A broad spectrum of infections can occur in the oral cavity. These can be classified according to the etiological agent in bacteria, viruses and fungi. The most common bacterial infections are more putative in the hard tissues of the teeth, the pulp organ and periodontal tissues. Fungal infections are caused by opportunistic fungi that are generally present in the oral microbiota. In the oral and perioral regions, they are mainly attributed to Candida albicans. As far as viral infections are concerned, the oral and perioral cavity can be infected with numerous viruses, each capable of determining a rather distinct clinical-pathological picture. Herpes viruses are the most common and, in most cases, cause local disease in the short term. Human papillomaviruses are responsible for clinically distinct, rosy-white, exophytic verruca-papillary lesions with a typical surface alteration that gives a granular or cauliflower appearance.

The oral tissues, for obvious anatomical reasons, are exposed to continuous mechanical and inflammatory traumatic insults. Both reactive and pure traumatic hyperplastic injuries have been dealt with in this chapter. Reactive hyperplastic lesions are tumor-like hyperplasias caused by a tumor-like non-neoplastic proliferation due to chronic irritative stimuli. The most common reactive lesions include morsicatio labiorum, buccarum and traumatic fibroma. Among the purely traumatic ones, hematoma, ecchymosis and mucocele (affecting the minor salivary glands) stand out. These lesions can be generalized to large areas of the mucous membrane of the oral cavity or localized as solitary neoformations. Furthermore, according to the clinical aspect, they can be divided into plain (e.g., keratosis), exophytic (e.g., mucocele and fibroma) and endophytic (e.g., traumatic ulcers). Reactive traumatic injuries often present diagnostic challenges because they mimic other pathologies of a non-traumatic nature. 

Autoimmune diseases are caused by autoantibodies targeting structural proteins present in the skin and mucosa. The oral mucosa is frequently affected in these diseases, in particular by lichen planus, recurrent aphthous stomatitis, erythema multiforme, Stevens-Johnson syndrome and pemphigus. Clinical symptoms are heterogeneous and may present clinically with erythema, erosions and ulcers localized on the oral mucosa, causing a plethora of local and systemic symptoms, including pain, dysphagia, difficulty in eating and speaking and general malaise. The multiplicity and similarity of the clinical manifestations of these pathologies make an accurate diagnosis based only on the clinic extremely difficult. Therefore, to make a correct differential diagnosis, the clinic must be accompanied by a histopathological examination. The management of oral lesions accompanied by painful symptoms is challenging and requires a multidisciplinary approach. The main purpose of treatment is usually directed at reducing the pain and discomfort caused, controlling the worsening of the disease, and preventing complications.

The oral cavity reflects the general health of the organism. Signs of a systemic or syndromic pathology often appear first in the oral cavity rather than systemically. Systemic diseases that can cause oral manifestations include endocrinopathies, oncological, cardiovascular, gastrointestinal and neurological diseases. Oral lesions caused by the treatment of systemic diseases can also be clinically significant, including those caused by cancer therapies (mucositis) and drugs that alter salivary flow. Some clinically observable changes in the oral cavity are disease-specific, while others may simply increase the dentist's level of suspicion. This short chapter deals with some important systemic pathologies with labial manifestation: Crohn's disease, Melkersson-Rosenthal syndrome, and chemotherapy-induced mucositis in cancer patients.

Malformative lesions of vascular origin should be considered among the neoplasms of the facial soft tissues. These comprise a very heterogeneous group that can be classified into tumors and vascular malformations. Vascular malformations are characterized by a structural defect of blood vessels that have a physiological turnover of endothelial cells resulting from a malformation during development. They can, in turn, be sporadic or associated with genetic mutations. They are classically divided into low or high-flow vascular malformations. The former have no arterial component and are classified according to their predominant endothelial cell type as capillary, venous, lymphatic or combined. The latter has an arterial component and includes arterial malformations, arteriovenous malformations, arteriovenous capillary malformations and arteriovenous fistulas. Vascular tumors include benign and malignant neoplasms of endothelial cellular origin. Among the most common vascular tumors, hemangioma stands out. Pyogenic granuloma (lobular capillary hemangioma) is the most commonly diagnosed subtype of benign endothelial neoplasia in the oral cavity. Furthermore, most oral pyogenic granulomas are considered reactive rather than neoplastic proliferations. Among the malignant ones, much rarer, Kaposi's sarcoma and angiosarcoma emerge.

Labial potentially malignant disorders of the oral cavity are one of the main risk factors for the onset of oral cancer. Oral cancer now accounts for 3-5% of malignant tumors in Western world statistics. For this reason, the treatment of precancerous diseases of the oral cavity assumes an undeniable importance in preventing the onset of this pathology. Pre-cancers of the oral cavity include the forms with the highest risk of malignant transformation (erythroplasia, homogeneous and non-homogeneous leukoplakia) and the other forms with a low index of malignant transformation (lichen planus, oral submucosal fibrosis, leucoplakia, and chronic hyperplastic candidiasis). The cause of the onset of the precancerous oral cavity is unknown, but there are usually some risk factors that, alone or in combination, play an action favoring the appearance of the mucosal lesion. The main risk factors for precancerous lesions in the oral cavity are tobacco, alcohol, chronic local trauma, poor oral hygiene, chronic dietary and vitamin deficiencies, exposure to diagnostic and therapeutic ionizing radiation, viral and fungal infections and immunological factors. In this chapter, we will focus on actinic cheilitis, an extremely common precancerous condition of the lips, and oral cancer.

The diagnosis of oral mucosal pigmentations is complex, and histopathological evaluation may be necessary to clarify the nature of the lesion. Although most oral pigmented lesions are benign, it must be emphasized that melanoma of the oral cavity, probably the most aggressive epithelial tumor, is often underestimated and diagnosed late. The dentist, therefore, should have basic knowledge of the main epidemiological and clinical characteristics of this large group of lesions. Pigmented lesions associated with melanin include racial pigmentations, melanotic macules, smoking-associated melanosis, melanocytic nevi, melanoacanthoma, and melanoma. Some systemic diseases (for example, Peutz-Jeghers syndrome and Laugier-Hunziker syndrome) are also characterized by the presence of melanin lesions in the oral mucosa. In the literature, there are also some cases of pigmentation caused by melanin in association with the intake of drugs and as a consequence of some postinflammatory mechanisms. Pigmented lesions not associated with melanin are subdivided according to the nature of the pigment responsible for the discoloration. The pigmentations caused by the deposition of exogenous pigments are represented by some metals (for example, amalgam, tattoo), drugs, or their metabolites.

Photodynamic therapy (PDT) is one of the most innovative therapies currently available with no side effects. Initially introduced for the treatment of dermatological pathologies, it is now used in numerous medical fields, as well as in oral pathology. PDT has antimicrobial effects and can be used in several infections. The mechanism of action of PDT is based on the application of a dye called photosensitizer, which is activated by a precise wavelength. The photosensitizer is activated by specific wavelengths based on the chemical characteristics. Its activation involves the formation of reactive oxygen species that determine the death of the altered cells. Phototherapy is a therapeutic medical treatment based on the use of a special optical unit capable of emitting light, which can be used with or without UV radiation. Phototherapy acts as a natural and non-invasive therapy, capable of transferring energy to the cells of the organism, promoting regenerative capabilities. The aim of our work is to report our clinical experience in the treatment of some lip pathological conditions with phototherapy and PDT.