Ceramics: their place in dentistry.

A transfer molded ceramic coping material, Cerestore, and a castable ceramic, Dicor, are commercially available for fabrication of all-ceramic crowns. The manufacturers indicate their use should be in single unit anterior or posterior crowns. Tooth preparations are similar and should have rounded lines angles to avoid sharp points which may cause stress concentration. The amounts of tooth reduction are also similar and range from 1.0 to 2.0 mm depending on the location of surfaces. There are variations in fabricating procedures but both involve heat treatment and special equipment. Cerestore requires eventual veneer build-up and shading. Dicor requires surface shading. Both are evaluated and classified by the Council on Dental Materials, Instruments and Equipment of the American Dental Association. At least three other ceramic systems are being developed but are not yet commercially available.

Radiopacity of light-cured posterior composite resins.

Radiographic images of teeth and restorations were used to evaluate the radiopacity of 11 light-cured posterior composite resins. The radiopacity of these composite resins provided enough variation on radiographs so that clinicians distinguished the images of the restoration from adjacent tooth structure.

Irradiance of visible light-curing units and voltage variation effects.

The irradiance in the wavelength of 450 to 500 nm of nine visible light-curing units was measured at 120 V input voltage. The highest irradiance was more than 20 times that of the lowest. Irradiance was also measured at 90 to 130 V input. Irradiance and depth of cure at lower input voltages were also examined.

Bone-inducing materials: their place in dentistry.

Materials and techniques for use in the repair of periodontal defects, alveolar ridge augmentation, ridge maintenance and alveolar ridge recontouring are discussed. An increased sophistication in the use of freeze dried and frozen allogeneic bone banked materials is evident. The principal application in ridge augmentation is to provide a base for the construction of dentures or other appliances in the ageing patient. Recently developed ceramic materials, similar in composition to the normal tooth and/or bone, are being used today for both periodontal defect repair and to maintain or build-up the alveolar ridge. These materials are forms of hydroxylapatite or of beta tricalcium phosphate. Their role in causing bone growth, in providing a matrix for new bone growth and in providing a source of calcium and phosphate ions is discussed. Although the mechanism of action of the synthetic ceramics is not yet known, there is increasing evidence that some are safe and effective, especially in alveolar ridge augmentation. Effectiveness, however, depends very much on careful patient selection prior to surgery.

Evaluation of light transmission characteristics of protective eyeglasses for visible light-curing units.

Eyeglasses with protective filters are recommended for users of visible light-curing units to decrease the intensity of blue light reaching the eyes. The transmission curves of 20 commercially available filter glasses are obtained. The irradiance from eight curing units through these glasses is measured. The reduction in irradiance through the filter glasses is related to the transmission curves.

Noise level evaluation of dental handpieces.

We evaluated the noise level of fourteen air-driven handpieces, six low speed (less than 20,000 rev/min) and eight high speed (greater than 160,000 rev/min), with respect to a three-directional co-ordinate system and distances of 6, 12 and 18 in. in each chosen direction. A two-way analysis of variance of the noise level between handpieces and positions indicates that large significant differences exist amongst handpieces and in different positions, and that interaction is just barely significant. The ranking and least significant differences for the mean of all handpieces v. position and for the mean of all positions v. handpiece were compared with the results for the ranking and significances from the one-way ANOVAS for each handpiece v. position and for each position v. handpiece. A trend exists with some of the handpieces of straight design (all low speed) for increased noise levels in a direction perpendicular to the handpieces and decreased levels in a direction parallel to the handpieces. For handpieces of angled design (all high speed) both directions parallel and perpendicular (the perpendicular to the longitudinal turbine axis) to the rotor axis indicate increased noise levels. The parallel direction includes the exiting air from the exhaust port. The perpendicular direction can be indicative of an aerodynamic factor associated with the established air flow patterns. The extremes in noise level were 56.8 dBA for a low-speed handpiece of straight design at the 18 in. distance in a direction parallel to the handpiece, and 87.3 dBA for a high speed handpiece at the 6 in. distance in a perpendicular direction.

Recommendations for determining biocompatibility and safety for the clinical use of metals in dentistry.

Determining the safety of dental materials through laboratory and animal testing before widespread use of such products in humans is critical to the continued use of many materials in dentistry. The patient and the dentist have the right to expect that a manufacturer has adequately evaluated a product for safety as well as effectiveness for its intended use before making the product commercially available. Although the use of dental amalgam and casting alloys is widespread, there is insufficient documented evidence to recommend discontinuing the use of either dental amalgam or base metal casting alloys. Unless it can be shown that a patient is hypersensitive to the metal and that the hypersensitivity is indeed a causative factor in a systemic disease, replacement of existing restorations is not recommended. Nevertheless, there are specific areas of future research including actions a dentist should implement. The dentist should document cases of sensitivity to metals and become familiar with the symptoms arising from metal exposure. In screening new products for use in dentistry the FDI Technical Report No. 9, Recommended Standard Practices for Biological Evaluation of Dental Materials is relevant. The series of recommended tests for metals to be used in dentistry include initial tests to determine acute toxicity, secondary tests such as those to evaluate irritation to the tissues in contact with the metal and usage tests, i.e. tests in animals simulating intended clinical use in humans.

Bonding of restorative materials to dentine.

The potential advantages of bonding a filling material to dentine have long been recognized by the dental profession. Such bonding would prevent recurrent decay and would provide a long-lasting restoration. Bonding of suitable filling materials to enamel can be easily accomplished by first etching the enamel with acid. This opens up areas in the enamel and permits filling materials to flow into the openings and form mechanical locks. It is not possible to do this with dentine since the acid used to etch enamel would harm the pulp when applied to dentine. The present status of dentine bonding is that a small number of products are now being marketed with claims of bonding to dentine. In addition, research is being conducted on some experimental products. Results in the laboratory show that the bond strengths achieved by composite resins, using the commercially available materials on dentine, do not reach those obtained with acid etched enamel. The correlation of these results with clinical performance is unknown. Therefore, the amount of available information is at present insufficient to make recommendations on the effectiveness or ineffectiveness of commercially available dentine bonding systems. However, it appears that caution should be employed when using any product requiring an etchant or acidic cleansing agent. There is a need for further research to gain better understanding of the biological safety and effectiveness of both the present commercial and experimental dentine bonding systems.

A comparison of the effectiveness of dentine bonding agents.

Tensile and shear bond strengths between prepared surfaces of coronal dentine and cores of composite materials using different bonding systems were determined. Control procedures demonstrated that tensile bond strengths were approximately doubled by the use of bonding agents in systems requiring initial cleansing or etching of dentine. Similar increases were found in shear bond strengths. When bonding to different depths of dentine was compared shear and tensile bond strengths to the more occlusal dentine were greater than to more pulpally placed dentine. The factors which appear to affect bond strength under laboratory conditions are: etching of dentine (but beware of this procedure clinically); the smear layer and its removal; polymerization shrinkage of composite materials; the depth and plane of bonded dentine; the use of fresh or stored dentine; and the structure of the treated dentine.

Ultraviolet light stability of composite resins.

The ultraviolet light color stability of seven commercial composite resins was evaluated after 1, 8, and 15 days of exposure. Color differences between exposed and unexposed specimens stored for identical time periods were determined. Samples exposed to ultraviolet light showed large changes in Munsell Hue and Chroma, with smaller but significant changes in Value. Unexposed samples showed small changes in the Munsell components in some cases opposite those observed for the exposed samples. Statistical analysis showed that although significant color changes were observed, brands of composite resins could not be distinguished by length of storage in the dark. Time of exposure was a significant variable at 24 hours and 8 days. At 15 days a number of composite resins did not undergo additional significant color change. Scanning electron microscope showed a significant roughening of the surface of exposed composites with resin breakdown and exposure of the composite filler.

Alternative interpretations of water sorption values of composite resins.

Water sorption values for direct filling resins and an unfilled resin were much more similar at 30 days when expressed as mg/g organic matrix than as mg/cm2 or weight percent. This interpretation is indicative of the water sorption characteristics of resin matrices. The values are even more indicative when solubility or leaching is taken into consideration. With the specimen sizes used in this study, the effect of the kinetics of water sorption could be minimized by using values obtained after immersion in water for 30 days.

Effects of backing reflectance and mold size on polymerization of photo-activated composite resin.

The in vitro depth of cure of a visible-light-activated microfilled composite, as influenced by backing reflectance and mold size, was investigated using microhardness measurements. More extensive polymerization was obtained with higher values of backing reflectance. Mold size larger than the cross-sectional area of the photo-activating beam also increased the degree of polymerization. Backing reflectance and mold size are influential factors and need to be defined in depth-of-cure evaluations if in vitro measurements are to be valid predictors of clinical performance.