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INTRODUCTION
Orthodontic corrections are mostly achieved with fixed orthodontic appliances. One of the negative side-effects is the formation of white spot lesions (WSL) and incipient caries1,2. Prevention of white-spot lesions (WSL) during fixed appliances orthodontic treatment is still a challenge in today’s orthodontic treatment: There is evidence that neglecting oral hygiene during orthodontic treatment with fixed appliances can cause WSL formation within weeks3,4. Orthodontic patients develop significantly more WSL than non-orthodontically treated persons, mainly because oral hygiene is more difficult in patients with multi-bracket orthodontics than without fixed treatment. Not treating WSL has been shown to result in lesion progression to carious lesions, and moreover presents esthetic problems3. WSL formation has been described as a rapid process of few weeks duration, with a sharp increase in WSL numbers within the first six months4-6. The incidence of WSL in individuals treated with fixed appliances has been reported to be 72.9% of patients, of which 2.3% of lesions were cavitated7. Even inactive lesions which do not show a tendency to progress may constitute an esthetic problem in anterior teeth, and one that is often noticed by patients not during treatment, but following appliance removal. While in the case of cavitated lesions restoration is essential, non-cavitated lesions should receive preventive therapy aimed at arresting and remineralizing the lesion8. As a new way of inhibiting further demineralization and improving their appearance, lesion infiltration with low-viscosity light-curing resins (infiltrants) has been recently proposed9. A reduced visibility of infiltrated WS-lesions is an additional positive side-effect, which is due to the similar refractive index of the infiltrated and sound enamel areas. Other enamel alterations such as further enamel anomalies such as molar-incisor-hypomineralisation (MIH), or fluorotic enamel also require esthetic improvement10-13. It has been reported that beyond the aspect of treating post-orthodontic WSL, resin infiltration might be suitable for treating those enamel anomalies (Figure 1).
METHOD
Search strategy
A non-systematic review of the literature using the PubMed database and robust truncations was performed on Feb 16, 2016 with no restrictions, to characterise inhibition of lesion progression, and the esthetic effects induced by resin infiltration of decalcified enamel, enamel fluorosis, and molar-incisor hypomineralisation (MIH). The search terms used in the PubMed database were
RESULTS
PubMed database search yielded 21 results. Hand-search of references of retrieved articles yielded another 13 articles. Five articles were not considered as they were not related to the topic of esthetic improvement of WSL, MIH or fluorosis affected enamel appearance by resin infiltration. Table 1 gives an overview of the articles retrieved by Pubmed, and by additional hand search of references.
DISCUSSION
Post-orthodontic WSL in vitro
The positive effects of masking vestibular white spots as well as the color stability of infiltrated lesions have been quantified in vitro by several research teams9,14-18. Additionally, a current cost-effectiveness analysis indicates that non-invasive treatment of early WSL by infiltrating instead of or postponing restorative treatment can have an impact on improving oral health care as it lengthens the life-cycle of a tooth19. The surfaces of infiltrated lesions are described as protected enamel surfaces following appropriate polishing, in vitro20,21. These finding is underlined by the description of an increase of mechanical strength after resin infiltration by other authors22-24.
Infiltrated lesions seem to be protected against new acid induced demineralization, and based on different in vitro experiments, a combination of resin infiltration and several adhesive systems seems to be viable, thereby allowing for a proceeding with fixed orthodontic treatment following an infiltration intervention22,25,26. Even more, there seems to be an enhanced performance of adhesives compared to untreated demineralized enamel: Some research groups quantified the bond strength of orthodontic brackets to infiltrated enamel16,27-30) and found that a mechanical inforcement of infiltrated surfaces seems to reduce enamel cracks or surface damages after debonding, in vitro29. As for the masking effect, de Lacerda et al. found that the Icon infiltrant produced a greater lightness reduction of artificial white-spot lesions in vitro, when compared to other sealants. Ou et al. reported that an excellent masking effect, too, with a high color stability, and no differences in terms of the masking effect with treatment of high or low demineralized enamel. Yim et al. evaluated removed surface layers and infiltrated areas of human enamel surface thicknesses in vitro, using confocal laser scanning microscopy, and found that application of 37% H3PO4 with a brush for 30 seconds increased the pore volume of WSL surface layers and the percentage of infiltrated areas in comparison to the use of 15% HCl for 120 seconds. Cohen-Carneiro et al. used bovine enamel specimens to test the discoloration potential of different agents (saliva, coffee, and wine) of infiltrated and non-infiltrated WSL. They used very long immersion intervals and found that infiltrated WSL had a higher staining potential than non-infiltrated WSL, in vitro. In contrast, Paris found also in vitro that resin infiltration is suitable to mask artificial WSL, and that polished infiltrated lesions are resistant to staining in vitro.9
Yuan et al. compared the esthetic improvements of white-spot lesions (WSLs) treated by fluoride, casein phosphopeptide amorphous calcium phosphate (CPP-ACP), or resin infiltration in vitro, and found that resin infiltration was more effective than NaF or CPP-ACP in masking WSLs. Paris and Meyer-Lueckel described the potential of the infiltration technique in dental practice31 as an intervention that bridges non-invasive and restorative treatment options, by arresting and masking non-cavitated proximal caries lesions.
Adverse effects on WSL or sound enamel
Up until now, no adverse effects are reported for the use of WSL infiltration. The technique has been used in clinical application with excellent results inmicro-invasive treatment of early approximal / vestibular caries). During infiltration treatment, the sound enamel adjacent to the WSL is likewise treated; i.e., both areas, sound enamel and WSL, are etched with HCl gel and treated with the infiltrant. However, according to a recent RCT32 no adverse effects were seen following etching of sound enamel along with WSL infiltration. This is supported by a previous in-vitro research: Meyer-Lueckel et al. found no significant differences in erosion depths following etching between lesions and sound enamel33. Etching and subsequent infiltration of sound enamel does not alter its structure too much, and the etching removes more of the porous WSL enamel than of the sound enamel.
Post-orthodontic WSL in vivo
Several studies have been dedicated to the masking effects of post-orthodontic WSL by infiltration9,34,35. The effect of lesion progression as seen in approximal lesions was confirmed for labial lesions, also34,36. Furthermore, case reports and short-term studies9,32,34,35,37-45 describe a masking of WSL, up until 1 year following infiltration32,37,46.
Hammad et al. distinguished between infiltration of visible WSLs without surface disruption and WSLs with a roughened surface not requiring restoration, and reported significant improvement in both groups following infiltration. Likewise, Shivanna and Shivakumar, as well as Kugel et al. presented a case reports along with reviews on the subject of the infiltration technique, and characterised it as a significant addition to clinician’s caries.
Using an RCT design, Senestrao et al. noted a marked improvement of decalcified enamel following infiltration in comparison to control teeth, with color stable results eight weeks after treatment. Another recent long-term RCT32 assessed the assimilation of infiltrated WSL with surrounding sound enamel. Similar to Senestrao et al., these authors found an assimilation of WSL color to surrounding enamel following infiltration that was color stable, without significant changes over six months. The extent of assimilation was influenced by extent and depth of lesions, and lesion surfaces: the more superficial and ‚younger’ the lesion, the better the masking effect. The longer the time elapse between debonding and infiltration, the more etching intervals are needed to achieve camouflage effects, which are also less satisfying. In a follow-up study, the same authors assessed the stability of the results, again: Esthetic results remained stable of at least twelve months of observation. Further studies are required to assess the potential limits of the durability of infiltration. Adverse effects in terms of gingiva irritation or pain were assessed but not seen by this trial.
MIH-, fluorosis affected teeth
Infiltration of carious lesion has been characterised as a strategy to strengthen damaged enamel structures, and to reduce caries progression without surgical intervention31,47-50. Beyond the aspect of WSL and early caries treatment, several other investigators also described an esthetical improvement and mechanical stabilization of fluorotic teeth, traumatic white spots or teeth suffering from molar incisior hypomineralisation (MIH) by infiltration, which increases its use as a therapeutic alternative for esthetic purposes in different types of porous lesions51-56 . E.g., Kim et al.41 described the effects of infiltration on teeth with developmental enamel defect and post-orthodontic WSL. They found that 25% of developmental enamel defect were completely masked, whereas 35% and 40% were partially masked and unchanged, respectively. 61% of WSL teeth were completely masked, 33% partially masked, and 6% unchanged. Munoz et al. (2013) described in a case report the promising results and of the infiltration technique for a micro-invasive type of treatment in cases of mild-to-moderate fluorosis and hypoplasia stains. Likewise, Tirlet et al. report cases of fluorosis and traumatic hypo-mineralization lesions successfully treated by infiltration, thereby suggesting to extend the indication of the technique to those enamel alterations. In this sense, also Attal et al. provided a protocol to treat MIH affected enamel, deep lesions of traumatic origin, or those associated with fluorosis succesfully using the infiltration technique51. This was confirmed by Auschill et al. (2014) who used the infiltration technique on cases of white opaque and brown discolourations by dental fluorosis of moderate extent, following experiencing unsatisfying results of bleaching to improve the aesthetic appearance of the affected teeth. The treatment results achieved by resin infiltration were satisfying in contrast, and remained stable in terms of a camouflage when assessed six months after treatment, the remain masked.
CONCLUSIONS
• WSL infiltration is a micro-invasive treatment option to treat decacified enamel and to inhibit further demineralization.
• Both RCTs, case reports and in vitro research indicate a reduction of visibility of infiltrated WSL, which is due to the similar refractive index of the infiltrant and sound enamel areas.
• The durability of the camouflage effect following infiltration has been shown to last for at least six months on the evidence level of RCTs, and at least one year according to a follow-up study of cases included in an RCT.
• Duration and depth of WSL are co-factors that affect the extent of improvement of the esthetic appearance of demineralised teeth by infiltration.
