Indirect Digital Workflow for Virtual Cross-Mounting of Fixed

Implant-Supported Prostheses to Create a 3D Virtual Patient

Luca Lepidi, DDS, MDSc ,1 Matthew Galli, DDS,2 Aldo Grammatica, SDT,3 Tim Joda, DMD, MSc ,4
Hom-Lay Wang, DDS, MSC, PhD,2 & Junying Li, DDS, MS, PhD2
1
Department of Clinical and Experimental Medicine, University of Foggia School of Dentistry, Foggia, Italy
2
Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, MI
3
Private Practice, Corato, Italy
4
Department of Reconstructive Dentistry, University Center for Dental Medicine Basel, University of Basel, Basel, Switzerland

Keywords Abstract
Virtual cross-mounting; centric relation; 3D
virtual patient; digital mounting; virtual face
Mounting dental casts in an articulator is an important prerequisite for prosthodontic
bow; digital dentistry; face scan. rehabilitation cases where the design of an accurate static and dynamic occlusion is
needed. Virtual mounting can be achieved through the superimposition of various
Correspondence 3D images acquired from the hard and soft tissues of the patient. The purpose of
Luca Lepidi, DDS, MDSc, Department of this technical report is to describe a digital cross-mounting technique for patients
Clinical and Experimental Medicine, undergoing implant-supported fixed prosthetic treatment. Through the use of face
University of Foggia School of Dentistry, 48 scanning, intraoral scanning, and cone beam computed tomography, this technique
Via Luigi Rovelli, Foggia 71122, Italy. E-mail: enables creation of a 3D virtual patient with occlusal registration in centric relation.
lucadrlepidi@gmail.com Ultimately, the described methodology allows for the fabrication of definitive full-
mouth implant-supported fixed prostheses.
This research did not receive any specific
grant from funding agencies in the public,
commercial, or not-for-profit sectors.

The authors declare that there are no conflicts

of interest in this study.

Accepted August 26, 2020

doi: 10.1111/jopr.13247

The new possibilities for acquiring and processing digital can be used to guide the mandible into a stable CR position.
data from cone beam computed tomography (CBCT), intrao- In conjunction with intraoral scanning, the desirable maxillo-
ral scanners (IOS), desktop scanners (DS), face scanners (FS), mandibular relationship can then be recorded according to the
and computer assisted design software (CAD software) allow treatment goals.12
for the creation of a virtual dental patient.1 Mounting casts on In daily practice, cross-mounting describes the interchange-
an articulator is a necessary step in the treatment of complex able mounting on an articulator of maxillary and mandibu-
prosthetic cases, especially when re-establishment of the ver- lar cast relationships.13 Transferring the maxillo-mandibular
tical dimension of occlusion (VDO) in centric relation (CR) is relationship from the patient to an articulator may lead
involved.2 Several studies have reported techniques for mount- to discrepancies.14 The introduction of new digital cross-
ing the arches on a virtual articulator (VA) in maximal in- mounting workflows in prosthodontics highlights the need to
tercuspal position (MIP).3–6 The accuracy and reliability of study and validate the use of these procedures. Digital CR
using digital impressions for the fabrication of single-unit or registration and virtual cross-mounting workflows in fixed
short-span fixed dental reconstructions has been demonstrated, prosthetic cases have been reported in the literature.12,14,15
whereas in the case of full-arch rehabilitation, a conventional Techniques for recording and transferring the position of the
approach is still recommended due to a lack of evidence.7 upper jaw relative to the skull to a VA have been described by
VAs can be assembled using workflows that incorporate other authors.16 Although there are studies reporting on cross-
analog steps (indirect procedure) or entirely digitally (direct mounting techniques17 and 3D reconstruction of patients,18
procedure).8–11 The virtual dental space created with an in- previous articles did not describe a data transfer procedure for
direct digital method for virtual occlusal analysis has been maxillofacial hard and soft tissues allowing for digital cross-
considered repeatable.8 During bite registration and occlusal mounting in CR on a VA. Thus, the purpose of this article
analysis, a leaf gauge and Lucia jig are clinical tools that was to describe a technique for digital cross-mounting of fixed

Journal of Prosthodontics 00 (2020) 1–7 © 2020 by the American College of Prosthodontists 1

Virtual Cross-Mounting to Create a 3D Virtual Patient Lepidi et al

implant-supported provisional prostheses (FIPPs) in order to

construct a 3D virtual patient, ultimately allowing for fabrica-
tion of definitive full-mouth implant-supported prostheses.

Technique
A fully edentulous patient that received full-mouth implant
surgery and interim restorations is presented in this article. The
interim prostheses were based on the patient’s habitual occlu-
sion and were inserted four months prior to initiation of the
workflow described in this study and the patient was satis-
fied with the esthetics and occlusion. To fabricate the definitive
restorations with CAD/CAM, data from the master casts and
Figure 1 Virtual provisional prostheses using IOS. (A) STL file of the op- the existing occlusion of the patient were acquired digitally. To
tical scan of the upper fixed prosthesis. (B) STL file of the optical scan achieve this, a digital cross-mounting procedure involving four
of the lower fixed prosthesis. (C) Lucia jig between the arches used for
phases (scanning provisional prostheses, creating virtual mas-
occlusal registration. (D) STL file of IOS in CR position.
ter casts, digital facebow transferring, and virtual articulation
in CR) was performed. The devices used include: an intrao-
ral scanner (Cs 3600, Carestream Health, Rochester, NY), FS
(Dental Pro Bellus 3D; Bellus 3D Inc, Campbell, CA), desktop
scanner (Neway, Faro Technologies Inc., Brescia, Italy), and a
CBCT machine (Cs 9600 3D, Carestream Health, Rochester,
NY). The software used were a dental CAD software (Exocad;
exocad GmbH, Darmstadt, Germany) and a STL file editing
software (Meshmixer; autodesk, San Rafael, CA).
Maxillary arch data can be acquired through the use of IOSs
or DSs with either a direct or indirect workflow. In the present
technique, direct digital impressions of the provisional pros-
theses were performed in the following manner:
1. An optical scan of the upper and lower fixed prosthesis
was acquired.
2. A Lucia jig was digitally designed starting from vir-
Figure 2 Summary of steps in the workflow for fabricating virtual master tual scans. Occlusal registration was performed by us-
casts. (A) Intraoral view of the lower arch. (B) Master gypsum cast with ing a leaf gauge, and then a Lucia jig was fabricated via
implant analogues was fabricated using the temporary prosthesis. (C) milling.
Master gypsum casts. (D) Scan bodies on master gypsum cast ready to 3. An interocclusal record of the interim prostheses was ob-
be scanned by DS. tained by IOS while using the 3D printed anterior Lucia
jig to maintain the patient’s jaws in the desired CR and
VDO positioning (Fig 1).
An indirect technique was used to obtain the virtual master
cast as follows:
1. The temporary prostheses were removed from the pa-
tient. Implant analogues were connected to the prosthe-
ses. Gypsum was poured around the analogues to create
a master cast.
2. Together with the interim restorations, the casts were
scanned using the DS.
3. The interim restorations were detached and scan bodies
were mounted onto the upper and lower master gypsum
casts.
4. DS was used to scan the casts in order to acquire an
Figure 3 Summary of additional steps involved in the workflow for fabri-
impression of the implant positions through an indirect
cating virtual master casts. (A, B) Virtual master models with implant ana- method (Fig 2).
logues matched with a scan of the prostheses screwed onto the master 5. A digital master model with implant analogues that
casts. (C, D) Virtual masters casts. The red arrow shows the markers. matched with the indirect impression of each model was
subsequently constructed. The digital master casts were

2 Journal of Prosthodontics 00 (2020) 1–7 © 2020 by the American College of Prosthodontists

Lepidi et al Virtual Cross-Mounting to Create a 3D Virtual Patient

Figure 4 Digital cross-mounting procedure. (A, B) Upper and lower virtual master casts matched with STL files in CR by IOS. (C, D) Matching of upper
virtual master cast with STL file obtained by DS of the 3D printed model on the fork to allow for transfer of occlusal registration in CR onto the fork.
(E) Lower virtual master cast matched with STL file in CR by IOS. (F) Virtual master casts in CR after cross-mounting.

Figure 5 Digital facebow and transfer procedure. (A) Matching between the face scan with the fork and virtual casts on the fork in CR. (B) Matching
between the face scan with the fork and the face scan without the fork in the resting position. (C) Superimposition of the face scan and scans of the
arches with the fork in place. (D) Superimposition of the 3D skull with the previous step. (E, F) Virtual patient with and without the fork, respectively.

imported into the dental CAD software (Exocad; exo- 1. Three facial scans (a. with the facebow fork in the pa-
cad GmbH, Darmstadt, Germany) and the STL files were tient’s mouth; b. in a resting position; c. smiling) were
generated indirectly. obtained using an extraoral facial scanner (EOS) (Bellus
6. The upper and lower virtual master casts were then ob- 3D): The facial scans were exported as OBJ files.
tained (Fig 3). 2. A 3D printed maxillary interim prosthesis was posi-
tioned on the fork, and a scan was performed with the
In order to record the position of the maxilla relative to the DS.
patient skull, the following steps were followed:

Journal of Prosthodontics 00 (2020) 1–7 © 2020 by the American College of Prosthodontists 3

Virtual Cross-Mounting to Create a 3D Virtual Patient Lepidi et al

Figure 6 The virtual patient in the VA. (A) OBJ file (facial scan with the fork) matched to DICOM converted file and STL files (digital scan of the arches
in CR position). (B) 3D reconstruction of hard and soft tissues without the fork. (C) Definitive wax-up before milling the framework. (D) The definitive
occlusal plane of the framework can be oriented relative to reference planes such as the Frankfort (porion-infraorbital point) or Camper planes (porion-
anterior nasal spine). In this article, an arbitrary reference plane was used which was about 8° inferior to the Frankfort plane based on an esthetic
evaluation of the patient’s facial harmony.

Figure 8 Intraoral photographs of the provisional and definitive prosthe-

ses. (A) Pre-surgical photograph of edentulous ridges. (B) After immedi-
ate loading of implants with provisional prostheses. (C) After 4 months
with provisional prostheses fixed on implants. (D) After delivery of defini-
Figure 7 Occlusal discrepancy measurement between MIP/CR occlu- tive prostheses.
sion. A discrepancy of 1.811 mm was calculated between the MIP and
CR positions measured from the incisal edges of the anterior prosthe-
ses.
fraorbital point, and external acoustic meatus. The digi-
3. All previous STL files were matched in the right posi- tal imaging and communications in medicine (DICOM)
tions in order to conduct digital cross-mounting (Fig 4). files were then imported into exocad software and con-
4. With the interim restoration and Lucia jig in the patient’s verted into a 3D model.
mouth, a CBCT scan was obtained. This CBCT image 5. A 3D virtual patient with all the necessary data was cre-
contained the maxillary and mandibular restorations, in- ated by superimposing the acquired 3D images (Fig 5).

4 Journal of Prosthodontics 00 (2020) 1–7 © 2020 by the American College of Prosthodontists

Lepidi et al Virtual Cross-Mounting to Create a 3D Virtual Patient

The final step involved assembling the virtual models in the prostheses. The provisional prostheses were fabricated based
VA after importing all the STL files into the exocad software on the preexisting removable upper and lower prostheses (up-
tool. per tooth-retained overdenture and lower complete denture).
After 4 months, optical scanning of the interim prostheses was
1. The 3D virtual patient model was imported into the STL used to evaluate the occlusal relationship. Since centric occlu-
file editing software and the transverse horizontal axis sion did not coincide with MIP, a new MIP coincident with
of the edited skull model obtained in CR position was CR was used to fabricate the definitive prostheses (Fig 7).13
aligned with the joint axis of the VA.19. The subsequent steps involved prosthetic finalization and de-
2. A Panadent PCH articulator module was chosen for the livery of complete-arch fixed implant-supported zirconia pros-
VA in exocad software. The Frankfort horizontal plane theses (Fig 8). This workflow can also be applied to other
was aligned parallel to the upper arm of the articulator clinical scenarios such as planning for full-mouth immediate
(Fig 6). loading of implants placed by guided surgery and cephalomet-
ric analysis.20 Ultimately, this technique allows clinicians to
import clinical, radiographic, and cephalometric data from a
Summary physical patient into a virtual patient.
The main limitation of this digital cross-mounting technique
The virtual cross-mounting procedure described aims to re- is the need for provisional fixed implant-supported prostheses
produce the maxillo-mandibular relationship independent of in order to proceed with the reported workflow. Another limi-
occlusal contacts so that registration is repeatable. Accurate tation is that specific knowledge of 3D software is necessary.
mounting relies on the alignment of intraoral scan data with This report provides a technical description of digital cross-
the transverse horizontal axis of the patient (Bergstrom’s point mounting in CR for the creation of a virtual patient through su-
was chosen in this workflow) and a reference plane from perimposition of data from multiple sources. A main advantage
the patient’s head (Frankfort plane: inferior orbital rim and of this technique is the possibility of processing a smile design
bilateral porion as reference points) on the VA.19 One unique and a virtual diagnostic wax-up based on esthetic and func-
aspect of the present technique was that the position of the tional principles. Additional advantages include: 1) the poten-
maxilla was obtained via a virtual facebow by scanning the tial to improve communication and workflow efficiency in den-
facebow fork attached to the upper arch with an extraoral tal clinics and laboratories regarding treatment planning and
scanner (EOS). This position was then transferred using a DS definitive restorative goals; and 2) the ability to transfer the re-
scan of the 3D printed cast of the upper provisional prostheses lationship between the arches and the interocclusal record in
on the fork, and CBCT imaging in CR position using the CR to the VA in a digital workflow. A major benefit of adopt-
Lucia jig. The Lucia jig is recommended because it allows ing this technique is that the available provisional prostheses
maintenance of the maxillomandibular relationship in the can provide important information regarding the implant posi-
same position during all data acquisition steps. Although the tions and inter-arch relationship, thus eliminating the step of
Lucia jig introduced a slight augmentation of the VDO, this fabricating a new splinting framework. Therefore, clinic time
did not cause any visible impairment in speech or function. and cost are saved.
The present technique allows for the construction of a vir-
tual model of the patient’s maxillofacial soft and hard tissues
as well as the inter-arch relationship in CR. Furthermore, it can Acknowledgments
also be used for digital acquisition of esthetic facial references The authors would like to thank Dr. Carmela Suriano (Uni-
such as the bi-pupillary line, oral line, and Ricketts line. This versity of Foggia, Foggia, Italy) and DT. Domenico Faretra
technique makes it possible to carry out a CR mounting by (Corato, Italy) for their contributions to this manuscript.
positioning the maxilla and the intercondylar transverse hori-
zontal axis accurately and precisely because the landmarks are
cephalometric and not arbitrary. At this point, the virtual pa-
tient is ready for the final diagnostic wax-up and for any further References
steps of the CAM phase during prosthetic finalization. In align- 1. Joda T, Gallucci GO: The virtual patient in dental medicine.
ment with the ALARA principle (radiation exposure to the pa- Clin Oral Implants Res 2015;26:725-726
tient should be as low as reasonably achievable), it is justifi- 2. Abduo J: Safety of increasing vertical dimension of occlusion: a
able to apply this technique in any patient undergoing complex systematic review. Quintessence Int 2012;43:369-380
implant rehabilitation to aid with the diagnostic and planning 3. Solaberrieta E, Minguez R, Barrenetxea L, et al: Direct transfer
phases.19 In the specific case of virtual cross-mounting, we rec- of the position of digitized casts to a virtual articulator.
ommend obtaining a CBCT scan only after a sufficient waiting J Prosthet Dent 2013;109:411-414
time has elapsed with respect to a possible previous CBCT scan 4. Lam WY, Hsung RT, Choi WW, et al: A 2-part facebow for
CAD-CAM dentistry. J Prosthet Dent 2016;116:843-847
in accordance with ALARA principles.
5. Solaberrieta E, Garmendia A, Minguez R, et al: Virtual facebow
An edentulous patient underwent guided implant surgery and technique. J Prosthet Dent 2015;114:751-755
obtained provisional implant-supported prostheses in 2018. 6. Lam WYH, Hsung RTC, Choi WWS, et al: A clinical technique
The surgical guide was constructed based on an IOS of the for virtual articulator mounting with natural head position by
preexisting removable prostheses in conjunction with CBCT using calibrated stereophotogrammetry. J Prosthet Dent
imaging using radiopaque markers placed in the preexisting 2018;119:902-908

Journal of Prosthodontics 00 (2020) 1–7 © 2020 by the American College of Prosthodontists 5

Virtual Cross-Mounting to Create a 3D Virtual Patient Lepidi et al

7. Wulfman C, Naveau A, Rignon-Bret C: Digital scanning for 15. Lo Russo L, Ciavarella D, Salamini A, et al: Alignment of
complete-arch implant-supported restorations: a systematic intraoral scans and registration of maxillo-mandibular
review. J Prosthet Dent 2019 relationships for the edentulous maxillary arch. J Prosthet Dent
8. Ury E, Fornai C, Weber GW: Accuracy of transferring analog 2019;121:737-740
dental casts to a virtual articulator. J Prosthet Dent 2019 16. Solaberrieta E, Minguez R, Barrenetxea L, et al: Comparison of
9. Solaberrieta E, Otegi JR, Minguez R, et al: Improved digital the accuracy of a 3-dimensional virtual method and the
transfer of the maxillary cast to a virtual articulator. J Prosthet conventional method for transferring the maxillary cast to a
Dent 2014;112:921-924 virtual articulator. J Prosthet Dent 2015;113:191-197
10. Solaberrieta E, Garmendia A, Brizuela A, et al: Intraoral digital 17. Venezia P, Torsello F, D’Amato S, et al: Digital cross-mounting:
impressions for virtual occlusal records: section quantity and a new opportunity in prosthetic dentistry. Quintessence Int
dimensions. Biomed Res Int 2016;2016:7173824 2017;48:701-709
11. Gartner C, Kordass B: The virtual articulator: development and 18. Joda T, Bragger U, Gallucci G: Systematic literature review of
evaluation. Int J Comput Dent 2003;6:11-24 digital three-dimensional superimposition techniques to create
12. Radu M, Radu D, Abboud M: Digital recording of a virtual dental patients. Int J Oral Maxillofac Implants
conventionally determined centric relation: a technique using an 2015;30:330-337
intraoral scanner. J Prosthet Dent 2019 19. Lepidi L, Chen Z, Ravida A, et al: A full-digital technique to
13. The glossary of prosthodontic terms: ninth Edition. J Prosthet mount a maxillary arch scan on a virtual articulator.
Dent 2017;117:e1-e105 J Prosthodont 2019;28:335-338
14. Li Z, Xia Y, Chen K, et al: Maintenance of the 20. Lepidi L, Suriano C, Saleh MHA, et al: Prosthetic rehabilitation
maxillomandibular position with digital workflow in oral of edentulous patients with implants based on facial profile
rehabilitation: a technical note. Int J Prosthodont assessment: a case report. Implant Dent 2019;28:
2018;31:280-282 91-98

6 Journal of Prosthodontics 00 (2020) 1–7 © 2020 by the American College of Prosthodontists