Clinical evaluation of resin infiltration treatment masking effect on hypomineralised enamel surfaces

One of the developmental deficiencies of the enamel is clinically visible enamel opacity. These deficiencies can arise from different types of anomalies (e.g. molar incisor hypomineralisation (MIH), amelogenesis imperfecta, fluorosis and consequences of trauma to the primary teeth) [1]. MIH is a clinical manifestation of enamel hypomineralisation in which permanent incisors and one or more first permanent molars may be affected [2, 3]. It occurs when ameloblasts damaged during the maturation stage are not able to secrete the organic matrix appropriately [3, 4]. While the primary etiology of MIH is unknown, theoretically, it is indicated that, changes in the matrix pH during enamel maturation may lead to MIH. The potential aetiological factors are systemic diseases, antibiotic use, preterm delivery, environmental toxins, and malnutrition [1, 5].

Dentine sensitivity, post-eruptive enamel breakdown, pulpal inflammation, dental pain, and early tooth extraction are frequently seen in teeth affected by MIH [6, 7]. Further, MIH alters the tooth’s aesthetic features, such as opacity, translucency, and fluorescence [8]. The clinical characteristics of MIH are well-demarcated hypomineralised borders, porous defects and altered enamel translucency. These changes affect enamel colour which ranges from white cream to yellow brown, that allow clinicians to separate the adjacent normal enamel from the coloured enamel. The defective enamel has a smooth surface with average thickness; however, the enamel structure is defective. As a characteristic of MIH is that the cervical third is spared, but the two other thirds might be affected [9].

Resin infiltration treatment has been proposed recently as an alternative micro-invasive option for enamel defects [10]. In caries ethology, main purpose of the resin infiltration treatment, using resin sealing of the microporosities which causes diffusion pathways for acids and dissolved minerals, thus arresting the incipient caries lesion. The resin matrix can also strengthen the enamel structure mechanically. Removal of the surface layer might also weaken the lesion structure, but Meyer-Lueckel et al. [11] reported that 15% HCl is most suitable for removing approximately 40 μm of the hypermineralized surface layer. Moreover, in this study, no cavitation occurred after etching, even when the surface layer had been eroded completely. In practice, subsequent resin infiltration should ensure restrengthening of the lesion structure. In contrast, microabrasion, which has been commonly used in white spots, removes up to 360 μm of enamel [12]. 99% ethanol is used to remove the water stored inside the lesion body's microporosity and allow the resin to penetrate into the lesion body driven by capillary forces [13].

Enamel lesions can be examined by various methods other than clinical examination [14]. One such is laser fluorescence (DIAGNOdent Pen), which utilizes the lasers fluorescence diagnostic method [15]. The light absorbed by the teeth is reflected in the form of fluorescence. The fluorescent light's intensity increases with the lesion's increasing depth. Another method is cross-polarisation, which is more reliable than traditional intraoral photography as it enhances the appearance of enamel defects by reducing the reflection on the enamel surface [16]. The enamel's structural details on the tooth's anterior surface may not be visible in the clinic due to light reflection. Direct light reflection from the anterior surface of the teeth may cause loss of data enamel defects may combine or wholely remove degree of probable enamel defects [16].

As the resin infiltration protocol was developed for managing carious lesions, the application for treating hypomineralized lesions should be developed. In this study, it was aimed to quantitatively evaluate the masking effect of resin infiltration treatment (ICON) on hypomineralized enamel surface lesions by using DIAGNOdent Pen; changes in colour by using a spectrophotometer, changes in lesion size by using cross-polarisation photography in permanent incisor teeth with MIH after before treatment; immediately after treatment; 1; 3; and 6-month follow-up.

The study was approved by the Tokat Gaziosmanpaşa University Clinical Research Local Ethics Committee (Project no: 18-KAEK-094), and the protocol was registered at Clinical Trials.gov (NCT04685889). The data were presented in accordance with the CONSORT statement. The written informed consent form was obtained from parents of the children included in the study stating that they accepted the treatment. This study was performed in accordance with the ethical standards of the Declaration of Helsinki (1964) and its subsequent amendments.

A total of 116 permanent central incisors in a set of 37 patients, including 58 teeth with developmental enamel defects due to MIH and 58 healthy teeth, were evaluated in this study. The patients included 21 girls (mean age = 9.94 ± 2.04) and 16 boys (mean age = 9.43 ± 2.08) in the 8–14 years (9.70 ± 2.08) age group.

The use of infiltrants for masking enamel discolourations in hypomineralized teeth has spread more recently [9]. We evaluated the qualitative and quantitative clinical outcomes of resin infiltration on teeth with MIH for 6 months. Our results showed that resin infiltration using Icon® was a successful effect in masking of hipomineralised teeth in children with MIH.

The primary mechanism of DIAGNOdent is based on different absorption and scattering of laser fluorescence radiation of the carious lesion compared to the surrounding healthy tissue [15]. Changes caused by caries in tooth cause an increase in fluorescence at the exciting wavelength. It was reported that this high fluorescence is due to bacterial porphyrins in the carious lesion [15, 17]. In MIH, opacities structure differs from caries etiology [9, 18]. DIAGNOdent readings were recorded high in tooth with irregular enamel structure without dental caries as MIH [19]. One of the reasons for higher values in the non-carious but hypomineralised enamel tissue might be the increased protein in the enamel [20]. Another reason, the fluorescence of darker teeth due to intrinsic enamel stains is higher than whiter teeth [15]. In line with previous studies, the values obtained using the laser fluorescence (DIAGNOdent Pen) were higher in MIH (white-cream and yellow–brown localized opacities without cavitation) before the application of resin infiltrant compared to the healthy anterior teeth.

Histological studies have shown an increase in microporosity within the different layers of hypomineralised enamel lesions [2, 18]. The porous and enlarged intercrystalline spaces act as diffusion pathways for acids and dissolved minerals. The application of a low-viscosity resin infiltrant fills the pores and reduces the microporous structure. Assuming the resin does not penetrate the sublayers of the enamel lesion and is only limited to the outermost layer. In that case, the effectiveness of the resin infiltration treatment might be decreasing over time [21]. In our study, the fact that the values obtained using the laser fluorescence (DIAGNOdent Pen) in the teeth treated with resin infiltrant decreased and, after that, remained stable for 6 months might suggest that the resin was homogeneously infiltrated into the lesion.

Nowadays, many colour systems are used in restorative and prosthetic dental treatments; the most preferred system in recent years is the CIELAB (ΔEab) colour system [22]. The L*, a*, and b* numerical values in the CIE scale in both the treatment and control groups were determined by VITAEasy Shade Advance®, and the ΔE numerical values depicting the change between colours were also calculated. Although the ΔE value refers to the colour change in the tooth, it does not provide information about the direction of colour change. Therefore, ΔE and L* values were evaluated together in our study. An increase in the L* value of teeth with enamel lesions is considered an increase in the brightness of the lesion area, representing greater lesion depth. A decrease in the L* value is considered a masking of the lesion, i.e., darker-coloured lesion areas resembling healthy enamel [23, 24]. In our study, a significant decrease was observed in the L* value after 6 months, which implied that the colour of the hypomineralised lesions had darkened and approached the natural tooth colour.

In this study, we found that the ΔE values calculated immediately after resin infiltration treatment and those calculated 1, 3, and 6 months later were, on average, greater by a factor of ΔE 3.7 compared to the initial values. Moreover, the colour change was clinically perceptible after resin infiltration treatment, as reported in the literature. However, the colour change was less in the control group compared to that in the treatment group at all times [25, 26]. Further, when the resulting colour change was evaluated with the L* values, it was determined that the colour of the lesions had darkened. The discolouration observed before and immediately after resin infiltration treatment in the control group may have been caused due to isolation of the teeth from oral fluids and dehydration for approximately 30 minutes during the application of the material and the measurements being performed.

The length of etching and drying application time affects the homogeneity and depth of the resin infiltration. C. Kobbe, et al.[27] proposed that two or three etching to obtain better aesthetic results in resin infiltration in white spot lesions. Hypomineralized enamel teeth has high organic content as protein and this may be a reason for the more difficult penetration of the infiltrant [27]. In this study, the etching and drying application was applied one time. If these processes were applied more time, maybe higher success could be achieved.

In their study, Khanna et al.[28] investigated the masking effectiveness of resin infiltration. Photographs of 70 teeth with opaque enamel lesions were obtained before and after treatment, and L*, a*, and b* values of these teeth were obtained using the Image J software. Unlike the aforementioned study, the colour parameters in our study were determined directly using VITA EasyShare Advance®, thereby minimizing errors caused by reflection during the photo shoot. Image J was not used to analyze the colour but to measure and compare the areas of hypomineralised lesions in the photographs obtained by cross-polarisation photography.

Similar to the aforementioned studies, we observed a significant decrease in the lesion areas after resin infiltration treatment (Icon®), which remained stable for 6 months. Since measuring the lesion areas using Image J is an advanced and repeatable method, and millimetric measurements obtain accurate results, it may be preferred over measurements performed using a periodontal probe or the naked eye in the clinic. We consider that using cross-polarisation photography provides more accurate information about the severity of MIH compared to visual examination or regular photo shoots. Studies on this subject are rare, which warrants more studies to support this information.

Resin infiltration treatment (Icon®), provided effective results as a micro-invasive treatment of anterior teeth with MIH lesions. The cross-polarization photography technique may be use to evaluate the lesion size instead of photography with flash. However, there is a need for more clinical studies evaluating the long-term success of this material.