The Kennedy classification quantifies partial edentulism. An outline is covered at the removable partial denture article.

Physiologically, teeth provide for greater chewing ability. They allow us to masticate food thoroughly, increasing the surface area necessary to allow for the enzymes present in the saliva, as well as in the stomach and intestines, to digest our food. Chewing also allows food to be prepared into small boli that are more readily swallowed than haphazard chunks of considerable size. For those who are even partially endentulous, it may become extremely difficult to chew food efficiently enough to swallow comfortably, although this is entirely dependent upon which teeth are lost. When an individual loses enough posterior teeth to make it difficult to chew, he or she may need to cut their food into very small pieces and learn how to make use of their anterior teeth to chew. If enough posterior teeth are missing, this will not only affect their chewing abilities, but also their occlusion; posterior teeth, in a mutually protected occlusion, help to protect the anterior teeth and the vertical dimension of occlusion and, when missing, the anterior teeth begin to bear a greater amount of force for which they are structurally prepared. Thus, loss of posterior teeth will cause the anterior teeth to splay. This can be prevented by obtaining dental prostheses, such as removable partial dentures, bridges or implant-supported crowns. In addition to reestablishing a protected occlusion, these prostheses can greatly improve one's chewing abilities.

As a consequence of a lack of certain nutrition due to altered eating habits, various health problems can occur, from the mild to the extreme. Lack of certain vitamins (A, E and C) and low levels of riboflavin and thiamin can produce a variety of conditions, ranging from constipation, weight loss, arthritis and rheumatism. There are more serious conditions such as heart disease and Parkinson's disease and even to the extreme, certain types of Cancer. Treatments include changing approaches to eating such as cutting food in advance to make eating easier and less likely to avoid as well as consumer health products such as multivitamins and multi-minerals specifically designed to support the nutritional issues experienced by denture wearers.

Numerous studies linking edentulism with instances of disease and medical conditions have been reported. In a cross-sectional study, Hamasha and others found significant differences between edentulous and dentate individuals with respect to rates of atherosclerotic vascular disease, heart failure, ischemic heart disease and joint disease.

There are 4 aspects to the treatment of angular cheilitis. Firstly, potential reservoirs of infection inside the mouth are identified and treated. Oral candidiasis, especially denture-related stomatitis is often found to be present where there is angular cheilitis, and if it is not treated, the sores at the corners of the mouth may often recur. This involves having dentures properly fitted and disinfected. Commercial preparations are marketed for this purpose, although dentures may be left in dilute (1:10 concentration) household bleach overnight, but only if they are entirely plastic and do not contain any metal parts, and with rinsing under clean water before use. Improved denture hygiene is often required thereafter, including not wearing the denture during sleep and cleaning it daily. For more information, see Denture-related stomatitis.

Secondly, there may be a need to increase the vertical dimension of the lower face to prevent overclosure of the mouth and formation of deep skin folds. This may require the construction of a new denture with an adjusted bite. Rarely, in cases resistant to normal treatments, surgical procedures such as collagen injections (or other facial fillers such as autologous fat or crosslinked hyaluronic acid) are used in an attempt to restore the normal facial contour. Other measures which seek to reverse the local factors that may be contributing to the condition include improving oral hygiene, stopping smoking or other tobacco habits and use of a barrier cream (e.g. zinc oxide paste) at night.

Thirdly, treatment of the infection and inflammation of the lesions themselves is addressed. This is usually with topical antifungal medication, such as clotrimazole, amphotericin B, ketoconazole, or nystatin cream. Some antifungal creams are combined with corticosteroids such as hydrocortisone or triamcinolone to reduce inflammation, and certain antifungals such as miconazole also have some antibacterial action. Diiodohydroxyquinoline is another topical therapy for angular cheilitis. If "Staphylococcus aureus" infection is demonstrated by microbiological culture to be responsible (or suspected), the treatment may be changed to fusidic acid cream, an antibiotic which is effective against this type of bacteria. Aside from fusidic acid, neomycin, mupirocin, metronidazole, and chlorhexidine are alternative options in this scenario.

Finally, if the condition appears resistant to treatment, investigations for underlying causes such as anemia or nutrient deficiencies or HIV infection. Identification of the underlying cause is essential for treating chronic cases. The lesions may resolve when the underlying disease is treated, e.g. with a course of oral iron or B vitamin supplements. Patch testing is recommended by some in cases which are resistant to treatment and where allergic contact dermatitis is suspected.

Most cases of angular cheilitis respond quickly when antifungal treatment is used. In more long standing cases, the severity of the condition often follows a relapsing and remitting course over time. The condition can be difficult to treat and can be prolonged.

Common causes of drug-related cheilitis include Etretinate, Indinavir, Protease inhibitors, Vitamin A and Isotretinoin (a retinoid drug). Uncommon causes include Atorvastatin, Busulphan, Clofazimine, Clomipramine, Cyancobalamin, Gold, Methyldopa, Psoralens, Streptomycin, Sulfasalazine and Tetracycline. A condition called "drug-induced ulcer of the lip" is described as being characterized by painful or tender, well-defined ulcerations of the lip without induration. It is the result of oral administration of drugs, and the condition resolves when the drugs are stopped.

Also termed "lip dermatitis", eczematous cheilitis is a diverse group of disorders which often have an unknown cause. Chronic eczematous reactions account for the majority of chronic cheilitis cases.

It is divided into endogenous (due to an inherent characteristic of the individual), and exogenous (where it is caused by an external agent). The main cause of endogenous eczematous cheilitis is atopic cheilitis (atopic dermatitis), and the main causes of exogenous eczematous cheilitis is irritant contact cheilitis ("e.g.", caused by a lip-licking habit) and allergic contact cheilitis. The latter is characterized by a dryness, fissuring, edema, and crusting. It affects females more commonly than males, in a ratio of about 9:1.

The most common causes of allergic contact cheilitis is lip cosmetics, including lipsticks and lip balm, followed by toothpastes. A lipstick allergy can be difficult to diagnose in some cases as it is possible that cheilitis can develop without the person even wearing lipstick. Instead, small exposure such as kissing someone who is wearing lipstick is enough to cause the condition.

Allergy to Balsam of Peru can manifest as cheilitis. Allergies to metal, wood, or other components can cause cheilitis reactions in musicians, especially players of woodwind and brass instruments, "e.g.", the so-called "clarinetist's cheilitis", or "flutist's cheilitis". "Pigmented contact cheilitis" is one type of allergic cheilitis in which a brown-black discoloration of the lips develops. Patch testing is used to identify the substance triggering allergic contact cheilitis.