White spots, where the cause decides the treatment.

A white spot is enamel that scatters light differently from the enamel beside it, and there are several ways to arrive at that. The most common in orthodontic patients is demineralisation: acid from plaque has drawn mineral out of the enamel beneath an intact surface, leaving it porous. The tooth is not yet cavitated, which is precisely why it is worth treating now. Dental fluorosis is a different thing entirely, formed during enamel development from higher fluoride exposure, and it is usually symmetrical and present on several teeth. Developmental defects, including hypomineralisation, are the third group, formed while the tooth was still being built and often sharply demarcated.

The distinction matters because it changes what will work. A network meta-analysis of minimally invasive treatments for fluorosis found that the ranking of techniques was not the same as for post-orthodontic lesions, and that remineralising agents alone showed limited effectiveness in fluorosis ^[3]. Meanwhile a systematic review of orthodontically induced lesions confirmed 5% sodium fluoride varnish as effective for those, while noting that the evidence for CPP-ACP was thin ^[4]. Treating every white mark as the same condition is how people end up disappointed by a technique that was never indicated for their case.

A white spot looks white because the porous enamel underneath is full of air and water, which bend light very differently from solid enamel. Resin infiltration works on that optical problem rather than on the surface. The enamel surface layer is opened with an acid gel, dried, and a low-viscosity resin is drawn into the pore network by capillary action, then light-cured. Because the resin's refractive index is close to that of sound enamel, the treated area stops scattering light and the mark visually recedes into the tooth around it.

Two things follow from that mechanism, and both are advantages. Nothing is drilled, so no sound tooth structure is removed, and the treatment usually needs no anaesthetic. And because it is additive rather than subtractive, it does not close off later options: if the result is not enough, everything that could have been done before is still available afterwards. That is the same conservative logic that governs the rest of this practice, applied to a cosmetic complaint.

This is where most pages about Icon overstate the case, so it is worth being precise. A meta-analysis of four in vivo studies with six-month follow-up found that all authors reported an immediate improvement in both colour and brightness, and that the colour change remained statistically significant at six months, while the brightness change did not ^[2]. So the masking effect is real and measurable, and colour is the outcome that holds up best.

The most recent and by far the largest review is more cautious, and honesty requires quoting it rather than the friendlier papers. Covering 29 studies, 544 patients and 1,495 teeth, it concluded that resin infiltration shows inconsistent and heterogeneous effects across most outcomes ^[1]. Its largest analysis, of the colour difference between the treated lesion and the adjacent sound enamel, found no significant change between the post-treatment result and six months, which reads as the achieved result holding rather than fading. Patient satisfaction rose immediately after treatment, but that gain was no longer statistically significant by three months ^[1].

The reviewers are explicit about why the picture is muddy: small sample sizes, short follow-up, measurements that were often not blinded, and high heterogeneity between studies ^[1]. The same caution appears in the orthodontic literature, where resin infiltration is described as showing a promising masking effect while most of the underlying studies carry a high risk of bias ^[4]. The fair summary is that this is a genuinely useful technique with a real optical effect, studied mostly in small short trials, and that anyone promising you a permanent guaranteed result is going beyond what the evidence currently supports.

If the marks are fluorosis rather than post-orthodontic demineralisation, the hierarchy of treatments changes. A network meta-analysis of seven controlled studies covering 555 participants ranked the options for aesthetic masking of fluorosis. Microabrasion combined with in-office whitening ranked first and produced the largest colour improvements at immediate, three-month and six-month assessment ^[3]. Resin infiltration was the most effective single technique used on its own, with consistent and clinically meaningful effects, while microabrasion alone and remineralising agents alone were modest or unstable ^[3].

Microabrasion has its own supporting literature. A systematic review of eleven prospective studies found it to be an effective and reliable technique for managing enamel discolouration, particularly in fluorosis, though that review was conducted in paediatric dentistry and the authors called for better-powered randomised studies for other kinds of spot ^[5]. In practice this means fluorosis is often best treated in sequence rather than with one technique, and that the sequence is decided after looking at the teeth rather than before.

The order runs from least to most invasive, and we do not skip rungs without a reason. First, arrest and remineralise: for an active early lesion, fluoride varnish and a change in cleaning can stop it progressing, and 5% sodium fluoride varnish has direct evidence behind it for orthodontically induced lesions ^[4]. Some lesions improve visually on this alone, and no further treatment is needed. Second, resin infiltration where a visible mark remains after the lesion is stable. Third, microabrasion, alone or combined with whitening, particularly in fluorosis ^{[3] [5]}. Only then composite, and only in the minority of cases where enamel has actually been lost rather than merely discoloured.

There are white spots that infiltration will not fully resolve, and saying so in advance is more useful than discovering it afterwards. Deeper fluorotic and developmental lesions extend further into the enamel than the resin reliably penetrates, and the deeper the porosity, the less complete the masking. Very large or sharply demarcated defects may improve without disappearing. In those situations infiltration can still be worth doing as a first step, because it costs no tooth structure and leaves every other option open, but it should be offered as an attempt at improvement rather than as a promise of erasure.