Dental management of patients irradiated for head and neck cancer

Radiotherapy toxicity

Radiotherapy is used in >50% of patients with cancer, both for curative and palliative purposes. Radiotherapy uses ionizing radiation to target and kill tumour tissue, but normal tissue can also be damaged, leading to toxicity. Modern and precise radiotherapy techniques, such as intensity-modulated radiotherapy, may prevent toxicity, but some patients still experience adverse effects. The physiopathology of toxicity is dependent on many parameters, such as the location of irradiation or the functional status of organs at risk. Knowledge of the mechanisms leads to a more rational approach for controlling radiotherapy toxicity, which may result in improved symptom control and quality of life for patients. This improved quality of life is particularly important in paediatric patients, who may live for many years with the long-term effects of radiotherapy. Notably, signs and symptoms occurring after radiotherapy may not be due to the treatment but to an exacerbation of existing conditions or to the development of new diseases. Although differential diagnosis may be difficult, it has important consequences for patients.

Dental management prior to radiation therapy in patients with head and neck cancer

INTRODUCTION

Patients diagnosed with head and neck tumors, are treated by surgery, radiation therapy (RT), chemotherapy (CT) or a combination thereof. The goal is to describe the management protocol for patients subjected to radiation therapy (RT) and to study their long-term oral health status.

MATERIALS AND METHODS

A retrospective study was performed in a sample of 50 patients. We analyzed the oral health status and all the variables included applying the adapted protocol of pre-RT.

RESULTS

Prior to RT, 84% of patients required scaling and 32% conservative treatment. Around 74% of patients required at least one exodontia. The mean of exodontias for patients presenting Grade 3 of oral hygiene was 6.50 per person (p<0.0001). The pre-RT study of possible candida infection showed that 78% of patients were negative for this infection. The mean resting saliva production was 39.10 (SD: 23.30; range: 13-145), with a stimulated value of 64.78 (SD: 33.92; range: 16-200).

CONCLUSIONS

All patients should be protocoled to ensure that they present optimal oral conditions prior to initiating RT treatment.

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.

Association of Care Processes With Timely, Equitable Postoperative Radiotherapy in Patients With Surgically Treated Head and Neck Squamous Cell Carcinoma

Importance

Delays in initiation of postoperative radiotherapy (PORT) after surgery for head and neck squamous cell carcinoma (HNSCC) are common, predominantly affect racial minorities, and are associated with decreased survival. Details regarding the care processes that contribute to timely, equitable PORT remain unknown.

Objective

To determine care processes associated with timely, equitable PORT.

Design, Setting, and Participants

This retrospective cohort study included patients 18 years or older undergoing surgery for HNSCC at the Medical University of South Carolina (MUSC), Charleston, followed by PORT (at MUSC or elsewhere) with or without chemotherapy from January 1, 2014, through December 31, 2016. Data were analyzed from September 15, 2017, through June 28, 2018.

Main Outcomes and Measures

The main outcome measure was the proportion of timely, guideline-adherent initiation of PORT (≤6 weeks postoperatively). Secondary outcome measures included care processes associated with timely PORT. The association between process variables with timely PORT was explored using multivariable logistic regression analysis. Effect modification of the association between receipt of care processes and timely PORT by race was explored using interaction effects.

Results

A total of 197 patients were included in the analysis; they were predominantly white (157 [79.7%]) and male (136 [69.0%]) with a mean age of 59 years (range, 28-89 years). Overall, 89 patients (45.2%) experienced a delay initiating PORT. African American patients had a 13.5% absolute increase in the rate of delayed PORT relative to white patients (21 of 37 [56.8%] vs 68 of 157 [43.3%]). The adjusted multivariable regression showed that the following care processes were associated with timely PORT: preoperative radiotherapy consultation (odds ratio [OR], 8.94; 95% CI, 1.64-65.53), PORT at MUSC (OR, 6.21; 95% CI, 1.85-24.75), pathology report within 7 postoperative days (OR, 4.14; 95% CI, 1.21-15.86), time from surgery to PORT referral of no longer than 10 days (OR, 12.14; 95% CI, 3.14-63.00), time from PORT referral to consultation of no longer than 10 days (OR, 10.76; 95% CI, 3.01-49.70), and time from PORT consultation to its start of no longer than 21 days (OR, 4.80; 95% CI 1.41-18.44). Analysis of interactions revealed no statistically significant differences between African American and white patients in receipt of key processes associated with timely PORT.

Conclusions and Relevance

Specific care processes are associated with guideline-adherent initiation of PORT. Novel strategies appear to be needed to ensure that these processes are performed for all patients with HNSCC, thereby facilitating timely, equitable PORT.

How to improve root canal filling in teeth subjected to radiation therapy for cancer

The aim of this study was to evaluate the influence of radiation therapy on root canal sealer push-out bond strength (BS) to dentin and the sealer/dentin interface after different final irrigation solutions (NaOCl, EDTA, and chitosan). Sixty-four maxillary canines were distributed into two groups (n=30): non-irradiated and irradiated with 60 Gy. Canals were prepared with Reciproc-R50 and subdivided (n=10) for final irrigation (NaOCl, EDTA, chitosan) and filled. Three dentin slices were obtained from each root third. The first slice of each third was selected for BS evaluation, and the failure mode was determined by stereomicroscopy. SEM analysis of the sealer-dentin interface was performed in the remaining slices. Two-way ANOVA and Tukey's tests (α=0.05) were used. Lower BS (P<0.0001) was obtained after irradiation (2.07±0.79 MPa), regardless of the final irrigation solution used. The NaOCl group (P<0.001) had the lowest BS in the irradiated (1.68±0.72) and non-irradiated (2.39±0.89) groups, whereas the EDTA (irradiated: 2.14±0.77 and non-irradiated: 3.92±1.54) and chitosan (irradiated: 2.37±0.73 and non-irradiated: 3.51±1.47) groups demonstrated a higher BS (P<0.05). The highest values were observed in the coronal third (3.17±1.38) when compared to the middle (2.74±1.36) and apical ones (2.09±0.97)(P<0.0001). There were more cohesive failures and more gaps in irradiated specimens, regardless of the final solution. The present study showed that radiation was associated with a decrease in BS, regardless of the final solution used, whereas chitosan increased BS in teeth subjected to radiation therapy.

Coronectomy - An alternative approach to remove impacted teeth in oncological patients

Background

Coronectomy involves the section of the tooth crown leaving the roots in the socket. Possibility of inferior alveolar nerve injury and mandibular fracture are the main indications for this approach. Herein, we describe a case series of coronectomy to highlight its indication in normal and oncological patients.

Material and Methods

A total of 9 patients were submitted to coronectomy, 6 of them were oncological. Three patients were evaluated before head and neck radiotherapy (HNRT), 2 after HNRT and 1 before bone marrow transplantation.

Results

Mean age of the patients was 49 years, most of them male (n=7). Lower third molars were the main teeth that received this procedure, and all cases presented intimate anatomic relationship between the roots and the mandibular canal. Moreover, three cases also presented evident mandibular fracture risk in removing the tooth. During the follow-up period, none complications were observed related to coronectomy and oncological treatment.

Conclusions

Coronectomy is a safe approach including for cancer patients and it should be considered in high-risk impacted teeth extractions.

Key words:Coronectomy, impacted teeth, oncological patients, postoperative complications.

Adjunctive Treatments for the Prevention of Chemotherapy- and Radiotherapy-Induced Mucositis

Background: Chemoradiotherapy-associated mucositis can manifest as pain, inflammation, dysphagia, diarrhea, weight loss, rectal bleeding, and infection. Mucositis is a major dose-limiting side effect of chemotherapy, affecting nutritional intake and oral and intestinal function. Despite several interventions being available, there is a need for safe and effective preventative and treatment options for treatment-induced mucositis. The goals of this review are to discuss interventions based on foods and natural products and present the research to date. Methods: A narrative literature review identified 60 clinical studies examining various nutritional compounds and 20 examining probiotics. 9 studies on probiotics for the prevention of diarrhea were also assessed on methodological quality and limitations identified. Results: Several compounds have been posited as useful adjuvants for cancer treatment–related mucositis. Probiotics demonstrate efficacy for the prevention and treatment of chemoradiotherapy-induced gastrointestinal toxicity without significant side effects. Glutamine and activated charcoal were reported to reduce chemotherapy-induced diarrhea but not radiation-induced intestinal mucositis. Honey has been reported to decrease treatment interruptions, weight loss, and delays the onset of oral mucositis. Zinc, glutamine, and topical vitamin E were demonstrated efficacy for oral mucositis. Conclusion: There is plausible clinical evidence for the administration of several adjunctive treatments for the prevention and treatment of mucositis. Probiotics were reported to reduce the burden of intestinal mucositis and treatment-induced diarrhea. Activated charcoal and glutamine are beneficial for chemotherapy-induced diarrhea, whereas the administration of honey, zinc, and glutamine reduce the risk of developing oral mucositis during chemotherapy or radiotherapy.

Longevity of bond strength of resin cements to root dentine after radiation therapy

AIM

To evaluate the bond strength and adhesive interface between several resin cements and root dentine immediately and 6 months after radiotherapy.

METHODOLOGY

Sixty maxillary canines were selected and randomly assigned to two groups (n = 30): one group was not irradiated and the other one was subjected to a cumulative radiation dose of 60 Gy. The teeth were sectioned to obtain roots 16 mm long and the canals were prepared with the Reciproc system (R50) and filled using a lateral condensation technique with an epoxy resin sealer. Each group was divided into three subgroups (n = 10) according to the resin cement used for fibreglass fibre post cementation: RelyX-U200, Panavia-F2.0 and RelyX ARC. The posts were cemented in accordance with the manufacturer's recommendations. Three 1-mm-thick dentine slices were then obtained from each root third. The first two slices in the crown-apex direction of each third were selected for the push-out test. The failure mode after debonding was determined with a stereo microscope. The third slice from each root third was selected for scanning electron microscopy (SEM) analyses to examine the resin cement-dentine interface with 100, 1000, 2000 and 4000× magnification. Bond strength data were analysed by anova and Tukey's test (α = 0.05).

RESULTS

Significantly lower bond strength (P < 0.0001) was obtained after irradiation compared to nonirradiated teeth. RelyX-U200 cemented fibre posts had the higher bond strength (15.17 ± 5.89) compared with RelyX ARC (P < 0.001) and Panavia-F2.0 (P < 0.001). The evaluation after 6 months revealed lower bond strength values compared to the immediate values (P < 0.001) for irradiated and nonirradiated teeth. Cohesive failures occurred in the irradiated dentine. SEM revealed fractures, microfractures and fewer collagen fibres in irradiated root dentine. RelyX-U200 and Panavia-F2.0 were associated with a juxtaposed interface of the cement with the radicular dentine in irradiated and nonirradiated teeth, and for RelyX ARC, hybrid layer formation and tags were observed in both irradiated and nonirradiated teeth.

CONCLUSION

Radiation was associated with a decrease in the push-out bond strength and with lower resin cement/root dentine interface adaptation. Self-adhesive resin cement was a better alternative for fibre post cementation in teeth subjected to radiation therapy. The bond strength decreased after 6 months.

Potential cytotoxic and selective effect of new benzo[b]xanthenes against oral squamous cell carcinoma

Aim: The current work shows a new synthetic methodology to obtain 21 naphthoquinones that have been evaluated against oral cavity cancer. The compounds were obtained by a three-component reaction involving lawsone, dimedone and aromatic aldehydes catalyzed by lithium chloride under microwave irradiation to produce families of 1,4- and 1,2-naphthoquinones. Results: A clonogenic assay was performed on SCC9 cell line cultures with all compounds, revealing five very active compounds. In the 3,4,5-dimethylthiazol-2,5-diphenyltetrazolium bromide cell viability assay using three different cell lines (SCC9, SCC4 and SCC25), 8c had an average IC50 of approximately 1.45 μM capable of reducing tumor cell viability, approximately 90-times higher than carboplatin.Conclusion: Therefore, the xanthene-naphthoquinone derivatives show promising bioactivity for oral cavity cancer treatment.

Guide for health professionals addressing oral care for individuals in oncological treatment based on scientific evidence

OBJECTIVE

Oncological treatment can cause changes in the oral cavity compromising oral functions. The aim of the study was, based on a systematic review, to draft a guide directed at the team of health professionals involved in the oral care of oncological patients.

METHODS

A systematic search of the literature was performed for articles published between 2000 and April 2017. Searches were made of electronic databases and hand search. The inclusion criteria were systematic reviews of randomized clinical trials (RCTs) and RCTs published in English, involving pediatric and adult oncological patients and focused on the prevention and treatment of oral complications as well as studies addressing the maintenance of oral health. Among the 1237 studies identified, 129 were pre-selected and 54 were selected to form the basis for the clinical guide.

RESULTS

The studies analyzed stress the need for oral assessments as well as preventive and curative actions prior to oncological treatment. To minimize the severity of oral problems, the studies emphasize daily oral care, the treatment of xerostomia with saliva substitute and hydration, and low-level laser therapy, nystatin, acyclovir, respectively, for the prevention and treatment of oral mucositis, oral candidiasis, and infection by herpes simplex virus. Thus, the guide produced addresses oral assessments and professional and home care before, during, and after oncological treatment.

CONCLUSION

The guide drafted has the function of assisting health professionals involved in the oral care of patients with cancer, enabling the prevention or treatment of oral complications stemming from oncological treatment.

Radiation-induced dental caries, prevention and treatment - A systematic review

Treatment of head and neck cancers (HNCs) involves radiotherapy. Patients undergoing radiotherapy for HNCs are prone to dental complications. Radiotherapy to the head and neck region causes xerostomia and salivary gland dysfunction which dramatically increases the risk of dental caries and its sequelae. Radiation therapy (RT) also affects the dental hard tissues increasing their susceptibility to demineralization following RT. Postradiation caries is a rapidly progressing and highly destructive type of dental caries. Radiation-related caries and other dental hard tissue changes can appear within the first 3 months following RT. Hence, every effort should be focused on prevention to manage patients with severe caries. This can be accomplished through good preoperative dental treatment, frequent dental evaluation and treatment after RT (with the exception of extractions), and consistent home care that includes self-applied fluoride. Restorative management of radiation caries can be challenging. The restorative dentist must consider the altered dental substrate and a hostile oral environment when selecting restorative materials. Radiation-induced changes in enamel and dentine may compromise bonding of adhesive materials. Consequently, glass ionomer cements have proved to be a better alternative to composite resins in irradiated patients. Counseling of patients before and after radiotherapy can be done to make them aware of the complications of radiotherapy and thus can help in preventing them.

Applying orthodontic tooth extrusion in a patient treated with bisphosphonate and irradiation: a case report

Bisphosphonates and irradiation are useful medical treatments, but can often cause oral complications such as medication-related oral necrosis of the jaw (MRONJ) and osteoradionecrosis (ORN) during oral surgery, including tooth extraction. Therefore, we should take all risks into consideration carefully before choosing dental treatment for patients with a medical history of such therapies. A 55-year-old woman who underwent cord blood transplantation to treat extranodal natural killer T (NK/T) cell lymphoma (nasal type IVB) had a medical history of bisphosphonate and irradiation treatments. We treated her residual tooth root by applying orthodontic extrusion to avoid extraction and successfully restored the tooth. Application of an orthodontic tooth extrusion technique for conservative treatment of a residual tooth is a useful means of avoiding MRONJ or ORN in patients who have a medical history of bisphosphonate and irradiation treatments.

Head and neck intensity modulated radiation therapy leads to an increase of opportunistic oral pathogens

OBJECTIVES

The introduction of intensity modulated radiation therapy (IMRT) has led to new possibilities in the treatment of head and neck cancer (HNC). Limited information is available on how this more advanced radiation technique affects the oral microflora. In a prospective study we assessed the effects of various advanced treatments for HNC on the oral microflora, as well as the effects of elimination of oral foci of infection.

MATERIALS AND METHODS

All consecutive dentate patients >18years, diagnosed with a primary oral or oropharynx carcinoma and seen for a pre-treatment dental screening (May 2011-May 2013) were included. Patients were grouped by oncologic treatment: surgery (SURG), IMRT (IMRT) or IMRT+chemotherapy (CHIMRT). Dental screening data, demographic data, subgingival biofilm samples, oral lavages and whole saliva samples were obtained to microbiologically analyze the effects of cancer treatments (1-year follow-up).

RESULTS

This study included 82 patients (29 SURG, 26 IMRT and 27 CHIMRT). The trends in changes in prevalence and proportions of microorganisms were comparable in the IMRT and CHIMRT group. However, relative to the SURG group, increased prevalence of enteric rods, staphylococci and Candida species was observed in the IMRT and CHIMRT groups. In these groups, elimination of oral foci decreased the frequency of detection of pathogens such as Porphyromonas gingivalis, Tannerella forsythia and Streptococcus mutans.

CONCLUSION

Different treatments in HNC patients result in different changes in the oral microflora. Opportunistic pathogens such as staphylococci, enteric rods and Candida sp. tend to increase in prevalence after IMRT with or without chemotherapy, but not after surgical intervention.

The wolf in sheep's clothing: Microtomographic aspects of clinically incipient radiation-related caries

Background

Radiation-related caries (RRC) can cause rapid progression, with a high potential for dental destruction affecting mainly cervical and incisal areas. Unlike the injuries that occur in the conventional caries, incipient RRC present in unusual surfaces have difficult diagnosis and classification stages of cavitation.

Material and Methods

Evaluate the radiographic patterns of demineralization of RRC by using micro-CT. Ten teeth with incipient RRC and 10 teeth with incipient conventional caries (control group) matched by anatomic teeth group and caries affected surfaces were evaluated by X-ray microtomography (micro-CT) Skyscan 1174V2 (50Kv, 1.3 megapixel, Kontich, Belgium). Teeth were placed in a standard position for micro-CT (coronal, transaxial and sagittal sections) during images acquisition. Lesions were classified according to the depth of invasion and relationship with enamel, dentin and pulp.

Results

RRC samples presented deeper lesions with higher involvement of enamel and dentin. Control group presented focal and superficial lesions with lower involvement of enamel and dentin.

Conclusions

Incipient RRC present aggressive microtomographic patterns of demineralization when compared to conventional caries, as indicated by deep lesions, regardless of its clinically incipient aspects.

Key words:Head and neck cancer, radiotherapy, microtomography, radiation caries.

Wound Dehiscence after Wisdom Tooth Removal in Mandibular Mesioangular Class IB Impactions: Triangular Transposition Flap versus Envelope Flap

Background and aims. Wound dehiscence after lower third molar surgery extends the postoperative treatment period and may cause long-standing pain. The aim of this study was to compare wound dehiscence after removal of wisdom teeth in the most prevalent mandibular impaction (mesioangular class IB) by two different soft tissue flap designs.

Materials and methods. Partially-erupted mandibular third molars with mesioangular class IB impaction (Pell and Gregory classification) were selected. Split mouth technique was used to compare the two flap designs (envelope vs. triangular transposition flap—TTF). The patients were recalled one week and a month later and rechecked for dehiscence, infection, and dry socket formation.

Results. There were no cases of infection in either group. However, three cases of dry socket in the envelope group and four in the TTF group were recorded. In the envelope group, dehiscence occurred in 43% of cases during the first week, with 67% of cases being a large dehiscence (diameters of more than 5 mm). Extra appointments (those requested by the patient exclusively related to the problem of the hole distal to the second molar) were scheduled in 10% of cases in the envelope group. In the TTF group, dehiscence occurred during the first week for the same impaction in 19% of cases with large dehiscence cases occurring in 65% of cases and extra appointment rate at 4.1%.

Conclusion. According to theresults in the evaluated operation, TTF may prevent postoperative wound dehiscence more probably than the envelope flap.

[Dental state in patients with head and neck cancers]

In France, in 2005, there were approximately 16,000 new cases of head and neck cancer. These cancers have an unfavourable prognosis: the survival rates at 3 and 10 years are 50% and 10% respectively. The consumption of alcohol and tobacco is the most important risk factor; in some countries HPV infection was identified as a risk factor of head and neck tumours. Furthermore, a poor oral hygiene seems to raise this risk. We found many decay and periodontium problems in patients with an upper aerodigestive tract cancer. An evaluation of dental state is necessary before any cancer treatment. Treatments by radiotherapy engender noxious effects: hypocellular, hypovascularization, hypoxie of the irradiated tissues, which lead to immediate and chronically oral complications such as mucositis, fibrosis, xerostomia, decay, or osteoradionecrosis. An oral follow-up of these patients can prevent these complications, or reduce the severity of oral complications, and promote a good oral state.

Pharmacological activation of the EDA/EDAR signaling pathway restores salivary gland function following radiation-induced damage

Radiotherapy of head and neck cancers often results in collateral damage to adjacent salivary glands associated with clinically significant hyposalivation and xerostomia. Due to the reduced capacity of salivary glands to regenerate, hyposalivation is treated by substitution with artificial saliva, rather than through functional restoration of the glands. During embryogenesis, the ectodysplasin/ectodysplasin receptor (EDA/EDAR) signaling pathway is a critical element in the development and growth of salivary glands. We have assessed the effects of pharmacological activation of this pathway in a mouse model of radiation-induced salivary gland dysfunction. We report that post-irradiation administration of an EDAR-agonist monoclonal antibody (mAbEDAR1) normalizes function of radiation damaged adult salivary glands as determined by stimulated salivary flow rates. In addition, salivary gland structure and homeostasis is restored to pre-irradiation levels. These results suggest that transient activation of pathways involved in salivary gland development could facilitate regeneration and restoration of function following damage.