Restorative dentistry
Digital Technologies
Dr. Zaid Abu Zaid
Digital Technologies for Restorative Dentistry. Doctor Zaid Abu Zaid. We move from how we capture the mouth, to how we manufacture, to how we design, and finally to the virtual patient. The thread through the whole talk is one file: the mouth becomes data, the data becomes a design, the design becomes a restoration, and in the best case all of it happens in one appointment. Every screen shows a mechanism; I fill in the detail.
The route
One digital thread .
From the mouth, to the file, to the restoration. Four chapters.
One digital thread. The digitization process is usually achieved by optically scanning oral structures, either directly or indirectly. Both roads end at the same place: a digital file we can design on. Four chapters. Chapter one, digitization of oral structures, direct and indirect, and every factor that decides whether it is accurate. Chapter two, CAD and CAM, computer aided design and computer aided manufacturing. Chapter three, virtual design, how the software proposes a restoration and how we evaluate it. Chapter four, the virtual patient, virtual smile design, the virtual articulator and the virtual facebow.
Digitization
Capture the mouth as data.
CAD/CAM
Design it. Make it.
Virtual design
The software proposes.
The virtual patient
Esthetics and function, before anything is made.
The map for the next thirty minutes. Chapter one, digitization: capturing the mouth as data, directly with an intraoral scanner or indirectly through an impression or a cast, and the twenty one factors that decide the accuracy. Chapter two, CAD and CAM: software and hardware that digitize the impression, model the restoration in three dimensions, and fabricate it with micrometric precision. Chapter three, virtual design: the automatic proposal, how we evaluate it on real records, and the fact that the design principles do not change. Chapter four, the virtual patient: virtual smile design, the virtual articulator, the virtual facebow, and what the evidence actually says. Implant dentistry is in the source material but is not covered today.
Chapter one
Digitization.data .
Optically scanning oral structures, directly with a hand-held scanner or indirectly through an impression or cast.
Chapter one. The digitization process is usually achieved by optically scanning oral structures either directly or indirectly. Directly means a hand-held intraoral scanner in the mouth. Indirectly means a conventional impression or a stone cast scanned on a laboratory scanner. Both roads produce the same thing, a digital model, and the rest of this chapter is about which road to take and what makes each one accurate.
Direct digitization
Direct. The intraoral scanner. Faster, more comfortable, more convenient. Accuracy now comparable to polyvinyl siloxane impressions.
Teeth and other oral structures can be scanned directly using a hand-held intraoral scanner. This procedure is known as a digital impression or intraoral scanning. It is widely used because it is faster, more comfortable for the patient, and more convenient than conventional impressions. Over the past decade the accuracy and ease of use of intraoral scanners have improved significantly, and most recent studies have shown that the accuracy of intraoral scanning is comparable to conventional polyvinyl siloxane impressions. Therefore intraoral scanning is considered suitable for single-tooth restorations and short-span fixed dental prostheses.
Single unit
One tooth, five angles. Suitable for single-tooth restorations and short-span fixed dental prostheses.
A prepared tooth captured from every direction: occlusal, buccal, lingual, mesial and distal, plus the adjacent and opposing teeth. This is the case intraoral scanning is best at. Most recent studies show accuracy comparable to conventional polyvinyl siloxane impressions, which makes it suitable for single-tooth restorations and for short-span fixed dental prostheses. The fewer images the scanner has to stitch together, the less error it can accumulate.
Errors add up over a long span.
The scanner stitches many small images.
Each join carries a tiny error.
Over a full arch, the errors accumulate.
The first limitation of intraoral scanning: distortion in large scanning areas. When scanning a large area the scanner needs to combine multiple images together. As the scanning distance increases, small errors can accumulate, leading to progressive distortion of the final digital impression. Notice there are no units on this drawing. The point is the direction of travel, not a number: the further you go from where you started, the more the model has drifted from the mouth.
A full arch is a long path.
The same arch, split into segments
The manufacturer's own advice for a full arch is to split it into segments.
A full arch is the long case. The scanner must travel from the last molar on one side, across the anterior teeth, to the last molar on the other side, stitching the whole way. That is why the manufacturers themselves recommend splitting a full arch into segments rather than one continuous sweep. On the left, the path across the arch. On the right, the same arch handled as segments. Splitting shortens each chain of joins, and a shorter chain accumulates less error.
Movable tissue cannot be captured.
Firm, attached mucosa: accurate.
Mobile mucosa changes shape during the scan.
Border molding cases: not always predictable.
The second limitation. Intraoral scanners cannot accurately capture movable soft tissues, because the shape of these tissues can change during scanning. Intraoral scanners can reproduce firm and attached mucosa with accuracy similar to conventional impression techniques. Mobile mucosa and movable tissues are much harder, and this limitation is seen with every scanner system, so it is related to the movement of the tissue and not to a particular brand. For this reason intraoral scanning is not always predictable for removable prostheses, especially when border molding is required. Scanning a long edentulous area may not be indicated when border molding is needed.
Accuracy
It depends on the patient
10
patient-related factors
1 Tooth type
2 Interdental spaces
3 Arch width variations
4 Palate characteristics
5 Wetness
6 Existing restorations
7 Surface characteristics, edentulous areas
8 Interimplant distance
9 Position, angulation and depth of implants
10 Implant scan body selection
11
operator factors
1 Scanner technology and system
2 Scanning head size
3 Calibration
4 Scanning distance
5 Ambient temperature changes
6 Ambient humidity
7 Ambient lighting conditions
8 Operator experience
9 Scanning pattern
10 Extension of the scan
11 Cutting off, rescanning, overlapping
The overall accuracy of an intraoral scanner can be affected by several factors. Operator skills, the experience and the scanning technique. Handling technique, incorrect handling or scanning decisions. And intraoral conditions, such as saliva, blood, limited space or difficult-to-reach areas. The source lists ten patient-related factors: tooth type, interdental spaces, arch width variations, palate characteristics, wetness, existing restorations, characteristics of the surface being digitized including edentulous areas, interimplant distance, the position, angulation and depth of existing implants, and implant scan body selection. And eleven operator factors: the scanner technology and system selection, scanning head size, calibration, scanning distance, ambient temperature changes, ambient humidity, ambient lighting conditions, operator experience, scanning pattern, extension of the scan, and cutting off, rescanning and overlapping procedures. The message is simple: accuracy is not a property of the box you bought. It is a property of the case and of the hands.
Interdental space
Under 3 mm, errors appear.
3 mm
errors, direction-dependent
3.5 mm
no significant effect
The distance between the prepared tooth and the adjacent tooth affects accuracy. When the interdental space is less than three millimetres, scanning errors may occur, and the errors vary with the scanning direction. When the distance is greater than three point five millimetres, accuracy is generally not significantly affected. As the distance increases, errors around the preparation margin decrease. The presence of an adjacent tooth makes scanning more difficult because it reduces scanner accessibility and may decrease both trueness and precision. And when data are missing or uncertain, the scanner software interpolates the missing areas. That smooths the surface and can create artificial bulges around the preparation margin, which appear as positive deviations. More interdental space means better accessibility and a more accurate scan.
The patient's mouth sets the terms.
Tooth type
Posterior teeth are harder to reach. Most scanners drift toward the buccal side as the scan moves back; the i500 drifts lingually.
Arch width
Trueness holds, precision falls. A wider arch means more variation between repeated scans.
Palate
Exclude the palate when you can. The higher the vault, the larger the discrepancy.
Tooth type. Posterior teeth are generally more difficult to scan accurately because they have more complex anatomy and are harder to access. As the scan moves toward the posterior region some scanners show horizontal displacement; most of the scanners evaluated displaced toward the buccal side, while the i500 displaced toward the lingual side. Arch width. Clinical studies found that changes in arch width did not significantly affect trueness, but as arch width increases precision decreases, meaning more variation between repeated scans. On intermolar width, in most systems except the i500 a greater intermolar width was associated with greater discrepancies; the i500 showed its highest discrepancies at both extremes, the narrowest and the broadest. Palate. Higher trueness and precision were obtained when the palate was not included in the maxillary scan, and as the palatal vault became higher discrepancies tended to increase, although those differences were not statistically significant.
Dry it. Matte it.
Wetness
Water scatters the light. Keep the field dry.
Existing restorations
Polished beat glazed. A thin, even layer of powder cuts reflections.
Wetness. Moisture on the tooth surface negatively affects accuracy. When the surface is wet, water changes the way light is reflected, and that interferes with the scanner's ability to capture surface detail. Keep the scanning area as dry as possible. Existing restorations. Scanning performance varies with the reflective properties of the restorative material: the type of material, the translucency, and the surface finish. In zirconia crowns, polished surfaces showed higher trueness than glazed surfaces. Scanning powder reduces reflection from highly reflective restorations, makes the surface easier to capture, and may also reduce scanning time. A thin and uniform layer is what is recommended, when it is needed at all.
The preparation itself.
Sharp, rough, irregular: lower accuracy.
Undercuts and deep floors: shadow, missing data.
Supragingival scans best; equigingival and subgingival worst.
The surface characteristics and the geometry of the preparation significantly affect accuracy. Sharp angles, irregular shapes and rough surfaces reduce accuracy; the more complex the preparation, the harder it is to scan. Preparations for full-coverage restorations such as crowns generally show higher accuracy than intracoronal preparations such as inlays, and for full-coverage preparations a higher occlusal convergence angle tends to improve accuracy, just as a greater divergence angle helps for intracoronal preparations. Undercut areas below the height of contour are difficult for the scanner to access; they appear as shadow regions with inaccurate or missing data. Location matters too: posterior teeth show lower accuracy than anterior teeth. So does depth: the deeper the pulpal and gingival floors, the higher the discrepancy. And the finish line: a finish line placed more gingivally or subgingivally is harder to capture, and equigingival and subgingival finish lines showed the lowest accuracy and the highest number of scanning deficiencies. Anterior, shallow, supragingival is the easy case. Posterior, deep, subgingival is the hard one.
The operator's discipline.
Calibrate daily
Most systems need it before scanning. iTero Element and TRIOS 5 self-calibrate.
Head size
Small heads reach further. Large heads may be more accurate.
Distance
There is no universal optimum. Follow the manufacturer's focal depth.
Temperature
A change in ambient temperature can cost you the calibration. Recalibrate.
Calibration is important to maintain accuracy. Most systems require the operator to calibrate before scanning, although some scanners, such as the iTero Element and the TRIOS 5, have an integrated self-calibration system. Establish a routine protocol for daily calibration before starting. Scanning head size: smaller heads are useful when access is limited, for example in patients with limited mouth opening, but larger heads may provide higher accuracy. Scanning distance is the distance between the surface and the tip of the scanner; changing it can cause discrepancies, and there is no single optimal distance for every scanner because the ideal distance and focal depth depend on the hardware and design of the specific system. Ambient temperature: changes in the surrounding temperature can make the scanner lose its calibration, which leads to errors, so calibrate before starting each workday.
1000 lux
teeth: chair light off, ceiling light on
500–800 lux
implant scan bodies
Follow the manufacturer's scanning pattern. Experience helps; newer systems depend on it less.
Ambient lighting significantly affects the accuracy of intraoral scanning, especially in dentate patients. Most scanners perform better under approximately one thousand lux, which is similar to normal room lighting. To get there, the dental chair light should be turned off while the room ceiling light stays on. The optimal level differs with what is being scanned: natural teeth at about one thousand lux, implant scan bodies at a lower intensity, roughly five hundred to eight hundred lux. On the clip, the scanning pattern. The scanning sequence significantly affects accuracy, different paths produce different levels of accuracy, so follow the sequence provided by the manufacturer of that specific scanner. Operator experience matters as well: more experienced operators achieve more accurate scans, and the effect is more noticeable with older generations of scanners, while newer systems are easier to use and less dependent on experience.
Scan it right the first time.
Cut-off and rescan: merge errors.
More and larger holes: more accuracy lost.
Overlapping rescans: lower accuracy.
Cutting off and rescanning parts of a digital scan reduces the overall accuracy. When a previously scanned area is removed and then rescanned, errors occur when the new data are merged with the existing data. The larger the number and the diameter of the mesh holes that are rescanned, the greater the potential loss of accuracy. Studies also showed lower accuracy when overlapping areas were present during the rescanning process. More cutting off, more rescanning and more overlapping all point the same way: lower accuracy. One clean pass is worth more than three corrections.
Indirect
When the mouth will not scan,cast .
Impression
Possible distortion
Stone cast
Possible distortion
Laboratory scanner
Higher accuracy
Digital model
The file we design on
Preferred for full-arch work where cross-arch accuracy is critical. Final accuracy is the accuracy of the impression or cast.
When direct intraoral scanning is not suitable, digitization can be performed indirectly: a conventional impression or a stone cast is scanned using a laboratory scanner. It takes more time than direct scanning, but it is a reliable way to obtain a digital model, provided the impression or cast is accurate and properly made. Laboratory scanners generally provide higher scanning accuracy than intraoral scanners. But with indirect digitization we have to consider the dimensional changes and distortions that can occur while making the impression and while pouring and producing the stone cast. Those two amber steps are where the error enters. Indirect digitization is still preferred for full-arch scanning when high cross-arch accuracy is required, because laboratory scanning gives better control over long distances across the arch. The final digital accuracy depends mainly on the quality of the original impression or cast.
Laboratory scanners.
Early: fixed light, one angle.
Modern: the object or the optics move.
Limited movement: two-step scanning.
Indirect digitization is commonly performed by scanning stone casts on a laboratory scanner. The cast is fixed on the scanning table, and the scanner precisely controls the movement of the light source, of the table, or of both, so it can capture the surface and build a digital three dimensional model. Early laboratory scanners used a fixed light source and scanned the object from one fixed angle. Modern scanners can move the object or the scanning components during the process, so the object is captured from multiple angles and more surface detail is recorded. Even so, their range of movement is still more limited than a hand-held intraoral scanner, so some areas remain difficult to capture clearly, especially undercuts and interproximal areas. If an important area is missed, a two-step scanning technique is used: the missed area is rescanned separately and then combined with the original scan.
Without pouring a cast
Shallow, no undercuts, accessible:impression itself.
Triple-tray impressions can be scanned and reach clinically acceptable accuracy. A stone cast is still needed for a physical try-in.
In some cases a conventional impression can be scanned directly, without first producing a stone cast. That is possible when the impression is relatively shallow, when there are no major undercuts in critical areas, and when the important areas are easily accessible to the scanner. Interestingly, posterior areas of conventional impressions may be easier to scan successfully than anterior areas. Virtual models obtained by directly scanning a conventional impression can have clinically acceptable accuracy. But a stone cast is still required whenever a physical model is needed, for the try-in of the definitive restoration and for adjustment or modification of the restoration.
Chapter one, in one line
Choose the roadcase .
Direct for single units and short spans. Indirect for full arches, border molding, and mouths that will not scan.
The summary of chapter one. Direct intraoral scanning is the road for single-tooth restorations and short-span fixed dental prostheses: faster, more comfortable, more convenient, and with accuracy comparable to conventional polyvinyl siloxane impressions. Fewer stitched images means fewer joins and less accumulated error. Indirect digitization is the road for full-arch work where cross-arch accuracy is critical, for removable cases that need border molding, and for any mouth that will not scan well. Laboratory scanners are more accurate than intraoral scanners, but the impression and the cast can distort, so the final accuracy is the accuracy of what you scanned. Choose the road by the case, not by the gadget.
Chapter two
CAD/CAM.Make it.
Computer-aided design and manufacturing: digitize, model in 3D, fabricate with micrometric precision. Since the 1980s, Dr. François Duret and CEREC.
Chapter two. Digital restorative engineering. CAD and CAM refers to software and hardware systems that digitize dental impressions, model restorations in three dimensions, and fabricate prosthetics with extreme micrometric precision. It originated in the nineteen eighties with Doctor Francois Duret and the CEREC system, and it replaces physical elastomeric impressions and manual waxing with a streamlined digital workflow. In this chapter: the three stages, the clinical pathway, what the patient gets, the honest comparison with the conventional method, and the honest disadvantages.
Three stages.
Acquire
3D optical coordinates of the preparation and the soft tissue, as a high-density point cloud and an open STL or PLY model.
Design
Occlusal clearance, emergence profile, margin and contacts, adjusted in real time.
Fabricate
CNC multi-axis milling or 3D printing of ceramic, zirconia or resin.
The core digital architecture, in three stages. One, digital acquisition: intraoral scanners capture three dimensional optical coordinates of the prepared teeth and the soft tissues, generating high-density point clouds and open-format STL or PLY digital models. Two, CAD virtual design: specialised software analyses dynamic occlusal clearance, designs accurate emergence profiles and marginal fit lines, and simulates contact parameters in real time. Three, CAM fabrication: computer-numerical-controlled multi-axis milling units, or stereolithography three dimensional printers, shape monolithic ceramic, zirconia or resin blocks into the physical restoration.
No stone model. No transit time.
Step one
Preparation
Standardised reduction and a clear supragingival or equigingival finish line, so the camera can see the margin.
Step two
Optical capture
Both arches and the interocclusal registration, in minutes, with no impression material.
The CAD and CAM clinical pathway eliminates stone models and conventional transit times. Step one, tooth preparation: a standardised reduction with a clear supragingival or equigingival finish line. Step two, optical capture: direct intraoral scanning of the arches and the interocclusal registration, in minutes. Step three, parametric modelling: the biogeneric algorithm calculates tooth morphology based on the adjacent anatomy. Step four, sintering and crystallisation: fast furnace firing achieves the optimal flexural strength and esthetics. Nothing leaves the building, and nothing waits for a courier.
Modelled, then fired.
Step three
Parametric modelling
A biogeneric algorithm calculates the morphology from the adjacent anatomy, then the clinician adjusts it.
Step four
Sintering and crystallisation
Fast furnace firing brings the block to its final flexural strength, shade and translucency.
Step three, parametric modelling. The design software proposes the restoration from the selected shape, the adjacent teeth, the opposing teeth and the surroundings. A biogeneric algorithm calculates the morphology from the neighbouring anatomy, and the clinician adjusts occlusal clearance, emergence profile, margin and contacts in real time. Step four, sintering and crystallisation. The milled block is fired in a fast furnace, which brings it to its final flexural strength, its shade and its translucency. Together with steps one and two, that is the whole chairside pathway: no stone model, no transit time to a laboratory, no second appointment.
For the patient
One visit.
60–90 min
a complete crown, with no temporary
1
numbing injection: preparation and placement in the same appointment
0
gagging: an optical camera, not a putty tray
The major clinical advantages, first for the patient. Same-day treatment: a complete crown in one visit of sixty to ninety minutes, with no temporary teeth needed. No gagging, because a clean optical camera replaces messy impression trays and putty. And one numbing injection, because the preparation and the final placement happen in the same appointment. Then quality and precision: exceptional accuracy, because computer-controlled margins mean a tighter fit and fewer leaks; stronger materials, because factory-pressed zirconia and ceramic blocks have zero porosity; and saved digital files, so if a crown breaks it can be re-milled instantly without a new appointment.
Placed the same day.
Computer-controlled margins: tighter fit, fewer leaks. Factory-pressed blocks, zero porosity. A saved file: if a crown breaks, re-mill it instantly.
The restoration is seated in the same appointment in which the tooth was prepared. Exceptional accuracy: computer-controlled margins mean a tighter fit and fewer leaks. Stronger materials: factory-pressed zirconia and ceramic blocks have zero porosity, unlike anything layered by hand. And the file is kept: if the crown breaks, it can be re-milled instantly from the saved design, without a new appointment and without a new impression.
Traditional versus CAD/CAM.
Traditional method
CAD/CAM digital method
Impression
Putty tray, often triggers gagging
3D optical scan: fast, comfortable, clean
Appointments
Two visits, two to three weeks apart
One visit, finished in one to two hours
Temporary tooth
Needed for weeks; can break or fall off
None: the permanent tooth is placed today
Remakes
Repeat the full impression and wait weeks
Instant re-mill, straight from the saved file
Traditional versus CAD and CAM at a glance. Impression: a gooey putty tray that often triggers gagging, against a three dimensional optical scan that is fast, comfortable and clean. Appointments: two visits required, two to three weeks apart, against a single visit finished in one to two hours. Temporary tooth: needed for weeks, and it can break or fall off, against none needed, because the permanent tooth is placed today. Remakes and duplicates: you must repeat the full impression and wait weeks, against an instant re-mill, milled directly from the saved file. Same clinical result, one visit, and we keep the file.
What it still costs
Honest about the price.
$40,000–120,000+
scanners, mills, software licences
A learning curve: scanning, 3D software, digital occlusion.
Moisture and blood hide margins: cord retraction still matters.
Burs have a minimum thickness: tiny crevices get over-milled.
The honest disadvantages. High initial cost: intraoral scanners, milling machines and CAD software licences require a major upfront equipment investment, forty thousand to over one hundred and twenty thousand dollars. Learning curve: doctors and dental assistants need dedicated training to master optical scanning, three dimensional software tools and digital occlusion. Moisture and blood sensitivity: optical scanners cannot see through saliva or bleeding, and margins hidden under swollen gums still require careful cord retraction. And a physical limit: milling burs have a minimum thickness, so extremely tiny internal crevices may be slightly over-milled. That last one is not a software problem. It is geometry: a round bur cannot enter a sharper corner than its own radius.
Chapter three
Virtual design.proposes , the clinician decides.
Chapter three, computer-aided design. The restoration exists as a file before it exists as an object. Most CAD software can automatically generate an initial restoration design from the selected tooth shape, the adjacent teeth, the opposing teeth and the surrounding oral structures. In this chapter: how good that automatic proposal actually is, which digital records we use to evaluate and improve it before anything is fabricated, and the point that matters most, that CAD makes the design process faster and more efficient but does not change the basic biological, functional and mechanical principles of prosthetic design.
The automatic proposal.
From the selected shape, the adjacent teeth, the opposing teeth and the surroundings. Single units: usually satisfactory. Multiple units and extensive FDPs: more adjustment.
Most CAD software can automatically generate an initial restoration design based on the selected tooth shape, the adjacent teeth, the opposing teeth and the surrounding oral structures. The initial design is usually more satisfactory for single-tooth restorations. Designing multiple restorations, or extensive fixed dental prostheses, is more challenging and may require considerably more adjustment by the operator. A single restoration is the easier and more predictable virtual design; multiple restorations and extensive prostheses are more complex and need more adjustments.
Evaluate on real records.
Scanned diagnostic models.
Provisionals and intraoral mock-ups.
Adjust, then fabricate.
Different virtual images and digital records can be used to evaluate and improve the proposed restoration design. These include scanned diagnostic models, interim or provisional restorations, intraoral mock-ups, and other types of trial restorations. These digital records help the clinician and the technician evaluate the shape, the position and the overall design of the planned restoration before fabrication. The proposal is a starting point, not a verdict: we pull it toward what we already know works in this mouth, and only then do we fabricate.
CAD makes the design faster.design .
The biological, functional and mechanical principles of conventional prosthetic design still apply.
Computer-aided design is a modern tool that makes the dental prosthesis design process faster and more efficient. However, CAD does not change the basic principles and the conventional design criteria used for dental prostheses. In other words, CAD is a tool that helps us design, but we still need to follow the same biological, functional and mechanical principles used in conventional prosthetic design. CAD improves the design process. It does not replace conventional prosthetic principles.
Chapter four
The virtual patient .
Virtual smile design and the virtual articulator: better esthetic and functional planning.
Chapter four. Modern dental CAD software includes advanced virtual simulation tools that help create a more ideal restoration design. Two of them matter here. Virtual smile design, which helps evaluate and plan the patient's smile and esthetics digitally. And the virtual articulator, which simulates the movements and the relationship between the upper and the lower jaws. Together they build what we call the virtual patient, and they lead to better esthetic and functional planning.
From one angle to the whole face.
2D: lines and calipers on a photograph, then a wax-up; one viewing angle.
3D: facial scanning judges esthetics from every angle; smartphone apps make it accessible.
For migrated, malposed or damaged teeth.
Many modern CAD programs include virtual esthetic simulation, known as virtual smile design or digital smile design. It lets the operator digitally simulate changes in the position, the shape and the appearance of the teeth, and it is particularly useful for migrated, malposed or damaged teeth, to plan their ideal position and their relationship with the patient's facial features. In the early stages, operators used two dimensional facial photographs: lines and virtual measurements were drawn on the photograph with a virtual caliper, and then a diagnostic wax-up was needed to transfer the digital plan to a physical model, so the result depended on the operator's ability to convert a two dimensional drawing into a three dimensional design. The important limitation is that a photograph allows evaluation from only one specific angle. Three dimensional facial scanning removes that limitation: esthetics can be evaluated from multiple angles, giving a more complete understanding of how the planned treatment affects the whole face. Its use is expected to increase, because three dimensional facial scanning is now available in some smartphone applications.
The virtual articulator.
Reproduces the interarch relationship and simulates jaw movement, so occlusion and function are checked before anything is made.
A virtual articulator is a computer software tool used to simulate the relationship between the upper and the lower teeth and to reproduce jaw movements digitally. It helps clinicians and dental technicians evaluate the occlusion and the function of a planned restoration before it is fabricated. There are two main types: the completely adjustable virtual articulator and the mathematically simulated virtual articulator.
Two kinds.
Completely adjustable
Records the real mandibular paths with an electronic jaw registration system. Complex cases. Rarely used.
Mathematically simulated
Calculates the movements from entered values.
The completely adjustable virtual articulator records and reproduces the actual movement paths of the mandible using an electronic jaw registration system. It is useful in complex cases where accurate evaluation of occlusion during mandibular movement is required. It is not widely used, because it requires additional equipment, the system is more complex to use, and many dentists are simply not familiar with it. The mathematically simulated virtual articulator reproduces mandibular movements by calculating the paths from specific values entered into the software. Depending on the system, the adjustable settings include the Bennett angle, the horizontal condylar inclination, the vertical dimension of occlusion, and the incisal table inclination. So: completely adjustable records the real movements, mathematically simulated calculates them from preset values.
Getting the jaws into the software.
Arbitrary mounting
Cephalometric radiograph
3D facial scan with extraoral markers
Photographs converted to a 3D scan
Digital axiography
Stereophotogrammetry
Standardised extraoral photographs
CBCT-based methods
To use a virtual articulator, the position of the patient's maxilla and mandible must first be transferred accurately into it. That procedure is called a virtual facebow transfer: transferring the patient's three dimensional jaw position to the virtual articulator. Several techniques can be used: arbitrary mounting, cephalometric radiography, three dimensional facial scanning using extraoral markers, converting a series of photographs into a three dimensional facial scan, digital axiography, stereophotogrammetry, standardised extraoral photographs, and CBCT-based methods. All of them do the same job: they establish the three dimensional position and relationship of the jaws inside the virtual articulator.
Evidence
Under 100 micrometres.
< 100 μm
dynamic articulation, in vitro, versus a mechanical articulator
Hsu MR, Driscoll CF, Romberg E, et al. Accuracy of dynamic virtual articulation: trueness and precision. J Prosthodont 2019;28(4):436–443.
An in vitro study evaluated the accuracy of eccentric mandibular movements using a mathematically simulated virtual articulator. The accuracy of the virtual articulator was similar to that of a mechanical articulator, and during dynamic mandibular movements the deviations were less than one hundred micrometres. That suggests mathematically simulated virtual articulators can provide clinically acceptable accuracy for dynamic articulation. The references on screen: Hsu, Driscoll, Romberg and colleagues, Journal of Prosthodontics two thousand nineteen, volume twenty eight, issue four, pages four hundred thirty six to four hundred forty three. And Lepidi, Galli, Mastrangelo and colleagues, Journal of Prosthodontics two thousand twenty one, volume thirty, issue one, pages twenty four to thirty five.
An additional tool.replacement .
Static articulation is clinically acceptable and comparable to mechanical articulators. Especially useful when the vertical dimension changes. More clinical research is still needed.
Most studies evaluating the accuracy of virtual articulators have focused on static articulation, the relationship between the upper and lower teeth in a fixed position. Several factors influence it: the alignment method, the arch length, the type of scanner, the articulation method, the virtual articulation algorithm, and the use of a mechanical articulator. Despite all of those, most studies find that the accuracy of static articulation with virtual articulators is clinically acceptable, and generally comparable to conventional mechanical articulators. The virtual articulator is currently recommended as an additional diagnostic and treatment-planning tool, rather than a complete replacement for the mechanical articulator. It is particularly useful in complex cases, especially when there are changes in the vertical dimension of occlusion. The clinical use of dynamic virtual articulators involves many additional variables, so further clinical research is still needed before virtual articulators can completely replace mechanical ones.
Everything connected.
The finale. Press the arrow key, or click the right of the screen, to add each station in turn. One: the intraoral scan turns the arch into data. Two: the face scan captures the esthetic frame from multiple angles. Three: the virtual facebow transfers the real three dimensional position of the maxilla and the mandible into the software. Four: the virtual articulator reproduces the interarch relationship and simulates the movements. Five: CAD proposes the restoration from the neighbours and the opposing teeth. Six: CAM cuts it out of a block. Seven: the restoration is seated the same day. When the last station lands, the thread connects all seven: one thread of data, seven stations, one patient.
Five things
1 Intraoral scanning is accurate for single units and short spans. Errors accumulate over long spans and over mobile tissue. 2 Accuracy is controllable: a dry field, good access, supragingival margins, daily calibration, about 1000 lux, one clean pass. 3 Indirect digitization still wins for full-arch work where cross-arch accuracy is critical. 4 CAD/CAM gives same-day, precise, repeatable restorations. The principles of design do not change. 5 The virtual patient, smile design plus articulator plus facebow, is an additional planning tool. Not yet a replacement.
Five take-home points. One: intraoral scanning is accurate for single units and short spans; errors accumulate over long spans and over mobile tissue. Two: accuracy is controllable by us, with a dry field, good access, supragingival margins, daily calibration, about one thousand lux of ambient light, and one clean pass without cutting and rescanning. Three: indirect digitization still wins for full-arch work where cross-arch accuracy is critical. Four: CAD and CAM gives same-day, precise, repeatable restorations, and the principles of design do not change. Five: the virtual patient, smile design plus articulator plus facebow, is an additional diagnostic and planning tool, not yet a replacement for the mechanical articulator, and it is most useful when the vertical dimension of occlusion changes.
Thank you.
Dr. Zaid Abu Zaid
Hsu MR, Driscoll CF, Romberg E, et al. Accuracy of dynamic virtual articulation: trueness and precision. J Prosthodont 2019;28(4):436–443.
Thank you. References on screen: Hsu and colleagues, Journal of Prosthodontics two thousand nineteen, volume twenty eight, pages four hundred thirty six to four hundred forty three, on the trueness and precision of dynamic virtual articulation. Lepidi and colleagues, Journal of Prosthodontics two thousand twenty one, volume thirty, pages twenty four to thirty five. Source lecture material adapted for this presentation. Questions.