.2). Intriguingly, F⁻-treated rats demonstrated a striking decrease in transcripts expressed during the maturation stage of enamel development (Klk4 and Amtn). In contrast, the expression of secretory stage genes, AmelX, Ambn, Enam and Mmp20, was unaffected.

Conclusions

The low pH environment of maturation stage ameloblasts facilitates the uptake of F⁻, causing increased cell stress that compromises ameloblast function, resulting in dental fluorosis.

Fluoride-induced thyroid dysfunction in rats: roles of dietary protein and calcium level

To assess the roles of dietary protein (Pr) and calcium (Ca) level associated with excessive fluoride (F) intake and the impact of dietary Pr, Ca, and F on thyroid function, 144 30-day-old Wistar albino rats were randomly allotted to six groups of 24 (female:male = 1:1). The six groups were fed (1) a normal control (NC) diet (17.92% Pr, 0.85% Ca = NC group); (2) the NC diet and high F (338 mg NaF [=150 mg F ion]/L in their drinking water = NC+F group); (3) low Pr and low Ca diet (10.01% Pr, 0.24% Ca = LPrLCa group); (4) low Pr and low Ca diet plus high F = LPrLCa+F group; (5) high Pr and low Ca diet plus high F (25.52% Pr, 0.25% Ca = HPrLCa+F group); and (6) low Pr and high Ca diet plus high F (10.60% Pr, 1.93% Ca = LPrHCa+F group). The areas of thyroid follicles were determined by Image-Proplus 5.1, and triiodothyronine (T3), free T3 (FT3), thyroxine (T4), and free T4 (FT4) levels in serum were measured by radioimmunoassay. The histopathological study revealed obviously flatted follicular epithelia cells and hyperplastic nodules, consisting of thyroid parafollicular cells that appeared by excessive F ingestion, on the 120th day. Pr or Ca supplementation reverses the F-induced damage in malnutrition. The serum T3, FT3, T4, and FT4 levels in the NC+F group were significantly decreased and significantly increased in the LPrLCa+F group. Thus, excessive F administration induces thyroid dysfunction in rats; dietary Pr and Ca level play key roles in F-induced thyroid dysfunction.

Fluoride induces endoplasmic reticulum stress and inhibits protein synthesis and secretion

BACKGROUND

Exposure to excessive amounts of fluoride (F(-)) causes dental fluorosis in susceptible individuals; however, the mechanism of F(-)-induced toxicity is unclear. Previously, we have shown that high-dose F(-) activates the unfolded protein response (UPR) in ameloblasts that are responsible for dental enamel formation. The UPR is a signaling pathway responsible for either alleviating endoplasmic reticulum (ER) stress or for inducing apoptosis of the stressed cells.

OBJECTIVES

In this study we determined if low-dose F(-) causes ER stress and activates the UPR, and we also determined whether F(-) interferes with the secretion of proteins from the ER.

METHODS

We stably transfected the ameloblast-derived LS8 cell line with secreted alkaline phosphatase (SEAP) and determined activity and localization of SEAP and F(-)-mediated induction of UPR proteins. Also, incisors from mice given drinking water containing various concentrations of F(-) were examined for eucaryotic initiation factor-2, subunit alpha (eIF2alpha) phosphorylation.

RESULTS

We found that F(-) decreases the extracellular secretion of SEAP in a linear, dose-dependent manner. We also found a corresponding increase in the intracellular accumulation of SEAP after exposure to F(-). These changes are associated with the induction of UPR proteins such as the molecular chaperone BiP and phosphorylation of the UPR sensor PKR-like ER kinase, and its substrate, eIF2alpha. Importantly, F(-)-induced phosphorylation of eIF2alphawas confirmed in vivo.

CONCLUSIONS

These data suggest that F(-) initiates an ER stress response in ameloblasts that interferes with protein synthesis and secretion. Consequently, ameloblast function during enamel development may be impaired, and this may culminate in dental fluorosis.

Detection of dental fluorosis-associated quantitative trait Loci on mouse chromosomes 2 and 11

Systemic exposure to greater than optimal fluoride (F) can lead to dental fluorosis (DF). Parental A/J (DF-susceptible) and 129P3/J (DF-resistant) inbred mice were used for histological studies and to generate F2 progeny. Mice were treated with 0 or 50 ppm F in their drinking water for 60 days. A clinical criterion (modified Thylstrup and Fejerskov categorical scale) was used to assess the severity of DF for each individual F2 animal. Parental strains were subjected to histological examination of maturing enamel. F treatment resulted in accumulation of amelogenins in the maturing enamel of A/J mice. Quantitative trait loci (QTL) detection was performed using phenotypic extreme F2 animals genotyped for 354 single nucleotide polymorphism-based markers distributed throughout the mouse genome followed by chi(2) analysis. Significant evidence of association was observed on chromosomes 2 and 11 for a series of consecutive markers (p < 0.0001). Further analyses were performed to examine whether the phenotypic effects were found in both male and female F2 mice or whether there was evidence for gender-specific effects. Analyses performed using the markers on chromosomes 2 and 11 which were significant in the mixed-gender mice were also significant when analyses were limited to only the male or female mice. The QTL detected on chromosomes 2 and 11 which influence the variation in response to fluorosis have their effect in mice of both genders. Finally, the QTL in both chromosomes appear to have an additive effect.

In Vivo Bonding of Orthodontic Brackets to Fluorosed Enamel using an Adhesion Promotor

Objectives: To determine the success of bracket retention using an adhesion promoter with and without the additional microabrasion of enamel.

Materials and Methods: Fifty-two teeth with severe dental fluorosis were bonded in vivo using a split-mouth design where the enamel surfaces of 26 teeth were microabraded with 50 μm of aluminum silicate for 5 seconds under rubber dam and high volume suction. Thirty-seven percent phosphoric acid was then applied to the enamel, washed and dried, and followed by placement of Scotchbond Multipurpose Plus Bonding Adhesive. Finally, precoated 3M Unitek Victory brackets were placed and light cured. The remaining teeth were bonded using the same protocol but without microabrasion.

Results: After 9 months of intraoral service, only one bond failure occurred in the control group where microabrasion was used. Chi-square analysis revealed P = .31, indicating no statistical significance between the two groups.

Conclusions: Bonding orthodontic attachments to fluorosed enamel using an adhesion promoter is a viable clinical procedure that does not require the additional micro-mechanical abrasion step.

Micromolar fluoride alters ameloblast lineage cells in vitro

Fluorosed enamel is caused by exposure to fluoride during tooth formation. The objective of this study was to determine whether epithelial ameloblast-lineage cells, derived from the human enamel organ, are directly affected by micromolar concentrations of fluoride. Cells were cultured in the presence of fluoride, and proliferation was measured by BrdU incorporation. The effect of 0, 10, or 20 microM fluoride on apoptosis was determined by the flow cytometry apoptotic index. The effects of fluoride on gene expression were investigated by SuperArray microarray analysis and real-time PCR. Fluoride had a biphasic effect on cell proliferation, with enhanced proliferation at 16 microM, and reduced proliferation at greater than 1 mM F. Flow cytometry showed that both 10 microM and 20 microM NaF significantly increased the apoptotic index of ameloblast-lineage cells. There was no general effect of fluoride on gene expression. These results indicate multiple effects of micromolar fluoride on ameloblast-lineage cells.

Caries susceptibility of human fluorosed enamel and dentine

OBJECTIVE

Objective of our laboratory study was to determine the impact of dental fluorosis severity on the formation of caries in the human enamel and dentine.

MATERIALS AND METHODS

Thirty-three human molars were grouped according to modified Thylstrup-Fejerskov index (TFI) into normal (N, TFI 0), mild fluorosis (ML, TFI 1-3) and moderate fluorosis (MD, TFI 4-6). Three mesio-distal sections were made in corono-apical axis of the tooth, giving enamel and dentine samples. They were embedded in an epoxy resin, and polished. Half of the polished surface was covered with an acid resistant varnish and immersed in standard acidified buffer solution (pH 4.5) for 48 h to create artificial caries lesions. They were treated with 5% NaOCl for 45 min and sectioned longitudinally along the center into two halves. Cut surfaces were polished and observed under a confocal laser scanning microscope for depth of demineralization. Morphology of the demineralized zones was observed under a field emission scanning electron microscope (FE-SEM). Data were analyzed using one-way ANOVA and Sheffe test (p=0.05).

RESULTS

Statistically significant difference in depth of demineralization was found between N and MD groups (p=0.046) in the enamel, and between N and ML (p=0.002), N and MD (p<0.001), ML and MD (p=0.029) in dentine. FE-SEM observation of the normal enamel showed direct dissolution with large fissures. Spongy appearance of intertubular dentine gradually disappeared from N to MD.

CONCLUSIONS

Moderately fluorosed enamel showed a significant caries resistance. In contrast, mild and moderately fluorosed dentine was significantly caries susceptible in vitro.

Lack of DNA damage induced by fluoride on mouse lymphoma and human fibroblast cells by single cell gel (comet) assay

Fluoride has widely been used in Dentistry because it is a specific and effective caries prophylactic agent. However, excess fluoride may represent a hazard to human health, especially by causing injury on genetic apparatus. Genotoxicity tests constitute an important part of cancer research for risk assessment of potential carcinogens. In this study, the potential DNA damage associated with exposure to fluoride was assessed by the single cell gel (comet) assay in vitro. Mouse lymphoma and human fibroblast cells were exposed to sodium fluoride (NaF) at final concentration ranging from 7 to 100 microg/mL for 3 h at 37 degrees C. The results pointed out that NaF in all tested concentrations did not contribute to DNA damage as depicted by the mean tail moment and tail intensity for both cellular types assessed. These findings are clinically important because they represent a valuable contribution for evaluation of the potential health risk associated with exposure to agents usually used in dental practice.

Effects of systemic fluoride and in vitro fluoride treatment on enamel crystals

Systemically administered fluoride at a concentration of 75 ppm increases the surface roughness of developing enamel crystals in rats, which may be significant in advancing our understanding of the biological mechanism of fluorosis. Thus, the aim of this study was to investigate whether the increased surface roughness may be a result of surface restructuring by the direct action of fluoride at the crystal surface. We examined the fluoride dose-dependent roughening of enamel crystal surfaces in vivo, in the rat, and whether this roughening could be mimicked by the in vitro treatment of rat enamel crystals with neutral pH fluoride solutions. Our results showed that enamel crystal surface roughness increased after treatment with increasing fluoride ion concentrations, whether applied in vitro or administered systemically. This suggests a mechanism, alongside others, for the increased surface roughness of crystals in fluorotic enamel.

Fluoride down-regulates the expression of matrix metalloproteinase-20 in human fetal tooth ameloblast-lineage cells in vitro

Fluoride is associated with a decrease in the incidence of dental caries, but excessive fluoride intake during tooth enamel formation can result in enamel fluorosis. Fluorosed enamel has increased porosity, which has been related to a delay in the removal of amelogenin proteins as the enamel matures. This delay in protein removal suggests that fluoride may affect either the amount or the activity of enamel matrix proteinases. In this study, we investigated the role of fluoride in the synthesis and secretion of matrix metalloproteinase-20 (MMP-20), the proteinase primarily responsible for the initial hydrolysis of amelogenin during the secretory stage of enamel formation. Cultured human fetus tooth organ ameloblast-lineage cells were exposed to 10 microM fluoride and analyzed for synthesis of MMP-20. Immunoblotting showed that 10 microM NaF down-regulated the synthesis of MMP-20 by 21% compared with control cells, but did not alter the amount of amelogenin or kalikrein-4 (KLK-4) synthesized by the cells. Real-time polymerase chain reaction (PCR) showed that 10 microM NaF down-regulated MMP-20 mRNA expression to 28% of the levels found in the non-treated cells. These in vitro results suggest that fluoride can alter the expression of MMP-20 by ameloblasts, resulting in a disturbance of the balance between MMP-20 and its substrate that may contribute to the retention of amelogenins in the formation of fluorosed enamel.

Fluoride content of UHT milks commercially available in Bauru, Brazil

OBJECTIVES

The aims of the present study were to evaluate the fluoride (F) concentrations in whole, defatted and chocolate milks commercially available in Brazil and to estimate the daily F intake from these sources.

MATERIAL AND METHODS

F concentrations were determined for 23 brands of milks, after HMDS-facilitated diffusion, using a F ion-specific electrode. Possible F ingestion per kg body weight was estimated, based on suggested volumes of formula consumption, for infants aging 1 to 12 months.

RESULTS

F concentrations ranged from 0.02 to 1.6 microg/mL F for all brands analyzed. Whole and defatted milks had the lowest F concentrations, ranging from 0.02 to 0.07 microg/mL. With respect to chocolate milks, three brands had F concentrations above 0.5 microg/mL. Some brands of chocolate milks exceeded the dose regarded as the threshold level for the development of dental fluorosis, without taking into account other sources of fluoride intake.

CONCLUSION

The high fluoride concentrations found in some brands of chocolate milks in the present study indicate that many products may be important contributors to the total fluoride intake, reinforcing the need of assaying fluoride content of foods and beverages consumed by small children.

Fluoride does not induce DNA breakage in Chinese hamster ovary cells in vitro

Fluoride has been widely used in dentistry because it is a specific and effective caries prophylactic agent. However, excess fluoride may represent a hazard to human health, especially by causing injury to genetic material. Genotoxicity tests represent an important part of cancer research to assess the risk of potential carcinogens. In the current study, the potential DNA damage associated with exposure to fluoride was assessed by the single cell gel (comet) assay in vitro. Chinese hamster ovary cells were exposed to sodium fluoride (NaF) at final concentration ranging from 7 to 100 micro/ml for 3 h, at 37 dgrees C. The results pointed out that NaF in all concentrations tested did not contribute to DNA damage as depicted by the mean tail moment and tail intensity. These findings are clinically important since they represent an important contribution to a correct evaluation of the potential health risk associated with the exposure to dental agents.

Micro-shear bond strength and morphological analysis of a self-etching primer adhesive system to fluorosed enamel

PURPOSE

The aim of this study was to evaluate micro-shear bond strength and morphological analysis of a self-etching primer adhesive system to fluorosed enamel.

MATERIALS AND METHODS

Extracted human molars were classified according to the severity of fluorosis using Thylstrup and Fejerskov index into four groups (TFI: 0, normal; 1-3, mild fluorosis; 3-6, moderate fluorosis; 6-7, severe fluorosis) and divided into following two sub-groups. For the first sub-group, a self-etching primer adhesive system was applied to the ground enamel surfaces and the other sub-group was conditioned with 37% phosphoric acid for 30s prior to application of the same adhesive system. Teeth were then restored with a resin composite, stored for 24h in water and micro-shear bond strengths were measured. After shear testing, the fracture modes were observed under a laser scanning microscope. Morphological study of etching patterns and adhesive interface was done under a scanning electron microscope (SEM). The data were analyzed using two-way ANOVA and Sheffe test (p=0.05).

RESULTS

No statistically significant difference was there between the different degrees of fluorosis in each sub-group. However, significant difference in the bond strengths between phosphoric acid etching and self-etching was found in moderate and severe groups. The SEM observations showed at the resin-enamel interface, thick resin tag like extensions penetrated around 3.5 microm into the enamel etched with phosphoric acid, while self-etching primer created, 1 microm lamina like penetration.

CONCLUSION

Severity of fluorosis affects the micro-shear bond strength of a self-etching bonding system to fluorosed enamel.

No relationship between subchronic fluoride intake and DNA damage in Wistar rats

Fluoride has been widely used in dentistry because it is an effective caries prophylactic agent. However, excess fluoride may represent a hazard to human health, especially by causing injury on the genetic apparatus. Genotoxicity tests form an important part of cancer research and risk assessment of potential carcinogens. In the current study, the potential DNA damage associated with exposure to fluoride was assessed by the single cell gel (comet) assay in peripheral blood, oral mucosa and brain cells in vivo. Male Wistar rats were exposed to sodium fluoride (NaF) at a 0, 7 and 100 ppm dose for drinking water during 6 weeks. The results pointed out that NaF did not contribute to the DNA damage in all cellular types evaluated as depicted by the mean tail moment and tail intensity. These findings are clinically important since they represent an important contribution to the correct evaluation of the potential health risk associated with dental agents exposure.

Tooth quality in dental fluorosis genetic and environmental factors

Dental fluorosis (DF) affects the appearance and structure of tooth enamel and can occur following ingestion of excess fluoride during critical periods of amelogenesis. This tooth malformation may, depending on its severity, influence enamel and dentin microhardness and dentin mineralization. Poor correlation between tooth fluoride (F) concentration and DF severity was shown in some studies, but even when a correlation was present, tooth fluoride concentration explained very little of DF severity. This fact calls into question the generally accepted hypothesis that the main factor responsible for DF severity is tooth fluoride concentration. It has been shown previously that genetic factors (susceptibility to DF) play an important role in DF severity although DF severity relates to individual susceptibility to fluoride exposure (genetics), tooth fluoride concentration relates to fluoride ingestion (environmental). The objective of this study was to investigate the correlation between tooth fluoride concentration, DF severity, and tooth mechanical and materials properties. Three strains of mice (previously shown to have different susceptibility to DF) at weaning were treated with four different levels of F in their water (0, 25, 50, and 100 ppm) for 6 weeks. Mice teeth were tested for fluoride by instrumental neutron activation analysis (INAA), DF severity determined by quantitative light-induced fluorescence [QLF], and tooth quality (enamel and dentin microhardness and dentin mineralization). Tooth fluoride concentration (environment factor) correlated positively with DF severity (QLF) (rs=0.608), fluoride treatment group (rs=0.952). However, tooth fluoride concentration correlated negatively with enamel microhardness (rs=-0.587), dentin microhardness (rs=-0.268) and dentin mineralization (rs=-0.245). Dental fluorosis (genetic factor) severity (QLF) correlated positively with fluoride treatment (rs=0.608) and tooth fluoride concentration (rs=0.583). DF severity correlated negatively with enamel microhardness (rs=-0.564) and dentin microhardness (rs=-0.356). Genetic factors (DF severity) and the environmental factor (fluoride concentration in tooth structure) have similar influence on tooth biomechanical properties, whereas only the environmental factor has an influence on tooth material property (mineralization).

Patterns of fluoride intake from 36 to 72 months of age

OBJECTIVES

This paper reports on estimated daily fluoride intake from water by itself, beverages, selected foods, dentifrice, and dietary supplements, both individually and combined (mg and mg F/kg bw), among 785 children in the Iowa Fluoride Study from 36 to 72 months of age.

METHODS

Children were recruited in 1992-95, with questionnaires sent at four- to six-month intervals. Dietary fluoride intake estimates used community and individual water fluoride levels and average fluoride levels of beverages and foods prepared with water. Descriptive statistics and generalized linear models (GLM) assessed levels and associations with demographic factors.

RESULTS

There was substantial variation in fluoride intake, with some individuals' intakes greatly exceeding the means. Daily water fluoride intake estimates (in mg) increased with age, fluoride intake from other beverages and dentifrice both decreased slightly, and combined intake was quite consistent. For combined intake per unit body weight (mg F/kg bw), there was a steady decline with age. Therefore, the percentages with estimated intake exceeding possible thresholds for dental fluorosis also declined with age.

CONCLUSIONS

Daily mean fluoride intakes from single and combined sources are relatively stable from 36-72 months of age among these children.

Fluorine content of several brands of chocolate bars and chocolate cookies found in Brazil

Chocolate bars and chocolate cookies are foodstuffs highly appreciated by children. The possibility of having fluorine (F) among their components, associated with an excessive consumption, may make them decisive contributors to the total daily F intake. Thus, they could participate in the establishment of dental fluorosis. The aim of this study was to analyze the fluorine concentration [F] of the chocolates bars (CB) Baton, Confeti, Garoto Ball, Kinder Ovo, M&M s, Milkybar, Nescau, Nescau Ball, Surpresa, Surpresa Bichos, Tortuguita; and of the chocolate cookies (CC) Danyt s, Hipop , Nescau, Passatempo, Pokémon, S tio do Pica-Pau Amarelo and Trakinas. Samples were purchased in Bauru, São Paulo, Brazil. Three grams of each product were previously ashed at 525 C (CB and cookies fillings) and at 550 C (cookies dough), during 4 hours. Fluorine was separated from the ash by hexamethyldisiloxane (HMDS)-facilitated diffusion. Fluorine analysis was carried out with the specific electrode. Mean [F]s SD and amplitude (unit mg/g) were: CB = 0.30 0.45 (0.07 - 1.60, n = 12) and CC = 1.08 2.64 (0.04 - 7.10, n = 7). It was concluded that some of the analyzed foods may be important contributors to the total daily F intake. As for the product that had the highest [F] (Danyt s), when only 3 units are consumed just once a day, they may supply up to 40% of the maximum recommended daily F intake (0.07 mg/kg body weight) for a 2-year-old child (12 kg). The [F] in these products should be informed on their labels.

Effect of fluorosis on dentine shear bond strength of a self-etching bonding system

The purpose of this study was to investigate the effect of dental fluorosis on shear bond strength of a composite material to dentine. Forty human premolar teeth were classified according to the severity of fluorosis using the Thylstrup and Fejerskov index and were divided into four groups (TFI scores of 0, 3, 4 and 5) of 10 teeth. Non-fluorosed teeth (TFI score of 0) served as the control group. A self-etching light-cured bonding system, Clearfil SE Bond, and a micro-hybrid light-cured composite, Clearfil AP-X were selected for the study. Buccal surfaces of mounted teeth were ground flat to expose the dentine. Composite cylinders, 4 mm diameter and 4 mm length, were bonded to the treated dentine surfaces. Shear bond strength was measured with an universal testing machine at a cross-head speed of 0.5 mm min-1. After failure, the fracture surfaces were examined under a stereo microscope. The mean bond strength was 24.37 +/- 3.54 MPa for non-fluorosed teeth and varied between 22.72 +/- 3.52 and 27.02 +/- 5.91 MPa for fluorosed teeth. The difference between the mean values for bond strength was not statistically significant (P > 0.05). Adhesive mode of failure was most prevalent in non-fluorosed teeth. It can be concluded that fluorosis does not affect the shear bond strength of composite material to human dentine.