Background: Type 1 diabetes mellitus (T1DM) is the most common form of diabetes in children and adolescents, and its incidence and prevalence are rising worldwide. The disease has a profound impact on lifestyle, and the oral cavity is among the most frequently affected organs. Evidence from previous research suggests a complex association between TIDM and dental caries, yet the influence of metabolic control on oral health remains insufficiently defined. This study aimed to assess caries status in the permanent dentition of children and adolescents with T1DM and to determine whether poor metabolic control, measured by glycated hemoglobin (HbA1c), is associated with oral health outcomes. Methods: A cross-sectional study was conducted at the Dental Clinic of the University of Salamanca (Spain) between 2020 and 2025. The study included 300 children aged 6–12 years with T1DM, divided into two groups according to the International Society for Paediatric and Adolescent Diabetes (ISPAD) criteria: 150 with good metabolic control (HbA1c <7%) and 150 with poor metabolic control (HbA1c >7%). Oral health was evaluated using the Decayed, Missing, and Filled Teeth index (DMFT) for permanent teeth. Results: The mean age of participants was 9.14 ± 1.92 years; 53.3% were boys and 46.7% were girls. The DMFT index ranged from 0 to 6, with a mean of 2.74 ± 1.81. Neither age nor sex significantly influenced DMFT values. Children with good metabolic control had a lower mean DMFT score (2.41 ± 1.76) compared with those with poor control (3.08 ± 1.80), and this difference was statistically significant (p < 0.01). Conclusions: Poor metabolic control (HbA1c >7%) was associated with a higher burden of dental caries in children with T1DM.