Biomechanical and morphological changes produced by ionizing radiation on bone tissue surrounding dental implant

Effects of different doses of ionizing radiation on alveolar bone repair in post-extraction tooth socket: an experimental study in rats

OBJECTIVE

This study aimed to evaluate the dose-response effects of ionizing radiation (IR) on alveolar bone repair and bone strength after tooth extraction.

MATERIALS AND METHODS

A total of 32 male Wistar rats were used in the study, 28 animals were included in the final analysis, and n = 7 for each experimental group. Mandibular first molars were extracted. After 7 days, the animals were randomly divided into four groups according to single-dose irradiation: NIr, control group; Ir15, irradiated at 15 Gy; Ir20, irradiated at 20 Gy; and Ir30, irradiated at 30 Gy. The tooth extraction sites were subjected to micro-computed tomography (micro-CT), histological, histomorphometric, and biomechanical analyses 14 days after extraction. Data were analyzed using one-way ANOVA followed by Tukey's post hoc test (α = 0.05).

RESULTS

Micro-CT analysis revealed that IR led to lower values of bone volume (BV, in mm3) (0.68 ± 0.08, P < 0.001) and bone volume fraction, ratio of the segmented bone volume to the total volume of the region of interest (BV/TV, in %) (44.1 ± 8.3, P < 0.001) for the Ir30 group compared to the control group. A significantly lower amount of newly formed bone was observed in the Ir30 (P = 0.005) than in the Ir15 group. The histomorphometric results of quantification of bone matrix neoformation and the micro-CT were in agreement, demonstrating greater damage to the Ir30 group. IR30 cells showed a lower percentage of densely packed collagen than control cells. No significant differences were found in the biomechanical parameters.

CONCLUSION

IR affects alveolar bone repair. A dose of 30 Gy reduced the bone healing process owing to a smaller amount of newly formed bone and a lower percentage of densely packed collagen. Therefore, a dose of 30 Gy can be used to successfully establish an animal model of an irradiated mandible that mimics the irradiated clinical conditions.

CLINICAL RELEVANCE

Radiotherapy can lead to severe side effects and tooth extraction is a major risk factor. A proper understanding of the pathological mechanisms of radiation in alveolar bone repair requires the establishment of a suitable animal model of clinical conditions.

Radioiodine-131 Therapy Used for Differentiated Thyroid Cancer Can Impair Titanium Dental Implants: An In Vitro Analysis

BACKGROUND

The aim was to assess, in vitro, the effects of radioiodine-131 (I-131) on the structure of titanium implants.

MATERIAL AND METHODS

A total of 28 titanium implants were divided into 7 groups (n = 4) and irradiated at 0, 6, 12, 24, 48, 192 and 384 hours. At the end of the experiment, each sample was investigated via scanning electron microscopy (SEM) and electrochemical measures.

RESULTS

The control sample revealed a smooth and compact surface. The small micro-sized porosity is slightly visible at the macroscopic level, but the precise details cannot be observed. A mild exposure to the radioactive solution for 6 to 24 h showed a good preservation of the macro-structural aspects such as thread details and surface quality. Significant changes occurred after 48 h of exposure. It was noticed that the open-circuit potential (OCP) value of the non-irradiated implants move toward more noble potentials during the first 40 min of exposure to the artificial saliva and then stabilizes at a constant value of -143 mV. A displacement of the OCP values toward more negative values was observed for all irradiated implants; these potential shifts are decreasing, as the irradiation period of the tested implants increased.

CONCLUSION

After exposure to I-131, the structure of titanium implants is well preserved up to 12 h. The eroded particles start to appear in the microstructural details after 24 h of exposure and their numbers progressively increase up to 384 h after exposure.

Definition of the Region of Interest for the Assessment of Alveolar Bone Repair Using Micro-computed Tomography

The objective of this study was to evaluate the influence of the extraction socket (distal or lingual root) and the type of region of interest (ROI) definition (manual or predefined) on the assessment of alveolar repair following tooth extraction using micro-computed tomography (micro-CT). The software package used for scanning, reconstruction, reorientation, and analysis of images (NRecon®, DataViewer®, CT-Analyzer®) was acquired through Bruker <  https://www.bruker.com  > . The sample comprised the micro-CT volumes of seven Wistar rat mandibles, in which the right first molar was extracted. The reconstructed images were analyzed using the extraction sockets, i.e., the distal and intermediate lingual root and the method of ROI definition: manual (MA), central round (CR), and peripheral round (PR). The bone volume fraction (BV/TV) values obtained were analyzed by two-way ANOVA with Tukey's post hoc test (α = 5%). The distal extraction socket resulted in significantly lower BV/TV values than the intermediate lingual socket for MA (P = 0.001), CR (P < 0.001), and PR (P < 0.001). Regarding the ROI, when evaluating the distal extraction socket, the BV/TV was significantly higher (P < 0.001) for MA than for CR and PR, with a lower BV/TV for CR. However, no significant difference was observed for MA (P = 0.855), CR (P = 0.769), or PR (P = 0.453) in the intermediate lingual extraction socket. The bone neoformation outcome (BV/TV) for alveolar bone repair after tooth extraction is significantly influenced by the ROI and the extraction socket. Using the predefined method with a standardized ROI in the central region of the distal extraction socket resulted in the assessment of bone volume, demonstrating the most critical region of the bone neoformation process.

Characterizations of alveolar repair after mandibular second molar extraction: an experimental study in rats

BACKGROUND

Characterizations of rat mandibular second molar extraction socket with significantly different buccal and lingual alveolar ridge width remain unclear.

OBJECTIVE

To observe alterations in the alveolar ridge after extraction of mandibular second molars, and to examine processes of alveolar socket healing in an experimental model of alveolar ridge absorption and preservation.

METHODOLOGY

Eighteen Wistar rats were included and divided into six groups regarding healing time in the study. Bilateral mandibular second molars were extracted. The rats with tooth extraction sockets took 0, 1.5, 2, 3, 4 and 8 weeks of healing. Histological observation, tartrate-resistant acidic phosphatase (TRAP) staining, Masson's trichrome staining, immunohistochemical staining and micro-computed tomography (micro-CT) were applied to estimate alterations in the alveolar ridge.

RESULTS

Different buccal and lingual alveolar ridge width led to different height loss. Lingual wall height (LH) decreased significantly two weeks after tooth extraction. Buccal wall height rarely reduced its higher ridge width. From two to eight weeks after extraction, bone volume (BV/TV), density (BMD), and trabecular thickness (Tb.Th) progressively increased in the alveolar socket, which gradually decreased in Tb.Sp and Tb.N. LH showed no significant change during the same period. Osteogenic marker OCN and OPN increased during bone repair from two to eight weeks. The reduced height of the lingual wall of the tooth extraction socket was rarely repaired in the later repair stage. Osteoclast activity led to absorption of the alveolar ridge of the alveolar bone wall within two weeks after operation. We observed positive expression of EMMPRIN and MMP-9 in osteoclasts that participated in the absorption of the spire region.

CONCLUSION

Extraction of rat mandibular second molars may help the study of alveolar ridge absorption and preservation. The EMMPRIN-MMP-9 pathway may be a candidate for further study on attenuating bone resorption after tooth extraction.

Irradiation affects the structural, cellular and molecular components of jawbones

PURPOSE

Emerging evidence shows that changes in the bone and its microenvironment following radiotherapy are associated with either an inhibition or a state of low bone formation. Ionizing radiation is damaging to the jawbone as it increases the complication rate due to the development of hypovascular, hypocellular, and hypoxic tissue. This review summarizes and correlates the current knowledge on the effects of irradiation on the bone with an emphasis on jawbone, as these have been a less extensively studied area.

CONCLUSIONS

The stringent regulation of bone formation and bone resorption can be influenced by radiation, causing detrimental effects at structural, cellular, vascular, and molecular levels. It is also associated with a high risk of damage to surrounding healthy tissues and an increased risk of fracture. Technological advances and research on animal models as well as a few human bone tissue studies have provided novel insights into the ways in which bone can be affected by high, low and sublethal dose of radiation. The influence of radiation on bone metabolism, cellular properties, vascularity, collagen, and other factors like inflammation, reactive oxygen species are discussed.