Retentive Strength of Y-TZP Crowns: Comparison of Different Silica Coating Methods on the Intaglio Surfaces

Objective:

To evaluate the effect of different methods of silica deposition on the intaglio surface of yttrium oxide stabilized zirconia polycrystal (Y-TZP) crowns on the retentive strength of the crowns.

Methods:

One hundred simplified full-crown preparations produced from fiber-reinforced polymer material were scanned, and 100 Y-TZP crowns with occlusal retentions were milled. Crown/preparation assemblies were randomly allocated into five groups (n=20) according to the treatment of the intaglio surfaces: TBS = tribochemical silica coating via air-abrasion with 30-μm silica-coated alumina particles; GHF1 = application of thin glaze layer + hydrofluoric acid (HF) etching for 1 minute; GHF5 = glaze application + HF for 5 minutes; GHF15 = glaze application + HF for 15 minutes; NANO = silica nanofilm deposition (5 nm) via magnetron sputtering. All groups received a silane application. The surfaces of the preparations (polymer) were conditioned with 10% HF for 30 seconds and silanized. The crowns were cemented with resin cement, thermocycled (12,000 cycles; 5°C/55°C), stored for 60 days, and subjected to a retentive strength test (0.5 mm/min until failure). The retention data (MPa) were analyzed using one-way analysis of variance, Tukey tests, and Weibull analysis. Failures were classified as 50C (above 50% of cement in the crown) and 50S (above 50% of cement on the substrate).

Results:

The TBS (5.6±1.7 MPa) and NANO groups (5.5±1 MPa) had higher retentive strength than the other groups (p<0.0001) and had the highest values of characteristic strength. There was no difference in Weibull modulus, except for the GHF1 group (lower values). The TBS and GHF15 groups, respectively, had 60% and 70% of their failures classified as 50C, while most of the other groups had 50S failures.

Conclusion:

Tribochemical silica coating and silica nanofilm deposition on the inner surface of zirconia crowns promoted a higher retentive strength.

Photon correlation spectroscopy applied to tear analysis

This study aims to deepen the knowledge on tear film properties by the development of a protocol for analyses of Photon Correlation Spectroscopy (PCS) on human tears and by the comparison between PCS results obtained on tears of contact lens wearers and non-wearers. Tears (5μL) were collected by a glass capillary. The analyses provide the hydrodynamic diameter of tear components by analyzing intensity fluctuations in time of scattered light. PCS appears a promising technique for studying tear features and for shedding light on specific eye conditions, such as on the clinical effects of CL wear. In fact, statistical difference (p<0.001) was found between the measured mean hydrodynamic diameter of tear components of wearers and non-wearers, the resulting value significantly higher for CL wearers. The scenario does not substantially change after (25±5)min from the CL removal. The difference is attributed to changes in the interactions between tear constituents due to CL wear. In order to get deeper insights on the influence of CL wear on aggregation and structure of tear components, a preliminary Electron Spin Resonance (ESR) investigation was performed, monitoring Fe³⁺ species. ESR spectra on tears of both CL wearers and non-wearers showed the presence of intense signals, probably associated to iron (III) centers in proteins such as lactoferrin, and a weaker resonance attributable to Fe³⁺ species interacting with S-S bridges of lysozyme. Differences in ESR spectra between CL wearers and non-wearers were detected and tentatively ascribed to changes in coordination or in local environment of Fe³⁺ centers connected to aggregation phenomena induced by CL wear, which promote their interaction with other neighboring iron species.

Different Methods for Inlay Production: Effect on Internal and Marginal Adaptation, Adjustment Time, and Contact Point

The aim of this study was to evaluate the effect of different production methods of resin and ceramic inlays on marginal and internal adaptation, adjustment time, and proximal contacts. Forty premolars were selected, embedded (their roots), and prepared to receive inlays that were made as follows (n=10): LaRe-digital impression with a Lava C.O.S. scanner, followed by milling of Lava Ultimate block (composite resin) in a milling center; CeRe-digital impression with a Cerec 3D Bluecam scanner, followed by milling of Lava Ultimate block in Cerec; CeDis-digital impression with a Cerec 3D Bluecam scanner, followed by milling of IPS e.max CAD block (lithium disilicate) in Cerec; and PresDis-impression with polyvinyl siloxane, inlay made using the lost wax technique and IPS e.max Press pressed ceramic (lithium disilicate). Marginal and internal adaptations were measured using the replica technique. The inlay adjustments were performed using diamond burs in a contra-angle hand piece, and the time for adjustment was recorded using a timer, in seconds. The tightness of the proximal contact was measured using standardized metal blades. The statistical analyses for marginal fit data showed that at the cervical edge, CeDis (177.8 μm) had greater misfit than CeRe (116.7 μm), while all the groups had similar adaptation at the occlusal edge. The groups had similar internal fit at the pulpal wall, while LaRe (104.7 μm) > CeDis (66.7 μm) = CeRe (76.7 μm) at the axial wall. The groups restored with lithium disilicate ceramic took more time for adjustment when compared to the resin restorative material. The lowest proximal contact, in micrometers, was seen in the CeRe group (8.8 μm).

Customized hybrid biomimetic hydroxyapatite scaffold for bone tissue regeneration

Three-dimension (3D) scaffolds for bone tissue regeneration were produced combining three different phases: nanometric hydroxyapatite (HA) was synthesized by precipitation method and the crystals nucleation took place directly within collagen fibrils following a biologically inspired mineralization process; polycaprolactone was employed to give the material a 3D structure. The chemico-physical analysis carried out to test the material's properties and composition revealed a high similarity in composition and morphology with biologically mineralized collagen fibrils and a scaffold degradation pattern suitable for physiological processes. The micro- computerized tomography (micro-CT) showed 53.53% porosity and a 97.86% mean interconnected pores. Computer-aided design and computer-aided manufacturing (CAD-CAM) technology was used for molding the scaffold's volume (design/shape) and for guiding the surgical procedure (cutting guides). The custom made scaffolds were implanted in sheep mandible using prototyped surgical guides and customized bone plates. After three months healing, scanning electron microscopy (SEM) analysis of the explanted scaffold revealed a massive cell seeding of the scaffold, with cell infiltration within the scaffold's interconnected pores. The micro-CT of the explanted construct showed a good match between the scaffold and the adjacent host's bone, to shield the implant primary stability. Histology confirmed cell penetration and widely documented neoangiogenesis within the entire scaffold's volume. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 723-734, 2017.

IgG4-related disease in Italy: clinical features and outcomes of a large cohort of patients

OBJECTIVES

To describe the clinical features, treatment response, and follow-up of a large cohort of Italian patients with immunoglobulin (Ig)G4-related disease (IgG4-RD) referred to a single tertiary care centre.

METHOD

Clinical, laboratory, histological, and imaging features were retrospectively reviewed. IgG4-RD was classified as 'definite' or 'possible' according to international consensus guidelines and comprehensive diagnostic criteria for IgG4-RD. Disease activity was assessed by means of the IgG4-RD Responder Index (IgG4-RD RI).

RESULTS

Forty-one patients (15 females, 26 males) were included in this study: 26 with 'definite' IgG4-RD and 15 with 'possible' IgG4-RD. The median age at diagnosis was 62 years. The median follow-up was 36 months (IQR 24-51). A history of atopy was present in 30% of patients. The pancreas, retroperitoneum, and major salivary glands were the most frequently involved organs. Serum IgG4 levels were elevated in 68% of cases. Thirty-six patients were initially treated with glucocorticoids (GCs) to induce remission. IgG4-RD RI decreased from a median of 7.8 at baseline to 2.9 after 1 month of therapy. Relapse occurred in 19/41 patients (46%) and required additional immunosuppressive drugs to maintain long-term remission. Multiple flares occurred in a minority of patients. A single case of orbital pseudotumour did not respond to medical therapy and underwent surgical debulking.

CONCLUSIONS

IgG4-RD is an elusive inflammatory disease to be considered in the differential diagnosis of isolated or multiple tumefactive lesions. Long-term disease control can be achieved with corticosteroids and immunosuppressive drugs in the majority of cases.

The filler-rubber interface in styrene butadiene nanocomposites with anisotropic silica particles: morphology and dynamic properties

Silica-styrene butadiene rubber (SBR) nanocomposites were prepared by using shape-controlled spherical and rod-like silica nanoparticles (NPs) with different aspect ratios (AR = 1-5), obtained by a sol-gel route assisted by a structure directing agent. The nanocomposites were used as models to study the influence of the particle shape on the formation of nanoscale immobilized rubber at the silica-rubber interface and its effect on the dynamic-mechanical behavior. TEM and AFM tapping mode analyses of nanocomposites demonstrated that the silica particles are surrounded by a rubber layer immobilized at the particle surface. The spherical filler showed small contact zones between neighboring particles in contact with thin rubber layers, while anisotropic particles (AR > 2) formed domains of rods preferentially aligned along the main axis. A detailed analysis of the polymer chain mobility by different time domain nuclear magnetic resonance (TD-NMR) techniques evidenced a population of rigid rubber chains surrounding particles, whose amount increases with the particle anisotropy, even in the absence of significant differences in terms of chemical crosslinking. Dynamic measurements demonstrate that rod-like particles induce stronger reinforcement of rubber, increasing with the AR. This was related to the self-alignment of the anisotropic silica particles in domains able to immobilize rubber.

Evaluation of tensile retention of Y-TZP crowns cemented on resin composite cores: effect of the cement and Y-TZP surface conditioning

This study evaluated the effect of the cement type (adhesive resin, self-adhesive, glass ionomer, and zinc phosphate) on the retention of crowns made of yttria-stabilized polycrystalline tetragonal zirconia (Y-TZP). Therefore, 108 freshly extracted molars were embedded in acrylic resin, perpendicular to their long axis, and prepared for full crowns: the crown preparations were removed and reconstructed using composite resin plus fiber posts with dimensions identical to the prepared dentin. The preparations were impressed using addition silicone, and Y-TZP copings were produced, which presented a special setup for the tensile testing. Cementation was performed with two adhesive resin cements (Multilink Automix, Ivoclar-Vivadent; RelyX ARC, 3M ESPE, St Paul, MN, USA), one self-adhesive resin cement (RelyX U100, 3M ESPE), one glass ionomer based cement (RelyX Luting, 3M ESPE), and one zinc phosphate cement (Cimento de Zinco, SS White, Rio de Janeiro, Brazil). For the resin cement groups, the inner surfaces of the crowns were subjected to three surface treatments: cleaning with isopropyl alcohol, tribochemical silica coating, or application of a thin low-fusing glass porcelain layer plus silanization. After 24 hours, all groups were subjected to thermocycling (6000 cycles) and included in a special device for tensile testing in a universal testing machine to test the retention of the infrastructure. After testing, the failure modes of all samples were analyzed under a stereomicroscope. The Kruskal-Wallis test showed that the surface treatment and cement type (α=0.05) affected the tensile retention results. The Multilink cement presented the highest tensile retention values, but that result was not statistically different from RelyX ARC. The surface treatment was statistically relevant only for the Multilink cement. The cement choice was shown to be more important than the crown surface treatment for cementation of a Y-TZP crown to a composite resin substrate.

Mechanical properties and micro-morphology of fiber posts

OBJECTIVES

To evaluate flexural properties of different fiber posts systems and to morphologically characterize their micro-structure.

METHODS

Six types of translucent fiber posts were selected: RelyX Post (3M ESPE), ParaPost Taper Lux (Colthéne-Whaledent), GC Fiber Post (GC), LuxaPost (DMG), FRC Postec Plus (Ivoclar-Vivadent), D.T. Light-Post (RTD). For each post system and size, ten specimens were subjected to a three-points bending test. Maximum fracture load, flexural strength and flexural modulus were determined using a universal loading device (5848 MicroTester(®), Instron). Besides, for each system, three intact posts of similar dimensions were processed for scanning electron microscopy to morphologically characterize the micro-structure. The following structural characteristics were analyzed: fibers/matrix ratio, density of fibers, diameter of fibers and distribution of fibers. Data were statistically analyzed with ANOVA.

RESULTS

Type and diameter of posts were found to significantly affect the fracture load, flexural strength and flexural modulus (p<0.05). Regarding maximum fracture load, it was found to increase with post diameter, in each post system (p<0.001). Regarding flexural strength and flexural modulus, the highest values were recorded for posts with the smallest diameter (p<0.001). Finally, structural characteristics significantly varied among the post systems tested. However, any correlation has been found between flexural strength and structural characteristics.

SIGNIFICANCE

Flexural strength appeared not to be correlated to structural characteristics of fiber posts, but it may rather be affected by mechanical properties of the resin matrix and the interfacial adhesion between fibers and resin matrix.

Effect of ferrule and post placement on fracture resistance of endodontically treated teeth after fatigue loading

OBJECTIVES

To evaluate the influence of the ferrule effect (1) and the fibre-post placement (2) on the fracture resistance of endodontically treated teeth subjected to cyclic fatigue loading.

METHODS

40 extracted single-rooted upper pre-molars were sectioned at the CEJ (groups a and b) or 2mm above the CEJ (groups c and d), and subsequently endodontically treated. After 24-h water storage at 37°C, specimens were restored according to four build-up approaches (n=10 per group): (a) NF-NP (no ferrule, no post), (b) NF-P (no ferrule, fibre-post), (c) F-NP (ferrule, no post) and (d) F-P (ferrule, fibre post). RelyX Posts (3M-ESPE) were used in groups NF-P and F-P, and were cemented with Panavia F 2.0 (Kuraray). A standardized composite core was built, after which specimens were restored with an all-ceramic crown (IPS Empress CAD, Ivoclar-Vivadent) Specimens were fatigued by exposure to 1,200,000 cycles using a chewing simulator (Willytech). All specimens that survived fatigue loading were fractured using a universal loading device (Micro-Tester, Instron). A two-way analysis of variance was used to determine the statistical significance of the factors ferrule and post on fracture resistance.

RESULTS

Only one NF-NP specimen failed under fatigue. The ferrule effect significantly enhanced the fracture resistance of the restored teeth, regardless the use of a post (p=0.003). F-NP obtained the highest fracture resistance (758.52±121.89N), which was not significantly different from F-P (647.58±132.95N); NF-NP presented the lowest fracture resistance (361.52±151.69N). For all groups, only 'repairable' failures were recorded.

CONCLUSIONS

Avoiding extra-removal of sound tooth structure, rather than placing a fibre post, can protect endodontically treated teeth against catastrophic failure. However, when any ferrule can be preserved, a fibre-post may improve the retention and fatigue resistance of the restoration.

Direct metal laser sintering (DMLS) of a customized titanium mesh for prosthetically guided bone regeneration of atrophic maxillary arches

This study describes a protocol for the direct manufacturing of a customized titanium mesh using CAD-CAM procedures and rapid prototyping to augment maxillary bone and minimize surgery when severe atrophy or post-oncological deformities are present. Titanium mesh and particulate autogenous plus bovine demineralised bone were planned for patient rehabilitation. Bone augmentation planning was performed using the pre-op CT data set in relation to the prosthetic demands, minimizing the bone volume to augment at the minimum necessary for implants. The containment mesh design was used to prototype the 0.6 mm thickness customized titanium mesh, by direct metal laser sintering. The levels of regenerated bone were calculated using the post-op CT data set, through comparison with the pre-op CT data set. The mean vertical height difference of the crestal bone was 2.57 mm, while the mean buccal-palatal dimension of thickness difference was 3.41 mm. All planned implants were positioned after an 8 month healing period using two-step implant surgery, and finally restored with a partial fixed prosthesis. We present a viable and reproducible method to determine the correct bone augmentation prior to implant placement and CAD-CAM to produce a customized direct laser-sintered titanium mesh that can be used for bone regeneration.

Design and manufacturing of ear prosthesis by means of rapid prototyping technology

In this paper, the complete procedure to design and construct reusable moulds for implant-based ear prosthesis and manufacture substructures by means of a computer aided design-computer aided manufacturing (CAD-CAM) procedure and rapid prototyping (RP) technology is presented. The scan of the healthy ear, the virtual superimposition of its mirrored image on to the defective side, and the rapid manufacturing of the substructure and of the mould eliminate several steps of traditional procedures (wax, stone, try-in). Moreover, the precise design and customization of the substructure is presented, with the original and engineered shape for the retention of the silicone. The time and cost saving results of this protocol are presented together with a discussion of the main design features that make the prosthesis a stable and reproducible system to improve rehabilitation of patients with auricular defects or absence.

3-T MRI with phased-array surface coil in the local staging of rectal cancer

PURPOSE

This study sought to evaluate the diagnostic accuracy of surface-coil 3T magnetic resonance (MR) imaging in the preoperative study of patients with rectal cancer.

MATERIALS AND METHODS

Thirty patients with histologically proven rectal cancer underwent surface-coil 3T MR imaging with sagittal, paracoronal and para-axial T2-weighted turbo spin echo (TSE) sequences. Slice thickness was 3 mm without gap, field of view 24 cm, matrix 400 × 512. Images were assessed for infiltration of the rectal wall, perirectal fat and pelvic structures. Tumours were staged according to the TNM system, and the MR imaging results were correlated with histopathology.

RESULTS

In the patients who underwent MR imaging before and after radiotherapy (group 1), the diagnostic accuracy of 3T MR imaging was 88% for T2, 94% for T3 and 88% for T4 cancers. In those who underwent surgical treatment without preoperative radiotherapy (group 2), the diagnostic accuracy was 90% for T2, 87% for T3 and 87% for T4 cancers.

CONCLUSIONS

The high signal-to-noise ratio coupled with a large field of view enables surface-coil 3T MR imaging to achieve high levels of diagnostic accuracy in the local staging of rectal cancer, and in particular in assessing infiltration of mesorectum and mesorectal fascia.

CAD-CAM construction of a provisional nasal prosthesis after ablative tumour surgery of the nose: a pilot case report

The computer-aided design of a nasal prosthesis based on pre-operative virtual laser scanning of the affected site was virtually adapted to the post-operative laser-scanned surface. The designed volume of the nose was rapidly prototyped and used to fabricate a provisional prosthesis and a computed tomography diagnostic template to check the available premaxilla bone for implants. The mould for the nasal prosthesis was prototyped using a computer-aided design and manufacturing (CAD-CAM) procedure. In addition, the mesiostructure of an eyeglasses-supported provisional prosthesis was also designed and prototyped using CAD-CAM procedures.

Effect of Mechanical Cycling on the Push-out Bond Strength of Fiber Posts Adhesively Bonded to Human Root Dentin

When adhesively cemented, tested fiber posts are fatigue resistant and appear to have no affect on bond strength to root dentin. Thus, the retention strength of these fiber posts could be maintained for an extended period; however, further studies should be conducted.

Maxillofacial rehabilitation after rhinectomy using two different treatment options: clinical reports

The aim of these clinical reports was to describe two different approaches to prosthetic rehabilitation after facial disfigurement because of a total rhinectomy. A man with a total rhinectomy was scheduled for craniofacial implants in the nasal residual defect. Three oral implants were used instead of craniofacial ones. A conventional framework was designed to connect the prosthesis to the implant abutments in the anterior nasal floor, and a custom-made ball attachment was positioned in the glabella abutment. A woman with a free rectum abdomis flap covering the defect of the middle face was scheduled for a nasal prosthesis. A titanium framework with a novel connection between the eyeglasses and the prosthesis was manufactured. The two clinical reports presented in this article illustrate favourable clinical treatment outcomes in the rehabilitation of disfigurement.

Early biofilm colonization on polished- and glazed-zirconium ceramic surface. Preliminary results

AIM

The purpose of this study was to evaluate the effect of ceramic surface polishing procedure on the early dental biofilm formation on zirconium ceramics.

METHODS

Twenty samples (discs shape) of tetragonal zirconium polycrystal stabilized with yttrium ceramics (Y-TZP) for LAVA system were fabricated (5 mm diameter and 1.5 mm thickness). Two patients with high level of dental hygiene were selected for this study. Oral devices covering the crowns of the upper premolars and molars were fabricated for each participant. Glazed and polished samples of Y-TZP ceramics were fixed on the vestibular and palatal zones of the devices. After 20 min (8 samples) and 1 h (8 samples) in the oral environment, the samples were removed and analyzed in a scanning electron microscope. The surface topographies of 4 ceramic samples (2 glazed and 2 polished) were analyzed (control group: without exposition in oral environment).

RESULTS

The glazed samples showed a more irregular surface than polished samples. Deposition of granular aggregates was verified on all the samples in the two times of the study analyzed. This granular material coated more intensely on irregular areas, and its thickness increased after 1 h. No difference was observed as to bacterial morphology in any time of the study. Cocci and rods-shaped prevailed.

CONCLUSIONS

Glazed surfaces presented larger tendency to dental biofilm accumulation.

The prosthetically guided osteodistraction of the mandible in the microvascular bone reconstruction after cancer surgery

The rehabilitation of the mandible after ablation cancer surgery is a challenge. Furthermore, osteodistraction in the microvascular fibula flap makes it difficult to predict adequate bone lengthening. The aim of this article is to evaluate a protocol used to manufacture templates for measuring osteodistraction, in terms of force vectors and definitive height. An accurate prosthetic wax-up with guide pins measuring the quantity of bone lengthening must be performed to manufacture the template. This device may be used to establish the end of the osteo-distraction in respect to the vertical dimension of the definitive occlusion.

Home care maintenance protocol for ear prostheses

Hygienic home care maintenance for patients who have received a maxillofacial prosthesis is very important in order to secure a long-term success of a facial rehabilitation. Craniofacial implant therapy requires a specific protocol to care for the peri-implant tissues and material used for the prosthesis. This article presents the maintenance and care protocol for proper follow-up management of a maxillofacial ear prosthesis. Home care methods for the prosthesis hygiene are described, including: the insertion and the disconnection of the ear prosthesis, hygiene of the bar abutments before and after postdefinitive connection to the craniofacial fixtures, washing of the device, professional follow-up.

Neuroradiologic differential diagnosis of cerebral intraparenchymal hemorrhage

Cerebral intraparenchymal hematoma (IH) is one of the most common causes of sudden onset of focal neurologic deficit. This is particularly true in the acute phase, in which IH appears hyperdense compared to the cerebral tissue. By three to four weeks, it becomes isodense with the cerebral gray matter and hypodense within 2 to 6 months. After contrast media administration, IH shows a peripheral ring of enhancement owing to the breakdown of the blood brain barrier. On magnetic resonance imaging (MRI), the appearance of IH depends upon the paramagnetic effects of the different derivates of hemoglobin and both the magnetic field strength and type of sequences used. In the hyperacute phase, IH appears hyperintense on T2 and hypointense on T1 owing to the presence of oxyhemoglobin. In the acute phase, IH is hypointense on T2 and iso-hypointense on T1 as a consequence of the presence of deoxyhemoglobin, which is converted into methemoglobin by 3 to 5 days. Methemoglobin has a strong paramagnetic effect, so in this phase IH becomes hyperintense on T1 and hypointense on T2. After 2 weeks, methemoglobin is converted in hemosiderin, responsible of the ring of hypointensity surrounding the lesion on T2WI. When an IH has been diagnosed, someone should think about the origin of bleeding. Among the different differential diagnosis, one should think about the possible origin, taking into account some parameters, such as: anamnestic data, site of the lesion, number of lesions, appearance on CT and MRI, and presence of perilesional edema. Computed tomography is a reliable and very fast tool for the diagnosis of IH, but MRI is able to provide additional information about the spontaneous or secondary nature of the hematoma, thus allowing a better characterization of the hemorrhagic lesion.

Residual facial disfigurement after the ablative surgery of a lachrymal gland carcinoma: a clinical report of the prosthetic rehabilitation

Facial disfigurement after ablative surgery of a massive adeno-carcinoma of the lachrymal gland is described. A rehabilitation with a maxillofacial prosthesis was proposed to restore the aesthetic appearance of the patient without inserting craniofacial implants. Retention of a maxillofacial prosthesis, that is not anchored to implants, depends on the use of adhesives or on mechanical devices like glasses. This clinic report describes a residual anatomic defect which allowed for the double choice of wearing the facial prosthesis both with or without glasses. A retentive backside of the prosthesis was developed to engage the facial defect undercuts, which enhanced retention when the patient used the skin glue without glasses. A unique foam silicone was utilized to reduce the weight of the prosthesis and to permit its retention only by skin adhesive.

[New aesthetic results with auricular prosthesis: two case reports]

The extrinsic and intrinsic coloration of maxillo-facial silicone elastomers has always been a challenge for the clinician in order to obtain a perfect, durable integration with the surrounding skin tissues. This preliminary report describes the method for obtaining good aestethetic results for maxillo-facial prosthesis. This study shows the aesthetic results of a new silicone for the laboratory technique of creating color of the basis for a maxillo-facial prosthesis, with a good matching with human skin. The technique is useful for the direct extrinsic coloration of the surface onto the skin of the patient by means of the RTV version of the same silicone. The technological properties of this material also make it easy to reproduce the emerging profile of the prosthesis from the human skin, avoiding anaesthetic overcounturings. The 12 month follow-up shows excellent and stable aesthetic results, which are not influenced by home care procedures and by the weathering effect on color and on physical properties.

[Overdenture supported by natural teeth: analysis of clinical advantages]

Hybrid prosthesis supported by natural teeth (overdenture) is widely used in clinical practice and should be executed whenever the clinical conditions suggest it. Through a critical review of the literature, the anatomical, functional, psychological and clinical advantages are emphasized. Among the first ones, the prophylaxis of residual anatomical components, due to the limitation of bone resorption, and the preservation of sensorial proprioception are relevant. Important advantages are also represented by a better crown-root ratio of residual teeth supporting overdenture, with the consequent improvement of the longitudinal prognosis of such teeth. The greater retention and stability of overdenture in comparison with complete denture greatly improve the masticatory efficacy. The psychological advantages resulting from the dental anchorage, which allows the patient to be more confident in social life, are also relevant. Finally, when the dental support is lost, converting overdenture into complete denture is simple and quick, and makes easier the longitudinal clinical maintenance of the denture.

What is community? An evidence-based definition for participatory public health

Increased emphasis on community collaboration indicates the need for consensus regarding the definition of community within public health. This study examined whether members of diverse US communities described community in similar ways. To identify strategies to support community collaboration in HIV vaccine trials, qualitative interviews were conducted with 25 African Americans in Durham, NC; 26 gay men in San Francisco, Calif; 25 injection drug users in Philadelphia, Pa; and 42 HIV vaccine researchers across the United States. Verbatim responses to the question "What does the word community mean to you?" were analyzed. Cluster analysis was used to identify similarities in the way community was described. A common definition of community emerged as a group of people with diverse characteristics who are linked by social ties, share common perspectives, and engage in joint action in geographical locations or settings. The participants differed in the emphasis they placed on particular elements of the definition. Community was defined similarly but experienced differently by people with diverse backgrounds. These results parallel similar social science findings and confirm the viability of a common definition for participatory public health.