The cutting effectiveness of carbide fissure burs on teeth

The cutting effectiveness of the burs decreased with time. While the multivariate analysis of variance showed an overall difference among the three groups, these differences appeared to be due to the shape of the curves (the linear and quadratic components) rather than to their average location (the mean). Therefore there were no significant differences in cutting among the three types of burs tested. The SEM photomicrographs showed that there was no gross bur damage after the burs were used for cutting tooth structure. The cutting mechanism of a carbide bur on tooth structure needs further investigation.

Comparison of the retentive strength of two cast gold pin techniques

The retention contributed by the use of pins with gold castings can be substantially increased by the technique of placing a threaded pin in the dentin and making a casting with a threaded receptacle to fit the pin. The basis for the improvement is the greater retention of threaded pins to dentin compared to that of smooth, cemented pins that are part of the casting. The limitation on the retention achieved with the new technique is the cohesive strength of the cement. Zinc phosphate cement provided the highest retention, and EBA and polycarboxylate cements provided lower and similar retention when threaded pins were cemented to threaded receptacles.

Acid etch bonded cast orthodontic retainers

We have described a technique which involves the use of a cast orthodontic retaining appliance bonded by the acid etch technique and composite resin for semipermanent retention. The technique provides an alternative form of treatment which offers some unique advantages over previous retentive techniques.

Dentinal crazing and interpin distance

All three types of self-threading plus cause dentinal crazing. The frequency and degree of damage done to the dentin varies significantly between the three types of pins and depends upon the differences in the diameters of the drill and the pin. When two or more pins are placed in dentin, the potential for dentinal damage increases. Minikin pins (0.019-inch diameter) caused the least damage, in terms of both degree and frequency. The optimum and safe interpin distance using Minikin pins suggested by this study is 3 mm. Minim and Regular pins (0.023- and 0.031-inch diameters, respectively) caused more injury than Minikin pins. The Regular pins showed more damaging effects on dentin than Minim pins, both in terms of degree and frequency. On the basis of this study, the minimum interpin distance using Minim or Regular pins should be 5 mm. These minimum interpin distances are applicable only in situations where the dentin is not dehydrated or embrittled due to endodontic treatment. In teeth that have been endodontically treated, it would be advisable to use only the smallest self-threading pins and possibly increase the interpin distance if two or more pins are to be used.

The effect of finishing on the anodic polarization of high-copper amalgams

The influence of surface finishing procedures on the corrodibility of high-copper amalgams was measured. Anodic polarization curves were determined in Ringer's solution for amalgam samples made from a dispersion and a ternary alloy. Three types of finishes were compared: as carved, burnished, and polished. The polarization curves of the burnished and polished specimens were statistically similar (P greater than 0.05) at all potentials investigated. The carved samples exhibited higher corrosion currents at most of the potentials investigated.

The effect of surface finish on the anodic polarization of a conventional spherical amalgam

The corrosion of carved, burnished, polished, and burnished--polished samples of a conventional spherical amalgam was studied by anodic polarization in Ringer's solution. The effect of the variation of the mercury content from 40 to 60 wt% on the corrosion of burnished or polished samples was also investigated. It was found that burnished and burnished--polished samples corrode the least and carved samples the most. The current-density peak associated with gamma2 was of greater magnitude in polished specimens than in burnished specimens throughout the range of mercury concentrations investigated. It is hypothesized that lower porosity and more ready passivation of the surface due to a high amount of gamma2 are the reasons that burnished samples corroded less than polished samples in this anodic polarization test.

Microleakage and enamel finish

Cavity preparations that are finished with hand instruments allow significantly less marginal leakage than those which are completed only with rotary instruments. This does not mean that hand-instruments walls are perfectly smooth; it only means that these walls allow less marginal leakage. Cavity preparations restored with composite resin showed more marginal leakage than those restored with amalgam. Also, the degree of marginal leakage was greater in cavity preparations restored with composite resin than in those restored with amalgam. Cavity preparations are more prone to marginal leakage at sharply defined cavosurface acute angles than at the smooth or straight surfaces of the cavity. This pattern of marginal leakage was true for both amalgam restorations and composite restorations, but the degree of marginal leakage was greater when composite resin was used as a restorative material. Since less marginal leakage was found in the finished cavity preparations, it is obvious that all cavity preparations must be finished with hand instruments. This may not completely eliminate the problem of marginal leakage, but it will reduce the potential secondary caries both in degree and frequency. Also, since sharply defined acute angles did exhibit more marginal leakage, this part of the cavity preparation needs special attention. With amalgam and composite restorations at least, these angles should not be sharply defined but should be slightly round, so that better condensation of restorative materials can be obtained. This may reduce the degree of marginal leakage.

Estimation of the phase distribution in dental amalgam with the electron microprobe

The phase distributions of several dental amalgams have been determined by two methods: calculation from elemental analysis data obtained with the microprobe, and measurement of phase areas on backscattered electron photographs with the image analyzer. The results of these methods agree, in general, with the distributions predicted by the stoichiometric equations.

Effect of surface preparation on phase distribution of amalgam surfaces

Several types of amalgams were prepared with carved, burnished, or polished surfaces. Elemental analyses were made of these surfaces with the electron microprobe and the phase fractions were calculated from these data. The phase distributions were found to vary with the technique of finishing.

The strength of multilayer and repaired composite resin

Composite resin surfaces that formed against a plastic matrix or that polymerized while exposed to air were excellent substrates for the adhesion of new resin. Samples formed by the addition of composite resin to a cut surface had a tensile strength of one half of the cohesive strength of the resin. Coating the cut surface with a thin layer of unfilled resin enhanced bonding of the second composite resin layer. The use of a thin layer of unfilled catalyst resin as a bonding agent caused the most rapid development of strength and the greatest strength in samples tested after 7 days.

Scanning electron microscope study of marginal adaptation of amalgam in restoration finishing techniques

Voids and gaps between the surfaces of the amalgam and the cavity preparation were apparent in the carved and the polished samples. These spaces in the burnished specimens were filled with an amorphous bulk of amalgam apparently caused by the burnishing process. Since the margins of burnished amalgam restorations have been shown to leak less than those of carved and polished specimens, it is hypothesized that this is due to the improved marginal adaptation attained through the burnishing process.

Microstructure of amalgam surfaces

The polished amalgam surface was smoother than the burnished and the carved surfaces. The burnished surface was smoother than the carved surface. The granular structures on the burnished amalgam surface were found to be of tin-mercury alloy. Polishing appears to be the best finishing technique for amalgam restorations, and there is no substitute for it.

The effect of varnish on dentinal bonding strength of five dental cements

1. The following dental cements are listed in order of decreasing mean bonding strenghts on varnish-free dentin: polycarboxylate, zinc phosphate, EBA, Fynal, and CBA. 2. The application of either Copalite or Varnal decreased the dentinal bonding strength of polycarboxylate and zinc phosphate cements. There was no change for CBA cement. 3. The application of Copalite and Varnal increased the dentinal bonding strength for Fynal to the level of zinc phosphate cement on varnish-free dentin. 4. The dentinal bonding strength of EBA cement increased with the application of Varnal but not with Copalite.

Dicarbenes. Dicarbenoid species from the reaction of 1,3-Bis(diazomethyl)benzene with zinc halides

The reaction of 1,3-bis(diazomethy1)benzene with zinc halides in diethyl ether and tetrahydrofuran gave dicarbenoid intermediates which could be trapped by olefins to give moderate yields of dicyclopropylderivatives. Insertion into a-C-H bonds of the ethereal solvents occurs in the absence of olefins. The dicarbenoid species m-C6H4(CHIZnI)2 in tetrahydrofuran was found to have a half-life of about 4h at 0�C.

Comparison of the retentive property and dentinal crazing ability of retention pins and machinist's taps

A comparison was made of the dentinal crazing formation and pull-out strength of conventional retention pins and modified machinist's taps. Modified machinist's taps produced less dentinal crazing in wet, fresh, and dried dentin than the conventional retention pins. Modified taps have sufficient pull-out strength to retain restorations on teeth with fresh dentin, in clinical situations.

Radical nature of the reaction of 4-nitrobenzal chloride with sodium hydroxide

The reaction of 4-nitrobenzal chloride with sodium hydroxide in aqueous methanol gave products which can be accounted for as arising from the dimerization and cross-coupling of the radicals 4-O2NC6H4CCl2 and 4-O2NC6H4CHCl.

Quantitative measure of mercury vapor emission from setting dental amalgam

The rate of mercury vapor emission from setting dental amalgam was measured by use of an ultraviolet light absorption technique under nondiffusion-controlled conditions. An average of 0.3 X 10-6 gm mercury per square centimeter was emitted at the experimental temperature. At 37 C, this amount was estimated to be 1.2 × 10 -6 gm/ cm2.

Effect of retainer margin and distribution of mercury on dental amalgem mercury vaporization patterns

The results of this study showed that mercury vaporization patterns were not related directly to specimen postset mercury distribution. During the setting process, amalgam specimen retainer configurations affected these patterns significantly.

Mercury vapor emission from dental amalgam

The patterns of mercury vapor emission from carved, burnished, and polished surfaces made from four commonly used dental amalgam alloys were determined with the use of a selenium sulfide detection method. Mercury vapor was emitted more intensely from the marginal region; carved and burnished surfaces emitted the same amount. There was a difference in the amounts emitted from the different alloys tested.

Effect of surface treatment on the corrodibility of dental amalgam

Potentiostatic anodic polarization data for unfinished, burnished, and polished amalgam surfaces were taken. From the standpoint of corrodibility, these tests indicated that physically improved amalgam restorations can be obtained by burnishing rather than by polishing or leaving amalgam carved and unfinished.