The effect of urea on the corrosion behavior of different dental alloys.

OBJECTIVE: Intraoral corrosion of dental alloys has biological, functional, and esthetic consequences. Since it is well known that the salivary urea concentrations undergo changes with various diseases, the present study was undertaken to determine the effect of salivary urea concentrations on the corrosion behavior of commonly used dental casting alloys. MATERIALS AND METHODS: Three casting alloys were subjected to polarization scans in synthetic saliva with three different urea concentrations. RESULTS: Cyclic polarization clearly showed that urea levels above 20 mg/100 ml decreased corrosion current densities, increased the corrosion potentials and, at much higher urea levels, the breakdown potentials. CONCLUSION: The data indicate that elevated urea levels reduced the corrosion susceptibility of all alloys, possibly through adsorption of organics onto the metal surface. This study indicates that corrosion testing performed in sterile saline or synthetic saliva without organic components could be misleading.

Adhesion and cohesion.

The phenomena of adhesion and cohesion are reviewed and discussed with particular reference to dentistry. This review considers the forces involved in cohesion and adhesion together with the mechanisms of adhesion and the underlying molecular processes involved in bonding of dissimilar materials. The forces involved in surface tension, surface wetting, chemical adhesion, dispersive adhesion, diffusive adhesion, and mechanical adhesion are reviewed in detail and examples relevant to adhesive dentistry and bonding are given. Substrate surface chemistry and its influence on adhesion, together with the properties of adhesive materials, are evaluated. The underlying mechanisms involved in adhesion failure are covered. The relevance of the adhesion zone and its importance with regard to adhesive dentistry and bonding to enamel and dentin is discussed.

What every dentist should know about zinc.

Zinc plays an important role in human physiology, from its involvement in the proper function of the immune system to its role in cellular growth, cell proliferation, and cell apoptosis as well as its essential role in the activity of numerous zinc-binding proteins. However, zinc also plays a key pathophysiological role in major neurological disorders and diabetes. Zinc deficiency is a worldwide problem, whereas excessive intake of zinc is relatively rare. Many patients are exposed to zinc on a regular basis through dentistry as a result of its use in certain restorative materials, mouthwashes, toothpastes and, notably, denture adhesives. Of particular importance to dental professionals are various case reports concerning the neurologic effects of excess zinc intake by patients who routinely use large quantities of zinc-containing denture adhesives. This review presents relevant information concerning the use of zinc in dentistry.

Factors involved in microbial colonization of oral prostheses.

The presence of biofilm or denture plaque on the tissue contacting the (intaglio) surface of a denture is a major etiologic factor in the pathogenesis of both denture stomatitis and inflammatory papillary hyperplasia. This article reviews the literature concerning the various factors that contribute to the development of denture plaque and its colonization by Candida albicans and other microorganisms.

Strength analysis of 6 resorbable implant systems: does heating affect the stress-strain curve?

PURPOSE: The objective was to directly compare the strength of 6 different resorbable implant plating systems using an in vitro model before and after heating. MATERIALS AND METHODS: Red oak wood was cut and fixated using various resorbable plates and screws. Vertical load was applied and the specimens fractured, while a test machine gathered data. This was repeated after heating of the specimens. RESULTS: Several parameters were analyzed, and force versus displacement curves were plotted for each specimen. CONCLUSIONS: There were no statistically significant differences for total maximum loads between heat-treated and non heat-treated specimens. There were differences in strengths amongst the various systems.

The leakage resistance of endodontic fiber obturators.

Fiber obturators have been introduced into endodontics but few reports exist regarding their efficacy compared to standard obturation materials. This study evaluated the leakage resistance of fiber obturators compared with other obturation materials. All specimens showed a progressive increase in leakage with time. The data indicate that fiber obturation and a new cone/sealer system provide the best canal obturation as evidenced by the leakage behavior.

The effect of mucine, IgA, urea, and lysozyme on the corrosion behavior of various non-precious dental alloys and pure titanium in artificial saliva.

The corrosion of dental alloys has biological, functional, and aesthetic consequences. Various studies have shown that protein solutions can inhibit the corrosion of alloys. This study is planned to determine the relationship of organic constituents of saliva and the corrosion of dental alloys. The organic constituents are IgA, mucine, urea, and lysozyme which are encountered in the highest amounts in saliva and the dental materials are titanium (Ti), Co-Cr-Mo and Ni-Cr-Mo alloys, and dental amalgam, the most often used metallic components in dentistry. In particular, the interactions between the commonest salivary proteins, IgA, mucine, urea and lysozyme, and Ti, Co-Cr-Mo, Ni-Cr-Mo and dental amalgam were investigated. Each alloy was evaluated by cyclic polarization in each medium. The general anodic and cathodic behavior during forward and reverse cycles, the corrosion and passivation current densities (muA/cm2 ), and the corrosion and the pitting potentials (mV) were determined. The results have shown that Ni-Cr-Mo and dental amalgam alloys are highly susceptible to corrosion in all the investigated media. The Co-Cr-Mo alloy has shown high passive current densities in the solution of mucine and lysozyme in artificial saliva. Titanium instead, has shown a high resistance to corrosion and a stable passive behavior in all media, especially in a solution of mucine and IgA in synthetic saliva. Mucine and IgA, as well as urea and lysozyme, appeared to enhance the formation of a passive film layer on the Ti metal surface, thus inhibiting the corrosion. Based on the study findings, and especially considering the problem of nickel allergy and toxicity of mercury released from dental amalgam, the use of Co-Cr-Mo alloys and Ti to Ni-Cr-Mo alloys is recommended and alternatives to dental amalgam should be sought for patients with impaired salivary flow.

The effect of a mouthrinse containing essential oils on dental restorative materials.

Mouthrinses that contain essential oils are effective for controlling plaque and periodontal disease. Recent studies have shown that such mouthrinses are effective at preventing the formation of biofilm in dental unit waterlines. However, there is no information in the literature regarding the effect of such mouthrinses on restorative materials used within the oral cavity. Specimens of three common restorative materials (a glass ionomer, a composite resin, and amalgam) were subjected to continuous exposure to Listerine and distilled water for 10 days; at that time, the strength, fluid sorption, and surface appearance of the specimens were compared. Specimens of the test materials also were placed in intraoral devices; volunteer patients wore these devices for 12 hours per day for a period of 10 days. During that time, the patients were instructed to rinse twice daily for 30 seconds with Listerine Cool Mint or a non-active mouthrinse. After 10 days, the specimens were salvaged from the devices and inspected by visible and SEM examination. This study indicates that routine use of mouthrinses containing essential oils (or even prolonged exposure to such mouthrinses) has no adverse effects on restorative materials that might be expected to react to such mixtures because of their chemical compositions. It was concluded that active mouthrinses do not appear to have any adverse effects on a variety of restorative biomaterials.

Resin-based sealing of root canals in endodontic therapy.

This study evaluated the effect of the obturation technique on leakage, which may be the primary cause of failure in endodontic treatment. The apical seal and leakage behavior of teeth obturated with a resin-based sealer and gutta-percha alternative were compared to conventionally obturated teeth. Sound premolars (N = 10) were instrumented and treated by conventional root canal obturation. A second group (N = 10) was treated with the Resilon-Epiphany system and the remaining 10 roots were divided into two groups (N = 5) and obturated without sealer. A detector electrode was placed coronally in each root in contact with the obturation system and sealed in place and the apices were left patent. The teeth were immersed in 0.9% sodium chloride with a stainless steel counter electrode. A 20V potential was connected between the stainless steel and each tooth in turn with current flow determined by voltage drop across a standard resistor. Leakage was followed for 30 days and statistically analyzed for differences between groups. All teeth in Groups 1, 3A, and 38 (p > 0.05) leaked at 30 days. In Group 2, four roots showed no leakage, five roots showed minimal leakage, and one root exhibited a leakage current at a greater magnitude than the others in the group. A significant difference (p < 0.005) was found between Groups 1 and 2 but not between Group 1 and Groups 3A and 3B (p > 0.05) or between Group 2 and Groups 3A and 3B.

Leakage resistance of the InnoEndo fiber obturation system.

To ensure long-term function, endodontic restorations require proper sealing of the root canal system. Recent studies have recognized that microleakage in endodontically treated teeth has negative consequences (ie, apical migration of bacteria) on their prognosis, often resulting in failure. Findings in the dental literature suggest that the innovative technology, consisting of fiber-based obturation and adhesive obturation materials, can minimize this leakage. As demonstrated in this article, the ability to achieve an adequate marginal seal represents a significant advance in endodontic therapy.

The effect of base/liner use on restoration leakage.

Central to the success of a restoration is the quality of the restoration-dentin interfacial seal; any compromise of the seal can lead to secondary or recurrent decay. Class V restorations have a high leakage propensity and this study evaluates the effect of base/liner placement on leakage behavior. Class V intracoronal half enamel/half dentin preparations (3.0 x 2.0 x 2.0 mm) were cut in four groups (n = 10) of extracted human teeth with a new bur used for each cavity preparation. All teeth were single-rooted, single-canal anterior teeth. Base/liner usage differed between each group. The first group of teeth had no liner or base, while a liner was placed in the second group of teeth prior to conditioning and restoration. A base was placed in the third group of cavity preparations and both the base and liner were placed in the fourth group. After preparation, a small diameter bare-end PVC-insulated copper wire was inserted within the root canal of each tooth from the apex to firm contact with the pulp chamber roof. The tooth-wire interface and root surface was sealed and leakage was followed electrochemically for 35 days in 0.9% NaCl solution. All of the teeth leaked to some degree; however, teeth that were restored without liner or base demonstrated the smallest amount of leakage. The greatest leakage was noted in teeth restored with both a base and a liner; teeth restored with only a base showed greater leakage than those restored with only a liner. The findings indicate that the presence of a base and/or a liner results in greater leakage compared with intracoronal Class V preparations that were conditioned and restored only. The data suggest that placing both a base and a liner increases restoration leakage significantly.

Screw-retained prosthesis for Straumann implant sites with limited interocclusal clearance.

This article reports a technique that addresses the problem of the restricted interocclusal distance when screw-retained prostheses are selected.

Microleakage within endodontically treated teeth using a simplified root canal preparation technique: an in vitro study.

This study evaluated the effects of two canal preparation methods on leakage in endodontically treated teeth, comparing the relative leakage rates for conventionally prepared teeth and those instrumented and obturated with the Ultradent Endo-Eze system. Two groups (n=11) of freshly extracted human premolars (and some canines) with closed apices and single roots were used. The roots in the first group were instrumented with conventional stainless steel hand files and obturated with gutta-percha and Sealapex. The experimental group were instrumented and obturated using the Ultradent Endo-Eze system. Radiographic examination showed no difference in the level or quality of root canal fill for teeth prepared conventionally and those prepared using the Endo-Eze system. Leakage followed a linear trend for both groups of teeth but the rate of leakage increase was approximately twice as high (that is, 80% greater) for the conventional group than for the Endo-Eze teeth. This difference was not statistically significant due to the wide variability in the conventional group data. It was noted that canal preparation time for the Endo-Eze teeth was approximately 50% shorter than that required for conventional root canal therapy.

Success or failure of dental implants? A literature review with treatment considerations.

This study reviews the literature concerning the success or failure of dental implants and provides the general dentist with information to decide whether to recommend dental implant therapy to a patient. The authors conducted an extensive literature search for articles relating to dental implant failure. Metaanalyses and multi-center studies were predominant in the selection. Predictors of dental implant success or failure were gleaned from various articles and presented in the form of text and tables. The main predictors for implant success are the quantity and quality of bone, the patient's age, the dentist's experience, location of implant placement, length of the implant, axial loading, and oral hygiene maintenance. Primary predictors of implant failure are poor bone quality, chronic periodontitis, systemic diseases, smoking, unresolved caries or infection, advanced age, implant location, short implants, acentric loading, an inadequate number of implants, parafunctional habits and absence/loss of implant integration with hard and soft tissues. Inappropriate prosthesis design also may contribute to implant failure.

Fracture resistance of human root dentin exposed to intracanal calcium hydroxide.

The purpose of the present study was to determine if exposure to intracanal calcium hydroxide [Ca(OH2)] alters the fracture resistance of human root dentin. One hundred and two freshly extracted single rooted human teeth divided into three groups of 34 teeth each. Coronal access and endodontic instrumentation using round burs, stainless steel files, and Profile GT rotary files were completed for each tooth. The prepared root canal system of each tooth was filled with saline solution (group 1), USP Ca(OH)2 (group 2), or Metapaste (group 3). The apicies and access openings were sealed with composite resin and the teeth were immersed in saline. After 30 days, the roots of 17 teeth from each group were sectioned horizontally into 1-mm thick disks and each disk was loaded to fracture at 2.5 mm/min with a SATEC universal-testing machine. After 180 days the same procedure was performed on the remaining 17 teeth in each of the 3 groups. The peak load at fracture was measured for each dentin disk. Data were analyzed using one-way ANOVA and a post hoc Student-Newman-Keuls test. After 30 days exposure to the test solution, there was no difference in the peak load at fracture for the three groups of teeth. However, after 180 days, the roots of the teeth exposed to USP Ca(OH)2 showed a significant decrease in peak load at fracture when compared to the 30-day groups and the 180-day groups exposed to saline or Metapaste.

Camouflaging changes in the appearance of a patient with ectodermal dysplasia.

This clinical report describes an innovative method to ease the transition of a patient from old implant-retained prostheses to enhanced prostheses that altered the vertical dimension, esthetics, smile, and overall facial appearance. This procedure was accomplished by a customized labial bow, such as the one commonly used for a removable Hawley-type retainer, adjusted to follow the contour of teeth waxed into a denture. This option was adopted because it is reversible, nondamaging to the denture teeth, yet still camouflages the appearance of the maxillary denture and changes in facial contour during the early transition stage from the old to the new prostheses.

Strength analysis of titanium and resorbable internal fixation in a mandibulotomy model.

PURPOSE: Mandibulotomy is used to access various tumors of the tongue base, posterior oral cavity, pharynx, parapharyngeal space, and cranial base. Internal fixation using titanium plates and screws is the most common method of stabilization. These have the potential for interference with radiotherapy delivery. This in vitro study compares the strength of titanium and resorbable internal fixation in a mandibulotomy model by analyzing the force required for plate and screw breakage. MATERIALS AND METHODS: Red oak wood board was used to simulate the mandible. Titanium and resorbable plates and screws in various configurations were used to stabilize pieces of the wood. They were arranged in 6 different groups. The specimens were individually tested with a vertical load, while the test machine recorded the force-versus-displacement behavior automatically. RESULTS: Plate type and configuration affected the applied load required to induce displacement of the simulated mandibulotomy. Heating and cooling the resorbable plates prior to strength testing also affected the load-versus-displacement curve. CONCLUSIONS: Overall, the titanium system we studied exhibited greater resistance to deformation from a vertical load than did the resorbable plate groups.