Many patients who have had whitening treatment see the benefit of having a beautiful white smile and are motivated to seek further esthetic treatment. They may request further esthetic changes such as a midline diastema or bonding of a peg-shaped lateral tooth. This chapter will examine the important information related to bonding after whitening treatment and the issues that will need to be addressed before esthetic dentistry is undertaken. A brief overview will describe the types of esthetic treatments that may be requested after whitening treatment has been completed.
Patients who have whitened their teeth are usually delighted with the results. They often elect to have further esthetic dentistry undertaken (Tables 17.1–17.4). Renewing any necessary composites can be undertaken 2–3 weeks after cessation of whitening, once the enamel bond strength has returned. Cosmetic contouring can be undertaken immediately. Preparation of anterior crowns or porcelain veneers should be delayed for at least 1 month to allow the shade to settle and to allow for any rebound shade shift, which can be one shade difference on the value-orientated shade guide. It is important to wait before making any new crowns because the teeth appear whiter and also brighter. The shade may change and settle very slightly by 1 week after whitening treatment has ceased.
REDUCTION IN BOND STRENGTH AFTER HOME WHITENING TREATMENTS
The reduction in bond strength of adhesive restorations to tooth structure after dental whitening has been investigated widely in the literature. Some authors have attributed the decrease in bond strength to the presence of residual peroxide on the tooth surface, which interferes with resin bonding and prevents its complete polymerization (Dishman et al. 1994). Others have mentioned that vital whitening will alter the protein and mineral content of the superficial layers of enamel, which may be responsible for reduced bond strength (Perdigão et al. 1998). Titley et al. (1991) reported that, in the scanning electron microscope (SEM) evaluation of whitened specimens, large areas of enamel surface were resin free and tags were poorly defined and fragmented and penetrated to a lesser depth when compared with those in the unwhitened control groups. In another study, SEM examination of resin and whitened enamel interfaces displayed a porous and granular view with a bubbly appearance (Titley et al. 1992).
Several authors have published articles on the effect of the decreased strength of the bond to the enamel and dentin after home whitening treatment. It seems that there is a reduction in bond strength of around 20% (the effect is not as severe with teeth treated with power whitening). The bond strength will recover fully over time, and it is important to wait before undertaking any esthetic treatment. Even though the enamel bond strength of teeth whitened with power whitening is not as severely affected, it is important to wait for the shade to “settle”—to readjust to the new lightened color so that the composite shade can be well blended and the restoration appears invisible.
The reduction in the bond strength may be attributable to the residual oxygen left inside the tooth. It is thought that it takes a further 2 weeks for all the oxygen to dissipate out of the tooth and for the bond strength to return to normal. The reduction in bond strength interferes with the resin infiltration into the etched enamel or demineralized dentin, inhibiting the polymerization of the resin placed immediately after whitening (Khoroushi et al. 2010). It may be preferable to wait 2 weeks for the bond strength to be restored before undertaking bonding treatment. Sometimes it may be preferable to wait longer—for instance, before undertaking porcelain laminate veneers or anterior crowns.
METHODS OF REVERSING THE REDUCTION IN BOND STRENGTH
1. Delaying bonding for 1 to 3 weeks. This a simple option that will allow all the oxygen to dissipate from the tooth and the bond strength to return to normal.
2. Using an antioxidant such as ascorbic acid to improve immediate bond strength.
Sodium ascorbate and its salt (vitamin C) has several functions in reversing the bond strength. First, it is an antioxidant that can neutralize the oxygen. It is thought that the antioxidant reduces the oxidative compounds, especially free radicals. There are a few papers on the use of ascorbic acid to immediately reduce the effect of the bond strength reduction (Titley et al. 1992, Türkün et al. 2000, Kimyai and Valizadeh 2008). The clinical product is also known as hydrogel; it can be applied to the surface of the tooth or into the access cavity immediately after non-vital whitening.
• Composite restorations:
1. Simple—replacement of anterior and posterior composite restorations
2. Repairing and resurfacing of restorations
3. Peg-shaped lateral buildups
5. Composite bonding for smile creation
• Cosmetic contouring and reshaping teeth to improve smile proportions; can be undertaken on both upper and lower teeth
• Orthodontic treatment: clear aligning treatment, fixed braces, retainer upgrades
• Porcelain treatments
1. Porcelain veneers
2. Porcelain inlays and onlays, crowns
• Multidisciplinary treatments involving a combination of procedures such as full-mouth rehabilitation and wear cases
• Advanced implant treatments
• Composite bonding: 1–3 weeks (at least 2 weeks)
• Porcelain veneers: 6 weeks (to let the shade settle, to select the correct shade, and to allow bond strength of enamel to return to normal levels)
• Porcelain crowns adjacent to whitened teeth: 6 weeks (helps with shade selection because sometimes too light a shade is selected)
• The color of the natural tooth
• The color of the composite
• The color of the dehydrated tooth
• The color of the whitened tooth
Allow the patient to visualize the closure of the diastema
• Place a composite mock-up to show the patient what the result could look like.
• Take photographs to show the patient.
• Take pretreatment and post-treatment photographs.
• Diagnostic cast
• Diagnostic wax-up
• See both before and after casts
• Plastic blow-down model
• Silicone index
Second, the antioxidants have a positive effect on the quality of the bond and the polymerization of the resin. Soeno et al. (2008) reported that surface treatment with ascorbic acid and ferric chloride strengthened the bond of the bonding agent, contributing to effective adhesion.
Third, it has been reported that ascorbic acid is capable of reversing the effect of dentin deproteinization by sodium hypochlorite and improving the bond strength of resin and dentin (da Cunha et al. 2010).
Fourth, other ways of increasing the bond strength after whitening include the following:
• Air abrasion—use of Sylc material for cleaning and increasing the bond strength (see Figure 17.3G).
• Double etching with 37% phosphoric acid for 15 seconds (see Figure 17.3M).
• Beveling of the surface of the restoration.
• Enamel surface treatment with a fast handpiece by removing the fine outer layer of the enamel and reshaping the restoration.
CLINICAL PRODUCTS THAT CAN BE USED FOR ENAMEL SURFACE TREATMENT TO NEUTRALIZE THE REDUCTION IN BOND STRENGTH
Several products are available to eliminate free radicals from dental surfaces after whitening procedures, and many studies have been conducted to assess the best product to use for this purpose. Garcia et al. 2012 assessed many different products to reverse the decrease in bond strength and rated the potential of each product to do this. They evaluated the percentage of antioxidant activity (AA%) of 10% ascorbic acid solution (AAcidS), 10% ascorbic acid gel (AAcidG), 10% sodium ascorbate solution (SodAsS), 10% sodium ascorbate gel (SodAsG), 10% sodium bicarbonate (Bicarb), Neutralize (NE), Desensibilize (DES), catalase C-40 at 10 mg/mL (CAT), and 10% alcohol solution of α-tocopherol (VitE).