[A preliminary study on the forming quality of titanium alloy removable partial denture frameworks fabricated by selective laser melting].

Objective: To evaluate the processing accuracy, internal quality and suitability of the titanium alloy frameworks of removable partial denture (RPD) fabricated by selective laser melting (SLM) technique, and to provide reference for clinical application. Methods: The plaster model of one clinical patient was used as the working model, and was scanned and reconstructed into a digital working model. A RPD framework was designed on it. Then, eight corresponding RPD frameworks were fabricated using SLM technique. Three-dimensional (3D) optical scanner was used to scan and obtain the 3D data of the frameworks and the data was compared with the original computer aided design (CAD) model to evaluate their processing precision. The traditional casting pure titanium frameworks was used as the control group, and the internal quality was analyzed by X-ray examination. Finally, the fitness of the frameworks was examined on the plaster model. Results: The overall average deviation of the titanium alloy RPD framework fabricated by SLM technology was (0.089±0.076) mm, the root mean square error was 0.103 mm. No visible pores, cracks and other internal defects was detected in the frameworks. The framework fits on the plaster model completely, and its tissue surface fitted on the plaster model well. There was no obvious movement. Conclusions: The titanium alloy RPD framework fabricated by SLM technology is of good quality.

Corrosion of dental alloys in artificial saliva with Streptococcus mutans.

A comparative study of the corrosion resistance of CoCr and NiCr alloys in artificial saliva (AS) containing tryptic soy broth (Solution 1) and Streptococcus mutans (S. mutans) species (Solution 2) was performed by electrochemical methods, including open circuit potential measurements, impedance spectroscopy, and potentiodynamic polarization. The adherence of S. mutans to the NiCr and CoCr alloy surfaces immersed in Solution 2 for 24 h was verified by scanning electron microscopy, while the results of electrochemical impedance spectroscopy confirmed the importance of biofilm formation for the corrosion process. The R(QR) equivalent circuit was successfully used to fit the data obtained for the AS mixture without S. mutans, while the R(Q(R(QR))) circuit was found to be more suitable for describing the biofilm properties after treatment with the AS containing S. mutans species. In addition, a negative shift of the open circuit potential with immersion time was observed for all samples regardless of the solution type. Both alloys exhibited higher charge transfer resistance after treatment with Solution 2, and lower corrosion current densities were detected for all samples in the presence of S. mutans. The obtained results suggest that the biofilm formation observed after 24 h of exposure to S. mutans bacteria might enhance the corrosion resistance of the studied samples by creating physical barriers that prevented oxygen interactions with the metal surfaces.

Influence of recasting on the quality of dental alloys: A systematic review.

STATEMENT OF PROBLEM: Dental alloy manufacturers advise against the reuse of previously melted alloy. However, for economic reasons, dental laboratories often reuse the casting surplus (sprue and metal remaining in the crucible former). Such reuse remains a controversial topic in dental practice. PURPOSE: The purpose of this systematic review was to assess the effects of remelting dental alloys by evaluating the following parameters: reasons for recasting and associated processes, feasible number of recastings, treatment of alloys before recasting and its effects on cytotoxicity, color of opaque porcelain, castability of alloys, marginal accuracy, mechanical properties, porcelain-metal interfaces, and corrosion. MATERIAL AND METHODS: The systematic review included all studies on dental alloy recasting. MEDLINE, Dentistry and Oral Science Source, Science Direct, and ISI Web of Science were searched (up to July 2014). Data were extracted and the quality of studies was assessed. RESULTS: Thirty-four studies published between 1983 and 2014 were included. The number of recastings ranged from 1 to 10. The percentage of new alloy ranged from 0 to 100 wt%, although the mean value was 50 wt%. CONCLUSIONS: Evidence for the feasibility of adding 50% new metal at each recasting is limited. The number of recastings should be limited to a maximum of 4. No general test protocol can be deduced from these studies, which limits the comparison and exploitation of data. Furthermore, no consensus protocol exists for the evaluation of recasting. Future studies should work toward establishing a standard protocol.

Interventions for replacing missing teeth: partially absent dentition.

BACKGROUND: Management of individuals presenting with partial loss of teeth is a common task for dentists. Outcomes important to the management of missing teeth in the partially absent dentition should be systematically summarized. This review recognizes both the challenges associated with such a summarization and the critical nature of the information for patients. OBJECTIVES: To assess the effects of different prostheses for the treatment of partially absent dentition in terms of the following outcomes: long-term success, function, morbidity and patient satisfaction. SEARCH METHODS: We searched the Cochrane Oral Health Group's Trials Register (to 21 March 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE via OVID (1950 to March 2011) and EMBASE via OVID (1980 to March 2011). There were no restrictions regarding language or date of publication. We contacted several authors to identify non-published trials. SELECTION CRITERIA: Randomized controlled trials (RCTs) comparing different methods (including the design and materials used) of treating partial edentulism, with clinically relevant outcomes, were included in this review. Trials reporting only surrogate outcomes, such as plaque accumulation or gingival volume, were excluded from this review. DATA COLLECTION AND ANALYSIS: Two review authors independently carried out the screening of eligible studies, assessment of dimensions of quality of trials, and data extraction. Results were expressed as mean differences for continuous data, risk ratios for dichotomous outcomes, and hazard ratios with 95% confidence intervals for time-to-event data. MAIN RESULTS: Twenty-one trials met the inclusion criteria for this review. Twenty-four per cent of these were assessed as being at high risk of bias and the remainder were at unclear risk of bias. The clinical heterogeneity among the included studies precluded any attempt at meta-analysis. There was insufficient evidence to determine whether one type of removable dental prosthesis (RDP) was better or worse than another. With fixed dental prostheses (FDPs), there was no evidence that high gold alloys are better or worse than other alloys, nor that gold alloys or frameworks are better or worse than titanium. There is insufficient evidence to determine whether zirconia is better or worse that other FDP materials, that ceramic abutments are better or worse than titanium, or that one cement was better or worse than another in retaining FDPs. There is insufficient evidence to determine the relative effectiveness of FDPs and RDPs in patients with shortened dental arch or to determine the relative advantages of implant supported FDPs versus tooth/implant supported FDPs. AUTHORS' CONCLUSIONS: Based on trials meeting the inclusion criteria for this review, there is insufficient evidence to recommend a particular method of tooth replacement for partially edentulous patients.

Analysis of an administrative database of indirect restorations over 11 years.

AIM: This paper describes the database used to assess the survival of indirect restorations and presents general data on survival of these restorations. METHODS: Data, based on the complete attendance and treatment history, over the 11 years from 1991 to 2001, of a statistically representative sample of 23,165 General Dental Services' (GDS) patients in England and Wales, all of whom received at least one indirect restoration during the observation period, have been analysed. The patients on the database received a total of 36,397 courses of treatment, and there were 52,481 indirect restorations placed. The method of analysis involved the estimation of the probability that the patient will eventually return, given an interval without attending, by analysing the observed patterns of re-attendance. This estimated probability of re-attendance was then used to modify the standard Kaplan-Meier procedure to produce realistic estimates of the hazard of re-intervention. RESULTS: Overall, 75% of indirect restorations remained without re-intervention after 5 years, and 61% after 10. Crowns outperformed other types of indirect restoration. Multi-surface metal inlays, by contrast, had a median interval to re-intervention of less than 8 years. CONCLUSIONS: The times to re-intervention for different types of indirect restoration have been successfully estimated and crowns shown to outperform veneers and inlays.

Ten-year outcome of crowns placed within the General Dental Services in England and Wales.

AIM: It is the aim of this paper to consider the factors associated with the need for re-intervention on a crown, and the times to re-intervention. METHODS: A data set was established consisting of patients, 18 years or older, whose birthdays were included within a set of a randomly selected dates, one of which was chosen in each possible year of birth and whose restoration records contained the placement of one or more indirect restorations on courses of treatment with last date on the claim form after 31st December 1990, and with date of acceptance after September 1990 and before January 2002. For each tooth treated with a crown, the subsequent history of intervention on that tooth was consulted, and the next date of intervention, if any could be found in the extended data set, was obtained. Thus, a data set was created of crowns which have been placed, with their dates of placement and their dates, if any, of re-intervention. RESULTS: Data for over 80,000 different adult patients were analysed, of whom 46% were male and 54% female. A total of 47,474 crown restoration occasions were obtained from the data over a period of 11 years. Metal crowns were found to have the longest survival-68% at 10 years, and all-porcelain crowns the shortest-48% at 10 years. Factors which were found to influence outcome of crowns included type of crown, age of patient, patient payment exemption status, patient attendance pattern and placement of a root filling in the same course of treatment as a crown. CONCLUSIONS: Full-coverage all-metal crowns have longer survival times before re-intervention than metal-ceramic crowns and all-ceramic crowns. Root fillings are associated with reduced survival time of the crowns examined in this study.

Forces in stainless steel, TiMolium and TMA intrusion arches, with different bending magnitudes.

The present study compared forces in stainless steel, TiMolium and TMA, V-bend intrusion arches with different magnitudes of flexion. The sample consisted of rectangular-section wires, caliber .017" x .025", with ten arches of each alloy. All V-bends were made 48 mm from the midline, using the same phantom upper jaw, maintaining the same distance between the tubes fixed to the molars and the midline. Loads necessary to deflect the arches by 5, 10, 15 and 20 mm were measured by means of an Instron dynamometer with a 1 kgf load cell. Calculations for sample size confirmed the suitability of using 10 arches of each alloy. Variance tests (ANOVA) of one factor and three levels, complemented by the Tukey test for multiple comparisons, identified that TMA(R) intrusion arches required a smaller quantity of load in relation to conventional steel and TiMolium at all levels of flexion. Furthermore, TiMolium presented intermediary characteristics between steel and TMA, and in all alloys increase in distance entailed a significant increase in force between all registered values, and that the increase in load necessary to deflect the arches at the intervals tended to decrease from first to last interval, these differences being more significant in steel, less in TiMolium and practically non-existent in TMA.

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.

Forces in stainless steel, TiMolium® and TMA® intrusion arches, with different bending magnitudes

The present study compared forces in stainless steel, TiMolium® and TMA®, V-bend intrusion arches with different magnitudes of flexion. The sample consisted of rectangular-section wires, caliber .017" x .025", with ten arches of each alloy. All V-bends were made 48 mm from the midline, using the same phantom upper jaw, maintaining the same distance between the tubes fixed to the molars and the midline. Loads necessary to deflect the arches by 5, 10, 15 and 20 mm were measured by means of an Instron dynamometer with a 1 kgf load cell. Calculations for sample size confirmed the suitability of using 10 arches of each alloy. Variance tests (ANOVA) of one factor and three levels, complemented by the Tukey test for multiple comparisons, identified that TMA® intrusion arches required a smaller quantity of load in relation to conventional steel and TiMolium® at all levels of flexion. Furthermore, TiMolium® presented intermediary characteristics between steel and TMA®, and in all alloys increase in distance entailed a significant increase in force between all registered values, and that the increase in load necessary to deflect the arches at the intervals tended to decrease from first to last interval, these differences being more significant in steel, less in TiMolium® and practically non-existent in TMA®.

O presente estudo comparou as forças em arcos de intrusão com dobra V confeccionados em aço inoxidável, TiMolium® e TMA®, com diferentes magnitudes de deflexão. A amostra constou de fios de secção retangular e calibre 0,017" x 0,025", com dez arcos de cada liga. Todas as dobras em V foram confeccionadas a 48 mm distantes da linha média, e foi utilizado o mesmo manequim de maxila para manter a mesma distância entre os tubos fixados nos molares e a linha média. As cargas necessárias para defletir os arcos em 5, 10, 15 e 20 mm foram mensuradas por meio de dinamômetro com célula de carga de 1 kgf, da marca Instron. O cálculo para o tamanho de amostra confirmou a possibilidade de se utilizar dez arcos de cada liga. Os testes de variância (ANOVA) de um fator e três níveis, complementados com os testes de Tukey para comparações múltiplas, identificaram que os arcos de intrusão de TMA® requereram menor quantidade de carga em relação ao aço convencional e ao TiMolium® em todos os níveis de deflexão; que o TiMolium® apresentou características intermediárias entre o aço e o TMA®; que em todas as ligas o aumento das distâncias implicou em aumento significativo da força entre todos os valores registrados; e que os incrementos de carga necessários para defletir os arcos nos intervalos tenderam a decrescer do primeiro ao último intervalo, sendo essas diferenças mais significantes no aço, menores no TiMolium® e praticamente inexistentes no TMA®.

Weld characteristics of orthodontic archwire materials.

Welding attachments to archwires can produce change in their physical as well as mechanical properties. This study evaluated three archwire alloy materials-stainless steel, Beta titanium, and Timolium for their weld characteristics. The study was divided into tensile-shear test using instron universal testing machine, surface evaluation with the help of scanning electron microscope, and metallographic examination with optical microscope. Six specimens were used for evaluation of each parameter. Increased strength in tensile-shear test and smooth surface and characteristic nugget formation in scanning and optical micrographs, respectively, clearly indicated superior weld characteristics for Beta titanium alloys when compared with the other two archwire alloys. Stainless steel was found to be intermediate in nature, whereas Timolium exhibited poor weld characteristics.

[Effects of investment materials on cast shrinkage of base metal alloys].

OBJECTIVE: To compare the influence of different investment materials, methods and crown height on the cast shrinkage of full crowns made of dental base metal alloy. METHODS: All of the 288 wax patterns were made and divided into three groups according to their crown height. In every group, wax patterns were invested in metal rings and paper rings with three types investment material and cast with base metal alloys. Then the inside diameters of castings were measured and analyzed by statistical package SPSS. RESULTS: Differences between groups invested with the three types of material were significant(P < 0.01). There were significant difference between the groups investing with metal rings and paper rings(P < 0.01). CONCLUSION: The component of investment material and invested ring can affect the cast shrinkage of dental base metal alloy apparently.

A 3-year clinical evaluation of a gallium restorative alloy.

Several alternative materials have been suggested to take the place of amalgam, because of the environmental toxic effects of its mercury component. One such material is gallium-based alloy restoratives. The aim of this in vivo study was to compare the long-term clinical performance of a commercial gallium alloy with an admixed high copper amalgam alloy. For this purpose, 32 gallium and 32 amalgam restorations were placed in molar teeth in 14 human subjects. All the selected patients had at least two molar teeth that required restoration. In this way both restoratives were used in the same oral cavity. The restorations were examined at baseline, 6 months, 1, 2 and 3 years. At baseline, six teeth restored with gallium alloy showed post-operative sensitivity, whereas none of the amalgams were sensitive. At the end of 3 years, only a few amalgam restorations showed slight surface tarnish and marginal integrity loss. None of them needed replacement. Of the 32 gallium restorations placed, five had to be removed because of sensitivity, corrosion and tooth fracture. Also dramatic surface roughness and corrosion were noticed in 12 gallium restoration. According to the results of this clinical study, gallium-based restoratives should not be used before their physical properties are improved.

Titanium applications in dentistry.

BACKGROUND: The ADA Council on Scientific Affairs outlines the status of titanium and titanium alloys used in dentistry and provides its recommendations concerning their use in clinical practice. CONCLUSIONS: Titanium and titanium alloys, based on their physical and chemical properties, appear to be especially suitable for dental implants and prostheses. For the construction of endosseous implant devices, titanium and its alloys have become well-accepted and can be considered the materials of choice. CLINICAL IMPLICATIONS: For crown and bridge prostheses, dentists can consider titanium and its alloys as viable options to more traditional noble and base metal alloys, but careful selection of processing methods and laboratory skill are necessary to ensure success.

Suggested guidelines for the topographic evaluation of implant surfaces.

The bone anchorage components of commercially available oral implant systems differ in surface roughness by at least sixfold. Correct reporting of the surface roughness of implant systems is important, since one cannot exclude the possibility that surface roughness will influence clinical results. However, many confusing statements are found in the literature when the surface topography of implants is described. Different measuring instruments and techniques strongly influence the outcome of a topographic characterization. Furthermore, a screw-type design introduces problems for most measuring instruments. Without a standard procedure, it is generally impossible to compare values from one study with another. The aim of the present study was to suggest standards for topographic evaluation of oral implants in terms of measuring equipment, filtering process, and selection of parameters. It is suggested that the measuring instrument be able to measure all parts of a threaded implant if the investigation relates to such a design. Preferably, 3-dimensional measurements should be performed. On screw-type implants, tops, valleys, and flanks should be evaluated. At least 3 samples in a batch should be evaluated, filter size must be specified, and at least one of each height, spatial, and hybrid parameter should be presented.

[The study on mechanical properties of laser welds of titanium in dentistry].

OBJECTIVE: To explore the mechanical properties of laser welds of titanium under different conditions. METHODS: Home-made Nd: YAG laser welding apparatus was used to weld TA2 and Ti-6Al-4V under different laser energy. Instron universal testing machine was adopted to measure the tensile load, 0.2% yield load and absolute elongation. The fractured surface was observed under SEM, Vickers microhardness values at welding area were measured and the mechanical properties after immersion in artificial saliva were detected. RESULTS: The mechanical strength of laser welds were related with material, voltage and the combination of them. At 700V-750V, there was no significant difference between tensile load of TA2 laser welds and that of the original material. For Ti-6Al-4V, At 750V. The mechanical strength of laser welds before and after immersion in artificial saliva made no statistic difference. CONCLUSION: It is suggested that the heat-affected zone of laser welding might be small and the corrosion resistance in artificial saliva might be high. The mechanical strength of titanium laser weld might meet the clinical demands at 19-20J/P.

[Effect of manifacturing technology on the resistance to corrosion of amalgam fillings and speed of mercury emission]. / A fogászati amalgám gyártástechnológiájának hatása az amalgámtömés korrózióállóságára és a higany kibocsátásának sebességére.

The study investigates the influence of the various manufacturing technological alternatives of a given alloy on the corrosion properties, as well as it evaluates the quantity of mercury release from the amalgam filling having the same alloy. The resistance of dental amalgams to corrosion is the function of their precious metal (mercury and silver) content. The release speed of the mercury depends on the original condition of the alloy. The highest values were given for filing amalgam. When investigating the composition of amalgam mainly in spherical form, a significant decrease could be here determined.

Thermal cycling distortion of porcelain fused to metal fixed partial dentures.

STATEMENT OF PROBLEM: The initial fit of porcelain fused to metal restorations deteriorates during the firing cycle of porcelain. PURPOSE: This study evaluated thermal cycling distortion of 3-unit porcelain fused to metal frameworks at different firing stages. MATERIAL AND METHODS: A master model was designed to represent the 2 abutments of a 3-unit fixed partial denture replacing a missing mandibular molar. Standard techniques were used to fabricate 10 castings. Half of the copings were cast in a Ni-Cr alloy and the other half in a Pd-Cu alloy. Framework distortion was measured by means of inner fit changes, horizontal linear measurements of the framework length, and vertical fit changes of each retainer. Measurements were made (1) initially, (2) after degassing firing, and (3) after glaze firing. Differences between the firing cycles created distortion values of the retainers in 3 dimensions. Repeated measures ANOVA was used to analyze data statistically. RESULTS: Measured differences between the 2 firing stages ranged from -47 to 81.7 micrometer. For both alloy groups, retainers showed increase in vertical gap that implied poorer vertical fit after porcelain application. Mean values of inner fit change recorded for porcelain application firing were higher in magnitude than the values of metal-conditioning firing. In addition, no statistically significant differences were found among alloy types. CONCLUSIONS: A 3-dimensional distortion was observed both in Pd-Cu and Ni-Cr frameworks during porcelain firing cycle. The distortion seen after porcelain application firing was significantly greater than that seen after metal-conditioning firing. This result can be attributed to these factors, contamination of porcelain to the inner surface of metal coping and reduction in resilience of metal.

Metodología aplicada al desarrollo de aleaciones dentales / Methodology applied to the development of dental alloys

Se presenta una metodología de desarrollo de aleaciones dentales y se aplica en plata-paladio con bajo contenido en metales nobles. El trabajo contempla obtención de aleaciones y evaluación de propiedades metalúrgicas y clínicas. Los resultados obtenidos con el grupo de aleaciones Ag-Pd muestran que el comportamiento "in vitro" permite predecir, con suficiente certeza, un comportamiento aceptable en boca. Esta predicción adquiere mayor validez al incorporar a la evaluación clínica aleaciones desarrolladas en trabajos anteriores, instaladas hace 4 o más años. Para una muestra global de 53 restauraciones, un 96 por ciento entrega resultados satisfactorios y sólo un 4 por ciento aparece como no aceptable. Se concluye que el trabajo desarrollado ofrece una aceptable metodología de prueba de toda nueva aleación propuesta como material dental restaurador (AU)