Color and translucency changes during and after curing of esthetic restorative materials

OBJECTIVES

This study was conducted to evaluate various types of contemporary resin composites and glass ionomer restorative materials for color differences that occur during light curing and after submersion in water. Additionally, translucency was evaluated through the use of a translucency parameter for each of these materials at these times.

METHODS

A translucency parameter was calculated from observed colors of 2 mm thick layers of light, medium and dark shades of popular restorative materials on black and white backings. The colors of these materials were also calculated, based on Kubelka-Munk theory, for layers on a B2 shade backing. Repeated measures analyses of variance were used to identify statistically significant factors for color differences and translucency parameters.

RESULTS

A statistically significant interaction was found between the products, shades and time intervals or times studied for both color difference and translucency parameter. There is relatively high variability in both lightness and translucency changes among these popular products, with some products increasing and others decreasing in these parameters with curing and subsequent water submersion.

SIGNIFICANCE

Kubelka-Munk theory can be used to calculate the color of a layer of material on a backing other than those used to determine the Kubelka-Munk coefficients, thereby increasing the efficiency of research into the optical properties of esthetic restorative materials. The relatively large optical changes which occur as popular esthetic restorative materials are cured and subsequently submersed in water indicate that these changes should be taken into account during any initial clinical appearance match at placement of the unset material.

Irreversible hydrocolloid and gypsum interactions

This study examined the compatibility of nine popular gypsum products with three more recently developed irreversible hydrocolloid impression materials, some of which were disinfected before pouring. A test die and evaluation procedure conforming to ANSI/ADA specification no. 18 standards were used to evaluate detail reproduction of the impression materials and detail transfer and roughness of the resultant die. Statistical evaluation of the data revealed that there continue to be deleterious surface interactions between specific irreversible hydrocolloid materials and gypsum products. Analysis also confirmed that the phenolic disinfectant used in this study did not influence the surface interaction between materials nor alter the resultant dimensional properties of the gypsums used.

Mechanical property and microstructural variations for recast low-gold alloy

Using polystyrene plastic patterns meeting the dimensional requirements of ANSI/ADA specification no. 5, tension test specimens were recast multiple times from a popular Type III gold (46%) alloy. The alloy was melted by electrical heating in a graphite crucible and four conditions were compared: new alloy and alloy cast two, three, and four times (n = 4). After casting, age-hardened specimens were loaded at an elongation rate of 0.5 mm/min until failure, and the stress-strain plots were recorded. Values of yield strength, tensile strength, and percentage elongation for the specimen groups were analyzed by one-way analysis of variance, followed by the Student-Newman-Keuls multiple range test. Significant decreases (P < .01) in yield strength and percentage elongation occurred with recasting, although there were no significant differences (P > .05) in tensile strength. Scanning electron microscope examination revealed that the number of casting defects increased with remelting, and that their presence dominates the tensile fracture process. The variation in mechanical properties of the alloy with remelting was attributed to these casting defects.

A comparison of an accelerated technique for casting post-and-core restorations with conventional techniques

PURPOSE

This project compares an accelerated technique for the casting of post-and-core restorations with four traditional techniques. The accelerated technique uses two phosphate-bonded investments and the traditional techniques use a gypsum- and a phosphate-bonded investment. The study measures and compares the differences between the seating of the casting and the seating of the acrylic resin pattern. The effects of the techniques on the fit of castings with and without a ferrule are also compared.

MATERIALS AND METHODS

Six groups of 10 castings were made from plastic patterns formed on a stainless steel test die. A different investment and/or burnout method was used for each group. Each group had two subgroups: ferruled and nonferruled. The fit of the plastic patterns was measured at two time intervals after forming, 2 weeks and 3 months. The patterns were invested immediately after the 3-month measurement, and the difference in fit of the castings was calculated. An ANOVA and Tuckey-Kramer test were done to determine the statistical validity.

RESULTS

The seating of the patterns after 3 months of storage was consistently worse than the 2-week measurements of fit. The ferrule and nonferrule patterns were not statistically different in seating. Measurement of the castings showed that the ferruled castings seated significantly worse than the nonferrule castings. The difference in the seating of the castings as compared with the patterns was considered clinically unacceptable, showing a range of 0.301 mm to 0.528 mm. The nonferrule castings showed a significant difference in seating among groups. The difference ranged from -0.099 mm to 0.322 mm.

CONCLUSIONS

The castings of the ferrule subgroups were considered clinically unacceptable and were not analyzed for significance. Among the nonferrule castings, the group using a gypsum investment and conventional technique for investing and burnout but no ring liner showed the best seating. The accelerated technique was intermediate in seating with a difference of 0.148 mm from the seating of the patterns. This group was significantly different from the two best groups but not from the remaining three groups.

Incisal-edge strength of porcelain laminate veneers restoring mandibular incisors

Porcelain laminate veneers can be used to increase incisal-edge length. The purpose of this study was to determine the fracture resistance of porcelain veneer restorations on Cymel 1077 mandibular incisors that were incisally reduced 0.0, 0.5, 1.0, and 2.0 mm. Variables studied were incisal-edge length and the angle of applied force. Sixty-one porcelain laminate veneers were made to restore incisal-edge length and bonded to the prepared teeth. Samples were fractured at force angles of 130 degrees and 137 degrees. No significant difference was found between varying incisal-edge lengths (P > .05). However, the lower applied angle required greater average force to fracture (P = .005) as tested by ANOVA.

Cement luting thickness beneath porcelain veneers made on platinum foil

Porcelain laminate veneers were made using a platinum foil matrix and were subsequently cemented to mandibular anterior Cymel teeth. Cement film thickness was measured in six predetermined locations. Repeated measures analysis of variance and single degree of freedom contrasts delineated a significant difference between marginal openings at the incisal edge where foil is folded and in four of the other vertical areas (132 versus 74.1 microns). Marginal cement film thickness of veneers made on platinum foil is less than that reported for veneers made on a refractory investment.

Occlusal accuracy of casts made and articulated differently

This study evaluated the occlusal accuracy of gypsum casts constructed from irreversible hydrocolloid and selected nonaqueous elastomeric materials. Master metal casts were attached to a vertically moving apparatus that allowed their occlusal surfaces to produce repeatable contacts. Impressions were made with irreversible hydrocolloid, polysulfide, and vinylsiloxane. Resulting maxillary casts were mounted with a constant positioning device and mandibular casts were mounted with zinc oxide-eugenol paste records or by maximum intercuspation. Four specific master occlusal contacts were compared with contacts generated from the mounted gypsum casts; a perfect score was 40 (four contacts x 10 casts). A chi-square linear model for category data was used to compare groups. Results indicated that casts made from irreversible hydrocolloid should not be articulated with the use of a zinc oxide-eugenol paste but are best articulated by using maximum intercuspation (32/40 contacts).

Prosthetic and surgical management of osteogenic sarcoma of the maxilla

Maxillary surgical defects resulting from resection of oral neoplasms vary in size from small perforations of the hard and soft palate to complete removal of these structures. Osteogenic sarcoma is of unknown etiology and is a rapidly growing tumor that may produce pain, paresthesia, and anesthesia. The recommended treatment of radical resection often results in defects that produce significant orofacial disfigurement. These defects, regardless of size, present significant functional disability, with compromised esthetics, mastication, and deglutition. Restoration with a maxillary obturator prosthesis can reestablish the physical separation between oral and nasal cavities and, in soft palate defects, enable normal palatopharyngeal function. Most patients can be rehabilitated successfully with restoration of speech and swallowing to normal levels and significant improvement in appearance.

The effects of a liquid dispersing agent and a microcrystalline additive on the physical properties of type IV gypsum

This study evaluated the effects of a liquid dispersing agent (LDA) and a microcrystalline additive (MCA) on selected physical properties of type IV gypsum. Working consistency, setting time, setting expansion, and compressive strength (1 hour and 7 days) were determined, following ADA Specification No. 25, on a standard, LDA (0.5, 1, 1.5, and 2 mL), MCA (21.1, 24.1, and 27.1 gm), and combination (LDA 0.75 mL + MCA 12.05 gm) mixes per 300 gm of gypsum. Results indicate that the additives affect the consistency of the mix, but consistency can be kept close to that of the standard by lowering the water/powder ratio. Statistical analysis of the data indicated that the additives significantly affected the setting time, setting expansion, and both the 1-hour and the 7-day compressive strengths. SEM examination of fractured surfaces of test mixes indicated improved crystal packing. The properties of type IV gypsum can be improved by optimizing the amount of LDA and MCA additives.

Precious and noble-based casting alloys

Some medium-gold and midrange gold alloys are satisfactory substitutes for Type III alloys, but tarnish may occur. Considering all factors, Type III alloys remain unparalleled as fixed restorative alloys. Some medium-gold and midrange gold metal-ceramic alloys are superior to their high-gold counterparts and are the choice for metal-ceramic restorations.

Post-ceramic soldering of various alloys

A base metal alloy was soldered to precious and semiprecious alloys using a post-ceramic soldering technique. The specimens were tested by the tensile mode and the results statistically analyzed. The solder joints involving the base metal had strengths comparable to the precious and semiprecious joints. However, a high percentage of the base metal joints were too weak to be tested. Further study using other solders is indicated.

Measurement of paint-on die spacers used for casting relief

Three paints used for die spacing were measured for film thickness. Two of the materials are marketed as die spacers, and the third is sold as a model airplane paint. The materials were applied to stone dies in multiple coats. They were embedded in resin, sectioned, and measured photographically through a microscope. The three die spacing materials were capable of achieving clinically acceptable relief in the range of 20 to 40 mu by using a variable number of coats. Different paints produced different thicknesses. The two paints sold specifically for die spacing gave 11 to 13 mu per coat. The hobby shop paint had the smallest film thickness per coat, yielding approximately 5 mu per layer. It also had the smallest standard deviation. This control plus the relative low cost and availabilty make it attractive for this purpose.

An investigation of epoxy resin dies

1. Complete crown epoxy resin dies are undersized. 2. MOD onlay epoxy resin dies are accurate. 3. Detail duplication of epoxy resin dies is comparable to that of die stone. 4. Hardness values of epoxy resin are generally less than those of die stone. The hardness of Epoxydent closely approached that of die stone.

The effect of nonionic surfactants on bubble entrapment in elastomeric impression materials

The incorporation of certain nonionic surfactants into silicone and polysulfide elastomers increases their wettability by gypsum products and consequently results in less bubble entrapment in poured casts. The choice of the most effective surfactant is critical and differs not only between types of elastomer, but also between brands of a single type. The beneficial effect of the optimal surfactant is not reduced by rinsing the impression prior to pouring. While the working time of silicone is increased by surfactant additions, that of polysulfide is essentially unaffected, as are the dimensional accuracies and permanent deformations of both materials.

Prediciting the clinical success of restorative dental materials

This paper discusses dental restorative resins, alloys, cements and implants and emphasizes the need for useful laboratory information that will predict the clinical behavior of these materials and structures.

A flexural method for evaluation of metal-ceramic bond strengths

A test technique is presented for evaluating metal-ceramic bond strengths. The test piece consists of a four-point loaded metal beam with porcelain bonded to the central tension side of the beam. The test produced failures at predictable locations and was able to differentiate between metal surface treatments.

Amalgam containing nickel or tungsten dispersions. I

Wetting tests were conducted to determine compatability between select dispersion powders and Ag3Sn. Subsequently, a method was perfected for incorporating nickel or tungsten powder into the Ag3 Sn ingot. Initial studies reveal good distributions of the dispersed phase in the ingots and the comminuted alloys, after amalgamation, appear to retain their normal working characteristics.

Amalgam containing nickel or tungsten dispersions. II

The technique of injecting dispersed phase particles into an Ag-Sn melt followed by rapid quenching was utilized. Results of this investigation show that a marked improvement of the brittle amalgam alloy occurs.

Improving the fracture resistance of dental ceramic

A time-temperature sequence for optimally strengthening dental ceramic by ion exchange was investigated. Stress relaxation occurs at higher temperatures and/or longer times. Improved strenghts are obtained in a reasonable period of time that could be used for clinical application.

The effect of added particles on the properties of Ag3 Sn-additive amalgams

Physical and chemical properties of amalgam alloys containing varying amounts of copper were evaluated. Evidence presented refutes the theory of physical strengthening due to the addition of silver-copper by its eutectic. Results suggest that reactive copper could be more advantageously added to the system by using fewer copper additive particles; these particles may need to have a greater copper content that those used in Dispersalloy.

Loading rate and temperature as variables in amalgam bending

Three commercial dental amalgams of known dissimilar clinical properties were evaluated in pure blending at widely different loading rates and temperatures. Comparative data of fracture stress at 140 F rank these alloys according to their clinical fracture resistance; the phenomenon of creep may account for early marginal fracture prior to corrosion-induced fracture.

Adherence of ceramic coatings on chromium-cobalt structures

A method has been developed for the consistent adherence of flame-sprayed ceramic coatings to Vitallium. The critical step involves etching the metal by the anodic polarization technique. This procedure allows complex geometrics to be corroded evenly, and, by suitable choice of etching solution and conditions, enables any metal to be substituted. The bond is capable of sustaining more severe deflections than are experienced during intraoral function. Despite the number of cracks generated during testing, the ceramic layer remains intact. The ceramic-metal bond is mechanical. The corroded surface provides greater surface area, thus permitting a number of retention sites. Analysis of the ceramic microstructure finds it to be suitable for tissue ingrowth.

Preceramic and postceramic solder joints

This investigation evaluated preceramic and postceramic soldering procedures. Three gap spaces and two soldering methods were evaluated. Wider gaps produced stronger joints. The strongest joints were achieved by using wider gaps and the oven soldering technique. Very wide gaps (0.76 mm.) are not recommended because of possible distortion through excessive solder shrinkage. However, in practice, many solder joints exceed the 0.31 mm. recommended minimum; these joints will not show decreased strength.

Selection of a resin system for anterior fracture treatment

The tensile strength of the bond formed between etched bovine enamel and selected resin systems was evaluated; also, the need for a resin pulpal barrier was examined. Results indicate that the BIS-GMA unfilled primer is unnecessary for strength or as a pulpal protectant. The large scatter of results substantiates the clinical hypothesis that the effectiveness of the acid etch is highly variable.

Laser fusion of selected dental casting alloys

Laser-fused precious, nonprecious, and mixed metal welds were investigated for optimum weld energy requirement as determined by tensile strength tests. These strengths were compared to soldered unions. Laser fusion is as good as, or better than, unions created by conventional dental joining methods.

Small specimen strain measurement by moiré fringes

The moiré fringe technique of strain analysis was applied to small beams of resin restorative materials. The feasibility of using this technique on small dental materials specimens was established.

Wear characteristics of burs

A wear test was conducted to evaluate carbide dental burs. There is great variability within each bur type, which renders a particular bur highly unpredictable; this can be correlated to the variability in the carbide material. There is little hope that existing burs will be improved through changes in the sintered carbide system alone.

Effect of viscosity on the accuracy and stability of elastic impression material

A ram and cylinder penetrometer was designed to measure the viscosity of impression materials at their time of placement. Viscosity had no effect on accuracy or stability of the impression materials within the viscosity ranges studied.

Marginal fracture vs mechanical properties of amalgam

The clinical marginal fracture characteristics of three commercial dental amalgams were evaluated and compared with a number of their mechanical properties to determine which properties would relate best to clinical performance. It was found that compressive strength, tensile strength, transverse strength, transverse deflection, and flow as determined by ADA Specification No. 1 were ineffective, whereas the rheological properties of dynamic creep, static creep, and slow compressive strength appeared effective in relating to marginal fracture.