Compressive strength recovery by composite onlays in primary teeth: Substrate treatment and luting agent effects

Objectives To evaluate 1% NaOCl treatment and two resin luting agent effects on compressive strength recovery in composite onlays on primary teeth and to analyze the fractures type. Methods Forty sound primary molars crowns were prepared in the standard machine and randomly divided into four groups (n = 10): G1 (1% NaOCl/ 30 min + EnForce); G2 (without 1% NaOCl EnForce); G3 (1% NaOCl/ 30 min + Rely X); G4 (without 1% NaOCl + Rely X). The onlays were made using Z250 composite on plaster models. Ten sound teeth were used as control group (CG). All groups were submitted to compression mechanic test in a universal test machine INSTRON at 1 mm/min cross-head speed. After that, the data (kgf) were submitted to ANOVA test (α = 0.05). Finally, the fracture types were classified in a crescent scale (1–5) related with severity degree and submitted to Fisherʹs Exact Test (p < 0.05). Scanning electronic microscope analysis was done in order to illustrate the fractures sites. Results The values of compressive strength of experimental groups did not differ each others neither from control group (p > 0.05). The results from fracture type showed that types 5 and 4 fractures (most severe) present the highest percentage to experimental groups. Conversely, the CG showed higher percentage of fracture types 2 and 3. Conclusions This research found that the composite onlays recovered the compressive strength compared to sound teeth, regardless of the substrate treatment and cement agent used. Nevertheless, no group showed similar type of fractures to CG, which had more frequency of less severe fracture types.