Engineering prosthetic axes for unparallel full arch implants by the virtual selection of abutment orientation and angulation

Abstract

A technique for virtual determination of the abutments’ angulation, orientation, and gingival height for unparalleled osseointegrated dental implants is described. A cone beam computed tomography (CBCT) and an optical scan were performed for the arch to be restored. The wax-up prosthesis was designed using the Exocad software program, and implants were virtually placed over the osseointegrated implants appearing in the CBCT using an implant planning software program. The abutments were virtually placed, and their angulation and orientation were selected according to the virtually designed prosthesis. This technique offers a time- and cost-effective digital solution for engineering unparallel implants’ prosthetic axes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-026-07808-4.

Introduction

Osseointegration is a natural healing process involving direct contact between bone cells (osteoblasts) and implant threads [1, 2]. Osseointegrated dental implants are in direct contact with bone with no supporting periodontal ligament [3]. Therefore, an unpassive prosthesis causes biological and mechanical complications such as screw loosening, fracture, or even failure of implant osseointegration [4–9].

The screw-retained implant-supported fixed prosthesis consists of implants, transmucosal abutments, and the prosthesis either as one unit or with a bar superstructure [10]. This type of prosthesis offers rigid splinting between dental implants, easy retrievability during maintenance visits, and fewer biological complications that may arise from excess cement in the cement-retained prosthesis [11–14]. The fabrication of screw-retained prostheses requires either parallel implants or parallel prosthetic axes with screw access holes emerging from the cingulum of anterior teeth for a better aesthetic outcome [12].

Unfavorable implant position and angulations may be due to anatomic limitations such as the position of the inferior alveolar nerve, pneumatization of the maxillary sinus, and the amount of remaining bone after alveolar ridge resorption, or even due to improper planning during implant placement. These factors lead to a complicated treatment plan and poor esthetic outcomes [11, 12].

Multiunit abutments have different angulations and gingival heights. They are greatly valuable to correct the prosthetic axes of unfavorable implant angulations, facilitate prosthesis fabrication, and change the screw access hole to an esthetically favorable position [3, 12]. In addition to multiple angulations, multiunit abutments have many possible orientations intraorally depending on the abutment implant connection [11, 13]. Intra-oral selection of the abutments’ angulation, orientation, and gingival height is a time- and cost-consuming procedure that requires high skill from the operator and multiple visits [11, 13, 14].

Computer-aided designing software can be classified into two main categories: specialized dental software for either prosthesis fabrication or implant planning and non-specialized free form software that mainly fill the gaps between the specialized ones. Recently the dental software are developing rapidly to by the addition of free forming features [8, 15].

This continuous development in digital prosthodontics and dental software programs has greatly affected both implant and prosthesis planning by simplifying the workflow in a smaller number of visits and time [16]. However, reports on the engineering of the prosthetic axes by the virtual selection of abutments’ orientation, angulation, and gingival heights are lacking.

The objective of this technique was to virtually determine prosthetic axes with an esthetic screw access hole and a common path of insertion for multiple unparallel implants by introducing a time- and cost-effective digital method for selecting abutment angulation, orientation, and gingival height.

Technique

This technique is indicated for patients with multiple unparallel osseointegrated implants; it offers a digital solution for determining the best angulation, orientation, and gingival height of the abutments according to the esthetics and function of the prosthesis through obtaining a cone beam computed tomography (CBCT) and an optical scan.

1. Data acquisition.

1. Obtain an optical scan of the jaw to be restored and its antagonist using an intraoral scanner (Medit i700; Medit). Export the 3D data in the form of standard tessellation language (STL) files (Fig. 1). Also perform a CBCT scan for the patient and export the medical image as a Digital Image and Communication in Medicine (DICOM) file.

• b.prosthesis waxing-up

1. Import the STL files of the jaw scans into the wax-up pontic module of a CAD software program (Dental CAD; Exocad GmbH). Design the prosthesis wax up by setting the teeth virtually using the rotate and move software tools [15] (Fig. 2).

2. Import the DICOM file and STL files of the jaw scans and the wax-up prosthesis into an implant planning software program (Real Guide 5.2 software, 3DIEMME), then align between the STL and DICOM files of the jaw using the assisted artificial intelligence software tool [17] (Fig. 3).

• c.virtual implant placement

• 4.To manipulate the prosthetic axes, start with placing virtual implants over the osseointegrated implants appearing in the DICOM file. The virtual implants should have the same diameter, length, and 3D orientation as the osseointegrated ones regarding angulation and vertical and horizontal position (Figs. 4 and 5).

• d.Virtual selection of abutment orientation, angulation and gingival height

• 5. Control the prosthesis axes by placing virtual abutments over each implant and selecting the appropriate angulation to have parallel prosthetic axes with screw channels opening at the cingulum of anterior teeth for esthetics by virtually rotating the abutments (Figs. 6 and 7; Supplementary Video 1, available online). You can select the gingival height of the abutment by measuring the distance between the implant crest appearing in the DICOM file and the STL file representing the soft tissue (Fig. 8).

• e.intraoral abutment insertion and prosthesis fabrication.

• 6. After recording abutments’ angulation, orientation, and gingival height, tighten each abutment intraorally with the torque recommended by the manufacturer and proceed with the steps of prosthesis construction either in a conventional workflow using impression transfers and conventional impression or in a digital workflow using scan bodies and intraoral scanner (Figs. 9, 10 and 11).

Fig. 1.

The STL files represent optical scans of the maxillary and mandibular arches

Fig. 2.

The virtual wax-up of the prosthesis will guide the selection of abutment orientation and angulation

Fig. 3.

Virtual alignment between the DICOM file representing the implants and the bone and the STL file representing the soft tissue

Fig. 4.

3D alignment between virtual implants and osseointegrated ones appearing in the DICOM file

Fig. 5.

Multiple osseointegrated implants with unfavorable angulation

Fig. 6.

Virtual abutment placement with controlling angulation and orientation

Fig. 7.

Engineering the abutment orientation and angulation with favorable prosthetic axes

Fig. 8.

Virtual measurement of the soft tissue thickness for selection of abutment gingival height

Fig. 9.

Intraoral occlusal view of the prosthetic axes after virtual selection of abutment orientation and angulation

Fig. 10.

The finalized permanent prosthesis with favorable prosthetic axes and esthetic screw access hole openings

Fig. 11.

The screw axes holes appearing in the palatal side of the prosthesis

Discussion

This technique introduces how to use digital technology to engineer prosthetic axes for multiple implants with unfavorable angulations by the virtual selection of the abutments’ angulation, orientation, and gingival height. Previous techniques have reported only how to replace old abutments for an existing prosthesis [3, 10] but to the authors’ knowledge, there are no previous articles that discussed the virtual selection of abutments’ angulation and orientation.

Although abutment selection could be performed intraorally, it is a time- and cost-consuming procedure and very exhausting for the prosthodontist and the patient, especially in full-arch misaligned implant situations. The intra-oral abutment selection requires trying many abutment angulations with many possible orientations until reaching a favorable angulation, which requires the presence of an abutment stock of different angulations, and gingival heights. The technique introduced allows the dentist to select the best possible orientation and angulation of the abutment before the start of clinical visits in approximately thirty minutes.

This technique discussed many challenges, starting with the virtual transferring of the 3D position and angulation of osseointegrated implants to dental software. Also employing the available implant planning software to virtually determine the screw access hole position and changing the prosthesis axes from an unfavorable orientation to a favorable one.

The virtual design of the prosthesis wax-up was conducted before abutment selection to allow the placement of the screw access hole in an aesthetically and functionally favorable position. The virtual implants should have the same diameter, length, and 3D orientation as the osseointegrated ones, which will help to check the quality of the virtual superimposition step in the axial, coronal, and sagittal planes of the DICOM file.

Limitations of this technique are related to the digital implant and prosthetic skills of the prosthodontist and the availability of implant planning software programs, optical scanners, and CBCT machines in the dental clinic. Also, the unavailability of some implants and abutment brands in the library of implant planning software is considered a limitation of this technique.

The future prospectives related to this technique may discuss the possibility of guide fabrication for accurate seating of the multiunit abutment in the preplanned position. Also, it is recommended to conduct studies evaluating the accuracy of this protocol especially with engaging abutment connections.

Summary

The technique presented depends on CBCT and digital technology to provide a time- and cost-effective solution to engineer the prosthetic axis and control the position of the screw access hole by the selection of the abutments’ orientation, angulation, and gingival height.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

Authors Contribution:1- Medhat Sameh Abdelaziz: (concept -design - writing of the manuscript- interpretation -software- operator in all the practical work.)

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Data availability

Data availability: The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.