A patient was referred to the Master in Lifelong Training in Aesthetic Restorative Dentistry and Endodontics at Rey Juan Carlos University for aesthetic treatment of her WSLs. She was a 33-year-old woman with no medical conditions recorded in her medical history. She reported that she had been born in Orense and raised in Málaga and Madrid, Spain. Clinical examination revealed generalized WSLs in the incisal third of the maxillary anterior teeth and isolated lesions in the posterior regions. The lesions showed a homogeneous distribution and color pattern (Figure 1). A photographic record was also obtained using a Nikon D7200 camera and an AF-S Micro-Nikkor 105 mm lens. This was supplemented with photographs taken using a polarizing filter (Polar_eyes; Nikon R1C1) and with transillumination, for which the tip of a Mini LED light-curing unit (Acteon Satelec, France) was positioned palatally. These non-invasive adjunctive examinations made it possible to determine the extent and depth of the WSLs.

Most lesions were superficial and well demarcated, with a homogeneous lesion body (type I), according to the transillumination-based classification of Marouane and Manton (2021)²¹.

Because WSLs were present on nearly all the teeth and the information obtained during history-taking did not indicate another cause, a diagnosis of type II AI, hypomaturation subtype IIC (“snow-capped enamel” or “snow-capped teeth”), was made13,14. Because as it is a genetically determined disorder, genetic testing is required to confirm the diagnosis and determine the inheritance pattern; however, the patient did not consider it necessary to undergo this test.

These superficial, well-demarcated lesions are considered to respond better to resin-infiltration treatment than deep lesions with heterogeneous lesion bodies, which may require modifications to the infiltration protocol or more invasive restorative treatments²¹.
A combined treatment was therefore proposed, beginning with tooth bleaching followed by resin infiltration of the WSLs, as this was the most conservative option^15,16.

After basic periodontal treatment had been completed, at-home bleaching was initiated using 16% carbamide peroxide (Pola Night, SDI, Australia), applied overnight in custom-made trays fabricated from thermoplastic sheets. The initial shade, 3M1, was recorded using the VITA Toothguide 3D-MASTER shade guide (VITA Zahnfabrik, Bad Säckingen, Germany). The aim of bleaching was to reduce the contrast between the lesions and the sound enamel. During the final week of treatment, the patient was instructed to apply the bleaching agent every other day because she developed mild tooth sensitivity. After 4 weeks of application, a final shade of 1M1 was obtained(VITA Toothguide 3D-MASTER shade guide), and bleaching was discontinued because the aesthetic objective was considered to have been achieved (Figure 2).

Despite the marked tooth-whitening effect, the WSLs were not completely masked (Figure 3); resin infiltration was therefore performed. Before resin infiltration, photographs were taken using a polarizing filter and transillumination to confirm the extent and homogeneity of the lesions (Figure 4).

The Icon Vestibular resin infiltration kit (DMG, Hamburg, Germany) was used in accordance with the manufacturer’s instructions, with slight modifications to the protocol. Absolute isolation was achieved from teeth 15 to 25 using a Nic Tone rubber dam (MDC Dental, Mexico) and No. 00 clamps (Figure 5).

The WSLs were etched with Icon Etch, a 15% hydrochloric acid, for 2 minutes (Figures 6 and 7). The treated surfaces were then rinsed with water spray and dried. A 99% ethanol solution (Icon Dry) was then applied. Three seconds after its application, transillumination was used to determine whether the lesions disappeared, in what is known as the ethanol test^19,21.

As the lesions did not disappear, the etching procedure was repeated four times. The number of applications was therefore increased beyond that recommended by the manufacturer in order to achieve deeper etching of the lesions and improve the degree of infiltration22-24. The hydrochloric acid was also applied actively to eliminate CO₂ bubbles, improve lesion conditioning²⁴ and achieve deeper removal of the superficial hypermineralized layer.
Icon Dry was then applied for 30 seconds (Figure 8), followed by drying with moisture-free air for 30 seconds. The principal function of ethanol is to dehydrate the microporosities of the WSLs and facilitate resin infiltration. It is recommended that the process be repeated at least once to remove as much water as possible. However, as noted above, it may also help predict whether the lesion can be masked by infiltration: if the lesion disappears within the first 3 seconds after being moistened with ethanol^20,21,23,24.

The low-viscosity infiltrating resin, Icon Infiltrant, was then applied to the white spot lesions and left in place for 3 minutes, after which it was light-cured for 40 seconds using a Mini LED light-curing unit (Acteon Satelec) (Figures 9 and 10). The procedure was repeated, allowing the infiltrant to remain in place for 1 minute, after which it was light-cured again for a further 40 seconds²⁵.

Once infiltration had been completed, the interproximal excess was carefully removed using dental floss and a No. 12 scalpel blade (Swann-Morton) (Figure 11), and the isolation was removed. The facial surfaces were polished using fine- and superfine-grit Sof-Lex discs (3M ESPE, USA), DIACOMP PLUS TWIST polishers (EVE, Germany), and Enamelize aluminum oxide polishing paste (Cosmedent,USA). At a follow-up appointment 7 days later, the lesions on teeth 23, 24 and 25 had not completely disappeared (Figure 12). A further application of Icon Vestibular was therefore performed on these teeth after roughening the lesion surfaces with a medium-grit Sof-Lex disc. The entire procedure described above was repeated, with favorable aesthetic results (Figure 13).

After 4 months, the results were reviewed (Figures 14 and 15), and polarized-light and transillumination photographs were taken again (Figure 16)

AI is a genetically determined disorder of enamel formation that, in its mild forms, may present solely as WSLs. The treatment of aesthetic alterations represents a challenge for the clinician, and the treatment approach is selected according to lesion severity, the patient’s age and the patient’s aesthetic expectations^12,15,16. This case demonstrates the good aesthetic results achieved by combining tooth bleaching with low-viscosity resin infiltration (Figures 17 and 18). These microinvasive procedures should therefore be considered before conventional procedures when treating these clinical presentations of AI.
Tooth bleaching is a non-invasive procedure that, in this case, partially masked the WSLs by reducing the differences between sound and affected enamel and improved the substrate for subsequent resin infiltration¹⁶. Therefore, even when tooth bleaching does not achieve the desired result, it may improve the final outcome when combined with other procedures, as it removes other types of stains, such as the brown stains present in this case, which is necessary before the infiltration procedure²⁶.
With regard to resin infiltration, the greatest challenge is adequately conditioning the hypermineralized surface enamel layer, because if this layer remains, the resin cannot infiltrate or mask the subsurface lesion. The use of 15% hydrochloric acid has been shown to be the best option for conditioning the surface enamel layer, removing approximately 34 μm of tooth structure with each application performed according to the manufacturer’s recommended protocol. In this case, the conditioning protocol was modified because, when the ethanol test and transillumination were performed during the first 3 seconds after application of Icon Dry, some lesions showed a negative ethanol-test pattern. It was therefore necessary to repeat the Icon Etch application procedure, as indicated by Marouane and Manton²¹. Arnold et al. (2015)²² had previously found that repeating the conditioning procedure increases the etching depth. Other authors have reported that the number of hydrochloric acid applications may be increased, provided that no more than seven applications are performed^22-25. Although the number of applications recommended by the manufacturer was exceeded, resin infiltration would still be more conservative than microabrasion, which may remove up to 360 μm of enamel²², or the use of a bur.

The low-viscosity TEGDMA resin fills the microporosities of the lesion by capillary action, preventing them from being occupied by oral fluids or air. Its ability to penetrate the lesion is determined by the previous conditioning of the enamel and the resin infiltration time. Although a 3-minute application is recommended, the infiltration time may be extended to up to 15 minutes to achieve a greater degree of infiltration^25,27,28. However, in our case, the application time was not extended because the ethonol test was positive, which led us to expect a good response to infiltration²¹.

The advantages of this resin infiltration procedure are that it is microinvasive, preserves tooth structure, is safe and rapid, provides good aesthetic results in a single visit, and is highly acceptable to patients^29-32. One disadvantage is that it does not achieve complete masking in deep lesions and that, despite producing a good aesthetic result, its application does not remineralize the lesion but only masks it^28,33.
Finally, although the color stability of infiltrated WSLs has been questioned, published clinical studies agree that the aesthetic results are maintained³⁴, even 6 years after infiltration³⁵.

Resin infiltration, preceded by tooth bleaching, is an effective and conservative alternative for treating WSLs caused by a mild form of AI. This therapeutic combination not only provides satisfactory aesthetic results but also preserves tooth structure. The use of ethanol and simultaneous observation of its effect using transillumination are valuable diagnostic tools that can predict the success of resin infiltration, thereby optimizing the clinical management of these lesions.