Treatment of white spot lesions with ACP paste and microabrasion

Current literature suggests that the appearance of white spot lesions (WSLs) can be improved by treatment with casein phosphopeptide amorphous calcium phosphate (CPP-ACP). Enamel demineralization is an unfortunate but common sequela to orthodontic treatment with fixed appliances. The increased number of plaque retention sites created by orthodontic appliances makes optimal oral hygiene a challenge, resulting in elevated Streptococcus mutans levels1 and a lower resting pH2 of dental plaque. WSLs are early smooth surface carious lesions that occur when the acidic environment results in subsurface demineralization of enamel. Beneath an intact hypermineralized surface, the lower mineral content of the body of the lesion produces an altered refractive index relative to sound enamel, resulting in the clinical appearance of an unesthetic white spot.3 Despite a great amount of discussion within the literature4 on their prevention, and with recent studies reporting incidence rates ranging from 36%–46%,5,6 WSLs are indeed a continuing problem in the practice of orthodontics.

Conservative treatment options for WSLs aim to bypass the superficial layer and remineralize the subsurface zone of the lesion. This is accomplished in two distinct ways: with the application of low levels of fluoride and calcium ions, which can penetrate deep into the WSL,7 or by reactivating the superficial enamel substrate via mechanical and chemical abrasion.8 One heavily researched method of delivery of low-concentration calcium and fluoride ions for the remineralization of early caries is the milk derivative casein phosphopeptide amorphous calcium phosphate (CPP-ACP). The CPP-ACP complexes act as a calcium and phosphate reservoir helping to maintain a state of super saturation of these minerals, which can enhance enamel remineralization.9 Presently, CPP-ACP complexes are available in a variety of gels, creams, and mousses and may also be incorporated into chewing gums. Microabrasion, the application of an acidic and abrasive compound to the surface of enamel, has been previously presented as a successful means to reduce or eliminate WSLs.10 The microabrasion process abrades the surface enamel while also polishing it, causing it to reflect light differently than natural enamel. Esthetics are improved as a portion of the whitened enamel is removed and a portion is camouflaged by the highly polished surface.11 Ardu et al.8 recently described a technique in which microabrasion was combined with the application of an CPP-ACP cream. They suggested that microabrasion to remove the hypermineralized superficial layer of enamel, followed by daily home application of CPP-ACP, could eliminate WSLs without involving invasive restorative procedures. However, beyond clinical case reports, a quantitative assessment of the effectiveness of this combined technique has yet to be published.

In this study, quantitative light-induced fluorescence (QLF) is used to assess the remineralization of artificially-induced WSLs in bovine enamel. QLF is a commonly used and validated instrument for the assessment of mineral content of smooth surface lesions,12 which allows for the quantitative analysis of mineral loss or gain from an enamel lesion. The aim of this in vitro study was to examine the effects of application of CPP-ACP paste and microabrasion treatment on the remineralization of WSLs using QLF analysis. The null hypothesis tested is that there will be no difference in WSL regression between treatment groups with or without application of CPP-ACP paste.

Sixteen freshly extracted bovine incisors, without cracks or erosions, were cleaned and stored in physiological saline. Each tooth was cut into four sections, and sections from the same tooth were randomly placed into distinct treatment groups to reduce the variability between teeth. The sections were then painted with an acid-resistant nail varnish exposing a window of 2 × 2 mm on the center of the labial surface. The varnish was allowed to dry, and then the 64 sections of teeth were soaked for 2 weeks at room temperature in demineralizing solution (Table 1) to create a WSL. To produce a remineralized surface zone to simulate the anatomy of the WSLs induced by orthodontic treatment, the teeth were then placed in remineralizing solution (Table 2) for 1 week.

At the end of this week, the relative fluorescence loss was recorded as ΔF_initial and used as the baseline value for the starting mineral content of the WSLs pretreatment (T1). The light-induced fluorescent images were captured using an intraoral fluorescence camera (Inspektor Research Systems BV, Amsterdam, the Netherlands) on a personal computer using image-capturing software (Inspektor Pro version 2.0.0.38).

The four treatment groups were assigned as follows:

Samples were rubbed with a cotton swab (Q-tip) and deionized water twice a day.

Samples were rubbed with 1∶1 diluted MI Paste (Tooth Mousse RECALDENT [CPP-ACP], GC America Inc, Tokyo, Japan, 070118M) and deionized water for 20 seconds twice daily. The samples were not rinsed before returning to the remineralization solution.

Once at the start of the 2-week treatment period, a 2-minute 35% phosphoric acid etch was applied with Gel-Etch Semi Gel (Temrex Corp, Freeport, NY) and rinse, followed by a 20-second pumice with Topex Prep & Polish Paste (Sultan Dental Products Inc, Englewood, NJ) with a rubber cup, attached to a slow-speed handpiece, in a clockwise direction followed by a rinse. Samples were then rubbed for 20 seconds with deionized water twice a day for the 2-week treatment period.

The same microabrasion application was applied at the start of the 2-week period, followed by twice-daily application of 1∶1 diluted MI Paste and deionized water for 20 seconds. Again, samples were not rinsed before returning to the remineralization solution.

All samples were stored in remineralization solution (Table 2), which was replenished daily, for the duration of the 2-week period. This 2-week interval was chosen based on the manufacturer's directions for treatment and reevaluation of WSLs (www.mipaste.com). A 1∶1 dilution of the MI Paste was used to simulate the dilution that occurs on paste application to teeth with the at-home application.

QLF values for each sample were measured at the end of 2 weeks (T2) and recorded as ΔF_final. The difference between ΔF_final and ΔF_initial, ΔF, was calculated to quantify the change in fluorescence for each sample. The change in fluorescence for each tooth section was analyzed with a two-within-subject factor analysis of variance (ANOVA) for comparison of treatment outcomes at α  =  .05. The fluorescence values among treatment groups at T1 were analyzed with an ANOVA to determine any differences among the mineral content of the WSLs between groups at the start of treatment.

From the initial 64 tooth sections used in this study, three were rejected owing to a WSL that was too minimal to distinguish from sound enamel (ΔF < 8%). Of the remaining sections, there was no significant difference between the mean ΔF_initial among all four groups.

The control group and paste-only group showed the smallest gain in fluorescence from T1 to T2 at 2.9% and 3.1%, respectively (Figure 1). The difference between these two groups was not statistically significant (P > .05). The microabrasion-only group and the paste and microabrasion group showed the largest gains in fluorescence at 6.8% and 8.2%, respectively, both significantly (P < .05) greater than the paste-only and control groups. This increase in fluorescence reflected a gain in mineral content.

Comparing the effects of microabrasion and CPP-ACP paste, the two-within-subject factor ANOVA indicates that the interaction between CPP-ACP paste and microabrasion was not statistically significant. While microabrasion led to a statistically significant gain in fluorescence (P  =  .0058), application of CPP-ACP did not (P  =  .40).

The results of this study indicate that a microabrasion technique may be a successful treatment for the regression of WSLs. As assessed by QLF, treatment of artificially-induced WSLs in bovine enamel with a microabrasion technique resulted in significant gains in mineral content after a 2-week treatment period. The combination of microabrasion and CPP-ACP for the successful treatment of WSLs has been advocated by the makers of MI Paste13 and others8; however, this appears to be based solely on anecdotal case reports. In this study, the application of CPP-ACP in the form of MI Paste did not convey any additional advantage to the microabrasion technique in the regression of WSLs.

To our knowledge, this is the first study to directly compare the effects of microabrasion and the application of CPP-ACP on WSL remineralization. Microabrasion on its own has been previously presented as a successful minimally invasive procedure to treat WSLs14; however, until now, the studies have been largely descriptive in nature.15 In one of the few quantitative investigations, Murphy et al.10 examined the visible change in WSL surface area following microabrasion of WSLs in eight postorthodontic patients. Using standardized intraoral images and image-processing software, they found that the technique significantly reduced visible enamel lesions with a mean reduction in lesion size of 83%. Though limited to the visible cosmetic improvement of WSLs, these results are in line with those of the present study, in which microabrasion resulted in a significant gain in WSL fluorescence value. It would appear that disturbance of the hypermineralized surface layer of WSLs plays an important role in the process of remineralization. This is also evident in the work of Al-Khateeb et al.,16 who examined the longitudinal effects of acid etching on the remineralization rate of WSLs in extracted premolars using QLF and microradiography. They too found that etching enhanced the remineralization process of WSLs and resulted in a more pronounced reduction of lesion depth compared with nonetched lesions.

In our in vitro study using bovine enamel and artificially induced WSLs, application of CPP-ACP paste alone did not result in any significant gain in mineral content above that of the control group. The remineralization of WSLs with CPP-ACP complexes has been previously studied with conflicting results. Using a pH cycling model of early caries in bovine enamel, Ogata et al.17 reported an insufficient effect of remineralization on enamel subsurface lesions with the use of CPP-ACP alone. As assessed by polarized light photomicrographs and microradiographs, the CPP-ACP–only group was not significantly different from the control with respect to mineral loss; the addition of low levels of fluoride was needed to see lesion regression. In contrast, Wu et al.,18 examining WSLs in bovine enamel with circularly polarized images, found that ACP with or without fluoride reduced WSL size. However, perhaps showing the importance of treatment length, the effect over controls became evident only after 6 weeks. Interestingly, their final results after 12 weeks showed that the application of fluoride toothpaste alone was equally effective as ACP treatment at lesion remineralization. The present study was limited to comparing CPP-ACP in the absence of fluoride with the effects of microabrasion on WSLs. Further studies are required to examine the potential benefits of fluoride, with or without CPP-ACP, on the microabrasion treatment of demineralization. The 2-week interval studied also may have limited the effectiveness of the CPP-ACP treatment; however, the microabrasion technique employed was found to be effective at increasing the mineral content of the WSLs in this time frame.

In one of the first clinical trials of CPP-ACP cream used specifically for treatment of postorthodontic WSLs, Bailey et al.19 reported that use of CPP-ACP cream enhanced the regression of WSLs compared with placebo. However, more recent clinical investigations show less promising results. In a prospective, randomized, and blinded clinical study, Beerens et al.20 compared a fluoride-containing CPP-ACP paste with a control paste in 54 subjects. After a 3-month treatment period, they found no advantage for use of the fluoridated CPP-ACP paste over regular oral hygiene in WSL regression as measured by QLF. Similarly, Bröchner et al21 in a prospective clinical trial using nonfluoridated CPP-ACP paste found WSL regression to be comparable with traditional toothpaste after a 4-week treatment period. The conflicting results of these clinical trials may be related to the method of assessment of WSL regression. The Bailey group used visual inspection to rate WSLs, while similar to the present study, the Beerens and Bröchner groups used a more objective assessment based on QLF computer imaging of teeth.

Clearly, further study is required to delineate the most effective way of treating postorthodontic WSLs, although the present study demonstrates that microabrasion shows promise in treating this common side effect of orthodontic treatment. While in theory, CPP-ACP would seem like an ideal remineralizing agent for early caries, as discussed in a recent review by Zero,22 the clinical benefits of CPP-ACP paste for the treatment of WSLs are not yet substantiated by credible scientific evidence.

• The null hypothesis could not be rejected: the application of a CPP-ACP paste confers no advantage to the regression of WSLs in this study.

• The application of a microabrasion technique results in significant regression of WSLs. The technique was successful regardless of whether it was performed with or without CPP-ACP paste.