Fab

CAD

Luis Infante, DD

aAssistant Professor, Louisiana StatebAssistant Professor, Division of RescProfessor, Division of Restorative andAdjunct Clinical Professor, Division

Infante et al

ricating complete dentures with

/CAM technology

S,a Burak Yilmaz, DDS, PhD,b

Edwin McGlumphy, DDS, MS,c and Israel Finger, DDS, MSd

School of Dentistry, Louisiana State University Health Sciences Center,New Orleans, La; Division of Restorative and Prosthetic Dentistry, TheOhio State University, College of Dentistry, Columbus, Ohio

Conventional complete denture prosthetics require several appointments to register the maxillomandibular relationship andevaluate the esthetics. The fabrication of milled complete dental prostheses with digital scanning technology may decrease thenumber of appointments. The step-by-step method necessary to obtain impressions, maxillomandibular relation records, andanterior tooth position with an anatomic measuring device is described. The technique allows the generation of a virtualdenture, which is milled to exact specifications without the use of conventional stone casts, flasking, or processing techniques.(J Prosthet Dent 2014;-:---)

Present-day advances have led tothe incorporation of computer-aideddesign/computer-aided manufacturing(CAD/CAM) technology into thedesign and fabrication of dental res-torations, including complete den-tures. Different systems for makingimpressions and fabricating casts of apatient’s dental structures have beenintroduced,1,2 some of which alsoallow for the production of specificrestorations in the laboratory, in thedental office, or at a centralized pro-duction center.3-5

The information for the develop-ment of a CAD/CAM cast or restora-tion can be acquired extraorally froman impression or from a cast ofthe object or intraorally by directlyrecording the structures intraorally.Different systems use different tools tocollect this information. Mechanicaldigitizing systems rely on touch probes(tactile),6,7 whereas optical digitizingsystems use cone beam computed to-mography,8,9 laser,5 or light-emittingdiode scanners.5,6 These data are pro-cessed by software and then usedto fabricate the desired object or

Universitytorative and Prostheof Restor

restoration with the CAM portion ofthe system.

In 2007, Quaas et al6 studied themeasurement uncertainty and the 3-dimensional accuracy of a mechanicaldigitizing system and concluded thatthe measurement uncertainty for thesystem was low and the precision washigh. However, they discouraged theapplication of this method for thedigitization of flexible impression ma-terials because the physical contact ofthe probe with the soft material mightlead to deformation and increased in-accuracy. In 2012, Goodacre et al2

proposed a technique to obtain maxil-lary and mandibular definitive impres-sions of the edentulous arches so thesecould be scanned and data acquired tomill denture bases with CAD/CAMtechnology. They also described theprocess for recording the neutral zone,the maxillary and mandibular anteriorteeth position, the palatal morphology,the occlusal vertical dimension, and theinterocclusal relation so these could beincluded as part of the process offabricating the bases. Furthermore, theyused a prototype of 3-dimensional

Health Sciences Center.d Prosthetic Dentistry, The Ohio State Universtic Dentistry, The Ohio State University.ative and Prosthetic Dentistry The Ohio State U

software that allowed the milling ofthe tooth sockets in the denture baseaccording to the desired arrangement.

The use of computer-generateddentures is changing the proceduresfor denture fabrication. CAD/CAMtechnology differs from the conven-tional method in that the laboratorywork is simplified and fewer appoint-ments are needed.10 Recently, Bidra11

reported the use of CAD/CAM tech-nology for the fabrication of mandib-ular implant-retained overdentures inonly 2 clinical appointments. Thisreport describes a technique to fabri-cate a complete dental prosthesis withCAD/CAM technology. The techniquepresented uses a standard clinical pro-cedure to fabricate dentures for a pa-tient with existing dentures in only 2appointments. The measurements wererecorded at the first appointment andinserted at the second appointment.

TECHNIQUE

1. Make a definitive impressionwith the impression materials and ther-moplastic moldable trays which are

ity.

niversity.

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available in different sizes (AvaDent).Initially, mix the 2 part heavy-consistencypolyvinyl siloxane (PVS) and press itinto the existing denture to create aPVS cast.

2. Measure the residual ridge andselect the appropriate thermoplastictray. Place the tray in a hot water bath(77�C) and mold to the cast.

3. Evaluate the tray intraorally toensure it covers all the appropriateanatomic areas and adjust the bordersas needed. As with any conventionaledentulous impression technique, drythe tissue with gauze. First, border themold with heavy-body material andmake the definitive impression with aregular-set light-body PVS material(Figs. 1, 2).

4. Choose the correct size anatomicmeasuring device (AMD) (1 of 3 avail-able sizes) (AvaDent) by using thecaliper to measure the widest part of

1 Maxillary definitive impression.

3 Maxillary and mandibular anatomic m(AMDs).

The Journal of Prosthetic Dentis

the residual ridge (Fig. 3). If the residualridge is between sizes, use the smallerAMD size. With the existing dentures inthe mouth, assess the occlusal verticaldimension (OVD) and rest positionwith a preferred assessment method.12

Establish whether these dimensions arecorrect or whether they need to bealtered. Once established, place dotson the patient’s facial features and re-cord the OVD with a caliper.

5. Coat the AMD maxillary traywith the specified adhesive (Express fastset polyvinyl siloxane PVS max-illomandibular registration record; Xer-tec) material onto the tray and placeintraorally to stabilize the AMD on theresidual ridge before making the re-cords. Coat the AMD mandibular traywith adhesive, express the PVS max-illomandibular relationship record ma-terial onto the tray, and place the trayin the mouth. Extend the mandibular

2 Mandibular defini

easuring devices 4 Maxillomandibulaexpressed into AMD m

try

AMD as far posteriorly as possible andplace it horizontally (Fig. 4).

6. Place both AMDs into themouth and attach the AvaDent ruler(Fig. 5). Align the ruler parallel to theinterpupillary line and record the anglethat will be used to correlate thecompleted AMD to the virtualmounting with software algorithms.With the central bearing tracing deviceresting on the mandibular tray, adjustthe OVD by turning the fitting on theside of the AMD to raise and lower thecentral bearing pin (Fig. 6). Thenconfirm the OVD. To confirm thecentric relation with a gothic archtracing, coat the tip of the bearing pinwith a marking agent, coat themandibular tray with occlusal spray, orrub it with occlusal paper. Guide thepatient’s mandible back and tracelateral, anterior, and posterior excur-sions on the mandibular tray with the

tive impression.

r relationship record material beingaxillary tray.

Infante et al

5 Registration of interpupillary line. 6 OVD adjustment by turning screw on side of AMD.

7 Stabilization of AMD by injecting maxillomandibularrelationship record material into area between maxillary andmandibular trays.

8 Use of composite resin to stabilize transparent guide.

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bearing pin. Direct the patient to “keepjaws together,” “slide lower jaw as farforward as possible,” “as far back aspossible,” and “as far left and right aspossible.” Create the gothic archtracing accordingly.

7. Remove the mandibular tray anddrill a divot into the tray at the tip ofthe arrow. Replace the tray intraorally,place the tip of the pin into the divot,and stabilize the AMD by liberallyinjecting maxillomandibular relation-ship record material into the area be-tween the maxillary and mandibularAMD trays (Fig. 7). Remove any recordmaterial from the maxillary AMD thatmight interfere with the drape of the lip.Adjust the lip support to the desired lipfullness by turning the fitting on theanterior of the lip support.

8. As a guide for selecting theappropriate denture tooth mold, overlay

Infante et al

the esthetic transparent guide onto theexisting denture. Use 1 of 3 overlayesthetic transparent guides, which repre-sent different tooth sizes. Once theproper transparent guide is chosen,establish the desired gingival height andmark it on the prescription. Mark themidline and incisal edge for the anteriorteeth on the lip support. Place compositeresin (Tetric EvoFlow; Ivoclar Vivadent)onto the transparent guide and adherethis to the lip support. With the AMD inthe mouth, verify the esthetics and OVD(Fig. 8).

9. Send both the completed im-pressions and the final AMD to thelaboratory for fabrication of thedentures.

10. Examine the digital preview vir-tual setup sent by the laboratory, andmodify the design of the denture ifneeded (Fig. 9).

11. Once processed, the dentures arereturned to the dentist for delivery tothe patient (Fig. 10).

DISCUSSION

Many materials have been used inthe fabrication of denture bases. Fromwood to porcelain, no material hasreceived the same attention or gainedthe same popularity as PMMA [poly(-methyl methacrylate)].13-15 Althoughit is the most common materialused today, PMMA is not withoutproblems. These problems are related toprocessing, porosity, fracture strength,dimensional stability, color stability,and biocompatibility (allergenic re-actions).16,17 Challenges with the use ofPMMA bases are being met by eitherimproving the qualities and properties

9 Virtual arrangement.

10 Maxillary and mandibular complete dental prosthesis.

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of the material or the use of alternativematerials.18-22 The AvaDent denturesare produced by machining a pre-formed cylinder of acrylic resin mate-rial. This cylinder is produced underhigh pressure and heat, which preventsshrinkage of the definitive milled pros-thesis. As a result of the highly con-densed resin, there is a decrease in freemonomer, a decrease in the porositywhen compared to a conventionallyprocessed denture, and a decrease inthe retention of Candida albicans by thedenture base.10 Manufactured acrylicresin teeth, which are not CAD/CAMproduced, are used.

The fabrication in the laboratorystarts with relating the scanned maxil-lary and mandibular impressions to thescanned AMD. The 2 files are digitallyoverlaid and merged by best-fit trian-gulation. Millions of digital trianglesoverlap each other to form a verticalrepresentation of jaw position and

The Journal of Prosthetic Dentis

vertical height. A virtual record base iscreated, and functional controls arethen applied. The algorithms for theocclusal arrangement are written usingtraditional rules.12 The occlusal planeis set from the incisal edges of themandibular teeth to halfway up theretromolar pad, and the curves ofSpee and Wilson are incorporated intothe software to create the optimumocclusal arrangement on the basis ofthe operator’s preference. Lingualizedor monoplane occlusal schemes may bechosen.23 The designed software ar-ranges the teeth according to the spe-cific guidelines of the desired occlusion,with the transparency being the guidefor the maxillary anterior teeth. A digitalpreview is sent to the dentist, who canexamine the virtual setup and modifythe design of the denture.

Once the design of the teeth isaccepted by the clinician, the intagliosurfaces of the denture and tooth

try

sockets are milled with a 5-axis millingmachine. The sockets for the selectedteeth are milled according to the posi-tion of the selected teeth. The selectedteeth are chemically bonded to theAvaDent base material by means of aproprietary PMMA bonding techniquethat uses heat and pressure, or ifrequested, a clinical evaluation of thedenture can be selected. The teeth areset into the milled sockets in wax andreturned to the dentist for evaluation,allowing for movement of the anteriorand posterior teeth, adjustment ofthe occlusion, and adjustment of thedenture base. In the wax evaluationmethod, the teeth are attached to thebase with conventional techniques.

Should the patient not have existingdentures, irreversible hydrocolloid im-pressions are made and casts arepoured. The thermoplastic trays areadapted to these casts. The verticaldimension of rest is obtained by the useof phonetics, specifically the bilabialsounds. Once obtained, the OVD iscalculated. The same technique is thenfollowed as with a patient who hasexisting dentures.

The stability of a denture, that is theability to “resist displacement by func-tional horizontal or rotational stresses,”depends to a great degree on the oc-clusion and base adaptation.24 Thetransfer of concentrated stresses fromthe denture base to the underlyingsupporting structures has been associ-ated with trauma to the tissues andaccelerated bone resorption.25-27 In thecurrently described technique, thereshould be reduced dimensional sta-bility problems because the denture ismilled from preformed acrylic resin.This quality should compare favorablyto bases fabricated with conventionalprocessing techniques. This may con-tribute to the improved stability andretention of the denture base with lesstrauma and fewer postinsertion ad-justment visits.

The digital system facilitates thecompletion of dentures in 2 visits. Im-pressions, occlusal relation records, andan orientation record are made at thefirst visit and the dentures inserted at the

Infante et al

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second. This significantly reduces thetime the patient spends in the dentaloffice. Unlike in the fabrication of con-ventional dentures, there is no facebowrecord. If the maxillomandibular recordis made at the correct OVD, the lack offacebow should not cause any error. Arepository of the digital record is stored,and an exact duplicate denture can bereproduced at any time. The denture canbe designed according to the dentist’sspecifications. Bases can be fabricatedwith various anatomic features, in-cluding stippling, rugae, thickness ofthe actual base, and borders of thedentures. A wax evaluation can also berequested. Various shades of acrylicresins are available for the fabrication ofthe bases, and manufactured acrylicresin teeth are used. The denture teethare placed virtually and the bases withtooth sockets milled. The exact positionsof the teeth are recorded. These toothpositions are compared to a scan madeof the denture and tooth positions afterthe dentures have been fabricated. Avirtual remount is possible, and wherediscrepancies are noted, the equilibra-tion of the teeth is completed in themilling center and clinical remountprocedures are avoided. A denture kit isprovided with all the materials requiredto make the initial records and impres-sions. The actual scanning of records ismade off-site, eliminating the need forthe dentist to purchase expensive ma-chines. Commercial laboratories cannow scan impressions and design thedentures; however, all denture basemilling is done at the central laboratory.Complete dentures, immediate den-tures, and implant dentures can befabricated with this system.

Although initial results are prom-ising, the technique has some disad-vantages. The central bearing tracingdevice can be a challenging method ofrecording jaw relationships. Althoughthe recording of the gothic arch tracingin some patients may be difficult,

Infante et al

alternative techniques are being intro-duced. Further, the system does notprovide for all schemes of occlusion,and no long-term results have beenpublished. Long-term clinical trialsshould be performed to evaluate thesuccess of the technique presented.

SUMMARY

A technique for the fabrication of aCAD/CAMdenture is described. By usingan AMD, the dentist can make clinicalrecords in 1-step appointments. TheAMD allows the clinician to gather all theclinical information needed with a singleintraoral device. The virtual denture ismilled to exact specifications without theuse of conventional stone models orflasking and processing techniques.

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Corresponding author:Dr Burak YilmazThe Ohio State University, College of DentistryDivision of Restorative and Prosthetic DentistryColumbus, Ohio 43210E-mail: yilmaz.16@osu.edu

Copyright ª 2014 by the Editorial Council forThe Journal of Prosthetic Dentistry.