Prosthodontic biomaterials and adverse reactions: a critical review of the clinical and research literature

Technical complications with tooth-supported fixed dental prostheses (FDPs) of different span lengths: an up to 15-year retrospective study

BACKGROUNDS

Long-span dental bridges may cause excessive load on abutment teeth and the periodontal area, which may lead to bridge fractures or periodontal problems. However, some reports have revealed that short- and long-span bridges can provide a similar prognosis. This clinical study aimed to investigate the technical complications associated with fixed dental prostheses (FDPs) of different span lengths.

METHODS

All patients with previously cemented FDPs were clinically examined during their follow-up visits. Several data related to FDPs were registered, such as design, material type, location, and type of complication. The main clinical factors analyzed were technical complications. Life table survival analyses were performed to calculate the cumulative survival rate of FDPs when technical complications were detected.

RESULTS

The study examined 229 patients with a total number of 258 prostheses and an average of 98 months of follow-up. Seventy-four prostheses suffered from technical complications, and the most common complication was ceramic fracture or chipping (n = 66), while loss of retention occurred in 11 prostheses. The long-term evaluation of long-span prostheses revealed a significantly higher technical complication rate compared to short-span prostheses (P = ,003). The cumulative survival rate for short-span FDPs was 91% in year 5, 68% in year 10, and 34% in year 15. For long-span FDPs, the cumulative survival rate was 85% in year 5, 50% in year 10, and 18% in year 15.

CONCLUSION

Long-span prostheses (5 units or more) can be associated with a higher technical complication rate compared to short-span prostheses after long-term evaluation.

Metallic nanoparticles as effective sensors of bio-molecules

This work describes biologically important nanostructures of metals (AgNPs, AuNPs, and PtNPs) and metal oxides (Cu₂ONPs, CuONSs, γ-Fe₂O₃NPs, ZnONPs, ZnONPs-GS, anatase-TiO₂NPs, and rutile-TiO₂NPs) synthesized by different methods (wet-chemical, electrochemical, and green-chemistry methods). The nanostructures were characterized by molecular spectroscopic methods, including scanning/transmission electron microscopy (SEM/TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-vis), dynamic light scattering (DLS), Raman scattering spectroscopy (RS), and infrared light spectroscopy (IR). Then, a peptide (bombesin, BN) was adsorbed onto the surface of these nanostructures from an aqueous solution with pH of 7 that did not contain surfactants. Adsorption was monitored using surface-enhanced Raman scattering spectroscopy (SERS) to determine the influence of the nature of the metal surface and surface evolution on peptide geometry. Information from the SERS studies was compared with information on the biological activity of the peptide. The SERS enhancement factor was determined for each of the metallic surfaces.

Spectroscopic characterization and in vitro studies of biological activity of bradykinin derivatives

Eleven multiple analogs of bradykinin-a peptide that is a natural ligand of B1 and B2 receptors but does not bind or activate the B1 receptor unless Arg⁹ is removed from the sequence by the action of carboxypeptidase N-were synthesized. Their biological activity was examined on T-REx cell lines expressing B1 or B2 receptors using the intracellular IP1 assay. The mRNA expression of B1R and B2R in the lysate of tumor cell lines, e.g., U87-MG (human astrocytoma), SHP-77 (human small cell lung cancer), and H4 (human brain glioma), was determined. For five B1R antagonists, adsorption at the liquid/solid interface (Au nanoparticles (AuNPs) served as the solid surface) was discussed in terms of the vibrations of molecular fragments (structural factors) responsible for the biological properties of these analogs.

Osseointegration Improvement of Co-Cr-Mo Alloy Produced by Additive Manufacturing

Cobalt-base alloys (Co-Cr-Mo) are widely employed in dentistry and orthopedic implants due to their biocompatibility, high mechanical strength and wear resistance. The osseointegration of implants can be improved by surface modification techniques. However, complex geometries obtained by additive manufacturing (AM) limits the efficiency of mechanical-based surface modification techniques. Therefore, plasma immersion ion implantation (PIII) is the best alternative, creating nanotopography even in complex structures. In the present study, we report the osseointegration results in three conditions of the additively manufactured Co-Cr-Mo alloy: (i) as-built, (ii) after PIII, and (iii) coated with titanium (Ti) followed by PIII. The metallic samples were designed with a solid half and a porous half to observe the bone ingrowth in different surfaces. Our results revealed that all conditions presented cortical bone formation. The titanium-coated sample exhibited the best biomechanical results, which was attributed to the higher bone ingrowth percentage with almost all medullary canals filled with neoformed bone and the pores of the implant filled and surrounded by bone ingrowth. It was concluded that the metal alloys produced for AM are biocompatible and stimulate bone neoformation, especially when the Co-28Cr-6Mo alloy with a Ti-coated surface, nanostructured and anodized by PIII is used, whose technology has been shown to increase the osseointegration capacity of this implant.

Periodontal clinico-morphological changes in patients wearing old nickel-chromium and copper alloys bridges

Elderly population frequently presents more than one prosthetic restoration realized from different types of dental alloys which, in time, suffer various alterations in the oral environment. Metallic ions are released in saliva due to its electrolytic qualities, interacting with the contact tissues. Studies regarding cytotoxicity of dental alloys are providing contradictory results. Besides biocompatibility, the microbial factor is also greatly influencing the long-term success of the prosthetic rehabilitation. This study's aim was to assess the response of the gingival tissue to nickel-chromium (Ni-Cr) and copper (Cu)-based dental casting alloys from fixed dentures present in many patients from Romania. Gingival samples were taken from 124 patients wearing fixed dental restorations made from these two types of alloys from injured areas surrounding the abutment teeth; histological specimens were prepared, fixed in 10% neutral buffered formalin, paraffin-embedded and stained with Hematoxylin-Eosin (HE). Histological analysis showed the existence of a chronic inflammatory infiltrate in the gingival chorion, necrosis areas, and vascular congestion. Various morphological alterations appeared, depending on the intensity of the inflammation and the immune response. The surface epithelium suffered a hyperplasic reaction, either limited to acanthosis or involving the whole epithelium, the release of the Cu(2+) and Ni(2+) ions from the dental alloys used in bridges and crowns being responsible for inducing gingival hyperplasia and a chronic inflammation in the areas situated around the abutment teeth. The immunohistochemical study allowed us to observe an increased number of positive cluster of differentiation 3 (CD3) T-lymphocytes in periodontium, proving that the cellular immune response is rapid and intense.

Methacrylate perspective in current dental practice

OBJECTIVE

To provide a current perspective concerning dental personnel sensitivity to methacrylate materials.

OVERVIEW

Methacrylate related sensitivity and allergies are currently beyond traditional thoughts concerning denture base resins and methyl methacrylate provisional materials. Methacrylates are now ubiquitous in current dental practice and dental personnel should be aware that dental adhesives contain potent sensitizers that may also cross-sensitize individuals to other methacrylates not experienced. The growing sensitivity to 2-hydroxyethyl methacrylate (HEMA) has been described to be epidemic in nature due to the artificial nail industry with dental patients and dental personnel may be more susceptible to dental methacrylate sensitization. While contact dermatitis remains the most prevalent methacrylate-related clinical presentation, respiratory complications and asthma are increasing associated with methacrylate exposure. While additional personal protective equipment (PPE) is thought to be first protective choice, the National Institute for Occupational Safety and Health (NIOSH) considers PPE overall largely ineffective and should be considered only as a last resort.

CONCLUSION

Dental personnel need to be more aware of methacrylate sources and use workplace control measures to limit methacrylate exposures to both dental personnel and patients.

CLINICAL SIGNIFICANCE

Sensitivity to methacrylate materials is a growing dental workplace major concern and dental personnel should be aware of both the methacrylate content of current materials and the products that contain ingredients with the most sensitization potential.

The contribution of orthodontic braces to aluminum exposure in humans: an experimental in vitro study

There is limited information on whether metals such as aluminum (Al) can migrate from orthodontic braces to saliva and subsequently contribute to its exposure in humans. This study aimed to assess this experimentally by incubating elastomeric orthodontic ligatures in artificial saliva for 30 days and other components of orthodontic braces (brackets, arch wires, and retainers) up to 180 days. As demonstrated, significantly higher levels of Al were leached from elastomeric ligatures (mean ± SD 28.2 ± 6.8 μg compared with their stainless steel counterparts (3.6 ± 0.1 μg) during 30 days. The higher the incubation time, the greater levels of Al leaching to artificial saliva were observed with the highest levels found for CNA β arch wire (252 ± 12 μg), Ni-Ti-Al arch wire (224 ± 11 μg), ceramic brackets (199 ± 10 μg), stainless steel arch wire (108 ± 5 μg), and metallic brackets (81.0 ± 4.2 μg) after 180 days of incubation. However, considering the tolerable weekly intake (TWI) established by the European Food Safety Authority, the intraoral use of orthodontic braces considered in this study would in the worst case constitute 0.04% and 0.09% of TWI in 70-kg adults and 30-kg children, respectively. In conclusion, the orthodontic braces considered in this study have no contribution to Al exposure in humans and can be considered safe in this regard.

Oral care of a patient with a SAPHO syndrome and a nickel allergy

SAPHO is an acronym for Synovitis, Acne, Pustulosis, Hyperostosis and Osteitis. The syndrome is difficult to diagnose because it may present many different manifestations in adults and children. Its origin is still unknown, although some infectious, genetic and immune hypotheses have been put forward. We report the case of a 49-year-old woman with SAPHO syndrome, who developed a serious cutaneous allergy following the insertion of a removable partial denture (RPD). The oral care and treatment of this patient are described.

Mechanical properties of cobalt-chromium 3-unit fixed dental prostheses fabricated by casting, milling, and additive manufacturing

STATEMENT OF PROBLEM

New additive manufacturing techniques for nonprecious alloys have made the fabrication of metal-ceramic fixed partial dentures (FPDs) less expensive and less time-consuming. However, whether the mechanical properties produced by these techniques are comparable is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical properties of cobalt-chromium frameworks for FPDs fabricated by 3 different techniques.

MATERIAL AND METHODS

Thirty frameworks for 3-unit FPDs were fabricated by traditional casting, computer-aided design and computer-aided manufacturing (CAD-CAM) milling, and selective laser melting (SLM), with n=10 in each group. The frameworks were weighed, and distal and mesial connector areas measured. The frameworks were cemented and loaded centrally (0.5 mm/s) until deformation above 1 mm occurred. Stiffness was measured as the slope of the axis between 500 and 2000 N. Microhardness was measured on sectioned specimens by Vickers indentation. The microstructure was also analyzed by scanning electron microscopy. One-way ANOVA with Tukey post hoc analysis was used to compare the groups (α=.05).

RESULTS

The framework design differed among the groups, making a comparison of strength impossible. The milled frameworks appeared bulky, while the cast and SLM frameworks were more slender. Statistically significant differences were found in microhardness, stiffness, wall thickness, weight, and connector size (P<.05), and a significant correlation was found between hardness and stiffness (-0.4, P<.005).

CONCLUSIONS

Fabrication method affects the design, stiffness, microhardness, and microstructure of cobalt-chromium FPD frameworks. The SLM frameworks were stiffer and harder than the cast and milled specimens.

Cobalt release and complications resulting from the use of dental prostheses

BACKGROUND

Cobalt release from dental prostheses has been shown to elicit allergic reactions in cobalt-allergic patients. It is therefore important to investigate whether these prostheses are possible sources of sensitization.

OBJECTIVES

To assess (i) cobalt release from dental prostheses and (ii) allergic reactions to components of dental prostheses, and (iii) to investigate the oral mucosa for inflammation 1-5 years after insertion of the prostheses.

METHOD

Clinical oral examination was conducted in 66 patients with 84 dental prostheses. Cobalt release from 84 functional (used) and 32 non-functional (new) prostheses was investigated with the cobalt spot test. Contact allergy was assessed by patch testing. Smear tests for Candida spp. were performed in patients showing signs of inflammation of the oral mucosa. The prostheses were assessed for biological and technical complications.

RESULTS

None of the functional prostheses released cobalt, whereas this was observed in 24 of 32 non-functional prostheses. None of the patients had contact allergy to cobalt. Of the 66 patients, 11 showed signs of inflammation of the oral mucosa, 2 had oral candidiasis, 16 had ill-fitting prostheses, and all had insufficient oral hygiene.

CONCLUSIONS

Dental prostheses released cobalt during the fabrication stages, but not 1-5 years after insertion. No allergic reactions were observed. Signs of inflammation were related to candidiasis, insufficient oral hygiene, and ill-fitting prostheses.

Cobalt deposition in mineralized bone tissue after metal-on-metal hip resurfacing: Quantitative μ-X-ray-fluorescence analysis of implant material incorporation in periprosthetic tissue

Most resurfacing systems are manufactured from cobalt-chromium alloys with metal-on-metal (MoM) bearing couples. Because the quantity of particulate metal and corrosion products which can be released into the periprosthetic milieu is greater in MoM bearings than in metal-on-polyethylene (MoP) bearings, it is hypothesized that the quantity and distribution of debris released by the MoM components induce a compositional change in the periprosthetic bone. To determine the validity of this claim, nondestructive µ-X-ray fluorescence analysis was carried out on undecalcified histological samples from 13 femoral heads which had undergone surface replacement. These samples were extracted from the patients after gradient time points due to required revision surgery. Samples from nonintervened femoral heads as well as from a MoP resurfaced implant served as controls. Light microscopy and µ-X-ray fluorescence analyses revealed that cobalt debris was found not only in the soft tissue around the prosthesis and the bone marrow, but also in the mineralized bone tissue. Mineralized bone exposed to surface replacements showed significant increases in cobalt concentrations in comparison with control specimens without an implant. A maximum cobalt concentration in mineralized hard tissue of up to 380 ppm was detected as early as 2 years after implantation. Values of this magnitude are not found in implants with a MoP surface bearing until a lifetime of more than 20 years. This study demonstrates that hip resurfacing implants with MoM bearings present a potential long-term health risk due to rapid cobalt ion accumulation in periprosthetic hard tissue. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1855-1862, 2017.

Recommendations for post-adaption care of an ocular prosthesis: A review

An ocular prosthesis must be maintained in a suitable state of cleanliness, fit and preservation. Otherwise its functioning may be compromised, leading to a variety of diseases. However, there is a lack of consensus on the care of such prostheses. This review assembles and attempts to update existing knowledge in this area and discusses the most appropriate care regimes.

Accuracy of interchangeable implant impression systems: an in vitro pilot study

PURPOSE

To evaluate the accuracy of impressions on changing the implant component (coping and abutment replica) between Brånemark and BIOMET 3i and between Straumann and Allfit.

MATERIALS AND METHODS

Two master casts were constructed, one containing pair of Brånemark self-tap Mk II fixtures (Nobel Biocare) labeled Master cast I and the other containing pair of Straumann Standard plus implant, SLA fixtures (Straumann) labeled Master cast II. Ten impressions of each master cast were made by open tray technique using polyether impression material. Five out of 10 impressions made from master cast I contained Brånemark pair of coping and replica and the other 5 contained 3i (Implant Innovations). Five out of 10 impressions made from master cast II contained Straumann pair of copings and replica and the remaining 5 contained Allfit implants (Ihde Dental). Duplicated casts were prepared, and distances between copings were measured using traveling microscope and compared the distance in master casts.

RESULT

No significant difference was observed in mean value between 2 master casts and their duplicates.

CONCLUSION

The interchangeability of coping and abutment replica between Brånemark and BIOMET 3i and between Straumann and Allfit was found to be possible without compromising the quality of impressions.

Electrochemical corrosion and surface analyses of a ni-cr alloy in bleaching agents

PURPOSE

The aim of this study was to evaluate the corrosion behavior of a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) and 10% carbamide peroxide (CP) bleaching solutions and to determine the composition of the surface oxide layer formed on the alloy specimens.

MATERIALS AND METHODS

Ten cylindrical specimens (4 mm in diameter × 25 mm in height) were cast from a Ni-Cr alloy (Wiron 99) and divided into two groups (n = 5). A potentiodynamic polarization test was used to compare the corrosion rates of specimens in HP and CP (pH = 6.5). Before cyclic polarization tests, all alloy specimens were allowed to reach a steady open circuit potential (Ecorr ) for a period of 1 hour. Then tests were initiated at 100 mV versus standard calomel electrode (SCE) below Ecorr and scanned at a rate of 1 mV/s in the anodic direction until reaching 1000 mV over the Ecorr value. The scan then was reversed back to the Ecorr of the specimens. The open circuit potentials (Ecorr ) and the current densities (Icorr ) were determined using the anodic Tafel regions extrapolating from the curves. Differences in Ecorr and Icorr were determined using one-way ANOVA (α = 0.05). In addition, corrosion rates were calculated from these curves. Before and after polarization tests, a scanning electron microscope (SEM) examination accompanied by energy dispersive X-ray spectroscopy (EDS) was used to analyze the surface morphology. The surface characterization of the passive film formed on alloy specimens was also performed by using X-ray photoelectron spectroscopy (XPS).

RESULTS

In this study, bleaching agents had an effect on the anodic process for two groups. Although no statistical difference was identified between the groups for both corrosion parameters, results indicated that the effect of CP on the corrosion behavior was less than that of HP. These results agreed with the SEM observations. XPS data showed that oxide layers formed on all groups contained mainly Cr2 O3 , NiO, and MoO3 , and the amounts of oxides formed on CP-treated specimens were higher than HP treated ones. Also, molybdenum rates were increased with CP application compared to HP.

CONCLUSIONS

The comparison of the effects of the two bleaching agents at 10% showed that the alloy suffered less corrosion with CP than HP. This result was also confirmed by the SEM and XPS data. The presence of Mo on the oxide layer affected the oxide layer, leading to lower corrosion rates.

Digital imaging and fabrication

Bioceramics have been adopted in dental restorations for implants, bridges, inlays, onlays, and all-ceramic crowns. Dental bioceramics include glass ceramics, reinforced porcelains, zirconias, aluminas, fiber-reinforced ceramic composites, and multilayered ceramic structures. The process of additive manufacturing is ideally suited to dentistry. Models are designed using data from a computed tomography scan or magnetic resonance imaging. Since its development in 2001, direct ceramic machining of presintered yttria tetragonal zirconia polycrystal has become increasingly popular in dentistry. There are wide variety commercially available cements for luting all-ceramic restorations. However, resin cements have lower solubility and better aesthetic characteristics.

Implant-supported full-arch zirconia-based mandibular fixed dental prostheses. Eight-year results from a clinical pilot study

OBJECTIVE

The purpose of this pilot study was to evaluate the long-term clinical performance of implant-supported full-arch zirconia-based fixed dental prostheses (FDPs).

MATERIALS AND METHODS

Ten patients received full-arch zirconia-based (Cercon) mandibular FDPs supported by four implants (Astra Tech). Nine patients received 10-unit FDPs and one patient received a 9-unit FDP. The FDPs were cemented onto individually prepared titanium abutments and were evaluated at baseline and after 12, 24, 36 and 96 months.

RESULTS

Nine patients attended the 8-year follow-up. None of the restorations showed bulk fracture, all FDPs were in use. Fractures of the veneering porcelain were, however, observed in eight patients. A total of 36 out of 89 units (40%) showed such fractures. Patient satisfaction was excellent despite the veneering material fractures.

CONCLUSION

Results from this 8-year pilot study suggest that implant-supported full-arch zirconia-based FDPs can be an acceptable treatment alternative.

Dendrimer/methyl methacrylate co-polymers: residual methyl methacrylate and degree of conversion

Dendrimer/methyl methacrylate co-polymers were studied for use in dental composites. The aim was to determine the effects of methyl methacrylate concentration in the resin mixture and polymerization method on the degree of conversion and residual monomer content of the copolymers. Two dendrimers were studied, D12 with 12 reactive methacrylate groups and D24 with 24 reactive groups. The concentration of methyl methacrylate varied from 20 wt% to 50 wt% of monomers. Camphorquinone (CQ) was used as the light-activation initiator and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) as the activator, both in the quantity of 3.0 wt%. Three polymerization methods were used: photo-polymerization, photo-polymerized immediately followed by post-polymerization at 120 degrees C for 15 min, and photo-polymerization followed by postpolymerization after 7 days. The degree of conversion was determined using FT-IR. Residual monomers were extracted with tetrahydrofuran and methanol and analyzed with HPLC. The highest degrees of conversion were 65 and 62%, and the lowest residual monomer contents 1.0 and 1.5% for D12 and D24, respectively. These were measured after heat-induced post-polymerization. For D12, increasing the proportion of methyl methacrylate decreased the degree of conversion and increased the residual monomer content after photo-polymerization. Post-polymerization enhanced the polymerization of the dendrimer co-polymers in respect of degree of conversion and residual monomer content. The present study suggested that the tested dendrimer/methyl methacrylate copolymers require heat-induced polymerization to reach the generally accepted levels of degree of conversion and residual monomers.

Determination of susceptibility to sensitization to dental materials in atopic and non-atopic patients

Introduction: Some studies report that atopic patients have a greater frequency of delayed-type sensitization than non-atopic patients. Objective: To determine the influence of the atopic condition on delayed sensitization to dental materials. Design: cross-sectional study. Methods: Forty (40) atopic subjects and forty (40) non-atopic subjects, of both sexes, between 20 and 65 years of age were included. The determination of delayed sensitization to dental materials was performed using patch test. An oral exam was also carried out to check for lesions of the oral mucosa. Results: 61.25% of the patients were positive for delayed-type sensitization to one or more allergens, being palladium chloride (21.25%), ammoniated mercury (20%), benzoyl peroxide (12.5%) and amalgam (10%) the most frequent. The frequency of sensitization was 67.5% in the group of atopic patients, compared to 55% in the non atopic group (p>0.05). The materials with the greatest difference of sensitization in atopic compared to non-atopic patients were ammoniated mercury, benzoyl peroxide, amalgam and Bisphenol A Dimethacrylate (BIS-GMA). Conclusion: The atopic condition is not related to a higher frequency of delayed sensitization to a battery of dental materials.

Key words: Patch test, delayed-type sensitization, allergy contact, atopia, dental materials.

Effect of temperature variation on the cytotoxicity of cast dental alloys and commercially pure titanium

Cell culture system has been used to evaluate alloy cytotoxicity under different environments, testing the extracts, but the effect of temperature variation on the cytotoxicity of dental alloys has not been analyzed. Objective: The aim of the present study was to investigate if temperature variation could affect dental alloy cytotoxicity, testing alloy extracts in an epithelial cell culture system. Material and methods: Discs of Ni-Cr, Co-Cr-Mo, Ni-Cr-Ti, Ti-6Al-4V and commercially pure titanium (cp Ti) were cast by arc melting, under argon atmosphere, injected by vacuum-pressure. Discs were immersed in artificial saliva and subjected to different temperatures: 37°C and thermocycling (37°C/5°C/37°C/55°C/37°C). After thermocycling, extracts were put in a subconfluent culture during 6 h, and the number of cells and their viability were used to evaluate cytotoxicity in these temperatures. For each alloy, data from temperature conditions were compared by Student's t-test (α=0.05). Results: The cytotoxicity tests with alloy/metal extracts showed that Ni-Cr, Co-Cr-Mo, Ti-6Al-4V and cp Ti extracts (p>0.05) did not affect cell number or cell viability, while Ni-Cr-Ti (p<0.05) extract decreased cell number and viability when the alloy was subjected to thermocycling. Conclusion: Within the limitations of the present study, the Ni-Cr-Ti alloy had cell number and viability decreased when subjected to temperature variation, while the other alloys/metal extracts did not show these results.

Chromium release from new stainless steel, recycled and nickel-free orthodontic brackets

OBJECTIVE

To test the hypothesis that there is no difference in the amounts of chromium released from new stainless steel brackets, recycled stainless steel brackets, and nickel-free (Ni-free) orthodontic brackets.

MATERIALS AND METHODS

This in vitro study was performed using a classic batch procedure by immersion of the samples in artificial saliva at various acidities (pH 4.2, 6.5, and 7.6) over an extended time interval (t(1) = 0.25 h, t(2) = 1 h, t(3) = 24 h, t(4) = 48 h, t(5) = 120 h). The amount of chromium release was determined using an atomic absorption spectrophotometer and an inductively coupled plasma atomic emission spectrometer. Statistical analysis included a linear regression model for repeated measures, with calculation of Huber-White robust standard errors to account for intrabracket correlation of data. For post hoc comparisons the Bonferroni correction was applied.

RESULTS

The greatest amount of chromium was released from new stainless steel brackets (0.52 +/- 1.083 microg/g), whereas the recycled brackets released 0.27 +/- 0.38 microg/g. The smallest release was measured with Ni-free brackets (0.21 +/- 0.51 microg/g). The difference between recycled brackets and Ni-free brackets was not statistically significant (P = .13). For all brackets, the greatest release (P = .000) was measured at pH 4.2, and a significant increase was reported between all time intervals (P < .002).

CONCLUSION

The hypothesis is rejected, but the amount of chromium released in all test solutions was well below the daily dietary intake level.

Comparative study of chemical and mechanical retentive systems for bonding of indirect composite resin to commercially pure titanium

This study evaluated the effect of chemical and mechanical surface treatments for cast metal alloys on the bond strength of an indirect composite resin (Artglass) to commercially pure titanium (cpTi). Thirty cylindrical metal rods (3 mm diameter x 60 mm long) were cast in grade-1 cpTi and randomly assigned to 6 groups (n=5) according to the received surface treatment: sandblasting; chemical treatment; mechanical treatment - 0.4 mm beads; mechanical treatment - 0.6 mm beads; chemical/mechanical treatment - 0.4 mm; and chemical/mechanical treatment - 0.6 mm beads. Artglass rings (6.0 mm diameter x 2.0 mm thick) were light cured around the cpTi rods, according manufacturer's specifications. The specimens were invested in hard gypsum and their bond strength (in MPa) to the rods was measured at fracture with a universal testing machine at a crosshead speed of 2.0 mm/min and 500 kgf load cell. Data were analyzed statistically by one-way ANOVA and Tukey test (alpha=5%). The surface treatments differed significantly from each other (p<0.05) regarding the recorded bond strengths. Chemical retention and sandblasting showed statistically similar results to each other (p=0.139) and both had significantly lower bond strengths (p<0.05) than the other treatments. In conclusion, mechanical retention, either associated or not to chemical treatment, provided higher bond strength of the indirect composite resin to cpTi.

Biocompatibility of dental materials

With the long history of use of many materials in dental surgery, biocompatibility concerns are not as great a concern as other issues, such as long-term degradation, mechanical strength problems, and prevention of secondary caries. It is important, however, not to forget that the potential exists for adverse tissue responses to synthetic materials used in repair, augmentation, and repair of natural tissue structures. As new materials and repair techniques become available and the sophistication of cell-level and subcellular response evaluations increases, the concerns to be addressed and the methods to be used may change. The advent of tissue-engineered medical products may mean that new questions must be addressed.

Biocompatibility evaluation of a novel hydroxyapatite-polymer coating for medical implants (in vitro tests)

Nanocomposites consisting of hydroxyapatite (HA) and a sodium maleate copolymer (maleic polyelectrolyte), synthesized by hydrothermal method and deposited on titanium substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique were tested for the biological properties. Coating bioanalysis was carried out by triple staining of actin, microtubules and nuclei followed by immunofluorescence microscopy. Within 24 h cells that occupied the biomaterial surface displayed the morphology and cytoskeleton pattern similar to the controls. Cells grown on nanocomposite coated surfaces had a higher proliferation rate than their counterparts grown on Ti coated with HA alone, indicating that maleic polyelectrolyte improved surface bio-adhesive characteristics. The capacity to induce cell attachment, spreading and proliferation demonstrated the potential of Ti coated with HA-polymer nanocomposites to be used as scaffolds in dental or orthopedic implantology.

FDI report on adverse reactions to resin-based materials

Resin-based restorative materials are considered safe for the vast majority of dental patients. Although constituent chemicals such as monomers, accelerators and initiators can potentially leach out of cured resin-based materials after placement, adverse reactions to these chemicals are rare and reaction symptoms commonly subside after removal of the materials. Dentists should be aware of the rare possibility that patients could have adverse reactions to constituents of resin-based materials and be vigilant in observing any adverse reactions after restoration placement. Dentists should also be cognisant of patient complaints about adverse reactions that may result from components of resin-based materials. To minimise monomer leaching and any potential risk of dermatological reactions, resin-based materials should be adequately cured. Dental health care workers should avoid direct skin contact with uncured resin-based materials. Latex and vinyl gloves do not provide adequate barrier protection to the monomers in resin-based materials.

Dendritic copolymers and particulate filler composites for dental applications: degree of conversion and thermal properties

OBJECTIVES

The aim of this study was to determine the degree of double bond conversion and thermal properties of photopolymerized dendritic copolymers and particulate filler composites that may be used as dental restorative materials.

METHODS

The resins consisted of a multifunctional dendritic monomer, methyl methacrylate and varying proportions of acetoacetoxyethyl methacrylate. In addition, one of the composites contained 1,4-butanediol dimethacrylate. Camphorquinone and 2-(N,N-dimethylamino)ethyl methacrylate were used as the light-activated initiation system. The degree of conversion was determined with Fourier transform infrared spectroscopy and the thermal properties with differential scanning calorimetry.

RESULTS

The degree of conversion of copolymers varied from 52 to 60% and increased with increasing concentration of acetoacetoxyethyl methacrylate. The values for the composites were 32-44%. Reaction exotherms of 0.2-9.6J/g were measured for the photopolymerized experimental materials indicating residual reactivity that increased with increasing concentration of acetoacetoxyethyl methacrylate. The residual reactivity trend seemed counter intuitive to the degree of conversion. The glass transition temperatures for the completely polymerized copolymers containing acetoacetoxyethyl methacrylate were 112-116 degrees C and for the particulate filler composites 84-87 degrees C.

SIGNIFICANCE

The addition of acetoacetoxyethyl methacrylate increased the degree of conversion. The polymerization characteristics of the experimental materials were comparable to those of control materials.

[Chronic cobalt poisoning in endoprosthetic replacement]

This article outlines symptoms and therapeutic options in chronic cobalt poisoning including a case report in which metallosis caused by a ceramic-metal articular pairing led to almost complete loss of sight and hearing after revision of a total hip prosthesis. At primary revision the firmly incorporated stem was left in place. For a better offset only the head was exchanged from a ceramic to a metal model which articulated with a socket containing a ceramic inlay. Postoperatively, movement of the hip joint became increasingly uncomfortable and painful. After 2 years, the patient started complaining about increasing impairment of his eyesight followed by a gradual loss of hearing. In a second revision, examination of the explanted material showed almost complete deterioration of the metal femoral head and a partially fractured ceramic inlay with extensive contamination of the bone and surrounding soft tissue by metal debris. At the time of revision increasing concentrations of the alloy elements cobalt, chromium, and molybdenum were measured in the serum and liquor. The concentration of cobalt, in particular, was remarkably high. Treatment options in cases with chronic cobalt poisoning include chelation therapy with EDTA or BAL/DMPS.

Effect of toothbrushing on titanium surface: An approach to understanding surface properties of brushed titanium

OBJECTIVES

This in vitro study aimed to characterize the surface morphology and composition of tooth-brushed titanium casting and thereby to elucidate interactions between the metal and abrasive material in dentifrice.

METHODS

Specimens were cast from CP Ti ingots and then mirror-finished. Two fluoride-free toothpastes containing crystalline CaHPO4.2H2O and amorphous SiO2 particles as abrasive were slurried with distilled water (15 g/30 mL). While toothbrushes were reciprocated at 120 strokes/min for 350,400 strokes, the specimens were brushed with the respective slurries under a load of 2.45 N. The brushed and non-brushed surfaces were characterized by means of SPM, EPMA, and XPS. SPM data were analyzed using one-way ANOVA, followed by post hoc Tukey test (p<0.01).

RESULTS

Irrespective of toothpastes, toothbrushing had a significant influence on surface roughness. The CaHPO4.2H2O-containing paste produced much rougher surface than the SiO2-containing paste. Both the surfaces were chemically altered due to reactions with the respective abrasive materials. Abrading chips had dimensions of micron to submicron order. A number of chips were attached to abrasive particles.

SIGNIFICANCE

The alterations of surface morphology and composition may affect biological responses of titanium in the oral environment. Dentifrice with lower abrasivity might be advisable for daily oral hygiene practice of patients with dental titanium devices.

Toxic effect of nickel in an in vitro model of human oral epithelium

Nickel is a metal widely employed in dental alloys, and due to peculiar properties of certain nickel-based materials, it cannot be substituted with other metals in some applications. The release of nickel ions from dental alloys placed into long-term contact with mouth soft tissues is alarming because of the toxic, immunological and carcinogenic effects which have been well documented for some nickel compounds. Our study was focussed on the toxic effects induced "in vitro" on human oral epithelium by the exposure to low concentrations of nickel chloride. In view of this, we adopted a three-dimensional model of epithelial cultures, reconstituted from TR 146 cells, resembling the physiological environment of the oral cavity and useful for biocompatibility testing. The effects on cell viability, apoptosis, cellular content of reduced and oxidized glutathione (GSH and GSSG) and release of prostaglandin E(2) (PGE(2)), interleukin-8 (IL-8) and interleukin-6 (IL-6) were investigated following topical application of a NiCl(2) solution ranging from 7.6mM to 0.05 mM for 72 h. Our findings show that nickel concentrations, which do not significantly modify cell viability and inflammation mediator release, can affect the redox equilibrium and stimulate apoptosis in oral epithelium cells. Further studies are needed to demonstrate the hypothesis that the oxidative imbalance induced by nickel might be implicated in the induction of apoptosis.

Investigation of reactions to dental materials

Patients undergoing dental treatment can be exposed to a wide range of potential allergens, but adverse events seem infrequent. Patients with symptoms or signs of stomatitis, burning, tingling, cheilitis, oral lichenoid lesions, lip and facial swelling may relate their problems to dental treatment or to the use of dental products. Investigation for immediate type or delayed type hypersensitivity is indicated using patch testing, prick testing and blood tests for allergen-specific IgE. The main allergic reactions found in patients include contact allergy to metals, cosmetics, food additives, flavours and acrylates, and immediate type allergy to latex. Adverse reactions following the administration of local anaesthetics are seen in about 0.5% of cases, but immediate type allergy to these agents is rare. In dental staff, occupationally related problems are common and usually take the form of hand or facial dermatitis or respiratory disease. The most common allergic reactions in dental staff are immediate type allergy to latex, and contact allergy to rubber additives, fragrances, acrylates and formaldehyde. Occupational irritant problems causing hand dermatitis are probably more common in dental personnel than is dermatitis caused by contact allergy. Patch testing and tests for immediate type allergy are useful investigative methods in the investigation of patients who present with oral or facial symptoms possibly related to dental treatments and are also beneficial in dental personnel who present with hand or facial dermatitis or respiratory symptoms.

Patients' choice of dental treatment following examination at a specialty unit for adverse reactions to dental materials

The Dental Biomaterials Adverse Reaction Unit in Bergen, Norway, is a national unit for the examination of patients with suspected adverse reactions to dental materials. The aim of this study was to investigate whether patients with suspected adverse reactions to dental materials experienced improvement in health after dental restorations had been replaced, and whether they had acted according to the recommendations of the Unit. A questionnaire was sent to 358 patients who had been examined at the Unit 18 months to 7 years earlier. Of the 207 patients who completed the questionnaire, 85 had had restorative materials replaced with other types of materials. A majority had had amalgam fillings replaced. After replacement, 51 patients reported an improvement in health. Twelve patients reported that they felt worse after replacement. The Unit recommended replacement of materials in 31 patients, of whom 24 followed the recommendation. Among 176 patients who were not given specific recommendations as to replacement of dental materials, 67 had had their restorations replaced, and 40 had started to have them replaced. It appears that the examination at the Dental Biomaterials Adverse Reaction Unit is one of several inputs that influence a person's decision to replace dental materials.

The national survey of adverse reactions to dental materials in the UK: a preliminary study by the UK Adverse Reactions Reporting Project

OBJECTIVE

Dental treatment involves the use of a wide range of materials. Many of the dental materials or their components pose a potential risk to the patient and member of the dental team. Pre-market biocompatibility testing cannot guarantee absolute safety, making monitoring of materials likely to cause an adverse reaction essential. The prevalence of adverse reactions to dental materials amongst dental patients and staff has not been systematically monitored in the UK. This project aims to develop a systematic approach to the evaluation and monitoring of the extent and severity of adverse reactions to dental materials in the UK.

METHOD

Through the distribution of reporting forms to dental surgeries and laboratories in the UK, the ARRP has received 1,075 complete reports relating to adverse reactions seen or experienced by dental staff and patients.

RESULTS

The main findings were that different materials cause adverse reactions to different groups of people. The largest proportion of patient related adverse reactions were reported to be due to metals (n = 175). These were mainly amalgam associated oral lichenoid reactions (n = 124). Dental technicians reported acrylic resin as the causal factor of hand dermatitis in 61% (44 out of a total 72) of cases reported. Finally, dental surgery staff reported gloves as causing hand dermatitis in 75% of cases (398 out of a total 531).

CONCLUSIONS

Different dental materials affect different person groups depending on their exposure to the material. Dental staff are most at risk from an adverse reaction to latex gloves, whereas most reported reactions for patients were due to metals. For dental technicians the biggest danger of an adverse reaction was from acrylic resins. There is a need to continue to raise the awareness among dental professionals of the existence of the Adverse Reactions Reporting Project so as to overcome problems of under-reporting.