24 Spectrum dialogue – Vol. 14 No. 1 – January 2015

Abstract

The number of totally edentulouspatients is steadily increasing,but so is the number of

solutions to their problems. Thepercentage of patients wearingcomplete dentures who are dissatisfiedwith their comfort and functionality ishigh, and the solution is to combinethese dentures with implant retention.

Removable implant-retainedoverdentures are a challenge both forthe clinician and for the technician,but this may be a comfortable,aesthetic and functional option for atotally edentulous patient who cannotafford a large number of implants, or ifinserting more implants positionedonto the whole surface of the dentalarch is not possible.

Case presentation

A55-year-old patient wearingmaxillary dentures decided that

he wanted to improve his level

of comfort, the aesthetics andfunctionality of the work.

The concept of removable implant-retained overdentures using theDolder bar is popular in Europe, but ithas been improved with theemergence of new technologies andmaterials.

The solution is to use a zirconia bar,milled at 2° with 2 anchor systems(attachments) at the distal end of thebar, with a golden secondary structureobtained by Galvanoforming.

This approach gives us theadvantage of a tension-free primarystructure made of zirconia, asecondary structure that offers us theadvantage of hydraulic retention anda tertiary structure that provides theendurance needed for a removablework.

In order to reach the next stage, weneed a dental impression that willreflect the exact position of theimplants and their axes. This stage is

very important, because the accuracyof the primary structure depends, to agreat extent, on the manner in whichthe position of the implants istransferred.

An open individual tray wasproduced on the first model, and theimpression abutments were connectedin the lab by means of a light cureduniversal modeling resin by primotecUSA/Germany: Primopattern Gel.(Figs. 1 & 2)

In order to facilitate the insertion ofthe impression abutments and to easethe practitioner’s job, theprimopattern bar was sectioned, thusobtaining an individual impressionguide. (Figs. 3)

The final impression was taken afterpositioning the abutments onto theimplants and reconnecting the bar inthe oral cavity by means ofPrimopattern Gel.

Implant Retained Overdentures– The Advantages of Zirconia

Cristian Petri, CDT

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Spectrum dialogue – Vol. 14 No. 1 – January 2015 25

Fig. 1

Fig. 3

Fig. 2

This procedure is useful to thepractitioner if he wishes to double-check his work, because the positionof the bar on the model must beidentical to its position inside the oralcavity.

The first step is to determine theshape and color of the teeth to beused. Although most reach this stagetowards the end of the work, it is veryimportant that, in the case of this typeof protocol, this step is placed at thevery beginning.

Why?

Because, after the occlusal relationdetermined and transferred it

into the articulator, an aesthetic andfunctional set-up is produced. Thisset-up is tried in inside the

oral cavity, and the rest of the stepsare to be carried out after the patientgives his consent about the aestheticaspect; all the other stages will beguided by the volume of the set-up.

Even though CAD is easy to use,i.e. automatically positioning the barand giving us all the accessoriesneeded to adjust or correct the

structure, if we know the finalposition of the teeth from the set-up,we will be able to place the structuresin the correct position and our workprocess will be streamlined.

The primary structure

The creation of a new work modelwas necessary: the master model,

cast in type IV plaster into theimpression taken with the individualtray. In the area of the implants,elastic silicone gum was used tofacilitate the transition at implantlevel, thus easily controlling thecheck-up of the structures’ adaptationto the implant platform.

Once the work models wereobtained and the intermaxillaryrelations were recorded using occlusalpatterns, all the information wastransferred into an articulator.

The mounting of the teeth was made

according to theestablished rules, but

also taking intoaccount the

antagonisticworks, the

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patient’s requests and the dentist’sinstructions. A silicone key was madeover the set-up, on both the vestibularand palatal sides, to guide us whenproducing the structures.

In addition to the advantages ofproductivity and precision,CAD/CAM also makes it easy for usto create a Dolder structure. At thefirst step the standard Titanium non-hex abutments (Fig. 4) wereprepared to obtain custom abutmentsand after that scans of the Titaniumbase non-hex abutments (Fig. 5), ofthe model and a double scan of theset-up were made. This scan of theset-up is the equivalent of siliconekeys made at the beginning in orderto guide ourselves on the model, thusobtaining the volume of the finalwork in 3D format, a volume that, aspreviously mentioned, guides us incorrectly positioning the bar. TheCAD library includes various types ofbars, shapes, positioning andmodelling instruments, but at thesame time it has certain restrictions; ifone wishes to change certain portionsof the bar that may jeopardize the

correct result, the software will blockthese operations.

These restrictions represent anadvantage for those who areinexperienced with this type ofstructures.

At the distal end of the structure,we positioned 2 Swift ART slidinganchor attachments from the CADlibrary. The 3D information of theanchor systems may be found in thelibrary of the software, depending onthe system we choose.

The attachments are positioned inthe insertion axis of the bar or, if onewishes, the axes may be modified. The

relation to the prosthetic field may beadjusted as needed.

The structure was milled in zirconia,with the help of CAD/CAM, andthen sintered (Fig. 6).

In order to secure the exact andrepetitive position of the Titaniumnon-hex abutments, we created a keymade of primotec’s Primosplint lightcured splint material, using it eachtime the abutments needed to bedetached from the model (Fig. 7).

Using dual cements, the titaniumabutments (Fig. 8) were sandblastedand cemented onto the zirconiastructure; thus, we obtained a passive-

26 Spectrum dialogue – Vol. 14 No. 1 – January 2015

Fig. 6

Fig. 4

Fig. 5

Fig. 8

Fig. 7

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28 Spectrum dialogue – Vol. 14 No. 1 – January 2015

Fig. 11

Fig. 9 Fig. 10

Fig. 12

Fig. 15

Fig. 13

Fig. 14

fit structure (Figs. 9, 10 & 11, Periapical x-rayobtained after 1 year. Bone adaptation is excellent)

Next, special attention was given to the finalfinishing of the zirconia structure, in order to obtaina bar milled at 2°. The finishing was carried out bymeans of the lab turbine and parallelometer. Thewalls of the structure were given their finishing usingdiamond milling tools and the sufficient amount ofwater spray. (Figs. 12 & 13)

At the extremities the attachments have beenchecked and the matrixes have been added. (Figs. 14 & 15)

The secondary structure

The zirconia structure was prepared in order toproduce the secondary structure by the

Galvanoforming process. The screws were positionedonto the bar and the retentive areas were covered inPrimopattern Gel, thus also obtaining a base for theGalvanoforming. (Fig. 16)

The zirconia bar was covered with a conductivesilver coating by the airbrush method. (Fig. 17) Fig. 16

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After the Galvanoforming process, (Fig. 18) the galvanizedgold structure was detached from the zirconia bar and theconductive silver coating was removed by means of a nitricacid based solution. (Figs. 19-21)

The tertiary structure

All components were repositioned onto the work model,and the retentive areas were blocked out with wax.

(Fig. 22) The entire surface of the golden secondary structurewas covered with a thin layer of wax, which is meant tocreate the space necessary for the cement film that would beused to cement the two structures. (Fig. 23)

In order to save time, the method of using a duplicatemodel was avoided. Instead, the tertiary structure was builtdirectly on the work model over the existing structures (Fig. 24) very efficiently using Primopattern Gel. Next, thecasting sprues were positioned and the tertiary structure wasinvested for casting. The silicone key was used at this stageas well, in order to check that enough space would be left atthe end for the aesthetic component and to make sure thatthe structure could be modeled so that the result would bedurable.

The tertiary structure was cast in CoCr alloy by theinduction method. After checking and polishing the tertiarystructure (Fig. 25), the golden structure was cemented into theCoCr tertiary structure, and the entire resulting structure wascoated with light-curing opaque material. (Fig. 26)

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Fig. 21

Fig. 17Fig. 18

Fig. 19

Fig. 20

Fig. 22

Fig. 23 Fig. 24

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The silicone guide was used again, inorder to reposition the denture teethin wax on top of the tertiary structure.The occlusal relation was checkedonce more; then, we went on totransform the physiognomiccomponent. In order to obtainimproved aesthetics for the artificialgum as well, several gingival masseswere used after injection. The colorswere placed directly into the siliconekey, in order to obtain as natural anaspect as possible for the artificial gum.The extra amount of gum needed wasinjected manually and polymerized at45°C, under a 2-bar pressure.

After the final polymerization, thedentures were divested, the surpluseswere removed and the work wascarefully processed by means of varioustypes of grinding tools, brushes andthreads. The final polishing wascarried out by means of biaxial brushesand pads. (Fig. 27, 28 & 29)

• Special thanks to Dr. Alina Picos for thecollaboration on this work.

Conclusion

In the attempts to restore oralimplants in the edentulous mandible,Dolder bars appear to offer a high rateof implant survival, good stability ofthe peri-implant tissue, and a low rateof prosthetic complications.

Additionally, the evolution oftechnology and materials makes itpossible for us to find varied solutionsand increase our productivity, whilealso improving precision. The comfortof totally edentulous patients whochoose this way of treatment is alsoimproved. In the end, it is up to eachtechnician to offer the patient acustomized smile.

32 Spectrum dialogue – Vol. 14 No. 1 – January 2015

Fig. 29

About the Author

Cristian Petri successfully completedhis 2-year dental technician college inCluj-Napoca, Romania in 1999.Subsequently, he worked as a dentaltechnician until 2001. He thendecided to work in the USA and

Germany as a dental technician for almost 2 years.(May – Oct. 2001: New Jersey and Dec. 2001-Nov. 2002: Althausen-MDT Alexander Konig).

In November 2002, he opened his own laboratory,Artchrys, in Cluj-Napoca. He has continued tofurther specialize as he has partaken in coursesconducted by Prof. Rudolf Slavicek, MTDMassimiliano Trombin, MTD Achim Ludvig, MTDJan Langner and MTD Haristos Girinis. Since 2011,he has lectured and published information regardingthe fabrication of complex implant restorations with afocus on function and aesthetics.

Since 2013, he has been the pilot lab forPrimotec/Germany and also the opinion leader inRomania for Artiglio-Italy.

Fig. 25 Fig. 26

Fig. 27

Fig. 28

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