Background: In recent years, scientific interest in probiotics in oral health has grown exponentially. This systematic review aims to analyze the effectiveness of probiotic use in dentistry, specifically in two areas: orthodontics and pediatric dentistry. Methods: Forty studies (RCTs, systematic reviews, clinical and preclinical studies) published between 2001 and 2025 were selected from the literature (PubMed) to evaluate the impact of probiotics on clinical, microbiological, and patient-specific parameters. Results: Results generally indicate that the most observed effect is the reduction in Streptococcus mutans levels, while in orthodontics, probiotics have proven beneficial primarily in reducing halitosis and traumatic lesions. In pediatric dentistry, early and prolonged use of probiotics has been shown to benefit both the reduction in caries and the improvement of gingival health, with significant results also observed in pediatric patients with special needs. Conclusions: Although the data obtained so far are very encouraging, further clinical studies are needed to define standardized protocols, identify the most effective strains, and evaluate the effects of long-term probiotic use. Probiotics therefore represent a promising and potentially valuable addition to preventive strategies in dentistry, particularly in orthodontics and pediatric dentistry, when integrated into a sustainable and personalized approach to patient oral health.