materials. it does not affect porcelain, other ceramics, or dental gold. however, it can slightly affect restorations made with composite materials, cements and dental amalgams. tooth whitening will not restore color of fillings, porcelain, and other ceramics when they become stained by foods, drinks, and smoking, as these products are only effective on natural tooth structure. as such, a shade mismatch may be created as the natural tooth surfaces increase in whiteness and the restorations stay the same shade. whitening agents do not work where bonding has been used and neither is it effective on tooth-colored filling materials. other options to deal with such cases are the porcelain veneers or dental bonding. individuals with poor oral hygiene risks some of the common side effects involved in teeth whitening are increased sensitivity of the teeth, gum irritation, and extrinsic teeth discolouration. hypersensitivity main article: dentine hypersensitivitythe use of bleach with extremely low ph levels in the tooth whitening procedure may lead to hypersensitive teeth, as it causes the dentinal tubules to open. exposure to cold, hot, or sweet stimuli may further exacerbate the intensity of the hypersensitive response. amongst those who receive in-office whitening treatment, between 67 and 78% of the individuals experience sensitivity after the procedure where hydrogen peroxide and heat is utilized. although it varies from person to person, sensitivity after whitening treatment can last up to 4–39 days. potassium nitrate and sodium fluoride in toothpastes are used to ease discomfort following bleaching, however, there is no evidence to suggest that this is a permanent method to eradicate the issue of hypersensitivity. irritation of mucous membranes hydrogen peroxide is an irritant and cytotoxic. hydrogen peroxide with concentrations of 10% or higher can cause tissue damage, be corrosive to mucous membranes and cause burning sensation to the skin. chemical burns can commonly occur whilst bleaching, irritation and discolouration of the mucous membranes may occur if a high concentration of oxidising agent comes in to contact with unprotected tissue. poorly fitting bleaching trays are amongst the most common reasons for chemical burns. the temporary burning induced by whitening treatments can be reduced by using custom-made plastic trays or nightguards provided by the dental professional. this prevents the leakage of solution onto the surrounding mucosa. uneven results uneven results are quite common after bleaching. consuming less foods and drinks that cause surface staining of teeth can contribute to attaining a good result from tooth whitening. return to original pre-treatment shade nearly half the initial change in colour provided by an intensive in-office treatment (i.e., one hour treatment in a dentist's chair) may be lost in seven days. rebound is experienced when a large proportion of the tooth whitening has come from tooth dehydration (also a significant factor in causing sensitivity). as the tooth rehydrates, tooth colour "rebounds", back toward where it started. over-bleaching over-bleaching, more often known as the "bleached effect", occurs among treatments that promise a large change over a short period of time e.g., hours. over-bleaching can emit a translucent and brittle appearance. damage to enamel teeth enamel can have an adverse negative effect by whitening treatment. evidence from studies show that carbamide peroxide present in whitening gels can damage the enamel surface. although this effect is not as damaging as phosphoric acid etch, the increased irregularity of the teeth surface makes the teeth more susceptible to extrinsic staining, thus having an increased detrimental effect on the aesthetics. the increased porosity and changes in surface roughness may have an impact on the formation of supra- and subgingival plaque, thus increasing the adhesion of bacterial species such as streptococcus mutans and streptococcus sobrinus, significant contributors to dental cavities. dental restorations are susceptible to unacceptable colour change even when using the home-based systems. weakened dentine intracoronal bleaching is a tooth whitening method that uses 30% more hydrogen peroxide. such tooth whitening methods can weaken the mechanical properties of dentine and could potentially lead to severe tooth sensitivity. effects on existing restorations dental restorations are susceptible to unacceptable colour change even when using the home-based systems. ceramic crowns – aggressive bleaching can chemically react with ceramic crowns and reduce their stability. dental amalgam – exposure to carbamide peroxide solutions increase mercury release for one to two days. the release of amalgam components is said to be due to active oxidation. this increase in amalgam mercury release is proportional to the concentration of carbamide peroxide. resin composite – bond strength between enamel and resin based fillings become weakened. many studies have found that 10-16% carbamide peroxide tooth bleaching gels (containing approximately 3.6-5.76% hydrogen peroxide) leads to an increase in the surface roughness and porosity of composite resins. however, the saliva may exert a protective effect. in addition, changes in the reflectance of the composite have been analysed following whitening with high concentration (30-35%) hydrogen peroxide. this suggests that tooth whitening negatively impacts composite resin restorations. glass ionomer and other cements – studies suggest that solubility of these materials may increase. bleachorexia bleachorexia is the term that is used to describe an individual that develops an unhealthy obsession with teeth whitening. this condition is similar to body dysmorphic disorder. the characteristics of bleachorexia are the continuous use of whitening products even though the teeth cannot possibly become whiter, despite the provision of repeated treatment. a person with bleachorexia will continually seek out for different whitening products, hence, it is recommended that a target shade is agreed upon before starting the treatment procedure to help with this problem. home teeth whitening risks the use of personalised home whitening trays is a patient administered therapy that is prescribed and dispensed by a dentist. patients need to actively participate in their treatment and follow the guidelines given by the dentist accurately. erratic or inaccurate use of the bleaching trays could cause harm to the patient such as blistering or sensitivity of the teeth and the surrounding soft tissue. inconsistent use of the bleaching trays can lead to the slowing and irregularity of the whitening process. some patients with a substantial gag reflex may not be able to tolerate the trays and would need to consider other methods of teeth whitening. other risks evidence suggests that hydrogen peroxide might act as a tumour promoter. although cervical root resorption is more evidently observed in thermocatalytic bleaching methods, intracoronal internal bleaching may also lead to tooth root resorption. moreover, severe damage to intracoronal dentine and tooth crown fracture can occur due to this bleaching method. however, the international agency of research on cancer (iarc) has concluded that there is insufficient evidence to prove that hydrogen peroxide is a carcinogen to humans. recently, the genotoxic potential of hydrogen peroxide was evaluated. the results indicated that the oral health products that contain or release hydrogen peroxide up to 3.6% will not increase the cancerous risk of an individual, hence, it is safe to use in moderation. maintenance despite achieving the results of treatment, stains can return within an initial couple of months of treatment. various methods may be employed to prolong the treatment results, such as: brush or flush out mouth with water after eating and drinking floss to remove plaque and biofilms between the teeth take special care during the first 2 days – the first 24–48 hours after the whitening procedure is seen as the most crucial period in which you must protect for your teeth the most. hence, it is vital that non-staining drinks or foods are eaten during this time as enamel is prone to adhere to stains. drink fluids that may cause staining through a straw depending on the method used to whiten the teeth, re-treatment every six months or after a year may be required. if an individual is a smoker or they consume beverages with the capacity to stain, regular re-treatments would be required. history teeth whitening remedies have been present since ancient times. despite seeming absurd, some methods were somewhat effective in their results. ancient roman dentists believed in using urine with goat milk to make their teeth look whiter. pearly white teeth symbolized beauty and marked wealth. in the auyrveda medicine system, oil pulling was used as an oral therapy. for this process today, swish coconut or olive oil in your mouth for up to 20 minutes each day. in the late 17th century, many people reached out to barbers, who used a file to file down the teeth before applying an acid that would, in fact, whiten the teeth. although the procedure was successful, the teeth would become completely eroded and more prone to becoming decayed. guy de chauliac suggested the following to whiten the teeth: "clean the teeth gently with a mixture of honey and burnt salt to which some vinegar has been added." in 1877, oxalic acid was proposed for whitening, followed by calcium hypochlorite. in the late 1920s, mouthwash containing pyrozone (ether peroxide) was found to reduce cavities while providing a whiter appearance to the teeth. by 1940s and 1950s, ether and hydrogen peroxide gels were used to whiten vital teeth, whereas non-vital teeth were whitened using pyrozone and sodium perborate. in the late 1960s, dr william klusmeier, an orthodontist from fort smith, arkansas, introduced the custom tray bleaching. however, it was not until 1989 that haywood and heymann published an article in support of this method. carbamide peroxide with a shelf life of one to two years, as opposed to hydrogen peroxide with a shelf life one to two months, was seen as a more stable agent for whitening teeth. society and culture teeth whitening has become the most promoted and mentioned methodology in cosmetic dentistry. in excess of 100 million americans brighten their teeth using different methods; spending $15 billion in 2010. the us food and drug administration only endorses gels that are under 6% hydrogen peroxide or 16% or less of carbamide peroxide. the scientific committee on consumer safety of the eu consider gels containing higher fixations can be dangerous. as per european council guidelines, only a certified dental professional can lawfully give tooth whitening products utilizing 0.1–6% hydrogen peroxide, provided the patient is 18 years of age or older. in 2010, the uk general dental council became concerned of the "risk to patient safety from poor quality tooth whitening being carried out by untrained or poorly trained staff." a public attitudes survey, conducted by the gdc, showed that 83% of people support "policies of regulating tooth whitening to protect patient safety and prosecuting illegal practice." a group of dental professionals and associations called the tooth whitening information group (twig) was founded to advance protected and beneficial tooth whitening information and assistance to the general population. reports can be made to the twig through their website with respect to any individual giving unlawful tooth whitening services, or if an individual has personally undergone treatment done by a non-dental professional. in brazil, all whitening items are classed as cosmetics (degree ii). there are worries that this will bring about increasing abuse of whitening products and thus there have been calls for reanalysis. according to research, tooth whitening can produce positive changes in young participants’ oral health related quality of life (ohrqol) in aesthetic areas such as smiling, laughing, and showing teeth without embarrassment. however, its main side-effect, tooth sensitivity, does negatively affect quality of life.