The Effect of Fissure Sealants on the Values of Two Different Caries Detection Devices

Abstract

Objective: The aim of this in vitro study was to evaluate the effects of clear and opaque fissure sealants on readings of laser fluorescence (LF) and light-emitting diode (LED) based caries detection devices. Background data: When planning patient care, the practitioner needs to consider any changes in the status of the sealed surface for the long-term success of the sealant. As visual inspection is difficult to perform on sealed surfaces, adjunct diagnostic methods must be used to improve follow-up assessments and increase the accuracy of caries diagnosis. Methods: Forty-six freshly extracted permanent human molars were selected and divided into two groups. Each group was treated with a different sealant (clear and opaque). The teeth were measured twice by two blinded observers using an LF-based and an LED-based device before and after sealing. The data were analyzed using Wilcoxon's matched-pairs signed-rank test and a paired t-test. Cohen's κ and the intraclass correlation coefficient were used to examine intra- and inter-examiner repeatability. Results: The values of the LED device were significantly higher after the application of the opaque sealant, but there was no statistically significant difference after the application of the clear sealant (p=0.15). The LF-based device readings were also significantly lower after both the clear and the opaque sealant applications (p<0.001). Conclusions: The readings from the LF-based device were affected by both sealants. The readings from the LED-based device were affected by the opaque sealant but not by the clear sealant.

Introduction

O cclusal surfaces are particularly vulnerable to caries development because of their morphological complexity, which makes them vulnerable to plaque accumulation and difficulty in exposure to fluoride. To deal with this problem, practitioners apply pit-and-fissure sealant, which is recognized as the most effective method for the prevention of pit-and-fissure caries. The sealant has also been proposed for the management of carious lesions in enamel and for preventing incipient caries activity.^1
–3 When planning patient care, the practitioner needs to consider any changes in the status of the sealed surface for the long-term success of the sealant. Research has demonstrated that practitioners can diagnose caries under clear sealants, but that they tend to underestimate the severity of any lesion present.⁴ As visual inspection is difficult to perform on sealed surfaces, adjunct diagnostic methods must be used to improve follow-up assessments and to increase the accuracy of diagnosing caries.⁵

Recently, several methods have been developed and recommended as diagnostic aids to identify caries lesions on occlusal surfaces.^4,5 One such method, a laser fluorescence (LF) based device, illuminates the surface with laser light, and detects fluorescence associated with caries. This instrument functions on the principle of the excitation of a 655 nm monochromatic light and measurement of back-scattered fluorescence. At this wavelength, apart from autofluorescing the tooth substance, fluorescing objects have been identified metabolites of oral bacteria as protoporphyrins.⁶ Although its usefulness as a diagnostic tool is limited, according to a systematic review,⁷ some studies showed that the LF method has relatively good validity and reproducibility both in vivo and in vitro, and that it is a valuable tool for caries detection.^8

–11

Previous studies have reported that fissure sealants do not affect LF readings.^12

–15 However, other studies^16

–19 have shown that the presence of sealants and composite filling materials might complicate the interpretation of the LF readings, leading to false-positive results.

The light emitting diode (LED) based caries detection device, which is a newly developed system, uses a combination of LED and fiberoptic technologies to detect caries lesions quantitatively. The detection handpiece is portable and functions with visual and audible caries-detection signals. If the enamel is healthy, the LED light is absorbed into the tooth, and the green light remains on. If the enamel is demineralized and decay is present, the LED light will be reflected, refracted, or scattered. The colorless receiving fiber captures this light, and the green light is extinguished. A red light is illuminated, and the device emits an audible tone, alerting the clinician that there is a change in the tooth's structure. Three different types of audible tones denote the extent of the decay. The technology of LED reflectance and refraction has been approved by the Food and Drug Administration for both occlusal pit-and-fissure caries and for interproximal evaluation of caries.^20

–23

Several studies^{5,12,14

–19,24} have focused on the influence of pit-and-fissure sealants on fluorescence measurements; however, the effect of these sealants on readings of LED-based caries-detection devices remain unknown.

The aim of this in vitro study was to evaluate the effects of clear and opaque fissure sealants on readings of LF-based and LED-based caries-detection devices, regardless of the type of the caries. The null hypothesis was that the application of the clear and the opaque sealant would not affect the values obtained for the LF- and LED-based caries-detection devices.

Methods

Material selection

Forty-six freshly extracted permanent human molars were selected for the study. The time span between tooth extraction and the following diagnostic examination did not exceed 1 week. Both sound teeth and teeth with different levels of caries were used. Teeth with restorations, sealants, large cavitations, and cracking or developmental defects (such as hypoplasia) were excluded. Before proceeding, the occlusal surfaces of the teeth were cleaned with a brush mounted on a slow-speed handpiece without pumice or a polishing paste. The study was approved by ethics committee of Gaziantep University (03-2009/78).

Standardization of the method

Two examiners determined the suspected sites for easy relocation of the test sites for future measurements. All the examiners had 7 years of experience in the area of caries detection and had experience in calibrating the devices. Maps of the fissures were drawn for each tooth's surface on paper. Then, all measurements were independently taken twice by two blinded dentists within the same groups, with a 1 week interval between the measurements. To avoid dehydration of the teeth, they were stored in distilled water in the intervening period.

Baseline measurements

LF examination

A pen-type DIAGNOdent device (KaVo, Biberach, Germany) was used for the LF measurements. Prior to each examination sequence, the device was calibrated on the ceramic standard in accordance with the manufacturer's instructions. The “A” tip (designed for occlusal surfaces) was used, and the tip was moved around the occlusal surface and rotated on its central axis until the highest value was obtained. The device can give a range of readings from 0 (sound) to 99 (deep dentinal caries). The values displayed on the screen were recorded. According to the average fluorescence values obtained with the LF device and the cutoff limits suggested by the manufacturer, the cutoff limits of the DIAGNOdent readings were as follows: score 0–13, sound tooth surface (code 1); 14–20, enamel carious lesion (code 2); 21–29, initial dentinal lesions (code 3); and ≥30, advanced dentinal lesions (code 4).

LED device reading

The LED-based device (Midwest Caries I.D. Detection Handpiece, DENTSPLY Professional, NY) uses a specific optic signature to detect the difference between healthy and decalcified teeth. The device was used to take measurements after it was calibrated with the ceramic standard. The tip of the probe was always parallel to the long axis of the tooth on the occlusal surface. According to the manufacturer's instructions; a non-red or greenish light indicates a healthy tooth structure (code 1), the presence of a red light with an audible tone indicates decalcification of the tooth's structure, a slow pulse indicates a small amount of decalcification (code 2), a medium pulse indicates a medium level of decalcification (code 3), and a rapid pulse indicates a high level of decalcification (code 4).

The teeth were then randomly divided according to the material for pit-and-fissure sealing. The groups were arranged as follows:

Group I–clear sealant (Smartseal & loc; Detax, Ettlingen, Germany), 20 teeth, 76 fissures

Group II–opaque sealant (Fissurit FX, Voco, Cuxhaven, Germany), 26 teeth, 70 fissures

Sealant placement

The occlusal surfaces were etched with 35% phosphoric acid gel for 30 sec, rinsed with water for 15 sec, and dried for 5 sec with an air syringe. After the enamel conditioning procedures, the sealants were applied using an explorer. The time for penetration of the sealants was 15 sec, and the sealants were then light-cured for 20 sec. After sealing, the same examiners re-measured the teeth using the LF device as described previously.

Statistical methods

The average of the maximum values was obtained by the two examiners during the first and the second assessments. The data from the two measurements performed by each examiner in each phase were combined, and the average readings from the LF and the LED-based devices were obtained for each tooth. The level of significance chosen was p<0.05.

Validity

The numerical readings from the LF-based device were transformed to categorical values according to the cutoff limits suggested by the manufacturer's instructions. Directional changes between the diagnosis of the unsealed and sealed surfaces were compared by performing the Wilcoxon's matched-pairs signed-ranks test for the two methods. As the data were not normally distributed, the codes were not condensed for this analysis. However, the data for the LF readings were normally distributed and were analyzed by a paired t-test. The Bonferroni correction was used for the statistical analysis of the results.

Reproducibility

Cohen's κ was calculated to examine the intra- and inter-examiner repeatability for the categorical data (LED device). It has been suggested that a κ score of 0–0.20 indicates slight agreement, 0.21–0.40 fair agreement, 0.41–0.60 moderate agreement, 0.61–0.80 substantial agreement, and>0.81 near-perfect agreement.²⁵ The intra-class correlation coefficient was used to assess intra- and inter-examiner reproducibility for the continuous data (LF pen readings).²⁶ The reproducibility indicates the closeness of the agreement between the results of the measurements taken under the different conditions.

Results

Table 1 presents the κ scores and the intra-class correlation scores for the intra- and inter-examiner agreement diagnostic thresholds for each of the diagnostic methods. The intra- and inter-observer accuracy values of the two observers for all the diagnostic methods showed near-perfect agreement (p<0.001).

Table 1.

Intra- and Inter-Examiner Reproducibility Values Before and After Sealing

		Intra-examiner		Inter-examiner
		Examiner 1	Examiner 2	Examiner 1-2
LF-based device	Before	0.984^a	0.970^a	0.955^a
	After	0.981^a	0.986^a	0.962^a
LED-based device	Before	0.999^a	0.999^a	0.863^a
	After	0.999^a	0.999^a	0.833^a

p<0.05.

LF, laser fluorescence; LED, light-emitting diode.

The mean LF pen readings showed a significant decrease after sealing. As shown by the results of the paired t-test presented in Table 2, there was a statistically significant difference (p=0.001) between the LF readings before and after sealing for both materials.

Table 2.

Mean LF-Based Device Values Before and After Sealing

LF-based device (n⁰:46)			Mean±SD	p Values
Clear sealant (n¹:76)	Examiner 1	Before sealant	19.50±14.14	0.001^a
		After sealant	13.51±14.03
	Examiner 2	Before sealant	19.91±13.81	0.001^a
		After sealant	12.98±13.25
Opaque sealant (n²:70)	Examiner 1	Before sealant	26.65±22.18	0.001^a
		After sealant	21.59±20.57
	Examiner 2	Before sealant	28.86±21.50	0.004^a
		After sealant	21.96±19.96

p<0.05.

n⁰, total number of teeth used in the present study.

n¹, number of occlusal pit or fissures clear sealant applied.

n², number of occlusal pit or fissures opaque sealant applied.

LF, laser fluorescence.

A comparison of the difference in the values of the LED device before and after sealing between the two materials showed a statistically significant increase with the opaque sealant (p<0.001), but there was no statistically significant difference with the clear sealant (p=0.15), with the mean values similar before and after sealing. However, the LF pen readings showed a significant decrease after the application of the clear and the opaque sealants according to the Wilcoxon's matched-pairs signed-ranks test (p<0.001). The Z values (mean/standard error of the mean) were calculated from the signed ranks (Table 3).

Table 3.

The z-Values and Their Significance from the Comparisons Before and After Sealing Between Sealants

		LED-based device		LF-based device
		z-Values	p Values	z-Values	p Values
Clear sealant	Examiner 1	−1.414	0.15	−4.394	0.000^a
	Examiner 2	−1.000	0.31	−4.256	0.000^a
Opaque sealant	Examiner 1	−6.472	0.00^a	−4.001	0.000^a
	Examiner 2	−6.464	0.00^a	−2.995	0.003^a

p<0.05.

LF, laser fluorescence; LED, light-emitting diode.

The scores for the LF and the LED devices before and after the application of the clear (Table 4) and the opaque (Table 5) sealants are compared in cross-sectional tables.

Table 4.

Cross-Sectional Table Comparing Scores of LF- and LED-Based Devices Before and After Clear Sealant

	LED-based device
LF-based device	Code 1	Code 2	Code 3	Code 4	Total
Before clear sealant
Code 1	29	20	7	3	59
Code 2	-	-	2	5	7
Code 3	-	-	3	4	7
Code 4	-	-	1	2	3
Total	29	20	13	14	76
After clear sealant
Code 1	52	2	-	5	59
Code 2	1	1	3	-	5
Code 3	2	3	-	2	7
Code 4	2	1	-	2	5
Total	57	7	3	9	76

LF, laser fluorescence; LED, light-emitting diode.

Table 5.

Cross-Sectional Table Comparing Scores of LF- and LED-Based Devices Before and After Opaque Sealan

	LED-based device
LF-based device	Code 1	Code 2	Code 3	Code 4	Total
Before opaque sealant
Code 1	19	10	7	5	41
Code 2	1	-	3	17	21
Code 3	-	-	2	3	5
Code 4	-	-	-	3	3
Total	20	10	12	28	70
After opaque sealant
Code 1	3	-	1	1	5
Code 2	13	4	3	2	22
Code 3	6	1	-	2	9
Code 4	13	2	6	13	34
Total	35	7	10	18	70

LF, laser fluorescence; LED, light-emitting diode.

Discussion

Pit-and-fissure sealants are used for caries prevention in pediatric dentistry. Therefore, it is important that reliable clinical follow-up should be done to determine whether caries are present under the fissure sealant. Some diagnostic methods have been developed for this purpose.^4,5 The LF-based device is one of the most useful and well-known caries-detection devices, with a number of studies evaluating the effect of the fissure sealant on the device's readings.^{5,12,14

–19,23} As the LED-based device is a new caries-detection technology, there were several studies related to its diagnostic efficacy in the literature.^21,22,25 Therefore, the present study was aimed at identifying potential differences before and after fissure sealant application in the readings of LF and LED devices, regardless of the caries. This is the first study to investigate whether pit-and-fissure sealant applications affect the readings of LED-based device.

Tests of various sealant materials have been reported in the literature.^{5,14,15,19,23} In the present study, we used Smartseal clear (Smartseal & loc; Detax, Germany) as the clear sealant. The LF readings were lower after its application, with statistically significant difference. These results disagree with those of Diniz et al.⁵ who reported that LF pen values tended to increase after clear sealing, but agree with those of some previous studies.^14,17 Krause et al.¹⁵ reported no difference between readings before and after clear sealing. An in vivo study¹³ also reported that clear sealants did not affect LF values in primary and permanent teeth. Askaroglou et al.¹⁹ found statistically significant increases after sealing with clear sealant in primary teeth. Although differences between in vitro studies may be attributed to differences in the study design, such as tooth type, storage medium, sample size, disease level at the examination sites, and etching time, the differences in this study may be because of the different composition of the materials used. Smartseal & loc, whose first use was reported in the literature, is a new material containing ∼50% filler, but the particle size is inside the nanorange at >1 μm. In nanostructured composites, a greater number of particles are present, which permits higher filler loading than with conventional composites. Moreover, the size of the particles is far below the wavelength of light, making them unmeasurable by the refractive index. When light enters, long wavelength light passes directly through materials showing high translucency.^15,24 No statistically significant difference between LF values before and after an experimental nanofilled clear sealant was reported.^5,15

Other authors have also reported a decrease in LF readings in various opaque sealant materials. ^{5,12,15,16,19} The decrease in the LF readings resulted in caries underestimation in the present study. This result is in accordance with the findings of Sönmez et al.¹⁸ who tested the same opaque sealant.

Titanium dioxide, which is included in some sealants, has variable levels of intrinsic fluorescence.¹⁷ It also has a profound effect on the fluorescence transmission of the underlying simulated caries. As the concentration of titanium dioxide approaches 0.5%, the fluorescence signal is almost fully attenuated¹⁷ by interfering with the LF signal transmission, which absorbs either the light emitted by the device or the fluorescence emitted by the carious tissue.^12,16 Takamori et al.¹² attributed the lower LF values in opaque sealants to the fluorescence, absorption, and scattering of irradiation and reflected beams, as these would be different from those in the clear sealants. Fissurit FX used in the present study contains 55% inorganic and glass ionomer filler, in addition to Bis-GMA and 2% NaF and titanium dioxide.¹⁸ The lower LF readings induced by this sealant are consistent with results of another study that used a glass ionomer sealant.¹⁶ In addition, LF values have been reported to significantly increase in demineralized enamel after the acid-etching procedure.¹⁵ Changes in the optical properties of the mineral are caused by an increased pore volume in demineralized enamel.²⁶ Thus, LF detects substantially more fluorophores within these pores than within healthy enamel.^27,28 A study has shown that hydroxyapatite crystals contribute significantly to scattering.²⁹ In light of these considerations, the fluor and glass ionomer filler content of the opaque sealant rather than the titanium dioxide may explain the decrease in LF values in the Fissurit FX group.

Although the LED light is absorbed in healthy enamel, it was not absorbed into the tooth because of the titanium dioxide used as a pigment in the opaque sealant. and was thought to be refracted or scattered. This may explain the rise in the values of the LED-based devices after the application of the opaque fissure sealant in this study. Therefore, false positive responses occurred. As there is no substance that permits the LED light to pass through clear sealant, the difference between the values before and after the application of the clear sealant was not significant in the present study.

Although the readings of the LED-based device before and after the application of the transparent sealant were consistent with each other, the opaque sealant scores of the LED-based device were incompatible. The readings of the LF-based device were not consistent before and after the application of either sealant. According to these results, within the limitations of the study, the LED-based device may be used as a more reliable means of assessing any changes in the status of the dentin under clear sealants. This diagnostic method makes it possible to eliminate operative procedures such as fissure sealant opening during control session of fissure sealant clinically.

The limitation of this in vitro study is that optical properties of the teeth and the materials may be affected by the in vivo condition. Previous in vitro studies have reported that LF values increased after sealant thermocycling,⁵ aging in saline.¹⁵ Therefore, aging, staining, and thermocycling should be evaluated in further studies. The interpretation of the results is also limited because there is no study in the literature related to the effect of fissure sealants on measurements obtained by LED-based devices. In addition, because of the differences in the working principle of the two devices (the LED-based device does not produce numerical values, whereas the LF-based device does), the results of these devices are not comparable.

Conclusions

In the present study, the null hypothesis was rejected for the two devices, except for the clear group of LED device. As there was no significant difference among the measurements with the LED-based device before and after the application of the clear sealant, the device may be used to determine presumptive caries under the sealant without any operative procedure. However, because the measurements in both the LED- and LF-based devices before and after opaque sealing showed a significant difference, these devices may not be used to diagnose caries under opaque sealant. Further studies are required to achieve more accurate results in relation to the performance of LED-based devices, because the optical properties of restorative materials may be affected by clinical situations.

Footnotes

Author Disclosure Statement

We declare that we have no conflict of interest.

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