Atraumatic Restorative Treatment (ART) was proposed as a new and effective method in the 1990s to provide conservative dental treatment to the people living in economically underdeveloped countries, due to lack of dental treatment facilities. In the technique, after the carious dentin is removed by excavation with hand instruments, the powder-liquid system conventional glass ionomer cement (GIC) which does not require special devices for mixing and hardening is used as a filling material. Because of these advantages of the treatment, the usage fields of ART have been expanded considering that it can be applied in the cases that working with rotary instruments is difficult or even impossible. But only a few research has been conducted on ART in adults and it must be investigated in terms of the clinical safety of ART by the studies focused on the counts and activities of the microorganisms in carious dentin left on the cavity floor. The purpose of this study is to investigate the reliability of ART in adult individuals related to the marginal adaptation of the restorations and the microbiological changes in the left carious dentin using in vitro and in vivo methods. In the in vivo part of the study, occlusal dentin carious of 25 participants at high risk of caries were removed with hand instruments and microorganisms of the last removed carious dentin were evaluated quantitatively concerning the bacterias playing a major role in caries lesions. The restorations of the teeth were carried out using ART technique with a GIC which has been proven its effectiveness in preventing the caries progression and recurrent caries in the practice of dentistry for many years. After six months, the microbiological assessment was repeated such as baseline. Marginal adaptation and the presence of the gaps in the ART restorations on the replicas created with the impression materials at the baseline and sixth month were investigated under scanning electron microscope. At the end of the study, the teeth were restored by the conventional methods and using composite material.

Inclusion Criteria:

Patients:

• 19-35 years of age;
• Good general health;
• High risk of caries;
• No evident signs of occlusal parafunctions.

Tooth:

• Molar tooth;
• 3-4 mm depth occlusal dentin caries;
• Vital;
• In occlusion;
• Proper tooth axes.

Exclusion Criteria:

Patient:

• Using regular medication;
• Pregnancy or lactation;
• Received radiotherapy or chemotherapy;
• Tooth clenching, bruxism.

Tooth:

• Spontaneous pain;
• Radiographic alterations in the periapical region;
• Presence of tooth mobility;
• Previously restored;
• Broken and/ or cracked.