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Active Management of Incipient Caries and Choice of Materials
1 Department of Pediatric Dentistry and Correspondence: * corresponding author, ctrairat{at}yahoo.com
Evidence of the effects of various sealant and fluoride materials in stabilizing or reversing incipient caries lesions has been reported. However, a knowledge gap still exists as to what material yields the best results. Thus, the objective of this study was to find the most effective material by comparing the effects of a resin-based sealant (sealant), a fluoride-containing sealant (F-sealant), a fluoride varnish (F-varnish), and a glass-ionomer cement (GIC) on deremineralization of incipient artificial caries and adjacent intact enamel on proximal surfaces of posterior teeth. The 4 materials were applied to lesions created on proximal surfaces. Areas of intact enamel 0.5 mm adjacent to the materials were also studied. The specimens were thermo- and pH-cycled. Cross-sections of the two areas were analyzed under polarized light microscope and quantified with Image-Pro plus®. The most effective material in reducing the carious areas was GIC, followed by F-varnish, F-sealant, and sealants. GIC followed by F-varnish was most efficient in inhibiting new caries lesions 0.5 mm adjacent to the materials.
Key Words: remineralization • artificial caries • fluoride-releasing material • sealant Abbreviations: resin-based sealant (sealant) • fluoride-containing sealant (F-sealant) • fluoride varnish (F-varnish) • glass-ionomer cement (GIC)
Caries is a dynamic process; therefore, the recent trend in management of non-cavitated lesions has been a shift from the operative to a more conservative approach to inhibiting and reversing lesion progression. Sealants have been shown to be effective in inhibiting caries progression when applied to incipient lesions (Garcia-Godoy et al., 1997a; Martignon et al., 2006). However, attempts to promote remineralization by augmenting sealants with fluoride have shown conflicting results (Tanaka et al., 1987; Vatanatham et al., 2006). Application of both F-varnish and glass-ionomer cement (GIC) to white-spot lesions has been reported to be effective in reversing the lesions (Weinstein et al., 1994; Hicks et al., 2000). Remineralization was also observed to extend beyond the perimeter, owing to leachable fluoride in the material (Hicks and Flaitz, 1992; Castellano and Donly, 2004). Observations of proximal caries lesion reversal when the lesion is close to the GIC have been reported (Marinelli et al., 1997). While this is suggestive of potential treatments, there is no accepted method of effective remineralization or reversal of caries lesions on proximal surfaces. The hypothesis for this study was that there are differences in de-remineralization results among a sealant, a F-sealant, a F-varnish, and a GIC used in artificial proximal caries lesions and adjacent intact enamel.
Tooth Selection and Preparation For this study, we selected 32 premolars and third molars extracted for orthodontic reasons and free from macroscopic defects or staining on the proximal surfaces. The use of these teeth satisfied the requirements of the Chulalongkorn University IRB, and informed patient consent was obtained. The teeth were cleaned with distilled water to remove debris, stored in saline solution to prevent dehydration, and subsequently coated with an acid-resistant nail varnish on all enamel surfaces, except for 3 1x4 mm2 enamel windows on the same level of mesial and distal surfaces that were the targeted areas of the study. The upper halves of all windows were masked with another acid-resistant nail varnish to preserve enamel intact for the continuation of the study.
Formation of Artificial Caries-like Lesions
Tooth Sectioning
The middle windows of both surfaces were used as controls, while, to the left and right lower-half windows of the mesial surface, we applied light-cured Delton® (Dentsply, Milford, DE, USA) and light-cured Teethmate F-1® (Kuraray Medical, Okayama, Japan), respectively. In the same sequence, we applied, to the distal surfaces, Duraphat® (Colgate, Canton, MA) and Fuji VII® (a.k.a. Fuji Triage®) (GC Corporation, 2003). Application of each material was carried out according to the respective manufacturer’s instructions (Fig. 1
Thermocycling and pH-cycling Model The control sections were kept in artificial saliva at 37°C, while the experimental groups were thermocycled 500x in artificial saliva at 5°C and 55°C, with one-minute dwell times. All control and experimental specimens were then removed, rinsed with distilled water, and dried with absorbent papers. They were then subjected to a five-day pH-cycling model, stimulating a high caries challenge (Featherstone et al., 1986). They were individually immersed in 15 mL of the demineralizing solution used in the artificial caries system for 6 hrs, at 37°C. They were then washed with 40 mL of distilled water for 60 sec, dried with absorbent papers, and immersed in 15 mL of remineralizing solution containing 1.5 mM calcium, 0.9 mM phosphate, and 150 mM of KCl in 0.1 M Tris buffer at pH 7.0 for 18 hrs at 37°C. The solutions were changed daily. At the end of the cycle, the specimens were rinsed with distilled water several times to remove any solution residue.
Embedding of Specimens
Calculating the Lesion Area
Statistical Analysis Statistical analysis was performed with SPSS software (Chicago, IL, USA). Mean values for lesion area and demineralized enamel adjacent to the lesion were checked for a normal distribution by the Kolmogorov-Smirnov test. The differences between the caries lesion area and demineralized enamel adjacent to various materials were analyzed with one-way ANOVA and multiple comparisons. A paired t test was used to test the difference between the lesion area of control groups and the net gain in area (  mean) among experimental groups. A 95% significance level was chosen to test differences in means, as well as means, of various materials.
Results confirmed that the mean (± SD) of both control areas (upper and lower middle sections) of mesial and distal surfaces were not statistically significant (p > 0.05; t test) (see Table 1  ). Therefore, the experimental windows were compared with control windows and with each other on both surfaces. An analysis of variance also indicated that all lesion areas underneath the materials applied to the experimental groups were significantly smaller compared with those of the control group (p < 0.05). There were also statistically significant differences in the mean lesion areas between the groups, except between F-sealant and F-varnish groups; corresponding means among the groups followed the same pattern (p < 0.05).
At 0.5 mm adjacent to the materials, GIC yielded the least demineralized area of 0.112 ± 0.07 mm2, but its mean area was not significantly different from that of the F-varnish group (0.138 ± 0. 05). However, both areas showed statistically significant differences compared with all other groups, except F-sealant vs. F-varnish. Nonetheless, the means showed statistically significant differences among all groups (p < 0.05) (Table 1 ).
The percentage reductions in area under the material (A) and new lesion area adjacent to the material (B), compared with those in controls, are shown in Table 2
This is the first study to compare, in one setting, 4 materials commonly suggested for application to incipient lesions. A previous study investigated sealant with and without fluoride (Jensen et al., 1990), GIC, and both sealants (Hicks and Flaitz, 1992), limiting the comparison to 3 materials. The materials chosen to represent each generic group in the study were: Delton®, due to its wide use as a conventional sealant; Teethmate F-1®, because it was found to release the highest level of fluoride among the F-sealants (Garcia-Godoy et al., 1997b); Duraphat®, which has been found to release fluoride better than Duraflor® (Castillo et al., 2001), and which yielded a higher concentration of fluoride in saliva than did Fluor-Protector® (Twetman et al., 1999); and Fuji VII®, which, according to the manufacturer’s product information (GC Corporation, Tokyo, Japan), releases higher fluoride levels than both Fuji II® and Fuji IX®. The differences in lesion size in this study may reflect the different mechanisms of each material in inhibiting demineralization and promoting remineralization. The least demineralized area found with GIC in this study correlated with its highest fluoride content (at 10–23%) (Smith, 1990), while the content in F-sealant was 2.28% (Tanaka et al., 2000). It has been shown that GIC’s increased fluoride content allows for a greater degree and more prolonged release of fluoride compared with other dental materials (Forsten, 1990). Much higher fluoride release of GIC was observed compared with F-sealant at day 1 (249 vs. 2.09 µg/cm2) and at 2 wks (77.28 vs. 8.02 µg/cm2) (Garcia-Godoy et al., 1997b; Gandolfi et al., 2006), resulting in a greater reduction of carious areas under and adjacent to GIC when compared with those of F-sealant. The non-F-sealant specimens showed the largest mean lesion area among the 4 materials, because sealant acted only as a physical barrier and shielded the enamel from further acid challenge. Even though remineralization of saliva may be facilitated through microleakage (Silverstone, 1983), the access of the saliva through sealant in our study was minimal. However, leakage between the enamel surface and GIC or F-sealant was greater than that of sealant (Cooley et al., 1990; Ganesh and Shobha, 2007). Besides the higher concentration of fluoride, these larger microleakages of GIC and F-sealant may aid in remineralization effects of the saliva, along with the release of fluoride on these materials’ surfaces. The significant enamel fluoride uptake adjacent to GIC can be explained by enamel mineral being continuously lost and regained, as occurs during the pH-cycling process. GIC fluoride release is pH-controlled (Rezk-Lega et al., 1991). During demineralization, GIC would release fluoride to the environment, and during remineralization, the fluoride would be taken up by the enamel. Even though the percentage of sodium fluoride in F-varnish is only 2.26%, the second least carious area found, next to GIC, may be explained by the prolonged retention of F-varnish on the tooth surface for several hrs, even after in vitro demineralization challenge and sonication (Sorvari et al., 1994), resulting in the exceptionally large fluoride uptake of the sound enamel and incipient caries lesion (Retief et al., 1980). The elevated fluoride in the saliva took 24 hrs to return to baseline (Eakle et al., 2004), adequate time for significant uptake of fluoride in the demineralized tooth structure. It could also be easily accessed by saliva. It has been found that placement of F-varnish either over or around the lesion will promote remineralization equally, and suggested that the dissolution of varnish by the moist environment could expose the caries lesion to saliva supersaturated with calcium phosphate and fluoride from the remaining varnish (Castellano and Donly, 2004). Many studies have indicated that CaF2 is the major, or even the only, product formed when enamel is treated with F-varnish (Dijkman et al., 1983; Øgaard et al., 1984; Bruun and Givskov, 1991). Coating of CaF2 at neutral pH by pellicle proteins and secondary phosphate prolongs the retention of CaF2 on the enamel. At lower pH, such as during demineralization, the pellicle protein and phosphate coating of CaF2 is lost, and an increase in the dissolution rate of CaF2 occurs (Rølla and Øgaard, 1985). The fluoride ions released may adsorb onto the enamel surface and inhibit dissolution (Arends and Christofferson, 1990), or increase the rate of remineralization of lost mineral. After demineralization, the CaF2 globules are again stabilized by the adsorption of proteins and phosphate (Øgaard, 1990). It has been shown that no firmly bound fluoride was present immediately after F-varnish treatment (Cruz et al., 1992). The firmly bound fluoride observed following Duraphat treatment (Øgaard et al., 1984; Seppä, 1984) is most likely formed later as a result of remineralization during pH cycling in plaque (Rølla, 1988). The results of our study showed that observation of incipient caries alone is not an adequate treatment option. Progression of lesions is likely and may lead to cavitation that makes reversal of the lesion impossible. When the sealant or fluoride-releasing materials were applied to the lesions in our study, the lesion area was reduced. In relation to patient care, a prescription of fluoride-containing products for home use requires constant cooperation from the patient. If the patient complies, remineralization may occur on the surfaces easily accessed by the saliva, such as buccal and lingual surfaces, but not likely on the proximal surface. The application of one of these materials after tooth separation with an elastic band may be a better choice for intervention. As shown in our study, even the use of sealant, which acts as a physical barrier, could reduce lesion size. This is supported by an 18-month clinical study, which demonstrated that only 22% of the sealed incipient proximal caries lesions progressed, compared with the 47% of the group left with no intervention other than instructions for patients to floss regularly (Martignon et al., 2006). However, our study also found that the application of fluoride-releasing materials to the lesion had significantly greater impact on the inhibition of demineralization and promotion of remineralization than did materials that cannot release fluoride. Furthermore, the remineralization effect with the use of GIC and F-varnish extended to inhibiting the demineralization of intact enamel adjacent to the materials. Future clinical studies would help to confirm the effectiveness of these 4 materials in the oral cavity. If similar results are found, a new regimen of intervention could be developed to maximize the conservation of tooth structure on proximal surfaces.
This study was supported by the Dental Research Fund, Dental Research Project 3205-312, Faculty of Dentistry, Chulalongkorn University. The authors thank Dr. Chanchai Hosanguan and Dr. Patita Bhuridej for their statistical analysis advice. Received for publication February 7, 2007. Revision received October 29, 2007. Accepted for publication November 26, 2007.
Journal of Dental Research, Vol. 87, No. 3,
228-232 (2008)
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ABSTRACT
INTRODUCTION
