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    Inside Dental Technology

    January 2014, Volume 5, Issue 1
    Published by AEGIS Communications


    Indirect Conversion Technique

    Implant therapy that can be individualized for each patient

    Robert Kreyer, CDT
    William Perry, DDS

    Implant prosthetics is a rapidly growing segment of modern prosthetic dentistry.

    The demand for implant placement in edentulous patients is driven by their awareness of complete denture treatment options through media and Internet marketing. In the coming years, there is likely to be an evolution of prosthetic implant treatment options, so the practitioner should always consider what is best for the individual compromised edentulous patient.

    This article presents an indirect conversion technique for immediate loading of a complete implant-supported provisional. This technique is not revolutionary, but it provides the clinician and technician with a flexible implant treatment option that can accommodate an individual patient’s prosthetic factors and variables.

    Implant Prosthetic Case Planning

    As with any implant prosthetic case, a successful outcome depends on the clinical and technical time invested in diagnostic planning from the beginning of the case. Understanding a prosthetic patient’s esthetic expectations and functional desires is a critical part of developing a case plan. Evaluating existing restorative space with mounted casts on a dental articulator is an essential part of the implant design process and case planning. Once these implant prosthetic variables are communicated, a diagnostic denture is created within established restorative space.

    Diagnostic Denture

    During diagnostic planning procedures, a traditional complete denture is designed and created according to the patient’s esthetic expectations and established restorative space. This diagnostic denture allows the clinician and technician to evaluate the restorative space and function of the proposed implant prosthetic treatment as a team. The diagnostic denture can also be converted to a radiographic stent for CBCT scans. Using these scans, one can plan the intraoral position of the guide pin, thus providing a reference point for vertical dimension and screw access in relation to tooth placement (Figure 1). The problem with using an existing or old denture for case planning and scanning concerns residual ridge resorption, the result of which is that denture teeth are not in their optimal position. The ideal prosthetic tooth position is in line with the vector forces of occlusion to the long axis of implant body. The best way to plan for implant placement and functional occlusion is through the use of a diagnostic denture on a semi-adjustable articulator. The waxed denture tooth arrangement is then processed, finished, and polished to include all of the hard edentulous anatomy that will provide support to the complete denture prosthesis.

    Direct Implant Conversion

    With the demand for implant-supported prosthetics rapidly increasing, it is necessary to examine the techniques currently being used and re-evaluate their efficiency and predictability.

    The direct conversion technique for immediate loading of implants has been used widely for converting mucosal-supported dentures to implant-supported ones. The direct conversion of a complete denture provisional prosthesis can be very time consuming clinically. It is also difficult to maintain established records such as the vertical and centric plus midline esthetic relationship. The direct conversion technique is usually performed either in the operatory of the surgeon or that of a restorative dentist by a clinician and technician. Such a conversion could tie up chairtime for most of the day, costing the clinician in lost time and labor. A positive benefit of direct implant conversion for patients is that they leave after surgery with a provisional restoration.

    Indirect Implant Conversion

    The indirect conversion technique presented in this article offers a predictable prosthetic option that places the conversion back in the dental laboratory and provides the clinician and patient with optimal restorative implant results. The technique also maintains established occlusion of vertical dimension (OVD) and centric relation records. Since the diameter of the holes for cylinders is minimal, the strength of the provisional is not compromised.

    Using the indirect conversion technique, implants are placed in a single day. The patient then goes home and comes back to the clinician’s office the next day, when the converted provisional is delivered and fitted.

    After implant placement, an intraoral verification jig is made with a resin or composite bar 2 mm above the mucosal surface. For accurate transfer to the articulator, occlusal records are taken over the jig for mounting (Figure 2, Figure 3 and Figure 4). A 2 mm layer of VPS impression material is then extruded onto the intaglio surface to provide space for acrylic resin. Gypsum stone is then mixed, and a verification master cast base is created for conversion of the mandibular complete denture (Figure 5, Figure 6 and Figure 7).

    The verification cast is then articulated to the mounted maxillary cast with the occlusal record (Figure 8). The verification cast intaglio surface is then analyzed as compared to the complete mandibular denture and the amount of gingival denture base that needs to be cut back is visualized (Figure 9 and Figure 10).

    The vertical dimension record is then verified with the guide pin relationship (Figure 11 and Figure 12). The crest of the residual ridge is marked on the intaglio of the denture base to gauge gingival cut-back (Figure 13, Figure 14 and Figure 15). The denture is attached to the maxillary, and the intaglio is relieved according to markings on the VPS surface (Figure 16 and Figure 17). After the intaglio surface is relieved, the OVD is verified by maintaining incisal pin contact (Figure 18).

    A hard VPS matrix is made for the denture by extruding heavy-body material around the labial, buccal, and lingual surfaces for relining of the intaglio surface (Figure 19, Figure 20 and Figure 21).

    Guide pins are then screwed into implant model analogs, allowing the denture to line up to the milling machine when drilling screw access holes (Figure 22, Figure 23 and Figure 24).

    Temporary cylinders are then measured, cut, and screwed into place according to the guide pin paths and relieved denture base surface (Figure 25 and Figure 26).

    The cut-back denture is then placed over the cylinders and into the matrix with guide pins screwed into place (Figure 27 and Figure 28) The denture is now relined, and the technician may attach temporary cylinders and create a convex intaglio surface (Figure 29 and Figure 31). Finally, the provisional implant-supported prosthesis is finished, polished, and delivered to the patient. (Figure 32 and Figure 33).

    Summary

    There are many modifications of the direct and indirect conversion techniques that include capturing implant placement with a quick impression, creating a fast master cast, and doing the conversion on a cast or in the mouth. A clinician or technician may choose a combination of both techniques, allowing most of the conversion to be done out of the intraoral environment. The trick is to select the best conversion technique based on the clinical implant restorative plan and the patient’s expectations and desires.

    About the authors

    Robert Kreyer, CDT
    Partner
    Custom Dental Prosthetics Inc.
    Los Gatos, CA

    William Perry, DDS
    Owner
    Private Practice
    Los Gatos, CA


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    Image Gallery

    Using digital guided planning, the implant is placed in relation to tooth with the vertical guide pin serving as a reference for vertical dimension and screw access.

    Fig 1.

    After implants are placed, the resin jig is bonded together and an intra-oral registration is taken to record the OVD and centric relation.

    Fig 2.

    The resin jig is removed from mouth, model analogs are screwed into temporary cylinders, and a 2 mm layer of VPS is injected onto the intaglio surface.

    Fig 3.

    Intaglio view of VPS and model analogs. The 2 mm thickness allows for space under the resin jig.

    Fig 4.

    The VPS occlusal registration record.

    Fig 5.

    A model base is poured of the intaglio surface and analogs as a master cast and verification jig.

    Fig 6.

    The occlusal record is place on a resin jig after indexing base.

    Fig 7.

    The mandibular based jig is now mounted to maxillary facebow mount with dental plaster.

    Fig 8.

    After mounting is completed, the occlusal record and resin jig with VPS intaglio is removed.

    Fig 9.

    The mounted implant-based master cast is shown with the complete mandibular denture, which will be converted to an implant-supported provisional.

    Fig 10.

    A guide pin is screwed into an implant analog showing angulations of access holes.

    Fig 11.

    The guide pin verifies OVD.

    Fig 12.

    Complete denture flanges are cut back. Note that the black line on the intaglio surface is the crest of the ridge used as a guide to remove acrylic.

    Fig 13.

    Lingual view of cut-back of flanges.

    Fig 14.

    The mandibular complete prosthesis is mounted with the bite record to a maxillary cast for adjustment of the intaglio surface against the yellow 2 mm VPS spacer that was under the jig.

    Fig 15.

    The VPS ridge spacer is marked with red articulating paper as the prosthesis is closed down.

    Fig 16.

    Red markings indicate where the intaglio surface should be relieved before final reline processing.

    Fig 17.

    After the intaglio surface is adjusted, a space is shown where the surface will be relined.

    Fig 18.

    Hard bite registration is extruded around the periphery of cut-back prosthesis to act as a labial, lingual, and buccal matrix during the reline procedure.

    Fig 19.

    The prosthesis surrounded by hard VPS bite registration material.

    Fig 20.

    The prosthesis is removed, showing the yellow VPS material that the denture will be converted against during the reline.

    Fig 21.

    A milling machine is lined up with each guide pin, and screw access holes are drilled according to individual angulations of the implant.

    Fig 22.

    Guide pin in position and drill bit lined up with implant analog.

    Fig 23.

    The prosthesis is then placed back on the implant master cast, and access holes are drilled.

    Fig 24

    Temporary cylinders are screwed into implant model analogs and cut accordingly.

    Fig 25.

    Cut temporary cylinders in place for rebase of provisional prosthesis.

    Fig 26.

    The complete prosthesis is placed over cylinders with screw access holes visible.

    Fig 27.

    Guide pin screws are screwed into cylinders through access holes.

    Fig 28.

    The provisional prosthesis is removed, leaving guide pins in cylinders, and cold-curing resin is placed into the VPS cast for rebase of the intaglio and attachment of cylinders.

    Fig 29.

    The provisional prosthesis with master cast is removed from the reline jig after curing.

    Fig 30.

    The rebased provisional is now ready for final finishing and polishing.

    Fig 31.

    The converted provisional implant prosthesis is placed back on the master cast for verification.

    Fig 32.

    The implant-supported converted provisional hybrid is delivered to the patient. Since all verification of cylinders to analogs and occlusion was done in the lab, delivery takes very little clinical chairtime.

    Fig 33.