A Rare Case of Peripheral Compound Odontoma and Review of the Literature

Abstract

Peripheral or extraosseous odontogenic tumors are rare oral soft tissue enlargements which demonstrate the same histologic features of their intraosseous counterparts but emerge in gingiva and mucosa. In this paper we report a case of peripheral odontoma in a 12-years-old female patient presented asymptomatic swelling in the palatal site. After the clinical and radiographic examination, excisional biopsy was applied to the lesion located entirely in the soft tissue of maxillary incisors. Histopathologically presence of tooth-like structures containing dentin with regular canals and partly enamel matrix were observed. Our aim is to present the extremely rare case of peripheral odontoma and to review the literature for demonstrating the frequency and clinicopathologic features of this entity.

Introduction

Odontogenic tumors are a heterogeneous group of lesions of diverse clinical behavior and histopathologic types, ranging from hamartomatous lesions to malignancy. The interactions between ectodermal and mesenchymal layers of odontogenic tissues can pioneer odontogenic tumors which are encountered commonly in intraosseous and fewer in soft tissues [1, 2].

Peripheral or extraosseous odontogenic tumors are oral soft tissue enlargements which demonstrate the same histologic features of their intraosseous counterparts but emerge in gingiva and mucosa. Mostly it is believed that it originates from the rests of Serres (remnants of the dental lamina) located supraperiosteally in the gingiva. Various factors like inflammation or trauma may affect proliferation of these remnants [3, 4].

In the current WHO classification, odontomas are classified under the benign odontogenic mixed tumors which descripted as tumour-like malformations (hamartomas) composed of dental hard and soft tissues [5]. This benign entity is subdivided into two types: compound and complex. Compound odontomas are organized tooth-like structures and complex odontomas are amorphous masses of odontogenic tissues with lack of organization. The degree of morpho-differentiation varies [6, 7]. It is thought that WNT/β-catenin pathway activation in embryonic SOX2 positive dental stem cells may play a role in odontoma pathogenesis [8].

Odontomas can rarely occur in extraosseous locations and are termed as peripheral odontomas. These lesions are asymptomatic, have limited growth over time and are not related to bone. It is primarily diagnosed in children without distinct gender predilection [9]. Peripheral odontomas also occur either compound or complex types [10]. To date, there is no consensus about the etiology of peripheral odontomas. One possible suggestion is that soft tissue remnants of the odontogenic epithelium with epithelial-mesenchymal interactions could form tooth-like structures [9, 11].

Peripheral odontomas are quite rare and 16 well-documented cases were reached in the English literature. The aim of this paper is to report a peripheral compound odontoma case and to review the literature for recognition the clinical, radiological and histopathological features of this entity.

Case Report

A 12 years-old female patient referred to our oral surgery clinic with painless, slowly growing swelling on palatal aspect of right incisors. Clinical examination revealed a 0.6 × 0.5 cm hard nodular mass covered with normal colored mucosa. Other than that, the overall medical, social and family histories were unremarkable. No history of trauma or infection was detected. There was no caries and periapical lesions found in the panoramic radiography (Fig. 1A). For further radiographic examination, cone-beam computed tomography (CBCT) was requested. In sagittal sections, radiopaque masses that were entirely located in soft tissue and not related to bone were clearly seen (Fig. 1B). Excisional biopsy was performed and tooth-like structures within their capsules were excised from the palatal mucosa (Fig. 2). The clinical diagnosis of odontoma was raised and macroscopically four oval-round hard tissue specimens in size from 0.2 to 0.3 cm were sent to the pathology department for the evaluation. In the histopathologic sections multiple, small, tooth-like structures containing dentin with regular canals and partly enamel matrix were observed. Ghost cells were also shown in the loose connective tissue surrounding these structures (Fig. 3). Thus, a histopathological diagnosis of peripheral compound odontoma was established. No complication was detected in the control examination. The patient has been undergoing follow-up and no recurrence has been recorded for ten months.

Fig. 1.

A No sign in the panoramic radiography, B in sagittal sections of CBCT, radiopaque masses unrelated to bone were clearly seen (arrows)

Fig. 2.

A Intraoperative appearance and B excisional biopsy specimens

Fig. 3.

A Decalcified histopathologic sections showing a tooth-like hard tissue (thick arrow) and mesenchymal soft tissue (thin arrow), B A tooth-like structure composed by enamel matrix (e) and dentin (d), also ghost cells (g) were observed (H&E ×40, ×200, respectively)

Discussion

Odontomas are benign tumor-like lesions which originate from epithelial and ectomesenchymal components. They are one of the most frequent odontogenic lesions in the series of odontogenic tumors. Clinically 3 types are recognized in the literature: intraosseous, peripheral (extraosseous), and erupted [12]. All types can be found as complex or compound types. Intraosseous odontomas are reported as odontogenic lesions with a frequency of up to 45.8% [13] whereas peripheral odontomas are extremely rare. Peripheral odontomas are more common in the maxilla and usually affect children [14, 15]. Table 1 summarizes the demographic and clinicopathologic features of previously reported peripheral odontoma cases in the literature and the present case.

Table 1.

Previously reported peripheral odontoma cases in the literature

	Author (Year)	Gender/Age	Localization	Clinical diagnosis	Histopathological diagnosis
1	Present case (2021)	Female/12 years	Maxilla, alatal region	Odontoma	Peripheral compound odontoma
2	Da Silva Rocha et al. [10] (2020)	Female/11 years	Maxilla, palatal region	Fibroma	Peripheral compound odontoma
3	De Oliveira et al. [16] (2019)	Male/30 years	Maxilla, anterior region	Maxillary exostosis	Peripheral compound odontoma
4	Custódio et al. [17] (2018)	Female/11 years	Maxilla, anterior region	Peripheral ossifying fibroma, peripheral giant cell granuloma	Peripheral complex odontoma
5	Koneru et al. [26] (2014)	Male/15 years	Maxilla, anterior region	A benign tumor of soft-tissue origin	Peripheral complex odontoma
6	Hanemann et al. [11] (2013)	Female/15 years	Maxilla, anterior region	Peripheral compound odontoma	Peripheral compound odontoma
7	Mikami et al. [14] (2013)	Male/9 months	Maxilla, palatal region	Unspecified	Peripheral developing odontoma
8	Friedrich et al. [15] (2010)	Male/3 years	Maxilla, palatal region	Unspecified	Peripheral developing odontoma
9	Silva et al. [9] (2009)	Male/8 months Male/5 months	Maxilla, palatal region Maxilla, palatal region	Congenital epulis Congenital epulis	Peripheral developing odontoma Peripheral developing odontoma
10	Ide et al. [23] (2008)	Female/7 years	Mandible, lingual region	Unspecified	Peripheral developing odontoma
11	Bernardes et al. [25] (2008)	Male/12 years	Maxilla, anterior region	Pyogenic granuloma, periodontal abscess, and peripheral ossifying fibroma	Peripheral developing compound odontoma
12	Kintarak et al. [19] (2006)	Female/13 years	Maxilla, palatal region	Irritation fibroma	Peripheral developing odontoma
13	Ide et al. [18] (2001)	Male/39 years	Maxilla, anterior region	Peripheral osteoma	Peripheral complex odontoma
14	Ledesma-Montes et al. [4] (1996)	Female/3 years	Mandible/lingual posterior region	Peripheral odontogenic fibroma	Peripheral compound odontoma
15	Giunta and Kaplan [20] (1990)	Female/5 years Male/21 years	Maxilla, palatal region Mandible/lingual posterior region	Periodontal abscess Peripheral odontoma, implanted tooth fragment, or foreign body	Peripheral compound odontoma Peripheral compound odontoma

Various terms have been suggested for this pathology such as peripheral odontoma [11, 16], gingival odontoma [4, 17], gingival peripheral odontoma [18], extraosseous odontoma [19], and soft tissue odontoma [20]. Ide et al. described this entity as peripheral developing odontoma to emphasize its origin, nature, and histopathology [21].

In the previous reviews, erupted odontomas were considered as peripheral odontoma [16]. But these erupted cases are intraosseous odontomas located superficially in bone and then eventually erupt into the oral cavity [18]. There is also debate that peripheral odontomas may erupt if left untreated [11, 22]. However, since there is no periodontal tissue and bone around the peripherally developing odontoma, it does not seem possible to mature into a real tooth and erupt over time. [18, 21].

The etiology of peripheral odontoma is complex. Randomly entrapped dental lamina rests in gingiva may be the reason for peripheral odontoma formation [9, 16, 17, 23]. No consensus has been made about what could be activating these dental lamina remnants and initiate proliferation for the extraosseous counterpart of odontomas. Depending on the developmental stage of the tooth germ, various morphologies can be seen in the peripheral odontoma, including mixed odontogenic lesions without dental hard tissue, developing odontomas, denticles and hard tissue masses without enamel organ [9, 22]. The absence of bone relation clarifies that it develops in the soft tissue, and is different from an erupted odontoma [4]. It has also been suggested that peripheral odontoma may arise from the basal layers of the surface epithelium. [24]. Another possible explanation has been described by Moghadam and Moktari as ectopic neural crest cells with differentiation ability can form tooth germ [22]. In two different reported cases, peripheral compound odontoma encountered in the missing premolar tooth areas and suggested they may arise from permanent tooth germ [11, 20]. Theories for trauma, infection, hereditary influence and genetic mutation were also reported in the literature [25, 26].

Majority of the reported peripheral odontoma cases are asymptomatic and present slowly growing mass. They can be encountered in maxilla or mandible, palatal/lingual or vestibule locations [4, 9, 18, 19, 21]. In the present case, painless swelling of the hard palate was observed.

Radiographies can be requested for further examination of peripheral odontoma to exclude other possible diagnosis. No changes are usually observed in periapical and panoramic radiography [10, 14, 18–20]. However, either it might be seen as irregular tooth-like structures [11] or seen as just radiopaque mass [16, 23]. If the lesion is not detectable in conventional methods, CBCT might be requested for the differential diagnosis [15]. In the current case, CBCT was used to assess the nature of the lesion and showed radiopaque masses entirely localized in soft tissue with no bone contact.

Due to the rarity of peripheral odontoma, it is not usually included in the differential diagnosis of soft tissue lesions [3]. However, the clinical differential diagnosis of peripheral odontoma can include fibroma [10], peripheral giant cell granuloma [17], periodontal abscess or cyst, pyogenic granuloma, misplaced tooth germ [20], reactive fibrous hyperplasia, focal fibrous hyperplasia, and peripheral ossifying fibroma [19]. It is also important to distinguish compound peripheral odontoma from supernumerary teeth. Clinically supernumerary teeth do not grow over time and cause swelling [10].

The treatment modality of peripheral odontoma is local excision. No recurrence has been reported yet to date.

In conclusion, peripheral odontomas are uncommon asymptomatic, slowly enlarging benign lesions in soft tissues of the oral cavity. Compound or complex types can be seen as their intraosseous counterpart. It has a wide clinical differential diagnosis when presented with mucosal swelling. Localization varies but usually occurs in the maxilla anterior region and mostly affects children. It might be detected in conventional radiographies, but CBCT can be requested to ensure. The treatment modality is total excision. Being aware that odontomas can also develop peripherally makes the diagnosis of peripheral compound odontoma easier. In addition, it is important to report all detected cases to reveal the frequency and characteristics of this rare entity.

Funding

The authors declare they have no financial interests.

Data Availability

The data including clinical information, radiograph, and histopathologic preparations are available upon request.

Declarations

Conflict of interest

The authors declare that there is no conflict of interest to disclose.

Ethical Approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institution and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of retrospective case report, formal consent is not required. The tissue included in the manuscript was obtained as part of the standard of care for the patient and retrospectively collected for the case report.