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Objectives: This study aimed to compare the accuracy of digital complete‐arch implant impressions with prefabricated aids using three intraoral scanners (IOSs) and explore the correlation between virtual deviation measurement and physical framework misfit. Materials and Methods: Four edentulous maxillary master models with four and six parallel and angular implants were fabricated and scanned by a laboratory scanner as reference scans. Ten scans of each master model were acquired using three IOSs (IOS‐T, IOS‐M, and IOS‐A) with and without prefabricated aids. Trueness and precision of root mean square (RMS) errors were measured. Ten aluminum alloy frameworks were fabricated, and the misfit was measured with a micro‐computed tomography scan with one screw tightened. Results: Trueness and precision showed significant improvement when prefabricated aids were used for all three IOSs (p < 0.010). Median (interquartile range) RMS errors of trueness reduced from 67.5 (30.4) to 61.8 (30.3) μm, from 100.6 (35.4) to 45.9 (15.1) μm, and from 52.7 (33.2) to 41.1 (22.5) μm for scanner IOS‐T, IOS‐M, and IOS‐A, respectively (p < 0.010). The precision of IOS‐A and IOS‐M was significantly better than IOS‐T when using prefabricated aid (p < 0.001). RMS errors and the maximum marginal misfit of the framework were significantly correlated (p < 0.001, R2 = 0.845). Conclusions: With the prefabricated aids, the accuracy of IOSs enhanced significantly in digital complete‐arch implant impressions. Three IOSs showed different levels of improvement in accuracy. Virtual RMS errors <62.2 μm could be the clinically acceptable threshold (150 μm) for framework passive fit. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the vertical misfit, stress distribution around dental implants, and cantilever fracture strength of 3‐unit implant‐supported cantilever fixed partial dentures (FPDs) using frameworks made from different materials and manufacturing techniques. Materials and Methods: Forty FPDs were fabricated and divided into 5 groups (n = 8) based on the framework material used: LAS Co‐Cr (Conventional casting—laser welding); TIG Co‐Cr (Conventional casting –TIG welding); OP Co‐Cr (Conventional casting—one‐piece); CAD Co‐Cr (CAD‐CAM); and CAD Zr (CAD‐CAM ZrO2). The vertical misfit was evaluated before porcelain application (T1) and before (T2), and after thermomechanical cycling (T3) by stereomicroscopy. Cantilever fracture strength was tested with a 50 kN (5000 kgf) load cell at a crosshead speed of 0.5 mm/min. Qualitative and quantitative photoelastic analysis was performed to evaluate stress distribution at seven specific points in five FPDs (n = 1/group) subjected to occlusal loading. Results: Only the molar showed interaction among the three factors (G × S × T; F(20.932) = 1.630; p = 0.044). Thermomechanical cycling (T2 vs. T3) had a significant effect on intra‐group vertical misfit in molar, especially in LAS Co‐Cr (Δ = 5.87; p = 0.018) and OP Co‐Cr (Δ = 5.39; p = 0.007), with no significant effect in premolar (p > 0.05). Ceramic application combined with thermomechanical cycling (T1 vs. T3) caused a significant intra‐group increase in vertical misfit in all groups, both in the molar and premolar (p < 0.05). OP Co‐Cr was associated with greater vertical misfit and stress concentration. Frameworks manufactured by the CAD‐CAM system exhibited lower vertical misfit and better stress distribution. FPDs with metal frameworks (>410.83 ± 72.26 N) showed significantly higher fracture strength (p < 0.05) than zirconia (277.47 ± 39.10 N), and the first signs of ceramic veneering fracture were observed around 900 N. Conclusions: FPDs with frameworks manufactured using a CAD‐CAM system appear to be associated with lower vertical misfit and better stress distribution, although the section of the frameworks followed by welding may be a viable alternative. In addition, metal frameworks exhibit high fracture strength. [ABSTRACT FROM AUTHOR]

Background: Despite computer‐aided design and computer‐aided manufacturing (CAD/CAM) technology improving prosthesis fit, errors inherent to digital workflow still exist. Purpose: To measure scanning/milling errors, and identify factors influencing marginal (MD) and internal discrepancy (ID). Materials and Methods: After scanning, 22 conical abutments in 5 master casts, 6 suprastructures with more than 2 implants (3, 4, and 6) were CAD designed. Angular deviation and errors in the vertical/horizontal planes were analyzed using a coordinate measuring machine (CMM). CAD suprastructures were milled and MD/ID evaluated with micro‐computed tomography (CT) and optic microscopy (OM) at one screw test (OST) and final fit test (FFT). Results: Mean scanning errors, at the vertical/horizontal planes, and angulation error were 3 μm ± 13, 44 μm ± 34, 0.3° ± 0.2°, respectively. Angulation errors nearly double in structures >3 abutments (0.26°vs 0.4°). OM MD in FFT/OST was 57.7 μm ± 13.9/100.7 μm ± 34.6, respectively. Micro‐CT FFT‐MD was 38.9 μm ± 12.8. Lineal/perimetral ID was 49.6 μm ± 11.9 and 108.2° ± 41.8, respectively. Structures >3‐implants were 2.3 times more likely to present higher MD (CI95%:0.4‐13.6). Nearly all the internal horizontal gap was due to scanning errors (44 of 49.6 μm). Horizontal scanning errors were three times more likely to present greater ID (CI95%:0.5‐17.4). Conclusion: Horizontal plane scanning errors are greater than vertical errors. Scanning angulation/milling errors are higher for suprastructures>3implants. Scanning/milling errors are associated with ID/MD, respectively, leading to micro‐gap formation. A CMM reduces scanning errors in >3‐implant‐frameworks before milling the final piece. [ABSTRACT FROM AUTHOR]

Purpose Precise implant-supported restorations require accurate impressions. Transfer, pick-up, and splinted pick-up are commonly used techniques. Several in vitro studies have compared these impression techniques; however, all studies used mechanical evaluation methods. The purpose of this study was to compare the discrepancies of these impression techniques digitally in vitro and in vivo. Materials and Methods Four dental implants were inserted in ten polymer mandibular models bilaterally in the regions of the first molars and canines. Three different impressions were made of each model and the models (original and stone casts) were scanned and digitized. Clinically, four implants were inserted in ten edentulous jaws; transfer and splinted pick-up impressions were made. With inspection software, discrepancies between the different impressions were calculated. Results The mean discrepancies in the in vitro study of the original polymer model to stone casts were 124 ± 34 μm for the transfer type, 116 ± 46 μm for the pick-up type, and 80 ± 25 μm for the splinted pick-up type, resulting in a mean discrepancy between the transfer and splinted pick-up type of 44 μm (124 - 80 μm). Clinically, the mean discrepancy between these two impression techniques was 280 μm. Conclusions The differing results between the transfer and splinted pick-up techniques of in vitro and in vivo data showed the need for clinical data; however, splinted pick-up impressions seemed to produce the most precise results. [ABSTRACT FROM AUTHOR]

Purpose The study aims to evaluate three-dimensionally (3 D) the accuracy of implant impressions using a new resin splinting material, 'Smart Dentin Replacement' ( SDR). Materials and Methods A titanium model of an edentulous mandible with six implant analogues was used as a master model and its dimensions measured with a coordinate measuring machine. Before the total 60 impressions were taken (open tray, screw-retained abutments, vinyl polysiloxane), they were divided in four groups: A (test): copings pick-up splinted with dental floss and fotopolymerizing SDR; B (test): see A, additionally sectioned and splinted again with SDR; C (control): copings pick-up splinted with dental floss and autopolymerizing Duralay® (Reliance Dental Mfg. Co., Alsip, IL, USA) acrylic resin; and D (control): see C, additionally sectioned and splinted again with Duralay. The impressions were measured directly with an optomechanical coordinate measuring machine and analyzed with a computer-aided design ( CAD) geometric modeling software. The Wilcoxon matched-pair signed-rank test was used to compare groups. Results While there was no difference ( p = .430) between the mean 3 D deviations of the test groups A (17.5 μm) and B (17.4 μm), they both showed statistically significant differences ( p < .003) compared with both control groups ( C 25.0 μm, D 19.1 μm). Conclusions Conventional impression techniques for edentulous jaws with multiple implants are highly accurate using the new fotopolymerizing splinting material SDR. Sectioning and rejoining of the SDR splinting had no impact on the impression accuracy. [ABSTRACT FROM AUTHOR]

Objective To compare the precision of fit of long-span vs. short-span implant-supported screw-retained fixed dental prostheses ( FDPs) made from computer-aided-design/computer-aided-manufactured ( CAD/ CAM) titanium and veneered with ceramic. The null hypothesis was that there is no difference in the vertical microgap between long-span and short-span FDPs. Materials and methods CAD/ CAM titanium frameworks for an implant-supported maxillary FDP on implants with a flat platform were fabricated on one single master cast. Group A consisted of six 10-unit FDPs connected to six implants ( FDI positions 15, 13, 11, 21, 23, 25) and group B of six 5-unit FDPs (three implants, FDI positions 21, 23, 25). The CAD/ CAM system from Biodenta Swiss AG (Berneck, Switzerland) was used for digitizing (laser scanner) the master cast and anatomical CAD of each framework separately. The frameworks were milled ( CAM) from a titanium grade V monobloc and veneered with porcelain. Median vertical distance between implant and FDP platforms from the non-tightened implants (one-screw test on implant 25) was calculated from mesial, buccal, and distal scanning electron microscope measurements. Results All measurements showed values <40 μm. Total median vertical microgaps were 23 μm (range 2-38 μm) for group A and 7 μm (4-24 μm) for group B. The difference between the groups was statistically significant at implant 21 ( P = 0.002; 97.5% CI −27.3 to −4.9) and insignificant at implant 23 ( P = 0.093; −3.9 to 1.0). Conclusions CAD/ CAM fabrication including laboratory scanning and porcelain firing was highly precise and reproducible for all long- and short-span FDPs. While all FDPs showed clinically acceptable values, the short-span FDPs were statistically more precise at the 5-unit span distance. [ABSTRACT FROM AUTHOR]

Objective: To compare the precision of fit of full-arch implant-supported screw-retained computeraided designed and computer-aided manufactured (CAD/CAM) titanium-fixed dental prostheses (FDP) before and after veneering. The null-hypothesis was that there is no difference in vertical microgap values between pure titanium frameworks and FDPs after porcelain firing. Materials and methods: Five CAD/CAM titanium grade IV frameworks for a screw-retained 10-unit implant-supported reconstruction on six implants (FDI tooth positions 15, 13, 11, 21, 23, 25) were fabricated after digitizing the implant platforms and the cuspid-supporting framework resin pattern with a laser scanner (CARES® Scan CS2; Institut Straumann AG, Basel, Switzerland). A bonder, an opaquer, three layers of porcelain, and one layer of glaze were applied (Vita Titankeramik) and fired according to the manufacturer's preheating and fire cycle instructions at 400-800°C. The one-screw test (implant 25 screw-retained) was applied before and after veneering of the FDPs to assess the vertical microgap between implant and framework platform with a scanning electron microscope. The mean microgap was calculated from interproximal and buccal values. Statistical comparison was performed with non-parametric tests. Results: All vertical microgaps were clinically acceptable with values <90 µm. No statistically significant pairwise difference (P = 0.98) was observed between the relative effects of vertical microgap of unveneered (median 19 µm; 95% CI 13-35 µm) and veneered FDPs (20 µm; 13-31 µm), providing support for the null-hypothesis. Analysis within the groups showed significantly different values between the five implants of the FDPs before (P = 0.044) and after veneering (P = 0.020), while a monotonous trend of increasing values from implant 23 (closest position to screw-retained implant 25) to 15 (most distant implant) could not be observed (P = 0.169, P = 0.270). Conclusions: Full-arch CAD/CAM titanium screw-retained frameworks have a high accuracy. Porcelain firing procedure had no impact on the precision of fit of the final FDPs. All implant microgap measurements of each FDP showed clinically acceptable vertical misfit values before and after veneering. Thus, the results do not only show accurate performance of the milling and firing but show also a reproducible scanning and designing process. [ABSTRACT FROM AUTHOR]

Objective To analyze the precision of fit of implant-supported screw-retained computer-aided-designed and computer-aided-manufactured ( CAD/ CAM) zirconium dioxide ( ZrO) frameworks. Materials and methods Computer-aided-designed and computer-aided-manufactured ZrO frameworks ( NobelProcera™) for a screw-retained 10-unit implant-supported reconstruction on six implants ( FDI positions 15, 13, 11, 21, 23, 25) were fabricated using a laser ( ZrO- L, N = 6) and a mechanical scanner ( ZrO- M, N = 5) for digitizing the implant platform and the cuspid-supporting framework resin pattern. Laser-scanned CAD/ CAM titanium ( TIT-L, N = 6) and cast Co Cr W-alloy frameworks (Cast, N = 5) fabricated on the same model and designed similar to the Zr O frameworks were the control. The one-screw test (implant 25 screw-retained) was applied to assess the vertical microgap between implant and framework platform with a scanning electron microscope. The mean microgap was calculated from approximal and buccal values. Statistical comparison was performed with non-parametric tests. Results No statistically significant pairwise difference was observed between the relative effects of vertical microgap between ZrO- L (median 14 μm; 95% CI 10-26 μm), Zr O- M (18 μm; 12-27 μm) and TIT- L (15 μm; 6-18 μm), whereas the values of Cast (236 μm; 181-301 μm) were significantly higher ( P < 0.001) than the three CAD/ CAM groups. A monotonous trend of increasing values from implant 23 to 15 was observed in all groups ( Zr O- L, Zr O- M and Cast P < 0.001, TIT-L P = 0.044). Conclusions Optical and tactile scanners with CAD/ CAM technology allow for the fabrication of highly accurate long-span screw-retained Zr O implant-reconstructions. Titanium frameworks showed the most consistent precision. Fit of the cast alloy frameworks was clinically inacceptable. [ABSTRACT FROM AUTHOR]

The ideal fixed, detachable framework sits passively on the implants and does not introduce any stress. Several techniques in the literature compensate for an ill-fitting framework. These techniques require extra visits, chairtime, and laboratory time and only mitigate the stress; the stress is not eliminated. A framework is presented here that eliminates the stress transmitted to the implants by encircling the abutment cylinders and not directly incorporating them into the framework. Furthermore, the framework mitigates the stress from the polymerization distortion of acrylic when processing the acrylic onto the prosthesis. [ABSTRACT FROM AUTHOR]

In this clinical report, following computer-guided (3D Procera Software Planning Program, Nobel Biocare, Yorba Linda, CA) placement and immediate provisionalization of 12 dental implants (NobelSpeedy™ Replace, Nobel Biocare), misfits of the prefabricated screw-retained interim prostheses were noted at several implant-abutment junctions. Nevertheless, adaptation of the misfits was observed 10 days later, after the loosened screws were tightened. While a high mean marginal bone loss of 2.1 mm (range: 1.4 to 3.5 mm) was noted, all implants remained osseointegrated at 3-year follow-up. [ABSTRACT FROM AUTHOR]

This study evaluated the precision of fit of implant frameworks cast in titanium (cp Ti) and palladium–silver alloy (Pd-Ag), made by the one-piece cast and laser welding techniques. From a metal matrix with five implants, 20 master casts were obtained, to which replicas of implants were incorporated. On these masters 10 frameworks were made for each type of material (cp Ti and Pd-Ag alloy). Half of these were made by the one-piece cast technique and the other half by the laser welding technique. The implant/prosthesis interface was analysed and measured in the vestibular and lingual regions of the central and distal implants with the help of a measuring microscope. The results indicated that in the central cylinders, the Tukey test ( P < 0·0005) showed a significant difference in the passive fit between the laser-welded frameworks (34·73 μm) and those one-piece cast frameworks (151·39 μm), and as regards materials, the palladium–silver alloy (66·30 μm) showed better results than the titanium (119·83 μm). In the distal cylinders there was no significant difference between the frameworks cast in titanium and palladium–silver by the one-piece technique. However, after laser welding, there was a significant difference for the frameworks cast in titanium (31·37 μm) and palladium–silver (106·59 μm). [ABSTRACT FROM AUTHOR]

Purpose: Implant-borne fixed partial dentures (FPDs) should fit passively in order to avoid complications ranging from screw loosening to loss of osseointegration. The aim of this study was to measure the strain development of three-unit and five-unit screw- and cement-retained implant-supported FPDs. Additionally, the influence of the parameters retention mechanism and FPD span were evaluated. Materials and Methods: Three Straumann implants were anchored in a measurement model based on a real-life patient situation and strain gauges (SGs) were fixed mesially and distally adjacent to the implants and on the pontics of the superstructures. During cement setting and screw fixation of 40 implant FPDs (10 samples from each group: three-unit cementable; five-unit cementable; three-unit screw-retained; five-unit screw-retained), strain development was recorded. For statistical analysis, multivariate two-sample tests were performed with the level of significance set at p= 0.1. Results: The mean strain values for the four FPD groups at the different SG sites ranged from 26.0 to 637.6 μm/m. When comparing the four groups, no significant differences in strain magnitude could be detected. Similarly, a comparison of the two FPD spans revealed no significant difference ( p= 0.18 for cementable FPDs; p= 0.22 for screw-retained FPDs). A comparison of the two fixation modes also revealed no significant difference ( p= 0.67 for three-unit FPDs; p= 0.25 for five-unit FPDs). Conclusion: FPD span and retention mechanism appear to have only a minor influence on strain development in implant FPDs. As implant-supported restorations have proven to be successful over time, the question arises as to whether an “absolute” passive fit is a prerequisite for successful implant restorations. [ABSTRACT FROM AUTHOR]

Objectives: To present the clinical and radiographic outcome of early loading of implants inserted into fresh extraction sockets and to present a treatment protocol for early loading of the implants by ‘passively fitting’ abutment-free permanent fixed complete dentures (implant FCDs). Material and methods: The study included 19 dentate patients treatment planned for extraction of all remaining maxillary teeth. In all, 116 Straumann-implants with sandblasted, large grit and acid etched (SLA) surface were placed: 77 (66%) inserted in fresh extraction sockets and 39 (34%) in healed bone. At least six implants were placed in each maxilla. One hundred and ten implants were loaded by permanent FCDs within 10 days after placements and six after 14 days. The patients were reexamined clinically and radiographically after 2–3 years of clinical function. All FCDs were removed for control of implant stability and evaluation of the peri-implant status. Results: Owing to framework fracture, two implants were lost, corresponding to a failure rate of 2%. The radiographic measurements after 2–3 years did not reveal any difference in bone height mesial and distal of the implants placed in extraction sockets vs. in healed bone. This was interpreted as a bone gain around the implants placed in extraction sockets and a slight bone loss around the implants placed in healed bone. Conclusion: Early functional loading of SLA-surfaced implants following immediate placement in maxillary extraction sockets by rigid and passively fitting permanent implant FCDs is a reliable treatment alternative. [ABSTRACT FROM AUTHOR]

Background: It has been considered that implant prostheses ought to display passive fit. The objective of this finite element analysis (FEA) was to simulate the bone loading resulting from the fixation of implant-supported three and five-unit fixed partial dentures (FPDs).Methods: Based on a patient case, six different FPD-groups were fabricated using either two or three implants for support. Strain gauges on the pontics of the prostheses were used for in vivo measurements. Based on the values obtained, bone loading models were simulated using three-dimensional finite element analysis and the results obtained were represented as von Mises equivalent stress.Results: The mean strain (epsilon) values ranged from 15 micro epsilon to 170 micro epsilon for the three-unit FPDs and from 32 micro epsilon to 302 micro epsilon for the five-unit FPDs. FEA revealed von Mises stresses up to 30 MPa in the cortical area, while in trabecular bone values up to 5 MPa were observed. Static implant loading of similar magnitude can be provoked through 200 N axial load.Conclusions: Although the in vivo measured strain levels (epsilon) were of higher magnitude for the five-unit prostheses, FEA revealed bone loading of comparable magnitude for both three- and five-unit FPDs. Multi-unit prostheses may demonstrate greater inaccuracies compared with single implant restorations, but due to the absence of moment loading the multi-implant configuration appears to compensate for the higher strain development. [ABSTRACT FROM AUTHOR]

Implant-borne fixed partial dentures (FPDs), whether cementable or screwable superstructures, ought to display a true passive fit. The objective of this in vivo-based finite-element analysis is, therefore, to quantify the degree of stress which occurs in the bone around the implants as a result of the fixation of cemented and screw-retained FPDs. On the basis of a simulated patient situation with two implants, six groups of implant-supported superstructures containing 10 samples each were fabricated. Strain gauges which were mounted on the pontics of the restorations were subsequently used to take in vivo measurements (Ethics Commission Approval No. 2315). Taking the values obtained as a basis, the von Mises equivalent stress was chosen to illustrate bone loading in three-dimensional finite-element models. Superstructure fixation caused residual interface stress as high as 30 MPa. Similar stress magnitudes can be observed for axial implant loading of 200 N. Assuming that the axial loading of a single implant with 200 N is within the bone's physiological range, it can be concluded that the degree of stress resulting from the fixation of superstructures alone does not constitute a risk. [ABSTRACT FROM AUTHOR]

When fixing implant-supported fixed partial dentures (FPDs), it is important to achieve passive fit. The objective of the in vivo study presented was to quantify the strain development during the fixation of screw- and cement-retained FPDs. After informed patient consent had been obtained (Ethics commission Approval No. 2315; FAU Erlangen-Nuremberg, Germany), four groups of five-unit FPDs (five samples per group) were fabricated and investigated in vivo. Group 1: Cementable, repositioning technique impression, burn out plastic coping; Group 2: Screwable, pickup technique impression, burn out plastic coping; Group 3: Screwable, pickup technique impression, cast to gold cylinder; Group 4: Screwable, pickup technique impression, bonded to gold cylinder. Two strain gauges (SG) were attached to the pontics of each bridge (SG-M and SG-D) to measure the strains that occurred during either the cementing or screw-in process. The final values were recorded for analysis. The mean strain values (μm/m) for each SG were: Group 1: SG-M 32 μm/m, SG-D: 89 μm/m; Group 2: SG-M 302 μm/m, SG-D: 197 μm/m; Group 3: SG-M 458 μm/m, SG-D: 268 μm/m; Group 4: SG-M 269 μm/m, SG-D: 52 μm/m. Although the bridges were clinically acceptable, none of them revealed a truly passive fit with zero microstrain. In contrast to conventional screw-retained bridges, cement retention seems to result in lower strain levels. Bonding bridge pontics to prefabricated implant components seems to allow both the retrievability of a screw-retained bridge and produce moderate strain values. [ABSTRACT FROM AUTHOR]

It is generally assumed that passively fitting superstructures are a prerequisite for long-lasting implant success. In the study presented, the strain development of three-unit implant fixed partial dentures (FPDs) was evaluated at the bone surrounding the implant and on the superstructure using a strain gauge technique. Six groups of three-unit FPDs representing the commonly used techniques of bridge fabrication were investigated with 10 samples each, in order to quantify the influence of impression technique, mode of fabrication and retention mechanism on superstructure fit. Two ITI implants (Straumann, Waldenburg, Switzerland) were anchored in a measurement model according to a real-life patient situation and strain gauges were fixed mesially and distally adjacent to the implants and on the bridge pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate two sample tests were performed setting the level of significance at P=0.1. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. The two impression techniques used did not reveal any significant differences in terms of precision. Both modes of fixation – i.e. cement and screw retention – provoked equally high stress levels. In the fabrication of screw-retained FPDs, similar results were obtained from the use of burn-out plastic copings and the technique of casting wax moulds to premachined components. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development. To cite this article: Heckmann SM, Karl M, Wichmann MG, Winter W, Graef F, Taylor TD. Cement fixation and screw retention: parameters of passive fit. An in vitro study of three-unit implant-supported fixed partial dentures. Clin. Oral Impl. Res. xx, 2003; 000–000 doi: 10.1111/j.1600-0501.2004.01027.x [ABSTRACT FROM AUTHOR]