The aim of this randomized, controlled, three-arm parallel-group, double-blinded clinical trial was to evaluate the clinical, radiographic, and histopathological success of three different pulp-capping materials in one-stage indirect pulp treatment of primary teeth.

The study included a total of 109 patients aged 5-9 years who had primary teeth with deep carious lesions with or symptoms of irreversible pulpitis. The teeth were divided into three groups according to the pulp-capping agents: (I) Calcium hydroxide (Ca[OH]2) (control group) (n=36), (II) bioactive tricalcium silicate (Biodentine) (n=37), and (III) resin-based tricalcium silicate (TheraCal LC) (n=36). All the teeth were evaluated clinically and radiographically at postoperative months 6, 12, 18, and 24. A total of 23 primary mandibular second molars that were in their regular exfoliation period (24-40 months) were extracted and fixed in 10% formaldehyde solution. The specimens were evaluated histologically to assess the integrity of the odontoblastic layer, tertiary dentin formation and the quality of the dentin formed, severity of pulpitis, and other pulpal changes.

Following the clinical and radiographic examinations, pulp vitality was assessed with cold thermal test (Chloraethyl; Wehr, Baden, Germany) and electrical pulp test. After local anesthesia injection, rubber-dam isolation was performed. In the first step of the IPC procedure, cavity preparation was performed and the caries were removed using a high-speed dental handpiece with a diamond bur. In the second step, the carious peripheral dentin was removed at the enamel-dentin junction using a high-speed tungsten-carbide bur and the infected and necrotic soft dentin layer in the center was carefully removed to prevent pulp exposure. Cavity excavation was stopped when the residual dentin over the pulp tissue showed increased resistance to manual instrumentation, and the demineralized dentin (affected dentin) was left at the floor of the cavity.

After this stage, the teeth were randomly divided into 3 groups:

Ca(OH)2 Group (Control): The residual demineralized dentin was covered with a thin layer of Ca(OH)2 (Dycal; Dentsply/Caulk, Dentsply International Inc. Milford, DE, USA) in accordance with the recommendations of the manufacturer.

Biodentine Group: A thin layer of tricalcium silicate-containing pulp-capping material (Biodentine, Septodont, France) consisting of powder and liquid was applied to the demineralized dentin tissue and a 12-min setting time was allowed for hardening, in accordance with the recommendations of the manufacturer.

TheraCal LC Group: Flowable form of resin-reinforced tricalcium silicate-containing material (TheraCal LC, Bisco Inc, IL, ABD) was applied directly onto the demineralized dentin at a maximum thickness of 1 mm and was polymerized for 20 sec (Valo LED, Ultradent Products Inc., South Jordan, USA), in accordance with the recommendations of the manufacturer.

Afterwards, in all three groups, capsule glass ionomer cement (Capsule; GC Corporation, Tokyo, Japan, Corporation, Tokyo, Japan) was placed on each capping material. Following the etching and bonding process, permanent restoration was finished with composite resin (Filtek Z250 Universal Restorative System, 3M ESPE Dental products, USA).

Histological examination A total of 23 primary mandibular second molars that were in their regular exfoliation period (in which the underlying permanent tooth germ had completed 2/3 of root formation) (24) and were found to be clinically and radiographically successful following IPC were extracted by the researcher and were processed for histological examination .All the extracted teeth were fixed in 10% formaldehyde solution. Three out of 23 specimens were excluded from the study since they were unsuitable for sectioning.

Inclusion Criteria:

• Previously untreated, vital and asymptomatic lower primary molars with deep caries lesions considered likely to result in pulp exposure if they were treated by a single and terminal excavation
• Positive pulp sensibility tested by an electric pulp tester and cold stimulation,
• Mild discomfort from chemical and thermal stimuli,
• Cooperative children and parents willing to follow the instructions and report for follow-up.

Exclusion Criteria:

• Signs of irreversible pulpitis (spontaneous pain, prolonged pain response etc.)
• The presence of percussion or palpation sensitivity, pathological mobility, or infection symptoms like fistula or abscess or discoloration in the clinical examination,
• Absence of normal lamina dura and periodontal range, presence of lesion, internal or external resorption or calcification in or around the root in the radiological examination,
• Children with special health care needs.