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English version: EXPERIMENTAL JUSTIFICATION OF SELECTING THE EFFECTIVE EXPOSURE DOSES FOR PATIENTS WITH MAXILLOFACIAL AREA TUMORS FOR ESTABLISHING THE RETENTION POINTS (EXPERIMENTAL STUDY)*
Mukovoz O. Ye.
Higher State Educational Establishment of Ukraine "Ukrainian Medical Stomatological Academy", Poltava, Ukraine
For building the mandibular defects the avascular autotranspiants, formaiinized or iyophiiized allotransplants, as well as their combination (autoallotransplants) or combined osteoplasty are used. Atthough the technical performance of the lower jaw defects operations by these ways is rather simple, it is characterized by a large number of drawbacks. The main disadvantages of avascular bone grafts are rejection, their common resorption, the difficulty of fixing the denture during the rehabilitation period, etc. Implantation represents a way to replace missing teeth with artificial counterparts. One of the positive aspects of this technology is that the implants are properly fixated and thus provide an effective resumption of chewing function and aesthetic forms of face; in such a manner, the orthopedic rehabilitation of patients is also performed. One of the ways to solve this problem is replacement of large defects of the lower jaw wtth simultaneous creation of retention points and implantation of dental implants. However, it is known that radiation therapy significantly worsens the conditions for prosthetic implants. The latter task is of particular relevance during the replacement of major defects wtth bone grafts and implantation after which the radiation therapy will be held.
Key words: radiation dose, implants, rats, prosthetic care
Introduction
In order to replace the lower jaw defects, the avascular autotransplants, formalinized or lyophilized allotransplants, and their combination (autoallotransplantation) or combined osteoplasty are used [1, 4]. Although the lower jaw defects replacements are not technically difficult, these surgeries are characterized by a large number of shortages. The main disadvantages of avascular bone grafts are their rejection, frequent resorption, the difficulty of fixing the denture in the rehabilitation period, and others. Implantation is a way of replacing the missing teeth with artificial counterparts [3, 6, 7, 11]. One of the positive aspects of this technology is the fact that implants are properly fixated, and thus they ensure the effective restoration of masticatory function and facial aesthetic forms; in such a way, the orthopedic rehabilitation of patients is performed [10]. One aspect of solving this problem is the replacement of lower jaw large defects with the singlestep creation of retention points and implantation of dental implants. But it is known that radiation therapy worsens the conditions for prosthetic care. The latter task is of particular relevance during the replacement of significant defects with bone graft and implantation which will be held after radiotherapy [5, 9, 12, 13].
The aim of the research is to perform the calculations for the most optimal dose of local irradiation which does
not cause the significant disturbances in the process of titanium implants implantation.
Materials and methods of the research
The comprehensive treatment of patients with maxillofacial area tumors which includes chemoradiotherapy, surgery and prosthetics with removable structures, or simultaneous surgical treatment with the formation of the prosthesis retention points has been performed at Higher State Educational Establishment of Ukraine "Ukrainian Medical Stomatological Academy" at the department of oncology and radiology with radiation medicine (Poltava Regional Clinical Oncological Dispensary) together with the prosthetic dentistry department since 2010. However, it is known that radiation therapy worsens the conditions for prosthetics. Thus, the question was raised to calculate the optimal dose that would not lead to osteoporosis and sequestration, and would provide the retention of titanium pins for subsequent prosthesis.
The paper used the radiation pattern of X-irradiation on the apparatus RUM-17m at the right cheek of 70 mature white laboratory rats of Wistar breed with average weight of 200-220 grams (anesthetized using aminozin -125 mg / kg and ketamine - 250 mg / kg and fixed ) at a dose of 20.0 Gy under the following conditions: tube voltage 130 kV, current strength 13 mA, without filter, tube F
To cite this English version: Mukovoz O. Ye. . Experimental justification of selecting the effective exposure doses for patients with maxiilofacial area tumors for establishing the retention points (experimental study / / Problemy ekologii ta medytsyny. - 2013. - Vol 17, № 3-4. - P. 53 -55.
TOM 17. N 3-4 2013 P.
- 45 cm, dose rate of 1.36 Gy / min, the dose of 20.0 Gy Eef. = 40.0 keV, subject to the rules of humane treatment of animals. Animals were kept in vivarium at room temperature with 12 hours-cycle light / darkness, with free access to food and water on a standard diet in accordance with the norms of laboratory animals maintenance [8].
Results and discussion
The lower jaw bones in intact rats are characterized by the parameters typical for this type of laboratory animals (Fig. 1). The shape and size of alveoli correspond to the roots of teeth which are in them. Alveolar wall is covered with compact plate which is visualized as clear areas of osteosclerosis. Periodontal gap is defined as a thin strip of dark substance without pathological changes. Alveolar process bone has a trabecular structure, with no degenerative signs. Cortical plate of the alveolar process is not changed. Crowns and roots of teeth do not reveal pathological changes [15, 16].
Another experimental group consisted of rats that underwent local irradiation of the lower jaw with inserted implant and the minimum dose of 20-40 Gy. It has been found that the lower jaw bone after implantation reveals similar radiological characteristics as compared to the previous group of animals without irradiation; however, a slightly marked hypertrophy of bone tissue on the 21st day of the experiment has been discovered (Fig. 3). The bone tissue has revealed a pronounced trabecular structure around the titanium implant. The signs of degradation are not seen at the radiographs. The condition of cortical plate of the alveolar process is satisfactory. It should be noted that the exclusion of titanium implants in the early and subsequent periods after implantation in this group of animals was not observed.
Fig. 1. Lower jaw radiograph of the intact rat.
The next group consisted of animals which underwent implantation without irradiation after the tooth removal (the control group). During the analysis of X-ray it has been revealed that the lower jaw bone after implantation is characterized by the absence of bone hypertrophy (Fig. 2). The bone tissue reveals a marked trabecular structure around the implant. The signs of degradation are not revealed. The cortical plates of alveolar ridge are in good condition.
1
Fig. 3. The condition of the lower jaw bone after dental implantation by the development of osseointegration against the backdrop of local irradiation of 20-40 Gy., the 21st day (X-ray).
The lower jaw bone after implantation, followed by local irradiation which corresponds to a dose of 41-60 Gy reveals the presence of a high density foreign body in the alveolar socket of the removed tooth. The bone tissue around the implant demonstrates the signs of slight inflammation and regeneration. (Fig. 4). The bone tissue around the implant reveals a pronounced trabecular structure. Signs of degradation have not been reported. Cortical plate of the alveolar process is in good condition. Meanwhile, the titanium implant rejection was observed in 1 out of 10 animals in the early period after implantation (p> 0,25 p2) as compared to the control group.
Fig. 2. The condition of the lower jaw bone in the place of molars removal and dental implantation by the development of reparative processes without irradiation, the 21st day (X-ray).
Fig. 4. The condition of the lower jaw bone after dental implantation by the development of osseointegration against the backdrop of local irradiation of 41-60 Gy, the 21st day (X-ray).
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A somewhat different picture is observed in the X-ray experimental animals that underwent local irradiation at a dose of 61-70 Gy. A high density foreign body in the alveolar socket of the removed tooth was revealed in rats at the lower jaw radiographs after dental implantation and irradiation on the 21st day which corresponded to the inserted metal implant (Fig. 5).
The bone tissue around the implant demonstrated the signs of inflammation. Spongy substance of alveolar process revealed the insufficiently pronounced trabecu-lae. The cortical plate of alveolar process demonstrated unclear contours and abnormal phenomena in the form of osteoporosis. In 4 out of 10 rats of this group the loss of the inserted implant was observed at the early stages of the experiment (p <0,001 p2) as compared to the control group of animals without irradiation.
Fig. 5. The condition of the lower jaw bone after dental implantation by the development of osseointegration against the backdrop of local irradiation 61-70 Gy., the 21st day (X-ray).
In experimental animals with X-ray irradiation at a dose of > 70 Gy the loss of the inserted titanium implants was recorded in all cases at the early stages after implantation. The bone tissue around the implant at the radiographs revealed the significant signs of inflammation and osteoporosis.
Conclusions
Thus, the analysis of the experimental data shows that local irradiation of animals at doses of 20-40 Gy and 41-60 Gy does not significantly impair the processes of reparation and regeneration, and does not lead to the rejection of titanium implants in the early and late periods of implantation. In addition, the increasing of the dose from 61 Gy and more was accompanied by the development of inflammation of the tissue around the implant, by pathological changes in the trabeculae of spongy substance and cortical plate of the alveolar process, as well as by such phenomena as osteoporosis. It should be noted that these changes in bone tissue did not contribute to the normal development process of implantation of titanium implants and led to their rejection during different periods of the experiment. Through the performed experiment, one can predict the consequences for the patient after radiotherapy more than 70 Gy and therefore do not use the method of titanium implants rehabilitation; instead one can resort to the avascular autotransplants, formalinized or lyophilized allotransplants and combined osteoplasty.
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