Push-out bond strength of fiber posts to irradiated and non-irradiated intraradicular dentin.

OBJECTIVES: The aim of this study is to evaluate the influence of ionizing radiotherapy on the resin-dentin interface in endodontically treated teeth restored with fiber posts using a dual-cure resin cement performed with the etch-and-rinse (ER) and self-etch (SE) approaches in terms of push-out bond strength (MPa), and to analyze the post/cement/dentin interface using scanning electron microscopy (SEM). MATERIALS AND METHODS: Seventy-six single-rooted human teeth were used and randomly assigned into two main groups (n = 38): one non-irradiated group (NoRad) and one group subjected to a cumulative radiation dose of 60 Gy (Rad). All root canals were instrumented and were further subdivided into two subgroups (n = 19) following the adhesive approach: ER (RadER; NoRadER) and SE (RadSE; NoRadSE) used for fiber post luting with the universal adhesive and dual cure resin cement. Each root was sectioned perpendicularly to its long axis and sections from the middle third of the roots were chosen for SEM analysis and push-out bond strength test. Two-way ANOVA with post hoc Tukey tests and a dummy variable linear regression analysis were used for data analysis. RESULTS: Regardless of the adhesive approach, push-out bond strength in irradiated teeth resulted in significantly lower values than non-irradiated teeth (p = 0.0001). There were no significant differences between the ER and SE approaches in non-irradiated teeth (p = 0.955), whereas the ER approach showed significantly higher bond strengths than the SE approach in irradiated teeth (p = 0.0001). CONCLUSIONS: Ionizing radiotherapy resulted in dentin structure disruption and negatively affected the push-out bond strength of fiber posts to intraradicular dentin. The reduction in bond strength was also more significant with the SE approach than with the ER approach. CLINICAL RELEVANCE: The alterations resulting from root dentin irradiation seem to influence adhesive systems bond strength to dentin, as these changes contribute to lower push-out bond strength in irradiated groups before fiber post luting. Thus, clinicians should prepare patients with a reasonable restorative treatment plan prior to radiotherapy and simultaneously initiate a preventive program during radiotherapy.

Is fractionated robotic stereotactic body radiosurgery optional salvage treatment for the re-irradiation of locally recurrent nasopharyngeal carcinoma?

Purpose: Recurrent nasopharyngeal carcinoma (NPC) after previous radiation therapy is a significant problem. This study was to determine the potential benefits from re-irradiation by fractionated stereotactic body radiotherapy (FSRT) on survival benefits and effects of severe late toxicities. Materials and Methods: Between 2009 and 2018, treatment outcomes were evaluated retrospectively in 26 patients with locally recurrent NPC treated using FSRT with CyberKnife. Five patients who had metastatic disease and one who had second recurrence were excluded from the study, and the remaining 20 patients were analyzed. The median age was 52 years (range, 28-80 years); re-treatment T stage was as follows: 6 (30%) - T2, 5 (25%) - T3, and 9 (45%) - T4. The median time from initial RT to recurrence was 22 months (range, 8-159 months). The median re-irradiation FSRT dose was 30 Gy in 5 fractions. Results: The median follow-up was 44 months; the overall survival (OS), local failure-free survival, and disease progression-free survival rates at 3 years were 89%, 73%, and 53%, respectively. All patients were evaluated for response after treatment: 9 (45%) had complete, 3 (15%) had partial, and 6 (30%) had no response. Univariate analysis demonstrated that higher cumulative total radiotherapy dose, gross tumor volume, and recurrent time interval were prognostic factors for local failure-free survival. The recurrent time interval was also an independent factor for progression-free survival and OS. The incidence of temporal lobe necrosis and trismus was 10% and 20%, respectively. One patient had Grade 5 toxicity to treatment-related bleeding. Conclusion: Tumor dose coverage is important for treating recurrent NPC, and treatment-related mortality was vascular in nature. FSRT is a promising treatment modality for recurrent NPC.

Acoustic diagnosis of elastic properties of human tooth by 320 MHz scanning acoustic microscopy after radiotherapy treatment for head and neck cancer.

BACKGROUND: On the elastic profiles of human teeth after radiotherapy for head and neck cancers, generation of dental complications, which may bring several side effects preventing the quality of life, has not well clarified. Thus, we aimed to show the applicability of using 320 MHz Scanning Acoustic Microscopy (SAM) in the evaluation of the tooth damage acoustically at the micrometer level following radiation therapy, and also in the determination of the safe dose limits to impede severe dental damage. METHODS: This prospective study was performed by SAM employed at 320 MHz by an azimuthal resolution of 4.7 µm resolving enamel and dentin. A total of 45 sound human third molar teeth collected between September 2018 and May 2019 were used for the acoustic impedance measurements pre- and post irradiation. Nine samples for each group (control, 2 Gy, 8 Gy, 20 Gy, 30 Gy and 60 Gy) were evaluated to acquire the acoustic images and perform a qualitative analysis. Scanning Electron Microscopy (SEM) images were obtained to establish a relationship between micromechanical and morphological characteristics of the teeth. Statistical analysis was conducted using the Student t-test succeded by Mann-Whitney U investigation (p < .05), while SEM images were assessed qualitatively. RESULTS: The analysis included 45 sound teeth collected from men and women 18 to 50 years old. Post irradiation micromechanical variations of human teeth were significant only in the radiation groups of 30 Gy and 60 Gy compared to pre-irradiation group for enamel (7.24 ± 0.18 MRayl and 6.49 ± 028 MRayl; p < 0.05, respectively). Besides, the teeth subjected to radiation doses of 20, 30 and 60 Gy represented significantly lower acoustic impedance values relative to non-irradiated group for dentin (6.52 ± 0.43 MRayl, 5.71 ± 0.66 MRayl and 4.82 ± 0.53 MRayl p < 0.05), respectively. CONCLUSIONS: These results are evidence for a safe acoustic examination device which may be a useful tool to visualize and follow the safe dose limits to impede severe dental damage through the radiation therapy treatment for head and neck cancers.