Enamel microabrasion: An overview of clinical and scientific considerations

Abstract

Superficial stains and irregularities of the enamel are generally what prompt patients to seek dental intervention to improve their smile. These stains or defects may be due to hypoplasia, amelogenesis imperfecta, mineralized white spots, or fluorosis, for which enamel microabrasion is primarily indicated. Enamel microabrasion involves the use of acidic and abrasive agents, such as with 37% phosphoric acid and pumice or 6% hydrochloric acid and silica, applied to the altered enamel surface with mechanical pressure from a rubber cup coupled to a rotatory mandrel of a low-rotation micromotor. If necessary, this treatment can be safely combined with bleaching for better esthetic results. Recent studies show that microabrasion is a conservative treatment when the enamel wear is minimal and clinically imperceptible. The most important factor contributing to the success of enamel microabrasion is the depth of the defect, as deeper, opaque stains, such as those resulting from hypoplasia, cannot be resolved with microabrasion, and require a restorative approach. Surface enamel alterations that result from microabrasion, such as roughness and microhardness, are easily restored by saliva. Clinical studies support the efficacy and longevity of this safe and minimally invasive treatment. The present article presents the clinical and scientific aspects concerning the microabrasion technique, and discusses the indications for and effects of the treatment, including recent works describing microscopic and clinical evaluations.

Key Words: Dental bleaching, Enamel microabrasion, Enamel surface, Esthetic treatment, Fluorosis, Hypoplasia

Core tip: Enamel microabrasion is indicated for the removal of superficial stains and irregularities of the enamel, mainly located in esthetic areas. The technique involves the mechanical rubbing of acidic and abrasive agents on the altered surface. Recent studies show that the technique is a conservative treatment when the enamel wear is minimal and clinically imperceptible, and is effective and long lasting. The present literature review aims to discuss indications and clinical and scientific aspects of the microabrasion technique, as well as its effects on the enamel surface.

INTRODUCTION

Several treatments have been introduced to the dental market for the restoration of dental appearance to a level that satisfies what patients seek regarding dental esthetics. These techniques are still being evaluated in order to ensure an efficient treatment with minimal chair time and low cost that is safe for professionals and patients. For superficial enamel stains or defects, enamel microabrasion is preferred, as it is considered an esthetic and conservative treatment[1-3]. Since its introduction by Croll et al[4] in 1986, there have been numerous reports describing various approaches[5-8], related products, and clinical successes[9-12].

The main indication for enamel microabrasion is intrinsic discoloration or texture alteration due to enamel hypoplasia, amelogenesis imperfecta, or fluorosis[13]. The technique removes the porous surface enamel layer, as well as the entrapped stains, by rubbing a gel that contains an acid and an abrasive compound in a similar way that a dental prophylaxis with pumice and water is performed. The enamel stain or defect is removed by a combination of the erosive and abrasive effects of the recommended mixture containing low acid concentrations and an abrasive agent, applied mechanically using a low-rotation micromotor[13-15]. It should be the first option for the management of teeth with intrinsic stains because it removes opaque, brown stains and smoothens surface irregularities by providing a more regular and lustrous surface[13,16]. As the technique is considered safe and minimally invasive, it can also be combined with tooth bleaching when necessary[1,9,10,13].

The success of enamel microabrasion is directly related to the correct indication of the clinical case and the proper execution of the technique. This review discusses aspects of microabrasion, such as its evolution, indications, advantages, clinical steps, and effects on the enamel structure, in order to address some concerns regarding newer trends presented in the latest research and clinical reports.

EVOLUTION OF THE TECHNIQUE

Enamel microabrasion was initially performed for the removal of fluorotic white spots using 36% hydrochloric acid, as recommended by Kane in 1926[14,17,18]. A heated metallic instrument was used to apply the acid to the altered enamel to increase its penetration[14,18] and hasten the chemical reaction between the acid and the enamel[3]. Concerned about the safety of the technique, Raper et al[19] suggested the use of 18% hydrochloric acid applied and rubbed with a wooden spatula wrapped with cotton for a maximum time of 10 min[19]. The authors drew attention to the thickness of the enamel, particularly at the cervical third of the tooth, which is thinner compared to the medium and incisal third. They also recommended the use of sodium bicarbonate to neutralize the effects of the hydrochloric acid.

Mechanical application with a low-rotation micromotor was first indicated in the 1970s, using a mixture of 18% hydrochloric acid, hydrogen peroxide and ether[20]. Combination with an abrasive agent was later indicated by Murrin et al[21] in 1982, who added pumice to 36% hydrochloric acid, resulting in a slurry that was applied using a rubber cup coupled to a micromotor[21]. Concerned about the acid concentration, Croll et al[4] recommended the use of the same mixture but with 18% hydrochloric acid. Croll later stated that an ideal microabrasive system should include a low acid concentration and abrasive particles in a water-soluble mixture that are applied with a low-rotation handpiece to avoid scattering the compounds, thus making the procedure safer[14]. The author again proposed the use of an extra-fine diamond bur prior to the use of the microabrasive agents to reduce the clinical time needed to perform the procedure[22].

The association of hydrochloric acid to abrasive particles resulted in the development of commercially available products. Prema Compound (Premier Dental Company, Philadelphia, PA, United States), which contains 10% hydrochloric acid, was the first to be introduced to the market. Currently, a lower concentration of hydrochloric acid is used, approximately 6.6%, under the commercial product name of Opalustre (Ultradent Products Inc., South Jordan, UT, United States). Both products use silicon carbide as an abrasive with different granulations (Table 1) dispersed in a water-soluble gel for easy removal[13]. The use of 35% phosphoric acid instead of hydrochloric acid was proposed by Kamp in 1989, and was considered advantageous as it is commonly used in clinical practice for other procedures[3,23].

Table 1 Commercial products used for microabrasion.

Material	Manufacturer	Acid	Abrasive	Particle size (mm)
Prema compound	Premier Dental Company (Philadelphia, PA, United States)	10% hydrochloric acid	Silicon carbide/dioxide	30-60
Opalustre	Ultradent Products (South Jordan, UT, United States)	6.6% hydrochloric acid	Silicon carbide	20-160
Pumice	Pumex (Newcastle-under-lyme, Staffordshire, United Kingdom)	-	Pumice	30-50

INDICATIONS FOR ENAMEL MICROABRASION

The proper indications for enamel microabrasion are summarized in Table 2. Dental fluorosis is the most common indication[16], which results from demineralization of enamel caused by excessive fluoride intake. Fluorosis produces opaque white areas or yellow to dark brown discolorations with porosities on the enamel surface, depending on severity[24,25]. Fluoride-induced enamel changes range from thin, white, opaque lines corresponding to perikymata running across the tooth surface, to an entirely chalky white surface[24]. They are characterized by the presence of bilateral, diffuse, and horizontal striations[25] observed on all teeth that mineralize at the same time (Figure 1A). Enamel microabrasion usually improves esthetic appearance in cases of mild and moderate fluorosis (Thylstrup-Fejerskov Index 1-7)[16,26,27], and should always be considered the first option in the management of these cases[13,16]. Even in situations with yellow or brown discolorations, enamel microabrasion can improve the esthetic appearance of the teeth[28]. As these stains are formed by the discoloration of demineralized surfaces and from external sources, the depth of the stain is likely associated with the penetration of the staining agents[16].

Figure 1 Indications for enamel microabrasion. Tooth staining from A: Fluorosis; B: Mineralized white spots.

Table 2 Summary of indications and advantages of the microabrasion technique.

Indications	Requirements	Advantages
Stains or defects restricted only to enamel	Shallow alterations just in the enamel surface	Safe and conservative treatment
Dental fluorosis	Use of rubber dam	Minimal loss of enamel
Mineralized white stains	After completion of orthodontic treatment, if necessary	Leaves enamel surface lustrous, shiny and glass-like
Correction of surface irregularities	Supplemented with bleaching, if necessary	Roughness and microhardness alterations easily resolved by saliva
Localized enamel hypoplasia		Reduced bacterial colonization on enamel surface
Polishing of enamel and auxiliary removal of composite resin residues after orthodontic therapy		Lasting and stable esthetic results

Microabrasion treatment may be indicated for correction of surface irregularities on dental enamel, which may be caused by imperfect enamel formation or acquired after the removal of orthodontic appliances[13], such as the removal of residual resin composite from brackets with diamond burs, and resulting in a smooth and polished enamel surface[29]. Microabrasion is also indicated for opaque, white areas or discolorations, even with porosities, from the demineralization/remineralization process common in the enamel region adjacent to orthodontic bands or brackets (Figure 1B), or from disturbances in the mineralization process, such as hypocalcification[7,13,30]. The white spots caused by orthodontics should first be treated with mineralizing agents, such as sodium fluoride[12,31], or with an infiltration technique[29]. Infiltration of the enamel by resin was recently developed as a way to obstruct the diffusion pathways for acids and dissolved minerals[32]. The resins used have low viscosity, high surface tension, and low contact angle with the enamel, as well as a refraction index similar to enamel[33]. The infiltration technique may also be used in cases of mineralized lesions[29,34]. The technique requires pre-conditioning of the surface with 15% hydrochloric acid, which removes approximately 40 μm of enamel surface, to ensure resin penetration[32]. In this way, the thickness of the enamel removed for resin infiltration is similar to microabrasion. However, there are no clinical trials evaluating the staining, abrasion wear or bacterial colonization of resin-infiltrated surfaces.

Microabrasion may be utilized in cases of localized or idiopathic enamel hypoplasia that is limited to the outer enamel layer[15,35]. Although this condition can sometimes require a restorative approach with composite resin or laminate veneer[36] (Figure 2), microabrasion should be considered as the first treatment option[16,36]. In addition to improving esthetics, it may reduce the need for enamel wear for a restorative approach, which is mainly important in young patients[36]. Otherwise, the infiltration technique may be used in cases with deeper stains not resolved by microabrasion, and may be an alternative for the invasive restorative approach[37,38]. Even if all whitish parts of a lesion do not completely disappear, the infiltration technique usually leads to considerable improvement in appearance[37] and masks the enamel stain[34,38].

Figure 2 Deep enamel staining due to hypoplasia. A: Hypoplasia; B: Ineffective microabrasion treatment of the right central incisor.

Enamel microabrasion is not indicated if the patient presents deficient lip sealing, as the teeth are always exposed to air and dehydrate more easily, thus a moistened film is not formed under the enamel. With this condition, the stained appearance of the tooth is more evident, and it may characterize the failure of the microabrasion. Therefore, these patients are encouraged to first seek orthodontic treatment and/or speech therapy[1,13].

The most important factors contributing the success of enamel microabrasion are the location and depth of the enamel stain or defect[8,13,16]. The alteration must be restricted to enamel tissue, without involvement of the dentin[13]. Deeper, opaque stains, such as those resulting from hypoplasia, cannot be resolved with microabrasion, and require a restorative approach[36]. An LED/light curing unit positioned in the palatine or lingual face of the tooth can help the clinician to examine the enamel stain (Figure 3). This can be used to estimate the lesion depth, as a darker color indicates deeper staining[9]. It is also important to perform the diagnosis in wet conditions, as the difference in the refractive index between air and enamel is greater than between water and enamel[12]. Commonly, white spots are more obvious on dry teeth, thus a lesion visible on a wet tooth can be considered deeper than a lesion visible only on dry enamel.

Figure 3 Transillumination to determine staining depth. A: Enamel hypoplasia in both central incisors; B, C: Transillumination to evaluate the staining.

TECHNIQUE

An ideal microabrasion technique should produce insignificant enamel loss, no damage to pulp or periodontal tissues, and satisfactory and permanent results in a short clinical time without discomfort to the patient[4]. The use of a rubber cup coupled to the rotatory mandrel enables precise application of the compound on the enamel surface, which eliminates splattering of the compound and makes the procedure safer, easier, and quicker[13]. For the safety of the patient, a rubber dam should be in place[39], though this may be difficult when the teeth are not completely erupted[13]. It is also important that the patient, clinician, and assistants all wear eye protection during the procedure[1].

The number of applications can vary according to the severity of the enamel staining[1,9,10,12]. To reduce the clinical time, the enamel can first be “regularized” with a tapered fine-diamond bur to lightly abrade the affected area, referred to as enamel macroreduction[1,9,13,30]. With this procedure, the application of microabrasive slurry can be reduced to two or three applications to remove the remaining stains and to smooth the enamel surface ground with the diamond bur[1]. Afterwards, polishing of the microabraded surface with felt discs and polishing[26] or fluoridated[1,9,10,40] pastes is recommended. Application of sodium fluoride gel[1,9,26] is also recommended to promote the remineralization process.

Because enamel microabrasion is a noninvasive technique, it can be supplemented with bleaching procedures[1,9,13,15,41]. Often, this is necessary as microabraded teeth can acquire a darker or yellowish coloration after treatment, and the remaining enamel is thinner and more clearly reveals the dentin. Bleaching is also indicated to reduce the contrast between the remaining white-spotted lesions and the tooth surface[26,42,43]. In either situation, a low concentration of carbamide peroxide is recommended using the home-bleaching technique[1,9,10,13].

CLINICAL AND SCIENTIFIC CONSIDERATIONS

Effects of the technique

Enamel microabrasion has been shown as an effective and conservative treatment[1,9,13,15,43]. According to reports by Sundfeld et al[13,43,44], 5 to 10 applications of microabrasive systems (35% phosphoric acid with pumice, Opalustre) can result in the loss of 25 to 200 μm of enamel, which is acceptable for clinical conditions (Figure 4). A recent study showed that 120 s of microabrasive treatment reduces approximately 10% of the enamel thickness[5], suggesting it is a safe and conservative procedure. According to Dalzell et al[45], the pressure used during the microabrasion procedure is crucial for total enamel removal, such that the higher the pressure, the greater the quantity of enamel removed. In addition, enamel wear from the microabrasion technique is time-dependent[46].

Figure 4 Depth of enamel removal. Polarized light microscopy showing the ground tooth section after enamel microabrasion with Opalustre (reprinted with permission from Sundfeld et al[44]).

In addition to the removal of discolored enamel, the microabrasion technique changes the optical characteristics of the enamel surface, called the “abrasion effect”[47,48]. The simultaneous abrasion and acid erosion of enamel prisms may compact mineralized tissue within the organic area, replacing the outer layer of prism-rich enamel with a densely compacted, prism-free region[48]. Microabrasion presents a lustrous, shiny, and glass-like surface of the enamel, which may reflect and refract light differently[13,41]. These optical properties may be able to camouflage any remaining subsurface enamel stains[48]. Tooth hydration by saliva augments these favorable optical properties[47,48]. Schimdlin et al[2] found that the luminescence and fluorescence of enamel after microabrasion of demineralized lesions was decreased in comparison with the untreated demineralized enamel.

Several studies have examined the effects of micro-abrasion on the remaining enamel surface[2,5-8,46,49-51]. The potential erosive and abrasive effects depend on several parameters, including the type, concentration and pH of the acid used, the abrasive medium, time of instrumentation, application mode, force applied, and revolutions per minute[8,50]. The microabrasion technique increases the roughness of the enamel surface, regardless of whether 18% or 35% phosphoric acid or 6.6% hydrochloric acid with abrasive was used[5,7,44,51]. Similarly, enamel microabrasion is also related to reduced enamel microhardness[6,49]. However, both effects can be reversed by the polishing procedure or saliva exposure[5,6,49,51]. Rodrigues et al[5] found that unlike that seen with microabrasion, the enamel surface maintained the same roughness through all the evaluated stages when mechanically treated with a silicon polisher; the authors suggested that the chemical features of enamel microabrasion are responsible for the roughness effects. Despite their concentration differences, phosphoric acid and hydrochloric acid have similar erosive effects[5,6,49], such as alterations in the enamel micromorphology with exposition of the interprismatic spaces, similar to the enamel conditioning patterns[7,46]. Although the microabrasive system causes change in the enamel surface, which can be observed by scanning electron microscopy, confocal imaging demonstrates that the subsurface is not altered (Figure 5). The smoother, dense, mineralized enamel layer created by microabrasive systems is also less favorable for bacterial colonization, particularly by Streptococcus mutans[52]. Additionally, Hoeppner et al[53] reported that the enamel surface was more resistant to demineralization four months after microabrasion with 35% phosphoric acid.

Figure 5 Enamel alterations after microabrasion. Scanning electron microscopy showing the acid conditioning pattern on the enamel surface caused by microabrasion with A: Phosphoric acid and pumice; B: Opalustre; C: Confocal laser scanning microscopy showing the minimal alteration of the enamel surface, but intact subsurface, after microabrasion with Opalustre.

Bertoldo et al[49] recently reported that microabrasion with 6.6% hydrochloric acid and silica results in the incorporation of chloride ions and silica into the enamel. These, along with results from additional studies concerning the effects of artificial[6,49] and human[51] saliva on microabraded enamel, should encourage clinicians to consider this method. Chloride ions are strongly associated with enamel rehardening, as they account for more than 60% of the ionic strength of saliva[54,55], and the silica compound is used in a bioactive material (Ca₃SiO₅) that efficiently induces a new apatite layer on acid-etched enamel[56]. Some authors believe that these properties should be maximized and, rather than polishing the microabraded enamel, a light polishing with a feltrum disc and fluoridates or diamond toothpaste with low granulation should be applied[1,5,9].

Clinical success

Several case reports demonstrate the lasting and stable esthetic results of the microabrasion technique[1,9,10,12,35,41]. According to clinical results, enamel microabrasion produced permanent color modification of superficial enamel coloration defects because the discolored enamel was removed, rather than altered or masked[57]. Microabraded enamel surfaces achieved a brilliant luster over time[13,57]. An example clinical result of enamel microabrasion is presented in Figure 6[58].

Figure 6 Resolution of fluorosis staining by microabrasion. A: Clinical case of fluorosis before treatment; B: Results after enamel microabrasion (reprinted with permission Machado et al[58]).

Loguercio et al[59] compared two commercially available products for microabrasion for removal of fluorosis stains, and found that treatment with Opalustre was more effective than Prema Compound. This effect was possibly due to the larger size of the silica granules in the Opalustre. However, both products were efficient, and the patients were highly satisfied with the results. Similarly, Sheoran et al[57] compared 35% phosphoric and 18% hydrochloric acid with pumice, and found no clinical difference between them, with microabrasive compounds successful in treating enamel opacities.

Enamel microabrasion is considered effective in cases of white, yellow or brown stains located in the outer enamel layer[60]. However, it is important to recognize the severity of enamel stains when facing fluorosis. Celik et al[16] performed enamel microabrasion with Opalustre in mild-to-severe fluorosed teeth and found that more applications were needed when lesions were more severe. Mild staining was treated with five applications, whereas moderate to severe staining needed ten applications. Train et al[27] also showed that the appearance of mildly fluorosed teeth was moderately improved, but microabrasion only slightly improved the appearance of severely fluorosed teeth. However, enamel microabrasion should still be the first option for patients that seek minimally invasive treatment, even in cases with severe fluorosis. In such cases, removal of opaque white areas or brown stains may increase the success of further treatment, such as bleaching, to achieve a uniform tooth shade[16]. Castro et al[26] showed that enamel microabrasion combined with at-home tooth bleaching effectively reduced staining in cases of mild to severe fluorosis, improving the esthetic appearance of the teeth and the self-perception of the patient, without incidence of side effects such as tooth sensitivity.

CONCLUSION

Accumulating evidence suggests that enamel micro-abrasion is efficient and effective for producing esthetic improvements. This technique involves minimal enamel loss, leaving a smooth and shiny enamel surface with permanent results. The procedure is considered a safe, conservative, atraumatic method for removing superficial enamel stains and defects. The laboratory and clinical results presented in these articles support the use of enamel microabrasion as a first treatment option for patients who prefer a less-invasive approach.