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INTRODUCTIONAs clinicians, we must often make decisionson the restoration of our dental implantdesign. In years past, screw-retained prosthe-ses were the norm, often with custom-pre-pared screws or screw-retained infrastruc-tures. Issues with past implant designscaused some problems with this type ofcrown. Screws could loosen, causing stressto the practitioner. Design corrections weremade with advent of the UCLA abutment,1,2which would engage the implant body andallow for either a screw-retained or cement-on crown. Since most implants today areinternally designed with some type of inter-nal stabilizing connection (such as a hex, tri-lobes, or morse tapers), loosening of abut-ments and screws has been dramaticallyreduced as long as the screws are properlytorqued to the manufacturer’s requirements.

As screw-retained crowns were replacedby screw-retained abutments and cement-oncrowns, other issues began to arise. Most prob-lems with cement-on crowns were the resultof abutments loosening under a cemented-onimplant-retained crown, resulting in the needto remove the crown to re-torque the abut-ment or drill an access opening through thecrown to tighten the abutment screw.

Another issue becoming popular in theliterature is the periodontal bone loss aroundimplants restored with cemented-retainedcrowns. Depending on the type of cementused, such as silicone cements, glass iono -mers, and resin cements, if the practitionerdoes not completely remove the excess sub-gingival cement, the body’s natural responseis to lose bone around the necks of the im -plants.3 Obviously, this problem can be mini-mized with supragingival margins or marginsplaced at, or very near, the gingival crest level.The problem is serious enough that screw-retained prostheses have again become popu-lar. So, it may be appropriate to review whenscrew-retained crowns and cement-on im -plant-retained crowns are to be used.

Choosing Between Screw-Retained andCement-Retained Crowns

As previously mentioned, nonresorbablecements that are not thoroughly removed

subgingivally can result in peri-implantitis,which is inflammation of the soft tissuearound the implant that can result in boneloss.4 Obviously, eliminating the cementwith a screw-retained crown will eliminatethis potential problem. As abutments aretorqued into place in a cement-on crownsituation, any issues with mobility of theabutment throughout time can be stressful,depending on the type of cement used toretain the crown. Using a soft or semi-flexi-ble temporary cement (such as Temp-Bond/Temp-Bond Clear [Kerr]; Retrieve[Parkell]; Improv [Alvelogro]; TempSpan[Pentron]; or Telio CS Link [Ivoclar Viva -dent]) allows for retrievability of the crownfrom the abutment; however, this can alsobe an issue if the crown comes off duringuse by the patient. Any type of porcelainfracture or movement of teeth resulting inopen contacts can be difficult to repair.Screw-retained crowns can be removed andcorrected if problems arise.

Also, it is imperative that the clinicianevaluate the circumstances prior to any sur-gical intervention and implant placement.What does that mean? The interocclusal dis-tance must be evaluated. An abutment for acemented-on crown must have a minimalheight of 5.0 mm, from the prepared marginto the top of the abutment, to have adequateretention. More height is even better, butwith any less than 5.0 mm, the cementedcrown may not be retentive long-term andmay possibly result in several re-cementa-tions, so a screw-retained crown is indicated.

Placement of the implant must be madeideal when considering a screw-retainedcrown. This means palatal in the anteriormaxilla, in the cingulum area, and ideallyin the center of a posterior tooth, down thelong axis of the crown. Angulation issueswith our implants can often be correctedeasier with custom prepared abutmentsand cement-on crowns.

TimothyKosinski, DDS

Single Posterior Implant CrownFabrication

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IMPLANTS

Cement-On Versus Screw-Retained Crowns

Dr. Kosinski: Please provide captions for the 3 images of

you and your staff. Thanks!

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The clinician must be aware ofthe advantages and disadvantages ofhaving a screw hole in the occlusalsurface of posterior surface, or lin-gual surface in anterior teeth, of anew crown. Also, we must observethe emergence of the screw in ascrew-retained crown. Of course, ascrew cannot come out of the facialaspect of the crown in the aestheticzone. The patient must be madeaware that the screw access mayshow a bit. Our best composites do anice job in filling the access hole, butfor some patients this may not be aes-thetic enough.

Finally, screw-retained implant-retained crowns can end up beingslightly more expensive than prepar-ing stock abutments and fabricatingbasically a normal crown over theabutment. Custom abutments, whencircumstances warrant, can be moreexpensive to the practitioner.

Indications for cement-on im -plant-retained crowns over preparedabutments and those indicated forscrew-retained prosthesis will bedemonstrated with the following 5clinical cases.

CASE REPORTSCases 1 and 2 describe the use ofscrew-retained implant crowns. Withthe use of either CT scanning and

diagnosis or evaluation of conven-tional hard models made from con-ventional impression techniques, thedental laboratory team can create theimplant position, interocclusal dis-tance from the opposing arch, andinterproximal distances from theadjacent natural teeth.

Case 1In this case, our dental laboratoryteam created a custom contouredhealing abutment and transitionalcrown using digital design (Figure 1).The Glidewell tapered dental implantwith internal hex design (GlidewellLaboratories) is nicely positioned inthe center of the edentulous ridge in

the mandibular second bicuspid areausing standard surgical protocol. Theimplant was torqued above 35 Ncmand the custom-contoured abutmentwas immediately positioned into theimplant (Figure 2). The concept is tocreate ideal tissue contours for thedelivery of the final implant-retainedcrown. The transitional crown wascemented onto the prepared abut-ment with a temporary cement(Temp-Bond). The margins of thecrown were placed at the soft-tissuelevel, allowing for easy cleanup of theexcess cement, thus eliminating anypotential periodontal issues from thevery beginning. After approximately3 months of integration of the

implant, the cemented transitionalcrown was removed, showing theincredibly healthy tissue response tothe digitally designed transitionalabutment. Healthy tissue contourswere created by using a custom-fabri-cated abutment that allowed for idealemergence profile in the finalimplant-retained crown (Figure 3). Ascan be seen by the transitional abut-ment, the interocclusal distance waslimited. Following the guideline ofhaving a least 5.0 mm of abutmentheight for predictable retention, itwas determined that a more effectivelong-term restoration would be ascrew-retained monolithic zirconiacrown (BruxZir [Glidewell Labora -tories]) (Figure 4). The implant crownwas passively seated into the implant(Figure 5), and them proximal andocclusal contacts were checked. Atorque wrench was used to complete-ly seat the retaining screw to 25 Ncm.Ideal emergence profile was estab-lished using the screw-retainedimplant crown (Figure 6), and a digi-tal periapical radiograph was takento ensure the complete seat of theprosthesis (Figure 7).

Case 2Maxillary second molar implantreplacement areas should be evaluat-ed carefully for interocclusal dis-tance. A short abutment and cement-on crown in this area can prove to be

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CASE 1. MANDIBULAR SECOND BICUSPID

Figures 1 and 2. The dental laboratory (Glidewell Laboratories) fabricated a digital transitional abutment and crown to be placed immediately after implant placement. Theimplant had been torqued to 35 Ncm, allowing the use of the custom-healing abutment.

Figure 4. Because of the limited interocclusal distance, a screw-retainedmonolithic zirconia (BruxZir [GlidewellLaboratories]) crown was used.

Figure 5. The implant crown was passivelyseated into the implant, proximal andocclusal contacts were checked, and thenthe retaining screw was torqued to 25Ncm.

Figures 6. Ideal emergence profile wasestablished using the screw-retainedimplant crown.

Figure 7. A digital periapical radiographwas taken to verify a complete seat.

Figure 3. After approximately 3 months ofintegration, the cemented-on temporarycrown was removed, showing the healthytissue response to the digitally createdimmediate transitional abutment.

After approximately 3months of integration ofthe implant, the cementedtransitional crown wasremoved, showing theincredibly healthy tissue....

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disastrous due to inadequate reten-tion with a high potential for crownsto become uncemented. Case 2demonstrates the use of a screw-retained implant crown to replacethe missing maxillary left secondmolar. The dental laboratory teamcreated a soft-tissue model with ascrew-retained crown due to the lim-ited interocclusal distance. A pre-pared abutment would have beenmuch too short to have successfullyretained a cement-on crown. Figure 9shows the stock healing abutment inplace approximately 3 months afterimplant placement. After the healingabutment was removed, good tissuehealth around the tapered dentalimplant (Glidewell Laboratories)could be observed. The implantcrown was then positioned andtorqued intraorally (Figure 10). Theaesthetic and functional maxillarysecond molar exhibited nice emer-gence profile. The final periapicalradiograph (Figure 11) indicated acomplete seating of the screw-retained implant crown.

Case 3Even with the increased popularity of

screw-retained implant crowns, in mypractice, I tend to use more cement-oncrowns over prepared stock or customabutments. The important issues toremember are that abutment marginsshould be just slightly subgingival, ifusing a titanium material, but can be atthe tissue level when using tooth-col-ored monolithic zirconia material.Being aware of margin design withyour abutment can make the finalresult aesthetic and periodontally

sound. Using stock abutments mayhinder your ability to manage marginposition, so considerations for customabutments should be made and consid-ered when treatment planning anddetermining proper fees. Figure 12illustrates a healing abutment placedin the mandibular right first molararea. The implant and tissue wereallowed to heal for about 3 months.After removal of the healing abutment,there was good tissue health around

the Glidewell implant. The implantitself was approximately 2.0 mm sub-gingival (facial aspect). Because there isplenty of interocclusal space, a pre-pared titanium abutment was seatedinto position and torqued to 25 Ncm.The interocclusal distance allowed fora tall and retentive prepared customabutment for a cemented crown(Figure 13). The abutment, ideally con-toured and in the center of the ridge,allowed for occlusal forces to be main-tained down the long axis of theimplant (Figure 14). The implant-retained crown was cemented to placeand the occlusion checked. I cementimplant-retained crowns with a tempo-rary cement (Temp-Bond). Thesecements are strong enough to hold thecrown in place as long as the abutmentis properly formed and yet, if any prob-lems were to arise down the road, suchas abutment loosening, they could bemore easily handled. Figure 15 showsthe final radiograph of the cementedcrown. No excess cement was leftbehind because the subgingival mar-gin, at about 1.0 mm, was not placeddeeply.

Case 4Dental implants in certain circum-stances can also be used to maintain

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CASE 2. MAXILLARY LEFT SECOND MOLAR SCREW-RETAINED IMPLANT CROWN

Figure 8. A soft-tissue model with thescrew-retained crown was chosen due tolimited interocclusal space. A short prepared abutment (less than 5.0 mm)would not have had adequate retention toretain a cemented crown in this case.

Figure 9. Stock healing abutment, 3months after implant placement in themaxillary left second molar area. After thehealing abutment was removed, we havegood tissue health around the Glidewellimplant.

Figure 11. Final periapical radiograph ofthe implant crown in place.

Figure 10. The aesthetic and functionalmaxillary second molar has a nice emergence profile.

CASE 3: CEMENT-ON IMPLANT-RETAINED MANDIBULAR FIRST MOLAR CROWN

Figure 12. Note the healthy tissue aroundthe Glidewell implant after removal of thehealing abutment.

Figure 13. A prepared titanium abutmentwas seated and torqued into position. The interocclusal distance allowed for a retentive prepared abutment for a cemented crown.

Figure 15. Final radiograph of the cemented in crown verifying that no excesscement remained subgingivally.

Figure 14. Occlusal view of the abutmentideally contoured and positioned in theridge. The implant-retained crown wascemented to place and occlusion checked.

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bridges. This case illustrates the useof an maxillary posterior, implant-retained, cemented fixed partial den-ture (FPD). Once the healing abut-ments were removed, healthy tissuewas observed around the Glidewelldental implants (Figure 16). A soft-tis-sue model showed that the marginsof the abutments were only slightlysubgingival, allowing for emergenceprofile, proper aesthetics, and easymaintenance of any cement (Figure17). With the Glidewell implant sys-tem, seating stents are provided(Figure 18). The seating stent allowsfor proper placement of the preparedcustom abutments. A torque wrenchwas used to properly seat the pre-pared abutments to 25 Ncm. Theabutments were positioned for acemented 3-unit, implant-retainedFPD (Figures 19 and 20). The laborato-

ry team was able to ideally contourthe abutments for proper draw andemergence profile. A radiograph wastaken to ensure complete and properseating of the prosthesis (Figure 21).

Case 5In this, the final case presented, thepreoperative radiograph of a non-restorable mandibular right secondmolar is shown (Figure 22). Afterapproximately 4 months of healing, aGlidewell implant was surgicallyplaced and torqued to 35 Ncm. Uponremoval of the healing abutmentafter an additional 3 months, the tis-sue contours were good and the tis-sue was healthy (Figure 23). Theinter occlusal distance allowed for along and retentive prepared customabutment to be torqued into positionto 25 Ncm (Figure 24), and the mono-lithic zirconia crown (BruxZir) wascemented into place (Figure 25). Thefinal periapical radiograph was taken

to verify proper seating and demon-strated no excess cement remained(Figure 26).

CLOSING COMMENTSPreparation for the surgery of dentalimplants must be predicated by anunderstanding of the final prostheticreconstruction. Visualizing the casefinished before, along with any need-ed surgical intervention, is importantif we keep in mind that dentalimplants are prosthetically driven.Mounted diagnostic casts are impor-tant in helping the clinician and labo-ratory team determine interocclusalspace. Discussions about aestheticrequirements/expectations with ourpatients should be done prior to theplacement of any implants. The bene-fits and risks of cement-on implant-retained crowns versus screw-retained crowns must be clearlyunderstood.

With the advent of new polycrys-talline dental materials (such asmonolithic zirconia and monolithiclithium disilicate (IPS e.max [IvoclarVivadent]) clinicians can deliver aes-thetic and strong restorations in theposterior regions, nearly eliminatingthe risks of fracture as experiencedhistorically using traditional porce-lains. These new high-strength, all-ceramic materials (used for abut-ments, crowns, and FPDs) can alsoimprove the aesthetics around theaccess opening of the screw-retainedcrown. Ideal placement of implantsso that occlusal forces are maintaineddown the long axis of the implant canbe determined by proper planning.The newest techniques for designingthe proper form and function for animplant-retained crown make deci-sions that much easier. CT diagnos-tics can allow for determining ideal

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CASE 4: CEMENT-ON, IMPLANT-RETAINED MAXILLARY POSTERIOR BRIDGE

Figure 16. Healthy tissue around Glidewelldental implants after healing abutmentswere removed.

Figure 17. Soft-tissue models showingmargins of the abutments were onlyslightly subgingival; allowing for emergence profile, proper aesthetics, and easy removal of cement.

Figures 18 and 19. A seating stent, provided with Glidewell implants, was used to properly position and seat the abutments. The abutments were positioned for a cement-on, 3-unit, implant-retained bridge. The laboratory (Glidewell Laboratories) wasable to contour the abutments for proper draw and emergence.

Figures 20 and 21. Occlusal and radiographic view of the implant-retained, cemented, 3-unit fixed partial denture.

CASE 5: CEMENT-ON MANDIBULAR SECOND MOLAR

Figure 22. Preoperative radiograph of nonrestorable mandibular right secondmolar to be extracted. After approximately4 months of healing, a Glidewell implantwould be surgically placed and torqued to35 Ncm.

Figure 23. Upon removal of the healingabutment, the tissue looked healthy.

Figure 24. Interocclusal space allowed fora retentive prepared abutment to betorqued to 30 Ncm. Since the interocclusaldistance was greater than 5 mm, a customabutment and cement-on implant-retainedcrown was used.

Figure 25. The final monolithic zirconia(BruxZir) crown was cemented into position.

Figure 26. The final radiograph was takento verify proper seating and no remainingexcess cement.

Visualizing the case fin-ished before, along withany needed surgical inter-vention, is important if wekeep in mind that implantsare prosthetically driven.

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position, type, and size of implant tobe utilized prior to any surgery. Thefinal crown can even be designedbefore ever bringing a surgical bur tothe patient’s mouth.5

We all want what is best of ourpatients. With proper clinical train-ing and an experienced and skilledlaboratory team, the modern materi-als and techniques that are now avail-able allow clinicians to providepatients with the best in implant andrestorative services.�

References1. Wu T, Liao W, Dai N, et al. Design of a customangled abutment for dental implants using com-puter-aided design and nonlinear finite elementanalysis. J Biomech. 2010;43:1941-1946.

2. Lewis SG, Llamas D, Avera S. The UCLA abut-ment: a four-year review. J Prosthet Dent.1992;67:509-515.

3. Sheets JL, Wilcox C, Wilwerding T. Cement selec-tion for cement-retained crown technique withdental implants. J Prosthodont. 2008;17:92-96.

4. Wilson TG Jr. The positive relationship betweenexcess cement and peri-implant disease: aprospective clinical endoscopic study. JPeriodontol. 2009;80:1388-1392.

5. Ganz SD. Restoratively driven implant dentistryutilizing advanced software and CBCT: realisticabutments and virtual teeth. Dent Today.2008;27:122-127.

Dr. Kosinski received his DDS from theUniversity of Detroit Mercy Dental School andhis mastership in biochemistry from WayneState University School of Medicine. He is aDiplomate of the American Board of OralImplantology/Implant Dentistry, the Interna -tional Congress of Oral Implantologists, andthe American Society of Osseointegration. Heis a Fellow of the American Academy ofImplant Dentistry and received his Mas -tership in the AGD. He has received manyhonors, including Fellowship in the Americanand International Colleges of Dentists andthe Academy of Dentistry International. He isa member of OKU and the Pierre FauchardAcademy. He is currently an adjunct clinicalprofessor at the University of Detroit MercySchool of Dentistry, serves on the editorialreview board of REALITY and the MichiganDental Association Journal, and became theeditor of the Michigan AGD, of which he isimmediate past president. He has publishedmore than 150 articles on the surgical andprosthetic phases of implant dentistry andwas a contributor to the textbooks Principlesand Practices of Implant Dentistry and 2010’sDental Implantation and Technology. He wasthe University of Detroit Mercy School ofDentistry Alumni Association’s “Alumnus ofthe Year,” and in 2009 and 2014 received theAGD’s Lifelong Learning and ServiceRecognition Award. He was featured on NobelBiocare’s Nobelvision and lectures extensive-ly. He can be reached at (248) 646-8651 ordrkosin@aol.com.

Disclosure: Dr. Kosinski reports no disclosures.

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