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Journal of Prosthetic Dentistry

Using an existing denture to design a radiographic template for a two-implant mandibular overdenture

      This article describes a technique for modifying an existing mandibular complete denture for use as a radiographic template with a radiopaque light-activated calcium hydroxide (Ca(OH)2) preparation. This allows prosthetically driven treatment planning and the surgical placement of 2 implants to support the existing mandibular denture.
      The 2002 McGill consensus statement on overdentures suggested that a 2-implant–supported overdenture may represent the minimum standard of care for the treatment of patients with a completely edentulous mandible.
      • Feine JS
      • Carlsson GE
      • Awad MA
      • Chehade A
      • Duncan WJ
      • Gizani S
      • et al.
      The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients.
      Similarly, in 2009, the British Society for the Study of Prosthetic Dentistry (BSSPD) and a panel of experts in the prosthetic rehabilitation of completely edentulous patients reiterated this finding (York consensus).
      • Thomason JM
      • Feine J
      • Exley C
      • Moynihan P
      • Müller F
      • Naert I
      • et al.
      Mandibular two implant-supported overdentures as the first choice standard of care for edentulous patients–the York Consensus Statement.
      In a recent review of the literature supporting both the McGill and York consensus statements, the 2-implant overdenture was held to represent a cost-effective treatment.
      • Thomason JM
      • Kelly SA
      • Bendkowski A
      • Ellis JS
      Two implant retained overdentures–a review of the literature supporting the McGill and York consensus statements.
      Accurate diagnosis and implant placement are dependent on radiographic templates.
      • Engelman MJ
      • Sorensen JA
      • Moy P
      Optimum placement of osseointegrated implants.
      • Misch CE
      • Crawford EA
      Predictable mandibular nerve location–a clinical zone of safety.
      Traditional radiographs such as panoramic and periapical films were found to be of limited diagnostic value owing to their 2-dimensional nature.
      • White SC
      • Heslop EW
      • Hollender LG
      • Mosier KM
      • Ruprecht A
      • Shrout MK
      • et al.
      Parameters of radiologic care: An official report of the American Academy of Oral and Maxillofacial Radiology.
      The development of computed tomography (CT) assessments enabled cross-sectional views of the recipient sites for implant placement. However, they are expensive and deliver a relatively high radiation dose to the patient.
      • Guerrero ME
      • Jacobs R
      • Loubele M
      • Schutyser F
      • Suetens P
      • van Steenberghe D
      State-of-the-art on cone beam CT imaging for preoperative planning of implant placement.
      More recently, cone beam computed tomography (CBCT) has allowed the capture of cross-sectional images at lower radiation doses. Moreover, when compared to conventional CT, CBCT produces superior images of bony structures.
      • Guerrero ME
      • Jacobs R
      • Loubele M
      • Schutyser F
      • Suetens P
      • van Steenberghe D
      State-of-the-art on cone beam CT imaging for preoperative planning of implant placement.
      • Monsour PA
      • Dudhia R
      Implant radiography and radiology.
      Numerous detailed designs for radiographic templates that address the radiographic approaches used in diagnosis and treatment planning for dental implants have been published.
      • Engelman MJ
      • Sorensen JA
      • Moy P
      Optimum placement of osseointegrated implants.
      • Basten CH
      • Kois JC
      The use of barium sulfate for implant templates.
      • Pesun IJ
      • Gardner FM
      Fabrication of a guide for radiographic evaluation and surgical placement of implants.
      • Fondriest JF
      • McClenahan DC
      Fabricating radiographic stents in implant treatment planning.
      Although varied in type and materials used, the ultimate aim of each of these designs is to enhance the collection of accurate and precise records of the operative site(s). Traditionally, treatment planning for mandibular overdentures has involved the laboratory fabrication of a clear acrylic resin replica of the denture incorporating barium salts,
      • Basten CH
      • Kois JC
      The use of barium sulfate for implant templates.
      gutta percha,
      • Pesun IJ
      • Gardner FM
      Fabrication of a guide for radiographic evaluation and surgical placement of implants.
      or metal bearings
      • Engelman MJ
      • Sorensen JA
      • Moy P
      Optimum placement of osseointegrated implants.
      located at the proposed sites for implant placement.
      • Fondriest JF
      • McClenahan DC
      Fabricating radiographic stents in implant treatment planning.
      However, this approach involves a considerable expenditure of time and money.

      Technique

      Radiographic template fabrication

      1. Ensure that the existing mandibular denture can be seated comfortably on the alveolar ridge and is in occlusal harmony with the maxillary denture and seated in maximum intercuspation (MI).
      2. Immediately before CBCT assessment, extrude a 2-mm wide vertical ribbon of radiopaque, light-activated, calcium hydroxide liner (Ultra-Blend Plus; Ultradent Products, Inc, South Jordan, Utah) onto the facial and lingual cameo surfaces. Extend the ribbon in the same vertical plane onto the intaglio surface in a line that coincides with the distal line angle of the mandibular canine (Fig. 1). Document the location of the marking on the denture to allow for the transfer of this location during the surgical procedure.
      Figure thumbnail gr1
      Fig. 1Application of radiopaque reference marks at distal line angle of canines.
      3. Light activate the liner with an appropriate light-emitting diode (LED) light according to the manufacturer's instructions (Fig. 2). Following the CBCT acquisition, mechanically remove the light-activated Ca(OH)2 ribbon from all surfaces where applied by using a scaler or other hand instrument.
      Figure thumbnail gr2
      Fig. 2Prosthesis with reference markings on cameo and intaglio surfaces of prosthesis.

      Diagnostic planning

      • 1.
        Review the acquired CBCT record by using a 3-dimensional viewer (Planmeca Romexis Viewer, v2.3.0.R; Planmeca Oy, Helsinki, Finland) to make a thorough assessment before implant placement.
      • 2.
        Orient the image so that the vertical plane is perpendicular to the axis of the ridge for optimal accuracy when measuring available bone dimensions for implant placement. For treatment planning purposes, move the cross-sectional slices in 3 different planes (sagittal, vertical, and horizontal) as follows: Displace the sagittal and vertical planes on the viewer so that they intersect at the site of the prospective implant, which coincides with the radiopaque marking of the Ca(OH)2 ribbon. Place the horizontal plane at the level of the mental foramen to evaluate the distance between the prospective implant site and the mental foramen (Fig. 3).
        Figure thumbnail gr3
        Fig. 3Screenshot from 3D-viewer with slices oriented to plan implant placement at distal site of mandibular right canine.
      • 3.
        On the vertical cross-section, determine the available bone height and width as well as the restorative space, which is represented by the distance between the crest of the residual ridge and the most coronal Ca(OH)2 radiopaque marking (Fig. 4).
        Figure thumbnail gr4
        Fig. 4Presurgical determinations, including available bone width (6.0 mm) and length (14.0 mm). Distance from crest of alveolar bone to most coronal point of radiopaque marking represents restorative space available (8.4 mm).
      • 4.
        Determine the buccolingual angulation of the implant bed in relation to the alveolar contour. Based on this information, determine how much crestal alveolar bone reduction is necessary to accommodate the minimal restorative space needed for the prosthetic rehabilitation. For example, note that a Straumann Tissue Level Standard Plus Implant (Institut Straumann AG, Basel, Switzerland) with a Locator (Zest Anchors Inc, Escondido, Calif) attachment incorporated in a mandibular overdenture requires a minimum of 7.3 to 8.3 mm (1.8 mm of smooth implant collar, 1 mm for the soft tissue collar built into the Locator abutment, 2.5 mm height of denture cap which includes the patrix Locator attachment, and 2 to 3 mm of acrylic resin).
      • 5.
        Finally, by using the shape of the alveolar ridge as a reference, determine the appropriate angle of the implant bed preparation in the buccolingual dimension. As an example, note that Figure 4 illustrates that the axis of the implant bed will be parallel to the lingual cortical bone.
      • 6.
        If needed, displace the site of the implant osteotomy based on the anatomy observed on the CBCT record, and then measure this displacement in relation to the radiopaque reference marking.

      Surgical procedure

      • 1.
        Use the patient's mandibular denture to transfer the location of the radiopaque markings (distal line angles of the canine) used during the CBCT acquisition. Mark these sites in the intaglio of the mandibular denture with a color transfer applicator (Dr Thompson's Color Transfer Applicators; Great Plains Dental Products Co Inc, Kingman, Kans) (Fig. 5).
        Figure thumbnail gr5
        Fig. 5Sites of previous radiopaque markings transferred to intaglio with color transfer applicator.
      • 2.
        Reposition the denture intraorally with slight pressure to impress the mucosa with the reference point markings from the prosthesis intaglio (Fig. 6).
        Figure thumbnail gr6
        Fig. 6Radiopaque reference markings transferred to patient's alveolar mucosa.
      • 3.
        Incise the mucosa and slightly elevate a mucoperiosteal flap to mark the alveolar crest with a small round bur at the sites where the mucosa has been impressed. Alternatively, if the site has been displaced during the CBCT-based treatment planning, mark the alveolar crest at the desired distance, taking the color marking on the mucosa as a reference point (Fig. 7).
        Figure thumbnail gr7
        Fig. 7Implant site (at distal site of mandibular left canine) marked by using round bur. Note that implant site was determined to be 8 mm distal to radiopaque marking based on CBCT record.
      • 4.
        Elevate a full thickness flap before proceeding with alveoloplasty, implant bed preparation, and placement according to the predetermined length, diameter, and angulation (Fig. 8).
      Note that the depth gauge and/or direction indicator placed in the implant bed and positioned toward the palatal cusp or cingulum of the opposing natural or prosthetic tooth ensures correct restoratively driven implant placement.

      Summary

      The goal of placing radiographic markers with the aid of cone-beam computed tomography is to provide accurate and reliable information when planning dental implants. This article describes a rapid diagnostic technique for template preparation using a patient's existing denture, onto which a light-activated radiopaque compound is temporarily placed. The diagnostic information is then transferred intraorally prior to surgery.
      The technique avoids the additional cost and treatment time related to the fabrication of a radiographic/surgical template by using a duplicate of the patient's denture. All diagnosis components are obtained with the patient's denture. One limitation is that this method does not guide the surgeon in a restrictive way during the osteotomy, thereby allowing implant misplacement if the surgeon does not control the osteotomy in relation to the existing prosthesis and opposing dentition.

      Acknowledgments

      The development of this report was supported by NIH/NIDCR grant R01 DE017882 .

      References

        • Feine JS
        • Carlsson GE
        • Awad MA
        • Chehade A
        • Duncan WJ
        • Gizani S
        • et al.
        The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients.
        Gerodontology. 2002; 19: 3-4
        • Thomason JM
        • Feine J
        • Exley C
        • Moynihan P
        • Müller F
        • Naert I
        • et al.
        Mandibular two implant-supported overdentures as the first choice standard of care for edentulous patients–the York Consensus Statement.
        Br Dent J. 2009; 207: 185-186
        • Thomason JM
        • Kelly SA
        • Bendkowski A
        • Ellis JS
        Two implant retained overdentures–a review of the literature supporting the McGill and York consensus statements.
        J Dent. 2012; 40: 22-34
        • Engelman MJ
        • Sorensen JA
        • Moy P
        Optimum placement of osseointegrated implants.
        J Prosthet Dent. 1988; 59: 467-473
        • Misch CE
        • Crawford EA
        Predictable mandibular nerve location–a clinical zone of safety.
        Int J Oral Implantol. 1990; 7: 37-40
        • White SC
        • Heslop EW
        • Hollender LG
        • Mosier KM
        • Ruprecht A
        • Shrout MK
        • et al.
        Parameters of radiologic care: An official report of the American Academy of Oral and Maxillofacial Radiology.
        Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2001; 91: 498-511
        • Guerrero ME
        • Jacobs R
        • Loubele M
        • Schutyser F
        • Suetens P
        • van Steenberghe D
        State-of-the-art on cone beam CT imaging for preoperative planning of implant placement.
        Clin Oral Investig. 2006; 10: 1-7
        • Monsour PA
        • Dudhia R
        Implant radiography and radiology.
        Aust Dent J. 2008; 53: S11-S25
        • Basten CH
        • Kois JC
        The use of barium sulfate for implant templates.
        J Prosthet Dent. 1996; 76: 451-454
        • Pesun IJ
        • Gardner FM
        Fabrication of a guide for radiographic evaluation and surgical placement of implants.
        J Prosthet Dent. 1995; 73: 548-552
        • Fondriest JF
        • McClenahan DC
        Fabricating radiographic stents in implant treatment planning.
        CDS Rev. 1997; 90: 40-43