Efficacy of Constructing Digital Hybrid Skull-Dentition Images Using an Intraoral Scanner and Cone-Beam Computed Tomography

Effect of fabrication methods and number of supporting teeth on the surface accuracy and dimensional stability of implant surgical guides

STATEMENT OF PROBLEM

Implant surgical guides manufactured using different fabrication methods have been commonly used for computer-guided implant placement. However, how fabrication methods and the number of supporting teeth influence accuracy and stability remains uncertain.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of fabrication methods and number of supporting teeth on the surface accuracy and dimensional stability of implant surgical guides with 3 different 3-dimensional (3D) printers and 1 computer numeric controlled (CNC) milling machine.

MATERIAL AND METHODS

Two tooth-supported maxillary implant surgical guides with different number of supporting teeth (S: short span with 4 supporting teeth, L: long span with complete arch supporting) were used to fabricate the specimens. Eighty surgical guides were fabricated from 3 different 3D printers and 1 milling machine as follows: group SLA-S (n=10) and SLA-L (n=10) were fabricated with a desktop stereolithography (SLA) 3D printer and photopolymerizing resin; group PolyJet-S (n=10) and PolyJet-L (n=10) were fabricated with a PolyJet 3D printer and photopolymerizing resins; group DLP-S (n=10) and DLP-L (n=10) were fabricated with a desktop digital light processing (DLP) 3D printer and photopolymerizing resin; and group MILL-S (n=10) and group MILL-L (n=10) were fabricated with a 5-axis milling machine and polymethyl methacrylate (PMMA) blanks. All surgical guides were digitized immediately after postprocessing and after 1, 2, and 3 months using a desktop scanner. The congruency between design files and digitized files was quantified with the root mean square (RMS) error with a metrology program (Geomagic Control X). Two-way ANOVA was used to analyze trueness, and the Levene test was used to assess precision (α=.05).

RESULTS

The fabrication methods and number of supporting teeth significantly affected the surface trueness of the guide (P<.001). Milled guides had the lowest mean RMS value for surface trueness, 45 µm for guides with 4 supporting teeth and 59 µm for guides with complete arch supporting. Regarding precision, the Levene test revealed significant difference among fabrication methods (P<.05), while no significant difference was found in the same fabrication method group (P>.05). After 3 months of storage, RMS values increased significantly in the complete arch supporting group comparison of SLA, PolyJet, and DLP (P<.001, P<.001, and P=.015, respectively). RMS values remained similar in other groups.

CONCLUSIONS

The trueness and dimensional stability of the surface of the implant surgical guides were affected by fabrication methods and the number of supporting teeth. However, the precision was only affected by fabrication methods. Milled surgical guides showed higher accuracy and better dimensional stability after storage than those produced with 3D printers. Among the groups of 3D printing, guides with 4 supporting teeth showed higher trueness and a lower degree of deformation after storage.

A chairside digital radiographic guide for registering digital casts to cone beam computed tomography scans with strong metallic artifacts

Accurate registration of digital casts and cone beam computed tomography (CBCT) scans with strong metallic artifacts is essential for the accuracy of guided implant surgery. This article describes a procedure for mapping digital casts onto CBCT scans containing significant scatter artifacts in the virtual implant planning stage. The technique uses a chairside segmented occlusal wing-like radiographic guide, which is constructed of digital splints fabricated using a desktop 3-dimensional printer and composite resin spheres as markers to accurately superimpose the bimaxillary digital scans onto the CBCT scans in a single procedure. This cost-effective technique is timesaving for clinicians and patients, and the digital information for implant planning can be collected in a single visit.

Automatic removal of soft tissue from 3D dental photo scans; an important step in automating future forensic odontology identification

The potential of intraoral 3D photo scans in forensic odontology identification remains largely unexplored, even though the high degree of detail could allow automated comparison of ante mortem and post mortem dentitions. Differences in soft tissue conditions between ante- and post mortem intraoral 3D photo scans may cause ambiguous variation, burdening the potential automation of the matching process and underlining the need for limiting inclusion of soft tissue in dental comparison. The soft tissue removal must be able to handle dental arches with missing teeth, and intraoral 3D photo scans not originating from plaster models. To address these challenges, we have developed the grid-cutting method. The method is customisable, allowing fine-grained analysis using a small grid size and adaptation of how much of the soft tissues are excluded from the cropped dental scan. When tested on 66 dental scans, the grid-cutting method was able to limit the amount of soft tissue without removing any teeth in 63/66 dental scans. The remaining 3 dental scans had partly erupted third molars (wisdom teeth) which were removed by the grid-cutting method. Overall, the grid-cutting method represents an important step towards automating the matching process in forensic odontology identification using intraoral 3D photo scans.

Diagnostic Applications of Intraoral Scanners: A Systematic Review

In addition to their recognized value for obtaining 3D digital dental models, intraoral scanners (IOSs) have recently been proven to be promising tools for oral health diagnostics. In this work, the most recent literature on IOSs was reviewed with a focus on their applications as detection systems of oral cavity pathologies. Those applications of IOSs falling in the general area of detection systems for oral health diagnostics (e.g., caries, dental wear, periodontal diseases, oral cancer) were included, while excluding those works mainly focused on 3D dental model reconstruction for implantology, orthodontics, or prosthodontics. Three major scientific databases, namely Scopus, PubMed, and Web of Science, were searched and explored by three independent reviewers. The synthesis and analysis of the studies was carried out by considering the type and technical features of the IOS, the study objectives, and the specific diagnostic applications. From the synthesis of the twenty-five included studies, the main diagnostic fields where IOS technology applies were highlighted, ranging from the detection of tooth wear and caries to the diagnosis of plaques, periodontal defects, and other complications. This shows how additional diagnostic information can be obtained by combining the IOS technology with other radiographic techniques. Despite some promising results, the clinical evidence regarding the use of IOSs as oral health probes is still limited, and further efforts are needed to validate the diagnostic potential of IOSs over conventional tools.

Effectiveness of creating digital twins with different digital dentition models and cone-beam computed tomography

Distortion of dentition may occur in cone-beam computed tomography (CBCT) scans due to artifacts, and further imaging is frequently required to produce digital twins. The use of a plaster model is common; however, it has certain drawbacks. This study aimed to assess the feasibility of different digital dentition models over that of plaster casts. Plaster models, alginate impressions, intraoral scan (IOS) images, and CBCT images of 20 patients were obtained. The desktop model scanner was used to scan the alginate impression twice, five minutes and two hours after impression-making. Using an IOS, the full arch was scanned in segments using CS 3600 and simultaneously with i700 wireless. The digital twins obtained from the alginate impression and IOS were superimposed with those obtained from the plaster cast. The differences and distances at each reference point were measured. Scans of alginate impressions after two hours showed the greatest discrepancies, but these were all less than the CBCT voxel size of 0.39 mm. Alginate impression scans and IOS are suitable supplements to CBCT compared to the plaster model. Accuracy can be improved by scanning the alginate impression within five minutes or by intraoral scanning of the entire arch with segmentation.