Dr. Massimiliano Mosella
• Founder of Bernard e Mosella, with expertise in prosthetic and digital dental technologies, focused on innovative digital workflows and advanced prosthetic solutions
• Earned a First-Level Master’s Degree in Digital Dental Technology (SDT) in 2016
• Completed a First-Level Master’s Degree in the Medical-Surgical field (TDP) in 2018
• Attended advanced international training programs with leading professionals; specialized training in Toronto prosthetic rehabilitation, 3 Step Technique, BOPT, oral rehabilitation, and occlusal design
• Inventor of the BEMARC Digital Facebow system and developer of the AFG digital keys
• Holder of two industrial invention patents and one international patent related to the BEMARC project
NHP is specific to each patient: Is it measurable, random, and related to gravity?
Introduction
Introduction
The evolution of digital dentistry is progressively shifting clinical practice from an empirical approach to one based on objective, measurable, and reproducible data.
In this context, data acquisition using BEM–ARC (digital facebow) is an innovative tool for obtaining reliable 3D information, enabling accurate recording of the maxillary position relative to cranial reference planes.
Particularly important are the measurement of the natural head position (NHP) and the definition of the horizontal reference plane.
The facebow, also known as a transfer bow, is an instrument used in dentistry for the accurate stereometric recording of the maxillary position relative to predefined reference planes. Stereometric vision refers to 3D visualization. The term “stereometry” derives from the Greek: sterèos “solid” and metrìa “measurement “.
Limitation of the facebow
Limitation of the facebow
The use of the transfer facearch implies that a reference plane is chosen. Adopting one reference plane rather than another directly affects the orientation of the models in the articulator, conditioning the esthetic aspect of the prosthetic restoration and, even more importantly, its functional result (Fig. 1).
“Data acquisition using BEM-ARC (digital facebow) represents an innovative tool for obtaining reliable three-dimensional information, enabling accurate recording of the maxillary position in relation to cranial reference planes.”
Analog Workflow Interpretations
Analog Workflow Interpretations
The main problem encountered during facebow transfer is that the articulator is symmetrical and orthogonal, whereas human anatomy is inherently asymmetrical. During an analog facebow transfer, discrepancies may occur in the horizontal, sagittal, and frontal planes (Fig. 5).
It is now understood that incorporating bubble levels into the facebow can improve data transfer to the articulator by using the horizontal plane as a reference (Fig. 6).
a New Reference
a New Reference
In this review, Prof. Orthlieb states that the first step in any reconstruction process is to establish a single horizontal reference plane, which is most often perpendicular to the gravitational vertical axis. Currently, the most commonly used plane is the axis-orbital plane (AOP).
In recent years, however, it has been demonstrated that the AOP does not accurately reproduce the patient’s natural horizontal orientation in the sagittal plane, corresponding to the position of the head in space when standing upright and looking at the horizon.
For this reason, the NHP should be used as the reference (Fig. 7).
In this technique, the patient is asked to perform a series of neck flexion exercises (as described by Madsen et al. [16]) and then to focus on an object at an infinite distance, or, alternatively, to look into their own eyes in a mirror approximately 3 feet away. When the patient is in the NHP, the visual axis is parallel to the floor. Cooke and Wei suggested that, once the patient is oriented in the NHP, they should stand with their feet comfortably apart to minimize body sway.
After the patient has been positioned in the NHP, it becomes easier to orient the teeth and jaws, using the occlusal plane as a reference in relation to the remaining craniofacial structures (Fig. 8–10).
The NHP is specific to each patient because it depends on several factors, including the following:
- Muscle balance
- Overall body posture
- Adaptation to gravity
- The individual neuromuscular pattern
- Thus, each patient has their own unique NHP.
The NHP is not random or constantly changing; rather, it represents a habitual and spontaneous position.
Why is the NHP related to gravity?
The body organizes itself in space in relation to gravity, seeking:
- Visual balance (horizon orientation)
- Visual comfort
- Postural stability
Thus, the NHP results from the interaction between the visual, vestibular, muscular, and skeletal systems.
The NHP reflects how the patient functions in space and integrates function, esthetics, and posture.
We also must identify and measure a reference plane capable of counteracting the force that most influences the human body: gravity. This reference is the horizontal plane.
BEM-arc
BEM-arc
BEM–ARC uses inertial sensors, which comprise gyroscopes, accelerometers, and magnetometers. These sensors are derived from the technology used in aircraft to maintain proper spatial orientation during flight, known as the Attitude and Heading Reference System (AHRS).
BEM–ARC sensors can analyze movement in the three spatial planes through roll, pitch, and yaw motions (Fig. 12A, B).
BEM–ARC uses both analog and digital measurement devices, including an asymmetrical facebow designed to record the spatial position of the condyles (Fig. 13–17). Today, facial scanners and photogrammetry applications can also be used to acquire this information digitally.
Real-time recording of head and jaw orientation in space is managed via a smartphone application that provides the operator with measurement data and video recordings.
The collected data can then be integrated into CAD software through a dedicated module, allowing the entire workflow to be managed digitally.
“Professionals involved in postural assessment may also perform motion analysis, allowing the calculation of an average head position.”
Clinical Application
Clinical Application
The first step is to place adhesive skin markers to identify the position of the condyles on the skull and, if required, additional cephalometric reference points. The clinician then acquires the intraoral scans and the previously recorded bite fork registration, both recorded in silicone, and exports them as STL files. A facial scan is subsequently performed using currently available scanning devices.
BEM–ARC uses a dedicated application for recording the NHP. The system combines inertial sensors to measure head orientation in real time within a few seconds. Multiple video recordings can be captured to provide the dental technician with as much information as possible.
Professionals involved in postural assessment may also perform motion analysis, allowing the application to calculate an average head position in space. The system then generates a report containing the recorded measurements.
Finally, the clinician sends the intraoral scans, bite fork data, videos, and facial scans to the dental technician via email, WhatsApp, or other digital platforms (Fig. 18).
Within the software, two bite forks are oriented according to the reference planes. Measurement values from the report are entered into the first fork, and the second fork is automatically aligned with it without requiring additional angular values, as it is already oriented in the horizontal plane.
Once the procedure is completed and saved, the data are exported to the CAD software as STL files (Fig. 19).
Then, the coupling is performed according to the reference planes. The fork oriented in the horizontal plane can be easily aligned and subsequently adjusted one plane at a time to correctly position the three spatial planes.
This procedure allows precise spatial orientation of the digital records and ensures accurate transfer of the patient’s maxillomandibular relationships within the virtual environment (Fig. 20A, B).
The helmet serves as a reference system between the scanning procedure and the CAD environment, with millimetric scales engraved on the arms inserted into the auricular region (Fig. 21–24).
“The dental technician’s software allows the preparation of models for printing already oriented according to the Natural Head Position.”
Using this module, the dental technician’s software prepares models for printing, already oriented according to the NHP.
In conclusion, integrating digital acquisition systems, inertial-based postural analysis, and CAD-oriented workflows enables a more accurate, reproducible, and clinically consistent transfer of maxillomandibular relationships, thereby improving diagnostic precision and prosthetic outcomes in a fully digital environment.
References
1) Using an additively manufactured natural head position reference device to transfer the horizon orientation plane and integrate it with a 3-dimensional virtual patient: A dental technique
The Journal of Prosthetic DentistryJanuary 2024
- Alberto Rosmaninho
- Jonathan M. Zeitler
- Marta Revilla-León
2) Digital workflow for fabricating printed complete dentures by integrating the true horizontal plane for articulator mounting and virtual patient integration
The Journal of Prosthetic DentistryAvailable online 9 October 2025
- Edgar García-Zea
- Marta Revilla-León
3) True horizontal or gravity plane for transferring the maxillary cast into the virtual articulator by using an optical jaw tracking system
The Journal of Prosthetic DentistryOctober 2025
- Marta Revilla-León
- John C. Kois
4) Accuracy of the maxillary cast transfer into the virtual semi-adjustable articulator by using analog and digital facebow record methods
The Journal of Prosthetic DentistryOctober 2025
- Marta Revilla-León
- Jonathan M. Zeitler
- John C. Kois
5) Accuracy comparison of the maxillary cast transfer into the virtual semi-adjustable articulator between an analog facebow record and a digital photography technique
The Journal of Prosthetic DentistryOctober 2025
- Marta Revilla-León
- Jonathan M. Zeitler
- John C. Kois
6) True horizontal or gravity plane registration for transferring the maxillary scan into the virtual articulator by using a facial scanner without the need for an additional device
The Journal of Prosthetic DentistryNovember 2025
- Marta Revilla-León
- John C. Kois
7) Using a three-dimensional natural head position precise recording and transferring device to translate the natural head position into a 3-dimensional virtual patient: A dental technique
The Journal of Prosthetic DentistryNovember 2025
- Lin Wang
- Kai Chen
- Guomin Wu
8) A new method to orient a 3-dimensional facial model to natural head position: A preliminary report on accuracy and reproducibility
Journal of Stomatology, Oral and Maxillofacial SurgeryOctober 2024
- An-an Yin
- Yu Dong
- Shi-zhu Bai