Photogrammetry presents some advantages as the acquisition procedure is not influenced by external factors such as ambient light conditions or the presence of edentulous areas. Nonetheless, at the moment, PG is not capable of reproducing soft tissues in an accurate form. Accordingly, photogrammetry needs to be developed to include accurate 3D scanning simultaneously with capturing implant coordinates. For that reason, a second method is still mandatory to register soft tissue information and complement the transferred implant position.63,67 Usually, this is made by resorting to an IOS or conventional impressions, and the merge of the two resulting digital files accurately representing the intraoral condition.
Therefore, some of the IOS errors are added to the impression, reducing the overall accuracy of the merged file.36,63,64,67 Alternatively, the impression of the soft tissues can be taken with conventional materials, such as polyether or alginate, and the obtained casts scanned afterward, possibly introducing material deformation. Nevertheless, the methods of all included studies described the use of a second impression being made, either with conventional methods or with different IOS systems. However, none of the in vitro studies simulated intraoral conditions, especially those using conventional methods.
After CMM machine (presented in 7 in vitro articles), 3D analysis and superimposition of the different STL files were the most observed comparison methods among the included articles.48,49,56,58,60 The usage of RMS values to offset both poles of deviations can avoid the impact of inevitable inherent errors of the ‘best-fit’ algorithm.70 Nevertheless, some studies evaluated the position of implant abutment replicas, whereas others considered the position of scan bodies on the implants, transforming that location into 3D locations of implants and abutments, which may not represent true clinical procedures. Tohme et al. referred to the flat angled portions of the scan bodies as crucial pieces, as ‘errors in these areas can shift the centroids of the objects and affect the implant position determination, which then affects the passivity of the implant-supported fixed complete-arch prostheses.48 However, the same article concluded that PG performed the worst in these particular portions, despite performing the best when the whole scan body was the object of interest. This fact does not seem to affect overall accuracy when considering the implant positions, probably because each photogrammetric system uses its own set of encoded marks, calibrated for that specific camera device. However, it may present some technical complications to DSLR systems. Across the case reports, photogrammetry was described as feasible and available for clinical use59, precise, reliable64, rapid, convenient for dentists and patients62,63,68, providing optimal passive framework fit36,63,64,68, and adequate esthetic and functional outcomes.62 Furthermore, considering 150 µm
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as the threshold established for this review for clinical acceptance, photogrammetry is well within that range, as the error associated with PG ranged from 20 to 77.6 µm, across the included studies.53,54
Commercially distributed systems, such as PIC Camera and iCam4D, were the most used across all studies. Although DSLR techniques were used in in vitro studies, their application at a clinical level is difficult, as an elevated amount of standardization is needed to ensure proper accuracy levels. Nevertheless, even with the need of a second impression to register soft tissue information, photogrammetric techniques offer shorter working times.67 Also, it may reduce the need for multiple consultations in full arch rehabilitations, as contraction material errors are eliminated, possibly resulting in lower misfit rates and deformation during travel to the laboratory.
Despite its high accuracy, developments in PG technology are still needed, to provide a favorable daily usage within a simple workflow. As Forlani et al. described, the resolution of the capturing device is capable of influencing precision of these systems56, and so improved sensors and processors for better image acquisition will deliver more accurate results. In addition, soft tissue scanning integration in the same device would remove the need for an additional impression, thus reducing error and working time. Finally, a reduction in cost would make the technology more accessible to clinicians, and also allowing for improvements in software.56
In the literature, Romero et al.59 compared the operating costs of a conventional approach with a fully digital methodology, reporting better results for the latter.59However, it failed to explain how the reported numbers were obtained in a systematic form. Nonetheless, a procedure with fewer steps to achieve a similar or better result than another method can be perceived as more encouraging to clinicians, especially for the ones with less experience in digital technologies. The rationale behind this statement is that fewer steps and shorter time spent in the procedure provide more time to execute each step with higher security and clarity.
Even considering a learning curve intrinsic to new technologies, the use of photogrammetry as a simpler method can possibly reduce operator error.
Articles that used DSRL as their photogrammetric capturing device had well-controlled conditions, with rotating plates and standardizes protocols. Although that ensures good results in the in vitro study itself, it does not represent a true clinical environment, where the outcome can be influenced by external factors, such as patient and professional movement, inconsistency, and possible failure of equipment.
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All the clinical reports and case series included extended their follow-up no further than 2 years after the intervention took place and presented some concerns about the quality and risk of bias assessment performed.
4.1. Limitations of the Present Review
The obtained results of the present systematic review are not robust due to limitations.
Most of the studies included are in vitro or case reports/series, offering lower standards of evidence. Moreover, regarding quality assessment and risk of bias, most articles rated low in both fields, raising questions about the methods used, especially on in vitro records, where the extrapolation of results needs to be cautiously evaluated. Also, this type of studies are not able to fully represent the variables of the oral cavity, as intraoral conditions moderately affect the precision and trueness of IOS systems.72 For that reason, the results of in vitro accuracy studies cannot be directly transferred to the clinical field.72
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