Radiotherapy effect on nano-mechanical properties and chemical composition of enamel and dentine

Assessing push-out bond strength in re-irradiated teeth: Universal resin cement performance in self-etch and self-adhesive modes

OBJECTIVES

To investigate the effect of cumulative doses of radiation on the pushout bond strength (BS) of a universal resin cement used in the self-etch (SE) and self-adhesive (SA) modes to the intraradicular dentin.

MATERIALS AND METHODS

Forty-eight human teeth were distributed into three groups (n = 16) according to the radiation therapy dose (RT): NoRT (no-radiotherapy), 70RT (70 Gy), and 70 + 70RT (70 Gy + 70 Gy). The teeth were redistributed into two subgroups (n = 8), according to the adhesive mode: SE (NoRT-SE, 70RT-SE, and 70 + 70RT-SE) and SA (NoRT-SA, 70RT-SA, and 70 + 70RT-SA). Data were statistically compared after BS test (ANOVA, Tukey's post hoc test, and Fisher's exact test).

RESULTS

In the SA mode, BS was significantly higher in nonirradiated teeth compared with 70RT and 70 + 70RT (p < 0.0001). There were no significant differences between SE and SA modes in nonirradiated teeth (p = 0.14). In the 70RT group, SE mode increased BS compared with SA mode (p < 0.0001). Most specimens had adhesive and mixed failures in SA and SE modes, respectively.

CONCLUSIONS

The universal resin cement in the SE mode had greater BS to the irradiated dentin. When teeth were re-irradiated, the universal resin cement had similar performance in terms of BS, regardless of the adhesive approach.

CLINICAL SIGNIFICANCE

There is no research establishing a correlation between radiotherapy and its impact on the BS of a universal resin cement used in SE and SA modes to intraradicular dentin.

The effects of re-irradiation on the chemical and morphological properties of permanent teeth

This study aimed to assess the in vitro effects of re-irradiation on enamel and dentin properties, simulating head and neck cancer radiotherapy retreatment. Forty-five human permanent molars were classified into five groups: non-irradiated; irradiated 60 Gy, and re-irradiated with doses of 30, 40, and 50 Gy. Raman spectroscopy, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) were employed for analysis. Raman spectroscopy assessed intensity, spectral area, and specific peaks comparatively. Statistical analysis involved Kolmogorov-Smirnov and One-Way ANOVA tests, with Tukey's post-test (significance level set at 5%). Significant changes in irradiated, non-irradiated, and re-irradiated enamel peaks were observed, including phosphate (438 nm), hydroxyapatite (582 nm), phosphate (960 nm), and carbonate (1070 nm) (p < 0.05). Re-irradiation affected the entire tooth (p > 0.05), leading to interprismatic region degradation, enamel prism destruction, and hydroxyapatite crystal damage. Dentin exhibited tubule obliteration, crack formation, and progressive collagen fiber fragmentation. EDX revealed increased oxygen percentage and decreased phosphorus and calcium post-reirradiation. It is concluded that chemical and morphological changes in irradiated permanent teeth were dose-dependent, exacerbated by re-irradiation, causing substantial damage in enamel and dentin.

Radiotherapy in the head and neck region influences the chemical and mechanical properties of intraradicular dentin

OBJECTIVES

To investigate the chemical and mechanical properties of intraradicular dentin submitted to radiotherapy.

MATERIALS AND METHODS

Sixteen mandibular incisors were divided into two groups (n = 8): non-irradiated and irradiated. The irradiated teeth were obtained from head and neck radiotherapy patients, with a total dose ranging from 70.2 to 72 Gy divided into 1.8 Gy daily. After sample preparation, intraradicular dentin slices of each root third were evaluated by Raman spectroscopy, energy dispersive spectroscopy and Knoop microhardness test. Data were analyzed by Two-way ANOVA and Tukey's test (α = 0.05).

RESULTS

In Raman spectroscopy, carbonate and amide III showed a significant difference for irradiation and third (carbonate p = 0.021 and p < 0.001; amide III p < 0.001 and p = 0.001, respectively). For amide I, there was a significant difference for third (p < 0.001). For carbonate/mineral ratio, there was a significant difference for irradiation (p = 0.0016) and third (p < 0.001), with the irradiated middle third showing the lowest values. For amide I/amide III ratio, there was a significant difference for irradiation (p = 0.005) in the cervical third. In energy dispersive spectroscopy, carbon (p = 0.004; p = 0.020), phosphorus (p < 0.001; p = 0.009) and calcium (p = 0.008; p = 0.007) showed differences for irradiation and third, with the irradiated groups presenting lower values in cervical and middle thirds. For calcium/phosphorus ratio, there was a significant difference for irradiation (p < 0.001) in cervical and middle thirds. Regarding microhardness, there was a significant difference for irradiation (p < 0.001), with all irradiated groups showing lower microhardness values.

CONCLUSIONS

The radiotherapy altered the chemical and mechanical properties of intraradicular dentin, mainly in the cervical and middle root thirds.

Activation of gelatinases in permanent human teeth after different experimental radiotherapy protocols

The objective of this study was to compare the activation of gelatinases in dentin-enamel junction (DEJ) and underlying dentin of permanent teeth after experimental radiotherapy in conventional and hypofractionated modalities. Newly extracted third molars (n = 15) were divided into three experimental radiotherapy groups: control, conventional (CR), and hypofractionated (HR) (n = 5 per group). After in vitro exposure to ionizing radiation, following standardized protocols for each modality, a gelatinous substrate was incubated on the tooth slices (n = 10 per group). Activation of gelatinases was measured by in situ zymography, expressed in arbitrary fluorescence units (mm2) from three tooth regions: cervical, cuspal, and pit. Fluorescence intensity was compared among radiotherapy protocols and tooth regions in each protocol, considering a significance level of 5%. Considering all tooth regions, the fluorescence intensity of the CR group was higher than the HR and control groups, both in DEJ and underlying dentin (p <0.001). In addition, the fluorescence intensity was higher in underlying dentin when compared to DEJ in all groups (p <0.001). Considering each tooth region, a statistically significant difference between CR and HR was only observed in the pit region of underlying dentin (p <0.001). Significant and positive correlations between fluorescence intensities in DEJ and underlying dentin were also observed (p <0.001). Experimental radiotherapy influenced the activation of gelatinases, as well as exposure to the conventional protocol can trigger a higher activation of gelatinases when compared to hypofractionated, both in DEJ and underlying dentin.

Antibacterial, antibiofilm and anticaries effect of BioXtra® mouthrinse for head and neck cancer (HNC) patients under a microcosm biofilm model

BACKGROUND AND PURPOSE

Considering the lack of studies investigating salivary substitutes to control post-radiation caries for patients with head and neck cancer (HNC), this study aimed to evaluate the antibacterial, antibiofilm, and anticaries effects of BioXtra® on the microcosm biofilm formed on different enamel types (non-irradiated and irradiated) and from distinct saliva sources (control and HNC patients).

MATERIALS AND METHODS

Non-irradiated and irradiated enamel specimens were treated with BioXtra®, phosphate-buffered-saline (PBS; negative control), or 0.12% chlorhexidine (CHX; positive control) for 1 min. Biofilm was produced from human saliva (healthy participants with normal salivary flow for the control group or irradiated HNC patients with hyposalivation for the HNC group), mixed with McBain saliva, under 0.2% sucrose exposure, daily submitted to the treatments (1 min), for 5 days. Bacterial metabolic activity, biofilm viability, CFU counting, and enamel demineralization were determined.

RESULTS

BioXtra® significantly reduced the bacterial metabolic activity for both enamel types and the inoculum sources, being more effective for the irradiated enamel or for the saliva from the control group. Similarly, BioXtra® significantly reduced the biofilm viability, the CFU for total microorganisms, mutans streptococci, and lactobacilli, and was able to significantly reduce the mineral loss and the lesion depth compared to PBS. CHX was an effective treatment to significantly reduce all parameters, performing better than BioXtra® and reinforcing its reliable efficiency as a positive control.

CONCLUSION

Regardless of the enamel type and the inoculum source, BioXtra® presented antibacterial, antibiofilm, and anticaries effects under this experimental model, which should be confirmed in further clinical studies.

Does radiation therapy affect adhesion of tricalcium silicate cements to root dentin?

OBJECTIVE

This study aimed to analyze the effect of irradiation on the push-out bond strength of mineral trioxide aggregate (MTA) and Biodentine to radicular dentin.

METHODOLOGY

A total of 60 extracted mature human teeth with single root canals were categorized into two groups (irradiated and non-irradiated) (n=30). Each group was further divided into two sub-groups based on cements used (Biodentine and MTA). Then, a cumulative radiation dose of 60 Gy was divided into 30 fractions (two Gy for every fraction) and administered for five successive days per week over six weeks. Obturation was then performed using MTA and Biodentine. Afterwards, 1.5 mm thick horizontal sections were procured from the middle one-third of all the specimens and then subjected to push-out bond test. Results were analyzed using one-way analysis of variance with post-hoc Tukey's test.

RESULTS

The bond strength of Biodentine and MTA to irradiated teeth was lower than non-irradiated teeth. Highest push-out bond strength was observed in non-irradiated specimens filled with Biodentine (p=0), followed by irradiated specimens filled with Biodentine (p=0); non-irradiated specimens filled with MTA (p=0); and irradiated specimens filled with MTA (p=0.9).

CONCLUSION

The push-out bond strength of Biodentine and MTA to root canal dentin decreased significantly post irradiation.

Ex-vivo analysis of demineralisation on irradiated teeth using optical coherence tomography

Head and neck cancer patients are prone to dental caries after radiotherapy. An ex-vivo study was conducted to assess the feasibility of optical coherence tomography (OCT) to detect tooth demineralization due to caries in irradiated teeth. Thirty-nine human molar teeth were subjected to caries lesion induction through irradiation (Group 1), pH cycling (Group 2-1), and both (Group 2-2). The OCT signal attenuation coefficient, µR was assessed and validated against microhardness test and scanning electron microscope (SEM). The µR for Group 1 increased from 10 Gy to 40 Gy, and subsequently decreased after irradiated to 50 Gy and 60 Gy due to damaged enamel microstructure. In Group 2-1, the µR decreased with duration of pH cycling from day 1 to day 14 due to the increase of porosity in enamel layer. However, the µR showed decreasing trend from day 14 to day 28 of pH cycling, resulted from mineral deposition in the enamel layer. Although no significant difference was found in the µR between Group 2-1 and 2-2, SEM of Group 2-2 demonstrated visually higher porosity and larger gaps between microstructures. Irradiation may accelerate caries damage to tooth microstructure by increasing its porosity and brittleness, but larger sample size may be needed to further prove the effect. OCT could potentially be used for early detection of tooth demineralization in vivo based on the measurable µR changes for all groups which are shown negatively correlated with microhardness value (p < 0.05).

Does irradiation of the tooth structure interfere with oxygen saturation measured by pulse oximetry?-An ex vivo laboratorial study

The effect of tooth structure subjected to ionising radiation on oxygen saturation levels (SpO2 ) measured by pulse oximetry was investigated. Fifty-four extracted human third molars were sectioned mesiodistally. Pulse oximeter diodes were placed in prefabricated silicone moulds, secured on a vise with tooth surfaces placed between the diodes and the participant's finger, and SpO2 levels were measured. After that, the tooth surfaces were subjected to ionising radiation in fractionated doses of up to 70 Gy, and SpO2 was measured according to the protocol described. The Kolmogorov-Smirnov test was used for the analysis of normality of the quantitative variables, and Student's t-test compared mean SpO2 levels before and after irradiation. Mean SpO2 after irradiation was 94.6 ± 0.9%, without a statistically significant difference from SpO2 before irradiation, which was 94.7 ± 0.6%. Irradiation of the tooth structure did not interfere with SpO2 levels measured by pulse oximetry.

Remineralization effects of Er,Cr:YSGG and/or bioactive glass on human enamel after radiotherapy-an in vitro study

The aim was to evaluate the effects of Er,Cr:YSGG and/or bioactive glass 45S5 (BG) on the chemical and physical properties of enamel after radiotherapy. Third molar crowns were cut in half (buccal-lingually), and the mid part of the labial/oral surface was subjected to different protocols. All samples were treated with standard 70 Gy. After radiotherapy, enamel was treated with either Er,Cr:YSGG (2780 nm; pulse 60 μs) and BG or only BG, and control samples were kept in deionized water. Vickers microhardness, scanning electron microscopy (SEM), and characteristic X-ray spectroscopy (EDS) were performed before, after radiotherapy, and after treatment. Analysis of variance (ANOVA) was used. A significant drop in enamel microhardness was observed after radiotherapy (p < 0.001). After Er,Cr:YSGG and BG or BG alone, there was a significant increase in microhardness (p < 0.001), which was on average significantly higher compared to the initial measurements for Er,Cr:YSGG with BG (p < 0.001), but not observed in BG alone (p = 0.331). After radiotherapy, SEM showed increased surface roughness with eroded prisms. Er,Cr:YSGG and BG or BG alone both showed disorderly packed glass particles on the enamel surface. Radiotherapy noticeably reduced the concentrations of calcium and phosphorus. Er,Cr:YSGG and BG treatment increased the concentrations of calcium, sodium, phosphorus, and silicate. BG treatment alone increased the concetration of calcium and phosphorus. Directly induced radiotherapy led to potential damage of enamel, but afterwards treatment with Er,Cr:YSGG laser and BG resulted in a higher increase of enamel microhardness compared to BG alone, reflecting in a possible better remineralization effect.

Impact of radiotherapy on the morphological and compositional structure of intra-radicular dentin

Considering the side effects in the oral cavity and dental structures of radiotherapy (RDT) for head and neck cancer, this study aimed to evaluate the effects of RDT on the root dentin concerning the obliteration of dentinal tubules, the inorganic composition of intra-radicular dentin, and the integrity of collagen fibers. Thirty human canines were selected from a biobank and randomly divided into two groups (n=15). The samples were sectioned buccolingually, and a hemisection was used for structural analysis by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). Low-vacuum SEM images were obtained at 2000-x magnification to observe the obliteration of the dentinal tubules. Moreover, compositional evaluation was performed using EDS. After RDT, the SEM and EDS analyses were repeated using the same methodology. RDT was applied fractionally at 2 Gy per day, 5 days per week, for 7 weeks, resulting in a total dose of 70 Gy. The collagen integrity of the irradiated and non-irradiated samples was analyzed using Masson's trichrome and picrosirius red staining polarization microscopy. Samples subjected to RDT exhibited dentinal tubule obliteration (p < 0.001); low integrity of type I and III collagen fibers (p < 0.05); compositional reduction of calcium (p = 0.012), phosphorus (p = 0.001), and magnesium (p < 0.001); an increased Ca/P ratio (p < 0.001). RDT affects the structure of dentinal tubules, the inorganic composition of intra-radicular dentin, and the collagen fiber integrity in the root dentin, which may interfere with the effectiveness and durability of dental procedures.

Dosimetric parameters and radiotherapy simulation methods used in preclinical studies of radiation damage to the dentition: a systematic review

OBJECTIVE

This systematic review investigated the dosimetric parameters used in preclinical studies.

STUDY DESIGN

Searches were performed in 3 databases (PubMed, Scopus, and Embase) and gray literature to identify studies for review. In vitro and ex vivo studies that examined the effect of radiation on human permanent teeth were included. The modified Consolidated Standards Of Reporting Trials checklist of items for reporting preclinical in vitro studies was used to assess the risk of bias.

RESULTS

In total, 32 studies met the inclusion criteria. The average radiation dose of in vitro studies was 53 (±22) Gy and in ex vivo studies was 69 (±1) Gy. Twenty-two studies used 5 different fractionation schemes. Twenty-two of the included studies did not report the radiotherapy modality of those reporting. Twenty studies used linear accelerators, and 7 used Cobalt-60 with the source-surface-distance of radiation ranging from 1.5 to 100 cm. Distilled water was the storage solution for the dental structure used most commonly. Biases were observed, including small sample sizes, lack of randomization, and blinding processes.

CONCLUSION

The dosimetric parameters used in the preclinical studies, including radiation dose, radiotherapy modality, fractionation regime, and the storage solutions used did not support the hypothesis of direct effects of radiation on the dental structure.

The Effects of Radiotherapy on Microhardness and Mineral Composition of Tooth Structures

OBJECTIVE

 The purpose of this study was to evaluate the microhardness and mineral composition alterations in enamel and dentine after radiotherapy.

MATERIALS AND METHODS

 Forty human maxillary premolar teeth (20 pairs) were assigned to nonirradiated and irradiated groups, the latter irradiated by fractional radiation to achieve a total dose of 70 Gy. Microhardness measurement was performed on a Knoop microhardness tester. Chemical components were analyzed using energy dispersive spectroscopy and Fourier transform Raman spectroscopy. The morphology was observed using a scanning electron microscope. The microhardness data were analyzed using a paired t-tested and one-way repeated analysis of variance (ANOVA), and the mineral composition data using related-samples Wilcoxon signed rank test and related-samples Friedman's two-way ANOVA by ranks.

RESULTS

 The irradiated teeth had a significantly lower microhardness in both enamel and dentine compared with the nonirradiated teeth. The irradiated dentine at 50 μm from the external tooth surface at the cemento-enamel junction showed the lowest microhardness compared with other locations. There was no statistically significant difference in calcium:phosphate ratio and chemical components. There was a reduction in protein:mineral ratio in dentine and at the cemento-enamel junction after irradiation. The irradiated teeth exhibited crack lines at the dentine-enamel junction and in dentine.

CONCLUSION

 Fractional radiation reduced microhardness in both enamel and dentine. The cervical dentine exhibited the highest microhardness reduction compared with other enamel and dentine locations.

Effect of experimental and commercial artificial saliva formulations on the activity and viability of microcosm biofilm and on enamel demineralization for irradiated patients with head and neck cancer (HNC)

The effect of different artificial saliva formulations on biofilm activity and viability, and on enamel demineralization for head and neck cancer (HNC) patients was evaluated. Irradiated enamel samples were treated (1 min) with BioXtra® or with experimental formulations containing carboxymethylcellulose plus inorganic constituents alone (AS) or containing 0.1 mg mL^-1 CaneCPI-5 (AS + Cane), 1.0 mg mL^-1 hemoglobin (AS + Hb) or combination of both (AS + Cane + Hb). Phosphate-buffered-saline and chlorhexidine (0.12%) were negative and positive control, respectively. Biofilm was produced from the saliva of five male HNC patients, under 0.2% sucrose exposure for 5 days, and daily treated with the formulations (1 min). No significant effects were observed for the different experimental treatments. BioXtra^® significantly reduced lactobacilli, demonstrating antibacterial potential for this group. Chlorhexidine was an effective treatment to significantly reduce all parameters, being an important antimicrobial and anticaries agent. Future in vitro studies must be performed using a new approach for the design of the experimental formulations.

Structure-function relationships in dog dentin

Investigations into teeth mechanical properties provide insight into physiological functions and pathological changes. This study sought to 1) quantify the spatial distribution of elastic modulus, hardness and the microstructural features of dog dentin and to 2) investigate quantitative relationships between the mechanical properties and the complex microstructure of dog dentin. Maxillary canine teeth of 10 mature dogs were sectioned in the transverse and vertical planes, then tested using nanoindentation and scanning electron microscopy (SEM). Microstructural features (dentin area fraction and dentinal tubule density) and mechanical properties (elastic modulus and hardness) were quantified. Results demonstrated significant anisotropy and spatial variation in elastic modulus, hardness, dentin area fraction and tubule density. These spatial variations adhered to a consistent distribution pattern; hardness, elastic modulus and dentin area fraction generally decreased from superficial to deep dentin and from crown tip to base; tubule density generally increased from superficial to deep dentin. Poor to moderate correlations between microstructural features and mechanical properties (R² = 0.032-0.466) were determined. The results of this study suggest that the other constituents may contribute to the mechanical behavior of mammalian dentin. Our results also present several remaining opportunities for further investigation into the roles of organic components (e.g., collagen) and mineral content on dentin mechanical behavior.

Microbial Poly-γ-Glutamic Acid (γ-PGA) as an Effective Tooth Enamel Protectant

Poly-γ-glutamic acid (γ-PGA) is a bio-derived water-soluble, edible, non-immunogenic nylon-like polymer with the biochemical characteristics of a polypeptide. This Bacillus-derived material has great potential for a wide range of applications, from bioremediation to tunable drug delivery systems. In the context of oral care, γ-PGA holds great promise in enamel demineralisation prevention. The salivary protein statherin has previously been shown to protect tooth enamel from acid dissolution and act as a reservoir for free calcium ions within oral cavities. Its superb enamel-binding capacity is attributed to the L-glutamic acid residues of this 5380 Da protein. In this study, γ-PGA was successfully synthesised from Bacillus subtilis natto cultivated on supplemented algae media and standard commercial media. The polymers obtained were tested for their potential to inhibit demineralisation of hydroxyapatite (HAp) when exposed to caries simulating acidic conditions. Formulations presenting 0.1, 0.25, 0.5, 0.75, 1, 2, 3 and 4% (w/v) γ-PGA concentration were assessed to determine the optimal conditions. Our data suggests that both the concentration and the molar mass of the γ-PGA were significant in enamel protection (p = 0.028 and p < 0.01 respectively). Ion Selective Electrode, combined with Fourier Transform Infra-Red studies, were employed to quantify enamel protection capacity of γ-PGA. All concentrations tested showed an inhibitory effect on the dissolution rate of calcium ions from hydroxyapatite, with 1% (wt) and 2% (wt) concentrations being the most effective. The impact of the average molar mass (M) on enamel dissolution was also investigated by employing commercial 66 kDa, 166 kDa, 440 kDa and 520 kDa γ-PGA fractions. All γ-PGA solutions adhered to the surface of HAp with evidence that this remained after 60 min of continuous acidic challenge. Inductively Coupled Plasma analysis showed a significant abundance of calcium ions associated with γ-PGA, which suggests that this material could also act as a responsive calcium delivery system. We have concluded that all γ-PGA samples tested (commercial and algae derived) display enamel protection capacity regardless of their concentration or average molar mass. However, we believe that γ-PGA D/L ratios might affect the binding more than its molar mass.

Effectiveness of glass ionomer cements in the restorative treatment of radiation-related caries - a systematic review

PURPOSE

The aim of this systematic review was to investigate the clinical effectiveness of glass ionomer cements (GICs) compared to other restorative materials in the treatment of radiation-related caries.

METHODS

Two independent researchers searched literature databases (PubMed, Scopus, Web of Science, Cochrane Library, Lilacs/BBO) and the grey literature to identify clinical trials that compared GICs with other restorative materials for the treatment of radiation-related caries. The clinical criteria considered for the performance of the restorations were based on the parameters of marginal adaptation/anatomical form, secondary caries, retention, and cumulative failures of the restorations. The methodological quality and risk of bias were evaluated using the Cochrane Collaboration tool.

RESULTS

From a total of 511, only four articles fulfilled the inclusion criteria. Conventional GIC restorations presented higher marginal adaptation failures than the resin-modified glass ionomer cements (RM-GICs) and composite restorations in all of the follow-up periods. Secondary caries was not observed in conventional GIC restorations throughout the follow-up periods, in three out of four of the included studies. RM-GICs and composite restorations showed significantly lower cumulative failure rates than conventional GICs at 6-, 12-, and 18-month follow-ups.

CONCLUSION

Due to insufficient scientific evidence, it was not possible to conclude that GICs are more effective than other restorative materials for the treatment of radiation-related caries.

Effect of Preirradiation Fluoride Treatment on the Physical Properties of Dentin

Objective. To determine the effects of preirradiation fluoride treatments on the Knoop hardness of dentin. Materials and Methods. Human posterior teeth mounted into acrylic resin molds were polished with silicon carbide (SiC) abrasives and 3-micron diamond paste. The Knoop hardness of dentin was measured with a Leco hardness instrument. The teeth were divided into groups of ten teeth per group as follows: no treatment (control), treatment with silver diamine fluoride (SDF), MI varnish (MI), and cavity shield (CS). The teeth were exposed to 2 Gy of daily radiation for six weeks using an X-Rad 320ix biological irradiator. Hardness was measured weekly, before, during, and after irradiation. The teeth were stored in artificial saliva at 37oC between radiation treatments. Results. In preirradiation dentin, a Knoop hardness value of 58.8 (14.1) KHN was obtained. Treatment with SDF significantly increased KHN before irradiation. Immediately after radiation treatment, hardness was significantly reduced in all experimental groups. Postirradiation fluoride treatments increased the hardness of dentin to varying degrees. Conclusions. Preirradiation fluoride treatment does not provide protection from decreases in the hardness of dentin. Treatment of teeth with fluoride formulations after radiation progressively restores the hardness of dentin to different degrees.

Direct Induced Effects of Standard and Modified Radiotherapy Protocol on Surface Structure of Hard Dental Tissue

Introduction

Radiotherapy is used to treat neo plasmatic lesions and the common side effects of this process are pain, swelling and sensitivity of mucous membranes in domain of radiation, reduced salivation, caries, and periodontal disease and, in total, low life quality. The purpose of this research was to estimate the outcome of direct irradiation on physical and surface characteristics of hard dental tissues.

Materials and methods

Twenty, caries free third molars were involved in the research. Prior to different submission protocols, tooth halves were randomly assigned to subject and control groups by using a draw method. The first group (n=20) was submitted to conventional irradiation protocol (2 Gy for 35 days), second group (n=20) was submitted to one powerful, exploratory dose of 70 Gy. Each sample served as its own control. Radiation was performed with a linear accelerator radiotherapy unit. The surface microhardness and roughness were measured at the beginning (initially), and upon completion of irradiation procedure. The average change in microhardness and roughness after different treatments was compared by t-test for independent samples. Normality was tested by the Shapiro-Wilk test.

Results

Significant differences were found after the standard radiation protocol and the exploratory dose of 70 Gy, with decreased mean microhardness and increased mean roughness (p<0.001) of both hard dental tissues. Enamel and dentin surface microhardness and roughness did not vary notably with regards to different irradiation protocols.

Conclusion

Head and neck conventional irradiation protocol leads to possible breakdown of enamel and dentin with reduced microhardness and increased surface roughness regardless of used irradiation protocol.

A machine learning approach to investigate the materials science of enamel aging

Understanding aging of tooth tissues is critical to the development of patient-centric oral healthcare. Yet, the traditional methods for analyzing the composition-structure-property relationships of hard tissues have limitations when considering aging and other factors.

OBJECTIVE

To apply unsupervised machine learning tools to pursue an understanding of relationships between the composition and mechanical behavior of aging enamel.

METHODS

Molar teeth were collected from primary (age ≤ 8), young adult (24 ≤ age ≤ 46) and old adult (55 ≤ age) donors. The hardness and elastic modulus were quantified using nanoindentation as a function of distance from the Dentin Enamel Junction (DEJ) within the cervical, cuspal and inter-cuspal regions of the enamel crown. Similarly, a co-located analysis of the chemical composition and structure was performed using Raman spectroscopy. A Self-Organizing Maps (SOMs) algorithm was implemented to identify multi-dimensional composition-property relationships.

RESULTS

The hardness and elastic modulus are positively correlated to crystallinity and negatively correlated with carbonate substitution. Furthermore, the effects from fluoridation on the age-dependent properties of enamel is non-linear and depends on its location. The contributions of fluoridation to the enamel properties are different in the cervical and non-cervical regions and appear to be unique within primary and senior adult teeth.

SIGNIFICANCE

Based on the findings, unsupervised learning methods can reveal complicated non-linear structure-property relationships in tooth tissues and help to understand the materials science of aging and its consequences.

Direct Radiotherapy-Induced Effects on Dental Hard Tissue in Combination With Bleaching Procedure

Introduction: The aim of this study was to evaluate the effects of radiation and tooth bleaching on the physical and morphological properties of enamel and dentin on permanent teeth.

Materials and Methods: Eighty fresh, non-carious third molars were used in this study. Before cutting the crown in half, the teeth samples were randomly allocated to treatment and control groups by using a lottery method. The first group (n = 20) underwent standard radiation protocol (2 Gy/fraction/day, 5 days/week) with bleaching treatment afterward using 16% carbamide peroxide gel, the second group (n = 20) underwent standard radiation protocol with afterward bleaching treatment using 38% hydrogen peroxide, the third group (n = 20) underwent a short, one strong, experimental dose of 70 Gy with afterward bleaching treatment using 16% carbamide peroxide gel, and the fourth group (n = 20) underwent one strong, experimental dose of 70 Gy with afterward bleaching treatment using 38% hydrogen peroxide gel. Groups 5–8 (n = 20) served as control as they underwent only bleaching treatment. Vickers microhardness and surface roughness were performed before (initial) and after irradiation and before bleaching or after only bleaching. The effects of irradiation and bleaching on microhardness (or roughness) of enamel and dentin were analyzed in the repeated-measures ANOVA model.

Results: Enamel microhardness after experimental single 70-Gy irradiation or after standard radiation protocol and bleaching with 16 or 38% gel was not statistically significant from microhardness in the control group (p &gt; 0.05). There was a statistically significantly greater reduction in the average microhardness of enamel and dentin during bleaching with 38% gel compared to 16% for both radiation protocols (p &lt; 0.001). After experimental 70-Gy irradiation and bleaching, a 16% statistically significant increase in surface roughness was found for enamel (p = 0.006) and dentin (p = 0.018), while this was not recorded for 38% gel. There was a statistically significantly greater increase in the average roughness of enamel and dentin during bleaching with 38% gel compared to 16% (p &lt; 0.001) for both radiation protocols.

Conclusions: Directly induced radiation leads to potential damage of hard dental tissues, which can be further damaged by additional bleaching. If teeth whitening is necessary after irradiation, it is suggested to use lower concentrations of whitening gels.

The effect of saliva substitute on the color stability of three different nanocomposite restorative materials after 1 month: An in vitro study

Context (Background):

The color stability of an esthetic material like composite resin may be hampered, due to the constant presence of oral microflora, saliva, and the frequent intake of food. However, as the oral cavity has a dynamic environment, the color stability of these restorative materials has been a challenge to dentistry.

Aim:

The aim of this study was to evaluate the effect of a saliva substitute (SS) on the color stability of three different nanocomposite restorative materials.

Materials and Methods:

A total of 66 disc-shaped samples of test materials were prepared using a polycarbonate mold measuring 15 mm diameter and 2 mm height and were randomly assigned to three groups of 22 samples each based on the test material used: Group I – Estelite Sigma Quick, Group II – Solare sculpt, and Group III – Beautifil II LS. They were further divided into two subgroups A and B with 11 samples each based on the immersion solutions, namely distilled water (DW) and saliva substitute (SS), respectively. The samples were immersed for 30 days. Baseline and post immersion color analysis were done with a spectrophotometer. The CIE L*a*b* values were measured and CIE ΔE values obtained were tabulated. Data were analyzed using the two-way-ANOVA test and Tukey's multiple post hoc test.

Results:

The mean color difference (ΔE) among the three different nanocomposite restorative materials ranged from 4.0 ± 0.26 to 10.62 ± 1.92. Group I showed the lowest color change (7.80 ± 0.55 and 4.00 ± 0.26), followed by Group III (8.59 ± 0.29 and 6.24 ± 0.66) and Group II (10.62 ± 1.92 and 6.85 ± 0.46) when immersed in SS and DW, respectively.

Conclusion:

All the specimens when immersed in SS showed greater discoloration than compared to the specimens immersed in DW. Group I showed greater resistance to color change compared to other groups.

Effects of radiation therapy on the dislocation resistance of root canal sealers applied to dentin and the sealer-dentin interface: a pilot study

Objectives

This study evaluated and compared the effects of radiation therapy on the dislocation resistance of AH Plus and BioRoot RCS applied to dentin and the sealer-dentin interface.

Materials and Methods

Thirty single-rooted teeth were randomly assigned to 2 groups (n = 15 each): AH Plus (Dentsply DeTrey) and BioRoot RCS (Septodont). Each group was subdivided into control and experimental groups. The experimental group was subjected to a total radiation dose of 60 Gy. The root canals of all samples were cleaned, shaped, and obturated using the single-cone technique. Dentin slices (1 mm) were sectioned from each root third for the push-out test and scanning electron microscopy (SEM) was done to examine the sealer-dentin interface. The failure mode was determined using stereomicroscopy. Bond strength data were analyzed by the independent t-test, 1-way analysis of variance, and the Tukey post hoc test (α = 0.05).

Results

Significantly lower bond strength was observed in irradiated teeth than non-irradiated teeth in the AH Plus group (p < 0.05). The BioRoot RCS group showed no significant reduction in bond strength after irradiation (p > 0.05) and showed a higher post-irradiation bond strength (209.92 ± 172.26 MPa) than the AH Plus group. SEM revealed slightly larger gap-containing regions in irradiated specimens from both groups.

Conclusions

The dislocation resistance of BioRoot RCS was not significantly changed by irradiation and was higher than that of AH Plus. BioRoot RCS may be the sealer of choice for root canal treatment in patients undergoing radiation therapy.

Conformational and constitutional analysis of dental caries following radiotherapy for head and neck cancer

Background

This study aimed to investigate the morphology and chemical composition of dental caries related to ionizing radiation (DCIR), an aggressive and progressive disease that affects dental hard tissues.

Materials and methods

Eight human teeth with DCIR were paired with sixteen control teeth (8 teeth with conventional caries and 8 without caries) and included in this study. An analysis of the morphology of the lesions was performed using the following techniques: periapical radiography, cone beam computed tomography, computed microtomography, and scanning electron microscopy. The chemical composition was assessed using X-ray dispersive spectroscopy.

Results

There was more demineralization in DCIR lesions when compared to conventional dental caries, even though there was no cavitation in the cervical region of the teeth. The superficial roughness and topography of DCIR lesions were similar to those of healthy teeth. On the other hand, lesions of conventional dental caries showed greater surface and topographic irregularity when compared to DCIR and healthy teeth (p = 0.001). Calcium (Ca) and phosphorus (P) levels were lower in DCIR lesions when compared to controls. However, higher levels of carbon (C) have been observed in DCIR lesions. There was a greater loss of the mineral matrix in DCIR followed by conventional caries. The reduction in the mineral matrix (Ca and P) was compatible with the imaging patterns observed in teeth with DCIR and conventional caries.

Conclusion

Despite their rapid evolution, DCIR presents an irregular, apparently intact surface with significant changes in the amount of Ca, P, and C.

Effect of ionizing radiation and cariogenic biofilm challenge on root-dentin caries

OBJECTIVES

To evaluate the effect of ionizing radiation and cariogenic biofilm challenge using two continuous flow models, normal and reduced salivary flow, on the development of initial root-dentin caries lesions.

MATERIALS AND METHODS

Microcosm biofilms were grown under two salivary flow rates (0.06 and 0.03 mL min^-1) and exposed to 5% sucrose (3 × daily, 0.25 mL min^-1, 6 min) dripped over non-irradiated and irradiated root-dentin blocks for up to 7 days. The vibration modes of root dentin, matrix/mineral (M/M), and carbonate/mineral (C/M) ratios were evaluated by FTIR. The mineral density was assessed by micro-CT.

RESULTS

With normal salivary flow, FTIR revealed an increase in the organic matrix (amide III) and a decrease in the mineral phase (ν_4, ν₂ PO₄^3-, AII + ν₂ CO₃^2-, C/M) in caries lesions. Irradiated dentin exhibited a reduction in the mineral phase (ν₁, ν₃ PO₄^3-, ν₂ CO₃^2-, C/M). Differences in mineral densities were not significant. With reduced salivary flow, FTIR also revealed increased organic matrix (amide III) for irradiated caries lesions and decrease in mineral phase (v_4, v₂ PO₄^3-, v₂ CO₃^2-, and C/M) in caries lesions. ν₁, ν₃ PO₄^3- precipitated on the surface of irradiated dentin and a lower mineral density was observed.

CONCLUSIONS

Initial caries lesions differed between non-irradiated and irradiated dentin and between normal and reduced salivary flow rates. Significant mineral loss with exposure of the organic matrix and low mineral density were observed for irradiated dentin with a reduced salivary flow rate.

CLINICAL RELEVANCE

Ionizing radiation associated with a reduced salivary flow rate enhanced the progression of root-dentin caries.

Protective effect of titanium tetrafluoride and silver diamine fluoride on radiation-induced dentin caries in vitro

This in vitro study evaluated the protective effect of titanium tetrafluoride (TiF₄) varnish and silver diamine fluoride (SDF) solution on the radiation-induced dentin caries. Bovine root dentin samples were irradiated (70 Gy) and treated as follows: (6 h): 4% TiF₄ varnish; 5.42% NaF varnish; 30% SDF solution; placebo varnish; or untreated (negative control). Microcosm biofilm was produced from human dental biofilm (from patients with head-neck cancer) mixed with McBain saliva for the first 8 h. After 16 h and from day 2 to day 5, McBain saliva (0.2% sucrose) was replaced daily (37 °C, 5% CO₂) (biological triplicate). Demineralization was quantified by transverse microradiography (TMR), while biofilm was analyzed by using viability, colony-forming units (CFU) counting and lactic acid production assays. The data were statistically analyzed by ANOVA (p < 0.05). TiF₄ and SDF were able to reduce mineral loss compared to placebo and the negative control. TiF₄ and SDF significantly reduced the biofilm viability compared to negative control. TiF₄ significantly reduced the CFU count of total microorganism, while only SDF affected total streptococci and mutans streptococci counts. The varnishes induced a reduction in lactic acid production compared to the negative control. TiF₄ and SDF may be good alternatives to control the development of radiation-induced dentin caries.

Effects of fractionation and ionizing radiation dose on the chemical composition and microhardness of enamel

OBJECTIVE

To evaluate the chemical and mechanical properties of enamel submitted to different in vitro radiation protocols.

DESIGN

Third molars were divided into seven groups (n = 8): non-irradiated (NI); a single dose of 30 Gy (SD30), 50 Gy (SD50), or 70 Gy (SD70) of radiation; or fractional radiation doses of up to 30 Gy (FD30), 50 Gy (FD50), or 70 Gy (FD70). Hemisections were analysed by Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS) and Knoop microhardness (KHN) test. One-way ANOVA followed by Bonferroni's post-hoc test compared the test groups with the NI. Two-way ANOVA was performed for the fractionation and radiation dose, followed by Bonferroni's test (α = 0.05).

RESULTS

FTIR revealed differences for the amide I band between the NI and FD50 and NI and FD70 groups (p < 0.001). For the organic matrix/mineral ratio, the FD70 group presented a lower ratio compared to NI (p = 0.009). Excluding the NI group, there were differences between the FD30 and FD50 (p = 0.045) and the FD30 and FD70 groups (p < 0.001). For EDS, there were differences for Ca (p = 0.011) and Ca/P (p < 0.001), with the FD70 group presenting lower values compared to NI (p = 0.015; p < 0.001). For KHN, the FD70 group presented lower values than the NI (p = 0.002). Two-way ANOVA showed difference for the dose (p < 0.001), with the 70 Gy group presenting a lower KHN value within the fractionated groups.

CONCLUSION

Fractional doses 70 Gy irradiation caused chemical and mechanical changes to enamel. Radiation applied in single or fractional doses produced different effects to enamel.

Demineralization of tooth enamel following radiation therapy; An in vitro microstructure and microhardness analysis

Objective

The objective of this study is to evaluate the effects of radiotherapy doses on mineral density and percentage mineral volume of human permanent tooth enamel.

Materials and Methods

Synchrotron radiation Xray microcomputed tomography (SRμCT) and microhardness testing were carried out on 8 and 20 tooth samples, respectively. Enamel mineral density was derived from SRμCT technique using ImageJ software. Microhardness samples were subjected to Vickers indentations followed by calculation of microhardness and percentage mineral volume values using respective mathematical measures. Data were analyzed using paired t-test at a significance level of 5%. Qualitative analysis of the enamel microstructure was done with two-dimensional projection images and scanned electron micrographs using μCT and field emission scanning electron microscopy, respectively.

Results

Vickers microhardness and SRμCT techniques showed a decrease in microhardness and an increase in mineral density, respectively, in postirradiated samples. These changes were related to mineral density variation and alteration of hydroxyapatite crystal lattice in enamel surface. Enamel microstructure showed key features such as microporosities and loss of smooth homogeneous surface. These indicate tribological loss and delamination of enamel which might lead to radiation caries.

Conclusions

Tooth surface loss might be a major contributing factor for radiation caries in head-and-neck cancer patients prescribed to radiotherapy. Such direct effects of radiotherapy cause enamel abrasion, delamination, and damage to the dentinoenamel junction. Suitable measures should, therefore, be worked out to protect nontarget oral tissues such as teeth while delivering effective dosages to target regions.

Irradiation therapy and chewing simulation: effect on zirconia and human enamel

PURPOSE

Ionizing radiation therapy (RT) is the main option for head and neck cancer treatment, but it is associated with multiple side effects. This study aimed to evaluate the effect of RT associated with chewing simulation on the surface of human enamel and Yttria-partially stabilized zirconia (Y-TZP).

METHODS

Maxillary premolar cusps and Y-TZP slabs were divided in 7 experimental groups: CO: no RT (control); EZ groups had irradiation applied to both, enamel and zirconia samples (simulating restoration prior to RT); E groups had irradiation applied to enamel only (simulating restoration after RT). RT doses were either 30, 50 or 70 Gray (Gy). Enamel cusps were abraded against zirconia slabs in a chewing simulator (CS - one million cycles/ 80 N/ 60 mm/min, 2 mm horizontal path, artificial saliva, 37˚ C). Zirconia hardness was evaluated before CS; zirconia roughness and enamel volume (wear) were evaluated before and after CS. Hardness and wear data were analyzed by one-way Analysis of Variance and Tukey post hoc test. Roughness was analyzed by Repeated Measures test and Bonferroni test (p=0.05).

RESULTS

There was no significant effect of enamel or zirconia irradiation on enamel cusp wear (p=0.226), regardless of the irradiation dose used - up to 70 Gy. Irradiation also did not affect Y-TZP surface roughness (p=0.127) and hardness (p=0.964).

CONCLUSIONS

RT does not promote significant changes to the surface characteristics of zirconia. Irradiated enamel abraded against zirconia does not show higher wear volume when compared to non-irradiated enamel.

Effect of ionizing radiation and chewing simulation on human enamel and zirconia

PURPOSE

To evaluate the effect of ionizing irradiation on human enamel and zirconia after chewing simulation.

METHODS

Twenty enamel and twenty translucent Yttria-stabilized zirconia (Y-PSZ) specimens were divided in 4 groups: Co (control) - no irradiation on enamel cusps/opposing zirconia slabs; E70 - irradiated (70 Gray) enamel cusps/opposing irradiated enamel slabs; Z70 - irradiated zirconia cusps/opposing irradiated zirconia slabs; EZ70 - irradiated enamel cusps/opposing irradiated zirconia slabs. Cusps were abraded against slabs in a chewing simulator (CS - one million cycles, 80 N, artificial saliva, 37˚C). Wear and roughness of zirconia and enamel were analyzed using a stylus profilometer. The abraded enamel was analyzed by Electron probe micro-analyzer (EPMA) and zirconia was characterized by nanoindentation and X-ray diffraction. One-way analysis of variance (ANOVA) and Tukey test were used for analysis of wear, Repeated Measures and Bonferroni test for roughness, and hardness and modulus values were compared using Wilcoxan Mann Whitney rank sum test (overall 5% significance).

RESULTS

Significantly higher volume loss was presented by cusps in the E70 group (p<0.001). Wear was similar between Co and EZ70 groups. There was no significant effect of irradiation on roughness of enamel or zirconia slabs (p=0.072). Irradiated Y-PSZ slabs had significantly higher hardness and modulus than non-irradiated ones and a 7% increase in m phase content was detected after irradiation.

CONCLUSIONS

The opposing surface characteristics played a more significant role on enamel wear than did ionizing radiation. However, radiation affects Y-PSZ crystalline composition, hardness and modulus of elasticity.

Effect of different doses of radiation on morphogical, mechanical and chemical properties of primary and permanent teeth-an in vitro study

Background

Radiotherapy, applied to the head and neck region, can cause radiation side effects such as reduction of saliva and radiation caries. The aim of this study was to perform an in vitro assessment of the effects of radiation therapy on the morphological, mechanical, and chemical properties of primary and permanent teeth.

Methods

One hundred four extracted human teeth (52 impacted wisdom teeth, 52 primary molar teeth) were used. The teeth were divided into two parts in the mesiodistal direction. Of the 98 teeth, the vestibular sections were used for the vickers analysis and lingual sections were used for the Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) analysis. The teeth in the experimental group were fixed to wax models. Each model had an equal number of teeth (n = 7). The doses were applied to the teeth for 6 weeks; 5 week days and 2Gy daily. After the radiotherapy was conducted weekly, a wax model was taken from radiation reception. Along with the elemental contents (Na, K, Mg, P, and Ca) of the teeth, enamel and dentin microhardness was evaluated, and SEM analyzes were performed on 6 teeth.

Results

Radiation caused a decrease in microhardness of enamel and dentin (p < 0.05). In the elemental analysis by ICP-OES, it was observed that there were decreases in all elements after 60Gy compared to the control group (p < 0.05). In the experimental groups, amorphous structures were encountered in SEM images.

Conclusions

Radiation has negative effects on the teeth structure and additional studies are needed in this regard. This study indicates that radiotherapy patients are at a higher risk for dental caries.

Morphological patterns of circumpulpal dentin affected by radiation-related caries

BACKGROUND

The aim of this work was to evaluate the microscopic characteristics through polarized light microscopy, scanning electron microscopy and the mineral content of circumpulpal dentin of irradiated (IT) and non-irradiated teeth (NIT), with deep caries that reached the root canal.

MATERIAL AND METHODS

A total of 25 IT were analyzed macroscopically, and radiographed. 5 NIT were used as controls. Two 100-μm-thick sections, per specimen, were evaluated in a polarized light microscopy and a scanning electron microscope. Demographics and clinical data were collected.

RESULTS

The results did not demonstrate distinct morphology of the IT compared with NIT. Mineral content values by weight percentage of Ca and P were also similar, corresponding to 66.65% and 33.21% in the IT and 66.60% and 33.29% in the NIT. The Ca/P ratio did not show statistical differences between groups being respectively 2.74 and 2.72, in the IT and NIT (p> 0.05).

CONCLUSIONS

Radiotherapy does not change morphology and mineral content of circumpulpal dentin in IT. Key words:Root canal, radiation-related caries, polarization microscopy, scanning electron microscopy, radiotherapy, oral neoplasms, dentin.

The DMFS160: A new index for measuring post-radiation caries

The current systems used to measure post-radiation caries underestimate the severity of the disease by failing to account for the unique spread of post-radiation caries, including incisal-edge and cusp tip decay, enamel delamination and crown amputation. A novel and clinically applicable index to measure post-radiation caries is proposed. The DMFS160 index counts 5 surfaces per tooth, accounting for incisal-edge caries, and is broken down into missing surfaces and decayed/filled surfaces. A staging and grading system is used to capture enamel delamination and crown amputation. The staging and grading provides a clinically-relevant measure at the whole-mouth level and is paired with evidence-based treatment strategies. In this paper the DMFS160 index is applied to three cases and compared to the DMFS index, demonstrating the improved accuracy of the DMFS160 index in measuring the extent of post-radiation caries.

Relationship between Changes in Chemical Composition of Enamel Subsurface Lesions and the Emitted Nonlinear Optical Signals: An in vitro Study

The development of new diagnostic technologies based on the light scattering and autofluorescence properties of dental tissues is required to improve the diagnostic ability of initial caries lesions earlier than previously done and promoting the potential of treatment without surgical intervention. The aim of this study is to correlate fluorescence-based results provided by multiphoton microscopy (MPM) with confocal Raman microscopy records using phosphate level at 960 cm-1 and the organic matrix at ∼2,931 cm-1 in healthy and demineralized human enamel. Measurements on 14 teeth were made using two incident lights of different wavelengths, released by confocal Raman microscopy and MPM. Raman phosphate peak intensity at 960 cm-1 along with organic to mineral ratio at (2,931/430 cm-1) and nonlinear optical signals (second harmonic generation [SHG] and intrinsic two-photon excited fluorescence [I2PEF]) were recorded from the demineralized and healthy enamel sites. Raman spectral maps showed that the higher the organic/mineral ratio in the demineralized enamel, the lower the intensity of mineral component in the same zone. MPM revealed new optical indicators of carious lesion as shown by the presence of a red-shifted fluorescence peak in the 650- to 750-nm area of the fluorescence spectrum of demineralized enamel. Moreover, on sample regions with insignificant autofluorescence, the emergence of the SHG signal could be noted. By comparing I2PEF images with the structural motifs observed by the confocal Raman imaging system, the morphological similarity of the acquired images was quite evident. Any change in the I2PEF spectra reflects alterations in the chemical composition of enamel. These findings may provide an important basis for potentially valuable applications of photonic tools in the clinical diagnosis of tooth pathological conditions, besides exposing the fundamental role of organic matrix in enamel integrity and reparation.

The impact of head and neck radiotherapy on the dentine-enamel junction: a systematic review

Background

Radiotherapy is widely used in contemporary head and neck cancer treatment protocols. The ability of head and neck radiotherapy (HNRT) to cause direct radiogenic destruction to the teeth is one of the most controversial topics in the field of oral oncology. Therefore, this systematic review aimed to investigate ionising radiation as an independent factor for physical and chemical changes on the dentine-enamel junction (DEJ), a pivotal dental topography for the onset and progression of radiation-related caries (RRC) and enamel delamination.

Material and Methods

Systematic searches were conducted on three databases: Scopus, MEDLINE (Via PubMed) and Embase (Elsevier). Laboratory studies evaluating the effects of simulated or in vivo HNRT on the DEJ were included. The GRADE tool adapted for in vitro studies was used to assess the methodological quality.

Results

Of the 154 initially selected studies, eight met the inclusion criteria, from which five studies were graded as high quality of evidence, two studies were graded as moderate quality and one as low quality. Two studies did not demonstrate DEJ alterations following HNRT while the other six articles described several organic and inorganic changes in the DEJ of irradiated teeth samples. These radiogenic events were mostly detected through micro and nanoindentation, Raman micro-spectroscopy, confocal microscopy, Western blotting and optical coherence tomography.

Conclusions

HNRT may have a negative impact on the physical and chemical aspects of the DEJ, predisposing cancer patients to RRC and enamel delamination.

Key words:Cancer, radiotherapy, radiation-related caries, dentin-enamel junction, systematic review.

Effects of different anti-caries agents on microhardness and superficial microstructure of irradiated permanent dentin: an in vitro study

BACKGROUND

To compare different anti-caries agents on microhardness and micromorphology of irradiated permanent dentin in vitro, and try to find the most effective agent to prevent radiation-dentin-destruction.

METHODS

A total of 120 dentin samples were prepared from 60 human teeth and randomly divided into 8 groups (n = 15), [ (1)] blank control [2]; irradiation control [3]; irradiation+ fluoride [4]; irradiation+ casein phosphate polypeptide-amorphous calcium phosphate (CPP-ACP) [5]; irradiation+ CPP-ACP+ fluoride [6]; irradiation+ infiltration resin [7]; irradiation+ infiltration resin+ fluoride [8]; irradiation+ infiltration resin+ CPP-ACP. Seven samples of each groups were chosen randomly for microhardness test and eight for scanning electron microscope observation.

RESULTS

A decrease of microhardness (P < 0.05) and an obvious morphological change were presented on dentin surface after radiotherapy. After applications of anti-caries agents, the morphological destructions were effectively restored. The infiltration resin plus fluoride group (56.00 ± 4.02 Kg/mm2), infiltration resin plus CPP-ACP group (56.05 ± 3.69 Kg/mm2), infiltration resin group (54.70 ± 4.42Kg/mm2) and CPP-ACP plus fluoride group (53.84 ± 6.23Kg/mm2) had the highest dentin microhardness value after radiotherapy, and no statistically significant difference were found between them.

CONCLUSIONS

Infiltration resin, CPP-ACP, fluoride and their pairwise combination can effectively prevent radiation-dentin-destruction. Among them, infiltration resin with CPP-ACP, infiltration resin with fluoride, CPP-ACP with fluoride, and infiltration resin have the most protective effects on irradiation-dentin-destructions.

Direct radiation-induced effects on dental hard tissue

Background

Radiation caries is a complication of radiotherapy characterized by enamel erosion and dentin exposure. The mechanisms of characteristic radiation caries formation are not well-understood. The aim of this study was to evaluate the direct radiation-induced effects on dental hard tissue and investigate their role in the formation of radiation caries.

Methods

Sixty non-carious third molars were divided into three groups (n = 20), which would be exposed to 0 Gy, 30 Gy, and 60 Gy radiation, respectively. After radiation, microhardness and elastic modulus were measured at four depths by means of a Vickers microhardness tester and atomic force microscopy (AFM). The microstructure was observed by scanning electron microscopy (SEM). X-ray diffraction and Raman microspectroscopy were used to determine crystal properties and protein/mineral (2931/960 cm^− 1) ratios.

Results

A statistically significant decrease in microhardness and elastic modulus values 50 μm from the dentino-enamel junction (DEJ) in enamel was revealed in the 30-Gy and 60-Gy groups. With the increasing dose, destruction of interprismatic substance and fissures at the DEJ-adjacent region were found. A greater reduction of crystallinity was revealed in enamel compared with dentin. Raman spectroscopic analysis showed a slight increase of the protein/mineral ratio for enamel following accumulated radiation, while the protein/mineral ratio for dentin was decreased.

Conclusions

Radiation could directly alter the mechanical properties, micro-morphology, crystal properties, and chemical composition of dental hard tissue. The early destruction of DEJ-adjacent enamel, combined with decreased crystallinity of enamel under radiation exposure, may be related to the formation of characteristic radiation caries.

Peptide-Mediated Biomimetic Regrowth of Human Enamel In Situ

Mimicking the dynamics of mineral loss and gain involved in dental caries formation can help us evaluate and compare the mineralization efficacy of different treatment agents used in enamel remineralization. Here, we offer an abridged study design outlining the preparation of tooth samples, creation of artificial dental lesions, application of a peptide, and characterization of the regrown enamel-like mineral layer.

Effect of radiotherapy on the chemical composition of root dentin

BACKGROUND

The radiotherapy can directly affect the bond strength of the adhesive materials, interfering in the prognosis of restorative treatments, which may be caused by chemical changes in dentin structure.

METHODS

Twenty inferior homologues premolars were distributed in 2 groups (in vitro study) (n = 10): nonirradiated and irradiated. The specimens were submitted to the analysis of phosphate (ν₁ PO₄ ^3- ;ν₂ PO₄ ^3- ;ν₄ PO₄ ^3- ), carbonate (ν₃ CO₃ ^2- ), amide I, CH₂ , amide III, and amide I/III ratio by confocal Raman spectroscopy. Data were submitted to statistical analysis (T test, P < .05).

RESULTS

In intracanal dentin, the irradiated group had lower ν₄ PO₄ ^3- values (1.23 ± 0.06) compared to nonirradiated group (1.40 ± 0.18) (P < .05), with no difference for ν₁ PO₄ ^3- and ν₂ PO₄ ³ peaks (P > .05). The irradiated (1.56 ± 0.06) had lower carbonate, amide III (1.05 ± 0.19), and amide I/III ratio values (0.19 ± 0.06) compared to nonirradiated group (1.42 ± 0.10, 1.28 ± 0.24, and 0.31 ± 0.10, respectively) (P < .05). For medium dentin irradiated group (1.30 ± 0.12) had lower phosphate values compared to nonirradiated group (1.48 ± 0.22) (P < .05). In cementum, there was no statistical difference between the groups.

CONCLUSION

The radiotherapy was able to cause changes in ν₄ PO₄ ^3- , carbonate, and amide III peaks of root dentin.

Effect of fluoride application during radiotherapy on enamel demineralization

OBJECTIVE

Radiation-related caries are one the most undesired reactions manifested during or after head and neck radiotherapy. Fluoride application is an important strategy to reduce demineralization and enhance remineralizaton. To evaluate the effect of the topical application of fluoride during irradiation on dental enamel demineralization.

MATERIAL AND METHODS

Thirty molars were randomly divided into three groups: Non-irradiated (NI), Irradiated (I), Irradiated with fluoride (IF). Each group was subdivided according to the presence or absence of pH-cycling (n=5). In the irradiated groups, the teeth received 70 Gy. The enamel's chemical composition was measured using Fourier Transform Infrared Spectrometry (organic matrix/mineral ratio - M/M and relative carbonate content - RCC). Vickers microhardness (VHN) and elastic modulus (E) were evaluated at three depths (surface, middle and deep enamel). Scanning electron microscopy (SEM) was used to assess the enamel's morphology.

RESULTS

The FTIR analysis (M/M and RCC) showed significant differences for irradiation, pH-cycling and the interaction between factors (p<0.001). Without pH-cycling, IF had the lowest organic matrix/mineral ratio and relative carbonate content. With pH-cycling, the organic matrix/mineral ratio increased and the relative carbonate content decreased, except for IF. VHN was influenced only by pH-cycling (p<0.001), which generated higher VHN values. ANOVA detected significant differences in E for irradiation (p<0.001), pH-cycling (p<0.001) and for the interaction between irradiation and pH-cycling (p<0.001). Increased E was found for group I without pH-cycling. With pH-cycling, groups I and IF were similar, and showed higher values than NI. The SEM images showed no morphological changes without pH-cycling. With pH-cycling, fluoride helped to maintain the outer enamel's morphology.

CONCLUSIONS

Fluoride reduced mineral loss and maintained the outer morphology of irradiated and cycled enamel. However, it was not as effective in preserving the mechanical properties of enamel. Radiotherapy altered the enamel's elastic modulus and its chemical composition.