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Journal of Prosthetic Dentistry

Management of unfavorable implant positions and angulations in edentulous maxillae with different complete-arch fixed prosthetic designs: A case series and clinical guidelines

Published:November 24, 2020DOI:https://doi.org/10.1016/j.prosdent.2020.09.023

      Abstract

      Implant-supported fixed prostheses in the edentulous maxilla can be difficult because of anatomic limitations and high esthetic demand. The choice between cement and screw retention depends on factors such as esthetics, occlusion, retrievability, and passivity. The choice is also often governed by the ability to manage technical or biologic complications. In the edentulous maxilla, because of the bone trajectory and resorption pattern, unfavorable implant angulations may be encountered. In such situations, a conventional screw-retained prosthesis is difficult to design. This article describes the restoration of edentulous maxillae for a series of patients with different complete-arch fixed prosthesis designs. The clinical guidelines, including indications, advantages, and limitations of each design, were discussed.
      Implant-supported fixed prostheses in the edentulous maxilla can be difficult from a surgical as well as a prosthetic perspective.
      • Abdunabi A.
      • Morris M.
      • Nader S.A.
      • Souza R.F.
      Impact of immediately loaded implant-supported maxillary full-arch dental prostheses: a systematic review.
      The maxilla also presents anatomic limitations such as the proximity to the nasal floor and pneumatization of the maxillary sinus.
      • Abdunabi A.
      • Morris M.
      • Nader S.A.
      • Souza R.F.
      Impact of immediately loaded implant-supported maxillary full-arch dental prostheses: a systematic review.
      ,
      • Esposito M.
      • Felice P.
      • Worthington H.V.
      Interventions for replacing missing teeth: augmentation procedures of the maxillary sinus.
      The centripetal resorption pattern and bone configuration may lead to unfavorable implant angulations, and high esthetic demand makes treatment complex and technique sensitive. Maxillary edentulism may be treated successfully by using different approaches involving 4, 6, or more implants.
      • Gallucci G.O.
      • Avrampou M.
      • Taylor J.C.
      • Elpers J.
      • Thalji G.
      • Cooper L.F.
      Maxillary implant-supported fixed prosthesis: a survey of reviews and key variables for treatment planning.
      The procedural diagnostics, treatment, and maintenance for these different approaches all require advanced knowledge and careful communication among the therapeutic team.
      • Gallucci G.O.
      • Avrampou M.
      • Taylor J.C.
      • Elpers J.
      • Thalji G.
      • Cooper L.F.
      Maxillary implant-supported fixed prosthesis: a survey of reviews and key variables for treatment planning.
      While fixed prostheses can be cement or screw retained,
      • Jivraj S.
      Screw versus cemented implant restorations: the decision- making process.
      retrievable implant-supported fixed dental prostheses are preferred whenever feasible, as a retrievable screw-retained design facilitates the maintenance and management of technical problems and is preferable from a biologic perspective.
      • Sailer I.
      • Mu S.
      • Zwahlen M.
      • Hammerle C.H.F.
      • Schneider D.
      Cemented and screw-retained implant reconstructions: a systematic review of the survival and complication rates.
      For the fabrication of a screw-retained prosthesis, the implant angulations must be such that the access holes emerge through the occlusal surfaces of the posterior teeth and the lingual fossa of the anterior teeth. A cement-retained prosthesis design can be chosen when the access holes emerge labially or through the incisal edges of the anterior teeth. However, the cement-retained design makes retrievability for maintenance and intervention difficult. Moreover, residual excess cement has been reported to be a primary cause of peri-implant disease.
      • Staubli N.
      • Walter C.
      • Schmidt J.C.
      • Weiger R.
      • Zitzmann N.U.
      Excess cement and the risk of peri-implant disease - a systematic review.
      ,
      • Papavasileiou D.
      • Behr M.
      • Gosau M.
      • Gerlach T.
      • Buergers R.
      Peri-implant biofilm formation on luting agents used for cementing implant-supported fixed restorations: a preliminary in vivo study.
      The available vertical restorative space governs the selection of the implant prosthesis.
      • Tunkiwala A.
      • Kher U.
      • Bijlani P.
      Numerical guidelines for selection of implant supported prostheses for completely edentulous patients.
      When the implant angulations are unfavorable and there has been extensive bone resorption, it has been a common practice to use a metal framework along with the acrylic resin and the denture teeth.
      • Tunkiwala A.
      • Kher U.
      • Bijlani P.
      Numerical guidelines for selection of implant supported prostheses for completely edentulous patients.
      However, this type of prosthesis requires frequent repairs and maintenance.
      • Dario L.
      • Aschaffenburg P.
      • English R.J.
      • Nager M.
      Fixed implant rehabilitation of the edentulous maxilla: clinical guidelines and case reports. Part I.
      Figure 1 illustrates such a prosthesis where the implant angulations were such that the access holes emerged labially. Composite resin was used to seal the access holes. However, the seal discolored over time, and the esthetics were compromised. Therefore, although this prosthesis design is common, it is not recommended.
      • Kwon T.
      • Bain P.A.
      • Levin L.
      Systematic review of short- (5–10 years) and long-term (10 years or more) survival and success of full-arch fixed dental hybrid prostheses and supporting implants.
      This article presents clinical scenarios encountered with unfavorable implant angulations in the edentulous maxilla and describes fixed prosthetic design options.
      Figure thumbnail gr1
      Figure 1Unfavorable screw access holes in fixed metal-supported acrylic resin prosthesis.

      Clinical report

      This clinical report describes 5 patients with unfavorable implant trajectories in the maxillary arch who were treated with fixed implant-supported complete-arch prostheses by using different prosthetic abutment designs.
      Patient 1 was treated by using angled or custom abutments with a cement-retained prosthesis. A 67-year-old healthy woman reported with multiple missing teeth and multiple carious teeth (Fig. 2A, 2B ). All teeth were extracted, and 7 implants (Tapered Internal; BioHorizons) were placed on the same day. A removable denture was delivered on the day of surgery as an interim restoration. After 6 months of osseointegration, cement-retained angled abutments (BioHorizons) were placed on the anterior 4 implants, and straight abutments were placed on the posterior 3 implants (Fig. 2C). The prosthesis was cemented with elastomeric resin cement (Premier Implant Cement; Premier Dental Co) (Fig. 2D, 2E). Post-treatment periapical radiographs indicated proper fit of the abutment with no residual cement in the gingival sulcus (Fig. 2F). The mandibular arch was treated with a cast partial denture with acrylic resin denture teeth to restore the severely resorbed residual ridge in the bilateral posterior region. Excess cement in the sulcus can be avoided if custom abutments are used with buccal restorative margins at not more than 0.5 mm subgingivally and with supragingival palatal and proximal margins.
      • Pette G.A.
      • Ganeles J.
      • Norkin F.J.
      Radiographic appearance of commonly used cements in implant dentistry.
      Additionally, radiopaque cements are recommended.
      • Nematollahi F.
      • Beyabanaki E.
      • Alikhasi M.
      Cement selection for cement-retained implant-supported prostheses: a literature review.
      Figure thumbnail gr2
      Figure 2A, Pretreatment view of patient 1. B, Pretreatment cone beam computed tomograph. C, Angled abutments for cement-retained prosthesis. D, Cement-retained definitive prosthesis. Note convex tissue surface to facilitate cleaning. E, Post-treatment view indicating definitive metal-ceramic prosthesis in place. F, Post-treatment periapical radiographs.
      Patient 2 was treated with a screw-retained prosthesis with angled screw hole abutments. A 55-year-old healthy man presented with multiple missing maxillary posterior teeth and a worn anterior dentition (Fig. 3A, 3B ). Intraoral examination revealed a maxillary partially edentulous arch with 6 anterior teeth remaining. All remaining teeth were nonrestorable and were extracted. Six implants (Tapered Internal; BioHorizons) were placed immediately after extraction (4 in anterior region and 2 in posterior region). A complete denture was delivered as an interim restoration during the healing period. A screw-retained metal-ceramic definitive prosthesis was fabricated (Fig. 3C, 3D). Because the anterior implant trajectories were not favorable for a conventional screw-retained design, angulated screw access hole abutments were selected for the 4 anterior implants, and multiunit abutments were used for the 2 posterior implants (Fig. 3C, 3D). The angled screw hole abutments allowed angulation correction of 28 degrees (Dynamic abutments; Talladium International Implantology). This allowed the screw access hole to emerge lingually, providing an esthetic restoration (Fig. 3D, 3E). Post-treatment radiographs revealed a well-fitting complete-arch prosthesis (Fig. 3F). The mandibular arch was restored with an implant-supported metal-ceramic fixed dental prosthesis in the right posterior region and tooth-supported metal-ceramic crowns and fixed dental prostheses in the anterior and left posterior region. Dynamic abutments were considered ideal for situations where the interarch space was less than 15 mm.
      • Berroeta E.
      • Zabalegui I.
      • Donovan T.
      • Chee W.
      Dynamic abutment: a method of redirecting screw access for implant-supported restorations: technical details and a clinical report.
      ,
      • Gjelvold B.
      • Sohrabi M.M.
      • Chrcanovic B.R.
      Angled screw channel: an alternative to cemented single-implant restorations- three clinical examples.
      Figure thumbnail gr3
      Figure 3A, Pretreatment intraoral view of patient 2. B, Pretreatment cone beam computed tomograph. C, Tissue surface view of dynamic abutment in anterior region and multiunit abutment in posterior region. D, Occlusal view indicating dynamic abutments used in anterior region and multiunit abutments in posterior region. E, Frontal view indicating definitive prosthesis in place with no screw access hole on facial aspect. F, Post-treatment panoramic radiograph.
      Patient 3 was treated by using multiunit abutments. A 56-year-old man with advanced periodontitis (Fig. 4A, 4B ) required the extraction of all his remaining teeth. Six implants (Tapered Internal; BioHorizons) were placed in the maxillary arch (4 in anterior and 2 in posterior region). Angled multiunit abutments (Multi-unit abutment; BioHorizons) were used to correct the undesirable angulations in the anterior maxilla (Fig. 4C). A screw-retained fixed interim prosthesis was delivered after 6 months. The interim prosthesis was replaced with a definitive screw-retained prosthesis fabricated with a polyetheretherketone (PEEK) (BioHPP; bredent UK) framework and composite resin teeth (Fig. 4D, 4E). The post-treatment radiograph revealed a more radiolucent PEEK framework than the metal-ceramic prosthesis (Fig. 4F). The mandibular arch was also restored with a PEEK prosthetic framework. The multiunit abutments redirected the screw openings to the occlusal or cingulum areas of the prosthesis. The angled variant involves the use of 2 off-axis screws, one to fix the abutment to the implant and the second at an angle to secure the prosthesis to the abutment. However, to provide sufficient abutment structure to house the retention screw for the restoration, the long axis of the implant and path of the retention screw diverged significantly. The multiunit abutments raised the prosthesis platform from implant (or bone) level to abutment (supracrestal) level. The accuracy of the prosthesis fit was evaluated visually and from radiographs. Soft tissue impingement was minimized.
      Figure thumbnail gr4
      Figure 4A, Pretreatment intraoral view of patient 3. B, Pretreatment cone beam computed tomograph. C, Multiunit abutments tightened in position. D, Screw-retained definitive prosthesis. E, Frontal view indicating definitive prosthesis in place with no screw access hole on facial aspect. F, Post-treatment panoramic radiograph.
      Patient 4 was treated by using a screw-retained milled framework with cemented individual crowns.
      • Baig M.-R.
      • Rajan G.
      • Rajan M.
      Edentulous arch treatment with a CAD/CAM screw-retained framework and cemented crowns: a clinical case report.
      A healthy, 65-year-old woman presented with a failing and unrestorable maxillary dentition and the inability to masticate food (Fig. 5A, 5B ). All maxillary teeth were extracted and 7 implants (Nobel Biocare) were placed. After 6 months, the definitive impression was made with open tray impression copings and the definitive cast was mounted onto the articulator and assessed for the implant angulations (Fig. 5C). A milled interim restoration was fabricated and delivered at the second stage surgery and used as a template for the design the definitive prosthesis. The definitive prosthesis was fabricated as a milled titanium framework with individual struts that supported metal-ceramic crowns (Fig. 5D, 5E). The intact crowns (without vent holes) fabricated and cemented with an interim cement on the struts where the screw accesses emerge from the facial aspect (Fig. 5E). However, the crowns, on the struts having lingual or occlusal access, can be fabricated with corresponding vent holes to allow future abutment screw access. The gingival facial aspect was fabricated with resin, and the intaglio surface had titanium contacting the tissues (Fig. 5F). Post-treatment radiographs revealed a well-fitting prosthetic framework (Fig. 5G). The mandibular anterior teeth were restored with composite resin, and posterior teeth on both sides were replaced with implant-supported metal-ceramic fixed prostheses (Fig. 5G).
      Figure thumbnail gr5
      Figure 5A, Pretreatment intraoral view of patient 4. B, Pretreatment cone beam computed tomograph. C, Mounted maxillary final cast indicating implants placed in anterior region with unfavorable trajectory following angle of premaxilla. D, Screw-retained milled titanium framework with individual struts to receive individual cement-retained metal-ceramic crowns. E, Cement-retained definitive crowns. F, Individual metal-ceramic crowns cemented on milled titanium framework. G, Post-treatment panoramic radiograph.
      Patient 5 was treated with a screw-retained 1-piece metal-ceramic prosthesis with lateral screw abutments.
      • Lee J.H.
      • Lee J.B.
      • Kim M.Y.
      • Yoon J.H.
      • Choi S.H.
      • Kim Y.T.
      Mechanical and biological complication rates of the modified lateral-screw-retained implant prosthesis in the posterior region: an alternative to the conventional implant prosthetic system.
      A 58-year-old woman presented with all molar teeth missing and advanced periodontitis in both the maxillary and mandibular arch. All remaining teeth were extracted. Six implants (blueSKY; bredent UK) were placed in the maxillary arch and 4 implants (with 2 distal tilted implants) in the mandibular arch. The lateral screw abutments were used for all 6 implants in the maxillary arch (Fig. 6A ) to provide sufficient thickness to the metal-ceramic fixed prosthesis (Fig. 6B). The posterior lateral screw abutments helped compensate for the severe implant angulations and limited interocclusal space (Fig. 6B, 6C). The prosthesis was fabricated in single piece without screw-access holes on the occlusal or facial surfaces (Fig. 6D). The mandibular arch was restored with an implant-supported fixed complete-arch prosthesis.
      Figure thumbnail gr6
      Figure 6A, Lateral screw abutments in place for maxillary arch. B, Tissue surface view of lateral screw abutment prosthesis. C, Palatal aspect of lateral screw abutment of maxillary right posterior implant. D, Occlusal view with definitive prosthesis in place with no screw-access holes on occlusal or facial aspect.

      Discussion

      The maxillary edentulous ridge often leads to placement of implants in nonaxial positions that need to be addressed with the definitive prosthesis.
      • Tunkiwala A.
      • Kher U.
      • Bijlani P.
      Numerical guidelines for selection of implant supported prostheses for completely edentulous patients.
      The trajectory of the implants determines the type of retention of the prosthesis.
      • Jivraj S.
      Screw versus cemented implant restorations: the decision- making process.
      Table 1 outlines different prosthetic options for managing implant trajectories in the edentulous maxilla. Figure 7 depicts the different abutment designs used for the patients in this clinical report to manage unfavorable implant positions and angulations. Angled abutments are an option for correcting nonaligned implants, thereby facilitating prosthesis fabrication. This technique allows the placement of implants with increased width and height, avoiding guided bone regeneration (GBR) procedures and reducing treatment time and cost. However, angled abutments result in increased stresses and the application of unfavorable forces to screws, implant abutment connections, implants, or bone, although these increased stresses are usually within the limits physiological tolerance.
      • Cavallaro Jr., J.
      • Greenstein G.
      Angled implant abutments a practical application of available knowledge.
      • Sethi A.
      • Kaus T.
      • Sochor P.
      The use of angulated abutments in implant dentistry: five-year clinical results of an ongoing prospective study.
      • Saab X.E.
      • Griggs J.A.
      • Powers J.M.
      • Engelmeier R.L.
      Effect of abutment angulation on the strain on the bone around an implant in the anterior maxilla: a finite element study.
      An individualized abutment allows the dentist and the technician to provide screw-retained restorations and avoid a cemented prosthesis. However, abutments with angulations of more than 28 degrees are difficult to manage.
      • Berroeta E.
      • Zabalegui I.
      • Donovan T.
      • Chee W.
      Dynamic abutment: a method of redirecting screw access for implant-supported restorations: technical details and a clinical report.
      ,
      • Gjelvold B.
      • Sohrabi M.M.
      • Chrcanovic B.R.
      Angled screw channel: an alternative to cemented single-implant restorations- three clinical examples.
      These abutments are generally suited for fixed restorations which replace only the clinical crowns and some part of the soft tissue. In the authors’ opinion, they are not amenable to use in patients with excessive restorative space, as the biomechanical challenges are difficult to overcome.
      Table 1Advantages and limitations of different prosthetic designs for complete-arch fixed restorations in edentulous maxillae
      Type of Prosthetic DesignIndicationsAdvantagesLimitations
      Cement-retained prosthesis with angled abutmentsFavorable or unfavorable implant positions with adequate interarch spaceEase of fabrication

      Low cost
      Excess cement removal difficult
      • Pette G.A.
      • Ganeles J.
      • Norkin F.J.
      Radiographic appearance of commonly used cements in implant dentistry.


      Lack of retrievability
      Screw-retained prosthesis with angled screw-access holesUnfavorable implant positions with limited interarch spaceBest used in interarch space less than 15 mm
      • Berroeta E.
      • Zabalegui I.
      • Donovan T.
      • Chee W.
      Dynamic abutment: a method of redirecting screw access for implant-supported restorations: technical details and a clinical report.
      ,
      • Gjelvold B.
      • Sohrabi M.M.
      • Chrcanovic B.R.
      Angled screw channel: an alternative to cemented single-implant restorations- three clinical examples.


      Angle corrections up to 28 degrees
      • Berroeta E.
      • Zabalegui I.
      • Donovan T.
      • Chee W.
      Dynamic abutment: a method of redirecting screw access for implant-supported restorations: technical details and a clinical report.
      ,
      • Gjelvold B.
      • Sohrabi M.M.
      • Chrcanovic B.R.
      Angled screw channel: an alternative to cemented single-implant restorations- three clinical examples.


      Retrievable
      Not useful when more interocclusal space available
      Screw-retained prothesis with multiunit abutmentsUnfavorable implant positions with adequate interarch spaceRetrievable

      Ease of prosthetic steps
      Need more interocclusal space
      Screw-retained framework and cement retained crownsUnfavorable implant positions with adequate interarch spaceRetrievable

      Easy to repair
      Costly

      Technique sensitive
      Screw-retained prothesis with lateral screw abutmentsUnfavorable implant positions with limited interarch space for occlusal screw accessRetrievable
      • Lee J.H.
      • Lee J.B.
      • Kim M.Y.
      • Yoon J.H.
      • Choi S.H.
      • Kim Y.T.
      Mechanical and biological complication rates of the modified lateral-screw-retained implant prosthesis in the posterior region: an alternative to the conventional implant prosthetic system.


      Ease of maintenance
      • Lee J.H.
      • Lee J.B.
      • Kim M.Y.
      • Yoon J.H.
      • Choi S.H.
      • Kim Y.T.
      Mechanical and biological complication rates of the modified lateral-screw-retained implant prosthesis in the posterior region: an alternative to the conventional implant prosthetic system.


      More esthetic single piece prosthesis
      Technique sensitive
      Figure thumbnail gr7
      Figure 7Types of abutment designs used for complete-arch fixed prostheses in managing unfavorable implant positions and angulations.
      Multiunit abutments are a beneficial alternative in situations with unfavorable implant angulations and subsequent unesthetic screw access hole openings. They require sufficient abutment height to accommodate the retention screw of the prosthesis and are therefore suitable for patients with increased restorative space. Managing clinical scenarios with excessive resorption and consequent increased restorative space can be challenging, even with the use of multiunit abutments. The screw-retained prosthesis tends to be bulky, and casting the metal framework can be challenging. Lack of passivity of the definitive prosthesis along with the increased weight make the prosthesis biomechanically unfavorable. By using a screw-retained metal framework with individual crowns is an effective alternative in such situations.
      • Baig M.-R.
      • Rajan G.
      • Rajan M.
      Edentulous arch treatment with a CAD/CAM screw-retained framework and cemented crowns: a clinical case report.
      The framework can be customized easily and can be milled in titanium or zirconia with suitable layering of pink porcelain or composite resin.
      In addition to abutment design, the precision fabrication of complete-arch protheses is important for long-term success. Digital technologies, including computer-aided design and computer-aided manufacturing (CAD-CAM) or computer numeric controlled (CNC) milled titanium frameworks, can improve accuracy and passive fit compared with the technique-sensitive casting procedures.
      • Alfadda S.A.
      Vertical marginal gap evaluation of conventional cast and computer numeric controlled-milled titanium full-arch implant-supported frameworks.
      The different materials used for fabricating the teeth (and the occlusal surfaces) and prosthetic frameworks influence stress concentration in the teeth or frameworks or abutments.
      • Datte C.E.
      • Tribst J.P.
      • Dal Piva A.O.
      • Nishioka R.S.
      • Bottino M.A.
      • Evangelhista A.M.
      • et al.
      Influence of different restorative materials on the stress distribution in dental implants.
      The frameworks used in different patients in this report were fabricated from the cobalt-chromium alloy or PEEK and the occlusal surfaces from ceramic or composite resin.
      A balance between prosthetic and anatomic concerns should be established when planning and providing complex restorations. In severely resorbed maxillary arches, support for the upper lip is best provided by an overdenture with conventional labial flanges. Hygiene maintenance in complete-arch fixed implant restorations is a challenging task.
      • Maeda T.
      • Mukaibo T.
      • Masaki C.
      • Thongpoung S.
      • Tsuka S.
      • Tamura A.
      • et al.
      Efficacy of electric-powered cleaning instruments in edentulous patients with implant-supported full-arch fixed prostheses: a crossover design.
      ,
      • Menini M.
      • Setti P.
      • Dellepiane E.
      • Zunino P.
      • Pera P.
      • Pesce P.
      Comparison of biofilm removal using glycine air polishing versus sodium bicarbonate air polishing or hand instrumentation on full-arch fixed implant rehabilitations: a split-mouth study.
      Regardless of the technical or biologic complications that may occur, implant-supported prostheses may need to be removed for necessary restoration servicing, oral hygiene maintenance, or surgical treatment.
      • Gallucci G.O.
      • Avrampou M.
      • Taylor J.C.
      • Elpers J.
      • Thalji G.
      • Cooper L.F.
      Maxillary implant-supported fixed prosthesis: a survey of reviews and key variables for treatment planning.
      ,
      • Jivraj S.
      Screw versus cemented implant restorations: the decision- making process.
      ,
      • Zarone F.
      • Sorrentino R.
      • Traini T.
      • Di lorio D.
      • Caputi S.
      Fracture resistance of implant-supported screw- versus cement-retained porcelain fused to metal single crowns: SEM fractographic analysis.
      ,
      • Kern J.
      • Kern T.
      • Wolfart S.
      • Heussen N.
      A systematic review and meta-analysis of removable and fixed implant- supported prostheses in edentulous jaws: post-loading implant loss.
      As long as the tissue surfaces are relatively convex, within the limitations of esthetic demands, the surfaces can be maintained plaque free. Use of electric toothbrushes
      • Maeda T.
      • Mukaibo T.
      • Masaki C.
      • Thongpoung S.
      • Tsuka S.
      • Tamura A.
      • et al.
      Efficacy of electric-powered cleaning instruments in edentulous patients with implant-supported full-arch fixed prostheses: a crossover design.
      or professional oral hygiene with glycine air polishing
      • Menini M.
      • Setti P.
      • Dellepiane E.
      • Zunino P.
      • Pera P.
      • Pesce P.
      Comparison of biofilm removal using glycine air polishing versus sodium bicarbonate air polishing or hand instrumentation on full-arch fixed implant rehabilitations: a split-mouth study.
      has been reported to provide high levels of both cleaning efficacy and patient acceptance of such prostheses.

      Summary

      Advances in biomaterials and technology have greatly enhanced the prosthetic options available. This article summarizes the different prosthetic options available for managing unfavorable implant axes and aims to help clinicians plan and execute treatment for these challenging patients.

      Acknowledgments

      The authors thank Dr Burzin Khan (India) and Master Technician Vasile Bacilla (Romania) for providing the photographs and information of patient #5 managed with lateral screw abutments.

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