Analysis of Common Teeth Whitening Techniques

By Irfan Ahmad, UK

Editor’s Note: Teeth whitening, or bleaching, is an effective, economical, and minimally invasive technique for whitening discolored teeth. Since its introduction by Haywood and Haymann 20 years ago, this at-home treatment has proven to successfully improve the appearance of stained teeth. Bleaching also has therapeutic effects on periodontal health and contributes to oral hygiene. Additionally, the transient stimulation of both soft and hard tissue is harmless and reversible. This article provides a brief introduction to commonly used teeth whitening techniques in both clinical and at-home settings.

Mechanism of Teeth Whitening

Teeth can be whitened through three processes: etching, grinding, and oxidation. Oxidation is the most popular method, as etching and grinding may irreversibly change the tooth structure and damage dental hard tissues. Furthermore, excessive enamel loss can have a counterproductive effect on teeth whitening by exposing the darker dentin. The oxidation process involves bleaching agents penetrating the enamel matrix to convert stained carbon rings into lighter carbon chains. The higher the concentration of the bleaching agent, the better and faster the whitening effect. This process changes the microstructure of the enamel, affecting the organic and inorganic phases of hard tissues. One negative impact of oxidation is that low-pH bleaching agents can demineralize the enamel. However, this effect is usually temporary, as the enamel surface layer rematerializes through saliva and the use of fluoride toothpaste, reversing the effect.

Teeth Whitening Techniques

Common bleaching agents include carbamide peroxide (concentration: 1%–45%), hydrogen peroxide (concentration: 3%–50%), and sodium perborate. These substances can be prepared as gels, varnishes, powders, mouthwashes, and toothpaste. The concentration of the bleaching agent determines the duration of treatment. Higher concentrations can quickly whiten teeth in a shorter time, while lower concentrations require a longer time to be effective. There are two main bleaching methods: in-office bleaching and at-home bleaching (under professional supervision). The latter can be combined with in-office “power start” and then completed slowly at home.

Vital Tooth Whitening

Vital tooth whitening is used solely for whitening teeth or as part of a cosmetic treatment plan, such as before veneers, crowns, or “white” fillings. Independently, bleaching can be used to change the yellow, brown/gray, or tetracycline intrinsic stains displayed by teeth. This technique involves using custom plastic trays manufactured using a heat/vacuum-molding mechanism. These trays are filled with the selected agent, placed on the teeth for a specified time, and then brushed with toothpaste containing high-concentration sodium fluoride (2800 ppm). The treatment duration depends on the degree of discoloration; for daily use of 10% carbamide peroxide for 2–3 hours, the at-home bleaching process may take 2–6 weeks. The effects result in a color change of 2–10 shades on the Vita classical shade guide. However, a rebound of 1–2 shades may occur after 2–4 weeks. Therefore, it is advisable to wait for a period before undergoing new cosmetic restorations to match the stable color of the teeth after rebound. For severe staining, such as severe tetracycline staining, whitening may take 6–12 months. It is necessary to provide professional supervision throughout the entire treatment process and monitor changes through photographs and relevant shade guides (Figure 1).

Non-Vital Tooth Whitening

Non-vital tooth whitening is the third choice for reducing discoloration of teeth after root canal treatment, commonly known as internal bleaching or walking bleach technique. Before starting, it must be ensured that the existing root filling has a satisfactory apical seal to prevent the bleaching agent from penetrating the periapical area and causing root resorption. This technique involves placing the bleaching agent into the pulp chamber and sealing it with a glass ionomer or resin-based composite filling to prevent microleakage and penetration of bacteria. Light-activated whitening uses bleaching agents containing carotenoids to expedite the breakdown of active ingredients when exposed to high-intensity light or laser. However, light itself has no effect on teeth whitening, but the heat generated by light may accelerate the whitening effect of the bleaching agent. Additionally, the heat generated by light can dehydrate teeth, leading to increased postoperative sensitivity (Figure 2).

Protective Measures

Although bleaching is effective and simple, certain conditions must be met before undertaking it. (1) Protecting the teeth: Pre-treatment of sensitive areas, such as cervical regions or wedge-shaped defects, should be sealed with glass ionomer adhesives. Additionally, bleaching severely worn teeth with exposed dentin areas will cause further erosion of the dentin. Finally, noticeable fluorosis or developmental bands may require microabrasion to avoid uneven bleaching. (2) Protecting the gums: The use of rubber dams or other gingival barriers is necessary when using high-concentration bleaching gels in the office.

Side Effects of Teeth Whitening

Although teeth whitening is a relatively safe procedure, certain side effects need to be addressed. (1) Immediately after bleaching, the microhardness of tooth enamel (outer 25um surface) decreases and usually recovers through saliva remineralization in 3–4 weeks. (2) Excessive bleaching with high concentrations may lead to chemical and morphological changes in the enamel structure, resulting in increased porosity, pinpoint erosion, decreased fracture toughness, erosion, or lesions similar to early caries. (3) Teeth and gum sensitivity, especially with high-concentration bleaching agents, can be relieved by inducing remineralization with sodium fluoride, potassium nitrate, or sodium citrate. (4) Reduced dentin bonding strength (especially with sodium perborate), but enamel bonding strength is almost unchanged 1 week after bleaching. (5) Increased microleakage at the interface between dentin and restoration materials, but enamel margins remain intact. (6) Effects on restoration materials, especially composite materials and glass ionomer fillings, may make existing fillings more prominent. (7) Cervical root resorption.

Key Points of Teeth Whitening

Overall, bleaching is a simple, effective, and harmless method for teeth whitening. However, it is critical to have professional supervision and monitoring for optimizing treatment and mitigating side effects.

This article is excerpted from “A Glance,” one of the classic dental works of [UK] Irfan Ahmad, published by Science and Technology Press. The book is a new edition that integrates the latest technologies and scientific advancements in prosthodontics, featuring 3D printing technology, intraoral scanning, digital workflow and diagnosis, smile design, shade assessment, and the use of dermal fillers for facial enhancements, comprehensively introducing the role of digital technology and regenerative medicine in prosthodontics. The book is richly illustrated and systematically comprehensive, serving as a guidebook for clinical prosthodontists and an invaluable reference for dental students.