Accuracy of Conventional and 3D-Printed Casts for Partial Fixed Prostheses.

PURPOSE: To evaluate and compare the accuracy of conventional and 3D-printed casts using five different 3D printers. MATERIALS AND METHODS: In the control group (CG group, n = 5), five conventional impressions using light- and heavy-body polyvinyl siloxane were obtained from the master model, resulting in five stone models. In the test groups, five different scans were performed by a well-trained and experienced clinician using a TRIOS intraoral scanner. All data were exported in STL file format, processed, and sent to five 3D printers. Five casts were manufactured in each printer group: SG (CARES P20, Straumann); FG (Form 2, Formlabs); WG (Duplicator 7, Wanhao); ZG (Zenith D, Zenith); and MG (Moonray S100, Moonray). Measurements of the accuracy (trueness and precision) of the casts obtained from conventional elastomeric impressions and 3D-printing methods were accomplished using a 3D analysis software (Geomagic Control). RESULTS: The FG group showed the lowest values for trueness (indicating a value closer to real dimensions), which were similar to the SG group only (P > .05). MG, WG, and ZG groups presented higher values and were similar compared to each other. Data on precision demonstrated that all 3D-printed groups showed lower values for precision (smaller deviation) when compared to the CG. CONCLUSIONS: The trueness depends on the chosen 3D printer. All of the tested 3D printers were more precise than cast models obtained from conventional elastomeric impressions.

Microleakage at Different Implant-Abutment Connections Under Unloaded and Loaded Conditions.

PURPOSE: This study evaluated the microleakage at different implant-abutment (I-A) connections under unloaded and loaded conditions. MATERIALS AND METHODS: Forty implants, specially designed with an opening at the apex, were grouped according to the I-A and screw device: external hexagon implants with titanium (EH) or EH diamond-like carbon screws fixing the abutment; internal hexagon implants with titanium screws (IH); and Morse taper implants with solid (MT) or MT passing screws (MTps) abutments. The implants were fixed in a 2-compartment device, and toluidine blue solution (1.0 mg/mL) was placed at the I-A interface (upper compartment). The lower compartment was filled with purified water. Four implants of each group were loaded (50 N, 1.2 Hz) and after 50,000, 100,000, 200,000, and 300,000 cycles, aliquots were collected from the lower compartment for absorbance reading. Data were analyzed using analysis of variance for repeated measurements and Tukey (α = 0.05). RESULTS: Although microleakage increased over time in most of the groups, MTps group showed lower values when loaded (P < 0.05). The DLC on the EH screw did not prevent microleakage (P < 0.05). CONCLUSION: It can be concluded that MT connection is more effective to prevent microleakage.

Bacterial Adhesion and Surface Roughness for Different Clinical Techniques for Acrylic Polymethyl Methacrylate.

This study sought to assess the effect of different surface finishing and polishing protocols on the surface roughness and bacterial adhesion (S. sanguinis) to polymethyl methacrylates (PMMA). Fifty specimens were divided into 5 groups (n = 10) according to their fabrication method and surface finishing protocol: LP (3 : 1 ratio and laboratory polishing), NF (Nealon technique and finishing), NP (Nealon technique and manual polishing), MF (3 : 1 ratio and manual finishing), and MP (3 : 1 ratio and manual polishing). For each group, five specimens were submitted to bacterial adhesion tests and analyzed by scanning electron microscopy (SEM). Two additional specimens were subjected to surface topography analysis by SEM and the remaining three specimens were subjected to surface roughness measurements. Data were compared by one-way ANOVA. The mean bacterial counts were as follows: NF, 19.6 ± 3.05; MP, 5.36 ± 2.08; NP, 4.96 ± 1.93; MF, 7.36 ± 2.45; and LP, 1.56 ± 0.62 (CFU). The mean surface roughness values were as follows: NF, 3.23 ± 0.15; MP, 0.52 ± 0.05; NP, 0.60 ± 0.08; MF, 2.69 ± 0.12; and LP, 0.07 ± 0.02 (µm). A reduction in the surface roughness was observed to be directly related to a decrease in bacterial adhesion. It was verified that the laboratory processing of PMMA might decrease the surface roughness and consequently the adhesion of S. sanguinis to this material.

Fracture Resistance of Internal Conical and External Hexagon: Regular and Narrow Implant-Abutment Assemblies.

PURPOSE: The aim of this study was to compare the maximum load on the elastic limit of internal conical (IC) implants with regular external hexagon (REH) and narrow external hexagon (NEH) implants. MATERIALS AND METHODS: Thirty cylindrical implants were divided in 3 groups (n = 10): REH (3.75 mm); NEH (3.3 mm); IC (3.5 mm). The implants were evaluated by means of cantilever bending loads using a mechanical testing machine. A strain qualitative analysis and the corresponding angles were analyzed. Using single factor analysis of variance with Tukey Test and Friedman Test (P < 0.05) the statistical analysis for data were performed. RESULTS: REH (294.37 N) and IC (294.37 N) groups presented statistically greater Fle than NEH (189.16 N). Regarding to the strain, there were no significant differences among groups. However, there were a greater number of fissures and more fractures present on NEH group. CONCLUSION: The IC implant with smaller diameter did not result in reduction of elastic limit when compared with the REH implants. Nevertheless, the reduction of 0.45 mm of the hexagonal connection implant's diameter has significantly diminished the elastic limit.

A conservative approach to retrieve a fractured abutment screw - Case report.

INTRODUCTION: Regarding implant-supported prostheses, the most reported types of complications are related to loosening or fracturing of abutment or prosthesis screws. This case report shows a series of procedures that allowed a conservative solution for a fractured screw. It avoided removing the implant and also allowed the same prosthesis to be used after guided-drilling the fractured screw and re-tapping the implant internal threads. The same prosthesis was replaced immediately after the procedure. PATIENT: A 67-year-old male patient, who had a fractured abutment screw of the lower left first molar implant. The patient decided for the conservative treatment option and an attempt was made to remove the fractured screw. DISCUSSION: Parafunctional habits can generate excessive occlusal forces, which are risk factors associated with loosening and fracturing implant screws and even the fixtures themselves. This case report focus on the probable causes, difficulties and risks associated with this procedure and it also discusses the alternative approaches. CONCLUSION: The purposed treatment allowed a time and money saving resolution for fractured abutment screws.

Stress Over Implants of One-Piece Cast Frameworks Made With Different Materials.

This study aims to compare stress transmitted to implants and passive fit of one-piece cast frameworks fabricated with 3 different materials: commercially pure titanium (G1-CP Ti), cobalt-chromium alloy (G2-Co-Cr), and nickel-chromium-titanium alloy (G3-Ni-Cr-Ti). In total, 12 frameworks simulating bars for fixed prosthesis in a model with 5 implants were fabricated. The passive fit of the framework interface was measured using an optical microscope and the stresses transmitted to implants were measured using quantitative photoelastic analysis. Data were statistically analyzed by analysis of variance (ANOVA) and least significant difference (LSD) tests (α = 0.05). Mean and standard deviation values of passive fit and stress over implants are presented, respectively: G1 [472.49 (109.88) µm and 11.38 (9.23) KPa], G2 [584.84 (120.20) µm and 15.83 (9.30) KPa], and G3 [462.70 (179.18) µm and 16.39 (9.51) KPa]. For stress over implants, there were significant differences between G1, G2, and G3 (P = 0.035), being the lowest values for the G1. There were no significant differences for passive fit between G1 and G3 (P = 0.844), but both were statistically different from G2 (P = 0.028 and P = 0.035, respectively), which showed the worse results. It may be concluded that the stress over implants was affected by the tested materials. The CP Ti presented the best values for the evaluated items.

Influence of the Prosthetic Index Into Morse Taper Implants on Bacterial Microleakage.

PURPOSE: To evaluate the influence of Morse taper implant index on microleakage. MATERIALS AND METHODS: Thirty implants and abutments were divided into 3 groups (n = 10): CM1 (universal post and implant without index), CM2 (universal post and implant with index), and CM3 (abutment and implant with index). To evaluate the microleakage from the implant inner part, the implants were inoculated with Streptococcus sanguinis solution at a 0.5 McFarland and incubated for 7 days at 37°C in Eppendorf tubes with sterile broth. To evaluate the microleakage into the inner part of implant, these were inoculated with sterile Schaedler broth and immersed in a Fusobacterium nucleatum solution at a 0.5 McFarland. The samples were incubated for 30 days in an anaerobic chamber. RESULTS: Nine samples of each group of the first methodology showed no presented bacterial contamination. No samples of the second methodology demonstrated turbidity of the broth. CONCLUSION: The presence of the prosthetic internal index had no influence on bacterial microleakage of Morse taper implants under static conditions, for both methodologies.

Microcomputed tomography marginal fit evaluation of computer-aided design/computer-aided manufacturing crowns with different methods of virtual model acquisition.

This in vitro study used microcomputed tomography to evaluate the marginal fit of crowns fabricated using a chairside computer-aided design/computer-aided manufacturing (CAD/CAM) system with different methods of virtual model acquisition. Crowns were fabricated to fit in a cast containing a single human premolar. Four methods of virtual model acquisition were used: Group 1 (control), digital impressioning of a typodont; Group 2, digital impressioning of a powdered typodont; Group 3, digital impressioning of a regular impression; and Group 4, digital impressioning of a master cast. Statistically significant differences were found between the marginal gap of Group 2 and the other groups (P < 0.05); no differences were found among Groups 1, 3, and 4. The results showed that crowns fabricated using the chairside CAD/CAM system exhibited significantly smaller vertical misfit when a thin layer of powder was applied over the typodont before digital impressioning.

Correlation between vertical misfits and stresses over implants from castable frameworks made of different alloys.

This study aims to investigate a possible correlation between vertical misfits and the stresses transmitted to implants from one-piece casted frameworks fabricated with 3 different materials: commercially pure titanium, cobalt chromium alloy, and nickel chromium titanium alloy. Twelve frameworks simulating screw-retained prosthesis were fabricated from a master cast with 5 implants. Each framework was screwed (20 Ncm) over a metal cast and the vertical mesial and distal misfits were measured using an optical microscope. The stresses transmitted to the implants were measured in a third model by a quantitative photoelastic analysis. Stress and vertical misfit data were statistically analyzed by ANOVA and least significant difference tests and the correlation tests were performed using Pearson Correlation Test (α = 0.05). Mean and standard deviation values of vertical misfit and stress over implants are presented, respectively: commercially pure titanium (29.09 ± 13.24 µm and 11.38 ± 9.23 kPa), cobalt chromium alloy (27.05 ± 10.30 µm and 15.83 ± 9.30 kPa), nickel chromium titanium alloy (24.95 ± 11.14 µm and 16.39 ± 9.51 kPa). There were no significant differences for vertical misfit (P = 0.285). Regarding the stress analysis, there were significant differences between commercially pure titanium, cobalt chromium alloy, and nickel chromium titanium alloy (P = 0.035), with the lowest values for the commercially pure titanium. It may be concluded that stress over implants was affected by different procedures and materials for framework production.

Photoelastic stress analysis of mandibular fixed prostheses supported by 3 dental implants.

PURPOSE: To observe the photoelastic stress patterns generated around implants in relation to variations in the diameter and total number of implants supporting fixed complete-arch mandibular frameworks. MATERIALS AND METHODS: Three different implant configurations were analyzed (n = 3): 5 standard implants with diameters of 3.75 mm (C), 3 standard implants with diameters of 3.75 mm (3S), and 3 wide implants with diameters of 5.0 mm (3W). The samples were subjected to a vertical compressive load (1.33 kgf) applied at the end of the distal cantilever of the framework. The shear stresses were calculated around the implants, and the data were analyzed using one-way analysis of variance. RESULTS: The implants nearest to the loading showed higher stress values regardless of the group. The C group showed lower shear stress when compared with the other groups (P = 0.001). No significant difference was observed between the 3W and 3S groups (P = 0.785). CONCLUSION: A reduction in the number of implants, regardless of the implant diameter, showed higher stress concentration around the implants. Five-implant configuration showed lower stress concentration and seems to be more biomechanically predictable.

Micrometric precision of prosthetic dental crowns obtained by optical scanning and computer-aided designing/computer-aided manufacturing system.

The current study evaluated prosthetic dental crowns obtained by optical scanning and a computer-aided designing/computer-aided manufacturing system using micro-computed tomography to compare the marginal fit. The virtual models were obtained with four different scanning surfaces: typodont (T), regular impressions (RI), master casts (MC), and powdered master casts (PMC). Five virtual models were obtained for each group. For each model, a crown was designed on the software and milled from feldspathic ceramic blocks. Micro-CT images were obtained for marginal gap measurements and the data were statistically analyzed by one-way analysis of variance followed by Tukey's test. The mean vertical misfit was T = 62.6 ± 65.2 µm ; MC = 60.4 ± 38.4 µm; PMC = 58.1 ± 38.0 µm, and RI = 89.8 ± 62.8 µm. Considering a percentage of vertical marginal gap of up to 75 µm, the results were T = 71.5%, RI = 49.2%, MC = 69.6%, and PMC = 71.2%. The percentages of horizontal overextension were T = 8.5%, RI = 0%, MC = 0.8%, and PMC = 3.8%. Based on the results, virtual model acquisition by scanning the typodont (simulated mouth) or MC, with or without powder, showed acceptable values for the marginal gap. The higher result of marginal gap of the RI group suggests that it is preferable to scan this directly from the mouth or from MC.

Photoelastic stress analysis of different wide implant/abutment interfaces under oblique loading.

PURPOSE: There is a variety of implant/abutment (I/A) junctions for the connection of implant-supported prostheses. The aim of this work was to compare the shear stress distribution in three types of I/A interfaces after application of oblique loading on the abutments, simulating loading on an anterior tooth. MATERIALS AND METHODS: Similar wide unthreaded and cylindric implants (13.0 mm in length and 5.0 mm in diameter) and abutments were fabricated and embedded in photoelastic acrylic resin. The I/A assemblies featured three different I/A interfaces: external hex, internal hex, and internal taper. The samples were submitted to a compressive load of 0.6 kgf, which was applied to the abutment at an angle of 135 degrees. The maximum shear stresses were determined and observed at 21 points around the implants in the photoelastic models (n = 4). Graphics describing the maximum shear stress (y-axis) and the analyzed points (x-axis) were created, and the curve areas were calculated. The Kruskal-Wallis test was applied to analyze the results (P < .05). RESULTS: There were no statistically significant differences between the groups (P = .058). CONCLUSION: All of the wide-diameter I/A junctions presented similar behavior under oblique loading and appeared to be suitable to support prostheses that could receive this type of loading.

Retrieval technique for the Branemark Novum protocol: replacement of a lost implant.

In the past, the Branemark Novum protocol for the immediate functional loading of a mandibular fixed implant supported prosthesis provided an effective alternative for select patients. However, the manufacturer has discontinued this design, and only a few selected prosthetic-related replacement components are currently available. This clinical report presents the loss of an implant associated with a discontinued system. To take advantage of all of the preexisting components, it proposes a rescue procedure that allows continuous use of the original fixed restoration during the restoration of the tripod support at the implant level.

Clinical outcomes of single dental implants with external connections: results after 2 to 13 years.

PURPOSE: The aim of this retrospective study was to evaluate the long-term survival rates and the frequency of complications associated with single implants and their associated restorations. MATERIALS AND METHODS: A retrospective cohort study was performed in patients who received dental implants between 1997 and 2007. The cohort included patients who had a single implant restored with a cemented or screwed restoration that had been in function for more than 2 years. The cumulative implant survival rates and peri-implant conditions (marginal bone loss, pocket depth, and plaque, gingival, and bleeding indices), as well as prosthodontic maintenance requirements, were evaluated. Descriptive statistics, the chi-square test, and regression models were used. RESULTS: Seventy-three implants were placed in 44 patients (32 women, 12 men; mean age, 48 years). All implants were available for follow-up after 2 to 13 years (mean follow-up, 60 months). The overall cumulative 5-year survival rates for implants were 95.9%, and most of the prostheses (98.6%) remained functional throughout the observation period. The overall frequency of complications was 29.6% (4.3% inflammatory, 22.5% prosthetic, 2.8% operative). The average peri-implant marginal bone loss was 1.8 mm. Peri-implant soft tissue conditions such as plaque and bleeding indices and pocket depths were also satisfactory. However, the presence of inflammation was significantly associated with pocket depth and gingival keratinized mucosa. The need to retighten loose abutment screws (21%) was the most frequent prosthodontic maintenance performed. However, all loose abutment screws occurred in prostheses retained with titanium screws, and 92.9% of the prostheses had a UCLA-type abutment. CONCLUSION: The implants and the associated prosthetic constructions used in this study showed excellent survival rates. However, there was a high frequency of prosthetic complications associated with titanium screws and UCLA cast abutments. Other prosthetic components may have yielded different results.

Influence of methodologic aspects on the results of implant-abutment interface microleakage tests: a critical review of in vitro studies.

PURPOSE: This study sought to evaluate the influence of methodologic aspects on variations in the findings of in vitro microleakage studies of the implant-abutment interface. MATERIALS AND METHODS: The MEDLINE, EMBASE, and Cochrane Library databases were consulted for in vitro studies published between 1990 and August 2011. Date from the studies that met the inclusion and exclusion criteria were arranged in tables and subjected to descriptive analysis. RESULTS: Twenty-one studies were found to be eligible for the analysis after application of the inclusion/exclusion criteria. Sixteen studies used bacteria (76.2%), one used a bacterial toxin (4.76%), one used saliva (4.76%), two employed dyes (9.52%), and one used a combination of dyes and bacteria (4.76%). Eight studies evaluated microleakage from the inner portion of the implant to the external portion (38.1%) and nine examined the reverse (42.85%), while four studies investigated the relationship between them (19.05%). The volume inoculated inside the implants ranged from 0.1 to 5.0 mL. The bacterial concentrations used in the tests ranged from 2.41 x 106 to 8 x 108 colony-forming units/mL. Oral bacterial flora; mixtures of bacteria, toluidine blue, and gentian violet; and lipopolysaccharide of Salmonella enterica bacterial toxins were used. The monitoring period of test results ranged from 24 hours to 11 weeks for bacteria, 5 minutes to 7 days for dye, and 7 days for bacterial toxins. In four studies, microleakage was correlated with the size of the implant-abutment microgap. The external-hexagon implant configuration showed the greatest microleakage, followed by internal-trilobe, internal-hexagon, and internal-taper configurations. CONCLUSION: The lack of standardization hinderd comparisons of the studies and could explain the divergent results. It is suggested for future studies that special emphasis be placed upon inoculation and analysis of the specific volume for each system, lower concentrations of inoculated bacterial suspensions, and shorter follow-up time when using bacteria.

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.

Mandibular overdentures with immediate loading: satisfaction and quality of life.

PURPOSE: The aim of this study was to verify quality of life related to oral health and satisfaction with dentures. Conventional mandibular complete dentures were converted to overdentures retained by two implants with immediate loading (bar-clip system, n = 16). MATERIALS AND METHODS: The Brazilian short version of the Oral Health Impact Profile (OHIP-14Br) was used to evaluate the impact of oral health on quality of life. Satisfaction with the prostheses was obtained by means of a questionnaire addressing satisfaction with the present prostheses and through use of a visual analog scale (VAS). RESULTS: The results of the OHIP-14Br questionnaire were verified at 3 and 6 months after conversion from complete dentures to a mandibular overdenture. The satisfaction questionnaire for the mandibular prostheses obtained 43.75% satisfaction before conversion and 100% satisfaction at 1 week and 3 and 6 months after conversion. The satisfaction results of the prostheses, both maxillary and mandibular, were 68.75% before conversion, 93.75% at 1 week and 3 months after conversion, and 87.5% at 6 months. There was an immediate improvement in patients' satisfaction with the mandibular overdenture prostheses regarding stability and retention (Friedman test, P = .000) and quality of life (Friedman test, P = .001). CONCLUSION: The improvement seen justifies the immediate loading approach used in this study.

Overdenture with immediate load: mastication and nutrition.

Lower conventional complete dentures were converted to overdentures retained by two implants with an immediately loaded bar-clip system (n 16). The masticatory performance test was carried out using 'Optocal' after forty chewing strokes. Nutritional condition was evaluated by means of a Mini-Nutritional-Assessment questionnaire. No individual was classified as malnourished. The masticatory performance test demonstrated a statistically significant difference before conversion (baseline) and 3 and 6 months after conversion of the lower conventional complete denture to an implant-retained overdenture (paired-samples t test; P < 0·05). A statistically significant difference before and after 6 months of conversion for nutritional condition (Wilcoxon test; P < 0·05) was also observed. The association between masticatory performance and nutritional assessment demonstrated that a statistically significant difference between masticatory performance of the subgroups classified at baseline as nourished (22·43 %) and those at risk of malnutrition (3·9 %) was only evidenced before conversion (P = 0·006). After the conversion from a lower conventional complete denture to an implant-retained overdenture, at 3 months, the risk of malnutrition and nourished at baseline did not present significant differences in masticatory performance. Nonetheless, the mean masticatory performance potential was 19·86 and 31·98 % for subgroups classified at baseline as at risk of malnutrition and nourished, respectively (P = 0·187). The results before conversion were less favourable for masticatory performance and nutritional condition. The increased retention of the mandibular prosthesis allowed improvement in masticatory performance and nutritional condition.

Implant/abutment vertical misfit of one-piece cast frameworks made with different materials.

This study compared vertical and passive fit of one-piece cast frameworks made with 3 different materials: commercially pure titanium (CP Ti - G1), cobalt-chromium alloy (Co-Cr - G2) and nickel-chromium-titanium alloy (Ni-Cr-Ti - G3). Fifteen frameworks were obtained simulating bars for fixed prosthesis in a model with 5 implants. The passive and vertical fit of the framework interface was measured using an optical microscope at x30 magnification. Data were statistically analyzed by ANOVA and LSD tests (α=0.05). Mean and standard deviation values for passive fit and vertical fit were, respectively: G1 [472.49 (109.88) µm and 29.9 (13.24) µm], G2 [584.84 (120.20) µm and 27.05 (10.30) µm], and G3 [462.70 (179.18) µm and 24.95 (11.14) µm]. For vertical fit, there were no significant differences among G1, G2 and G3 (p=0.285). There were no significant differences for passive fit between G1 and G3 (p=0.844), but both differed significantly from G2 (p=0.028 and p=0.035, respectively), which showed the highest misfit values. It may be concluded that the vertical fit of frameworks was not affected by the tested materials, and that one-piece cast frameworks resulted in inadequate passive fit. The Co-Cr alloy presented the worst values for passive fit.