# Oral Fibroma: Pathology, Features, and Differential An oral fibroma is a benign, localized nodule of dense fibrous connective tissue covered by stratified squamous epithelium, most often arising in the oral cavity as a reactive response to chronic mechanical irritation. The term irritation fibroma (also written irritational fibroma) is the preferred name for this reactive lesion, and it is distinct from true fibroblastic neoplasms such as fibrosarcoma and from virally driven epithelial lesions such as papilloma. This lesion matters because it sits at the center of a common clinical problem. A firm, smooth, mucosa-colored lump in a dog's or cat's mouth is one of the most frequent reasons for an oral biopsy, and the same gross appearance can represent a reactive nodule, a benign neoplasm, or an early malignant tumor. Getting the diagnosis right changes the treatment and the prognosis. The oral cavity is also a site where reactive and neoplastic fibrous lesions overlap heavily in name and appearance, so a working knowledge of irritation fibroma keeps you from over-treating a harmless nodule or under-treating a fibrosarcoma. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## What an Oral Fibroma Actually Is The irritation fibroma is a reactive, non-neoplastic proliferation of fibrous tissue. It develops where oral mucosa is repeatedly traumatized: a tooth that bites the cheek, a sharp or fractured tooth, an ill-fitting appliance, a diastema that the tongue rubs against, or a chronic chewing habit. The lesion is a response to that injury, not a clone of transformed cells. The word "fibroma" is used loosely in both human and [veterinary medicine](/blog/careers/veterinary-medicine-careers-from-clinical-practice-to-public-health). In strict terms, a fibroma is a benign tumor of fibrous connective tissue. In practice, most lesions called fibroma in the mouth are reactive fibrous nodules, which is why the qualifier "irritation" or "irritational" is added. The most common sites are the buccal mucosa and the tongue, followed by the lip, hard palate, and gingiva [1][2]. A lesion at the site of a known bite is sometimes called a biting fibroma, and the clinical history of a prior tooth bite or chronic biting injury is a useful diagnostic clue [2]. The lesion is usually asymptomatic, small, mucosa-colored, and either pedunculated (on a stalk) or sessile (broad-based) [2]. It is typically solitary, though multiple lesions can occur [2]. Because it grows slowly and does not invade, most animals present for a cosmetic or mechanical problem rather than systemic illness. ### Reactive Nodule Versus True Neoplasm The central concept to hold onto is that irritation fibroma is a reactive process. Reactive lesions are polyclonal, driven by local factors, and they stop growing when the stimulus is removed. True neoplasms are clonal and grow autonomously. This distinction is not just academic. It determines whether removing the local cause is enough or whether you need wide margins and staging. A retrospective study of 659 reactive oral lesions found that inflammatory fibrous hyperplasia was the most common reactive lesion (47%), followed by pyogenic granuloma (27.16%), with peripheral giant cell granuloma the least common (1.6%) [3]. Most reactive lesions were 0.5 to 1 cm, most were present for less than one year, and 87.2% of patients had poor oral hygiene [3]. Recurrence occurred in 13.5% of surgically excised reactive lesions [3]. That recurrence figure is a reminder that removing the lump without removing the cause invites the lesion back. ## Etiology and Pathogenesis Chronic, low-grade mechanical irritation is the driving force. Reported triggers include repeated biting, sharp teeth, ill-fitting dentures or appliances, and chewing habits such as betel nut or tobacco use in human patients [1]. In veterinary patients, the analogous triggers are malocclusion, fractured or sharp teeth, foreign bodies, and repetitive chewing on cage bars or hard objects. A diastema between the mandibular incisors has been documented as a source of chronic trauma that produced a tongue-tip irritation fibroma [4]. The pathogenesis follows a predictable sequence: 1. Repeated mechanical injury to the mucosa causes local inflammation. 2. Fibroblasts and myofibroblasts are recruited and deposit collagen. 3. The collagen matures and organizes into a dense, well-circumscribed nodule. 4. The overlying epithelium responds with hyperplasia, hyperkeratosis, or atrophy, depending on the local forces. 5. If the irritant persists, the nodule enlarges. If the irritant is removed, growth stops and the lesion may partially regress. One study examined why irritation fibroma rarely ulcerates despite continuous trauma. Using CD31 and Ki-67 immunostaining in 17 buccal mucosa cases, the authors found that the number and area of blood vessels in the superficial lamina propria just below the lesion epithelium were smaller than at the margin, while the deep lamina propria vascular network was maintained [5]. The authors proposed that the deep vascular network compensates for nutrient supply to the covering epithelium, which helps explain the absence of ulceration [5]. This is a good example of how a reactive lesion adapts its local blood supply rather than breaking down. ## Gross and Microscopic Features ### Gross Appearance An irritation fibroma is a well-circumscribed, dome-shaped or polypoid nodule. It is firm on palpation, smooth-surfaced, and usually the same color as the surrounding mucosa, though it may be paler if the epithelium is hyperkeratotic [2]. It can be sessile or pedunculated. Size varies widely. Most reactive oral lesions measure 0.5 to 1 cm [3], but large lesions occur. One report described a 2.2 cm smooth, well-circumscribed nodule on a stalk attached to the hard palate [6], and another described a 16 by 20 by 11 mm pedunculated mass on the anterior hard palate [7]. These larger examples show that size alone does not distinguish reactive from neoplastic. ### Histology The classic histologic picture has two components: - **Stroma:** A mass of dense, well-circumscribed fibrous connective tissue. Collagen fibers are thick and interwoven. Cellularity is low, meaning there are relatively few fibroblasts and they are widely spaced. This low cellularity is a key feature that separates irritation fibroma from fibrosarcoma. - **Epithelium:** Stratified squamous epithelium covers the nodule. It may show hyperplasia, hyperkeratosis, or acanthosis (thickening of the epithelial layer). Focal low-to-medium grade hyperplasia and hyperkeratosis were reported in a hard palate case [6]. In another case, histopathology showed a fibrous nodule covered by stratified squamous epithelium with hyperkeratosis and acanthosis [7]. Inflammatory cells may be scattered through the stroma, especially near the surface, reflecting the chronic irritation. Some lesions show myxoid (mucoid) change in the stroma. A denture-related irritation fibroma with prominent myxoid stromal change was reported, with Alcian blue staining showing diffuse stromal positivity [7]. Myxoid change is a stromal variation, not a sign of malignancy. A useful immunohistochemical finding: in that myxoid case, the lesional stroma was negative for broad-spectrum cytokeratin while the epithelium was diffusely positive, and the Ki-67 labeling index was very low [7]. This pattern supports a mesenchymal (fibrous) origin for the stroma and confirms low proliferative activity. ### The Gingival Variant and Ossification Peripheral oral fibromas of the gingival and alveolar mucosa are a distinct subgroup. They are localized, cellular, small fibrous nodules, and some contain a central nidus of metaplastic woven bone, which defines the ossifying variant [8]. A study of 28 gingival peripheral oral fibromas found strong to moderate diffuse nuclear SATB2 immunoreactivity in all 10 ossifying lesions (100%) and in 8 of 18 non-ossifying lesions (44%), but in only 1 of 28 (3%) reactive fibrous lesions from non-gingival intraoral sites [8]. SATB2 is an osteoblastic transcription and differentiation factor. The authors proposed that gingival peripheral oral fibromas originate from periodontal ligament and that this origin explains their frequent ossification [8]. They also warned that this SATB2 positivity must be considered when assessing biopsies of SATB2-positive oral neoplasms to avoid misinterpretation [8]. In dogs, a related entity has been described. A case series of 27 lesions proposed the name gingival mucoperiosteal fibroma (GMPF) for benign fibrous masses characterized histologically by a lack of odontogenic tissue and various degrees of ossification [9]. These lesions affected adult dogs with an average age of 95 months (range 24 to 156 months), appeared as expansile growths with a superficial appearance matching the surrounding gingiva, and most commonly involved the mandibular incisive region (13 of 27 cases) [9]. Bone proliferation was seen radiographically in 14 cases and histologically in 17 lesions, though bony invasion by the mass was not noted [9]. Surgical resection was curative in all cases when performed, with no recurrence at follow-up [9]. This is a veterinary-specific entity that should be on the differential for gingival fibrous masses in dogs. ## Species Differences Species patterns matter for the differential list. **Dogs.** Oral tumors and tumor-like lesions are common. In a retrospective study of 486 oral cavity lesions in dogs and cats, 29.11% of canine lesions were benign tumors, 24.12% were hyperplastic lesions, and 14.7% were inflammatory lesions [10]. Among canine cases, gingival hyperplasia was diagnosed in 23.24% and peripheral odontogenic fibroma in 19.12% [10]. A separate Swiss study of 773 histopathologically confirmed canine oral neoplasms found that benign tumors made up 63%, with peripheral odontogenic fibroma the most common benign tumor (77.8% of benign tumors) [11]. Those figures are about neoplasms specifically, and they show that fibrous and fibro-osseous lesions dominate the benign oral mass category in dogs. The gingival mucoperiosteal fibroma adds another fibrous entity to the canine list [9]. **Cats.** In the same 486-case study, only 4.79% of feline lesions were benign tumors, 15.07% were hyperplastic, and 57.53% were inflammatory [10]. Chronic lymphoplasmacytic stomatitis accounted for 43.84% of feline cases [10]. This means that in cats, an oral mass is more likely to be inflammatory than neoplastic, and reactive fibrous lesions fit within that inflammatory and hyperplastic spectrum. **Cattle.** Oral fibroma is rare in cattle. The literature is dominated by case reports in dogs, cats, and humans, and the comparative burden of reactive oral fibrous lesions in cattle is low. When a bovine oral mass is encountered, other differentials (including infectious and neoplastic processes) should be weighted more heavily. This is a genuine species difference in prevalence, not a statement that the lesion cannot occur. **Other species.** A trauma-induced fibroma was documented in an Indo-Pacific bottlenose dolphin with a mandibular deformity and a long-standing oral mass. Histopathology showed prominent fibroblast proliferation and collagen deposition, and fibropapillomas and desmoid tumors were excluded by viral detection assays and beta-catenin accumulation analysis, supporting a reactive fibrotic rather than malignant phenotype [12]. This case reinforces the reactive nature of the lesion when the cause is identifiable trauma. ## Differential Diagnosis The differential for a firm oral nodule is broad. The table below compares the lesions most often confused with irritation fibroma. | Lesion | Etiology | Histology | Behavior | Treatment | |--|--|--|--|--| | Irritation fibroma | Chronic mechanical irritation | Dense, well-circumscribed collagen, low cellularity, few fibroblasts, covered by squamous epithelium | Benign, reactive, non-invasive, may recur if cause persists | Excision plus removal of the irritant | | Papilloma | Viral (papillomavirus) | Epithelial proliferation, finger-like projections, koilocytes, cytokeratin positive | Benign, often self-limiting, contagious | Often regresses. Excision if persistent or obstructive | | Fibrosarcoma | Neoplastic, clonal | Spindle cells, high cellularity, pleomorphism, mitotic figures, invasive | Malignant, locally invasive, may metastasize | Wide surgical excision, staging | | Peripheral odontogenic fibroma | Odontogenic origin | Fibrous stroma with odontogenic epithelium or inductive tissue | Benign, neoplastic | Excision | | Gingival mucoperiosteal fibroma (dog) | Uncertain, likely reactive or developmental | Poorly cellular fibrous tissue, thick interwoven collagen, variable ossification, no odontogenic tissue | Benign, expansile, non-invasive | Surgical resection, curative in reported cases | | Ossifying fibroma | Fibro-osseous, intraosseous | Fibrous matrix with mineralization and ossification, well-circumscribed and radiopaque | Benign but can be locally aggressive | Excision, imaging follow-up | | Pyogenic granuloma | Reactive, often vascular | Lobular vascular proliferation with inflammation | Benign, reactive, bleeds easily | Excision plus removal of cause | The most important distinctions to make are between irritation fibroma and papilloma, and between irritation fibroma and fibrosarcoma. ### Irritation Fibroma Versus Papilloma Papilloma is an epithelial lesion, not a fibrous one. It is caused by papillomavirus and shows epithelial proliferation with finger-like projections on histology. The stroma is a supporting element, not the primary proliferation. Irritation fibroma is the reverse: the stroma is the lesion and the epithelium is a covering. Immunohistochemistry separates them cleanly. Papilloma is cytokeratin positive in the proliferating cells. Irritation fibroma is cytokeratin negative in the stroma, with cytokeratin positivity confined to the overlying epithelium as an internal control [7]. Clinically, papillomas are often multiple, may have a cauliflower-like surface, and frequently regress spontaneously. Irritation fibromas are usually solitary, smooth, and persist until the irritant is removed. ### Irritation Fibroma Versus Fibrosarcoma This is the distinction with the highest stakes. Fibrosarcoma is a malignant spindle cell neoplasm. It is more cellular than irritation fibroma, shows pleomorphism (variation in cell and nuclear size and shape), and has mitotic figures. It invades local tissue rather than pushing it aside. Irritation fibroma is paucicellular, has bland uniform fibroblasts, and is well-circumscribed. The low Ki-67 labeling index in irritation fibroma [7] contrasts with the higher proliferation expected in fibrosarcoma. In dogs, fibrosarcoma accounted for 8% of malignant oral tumors in one Swiss series [11], so it is a real entity and not a rare curiosity. ### Irritation Fibroma Versus Oral Fibromatosis Oral fibromatosis is a separate proliferative entity. It is not simply a large irritation fibroma. Fibromatosis refers to a group of locally aggressive, non-metastasizing fibrous proliferations that infiltrate surrounding tissue and have a higher recurrence rate than reactive nodules. The key difference is the growth pattern: irritation fibroma is well-circumscribed and pushes tissue aside, while fibromatosis infiltrates. This distinction changes surgical planning, because fibromatosis requires wider margins to achieve control. Do not use the terms interchangeably. ### The Spindle Cell Problem Any oral biopsy showing a spindle [cell proliferation](/blog/guides/cell-proliferation) raises the question of a mesenchymal neoplasm. Immunohistochemistry helps. Vimentin is a mesenchymal marker and is positive in fibrous lesions. Cytokeratin is an epithelial marker and is negative in the stroma of irritation fibroma, with positivity in the overlying epithelium serving as an internal control [7]. This combination (vimentin positive, cytokeratin negative) supports a fibrous rather than epithelial origin. It does not by itself distinguish reactive from malignant. That distinction rests on cellularity, pleomorphism, mitotic activity, and the presence or absence of invasion. ## How the Diagnosis Is Made in Practice Diagnosis is a three-part process: clinical assessment, biopsy with margin evaluation, and histopathology with immunohistochemistry when needed. ### Clinical Assessment Start with the history. Ask about duration, growth rate, and any known trauma such as biting, chewing habits, malocclusion, or a diastema [4]. Examine the entire oral cavity, not just the visible mass. Look for the source of irritation. A sharp tooth, a fractured tooth, or an ill-fitting appliance may be sitting right next to the lesion. Palpate the lesion and note whether it is firm, movable, and well-circumscribed or fixed and infiltrative. Note the size and whether it is pedunculated or sessile. ### Biopsy and Margin Evaluation Excisional biopsy is both diagnostic and therapeutic for irritation fibroma. The lesion should be removed with a margin of normal tissue, and the base should be addressed to reduce recurrence. In one palatal case, the base of the lesion was cauterized to prevent recurrence [1]. In another, the lesion was excised with a 2 mm safety margin at the stalk and subperiosteal dissection [7]. Margin evaluation matters because it tells you whether the lesion was completely removed and whether the growth pattern was circumscribed or infiltrative. An infiltrative pattern pushes you toward fibromatosis or a malignant neoplasm. Submit the tissue in formalin with a description of the site and orientation. If the lesion is large or the diagnosis is uncertain, an incisional biopsy may be done first. In one case, an incisional biopsy revealed moderate epithelial dysplasia, which changed the management plan before definitive excision [7]. That example shows why histopathology should guide the next step rather than assuming every firm nodule is a simple fibroma. ### Immunohistochemistry Immunohistochemistry is used when the histologic picture is ambiguous or when a spindle cell neoplasm is on the differential. The panel typically includes: - **Vimentin:** Positive in fibrous stroma, confirming mesenchymal origin. - **Cytokeratin:** Negative in the stroma of irritation fibroma, positive in the overlying epithelium as an internal control [7]. - **Ki-67:** Low labeling index in irritation fibroma, reflecting low proliferative activity [7]. - **SATB2:** Positive in gingival peripheral oral fibromas, especially ossifying variants, and useful for identifying the gingival subset [8]. The cytokeratin result deserves emphasis. Broad-spectrum cytokeratin negativity in the lesional stroma, with diffuse epithelial positivity as an internal control, is a clean way to confirm that the proliferation is mesenchymal and not epithelial [7]. This is exactly the pattern that separates irritation fibroma from papilloma and from epithelial malignancies. ### What About Viral Co-infection? Several studies have looked for viral genomes in oral irritation fibroma as a comparison group for oral cancer research. Merkel cell polyomavirus DNA was detected in 30.6% of irritation fibroma samples in one study [13], and Epstein-Barr virus EBER sequences were detected in 3 of 36 irritation fibroma cases (8.3%) [14]. Co-infection with multiple viruses has also been examined in oral cavity lesions [15]. These findings are about viral detection in tissue, not about causation. There is no evidence that these viruses cause irritation fibroma, and the lesion remains a reactive process. The viral data are relevant mainly because irritation fibroma is used as a non-malignant comparison tissue in oral oncology research. ## Clinical Relevance, Limitations and Common Mistakes The clinical relevance of irritation fibroma is straightforward: it is a benign lesion that is cured by removing the lesion and the cause. The main risk is misdiagnosis. A reactive nodule that is actually a fibrosarcoma will recur and progress if treated as a simple fibroma. A papilloma that is excised unnecessarily is a minor harm, but a papilloma mislabeled as a fibroma may lead to unnecessary concern about contagion. Common mistakes students and clinicians make: 1. **Assuming every firm oral nodule is a fibroma.** The differential includes papilloma, fibrosarcoma, peripheral odontogenic fibroma, ossifying fibroma, and pyogenic granuloma. Histopathology is required. 2. **Skipping the search for the irritant.** If the cause is not removed, recurrence is likely. The 13.5% recurrence rate for excised reactive lesions [3] reflects this. 3. **Confusing irritation fibroma with oral fibromatosis.** Fibromatosis is infiltrative and locally aggressive. The terms are not interchangeable. 4. **Over-relying on gross appearance.** A 2.2 cm palatal nodule [6] and a 16 by 20 by 11 mm palatal mass [7] were both reactive fibromas. Size does not rule out a reactive lesion. 5. **Ignoring species patterns.** In cats, oral masses are more often inflammatory than neoplastic [10]. In dogs, fibrous and fibro-osseous benign tumors are common [10][11]. These patterns should shape the differential list. 6. **Forgetting the gingival subset.** Gingival peripheral oral fibromas can ossify and express SATB2 [8]. In dogs, gingival mucoperiosteal fibroma is a recognized entity [9]. A gingival fibrous mass is not the same as a buccal mucosal irritation fibroma. 7. **Treating immunohistochemistry as optional.** When the histology is ambiguous, vimentin and cytokeratin staining clarify the lineage, and Ki-67 helps assess proliferation [7]. Limitations: this article covers the pathology and differential of oral fibroma in domestic species. It does not cover surgical technique in detail, and it does not provide treatment protocols for malignant lesions. Individual cases require a veterinarian who can examine the patient, review the history, and interpret the biopsy in context. ### Quick Review - Irritation fibroma is a reactive, non-neoplastic fibrous nodule caused by chronic mechanical irritation. - Histology shows dense, well-circumscribed collagen with low cellularity and few fibroblasts, covered by squamous epithelium. - Common sites are buccal mucosa, tongue, lip, hard palate, and gingiva. - Vimentin positive and cytokeratin negative in the stroma confirms a fibrous origin. Ki-67 is low. - Papilloma is epithelial and viral. Fibrosarcoma is malignant and cellular. Fibromatosis is infiltrative. - Gingival peripheral oral fibromas may ossify and express SATB2. In dogs, gingival mucoperiosteal fibroma is a distinct entity. - Excision plus removal of the irritant is curative. Recurrence follows persistent irritation. ## Frequently Asked Questions ### What causes an irritation fibroma? Chronic mechanical irritation is the cause. Repeated biting, sharp teeth, malocclusion, a diastema, or a chewing habit traumatizes the mucosa, and the fibrous nodule forms as a reactive response. Removing the source of irritation is part of treatment. ### Is an oral fibroma cancer? No. An irritation fibroma is a benign reactive lesion, not a cancer. It does not invade or metastasize. However, other oral masses can look similar and be malignant, so histopathology is needed to confirm the diagnosis. ### How do you tell a fibroma from a papilloma? Papilloma is an epithelial lesion caused by papillomavirus, while irritation fibroma is a fibrous lesion caused by trauma. On histology, papilloma shows epithelial proliferation and is cytokeratin positive. Irritation fibroma shows a dense fibrous stroma that is cytokeratin negative, with cytokeratin positivity only in the overlying epithelium. ### What is oral fibromatosis? Oral fibromatosis is a separate proliferative entity, not a synonym for irritation fibroma. It is an infiltrative fibrous proliferation that is locally aggressive and has a higher recurrence rate. The infiltrative growth pattern distinguishes it from the well-circumscribed irritation fibroma. ### Are oral fibromas common in dogs and cats? Yes. Oral masses are common in dogs and cats, and reactive and hyperplastic lesions make up a large share of them. In cats, inflammatory lesions are especially common. In dogs, benign fibrous and fibro-osseous tumors are frequent. Oral fibroma is rare in cattle. ### Does an oral fibroma need to be removed? Excision is the standard treatment, and it is usually curative when the irritant is also removed. Small asymptomatic lesions may be monitored, but a biopsy is needed to confirm the diagnosis. Recurrence is possible if the source of irritation persists. ## Related Articles - [Chronic Inflammation: Causes and Morphologic Features](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/chronic-inflammation-causes-and-morphologic-features) - [Differential Diagnosis in Pathology: A Structured Approach](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/differential-diagnosis-in-pathology-a-structured-approach) - [What To Do If Your Dog Is Stung By A Bee In The Mouth](/knowledge/veterinary-medicine/dental-care/what-to-do-if-your-dog-is-stung-by-a-bee-in-the-mouth) - [Dog Stung By Bee In Mouth](/knowledge/veterinary-medicine/dental-care/dog-stung-by-bee-in-mouth) - [Chicken Pox in Humans: Etiology, Clinical Features, and Differential Diagnosis from Avian Diseases](/knowledge/bacteria/wildlife-bacteria/chicken-pox-virus-human-variants-differential) - [Multiplex Real-Time RT-PCR for Differential Diagnosis of Porcine Respiratory Pathogens in Oral Fluids](/knowledge/diagnostics/molecular/multiplex-real-time-rt-pcr-porcine-respiratory-pathogens-oral-fluids) - [Horse Pill: How to Give Oral Medication to Horses](/knowledge/veterinary-medicine/pet-medication-guide/horse-pill-how-to-give-oral-medication-to-horses) - [Brain Herniation: Types and Pathology](/knowledge/veterinary-medicine/veterinary-pathology-microbiology/brain-herniation-types-and-pathology) ## Sources 1. [A Large Irritation Fibroma of the Hard Palate: A Rare Clinical Entity.](https://pubmed.ncbi.nlm.nih.gov/39006648/) 2. [Biting Fibroma of the Lower Lip: A Case Report and Literature Review on an Irritation Fibroma Occurring at the Traumatic Site of a Tooth Bite.](https://pubmed.ncbi.nlm.nih.gov/36620845/) 3. [Reactive lesions of oral cavity: A retrospective study of 659 cases.](https://pubmed.ncbi.nlm.nih.gov/29456298/) 4. [Irritation Fibroma on the Tongue Tip Associated With Mandibular Incisors Diastema in a 53-Year-Old Woman: A Case Report.](https://pubmed.ncbi.nlm.nih.gov/41202000/) 5. [Histopathological analysis of the association between mucosal epithelial changes and the lamina propria vascular network in irritation fibroma.](https://pubmed.ncbi.nlm.nih.gov/34280532/) 6. [Large irritation fibroma of hard palate: a case report of a rare clinical entity.](https://pubmed.ncbi.nlm.nih.gov/33889227/) 7. [Denture-Related Irritation Fibroma With Myxoid Change of the Anterior Hard Palate: A Clinicopathologic Case Report.](https://pubmed.ncbi.nlm.nih.gov/42017097/) 8. [SATB2 is frequently expressed in ossifying and non-ossifying peripheral oral fibroma of the gingival region but not in reactive fibromatous lesions from other intraoral sites.](https://pubmed.ncbi.nlm.nih.gov/32252013/) 9. [Gingival Mucoperiosteal Fibroma-Clinical, Imaging, and Histological Review of a Novel Oral Fibroma in 27 Dogs.](https://pubmed.ncbi.nlm.nih.gov/39042866/) 10. [Canine and Feline Oral Cavity Tumours and Tumour-like Lesions: a Retrospective Study of 486 Cases (2015-2017).](https://pubmed.ncbi.nlm.nih.gov/31690420/) 11. [A retrospective analysis of oral tumors in dogs in Switzerland identifies peripheral odontogenic fibroma and melanoma as the predominant tumor types.](https://pubmed.ncbi.nlm.nih.gov/39442534/) 12. [From traumatic oral fibroma to fatal pneumonia: a multidisciplinary postmortem investigation in a long-term monitored Indo-Pacific bottlenose dolphin (Tursiops aduncus).](https://pubmed.ncbi.nlm.nih.gov/42365389/) 13. [Prevalence of Merkel Cell Polyomavirus (MCPyV) in the Oral Cavity Biopsies in Northern Iran.](https://pubmed.ncbi.nlm.nih.gov/34967573/) 14. [Detection of Epstein-Barr virus encoded small RNA genes in oral squamous cell carcinoma and non-cancerous oral cavity samples.](https://pubmed.ncbi.nlm.nih.gov/34615503/) 15. [Prevalence of Co-infection by Human Papillomavirus, Epstein- Barr Virus and Merkel Cell Polyomavirus in Iranian Oral Cavity Cancer and Pre-malignant Lesions.](https://pubmed.ncbi.nlm.nih.gov/36397808/)