Rodrigo Antonio de Medeiros

Surface characterization of lithium disilicate ceramic after nonthermal plasma treatment

STATEMENT OF PROBLEM Surface transformation with nonthermal plasma may be a suitable treatment for dental ceramics, because it does not affect the physical properties of the ceramic material. PURPOSE The purpose of this study was to characterize the chemical composition of lithium disilicate ceramic and evaluate the surface of this material after nonthermal plasma treatment. MATERIAL AND METHODS A total of 21 specimens of lithium disilicate (10 mm in diameter and 3 mm thick) were fabricated and randomly divided into 3 groups (n=7) according to surface treatment. The control group was not subjected to any treatment except surface polishing with abrasive paper. In the hydrofluoric acid group, the specimens were subjected to hydrofluoric acid gel before silane application. Specimens in the nonthermal plasma group were subjected to the nonthermal plasma treatment. The contact angle was measured to calculate surface energy. In addition, superficial roughness was measured and was examined with scanning electron microscopy, and the chemical composition was characterized with energy-dispersive spectroscopy analysis. The results were analyzed with ANOVA and the Tukey honestly significant difference test (α=.05). RESULTS The water contact angle was decreased to 0 degrees after nonthermal plasma treatment. No significant difference in surface roughness was observed between the control and nonthermal plasma groups. Scanning electron microscopy and energy-dispersive spectroscopy images indicated higher amounts of oxygen (O) and silicon (Si) and a considerable reduction in carbon (C) in the specimens after nonthermal plasma treatment. CONCLUSIONS Nonthermal plasma treatment can transform the characteristics of a ceramic surface without affecting its surface roughness. A reduction in C levels and an increase in O and Si levels were observed with the energy-dispersive spectroscopy analysis, indicating that the deposition of the thin silica film was efficient.

Evaluation of marginal bone loss of dental implants with internal or external connections and its association with other variables: A systematic review

STATEMENT OF PROBLEM Different factors can influence marginal bone loss around dental implants, including the type of internal and external connection between the implant and the abutment. The evidence needed to evaluate these factors is unclear. PURPOSE The purpose of this systematic review was to evaluate marginal bone loss by radiographic analysis around dental implants with internal or external connections. MATERIAL AND METHODS A systematic review was conducted following the criteria defined by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Initially, a population, intervention, comparison, and outcome(s) (PICO) question was defined: does the connection type (internal or external) influence marginal bone loss in patients undergoing implantation? An electronic search of PubMed/MEDLINE and Scopus databases was performed for studies in English language published between January 2000 and December 2014 by 2 independent reviewers, who analyzed the marginal bone loss of dental implants with an internal and/or external connection. RESULTS From an initial screening yield of 595 references and after considering inclusion and exclusion criteria, 17 articles were selected for this review. Among them, 10 studies compared groups of implants with internal and external connections; 1 study evaluated external connections; and 6 studies analyzed internal connections. A total of 2708 implants were placed in 864 patients. Regarding the connection type, 2347 implants had internal connections, and 361 implants had external connections. Most studies showed lower marginal bone loss values for internal connection implants than for external connection implants. CONCLUSIONS Osseointegrated dental implants with internal connections exhibited lower marginal bone loss than implants with external connections. This finding is mainly the result of the platform switching concept, which is more frequently found in implants with internal connections.

Toxicity analysis of ocular prosthesis acrylic resin with or without pigment incorporation in human conjunctival cell line

The aim of this study was to evaluate the influence of pigment incorporation on the cytotoxicity of ocular prosthesis N1 color acrylic resin. Nine samples were manufactured by heat-polymerization in water bath and divided into 3 groups: acrylic resin without pigment incorporation (group R), acrylic resin with pigment incorporation (group RP), and acrylic pigment (group P). Eluates formed after 72h of sample immersion in medium were incubated with conjunctival cell line (Chang conjunctival cells) for 72h. The negative control group consisted in medium without samples (group C). The cytotoxic effect from the eluates was evaluated using MTT assay (cell proliferation), ELISA assay (quantification of IL1β, IL6, TNF α and CCL3/MIP1α) and RT-PCR assay (mRNA expression of COL IV, TGF β and MMP9). Data were submitted to ANOVA with Bonferroni post-tests (p<0.05). All groups were considered non-cytotoxic based on cell proliferation. However, resin with pigment incorporation showed significant IL6 quantity increase. Resin without pigment incorporation exhibited higher mRNA expression of COL IV, MMP9 and TGF β, however it was also observed for the negative control group. The materials exhibited divergent biological behavior. Despite the pigment incorporation that resulted in an increase of IL6, no cytotoxicity was observed based on cell proliferation.

Stress distribution in implant-supported prostheses using different connection systems and cantilever lengths: digital photoelasticity

Abstract Photoelastic analysis was used to evaluate the biomechanical behaviour of implant-supported, double-screwed crowns with different connection systems and cantilever lengths. Three models were made in PL-2 photoelastic resin and divided into six groups, on the basis of the implant connection system (external hexagon [EH] or Morse taper [MT]), type of abutment (Mini Pilar [Neodent, Curitiba, Paraná, Brazil] or “UCLA”) and number of crowns in the cantilever (one or two). The implant-prosthesis unit was placed in a circular polariscope. Occlusal surfaces of the crowns were subjected to 100-N loads in the axial and oblique (45°) directions in a universal testing machine (EMIC). Generated stresses were recorded and analysed qualitatively in a graphics program (Adobe Photoshop). Under axial loading, all of the groups had similar numbers of fringes, which were increased when the crowns were subjected to oblique loading. The highest number of fringes was found during oblique loading in the EH + Mini Pilar group. In conclusion, although the type of implant connection system did not have a direct influence on the stress distribution for axial loading, the cantilever length did have a direct influence on stress distribution. Models with two crowns in the cantilever showed more stress, with a greater concentration of force on the cervical part of the implant.

Stress distribution in bone simulation model with pre-angled implants

Abstract The aim of this study was evaluate the biomechanical behaviour of prostheses screwed into conventional (0° angulation) and pre-angled experimental (8, 12 and 20°) external hexagon implants (13 × 4 mm) by photoelastic analysis. Eight casts were made in photoelastic resin. Casts were divided into groups of single crowns or three combined elements. Each unit was positioned in a circular polariscope. By using a universal testing machine, 100 N loads were applied in the axial and oblique (45°) directions to fixed points on the occlusal surfaces of the crowns. Generated stresses were recorded photographically and analysed qualitatively in a graphics program. In single-element prostheses, the number of high-stress fringes increased with increasing implant angle. However, in three-element prostheses, there was no difference in the stress distribution with implant angle, except for the 12° implant that had a higher degree of stress. For the other groups pre-angulation of the implant increases the concentration and intensity of stresses for single prosthesis and has similar stress distribution in three-element fixed prostheses.

Prosthetic Rehabilitation of a Patient with Gastroesophageal Reflux Disease: 4-Year Followup

The gastroesophageal reflux disease (GERD) is one of the main causes of dental erosion. The aim of this case presented is to describe the prosthetic rehabilitation of a patient with GERD after 4 years of followup. A 33-year-old male patient complained about tooth sensitivity. The lingual surface of the maxillary anterior teeth and the cusps of the upper and lower posterior teeth presented wear. It was suspected that the feeling of heartburn reported by the patient associated with the intake of sports supplements (isotonics) was causing gastroesophageal changes. The patient was referred to a gastroenterologist and was diagnosed with GERD. Dental treatment was performed with metal-free crowns and porcelain veneers after medical treatment of the disease. With the change in eating habits, the treatment of GERD and lithium disilicate ceramics provided excellent cosmetic results after 4 years and the patient reported satisfaction with the treatment.

Chromatic changes to artificial irises produced using different techniques.

Abstract. Ocular prostheses are important determinants of their users’ aesthetic recovery and self-esteem. Because of use, ocular prostheses longevity is strongly affected by instability of the iris color due to polymerization. The goal of this study is to examine how the color of the artificial iris button is affected by different techniques of artificial wear and by the application of varnish following polymerization of the colorless acrylic resin that covers the colored paint. We produce 60 samples (n=10) according to the wear technique applied: conventional technique without varnish (PE); conventional technique with varnish (PEV); technique involving a prefabricated cap without varnish (CA); technique involving a prefabricated cap with varnish (CAV); technique involving inverted painting without varnish (PI); and technique involving inverted painting with varnish (PIV). Color readings using a spectrophotometer are taken before and after polymerization. We submitted the data obtained to analyses of variance and Tukey’s test (P<0.05). The color test shows significant changes after polymerization in all groups. The PE and PI techniques have clinically acceptable values of ΔE, independent of whether we apply varnish to protect the paint. The PI technique produces the least color change, whereas the PE and CA techniques significantly improve color stability.

A photoelastic and strain gauge comparison of two attachments for obturator prostheses

Statement of problem. The rehabilitation of patients after a maxillectomy involves the use of an obturator to seal oral‐nasal‐sinus communication and to facilitate mastication, swallowing, and speech. Purpose. The purpose of this in vitro study was to evaluate different attachment systems used for implant‐retained obturators at dissipation loads and under shear forces. Material and methods. Photoelastic models were fabricated with 3 external hexagon implants at the incisor, canine, and first molar regions. Subsequently, overdentures were made, and metal hooks were placed at the incisor and first molar regions to displace the prostheses in the vertical, anterior, and posterior directions, with a constant speed of 50 mm/min. A photoelastic model with an O‐ring or bar‐clip system was placed in a circular polariscope, and tested with a universal testing machine. The images were recorded and high‐intensity fringes were counted using software. For strain gauge analysis, each strain gauge was placed horizontally at the mesial and distal sides of the implants. The registered strains were submitted to 2‐way ANOVA (&agr;=.05). Results. The O‐ring showed the lowest number of high‐intensity fringes in photoelastic imaging, while the strain gauge analysis showed the lowest stress values in the bar‐clip group (P=.007). Conclusions. The stress around titanium implant necks was more damaging to surrounding bone, while the bar‐clip attachment system had a better biomechanical performance. The bar‐clip presented the lowest strain values around the dental implants and few high‐intensity fringes.

Stress distribution on short implants with different designs: a photoelastic analysis

Abstract Short dental implants have been used as an attempt to avoid bone grafts surgery, however there are few literature reports that evaluate changes to their design. Therefore, the aim of this study was to assess the effect of different short implant design on stress distribution through photoelastic analysis. Six external hexagon (5 × 5 mm) short dental implants with different design were used. Each group was treated with a single crown and a three element fixed partial dental prosthesis, resulting in a total of 12 photoelastic models. The assembling photoelastic model-implant-prosthesis was set in a circular polariscope where loads of 100N were applied on the occlusal surface with a Universal Test Machine (UTM). The tension fringes were photographed and later assessed qualitatively by a graphic software (Adobe Photoshop). Less high-intensity fringes were observed on the short implants with triangular threads, short external hexagon and flat apical profile. In conclusion, the macrodesign influenced the amount of stress distributed to the bone when short dental implants are placed.

Biomechanical evaluation of spring system for implant-supported prosthesis: analysis by photoelasticity and extensometry

Abstract New systems are released in the odontological market with the objective of bringing improvements and advancements in the clinical success of implants and implant-supported prostheses. The distribution of tension for the bone/implant system of these new systems is important. The purpose of this work was to evaluate, by photoelastic analysis and strain gauges, the distribution of tension for the bone/implant system, using the Slim system. A photoelastic cast with an external hexagon implant was manufactured and a metal prosthesis was screwed below it, with or without the tested system. For the photoelasticity methodology, a photoelastic cast, with or without the tested system, was positioned in a circular polariscope, and axial loads of 100 N were applied to the centre of the crown. The pattern of tension generated was photographed and analysed qualitatively in an imaging programme. For the extensometry methodology, two extensometers were placed in the mesial and distal region of the implant in the photoelastic cast. The axial loads were applied to the group again, with or without the system (n = 10). The t test of independent samples with a significance level of 5% was used for this analysis. This study demonstrated greater tension values for both the photoelastic and extensometry methods when the tested system was used. Clinical studies must be performed to evaluate the tested system because the results might not be clinically significant to a bone reabsorption.