M. Sedda

Influence of coloring procedure on flexural resistance of zirconia blocks.

STATEMENT OF PROBLEM The white color of zirconia limits the possibility of a natural-looking restoration. Industrially precolored blocks and green-stage coloring liquids are used to obtain shaded zirconia. Several authors have reported that pigments may negatively affect the mechanical characteristics of the material. PURPOSE The purpose of this in vitro study was to investigate the effect of a recently marketed coloring system on the flexural strength (σ), Weibull characteristic strength (σ0), and Weibull modulus (m) of a zirconia for computer-aided design/computer-aided manufacturing (CAD/CAM) systems. MATERIAL AND METHODS Noncolored white blocks (In-Ceram YZ), industrially precolored blocks (In-Ceram YZ col. LL1p), and green-stage infiltration-shaded blocks in 4 colors (In-Ceram YZ Coloring Liquids) were tested. Industrially precolored specimens (n = 30) were assigned to the PREC group. Noncolored specimens were divided into 5 groups (n = 30). Group CNTR was not treated (control). Groups INF-N, INF-L, INF-M, and INF-I were subject to green-stage infiltration (neutral, light, medium, and intense, respectively). Specimens were tested in a 3-point bending apparatus following ISO 6872:2008 specifications. Data were analyzed by 1-way ANOVA. RESULTS The calculated flexural strengths (MPa) were CNTR 1232.56 ± 103.91; PREC 1215.16 ± 141.42; INF-N 1280.72 ± 160.10; INF-L 1218.92 ± 78.63; INF-M 1153.71 ± 176.80; and INF-I 1248.46 ± 111.73. No statistically significant differences were found among the tested groups (P = .195). CONCLUSIONS Unlike what has been reported for other combinations of zirconia and coloring liquids, the coloring technique tested in the present study did not negatively influence the flexural characteristics of the tested zirconia.

Evaluation of the fracture resistance of reattached incisal fragments using different materials and techniques

OBJECTIVES When coronal fracture occurs in anterior teeth, fragment reattachment can be a valid alternative to a direct restoration. The aim of this study was to evaluate the influence of the material and the technique used to reattach the fragment. MATERIALS AND METHODS Eighty sound maxillary and mandibular incisors were selected and randomly divided into eight groups (n = 10). The incisal third of each tooth was removed using a saw machine. The fragments in groups 1-4 were reattached using resin-based materials: group 1 adhesive, group 2 flow, group 3 composite, group 4 cement; in groups 5-8, the same materials mentioned before were used but a bevel was also performed on both labial and lingual surfaces. Shear bond strength (SBS) was calculated by applying a load incisal to the reattachment line. A two-way Anova was used to evaluate the influence of materials and techniques on the SBS. RESULTS The technique used was statistically significant (P < 0.001), while the material was not (P = 0.793). CONCLUSIONS The choice of material seems to have no influence on the SBS, whereas a bevel performed on the labial and lingual surfaces can significantly improve the SBS of the reattached fragment.

Flexural resistance of heat-pressed and CAD-CAM lithium disilicate with different translucencies

OBJECTIVE To compare flexural strength of CAD-CAM and heat-pressed lithium disilicate. METHODS For Pressed specimens (Group A), acrylate polymer blocks were cut with a saw in bars shape. Sprueing, investing and preheating procedures were carried out following manufacturers instructions. IPS e.max Press ingots (Ivoclar-Vivadent) were divided into subgroups (n=15) according to translucency: A.1=HT-A3; A.2=MT-A3; A.3=LT-A3; A.4=MO2. Ingots were then pressed following manufacturers instructions. For CAD-CAM specimens (Group B) blocks of IPS e.max CAD (Ivoclar-Vivadent) were divided into subgroups: B.1=HT-A3; B.2=MT-A3; B.3=LT-A3; B.4=MO2. Specimens (n=15) were obtained by cutting the blocks with a saw. Final crystallization was performed following manufacturers instructions. Both Press and CAD specimens were polished and finished with silica carbide papers of increasing grit. Final dimensions of the specimens were 4.0±0.2mm, 1.2±0.2mm, and 16.0±0.2mm. Specimens were tested using a three-point bending test. Flexural strength, Weibull modulus, and Weibull characteristic strength were calculated. Flexural strength data were statistically analyzed. RESULTS The overall means of Press and CAD specimens did not differ significantly. Within the Press group different translucencies were found to have similar flexural strength. Within the CAD group, statistically significant differences emerged among the tested translucencies (p<0.001). Specifically, MT had significantly higher flexural strength than HT and MO. Also, LT exhibited significantly higher flexural strength than MO. SIGNIFICANCE The choice between IPS e.max Press and IPS e.max CAD formulations can be based on different criteria than flexural resistance. Within each formulation, for IPS e.max Press translucency does not affect the flexural strength while for IPS e.max CAD it is an influential factor.