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    -  Zerener T
    -  Dırıcan B
    -  Yıldız S
    -  Sager O
    -  Karaoglanoglu S
    -  Beyzadeoglu M

 
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ORIGINAL ARTICLE
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Dosimetric evaluation of the effect of dental restorative materials in head and neck radiotherapy


1 Department of Restorative Dentistry, University of Health Sciences, Gulhane Faculty of Dentistry, Ankara, Turkey
2 Department of Oral and Maxillofacial Surgery, University of Health Sciences, Gulhane Faculty of Dentistry, Ankara, Turkey
3 Department of Radiation Oncology, University of Health Sciences, Ankara, Turkey
4 Department of Anatomy, University of Health Sciences, Ankara, Turkey

Date of Submission14-Oct-2019
Date of Decision22-Jan-2020
Date of Acceptance07-Apr-2020
Date of Web Publication27-Jan-2021

Correspondence Address:
Elif A Oktay,
Department of Restorative Dentistry, University of Health Sciences, Gulhane Faculty of Dentistry, Ankara
Turkey
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijc.IJC_897_19

PMID: 33753619

  Abstract 


Background: The aim of our study is to assess the dose enhancement from scattered radiation due to dental restorative materials used for occlusal and mesio-occlusal-distal (MOD) cavity filling during simulated head and neck radiotherapy.
Methods: We have studied the dose enhancement ratio (DER) of conventional amalgam, high-copper amalgam, and resin composite dental restorative materials at cadaver mandible teeth using 2 therapeutic photon energies of 1.25 MeV (Co-60 gamma ray) and 6 MV (Linac X-ray) for irradiation.
Results: DER values at buccal position for Co-60 and 6 MV X-ray were 1.250 ± 0.013 and 1.151 ± 0.012, respectively. For dental cavity fillings, DER values for 6 MV X-ray were 1.065 ± 0.021, 1.100 ± 0.014, and 1.162 ± 0.016 for resin composite filling, low-copper amalgam filling, and high-copper amalgam filling, respectively. Our results revealed that DER regarding irradiation energy was minimum for 6 MV X-rays. With respect to dental restorative filling material, DER was minimum for resin composite filling. Regarding the cavity type, our results with standard deviation (SD) calculations revealed that DER was slightly but not significantly different for both Co-60 gamma ray (1.25 MeV) and 6 MV X-ray energies for both occlusal and MOD cavities.
Conclusion: Our dosimetric results for a single beam geometry suggest that, among the three types of filling, resin composite filling is an ideal restorative filling material with minimal morbidity-inducing radiation dose enhancement that may result in increased osteoradionecrosis and secondary caries risk. There is a need for further dosimetric studies with actual clinical beam arrangements.


Keywords: Amalgam, composite, dental restoration, dose enhancement ratio (DER), radiotherapy
Key Message Dental restorative material selection should be performed vigilantly to avoid radiation-induced complications for head and neck cancer patients.



How to cite this URL:
Oktay EA, Zerener T, Dırıcan B, Yıldız S, Sager O, Karaoglanoglu S, Beyzadeoglu M. Dosimetric evaluation of the effect of dental restorative materials in head and neck radiotherapy. Indian J Cancer [Epub ahead of print] [cited 2021 May 5]. Available from: https://www.indianjcancer.com/preprintarticle.asp?id=308062





  Introduction Top


Head and neck tumors constitute an important subgroup of all cancers with their diverse natural histories. They are named with regard to their locations and subsites in the head and neck region.[1] Critical parts are located in this relatively small region of the human body, which carries out basic physiologic functions including nutrition, respiration, and expression. Respective of their location, size, and spread pattern, head and neck tumors may lead to profound deterioration of the patients' quality-of-life and social integration with debilitating consequences such as functional impairments and structural disfiguration. Radiation therapy plays a central part in multimodality management of head and neck cancers. However, besides its therapeutic benefits, irradiation of the head and neck region may also induce quality-of-life impairment particularly in cases of high-dose radiation exposure or reirradiation.

Precursor cells of a tissue are a major determinant of its radiosensitivity.[1] Inherent radiosensitivity of different cells may show diversities. Bergonie and Tribondeau law states that excessive amount of less-differentiated cells in the tissue, abundant number of active mitotic cells, and duration of active cell proliferation are critical factors associated with tissue radiosensitivity.[1],[2] In this context, mucosal lining of the head and neck region is radiosensitive with its rapid cellular turnover rate. High mucosal turnover rate of the oral cavity renders this region very prone to radiation-induced toxicity. Several acute and late radiation-induced complications may result from lethal and sublethal damage of oral tissues including mucositis, soft tissue necrosis, mandibular osteoradionecrosis, temporomandibular joint dysfunction, fibrosis, skin reactions, periodontal disease, and caries.

Since both the tumor and dental restorations are covered in the irradiation field, restorative material selection for head and neck cancer patients should be performed vigilantly to avoid radiation-induced complications.[3]

A multidisciplinary team approach is warranted for optimal management of head and neck cancers. Patients have higher life expectancies with significant advances in cancer treatment, and morbidity is gaining more importance as a measure of survival besides mortality.[4] In this context, avoiding radiation-induced toxicity with maintenance of functionality should be a critical aspect of head and neck cancer management. Metal objects in the path of X and gamma ray beams lead to considerable amount of scattered radiation associated with the atomic number of the scatterer, namely, amalgam and composite restorative materials in head and neck cancer radiotherapy. Existence of dental restorative filling materials may lead to osteoradionecrosis of the lower jaw and mucositis due to the electronic backscatter effect in radiotherapeutic management of head and neck cancers. The magnitude of dose enhancement is a function of the atomic number of the scatterer.[5],[6],[7],[8],[9],[10],[11],[12],[13],[14] Dose enhancement is maximum for materials with high atomic number (Z). Percentage of dose increase to tissue was assessed by film dosimetry in the study by Hudson et al., and dose enhancement was found to be 20% for steel (Z = 26) and 40% for copper (Z = 29) at the wax phantom-metal interface.[14]

Osteoradionecrosis is a deleterious complication of head and neck cancer radiotherapy which may manifest with pain, orocutaneous fistula, exposed necrotic bone, pathological fracture, and suppuration.[5],[15] Relatively decreased vascularity and increased bone density of the mandible render it more prone to osteoradionecrosis rather than the maxilla.[16] The mandible is typically exposed to a greater radiation dose than the maxilla in clinical practice.[16],[17] In the study by Manzano et al. assessing osteoradionecrosis in the jaws of patients with head and neck cancer, osteoradionecrosis was more frequent in the mandible (80.0%) as a region in close vicinity of several tumors such as oral floor, tongue, and retromolar trigone region cancers but was also observed in the maxilla at a lower rate (10.0%).[17]

As well as the radiation dose, other factors including dental trauma, tumor location, premorbid state of dentition, and concomitant chemoradiotherapy may give rise to the development of osteoradionecrosis of the lower jaw.[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[18],[19],[20],[21]

There is scarce data related to the effect of dental restorative materials in head and neck radiotherapy. In this context, we have studied the backscatter effect of conventional amalgam, high-copper amalgam, and resin composite filling materials at cadaver mandible teeth with occlusal and MOD cavity fillings during simulated head and neck radiotherapy using two therapeutic photon energies of Co-60 gamma ray (1.25 MeV) and 6 MV (Linac-xray) to assess the dose enhancement from scattered radiation due to restorative material that may lead to osteoradionecrosis and radiomorbidity of the lower jaw by using Thermoluminescent Dosimeter chips (TLD100) placed at five different sites on the same left first molar tooth in this study.


  Materials and Methods Top


This study was performed in compliance with the Declaration of Helsinki principles and its later amendments with review board approval (document number: 24329, date: 24th August 2015). A special phantom, actual human cadaver mandible surrounded by water with soft tissue density was used for measurements on the first left molar tooth [Figure 1].
Figure 1: Special phantom, actual human cadaver mandible (effective Z = 7.8) surrounded by water with soft tissue density (effective Z = 7.4) used for dose measurements

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Sources of irradiation were Co-60 Teletherapy machine (Theratron 780, Nordion, Ontario, Canada) and a dual-energy Linear Accelerator (Elekta Synergy, Elekta Medical Systems, Crawley, UK). Measurements were performed for 2 different cavities with the same volumes of occlusal and mesio-occlusal-distal (MOD) fillings as shown in [Figure 2]a and [Figure 2]b, respectively. Three different restorative filling materials of conventional amalgam, high-copper amalgam, and resin composite were used for the same molar tooth in all experiments with the aforementioned restorative materials [Table 1].
Figure 2: (a) Occlusal cavity. A = 1/3B (distance between tubercles) Isthmus width = 1.9 mm. B = distance between tubercles = 5.75 mm. C = 1/3D (buccolingual size of the tooth) = 3.7 mm. D = buccolingual size of the tooth = 11.1 mm. E = mesiodistal size of the tooth = 11.6 mm. F = height of cavity = 2.0 mm. (b) Mesio-occlusal-distal (MOD) cavity. A = 1/3B (distance between tubercles) Isthmus width = 1.9 mm. B = distance between tubercles = 5.75 mm. C = 1/3D (buccolingual size of the tooth) = 3.7 mm. D = buccolingual size of the tooth = 11.1 mm

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Table 1: Composition of the dental materials used in the study

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Dose measurements were all performed at the same left first molar tooth for pre-restoration and post-restoration conditions with restorative materials. Thermoluminescent dosimeter (TLD100) chips with square-prism shape (effective atomic number 8.2 soft tissue Zeff) and 3.2 × 3.2 × 0.9 mm3 size were used for assessments. TLD chips were calibrated for dose range of 0.1-6 Gy with the standard deviation value of 0.01. TLD reader (Victoreen 2800, Victoreen, Cleveland, Ohio) was used for radiation absorbed dose measurements. All TLD chips were calibrated for each irradiation beam energy. Five TLD100 chips were tightly packed and placed on 5 sites of the 1st molar tooth at mesial, distal, buccal, lingual, and occlusal positions as shown in [Figure 3].
Figure 3: Left mandibular 1st molar five TLD100 chip positions for measurement of scattered radiation (1 = distal, 2 = occlusal, 3 = mesial, 4 = buccal, 5 = lingual)

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Dose measurements were performed at all five sites for two different radiation energy levels, three different restorative filling materials, and two different cavity types.

Radiation field size was 6 × 6 cm2 and source-skin distance was 100 cm for the Linear Accelerator (6 MV X-ray) and 80 cm for Co-60 gamma ray (1.25 MeV) teletherapy machine. Beam axis was perpendicular to the TLD100 chips. The delivered dose was 1 Gy each time, and measurements were repeated 3 times for two different cavity types with 2 different energies of Co-60 gamma ray and 6 MV X-ray.

The scattered radiation for two different energy levels and restorative filling materials, and two different cavity types was assessed by using the dose enhancement ratio (DER), which is calculated by mean post-restoration dose divided by mean pre-restoration dose.


  Results Top


Dose enhancement ratio (DER) measurements with standard deviation calculations (post-restoration dose/pre-restoration dose) at bone-dental alloy interfaces as a function of cavity type and dental restorative filling material are shown in [Table 2].
Table 2: Dose enhancement ratios with standard deviation calculations (post-restoration dose/ pre-restoration dose) at bone.dental alloy interfaces as a function of cavity type and dental restorative filling material (TLD100 chip position 1=distal, 2=occlusal, 3=mesial, 4=buccal, 5=lingual)

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Our results revealed that DER regarding irradiation energy was minimum for 6 MV X-rays. With respect to dental restorative filling material, DER was minimum for resin composite filling. Regarding the cavity type, our results with standard deviation (SD) calculations revealed that DER was slightly but not significantly different for both Co-60 gamma ray (1.25 MeV) and 6 MV X-ray energies for both occlusal and MOD cavities [Table 2].


  Discussion Top


Patients with head and neck cancers are typically above the age of 50, comprising a patient group very likely to have restorative dental fillings.[5] These restorative filling materials may have different contents such as silver, tin, copper, zinc, mercury for amalgams with differing amounts and silica zircon particles for composite resin material.

Backscattering radiation from high atomic number materials is an important factor in head and neck radiotherapy. Scatter from high atomic number (Z) materials may lead to both soft and hard tissue complications in the oral cavity. Amalgam is a heterogeneous material composed of mercury (Z = 80), silver (Z = 47), tin (Z = 50), and zinc (Z = 30).[22]

Interaction of high-energy X and gamma rays with matter is explained with the Compton effect, pair production, and photoelectric effect for high Z materials. Photoelectric effect increases by the third power of Z (atomic number) as Z3 while decreasing with the cube of ionizing radiation energy as E-3. Compton effect, however, is independent of the atomic number, while pair production increases with the square of atomic number (Z2). In the Compton effect, photon collides with electrons in the material to produce a broad spectrum of secondary electrons through inelastic collision processes. In pair production, the photon is absorbed and a positron-electron pair is produced. Electron scattering differences of the bone-restorative filling material interface are a major determinant of the degree of Compton effect and high-energy electron dose enhancement. The Compton scattering process is independent of the material's atomic number (Z). Compton scattering increases as the electron density of the material increases, and pair production increases with Z2 of the material.[5] Most materials other than hydrogen have the same electron number per gram. Electron density expressed as number of electrons per cubic centimeter is given by density multiplied by the number of electrons per gram. The amalgam used in restorative filling in our study has 8 g/cm3 density, while mandibular bone density is 1.85 g/cm3 and soft tissue density is approximately 1 g/cm3.[5],[23],[24],[25]

Irradiated bone that has failed to heal in 3 to 6 months is termed osteoradionecrosis, which is a primary osseous complication resulting from radiation injury.[3],[5] Irradiation may lead to impairment of the bone's capability to resist trauma and avoid infections through direct osteocytic damage or injury to the small vasculature of the Haversian systems and the periosteum. As a result of the compromised bone's inadequate repair capability, pathologic fractures may occur. Other manifestations may include pain, fistula, infection, and complete or partial sensational loss. Retrospective series report varying incidences of osteoradionecrosis typically in the mandible after irradiation of the head and neck region. Traumas, oral infections, and intimate association of primary tumor with the bone are among the factors increasing the risk of osteoradionecrosis and radiomorbidity.[4]

Dental restorative materials to be preferred in patients with head and neck cancer requiring dental restoration before or after radiation treatment should include non-metallic dental restorative materials; however, resin-modified glass ionomers and conventional glass ionomers may be mechanically affected by ionizing radiation and dissolve indirectly.[26] Composite dental filling materials have several favorable properties such as excellent optic features and elastic modules similar to enamel and dentine.[3] Other favorable aspects of composite filling materials include acceptable clinical performance and higher biocompatibility compared to metallic restorations.

Since composite resin restorations interact with tooth hard tissues via the adhesive systems, maximal sparing to maintain minimal exposure of healthy dental tissues should be an important aspect of head and neck irradiation. However, biomechanical properties of dentine structures and microtensible bone strength may be adversely affected by irradiation despite the use of normal tissue sparing head and neck radiotherapy techniques. High-dose radiation exposure may result in impaired adhesion of restorative material and tooth hard tissue (enamel-dentine) that may lead to secondary caries. There are currently controversial opinions about the effects of ionizing radiation on composite resin and adhesive systems, which have yet to be defined.[3],[27]


  Conclusions Top


In light of the results of our study, we can draw the following conclusions:

  1. The quantity of the scattered radiation alone may not directly cause radiomorbidity but may increase the risk of osteoradionecrosis and secondary caries due to greater resultant absorbed dose to the mandible
  2. Regarding irradiation energy, our results revealed that backscatter was minimal for 6 MV X-ray
  3. With respect to dental restorative filling material, our results revealed that backscatter was minimal for resin composite occlusal and MOD filling
  4. Regarding the cavity type, our results revealed that backscatter was slightly but not significantly different for Co-60 (1.25 MeV) and 6 MV X-ray irradiations for both occlusal and MOD cavities.


Our dosimetric results for a single beam geometry suggest that, among the three types of filling, resin composite filling is an ideal restorative filling material with minimal morbidity-inducing radiation dose enhancement that may result in increased osteoradionecrosis and secondary caries risk. There is a need for further dosimetric studies with actual clinical beam arrangements.


  Acknowledgements Top


This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Madrid Troconis CC, Santos-Silva AR, Brandão TB, Lopes MA, de Goes MF. Impact of head and neck radiotherapy on the mechanical behavior of composite resins and adhesive systems: A systematic review. Dent Mater 2017;33:1229-43.  Back to cited text no. 3
    
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Beyzadeoglu M, Sager O, Dincoglan F. General concepts in head and neck radiotherapy. In: Beyzadeoglu M, Ozyigit G, Selek U, editors. Radiation Therapy for Head and Neck Cancers A Case-Based Review. Springer-Verlag Berlin, Heidelberg; 2015. p. 1-15.  Back to cited text no. 4
    
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Wang R, Pillai K, Jones PK. Dosimetric measurement of scattered radiation from dental implants in simulated head and neck radiotherapy. Int J Oral Maxillofac Implants 1998;13:197-203.  Back to cited text no. 15
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]



 

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