Introduction
Treatment of caries has evolved dramatically over the past decade. Advances in epidemiology of caries, dental materials, and technology as well as use of individual caries risk assessment have resulted in a much more conservative approach to surgical treatment of incipient lesions. While surgical intervention has become more microinvasive in order to retain maximum tooth structure, research has shown dental restorations will need to be replaced many times in a patient's life span. Therefore, preventing an incipient lesion from becoming cavitated is crucial to avoid surgical intervention and subsequent restoration.
Recently, a product marketed under the brand name of Icon (DMG America Company, Englewood, NJ), has become available for non-surgical treatment of non-cavitated caries on interproximal and smooth surfaces of permanent teeth. The basic technique involves etching the incipient lesion with a strong acid, rinsing and desiccation, then filling the caries with a low-viscosity resin. The resin is allowed to penetrate deeply into the enamel lesion (near the DEJ) and is then hardened with a curing light. Resin infiltration forms a diffusion barrier in the tooth and thereby seals the lesion from further acid attack.
Clinical studies using resin infiltration on interproximal lesions on permanent teeth have shown very promising results. This paper reports on the clinical use of resin infiltration in order to achieve maximum clinical benefits for patients.
Diagnosis and treatment thresholds for interproximal caries
Cavitation of enamel is thought of as a critical event in the caries process, as a formed microcavity may harbor a cariogenic biofilm and protect it from mechanical disruption.1 For this reason, cavitation of enamel is a common threshold for determining if caries lesions should be treated by surgical intervention. As diagnosis of interproximal caries is most commonly made through radiographic examination, and the clinician must determine the radiographic presentation that corresponds to interproximal enamel cavitation. Clinical studies have investigated the relationship between the radiographic display of the caries lesion and the presence of cavitation.2 Several studies determined that 52–78% of lesions that displayed radiographic evidence of caries lesions in the outer third of dentin were cavitated as assessed during cavity preparation.2 Other studies determined that 28–100% of lesions that displayed radiographic evidence of caries lesions in the outer third of dentin were cavitated as assessed by direct observation following tooth separation.2
With such variation in the reported correlation between radiographic display and enamel cavitation, the clinician is faced with ambiguity related to a threshold for surgical treatment. The International Caries Classification and Management System (ICCMS) was developed to help the clinician classify and treat caries lesions.3 This systems considers not only the radiographic display, but also the activity of the lesion and clinical staging. For example, an inactive lesion which is not likely to progress would not require surgical treatment. Clinical staging refers to the visual changes that can be seen in enamel throughout the caries process, including white demineralization bands, dark shadowing and frank cavitation. According to the ICCMS treatment matrix, active interproximal lesions without visual signs of caries activity do not require surgical treatment until radiographic display at the middle third of dentin. On the other 12hand, for an active lesion in the inner third of dentin with early visible surface changes to the enamel, the recommendation allows the clinician to decide whether to perform surgical treatment.
As it is ultimately the clinician who must decide if a caries lesion will receive surgical treatment, it is useful to survey practicing dentists to determine their radiographic threshold for treatment. A 2009 study from the US Dental Practice-Based Research Network surveyed 500 dentists in the United States and Scandinavia.4 The study reported that in high caries risk patients, 66% of dentists chose to surgically treat lesions radiographically observed in enamel only and 24% chose to wait until the lesions progressed to the inner third of the dentin. In low caries risk patients, 39% of dentists would treat the enamel only lesion surgically and 54% would wait until it progressed to the inner third of dentin. This survey demonstrates that many dentists perform invasive treatment to lesions that are radiographically evident in the enamel or inner third of the dentin despite evidence and professional recommendations that surgical treatment may not be necessary. The clinical niche for resin infiltration is to provide a treatment option to stop the progression of early caries lesions and prevent surgical treatment of savable tooth structure.
Development of resin infiltration for interproximal lesions
The histopathology of enamel caries can be summarized as acid dissolution and enlargement of intercrystalline spaces creating enamel porosity and channels for acid to progress to the dentin.2 The initial caries lesion, the white spot lesion, forms when the subsurface of the caries lesion becomes more porous than its outermost 10–30 micron surface. The surface of the enamel is more resistant to dissolution due to the presence of less acid soluble fluorapatite.5 The principle of resin infiltration is to occlude the porosity formed during the caries process and prevent pathways for acid to further dissolve the tooth structure.6 The two basic steps to achieve this goal are to remove the less-porous surface layer of enamel and allow resin to infiltrate the internal enamel porosities through capillary movement.
As the surface of a carious lesion may act as a barrier to resin infiltration, several preliminary studies evaluated different acid solutions for removal of the surface layer. A solution of 15% hydrochloric acid applied for 90–120 seconds was shown to almost completely remove the 45-micron thick surface layer of the lesion.7 Solutions of 5% hydrochloric acid and 37% phosphoric acid were only able to remove about half the depth of the surface layer of the lesion.7 Lesions etched with 15% hydrochloric acid could be infiltrated with a dental adhesive to a depth of 58 microns whereas the use of 37% phosphoric acid only allowed 18 microns of infiltration.6
After removing the surface layer of the caries lesion, the next step is to infiltrate resin into the porosities created during dissolution of intercrystalline enamel. The ability of several dental adhesives and 66 experimental resin infiltrants to penetrate porous enamel was estimated using their physical properties. Infiltrants containing triethylene glycol dimethacrylate (TEGDMA) showed the highest potential for penetration.8 An experimental infiltrant containing about 90% TEGDMA and 10% ethanol was shown to penetrate deeper into caries lesions than a commercially available dental adhesive,9 and later an infiltrant containing only TEGDMA was shown to penetrate deeper than other formulations of infiltrants.10
The commercially available resin infiltration product, Icon, was released in 2010. This product contains a 15% hydrochloric acid etchant, an ethanol solution for desiccating the enamel and a TEGDMA-based resin infiltrant. When applied for 3 minutes, the Icon infiltrant was shown to penetrate deep into non-cavitated interproximal caries lesions.11 Initial laboratory testing showed that infiltrating enamel lesions with Icon resin infiltration was able to inhibit the progression of demineralization in an acidic solution.12 There are some limitations. Salivary contamination of the infiltration process decreased its ability to prevent demineralization and infiltration is not able to fill the cavities present in cavitated interproximal lesions.1313
Evidence for the effectiveness of interproximal resin infiltration
In a split-mouth study of fifty 5–8-year-old children, 62% of untreated interproximal lesions progressed within a year, whereas, only 23% of those infiltrated showed radiographic progression.14 In another split-mouth trial of 39 adult patients, 32% of infiltrated, 41% of sealed, and 70% of untreated interproximal lesions showed progression after 3 years.15 In a third split-mouth trial of 29 young adult patients, 42% of untreated interproximal lesions progressed within 3 years, whereas, only 4% of those infiltrated progressed.16 In a split-mouth trial performed in a practice-based network, lesion progression was noted in 10 out of 186 infiltrated lesions and 58 out of 186 untreated lesions.17 Based on the results of these clinical studies, a Cochrane review for microinvasive treatments for managing dental decay concluded that microinvasive treatments for interproximal caries (such as resin infiltration) significantly reduces the likelihood of caries progression more than non-invasive treatments.18
Procedure for interproximal resin infiltration
The caries risk of the patient must be determined based on the presence of caries lesions and the patient's diet. Diet counseling should be performed and patient was encouraged to substitute sweetened beverages with water. The surfaces to be treated using resin infiltration should be identified in the treatment plan and informed consent should be obtained. A bitewing radiograph will indicate the extent of penetration of the interproximal lesion (Figure 1).
Prior to treatment, orthodontic rubber separators should be placed (Figure 2) between the teeth to be treated in order to facilitate placement of the interproximal foils. The clinician must balance the inconvenience of scheduling time to place the separators and the uncomfortableness of wearing the separators with the ease of performing treatment that can be achieved with long-term use of separators. A larger separator is preferred for maximum results. In most cases, the resin infiltration procedure will not be performed during the visit where the determination for the need for the procedure is made. Therefore, it is generally possible and preferred to allow a minimum of a 72-hour period for interproximal separation for the teeth prior to performing the Icon procedure.
An easy method to place the separators is to loop two pieces of floss through the separator (Figures 3a and b) and then pull the separator taut. One side of the floss can then be passed through the contact. The separator is then pulled through the gingival embrasure so it is positioned apical the contact. The separator is then pulled coronally to wedge it between the contact. In order to remove the separator without inducing discomfort, it should be cut with scissors to open it up and then pulled underneath the contact with hemostats.
Figures 3a and b: Technique for placement of orthodontic separator prior to use of resin infiltration.
After removing the orthodontic separator, a rubber dam is placed (Figure 4) to prevent saliva from contaminating the surface to be treated. It is also essential to avoid the hydrochloric acid from irritating the soft tissue, and the resin infiltrant producing an unpleasant taste to the patient. It is important to use a latex rubber dam with this treatment, as resin infiltrant can dissolve non-latex rubber dams. If the patient is allergic to latex, the rubber dam material to be used should be tested with some of the infiltrant to verify it will not be affected by the resin. Based on the amount of excess infiltrant that contacts the rubber dam, a non-latex dam can form a perforation prior to completing the first 3 minutes of infiltration if not verified that this effect will not occur. As demonstrated in this case, the tooth receiving treatment can be clamped as long as the wings of the clamp do not infringe on the space needed to place the interproximal foil (Figure 5).
When the orthodontic separator is placed in advance, the wedge is only needed to stabilize the matrix during the procedure and not to separate the teeth. Using a wedge might cause bleeding which could interfere with the need for a completely dry environment. The wedge should be directed through the contact initially ensuring that the tip of the wedge is seen on the other side of the tooth and that it was not inadvertently directed apically into the soft tissue. Generally, local anesthesia is not needed. Once the wedge is in place, it should not be removed until treatment is completed as removing the wedge will frequently cause bleeding that will contaminate the procedure. Note that the wedge should only be used to stabilize the matrix system and not to separate the teeth. Separation is easily achieved via use of orthodontic separators.
The next step was to etch the tooth with Icon-Etch hydrochloric acid (Figure 6). The film in the interpoximal foils is perforated on the side with the green border and unperforated on the side with the white border. Therefore, the foil is positioned with the green-bordered side facing toward the surface being treated.15
When sufficient separation is achieved, the foil can be easily placed by pushing the foil apically while slightly sliding the foil back-and-forth in the buccal-lingual direction (Figure 7).
If it is challenging to slide the foil through the contact (as demonstrated in the case above), the foil can be separated from the dispensing syringe so it is easier to manipulate. The foil is grasped with two fingers on one side and hemostats on the other in order to pull the film taut and prevent it from folding. It is then helpful to start at an occlusal point angle (mesiolingual-occlusal point angle) and gently saw the foil into the contact point. Generally, this last step is not needed when adequate separation exists via pre-placement of an orthodontic separator.
After etching for 2 minutes, the foil is removed and the tooth should be thoroughly rinsed with water for 30 seconds and dried completely. The air-water tip is placed in direct contact with the tooth to ensure it is completely dried (Figure 8).
The Icon-Dry alcohol solution should be applied to the interproximal area of the tooth. Several drops of the solution should be applied to the treated proximal surface so that desiccation of the surface can be achieved (Figure 9). After 30 seconds, the tooth should be completely dried with the air syringe after verifying that the spray will be completely dry.
A new foil is then placed between the teeth and the Icon-Infiltrant resin is introduced (Figure 10). Prior to dispensing the infiltrant, the overhead light must be adjusted with an orange filter to prevent premature polymerization of the resin. Over a 3-minute period, infiltrant is dispensed through the foil via rotation of the handle. Excess material should be removed with a low volume evacuator in order to prevent the patient from tasting the resin.
After removing the foil, a gentle stream of air and floss are used to remove excess resin (Figure 11).16
The infiltrant is polymerized with a light curing unit (minimum 1,000 mW/cm2). The light tip is placed in contact with the tooth and moved from the lingual to the occlusal to the buccal surfaces of the teeth for a total of 40 seconds (Figure 12).
The Icon-Infiltrant is then returned to the interproximal surface of the tooth with a new foil for the second application (Figure 13). The infiltrant is again applied for 1 minute and then the same clean-up and light polymerization procedures described previously are repeated. The wedge and the rubber dam should be removed, and the patient's mouth should be thoroughly rinsed. All of the elements of the product needed are available in a “kit” of Icon used for this interproximal lesion treatment purpose (Figure 14).
At the end of the visit, the patient is informed which teeth were treated with Icon resin infiltration and the treatment performed noted in the patient's chart. The patient must be informed that this treatment is not visible on radiographs, and therefore must be monitored through signs of radiographic progression.17
Resin infiltration for demineralized smooth surface lesions after orthodontic treatment
In the same way that resin infiltration is effective to arrest the progression of pre-cavitated interproximal caries lesions, it is also effective at halting progression of white lesions created as a result of inadequate oral hygiene during orthodontic treatment. Unfortunately, and too often, lesions appear around orthodontic brackets, which become highly visible and of great esthetic concern after orthodontic treatment. In the anterior region in particular, these white spot lesions can be highly unsightly. This is particularly problematic whereas a primary objective of orthodontic therapy is to improve esthetics. Because these lesions are specifically caries lesions, they can be treated using resin infiltration. The sequence of steps is the same except that the interproximal matrix is not needed. A separate “kit” of Icon is available specifically for this purpose (Figure 15).
An example of the immediate effect of resin infiltration treatment using the Icon system can be seen in Figures 16 and 17 (pre- and post-treatment).
Figure 15: Special “kit” for use of Icon resin infiltrant for anterior facial white spot treatments.
Conclusion
Clinicians are well aware of the need to always provide the most conservative treatment possible when deciding how to manage dental caries lesions. The use of resin infiltration (Icon) is one of the most conservative lesion management techniques in terms of halting progression of caries lesions. With careful post-treatment monitoring, excellent results and minimal overall loss of tooth structure is achieved with this technique.
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- Splieth CH, Ekstrand KR, Alkilzy M, et al. Sealants in Dentistry: Outcomes of the ORCA Saturday Afternoon Symposium 2007. Caries Res 2010; 44:3–13.
- Martignon S, Ekstrand KR, Ellwood R. Efficacy of sealing proximal early active lesions: an 18-month clinical study evaluated by conventional and subtraction radiography. Caries Res 2006; 40:382–388.