Before the start of the selected chemotherapy patients will be treated preventively for oral mucositis. A group will carry out the mouthwash with chlorhexidine 0.12% twice a day for five days and another will be held to damage preventive therapy (wavelength of 660nm, power 100mW and lluencia of 4 J / cm² per point, with distance of 2cm between points located on the right buccal mucosa, left buccal mucosa, hard palate, upper lip and lower lip). Patients who develop oral mucositis even after the prevention, will be divided into three groups for laser sessions with the purpose of treatment of oral mucositis. The group assignment obeyed severity of oral mucositis. Group 1 will include patients with oral mucositis grade 1. Sera used wavelength of 660nm, power 100mW and lluencia of 4 J / cm². Group 2 included patients with oral mucositis grade 2. Sera used with a wavelength of 660nm, power 100mW and lluencia of 8 J / cm². Group 3 included patients with oral mucositis grade 3 Sera used laser diode AsGaAl operating in continuous mode, with a wavelength of 790 nm, power of 100mW and fluency of 8 J / cm².

Before the start of the selected chemotherapy patients will be treated preventively for oral mucositis. A group will carry out the mouthwash with chlorhexidine 0.12% twice a day for five days and another will be held to damage preventive therapy (wavelength of 660nm, power 100mW and lluencia of 4 J / cm² per point, with distance of 2cm between points located on the right buccal mucosa, left buccal mucosa, hard palate, upper lip and lower lip). Patients who develop oral mucositis even after the prevention, will be divided into three groups for laser sessions with the purpose of treatment of oral mucositis. The group assignment obeyed severity of oral mucositis. Group 1 will include patients with oral mucositis grade 1. Sera used wavelength of 660nm, power 100mW and lluencia of 4 J / cm². Group 2 included patients with oral mucositis grade 2. Sera used with a wavelength of 660nm, power 100mW and lluencia of 8 J / cm². Group 3 included patients with oral mucositis grade 3 Sera used laser diode AsGaAl operating in continuous mode, with a wavelength of 790 nm, power of 100mW and fluency of 8 J / cm².

The assessment of oral mucositis will be held with the WHO classification: grade 0 = no mucositis; Grade I = erythema without injury; Grade II = ulcers, but can eat; Grade III = painful sores, but able to consume liquid food (nutrition), with support of analgesia; Grade IV = requires parenteral or enteral support and continuous analgesia.

The patient also conduct a self-assessment of pain by visual analog scale pain quantifying 0-10 before the laser section and after the first application.

Pediatric male or female, diagnosed with cancer who have not yet started cancer treatment, with otherwise healthy oral mucosa in the initial dental exam.

Patients who have already started treatment for cancer under radiotherapy or presenting traumatic factors (such as braces or restorations with sharp edges), or presenting ulcers in the mucosa at the initial examination.

Inclusion Criteria:

• Pediatric male or female, diagnosed with cancer who have not yet started cancer treatment, with otherwise healthy oral mucosa in the initial dental exam.

Exclusion Criteria:

• Patients who have already started treatment for cancer under radiotherapy or presenting traumatic factors (such as braces or restorations with sharp edges), or presenting ulcers in the mucosa at the initial examination.