Malnutrition is a clinical-social disease caused by multiple prenatal, intrauterine and postnatal factors as well as social, political and cultural determinants (distal causes). Despite the global and national reductions in the number of cases, malnutrition continues to be a public health problem, with greater prevalence in pockets of poverty found in the northern and northeastern regions of Brazil.

Episodes of malnutrition in early childhood, with consequent calcium, phosphate and vitamin A, C and D deficiencies, can increase one's susceptibility to dental caries through three probable mechanisms: defects in tooth formation (odontogenesis), delayed tooth eruption and alterations in the salivary glands.

It is likely that the significant increase in susceptibility to caries in malnourished individuals stems from alterations in the salivary secretion rate, since a reduction in salivary flow (salivary gland atrophy) increases the susceptibility to both dental caries and dental erosion. As saliva is the main defense factor of the oral cavity, a reduction/change in its physical properties (secretion rate and buffering capacity) can cause immunological disorders that affect an individual's defense capacity.

Studies have demonstrated that salivary immunoglobulin A (IgA) also plays an important role in the immunity of the oral mucosa. Indeed, patients with IgA deficiency can experience recurring upper airway (tonsillitis, ear infection and sinusitis), lower airway (pneumonia) and gastrointestinal (diarrhea and parasitosis) infections.

The investigation of mechanisms that can reduce the impact of malnutrition on the defenses of the organism is of the utmost important and interest to public health. Among such mechanisms, low-level laser therapy has demonstrated effectiveness in the treatment of diverse conditions and disease through the promotion of the biomodulation of the cell metabolism and due to its analgesic and anti-inflammatory properties with no mutagenic or photothermal effects.

Laser stimulation of the major salivary glands to produce more saliva occurs through the increase in local circulation due to vasodilatation, the induction of the proliferation of glandular cells and cell respiration/ATP (adenosine triphosphate) synthesis as well as the release of growth factors and cytokines to stimulate protein exocytosis. With regard to an increase in salivary IgA, low-level laser intensifies the activation of B lymphocytes, which differentiate into plasma cells, thereby contributing to the increase in immunoglobulin levels.

The study of salivary aspects in malnourished children and possible treatments that can be used to improve salivary quality and quantity in these children has significant social relevance, as saliva is one of the main mechanisms against infection and participates in essential functions of life, such as swallowing and the maintenance of oral health.

An experimental cross-sectional study is proposed, which will be conducted at the Center for Educational and Nutrition Recovery in the city of Maceió, state of Alagoas, Brazil, and University Nove de Julho (UNINOVE) in the city of Sao Paulo, Brazil. This project has been approved by CESMAC ethics committee (CAAE 71961317.1.0000.0039).

Inclusion Criteria:

• Children aged one to five years enrolled at the Center for Educational and Nutrition Recovery in the city of Maceió whose parent/guardians signed as statement of informed consent agreeing to the participation of the children.
• Children suffering of malnutrition.

Exclusion Criteria:

• Children aged one to five years not enrolled at the Center for Educational and Nutrition Recovery in the city of Maceió and children whose parents/guardians did not sign a statement of informed consent.
• Children not suffering of malnutrition.