Biomedical subjects

L C Sobrinho

Publications and source records attributed to L C Sobrinho.

9 recordsLinked to original sources

PubMed2001

Influence of loading types on the shear strength of the dentin-resin interface bonding.

Small differences in the shear bond test can make critical differences in the bonding strength values. The purpose of this study was to compare the influence of the orthodontic-looped wire, stainless steel tape and chisel systems used in shear bonding tests to verify the resistance in the dentin-resin interface. Forty-eight human teeth were used and divided in three groups. The teeth were ground until a flat smooth surface was achieved, that was delimited with an adhesive tape containing a hole of 4 mm diameter. After, the dentine surface was treated with Scotchbond Multi Purpose and the composite Z-100 was applied in layers, through a stainless steel mold. The samples were stored at 37 degrees C and 100% of relative humidity for 24 h and, then, submitted to 500 thermal cycles. After, they were taken to an universal test machine (Otto Wolpert) with crosshead speed of 6 mm/min. The results were statistically analyzed using a Tukey's test (p\lt 0.05). The orthodontic-looped wire determined the highest values of shear bond (13.33 MPa), following by chisel (7.81 MPa) and stainless steel tape (4.87 MPa). The debonding values depend on a complex stress combination produced during the loading of the samples. Small variations in test methodologies give statistically different values for shear bond strength. Different shear strength methods in vitro make the comparative clinical performance of the resin filling materials difficult.

Journal Article↗

PubMed2000

Correlation between light intensity and exposure time on the hardness of composite resin.

This study evaluated the correlation between light intensity emitted by the curing units and exposure time on the of degree polymerization of dental composites by measured Knoop hardness. Specimens with 5 mm diameter and 2 mm height were prepared in a copper mold, covered with a mylar strip and polymerized for 30 sec by curing units with 50, 130, 180, 220, 280 and 520 mW/cm(2), respectively. The output for all units was measured using a Curing Radiometer (Demetron). Other specimens were polymerized for 45, 60, 75, 90, 105, 120, 135, 150, 165 and 180 sec utilizing units of 130, 220 and 280 mW/cm(2). Knoop hardness values of the top and bottom surfaces were measured after 24 h. The results indicate that the curing units with higher light intensity presented improved values of Knoop hardness on the top and bottom regions. As expected, the top surface always presented improved Knoop hardness values in relation to the bottom, after exposure for 30 sec. The values obtained on the surface were statistically superior compared to the values on the bottom (p<0.05) for the intensity of 130, 220 and 280 mW/cm(2) after 30, 45 and 60 sec of exposure.

Journal Article↗

PubMed2000

Influence of curing tip distance on composite Knoop hardness values.

The purpose of this paper was to study the influence of curing tip distance on Knoop hardness values, at different depths, of two composites, Z100 and Silux Plus. Specimens (5 mm in diameter and 2.5 mm in height) were prepared in a copper mold, covered with mylar strip and polymerized for 40 s, at 3 tip-to-composite surface distances: 0 mm (surface contact), 6 and 12 mm, utilizing an XL 3000 curing unit, with 750 mW/cm2 power. The specimens were then stored at 37 degrees C for 24 h. Knoop hardness values were measured using a microhardness tester, with a load of 50 g for 30 s for each indentation. Four specimens were made for each distance and composite and eighteen indentations were made of each specimen. The results were submitted to analysis of variance and Tukey test at 5% significance level. The results indicated that 1) composite Z100: the larger the curing tip distance in relation to the composite, the lower the Knoop hardness values; 2) Silux Plus: increasing the curing tip distance did not produce a statistically significant difference in the Knoop hardness values; however, at 6 and 12 mm, the deeper layers showed lower Knoop hardness values in relation to the surface; 3) Z100: statistically superior in relation to Silux Plus at all three curing tip distances and at all depths (P < 0.05).

Analysis of Variance↗

PubMed1998

Comparison of the wet and dry fatigue properties of all ceramic crowns.

The purpose of this paper was to investigate the influence of fatigue on the fracture strength of In ceram, optimal pressable ceramic (OPCTM) and IPS Empress in both wet and dry environments. Twenty-six crown shapes 8 mm in diameter and 8.5 mm in height were fabricated for each ceramic system. For each ceramic system, ten specimens were tested for fracture strength without fatiguing. The second group was submitted to a fatigue and fracture test in a dry (eight specimens) and a third group in a wet (eight specimens) environment using an Instron testing machine. The results were statistically analysed using a Mann-Whitney test. The results indicated that: (i) the fracture strength for In ceram was significantly stronger than OPCTM and IPS Empress (p<0.05) - no difference was found between OPCTM and IPS Empress; (ii) fatiguing and fracture testing showed a significant decrease in the fracture strength for In ceram and IPS Empress in the wet environment and no difference was found in the dry environment - no difference was found for OPCTM; and (iii) when fatigued in a dry environment, In ceram crown shapes were significantly stronger than OPCTM and IPS Empress (p<0.05) - the same statistical differences were found when fatigued in a wet environment.

Journal Article↗

PubMed1998

Fracture strength of all-ceramic crowns.

This paper compares the fracture strength of three types of all-ceramic crown shape systems (In ceram, OPC and IPS Empress) cemented with either a commercial resin cement, zinc phosphate or glass ionomer. Twenty test crown shapes with 8 mm diameter and 8.5 mm height were fabricated for each type of ceramic. Ten In ceram crown shapes were luted on the die using zinc phosphate, while ten OPCTM and IPS Empress were luted using resin cement specified for the particular system. Another ten specimens each, of In ceram, OPC and IPS Empress, were luted on the die using a glass ionomer. The crown shapes were fractured in a mechanical testing machine (Instron) using a steel ball, 4 mm diameter, that contacted the occlusal surface and the resulting data were statistically analysed using a Mann-Whitney test. The results showed that: (1) In ceram crown shapes luted with zinc phosphate were significantly stronger than IPS Empress crown shapes luted with resin cement (p < 0.05), but no difference was observed compared with OPC crown shapes luted with resin cement. No statistical difference was found between OPC and IPS Empress crown shapes. (2) When the three ceramics were luted with glass ionomer, the In ceram was significantly stronger than OPC (p < 0.05) and IPS Empress (p < 0.05). OPC was significantly stronger than IPS Empress (p < 0.05).

Journal Article↗

PubMed1995

Effect of topical fluoride application on the surface roughness of composites.

The influence of fluoride solutions on the surface roughness of polished and nonpolished composites with Sof-Lex discs was verified. Concise and Herculite XR samples were exposed to the action of 1.23% acidulated phosphate fluoride rinse, 1.23% acidulated phosphate fluoride gel, and 0.2% neutral phosphate fluoride rinse for 4 min each. The average roughness values obtained by perfilometer showed that all fluoride solutions produced surface alterations in the samples. In the unpolished samples, more roughness was produced in Concise etched by 1.23% acidulated phosphate fluoride rinse. In the polished samples, the 1.23% acidulated phosphate fluoride gel produced greater alterations in Herculite XR, and the neutral rinse in Concise samples.

Acidulated Phosphate Fluoride↗

PubMedDate not supplied

Masticatory efficiency in children with primary dentition.

PURPOSE: The aim of this study was to evaluate masticatory efficiency in children with normal primary occlusion and malocclusion and to correlate efficiency with body variables. METHODS: Thirty children were divided into three groups: Group I with normal occlusion (n = 10), Group II with posterior crossbite (n = 10) and Group III with anterior open bite (n = 10). They chewed standardized silicone tablets for 20 strokes and the optical scanning system was used to calculate the particle size (area and perimeter). Results were compared among the groups. Body weight and height were correlated with masticatory efficiency. RESULTS: Group I fragmented the tablets into a greater number of particles with smaller sizes than Groups II and III, and the differences were statistically significant (p<0.05). There was no difference between the children with crossbite and children with open bite. Correlation coefficients between body variables and masticatory efficiency were weak (p>0.05). CONCLUSIONS: Occlusion is a factor of influence on masticatory process.

Analysis of Variance↗

PubMedDate not supplied

Effect of the photo-activation method on polymerization shrinkage of restorative composites.

This study measured the gap that resulted from polymerization shrinkage of seven restorative resin composites after curing by three different methods. Contraction behavior, according to the specimen region, was also characterized. The materials used for this study were Alert (Jeneric/Pentron, Wallingford, CT 06492, USA), Surefil (Dentsply Caulk, Milford, DE 19963, USA), P60 (3M Dental Products, St Paul, MN 55144, USA), Z250 (3M), Z100 (3M), Definite (Degussa-Hüls, Hanau, Germany) and Flow-it (Jeneric/Pentron). The composite was placed in a circular brass mold 7 mm in diameter and 2 mm in height. Photo-activation was performed by a) continuous light (500 mW/cm2) for 40 seconds; b) stepped light with low intensity (150 mW/cm2) for 10 seconds and high intensity (500 mW/cm2) for 30 seconds and c) intermittent light (450 mW/cm2) for 60 seconds. The top and bottom surfaces were then polished and after 24 +/- 1 hours, the contraction gap was measured by SEM at variable pressure (LEO 435 VP, Cambridge, England). Results were analyzed by ANOVA and the means compared by Tukey's test (5%). The results demonstrated 1) the continuous light method presented the greatest gap values (15.88 microm), while the other methods demonstrated lower polymerization shrinkage values (stepped light, 13.26 microm; intermittent light, 12.79 microm); 2) restorative composites shrunk more at the bottom surface (15.84 microm) than at the top surface (12.11 microm) and (3) the composites Alert (12.02 microm), Surefil (11.86 microm), Z250 (10.81 microm) and P60 (10.17 microm) presented the least contraction gaps, followed by Z100 (15.84 microm) and Definite (14.06 microm) and finally Flow-it (23.09 microm) low viscosity composite, which had the greatest mean value.

Analysis of Variance↗

PubMedDate not supplied

Investigation of the dry and wet fatigue properties of three all-ceramic crown systems.

PURPOSE: The aim of this study was to investigate the influence of fatigue on the fracture strength of In-Ceram (Vita Zahnfabrik), Optimal Pressable Ceramic (Opc, Jeneric Pentron), and IPS Empress (Ivoclar-Vivadent) in both wet and dry environments. MATERIALS AND METHODS: Twenty-six crown shapes measuring 8.0 mm in diameter and 8.5 mm in height were fabricated for each ceramic system. For each ceramic system, 10 specimens were tested for fracture strength without fatiguing. A second group (8 specimens) was submitted to a fatigue and fracture test in dry conditions, and a third group (8 specimens) was fatigued and fractured in a wet environment using a mechanical testing machine (Instron). The results were statistically analyzed using a Mann-Whitney test. RESULTS: The results indicated that: (1) The facture strength for In-Ceram was significantly stronger than IPS Empress. No difference was found between In-Ceram and Opc, and Opc and IPS Empress. (2) The strength of the three ceramic systems decreased significantly after fatiguing in both dry and wet environments compared with the nonfatigued specimens. No difference was found between fatiguing in dry and wet environments. (3) For the three systems fatigued in a dry environment and then fracture tested, In-Ceram and Opc were significantly stronger than IPS Empress, but no difference was found between the three systems fatigued in a wet environment. CONCLUSION: Significant differences in the fracture strengths of the different systems investigated may be seen that result from both the nature of the system and the environment in which the specimens were fatigued.

Aluminum Oxide↗