Bing Crosby sang about snow on Christmas Day, but people around the nation now sing praises about tooth whitening. Here`s what you need to know about the sweet dreams offered by dentistry.
Ellen S. Neuenfeldt, RDH, BS
Tooth whitening is one of the most common cosmetic dental procedures offered today. Recent surveys report that more than 96 percent of general dentists dispense and supervise at-home tooth-whitening systems.
Patients request tooth whitening for varying reasons. Many are exposed to consumer print and broadcast promotions of dental products, especially in the area of cosmetic and esthetic dentistry. Videos viewed in the dental office reception area also convey the message. Once patients learn about a certain procedure or treatment, they often request it. Consequently, a shift is occurring in the profession to elective esthetic dentistry, including tooth whitening.
Tooth whitening is one of the simplest means available to lighten teeth and diminish or eliminate stains in both vital and nonvital teeth. When patients have their teeth whitened, they often become interested in additional esthetic procedures, such as veneers, replacement of old restorations, and diastema closures. However, the success of the whitening treatment is dependent on appropriate patient selection, method of whitening, treatment planning, and attention to technique.
The dental hygienist plays an important role in establishing and maintaining tooth-whitening procedures. Patients are curious about this process, and want to know what method would be the best choice. During the preventive care appointment, the dental hygienist can introduce and explain the various tooth-whitening options that are available. Patients look to dental hygienists to help them make the right decision regarding tooth whitening.
This article presents an overview of tooth whitening, with an emphasis on professionally administered at-home whitening. This information will assist the dental hygienist when consulting with patients regarding this increasingly popular procedure.
In 1989, Haywood and Heymann introduced the nightguard vital bleaching technique. This technique utilized a 10 percent carbamide peroxide whitening gel applied in a custom fit tray overnight for two to six weeks of treatment. This method has evolved into an effective method of lightening intrinsically stained or discolored teeth.
Whitening has undergone an evolution of continuous improvement. Today, in-office and professionally administered at-home whitening treatments with custom trays have become routine in most general practices. Tooth whitening materials and methods offer several treatment options to meet patients` varying needs.
Whitening agents overview
The active ingredients in whitening agents must react in a short period of time with stains, be compatible with oral tissues, and be easy to use. Carbamide peroxide and hydrogen peroxide are the most common, and have been used for decades in dentistry.
Hydrogen peroxide is an oxidizing agent that quickly breaks down to water and oxygen, releasing oxygen within the first few seconds of contacting the tooth surface. Because of its low molecular density, hydrogen peroxide permeates the tooth enamel without abrasion to oxidize colorations, causing the teeth to lighten.
Carbamide peroxide is the most commonly used active ingredient in tooth-whitening materials. Carbamide peroxide breaks down into hydrogen peroxide and urea in an aqueous solution. Ten percent carbamide peroxide produces 3.6 percent hydrogen peroxide. Current dentist-administered, at-home tooth-whitening products commonly contain concentrations from 10 to 22 percent carbamide peroxide.
The stain molecules are released more quickly with whitening agents that have higher concentrations. Although faster results can be obtained, very high concentrations are more likely to irritate the gingival tissues and cause tooth sensitivity.
Carboxymethylene polymer, or carbopol, is added to many whitening solutions to allow for a timed or sustained release of the whitening agent. This quality, plus the thixotropic nature of carbopol-containing whitening materials, makes it ideal for custom tray whitening.
Methods for whitening
Dentist-administered, in-office whitening: High-power curing lights, such as argon lasers, are used to activate the bleach for accelerated whitening results. A concentration of hydrogen peroxide (usually 35 percent) is used. The high concentration of bleach necessitates rigid adherence to isolation techniques to protect the soft tissue. After isolation and placement of the whitening material, the teeth are exposed to a high-power curing light source. The total whitening treatment involves approximately one to three appointments. Patients who want quick results without concerns relative to compliance at home often request the in-office whitening procedure.
Dentist-supervised whitening: This procedure "jump starts" the take-home whitening procedure. A whitening tray loaded with a high concentration of carbamide peroxide (~35 percent) is placed in the patient`s mouth for 30 minutes. The patient can remain in the dental chair or sit in the reception area of the dental office while the whitening tray is in the mouth. On average, a two- to three-shade change can occur. Take-home whitening material is then provided to the patient for the completion of the whitening procedure.
Over-the-counter whitening products: These whitening products are available for sale directly to the public without dentist supervision. Four primary areas of concern differentiate professional prescribed at-home whitening materials from over-the-counter products:
- At-home whitening treatments should not be initiated until a complete examination of the teeth is made. Only a dental professional can complete these procedures. The uninformed consumer may attempt whitening when it may not be appropriate.
- Patients must be informed of possible esthetic situations that may be encountered as a result of successful whitening procedures. The patient must be informed that all existing composite restorations that previously matched the teeth may need replacement. Over-the-counter whitening products do not provide this assessment.
- When the dental professional performs a whitening treatment, a custom tray is fabricated and trimmed to conform to the patient`s free gingival crest. This helps to reduce any potential for tissue irritation. Over-the-counter products provide a generic "boil-and-fit" tray, which is considerably thicker and less comfortable than a custom tray and cannot be scalloped. A custom tray provides homogeneous application of whitening gel and less gel is swallowed.
- Over-the-counter products do not provide professional supervision of the whitening process. This supervision is important in dealing with any side effects associated with whitening, or with any anticipated concerns, such as tissue irritation. The dental professional also monitors the extent to which the patient whitens the teeth.
Professionally administered at-home whitening: This is the most popular tooth-whitening method. It is one of the most simple and least expensive means available to lighten discolored teeth and diminish or eliminate many stains in both vital and nonvital teeth. This technique is simple and safe for a majority of patients when dispensed and monitored by a dental professional. At-home whitening also requires less staff time and less chair time than dentist-administered or dentist-supervised whitening.
The technique involves applying a mild whitening agent to the teeth by utilizing a custom fit vacuum-formed tray. Whitening agents used for this method contain lower concentrations of carbamide peroxide, usually 10 to 22 percent.
Professionally dispensed at-home whitening is simple, within control of the patient, and effective. In most cases, it takes between two and four weeks to obtain optimal lightening. The daily exposure times to the whitening gel and the degree of discoloration in the teeth are the main determinants of the time necessary to achieve the desired final shade.
Indications for professional whitening systems
Whitening with custom trays achieves the best results for patients with yellow, orange, or light brown coloration. Patients with dark blue-gray staining due to a history of tetracycline intake usually do not respond well to whitening. Tetracycline stains have responded in two to six months of nightly treatment, although not to the extent of normal teeth. No detrimental effects on the patient or teeth have been noted with extended whitening time periods.
At-home custom-tray whitening is also indicated for the treatment of brown fluorosis stains. The brownish discolored areas respond quite well; however, the white opaque "spots" found in association with fluorosis stains are not removed. These "spots" usually become less apparent, though, because the surrounding tooth structure lightens, making the white spots less obvious.
At-home whitening with custom trays can also assist in lightening teeth that have been exposed to years of the staining influences of smoking, coffee, tea, and chromogenic foods. Often, teeth that have darkened by these factors no longer match adjacent or opposing crowns or other prostheses. This mismatch in color is frequently considered unsightly by the patient. The original shade can often be achieved and a match with other existing prostheses obtained by whitening the non-restored natural teeth.
There are several future indications for custom-tray whitening. These include the examination of carbamide peroxide to effect a reduction in root surface caries, and consideration for the treatment of gingival inflammation associated with gingivitis. However, definitive conclusions cannot be made regarding either of these potential uses. The primary use of the custom-tray whitening technique continues to be the lightening of discolored teeth.
Diagnosis and treatment planning
Diagnosis of tooth discoloration and assessing the condition of the teeth and mouth are important determinants to the success of tooth whitening. Additional factors that affect the outcome of the tooth whitening procedure are:
- The patient`s expectations and desire to achieve an esthetic result
- Willingness to work as a "team" with the dental staff and follow instructions
- Acceptance of the responsibility to modify behaviors that can affect tooth coloration.
Custom trays generally require only an initial consultation appointment, an appointment to review the procedure and dispense the material and custom trays to the patient, and brief periodic visits to monitor patient progress.
A thorough prophylaxis is essential to assess the extent of deep stains and to adequately prepare the teeth for treatment. The patient must understand that existing anterior restorations matching the pre-treatment shade of the teeth may require partial or total replacement, since these restorations will no longer match the lighter shade of the teeth after the whitening treatment.
Proper fabrication of the tray limits the contact area of the whitening gel to the teeth and prevents excess gel from touching the gingival tissue. A custom whitening tray is fabricated on a stone model from an impression of the teeth. Most whitening systems require the application of a block-out resin material on the facial surfaces of the stone model. When the vinyl tray material is vacuum-formed to the model, the block-out resin forms a reservoir in the tray, which helps to increase the amount of gel available in the tray for whitening.
A recently introduced whitening system utilizes the 3M™ Zaris™ Gel Retention Insert. This insert serves as a reservoir for the whitening gel and eliminates the need for block-out resin. In addition, the micro-replicated, capped projections on the surface of the insert act to retain the whitening gel against the tooth.
The tray is trimmed approximately .5mm short of the cervical margin of the teeth to reduce the amount of gel contacting the gingival tissue. It is inserted in the patient`s mouth to evaluate the overall fit, tissue adaptation, and retention. The proper method for filling the tray with the whitening gel and positioning the tray over the teeth is reviewed. Information regarding at-home whitening, including potential concerns or side effects, should be reviewed with the patient. The instructions should indicate that minor sensitivity might be encountered. Side effects related directly to the whitening gel are usually mild, transient, and dose-related. Temporarily discontinuing the treatment or reducing exposure time generally alleviates these problems. Clinical studies indicate that none of the side effects persist once the treatment is terminated.
All patients should be recalled periodically during the whitening treatment to check compliance, shade change, and address any questions or concerns they may have. Treatment should be discontinued once optimal lightening of the teeth has occurred. A final shade is taken and recorded in the patient chart.
Whitening with custom trays approaches an efficacy rate of 97 percent for non-tetracycline-stained teeth, and up to 90 percent for tetracycline-stained teeth with extended treatment time. Shade retention can be expected in up to 90 percent of patients one year after treatment, 62 percent at three years, and at least 35 percent at seven years.
Side effects of whitening treatment
Two primary side effects that may occur during the whitening treatment are transient sensitivity of the teeth to cold and/or irritation of the gingival tissues. Either alone or together, these side effects can occur in as many as two-thirds of patients. The majority of these side effects last one to four days, and all side effects cease upon the termination of treatment with no long-term effects noted. Patients who normally report tooth sensitivity to hot and cold - as well as an increased sensitivity after a prophylaxis - appear to be more prone to side effects.
When a patient experiences tooth sensitivity during whitening, possible explanations include extremely large pulps, exposed root surfaces, transient hyperemia associated with orthodontic tooth movement, severe loss of enamel, multiple changes of the active whitening solution within a 24-hour period, or too high of a concentration of whitening gel.
Sensitivity of the gingival tissues can be caused by fit of the custom tray, rigidity of the material used for the tray, soft-tissue coverage by the tray, over-filling the tray with gel, or rough areas on the tray.
The active treatment of sensitivity may include the use of desensitizing toothpaste during the treatment period, fluoride in the custom tray five minutes before or after the whitening procedure, and/or anti-inflammatory or pain medications. Fluoride blocks the dentinal tubules that, in turn, prevents sensitivity. Another agent useful in decreasing sensitivity is potassium nitrate, which decreases sensitivity by a chemical interference that prevents the pulpal sensory nerve from repolarizing after the initial depolarization.
A passive treatment would include a reduction in the time of wear (from nighttime to hourly daily wear), reduction in the frequency of application (skipping one or two days), or reduction in the concentration of the whitening gel.
Effect on restorative materials and bond strengths
Composite resins do not appear to change color, although there may be a cleansing effect at the margin and surface of the restoration. However, if there is a change, it is usually clinically insignificant relative to the overall change in the tooth color. Carbamide peroxide whitening gels may slightly roughen composite surfaces, but it is unlikely to have any clinical significance.
No effects of whitening on the color or physical properties of porcelain or other ceramic materials have been reported. However, methacrylate temporary resins exposed to carbamide peroxide can discolor, becoming orange in color. Polycarbonate crowns and bis-acryl composite temporary materials do not discolor.
Bonding to teeth may be somewhat difficult after the whitening treatment. It is speculated that residual peroxide and/or oxygen interferes with polymerization of resin adhesives and restorative materials to decrease bond strengths. It is recommended to delay bonding procedures a minimum of two weeks after whitening.
In addition, wait a minimum of two weeks after the treatment for tooth-whitening coloration to stabilize before placing restorations. If bonding cannot be delayed, water-clearing solvents such as acetone- or ethanol-based adhesive systems can reverse the adverse effects of whitening on enamel bond strength.
There rapid acceptance of the custom-tray whitening procedure by most dentists is due to simplicity and patient satisfaction. More than 500 published articles before 1990 and an additional 200 since that time, attest to the safety and nontoxicity of whitening materials when administered by a dental professional.
A 10 percent solution of carbamide peroxide is composed of 3 percent hydrogen peroxide and 7 percent urea. The hydrogen peroxide breaks down into water and oxygen, and the urea breaks down into carbon dioxide and ammonia. Normal body processes easily handle all four products. Enzymes called peroxidases scavenge hydrogen peroxide, which is a normally occurring body component. Urea, which raises the salivary pH, is also a normal body component found in saliva.
The acidic nature of the whitening solutions initially raised questions relative to the tooth structure and possible subsurface softening of the enamel. The concern was that teeth would be more susceptible to caries during the whitening procedure. Research has indicated that carbamide peroxide in the pH range of 5.3 to 7.2 does not cause a noticeable etching of the teeth. Studies also indicate no appreciable subsurface softening of the enamel from applications of carbamide peroxide whitening materials.
There has been no evidence of pulpal damage resulting from the use of carbamide peroxide agents. Tooth sensitivity has been related to the passage of hydrogen peroxide and urea through the enamel and dentin to the pulp. As is the case with 35 percent hydrogen peroxide solutions, resulting tooth sensitivity is most likely due to reversible pulpitis. Test results indicate that any effect to the pulp is either nonexistent or reversible after two months. Consequently, it would be expected that 10 percent carbamide peroxide, which is essentially 3 percent hydrogen peroxide, would have minimal effect on the pulp. Accumulated data continue to support the safety of this successful and well-accepted procedure for tooth whitening.
Due to the nature of the preventive care appointment, dental hygienists have the opportunity to listen to their patients and understand their oral health needs and goals. One of these goals is often the desire for "whiter and brighter" teeth. By partnering with the patient, the best treatment option can be determined. A "win-win" result occurs for the patient and the dental team. Patient expectations are met or exceeded, value continues to build in the dental hygiene department, and overall practice production is increased.
Ellen S. Neuenfeldt, RDH, BS, is a senior technical service representative for the 3M Dental Product Division in St. Paul, Minn.
References available upon request.