Effect of Self-etch Adhesives on Self-sealing Ability of High-Copper Amalgams.

STATEMENT OF THE PROBLEM: Similar to conventional amalgam, high-copper amalgam alloy may also undergo corrosion, but it takes longer time for the resulting products to reduce microleakage by sealing the micro-gap at the tooth/amalgam interface. PURPOSE: The aim of this study was to evaluate the effect of self-etch adhesives with different pH levels on the interfacial corrosion behavior of high-copper amalgam restoration and its induction potential for self-sealing ability of the micro-gap in the early hours after setting by means of Electro-Chemical Tests (ECTs). MATERIALS AND METHOD: Thirty cylindrical cavities of 4.5mm x 4.7mm were prepared on intact bicuspids. The samples were divided into five main groups of application of Adhesive Resin (AR)/ liner/ None (No), on the cavity floor. The first main group was left without an AR/ liner (No). In the other main groups, the types of AR/ liner used were I-Bond (IB), Clearfil S3 (S3), Single Bond (SB) and Varnish (V). Each main group (n=6) was divided into two subgroups (n=3) according to the types of the amalgams used, either admixed ANA 2000 (ANA) or spherical Tytin (Tyt). The ECTs, Open Circuit Potential (OCP), and the Linear Polarization Resistance (LPR) for each sample were performed and measured 48 hours after the completion of the samples. RESULTS: The Tyt-No and Tyt-IB samples showed the highest and lowest OCP values respectively. In LPR tests, the Rp values of ANA-V and Tyt-V were the highest (lowest corrosion rate) and contrarily, the ANA-IB and Tyt-IB samples, with the lowest pH levels, represented the lowest Rp values (highest corrosion rates). CONCLUSION: Some self-etch adhesives may increase interfacial corrosion potential and self-sealing ability of high-copper amalgams.

Effect of fluoride on nickel-titanium and stainless steel orthodontic archwires: an in-vitro study.

OBJECTIVES: The commonly used Nickel-Titanium (NiTi) archwires in orthodontic treatment are often exposed to fluoride-containing mouthwashes. The aim of this in-vitro study was to evaluate and compare the corrosion resistance of three commercially available NiTi archwires exposed to 0.05 wt% and 0.2 wt% fluoride mouthwashes. MATERIALS AND METHODS: Three different types of NiTi archwires, 0.016″ in diameter, from Dentaurum, Global, and GAC, and a stainless steel archwire from Dentaurum were examined to assess their corrosion resistance in Fusayama-Meyer artificial saliva and in two other artificial saliva containing 0.05 wt% and 0.2 wt% sodium fluoride (NaF). After the primary setup of wires, they were tested by potentiodynamic and potentiostatic polarization and corrosion potential/time analyses. Their surfaces were evaluated using a scanning electronic microscope (SEM). RESULTS: The results showed that all the wires were passive in artificial saliva. In contrast, by adding fluoride ions to the solution, the decrease in the archwires' corrosion resistance was in direct proportion to the increase in fluoride concentration. CONCLUSION: The NiTi wires experienced deterioration of their corrosion properties under the effect of fluoride but not as much as the stainless steel archwires.

Effects on shear bond strength and the enamel surface with an enamel bonding agent.

INTRODUCTION: The purpose of this study was to evaluate the shear bond strength of orthodontic brackets and the effect of an enamel bonding agent (EBA) on enamel surface after debonding. METHODS: Seventy-five extracted maxillary premolars were collected and randomly divided into 3 groups of 25. The enamel cracks were surveyed with a stereomicroscope. In the first group, 1 layer of EBA was applied before the adhesive resin. In the second group, 2 layers of EBA were used; in the third group, no EBA was used. Bonding was followed by incubation for 48 hours at 37 degrees C and thermocycling for 1000 cycles. Debonding was performed with a shear force. The surfaces of the teeth were evaluated, and the length, depth, direction of cracks, and adhesive remnants on the enamel surface were recorded. Data were analyzed by using analysis of variance and paired samples t tests. RESULTS: There were no significant differences between the shear bond strengths (P = 0.341) of the 3 groups, or in the direction, length, and depth of the cracks before and after debonding (P > 0.05). There was a significant increase in the number of cracks after debonding in the 3 groups (P < 0.05). The evaluation of adhesive remaining on the surface of the teeth indicated that most bond failures occurred at the resin-bracket interface. CONCLUSIONS: The use of EBA does not enhance bond strength or provide greater protection to the enamel surface during debonding.

Comparison between the external gonial angle in panoramic radiographs and lateral cephalograms of adult patients with Class I malocclusion.

The external gonial angle is an important angle of the craniofacial complex. It is significant for the diagnosis of craniofacial disorders. Lateral cephalogram and orthopantomograms can be used to determine this angle. In this study, we compared the external gonial angle determined from the two mentioned radiographs in Class I patients. We collected the radiographs of 70 patients with Angle's Class I (22 men and 48 women). The patients' age ranged from 15-30 years with a mean age of 18.24 years. The data gained were statistically evaluated by t-test. The following results were obtained. The mean value of the gonial angle in the lateral cephalogram was 125.00 degrees (men, 124.9 degrees and women, 125.04 degrees ) and in the orthopantomogram was 124.17 degrees (men 123.68 degrees , women 124.39 degrees ). The difference between these rates was 0.83 degrees (men 1.22 degrees , women 0.64 degrees ) and not significant (P = 0.406). Based on the obtained results, we can conclude that panoramic radiography can be used to determine the gonial angle as accurately as a lateral cephalogram. In addition, we can determine the right and left gonial angles of a patient in the orthopantomogram without interferences due to superimposed images of anatomical structures in a lateral cephalogram. For determination of the gonial angle, an orthopantomogram may be a better choice than a lateral cephalogram.

Endodontic treatment of a maxillary central incisor with three root canals.

Abnormal morphology of the root canal may exist in any tooth, even a maxillary central incisor. In this paper we report endodontic treatment for a rare example of a maxillary central incisor with one root and three root canals.