Biochemistry & Mechanism
Describe the primary chemical process by which bleaching agents lighten tooth color, naming the reactive species involved.
Oxidation via reactive oxygen species/free radicals (peroxide-derived radicals) that break down pigmented organic molecules (chromogens).
Name two common active ingredients used for vital tooth bleaching and one used for nonvital internal bleaching.
Vital: hydrogen peroxide and carbamide peroxide. Nonvital: sodium perborate (alone or with hydrogen peroxide).
Define the “walking bleach” technique and identify where the bleaching material is placed.
Walking bleach: bleaching material (e.g., sodium perborate with or without hydrogen peroxide) placed inside the pulp chamber of a nonvital, endodontically treated tooth; sealed and left for days.
State the most common side effect of vital bleaching and when it is most likely to occur.
Tooth sensitivity (most common), occurs predominantly in first 2 weeks2 weeks and may persist days to months.
Given a patient with generalized extrinsic coffee staining and good oral health who requests whitening, which bleaching mode (in‑office vs tray at home) would you recommend and why?
Recommend tray-based at‑home bleaching (night‑guard vital bleaching) because extrinsic coffee staining responds well, patient compliance allows safer lower‑concentration, long‑contact treatment with fewer sensitivity events and home maintenance.
Explain why dentin color change has a greater influence on overall tooth whitening than enamel color change.
Dentin has more intrinsic chromogenic organic material and transmits color through enamel; color of dentin therefore dominates perceived tooth shade.
Identify the role of potassium nitrate and sodium fluoride when included in bleaching formulations.
Potassium nitrate — reduces neural transmission causing desensitization; sodium fluoride — aids remineralization and reduces sensitivity.
List two essential steps to protect soft tissues during an in‑office bleaching session.
Use of rubber dam or liquid rubber to isolate soft tissues; apply gingival barrier and ensure trays are not overfilled for home use.
Name three patient groups or conditions for which cosmetic full‑arch bleaching is discouraged or contraindicated.
Contraindicated/discouraged: pregnant or lactating women; patients on photosensitizing medications or receiving photochemotherapy; young patients with mixed dentition (full‑arch cosmetic bleaching discouraged).
A patient presents with severe tetracycline intrinsic staining and asks for realistic expectations. What factors will influence the outcome and how should you counsel them about achievable results?
Factors: initial shade/darkness, depth (intrinsic vs extrinsic), age, enamel thickness/wear exposing dentin, concentration and duration of agent — counsel that severe tetracycline staining may need multiple modalities (extended bleaching, internal bleaching for affected teeth, or restorations) and that a maximum achievable shade exists.
Contrast the relative strengths and working times of hydrogen peroxide versus carbamide peroxide, and state how carbamide peroxide produces hydrogen peroxide.
Hydrogen peroxide is stronger and acts faster but has shorter working time; carbamide peroxide releases hydrogen peroxide slowly (carbamide peroxide → H2O2+ureaH2O2+urea), giving extended action.
Describe the function of carbopol and glycerin in bleaching gels and why viscosity matters.
Carbopol and glycerin act as thickening agents: carbopol prolongs release of peroxide; glycerin controls gel flow to avoid gingival spread; proper viscosity prevents soft tissue contact.
Summarize the typical professionally applied power/laser bleaching session: concentrations used, session length, number of applications range, and adjunct protection requirements.
Professional power bleaching: typically 30–40%30–40% hydrogen peroxide (or high % carbamide peroxide), each application 30–60 minutes30–60 minutes, total 1–6 applications; eye protection and rubber‑dam/liquid rubber isolation required.
Explain the effects bleaching can have on existing restorative materials and the recommended delay before performing restorative or bonding procedures after bleaching.
Bleaching does not change porcelain or composite shades; bonding strength to bleached enamel is reduced — delay restorative bonding procedures for at least 2 weeks2 weeks after bleaching; restorative procedures also postponed until shade stabilizes.
A 14‑year‑old with mixed dentition requests full‑arch cosmetic bleaching. According to professional guidance, what is the recommended approach and key reasons?
For mixed dentition: delay full‑arch cosmetic bleaching until permanent teeth have erupted; if treatment is necessary, use custom trays, limit gel, and supervise closely per pediatric dentistry guidance. 300 (alternate) — Use conservative approaches, prioritize eruption and enamel maturity, and avoid full‑arch aggressive protocols.
Explain how free radicals are formed during bleaching and how they interact with chromogens in enamel and dentin.
Peroxide decomposes to form reactive oxygen species (free radicals) that oxidize and fragment large chromogen molecules into smaller, less pigmented molecules within enamel matrix and dentinal tubules.
Explain why pH differences between hydrogen peroxide and carbamide peroxide matter for enamel/dentin health and remineralization.
Hydrogen peroxide has lower pH (more acidic) which can demineralize enamel if overused; carbamide peroxide breaks down to products that raise pH (urea → ammonia) facilitating bleaching with less demineralization risk.
Outline the steps for fabricating and delivering a night‑guard vital bleaching system (at‑home tray system) to a patient.
Impression taking; cast fabrication; vacuum‑forming thin, custom trays; trimming/adapting trays to prevent gingival overflow; patient education on gel volume, timing, hygiene; follow‑up schedule.
Describe systemic effects that may occur if concentrated bleaching agents are ingested and a brief rationale for counseling patients to avoid swallowing gel.
Ingestion may cause mucosal irritation/ulceration, esophageal/stomach irritation, nausea/vomiting and possible drug interactions — advise not to swallow gel and use minimal gel quantities.
For a tooth with an existing composite veneer that is discolored internally, explain the options and the limitations of bleaching relative to restorative approaches.
Composite veneer will not lighten with bleaching — consider replacement after bleaching (delay bonding for 2 weeks2 weeks) or restorative options (veneers/crowns) if bleaching alone insufficient.
Detail the timeline of penetration: how quickly bleaching products reach the pulp, the short-term dehydration effect on shade, and the typical time until final stabilized shade is observed.
Penetration to pulp: approximately 5–15 minutes5–15 minutes; immediate dehydration causes temporary lighter shade; final shade stabilizes in about 2 weeks2 weeks after treatment.
Discuss how high concentrations of hydrogen peroxide (>30%) can affect enamel microstructure and the potential visual consequence while remineralization occurs.
High concentrations of hydrogen peroxide (>30%) may remove enamel matrix and create microscopic voids that scatter light, producing increased whiteness until remineralization restores structure.
For a nonvital single discolored endodontically treated tooth, give the clinical prerequisites and the standard time the internal bleaching agent is left in place per cycle.
Requirements: healthy periodontium, well‑obturated root canal, sealed coronal restoration before bleach placement; typical internal bleaching cycle left for 3–7 days3–7 days before re‑evaluation.
Explain the risk of root resorption in bleaching: when it is more likely to occur (vital vs nonvital), and one practice recommendation to minimize this risk.
Root resorption risk is associated more with some internal bleaching and high concentrations; avoid placing agents on exposed cementum, ensure proper sealing of root canal filling, and limit exposure duration and concentration.
Create a short documentation checklist (6–8 items) that must be completed before, during, and after a bleaching treatment for professional standards and medicolegal safety.
Documentation checklist (example):