Amp W. Miller

In vitro investigation of the wear of human enamel by dental porcelain

STATEMENT OF PROBLEM Metal ceramic systems are advocated when both esthetics and strength are required. A major drawback to many porcelains is their wear and destruction of opposing natural dentition. PURPOSE This study evaluated the wear of enamel opposing 1 traditional and 2 recently introduced low-fusing feldspathic dental porcelains. MATERIAL AND METHODS Six blocks of Ceramco II, Finesse, and Omega 900 feldspathic porcelain materials were fabricated and fired according to manufacturer recommendations. Porcelain blocks were polished through 0.25 microm diamond polishing paste. Thirty-six enamel specimens were obtained and milled to a 2 mm (+0.5 mm) diameter. Enamel specimens were attached to an offset cam motor operating at 60 Hz. Enamel specimens were in constant contact with the stationary porcelain blocks under a load of 600 g and traversed a distance of 8 mm. Diameter and height of enamel specimens were measured at times of 0, 6, 12, 24, and 48 hours and subsequent determination of enamel volume loss recorded. Profilometric surface roughness of the ceramic blocks was also measured for the corresponding times. RESULTS Statistical analysis revealed that both Finesse and Omega 900 feldspathic porcelains caused significantly less enamel volume loss when compared with Ceramco II porcelain at all time intervals. Surface roughness revealed no consistent significant differences among porcelains. CONCLUSION Both Finesse and Omega 900 porcelains were not as destructive to human tooth structure as Ceramco II porcelain. These results suggest an advantage of the new, lower-fusing porcelains in conditions where natural dentition wear is a concern.

Effects of interfacial variables on ceramic adherence to cast and machined commercially pure titanium

STATEMENT OF THE PROBLEM Titanium-ceramic bonding is less optimal than conventional metal-ceramic bonding, due to excessive oxidation of titanium during porcelain firing. PURPOSE This in vitro study evaluated the effects of porcelain firing atmosphere and gold sputter coating on titanium surfaces on porcelain bonding to machined and as-cast titanium substrates. Material and methods Eight groups of ASTM grade 2 commercially pure (CP) titanium specimens (13 mm x13 mm x1 mm) were prepared (n=10). A conventional Au-Pd-In metal-ceramic alloy (Orion) and an ultra low-fusing porcelain (Finesse) served as the control (n=10). Forty machined titanium specimens were prepared from 1.00-mm thick titanium sheets with a diamond band saw. Forty titanium specimens were produced in a centrifugal dental titanium casting machine. All titanium specimens were airborne particle abraded with 110-microm alumina particles, whereas the control specimens were airborne particle abraded with 50-microm alumina particles. Forty titanium specimens (20 specimens each of as-cast and machined titanium) were randomly selected for gold sputter coating before ceramic firing. An ultra low-fusing porcelain (Vita Titankeramik) was fused on the central 6-mm diameter circular area on each titanium specimen. Porcelain firing environments for the titanium specimens consisted of vacuum and a reduced argon atmosphere. Porcelain was debonded by a biaxial flexure, constant strain test at a cross-head speed of 0.25 mm/min. Specimens were analyzed by standardized SEM/EDS analysis 3 times throughout the study to determine the silicon atomic percentage (Si at %): (1) after airborne particle abrasion, before porcelain application; (2) after the application of the first layer of porcelain; and (3) after the fracture of porcelain from the metal substrate. The titanium-ceramic adhesion was characterized by determining the area fraction of adherent porcelain (AFAP). Results were analyzed by analysis of variance and the Student-Newman-Keuls test (alpha=.05). RESULTS Statistical analysis showed a significant difference in the AFAP values among all the groups. AFAP value of the control group was significantly higher (135.35 +/- 23.68) than those of the experimental groups (P<.001). For the machined titanium, AFAP value of gold sputter-coated/argon group (91.38 +/- 7.93) was significantly higher than the rest of the groups (P<.001). For the as-cast titanium fired in vacuum, significantly lower AFAP values (P<.001) were found in the gold sputter-coated group (50.2 +/- 11.26 vs 66.15 +/- 10.41). AFAP values between the argon groups with or without the gold coating were not significantly different (P=.303); however, both argon groups (93.83 +/- 4.65 and 98.09 +/- 6.35) showed significantly higher AFAP values compared with the vacuum groups (P<.001). CONCLUSION Firing porcelain in a reduced argon atmosphere significantly improved titanium-ceramic bonding for machined and as-cast titanium. The sputter-coated gold layer on titanium provided improved titanium-ceramic bonding only when combined with firing porcelain in reduced argon atmosphere. When porcelain was fired in vacuum in the presence of the gold layer, the titanium-ceramic bonding was weakened in as-cast titanium and was not affected in machined titanium. Conventional noble metal-ceramic bonding was superior to titanium-ceramic bonding regardless of the interfacial variables examined in this study.

Factors affecting the retention and fit of gold castings

A study was designed to simulate clinical conditions. Several factors were evaluated for effect on retention and fit (margin adaptation) of gold castings. Twenty-six castings (13 pairs) were made by different investigators using a standard preparation but with varying fabrication techniques. One of each pair of castings was made on a spaced die and one on an unspaced die. A significant difference in the postcementation retention was observed in the varying techniques of each investigator. Retentive values varied from 29 to 129 lbs. Complete seating of the castings during cementation was improved by the use of die spacer. Castings made on the spaced dies had more retention than corresponding unspaced castings. Die spacing has positive benefit when properly used. Moderate roughness of axial surfaces improves retention when zinc phosphate cement is used. Physical properties of restorative materials are important, but the individual technique and care of each investigator has a major effect on the ultimate fit and retention of the cast restoration.

Review of the pH of hemostatic agents used in tissue displacement

Newer hemostatic agents such as the tetrahydrozolines and oxymetazolines have a more acceptable pH and should be kinder to tooth structure and soft tissue than the conventional solutions. Although additional study is needed, it would seem prudent to be cautious in using low pH hemostatic agents and avoid the exposure to sensitive intraoral tissues-particularly delicate tissues--or tooth preparation close to the dental pulp.

Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method

STATEMENT OF PROBLEM Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy. PURPOSE This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods. MATERIAL AND METHODS Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test. RESULTS Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively. CONCLUSIONS A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.

Post and core systems: Which one is best?

Teeth with nonvital pulps or pulpless teeth demand special restorative attention. Post and core fabrication for these teeth can be handled in many ways. This article has described some of the prefabricated post systems currently available. The relative advantages and disadvantages have been compard. Prefabricated post systems in many instances can simplify and expedite restorative dentistry. Which system is best? The answer varies according to the restorative situation and the skills and preference of the dentist. A post and core should not jeopardize the remaining tooth structure, and the particular system mus be manageable.

Direct pattern technique for posts and cores.

The technique described results in a well adapted cast post and core with good retention (Figs. 18 and 19). The chances of perforation of the root and trauma to the patient are reduced, and the expense of the procedure is minimal. This system is adaptable to single- or multirooted teeth and continually produces good results with minimal problems.

The incompletely fractured tooth

Signs and symptoms of the incompletely fractured tooth have been presented with emphasis on the role of occlusion in etiology and diagnosis. Early recognition and treatment are paramount.

Comparison of the fracture strengths of ceramometal crowns versus several all-ceramic crowns

Fracture resistance to forces applied to the incisal edges of four types of anterior crowns was tested. Ceramometal crowns fractured at significantly higher values (720 psi) than the all-ceramic crowns (approximately 360 psi). No significant difference was found among the fracture values of the Dicor crowns, the aluminous porcelain jackets, and the crowns fabricated from Dicor veneered with aluminous body and incisal porcelain.