Teeth Whitener

Background

Teeth whiteners are products designed to enhance the appearance of teeth by removing stains and improving brightness. These whiteners typically contain bleaching agents, such as hydrogen peroxide or other peroxygen-type chemicals, that remove organic residue and oxidize stains so they are less visible. While teeth whiteners have been used by dentists for many years, they have only been commercially available since the mid-1990s. These products are available in two primary forms: as toothpastes that whiten teeth as they clean and as specialty liquids applied to teeth separate from the brushing process.

History

Teeth-whitening formulations were first developed for use in denture cleaning compounds. From there, they gained popularity among dentists for general teeth whitening. The first clinical treatments administered by dentists required several lengthy appointments that involved etching the teeth with an abrasive or an acid and then bleaching them with a 30-33% solution of hydrogen peroxide and applying heat. Finally, the teeth were polished to restore a lustrous surface. Dentists typically charged $50-150 for each of these clinical procedures.

In the 1990s, commercial tooth whiteners began appearing on the market for the general public. These products contained some of the same active ingredients as the professional products but at lower concentrations. To achieve significant whitening, they must be used for several minutes each day for four to six weeks. While they can improve the general appearance of teeth, these products are not effective in removing deeper stains such as those caused by tetracycline, fluorosis, jaundice, or internal bleeding. In the late 1990s, sales for teeth whiteners soared to $33.7 million. By comparison, consumers spent $2.43 billion on the entire oral hygiene category which include toothpastes and mouthwashes.

While the products currently on the market are generally recognized to be less effective than professional treatments, there is still concern that they may damage oral tissue. Therefore teeth whiteners are the source of some controversy. The U.S. Food and Drug Administration (FDA) has expressed concerns that these products should be considered drugs rather than cosmetics and the American Dental Association (ADA) says that overuse of these products may damage tissue, cause cell changes, or harm dentin and enamel. Although the products remain on the market, their future is not yet clear, and an extreme shift could occur if the FDA eventually rules that whiteners can no longer be sold as cosmetics.

Raw Materials

Water constitutes the largest portion of the formula and is used as diluent for the other ingredients. Dionized or demineralized water is used because the metal ions found in hard water can interfere with the action of the other raw materials.

Stain removal can be achieved chemically with bleaching agents such as hydrogen peroxide and physically with abrasives such as carbonates. Chemical bleaching agents include hydrogen peroxide, sodium percarbonate, and sodium perborate. Abrasive materials used in whiteners include calcium or magnesium carbonate, calcium phosphates, insoluble sodium metaphosphate, silica xerogels or aerogels, and hydrated aluminas.

Detergents are used in teeth whiteners to provide foam and help cleanse. These chemicals are surfactants such as sodium lauryl sulfate, sodium lauryl sarcosinate, sodium lauryl sulfoacetate, or dioctyl sodium sulfosuccinate.

Binders and thickeners increase the viscosity of the product. Some that are typically used are carboxymethylcellulose, carrageenan, gum tragacanth, gum karaya, Irish moss, sodium alginate, Carbopol resins, magnesium aluminum silicates, and block copolymers.

Therapeutic agents may also be added to the product. They include sodium citrate, which interferes with the metabolic activity of pathogenic bacteria and helps reduce gingivitis; and pyrophosphate, which is an effective tartar-control agent.

Humectants such as sorbitol, glycerin, and propylene glycol are used in the formulas to reduce moisture loss from the product; this prevents "crusting" if the cap is left off of the package for an extended time. Flavors are included to improve consumer appeal. Common flavors are peppermint, spearmint, wintergreen, sassafras, and anise. Additionally, sweeteners, such as saccharin, are added to further improve the taste of the product. Preservatives such as methyl and propyl paraben and sodium benzoate are used to prevent bacterial growth in the product. Finally, titanium dioxide, which contributes to teeth whitening; sodium bicarbonate, which controls pH; and certified colors are other common ingredients.

Design

Teeth whiteners for home use are carefully formulated to be efficacious and safe. The most significant challenge when designing these products is to eliminate potential incompatibility between the peroxygen bleaching agents (e.g., hydrogen peroxide) and the other ingredients in the formulation. Initially, this challenge was overcome by the development of a dual-delivery system where gelled hydrogen peroxide was kept separate from the rest of the formulation with a dual chambered package. With this

method, both portions of the product were co-extruded onto the toothbrush at the time of use. Eventually, stable formulations were designed which replaced hydrogen peroxide with a solid peroxygen bleaching agent (either sodium percarbonate or calcium peroxide) in an anhydrous formulation. This approach also allows the incorporation of other active ingredients such as baking soda and tartar-control agents. If care is taken to select compatible thickeners, and if contamination from other sources is controlled, these formulations can maintain shelf stability for the life of the product.

Aesthetic considerations also impact formula design. For example, taste, appearance, and consistency must be designed to the consumer's liking before these products can be commercially acceptable. Proper packaging must also be considered during the design phase of product development. Teeth whiteners may be designed as pastes that can be applied using a simple toothbrush or as liquids used in conjunction with plastic or rubber dental dams that hold the solution close to the tooth surface. This application process helps the product perform better. In addition, some teeth whiteners are designed with a pre-rinse treatment that eliminates some of the residue found on the tooth surface.

A number of manufacturers have marketed successful teeth whitening products. For example, Proctor and Gamble's Crest introduced its MultiCare Plus Extra Whitening toothpaste in the late 1990s. Other popular brands include Aquafresh Whitening Advanced Freshness by Smith Beacham; Rembrandt Daily Whitening Gel with Safe Peroxide by the Den-mat Corporation; and Mentadent Advanced Whitening by Cheseborough Ponds to name just a few.

The Manufacturing Process

Raw material staging

• 1 Raw materials are first analyzed to make sure they comply with all relevant specifications. Once they have been approved they are pre-weighed and staged in the manufacturing area in preparation for production.

Charging the batch tank

• 2 Toothpaste-like teeth whiteners are typically made in stainless steel batching tanks equipped with planetary-style mixers that stir the batch without whipping in excessive amounts of air. These tanks are sealed and equipped with an apparatus that uses a vacuum to pull out trapped air. This prevents the formation of bubbles in the finished product. Batching tanks range in size from 25-625 gal (100-2,500 L)

Mixing

• 3 The humectants (glycerine and sorbitol) are added first and the powdered thickening agents are dispersed in the liquid. By dispersing the powders in the non-aqueous solvents they will not clump when they come in contact with water.
• 4 After the powders are dispersed, the water is added to dilute the batch. The batch is mixed for about 20 minutes, allowing the water soluble ingredients to fully hydrate.
• 5 Then, a vacuum is applied to draw excess air from the batch. The sweeteners, surfactants, and other ingredients are mixed in and the batched is mixed for another 15 minutes.
• 6 Finally, the flavor chemicals are added and the batch is stirred for an additional 10 minutes until it reaches a smooth, bubble-free consistency.

Filling and packaging

• 7 The finished product is transferred to a filling machine via high pressure pumps. The filling machine consists of nozzles connected to a metered dispensing system. The packaging, usually plastic tubes, is fed under the filling nozzles via a conveyor belt. Each tube moves down the conveyor and as it passes under the filling head the nozzle dispenses a pre-set amount of product into the open end of the tube. The tube then moves down the conveyor to a sealing machine that clamps the tube shut and seals the plastic with heat or ultrasonic vibrations. Each tube imprinted with a batch code to allow the tracking of each lot. The sealed tubes are then transferred to cartons for shipping.

Quality Control

As with other personal care products, the quality of teeth whiteners are carefully monitored during production. Before manufacture begins, all raw materials are assessed to ensure they meet the established specifications. After the batch is complete, the finished product is checked for quality including basic chemical parameters such as pH and viscosity. Both these factors can affect the stability of the product as well as its aesthetic appeal. For example, if the pH is too low, the solubility and efficacy of the whitening agents may be affected. The batch is also checked to ensure it is free of microbial contamination.

The quality these products may be impacted by actions of the FDA. In February 1994, the FDA issued a Notice of Proposed Rule Making (NPRM) in the form of a tentative final monograph for oral antiseptic drug products. This monograph lists active ingredients and establishes testing and efficacy requirements for teeth whiteners. Active ingredients are classified Category II (not generally recognized as safe or effective) or Category III (more data needed to establish safety and effectiveness). As of the end of 2000, the FDA has not established when it will issue the final monograph on this category and it continues to regulate these products as cosmetics, not as drugs. The National Tooth Whitener Coalition, a trade organization composed of teeth whitener manufacturers, is fighting to ensure that the FDA does not over regulate this product category.

The Future

The primary factor affecting the future teeth whitener products is the regulatory environment. Depending on future actions by the FDA, these products may continue to be sold as cosmetics or they may be regulated as drugs. The fact that most of these products contain hydrogen peroxide continues to be of concern. In addition, chemists are continually developing improved formulations. While changes in the regulatory environment will impact the future of teeth whitening products, it is likely that advances in chemistry will result in products with improved performance, taste, and stability.