Photogrammetric measurements of implant positions. Description of a technique to determine the fit between implants and superstructures

Accuracy of intraoral optical scan versus stereophotogrammetry for complete-arch digital implant impression: An in vitro study

PURPOSE

To assess and compare the accuracies of intraoral scanners (IOS) and stereophotogrammetry (SPG) devices for complete-arch digital implant impressions.

METHODS

A 4-analog model was digitized using a desk scanner to obtain a reference file. Thirty test scans were conducted using the investigated IOS device, while an additional 30 scans were performed using the SPG device. Using the best-fit algorithm, the resulting 60 test files were aligned with the reference file. Linear (ΔX, ΔY, and ΔZ-axis) and angular deviations (ΔANGLE) were evaluated. Three-dimensional (3D) deviation was calculated based on the Euclidean distance (ΔEUC). The analysis was stratified according to the scanning device and implant position. Fisher's F and t-tests were used to compare the variances and expected values of the two scanning systems.

RESULTS

IOS expressed a higher 3D (ΔEUC) mean deviation than SPG (52.8 µm vs. 33.4 µm, P < 0.0001), with extreme measurements up to 181.9 µm. A significantly higher standard deviation (SD) was associated with IOS (37.1 µm vs. 17.7 µm, P < 0.0001). Considering angular deviations, the IOS showed slightly higher angular mean deviations (ΔANGLE) than the SPG (0.28° vs. 0.24°, P = 0.0022), with extreme measurements of up to 0.73°. The SPG SD values were significantly lower than the IOS SD values (0.14° vs. 0.04°, P < 0.0001).

CONCLUSIONS

The SPG showed significantly higher 3D and angular accuracies for complete arch implant impressions, with consistent repeatability. IOS scanning revealed significantly higher extreme deviations exceeding the acceptable threshold value. Despite study limitations, SPG appears more feasible than IOS for complete-arch digital implant impressions.

Influence of implant scan body design (height, diameter, geometry, material, and retention system) on intraoral scanning accuracy: A systematic review

PURPOSE

To evaluate the influence of implant scan body (ISB) design (height, diameter, geometry, material, and retention system) on the accuracy of digital implant scans.

MATERIAL AND METHODS

A literature search was completed in five databases: PubMed/Medline, Scopus, Embase, World of Science, and Cochrane. A manual search was also conducted. Studies reporting the evaluation of ISB design on the accuracy of digital scans obtained by using IOSs were included. Two investigators evaluated the studies independently by applying the Joanna Briggs Institute critical appraisal. A third examiner was consulted to resolve any lack of consensus. Articles were classified based on the ISB features of height, geometry, material, and retention system.

RESULTS

Twenty articles were included. Among the reviewed studies, 11 investigations analyzed the influence of different ISB geometries, 1 study assessed the impact of ISB diameter, 4 studies investigated the effect of ISB splinting, 2 articles evaluated ISB height, and 2 studies focused on the effect of ISB material on scan accuracy. In addition, 8 studies involved ISBs fabricated with different materials (1- and 2-piece polyetheretherketone and 1-piece titanium ISBs), and all of the reviewed articles tested screw-retained ISBs, except for 3 in vitro studies.

CONCLUSIONS

The findings did not enable concrete conclusions regarding the optimal ISB design, whether there is a relationship between IOS technology and a specific ISB design, or the clinical condition that maximizes intraoral scanning accuracy. Research efforts are needed to identify the optimal ISB design and its possible relationship with the IOS selected for acquiring intraoral digital implant scans.

Accuracy of 2 direct digital scanning techniques-intraoral scanning and stereophotogrammetry-for complete arch implant-supported fixed prostheses: A prospective study

STATEMENT OF PROBLEM

Conventional impression techniques for complete arch implant-supported prostheses are technique-sensitive. Stereophotogrammetry (SPG) and intraoral scanning (IOS) may offer an alternative to conventional impression making.

PURPOSE

The purpose of this prospective study was to compare the accuracy of IOS and SPG for complete arch implant scans and to evaluate the passive fit of frameworks fabricated with SPG.

MATERIAL AND METHODS

Laboratory scanning of gypsum casts, SPG, and IOS were performed for all participants. The data regarding the abutment platform were superimposed to calculate the 3D deviation of SPG and IOS compared with that of laboratory scanning as an evaluation of accuracy. The effect of implant position and number on accuracy was analyzed. The more accurate technique between SPG and IOS was used to fabricate the titanium frameworks, as was laboratory scanning. The passive fit of the frameworks was assessed by clinical examination, the Sheffield test, and panoramic radiography.

RESULTS

Seventeen participants (21 arches, 120 implants) were included. The accuracy of SPG ranged from 2.70 μm to 92.80 μm, with a median (Q1, Q3) of 17.00 (11.68, 22.50) μm, which was significantly more accurate than that of IOS, ranging from 21.30 μm to 815.60 μm, with a median (Q1, Q3) of 48.95 (34.78, 75.88) μm. No significant correlation was found between position or number of implants and 3D deviation in the SPG group. A weak positive correlation was found between implant number and 3D deviation in the IOS group. SPG and laboratory scanning were used to fabricate titanium frameworks. The passive fit between the frameworks and abutment platforms was confirmed.

CONCLUSIONS

SPG, which was not affected by position or number of implants, was more accurate than IOS and comparable with laboratory scanning. The frameworks fabricated based on SPG and laboratory scanning were comparable in their passive fit. The SPG technique may be an alternative to laboratory scanning for complete arch implant scans.

Photogrammetry technology in implant dentistry: A systematic review

STATEMENT OF PROBLEM

Photogrammetry technology may be useful in implant dentistry, but a systematic review is lacking and is indicated before routine use in clinical practice.

PURPOSE

The purpose of this systematic review was to assess the role of the photogrammetry technology used in implant dentistry and determine its validity as an accurate tool with clinical applications.

MATERIAL AND METHODS

Four major databases, PubMed MEDLINE, Google Scholar, Scopus, and Web of Science, were selected to retrieve articles published from January 2011 to February 2021 based on custom criteria. The search was augmented by a manual search. After screening of the collected articles, data, including study design and setting, type of application, digitizer used, reference body, method of evaluation, and overall outcomes, were extracted.

RESULTS

Twenty articles were included based on the selection criteria. Most of the articles confirmed that the use of photogrammetry was promising as an implant coordinate transfer system. However, few articles showed its use for 3-dimensional scanning, which might require more development.

CONCLUSIONS

The initial reports of using photogrammetry technology considered this method as a valid and reliable clinical tool in implant dentistry. More studies to develop the photogrammetry technology and to assess the results with evidence-based research are recommended to enhance its application in different clinical situations.

Comparison of the Accuracy of Two Transfer Caps in Positional Transmission of Palatal Temporary Anchorage Devices: An In Vitro Study

The aim of this study was to compare the positional information transfer accuracy of palatal temporary anchorage devices (TADs) of two different brands of transfer caps: PSM and Leone. Thirty plaster casts of maxillary dental arches were chosen for master models. A couple of Leone TADs were inserted in each master model. For each master model, two analysis models were created: using two transfer caps, Leone and PSM, the impressions were taken, the analogues were connected on the transfer caps, and the casts were poured. Using digital methods and equipment, such as a 3D scanner, a 3D analysis and a comparison of the accuracy of the two transfer caps in transferring the positional information of the TADs was then made. The data obtained were analyzed using the Mann-Whitney U-test at a significance level of α = 0.05. PSM transfer caps showed higher error frequency in almost all measurements. Only two measurements had a larger error in the analysis models made with Leone transfer caps. The Mann-Whitney U-test found a significant difference between the error levels of TADs found in the analysis models created with PSM transfer caps. Leone transfer caps showed greater reliability in TADs positional information transmission.

Comparison between stereophotogrammetric, digital, and conventional impression techniques in implant-supported fixed complete arch prostheses: An in vitro study

STATEMENT OF PROBLEM

Conventional impressions and digital intraoral scanning for implant-supported fixed complete arch prostheses still have many problems that influence accuracy. Although stereophotogrammetry may offer a reliable alternative to other techniques, it has seldom been investigated.

PURPOSE

The purpose of this in vitro study was to measure and compare the intraoral scan body deviations of the reference cast with the intraoral scan body distortions obtained by conventional, digital, and stereophotogrammetric techniques.

MATERIALS AND METHODS

An edentulous maxillary "all-on-four" cast was prepared with 2 straight and two 17-degree angled screw-retained abutments screwed on the implant. Three capture techniques were compared: the conventional impression technique (CI group) using impression plaster (IP), the digital intraoral scanning (DIS group) technique, and the stereophotogrammetry (SPG group) technique. A calibrated extraoral scanner was used to digitize the definitive cast to compare its intraoral scan body positions with those of the other techniques in terms of global angular distortion and 3D deviations of the whole scan body and flat angled surface alone by using an inspection and metrology software program and the best fit alignment technique. The Kolmogorov-Smirnov and Shapiro-Wilk tests showed normal distribution of the quantitative variables. Thus, the repeated measures analyses of variance followed by univariate analysis and Bonferroni multiple comparison tests were performed to analyze the data (α=.05).

RESULTS

Significant global angular discrepancies and 3D deviations of the whole scan body and flat angled surface were found among the CI, DI, and SPG groups for both trueness (P<.001) and precision (P<.001).

CONCLUSIONS

The stereophotogrammetry capture technique reported the highest accuracy in terms of trueness and precision for the intraoral scan bodies of all the techniques evaluated. However, at the flat angled surface region of the scan body, higher trueness was detected with the digital technique. Conventional impressions showed better trueness results than the digital ones, but the opposite was true of precision.

Trueness and precision of complete-arch photogrammetry implant scanning assessed with a coordinate-measuring machine

STATEMENT OF PROBLEM

Photogrammetry technology has been used for the digitalization of multiple dental implants, but its trueness and precision remain uncertain.

PURPOSE

The purpose of this in vitro investigation was to compare the accuracy (trueness and precision) of multisite implant recordings between the conventional method and a photogrammetry dental system.

MATERIAL AND METHODS

A definitive cast of an edentulous maxilla with 6 implant abutment replicas was tested. Two different recording methods were compared, the conventional technique and a photogrammetry digital scan (n=10). For the conventional group, the impression copings were splinted to an additively manufactured cobalt-chromium metal with autopolymerizing acrylic resin, followed by recording the maxillary edentulous arch with an elastomeric impression using an additively manufactured open custom tray. For the photogrammetry group, a scan body was placed on each implant abutment replica, followed by the photogrammetry digital scan. A coordinate-measuring machine was selected to assess the linear, angular, and 3-dimensional discrepancies between the implant abutment replica positions of the reference cast and the specimens by using a computer-aided design program. The Shapiro-Wilk test showed that the data were not normally distributed. The Mann-Whitney U test was used to analyze the data (α=.05).

RESULTS

The conventional group obtained an overall accuracy (trueness ±precision) value of 18.40 ±6.81 μm, whereas the photogrammetry group showed an overall scanning accuracy value of 20.15 ±25.41 μm. Significant differences on the discrepancies on the x axis (U=1380.00, P=.027), z axis (U=601.00, P<.001), XZ angle (U=869.00, P<.001), and YZ angle (U=788.00, P<.001) were observed when the measurements of the 2 groups were compared. Furthermore, significant 3-dimensional discrepancy for implant 1 (U=0.00, P<.001), implant 2 (U=0.00, P<.001), implant 3 (U=6.00, P<.001), and implant 6 (U=9.00, P<.001) were computed between the groups.

CONCLUSIONS

The conventional method obtained statistically significant higher overall accuracy values compared with the photogrammetry system tested, with a trueness difference of 1.8 μm and a precision difference of 18.6 μm between the systems. The conventional method transferred the implant abutment positions with a uniform 3-dimensional discrepancy, but the photogrammetry system obtained an uneven overall discrepancy among the implant abutment positions.

In vivo trueness and precision of full-arch implant scans using intraoral scanners with three different acquisition protocols

OBJECTIVES

To evaluate an in situ reference acquisition method for implant positions in complete edentulous maxillae using an industrial scanner and allowing for in vivo trueness analysis of the restorative workflow. To assess in vivo trueness and precision of intraoral scanners (IOS) using different acquisition protocols. Furthermore, to compare IOS trueness with impression-based models and implant-supported fixed dentures (IFD) in a parallel study on the same cohort using the same in situ reference scan.

METHODS

Six scan-bodies mounted to maxillary implants in five subjects were reference scanned (REF) using an industrial scanner. Subjects were scanned with IOS three times using three different protocols: control (CT), dental floss assisted (DF), and acrylic splint (SP). CAD-files of scan-bodies with inter-aligned analogues were geometry-aligned to REF, and SP. Scan-bodies were aligned to CT and DF in proprietary dental laboratory software and exported with analogue positions. Resulting six CAD-analogues per scan were Globally Aligned using a consistent geometry-based alignment. Deviations were computed after a Reference Point System Alignment at the implant/prosthetic platform for Cartesian axes with a linear Resultant.

RESULTS

Resultant trueness was CT: 41±11 µm, DF: 49±22 µm, SP: 55±8 µm. Resultant precision was CT: 48±7 µm, DF: 50±7 µm, SP: 45±6 µm.

CONCLUSIONS

This method is applicable for assessing trueness of maxillary full-arch implant scans in vivo. The CT protocol was most accurate. CT trueness showed no difference to digitised impression-based models in parallel study. CT was more accurate than IFD in a parallel study. CT displayed similar numerical trueness as existing in vitro studies.

CLINICAL SIGNIFICANCE

Using IOS to acquire full-arch implant scans is controversial. The modified protocol in this pilot shows promising results in the maxilla where great care was taken to manage non-attached tissues when a modified scanning pattern was used. However, other IOS may show varying results in vivo. A completed scan does not necessarily equate to an accurate scan.

In vivo trueness of full-arch implant-supported CAD/CAM restorations and models based on conventional impressions

OBJECTIVES

To evaluate a method for in situ reference acquisition of implant positions in complete edentulous maxillae using an industrial scanner. To assess in vivo trueness of full-arch implant-supported fixed dentures (IFD) and dental models based on conventional impressions.

METHODS

In five subjects, scan-bodies were mounted to six maxillary implants and scanned three times using an industrial scanner (REF). Original impression-based models used to manufacture existing IFDs, (MOD1), and models fabricated from new polyether impressions, (MOD2), were scanned three times with a laboratory scanner. Scan-bodies were aligned and exported with analogue positions corresponding to implant positions. Implant analogues were mounted onto existing IFDs and scanned three times (BRIDGE). CAD files of scan-bodies with inter-aligned CAD-analogues were geometry-aligned to REF. CAD-analogues were aligned to exported files of MOD1 and MOD2, and to BRIDGE. Resulting six CAD-analogues were Globally Aligned using a consistent geometry-based alignment. Deviations were computed after a Reference Point System Alignment at the implant/prosthetic platform for Cartesian axes and a linear Resultant.

RESULTS

REF precision was 9.3 ± 1 µm. In vivo trueness for Resultant was MOD1: 36±16 µm, MOD2: 28±7 µm and BRIDGE: 70±23 µm, where MOD1 and MOD2 were statistically significantly different from BRIDGE. In vitro manufacturing trueness of Resultant when MOD1 acted reference for BRIDGE was: 69 ± 22.

CONCLUSIONS

This method can be applied for assessing in vivo trueness. CAD/CAM processed IFD showed deviations twice that of impression-based models, however, errors from impressions and subsequent model scans were not additive to the entire workflow.

Digital Dental Models: Is Photogrammetry an Alternative to Dental Extraoral and Intraoral Scanners?

Background: 3D models are nowadays part of daily clinical practice. Photogrammetry is a brand-new method for transforming small objects into 3D models while keeping their original shape and size. The aim of this study was to evaluate the accuracy, in terms of precision and trueness, of a digital dental model acquired with photogrammetry compared with those obtained using extraoral scanners and intraoral scanners, starting from the same plaster model. Methods: A plaster model was converted into a digital model using photogrammetry, an extraoral scanner and an intraoral scanner. Different references were measured twice at a distance of 30 min for each model, on the digital models using the software Blender and on the plaster model using a calibre. The Interclass Correlation Coefficient was calculated for each pair of measurements. A volumetric analysis was performed by superimposing the digital models. The coefficient of variation was calculated. A two-way ANOVA test was conducted. Results: For each reference, the coefficient of variation was less than 3%, and the two ANOVA tests resulted in a non-significant value in both cases (p > 0.05). The volumetric analysis demonstrated good agreement between the models derived from the different acquisition methods. Conclusions: Photogrammetry seems to be a good method for acquiring digital models starting from a plaster model, all the methods tested seem to be good for obtaining an accurate three-dimensional digital model. Other studies are needed to evaluate clinical efficacy.

Accuracy of photogrammetry, intraoral scanning, and conventional impression techniques for complete-arch implant rehabilitation: an in vitro comparative study

Background

To compare the accuracy of photogrammetry, intraoral scanning and conventional impression techniques for complete-arch implant rehabilitation.

Methods

A master cast containing 6 implant abutment replicas was fabricated. Group PG: digital impressions were taken 10 times using a photogrammetry system; Group IOS: intraoral scanning was performed to fabricate 10 digital impressions; Group CNV: splinted open-tray impression technique was used to fabricate 10 definitive casts. The master cast and conventional definitive casts were digitized with a laboratory reference scanner. For all STL files obtained, scan bodies were converted to implant abutment replicas using a digital library. The accuracy of a digitizer was defined by 2 main parameters, trueness and precision. "Trueness" was used to describe the deviation between test files and reference file, and "precision" was used to describe the closeness between test files. Then, the trueness and precision of three impression techniques were evaluated and statistically compared (α = 0.05).

Results

The median trueness was 24.45, 43.45 and 28.70 μm for group PG, IOS and CNV; Group PG gave more accurate trueness than group IOS (P < 0.001) and group CNV (P = 0.033), group CNV showed more accurate trueness than group IOS (P = 0.033). The median precision was 2.00, 36.00 and 29.40 μm for group PG, IOS and CNV; Group PG gave more accurate precision than group IOS (P < 0.001) and group CNV (P < 0.001), group CNV showed more accurate precision than IOS (P = 0.002).

Conclusions

For complete-arch implant rehabilitation, the photogrammetry system showed the best accuracy of all the impression techniques evaluated, followed by the conventional impression technique, and the intraoral scanner provided the least accuracy.

Photogrammetric and Intraoral Digital Impression Technique for the Rehabilitation of Multiple Unfavorably Positioned Dental Implants: A Clinical Report

The aim of this clinical report is to describe the use of the photogrammetric system and intraoral scanning as a reliable technique to record the 3-dimensional implant positions of a full-arch maxillary implant–supported fixed rehabilitation in which the implants were unfavorably positioned. The stereo camera of the photogrammetric system was used to capture the 3-dimensional panoramic position of the implants. The information on soft tissues was obtained with an intraoral scanner. Then, the 2 digital files (standard tessellation language [STL] files) were subsequently superimposed using a best-fit alignment function to generate the definitive digital model with information on teeth, soft tissues, and implants.

Photogrammetry as an alternative for acquiring digital dental models: A proof of concept

Photogrammetry is a mathematical technique that generates three-dimensional coordinates of specific points identified from multiple images of the same object obtained at different angles. This technique may be a low-cost alternative for traditional scanning. The objective of this proof of concept was to evaluate the accuracy and precision in obtaining digital models (DM) from a plaster model (PM) using photogrammetry. Five DM were generated from 50 photographs taken surrounding the PM. The photographs were taken by a single operator on five consecutive days using natural light. The images obtained were processed on 3DF Zephyr Free software. The height and width of all teeth were recorded on both PM and DM, as well as the distance between the canine cusps (C-C) and between the mesiobuccal cusps of the first molars (1 M-1 M). For the PM the measurements were taken with a digital caliper, whereas the DM was measured using the software Blender. The DM and PM measurements presented a limit of agreement between -0.433 and 0.611 mm. The accuracy of DM measurements showed a SD of ±0.171 mm and a repeatability coefficient of 0.474. In the superimposition of all DM, it was possible to notice a greater discrepancy in the posterior region of the arch and palate, but this difference decreased when the region was segmented. It can be concluded that photogrammetry appears to be a viable technique for the digitization of dental models. Further studies need to be performed to evaluate its clinical application.

Internal Adaptation of Implant-Supported, Polymer-Infused Ceramic Crowns Fabricated by Two CAD/CAM Systems

PURPOSE

The aim of this in vitro study was to compare the internal 3D adaptation of polymer-infused ceramic crowns fabricated using two CAD/CAM systems: CEREC inLab MC XL and Ceramill Motion 2 (5X).

MATERIALS AND METHODS

Twenty-five implant-supported metal-ceramic crowns were fabricated conventionally using the lost-wax technique, and the outer contour was scanned to serve as a guide for designing the polymer-infused ceramic CAD/CAM crowns. Twenty-five crowns were fabricated using CEREC, and 25 crowns were fabricated using Ceramill. The cement space was set to 20 μm. The Zeiss Accura Microsystem Coordinate Measuring Machine (CMM), Calypso, and Geomagic software were used to measure the 3D accuracy of fit of all crowns to their respective implant abutments. To test for the statistical significance between groups in terms of 3D total distortion, a one-way ANOVA was conducted. The Kolmogorov-Smirnov test was used to investigate the differences in the x, y, and z coordinates. A p-value of 0.05 or less was considered statistically significant at an alpha level of 0.05.

RESULTS

Comparing the 3D misfit of metal-ceramic crowns to those of CAD/CAM crowns fabricated using CEREC revealed no significant difference (88.20 ± 36.59 μm vs. 102.45 ± 36.58 μm, p = 0.161). Similarly, no significant difference in 3D total distortion was identified between metal-ceramic crowns and crowns fabricated using Ceramill (88.20 ± 36.59 μm vs. 78.40 ± 31.03 μm, p = 0.336); however, the 3D total distortion of polymer-infused crowns made by Ceramill was significantly reduced compared to that of crowns fabricated by CEREC (78.3 ± 31.0 μm vs. 102.4 ± 36.5 μm, p = 0.019).

CONCLUSIONS

Polymer-infused ceramic crowns fabricated using CEREC exhibited the least accurate 3D fit. All misfit values of the tested groups were within clinically acceptable levels.

Discrepancy of complete-arch titanium frameworks manufactured using selective laser melting and electron beam melting additive manufacturing technologies

STATEMENT OF PROBLEM

Titanium frameworks for implant-supported prostheses can be additively manufactured using different powder-based fusion technologies, including selective laser melting (SLM) and electron beam melting (EBM). Some manufacturers have developed a technique that combines the printing of the framework with the subsequent machining of the implant interface. Whether these technologies produce frameworks with acceptable accuracies is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the discrepancy obtained from the digitizing procedures of the definitive cast, the implant-prosthesis discrepancy, and the distortion of the manufacturing processes in the fabrication of titanium frameworks for implant-supported complete-arch prostheses manufactured using SLM and EBM additive manufacturing technologies.

MATERIAL AND METHODS

A completely edentulous mandibular definitive cast with 4 implant analogs and a replica of a screw-retained interim restoration was obtained. A standard tessellation language (STL) file of the framework design was prepared using dental software (Exocad). Six frameworks were manufactured using either SLM (3D Systems) or EBM (Arcam) technologies. Discrepancy (μm) was measured at the x- (mesiodistal), y- (buccolingual), and z- (occlusogingival) axes by using the formula 3D=x²+y²+z² three times by best-fit superimposure of the definitive cast STL file, the definitive cast titanium framework, and the framework STL file by using a coordinate measuring machine (CMM) controlled by software (Geomagic). The Kruskal-Wallis and Mann-Whitney U statistical tests were used (α=.05).

RESULTS

The digitizing procedures of the definitive cast showed a mean accuracy of 3 ±3 μm. Except for the z-axis (P<.05), no significant differences were observed between the SLM and EBM technologies for implant prosthesis discrepancy for the x- or y-axis (P>.05). The most favorable results were obtained in the z-axis, representing the occlusogingival direction. Three-dimensional discrepancy measurements in all comparisons ranged between (60 ±18 μm and 69 ±30 μm) and were not statistically significant (P>.05). The highest discrepancy was observed in the y-axis (37 to 56 μm), followed by the x- (16 to 44 μm) and z- (6 to 11 μm) axes (P<.05).

CONCLUSIONS

The titanium frameworks analyzed for a complete-arch implant-supported prosthesis fabricated using either the SLM or EBM additive technologies showed a clinically acceptable implant-prosthesis discrepancy, where similar discrepancies on the x-, y-, and z-axes were found between the additive manufacturing technologies. Both technologies showed comparable abilities to manufacture the STL file additively on the x-, y-, and z-axes.

Strain gauge analysis of implant-supported, screw-retained metal frameworks: Comparison between different manufacturing technologies

Over the past decades, the technological development in the medical field, coupled with the ongoing scientific research, has led to the development and improvement of dental prostheses supported by screw-retained metal frameworks. A key point in the manufacture of the framework is the achievement of a passive fit, intended as the capability of an implant-supported reconstruction to transmit minimum strain to implant components as well as to the surrounding bone, when subject to any load. The fitting of four different kinds of screw-retained metal frameworks was tested in this article. They differ both in materials and manufacturing process: two frameworks are made by casting, one framework is made by computer-aided design and computer-aided manufacturing and one framework is made by electric resistance spot welding (WeldONE, DENTSPLY Implants Manufacturing GmbH, Mannheim, Germany). The passivity of the frameworks was evaluated on the entire system, composed of a resin master cast, the implant analogues embedded in the cast and the frameworks. Strains were recorded by means of an electrical strain gauge connected to a control unit for strain gauge measurements. The experimental tests were carried out in the laboratories of the Department of INdustrial engineering at the University of Bologna. The results of the test campaigns, which compared three samples for each technological process, showed that no significant differences exist between the four framework types. In particular, the frameworks made by the resistance welding approach led to a mechanical response that is well comparable to that of the other tested frameworks.

A comparative analysis of the accuracy of implant master casts fabricated from two different transfer impression techniques

Aim:

This study evaluated and compared two impression techniques in terms of their dimensional accuracies to reproduce implant positions on working casts.

Materials and Methods:

A master model was designed to simulate a clinical situation. Impressions were made using four techniques: (1) Stock open tray (SOT) technique; (2) stock closed tray (SCT) technique; (3) custom open tray (COT) technique; and (3) custom closed tray (CCT) technique. Reference points on the hexagonal silhouette of the implant on master model and onto the analogs of the obtained master casts were compared after using the four impression techniques. Measurements were made using an optical microscope, capable of recording under 50x magnifications. The means and standard deviations of all the groups and subgroups were calculated and statically analyzed using analysis of variance (ANOVA) and Tukey's test.

Results:

The open tray impressions showed significantly less variation from the master model and all the techniques studied were comparable.

Conclusion:

All the techniques studied shown some distortion. COT showed the most accurate results of all the techniques.

Impression of multiple implants using photogrammetry: description of technique and case presentation

Aim: To describe a technique for registering the positions of multiple dental implants using a system based on photogrammetry. A case is presented in which a prosthetic treatment was performed using this technique. Study Design: Three Euroteknika® dental implants were placed to rehabilitate a 55-year-old male patient with right posterior maxillary edentulism. Three months later, the positions of the implants were registered using a photogrammetry-based stereo-camera (PICcamera®). After processing patient and implant data, special abutments (PICabutment®) were screwed onto each implant. The PICcamera® was then used to capture images of the implant positions, automatically taking 150 images in less than 60 seconds. From this information a file was obtained describing the relative positions – angles and distances – of each implant in vector form. Information regarding the soft tissues was obtained from an alginate impression that was cast in plaster and scanned. A Cr-Co structure was obtained using CAD/CAM, and its passive fit was verified in the patient’s mouth using the Sheffield test and the screw resistance test. Results and Conclusions: Twelve months after loading, peri-implant tissues were healthy and no marginal bone loss was observed. The clinical application of this new system using photogrammetry to record the position of multiple dental implants facilitated the rehabilitation of a patient with posterior maxillary edentulism by means of a prosthesis with optimal fit. The prosthetic process was accurate, fast, simple to apply and comfortable for the patient.

Key words:Dental implants, photogrammetry, dental impression technique, CAD/CAM.

A sectional-splinting technique for impressing multiple implant units by eliminating the use of an open tray

Since the inception of root form implant dentistry by P-I Branemark in the early 1980's, so many technical advances have been put forward by several authors. However, the open tray impression technique is still performed for impressing multiple implant fixtures as it was first described in the original Branemark procedure manual. The most critical aspect for a successful implant-supported restoration is the passive and an accurate fit of superstructures to avoid preload and loading stresses. Splinting impression technique in multiple implants has gained popularity. Auto-polymerizing acrylic resin is among the most routinely practiced splinting material for multiple implant units. However, unfortunately, it exhibits shrinkage, which makes an impression quite inaccurate. This case report presents the solution to minimize the shrinkage of resin by utilizing sectional-splinting technique as advocated in the previous implant literature.

Effect of unilateral misfit on preload of retention screws of implant-supported prostheses submitted to mechanical cycling

PURPOSE

The aim of this study was to evaluate the effect of different levels of unilateral angular misfit on preload maintenance of retention screws of single implant-supported prostheses submitted to mechanical cycling.

MATERIALS AND METHODS

Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n=12). The crowns presented no misfit in Group A (control group) and unilateral misfits of 50 μm, 100 μm and 200 μm in the groups B, C and D, respectively. The crowns were attached to external hexagon implants with a titanium retention screw with torque of 30 N/cm. Oblique loading of 130 N at 2 Hz was applied on each replica, totalizing 5×10⁴ and 1×10⁶ cycles. Detorque values were measured initially and after each cycling period. Data were evaluated by analysis of variance and Tukey's HSD test (p<0.05).

RESULTS

All groups presented reduced initial detorque values (p<0.05) in comparison to the insertion torque (30±0.5 N/cm) and Group A (25.18 N/cm) exhibited the lowest reduction. After mechanical cycling, all groups presented detorque values from 19.5 N/cm to 22.38 N/cm and the mechanical cycling did not statistically influence the detorque values regardless the misfit level of the replicas.

CONCLUSION

The unilateral misfit influenced the preload maintenance only before mechanical cycling. The mechanical cycling did not influence the torque reduction.

Measurement of ridge alterations following tooth removal: a radiographic study in humans

OBJECTIVE

The aim of this study was a radiographic mesiodistal analysis of the shape of the bone crest 3 months after tooth removal.

MATERIAL AND METHODS

One hundred single tooth extractions were performed on 100 patients because of orthodontic or prosthetic causes. Bite blocks were used for two radiographs: one on the day of extraction and the other after healing of the socket, 3 months later. These X-rays were used to determine: (1) the most apical distance of alveolar ridge resorption, with baseline as the line between bone-to-teeth contact (the greatest distance in bone resorption height) and (2) the mesiodistal distance (MDD) and mesial and distal angles arising after bone tissue modeling.

RESULTS

Significant differences (P<0.05) emerged between the MDDs of multiple- [8 mm, 95% confidence interval (CI): 6.09, 9.90] and single-root teeth (5.60 mm, 95% CI: 4.80, 6.50). However, mesial or distal angles or the most apical distance of alveolar ridge resorption did not differ (mean distance in height=4.32 mm, 95% CI: 3.85, 4.78; mean angle=24 degrees ).

CONCLUSIONS

In this study, the post-extraction mesiodistal bone distance between teeth adjacent to the edentulous ridge depends on the size of the edentulous space. Nevertheless, the distance does not affect the distance in bone loss height. The distance of bone resorption height reaches a balance at the midpoint, which we consider indicative of stable healing. This resorption process must be considered when placing dental implants in fresh extraction sockets, especially in aesthetic sites, because the implant surfaces could be exposed after 3 months.

Optical three-dimensional scanning acquisition of the position of osseointegrated implants: an in vitro study to determine method accuracy and operational feasibility

PURPOSE

Manufacturing complex prosthetic framework on osseointegrated implants requires precision at every step of execution. The purpose of this study was to verify the possibility of applying the technology of image acquisition to determine the spatial position of osseointegrated implants.

MATERIALS AND METHODS

An optical three-dimensional scanning technique was employed: its measurement systematic error (bias) was calculated by comparing the results with the detection on a coordinates measuring machine. Measurements were carried out on master casts by doing an in vitro simulation of intraoral conditions.

RESULT

This study showed that the bias error value of the three-dimensional optical acquiring system was situated between 14 and 21 microm.

CONCLUSION

As far as the accuracy is concerned, it seems possible to use the three-dimensional image acquisition technology as a valid alternative to traditional impression-making procedures. However, the bias levels obtained in this in vitro study will have to be confirmed in a clinical trial.

A new optical method to evaluate three-dimensional volume changes of alveolar contours: a methodological in vitro study

OBJECTIVES

The aim of this study was to evaluate the reproducibility and the accuracy of volumetric measurements of specimens imitating localized alveolar ridge defects using an optical three-dimensional (3D) system.

MATERIAL AND METHODS

Eight pairs of specimens (five with a cuboid and three with a geometrically complex form) were used for the measurements. Each of them imitated a pre-operative ridge defect and a corresponding surgically corrected post-operative situation. The true volume differences between two corresponding specimens were either assessed by a mechanical 3D coordinate measuring machine or by computer calculation (controls). For the test measurements, an optical 3D system with a newly developed software for volume measurements was utilized. The volumes of the specimen pairs were captured and the data digitized. The volume differences between the simulated pre- and post-operative situations were calculated by subtracting the two values obtained. The accuracy of the optical 3D system was assessed comparing the test and the control values. The difference between these values described the systematic error of the test method. The reproducibility was evaluated by calculating the coefficients of variation of repeated test volume measurements. Descriptive statistics were applied.

RESULTS

The accuracy of the optical 3D system was very high with differences between test and control measurements never exceeding 1.5%. The systematic error of the test measurements was consistently below 2.5 mm3. The reproducibility of the measurements showed very low coefficients of variation ranging from 0.05% to 0.5%, indicating excellent reproducibility.

CONCLUSIONS

The tested optical 3D system showed excellent accuracy and high reproducibility for measuring volume differences between specimens imitating localized alveolar ridge defects before and after augmentation procedures.

Cross-sectional analysis of the implant?abutment interface

The purpose of this study was to develop a technique to evaluate the implant-abutment gap of an external hexagon implant system as a function of radius. Six implants of 3.75 mm in diameter (Conexao Sistema de Protese Ltda, Sao Paulo, Brazil) and their respective abutments were screw connected and torqued to 20 N cm(-1). The implants were mounted in epoxy assuring an implant long-axis position perpendicular to the vertical axis. Each implant was grounded through its thickness parallel to implant long-axis at six different distance interval. Implant-abutment gap distances were recorded along the implant-abutment region for each section. Individual measurements were related to their radial position through trigonometric inferences. A sixth degree polynomial line fit approach determined radial adaptation patterns for each implant. Micrographs along implant sections showed a approximately 300 mum length implant-abutment engagement region. All implants presented communication between external and internal regions through connection gaps and inaccurate implant-abutment alignment. Average gap distances were not significantly different between implants (P > 0.086). Polynomial lines showed implant-abutment gap values below 10 mum from 0 mum to approximately 250 mum of the implant-abutment engagement region. Gap distances significantly increased from approximately 250 mum to the outer radius of the implant-abutment engagement region. The technique described provided a broader scenario of the implant-abutment gap adaptation compared with previous work concerning implant-abutment gap determination, and should be considered for better understanding mechanical aspects or biological effects of implant-abutment adaptation on peri-implant tissues.

Photogrammetry and Conventional Impressions for Recording Implant Positions: A Comparative Laboratory Study

BACKGROUND

The development of digitized techniques for manufacturing implant frameworks has made possible alternative "impression" techniques for recording implant positions.

PURPOSE

The objective of the present study was to test the precision and accuracy of a three-dimensional photogrammetric technique to record implant positions in vitro and to compare casts made with this technique with conventional casts fabricated with two conventional impression techniques.

MATERIALS AND METHODS

Twenty casts were fabricated from 10 polyether (Impregum, ESPE Dental AG, Seefeld, Germany) impressions and 10 plaster (Kühns Abdrucksgips, Ernst Hirnischs GmbH, Goslar, Germany) impressions of one master model. The casts were measured in a coordinate measuring machine (Zeiss Prismo VAST, Oberkochen, Germany) and compared with the master model. Six separate three-dimensional photographs of the master model were taken with a special camera. After the photographs were measured with an analytic plotter, results were analyzed and compared to the coordinates of the original model and casts.

RESULTS

A systematic pattern of distortion in the x-axis was found for the two impression techniques. Expansion of the implant arch at the terminal implants (p < .01) averaged 22 microm and 94 microm on photographs and plaster casts, respectively. Polyether casts contracted an average of 52 microm when compared with the master (p < .01). In absolute figures, photogrammetry and the polyether technique reproduced the x-axis and three-dimensional parameters more accurately than the plaster technique did when cylinder center point distortion was compared (p < .05 to p < .001). However, angular cylinder distortion in absolute figures was greater with the photographic technique than with either of the impression techniques (p < .05-p < .001).

CONCLUSION

Photogrammetry is a valid option for recording implant positions and has a precision comparable to that of conventional impression techniques. At present, however, it is limited to framework fabrication techniques that are based on digital platforms.

Cyclic loading of implant-supported prostheses: changes in component fit over time

STATEMENT OF PROBLEM

Dental literature suggests that an implant-supported prosthesis must exhibit a passive fit to prevent implant fracture, component breakage, and screw loosening. From a practical standpoint, passive fit is impossible to achieve; instead, minimal misfit may be the clinical goal. To date no specific range of misfit (below which problems are minimal and above which catastrophic failure occurs) has been established.

PURPOSE

The purpose of this study was to determine whether the fit of an implant-supported prosthesis changes through cyclic loading and to quantify the amount of change between the gold cylinder and implant abutment over time.

MATERIAL AND METHODS

Fifteen implant-supported frameworks were fabricated with conventional casting techniques and were cyclically loaded under 3 different loading conditions. Five frameworks were loaded on the anterior portion of the framework, 5 were loaded on the left unilateral posterior cantilever, and 5 were loaded bilaterally on the posterior cantilevers with a servohydraulic testing machine. A cyclical load of 200 N was applied to each framework for up to 200,000 cycles. Linear measurements were made in micrometers of the gap between the prosthetic cylinder and the implant-supported abutment at 4 predetermined reference points. These measurements were recorded before the application of the cyclical load, after 50,000 cycles, and after 200,000 cycles. A repeated measures of variance model was fit separately to the data for each load location (P<.05).

RESULTS

There was a significant (P=.024) decrease in gap dimensions at individual reference points and a significant (P=.031) decrease in the average gap when the load was applied to the anterior portion of the framework. When the load was applied unilaterally or bilaterally on the posterior cantilever, significant gap closure was not observed (P=.33 and P=.35, respectively).

CONCLUSION

Within the limitations of this study, the fit between the prosthetic superstructure and the implant-supported abutment changed when simulated functional loading of the anterior portion of the prosthesis was performed. Simulated functional loading applied unilaterally or bilaterally to the posterior cantilever portion of the prosthesis did not result in changes in the measured gap sizes.

Fit of implant frameworks: an in vitro comparison between two fabrication techniques

STATEMENT OF PROBLEM

It has been suggested that a precise fit between the implant and the framework cylinder is necessary to ensure a satisfactory long-term clinical outcome.

PURPOSE

The purpose of this study was to compare the precision of fit between implant abutments and framework cylinders in frameworks fabricated by the Procera system and those fabricated from cast gold-alloy.

MATERIAL AND METHODS

A total of 19 frameworks, 14 made with the Procera system (type 1) and 5 made of a cast gold-alloy (type 2), were fabricated. A total of 95 implants, 70 type 1 and 25 type 2 frameworks, were evaluated. Three replicas of the space between the implant abutments and the framework cylinders of the master cast were made for each test specimen. The replicas were cut with a scalpel in 2 axial directions: buccal-lingual and right-left. For the purpose of measurement, a microscope with a precision of +/- 0.5 microm was used at original magnification x30. The Student t test was used to determine whether there were significant differences between the framework designs.

RESULTS

The buccal-lingual measurements for the type 1 and type 2 frameworks showed mean values of 28.1 microm (SD 9.8) and 42.0 microm (SD 1.8) on the buccal side, respectively, and 25.6 microm (SD 11.2) and 51.6 microm (SD 10.9) on the lingual side, respectively. For the right-left view, the mean measurements were 26.6 microm (SD 8.4) and 49.2 microm (SD 11.4) on the right side, respectively, and 27.4 microm (SD 8.5) and 44.4 microm (SD 6.5) on the left side, respectively. The total mean value for type 1 frameworks was 26.9 microm (SD 9.3); that for type 2 frameworks was 46.8 microm (SD 8.8).

CONCLUSION

Within the limitations of this experiment, it was demonstrated that the fit of frameworks made with the Procera system was significantly better than that of the frameworks made with cast gold-alloy (P<.01).

Fit of implant-supported fixed prostheses fabricated on master casts made from a dental stone and a dental plaster

STATEMENT OF PROBLEM

The impression and cast on which an implant-supported fixed prosthesis is fabricated must accurately reproduce the intraoral relations.

PURPOSE

The fit of fixed prostheses fabricated on master casts poured in a conventional die stone and in an ultra-low-expansion plaster was investigated in vitro.

MATERIAL AND METHODS

An impression was made of patient replicas with inter-implant abutment distances of 50 and 35 mm. Ten master casts were poured in a conventional die stone (Velmix, Kerr) and 10 in an ultra-low-expansion plaster (Gnathostone, Zeus). A simulated plaster fixed prosthesis was fabricated on each master cast and then returned in a random order to the appropriate patient replica. The fixed prostheses were screwed into place on one abutment with a torque of 10 Ncm. Vertical discrepancies were measured at the other abutment by an operator blinded to the cast on which the fixed prosthesis was fabricated. A 2-way analysis of variance was performed for distance and materials, and significant differences were identified with regression analysis.

RESULTS

For the 50-mm inter-abutment distance, die stone master casts produced a mean vertical discrepancy of 80 microm (SD 32.50 microm). Plaster master casts produced a mean vertical discrepancy of 42.8 microm (SD 12.17 microm). The means were significantly different (P=.01). For the 35-mm inter-abutment distance, the mean vertical discrepancy produced from the die stone and plaster master casts was 84.33 microm (SD 49.9 microm) and 0 microm (SD 0), respectively. The means were significantly different (P<.001). A significant difference was found between the mean vertical seating discrepancies of fixed prostheses produced from plaster casts with inter-abutment differences of 50 mm and plaster casts with inter-abutment distances of 35 mm (P=.003). No significant differences were found between mean vertical seating discrepancies for fixed prostheses fabricated on die stone casts.

CONCLUSION

In this in vitro study, master casts poured in an ultra-low-expansion plaster limited to a maximum inter-abutment dimension of 35 mm were more accurate than casts with 50-mm inter-abutment spans or those poured in a conventional die stone.

The significance of passive framework fit in implant prosthodontics: current status

The clinical and laboratory procedures employed for framework fabrication are inadequate to provide an absolute passive fit for implant-supported fixed superstructures. Although some prosthetic complications are attributed to the lack of passive fit, its effect on implant success is questionable. Nevertheless, the clinical results of increasing applications of advanced technology to improve framework fit seem promising. This article reviews the clinical significance of passive fit and the factors that affect the final fit of implant-supported frameworks.

Stress levels for well-fitting implant superstructures as a function of tightening force levels, tightening sequence, and different operators

STATEMENT OF PROBLEM

Unfavorable stress distribution and occlusal overload have been reported to result in failures ranging from screw loosening to loss of osseointegration.

PURPOSE

The purpose of this study was to assess the effect of different tightening forces and sequences, with different operators, on stresses generated on an accurately fitting implant superstructure on multiple working casts made with a splinted impression technique.

MATERIAL AND METHODS

The effects of different tightening forces (10 and 20 Ncm) were assessed with the use of 30 stone casts made from a metal master model with a splinted impression technique. Stresses generated were recorded by 4 strain gauges attached to the superior surface of the master framework. A multiple analysis of variance with repeated measures was performed to test for significant differences among the groups.

RESULTS

Tightening force values at 10 Ncm ranged from 150.43 to 256 Ncm. At 20 Ncm, microstrain values ranged from 149.43 to 284.37 Ncm. Microstrain values related to the sequence of tightening ranged from 150.8 to 308.43 Ncm (left to right) and 154.63 to 274.80 Ncm (right to left). For the different operators, microstrain values ranged from 100.13 to 206.07 Ncm. No statistically significant differences among the variables of tightening force, tightening sequence, and operators were found ( P >.05). The interaction between groups and strain gauges was also found to be nonsignificant (P >.05).

CONCLUSION

The potential of variable tightening force and tightening sequence to generate unfavorable preload stresses can be minimized through use of the splinted impression technique, which ensures an accurately fitting superstructure.

Experimental and computational approach for the evaluation of the biomechanical effects of dental bridge misfit

Dental bridges supported by osseointegrated implants are commonly used to treat the partially or completely edentulous jaw. The bridges are manufactured in metal alloy using a sequence of technological steps which well match the requirement to get custom overstructures but does not guarantee geometrical and dimensional tolerances. Dentists often experience that a perfect fit of the bridge with the abutments is almost impossible to achieve. When a misfitting bridge is forced on the abutments, deformations may occur inducing a permanent preload at the fixture-bone interface and the greater the misfit the greater is the preload and the risk of implant failure. This work gives an evaluation of the biomechanical effects induced by a misfitting bridge when forced on two supporting dental implants. The strains induced in the bridge have been measured using two purposely designed and fabricated experimental devices allowing different types of misfit. FEM 3D models of the bridge and of the bridge anchored to the bone by implants have been developed. The former has been validated by simulating the same loading conditions as in the experimental tests and comparing the bridge strains. Both models have been used for the evaluation of the stress induced in the bridge and at the fixture-bone interface by bridge length errors. The results show that the method may help to estimate the stress distribution in the bridge and bone as a consequence of different dental bridge misfits.

Measuring fit at the implant prosthodontic interface

Four centers in the United States and Sweden have been working for 2 years to develop systems and methods for measuring fit at the prosthodontic interface. Two systems are based on stylus contact techniques, one system uses a laser as its reader source, and one system is photogrammetric. All the systems are capable of providing data as three-dimensional x, y, and z axes coordinate values that can be transformed into linear and angular data that characterize the bearing surfaces of abutments or abutment replicas and their mating components in the prosthesis framework. The centroid, a single point computed from the collected data, was the measurement unit, derived for these bearing surfaces, that was used to compare the systems. All four methods can most likely detect misfits that are relevant in the clinical setting; however, only one system can be used intraorally. When any measurement system is assessed, the data should always be examined for repeatability to establish the reliability of the system. This investigation made comparisons among the measurement methods used at the four centers. It was apparent from this study that comparisons of data from measurement systems should be rounded to the nearest 10 microns. The SDs determined in the comparisons were larger than 5 microns and therefore misfits should be calculated in terms smaller than 10 microns. This final point is important to the clinician who relies on research reports about precision of fit when selecting treatment approaches in caring for the implant prosthodontic needs of their patients.

Three-dimensional distortion of gold alloy castings and welded titanium frameworks. Measurements of the precision of fit between completed implant prostheses and the master casts in routine edentulous situations

Thirty routine patients, provided with fixed prostheses supported by osseointegrated Brånemark implants in edentulous lower jaws, were arranged into three different groups with regard to design of the metal framework. Ten patients received cast gold alloy frames and the other two groups were provided with two different designs of welded titanium frames. The fit of the completed prostheses was measured in three dimensions (3-D) in relation to the master cast, by means of a photogrammetric technique, prior to insertion. Mean 3-D distortion of the centre point of the gold cylinder was 42 (s.d. 8) microns for the cast framework. The corresponding mean distortion for the two designs of titanium frameworks was 43 (s.d. 16) and 36 (s.d. 10) microns, respectively. Least distortion was observed in vertical direction for all three designs. None of the different designs of metal frames showed a significantly better fit (P > 0.05), but the cast and oldest titanium framework design presented a much wider range of distortion. This indicated a higher risk of sectioning and resoldering during the fabrication of the prostheses as compared to the more consistently fabricated prostheses, with a new titanium framework design.