Aisha Stumpf

Shear bond strength of metallic and ceramic brackets using color change adhesives

OBJECTIVE To determine the shear bond strength of orthodontic brackets using color change adhesives that are supposed to aid in removing excess of bonding material and compare them to a traditional adhesive. METHODS Ninety metallic and ninety ceramic brackets were bonded to bovine incisors using two color change adhesives and a regular one. A tensile stress was applied by a universal testing machine. The teeth were observed in a microscope after debonding in order to determine the Adhesive Remnant Index (ARI). RESULTS The statistical analysis (ANOVA, Tukey, and Kruskall-Wallis tests) demonstrated that the mean bond strength presented no difference when metallic and ceramic brackets were compared, but the bond resistance values were significantly different for the three adhesives used. The most common ARI outcome was the entire adhesive remaining on the enamel. CONCLUSIONS The bond strength was similar for metallic and ceramic brackets when the same adhesive system was used. ARI scores demonstrated that bonding with these adhesives is safe even when ceramic brackets were used. On the other hand, bond strength was too low for orthodontic purposes when Ortho Lite Cure was used.

Degradation of Dental Ceramics

Orthodontic appliances and dental ceramics are installed within the oral cavity and this environment presents a series of external factors that can influence the mechanical and physical properties of these devices. The environment of the oral cavity aggravates the low tensile strength of dental ceramics.

Microstructure of Ceramic Materials

The properties of ceramics depend on their microstructure, which is defined by the type, size, morphology, distribution, orientation and composition of the phases present and by the interface between the grains. In the latter case, a thick or thin layer of amorphous material may be found, originating from sintering additives. The variables involved can barely be controlled in an adequate manner, which makes it difficult to predict the final properties of a porcelain with a reasonable degree of reliability.

Ceramic Materials for Prosthetic and Restoration Use

The first uses of ceramics as dental material date from the early XVIII century. Today, ceramics are being used on a large scale as restorative materials in Dentistry. This includes materials for dental crowns, prosthesis cementation and total and partial dentures.

Ceramic Materials for Orthodontic Use

In the last three decades, great advances have been made in the mechanical properties of ceramics, reducing the presence of defects, increasing the degree of homogeneity and improving the microstructure in order to increase strength. The advent of the manufacture of laminated ceramic composites is improving the properties of ceramic materials.

Dental Alumina: Microstructure and Properties

Dense and polycrystalline alumina (α-Al2O3) is one of the most studied bioceramics due to the combination of its chemical inertness and its mechanical behavior (high compression strength and wear resistance), its good biocompatibility and high corrosion resistance.

Mechanical Behavior of Ceramic Materials

Ceramic materials are typically brittle materials, presenting very different mechanical behavior when compared to metallic and polymeric materials. Usually, the most important mechanical properties of ceramic materials concerning their mechanical behavior are tensile strength and fracture resistance, based on concepts of Fracture Mechanics.

In vitro force delivery of nickel-titanium superelastic archwires in vertical displacement

OBJECTIVE: The purpose of this study was to evaluate the force delivered by different superlastic nickel-titanium wires during vertical displacement, in order to determine whether their stress release meets the criteria for constant and light forces that are usually accredited to these archwires. METHOD: Ten samples of 6 brands of 0.016-in archwires (Ormco, GAC, Morelli, TP, American Orthodontics e Rocky Mountain) were tested in a complete metal model using Dynalock brackets (3M Unitek™). In the canine position, there was a sliding bracket connected to a pole. This set was related to a load cell of 0.5 kg attached to a universal testing machine (Autograph AG-199kNG, Shimadzu). The crosshead speed was 0.5 mm/min and the maximum displacement was 1.0 mm. The model was submerged in temperature-controlled water. The results were analyzed by ANOVA (p < 0.05), using the software SAS System 8.02, Cry, NC, USA. RESULTS: The TP archwire had the lowest force throughout the test, although the final force was high (277.91 g). The Rocky Mountain archwire had the highest force release (455.41 g). CONCLUSION: The different brands of wires tested in this study failed in delivering low and constant forces as expected from superlastic nickel-titanium wires. The forces were extremely heavy for a vertical tooth movement.