Karl F. Leinfelder

Pattern of Wear in Posterior Composite Restorations

Clinical evaluation of posterior restoratixe materials has showIn that wear proceeds at a mulch faster rate in coniposite resins than in amalams (PHILLIPS et al, J Prosth Dent 26:68. 197 1 28:164, 1972; LEINFELLDER et al, J Prosth Dent 33:407. 1975). With thc recent dexelopment of in vixo replication techniquies (e.g., TAx et a, Brit Dent J 137:463, 1974). wear patterns may be StUdied with the aid of the SEM. The purpose of the present iiote is to describe the Pattern of wear of posterior coinposite r estoratioris throrlh tIre LISC of c nox0cl tWO-Stagel Fre)p lication technique. C(ormcposite restoratiorns hic h hicac beuI llaced uinder clinic ally controlledcl ocnlitiolus tiP to four vears ago were relilicated in xixvo corin Xantopren BlcreU for both the negatix e imupressions arid the ptositixe replicas (R. P. Kusy and K. F L iNFiiDFoRn.tonprnlblishedc fter precoatin the seclond-staoe replica witli carbon. Au-PcI was deposited prior to observation witth the SEM.t Lsing an acceleratinxoltce,e of 2. 5 KV, condens-i ctirrert of 0.7-0.9 anipj). anJ a work-iug distainc of cLa 20 nmn, the c ciriccsl-t s

Three-year clinical study of UV-cured composite resins in posterior teeth

Four proprietary composite resins cured with ultraviolet light were inserted into Class I and II cavity preparations. The restorations were evaluated over a 3-year period for color match, interfacial staining, secondary caries, loss of anatomic form, marginal adaptation, and surface texture. The percent of restorations exhibiting no generalized loss of anatomic form ranged from 47% to 93%.

Two independent evaluations of ten amalgam alloys

Two independent research groups evaluated marginal failure and conducted creep tests on 10 commercial amalgam alloys. Correlation data determined that both laboratory tests and clinical results were essentially the same between the two studies. The 2-year clinical results indicate that five alloys, Cupralloy, Dispersalloy, Indiloy, Phasealloy, and Tytin give best results. Creep correlated with the rate of marginal failure within a study when all alloys were assessed; however, for the seven gamma-2-free alloys, there was no significant relationship between in vivo and in vitro data. Since creep tests did not predict marginal failure of the gamma-2-free alloys, the results of clinical studies should be the guide to selection of the better amalgam alloys.

In vitro Corrosion and in vivo Marginal Fracture of Dental Amalgams

The relationship between in vitro corrosion and in vivo marginal fracture of dental amalgams has been studied. The potentiodynamic cyclic polarization technique has been used to determine the in vitro corrosion index. The marginal fracture data have been obtained from previous clinical studies reported by three independent research groups. A linear regression analysis has been employed to determine the degree of correlation between in vitro and in vivo data. Depending on the method of corrosion index measurement and the source of clinical data, correlation coefficients (r) ranging from 0.82 to 0.94 (p < 01) have been obtained.

Hardening of Dental Gold-Copper Alloys

X-ray diffraction studies of several proprietary dental gold alloys demonstrated that hardening probably is a dual mechanism of precipitation and order-hardening. Lattice parameter measurements showed that the ordered structure was AuCu. In addition, it was shown that maximum hardness occurs at about 75% full order.

Hardening of Gold-Based Alloys

The relationships between composition, heat treatment, hardness and microstructure have been investigated for a number of commercial dental casting alloys and for several series of experimental gold-silver-copper compositions. The results indicate that at least two distinct hardening mechanisms must occur in these alloys.

In Situ Replication Techniques: I. Preliminary Screening and the Negative Replication Technique

Fourteen commercially available elastomeric materials were investigated for their suitability as in vivo replication media. After a preliminary screening on an annotated specimen, three materials were chosen for further study. Of all materials evaluated, Xantopren Blue and Silene silicone impression materials provided the best results in vivo. This study demonstrates that a high resolution (ca 1 micron) negative replication technique may prove useful for the clinical evaluation of single-surface phenomena.

Burnished amalgam restorations: A two-year clinical evaluation

Bu rnishing amalgam restorations has been a subject of discussion for more than 30 years. Generally, burnishing has been considered detrimental to an amalgam restoration due to a possible mercury enrichment of the surface.‘-” It was speculated that restorations treated in this manner would be more susceptible to corrosion and tarnish and thus exhibit a higher rate of marginal fracture than those finished in a conventional manner. Recently, however, a number of laboratory studies have demonstrated that postcarved burnishing of conventional amalgams does not produce the adverse effects predicted by a number of investigators.4-7 In fact, such a procedure was shown to be responsible for improving a number of physical properties. including increasing surface hardness, reducing porosity and residual mercury, and slowing the rate of corrosion. These findings have been substantiated by at least one clinical study.’ In addition to postcarved burnishing, Kanai5 and Jfirgensen and Saito” have suggested that precarved burnishing enhances the clinical longevity of conventional amalgam restorations. The technique, which consists of overfilling the cavity preparation and burnishing with heavy pressure prior to carving, supposedly causes a reduction in porosity as well as mercury content. It is the purpose of this study to evaluate the clinical performance of conventional amalgam restorations subjected to this technique.

Permeability and porosity of dental casting investments

Permeability of various gypsum- and phosphate-bonded investments was measured during conventional burn-out procedures. Porosity determinations were made on specimens cooled to room temperature after burn-out. As a group, the gypsum-bonded investments were found to be more permeable than the phosphate-bonded investments. Two phosphate-bonded investments were determined to be relatively impermeable to gas flow, while another exhibited permeability comparable to that of the gypsum-bonded investments. In spite of differences in permeability, the porosity of each type of investment was nearly constant. The porosity of the phosphate-bonded investment was approximately three-fourths that of the gypsum investments. These investments were modified by the addition of varying amounts of acrylic polymer for the purpose of altering permeability. The addition of acrylic polymer increased porosity and permeability of all of the materials included in this investigation. The acrylic additives, however, had no effect on the permeability of relatively impermeable investments unless used in high concentration. The results of this investigation would tend to substantiate the need for special spruing and venting procedures.

Evaluation of the frozen-slab technique for cementing cast restorations

C ooling the mixing surface of a glass slab to temperatures above the dew point improves the properties of zinc phosphate cement. Moisture condensation, however, produces a cement with inferior physical proper-u-s when conventional powder-liquid ratios are used.’ Cooling the mixing surface to 10” C or lower and increasing the powder-liquid ratio to establish a proper cementing consistency results in a cement mix that retains strength and solubility properties at acceptable levels.‘-’ Under these same conditions, the working time is reportedly doubled while the setting time is significantly reduced. Many studies involving the frozen-slab technique have dealt with orthodontic considerations. Little information has been reported on the use of the technique for cementing fixed restorations. The objective of this study, therefore, was to evaluate the frozen-slab technique for use in cementing cast restorations. A series of commercially available zinc phosphate cements were evaluated for film thickness, temperature rise during setting, and pH levels.