Prosthetic planning and project
Introduction :
Implantology is now an integral part of contemporary dental treatment. Therefore, it is important to integrate this technique into the overall treatment plans offered to patients. To achieve effective and stable long-term results, it is first necessary to integrate the implant into a sufficient bone volume. The second imperative of aesthetic implant treatment is proper implant positioning.
In view of these elements and in order to obtain a satisfactory result for both the practitioner and the patient, it appears necessary to anticipate this therapy to establish the right indications and to plan the preliminary and essential interventions (bone reconstruction, gingival, etc.). This anticipation must involve the realization of a prosthetic project in order to predict the final result.
1- Tools related to the construction of the prosthetic project
The tools related to the construction of the prosthetic project are all the means that allow information to be transferred to the prosthetic laboratory, because the treatment project is carried out upstream by the prosthetic technician. All elements must, therefore, be transmitted to him for easy implementation and equally easy clinical validation.
1-1- Photography:
Photography in dentistry is a key element which currently plays three main roles:
- Allows data to be recorded to create a precise and supported treatment plan outside of consultation time;
- Promotes the transmission of clinical data to the prosthetist;
- Allows the comparative aspect of the treatment (before/after).
1-2- Digital Smile Design (DSD):
The objective of the DSD is therefore to provide assistance by protocolizing the reflection and creation of a prosthetic project.
Virtual smile design is a conceptual, versatile protocol based on an analysis of patients in their facial and dental dimensions.
This analysis involves a predetermined series of high-quality digital photographs and videos, which, among other things, allow for the capture of still images that are more natural than photos.
The analysis of these documents highlights the relationships between the teeth, the gums and the lips, but also between the position of the latter in the smile and the face and its dynamics which allows the expression of emotions.
The DSD is thus an undeniable tool, used daily, in the optimization of treatments (analysis, diagnosis, implementation, but also monitoring). However, its use must be correlated with the artistic vision of the practitioner and the prosthetist as well as their respective skills.
1-3- Face design:
When treating completely edentulous patients, it remains difficult to “invent” teeth or to choose them from among various possibilities, with very little data. Face design can be an aid in this choice: it supports clinicians in the design of restorations that meet the aesthetic criteria and psychosocial characteristics relating to the image of each patient. These characteristics are closely related to emotions, sense of identity, behavior but also respect for the individual.
2- The prosthetic project:
2-1- The “prosthetic driven implantology” concept
The implant solution can be proposed for all types of edentulousness, whether single, multiple or total. Whatever the case, the implant has a prosthetic rehabilitation objective; it is the future prosthesis (single, bridge-mounted or complete prosthesis) which defines the position of the implant(s).
As such, it is important following the planning stage and during the surgical phase to respect the previously chosen implant position.
2-2- Analysis of the prosthetic project
If we strictly refer to the current concept of implantology “guided by the prosthetic objective”, all the stages must in theory and ideally arise from a clearly defined initial prosthetic project and materialized at the different stages of implant therapy.
It is therefore important and strongly recommended to test the latter in the mouth before the surgical intervention and the final prosthetic realization by going through the realization of a temporary prosthesis. It is also possible to use as is or to modify an existing prosthesis in use, provided that the latter meets all the required quality criteria. The necessary modifications will then be made and then the project validated in accordance with the patient’s feelings before continuing the therapeutic process.
The creation of a temporary prosthesis allows:
- To transpose into the mouth the information provided by diagnostic waxes for an essentially functional and aesthetic purpose.
- Allows the preview of various essential parameters including: lip support, DVO, neck position, location and shape of future prosthetic teeth.
- It also establishes a stable and repetitive intermaxillary relationship.
- Objective the occlusal-prosthetic space available for the different surgical and prosthetic components.
- Gives a concrete idea of the final aesthetic result to the patient as well as to the practitioner.
- Can also allow the patient who has never been fitted with a hearing aid to gradually get used to a volume and bulk that was previously unknown or forgotten.
- More important and interesting to achieve in the anterior sector, where aesthetics (subjective element) occupies a primordial place.
- Role of radiological guide allowing the validation of the prosthetic project, the choice of location and the placement of the implants.
- Future role of surgical guide by allowing the emergence of implants to be predicted based on the future prosthesis of use that it prefigures.
- It then allows the correct management of the embrasures during the prosthetic phase.
2-3- Different methods aimed at materializing the prosthetic project
- Wax up or diagnostic circ
- Master assembly : These circ models prefiguring the future prosthetic restoration are produced after assembly in an articulator.
- Attached prosthesis (temporary or for use, meeting quality criteria and validated)
These diagnostic elements can now be scanned and integrated into dedicated implant planning software (SimPlant®, etc.).
- Modeling by virtual wax up after optical impression of the edentulous site.
2-4- Interests of these models
2-4-1- The radiological guide
The radiological guide is made of:
- Duplicating wax up, director assembly or patient’s removable prosthesis.
- It can also correspond to the patient’s temporary or usual prosthesis, validated and fitted for this purpose.
This imaging guide must have characteristics allowing its use during 2 fundamental stages:
- the diagnostic stage of radiological acquisition (from which implant planning will be carried out) and
- the reference stage during surgery.
The quality of this initial guide, developed with respect for the prosthetic project, is essential since it allows the latter to be compared with anatomical considerations at the implant planning stage.
2-4-1-1- Radio guide specifications:
- Be radiopaque
- Do not emit parasitic noises, responsible for artifacts in imaging
- Determines the envelope of the prosthetic restoration
- Determines the thickness of soft tissues
- Informs about the axis of emergence of the implant(s)
- Be stable and retentive
2-4-1-2- Positioning fault:
The radiological guide stage occurs early in the implant treatment plan sequence. As such, a positioning error at this stage would have an influence on the future final implant position. To avoid any displacement of the guide, in certain situations (significant terminal edentulism or even complete edentulism) it is essential to make an occlusion key.
2-4-2- Purely digital planning:
In the context of digital planning, the virtual wax-up can be directly merged with the three-dimensional imaging data on dedicated planning software, not requiring the creation of a radiological guide to be worn during volume acquisition.
This system therefore allows matching between 3D images obtained in the mouth and three-dimensional radiological acquisition.
3- Radiological examination and implant planning:
Since precise knowledge of the sites to be implanted and of the neighboring anatomical structures can only be understood through rigorous radiographic analysis, radiological investigation techniques have evolved considerably in recent decades in response to the need to improve the precision of pre-implant diagnosis.
Sectional imaging now makes it possible to carry out reliable implant planning.
Imaging has become a determining element of the pre-operative assessment in oral implantology.
The different imaging techniques used in this indication are as follows:
- Conventional radiology techniques , including: panoramic radiography and long-cone retro-alveolar images
- Three-dimensional imaging techniques (3D imaging) : cone beam tomography, computed tomography or scanner, implant simulation (Simplant*, Nobleguide*, etc.) and robotic navigation (Robodent*, etc.) are applications of 3D imaging.
All these techniques do not seem to us to be competing but complementary in the context of implant surgery.
3-1- Panoramic radiography:
This is the first-line examination, essential but most often insufficient. The principle is that of curved tomography which results from a simultaneous and opposite movement of the X-ray source and the X-ray film during a rotation, producing a relatively thick tomographic slice including both arches on the same so-called panoramic image.
Benefits :
- Obtaining the entire dento-maxillary system in a single image.
- Rough estimate of bone height,
- Relatively low cost.
Disadvantages:
- Mesio-distal dimensions are unreliable because they vary greatly from one examination to another depending on the morphology of the maxilla and the position of the patient.
- Vestibulo-lingual dimension ignored.
- Limited by its thickness, 10 to 12 mm in the posterior regions and sometimes 6 to 10 mm in the anterior regions; this explains why only the structures included in this tomographic section are clear, and why the incisors are often blurred.
- Study of insufficient sinuses, and finally that important anatomical structures such as the foramen mentum or the mandibular canal or even a cyst or a residual root may go unnoticed.
- Necessity, for direct measurements of the use of a scale ruler of the desired magnification.
- Does not allow assessment of the quality of the cancellous bone, the thickness of the alveolar process, the deep location of obstacles such as the sinus or the mandibular canal or the quality of the cancellous bone.
3-2- Long-cone retroalveolar:
Allows obtaining 2D images without distortion, it is a more reliable approach to bone height and mesiodistal study than panoramic.
3-3- Cone beam computed tomography (cone beam CBCT):
Since the advent of cone beam tomography, the indications for traditional CT (computed tomography) have been called into question with regard to the exploration of the facial masses.
Principle and technique of cone beam data acquisition:
The conical X-ray beam passes through the object to be explored before being analyzed after attenuation by a detection system. The tube and the detection system rotate around the subject (192 to 360° depending on the manufacturer), several hundred analyses (shots) are carried out in the different planes of space, allowing, after transmission of the data to a computer, the volume reconstruction of a cube or cylinder containing the object (here, the jaws). The volume studied is composed of voxels whose side is the size of a pixel, measured in mm or microns (µm).
Advantages of the cone beam:
- Compared to the scanner, the cone beam has the advantage of less irradiation.
- Allows the surgical indication to be rigorously established, avoiding unnecessary surgical interventions and, conversely, allowing the placement of implants which seemed impossible based solely on the data from the dental panoramic scan.
- It also allows for an operative strategy to best predict the number, distribution, diameter, length and optimal orientation of the implants, depending on the available bone volume, as well as its quality and the prosthetic project.
- Forensic interest.
- The “cone beam” is considered the reference 3D imaging technique in implantology.
3-4- Dentascan or computed tomography (CT):
CT imaging uses X-rays and is based on the differential absorption of radiation by the different anatomical structures crossed.
Advantages of pre-implant scanning:
- Measurement study of bone volume in three dimensions and a more reliable approach to the quality of available bone;
- Compared to the cone beam, the scanner can be indicated in the case of uncontrollable or predictable kinetic artifacts, in elderly patients (Parkinson’s) or nervous patients or even in children, the optimization allowing the distribution of a minimal dose in an ultra-short exposure time (one second for certain machines).
- Assessment of bone volume and density:
- Bone typology (according to the Lekholm and Zarb classification: D1, D2, D3, D4)
- Bone thickness at the crest over the entire height of the alveolar process and the available bone height.
- Bone density.
- Location of critical anatomical obstacles:
- The maxillary sinus
- The lower dental canal
- The mental foramen
- Vessels and hemorrhagic risk
3-6- Implant planning itself:
In order to carry out this implant planning, the practitioner now has different tools at his disposal: Layers; Implant libraries.
Layers:
Conventional planning is carried out using layers provided by the manufacturers and indicating the outline of the available implants. They are superimposed on the radiological images in order to verify by transparency the volume of peripheral bone available as well as the proximity of anatomical structures.
The layers also indicate, by an apical mark, the position of the tip of the drill which will be used in order to provide a safety distance.
Layers correspond to tools that can be described as “static” and increase the risk of error and inaccuracy at the implant planning stage.
Implant libraries:
If the planning is carried out using simulation software, the practitioner who has implant libraries can carry out dynamic planning based on the prosthetic project and the anatomical information provided by the imaging, viewed in real time on the screen.
The three-dimensional positioning of the selected implant is then integrated into all available sections, within which it is possible to navigate with a vision of the “impact” of the implant positioning in the 3 dimensions of space.
4- Guided implant surgery:
Guided implant surgery is the process of planning implant surgery on a computer using the patient’s 3D radiological data.
The conventional method of using panoramic X-rays of the patient to plan implant surgery cannot transfer the plan exactly as planned. However, guided surgery can transfer the plan exactly as already planned.
To perform the operation exactly as planned, a customized surgical guide and a guided implant surgery kit are required.
The following are required for guided implant surgery:
- Patient cone beam.
- Planning software
- Guided Implant Surgery Drill Kit
- Personalized surgical guide.
The general workflow for guided implant surgery:
- Implant treatment plan
- Digital wax-up
- Preoperative CBCT acquisition
- Surgical guide design
- 3D printing of the guide
- Intraoral scanner
- Digital model
- Data merging
- Virtual placement of implants
- Machining the guide
- Implant surgery
The advantages of guided surgery are:
- Precise, safe and predictable.
- The surgery time is shorter.
- Generally performed as flapless surgery and shorter recovery time for the patient.
- Less invasive surgery, less blood and less pain for the patient.
- Immediate charging possible.
- Bone grafts can be minimized.
The disadvantages of guided implant surgery include:
- The cost is very high.
- In flapless surgery, the patient’s bone situation cannot be assessed.
- Planning surgery takes longer.
- The user must learn the scheduling software.
- It is difficult to cope with unforeseen situations during surgery.
- Surgical kits and surgical models must be purchased.
Conclusion :
Implant planning is a central element of the thinking and therefore of the implant procedure. It is born from the synthesis of all the data collected by the practitioner: interview, clinical examination and additional tests.
It will lead to the proposal of a treatment plan and its discussion with the patient to obtain their free and informed consent to the treatment plan.
The key element of this planning is the prosthetic project, which is transformed into a radiological guide. Its creation greatly facilitates the interpretation of images and the implementation of planning.
In any case, planning must be carried out seriously and meticulously, because as always, thinking must precede action.
Prosthetic planning and project
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