White spots lesions or creamy and yellow opacities on labial surface of teeth are dental problems often seen in children and adolescents. These lesions may include early caries changes, presenting as white opaque areas on which the lack of enamel shininess is caused by the subsurface loss of minerals, but also some form of developmental defects of enamel (DDE). Molar-incisor hypomineralisation (MIH) in form of well-demarcated from intact enamel, asymmetric, white, creamy or yellow to brownish opacities (larger than 1 mm) is an example of quantitative DDE (1-5). The most recent systematic review and meta-analysis revealed that overall prevalence of MIH in children was estimated at 13.5% (6). In addition to having poorly mineralized and at risk of post-eruptive breakdown first permanent molars, children diagnosed with MIH may also have one or more hypomineralized incisors. Then enamel opacities, tend to be located towards the incisal third of the labial surfaces, sparing the cervical enamel. MIH affected enamel has a high carbon and protein content, but lower calcium and phosphate concentrations than intact tissue (5, 7). Microscopically, MIH lesions present disorganized enamel prisms and large inter-prismatic spaces occupied by a protein-rich matrix, which is associated with decreased mineral density, hardness and fracture resistance (8). The presence of voids between the normally densely packed enamel rods alters the refractive index of the defective enamel and makes it appear more opaque (9). The incisor defects are usually less serious than those seen in molars with diminished risk of breakdown due to the absence of chewing forces, and these teeth tend not to be thermally sensitive (3, 7). Even though hypomineralized molars cause the most severe oral symptoms and functional limitations, MIH affected incisors, due to aesthetic reasons, had the largest negative effect on quality of life in aspect of the emotional and social well-being (10).

Available methods of white lesions and opacities treatment include remineralization with fluoride or casein phosphopeptide-amorphous calcium phosphate (CPP-ACP), which with patient’s adherence might be effective in arresting demineralization, but their effectiveness in an improvement of aesthetics is limited (1, 2). Microabrasion and bleaching can be used for camouflage of with spots of developmental origin and white opacities, however these methods are not free from side – effects e.g. aggressive reduction of enamel in microabrasive technique or post- bleaching teeth hypersensivity, which can be severe in MIH – affected teeth (1, 2, 5). Furthermore, according to Polish regulations, teeth bleaching with the use of agents in which the concentration of hydrogen peroxide present or released is between 0.1 and 6% is not recommended for patients under the age of 18 years (11). Possible treatment of enamel opacities includes also more invasive methods – direct composite resin restorations or veneers. Nevertheless, in children and adolescences due to the large pulp chambers, and thin layers of enamel and dentin conservation as much as possible of tooth tissue seems to be really essential (2), and when managing MIH affected incisors more invasive treatment needs to be postponed until complete maturation (5).

Infiltration with methacrylate-based resin is one of the newer minimally invasive procedure, which seems to provide an intermediary treatment modality between prevention and restorative therapy. It was design for treatment of caries lesions on smooth and proximal surfaces limited to enamel or crossing the enamel-dentin junction and reaching maximum up to 1/3 external layer of dentin (D1 according to radiological classification). The arresting of caries lesions is achieved by penetrating the low-viscosity and high surface tension resin into the enamel after having been etched with a 15% hydrochloric gel (HCl). Infiltration results in obstructing the diffusion pathways for carbohydrates and organic acids in the enamel and creating of diffusion barrier outside and inside the tissue, additionally it increases microhardness of infiltrated early enamel lesion (12, 13).

Additionally infiltration has positive aesthetic effect – masking of white spots lesions, which was proved in vitro and in clinical trials (14-20). A reduced visibility of infiltrated lesions or restoring of natural tooth color is due to filling of enamel micropores, formerly filled with air (refractive index RI = 1.00) or water (RI = 1.33), with low-viscosity resin of refractive index (RI = 1.52) more similar to intact enamel index (RI = 1.65), which is the same as that of hydroxyapatite. It results in alteration of the optical characteristics of the affected by caries process enamel and it seems like the surrounding sound tissue (9, 15, 16). That cosmetic effects of infiltration of initial caries lesions and post-orthodontic decalcifications encouraged practitioners to use that method in treatment of developmental enamel opacities on labial surfaces that are symptoms of fluorosis and MIH. Published reports suggest extending infiltration approach to these indications (1, 4, 7, 16, 17). An updated European Academy of Paediatric Dentistry policy document on “Best Clinical Practice guidance for clinicians dealing with children presenting with Molar-Incisor Hypomineralisation (MIH)”, published in 2021, mentions resin infiltration as one of treatment option of MIH-affected anterior teeth (2).

The aim of this study was to assess clinically the effectiveness of Icon infiltration technique in masking demarcated enamel opacities in MIH-affected permanent teeth in children and adolescents and to evaluate the stability of achieved visual effect.

The study was approved by the Bioethics Committee at the Medical University of Lodz (RNN 24/22/KE, 2022) and conducted in compliance with the principles of the Helsinki Declaration. 115 permanent incisors with demarcated opacities in 33 subjects (18 girls and 15 boys), aged from 8 to 18 years (mean age – 10.45 ± 2.97), diagnosed with MIH were treated with Icon infiltration (DMG, Hamburg, Germany). All participants were patients of the Department of Pediatric Dentistry of Medical University of Lodz. The study lasted from May 2022 to May 2023, and was conducted by a pediatric dentistry specialist and a doctor undergoing residency training in this field. Inclusion criteria: written consent of the patient and/or legal guardian to participate in the study, age up to 18 years, diagnosis by clinical examination of MIH and presence of demarcated enamel opacities on permanent incisal teeth in the form of white, cream or yellow to brownish discoloration. Exclusion criteria: the presence of post-eruptive mechanical damage within the enamel opacities in incisal teeth affected by MIH, the presence of enamel defects of other origin than incisor-molar hypomineralization on incisor teeth. Of maxillary teeth 61 were central incisors and 27 lateral incisors, whereas of mandibular teeth 21 were central incisors, 6 lateral incisors, which were 53.05 vs. 23.47% and 18.26 vs. 5.22% of all teeth included into the study, respectively (tab. 1). Colour, the extend of the lesion, and hypersensitivity when drying with air spray were analyzed (tab. 2). The extend of the demarcation opacities of labial surface was assessed according to criteria < 1\3, at least 1/3 < 2/3, at least 2/3 which is in line with the classification of the extent of MIH lesions proposed by Ghanim et al. (21).