Tumor-intrinsic perinuclear LOXL2: Prognostic relevance and relationship with YAP1 activation status in oral squamous cell carcinoma.

INTRODUCTION: Lysyl Oxidase-Like 2 (LOXL2) expression and function is frequently altered in different cancers, but scarcely explored in oral squamous cell carcinoma (OSCC). This prompted us to investigate the clinical relevance of LOXL2 expression pattern in OSCC and also a possible crosstalk with Hippo/YAP1 pathway signaling. METHODS: Immunohistochemical analysis of LOXL2 protein expression was performed in 158 OSCC patient samples, together with Yes-associated protein 1 (YAP1) activation status. Correlations with clinicopathological parameters and patient survival were assessed. RESULTS: Tumor cell-intrinsic LOXL2 expression showed two distinct expression patterns: diffuse cytoplasmic staining (64.6%), and heterogeneous perinuclear staining (35.4%). Remarkably, perinuclear LOXL2 staining was significantly associated with lymph node metastasis, advanced clinical stage and perineural invasion. Moreover, patients harboring tumors with perinuclear LOXL2 expression exhibited significantly poorer disease-specific survival (DSS) rates. Strikingly, we also found that perinuclear LOXL2 positivity gradually increased in relation to YAP1 activation, and patients harboring tumors with concomitant perinuclear LOXL2 and fully active YAP1 exhibited the worst DSS. Multivariate Cox analysis further revealed combined perinuclear LOXL2 and fully active YAP1 as a significant independent predictor of poor DSS. CONCLUSION: Tumor-intrinsic perinuclear LOXL2 emerges as a clinically and biologically relevant feature associated with advanced disease, tumor aggressiveness, and poor prognosis in OSCC. Moreover, this study unprecedentedly uncovers a functional relationship between perinuclear LOXL2 and YAP1 activation with major prognostic implications. Notably, combined perinuclear LOXL2 and fully active YAP1 was revealed as independent predictor of poor prognosis. These findings encourage targeting oncogenic LOXL2 functions for personalized treatment regimens.

Emerging Role of Decoy Receptor-2 as a Cancer Risk Predictor in Oral Potentially Malignant Disorders.

The aim of this study was to evaluate the expression of the senescence markers, Decoy Receptor 2 (DcR2) and Differentiated Embryo-Chondrocyte expressed gen 1 (DEC1), in oral potentially malignant disorders (OPMDs) to ascertain their possible association with oral cancer risk. The immunohistochemical analysis of DcR2 and DEC1 expression (along with p16 and Ki67 expression) was carried out in 60 patients with clinically diagnosed oral leukoplakia. Fifteen cases (25%) subsequently developed an invasive carcinoma. Correlations between protein marker expression, histological grade and oral cancer risk were assessed. DcR2, DEC1 and Ki67 protein expressions were found to correlate significantly with increased oral cancer risk, and also with an increased grade of dysplasia. Multivariate analysis demonstrated that DcR2 and Ki67 expression are independent predictors of oral cancer development. Our results evidence for the first time the potential of DcR2 as an early biomarker to assess oral cancer risk in patients with oral leukoplakia (HR = 59.7, p = 0.015), showing a superior predictive value to histology (HR = 4.225, p = 0.08). These findings reveal that the increased expression of DcR2 and DEC1 occurred frequently in OPMDs. In addition, DcR2 expression emerges as a powerful biomarker for oral cancer risk assessment in patients with oral leukoplakia.

Management of maxillofacial trauma in the elderly: A European multicenter study.

BACKGROUND/AIMS: Management of maxillofacial trauma in the geriatric population poses a great challenge due to anatomical variations and medical comorbidities. The aim of this study was to analyze the management variables, timing, and outcomes of facial fractures in elderly patients (aged 70 years or more) at several European departments of oral and maxillofacial surgery. MATERIALS AND METHODS: This study was based on a systematic computer-assisted database that allowed the recording of data from all geriatric patients with facial fractures from the involved maxillofacial surgical units across Europe between 2013 and 2017. RESULTS: A total of 1334 patients were included in the study: 665 patients underwent closed or open surgical treatment. A significant association (P < .005) was found between the presence of concomitant injuries and a prolonged time between hospital admission and treatment. The absence of indications to treatment was associated with comorbidities and an older age (P < .000005). CONCLUSIONS: Elderly patients require specific attention and multidisciplinary collaboration in the diagnosis and sequencing of trauma treatment. A prudent attitude may be kept in selected cases, especially when severe comorbidities are associated and function is not impaired.

Implant treatment in immunosuppressed renal transplant patients: A prospective case-controlled study.

OBJECTIVES: The aim of this clinical study was to evaluate long-term outcomes of implant therapy in a cohort of immunosuppressed renal transplant patients compared with a matched control group. MATERIAL AND METHODS: Pharmacologically immunosuppressed renal transplant patients received dental implant treatment between 2001 and 2011. Periodontal, clinical and radiographic parameters were prospectively measured with a mean follow-up of 116.8 months (range from 84 to 192 months). A matched controlled non-transplant sample receiving similar implant treatment in the same time was included as a control group. RESULTS: Implant survival rate was over 98% in both test and control groups (100% and 98.84%, respectively). Peri-implant mucositis was diagnosed in 46.80% of the implants in the study group and in 48.80% in the control group. Peri-implantitis occurred in 5.10% of the implants in the study group and in 8.10% of the controls. Wound healing and post-operative pain were similar in both groups. CONCLUSIONS: Despite the limitations of this study, pharmacological immunosuppression in renal transplant patients did not affect implant outcomes. Renal transplant patients should be carefully controlled periodically after implant treatment. CLINICAL IMPLICATIONS: The results from this investigation justify the use of dental implants for the dentalrehabilitation of immunosuppressed patients after renal transplantation provided they follow the necessarylong-term monitoring and regular maintenance of their oral and systemic health.

Implant treatment in pharmacologically immunosuppressed liver transplant patients: A prospective-controlled study.

OBJECTIVES: The main objective of this prospective study was to evaluate the long-term outcome of implant therapy in liver transplant patients (LTP). The secondary goal was to assess several implant- and patient-dependent variables, such as peri-implantitis (PI), peri-implant mucositis (PIM), bone loss (BL), and immediate postoperative complications. MATERIAL AND METHODS: Two groups, including 16 pharmacologically immunosuppressed LTP and 16 matched controls, received 52 and 54 implants, respectively, between 1999 and 2008. After evaluating the postoperative healing, a mean follow-up of more than 8 years was carried out, and radiographic, clinical, and periodontal parameters were recorded to evaluate implant survival and implant- and patient-dependent outcomes. RESULTS: The early postsurgical complications were similar in both groups. Implant survival rate was 100% in the LTP group and 98.15% in the CG. PIM was diagnosed in 35.42% of the implants and 64.29% of the patients of LTP group (LTPG) and in 43.40% of the implants and 56.25% of the patients in the CG. PI was detected in 4.17% of the implants and 7.10% of the patients in the LTPG and in 9.43% of the implants and 18.80% of the patients in the CG. CONCLUSION: Pharmacologically immunosuppression in liver transplant patients was not a risk factor for implant failure, nor for the incidence of peri-implant diseases. Liver transplant is not a contraindication for dental implant treatment, although these patients should be carefully monitored during follow-up care.

Clinicopathologic and Surgical Study of Pleomorphic Adenoma of the Parotid Gland: Analysis of Risk Factors for Recurrence and Facial Nerve Dysfunction.

PURPOSE: To determine whether clinicopathologic or surgical features are risk factors for recurrence and facial nerve dysfunction in pleomorphic adenoma (PA) of the parotid gland. PATIENTS AND METHODS: The records of 198 patients surgically treated for a PA of the parotid gland from 1999 through 2013 were retrospectively reviewed to identify patients who developed a tumor recurrence. The Fisher exact test and Mann-Whitney U test were used to analyze patient characteristics between recurrent and non-recurrent PAs. Logistic regression was used to determine the risks of recurrence and facial nerve dysfunction. RESULTS: Twenty-three patients (11.6%) developed a recurrence. Patients with tumor recurrence were notably younger than patients without recurrence. Of the 14 patients who underwent enucleation, 11 (78.6%) developed residual disease, as did 10 of 165 patients (6%) managed by a superficial parotidectomy (P < .0005). Furthermore, the risk of residual disease was 9.3 to 21.6 times higher in patients who underwent enucleation than in those who underwent a total or superficial parotidectomy. For tumor histology, recurrence was observed in 3 (15.8%) of the 19 cellular types, 18 (11.5%) of 157 classic cases, and 1 (4.8%) of 21 myxoid cases (P = .5). The risk of recurrence with positive resection margins was 49 times higher than with negative margins (P = .001). CONCLUSION: Young age, enucleation, and positive margins are risk factors for residual pleomorphic adenoma, and surgical technique and histomorphologic features are associated with increased facial nerve dysfunction.

Expression of the voltage-gated potassium channel Kv3.4 in oral leucoplakias and oral squamous cell carcinomas.

AIMS: The expression of the voltage-gated potassium channel Kv3.4 was investigated in both oral squamous cell carcinomas (OSCC) and oral leucoplakias to establish its clinical significance during the development and progression of OSCC. MATERIALS AND METHODS: Tissue specimens from 62 patients with oral leucoplakia were collected prospectively and 100 patients with OSCC who underwent surgical treatment were collected retrospectively, and Kv3.4 expression was analysed by immunohistochemistry. RESULTS: Thirty-nine of 100 tumours exhibited Kv3.4-positive expression, and staining was associated with the degree of differentiation (P = 0.05) but showed no impact on patient prognosis. Abnormal Kv3.4 expression was detected in 16% (7 of 43) hyperplastic lesions and at a significantly higher proportion in oral dysplasias (50%, 8 of 16 cases; P = 0.008), whereas expression was negligible in normal adjacent epithelia. Furthermore, patients carrying Kv3.4-positive lesions exhibited a higher progression risk than those with Kv3.4-negative lesions; however, histology but not Kv3.4 expression predicted oral cancer development significantly in this prospective cohort. CONCLUSION: This study provides original evidence to demonstrate the early occurrence and high prevalence of abnormal Kv3.4 expression in oral leucoplakias. Our results support a role for Kv3.4 potassium channel in OSCC tumorigenesis rather than tumour progression and disease outcome.

Prevalence of human papillomavirus in oral squamous cell carcinomas in northern Spain.

The aim of this study was to analyze the prevalence of high-risk HPV in oral squamous cell carcinoma (OSCC) in a northern Spanish population, as well as to ascertain the prognostic role of p16INK4a expression. The examination samples were collected from paraffin tissue blocks, from 125 patients surgically treated between 1996 and 2007. All cases were histologically evaluated, and the presence of HPV was assessed by p16 and p53immunohistochemistry followed by DNA detection by in situ hybridization (ISH) and polymerase chain reaction (PCR) amplification using the combination of consensus primers MY11/GP6 + . Fourteen cases (11 %) were p16-immunopositive, and p53 was scored positive in 73 cases (58 %). Five cases (4 %) showed a simultaneous p16-positive and p53-negative immunostaining. ISH was negative in all the cases. Among the p16INK4a-immunopositive cases, PCR amplification failed to reveal HPV DNA in any tumor samples. There were no statistically significant differences in any clinical or pathological characteristics of the patients regarding p16INK4a expression. T classification, neck-node metastasis, and clinical stage showed outcome relevance. However, no significant differences in cause-specific survival based on p16INK4a were observed. We did not find any high-risk HPV types in our patients, thus, are unlikely that HPV has an important role in the etiology of OSCC. p16INK4a protein was neither an accurate marker of HPV infection nor a prognosis marker in OSCC.

Relevance of level IIb neck dissection in oral squamous cell carcinoma.

BACKGROUND: The purpose of this study was to determine the prevalence of level IIb metastasis in patients with oral squamous cell carcinomas (OSCCs). MATERIAL AND METHODS: A prospective analysis of 56 patients with OSCC who underwent surgical treatment of the primary lesion with simultaneous neck dissection was performed. During neck dissection, level IIb lymph nodes were separately removed and processed. Neck dissection was bilateral in 26 patients (46%) and unilateral in 30 patients (54%). RESULTS: The mean number of nodes found in the level IIb specimens was 4.7 (range: 0-8 nodes). The prevalence of metastasis at level IIb was 0% in pN0 necks and 3.4% in pN+ necks, with an overall prevalence of 1.8%. A significant association between metastasis to level IIb and type of neck dissection was observed. There were no isolated metastases to level IIb without the involvement of other nodes in the remaining neck specimen. Four regional recurrences were observed during follow-up. CONCLUSIONS: Based on our findings, we suggest that dissection of the level IIb region in patients with OSCC may be required only in patients with multilevel neck metastasis or if level IIa metastasis is found intraoperatively.

Prognostic Significance of ß-Catenin in Relation to the Tumor Immune Microenvironment in Oral Cancer.

The aim of this study was to investigate the prognostic relevance of ß-catenin expression in oral squamous cell carcinoma (OSCC) and to explore relationships with the tumor immune microenvironment. Expression of ß-catenin and PD-L1, as well as lymphocyte and macrophage densities, were evaluated by immunohistochemistry in 125 OSCC patient specimens. Membranous ß-catenin expression was detected in 102 (81.6%) and nuclear ß-catenin in 2 (1.6%) tumors. There was an association between ß-catenin expression, tumoral, and stromal CD8+ T-cell infiltration (TIL) and also the type of tumor immune microenvironment (TIME). Tumors harboring nuclear ß-catenin were associated with a type II TIME (i.e., immune ignorance defined by a negative PD-L1 expression and low CD8+ TIL density), whereas tumors with membranous ß-catenin expression were predominantly type IV (i.e., immune tolerance defined by negative PD-L1 and high CD8+ TIL density). Combined, but not individual, high stromal CD8+ TILs and membranous ß-catenin expression was independently associated with better disease-specific survival (HR = 0.48, p = 0.019). Taken together, a combination of high stromal CD8+ T-cell infiltration and membranous ß-catenin in the tumor emerges as an independent predictor of better survival in OSCC patients.

The epidemiology and management of odontomas: a European multicenter study.

INTRODUCTION: Odontoma is the most commonly diagnosed odontogenic tumor of the oral cavity. The objective of the present study was to assess the demographic variables, patterns, diagnostic features, and management issues of odontomas treated at several European departments of maxillofacial and oral surgery. MATERIALS AND METHODS: This study was conducted at 8 European departments of oral surgery between January 1, 2004, and December 31, 2018. Only patients with odontomas were included. The following data were recorded for each patient: gender, age, comorbidities, site, size of odontomas, radiographic features, type of odontoma, treatment of odontomas, treatment of associated teeth, complications, and recurrence. RESULTS: A total of 127 patients (70 male and 57 female patients) with odontomas were included. The mean age was 22 years; 71 odontomas were found in the mandible, whereas 56 in the maxilla. In the mandible, the most frequently involved subsite was the parasymphysis, while in the maxilla, the most common subsite was the upper incisor region. The mean size of included odontomas was 15.3 mm. On the whole, 62 complex odontomas, 50 compound odontomas, and 15 mixed-type odontomas were observed. Complete excision of the odontomas was performed in 121 patients. In 24 patients, the extraction of deciduous teeth was performed, and in 43 patients, one or more permanent teeth were removed. Finally, in 9 patients, a partial excision of the odontoma was performed. Recurrence was observed in 4 cases out of 127 patients. CONCLUSIONS: Dental practitioners should be aware of the distinct clinical and radiographic features of odontoma in order to perform an appropriate and early diagnosis. Conventional radiography, such as panoramic radiograph, is often sufficient technique for a diagnosis after clinical suspicion or for an incidental diagnosis to prevent later complications, such as impaction or failure of eruption of teeth.

Implant treatment in patients with oral lichen planus: a prospective-controlled study.

OBJECTIVES: The main aim of this prospective-controlled study was to evaluate the implant survival rate in patients diagnosed with oral lichen planus (OLP). The secondary goals were to analyze the presence of implant- and patient-dependent variables. MATERIAL AND METHODS: Two groups, including 18 patients diagnosed with OLP and 18 controls, received 56 and 62 implants during the years 2003-2008. Pain and wound healing were evaluated after the procedure. After a mean follow-up of 53.5 and 52.3 months, clinical and radiographic assessments were used to evaluate implant survival and patient- and implant-dependent parameters. RESULTS: The implant survival rate was 100% for the OLP group. Immediate postsurgical complications were similar in both groups. Peri-implant mucositis (PIM) was detected in 44.6% of the implants and 66.6% of the patients with OLP. The presence of desquamative gingivitis (DG) was associated with a higher rate of PIM on those implants of the OLP group (P=0.004). Peri-implantitis (PI) appeared in 10.7% of the implants and 27.7% of the patients with OLP (P=NS). CONCLUSION: Despite the limitations of the small sample size, it seems that lichen planus is not a prominent local player in the genesis of implant failure. Patients with DG should be carefully examined during follow-up care.

Survival after free flap reconstruction in patients with advanced oral squamous cell carcinoma.

PURPOSE: The purpose of the present study was to assess the effect of free-flap reconstruction on the survival of patients treated for oral squamous cell carcinoma. PATIENTS AND METHODS: The present study was based on a retrospective cohort of 98 patients. Of the 98 patients, 49 underwent surgical reconstruction with microvascular tissue transfer (test group) and in 49 (control group), only local or regional flaps were used. RESULTS: For the free-flap group, the average follow-up period was 34.6 months. For the control group, the average follow-up was 39.8 months. At the end of the follow-up period, 23 (47%) and 33 (67.3%) patients had died of oral squamous cell carcinoma in the microvascular reconstructive and control group, respectively. The difference in the final status between the 2 groups was statistically significant (P = .03). In the free-flap group, the mean and median survival time was 65 and 60 months. In the locoregional flap group, the mean and median survival time was 54 and 24 months, respectively. No difference was seen in the survival time between the free-flap and local flap groups (P = .2). Univariate Kaplan-Meier analysis revealed that positive surgical margins were significantly associated with shortened survival in the free-flap group and that recurrence was significant in both reconstructive groups. On multivariate Cox regression analysis, the status of the resection margin (P = .07) and tumor recurrence (P < .0005) showed a significant relationship with survival. CONCLUSION: Patients with free-flap reconstruction of surgically created defects after oral cancer resection showed a trend toward better 5-year survival.

Use of autologous skin equivalents with artificial dermal matrix (integra) in donor site coverage in radial forearm free flaps: preliminary cases.

PURPOSE: The radial forearm flap is one of the most commonly used methods for intraoral reconstruction in oral carcinoma surgery. One of its disadvantages is the residual functional and unaesthetic defect in the donor site. The objective of this report is to describe preliminary cases of a novel method to cover such donor sites based on the use of autologous skin equivalents (ASEs) and an artificial dermal matrix (Integra, Prim, Barcelona, Spain). MATERIALS AND METHODS: The donor sites of 2 patients were treated with the artificial dermal matrix after raising a radial forearm flap. A skin biopsy and a blood sample were taken to construct an ASE. After 3 weeks, the ASE was applied over the dermal template and left to heal. The functional and esthetic results were recorded. RESULTS: Good functional and esthetic results were achieved, with correct wrist motility, although a natural skin color could not be achieved. Neither the Integra nor the ASE was rejected. Total wound coverage was achieved at 4 months, and completely normal skin was observed at 6 months. CONCLUSIONS: This technique of combining an artificial dermal matrix with an ASE could be an alternative method to cover the donor sites of radial forearm flaps.

The epidemiology and management of odontogenic keratocysts (OKCs): A European multicenter study.

The objective of the present study was to assess the epidemiology including demographic variables, diagnostic features, and the management of odontogenic keratocyst (OKCs) at several European departments of maxillofacial and oral surgery. This study is based on a systematic computer-assisted database that allowed the recording of data from treated OKCs. The following data were recorded for each patient: gender, age, voluptuary habits, comorbidities, site, size, radiographic features, treatment of OKCs, length of hospital stay, complications, recurrence, management and complications of eventual recurrence. A total of 405 patients, 249 male and 156 female, with 415 OKCs (407 sporadic and 8 syndromic lesions) were included in the study: 320 lesions were found in the mandible, whereas 95 were found in the maxilla. In the mandible, the most frequently involved subsite was the angle, whereas in the maxilla it was the molar region. The most frequently performed treatment option was enucleation plus curettage/peripheral ostectomy in 204 OKCs (recurrence rate, 9%). Decompression without residual cystectomy (recurrence rate, 66%), marsupialization with residual enucleation with the use of Carnoy's solution (recurrence rate, 50%), decompression with residual cystectomy (recurrence rate, 43%), and simple enucleation (recurrence rate, 24%) were the treatment options with the highest recurrence rates. An appropriate management of odontogenic keratocysts should be individualized, taking into consideration clinical and radiological findings, as well as patients' age and comorbidities.

Quality of life following maxillofacial trauma in the elderly: a multicenter, prospective study.

BACKGROUND/AIMS: When facial trauma involves elderly patients, the possible presence of frailty and comorbidities in victims of trauma may worsen the posttraumatic symptoms and decrease quality of life. The aim of this multicenter study was to assess the quality of life following surgical or non-operative management of maxillofacial trauma in elderly patients. MATERIALS AND METHODS: This cohort study was based on the administration of validated self-administered questionnaires to all the geriatric patients (70 years or more) with facial fractures from the involved maxillofacial surgical units across Europe, since 1st January 2019 to 31st June 2019. The following questionnaires were administered: SF36 questionnaire; the VFQ-25 questionnaire; the Oral Health Impact Profile - 14 (OHIP14). Outcome variables were VFQ-25 and OHIP-14 results. RESULTS: A total of 37 patients (14 male and 23 female patients) met the inclusion criteria and were included in the study. Elderly patients had an improvement in almost all the categories examined by the SF-36 questionnaire 6 months after trauma, with the only exception of a worsening as for role limitations due to physical health. An improvement was observed in almost all the categories at SF-36 test. A worsening of scores of OHIP-14 for all the considered dimensions in the whole study population was observed too. CONCLUSIONS: Elderly patients following facial trauma experience significant emotional, social, and functional disturbances. We observed that emotional problems, energy/fatigue, social functioning, and generally social limitations played a great role in the decrease of QoL in elderly patients following maxillofacial trauma.

Synchronous squamous cell carcinoma and chronic lymphocytic leukemia of the palate.

Although multiple synchronous malignancies of the same histological type have been described frequently in the upper aerodigestive tract, this is a less frequent phenomenon when dealing with tumors of different lineage. We present a case of a man who developed simultaneously an oral squamous cell carcinoma and chronic lymphocytic lymphoma of the palate without any previous risk factors. To the best of our knowledge, this is the first case well documented in the literature of synchronous oral squamous cell carcinoma and chronic lymphocytic lymphoma of the palate in the same sample. The presence of multiple primary malignancies of different histological types not only complicates the treatment but also worsens the prognosis of the patient.

Clinical and immunohistochemical analysis of orbital metastasis from prostate carcinoma.

Orbital tumors can present with different symptoms, especially ophthalmic disturbances. We describe 1 patient with an orbital metastasis from prostate carcinoma presenting with proptosis and give details of his presentation, diagnostic tools, and treatment. This is a rare case. Possible ocular spread of prostate adenocarcinoma and the diagnostic techniques used are discussed. It is stressed that immunohistochemical studies and comparison with primary tumor may be essential for a definitive diagnosis. The treatment of prostate orbital metastases is also reviewed.

Genes involved in the epithelial-mesenchymal transition in oral cancer: A systematic review.

OBJECTIVE: Epithelial-mesenchymal transition (EMT) is considered the initial step in the invasion-metastasis cascade. The aim of this systematic review was to study the signature of genes involved in the EMT process in oral cancer (OC) confirmed by protein expression and its possible relationship with oral squamous cell carcinoma (OSCC) prognostic variables. MATERIALS AND METHODS: A search of the scientific literature was carried out with no start date restriction until 17 September 2020 in the electronic databases Pubmed/MEDLINE, Web of Science, Cochrane Library and Scopus, following specific eligibility criteria. The methodological quality of the included studies was assessed using the Newcastle-Ottawa tool. RESULTS: A total of 8 retrospective cohort studies were included, all of them performed in China and with low risk of bias. Overexpression of the genes HNRNPC, ITGA5, HMGA2 and SRSF3, and low expression of ALDH3A1 and ARID2 promote EMT in OC. The more advanced clinical stages of the TNM classification were significantly associated with overexpression of HNRNPC, ITGA5, HMGA2 and SRSF3, and low expression of ARID2. CONCLUSIONS: HNRNPC, ITGA5, HMGA2, SRSF3, ALDH3A1 and ARID2 genes were associated with EMT process. Over- or under-expression of these genes is associated with worse stages of OSCC and/or worse prognosis of the tumor. Further studies on this topic are needed in different countries to be able to confirm these results, since the detection of these genes can help to know which tumors have a worse prognosis.

Effect of region-dependent viscoelastic properties on the TMJ articular disc relaxation under prolonged clenching.

The disc of the temporomandibular joint (TMJ) is located between the mandibular condyle and temporal bone, and has an important load-bearing and stress absorbing function. The TMJ disc presents viscoelastic characteristics that are largely dependent on its collagen fibre and proteoglycan composition and organization. The purpose of this study is to investigate the possible effects of region-specific dynamic viscoelastic properties on stress relaxation during prolonged clenching. Two finite element models were used to compare the stress distribution within the TMJ disc, namely, one with uniform disc material property and another one with region-specific disc material properties. Similar results were observed in both models with slight differences in the location of maximum stress. Larger stresses were observed in all cases for the model with uniform disc material property. Moreover, the higher values for the model with uniform disc material property appeared in the lateral region, while in the model with region-specific disc properties, these values moved to the lateral and central region. This investigation confirms that both models are sufficiently accurate to investigate stress distribution in the TMJ disc, and, particularly, the model with the region-specific disc material properties ensure better simulations of the TMJ disc behaviour.