Introduction

Idiopathic osteosclerosis (IO) is described as a non-expansible radiopaque alteration of trabecular bone of unknown origin, asymptomatic, with various shapes and sizes, affecting both the maxilla and the mandible, with higher prevalence in the mandibular molar and premolar region (1-9).

Its radiopacity may resemble other pathologies of the jaws, such as condensing osteitis, root segments, hypercementosis, cementoblastoma, impacted teeth, focal cemento-osseous dysplasia (6, 10), and, on rare occasions, complex odontomas [6]. However, accurate diagnosis can be based on detailed analysis of the lesions’ morphology as shown on radiographs and on clinical signs and symptoms.

The etiology of IO is unclear; traumatic occlusion being a hypothesis (1). Since it can be considered anatomical variation of trabecular bone (1, 5, 8, 10), no therapy is recommended, only radiographic monitoring (7, 8).

Clinicians often refer potential IO cases to radiologists for a second opinion or to surgeons for excision of the lesions. Although commonly found in radiographs, there are few studies on IO. The aim of this retrospective study was to report case series of patients with IO, to review the literature on the subject, and to discuss its main characteristics, diagnosis, differential diagnosis, and treatment.

Material and Methods

The sample consisted of 354 panoramic radiographs of patients who attended a radiology clinic in Maringá-PR, Brazil. Inclusion criteria were radiographs that showed the entire maxilla and mandible (condyles included), had no distortion, no asymmetry, and no error due to inadequate patient positioning for exposure (6). The radiographs were examined by a single dental radiologist on a standard light-box under dimmed lighting. The radiographs were taken for reasons other than IO examination, such as evaluation of third molar extraction, implant placement, or routine procedures.

As in MacDonald-Jankowski (1999) (6), a radiopaque area would be considered an IO when all the following criteria were satisfied:

1. Symptomless (8);

2. Not a mixed radiolucent-radiopaque lesion with the appearance of a fibro-osseous lesion (1, 11) or an odontoma (6);

3. Not directly associated with deep caries or large restorations (8, 9);

4. Not a thickening of the lamina dura (1, 11);

5. Not surrounded by a radiolucent halo (5);

6. Not associated with resorption of the adjacent teeth (6);

7. No evidence of displacement of the inferior alveolar canal, maxillary sinus floor or adjacent teeth to the lesion, suggesting an expansive lesion (2);

8. When remnants of deciduous or permanent teeth were clearly identifiable and excluded from the diagnosis (8);

9. Not typical of any other condition (3).

Results

Twenty-two foci of IO were identified in 20 out of the 354 patients—around 5.6% of the sample. Patients’ age and sex, and size, shape and location of the IOs are shown in Table 1. All patients were healthy with age ranging from 5 to 51 years (mean age = 29.8), and a male-female ratio of 3:2. Prevalence of IO did not show statistical differences for the variables age and sex. Of the 22 foci, 19 (95%) occurred in the mandible and, of those, 57% were in the molar region.

Most IOs were located in the premolar/molar region, at the root apices, between the roots, away from the teeth, laterally to the tooth, and in edentulous areas (Figures 1-5). They were equally distributed between right and left sides of the jaws. With the exception of one IO in the maxilla, between the premolars (Figure 3C), the remaining foci were in the mandible, with a statistical higher prevalence for the latter (p<0.01). Two cases occurred in the lower canine region (Figure 1D/1G).

Figure 1 Size, shape and localization of IOs in the mandible. The upper row displays radiographs of right side and the lower rows of the left side. A: 3mm-rounded IO near the first molar apex (female, 32 years); B: 5mm-ovoid IO away from the teeth (female, 43 years); C: 1.3cm-irregular shaped IO between premolar and molar (male, 19 years); D: 7mm-rounded IO away from the teeth, in the canine/premolar region (male, 21 years); E: 1cm-irregular shaped IO between the roots of deciduous molar (female, 7 years); F: 1cm-triangular IO in an edentulous area laterally to the second premolar region (female, 22 years); G: 1.2cm-elliptical IO in the canine region (male, 18 years); H: 11mm-rounded IO in the first premolar apex (male, 23 years).

Figure 5 Panoramic radiographs of two patients with two IOs (arrows) each in the mandible. A: female, 33 years; B: female, 21 years.

Figure 3 Radiographs of IOs and of root segments. A: IO in an edentulous area of the mandible (male, 43 years); B: root segment of mandibular molar; C: IO in the maxilla (female, 40 years); D: root segment of maxillary molar.

The radiographs showed IOs as localized, well-defined non-expansible radiopaque areas, mostly round or ovoid in shape but sometimes irregular. In some cases IOs were similar to condensing osteitis (Figure 2) or residual roots (Figure 3A).

Figure 2 IOs in the apices of healthy teeth (white arrows), which may be misdiagnosed as condensing osteitis (black arrows). A: female, 22 years; B: male, 20 years; C: male, 17 years; D: male, 22 years.

Of the 20 patients, 18 had one IO and 2 had two IOs in the mandible (Figure 4, 5). Two patients had lesions often included in the differential diagnosis of IO: a complex odontoma and a focal cemento-osseous dysplasia (Figure 6).

Figure 4 IOs (arrows) in patients differing in age; A: 5 years-old male patient, molar area; B: 51 years-old male patient, edentulous area.

Figure 6 Differential diagnosis of IOs. A: residual root (white arrow), complex odontoma (dashed arrow), IO (black arrow) (male, 37 years); B: focal cemento-osseous dysplasia (white arrow), IO (black arrow) (male, 41 years).

All IOs were asymptomatic and detected on panoramic radiographs. Some cases required periapical radiographs to confirm the diagnosis. Radiographic monitoring was the only management recommended for all cases, which showed no further complications.

Discussion

Austin and Moule (1984) (14) used the term osteosclerosis in 1984 to describe regions with increased bone density not directly related to infections or systemic diseases. They used bone sclerosis as a general term to describe areas of increased bone formation which lead to increased radiopacity. Although these bone alterations have several synonyms, such as bone sclerosis (14), dense bone island (3, 7, 15, 17), bone scar, focal periapical osteopetrosis, or enostosis [7], IO is often preferred because of their unknown origin (1, 2, 5, 6, 8, 10-12, 18-21).

Although the term idiopathic describes a lesion of unknown etiology, Goaz and White (1999) (4) assert that IO may be the result of retained deciduous molar roots that have been resorbed and replaced by sclerotic bone. In addition, there is evidence of association between increasing incidence of IO and colorectal cancer or adenoma (19), and some authors believe that IO is caused by traumatic occlusion [1]. Marques-Silva et al. (2007) (12) claim that IO may cause changes in tooth position or problems during orthodontic treatment, and reported a case of tooth resorption caused by ectopic eruption rote caused by IO (12). However, IO is usually considered a developmental variation of normal bone architecture unrelated to local stimuli (1, 5, 8, 10, 20), a viewpoint with which the authors of the present study agree. The cases reported in this study showed that IOs did not cause any harm to the patients, and no specific etiology was associated with the lesions.

Studies showed that the prevalence of IO varied from the lowest 1.96% among Greeks (13) to the highest 31% in a Chinese/Indo-Chinese population (14). The present study found an incidence of 5.6% in a Brazilian sample, with a male-female ratio of 3:2 that did not prove significant. Although some studies found higher prevalence of IO among women (3, 9, 10, 21), most found no significant difference between sexes (1, 2, 5, 6, 8, 11, 14-16, 18, 20). As for age, IO may occur in any stage [8], although it is more frequently found in the third and fourth decades of life (2, 3, 8, 10). In the present study, IO was found in patients ranging in age from 5 to 51 years.

On radiographic evaluation, IO is often round, elliptical or irregular in shape, with size varying from 2-3mm to 7 cm (1, 14, 16), although it may encompass the whole body of the mandible (6, 15). In the present study, the biggest IO measured 1.8cm and, similar to previous research, the lesions were found in different areas: near the root apices, between teeth, away from or adjacent to the teeth (6). Higher incidence of IO in the mandibular molar and premolar region was found in this study, as previously described (2, 9-11, 13, 15, 18, 20).

Since IO can be found near root apices (6) and tend to be associated with changes in the lamina dura, Petrikowski et al. (1997) (16) assert that IO may be misdiagnosed, given that on radiograph other lesions show similar characteristics. Condensing osteitis is one possibility in differential diagnosis of IO (10-12, 20). Although condensing osteitis also develops in the periapical areas, it is a response to a low-grade inflammatory stimulus, such as deep caries, large restoration, or pulpitis, and the associated teeth are usually non-vital or show considerable inflamed pulps. IOs, on the other hand, are developmental variations of normal bone unrelated to local stimuli (10, 20). In the present study, six IOs were near tooth apices (Figures 1H, 2, 6B), some being very similar to condensing osteitis. However, the associated teeth were healthy or had shallow restorations.

Other differential diagnoses of IO are root segments, exostosis, hypercementosis, foreign bodies, fibro-osseous lesions, odontomas, cementoblastomas, and even impacted teeth should be taken into consideration (6, 10-13). In this study, one case of IO in an edentulous area resembled root segment (Figure 3A), accurately diagnosed as IO through periapical radiographs.

Although IO can be found either in the maxilla or the mandible, the higher prevalence of IO in the inferior molar region (2, 3, 5, 8, 15, 16) may contribute to the diagnosis of IO. Differentiation of IO from root segments should take into consideration extraction history and lines of a residual root fragment, while accurate images of impacted teeth are enough to confirm the difference (10).

IOs are likely to undergo changes in a young population, showing potential to expand over time (16). Sclerotic lesions can either expand or stabilize (11). However, it is unclear whether periodic monitoring is sufficient or whether they should be considered insignificant findings and simply disregarded. The present study does not elucidate the matter, as monitoring is not an objective of the study.

Because IOs are not clinically significant, being asymptomatic and usually incidentally discovered on radiographs, it is difficult to determine their manifestation. In this study, all IOs were primarily diagnosed on panoramic radiographs, while few cases needed periapical radiographs to confirm the diagnosis. Diagnosis was based on bone morphology, no expansion or radiolucent halo, and lack of symptoms. The literature review showed that only three studies used conventional or cone beam computed tomography (CBCT) to diagnose IO (5, 9, 17). Araki et al. (2011) [9] state that CBCT may reveal the initial aspect of bone sclerosis, and Yonetsu et al. (1997) (5) affirm that CBCT allows the investigation of the internal density of IOs. However, clinical routine still uses panoramic radiograph as one of the main imaging examinations.

Although IO may cause root resorption, nerve compression, dental impaction, dental displacement, and difficulties in orthodontic movement (12), these are rare consequences, not found in this study. Because IOs are asymptomatic, not expansive, and with limited growth, surgical intervention is not recommended, while radiographic monitoring is suggested (7).

Conclusion

Incidence of IO in the Brazilian sample was 5.6%, age ranging from 5 to 51 years (mean=29.8), and male-female ratio of 3:2. The radiopaque lesions occurred in different locations, with significantly higher incidence in the mandible. The findings and the literature review corroborate the hypothesis that IO should be considered developmental variation of normal bone that do not require treatment.