Impacto da radioterapia de cabeça e pescoço nos tecidos dentários: alterações estruturais e efeito de dentifrícios fluoretados

Abstract

Radiotherapy is one of the main therapeutic modalities used in the treatment of head and neck cancer. However, it may lead to complex oral complications. Radiation-related caries (RRC) is characterized by a more rapid and aggressive progression than conventional dental caries, typically initiating with enamel cracking and delamination, followed by dentin exposure to the oral environment. The direct effects of ionizing radiation on dental tissues include changes in microhardness, disruption of the collagen network, and obliteration of dentinal tubules, making the management of this condition particularly challenging and highlighting the importance of preventive strategies. Although the efficacy of fluoride is well established, evidence regarding the effects of different fluoride concentrations on irradiated dental substrates remains limited. The aim of this thesis was to evaluate the structural alterations induced by radiotherapy in dental tissues and to investigate the effects of toothpastes containing different fluoride concentrations on irradiated tissues through complementary studies, encompassing structural and crystallographic changes as well as the response of dental tissues to fluoride-based preventive strategies. To achieve this, three in vitro laboratory studies were conducted, presented as Chapters 1, 2, and 3. Chapter 1 aimed to correlate the mechanical and solubility properties of enamel with radiation-induced crystallographic changes, considering the proximity to the dentino-enamel junction (DEJ). The methodologies included two-dimensional synchrotron radiation X-ray microdiffraction (SR-µXRD), Vickers microhardness, fracture toughness, and citric and lactic acid solubility tests. The irradiated enamel exhibited lower microhardness values and greater acid solubility than the non-irradiated enamel. Furthermore, SR-µXRD revealed changes in the crystallographic parameters and texture of irradiated hydroxyapatite. Chapter 2 investigated the effects of radiation on the surface properties of demineralized human dentin following pH cycling and toothpaste treatment. Knoop microhardness, Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM) were employed. Under the in vitro conditions of this study, irradiated and non-irradiated dentin showed similar behavior regarding microhardness and surface roughness after being subjected to the same pH-cycling protocol and treatment with fluoride toothpastes. Chapter 3 evaluated the effects of toothpastes containing different fluoride concentrations on the mechanical and surface properties of irradiated and non-irradiated dentin after pH cycling. The same methodologies described in Chapter 2 were used. The results demonstrated that different fluoride concentrations produced distinct responses in irradiated dentin. The toothpaste containing 5,000 ppm fluoride resulted in higher microhardness values and lower surface roughness than the fluoride-free toothpaste and the 1,450 ppm fluoride toothpaste. In conclusion, head and neck radiotherapy promotes significant structural changes in dental tissues, as evidenced by crystallographic alterations in enamel hydroxyapatite. Furthermore, fluoride toothpastes demonstrated the potential to mitigate the deleterious effects of ionizing radiation on dentin.