Introduction
Attempts have been made to develop a digital workflow that allows the subgingival form of the provisional restoration to be accurately transferred to the final restoration to provide appropriate cleansability, esthetics, and function.
Joda et al reported a method to manually individualize the scanbody, which has a circular diameter based on the emergence profile created by the provisional restoration.1 They developed a method for individualization of prefabricated implant transfer posts based on conventional impression-taking procedures.2,3 This method prevents supra-implant soft tissue collapse during intraoral scanning; however, a coronal configuration based on the provisional restoration cannot be assigned to the final restoration.
Monaco et al described an intraoral scanning method for replication of peri-implant soft tissue contours, as well as the emergence profile of the provisional restoration.4 They prepared an intraoral Standard Triangulation Language (STL) image to detect the implant position with a standardized implant scanbody (STL1). In this method, the lower part of the image, containing the inner surface of the supra-implant emergence profile and broken down, soft peri-implant tissue, is removed. The vestibular and palatal sides of the provisional restoration and adjacent teeth are intraorally detected, and the provisional restoration is removed from the mouth to scan its subgingival component (STL2). Data regarding the portion of the provisional restoration below the gingival margin, as well as the emergence profile and vestibular mucosa, are retained. STL1 and STL2 are digitally superimposed to produce STL3, comprising the scanbody, its relative 3D implant position, and data regarding the peri-implant soft tissue and emergence profile. This method uses subgingival data describing the provisional restoration; the coronal form of the final restoration is fabricated manually.
These methods transfer the provisional subgingival components to the final restoration; we hypothesized that data regarding the coronal form of the provisional restoration could enable provisional supra- and subgingival components to be assigned to the final restoration. Here, we report on the clinical application of our workflow that involves scanning and superimposing morphological data with an intraorally installed provisional restoration, intraorally connected scanbody, and extraorally scanned whole morphology of the provisional restoration. This approach could transfer the whole morphology from the provisional implant restoration to the final restoration. In addition, we digitally analyzed the volumetric discrepancies between the restorations.
Materials and Methods
Case
In this case, a 63-year-old male patient presented with a missing right mandibular second molar (tooth #31). He had previously received an implant body (ø4.1 × 12.0 mm Bone Level Implant RC, Straumann, Basel, Switzerland) and had undergone installation of a screw-retained, connected provisional restoration (Figures 1 and 2). Following installation, a dentist adjusted the provisional restoration (namely, its crown morphology and subgingival contour); function and cleansability were then confirmed to be appropriate for the patient. Therefore, the provisional restoration needed to be replaced with a final restoration; we opted to implement our novel procedure. The patient provided informed consent to participate in this study.
Reproduction of the morphology of the provisional restoration using a novel digital workflow
Initially, an intraoral scanner (TRIOS2, 3Shape, Copenhagen, Denmark) was used to digitize three morphological components in the form of 3OXZ data (all components were digitized in 3D) (Figure 3): (1) intraoral morphology data describing the whole mandible with the provisional restoration present; (2) intraoral morphology data describing the whole mandible with the implant scanbody (RC Straumann CARES Mono Scanbody, Straumann) connected to the implant body; and (3) morphology data describing the provisional restoration, linked using an implant replica buried in the plaster model to prevent the movement of the provisional restoration during the scanning process. Additionally, intraoral morphology data describing the whole maxillary dental arch and data describing both the maxillary and mandibular dental arches occluded at the intercuspal position were also digitized. Initially, Dental Designer (3Shape, Denmark) was used to transfer the 3OXZ data to Digital Imaging and Communications in Medicine format. Another software (Exchange, Delcam, Autodesk, Birmingham, UK) was then used to convert these intermediate data to the STL format. Finally, a dental computer-aided design (CAD) software (Exocad, Darmstadt, Germany) was used to visualize the data.
These STL data enabled superimposition of the intraoral 3D morphology data describing the whole mandible with the provisional restoration and of the data describing the whole mandible with the implant scanbody; this was performed using a least mean squares method based on the surface morphologies of the remaining teeth and gingival mucosa (Figure 4). Then, data describing the provisional restoration (ie, the 3D surface data) were overlapped onto the existing superimposed 3D image, with reference to the supragingival surface morphology of the provisional restoration. This enabled the provisional restoration and surrounding soft tissue configurations to be reproduced on the implant scanbody in a digital form (Figure 5).
In the next portion of the process, these three-layer image data were returned to the CAD design software (CARES Straumann, Straumann). Figure 6 (a, b) shows the provisional restoration and surrounding soft tissue forms as reflected in the CAD design software. The borderline between the abutment and the final restoration was determined from the provisional restoration configuration based on information regarding the soft tissue configuration surrounding the provisional restoration. The customized titanium abutment and full anatomical zirconium crown were then designed (Figure 6b-d).
Based on the definitive surface morphology, the configuration of the titanium base was digitally withdrawn. Using a 5-axis milling machine (DWX-50, Roland, Shizuoka, Japan), the final restoration was then prepared on a zirconia disk based on these data (Medium Plus, Adamant, Tokyo, Japan). After polishing and baking the zirconia using layering porcelain, an adhesive resin cement (Panavia V5 opaque, Kuraray Noritake Dental Inc, Tokyo, Japan) was used for fixation of the crown form, comprising the final restoration and titanium base (Figure 6e, f).
In silico assessment of restorations
Prior to installation, the discrepancies between the restorations were measured using in silico analysis, as previously reported by Kurosaki et al.5
Results
Figure 7 shows the similarity between the final and provisional restorations. Notably, no chairside adjustment was needed during installation of the final restoration. The respective volumetric discrepancies in the concave and convex components between the final and provisional restorations were 17.2 mm3 and 5.5 mm,3 as shown by in silico analysis; the total volumetric discrepancy was 22.7 mm.3 Moreover, the total discrepancy volume ratio was 4.7%.
An intraoral view after final restoration installation is shown in Figure 8. Notably, no inflammation was observed in the peri-implant tissues. Therefore, no volumetric discrepancy-related clinical issues were noted. Moreover, oral function was satisfactory; thus, the patient reported satisfaction with the treatment outcome.
Discussion
The use of an implant scanbody enables accurate 3D recognition of implant platform location; thus, digital implant impressions have increasingly been used with intraoral scanners and implant scanbodies.6 However, the standardized implant scanbody has a prefabricated circular diameter that differs from the provisional restoration configuration that supports the gingival morphology. Additionally, gingival tissue rapidly breaks down after provisional crown removal before scanning. Thus, simple digital scanning of the implant scanbody, which is connected to the implant body, cannot capture the gingival morphology where the provisional restoration is installed. In contrast, our novel digital workflow can reflect the gingival configuration by examining the subgingival contour within the provisional restoration. In addition, the supragingival configuration can also be reflected in the morphology of the final restoration. This enables accurate transfer from the provisional restoration for both functional and esthetic elements of crown morphology, which are assigned to the final restoration. This procedure does not require fabrication of a working cast and X-ray radiation to confirm the position of the impression coping.
In conclusion, clinically acceptable accuracy was achieved using our novel digital workflow for whole morphology reproduction of the provisional restoration, thereby facilitating transfer to the final restoration. Although this technique is only applicable when using an implant system that involves the implant scanbody, it is useful in clinical settings with minimum discomfort to the patient and facilitates achievement of appropriate function and esthetics.
Abbreviations
Note
The authors declare that there are no conflicts of interest.
