CLINICAL REPORT

aClinical AssiUniversity ofbDoctoral stuUniversity ofcPostgraduatdFull ProfessUniversity of

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Virtually guided alveolar ridge reduction combined withcomputer-aided implant placement for a bimaxillaryimplant-supported rehabilitation: A clinical report

Mario Beretta, DDS, MSc, PhD,a Pier Paolo Poli, DDS, MSc,b Sebastian Tansella, DDS,c andCarlo Maiorana, MD, DDS, MScd

ABSTRACTInsufficient crown height space, particularly in the interforaminal region of edentulous ridges withknife-edge morphology, may prevent successful prosthetic rehabilitation. Such conditions requireosteoplasty, which might complicate computer-guided implant placement. This clinical report il-lustrates the treatment of a patient with complete edentulism rehabilitated with a mandibularimplant-supported fixed dental prosthesis by using a virtually guided approach. Both alveolar ridgereduction and prosthetically driven implant insertions were computer-guided by surgical stents toincrease accuracy and predictability. This approach enabled the immediate loading of the implantswith an interim prosthesis before the delivery of a definitive screw-retained fixed prosthesis. At the1-year follow-up visit, clinical and radiographic examination revealed a stable outcome. (J ProsthetDent 2017;-:---)

Implant-supported fixed dentalprostheses (IFDPs) for patientswith complete edentulism areassociated with a high long-term survival rate.1 Immediateloading protocols have beencombined with software plan-ning and surgical guidingtechniques2 and have allowedflapless implant surgery.3-7

Benefits include less post-

operative pain and swelling8; less edema, hematoma,hemorrhage, and trismus9; reduced surgical time10; and areduced likelihood of implant positioning errors11

compared with free-hand, open-flap implant surgery. Inthe interforaminal region, a distance of 8 to 12 mm be-tween the bone crest and the occlusal plane is advisable toprovide space for the prosthetic components.12 In less-than-ideal situations, additional vertical height and hori-zontal width may be gained surgically with free-handosteoplasty.13 Recent evidence suggests that the use of asurgical guide based on the prospective interim prosthesisand fabricated on a stereolithographic cast permits guidedalveolar ridge reduction in a more precise manner.14 Thepurpose of the present report was to illustrate a novelapproach completely guided by surgical stents fabricatedfrom a virtual plan. The aim of the technique was to

stant Professor, Implant Center for Edentulism and Jawbone Atrophies, MaMilan, Milan, Italy.dent, Implant Center for Edentulism and Jawbone Atrophies, MaxillofacialMilan, Milan, Italy.e student, Department of Oral Rehabilitation, Italian Institute of Stomatologor, Implant Center for Edentulism and Jawbone Atrophies, Maxillofacial SuMilan, Milan, Italy.

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increase the accuracy of both the alveolar ridge reshapingand implant insertion.

CLINICAL REPORT

A 58-year-old white, partially edentulous woman re-quested maxillary and mandibular FDPs while seeking aminimally invasive approach. Her medical history wasnoncontributory and she was wearing removable partialdentures retained by teeth that were judged to have apoor prognosis (Fig. 1). However, her occlusal verticaldimension (OVD) was not reduced.

Preliminary complete-arch impressions were made ofboth arches with a polyether material (Impregum Penta;3M ESPE) in stock trays. Record bases and occlusion rimswere fabricated and inserted to replicate the OVD from

xillofacial Surgery and Odontostomatology Unit, Maggiore Policlinico Hospital,

Surgery and Odontostomatology Unit, Maggiore Policlinico Hospital,

y, University of Milan, Milan, Italy.rgery and Odontostomatology Unit, Maggiore Policlinico Hospital,

1

Figure 1. Presurgical clinical situation. A, Frontal view. B, Occlusal view of mandibular arch.

Table 1.Distribution of implant location and characteristics

Implant Location

ImplantWidth(mm)

ImplantLength(mm)

AbutmentAngulation(degrees)

Maxillary right first molar 4.3 13 0

Maxillary right first premolar 3.8 11 0

Maxillary right lateral incisor 3.3 11 17

Maxillary left lateral incisor 3.3 11 17

Maxillary left first premolar 3.8 11 0

Maxillary left first molar 3.8 11 17

Mandibular right first premolar 3.8 13 30

Mandibular right lateral incisor 3.8 13 0

Mandibular left lateral incisor 3.8 13 0

Mandibular right first premolar 3.8 13 30

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the removable partial dentures. Diagnostic casts and waxrims were mounted on a semi-adjustable articulator(Artex CT; Amann Girrbach AG) in the centric relationposition. A prefabricated radiographic stent was madewith a silicone elastomer (Evobite; 3DIEMME) and anextraoral radiopaque marker (3DMarker; 3DIEMME) fora cone-beam computed tomography (CBCT) scan. Op-tical scans of the diagnostic casts and the radiologicalstent alone were also made to overlap the acquiredstandard tessellation language (STL) data with the digitalimaging and communication in medicine (DICOM) dataobtained from the CBCT examination. The extraoralradiopaque marker visible in both sets of scans wassuperimposed. As a result, the 3-dimensional (3D) po-sition of the implants (CONELOG; CAMLOG Bio-technologies AG) could be planned by using dedicated3D software (3Diagnosys; 3DIEMME) (Table 1).

As the maxilla had adequate bone, a flapless approachwas planned. In the mandible, a vertical ridge reductionwas planned virtually to obtain a residual crest withoptimal anatomy and to position the implants correctly(Fig. 2). According to the virtual plan, 2 polymethylmethacrylate (PMMA) interim prostheses were fabri-cated. The entire virtual plan was transferred to thesurgical field by means of surgical guides fabricated witha 3D printer (DWS020D; Digital Wax Systems) and rapidprototyping techniques.

After tooth extraction, a stent was accurately placedon the mucosa with a silicone guide (Zetalabor; Zher-mack SpA) to prepare the holes precisely for the subse-quent insertion of the anchor pins (Fig. 3A). Amucoperiosteal flap was then raised to expose theinterforaminal region. At this point, a customizedbicomponent surgical stent was secured in the appro-priate position with 4 endosseous pins (RealGUIDE Kit;3DIEMME srl) inserted in the previously preparedreference holes (Fig. 3B). Thus, a ridge could be remod-eled according to the computer-guided virtual plan.

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Under saline irrigation, the osteoplasty of the residualalveolar ridge was completed with a pear-shaped surgicalbur aided by the flat part of the stent corresponding tothe virtually planned level of apicocoronal reduction(Fig. 3C). Thereafter, the upper component of the tem-plate was connected to the stent with 3 mini-screws(Tent Screw; Neo Biotech) serving as a surgical guidefor the forthcoming implant placement (Fig. 3D). Finally,implants were inserted in compliance with the virtualplan in the interforaminal region with an insertion torqueof at least 35 Ncm (Fig. 3E). The flaps were sutured with4/0 polyglycolic acid suture. Bar abutments (COMFOURSystem; CAMLOG Biotechnologies) and intermediateabutments were screwed to the implants. An autopoly-merizing composite resin (Unifast TRAD; GC Corp) wasplaced over the abutments to fix the PMMA interimprosthesis precisely with a silicone index. The screw ac-cess holes were closed with Teflon tape and light-polymerized interim composite resin (Telio CS; IvoclarVivadent AG) (Fig. 3F).

Healing proceeded uneventfully, and after 6 months,a definitive impression was made of both arches, andchromium-ceramic IFDPs were delivered (Fig. 4). A

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Figure 2. A, Virtual mandibular stent for guided interforaminal osteoplasty. B, Virtual 2-component surgical stent for mandibular guided implantinsertion.

Figure 3. A, First stent used to guide insertion of anchor pins. Reference lines guiding position of possible vertical releases visible in lower part of stent,distal to mental foramina. B, First stent of 2-component template used to guide alveolar ridge osteoplasty. C, Interforaminal alveolar ridge reductionaccording to virtual plan. D, Second stent of 2-component template used to guide insertion of implants according to virtual plan. E, Implant placed inprosthetically guided position according to virtual plan. Interim abutments screwed on implants. F, Immediately loaded screw-retained mandibularinterim prostheses in position.

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panoramic radiograph was made during the 1-yearfollow-up appointment (Fig. 5).

DISCUSSION

Little information is yet available on the application ofvirtual technology to plan an osteoplasty together withguided implant placement during open-flap procedures.The superimposition of the diagnostic casts with theDICOM data enabled simultaneous planning on bone,soft tissues, and virtual waxing. Therefore, the idealshape of the mandible could be planned to receive dentalimplants in a prosthetically driven position in compliance

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with the prosthetic waxing. Once the horizontal osteot-omy was planned, the virtual project was transferred to abone-supported surgical stent.

To place the template in the exact position, a pre-liminary stent was used to drill the holes for the sub-sequent insertion of the anchor pins. The position ofthis mucosa-supported stent was guided by a siliconeindex in occlusion with the maxillary arch and based onthe soft-tissue profile previously recorded and trans-ferred with the software through the optical scan of thedental casts. A disadvantage might be soft-tissuecompressibility or soft-tissue enlargement after localanesthesia. Hence, local anesthesia was performed deep

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Figure 4. A, Soft tissue healing and definitive abutments in position in mandible after 6 months of soft tissues conditioning. B, Intraoral view ofdefinitive prostheses.

Figure 5. Postoperative panoramic radiograph. Implants appearedstable, with no signs of peri-implant pathology.

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in the vestibule without altering the thickness of thecrestal soft tissues, and the stent was fitted by applyingsome compression so that the soft tissues underneathbecame ischemic.

Furthermore, the stent was provided with verticalgrooves located distally with respect to the mental fora-mens to guide the clinician as to whether releasing in-cisions were necessary. In the present patient, a crestalincision with no releasing incisions was judged sufficientto expose the residual ridge and the mental nerve. Theabsence of releasing incisions was also related to the factthat no bone grafting was needed. Flaps were raised toroughly 8 mm below the alveolar crest and then reposi-tioned with resorbable single and cross sutures.

The use of a bicomponent surgical stent allowedguided ridge reduction and subsequent computer-aidedimplant placement without switching between differenttemplates. Indeed, the surgical implant guide was con-nected to the first stent without modifying its position,possibly increasing the accuracy of the procedure.

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However, accuracy was not assessed and should be partof future clinical studies.

An important limitation is the cumulative effect oferrors. Deviations may reflect the sum of all errorsoccurring from impressions to imaging, planning, thetransformation of data into a guide, and the improperpositioning of the last during surgery.6 Moreover, theproposed technique involves additional costs to producethe surgical guides and related components.

SUMMARY

The present report illustrates a treatment approach toremodeling the alveolar ridge and to placing implants ina completely guided setting from a virtual plan byconsidering both anatomic and prosthetic data. Thisapproach might increase the accuracy of implant inser-tion and consequently enhance the predictability of theprosthetic outcome.

REFERENCES

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7. Beretta M, Poli PP, Maiorana C. Accuracy of computer-aided template-guided oral implant placement: A prospective clinical study. J PeriodontalImplant Sci 2014;44:184-93.

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8. Pozzi A, Tallarico M, Marchetti M, Scarfo B, Esposito M. Computer-guidedversus free-hand placement of immediately loaded dental implants: 1-yearpost-loading results of a multicentre randomised controlled trial. Eur J OralImplantol 2014;7:229-42.

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13. Malo P, Rangert B, Nobre M. “All-on-Four” immediate-function concept withBranemark System implants for completely edentulous mandibles: A retro-spective clinical study. Clin Implant Dent Relat Res 2003;5 Suppl 1:2-9.

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14. Faeghi Nejad M, Proussaefs P, Lozada J. Combining guided alveolar ridgereduction and guided implant placement for all-on-4 surgery: A clinicalreport. J Prosthet Dent 2016;115:662-7.

Corresponding author:Dr Pier Paolo PoliImplant Center for Edentulism and Jawbone AtrophiesMaxillofacial Surgery and Odontostomatology UnitFondazione Cà Granda IRCCS, Ospedale Maggiore PoliclinicoUniversity of MilanVia Commenda 10, 20122 MilanITALYEmail: pierpaolo.poli@unimi.it

AcknowledgmentsThe authors thank Riform dental technician laboratory for the support during thevirtual and prosthetic procedures.

Copyright © 2017 by the Editorial Council for The Journal of Prosthetic Dentistry.

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