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Implant positioning

Minimally invasive procedures and esthetics

SPECIAL ISSUE

Precisionand biologicalconsiderations

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NobelActive™

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It is undeniable that dental implantology has movedon in 20 years from research for osseointegrationand function to research for tissue integrationand esthetics.

This paradigm shift has switched the notion ofimplant survival to biological success, a mandatorycondition for tissue stability. This is the result ofmultiple factors and cannot be summed up in thesimple design of an implant or the choice of a pros-thetic device.It is not solely a question of an implant design, whichis the intelligent form for a given function, concen-trated in a few millimeters-subtleties that have adecisive impact on the primary and secondaryimplant stability. It is decisively based on bio-esthe-tic integration with the present peri-implant soft tis-sues, the reliability of the prosthetic connection, thesimplicity of the surgical procedure and the prostheticcomponents installation, just to give these examples.

The anterior region represents the most critical areafrom an esthetic standpoint and the most complexwith regard to the osseous and gingival architecture,and especially when the tooth loss occurs a defi-ciency of the hard tissues and/or soft tissues irrepa-rably complete the clinical status.

Traumas, fractures, cracks and injections generatebone and soft tissue defects, slow or sudden. It isessential to diagnose for establishing the sequencesin a surgical-prosthetic treatment plan, the methodsof tissue regeneration, the possibilities for immediateimplantation in a fresh extraction site, or more sim-ply (but more rarely) how to preserve tissues.

The clinical examination, which should be comple-ted by a radiographic and/or tomographic examina-tion, should take account of the periodontal biotypeand guide the clinician's decision-making.

At present, prior to the first surgical act, the treat-ment rationale is based on the following questions:

■ Orthodontic pre-treatment■ Bone volume augmentation■ Gingival and mucosal tissue enhancement■ Timing of these procedures before, during or after

implant placement ■ Provisionalization modalities■ Type of implant(s)

The choice of this last element depends from a large extenton the clinician experience, the surgical instrumentationat his/her disposal and his/her confidence,which is rela-ted somewhat from the use of a "family" of implants.

Tooth 11 is missing. Non invasive placement (semi-lunar incision) of a NobelActive™implant (Nobel Biocare).

Bio-esthetic considerations

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There is thus a kind of "routine" that only can be coun-teracted by understanding the features of eachimplant.It is therefore essential for the improvement of tis-sue integration to study these characteristics andtheir biological outcomes (this being one of the objec-tives of this special issue), and not to hesitate to usea new generation of implants in appropriate clinicalsituations, as there is no "universal" implant thatwould be suitable in all sites and for all indications.

But in the anterior region, partial edentulism, imme-diate implantation following extraction and implantin a healed site with a thin biotype generally repre-sent the greatest clinical challenges.Some of the popular implants consist in titaniumscrews called "one piece" if they are transmucosal, and"two piece" if it is the role of the prosthetic abutmentto provide an adherence surface for the three-dimen-sional biological space composed by the junctional epi-thelium and the connective attachment.

3mm healing abutment.

The “one-piece” screwed ceramiccrown.

Procera® zirconia crown (Nobel Biocare) on 11. A feldspathic ceramic“chip” has been bonded on 12 to compensate the too large spacefor 11.

for optimal implant positioningBY Bernard Touati

The bio-esthetic integration.

“Cone Beam” CT radiograph showing the concavehealing abutment (CURVY concept).

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BIO-ESTHETIC CONSIDERATIONS FOR OPTIMAL IMPLANT POSITIONING

Not all of these features are found within all modernimplant systems (and other variants sometimes pro-vide the same results), but overall this developmentseems to have influenced the last generation ofimplants designs recently, which also copy one ano-ther, "research and development" not being possiblefor all manufacturers…The use of an implant with modern characteristics isnot the only guarantee of harmonious integration.Three-dimensional seating is essential, and the litera-ture that abounds on the subject demonstrates this well.

This seating is a determining factor for bio-estheticintegration: it is responsible for the morphology ofthe prosthetic restoration, its emergence and angu-lation, and the architecture of the peri-implant softtissue at the level of the scalloped gingival marginsand inter-dental papillae.During the 1980s, implantology was guided by ana-tomical imperatives. Since then, prosthetic require-ments (such as the ideal position for a prostheticrestoration) and biological imperatives (such as tis-sue stability) rule all implant treatment.At present,with the advances made possible by 3-D ima-ging (Scanners and Cone Beams) and software forimplantology, guidance of implant positioning may beentirely computer-assisted with great precision and greatsafety with regard to the various anatomical landmarks.The seating of an implant should not negativelyaffect bone volume; if this is insufficient in terms ofheight or thickness it should be regenerated to sup-port the soft tissues ("The tissue is the issue but thebone sets the tone" Garber/Salama).

Horizontally the diameter of the implant should pro-mote inter-dental bone peak (where there are natu-ral teeth), the minimum thickness of which shouldnot be less than 1.5mm (Esposito, 1993).This boneportion determines a predictable factor of the gin-gival papillae (Salama 1998).Implant stability is required in an extraction socket,but not at the price of choosing the widest implantdiameter: it is here where the implant design playsan important role.In the case of adjacent implants the space should beincreased to 3 or 4millimeters, the biological condi-tions being different in the absence of Sharpey'sfibers, periodontal blood supply and a smaller andless firm fascicle of collagen fibers: the peri-implant

A contemporary implant presents the key-features asthe apex, the body ("core"), the threads, the collar,the external or internal connection system, and aosseoconductive surface.

Modern development has had a tendency to modifyall of these characteristics in the light of studies andexperience acquired during the last 20 or 25years.This tendency could be set out as follows:

■ The apex is quite narrow, and the threads makesit self-cutting, or self-tapping, which enables it tooperate in a narrower osteotomy and thus to gainin primary stability.The design of the threads also makes it "backward-cutting", enabling reorientation during placementof the implant in a bone with a compatible density.

■ The body, neither cylindrical nor tapered, has a spi-ral form with an osteotome effect, compressingthe bone and making it denser during the implantplacement.

■ The threads are more aggressive and their designdevelops along the height of the implant a variablecutting effect and that of compression. A doublethread spire allows for faster placement, the spa-cing between the thread spires and a groove faci-litating the escape of bone chips and reducingoverheating.

■ The collar is of a slightly smaller size compared tothe body of the implant, back tapered, and hasmini-threads or grooves on it, not smooth but tex-tured. Its design allows for a certain "rebound" ofthe cortex after the implant has been through it,and its macro- and micro-surfaces lead to osseoin-tegration of the implant neck in order to stabilizethe crestal bone at this level.

■ The connection system combines a Morse taperwith internal interlocking, hexagonal or otherwise,for improved hermeticity with regard to bacteria, bet-ter retention of prosthetic components (and there-fore less screw loosening), and a greater ease forseating these without necessarily need for positio-ning index and retro-alveolar radiography. Theconnection system, narrower than the diameter ofthe implant, allows a real platform-switching effect.

■ Finally, the surface of the titanium implants is rough,and has an oxidized layer that accelerates bone for-mation and thus leads for faster secondary stability.

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soft tissue is a scar tissue, and does not have thesame potentialities for repair as healthy gingiva,firmly-attached to the bone and highly-vascularized.

Vertically the implant should promote the volume ofthe soft tissue barrier that ensures a tight joint with regardto bacteria, toxins and all aggressive elements withinthe buccal environment, thanks to the adherence of thejunctional epithelium (which contains glycoproteins andhemi-desmosomes) and the connective tissue fibroblasts.This 3-D biological space should have a height ofaround 3 mm to ensure its stability, which is why thegingival biotype is important.When insufficient spacerecreates the necessary volume at the expense of the cres-tal bone, recession occurs.The thickness of the soft tis-sue should be sufficient around the implant collar andcan be achieved naturally (thick biotype), surgically(subepithelial connective tissue graft) or prosthetically(transmucosal-Curvy® abutment, Nobel Biocare® orplatform-switching concave implant abutment).

The reference point for this distance of 3 mm shouldbe the predetermined level of the marginal soft tis-sue in the case of a gingival graft: implant placementin the anterior region combined with soft tissuesregeneration implies prudence and skills.

Tooth 21 socket after extraction. The osteotomy is made onto the palatal bone.

Vertical positioning of the implant 3mm subgingivally. The buccal gap between the NobelActive™ implant and the socketwill be filled with BioOss (Geistlich).

“Cone Beam” CT of tooth 21

before extraction.The implant has been palatallyre-oriented and the buccal gapfilled with bone substitute.

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BIO-ESTHETIC CONSIDERATIONS FOR OPTIMAL IMPLANT POSITIONING

Sagitally the implant should not reduce the thicknessof the buccal bone wall, which should be a minimumof 1.5 mm, even 2 mm (Spray 2000).Nowadays the use of a countersink is not recom-mended.The crestal bone needs to be protected andthe horizontal component of the biological space isa key-issue to maintain it.In an extraction socket, the implant should be ancho-red in the palatal bone wall and not in the center ofthe alveolus (unless the buccal bone table is thick),allowing the emptied buccal space being filled witha bone substitute.This procedure is held to provide the longest-termimplant/bone contact and to recreate a thicker buc-cal bone wall (Abushahba 2008, Kan 2009).In natural teeth a thin buccal cortical plate withreduced or no spongy bone is viable, and may bestable, as the bone is stimulated by the Sharpey's fibersand take advantage of the rich blood supply provi-ded by the periodontal ligament.In the case of an implant, only a thick bone wall can

guarantee stability and play a counteract to various remo-deling patterns, as tissue stability depends on a num-ber of factors…Nowadays implant success is not reduced by theimplant design or position (although these parametersare important)and cannot be covered in a few lines.Contemporary dental implantology also has otherrequirements, like minimizing surgical trauma byapplying minimally invasive procedures,protecting theblood supply, reducing the handling steps of prosthe-tic components,using materials that are biocompatiblewith the transmucosal area, providing immediate sup-port to the soft tissues by means of a temporary esthe-tic restoration,preferably fixed,and sub-contouring alltrans-mucosal prosthetic components.All of these paradigm shifts lead our clinical and labo-ratory prosthetic concepts to do the same. Except insituations where a zirconium oxide abutment has beenprepared beforehand, as for a temporary restoration,prior to surgery using an advanced planning tech-nique, in all other cases our preference is for a screw-retained one-piece crown on a zirconia base. It has theadvantage of eliminating the abutment/crown jointand luting cement removal sub-mucosally.Today we have at our disposal an advanced planningstrategy, whether supported by digital technology ornot.A surgical-prosthetic co-ordination should faci-litate some prosthetic phases such as the productionof implant abutments andtemporary restorations. Forexample, these steps can beanticipated before the firstsurgery, giving a timing anda planning for the surgicalsequences over time. ■

“Curvy” abutment (Nobel Biocare) showing the transmucosalconcavity. It closes the mucosal biological barrier and thickens the connective tissue.

“One-piece” screwed Procera® zirconia crown showing the buccalconcavity and transmucosal cervical reduction.

The bio-esthetic integration. On tooth 12 a bonded laminate veneerchanges a canine into a laterale.

Dental Institute34, avenue Montaigne75008 Paris - France

Bernard Touati