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Use of digital technologies in fabrication of a custom healing stent after stage II implant surgery for advanced jaw reconstruction

Use of digital technologies in fabrication of a custom healing stent after stage II implant surgery for advanced jaw reconstruction



Use of digital technologies in fabrication of a custom healing stent after stage II implant surgery for advanced jaw reconstruction




Journal of Prosthetic Dentistry, 2021-03-01, Volume 125, Issue 3, Pages 545-550, Copyright © 2020 Editorial Council for the Journal of Prosthetic Dentistry


Abstract

This report describes the fabrication of a custom healing stent for second stage implant surgery in advanced jaw reconstruction. Postoperative computed tomography data and digital dental implant component libraries were used to create a custom healing stent to fit connected implant abutments without the need for a definitive abutment impression. After segmentation of the dental implants and importation into a computer-aided design software program, the appropriate digital implant componentry was aligned to the dental implants. The healing stent was then virtually designed, rapid prototyped, and then converted into a biocompatible and sterilizable material by using conventional laboratory methods. The methods presented offer clinicians the opportunity to insert a healing stent at second stage implant surgery with no need to create a stent or obtain an impression during the procedure.

The management of head and neck cancer involves surgery, radiotherapy, and/or chemotherapy. The surgical continuum involves resection, reconstruction, and rehabilitation. Advances in innovative techniques have provided advanced jaw reconstructive techniques which allow for nearly all surgical procedures to be carried out at the primary cancer surgery. This includes the introduction of the Alberta reconstructive technique (ART), , involving 2 stages: stage I—resection and reconstruction with a prefabricated fibula along with primary implant installation and stage II—implant exposure and abutment connection.

A stent refers to any device or mold used to hold a skin graft in place. Healing stents retained by implants rely on the use of either interim cylinders and intraoperative fabrication and bonding with photopolymerized materials or fabrication after obtaining a definitive impression. The challenges with intraoperative fabrication of a stent include exposure to free monomers and the heat from polymerization, as well as the need to ensure a sterile surgical field. When ART is being performed, the definitive fibula and implant positions are not complete until the definitive plating; therefore, the stent cannot be created until after the second stage surgery.

This technical report describes the use of digital technologies and additive manufacturing to make a patient-specific, abutment-fitting healing stent for stage II implant surgery as part of ART. The methods presented offer clinicians the opportunity to insert a healing stent at second stage implant surgery with no need for intraoperative creation of the stent. The described technique has been used routinely at the Institute for Reconstructive Sciences in Medicine during the implant exposure and abutment connection during stage II surgery for patients treated with the ART procedure.


Technique

  • 1.

    Use the postoperative computed tomography (CT) scan, routinely ordered for postoperative surgical surveillance and assessment and used after clinical evaluation for this technique.

  • 2.

    Import the Digital Imaging and Communications in Medicine data set into a segmentation program (Mimics; Materialise).

  • 3.

    Segment the data to isolate the installed implants ( Fig. 1 ).

    Segmented implants.
    Figure 1
    Segmented implants.
  • 4.

    Import a proprietary computer-aided design (CAD) file of the selected implant dimension (Trinex; Southern Implants) of the same width and length of each identified installed implant ( Fig. 2 ).

    Imported proprietary computer-aided design file of selected implant.
    Figure 2
    Imported proprietary computer-aided design file of selected implant.
  • 5.

    By using visual alignment, obtain the best fit between the CAD-generated implant to the installed implant ( Fig. 3 ). Repeat the process for each installed implant ( Fig. 4 ).

    Alignment of computer-aided design implant to segmented implant.
    Figure 3
    Alignment of computer-aided design implant to segmented implant.

    All computer-aided design implants aligned to segmented implants.
    Figure 4
    All computer-aided design implants aligned to segmented implants.
  • 6.

    Once the CAD generated implants have been aligned to the installed implants, export and save this design data as a standard tessellation language (STL) file.

  • 7.

    Into a CAD Program (Magics; Materialise), import a proprietary CAD file of a 5.00-mm (height) implant abutment ( Fig. 5 , Blue ) (Trinex; Southern Implants) and the Rohner Technique (RT) prosthetic screw ( Fig. 5 , Green ) (S-PROS-RT, FIRST System; Southern Implants). Proprietary CAD files provided by Southern Implants.

    Proprietary computer-aided design files of: Selected implant ( red ), 5.00-mm (height) implant abutment ( blue ), RT prosthetic screw ( green ), rescaled Rohner Technique (RT) prosthetic screw ( gray ), stacked image, merger of stacked IAR ( purple ). IAR, implant-abutment-rescaled RT prosthetic screw.
    Figure 5
    Proprietary computer-aided design files of: Selected implant (
    red ), 5.00-mm (height) implant abutment (
    blue ), RT prosthetic screw (
    green ), rescaled Rohner Technique (RT) prosthetic screw (
    gray ), stacked image, merger of stacked IAR (
    purple ). IAR, implant-abutment-rescaled RT prosthetic screw.
  • 8.

    Virtually rescale the RT prosthetic screw to increase the diameter of the head and shaft of the screw by 2.2 mm ( Fig. 5 , Gray ).

  • 9.

    Align the selected implant ( Fig. 5 , Red ), dental implant abutment ( Fig. 5 , Blue ), and the rescaled RT prosthetic screw ( Fig. 5 , Gray ) and stack it above the dental implant ( Fig. 5 , stacked image ). Repeat this for each dental implant location.

  • 10.

    Merge the stacked implant-abutment-rescaled RT screw (IAR) into 1 CAD file and export and save it as an STL file ( Fig. 5 , Purple ).

  • 11.

    Import the merged IAR STL file into CAD clay program (Geomagic Freeform Plus; 3D Systems) ( Fig. 6 , top ).

    Merged implant-abutment-rescaled RT screw (IAR) STL file ( top ). Initial design of healing stent ( middle ). Finalized design of healing stent flasking prototype ( bottom ). IAR, implant-abutment-rescaled; RT, Rohner Technique; STL, standard tessellation language.
    Figure 6
    Merged implant-abutment-rescaled RT screw (IAR) STL file (
    top ). Initial design of healing stent (
    middle ). Finalized design of healing stent flasking prototype (
    bottom ). IAR, implant-abutment-rescaled; RT, Rohner Technique; STL, standard tessellation language.
  • 12.

    Create a digital shape of the healing stent to encompass the length and width of the span of the implants. Design the healing stent to be ovate in shape to facilitate hygiene and comfort. The healing stent is not tissue-supported and therefore should only come to the level of the implant abutment interface ( Fig. 6 , middle ).

  • 13.

    Subtract the IAR assembly from the virtually designed digital healing stent ( Fig. 6 , bottom ). The resulting design is the healing stent flasking prototype.

  • 14.

    Save and export the healing stent as an STL file.

  • 15.

    Import the healing stent flasking prototype into a CAD program (Magics; Materialise) and verify the digital file is appropriate to be additively manufactured. Use the automatic file repair as needed.

  • 16.

    Save and export the healing stent flasking prototype as an STL file.

  • 17.

    Send the healing stent flasking prototype STL file to a 3D printer (Objet VeroWhitePlus material, Objet260 Connex3D printer; Stratasys Ltd) and additive manufacture ( Fig. 7 , top ).

    Healing stent flasking prototype in printed material ( left ); Polymerized and polished polymethyl methacrylate healing stent ( right ).
    Figure 7
    Healing stent flasking prototype in printed material (
    left ); Polymerized and polished polymethyl methacrylate healing stent (
    right ).
  • 18.

    Postprocess the printed healing stent flasking prototype according to manufacturers’ instructions (Objet VeroWhitePlus material, Objet260 Connex3D printer; Stratasys Ltd).

  • 19.

    Invest the healing stent flasking prototype in dental stone (COECAL Dental Stone; GC America) (SR Ivocap Injection System; Ivoclar Vivadent AG).

  • 20.

    Polymerize conventionally in heat-polymerizing polymethylmethacrylate (Clear SR Ivocap; Ivoclar Vivadent AG).

  • 21.

    Divest the processed healing stent, fit componentry (abutment and RT prosthetic screw; Southern Implants) into the stent to ensure reasonable fit. Trim and polish conventionally ( Fig. 7 , bottom ).

  • 22.

    Deliver the healing stent during Stage II implant surgery ( Fig. 8 ).

    Healing stent delivered during stage II implant surgery.
    Figure 8
    Healing stent delivered during stage II implant surgery.

Discussion

A healing stent can assist with the control of tissue growth around abutments during the healing phase after second stage implant surgery. Traditionally, an impression of the implant-to-abutment interface is required to fabricate a conventional healing stent. The procedure described elaborates the digital creation of the healing stent for the second stage surgery. The benefit of this method is being able to eliminate the need for intraoperative bonding or capturing a definitive abutment impression. Errors in segmentation, alignment, and polymerization could result in difficulty seating the healing stent. The number of manual steps and visual alignment could also result in errors, as the alignment of the CAD components to the CT scan is only as accurate as a single pixel viewed by eye because of limitations in automatic registration functionality.

The described procedure can only be used when postoperative scan data are available. The CT data used in this technique are routinely ordered for postoperative surgical surveillance and assessment and were used after clinical evaluation for this technique. Ordering additional scans to complete this technique would require clinical justification.

The 2.2-mm rescaling of the RT screw not only allows a degree of margin of error in positioning and aligning the healing stent to the abutments but also prevents the 4.3-mm abutments from sliding through the created access channel of 3.6 mm. The freedom described allows for any possible alignment error and reduces the need for operative adjustments through a process of loosening or tightening the RT prosthetic screws to achieve a fit. Thus far the team at the Institute for Reconstructive Sciences in Medicine has not had problems with gross alignment misfit or issues with differences in CT scan data to fitting. Currently, directly printing the definitive healing stent is not possible because of material validation and sterilization issues in the provincial health system. The steps in the described process could be significantly reduced if a complete digital workflow with the addition of an oral scanner with corresponding scan flags and additive manufacturing of the definitive device were available.


Summary

The described technique eliminates the need to have a definitive implant impression and the need to create the stent intraoperatively. The fabrication process by using imaging, digital manipulation, and traditional methods allows for the design of a tissue stent which is retained well on the implants, prevents tissue overgrowth, and is contoured for oral hygiene.

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