Genetic influences on dental enamel that impact caries differ between the primary and permanent dentitions

Clinically, primary and permanent teeth are distinct anatomically and the presentation of caries lesions differs between the two dentitions. Hence, the possibility exists that genetic contributions to tooth formation of the two dentitions are different. The purpose of this study was to test the hypothesis that genetic associations with an artificial caries model will not be the same between primary and permanent dentitions. Enamel samples from primary and permanent teeth were tested for microhardness at baseline, after carious lesion creation, and after fluoride application to verify association with genetic variants of selected genes. Associations were found between genetic variants of ameloblastin, amelogenin, enamelin, tuftelin, tuftelin interactive protein 11, and matrix metallopeptidase 20 and enamel from permanent teeth but not with enamel from primary teeth. In conclusion, our data continue to support that genetic variation may impact enamel development and consequently individual caries susceptibility. These effects may be distinct between primary and permanent dentitions.     

Role of remineralizing fluid in in vitro enamel caries formation and progression.

OBJECTIVE: To evaluate a remineralizing fluid for its influence on in vitro caries formation and progression. METHOD AND MATERIALS: Caries-free teeth (n = 12) were sectioned into 3 segments. Each segment was assigned to a treatment group: (1) remineralizing fluid for 2 minutes; (2) 1.23% acidulated phosphate fluoride (APF) gel for 1 minute; (3) no-treatment control. Following treatment, the tooth segments were rinsed in distilled/deionized water and exposed to synthetic saliva for 24 hours. In vitro caries were formed and longitudinal sections obtained. The tooth segments were treated again and rinsed as above, before undergoing in vitro caries progression. Longitudinal sections were evaluated for lesion depth (ANOVA, Duncan multiple range analysis). RESULTS: Following lesion formation, mean lesion depths were 173 +/- 19 microm for no-treatment control; 97 +/- 11 microm for APF gel; and 52 +/- 12 microm for remineralizing fluid. After lesion progression, mean lesion depths were 236 +/- 23 microm for no-treatment control; 184 +/- 26 microm for APF gel; and 112 +/- 17 microm for remineralizing fluid. Mean lesion depths for the remineralizing fluid and APF gel groups for the lesion formation and progression periods were significantly less than those for the control group (P < .05). After lesion formation and progression, the APF group had significantly greater mean lesion depths than did the remineralizing fluid group (P < .05). CONCLUSIONS: A remineralizing fluid containing calcium, phosphate, and fluoride in a carbopol base enhanced resistance against in vitro caries formation and progression when compared with APF treatment.     

Correlation between fissure discoloration, Diagnodent measurements, and caries depth: an in vitro study

PURPOSE: This in vitro study was performed to correlate the presence of discoloration on occlusal surfaces with its histological depth and assess its influence on Diagnodent measurements in a group of permanent and primary teeth. METHODS: Ninty-five primary and 95 permanent third molars were randomly selected from a pool of macroscopically intact teeth. One site of the fissure on each occlusal surface was selected and categorized according to its discoloration. Each site was measured 3 times with Diagnodent. The teeth were prepared histologically and evaluated according to their caries extent under a microscope (final magnification x 12.8). RESULTS: In the group of permanent teeth with dark brown or black discoloration (N=23), 13% showed dentinal caries, 57% were sound or had an initial enamel lesion, and 30% had a deep enamel lesion. In the group of primary teeth with dark brown and black discoloration (N=19), 42% presented dentinal caries, 42% showed deep enamel caries, and 16% had an initial enamel lesion. The difference between permanent and primary teeth was statistically significant (P<.05). Discolored fissures showed higher Diagnodent values than nondiscolored or opaque fissures in both groups (independent of their caries status). CONCLUSIONS: The presence of brown or dark spots on fissures were not useful for the prediction of dentinal caries for permanent teeth. In primary teeth, however, a higher correlation between fissure discoloration and dentinal lesions was found. Diagnodent tends to overscore discolored surfaces.     

Microhardness of dentine in primary teeth after topical fluoride applications

OBJECTIVES: This study measured the microhardness of arrested dentinal caries on primary teeth receiving regular fluoride applications after 30 months. METHODS: Caries on primary upper anterior teeth of preschool children were randomly assigned to receive 38% silver diamine fluoride every 12 months or 5% sodium fluoride varnish every 3 months. Lesions that were hard on probing were considered arrested. At 30 months, very mobile teeth were extracted, sectioned, and polished and they underwent Knoop hardness number (KHN) measurements at sites below the surface at the center of the carious lesion every 25 microm toward the pulp. Three sets of measurements were made on parallel tracks approximately 150-200 microm apart, and the median KHN at each depth were analyzed. RESULTS: Five arrested and five soft carious lesions were examined. Within the outer 25-200 microm, the median KHN of arrested carious lesions (range, 20-46 or 196-451 MPa) were greater than those of soft carious lesions (range, 5-20, or 49-196 MPa). The difference between them, however, was not statistically significant. At a distance of 225 microm or more from the surface of the lesion, the median KHN of both groups were between 20 and 30 (196-294 MPa). CONCLUSIONS: The outermost dentinal surface of carious lesions that had been arrested by topical fluoride application was harder than that of active carious lesions. At a distance of 225 microm or more from the lesion surface, the microhardness of both arrested and soft dentinal caries was similar.     

The influence of varying fluoride concentrations on in vitro remineralisation of artificial dentinal lesions with differing lesion morphologies

OBJECTIVE: The influence of low-level fluoride (F) concentrations and lesion characteristics on the remineralisation of sub-surface root caries was investigated in vitro. DESIGN: Experimentally produced dentinal carious lesions were exposed to artificial saliva in the presence of 0.00ppm, 0.48ppm, 2.49ppm or 4.91ppm F (as NaF) for 5 days. Calcium, phosphate and fluoride ion uptake was quantified by chemical assay. Baseline changes in the mineral content and distribution of the lesions were assessed by transverse microradiography (TMR). RESULTS: The uptake of calcium and phosphate was significantly increased (p<0.05) by fluoride, even at low concentrations. The action of fluoride was influenced by the mineral content and distribution of the lesions at baseline, however, with the location and degree of mineral deposition being strongly related to the mineral content of the lesions surface layer. CONCLUSIONS: The process of remineralisation of root dentine is multifactorial. The morphology of lesions at baseline significantly affected the location and quantity of mineral deposition.     

Argon laser irradiation and fluoride treatment effects on caries-like enamel lesion formation in primary teeth: an in vitro study

PURPOSE: To evaluate topical acidulated phosphate fluoride (APF) and low fluence argon laser (Ar) treatment effects on in vitro caries formation in primary tooth enamel. METHODS: 20 extracted or exfoliated primary teeth with sound buccal and lingual surfaces underwent soft tissue debridement and a fluoride-free prophylaxis. Treatment groups were: (1) Control [n=5]; (2) Ar [231mW, 10 seconds, 11.5J/cm2; n=5], (3) 1.23% APF for 4 minutes before Ar [n=5]; (4) Ar before APF [n=5]. Buccal and lingual enamel surfaces were treated, and then rinsed in deionized,distilled water (24 hours). An acid-resistant coating was applied leaving buccal and lingual sound enamel windows exposed. In vitro enamel caries was created (2.2 mM calcium, 2.2 mM phosphate, 5.0 mM fluoride, pH 3.90, 10 days). Following longitudinal sectioning, two lesions per primary tooth (10 lesions total) with each group were evaluated for lesion depth (polarized light, water imbibition) and compared (ANOVA, Duncan's Multiple Range). RESULTS: Argon laser irradiation alone provided a 41% reduction in lesion depth (176 +/- 21 microm, P< 0.05) when compared with that for the no treatment controls (297 +/- 31 microm). The combination of argon laser irradiation with APF treatment resulted in lesion depth decreases of slightly over 50% (140 +/- 23 microm for APF before ArTx; 124 +/- 17 microm for ArTx before APF, P< 0.05) compared with control lesion depths, and 20 to 30% over that for argon laser treatment alone (P< 0.05). There was no statistical difference in lesion depth regardless of whether fluoride treatment occurred before or after laser irradiation (P> 0.05).     

Comparative study to quantify demineralized enamel in deciduous and permanent teeth using laser- and light-induced fluorescence techniques.

Caries is a disease that affects both deciduous and permanent dentitions. Caries progresses more rapidly in deciduous enamel than in permanent enamel. Therefore, new caries diagnostic methods need to be tested on the deciduous teeth as well. Quantitative laser-induced fluorescence (QLF I) as well as the quantitative light-induced fluorescence (QLF II) seem promising for the quantification of mineral loss from dental caries but have only been tested on the permanent dentition. The objective of this study was to determine and compare the ability of QLF I and QLF II to quantify mineral loss from carious lesions in both deciduous and permanent teeth. Thirty sound deciduous and 30 sound permanent teeth were cleaned and divided into three groups each containing 10 deciduous and 10 permanent teeth. Windows on the buccal or labial enamel surfaces were demineralized for 48, 72, or 96 h. Images of demineralized enamel were captured using QLF I and QLF II. The images were analyzed to determine the mean change in fluorescence radiance (Delta F, %). The teeth were then sectioned for assessment of lesion depth (microm) and integrated mineral loss (IML, vol% x microm) using transverse microradiography (TMR), as the 'gold standard' for lesion analysis. The results indicated a good correlation for Delta F between QLF I and QLF II in both deciduous (r = 0.96) and permanent teeth (r = 0.98). There was a good correlation between Delta F and TMR (lesion depth and IML) in deciduous teeth (r = 0.76 and 0.84 with QLF I, r = 0.81 and 0.88 with QLF II). In permanent teeth, the correlation between Delta F and TMR (lesion depth and IML) was lower than in deciduous teeth (r = 0.07 and 0.53 with QLF I, r = 0.15 and 0.62 with QLF II). From these results it can be concluded that either QLF method is capable of quantifying mineral loss in early carious lesions in deciduous teeth. Moreover, under the conditions of this study, the use of either QLF method to quantify mineral loss in early carious lesions in deciduous teeth is slightly more accurate than in permanent teeth.     

In vitro caries formation in primary tooth enamel: role of argon laser irradiation and remineralizing solution treatment

BACKGROUND: The authors evaluated the effects of argon laser (AL) diation and remineralizing solution (RS) treatment alone and in combination on carieslike lesion formation in primary tooth enamel in an in vitro study. MATERIALS AND METHODS: The authors divided 10 caries free primary tooth enamel surfaces into four segments and assigned them to one of four treatment groups: no treatment control, AL irradiation alone at 13.5 joules per square centimeters (0.270 watts, 5-millimeter beam, 10 seconds), RS treatment alone for two minutes and AL irradiation before RS treatment. The authors created in vitro caries using a modified ten Cate solution. They evaluated longitudinal sections (three per tooth segment, 30 per treatment group) for mean lesion depth. RESULTS: After lesion formation, mean lesion depths (+/- standard deviation) were 179 +/- 16 micrometers for the no treatment controls, 137 +/- 19 microm for AL irradiation alone, 87 +/- 9 microm for RS treatment alone and 68 +/- 12 microm for AL irradiation before RS treatment. All treatment groups had mean lesion depths that were significantly less than those for the matched no-treatment control group (analysis of variance [ANOVA], Duncan multiple range [DMR] test, P < .05). AL irradiation before RS treatment significantly reduced lesion depth compared with AL irradiation alone or RS treatment alone (ANOVA, DMR test, P < .05). CONCLUSIONS: The maximum reduction in lesion depth in primary tooth enamel was achieved when the RS--which contained calcium, phosphate and fluoride in a carbopol base--was combined with AL irradiation. CLINICAL IMPLICATIONS: It would appear that to improve clinical caries resistance to enamel dissolution, AL irradiation before RS treatment could be used.     

Oral hygiene as a risk indicator of enamel and dentin caries

Dental researchers have postulated that the risk factors for enamel and dentin caries may not be the same. A review of the literature ascertained that data to support this theory are lacking. Objectives: To evaluate the risk indicators of enamel and dentin caries of the permanent dentition in a study group who had limited access to fluorides and made limited use of dental services. Methods: The study was conducted in Goa, India. Data came from a cross-sectional survey of 1189 seventh grade children, which consisted of a clinical dental examination and a self-administered questionnaire to their parents. The cavitated and non-cavitated criteria were used to score for caries, and the Silness-Loe index for plaque. Results: The mean age of the children was 12.2 years. The percentage of children caries free in the permanent dentition was 22.2%, the mean± s for dmfs, enamel and dentin lesions were 4.20±5.10, 2.59±2.89 and 1.61±3.30 respectively, and the mean plaque score was 1.00±0.48. Results of regression analyses showed that the risk indicators of prevalence and severity of caries differed depending on lesion type. The only variable that was consistently a risk indicator of presence and severity of both dentin and enamel caries was poor oral hygiene. Mother's highest level of education and presence of fluorosis were also risk indicators of enamel and dentin caries. The presence of decayed primary teeth was a risk indicator of enamel caries; and fluorosis severity, use of fluoride toothpaste at the time of the survey, and toothbrushing frequency were risk indicators of dentin caries. The observed caries-oral hygiene association seen is explored further.     

Association between clinical parameters and the presence of active caries lesions in first permanent molars

The aim of the present study was to evaluate the association between clinical parameters and the presence of active caries lesions on the occlusal surface of first permanent molars. Forty eight children (5.8-13.8 years-old) with at least one first permanent molar present were selected. The clinical parameters evaluated were gender, age, DMF-T and dmf-t, presence of active white spots in other teeth, general plaque index, tooth's dental arch (upper or lower), tooth's side (right or left), presence of visible plaque and eruption degree of the first permanent molars. The first permanent molars were evaluated through visual inspection by two examiners in order to assess the presence of active or inactive caries lesions on the occlusal surface. Univariate and multivariate analyses for determination of the association between clinical parameters and the presence of active caries lesions in these teeth were performed. The presence of active white spots in other teeth was associated with the presence of active caries lesions in the first permanent molars, in both univariate and multivariate analyses (Odds ratio = 8.8 and 1.9, respectively). The presence of abundant visible plaque on the occlusal surface of the first permanent molars (Odds ratio = 3.5 in the univariate analysis, and 3.9 in the multivariate one) also presented a significant association. In conclusion, the presence of active white spots in other teeth and the presence of considerable visible plaque were associated with the presence of active caries lesions on the occlusal surfaces of first permanent molars.     

Development of an in situ root caries model. A. In vitro investigations

OBJECTIVES: The paper describes preliminary in vitro investigations, the objectives of which were to examine the influence of certain experimental parameters on artificial carious lesion formation in root hard tissues, and their remineralisation. These experiments formed part of a wider study that aimed to develop an in situ model of root caries, based on the existing coronal caries model used in Liverpool. The present studies examined the effects (a) of the anatomical origin of the dentine, the presence or absence of cementum, the exposure time and the type of demineralising system, on lesion development, and (b) of baseline lesion size on the extent and location of mineral re-precipitation. METHODS: Mineral content parameters in plano-parallel sections taken from dentine lesions were determined by computer-controlled transverse microradiography. RESULTS: The importance of the anatomical origin of the dentine on lesion formation was investigated by comparing in vitro lesion formation in premolar and molar dentine, and in dentine from apical, middle and coronal thirds of the root: no difference was observed between these sites. Lesions formed more rapidly in acid buffer solutions than in acid gel systems, and were more reliably produced when cementum was removed. The effect of baseline lesion size on subsequent in vitro remineralisation demonstrated that a small baseline mineral content was associated with a larger percentage mineral gain. The location of mineral deposition throughout the lesion was also influenced by baseline mineral content parameters. CONCLUSIONS: The results form a basis for the further development of an in situ dentinal caries model, providing data to suggest that manipulation of parameters involved in the preparation of artificial carious lesions has a significant effect on the behaviour of the lesion, particularly the phenomenon of remineralisation. Further work is needed to investigate the behaviour of the model in situ.     

Effects of child formula dentifrices on artificial caries like lesions using in vitro pH-cycling: preliminary results

AIM: To compare the remineralisation effects of different child dentifrices on primary teeth. DESIGN: In vitro single-section technique and pH-cycling model. METHODS: Primary teeth were painted with nail varnish, leaving a 1 mm wide window before placing in demineralising solution for 96hr to produce artificial carious lesions 150-200 microm deep. Teeth were longitudinally cut into approximately 100-150 microm thick sections and assigned to three groups (n = 7). Sections in Group A were exposed to Perioe Children's Toothpaste (LG, Korea), Group B to Colgate Pokemon (Colgate-Palmolive, Thailand) and Group C to Vicco (Vicco Laboratories, India). Polarised light microscopy and microradiography was used to evaluate lesion depth, before and after 7 days pH cycle. RESULTS: Mean lesion depths in Groups A and C increased by 11% and 14% respectively, while Group B demonstrated a lesion reduction of 3%. Comparisons using ANOVA and Student-Newman-Keuls tests showed that Groups A and C were significantly different from Group B (p < 0.05), but there was no significant difference between Groups A and C. CONCLUSIONS: Based on the data obtained, Colgate Pokemon remineralised initial carious lesions. In addition, when compared to Colgate Pokemon, Perioe Children's Toothpaste failed to show 'healing' efficacy even though it is claimed to contain fluoride.     

Potential inhibition of demineralization in vitro by fluoride-releasing sealants

BACKGROUND: The incorporation of fluoride into sealants has been viewed as a viable way to prevent pit-and-fissure caries by potential inhibition of demineralization through the release of fluoride to enamel. The authors conducted a study to examine the effect of a recently introduced fluoride-releasing sealant (ProSeal, Reliance Orthodontic Products, Itasca, Ill.) on enamel demineralization in an in vitro artificial caries system. METHODS: The authors randomly assigned 45 extracted human third molars to three treatment groups receiving either conventional sealant without fluoride (Group 1), fluoride-releasing sealant (Group 2) or glass ionomer sealant with high fluoride release (Group 3). They placed cavity preparations on the buccal surfaces of the molars and filled them with the assigned material. They placed acid-resistant varnish on the specimens' enamel surfaces to within 1 millimeter of the sealant, leaving a 1-mm rim of sound enamel available for in vitro enamel caries formation. They thermocycled the teeth (500 cycles) in artificial saliva. They subjected the teeth to an in vitro artificial caries challenge for six weeks to produce caries-like lesions in enamel adjacent to the sealant materials. The authors took longitudinal sections from each tooth, immersed them in water and examined them via polarized light microscopy to determine wall lesion frequencies. RESULTS: The mean (+/- standard deviation) lesion depths were 232 +/- 17 micrometers for Group 1, 144 +/- 21 mum for Group 2 and 128 +/- 15 mum for Group 3. The wall lesion frequency was 12 percent for Group 1 and 7 percent for both Groups 2 and 3. There was a significant difference (P < .05) among the fluoride-releasing materials versus the nonfluoride-releasing material. This study indicates that the new fluoride-releasing sealant substantially reduces the amount of enamel demineralization adjacent to the material. CONCLUSION: ProSeal provided increased demineralization inhibition compared with a conventional sealant containing no fluoride, but less than that shown by a glass ionomer sealant. CLINICAL IMPLICATIONS: ProSeal's physical properties and cariostatic effects may allow for applications beyond traditional sealant use.     

Evaluation of restorative materials using a new perfusion system

PURPOSE: 1) To test a new perfusion device able to alternate demineralizing/nondemineralizing solutions, as an acid attack system, and 2) to standardize the dentin demineralization procedure, in order to define the in vitro secondary caries inhibiting potential of different restorative materials. MATERIALS AND METHODS: A fluoride-containing adhesive/composite resin (group A), an experimental adhesive/composite resin (group B), and a glass-ionomer cement (group C) were used to restore 24 Class II cavities in extracted molars. Optimal conditions to obtain dentin demineralization inside the perfusion device were identified and applied to restored teeth. Dentin demineralization after perfusion was analyzed by microradiography. The output parameters were lesion morphology, dentin mineral volume percentage, and integrated mineral loss (Delta Z, % volume x microm) of the exposed (outer lesions) and marginal (inner lesions or caries inhibition zones, CIZs) dentin. RESULTS: Demineralization increased as follows: group A < group B < group C. Group A behaved better than group B, probably due to fluoride content, as indicated by Delta-Z values, higher number of CIZs, and few inner lesions. Group C showed a marginal protective effect, demonstrated by the frequent CIZs and Delta-Z positive values. This effect, however, was unable to reduce the high demineralization, probably due to the critical handling characteristics, inducingthe worst marginal adaptation. CONCLUSION: A new dynamic perfusion device was tested and a reproducible procedure was standardized in order to achieve in vitro conditions that could better simulate the pH changes of oral environment. A limited fluoride protective effect was demonstrated by using the perfusion system, whereas a perfect marginal adaptation was shown as a paramount factor to prevent restoration failure.     

Early detection of white spot lesions with digital camera and remineralization therapy

BACKGROUND: In this paper, the characteristics of the early stage of dental caries are discussed and the methods we used to treat the early stage of dental caries to increase the number of caries-free patients are presented. Studies from in vitro to in situ experiments and a clinical study were carried out to support clinical remineralization therapy. METHODS AND RESULTS: To clarify the effect of time for remineralization, the degree of remineralization was assessed at 2 days, 6 days, and 10 days after 2-day demineralization in 0.01 M/L lactic acid buffer (pH 4.0 at 37 degrees ). The remineralization solution contained 3.0 mM/L Ca, 1.8 mM/L P, and 3 ppm fluoride adjusted to pH 7.0. A 10-day continuous remineralization with a 3 ppm fluoride resulted in a high fluoride concentration. To evaluate mineral loss from sound tooth structure and white spot lesions, thin sections (about 90 microm) including white spots (WS) were prepared and exposed to oral conditions for 2 weeks continuously. The mineral loss from sound tooth structure was found to be twice that from WS. In another experiment during the remineralization period, enamel samples were immersed in three different bicarbonate solutions; 0.5, 5.0 and 50 mM/L for 30 minutes, two times per day. Both the bicarbonate and fluoride applied groups showed higher improvement in acid resistance and the amount of remaining mineral was almost two times higher than the controls (p < 0.01). In a clinical study we demonstrated remineralization in patients who followed professional mechanical tooth cleaning and fluoride prophylaxis paste. Using this regime, in patients with deciduous caries present at baseline, over 80 per cent of permanent teeth were caries free at the age of 12 years. In these studies the digital camera with CasMaTCH and an image analysis system showed several advantages for monitoring in de- and remineralization. CONCLUSIONS: White spot lesions, rather than intact tooth surfaces, can be mineralized through the daily clinical procedures described in this paper.     

Comparison of the caries-preventive effect of a glass ionomer sealant and fluoride varnish on newly erupted first permanent molars of children with and without dental caries experience

Abstract

Purpose: This longitudinal clinic study evaluated the effect of a glass ionomer sealant (GIS) and a fluoride varnish (FV) in the prevention of dental decay on newly erupted permanent molars of children with and without caries experience. Materials and methods: Eighty children, aged 6–8 years, with all four newly erupted first permanent molars, were divided into two groups. Group 1 consisted of 53 children without caries experience and group 2 consisted of 27 children with dental caries experience. Permanent molars of the right side were sealed with GIS and the fluoride varnish was applied on the other two permanent first molars. Evaluation of GIS retention and the effectiveness of both materials in the prevention of dental caries were performed after 6, 12 and 18 months. Results: After 18 months, of the 299 teeth, 271 (91%) showed no caries lesions and 28 presented caries lesions (9%). Teeth sealed with GIS had more carious lesions (15) than teeth with fluoride varnish (13). Most of the teeth (70%) that presented carious lesions were in group 2. Of the 138 sealed teeth, only one showed GIS to be totally present, 95 were partially present and 42 teeth were absent. Conclusion: The caries-preventive effect was very similar between both treatments. The presence of dental caries prevailed in the children with caries experience.     

Dose-response effects of zinc and fluoride on caries lesion remineralization

The present mechanistic in vitro study aimed to investigate dose-response effects of zinc and fluoride on caries lesion remineralization and subsequent protection from demineralization. Artificial caries lesions were created using a methylcellulose acid gel system. Lesions were remineralized for 2 weeks using citrate-containing artificial saliva which was supplemented with zinc (0-153 μmol/l) and fluoride (1.1 or 52.6 μmol/l) in a 7 × 2 factorial design. Lesions were also remineralized in the absence of zinc and citrate, but in the presence of fluoride. After remineralization, all lesions were demineralized for 1 day under identical conditions. Changes in mineral distribution characteristics of caries lesions after remineralization and secondary demineralization were studied using transverse microradiography. At 1.1 μmol/l fluoride, zinc exhibited detrimental effects on remineralization in a dose-response manner and mainly by preventing remineralization near the lesion surface. At 52.6 μmol/l fluoride, zinc retarded remineralization only at the highest concentration tested. Zinc enhanced overall remineralization at 3.8-15.3 μmol/l. At 76.5 and less so at 153 μmol/l, zinc showed extensive remineralization of deeper parts within the lesions at the expense of remineralization near the surface. Citrate did not interfere with remineralization at 1.1 μmol/l fluoride, but enhanced remineralization at 52.6 μmol/l fluoride. Lesions exhibiting preferential remineralization in deeper parts showed higher mineral loss after secondary demineralization, suggesting the formation of more soluble mineral phases during remineralization. In summary, zinc and fluoride showed synergistic effects in enhancing lesion remineralization, however only at elevated fluoride concentrations.     

Reaction Paper: The Use of Topical and Systemic Fluorides in the Present Era

Systemic fluoride may enhance the resistance of the tooth by way of (1) an alteration in tooth morphology, and (2) a conversion of the hydroxyapatitic mineral to a fluoridated state with an attendant reduction in solubility and an enhancement of the remineralization phase of the caries process. It has been reported by a number of investigators, although it is not universally accepted, that the posterior teeth from fluoridated areas have a distinct morphology that is less susceptible to caries attack. Fluorapatite and hydroxyapatite do not differ appreciably with respect to the amount of mineral that dissolves at a specified concentration of acid. However, if solubility is considered as a function of pH at equilibrium, i.e., the final pH after the dissolution products have entered the solvent--a model more akin to the in vivo situation--hydroxyapatite is the conspicuously more soluble of the two minerals. In this connection, epidemiologic data suggest that children with unusually high levels of surface enamel fluoride have little or no caries. This observation is consistent with the finding that the solubility of solid apatite solutions with varying degrees of fluoride substitution was inversely related to fluoride content, with minimal solubility at 0.5 substitution, a value observed in natural teeth at the very outermost surface of the enamel. Evidence of a preeruptive effect of fluoride has also been shown in field studies in which subjects had reduced levels of caries with fluoride exposure in childhood only.     

Fluoride-releasing sealant and caries-like enamel lesion formation in vitro

OBJECTIVE: The aim of this laboratory study was to evaluate the effects of a fluoride-releasing pit and fissure sealant (FS) and a conventional non-fluoride-containing pit and fissure sealant (CS) on caries-like lesion formation in enamel. DESIGN: Twelve extracted, macroscopically caries-free human molar teeth underwent fluoride-free prophylaxis and were sectioned into toothquarters. Cavity preparations were placed in buccal and lingual surfaces of the toothquarters, acid-etched and filled with sealant material (per the manufacturer's instructions) as follows: 1) mesiobuccal and mesiolingual quarters--FS (Fissurit-F, VocoChemie); and 2) distobuccal and distolingual quarters--CS (Fissurit, VocoChemie). Prior to caries formation in an acidified gel, the toothquarters were thermocycled (500 cycles) in artificial saliva. Sections were taken following caries initiation (6 week gel exposure) and caries progression (9 week gel exposure), and examined by polarized light microscopy to determine mean primary surface lesion depth and presence or absence of wall lesions. RESULTS: Mean surface lesion depths were significantly different between FS and CS groups following caries initiation (FS = 119 microns; CS = 157 microns, p < 0.05, paired t-test) and progression (FS = 169 microns; CS = 221 microns, p < 0.05, paired t-test). Wall lesions were reduced in FS (14% initiation; 25% progression) when compared with CS (19% initiation; 35% progression); however, this was not significantly different (p > 0.05, paired t-test). CONCLUSION: A pit and fissure sealant containing releasable fluoride provided a caries inhibiting effect with a significant reduction in lesion depth in the surface enamel adjacent to the fluoride-releasing sealant and a tendency toward reduction in the frequency of wall lesions. CLINICAL SIGNIFICANCE: Fluoride release by pit and fissure sealants may provide additional protection against caries formation in cuspal incline enamel and smooth surfaces adjacent to sealed pits and fissures, and act as a fluoride reservoir with long-term release of fluoride into the immediately adjacent oral environment.     

Effect of Nd:YAG laser combined with fluoride on the prevention of primary tooth enamel demineralization

Most studies dealing with the caries preventive action of Nd:YAG laser have been done in permanent teeth and studies on primary teeth are still lacking. The aim of this study was to evaluate in vitro the effect of Nd:YAG laser combined or not with fluoride sources on the acid resistance of primary tooth enamel after artificial caries induction by assessing longitudinal microhardness and demineralization depth. Sixty enamel blocks obtained from the buccal/lingual surface of exfoliated human primary molars were coated with nail polish/wax, leaving only a 9 mm2 area exposed on the outer enamel surface, and randomly assigned to 6 groups (n=10) according to the type of treatment: C-control (no treatment); APF: 1.23% acidulated phosphate fluoride gel; FV: 5% fluoride varnish; L: Nd:YAG laser 0.5 W/10 Hz in contact mode; APFL: fluoride gel + laser; FVL: fluoride varnish + laser. After treatment, the specimens were subjected to a des-remineralization cycle for induction of artificial caries lesions. Longitudinal microhardness data (%LMC) were analyzed by the Kruskal-Wallis test and demineralization depth data were analyzed by oneway ANOVA and Fisher's LSD test (á=0.05). APFL and APF groups presented the lowest percentage of microhardness change (p<0.05). Demineralization depth was smaller in all treated groups compared with the untreated control. In conclusion, Nd:YAG laser combined or not with fluoride gel/varnish was not more effective than fluoride alone to prevent enamel demineralization within the experimental period.