They are infectious disease. Bacteria builds up at the tooth/gum junction, leading to relatively localised, inflammatory symptoms (gingivitis), or infiltrates further, causing a localised infection (periodontitis). These conditions progress particularly quickly if the patient’s immune defences are weakened (hereditary factors, general health status, immune deficiencies).
Dental decay (or caries) is also a bacterial infection. It leads to acidic demineralisation of the tooth enamel, developing following an imbalance in the mouth’s ecosystem.