Managing digital images.

Although most orthodontists can rely on their orthodontic image software, those who have the need to go beyond just the monitor display of the images will need to get behind the scenes. Understanding a little of what makes up digital images and how to manipulate the variables will enable them to get optimum image quality as well as conserve on time, file size, and storage media. For those who import bitmapped images into digital presentations, the ability to adjust these variables can enable them to create presentation files that are manageable in size, will display without delays, and are of optimum resolution.

An ex-vivo investigation into the effect of bracket displacement on the resistance to sliding.

This ex-vivo study investigated the effect that repeated bracket displacement has on sliding friction and the magnitude of bracket displacement, and hence tooth movement, required to release bracket/archwire binding. The design consisted of an ex-vivo laboratory study. A jig was designed that allowed repeated displacement of a bracket to occur, while the resistance to sliding (friction) was measured using an Instron universal testing machine. One type of stainless steel bracket was used in conjunction with four archwire types (0.016-inch stainless steel, 0.019 x 0.025-inch stainless steel, 0.021 x 0.025-inch stainless steel, 0.019 x 0.025-inch beta-titanium) and four magnitudes of displacement. Repeated bracket displacement has a significant effect on the sliding resistance at the bracket/archwire interface (P < 0.001). The reduction in sliding resistance noted with displacement depended on the archwire. Over the range of displacements tested, there was an 85 and 80 per cent reduction associated with 0.021 x 0.025-inch and 0.019 x 0.025-inch stainless steel, respectively. For 0.019 x 0.025-inch beta-titanium and 0.016-inch stainless steel, these reductions were 27 and 19 per cent, respectively. The importance of true friction, given the likelihood of bracket and/or archwire displacements in vivo, may be lessened.

Effect of microfiller fraction and silane treatment on resin composite properties.

A series of microfilled resin composites were formulated by incrementally mixing either agglomerated 20 nm or unagglomerated 50 nm silica microfillers into monomers composed of diphenyloxymethacrylate and TEGDMA. The microfiller particles were prepared with and without a gamma-methacryloxypropyl-trimethoxy silane coupling agent. Following polymerization, five material properties were tested: uniaxial tensile strength, Young's modulus in slow compression, Knoop hardness, water sorption, and toothbrush abrasion resistance. Results from these tests indicated that microfiller content clearly was the most influential parameter affecting material property performance. Composites containing 20 nm particles demonstrated greater water sorption, higher Knoop hardness, and better resistance to toothbrush wear. Surprisingly, the application of silane to microfiller surfaces did not greatly improve composite performance for most of the material properties tested in this study. However, water sorption behavior over a 3-year period was observed to be more stable for materials possessing silane-treated particles. Future evaluation of coupling agents should include long-term water storage prior to conducting mechanical tests.

The effect of using custom or stock trays on the accuracy of gypsum casts.

This study examined the linear dimensional stability of nonaqueous elastomeric impressions made from stock and custom trays by measuring casts derived from those impressions at 1 hour, 1 day, and 1 week. There was a small statistical difference among casts produced from stock versus custom trays compared to the master model. However, there was no significant difference in casts produced from impressions poured at 1 hour, 1 day, and 1 week. A custom tray with a 2.0 to 2.5 mm tray spacing had the least amount of variation, yet the differences between custom and stock trays may not be clinically significant.

The effects of varied etching time and etching solution viscosity on bond strength and enamel morphology.

The effects of varied etching time and etching solution viscosity on bond strength were evaluated by measuring the tensile bond strength of a composite resin to bovine enamel. Also, six enamel surfaces were examined to evaluate the effect of acid treatment on the morphology of etched enamel using scanning electron microscopy. There was no significant difference in tensile bond strength between three etchants of differing viscosity or between etch times. Light microscopy revealed that most bond failures were cohesive in nature. When the three etchants of differing viscosity were compared under the scanning electron microscope, the liquid and the thin gel produced a more even etch pattern than the thick gel. In addition, the thin gel appeared to produce the most well-defined pattern of the three conditioners.

Efficacy testing of visible-light-curing units.

This study evaluated (1) the effect of known reductions in the output of curing lights on the depth of cure of various resins as determined by hardness measurements, and (2) the ability of the clinician to detect reduced light output by use of an explorer to compare the hardness of the top and bottom surfaces of resin specimens. Curing light output was reduced stepwise from 10 to 70% with neutral density filters. Hardness values indicated polymerization of the top surface to be generally unaffected by light blockage. Bottom surfaces were greatly affected: more with a 30-second than a 60-second cure time. Three clinicians utilized an explorer to compare the tops and bottoms of specimens of known hardness. Evaluators were unable to routinely detect differences of less than 20 to 30 Barcol numbers. The data indicate that a light meter is a more efficacious means of monitoring curing light performance than is a tactile test of resin surface hardness.

Effect of root canal treatments on dentin permeability.

Calcium hydroxide has been used to slow or reverse external root resorption subsequent to trauma. In this study, an experimental model was established to study the diffusion of calcium ions from the canal to the root periphery after various intracanal treatments. Analyses of calcium ion concentrations from extraradicular samples revealed that dentin specimens varied in their rates of diffusion of calcium and that treatment of the canals with various agents affected the amounts of calcium recovered.

Class 5 composite resin restorations: margin configurations and the distance from the CEJ.

An in vitro study of 60 teeth examined the cervical microleakage of class 5 composite resin restorations in regard to preparation design and location from the cementoenamel junction (CEJ). Four groups of 15 teeth each were prepared for a class 5 composite resin restoration with the cervical margins finished as follows: a butt joint margin placed less than 1 mm from the CEJ, a beveled margin placed less than 1 mm from the CEJ, a butt joint placed greater than 1.5 mm from the CEJ, and a beveled margin placed greater than 1.5 mm from the CEJ. The teeth were acid etched, treated with an enamel bonding agent, and restored with a microfilled composite resin, and then sectioned for further analysis. The sectioned specimens were evaluated for cervical microleakage by Ca45 autoradiography. The butt joint margins placed less than 1 mm from the CEJ had significantly more microleakage than the other groups, indicating that all enamel margins of a class 5 composite resin restoration should be beveled to decrease microleakage regardless of their location relative to the cementoenamel junction.

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins.

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.

The glass-ionomer-lined cervical composite restoration: an in vitro investigation.

The marginal adaptation and microleakage of the glass-ionomer-lined composite resin restoration in simulated erosion and conventional class 5 preparations were evaluated. The most common site of leakage for all restorations was the gingival margin. In erosion lesion restorations, the etched thick liners were superior to the etched thin liners with respect to marginal leakage. Acid-etched and unetched liners in both the erosion lesion and the conventional class 5 restorations were comparable. Under the SEM a gap was often found in the liner rather than at the liner-resin interface in restorations with etched liners.

Influence of selected variables on adhesion testing.

Three variables associated with adhesion testing were examined: (1) the test mode, shear and tension; (2) design of the tensile apparatus; and (3) tooth substrate, human and bovine. Findings revealed no significant differences in bond strength by one tensile test and a shear test. However, the shear test produced more true adhesive failures; thus it may be preferable to use a shear test for adhesion testing. Bond strengths with some adhesive systems differed significantly when tested by two different tensile apparatus. Design of the test apparatus appeared to affect values. Bond strength measurements obtained with human and bovine enamel were essentially comparable. Values with dentin varied. There appeared to be a trend for higher bond strength values with bovine than with human dentin.

In vitro evaluation of the use of resin liners to reduce microleakage and improve retention of amalgam restorations.

This in vitro study evaluated the ability of three commercially available adhesive resins to reduce microleakage and provide retention between amalgam restorations and tooth structure. Results indicated that Amalgambond reduced leakage significantly more than Panavia EX, Prisma Universal Bond 2, and Copalite. In addition Amalgambond and Panavia EX exhibited the ability to bond amalgam to tooth structure. These results suggest that Amalgambond has the potential for serving successfully as a cavity liner with amalgam.

NuLYTELY (PEG 3350, sodium chloride, sodium bicarbonate and potassium chloride for oral solution).

NuLYTELY (PEG 3350, Sodium Chloride, Sodium Bicarbonate, and Potassium Chloride for Oral Solution), a product from Braintree Laboratories, Inc. is a modification of GoLYTELY (PEG 3350 and Electrolytes for Oral Solution) that has been found to have the same therapeutic advantages in terms of safety, efficacy, speed and patient acceptance. This product was developed to improve upon the taste of GoLYTELY. NuLYTELY represents an effective alternative for bowel cleansing prior to colonoscopy that may be more acceptable to some patients.

Dipentum (olsalazine sodium)

Dipentum (olsalazine sodium), a product by Pharmacia, represents the first oral delivery of sulfa-free 5-aminosalicylic acid therapy available for remission maintenance in sulfasalazineintolerant patients with ulcerative colitis. It provides a safe and well-tolerated treatment regimen that has been shown to be as effective as sulfasalazine in maintaining remission of ulcerative colitis.

Direct surface pH determinations of setting cements.

Surface pH measurements were made over a 24-hour period for several luting cements and glass-ionomer lining and restorative materials. Of the luting cements, the water-mixed glass-ionomer cement, Ketac-Cem, had the lowest initial pH and the polycarboxylate, Durelon, had the highest. Three glass-ionomer lining materials showed differences in pH that increased over the entire test period. Two of the three visible-light-cured glass-ionomer liners evaluated showed similar pH values, while the third exhibited a considerably lower pH. The lower pH values found with the water-mixed glass-ionomer luting agent suggest that acidity may contribute to the posttreatment sensitivity associated with this material.

Intron A (interferon-alpha-2b recombinant) for injection/Schering-Plough Corporation.

Intron A (Interferon-alpha-2b Recombinant) for injection, a product by Schering-Plough Corporation, is a recombinant DNA, genetically engineered copy of a naturally occurring protein which acts as an antiviral agent. This product is now approved in the United States for the treatment of chronic non-A, non-B hepatitis, also known as hepatitis C. Intron A represents an important advance in the treatment of chronic hepatitis non-A, non-B/C because until now, although many other drugs have been tried, there has been no effective treatment.

The effect of surface treatment on the Knoop hardness of Dicor.

One advantage cited for the use of Dicor over other ceramic materials is a reported Knoop hardness comparable to human enamel. However, when fabricating dental restorations, a Dicor glass-ceramic casting generally is subjected to several different surface treatments because of processing, esthetic, and functional requirements. Therefore, this study compared the Knoop hardness of Dicor specimens under three conditions: (1) cerammed, (2) cerammed and shaded, and (3) sectioned to reveal internal material. Knoop hardness differences between groups were significant (P less than or equal to .05). The cerammed surface was the hardest; it was harder than human enamel. Shaded specimens had a surface hardness comparable to dental porcelain. However, the internal glass-ceramic material, located beneath the shading porcelain and cerammed surface, had a Knoop hardness slightly higher than that of human enamel.