Color prediction of layered dental resin composites with varying thickness.

OBJECTIVE: The aim of this study was to assess the accuracy of a Principal Components Analysis (PCA)-based method for reflectance reconstruction and color estimation of layered dental resin-based composites with different thicknesses. METHOD: Bi-layered samples of different clinically relevant thicknesses were created using shades of VITAPAN Excell (VE), VITAPAN Dentine (VD) and VITA Physiodens (VP), combined with their corresponding enamel shades. Spectral reflectance of all samples was measured over a black background using a non-contact spectroradiometer with CIE 45∘∕0∘ geometry. Two different PCA-based models, built from two different configurations of known samples, were proposed to reconstruct the spectral data and color of unknown layered samples. Root Mean Square Error (RMSE), Goodness of Fit (GFC), as well as ΔE00 with corresponding 50:50% acceptability and perceptibly thresholds (AT and PT) were used as performance assessment. RESULTS: The 5-samples training set approach provided an average RMSE < 0.015 and GFC > 0.999 when measured and predicted spectral reflectances were compared, while for the 9-samples training set, RMSE < 0.0098 and GFC > 0.9999 were obtained. The overall mean color differences obtained with the 5-samples training set approach were ΔE00 = 0.99 (AT% = 96.25% and PT% = 32.50%), while using the 9-samples training set resulted in lower overall mean color differences: ΔE00 = 0.50 (AT% = 99.22% and PT% = 83.87%). SIGNIFICANCE: Within the framework of this study, the two proposed PCA-based configurations allow the prediction of the spectral reflectance of layered dental resin-based composites of different shades and thicknesses, with a high degree of accuracy.

Influence of Bleaching and Aging Procedures on Color and Whiteness of Dental Composites.

Bleaching can cause perceptible color changes on resin-based composite (RBC) restorations that may not be stable with aging. The objective of this study was to evaluate color stability and whiteness variations of RBCs after bleaching and aging procedures. Discs (10 mm in diameter and 1 mm thick) of shades A2 and A3 were fabricated from two RBCs (Filtek Z250 and Filtek Z350 XT) and divided into three subgroups (for each composite and shade) (n=5) as follows: control (no bleaching), at-home bleaching, and in-office bleaching. All specimens underwent an accelerated artificial aging up to 450 KJ/m2 and 900 KJ/m2 in an aging chamber (Suntest XXL+). A spectroradiometer (SpectraScan PR-670) was used to obtain CIE L*a*b* coordinates. CIEDE2000 color difference (ΔE00) and whiteness index for dentistry (WID) were used to evaluate color stability. Color and whiteness differences data were analyzed considering the 50:50% visual color difference thresholds (perceptibility [PT] and acceptability [AT]) and 50:50% whiteness thresholds (whiteness perceptibility [WPT] and whiteness acceptability [WAT]). Analysis of variance and Tukey tests (α=0.05) were used to statistically analyze the data. After bleaching, all specimens showed ΔE00 and ΔWID values below their corresponding acceptability thresholds (AT and WAT, respectively). After aging, L* and WID values decreased while b* values increased (p≤0.05), resulting in ΔE00 and ΔWID values above AT and WAT, respectively. Color changes after bleaching RBCs were clinically acceptable, while aging provoked clinically perceptible color changes.

Perioperative blood transfusion in cancer patients undergoing laparoscopic colorectal resection: risk factors and impact on survival.

BACKGROUND: Perioperative blood transfusion has been associated with a poor prognosis in patients undergoing surgery for colorectal cancer. The aim of this study was to evaluate risk factors for blood transfusion and its impact on long-term outcome exclusively in patients undergoing laparoscopic surgery for curable colorectal cancer. METHODS: Data were retrieved from a prospectively collected database of patients who underwent laparoscopic surgery for curable colorectal cancer over a 6-year period. Long-term data were collected from our outpatient clinic and personal contact when necessary. RESULTS: Two hundred and one patients underwent laparoscopic surgery for curable colorectal cancer (stage I-III). Sixty-eight (33.8 %) received blood transfusions during or after surgery. These patients were typically older, had lower preoperative hemoglobin levels, had a more advanced cancer, had a higher Charlson score, had a higher rate of complications and had a higher conversion rate. Kaplan-Meier overall survival analysis was significantly worse in patients who received blood transfusions (P = 0.004). Decreased disease-free survival was also observed in transfused patients; however, this did not reach statistical significance (P = 0.21). A multivariate analysis revealed that transfusion was not an independent risk factor for decreased overall and disease-free survival. The Charlson score was the only independent risk factor for overall survival (OR = 2.1, P = 0.002). Independent factors affecting disease-free survival were stage of disease, Charlson score and, to a lesser degree, age and body mass index. CONCLUSIONS: Perioperative blood transfusion is associated with decreased long-term survival in patients undergoing laparoscopic resection for colorectal cancer. However, this association apparently reflects the poorer medical condition of patients requiring surgery and not a causative relationship.

Metastatic lymph node ratio (LNR) as a prognostic variable in colorectal cancer patients undergoing laparoscopic resection.

BACKGROUND: Lymph node ratio (LNR: the ratio of metastatic to total retrieved nodes) has shown prognostic significance in several tumors. Its role in patients with colorectal cancer submitted to laparoscopic resection is still not clearly defined. The aim of this study was to evaluate the impact of LNR on long-term outcome in patients undergoing curative laparoscopic resection. METHODS: Patients' data were retrieved from our prospective in-hospital collected data of patients that underwent laparoscopic surgery for curable colorectal cancer over a 6-year period. Long-term data were collected from our outpatient's clinic data and personal contact when necessary. RESULTS: Two hundred and five patients underwent laparoscopic resection for curable colorectal cancer in the study period. Sixty-five patients were node positive. Receiver operating characteristic (ROC) analysis selected 0.13 as the best LNR cutoff value in this group. Kaplan-Meier 5-year survival analysis revealed a significant decrease in overall and disease-free survival in patients with an LNR above 0.13. Long-term outcome of patients with an LNR below 0.13 was similar to node-negative stage II patients. CONCLUSIONS: The lymph node ratio is a valuable prognostic factor in node-positive colon cancer patients undergoing laparoscopic resection. Patients with an LNR below 0.13 have the same long-term outcome as stage II node-negative patients. The laparoscopic approach presents the same trends in terms of overall survival and disease-free survival as conventional open access when LNR is considered.