excretion of porphyrins into teeth. the excretion of porphyrins produces purple-red pigments in teeth. hemolytic disease of the newborn: this disease occurs when a newborn's red blood cells are being attacked by antibodies from the mother caused by an incompatibility between the mother and baby's blood. this condition can produce green staining of teeth due to jaundice, which is an inability to excrete bilirubin properly. root resorption: root resorption is clinically asymptomatic; however, it can produce a pink appearance at the amelocemental junction. alkaptonuria: metabolic disorder which promotes the accumulation of homogentisic acid in the body and may cause brown colour pigmentation in the teeth, gums, and buccal mucosa. methods prior to proceeding to tooth whitening alternatives, it is advised that the patient comes into the dental office to have a comprehensive oral examination that consists of a full medical, dental, and social history. this will allow the clinician to see if there is any treatment that needs to be done such as restorations to remove cavities, and to assess whether or not the patient will be a good candidate to have the whitening done. the clinician would then debride (clean) the tooth surface with an ultrasonic scaler, hand instruments, and potentially a prophy paste to remove extrinsic stains as mentioned above. this will allow a clean surface for maximum benefits of whichever tooth whitening method the patient chooses. below will discuss the various types of tooth whitening methods including both internal application of bleaching and external application through the use of bleaching agents. in-office figure 3. shade guidesvita classical a1-d4 shade guide arranged according to valuevita classical a1-d4 shade guide arranged according to chroma; a: red-brown, b: red-yellow, c: grey, d: red-grey before the treatment, the clinician should examine the patient: taking a health and dental history (including allergies and sensitivities), observe hard and soft tissues, placement and conditions of restorations, and sometimes x-rays to determine the nature and depth of possible irregularities. if this is not completed prior to the whitening agents being applied to the tooth surface, excessive sensitivity and other complications may occur. the whitening shade guides are used to measure tooth colour. these shades determine the effectiveness of the whitening procedure, which may vary from two to seven shades. these shades may be reached after a single in office appointment, or may take longer, depending on the individual. the effects of bleaching can last for several months, but may vary depending on the lifestyle of the patient. consuming tooth staining foods or drinks that have a strong colour may compromise effectiveness of the treatment. these include food and drinks containing tannins such as; coffee, tea, red wines, and curry. in-office bleaching procedures generally use a light-cured protective layer that is carefully painted on the gums and papilla (the tips of the gums between the teeth) to reduce the risk of chemical burns to the soft tissues. the bleaching agent is either carbamide peroxide, which breaks down in the mouth to form hydrogen peroxide, or hydrogen peroxide itself. the bleaching gel typically contains between 10% and 44% carbamide peroxide, which is roughly equivalent to a 3% to 16% hydrogen peroxide concentration. the legal percentage of hydrogen peroxide allowed to be given is 0.1–6%. bleaching agents are only allowed to be given by dental practitioners, dental therapists, and dental hygienists. bleaching is least effective when the original tooth color is grayish and may require custom bleaching trays. bleaching is most effective with yellow discolored teeth. if heavy staining or tetracycline damage is present on a patient's teeth, and whitening is ineffective (tetracycline staining may require prolonged bleaching, as it takes longer for the bleach to reach the dentine layer), there are other methods of masking the stain. bonding, which also masks tooth stains, is when a thin coating of composite material is applied to the front of a person's teeth and then cured with a blue light. a veneer can also mask tooth discoloration. in-chair whitening is faster and more effective in comparison to the take-home bleaching options. some clinicians also make custom bleaching trays, which can take up to a week to create. after the whitening treatment is completed, the patient is able to use these trays for maintenance of their bleaching with at-home kits or for use with desensitising products. light-accelerated bleaching power or light-accelerated bleaching uses light energy which is intended to accelerate the process of bleaching in a dental office. different types of energy can be used in this procedure, with the most common being halogen, led, or plasma arc. use of light during bleaching increases the risk of tooth sensitivity and may not be any more effective than bleaching without light when high concentrations of hydrogen peroxide are used. a 2015 study showed that the use of a light activator does not improve bleaching, has no measurable effect, and rather is likely to increase the temperature of the associated tissues, resulting in damage. the ideal source of energy should be high energy to excite the peroxide molecules without overheating the pulp of the tooth. lights are typically within the blue light spectrum as this has been found to contain the most effective wavelengths for initiating the hydrogen peroxide reaction. a power bleaching treatment typically involves isolation of soft tissue with a resin-based, light-curable barrier, application of a professional dental-grade hydrogen peroxide whitening gel (25–38% hydrogen peroxide), and exposure to the light source for 6–15 minutes. recent technical advances have minimized heat and uv emissions, allowing for a shorter patient preparation procedure. for any whitening treatments, it is recommended that a comprehensive examination of the patient is done including the use of radiographs to aid in the diagnosis of the current condition of the mouth, including any allergies that may be present. the patient will need to have a healthy mouth and free of periodontal disease or cavities and to have had a debridement/clean done to remove any tartar or plaque build up. it is recommended to avoid smoking, drinking red wine, eating or drinking any deeply coloured foods after this as the teeth may stain considerably straight after treatment. nanoparticle catalysts for reduced hydrogen peroxide concentration a recent addition to the field is new light-accelerated bleaching agents containing lower concentrations of hydrogen peroxide with a titanium oxide nanoparticle-based catalyst. reduced concentrations of hydrogen peroxide cause lower incidences of tooth hypersensitivity. the nanoparticles act as photocatalysts, and their size prevents them from diffusing deeply into the tooth. when exposed to light, the catalysts produce a rapid, localized breakdown of hydrogen peroxide into highly reactive radicals. due to the extremely short lifetimes of the free radicals, they are able to produce bleaching effects similar to much higher concentration bleaching agents within the outer layers of the teeth where the nanoparticle catalysts are located. this provides effective tooth whitening while reducing the required concentration of hydrogen peroxide and other reactive byproducts at the tooth pulp. internal bleaching internal bleaching is a process which occurs after a tooth has been endodontically treated. this means that the tooth will have had the nerve of the tooth extirpated or removed through a root canal treatment at the dentist or by a specialist endodontist. internal bleaching is often sought after in teeth which have been endodontically treated as tooth discolouration becomes a problem due to the lack of nerve supply to that tooth. it is common to have this internal bleaching done on an anterior tooth (a front tooth that you can see when smiling and talking). a way around this is by sealing off the bleaching agent inside the tooth itself and replacing it every few weeks until the desired shade has been achieved. the amount of time between appointments varies from patient to patient and with operator preference until the desired shade has been achieved. even though this is a great option, the disadvantage of this treatment is a risk of internal root resorption of the tooth that is being internally bleached. this may not occur in every patient or every tooth, and its occurrence is difficult to determine prior to completing the treatment. at home at home tooth whitening products are available from dentists or 'over the counter' (otc). at home whitening methods include over-the-counter strips and gels, whitening rinses, whitening toothpastes, and tray-based tooth whiteners. otc products can be used for milder cases of tooth staining. home-based bleaching (following manufacturer's instructions) results in less tooth sensitivity than in-office bleaching. strips and gels the plastic whitening strips contain a thin layer of peroxide gel and are shaped to fit the buccal/labial surfaces of teeth. many different types of whitening strips are available on the market, after being introduced in the late 1980s. specific whitening strip products have their own set of instructions however the strips are typically applied twice daily for 30 minutes for 14 days. in several days, tooth colour can lighten by 1 or 2 shades. the tooth whitening endpoint does depend on the frequency of use and ingredients of the product. whitening gels are applied onto the tooth surface with a small brush. the gels contain peroxide and are recommended to be applied twice a day for 14 days. the tooth whitening endpoint like that of the whitening strips. rinses whitening rinses work by reaction of the oxygen sources such as hydrogen peroxide within the rinse and the chromogens on or within the tooth. it is recommended to use twice a day, rinsing for one minute. to see an improvement in shade colour, it can take up to three months. toothpastes whitening toothpastes differ from regular toothpastes in that they contain higher amounts of abrasives and detergents to be more effective at removing tougher stains. some whitening toothpastes contain low concentrations of carbamide peroxide or hydrogen peroxide which help lighten tooth colour however they do not contain bleach (sodium hypochlorite). with continuity of use over time, tooth colour can lighten by one or two shades. tray-based tray-based tooth whitening is achieved by wearing a fitted tray containing carbamide peroxide bleaching gel overnight or for two to four hours a day. if manufacturer's instructions are followed, tooth whitening can occur within three days and lighten teeth by one or two shades. this type of tooth whitening is available over-the-counter and professionally from an oral health professional. baking soda baking soda is a safe, low abrasive, and effective stain removal and tooth whitening toothpaste. tooth whitening toothpaste that have excessive abrasivity are harmful to dental tissue, therefore baking soda is a desirable alternative. to date, clinical studies on baking soda report that there have been no reported adverse effects. it also contains acid-buffering components that makes baking soda biologically antibacterial at high concentrations and capable of preventing growth of streptococcus mutans. baking soda might be useful for cavities-prone patients, as well as those who wish to have whiter teeth. pens whitening pens are a convenient way to touch up any dental surface. the plastic, convenient, tube contains a bleaching gel that can be easily applied in hard-to-reach spots. in order to work, the gel needs to stay on the tooth surface for around 20–30 minutes. indications tooth whitening may be undertaken for a variety of reasons, but whitening may also be recommended to some individuals by dental professionals. intrinsic tooth staining aesthetics dental fluorosis endodontic treatment (internal bleaching) tetracycline staining contraindications some groups are advised to carry out tooth whitening with caution as they may be at higher risk of adverse effects. patients with unrealistic expectations allergy to peroxide pre-existing sensitive teeth cracks or exposed dentine enamel development defects acid erosion receding gums (gingival recession) and yellow roots sensitive gums defective dental restorations tooth decay. white-spot decalcification may be highlighted and become more noticeable directly following a whitening process, but with further applications the other parts of the teeth usually become more white and the spots less noticeable. active periapical pathology untreated periodontal disease pregnant or lactating women children under the age of 16. this is because the pulp chamber, or nerve of the tooth, is enlarged until this age. tooth whitening under this condition could irritate the pulp or cause it to become sensitive. younger people are also more susceptible to abusing bleaching. persons with visible white fillings or crowns. tooth whitening does not change the color of fillings and other restorative