A clinical study of glass ionomer cement

The aim of this investigation was to compare the clinical performance of a glass ionomer cement (GIC) with a composite resin when used for direct bonding of standard edgewise orthodontic brackets. Fourteen patients (10 females, four males), in whom 242 teeth were bonded with brackets, were divided into two groups: GIC (121 teeth) and composite (121 teeth). The brackets were allocated to alternate quadrants and first-time failures were recorded over a period of 24 months. Data were analysed statistically (non-parametric chi-squared test). The results demonstrated a significantly lower unpreviewed debonding index (UDI) (15.7 per cent) for the composite than for the GIC (28.1 per cent) (P = 0.042). The use of heavy archwires was largely responsible for this difference. No difference was observed when light and medium archwires were used. GIC may be a viable alternative to composite for use with light archwires and with limited treatment objectives.

Resin bonding to various alloys by means of the Silicoater MD System

The aim of this research was to evaluate the effectiveness of the Silicoater MD System for bonding resin to four different Brazilian alloys. The alloys included the following proprietary materials: Duracast, Durabond II, Palad and Premium. Biobond II, a popular nickel-chromium alloy has been used as control. Dentacolor served as the veneering agent. All specimens were thermo-cycled for 24 hours between 41 degrees and 131 degrees C at a dwell time of one minute per temperature. Shear-bond strengths ranged from 1667 to 2842 psi. Scanning electron microscopic evaluation demonstrated no gap formations at the resin/metal interface for all of the aforementioned systems, the Silicoater MD System demonstrated acceptable retention efficiency in five types of metallic alloys.

VariGlass fluoride release and uptake by an adjacent tooth

PURPOSE

To quantitatively analyze in vitro the fluoride release from proximal VariGlass restorations and resulting uptake by the enamel of adjacent teeth.

MATERIALS AND METHODS

Sixty impacted third molars were used and assigned to three groups: C: control, teeth without restorations; RC: teeth with resin composite restorations (Prisma APH); and PMRC: teeth with polyacid-modified resin composite restorations (VariGlass). Each group consisted of four sets of five teeth each. In the latter two sets, by alternating restored and unrestored teeth, the proximal surfaces of three unrestored teeth with an area of exposed enamel were in contact with the restored proximal surfaces of two other teeth. The sets were submitted to high caries challenge conditions with demineralizing and remineralizing solutions for 14 days. The fluoride of each solution and the fluoride uptake were determined and statistical analyses were carried out (ANOVA and Tukey's test).

RESULTS

The highest mean fluoride concentration occurred with Group PMRC in both kinds of solutions (P < 0.01), but this value was higher in the demineralizing solution (P < 0.01). Over the 14 days, however, this mean gradually decreased in both solutions (P < 0.01). Group PMRC also showed the highest mean fluoride uptake (P < 0.01), which gradually decreased with depth in the enamel (P < 0.01).

Diffusion of calcium through dentin

The purpose of this research was to investigate whether calcium ions from a paste of calcium hydroxide [Ca(OH)2] and saline introduced into root canals diffuse through the dentin to reach the surface of the root. Six teeth were opened and submitted to a biomechanical process, after which all the smear layer was removed. The experiment was divided into three phases: dissolution, dissolution and diffusion I, and dissolution and diffusion II. Dissolution-each tooth, with no Ca(OH)2 paste in place, was sealed both cervically and apically and stored in 700 ml of deonized water until calcium losses from the tooth into the water were stabilized. Dissolution and diffusion I-each root canal was filled with a paste of Ca(OH)2 and saline, sealed again apically and cervically, and returned to its solution. Dissolution and diffusion II-samples were divided into three parts: the control group or group 1, containing the original paste; group 2, in which the existing paste was diluted and the teeth were resealed and replaced in their solutions; and group 3, in which the existing paste was removed and a fresh paste was introduced. The diffusion was greater in group 3, followed by group 2. In the control group, we found a diffusion of calcium, which is statistically null. The results showed that calcium diffusion was observed, in the first 16 days, in all situations in which there was Ca(OH)2 paste inside the root canals.

Clinical comparison between a glass ionomer cement and a composite for direct bonding of orthodontic brackets

The clinical performance of a glass ionomer cement for direct bonding of orthodontic brackets was compared with a composite resin routinely used in this procedure. Brackets were bonded, using both materials, in alternate quadrants of 16 patients of the Orthodontic Clinic of the State University of Rio de Janeiro. A total of 225 teeth, 112 in the glass ionomer cement group and 113 in the composite group, were tested. Bond failure frequencies were recorded for 12 months, and chi-square statistical test was carried out comparing the failure rates of the materials. The composite showed a statistically significant lower failure rate (7.96%) than the glass ionomer cement (50.89%), regardless of the dental arch tested. Although the glass ionomer cement presents important properties not observed in the composite, it is necessary to increase its cohesive strength to permit its clinical use for direct bonding of orthodontic brackets.

Direct bonding to porcelain

Orthodontic brackets were bonded to 180 faces of 45 porcelain cubes that were divided into three groups according to their surface preparation. In group I, the glaze had been removed with a sandpaper disk, whereas in group II, it was maintained. A solution of acidulated phosphate fluoride (APF) gel was applied to the samples in groups I and II for 5 minutes after pumicing. In group III, the glaze had been removed with a coarse diamond bur. Each group was further divided into four subgroups, depending on whether a priming agent had been used, and the type of composite used to bond the brackets. Shear force was used to debond the brackets, and the results showed that the APF solution was unable to provide enough retention on porcelain surface to bond brackets. Mechanical retention, obtained with a coarse diamond bur, was necessary to increase bond strength, which can be further improved by chemical bonding, with a silane priming agent. Therefore bonding to porcelain is clinically possible and is an acceptable procedure in orthodontic treatment.

Effect of different time intervals between sealant application and bracket bond on adhesive strength

The effect of variation of time between the use of the sealant and the composite itself on the bond strength of the enamel-resin-bracket system was tested in vitro for two composites. Eighty brackets were bonded to extracted human molars, half for each composite. The sealant was applied 1 minute, 2.5 minutes, 5 minutes, and 10 minutes before the use of the composite. The brackets were submitted to a shear force until debonding. Means and standard deviations were calculated. No statistically significant differences were found among the different times of sealant application and between the two composites tested, when a two-way analysis of variance was carried out.

Direct bonding brackets: unfilled versus unfilled/filled resins

The clinical and clinical/laboratorial performance of unfilled/filled and only unfilled resins for direct bonding of orthodontic brackets were evaluated. In the clinical part, brackets were bonded using both techniques in alternate quadrants of eleven patients of the Orthodontic Clinic, State University of Rio de Janeiro. A total of 118 teeth, 59 in each group, were tested and bond failure frequencies were recorded for six months. For the clinical/laboratory part, upper and lower premolars to be extracted for orthodontic reasons, were selected. Thirty-two brackets were bonded in vivo--16 using unfilled/filled and 16 using only unfilled resins--and the teeth were kept in the mouth for two months. After extraction, the teeth were secured in plastic rings and an Universal Instron Machine was used to debond the brackets. No statistically significant differences were observed for clinical failure rates, nor for laboratory debonding strength between the two techniques. Failures occurred preponderantly at the bracket/resin interface, so that most of the resin remained bonded to the enamel surface on both groups.

Polishing after debracketing: its influence upon enamel surface

The effect of different time periods of polishing, after debonding orthodontic brackets, upon enamel surface was investigated. Nine brackets were bonded onto nine healthy human teeth, extracted for severe periodontal disease. The brackets were removed after twenty-four hours and the composite was removed from the dental surface with a tungsten carbide bur. Three of these teeth were polished with a rubber cup, pumice and water for 30 seconds. Three others had the same procedure for 10 seconds and the last group did not received any polishing. The three groups were examined at the Scanning Electron Microscope and compared with the sound enamel of the same teeth. The results showed that pumicing is necessary after debracketing, although, even after 30 seconds of polishing, composite is still found on the enamel surface. The three procedures did not provide a surface equal to the sound enamel, but better results were obtained by increasing polishing time.

The standardized stop: a new concept in endodontics

This article presents a technique for making and using disposable standardized silicone stops. The stops have several diameters, colors, and thicknesses in order to make nonsurgical endodontics more efficient and improve the quality of therapy.

The orientation and direction of rods in dental enamel

Enamel rods are commonly accepted as perpendicularly oriented to the tooth surface and this concept has influenced the design of cavity preparations. This investigation studied the orientation and direction of enamel rods at the outer third of the enamel plate. Fifteen human molars were randomly selected and sectioned in the buccolingual, mesiodistal, and coronal directions. Angulations of the rods at the outer surface were measured by use of a protractor superimposed on the micrographs taken by scanning electron microscope. The mean angulation for axial surfaces was 60 degrees. The enamel rods were consistently parallel to the long axis of the tooth with 55-degree mean angulation. The conclusion was that enamel rods are not perpendicular to the surface except at the edge of the cusps and occasionally at the cervical area.

Sealant and resin viscosity and their influence on the formation of resin tags

The ability of resin to penetrate tooth enamel during orthodontic bonding may be affected by the viscosity of the resin and the presence of a sealant. Twenty-four extracted molars were randomly divided into six groups of four. Three resin viscosities were applied with and without sealant and resin tag formation was studied with a scanning electron microscope. Statistically larger resin tags resulted in the group using the more fluid composite resin (orthodontic Concise) in combination with the sealant, although the frequency, regularity and form of the tags did not differ significantly among the various viscosities.