for its use and can also contribute to lost time. the cost of dental dams is an expense to the dental practice and could also be a disincentive. although the rubber dams are inexpensive to purchase, initial costs for the armamentarium can be high. there is a risk of rubber dam clamps breaking during application due to the chemical effects of sodium hypochlorite, an antimicrobial solution used during root canal treatments, repeated stresses of clinical use, or autoclaving, all of which can potentially weaken the material. to avoid swallowing or aspiration of broken clamps, the dental practitioner should place floss around the clamp to allow its retrieval if it snaps or springs off during a procedure. as the dental dam clamp is placed along the gum line, this can cause some discomfort or pain (especially in a patient who does not require local anaesthesia), bleeding from the gums, damage to the periodontal ligament or abrasion of the cementum on the root of the tooth, which may cause an uneven surface on the tooth root that can retain plaque. the dental dam is placed over the mouth, effectively blocking off the airway, which means the patient must be able to comfortably breathe through their nose. this is a problem for patients with nasal airway obstruction such as the common cold, a broken nose, adenoids, recurring sinus issues, or those who habitually breathe through their mouths. patients can also find that communication is reduced between the dental practitioner and themselves, which may result in feelings of claustrophobia, vulnerability, and anxiety. those prone to dental phobia and individuals who have learning difficulties, disabilities or special needs may find the use of dental dams impossible and intolerable. to an extent, the use of a dental dam may lead to visual distortion of tooth morphology since the other teeth and the rest of the mouth are hidden from view. this may lead to perforation if an access cavity is incorrectly angled during root canal therapy. for this reason, endodontists may routinely begin their access cavity before applying the dam. this will ensure the correct orientation prior to commencing removal of the blood vessels, nerve tissue and other cellular entities from the tooth. the rubber dam, which is usually brightly coloured (blue or green), may alter the apparent colour of the tooth, which can lead to incorrect choice of shade, e.g. during placement of a dental composite during a restorative procedure. for this reason, dental practitioners should select the appropriate shade of material prior to the application of rubber dam. as the rubber dams are primarily made of latex, patients may experience reactions which range from uncomfortable (allergic contact dermatitis, allergic contact cheilitis, allergic contact stomatitis) to life-threatening (anaphylaxis). nitrile versions are available for those with latex allergies and adverse reactions can be avoided by patients informing dental practitioners of latex allergies prior to treatment or adverse reactions after rubber dam application. oral sex repurposing of a condom into a dam. flavoured dams packaged for sale as a safer sex product. dental dams are sometimes suggested for use as a physical barrier against the exchange of body fluids during cunnilingus and anilingus, especially for women who have sex with women to protect against sexually transmitted infections (stis). however, they are rarely used for this purpose, and there is no good evidence that their use reduces the risk of sti transmission, including the risk of hiv infection. after lubrication with a water-based lubricant, an unpunctured dental dam may be held over the vulva or anus, allowing oral stimulation of these areas without transmission of bodily fluids or direct physical contact. plastic cling wrap, condoms (repurposed by cutting off the tip and ring and cutting them lengthwise) or latex gloves (cut open longitudinally) can be used for sti protection in a similar manner as a dental dam, by providing a physical barrier to cover the vaginal or anal areas during oral sex and these alternative barrier methods are more affordable and readily available than dental dams. dental dams were initially promoted in the 1980s in some safer sex campaigns as a barrier to prevent transmission of stis during oral sex. they were introduced for use in some women's prisons in canada and australia (in the jurisdictions of new south wales, the australian capital territory, western australia, and south australia) in the 1990s as a form of sexual barrier protection after the world health organization (who) recommended that female prisoners should have access to dental dams. inmates have reported numerous problems with dental dam use, including the dam being too thick, lack of availability, poor taste, and reduced sensations when used for oral sex. dental dams are often reappropriated by prison inmates for other uses, such as hair elastics, placemats or shoelaces. they are relatively expensive and difficult to obtain outside of the prison system. rubber dams are not manufactured, marketed, registered, tested, or evaluated for their effectiveness as an sti prevention aid, and no studies exist (as of 2010) on their permeability to sti pathogens.