Fabrication of Metal-Reinforced Complete Dentures Using the CAD-CAM Technique

applied sciences

Technical Note Fabrication of Metal-Reinforced Complete Dentures Using the CAD-CAM Technique

Xing-Yu Piao , June-Sung Shim and Ji-Man Park *

Department of Prosthodontics, College of Dentistry, Yonsei University, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea; [email protected] (X.-Y.P.); [email protected] (J.-S.S.) * Correspondence: [email protected]

Abstract: The digital manufacture of complete dentures would greatly simplify the workﬂow; however, the metal-reinforced complete dentures production method has not been well established. This article describes a technique of fabricating metal-reinforced complete dentures in a milling machine using the geometry guide, a negative impression of the occlusal surface of the metal- reinforced complete denture designed using the computer-aided design software. The geometry guide supports and stabilizes the artiﬁcial teeth and metal framework in the correct position in the surrounding resin. Fabrication of metal-reinforced dental prosthesis using the digital technique is possible with this method.

Keywords: CAD-CAM; geometry guide; dental prosthesis; metal substructure

1. Introduction With the wide applications of digital technology in dentistry, research to establish a Citation: Piao, X.-Y.; Shim, J.-S.; Park, completely digital workﬂow for the fabrication of complete dentures has been underway J.-M. Fabrication of Metal-Reinforced since 1994 [1]. Currently, complete dentures are being fabricated using computer-aided Complete Dentures Using the design and computer-aided manufacturing (CAD-CAM) via milling or rapid prototyping CAD-CAM Technique. Appl. Sci. methods. The clinical feasibility of these dentures has been proven [2–5]. Additionally, 2021, 11, 7369. https://doi.org/ various advantages have been reported, such as better ﬁt, retention, easy reproduction, and 10.3390/app11167369 decreased manipulation [6,7]. However, fabricating metal-reinforced complete dentures

Academic Editor: Anming Hu using the digital technique is different, as these dentures are fabricated using at least two other materials.

Received: 5 July 2021 Metal-reinforced complete dentures are associated with improved retention, reduced Accepted: 29 July 2021 probability of fracture, and greater patient satisfaction in terms of comfort and pronunci- Published: 11 August 2021 ation compared to conventional resin-based complete dentures [8]. Metal denture bases, fabricated using selective laser melting, milling, stereolithography apparatus, or digital Publisher’s Note: MDPI stays neutral light processing techniques, have been found to be feasible for clinical use [9,10]. Digi- with regard to jurisdictional claims in tal fabrication of metal-reinforced complete denture bases using the current technology published maps and institutional affil- is difficult. iations. To overcome this limitation, considerable research has been conducted. Oh et al. [11] introduced a method to combine the digital technique and conventional flask procedure to fabricate a removable partial denture. Moreover, Park et al. [12] fabricated a digital denture by bonding the functional cusps of artificial teeth manufactured using a 3D metal printer Copyright: © 2021 by the authors. with the resin denture base. Nevertheless, a fully digital workflow for the fabrication of Licensee MDPI, Basel, Switzerland. metal-reinforced complete dentures, preserving the basic structure, has not been developed. This article is an open access article Hence, in this technical article, we report a novel method to add a metal framework distributed under the terms and structure to the complete denture milling procedure. A geometry guide, an indentation for conditions of the Creative Commons the complete denture, was designed to determine and replicate the correct positions of the Attribution (CC BY) license (https:// artificial teeth and metal framework. creativecommons.org/licenses/by/ 4.0/).

Appl. Sci. 2021, 11, 7369. https://doi.org/10.3390/app11167369 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 6 Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 6 Appl. Sci. 2021, 11, 7369 2 of 5

2. Materials and Methods 2. Materials and Methods 2.1.2. Materials Technical andNote: Methods Designing Process on the CAD Software 2.1. Technical Note: Designing Process on the CAD Software 1.2.1. TechnicalDigitize Note:the master Designing casts Processand the on occlusal the CAD relation Software record by scanning using a desktop 1.1. scannerDigitizeDigitize (T500;the master Medit, casts Seoul, and Korea);the occlusal re relationlation record by scanning using a desktop 2. Designscannerscanner the (T500; metal Medit, frameworks Seoul, Korea); with the attachments and complete dentures for both 2. archesDesignDesign separatelythe metal frameworks in the CAD with software the attachments (Exocad DentalCAD and complete 2.4 denturesdenturesPlovdiv; forforExocad bothboth GmbH,archesarches separately Darmstadt, in Germany) the CAD using softwaresoftware the acquired (Exocad(Exocad data; DentalCADDentalCAD 2.42.4 Plovdiv;Plovdiv; ExocadExocad 3. ReplaceGmbH,GmbH, Darmstadt, the denture Germany) base with using the correspondi the acquired ng data;tissue surface of the dental cast in 3. theReplaceReplace CAD the software denture (Meshmixer; base with theAutodesk, correspondingcorrespondi Inc., Sanng tissue Rafael, surface CA, USA) of thethe in dentaldentalthe imported castcast inin standardthethe CAD CAD softwaretessellation software (Meshmixer; language (STL) Autodesk, files. Inc.,CombineInc., SanSan Rafael,Rafael, the denture CA,CA, USA)USA) and indesignedin thethe importedimported metal frameworkstandardstandard tessellation (Figure 1); language (STL) ﬁles.files. Combine the denture andand designeddesigned metalmetal frameworkframework (Figure (Figure 11););

Figure 1. Design of metal-reinforced complete dentures. Yellow portion represents the metal frame- workFigure with 1. Design the attachments. of metal-reinforced (A) Maxillary complete denture. dentures. (B) Mandibular Yellow portion denture. represents the metal frameworkwork withwith thethe attachments.attachments. ((AA)) MaxillaryMaxillary denture.denture. ((BB)) MandibularMandibular denture.denture. 4. Extrude the metal portion by 1 mm and export the modified metal-reinforced com- 4. Extrude the metal portion by 1 mm and export the modiﬁed metal-reinforced complete 4. pleteExtrude denture the metal data; portion by 1 mm and export the modified metal-reinforced com- denture data; 5. Designplete denture the geometry data; guide for the metal-reinforced complete dentures using the 5. Design the geometry guide for the metal-reinforced complete dentures using the 5. “BooleanDesign the command” geometry inguide the CAD for the software metal-reinforced (Meshmixer; complete Autodesk, dentures Inc., San using Rafael, the “Boolean command” in the CAD software (Meshmixer; Autodesk, Inc., San Rafael, CA,“Boolean USA) command”that contains in the the negative CAD software impression (Meshmixer; of a part of Autodesk, the metal-reinforced Inc., San Rafael, com- CA, USA) that contains the negative impression of a part of the metal-reinforced pleteCA, USA) dentures that contains(Figure 2); the negative impression of a part of the metal-reinforced com- pletecomplete dentures dentures (Figure (Figure 2); 2);

Figure 2.2. Design process for thethe primaryprimary geometrygeometry guide of thethe maxillarymaxillary denture.denture. (A)) SelectingSelecting thethe regionregion coveringcovering thethe metalFigure base 2. Design and artiﬁcialartificial process teethteethfor the onon primary aa basebase structure. structure.geometry (guideB)) ExtrudingExtruding of the maxillary thethe selectedselected denture. areaarea inin(A a)a Selecting verticalvertical direction.direction. the region ((C covering)) ApplyingApplying the metal base and artificial teeth on a base structure. (B) Extruding the selected area in a vertical direction. (C) Applying “Boolean“Boolean Difference”Difference” commandcommand between the base structure and denture to eliminate the area occupied by the denture. “Boolean Difference” command between the base structure and denture to eliminate the area occupied by the denture. ((D)) DiscardingDiscarding thethe upperupper structurestructure afterafter thethe commandcommand isis performed.performed. ((EE)) InspectingInspecting thethe primaryprimary geometrygeometry guide.guide. (D) Discarding the upper structure after the command is performed. (E) Inspecting the primary geometry guide. Appl. Sci. 2021, 11, 7369 3 of 5 Appl. Sci. 2021,, 11,, xx FORFOR PEERPEER REVIEWREVIEW 3 of 6

6. Modify the geometry guide design by discarding the labial, mesial, and distal surfaces 6. Modify the geometry guide design by discarding the labial, mesial, and distal sur- of the teeth sockets (Figure3). Export the STL ﬁle of the geometry guide. faces of the teeth sockets (Figure 3). Export the STL file of the geometry guide.

FigureFigure 3.3. DesignDesign of the geometry guides. ( A)) MaxillaryMaxillary geometrygeometry guide.guide.guide. ( (B)) Mandibular Mandibular geometrygeometrygeometry guide.guide.

2.2.2.2. Technical Note:Note: FabricationFabrication ofof DentalDental ProsthesisProsthesis 1.1. MillMill the the artificial artiﬁcial teeth teeth from from a double a double cross-linked cross-linked resin resin disk disk (SR (SRVivodent Vivodent CAD; CAD; Ivo- clarIvoclar Vivadent Vivadent AG, AG, Schaan, Schaan, Liechtenstein). Liechtenstein). Fabricate Fabricate the themetal metal framework framework using using the the lost-wax casting technique after milling the wax pattern (Mazic Wax; VERICOM lost-waxlost-wax castingcasting techniquetechnique afterafter millingmilling thethe waxwax patternpattern (Mazic(Mazic Wax;Wax; VERICOMVERICOM Co.,Co., Co., Ltd., Chuncheon, Korea); Ltd., Chuncheon, Korea); 2. Mill the geometry guide from the gypsum poured on the metal holder attached to 2. Mill the geometry guide from the gypsum poured on the metal holder attached to the milling machine. Mill the designs in a milling machine (Rainbow Mill-Zr 2nd; the milling machine. Mill the designs in a milling machine (Rainbow Mill-Zr 2nd; Dentium Co., Ltd., Seoul, Korea) after calculating the toolpath; Dentium Co., Ltd., Seoul, Korea) after calculating the toolpath; 3. Bond the artiﬁcial teeth and the metal framework to the geometry guide (Figure4); 3. Bond the artificial teeth and the metal framework to the geometry guide (Figure 4);

FigureFigure 4.4. ArtiﬁcialArtificial teeth teeth and and metal metal framework framework bonded bonded to the totogeometry thethe geometrygeometry guide guideguide within withinwithin the metal thethe holder. metalmetal (holder.A) Maxillary (A)) MaxillaryMaxillary structure. structure.structure. (B) Mandibular ((B)) MandibularMandibular structure. structure.structure.

4.4. PourPour autopolymerizingautopolymerizing resinresin (Retec (Retec PRESS PRESS LT; LT; Retec Retec Kunststofftechnik Kunststofftechnik GmbH, GmbH, Ros- Rosbach,bach, Germany) Germany) to fillto fill the the space space above above the the geometry geometry guide. guide. Cure Cure the the resin resin using using a adental dental polymerization polymerization unit unit (Palamat (Palamat elite; elite; Kulzer Kulzer GmbH, GmbH, Hanau, Hanau, Germany)Germany) asas perper thethe manufacturer’s manufacturer’s instructions; instructions; 5.5. SetSet thethe metalmetal holder holder that that contains contains the the geometry geometry guide, guide, artificial artificial teeth, teeth, and metal and frame-metal frameworkwork in the in milling the milling machine. machine. Mill Mill the denture the denture according according to the to acquiredthe acquired modified modi- fieddenture denture data, data, in which in which themetal the metal portion portion is extruded is extruded by 1 by mm 1 mm (Figure (Figure5); 5); 6. Remove the attachments, gypsum, and resin covering the metal base. Finish the prosthesis by polishing (Figure6). Appl. Sci. 2021, 11, x FOR PEER REVIEW 4 of 6

Appl.Appl. Sci. 20212021,, 1111,, 7369x FOR PEER REVIEW 44 of of 56

Figure 5. Fabrication of metal-reinforced complete denture extruded by 1 mm.

6. Remove the attachments, gypsum, and resin covering the metal base. Finish the pros- Figurethesis 5. Fabrication by polishing of metal-reinforced (Figure 6). complete denture extruded byby 11 mm.mm.

6. Remove the attachments, gypsum, and resin covering the metal base. Finish the prosthesis by polishing (Figure 6).

FigureFigure 6. 6. FinalFinal prosthesis prosthesis after after polishing. polishing. ( (AA)) Maxillary Maxillary denture. denture. ( (BB)) Mandibular Mandibular denture. denture. ( (CC)) Intraoral Intraoral photograph. photograph.

3.3. Discussion Discussion Figure 6. Final prosthesis afterInIn polishing. this this technique, technique, (A) Maxillary the the denture denture denture. base base (B) Mandibulardesigned designed in in denture. the the CAD CAD (C )software softwareIntraoral photograph.was was first first replaced replaced withwith the the corresponding corresponding tissue tissue surface surface of of the the de dentalntal cast cast to to obtain obtain an an ideal ideal denture denture border border andand3. Discussion enhance enhance the the retention retention and and stability stability of of the the denture denture [13]. [13]. The The geometry geometry guide, guide, specially specially designeddesignedIn this through through technique, this this technique, technique,the denture functions functions base designed as as a a connector connector in the CAD to to maintain maintain software parts parts was of of first the the replaceddenture denture ininwith the the thecorrect correct corresponding position. position. To To tissue maintain maintain surface a a stable stable of the position, position,dental cast three three to obtainhemispheres hemispheres an ideal were were denture attached attached border to to thetheand maxillary maxillaryenhance flatthe flat retentionmetal metal base base and and and stability three three bars bars of the were were denture attached attached [13]. to to The the the geometrymandibular mandibular guide, metal metal specially frame- frame- work.work.designed The The through customized customized this technique,design design of of thefunctions the artifici artificial asal ateeth teeth connector ensures ensures to ideal idealmaintain teeth teeth parts arrangement of the denture and and interocclusalinterocclusalin the correct relationship relationshipposition. To as asmaintain per per individual individual a stable requirements. requirements.position, three In In hemispheres addition, addition, milling milling were attachedindividual individual to teethteeththe maxillary from from a a double double flat metal cross-linked cross-linked base and resin resinthree block block bars awere accordingccording attached to to the the to CAD CADthe mandibular data data provides provides metal adequate adequate frame- estheticsestheticswork. The and and customized accuracy. accuracy. design of the artificial teeth ensures ideal teeth arrangement and interocclusalOhOh et et al. al. [11]relationship [11] utilized utilized theas the per CAD-CAM CAD-CAM individual techniqu technique requirements.e to to mill mill Inthe the addition, denture denture millingbase base and and individual artificial artificial teethteeth fromfrom from a a doublewax wax disk. disk. cross-linked After After the the resinplacement placement block aofccording of the the wax wax to structure structurethe CAD dataand and metalprovides metal framework, framework, adequate conventionalconventionalesthetics and flaskingaccuracy. flasking and and injection injection molding molding were were performed. performed. Thus, Thus, the thepossibility possibility of in- of inevitable errors in these conventional flasking and packing procedures cannot be excluded. evitableOh errors et al. [11] in these utilized conv theentional CAD-CAM flasking techniqu and packinge to mill procedures the denture cannot base beand excluded. artificial However, in our technique, unexpected errors can be eliminated as the conventional However,teeth from in a our wax technique, disk. After unexpected the placement errors of can the be wax eliminated structure as theand conventional metal framework, man- manual procedures were replaced by the geometry guide and subtractive milling process. ualconventional procedures flasking were replaced and injection by the moldinggeometry were guide performed. and subtractive Thus, millingthe possibility process. of Ad- in- Additionally, polymerization shrinkage of the base resin will not affect the fit of the denture, ditionally,evitable errors polymerization in these conv shrinkageentional flaskingof the base and resin packing will proceduresnot affect the cannot fit of thebe excluded. denture, as the resin is cured before the milling procedure [7,14]. asHowever, the resin in is our cured technique, before the unexpected milling procedure errors can [7,14]. be eliminated as the conventional man- The limitation of this method is that additional efforts are required compared to the ual proceduresThe limitation were of replaced this method by the is thatgeometry additional guide efforts and subtractive are required milling compared process. to Ad-the commonly used commercial techniques, due to the lack of automatic function in the CAD commonlyditionally, usedpolymerization commercial shrinkage techniques, of thedue base to the resin lack will of aunottomatic affect thefunction fit of thein the denture, CAD software for replacing the palatal part of the denture base with the metal base. To protect softwareas the resin for isreplacing cured before the palatal the milling part of procedure the denture [7,14]. base with the metal base. To protect the milling burs from breakage while in contact with the metal base, the corresponding the millingThe limitation burs from of breakagethis method while is that in co additionalntact with efforts the metal are required base, the compared corresponding to the region should be extruded by 1 mm while designing. Thin remnant parts of pink resin and region should be extruded by 1 mm while designing. Thin remnant parts of pink resin gypsumcommonly should used becommercial removed aftertechni theques, milling due to process. the lack of automatic function in the CAD and gypsum should be removed after the milling process. softwareWith for the replacing geometry the guide palatal providing part of the support denture and base stability with the for allmetal components base. To protect in the rightthe milling position, burs this from technique breakage can while be applied in contact in edentulous with the cases.metal Furthermore,base, the corresponding additional clinicalregion should studies be are extruded needed to by comprehensively 1 mm while designing. evaluate theThin metal-reinforced remnant parts completeof pink resin den- and gypsum should be removed after the milling process. Appl. Sci. 2021, 11, 7369 5 of 5

tures fabricated using this method. In addition, research can be conducted for the adaption of this technique in the manufacturing of removable partial dentures and overdentures.

4. Conclusions This technique enables the fabrication of metal-reinforced complete dentures via the CAD-CAM technique using a specially designed geometry guide. The digital technique offers the possibility of fabricating dental prostheses using more than 2–3 materials.

Author Contributions: Conceptualization, X.-Y.P. and J.-M.P.; methodology, X.-Y.P. and J.-M.P.; software, X.-Y.P.; validation, X.-Y.P., J.-S.S. and J.-M.P.; formal analysis, J.-M.P.; investigation, X.-Y.P.; resources, J.-M.P.; writing—original draft preparation, X.-Y.P.; writing—review and editing, X.-Y.P. and J.-M.P.; visualization, X.-Y.P. and J.-M.P.; supervision, J.-M.P.; project administration, J.-M.P.; and funding acquisition, J.-S.S. and J.-M.P. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Korea Medical Device Development Fund grant funded by the Korea government, Grant number: 202011A02. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: The authors thank Jeon, J. of the Central Laboratory, Yonsei University for the technical assistance with CAD and laboratory procedures. Conﬂicts of Interest: The authors declare no conﬂict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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