The status of jaw lesions and medication-related osteonecrosis of jaw in patients with multiple myeloma.

BACKGROUND/PURPOSE: Myeloma jaw lesions are not uncommon. The study aimed to investigate the status of jaw lesions and medication-related osteonecrosis of jaw (MRONJ) in multiple myeloma (MM) patients. METHODS: One hundred and twenty-two consecutive newly-diagnosed MM patients seeking dental care at a hospital of southern Taiwan was examined according to jaw lesions with complete follow-up data. RESULTS: Median age of the patients was 67.8 years, and 88.5% of patients were of DS stage III and 41.0% were of ISS stage III at diagnosis. Median survival was 37.9 months for 43 (35.2%) patients with jaw lesions and 57.4 months for 79 patients without jaw lesions. 1-year, 5-year and >7-year overall survival rates for patients with jaw lesions versus patients without jaw lesions were 94.9%, 67.2%, 56.7% vs 83.7%, 51.8%, 26.8% respectively. Patients with jaw lesions had the worse survival (P = 0.03). Neither age nor stage affected survival. Jaw lesions involved the mandible more often than the maxilla and stopped progressing during remission, but did not repair. Jaw lesions were the first evidence or recurrent sign of MM in six (4.9%) patients. Long-term monthly antiresorptive therapy changed the radiographic patterns of jawbones and induced MRONJ developing in 16.7% (8/48) of patients. Five (62.5%) MRONJ sites spontaneously occurred without local risk factors. CONCLUSION: Nearly one-third of MM patients develop osteolytic jaw lesions that seem to be associated with poorer survival. Jaw lesion is an independent prognostic predictor of survival in myeloma. Antiresorptive drugs at less frequent dosing regimen are crucial to minimize spontaneous MRONJ.

Management of dental extractions in patients on warfarin and antiplatelet therapy.

BACKGROUND/PURPOSE: Planning dental extractions for Taiwanese patients on antithrombotic therapy remains controversial. This study aimed to examine management of dental extraction in patients on warfarin and antiplatelet therapy. METHODS: Subjects comprised 1331 patients, with (1) 60 on warfarin with intentional normalized ratio (INR) below 4.0 (warfarin continued: 28 patients/33 occasions; warfarin stopped and switched to heparin under hospitalization: 32 patients/37 occasions); (2) 183 on antiplatelet therapy (aspirin: 125 patients/185 occasions; clopidogrel: 42 patients/65 occasions; dual therapy: 16 patients/24 occasions); and (3) a control group of 1088 patients/1472 occasions without any antithrombotic therapy. The patient's clinico-demographic parameters, warfarin effectiveness (dose and INR levels) and antiplatelet therapy, number and type of dental extraction and incidence of postoperative bleeding were investigated. RESULTS: Incidence of postoperative bleeding in the warfarinized group (warfarin continued: 9.1%; warfarin stopped: 8.1%) was higher than in the antiplatelet group (aspirin: 1.1%; clopidogrel: 3.1%; dual antiplatelet: 4.2%), and the control group (0.7%), but these differences were not significant and unrelated to INR or number and type of dental extraction. Postoperative hemorrhage was managed successfully by repacking with Gelfoam impregnated with tranexamic acid powder in most patients. CONCLUSION: The study indicated that there is no need to interrupt warfarin (INR<4.0) and antiplatelet therapy before dental extractions in Taiwanese patients. A sufficient hemostasis could be obtained using local measures. This approach can save these individuals from becoming exposed to the risk of thromboembolism and the inconvenience of bridging anticoagulation with heparin.

Evaluation physical characteristics and comparison antimicrobial and anti-inflammation potentials of dental root canal sealers containing hinokitiol in vitro.

Hinokitiol displays potent antimicrobial activity. It has been used in toothpaste and oral-care gel to improve the oral lichen planus and reduce halitosis. The aim of this study was to evaluate the antimicrobial activity of 3 different dental root canal sealers with hinokitiol (sealers+H) and their physical and biological effects. AH Plus (epoxy amine resin-based, AH), Apexit Plus (calcium-hydroxide-based, AP), and Canals (zinc-oxide-eugenol-based, CA), were used in this study. The original AH and CA exhibited strong anti-methicillin-resistant Staphylococcus aureus (anti-MRSA) activity, but AP did not. The setting time, working time, flowability, film thickness, and solubility of each sealer+0.2%H complied with ISO 6876:2001. CA+0.2%H exhibited high cytotoxicity, but the others sealers+0.2%H did not. Because hinokitiol combined with Zn2+ in CA creates a synergistic effect. The physical tests of AP+0.5%-1%H complied with ISO 6876:2001, improved antimicrobial activity, inhibited inflammation genes cyclooxygenase-2 (COX-2) and hypoxia-inducible factor-1α (HIF-1α) mRNA in MG-63 cells and human gingival fibroblasts (HGF), and down-regulated lysyl oxidase (LOX) mRNA of HGF. In summary, AH and CA demonstrated strong antimicrobial activity, but AP did not. Application of hinokitiol increases AH anti-MRSA activity should less than 0.2% for keep well flowability. AP+0.5%-1% hinokitiol exhibited strong physical, antibacterial, and anti-inflammation potentials, and inhibited S. aureus abscess formation. Applying an appreciable proportion of hinokitiol to epoxy-amine-resin-based and calcium-hydroxide-based root canal sealers is warranted, but the enhanced cytotoxicity and synergistic effect must be considered.

Aberrant expression in multiple components of the transforming growth factor-ß1-induced Smad signaling pathway during 7,12-dimethylbenz[a]anthracene-induced hamster buccal-pouch squamous-cell carcinogenesis.

UNLABELLED: Transforming growth factor (TGF)-ß1 signaling controls a plethora of cellular processes including tumorigenesis. The TGF-ß1 ligand initiates signaling by binding to TGF-ßreceptor II (TßRII) and allowing heterodimerization with TGF-ßreceptor I (TßRI); thus, TßRI is phosphorylated by TßRII. After phosphorylation, Smad2 and Smad3 heterodimerize with Smad4, and this complex migrates to the nucleus to regulate the expression of specific target genes. However, Smad7 interrupts above signal transduction by preventing phosphorylation of Smad2 or Smad3. The objective of this study was to examine the TGF-ß1-induced Smad signaling pathway during 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch squamous-cell carcinogenesis. Fifty 6-week-old male Syrian golden hamsters were divided into three experimental and two control groups (10 animals in each). Both pouches of each animal in the experimental groups were painted with 0.5% DMBA solution, and both pouches of each animal of one of the control groups were similarly treated with mineral oil; the other control group remained untreated throughout the experiment. Animals from three experimental groups were sacrificed at the end of 3rd, 9th, and 14th-weeks after DMBA treatment, respectively, and animals from two control groups were all sacrificed at 14th-weeks after the treatment. Immunohistochemical staining for TGF-ß1, TßRI, TßRII, Smad2-4 and Smad7 were performed. RESULTS: A significant increase in the expression of Smad7 and significant decreases in the expression of TßRII, Smad 2, Smad3 and Smad4 were noted during hamster buccal-pouch carcinogenesis induced by DMBA. Our findings indicate that a disruption in TGF-ß1-induced Smad signaling occurs as a result of aberrant expression of multiple components in the TGF-ß1 signaling pathway during DMBA-induced hamster buccal-pouch carcinogenesis, leading to loss of TGF-ß1 growth-suppressive effects on transformed pouch keratinocytes.

Targeting l1 cell adhesion molecule using lentivirus-mediated short hairpin RNA interference reverses aggressiveness of oral squamous cell carcinoma.

The L1 cell adhesion molecule (L1CAM) has been implicated in tumor progression of many types of cancers, but its role in oral squamous cell carcinoma (OSCC) has not been investigated. In the present study, we demonstrated overexpression of L1CAM in OSCC cells, but not in normal keratinocytes, using both clinical specimens and cell lines. This overexpression demonstrated a strong correlation with less differentiation and a higher invasion potential of cancer cells, supporting the significance of L1CAM in human OSCC tumor progression. Targeting L1CAM gene expression in SCC4 cells overexpressing L1CAM using a lentivirus-mediated small hairpin RNA (shRNA) led to a significant reduction in cell proliferation in vitro via retardation of cell cycle at the G1 phase. In addition, shRNA knockdown of L1CAM strongly attenuated the migration and invasion of SCC4 cells, and this was also observed to parallel increased E-cadherin levels and decreased levels of vimentin, fibronectin, and Snail-family transcription factors, indicating that L1CAM expression was related to the epithelial-mesenchymal transition. Furthermore, while mice receiving orthotopically placed control SCC4 cells died within 40 days due to invasive tumor growth and regional lymph node metastasis, prolonged animal survival and complete suppression of tumor progression was observed in mice implanted with L1CAM-deficent SCC4 cells, further substantiating the fundamental importance of L1CAM in OSCC pathophysiology. Our findings suggested that L1CAM is a critical mediator of tumor progression in OSCC, and targeting L1CAM using lentivirus-mediated shRNA may be a useful molecular pharmaceutical approach for the treatment of advanced OSCC.

Detection of permanent three-rooted mandibular first molars by cone-beam computed tomography imaging in Taiwanese individuals.

This study determined the prevalence of permanent three-rooted mandibular first molars and their morphology among a Taiwanese population by using cone-beam computed tomography (CBCT). Images from 744 patients were screened to obtain 123 samples for this study. All permanent mandibular first molars were evaluated in axial sections from the pulpal floor to the apices of the roots to determine the number of roots. The interorifice distances from the distolingual (DL) canal to the mesiobuccal (MB) and distobuccal (DB) canals were also estimated. The prevalence of permanent three-rooted mandibular first molars was 33.33%, with a bilateral incidence of a symmetrical distribution of 53.65%. There was a significantly greater incidence of three-rooted teeth on the right side of the mandible than on the left, but gender did not show a significant relationship with this variant prevalence.The mean interorifice distances from the DL canal to the DB, MB, and ML canals of the permanent three-rooted mandibular molars were 2.7, 4.4, and 3.5 mm, respectively. The high prevalence of the DL root in permanent mandibular first molars among the Taiwanese (Chinese) population and estimations of the interorifice distance of such teeth might be useful for successful endodontic treatments.

Expression of inhibitors of apoptosis family protein in 7,12-dimethylbenz[a]anthracene-induced hamster buccal-pouch squamous-cell carcinogenesis is associated with mutant p53 accumulation and epigenetic changes.

Fifty outbred Syrian golden hamsters were equally divided into three experimental groups and two control groups. The pouches of the experimental groups were painted bilaterally with a 0.5% 7,12-dimethylbenz[a]anthracene (DMBA) solution thrice a week for 3, 7 and 14 weeks. One of the control groups was applied with mineral oil while another control group remained untreated throughout the experiment. Neither survivin nor cIAP2 could be detected in any of the control tissues, whereas survivin and cIAP2 were found to be significantly increased in 3-, 7- and 14-week DMBA-treated pouches compared with the control pouches. Expression of XIAP, cIAP1 and NAIP were noted for both the control and 3-, 7- and 14-week DMBA-treated pouches, but levels were found to be significantly elevated in the experimental groups compared with the control pouches. p53 was not detected in any control tissues, but was significantly increased in 3-, 7- and 14-week DMBA-treated pouches. Direct sequencing revealed a point mutation (C-->G) of p53 for pouch tissues treated with DMBA for 3 and 7 weeks, and there was a wide variation in the p53 sequence of the 14-week DMBA-treated pouch tissues, as compared with the control tissues. The control tissues had a survivin- and cIAP2-methylated allele, whereas the DMBA-treated tissues showed no evidence of survivin- and cIAP2-methylation. Neither the control nor DMBA-treated pouches showed evidence of XIAP-, cIAP1- or NAIP-methylation. Our results suggest that the expression of inhibitors of apoptosis family in DMBA-induced hamster buccal-pouch squamous-cell carcinogenesis may be modulated by both genetic (mutant p53) and epigenetic mechanisms.

Expression of p63 protein and mRNA in oral epithelial dysplasia.

BACKGROUND: Abnormalities in the TP53 are regarded as the most consistent findings in oral squamous cell carcinoma. Two related members of the TP53 family, p73 and p63, have shown remarkable structural similarity to TP53, indicating possible functional and biological interactions. The aim of the present study was to investigate the expression of p63 protein and mRNA in oral epithelial dysplasia. METHODS: Immunohistochemical p63 staining was compared for samples from 90 male patients with buccal epithelial dysplasias and 15 healthy individuals with normal buccal mucosa and 15 subjects with reactive epithelial hyperplasia of the oral mucosa secondary to traumatic insult. The buccal lesions consisted of mild, moderate and severe epithelial dysplasias (30 samples in each category). The mRNA expression using reverse transcription polymerase chain reaction (RT-PCR) was also included for a subset of available fresh tissue specimens (four samples in each category of mild and moderate epithelial dysplasia; five samples in severe epithelial dysplasia; five samples in each of normal and reactive epithelial hyperplasia). RESULTS: Nuclear p63 staining was demonstrated predominantly in the basal layers of the epithelium of the normal buccal mucosa and reactive epithelial hyperplasia specimens. For epithelial dysplasia lesions, however, staining was not restricted to the basal layers, extending to the middle spinous layer for samples in the mild category, with p63 immunoexpression observed across almost the full thickness of the dysplastic epithelium for analogous moderate and severe specimens. Compared with normal/reactive hyperplastic mucosa, p63 staining in the dysplastic mucosa was significantly increased. The severity of dysplasia was increased with the increase of p63 staining. Furthermore, Delta Np63mRNA was identified in all of the fresh tissue samples whereas expression of transactivation (TA) isotype was not detected. A subset of moderate epithelial dysplasia and severe variant showing p63-positive staining has undergone malignant transformation to squamous cell carcinomas in about 5 years follow-up. CONCLUSION: Our results indicate that impaired p63 immunoexpression (predominantly Delta N isoform) is associated with the severity of oral epithelial dysplasias and up-regulation of p63 may play a role in the early stage of human oral tumorigenesis.

Sialolipoma of the floor of the mouth: a case report.

Intra-oral lipoma is a well-known entity, but lipomatous tumors including salivary gland tissue containing clustered or peripherally located ducts and acinar cells are uncommon. They are a newly recognized entity of salivary gland lipoma, designated sialolipoma. We describe a case of sialolipoma arising in the floor of the mouth presenting with apparently normal salivary gland tissue, as demonstrated by both histologic and immunohistochemical findings, in a 67-year-old female. Complete surgical removal of the tumor with preservation of the sublingual gland was implemented after a careful examination confirming that the lesion did not originate from the sublingual gland.

p73 expression for human buccal epithelial dysplasia and squamous cell carcinoma: does it correlate with nodal status of carcinoma and is there a relationship with malignant change of epithelial dysplasia?

BACKGROUND: TP73, a p53 homologue gene, shares similar structural sequences with p53. The aim of this study was to investigate the p73 expression for human buccal epithelial dysplasia (ED) and squamous cell carcinoma (SCC). METHODS: Seventy-five samples of human buccal ED, including mild, moderate, and severe ED (25 samples in each category), were analyzed for p73 protein expression by means of immunohistochemistry. Twenty-five samples of human buccal SCCs were analyzed for p73 mRNA expression with reverse transcription-polymerase chain reaction (RT-PCR) and were also analyzed for protein expression with immunohistochemical analysis. RESULTS: By use of immunohistochemical analysis, nuclear staining of p73 protein was detected in a subset of normal mucosa, buccal ED, and SCC specimens. p73 nuclear staining was noted for the basal cells of normal buccal mucosa. For buccal lesions deriving from mild, moderate, and severe ED, p73 protein was observed in basal and parabasal layers and in more superficial cell layers corresponding to the spinous layer. For well-differentiated carcinomas, p73 immunoreactivity was chiefly observed among the less-differentiated cells in the periphery of carcinomatous clusters, whereas moderately differentiated carcinomas revealed homogeneous staining, involving nearly all of the tumor cells. On RT-PCR, the expression of p73 mRNA from buccal SCC was noted to be compatible with the findings of immunohistochemical analysis. An electrophoretic band with a 180-bp PCR product corresponding to p73 mRNA has been observed. The expression of p73 seemed to be significantly elevated for specimens of buccal ED (protein level) and SCC (protein and mRNA levels) compared with the analogous expression for normal control tissue (Fisher's exact test, p <.001). Also, p73 expression (protein and mRNA levels) correlated significantly with cervical lymph node metastasis for cases of buccal SCC (Fisher's exact test, p <.001). Eight cases of ED (protein level) showing p73 positivity have undergone malignant transformation to develop SCCs in 2 years follow-up, but no statistical significance was established (Fisher's exact test, p >.05). CONCLUSIONS: The data suggest that p73 expression may be (1) associated with the differentiation of oral stratified squamous epithelium, (2) an early event in human oral carcinogenesis, and (3) associated with the nodal status of patients with oral carcinoma and a possible indicator for malignant change of oral ED.

Composite lymphoma: angiocentric T-cell lymphoma (CD8+ cytotoxic/suppressor T-cell) and diffuse large B-cell lymphoma associated with EBV, and presenting clinically as a midfacial necrotizing lesion.

A composite lymphoma is defined as the simultaneous occurrence of two histologically different types of lymphomas situated in one anatomical location. Reports of composite B- and T-cell lymphomas, especially in the head and neck region, are rare. We describe a 76-year-old Taiwanese aboriginal female patient clinically presenting with a midfacial necrotizing lesion (MNL). Microscopic examination of the incisional biopsy specimen revealed extensive surface necrosis with infiltrates of inflammatory cells. Beneath the necrotic surface, there appeared to be two distinct populations of pleomorphic lymphoid cells exhibiting the characteristic features of the angiocentric distribution of the tumor cells and evidence of angiodestruction. Immunohistochemical staining revealed that these atypical lymphoid cells were positive for LCA, CD45, CD5, CD20, CD3 epsilon, CD8, bcl-2 and bcl-6 and negative for CD56, CD4, CD68, keratin, S-100, kappa and lambda. Furthermore, these atypical lymphoid cells also expressed EBV-encoded nuclear RNAs (EBERs) following in situ hybridization. Therefore, this was a case of composite lymphoma: angiocentric T-cell lymphoma (ATCL) (CD8+ cytotoxic/suppressor T-cell) and diffuse large B-cell lymphoma (DLBL) associated with the Epstein-Barr virus (EBV) and presenting clinically as MNL.

Peripheral osteoma of the mandibular condyle.

A rare case of peripheral osteoma, which developed in the right mandibular condyle of a 27-year-old man, is presented. Condylectomy with reconstruction of the condyle using a rib graft and subsequent mouth opening exercise as well as orthodontic treatment were performed. Occlusion disharmony and facial asymmetry were substantially improved, with no sign of recurrence two years after surgery. Long-term post-operative care of mouth opening exercise is highlighted. Orthodontic treatment is also indicated for better results on occlusal function and facial appearance. Therefore, a team composed of interdisciplinary specialists such as dentist, oral & maxillofacial and chest surgeons is indispensable to successful treatment.

Increased expression of inducible nitric oxide synthase for human buccal squamous-cell carcinomas: immunohistochemical, reverse transcription-polymerase chain reaction (RT-PCR) and in situ RT-PCR studies.

BACKGROUND: The inducible nitric oxide synthase (iNOS) is involved primarily in inflammatory and carcinogenesis processes. An enhanced expression of iNOS at the protein level has been reported previously for human oral squamous cell carcinoma; however, the expression of iNOS at the mRNA level has not yet been demonstrated. Furthermore, no studies have addressed whether iNOS expression at mRNA level correlates with cervical lymph node metastasis. METHODS: Specimens of the squamous cell carcinoma of the buccal mucosa obtained from tissue samples of surgically resected tumors from 25 male patients were evaluated with immunohistochemical assessment of iNOS protein and IS-RT-PCR, as well as RT-PCR for iNOS mRNA. We also analyzed the iNOS expression status with clinical parameters to determine whether it had any prognostic significance in this homogenous population. RESULTS: Inducible NOS protein (16 of 25, 64%) and mRNA (13 of 25, 53%) activities were detected for the oral carcinoma specimens examined in this study. Cytoplasmic and/or nuclear stainings were observed in the specimens of both well-differentiated SCC (10 of 15, 67%), and moderately to poorly differentiated SCC (6 of 10, 60%). The cellular location of iNOS mRNA was noted to be consistent with the finding using immunohistochemical technique (cytoplasm and/or nuclei stainings of the tumor islands). Using in situ RT-PCR, iNOS mRNA activity was detected in nine specimens of well-differentiated squamous cell carcinoma (9 of 15, 60%) and four specimens of moderately to poorly differentiated squamous cell carcinoma (4 of 10, 40%). With RT-PCR, an electrophoretic band corresponding to a 907-bp PCR product was observed for nine specimens of well-differentiated squamous cell carcinoma (9 of 15, 60%) and four specimens of moderately to poorly differentiated squamous-cell carcinoma (4 of 10, 40%). Neither iNOS protein nor mRNA was noticed in the samples of normal buccal mucosa or in the negative control samples. There was a significant relationship between iNOS expression (at both protein and mRNA levels) and whether patients had nodal disease. CONCLUSIONS: We have demonstrated an enhanced expression of iNOS protein and mRNA in a number of human buccal carcinomas compared with normal buccal mucosa. Such an observation suggests that the iNOS protein and mRNA expression is chiefly derived from a subset of oral cancerous tissues. Our observation also indicates that iNOS expression correlates with cervical lymph node metastasis in oral squamous cell carcinomas. Therefore, it may also indicate that a subset of oral cancers with greater metastatic potential, as evidenced by increased expression iNOS protein and mRNA, is identified.

Immunohistochemical demonstration of p73 protein in the early stages of DMBA-induced squamous-cell carcinogenesis in hamster buccal pouch.

The identification of a new protein, p73, with structural and functional similarities to p53 protein suggests that a family of p53-like proteins is likely to exist. This study investigated the status of p73 protein in the early stages of 7,12-dimethyl benz[a]anthracene (DMBA)-induced carcinogenesis. Outbred young (6-week-old) male Syrian golden hamsters (Mesocricatus auratus; 40 animals) were randomly divided into four equal groups: a 3-week DMBA-treated experimental group, a 6-week DMBA-treated experimental group, a mineral oil-treated control group, and a non-treated control group. Following this, a total of 80 specimens of pouch mucosa were obtained from the 40 animals in the four groups. Positive nuclear staining for p73 protein was randomly distributed throughout the whole epithelial layer of the DMBA-treated specimens and was absent in controls. Positive p73 staining was observed in 8 of the 20 (40%) 3-week, and 14 of the 20 (70%) 6-week DMBA-treated specimens. None of the 3-week DMBA-treated specimens revealed more than 25% p73-positive keratinocytes, but, in 12 (60%) of the 6-week-treated specimens, more than 25% of the keratinocytes examined were p73-positive. This suggests that the longer the DMBA painting period, the higher the proportion of p73-stained pouch keratinocytes. Furthermore, a p73-dependent mechanism may be associated with the early stages of oral carcinogenesis. Such a mechanism could be very important to an understanding of the participation of p73 in the development of oral squamous-cell carcinomas.

The mRNA expression of inducible nitric oxide synthase in DMBA-induced hamster buccal-pouch carcinomas using reverse transcription-polymerase chain reaction.

BACKGROUND: Three isoforms of NO synthase (NOS) have been identified: endothelial NOS, neuronal NOS, and inducible NOS (iNOS). The enhanced expression of iNOS, at the protein level, has been reported previously in certain chemically induced oral carcinomas in hamster buccal-pouch mucosa, however, the corresponding expression of iNOS, at the mRNA level, has not yet been demonstrated. The purpose of the present study is to assess the iNOS mRNA expression level in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas using a reverse transcription-polymerase chain reaction (RT-PCR). METHODS: Thirty-three outbred, young (six-weeks old), male, Syrian golden hamsters (Mesocricetus auratus) were randomly divided into one experimental group (13 animals) and two control groups (10 animals each). The pouches of a group of 13 animals of the experimental group were bilaterally painted with a 0.5% DMBA solution three times a week for 12 weeks. Each animal of one control group was similarly treated with mineral oil only, while the other control group of 10 animals remained untreated throughout the experiment. RESULTS: Areas of dysplasia and squamous-cell carcinomas, with a 100% tumor incidence, developed for all of the DMBA-treated buccal pouches. The mineral oil-treated and untreated pouches had no obvious changes. A band of 499-bp, corresponding to iNOS mRNA, was present in all the DMBA-treated hamster buccal-pouch mucosa animals, but not in the untreated animals or the animals treated with mineral oil. Upon direct sequencing, this 499-bp band was confirmed to be part of the iNOS gene. CONCLUSIONS: This study demonstrated that increased iNOS mRNA expression could contribute to the mechanism for experimentally induced oral carcinogenesis.