Implant-Supported Prosthesis Misalignment Related to the Dental Arch: A 14-Year Clinical Follow-up

The purpose of this study was to warn the dental community about a possible problem in function with partial implant-supported prostheses used for long periods. The misalignment between natural teeth and the implant-supported prosthesis on teeth 11 and 12, observed in a 14-year clinical follow-up, illustrates the fact. The metal-ceramic crowns were placed in 1995 after a rigorous occlusal adjustment. Evaluations were made at 4, 6, 9, and 14 years, when it was noticed that the restorations were positioned palatally and extruded in comparison with the natural teeth. After 9 years, a greater discrepancy was noticed, with anterior occlusion and esthetic changes. The possible causes have been discussed: occlusal problems, parafunctional habits, and natural movement. The first 2 options were discarded after clinical analysis and diagnosis. Therefore, the natural movement probably deriving from an interaction of mechanical and genetic factors might have been the cause. The implants do not have periodontal ligaments but rather ankylosis, so they do not suffer those movements. This case emphasizes the need to inform patients that implants can last more than 10 years in function, but this is not the case with restorations, which lose function and esthetics and must be replaced.

Three-Dimensional Finite Element Analysis of Stress Distribution on Different Bony Ridges With Different Lengths of Morse Taper Implants and Prosthesis Dimensions

This finite element analysis (FEA) compared stress distribution on different bony ridges rehabilitated with different lengths of morse taper implants, varying dimensions of metal-ceramic crowns to maintain the occlusal alignment. Three-dimensional FE models were designed representing a posterior left side segment of the mandible: group control, 3 implants of 11 mm length; group 1, implants of 13 mm, 11 mm and 5 mm length; group 2, 1 implant of 11 mm and 2 implants of 5 mm length; and group 3, 3 implants of 5 mm length. The abutments heights were 3.5 mm for 13- and 11-mm implants (regular), and 0.8 mm for 5-mm implants (short). Evaluation was performed on Ansys software, oblique loads of 365N for molars and 200N for premolars. There was 50% higher stress on cortical bone for the short implants than regular implants. There was 80% higher stress on trabecular bone for the short implants than regular implants. There was higher stress concentration on the bone region of the short implants neck. However, these implants were capable of dissipating the stress to the bones, given the applied loads, but achieving near the threshold between elastic and plastic deformation to the trabecular bone. Distal implants and/or with biggest occlusal table generated greatest stress regions on the surrounding bone. It was concluded that patients requiring short implants associated with increased proportions implant prostheses need careful evaluation and occlusal adjustment, as a possible overload in these short implants, and even in regular ones, can generate stress beyond the physiological threshold of the surrounding bone, compromising the whole system.

Deformation of Implant Abutments After Framework Connection Using Strain Gauges

When a cylinder is connected to an abutment it is expected that abutment and cylinder will be subjected to compression forces throughout their periphery because of the clamping force exerted by the screw. The deformation resultant of this compression should be measurable and uniform along the periphery of the abutment. Considering that multiple retainers connected to each other can affect the fit of a framework, as well as the use of different alloys, it is expected that the abutments will present different levels of deformation as a result of framework connection. The aim of this study was to evaluate the deformation of implant abutments after frameworks, cast either in cobalt-chromium (CoCr) or silver-palladium (AgPd) alloys, were connected. Samples (n = 5) simulating a typical mandibular cantilevered implant-supported prosthesis framework were fabricated in cobalt-chromium and silver-palladium alloys and screwed onto standard abutments positioned on a master-cast containing 5 implant replicas. Two linear strain gauges were fixed on the mesial and distal aspects of each abutment to capture deformation as the retention screws were tightened. A combination of compressive and tensile forces was observed on the abutments for both CoCr and AgPd frameworks. There was no evidence of significant differences in median abutment deformation levels for 9 of the 10 abutment aspects. Visually well-fit frameworks do not necessarily transmit load uniformly to abutments. The use of CoCr alloy for implant-supported prostheses frameworks may be as clinically acceptable as AgPd alloy.

Effect of framework soldering on the deformation of implant abutments after framework seating: a study with strain gauges

Introduction: Passive fit has been considered an important requirement for the longevity of implant-supported prostheses. Among the different steps of prostheses construction, casting is a feature that can influence the precision of fit and consequently the uniformity of possible deformation among abutments upon the framework connection. Purpose: This study aimed at evaluating the deformation of abutments after the connection of frameworks either cast in one piece or after soldering. Materials and Methods: A master model was used to simulate a human mandible with 5 implants. Ten frameworks were fabricated on cast models and divided into 2 groups. Strain gauges were attached to the mesial and distal sides of the abutments to capture their deformation after the framework’s screw retentions were tightened to the abutments. Results: The mean values of deformation were submitted to a 3-way analysis of variance that revealed significant differences between procedures and the abutment side. The results showed that none of the frameworks presented a complete passive fit. Conclusion: The soldering procedure led to a better although uneven distribution of compression strains on the abutments.

Aesthetic analysis of an implant-supported denture at the cleft area

Objective: To evaluate the aesthetics of an implant-supported denture at the cleft area, comparing the peri-implant tissues and prosthetic crown with the contralateral tooth. Settings: Hospital for Rehabilitation of Craniofacial Anomalies, Bauru, São Paolo, Brazil. Patients: A total of 39 individuals of both genders, with complete unilateral cleft lip and palate, who received secondary alveolar bone graft and were rehabilitated with single implant-supported dentures at the area of the missing maxillary lateral incisor after completion of orthodontic treatment. Interventions: The following parameters were analyzed in follow-up sessions: length and width of prosthetic crown and contralateral tooth, characteristics of implants, filling of interproximal space by the papilla, and smile height of the patients. Results: The implant-supported prosthetic crowns were longer than the contralateral tooth (p < .001). Among the 78 papillae analyzed, 29 (37.17%) received a score of 3; 32 (41.02%) papillae had a score of 2; and 17 (21.79%) received a score of 1. Concerning the smile height, among the 39 patients analyzed, 23 (56.41%) had a medium smile, 15 (38.46%) had a high smile, and two (5.12%) presented a low smile. Conclusion: The use of dental implants to rehabilitate the edentulous cleft area is an excellent option. However, adequate evaluation of the bone quantity and quality, positioning and shape of adjacent teeth, smile height, and patient expectations should be considered to achieve success and avoid aesthetic deformities such as elongated teeth and absence of gingival papillae.

Moving from surfactant-stabilized aqueous rhodium (0) colloidal suspension to heterogeneous magnetite-supported rhodium nanocatalysts: Synthesis, characterization and catalytic performance in hydrogenation reactions

Wet impregnation of pre-synthesized surfactant-stabilized aqueous rhodium (0) colloidal suspension on silica was employed in order to prepare supported Rh-0 nanoparticles of well-defined composition, morphology and size. A magnetic core-shell support of silica (Fe(3)O4@SiO2) was used to increase the handling properties of the obtained nanoheterogeneous catalyst. The nanocomposite catalyst Fe3O4@SiO2-Rh-0 NPs was highly active in the solventless hydrogenation of model olefins and aromatic substrates under mild conditions with turnover frequencies up to 143,000 h(-1). The catalyst was characterized by various transmission electron microscopy techniques showing well-dispersed rhodium nanoparticles (similar to 3 nm) mainly located at the periphery of the silica coating. The heterogeneous magnetite-supported nanocatalyst was investigated in the hydrogenation of cyclohexene and compared to the previous surfactant-stabilized aqueous Rh-0 colloidal suspension and various silica-supported Rh-0 nanoparticles. Finally, the composite catalyst could be reused in several runs after magnetic separation. (C) 2011 Elsevier B. V. All rights reserved.

Role of CCR2 in orthodontic tooth movement

Introduction: Cytokines and chemokines regulate bone remodeling during orthodontic tooth movement. CC chemokine ligand 2 (CCL2) is involved in osteoclast recruitment and activity, and its expression is increased in periodontal tissues under mechanical loading. In this study, we investigated whether the CC chemokine receptor 2 (CCR2)-CCL2 axis influences orthodontic tooth movement. Methods: A coil spring was placed in CCR2-deficient (CCR2(-/-)), wild-type, vehicle-treated, and P8A-treated (CCL2 analog) mice. In a histopathologic analysis, the amounts of orthodontic tooth movement and numbers of osteoclasts were determined. The expression of mediators involved in bone remodeling was evaluated by real-time polymerase chain reaction. Results: Orthodontic tooth movement and the number of TRAP-positive cells were significantly decreased in CCR2(-/-) and P8A-treated mice in relation to wild-type and vehicle-treated mice, respectively. The expressions of RANKL, RANK, and osteoblasts markers (COL-1 and OCN) were lower in CCR2(-/-) than in wild-type mice. No significant difference was found in osteoprotegerin levels between the groups. Conclusions: These data suggested a reduction of osteoclast and osteoblast activities in the absence of CCR2. The CCR2-CCL2 axis is positively associated with osteoclast recruitment, bone resorption, and orthodontic tooth movement. Therefore, blockage of the CCR2-CCL2 axis might be used in the future for modulating the extent of orthodontic tooth movement. (Am J Orthod Dentofacial Orthop 2012;141:153-60)

Internal fit of two all-ceramic systems and metal-ceramic crowns

Objectives: The aim of this study was to investigate the internal fit (IF) of glass-infiltrated alumina (ICA - In-Ceram Alumina), yttria-stabilized tetragonal zirconia polycrystals (Y-TZP - IPS e.max ZirCAD), and metal-ceramic (MC - Ni-Cr alloy) crowns. Material and Methods: Sixty standardized resin-tooth replicas of a maxillary first molar were produced for crown placement and divided into 3 groups (n=20 each) according to the core material used (metal, ICA or Y-TZP). The IF of the crowns was measured using the replica technique, which employs a light body polyvinyl siloxane impression material to simulate the cement layer thickness. The data were analyzed according to the surfaces obtained for the occlusal space (OS), axial space (AS) and total mean (TM) using two-way ANOVA with Tukey's multiple comparison test (p<0.05). Results: No differences among the different areas were detected in the MC group. For the Y-TZP and ICA groups, AS was statistically lower than both OS and TM. No differences in AS were observed among the groups. However, OS and TM showed significantly higher values for ICA and Y-TZP groups than MC group. Comparisons of ICA and Y-TZP revealed that OS was significantly lower for Y-TZP group, whereas no differences were observed for TM. Conclusions: The total mean achieved by all groups was within the range of clinical acceptability. However, the metal-ceramic group demonstrated significantly lower values than the all-ceramic groups, especially in OS.

Iron(III) Porphyrin Covalently Supported onto Magnetic Amino-Functionalized Nanospheres as Catalyst for Hydrocarbon and Herbicide Oxidations

This work describes the covalent immobilization of an ironporphyrin, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin iron(III) chloride (FeTFPP), onto maghemite/silica magnetic nanospheres covered with aminofunctionalized silica. The resulting material (gamma-Fe2O3/SiO2-NHFeP) was characterized by diffuse reflectance infrared spectroscopy (DRIFTS) and UV-Vis absorption spectroscopy. The catalytic activity of this magnetic ironporphyrin was investigated in the oxidation of hydrocarbons (styrene, (Z)-cyclooctene and R-(+)-limonene) and an herbicide (simazine) by hydrogen peroxide or 3-chloroperoxybenzoic acid. Hydrocarbon and simazine oxidation reaction products were analyzed by gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively. This catalytic system proved to be efficient and selective for hydrocarbon oxidation, leading to high product yields from styrene (89%), cyclooctene (71%) and R-(+) -limonene (86%). Simazine oxidation was attained with 100% selectivity for a dechlorinated product (OEAT), while several oxidation products were obtained for the same catalyst in homogeneous media. The catalyst can be easily recovered through application of an external magnetic field and washed after reaction. Catalyst reuse experiments for R-(+)-limonene oxidation have shown that the catalytic activity is kept at 90% after 10 consecutive reactions.

Linear parameter varying control design for rotating systems supported by journal bearings

Linear parameter varying (LPV) control is a model-based control technique that takes into account time-varying parameters of the plant. In the case of rotating systems supported by lubricated bearings, the dynamic characteristics of the bearings change in time as a function of the rotating speed. Hence, LPV control can tackle the problem of run-up and run-down operational conditions when dynamic characteristics of the rotating system change significantly in time due to the bearings and high vibration levels occur. In this work, the LPV control design for a flexible shaft supported by plain journal bearings is presented. The model used in the LPV control design is updated from unbalance response experimental results and dynamic coefficients for the entire range of rotating speeds are obtained by numerical optimization. Experimental implementation of the designed LPV control resulted in strong reduction of vibration amplitudes when crossing the critical speed, without affecting system behavior in sub- or supercritical speeds. (C) 2012 Elsevier Ltd. All rights reserved.

Preload Evaluation of Different Screws in External Hexagon Joint

Purpose: This study compared the maintenance of tightening torque in different retention screw types of implant-supported crowns. Materials and Methods: Twelve metallic crowns in UCLA abutments cast with cobalt-chromium alloy were attached to external hexagon osseointegrated implants with different retention screws: group A: titanium alloy retention screw; group B: gold alloy retention screw with gold coating; group C: titanium alloy retention screw with diamond-like carbon film coating; and group D: titanium alloy retention screw with aluminum titanium nitride coating. Three detorque measurements were obtained after torque insertion in each replica. Data were evaluated by analysis of variance (ANOVA), Tukey's test (P < 0.05), and t test (P < 0.05). Results: Detorque value reduced in all groups (P < 0.05). Group A retained the highest percentage of torque in comparison with the other groups (P < 0.05). Groups B and D retained the lowest percentage of torque without statistically significant difference between them (P < 0.05). Conclusions: All screw types exhibited reduction in the detorque value. The titanium screw maintained the highest percentage of torque whereas the gold-coated screw and the titanium screw with aluminum titanium nitride coating retained the lowest percentage. (Implant Dent 2012;21:46-50)

Buccal Bone Plate Remodeling After Immediate Implant Placement With and Without Synthetic Bone Grafting and Flapless Surgery: Radiographic Study in Dogs

Recent studies in animals have shown pronounced resorption of the buccal bone plate after immediate implantation. The use of flapless surgical procedures prior to the installation of immediate implants, as well as the use of synthetic bone graft in the gaps represent viable alternatives to minimize buccal bone resorption and to favor osseointegration. The aim of this study was to evaluate the healing of the buccal bone plate following immediate implantation using the flapless approach, and to compare this process with sites in which a synthetic bone graft was or was not inserted into the gap between the implant and the buccal bone plate. Lower bicuspids from 8 dogs were bilaterally extracted without the use of flaps, and 4 implants were installed in the alveoli in each side of the mandible and were positioned 2.0 mm from the buccal bone plate (gap). Four groups were devised: 2.0-mm subcrestal implants (3.3 x 8 mm) using bone grafts (SCTG), 2.0-mm subcrestal implants without bone grafts (SCCG), equicrestal implants (3.3 x 10 mm) with bone grafts (EGG), and equicrestal implants without bone grafts (ECCG). One week following the surgical procedures, metallic prostheses were installed, and within 12 weeks the dogs were sacrificed. The blocks containing the individual implants were turned sideways, and radiographic imaging was obtained to analyze the remodeling of the buccal bone plate. In the analysis of the resulting distance between the implant shoulder and the bone crest, statistically significant differences were found in the SCTG when compared to the ECTG (P = .02) and ECCG (P = .03). For mean value comparison of the resulting linear distance between the implant surface and the buccal plate, no statistically significant difference was found among all groups (P > .05). The same result was observed in the parameter for presence or absence of tissue formation between the implant surface and buccal plate. Equicrestally placed implants, in this methodology, presented little or no loss of the buccal bone. The subcrestally positioned implants presented loss of buccal bone, even though synthetic bone graft was used. The buccal bone, however, was always coronal to the implant shoulder.

Effectiveness of Tooth Wipes in Removing Babies' Dental Biofilm

Purpose: To assess the effectiveness of tooth wipes in removing dental biofilm from babies' anterior teeth, as well as to evaluate the babies' behaviour and the guardians' preference concerning hygiene methods. Materials and Methods: In this random blind cross-over study, 50 high caries risk babies, from 8 to 15 months old, were divided into two groups: babies with oral hygiene performed by caregivers (n = 25) or by their mothers (n = 25). The caregivers and mothers removed biofilm using three methods of oral hygiene (tooth wipes, toothbrushes and gauze), one in each experimental phase. Professional cleaning was done before each phase, which had 2 days of biofilm accumulation and 1 experimental day, when caregivers and mothers used one method to remove biofilnn. Examiners blinded to the study design assessed the biofilm index at baseline, prior to and following biofilm removal using each method. The babies' behaviour and the mothers'/caregivers' preference were assessed. Results: The tooth wipes, toothbrushes and gauze significantly reduced the amount of biofilm (P < 0.001). The mothers' group removed more biofilm than the caregivers' group, using toothbrushes or tooth wipes (P < 0.05). Babies in the mothers' group had better behaviour using tooth wipes than toothbrushes (P < 0.05). Mothers and caregivers preferred to use tooth wipes. Conclusions: Tooth wipes are effective in removing biofilrn from babies' anterior teeth and are the method best accepted by mothers, caregivers and babies.

Prosthetic misfit of implant-supported prosthesis obtained by an alternative section method

PURPOSE. Adequate passive-fitting of one-piece cast 3-element implant-supported frameworks is hard to achieve. This short communication aims to present an alternative method for section of one-piece cast frameworks and for casting implant-supported frameworks. MATERIALS AND METHODS. Three-unit implant-supported nickel-chromium (Ni-Cr) frameworks were tested for vertical misfit (n = 6). The frameworks were cast as one-piece (Group A) and later transversally sectioned through a diagonal axis (Group B) and compared to frameworks that were cast diagonally separated (Group C). All separated frameworks were laser welded. Only one side of the frameworks was screwed. RESULTS. The results on the tightened side were significantly lower in Group C (6.43 +/- 3.24 mu m) when compared to Groups A (16.50 +/- 7.55 mu m) and B (16.27 +/- 1.71 mu m) (P<.05). On the opposite side, the diagonal section of the one-piece castings for laser welding showed significant improvement in the levels of misfit of the frameworks (Group A, 58.66 +/- 14.30 mu m; Group B, 39.4.8 +/- 12.03 mu m; Group C, 23.13 +/- 8.24 mu m) (P<.05). CONCLUSION. Casting diagonally sectioned frameworks lowers the misfit levels. Lower misfit levels for the frameworks can be achieved by diagonally sectioning one-piece frameworks. [J Adv Prosthodont 2012;4:89-92]

Effect of the relationship between particle size, inter-particle distance, and metal loading of carbon supported fuel cell catalysts on their catalytic activity

The effect of the relationship between particle size (d), inter-particle distance (x(i)), and metal loading (y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5-3 nm) and x(i)/d (>5) values, was evaluated. It was found that for y < 30 wt%, the optimum values of both d and x(i)/d can be always obtained. For y >= 30 wt%, instead, the positive effect of a thinner catalyst layer of the fuel cell electrode than that using catalysts with y < 30 wt% is concomitant to a decrease of the effective catalyst surface area due to an increase of d and/or a decrease of x(i)/d compared to their optimum values, with in turns gives rise to a decrease in the catalytic activity. The effect of the x(i)/d ratio has been successfully verified by experimental results on ethanol oxidation on PtRu/C catalysts with same particle size and same degree of alloying but different metal loading. Tests in direct ethanol fuel cells showed that, compared to 20 wt% PtRu/C, the negative effect of the lower x(i)/d on the catalytic activity of 30 and 40 wt% PtRu/C catalysts was superior to the positive effect of the thinner catalyst layer.