Existence of an electrically insulating layer in amalgam-containing galvanic couples.

Objective: Avoiding the placement of amalgam and noble metal restorations in interproximal contact is recommended due to anticipated galvanic corrosion of the amalgam. There is a similar concern for amalgam/amalgam galvanic couples. It was the objective of this study to determine if an electrically insulating layer forms in the contact area of these galvanic couples.

Corrosion potential recovery of dental amalgam restorations following prophylaxis.

Objective: Dental amalgam restorations are subjected to abrasion during selective prophylaxis that can damage or remove the protective oxide and result in increased rates of corrosion and chemical dissolution of mercury. It was the objective of this research to study the corrosion potential change of dental amalgam restorations to obtain an indication of the time required for in vivo repassivation following prophylaxis.

Methods: The corrosion potentials of 27 Class I and Class II amalgam restorations were measured pre- and post-prophylaxis using a high impedance voltmeter and a Ag/AgCl micro-reference electrode.

Time-dependent corrosion potential of newly-placed admixed dental amalgam restorations.

Objective: It was the objective of this study to measure the corrosion potential over time of newly-placed admixed dental amalgam restorations as a possible indicator of corrosion activity.

Methods: The corrosion potentials of 271 amalgam restorations, 4-min to 24-month old were measured in a convenience sample of 81 subjects. The selected restorations had no occlusal or interproximal contact with other metallic restorations.

Corrosion potential variation of aged dental amalgam restorations over time.

Objective: The corrosion potential of a dental amalgam restoration is generally determined using a single measurement, even though environmental factors and abrasion can continuously alter the surface state and reactivity of this alloy. It was, therefore, the purpose of this study to determine the maximum variability of the corrosion potential of aged dental amalgam restorations, for 28 days.

Methods: The corrosion potentials of 148 aged dental amalgam restorations in 12 human subjects were measured at t = 0 and 4 h, and 4, 7, 14, 21 and 28 days.

In vivo galvanic currents of intermittently contacting dental amalgam and other metallic restorations.

Objective: It was the objective of this study to determine the magnitude of in vivo galvanic currents produced by simulating electrical contact between occluding metallic restorations, and to examine the influence of restoration age, difference in pre-contact corrosion potentials, and surface area.

Methods: A convenience sample of 106 human subjects was studied. A Ag/AgCl micro-reference electrode and a high impedance voltmeter were used to measure the pre-contact corrosion potentials.

Effectiveness of wet and dry mercury vapour suppressant systems in a faculty of dentistry clinic.

The objective of this study was to determine the effectiveness of a liquid and a dry commercial mercury vapour suppressant system. Measurements were made in a student dental clinic, using a mercury vapour detector for periods up to 76 weeks. The two products examined were Mercon vap liquid in a stock jar and the Mercon tainer dry jar system.

Dimensional stability and dehydration of a thermoplastic polycarbonate-based and two PMMA-based denture resins.

This study compared the dimensional stability and dehydration of a thermoplastic polycarbonate denture base resin with two conventional polymethyl methacrylate denture base resins. Maxillary complete dentures were fabricated from the three denture materials and the accuracy of fit along the posterior palatal border of the cast used in processing was measured. Measurements were conducted at five palatal locations immediately after processing and at 7 and 30 days during immersion in water (23 degrees C) and at 7 and 30 days during dehydration (23 degrees C, 65-75% relative humidity).

Considerations in measuring the electrical potentials of metallic restorations in vivo.

Many variables are believed to affect the accurate measuring of metallic restoration electrical potentials. This study examined the effects of intra- versus extra-oral location of the reference electrode, the type of metallic probe used to make contact with the restoration, and scratching and brushing of the restoration surface. Dental amalgam restorations were measured in 40 human subjects.

Corrosion and cytotoxicity evaluation of thermafil endodontic obturator carriers.

The purpose of this study was to evaluate the in vitro cytotoxicity of two metallic and two plastic Thermafil carrier materials, and to separately evaluate the in vitro corrosion behavior of the two metallic carriers. Stainless-steel, Ti-6AI-4V, Polysulfone, and Vectra carriers were evaluated for cytotoxicity using the ISO-recommended agar overlay test. The two metallic carriers were additionally corrosion tested in 0.

The effects of the coupling of titanium implants and dissimilar metal abutments on osteoblast differentiation in vitro.

This study evaluated the effect of titanium endosseous dental implants coupled to dissimilar materials on the capacity of preosteoblasts in bone marrow culture to differentiate, to form alkaline phosphatase-positive colonies, and to mineralize. Ten UCLA abutments were cast in each of 4 alloys: Type III gold, ceramometal gold, commercially pure grade I titanium, and titanium-aluminum-vanadium (Ti-6Al-4V); 10 ceramic abutments and 30 sterile Brånemark System implants were also used. Five abutments of each material and 5 implants were incubated individually in rat bone marrow culture, as were 5 of each abutment attached to an implant; bone marrow cultures not containing test samples were used as controls.

Improved fit of maxillary complete dentures processed on high expansion stone casts.

Purpose: Although relatively well-fitting dentures are produced at low cost and with easy-to-manipulate material, current denture base materials are not ideal. Because acrylic resin complete and removable partial dentures change dimensionally as a result of polymerization and thermal contractions, a high expansion stone was tested in this study to determine its ability to compensate for some of the dimensional change.

Material And Methods: Maxillary complete dentures were processed on type III dental stone and high expansion stone casts.

Posterior palatal seal adaptation: influence of a high expansion stone.

In this follow-up investigation, the ability of a new, high expansion stone to reduce acrylic resin denture base processing distortions was studied and compared with a previously reported investigation of bases processed on buff stone. Denture bases were processed by the continuous-injection and trial-pack techniques on flat vault palate casts and then trimmed and polished. Measurements were made at the posterior palatal border opening at 1 day and 1 week immersion in water (23 degrees C).

Mercury vapour suppression by various liquid media.

Fresh and used photographic fixer, Merconvap and water were evaluated for their ability to suppress the vapourization of mercury. Mercury vapour concentration above the four test storage liquids was measured at various times between 10 min and 335 days, using a mercury vapour measuring instrument. The data were analysed using a Student-Newman-Keuls multiple comparison test (P = 0.

Posterior palatal seal adaptation: influence of processing technique, palate shape and immersion.

Accuracy of fit of denture bases is critical to adequate retention. This study compared the dimensional change of a newer continuous-injection technique with a standard trial-pack technique as determined by measuring the posterior palatal border opening. The influence of palate shape and immersion were also assessed.

Surface topography of demineralized dentin preceded by formalin fixation.

Formalin treatment of dentin, prior to burnishing demineralization, results in a "tufted" collagen surface that may optimize bonding of hydroxyethyl methacrylate dentinal bonding agents. The purpose of this study was to determine if there is a clinically acceptable formalin treatment time that will yield a deeply tufted collagen surface. The exposed dentin of periodontally healthy and periodontally diseased human teeth was treated with formalin for various treatment times before "burnishing" demineralization with citric acid.

Crevice corrosion products of dental amalgam.

The objective of this study was to determine the in vitro corrosion products that resulted from crevice corrosion of low- and high-copper dental amalgams. Specimens were potentiostatically polarized in a chloride-containing electrolyte while set against a PTFE surface to form a crevice. After 16 h, corrosion products were examined by light microscopy, SEM, EDS, and XRD.

Chemical and molecular weight analyses of prosthodontic soft polymers.

A number of studies have been made investigating the properties of dental prosthodontic soft polymer materials. In such materials, which are used as short-term denture soft liners, the polymer component is complexed with one or more plasticizers. This lowers the glass transition temperature, Tg, of the polymer by allowing greater chain mobility and produces a more flexible material.

An in vivo and in vitro study of the loss of plasticizer from soft polymer-gel materials.

Polymer-gel materials used as short-term denture soft linings are blended with plasticizers to lower the glass transition temperature (Tg). A lower Tg allows for greater polymer chain mobility, thus producing a more flexible material. The present work evaluated the loss of plasticizers due to leaching both in vivo and in vitro.

Gel strength and rate of gelation of soft polymers.

A rheometer was used to characterize the gelation rate of six commercial short- to medium-term (chairside intra-oral gelation) denture soft-lining materials. Shear puncture force was measured from one to 60 days for six short- to medium-term materials as well as for three heat-cured (polymerizable) materials. The observed increase in puncture force with age of the specimen was considered to be a function of increased polymer chain entanglement and/or loss of plasticizer.

Clinical implications of resilient denture lining material research. Part II: Gelation and flow properties of tissue conditioners.

The clinical effectiveness of tissue conditioners and functional impression materials is influenced by their gelation and flow properties. Laboratory tests were previously conducted that simulated the conditions of clinical use to the extent possible on six commercial intraoral-gelling resilient denture liners. The liners were found to vary significantly in their gelation times and to flow throughout the 7-day study.

The dimensional accuracy of 12 impression material and die stone combinations.

This study determined the dimensional accuracy of dies made using a combination of four impression materials and three Type IV die stones. A metal die was prepared for a molar complete cast crown, and 10 stone replicas were made using 12 different combinations of impression materials and die stones. The distances between reference points on the metal and stone dies were measured in three directions with a traveling microscope.

Comparison of the dimensional stability of two waxes and two acrylic resin processing techniques in the production of complete dentures.

Two base plate waxes and two denture processing techniques were independently compared for dimensional stability. Occlusion rims were constructed from extra hard and medium soft base plate waxes and teeth were set. Acrylic resin bases were processed by a trial packing technique, and a continuous injection system.

Clinical implications of resilient denture lining material research. Part I: Flexibility and elasticity.

The clinical use of resilient denture liners is based on their flexibility and elasticity. The nine commercial resilient denture liners measured were less flexible during and after simulated chewing and clenching test sequences. The elasticity of the intraoral-cure liners reached maximal values at 24 hours.

Correlation of dental amalgam crevice corrosion with clinical ratings.

In vitro corrosion behavior of gamma 2-containing and gamma 2-free dental amalgams was examined under crevice conditions which simulated the amalgam-tooth interface. By means of potentiostatic testing, current-density/time behavior and integrated anodic current were measured for 16 hr. All of the amalgams demonstrated crevice corrosion susceptibility.