Immersion of a microhybrid composite resin in staining drinks: a colorimetric analysis and microhardness study

Background. The aim of this study was the colorimetric and microhardness evaluation of a microhybrid composite resin after immersion in hot staining drinks. Methods and materials. Sixty- four Filtek Z250 (3M ESPE) samples (4x4x2 mm) were prepared and photopolymerized on both sides (30+30 sec) under a mylar film. Half samples were polished with Soflex Pop-on disks (3M ESPE). Colorimetric analysis were performed by means of a spectrocolorimeter (CIELab parameter C); hardness evaluations were performed by means of a Vickers microdurometer. Four groups of 16 samples were identified, subdivided per type of polishing and immersion drinks: G1=mylar-coffee; G2=mylar-tea; G3=disks-coffee; G4=disks-tea. Samples were submitted to analysis before the treatment (t0), after one day immersion in the beverages at a temperature of 55°C (t1) and after three days immersion (t2) in the same conditions. Statistical analysis was carried out with on-way ANOVA, Scheffe post hoc test, independent-samples and paired-samples Student T test. Results. Vickers tests showed a general hardness increase after immersion in the beverages: HV=72,02±2,54 at t0 and HV=74,95±2,62 at t2 (p=0,000) for G1; HV=72,02±2,54 at t0 and HV=74,95±2,62 at t2 (p<0,01) for G2; HV=72,33±4,97 at t0 and HV=75±2,68 at t2 (NS) for G3; HV=73,66±4,97 at t0 and HV=82,39±2,68 at t2 (p=0,000) for G4. Colorimetric analysis showed an increase of the saturation parameter C (5,79±0,29 at t0, 13,1±0,38 at t2 for G1, p=0,000; 5,99±0,49 at t0, 7,57±0,57 at t2 for G2, p=0,000; 5,42±0,23 at t0, 8,62±0,62 at t2 for G3, p=0,000; 5,60±0,30 at t0, 6,51±0,12 at t2 for G4, p=0,000). Conclusions. It is useful to know patients diet and oral hygiene in order to plan a follow-up and a surface polishing of the restorations: a three-six months period for the first recall may be convenient.