Bond Strength and Surface Roughness of Two Ceramics After Metal Bracket Debonding.

Objective: The aims of this study were to compare the bond strength between metallic brackets and two different glass ceramics and to evaluate the ceramic surface roughness after different finishing protocols. Methods: The surface roughness of lithium disilicate and resin matrix ceramic samples was measured (initial). All samples were treated with hydrofluoric acid and silane and bonded to metallic brackets with orthodontic cement adhesive. Shear bond strength tests were performed using a universal testing machine (n=12). The surface roughness was measured again (intermediate, n=6) after removing the remaining cement adhesive from the ceramic surfaces with a diamond or 24-blade bur after polishing the ceramic surfaces (final, n=6). Results: The resin matrix ceramic had the highest bond strength. The rotatory instrument used for the removal of cement adhesive did not affect the surface roughness of the resin matrix ceramic or lithium disilicate (p=0.985 and p=0.504, respectively), but did affect the evaluation time (p<0.001) for both restorative materials. The intermediate roughness was the highest. For the resin matrix ceramic, polishing promoted a final surface roughness similar to the initial condition; however, changes in the surface shape of this ceramic could be visibly observed when using a 24-blade bur. Conclusion: The bond strength of metallic brackets bonded on resin-matrix ceramics is higher than bonding on lithium disilicate. The use of diamond burs for the removal of the remaining adhesive from the resin matrix ceramics is highly recommended.

Mechanical performance of monolithic materials cemented to a dentin-like substrate.

STATEMENT OF PROBLEM: Studies on the mechanical behavior of restorative materials bonded to tooth structure and considering the properties of the material and the bonding between both substrates are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the hardness, fracture toughness, load-to-failure, cyclic fatigue, and stress distribution of 4 computer-aided design and computer-aided manufacturing (CAD-CAM) materials when bonded to a substrate similar to dentin (G10). MATERIAL AND METHODS: Disks (11×1.2 mm) of lithium disilicate (LD), feldspathic ceramic (FC), polymer-infiltrated ceramic (PC), and a nanohybrid composite resin (NC) were fabricated (n=45) and had their surfaces polished. Microhardness was measured by the Knoop indentation (19.61 N, 12 seconds, n=5). Indented specimens were subjected to biaxial flexural strength testing, and the fracture origin defect was measured to calculate fracture toughness (n=5). Forty disks from each material were adhesively bonded to G10. Half of the specimens were subjected to load-to-failure testing, and remaining specimens (n=20) were subjected to cyclic fatigue (400 N, 106 cycles). The test was suspended every 200 000 cycles, and specimens were examined for cracks, debonding, or catastrophic failure. Obtained data were evaluated by analysis of variance and the Tukey post hoc test (α=.05). Weibull analysis was also performed. A 3D model of the tested specimens was constructed in a design software program, and the stress distribution was evaluated by finite element analysis, with the application of a 100-N load normal to the restoration surface. RESULTS: Hardness values with statistically significant differences were LD (540.4)>FC (474.6)>PC (176.6)>NC (58.26). Fracture toughness vales (MPa.m1/2) and statistical significance were as follows: LD (2.25)=NC (2.46)>FC (1.14)=PC (1.18). Load-to-failure values (N) were LD (2881.6)=FC (2881.6)=PC (3200.6)>NC (2367.5). A specimen each of LD and NC fractured during the fatigue test, and LD and PC had a high percentage of subsurface cracks (55% and 75%, respectively). The FC had the lowest debonding rate after load-to-failure testing and no catastrophic fractures or cracks during fatigue. CONCLUSIONS: The materials tested had different mechanical behaviors depending on the tests performed. Feldspathic ceramic had the best fatigue behavior when cemented to a dentin-like substrate.

Effect of interim cement application on bond strength between resin cements and dentin: Immediate and delayed dentin sealing.

STATEMENT OF PROBLEM: Despite the advances in materials and techniques, adhesion to dentin is challenging because of the complex composition of dentin's mineral, organic, and fluid phases. PURPOSE: The purpose of this in vitro study was to evaluate the bond strength of 2 different resin cements (conventional and self-adhesive) with or without previous dentin sealing and the effect of interim cement. MATERIAL AND METHODS: Forty-five molars were embedded into acrylic resin blocks and a flat dentin surface was exposed. Twenty teeth (n=5 per group) were treated with the conventional resin cement associated with etch-and-rinse or self-etch adhesive approaches, applied before (immediate dentin sealing) or after (delayed dentin sealing) the application/removal of interim cement. Another 25 teeth (n=5, per group) were treated with self-adhesive resin cement with (self-etch mode [immediate dentin sealing or delayed dentin sealing]) or without adhesive application. Furthermore, in the self-adhesive resin cement group, the application of polyacrylic acid for dentin etching before cementation was evaluated. Composite resin blocks were cemented onto flat, treated dentin surfaces, and the assemblies were sectioned into bar-shaped specimens for microtensile bond strength testing. The data were subjected to 1-way ANOVA followed by the post-hoc Tukey test (α=.05). The failure patterns were classified as cohesive, adhesive, or mixed. RESULTS: The application of adhesive before interim cement (immediate dental sealing) promoted the highest values of bond strength for both resin cements (P<.001). For self-adhesive resin cement, polyacrylic acid-enhanced bond strength after the application of interim cement. CONCLUSIONS: The application of dental adhesive immediately after tooth preparation (immediate dentin sealing) and before the use of an interim cement promoted the highest values of bond strength to dentin with the resin cements tested.

Effect of surface treatments on the bond strength of different resin teeth to complete denture base material.

Although different commercial brands of artificial teeth are available in the market, debonding from the denture base is still an issue when rehabilitating edentulous patients with conventional or implant-supported complete dentures. The purpose of this study was to investigate the effect of surface treatments on the bond strength of four artificial teeth brands to a denture base material polymerized by microwave energy. Forty anterior artificial teeth of each brand (Biolux, Trilux, Biotone IPN, and Vipi Dent Plus) were bonded to denture base material (VipiWave). Before processing, groups often specimens of each brand received surface treatment: control, monomer application (MA), air abrasion (AA) or diatoric cavity (DC). After processing, a blinded examiner conducted the bond test by applying load to the specimens (0.5 mm/min, to 45 degrees). Data were analyzed by one-way ANOVA followed by Tukey's test (alpha = 0.05). Biolux teeth have stronger bonding to denture base than Trilux (p < 0.05) in control group; higher bond values than Biotone IPN (p < 0.05) in MA group; and higher bond strength than Vipi Dent Plus and Trilux (p < 0.01) in DC group; AA had no differential effect for any of the brands. With regard to the effect of the surface treatments on bond strength within groups of commercial brand, statistical analysis revealed no difference among them. According to results in general, Biolux teeth had the strongest bonding to the denture base material polymerized by microwave energy. Results may assist dentists in selecting denture teeth from the standpoint of shear bond strength.

Influence of re-using reversible hydrocolloids on the linear alteration of coating models.

Reusing reversible hydrocolloids too many times may cause alterations of the coating model and produce unsatisfactory RPPs. The aim of this study was to analyze the linear alterations of coating models reproduced from molds obtained with two commercial brands of reversible hydrocolloid (RH) with 15 reuse cycles of the material. A metal model was used with 4 marks (A, B, C and D) on which the distances AB, BC, CD, DA, BD and AC could be measured lineally. Ten models were divided into two groups according commercial brand of RH: group VIPI-Duplicator VIPI and group K27--Duplicator K27l. The RH was heated in a microwave oven and poured into a flask containing the model. The mold was filled with the ethyl silicate coating, and after crystallization, refractory models were obtained. This was repeated in the 15 re-use cycles of each RH. The refractory models obtained from the 1st, 5th, 10th and 15th times of re-use of RHs were measured under a measuring microscope. The means were submitted to the Analysis of Variance, Tukey and Dunnet tests, to a 5% level of significance. Group VIPI showed linear alterations in relation to the plaster models, for distances AB (1 use = -1.25% and 5th re-use = -1.20%); AD (1st use = 0.76%, 10th re-use = 0.65% and 15th re-use = 0.52%); BD (1st use = 0.58%). Both commercial brands analyzed produced coating models with acceptable linear alterations in up to 15 reuse cycles, no statistical difference being observed between them.

Influence of different materials and techniques to transfer molding in multiple implants.

The aim of this study was to compare different materials and techniques used in transfer molding of multiple implants, by evaluating the space between implants and superstructure. Four external hexagon implants were fixed in a master template and the same on a superstructure. Transfer molding of implants were done using the direct and indirect techniques, with transfers united or not, using the union chemically activated acrylic resin (QA) and other groups polymerized acrylic resin (FT), and sectioned and not split. The casts were made with polyether and models divided into 8 groups (n = 5). The space between the superstructure and the master implants was measured with a microscope and the data was analyzed statistically by Student's t test (p < 0.05). For the material of union there was no significant difference, except when the groups were compared with the resin Duralay QA (G4) and the resin Duolay FT (G8) and groups using resins Duolay QA (G5) and Duolay FT (G7) for the union of the transfers. When comparing the groups who had the union between the transfers and sectioned again united with those in which the union was not severed there was no statistically significant difference. QA resin was superior to the FT with respect to the union of transfers. Techniques with united transfers or not were similar.

Influence of different flasking and polymerizing methods on the occlusal vertical dimension of complete dentures.

The flasking and polymerization technique for resins can introduce stresses during processing which may lead to denture base distortions, artificial teeth displacement and increases in the occlusal vertical dimension (OVD). This study investigated whether the association of microwave heat-activation (MH) and bimaxillary flasking (BF) minimizes the possible increases in OVD after prostheses processing. Forty pairs of complete dentures were waxed with the artificial teeth in closed occlusion and divided into four groups according to investing and heating methods: G1 (control) = monomaxillary/water bath; G2 = monomaxillary/microwave; G3 = bimaxillary/water bath and G4 = bimaxillary/microwave. OVD was measured using a digital caliper before and after prostheses processing. Results were submitted to statistical analysis (Student's t-test for multiple comparisons and post hoc ANOVA, alpha = 0.05). Comparison of values before and after processing showed that OVD increased in all groups after polymerization (p < 0.001), regardless of flasking and polymerization methods. Statistically, G2 had the greatest difference in OVD when compared to G1 (p = 0.014), G3 (p = 0.019) and G4 (p = 0.024). G3 and G4 showed similar results statistically when compared to G1 (control). Both investing and heating methods resulted in an increase in OVD after processing. However, the prostheses invested in bimaxillary flasks showed the lowest changes in OVD, regardless of the polymerization method.

Water sorption of heat-polymerized acrylic resins processed in mono and bimaxillary flasks.

This study evaluated water sorption in heat-polymerized acrylic resins processed in monomaxillary flasks by water bath and in bimaxillary flasks by microwave energy and water bath. Fifty heat-polymerized acrylic resin specimens were fabricated according to the 12th specification of the American Dental Association and assigned to 3 groups: group 1 was processed by water bath in monomaxillary metallic flask; group 2 was processed by microwave energy in bimaxillary PVC flask; and group 3 was processed by water bath in bimaxillary metallic flask. Specimens were submitted to water sorption test, means were calculated and analyzed statistically by Student's t-test. Means (in g/cm3) were: group 1--0.024085, group 2--0.025312 and group 3--0.022098. Microwave energy processing and the amount of stone and resin used in the bimaxillary PVC flask did not influence water sorption; specimens processed in bimaxillary metallic flask by water bath presented lower water sorption means, suggesting an inadequate polymerization of the acrylic resin mass.

Water sorption of heat-polymerized acrylic resins processed in mono and bimaxillary flasks

A finalidade deste estudo foi avaliar a sorção de água de resinas acrílicas ativadas termicamente quando processada em mufla monomaxilar para banho de água e mufla bimaxilar para banho de água e microondas. Foram confeccionados 50 corpos-de-prova de resina acrílica ativada termicamente de acordo com a especificação nº 12 da American Dental Asociation, divididos em três grupos: no grupo 1, os corpos-de-prova foram processados em mufla monomaxilar metálica para banho de água; no 2 foram processados em mufla bimaxilar de PVC para uso em microondas e no 3 foram processados em mufla bimaxilar metálica para banho de água. Os corpos-de-prova foram submetidos ao ensaio de sorção de água, os valores médios foram calculados e analisados pelo teste t de Student. Os valores obtidos (g/cm3) foram: grupo 1 - 0,024085, grupo 2 - 0,025312 e grupo 3 - 0,022098. A polimerização da resina acrílica por energia de microondas na mufla bimaxilar de PVC não influenciou a sorção de água em relação ao processamento em muflas monomaxilares, enquanto a polimerização feita em muflas bimaxilares metálicas aquecidas em banho de água diminuiu esse índice, sugerindo inadequada polimerização da massa de resina.

Is an elongated stylohyoid process prevalent in the elderly? A radiographic study in a Brazilian population.

BACKGROUND: Elongation and calcification of the stylohyoid ligament complex may be correlated with Eagle's syndrome. The styloid complex pathogenesis is still being debated. OBJECTIVE: The aim of this study was to investigate the prevalence of stylohyoid ligament complex elongation in panoramic radiographs of 2252 patients in a Brazilian adult, partially edentulous population, of both sexes. METHODS: The radiographs, taken in the Semiology Department at the Dental School in Brazil, were randomly selected from January 1997 to December 2000. The stylohyoid ligament complexes were measured from the cranial base up to the osseous tip of each process. Mineralisation of the complex of more than 25 mm in length on the radiograph was considered to be abnormal. The same operator made all the measurements. The lengths of the areas of mineralisation were recorded, and whether the condition was bilateral was noted. RESULTS: This abnormality was present in both sexes. A calcified complex was found in 451 of the 2252 patients. The majority of these calcified complexes (n = 248; 54.9%) were bilateral. Three hundred and fifty-six (39.5%) of them were longer than 25 mm (and so were abnormal), and the length varied from 26.1 to 65 mm. (average length = 27.8 mm). Forty (4.4%) of the abnormalities were longer than 50 mm, and of these 36 (90%) were in the 40-59 year age group. The mean length of a mineralised stylohyoid ligament complex in patients in the 60-79 year age group was 32.75 mm. CONCLUSIONS: The results suggested that an anatomical variant of the stylohyoid ligament complex was more frequently found in the elderly female population, although this abnormality was present in both sexes. There was a greater tendency for the abnormality to be present in patients between 60 and 79 years of age.