Localized Periodontitis in Young Individuals: Aggregatibacter JP2 Clone, Immunological Dysfunctions and Other Stories

Grade C molar-incisor pattern periodontitis (C-MIP) is the latest in a series of names given to a unique phenotype, characterized by an aggressive and rapid loss of tooth-supporting structures, starting early in life and usually affecting first molars and incisors. Although much less prevalent than the more generalized "chronic" forms of this disease in adults, it affects mostly young individuals of lower socioeconomic status and African descent, or from mixed-race populations, and shows a strong familial aggregation, pointing to a possible genetic contribution, yet not fully elucidated. Even though most of the studies report this disease in adolescents/young adults, it can also be diagnosed in the primary dentition, frequently in the first molar. Thus, proper periodontal examination and radiographs in children are crucial for early diagnosis and treatment. The rapid periodontal breakdown in this disease is also associated with specific microorganisms and a dysfunctional inflammatory response of the host. A. actinomycetemcomitans has been strongly implicated in C-MIP severity and progression, although newer technologies have pointed to the influence of other associated species implicated in this disease in different populations. Additionally, a pro-inflammatory profile along with hypo/hyperactivity of the cellular innate response has been observed in C-MIP. Genetic studies have supported evidence of family aggregation, although specific genes are yet to be identified. Several clinical therapies have been proposed to treat C-MIP over time, and non-surgical periodontal therapy with adjunctive systemic antibiotics has shown a favorable impact on clinical, immunological, and microbiological outcomes in the short and long term in both primary and permanent dentition. This paper aims to review this unique disease, its proposed pathogenic mechanisms, risk factors, treatment outcomes, and the remaining gaps that still require investigation.