3D Reconstruction of tomographic images of the jawbone for subperiosteal implants and its practical application

In the paper was worked out   research of the “design – to – implementation” cycle of widely used in Implantology subperiosteal implants. New approach of “design –manufacturing-implementation” was carried out without making a pattern, based on real bone copy after initial surgery intervention. The new approach used 3D tomographic image of the bone and subsequent 3D reconstruction. The reconstructed  bone   3D model can be used two ways - for the plastic materialization the model of the bone with the rapid prototyping technology and subsequent manual modeling the implant over the plastic bone and conventional casting, or using more progressive Virtual Engineering Technology, high-quality and fast direct virtual shaping in 3D the implant and it’s materialization physically using state of the art technology, called "selective laser melting- SLM" directly by CrCo or Titanium alloys.

INTRODUCTION

In our time, the restoration of partially or completely lost teeth we do end masse by placing intraosseous dental implants and subsequent semi-movable or immovable prosthetics. In many cases the bone is insufficient or the screws fall into places unsuitable for prosthetics, e.g. in the upper jaw - the sinus cavities, and in the lower - the lower jaw canal and the use of intraosseous implants is impossible or possible after bone grafting, surgery, which is expensive, time consuming and not guaranteed. Jaws that have advanced atrophy of the alveolar bone present a difficulty in prosthetics in dentistry, both with plaque prostheses and with intraosseous so-called enosal implants. Moreover, in cases of very severe atrophy, any bone grafting is impossible and even risky. For this reason, it is necessary to create supports for fixed prosthesis of the upper and lower jaw with the help of the so-called subperiosteal implants, which we use for completely and subtotally edentulous jaws.

The name comes from the Latin sub - which means "under" and periosteum - "periosteum", ie. under the periosteum. Thus, these implants we place on the bone and under the periosteum.

Through this restorative approach, we avoid complex, expensive and time-consuming bone augmentation surgeries to place enosal implants, as well as the high risk of mandibular fracture when using other methods (for example Trans mandibular implants). The dentist has the possibility to combine a subperiosteal implant and natural teeth, as well as to combine a subperiosteal implant with a bridge or joint connecting prosthetic structure. In addition, unlike intraosseous (intraosseous) implants, subperiosteal implants do not require a particularly large amount of bone.
A possible alternative is partial or total plaque prostheses, something most patients find unacceptable, despite widespread advertising of Corega-type denture adhesives.
Another alternative is subperiosteal implants. Although this method repelled patients for a long time, for several reasons [1]:
    1. Fear of the patient of two surgical interventions - one to take a bone impression and the second - to place the implant.
2. Insufficient height and thickness of alveolar bone for intraosseous implantation and related long-term surgical interventions to enlarge the bone to make it suitable for such.
3. Due to financial reasons.
4. Ignorance theoretically and lack of mastery of the operative technique of subperiosteal implantation by practicing dentists.

SUBPERIOSTAL IMPLANTS

Subperiosteal implants are one of the first forms of implants in general in the recent history of implantology. For the first time in 1943, Gustav Dahl [2] implanted a total subperiosteal grill with 4 stumps, on which he made a fixed prosthesis.


FIG. 1 Dahl subperiosteal implants. [2]


FIG. 2 Subperiosteal implants in 1943. [3]

A little later, in 1947, Goldberg and Gershkoff [4] implanted a massive subperiosteal gill on the lower jaw, which they fixed to the bone with screws.


FIG. 3 Subperiosteal implants on the Goldberg and Gershkoff pathway, in which they first use screws to fix it. [4]

Linkow undoubtedly gave a powerful impetus to the development of subperiosteal implants [5]. In his remarkable scientific work, Theories and Techniques of Dental Implants, Linkow summarizes the entire world's implant experience to date. He developed a slender and complete implant system, part of which is that for subperiosteal implants. An original solution in 1984 in this respect was the so-called tripodal subperiosteal implant. Tripodal, because there is no complete frame, and 3 separate subperiosteal frames are united by a common gingival splint with spherical joints for articulation of the prosthesis.


FIG. 4 Linkow's tripod implant. [5]

Implantologists have long avoided the use of subperiosteal implants because they cause inflammation of the bone with subsequent melting. Subsequently, they created a structure with extended free spaces, which allows the bone to feed properly and today the results of their use as a clinical success are comparable to those of intraosseous implants. They are a good alternative to intraosseous implants, which in many cases, due to insufficient bone, require bone grafting and a better alternative to removable dentures.

TECHNOLOGICAL STAGES IN CREATING SUPERIOSTAL IMPLANTS

1 - Fingerprinting. In it we take fingerprints from the jaws, cast plaster models and make bite patterns on them. After removing the bite, we arrange the teeth as for a prosthesis.
2 - Preliminary surgical intervention. We place the individual spoon on the jaw and with a round drill through the holes; we mark the places of the future stumps. We adjust the individual spoon on the bone and take an imprint. This is the two-step process. There is also a one-step process. In it we avoid the first surgical intervention, using a computed tomography reconstruction. A process that we will look at in this article. [3]
3 - We cast a model, followed by modeling with profile waxes, packaging and model casting. The prepared subperiosteal implant we sterilize in an autoclave and the next stage is ready.
4 - Actual surgical intervention. We perform it 3-4 weeks after the preliminary one.
We invite the patient daily until the removal of the sutures to remove the plaque on the stumps, which ensures the smooth healing of the wound.
5 - Orthopedic. We can blunt it a week to ten days after removing the sutures of the second operation, when there is no danger of opening the surgical wound and when the scar has already retracted. We take an impression in a bite by the usual method with solid and proofreading. We make a bridge structure. [3]

Constructions subperiosteal implants

The technique of subperiosteal implantation is an old alternative method to the first intraosseous implantation methods in the oral cavity.  We used to use Vitallium as a material. We now use mainly titanium alloys and to a lesser extent, the so-called "passivated" chromium-cobalt-molybdenum alloys. It is important to note that the crowns and bridges on these subperiosteal implants are made of cermets or photopolymer, and the metal base in both cases must be made of titanium alloy, to avoid electrical voltage between the prosthesis and the implant, etc. bi-poly-metallization. At values of this electrical voltage above 100 mV, as much as the natural electrical voltage of a living cell, there is damage to the bone cells, which is detrimental to the implant. If we make the implant from another alloy, then the crowns or bridges must be made of the same alloy for the above reasons.

Nowadays, implantologists use subperiosteal implants with wide spaces between the peripheral "frame" and the transverse "ribs", as shown in FIG. 5. The coronal part, the so-called "heads" of the subperiosteal implant vary in number and location.



FIG. 5 Modern subperiosteal implant.

They can be from 1 to 6 pieces, depending on whether it is distal unrestricted, intermediate or total edentulousness of the jaws. However, the method of operation has remained the same to this day. To make a subperiosteal implant, we need to deperiosteate the bone in the edentulous area - a routine surgical procedure that we use in many other dental surgeries and bone imprints, which in the presence of modern impression materials is not a problem and technically very similar to the impression techniques known from orthopedic dentistry. The subperiosteal implants lie on the bone (do not enter it) over a very large area and are fixed by the growth of fibrous connective tissue, which covers them completely (Fig. 6). There is no need for a period of bone integration. The periosteum (periosteum) and the lining of the gums heal on them in no more than 2 weeks.



FIG. 6 Subperiosteal implant - again model from 1943 (Dahl). [2]


FIG. 7 Modern subperiosteal implant. [3]



FIG. 8 Orthopantomography (X-ray) of total subperiosteal implants of the upper and lower jaw.

A problem related to the subperiosteal implant is the possibility for good distribution of the masticatory load on the bone, which depends primarily on two main criteria - the material of the implant and the geometry / design of the implant. In order to more evenly distribute the load during the chewing process (about 600 N), we recommend a gap between the rib supporting the head and the bone, as shown in fig. 9. [6]



FIG. 9 Gap between the rib supporting the head and the bone. [6]

We anticipate future optimization tasks in order to find the optimal shape of the implant that will load the bone as evenly as possible.


FIG. 10. How things look in our time.

Reconstruction from tomographic images

Tomography: Tomography is a method of studying bone tissue using X-rays. We use it widely in the field of dentistry because it allows taking a three-dimensional image of the jaw. In FIG. 11 shows a tomographic apparatus.




FIG. 11 General view of a 3D mammographic X-ray scanner.

During the exposure, the tomograph device fixes 300 incisions in the dental area in different projections, and then with the help of a computer specialized program, based on them, creates a 3D model of the examined area. The scanning time is 14 seconds, and the result is an impressive quality of the achieved three-dimensional images, such as exceptional clarity and precision, especially in view of the bone structure on which we plan to place a subperiosteal implant. With the help of tomography, we avoid the first preliminary surgical intervention, which saves significant effort and time on the part of the patient.
In FIG. 12 shows a typical 3D color tomographic image of the maxillofacial area.


FIG. 12 3D tomographic image.

We build a subperiosteal implant precisely based on the captured three-dimensional tomographic image in a specialized CAD software package.



Fig. 13. Cast subperiosteal implant (Cr-Co-Mo) based on the two-stage process (fingerprinting) on the left and a CAD model based on a tomographic image on the right in a single-stage process. [7]

Computed tomography dates back to 1972 by G. Hounsfield and A. Cormac, who later (1979) became Nobel laureates. The implants shown in the photo are cast models using classic technology.

Reconstruction from tomographic images

With the introduction of CAD / CAM - technologies, a new beginning in the field of SI. The first known experiment was by Fisher [8] from Australia, in 1993. He described a CAD / CAM method for subperiosteal implantation for the treatment of completely edentulous jaws. Thanks to this, we no longer make 2 operative interventions, but only one. From the captured three-dimensional computed tomography image, we extract all the information. Then we convert it into a 3D CAD model. We transfer it to the CAM part, where we perform milling. We process the received digital code (NCL - Number Cutter Location). We do this so that the control of the CNC milling machine can read it. We make the model on the machine. In fact, we produce a negative impression of the tomograph-scanned jaw from a block of technical wax. We fill the model with epoxy resin to create a positive replica of the jaw. [9]
From it we go to the method of casting on molten models.
To speed up the process, as well as to achieve a higher execution speed, we will pay special attention to the new techniques for the production of implants - the use of 3D printing.

Based on the obtained 3D CAD model, we can export the information in the form of a * .stl file, which will then go to a rapid prototyping machine, such as one working on stereolithography technology, in order to create a final model. We use it, then, as a base for casting on a molten model. Thus, although we use many modern and progressive methods of work, we come to the classic casting of molten models.

Based on the experiments performed in MTF at TU - Sofia with the help of a tomograph we created an accurate computer model of the jaw, which we made as a physical object of plastic using a prototyping machine available in the faculty, as shown in fig. 14.


FIG. 14. Physical prototype of the lower jaw made of plastic on a 3D printer in MTF at TU - Sofia.

The technology allows even on a virtual level based on the geometry of the jaw, which comes from the tomography apparatus, to make a precisely virtual model of a subperiosteal implant in a CAD 3D package, the model of which we see in fig. 15.



FIG. 15 Virtual model of a subperiosteal implant constructed in a 3D CAD software system based on a model of a virtual three-dimensional jaw obtained directly from a tomographic apparatus

In MTF at TU - Sofia is available for experiments the most modern prototyping machine - SLM 125 (Sinter Laser Melting - direct laser melting), which works with various metals and alloys (in powder form), incl. with Cr Co and Ti alloys. This allows her to create the final working model of a subperiosteal implant directly from the constructed virtual model.


FIG. 16 General view of the SLM 125 prototyping machine [10]

Conclusions. Subperiosteal implants - reasons for their rediscovery

Subperiosteal implantation is a relatively fast and not very difficult to perform implantation method, consisting of known elements of the surgical technique in other types of surgical dental interventions, known impression techniques and routine prosthetic methods. [11] It combines an optimal combination of speed of execution, price, functionality and aesthetics. We make the subperiosteal implants by the usual dental methods - modeling, casting and polishing, as well as by new advanced purely machine-building methods. [10] We have the ability to scan quickly via computed tomography and obtain a very accurate three-dimensional color model of the scanned area. Then transfer the image to a CAD software package. On it to complete the model in 3D view of the jaw. Then virtually model the subperiosteal implant (which can also be strongly sized and structurally optimized in order to distribute the masticatory load as evenly as possible [6]). Then we can transform this virtual model of the subperiosteal implant into a control program of a machine for direct metal construction (SLM 125) [10]. On this cup after the respective manipulations to produce a quality subperiosteal implant. In this way we eliminate almost completely the dental laboratory and the related numerous design and production difficulties. [1] [10] [11]. Finally yet importantly, we must mention the great convenience for the patient, because in this process he will undergo only one surgical intervention related to the placement of the implant (and not two, as in the classical technology until now, which to some extent is the main reason for the not very great popularity of this type of implants).

The finished subperiosteal implant we can see in the picture below, fig. 17. In FIG. 18 is a panoramic X-ray image of the same section and FIG. 19 shows the result in the same patient. [12].


FIG. 17 Photo of subperiosteal implant. [12]


FIG. 18 Panoramic X-ray of the same subperiosteal implant. [12]


FIG. 19 End result of the same patient. [12]

Bibliography

1. Dr. Hristo Hristov (2002). Subperiosteal implants - a good alternative for insufficient bone for intraosseous implantation. Newspaper "Dental World" issue 1, January 2002
2. Dahl, G.S. (1943) Om mojlighenten for implantation I kakan ov metallskelett som bas eller retention for fasta eller aavalagbara protesor. Odontol. Tidskr. 51, 440 - 449.
3. Iva Uzunova, Georgi Zapryanov. Subperiosteal implants - a good alternative for insufficient bone for intraosseous implantation.
4. Goldberg, N.I. & Gershkoff, A. (1949). The implant lower denture. Dental Digest 55: 490-495
5. Linkow, L. I., R. Chercheve (1970). Theories and techniques of oral implantology. St. Louis, Mosby.
6. G. Todorov, J. Sofronov, H. Hristov. Strength and deformation behavior of subperiosteal implants. Magazine of Mechanical Engineering and Electrical Engineering, issue 6 2013
7. A. Norman Cranin, DDS, Deng Michael Klein, DDS John P. Ley, DDS John Andrews, DDS Robert DiGregorio, PharmD. An in vitro comparison of the computerized tomography / cad-cam and direct bone impression techniques for subperiosteal implant model generation. Journal of oral implantology. Vol. XXIV / No. Two / 1998.
8. Fischer J.E. (1993), CAD / CAM subperiosteal implants in Australia. Case report, Aust Dent J. 1993 Oct; 38 (5): 413.
9. Marc L. M. McAllister, application of stereolithography to subperiosteal implant manufacture. Journal of oral implantology. Vol. XXIV / No. Two / 1998
10. G. Todorov, N. Nikolov, V. Mitov, J. Sofronov. Construction of a dental metal structure type-bearing insert through the technology "selective laser melting" in TU - Sofia.
11. Dr. Hristo Hristov (1999). Creation of supports for fixed prosthesis of the upper and lower jaw with advanced atrophy with the help of subperiosteal implants. Dental Almanac no. 1/1999
12. Kazuki Takaoka, Emi Segawa, Kazuma Noguchi, Hiromitsu Kishimoto, Masahiro Urade Maxillary subperiosteal implantitis that caused severe bone resorption of the maxilla with perforation of the maxillary sinus and sinusitis: A case report. Journal of Stomatology. 2013, 3, 226-229.

We conducted this study under project Project BG051PO001-3.3.06-0046 "Support for the development of doctoral students, postdoctoral students and young scientists in the field of virtual engineering and industrial technologies" at the Ministry of Education and Science.

For more information - email pfhristov@yahoo.com