Follow-up of idiopathic osteosclerosis on cone-beam computed tomography: a retrospective longitudinal study

Abstract

This study aimed to investigate the cone-beam computed tomography (CBCT) follow-up of adult patients with asymptomatic, incidentally encountered idiopathic osteosclerosis (IO) to demonstrate its natural course. Retrospectively, 37 patients (mean age, 40.5 years; 19 females and 18 males) with mandibular IO were included, based upon clinico-radiological features. Inclusion criteria were a baseline and at least one follow-up CBCT scan after 12 months or later, no periapical inflammatory lesion, and no previous endodontic or surgical treatment in the respective dentate region. Changes of maximum axial and cranio-caudal diameter and morphology (tooth relationship, lesional shape, radiodensity, endosteum and mandibular canal relationship, root resorption) were evaluated in 45 lesions and descriptively analyzed. The interreader agreement was calculated for diameter and morphological evaluation by intraclass correlation coefficient (ICC) and weighted κ statistics, respectively. The results showed that none of the lesions changed in diameter nor in morphology within the respective follow-up (mean, 19.0 months, maximum 96.0 months). Overall, there was high interreader agreement (up to ICC = 0.854, and weighted κ = 1). In conclusion, on CBCT, IO morphometrics and morphology may naturally remain unchanged in asymptomatic adults, even after up to eight years of follow-up. Consequently, once the diagnosis of IO has been established, CBCT follow-up might not be justified to prevent imaging overuse, which is associated with an excess of ionizing radiation exposure.

Introduction

Idiopathic osteosclerosis (IO) of the jawbones, also known as a dense bone island or enostosis, is a common and incidentally encountered benign intra-osseous lesion^{1, 2, 3–4}. A possible underlying developmental alteration of endochondral ossification has been discussed^{3, 4–5}. IO is mostly radiographically depicted in young adults with a strongly varying prevalence of up to over 30%, and in a singular or multiple fashion, up to a few centimeters in diameter^{3,6, 7, 8–9}. It occurs more often in the mandible than in the maxilla, and it may be seen in an inter-/periradicular or periapical location, either connected with the lamina dura of the adjacent vital teeth or separated^{1, 2, 3–4}. Histologically, IO represents focal mature compact bone within the cancellous bone, with distinctive thorn-like, thickened trabeculae that radiate into the surrounding spongiosa, frequently connected to the endocortex^3,10.

This translates into relatively specific features on panoramic and periapical radiographs, which may be sufficient to diagnose most lesions that are usually asymptomatic incidental imaging findings^8,11. In longitudinal radiographic studies, only minor changes of IO have been detected in adults with mostly unchanged lesions^{12, 13–14}. In children and adolescents, IO may infrequently hinder tooth eruption and orthodontic tooth movement^{13, 14, 15–16}. With the increasing, ubiquitous application of multiplanar cone-beam computed tomography (CBCT) for lesional diagnostics, studies have emphasized its advanced value in establishing the correct diagnosis of IO, through an analysis of its lesional appearance, and its effects on the adjacent anatomy, free of superimposition as on panoramic radiographs^{17, 18, 19–20}.

On CBCT, however, the follow-up of IO has not been systematically investigated yet. This raises the question of how far IO may exhibit changes within a time period of months or years, as analyzed on CBCT. It becomes even more important when keeping in mind that, once IO is confidently diagnosed on a clinico-radiological basis, it does not require further biopsy or treatment^3,20,21. Biopsy has rarely been described in case reports with an atypical IO appearance, such as tooth displacement and incomplete compact bone density in young individuals^10,16. Hence, further investigation could then aid in the clinical management strategy of patients with IO, to prevent over- or under-diagnostic imaging as well as treatment. This over-imaging issue particularly refers to the avoidance of an increased patient radiation dose of CBCT, compared to the lower dose of panoramic radiographs.

The purpose of the current study was, therefore, to investigate the natural course of incidental, asymptomatic IO, and thus potential changes in size and morphology, in adult patients who underwent follow-up CBCT scans.

Materials and methods

Approval and accordance statement

The protocol for this retrospective study (EK 1179/2024) was approved by the local institutional review board (IRB; i.e. the Ethics Committee of the Medical University of Vienna), and the procedure was performed in accordance with the Declaration of Helsinki. Written, informed consent for clinical dental CBCT was obtained from all individuals and informed consent for study inclusion was waived by the IRB.

Study population

This retrospective study was based on the chart review of dental CBCT examinations performed between July 2014 and October 2024 in 441 adult patients, 18 years of age or older, who had been referred to our tertiary referral center to undergo clinical and radiological work-up, reporting, inter alia, the incidental finding of IO. The following inclusion criteria were used to select patients with IO: (a) a baseline CBCT scan of the mandible that yielded the diagnosis of IO defined as a focal, variably shaped, compact bone density within the cancellous bone of the dentate mandibular areas, with radiating extensions into the adjacent spongiosa and/or attached to the endosteum, of a size ranging from a few millimeters to 3 cm in diameter; (b) one or multiple subsequent CBCT follow-up scans, after at least 12 months or later, that supported the diagnosis of IO; (c) no findings indicative of an endodontic lesion with associated reactive osteitis, including large carious defects or a negative pulp vitality test of the teeth adjacent to the IO; (d) absent symptoms in the region of the IO, such as local pain or soft tissue swelling; and (e) no history of endodontic therapy, or dental or jaw surgery involving the regions affected by IO.

Consequently, exclusion criteria were CBCT findings suggestive of any lesion other than IO, of odontogenic or non-odontogenic origin, such as: (a) radiopaque bone findings associated with mechanical stress, such as periodontal ligament widening with lamina dura thickening, marked dental malposition, or abutment teeth in fixed bridges or partial dentures; (b) radiopaque bone findings associated with tooth retention or impaction; (c) clinical and/or radiological findings suspicious for inflammation/infection, such as periodontal disease or chronic apical periodontitis with associated condensing osteitis, any osteolyses or cysts, periosteal reaction suggestive for osteomyelitis, as well as radiopacities at teeth with deep caries or large crown restorations; (d) cortical erosion or expansion; (e) regions affected by previous dental or jaw bone trauma; (f) dental regions with tooth remnants and radiopaque changes in edentulous areas (e.g., socket preservation). Further exclusion criteria were any present systemic, metabolic, malignant, or genetic disease, such as Gardner syndrome, that might be associated with jaw bone lesions²². Available histopathology demonstrating IO was not an inclusion criterion; however, any results indicative of findings other than IO, if available during chart review, were exclusion criteria.

CBCT imaging

All CBCT scans, covering the mandible from the lower margin to the occlusal level, were obtained using a KaVo 3D eXam CBCT unit (KaVo Dental GmbH, Biberach an der Riß, Baden-Württemberg, Germany) with the patient in the seated position, applying the following parameters: tube voltage, 120 kVp; tube current-exposure time product, 20 mAs; field of view, 8 × 16 cm; voxel size, 0.250 mm; and mean dose area product, 270 mGy*cm² (range, 250–310 mGy*cm²). The images were post-processed by the i-CATVision and eXamVision software version 1.9.3 (Imaging Sciences International, Hatfield, Pennsylvania, USA; https://icatvision.software.informer.com/1.9/), and imported into a picture archiving and communication system (PACS), the IMPAX EE R20 Release XIX (Agfa HealthCare, Mortsel, Belgium; https://www.agfahealthcare.com/enterprise-imaging-platform/) for analysis and storage.

Evaluation

On the PACS, the CBCT scans were anonymized and randomly presented by a study assistant to a dental imaging specialist (S. F. N., a board-certified radiologist with 22 years of experience in head and neck imaging). To assess the interobserver agreement, another imaging specialist (U. S. N., a board-certified radiologist with 12 years of experience in head and neck imaging) evaluated the same CBCT scans separately. Four weeks thereafter, the scans were re-evaluated by both readers to assess their intraobserver agreement. This re-evaluation to assess the interobserver and intraobserver agreement was performed using the patients’ baseline CBCT scans. Both readers were blinded to the patients’ data. Prior to the actual evaluation, based upon five different CBCT cases exhibiting IO, which were not included in the study due to a lack of follow-up, a calibration session in terms of a consensus reading was performed to ensure that both readers then applied the same standardized evaluation criteria.

For this study, the standard tooth numbering system according to the FDI World Dental Federation notation (ISO 3950:2016 Dentistry – Designation system for teeth and areas of the oral cavity) was applied, and each dentate mandibular region was checked for the presence of an IO lesion. Initially, the temporal course of each IO lesion, and thus, potential changes, were visually checked by using a PACS-integrated automated registration tool, to create an overlay scan of two comparative, consecutive CBCT studies that included the whole stack of transverse CBCT images (Fig. 1A-C). By moving a slider bar, the fusion could be accentuated toward each of the different CBCT studies, which enhanced the comparison of the extension, morphological appearance, and radiodensity of the IO lesions (Fig. 1A-C). Then, using the whole stack of CBCT slices of each scan, the respective lesional maximum axial diameter was obtained in the transverse plane, and the maximum cranio-caudal diameter in the orthoradial plane (Fig. 1D and E). In cases in which IO involved two or more adjacent dental regions, the entire maximum diameter was obtained. All morphometrics were recorded in millimeters, based upon single measurements using a PACS-integrated distance measurement tool. Furthermore, using the whole stack of slices of each scan, the localization and morphological appearance of each lesion was visually qualitatively assessed in detail. First, each lesion was classifed in relation to the respective tooth or teeth, as being situated either in a periapical or periradicular area with contact with the lamina dura, or in a periapical area but separated from the lamina dura. Second, the lesional shape was judged as (a) round or ovoid, (b) triangular, (c) square, or (d) irregular based on its appearance in the two imaging planes, and its radiodensity was determined to correspond to that of the adjacent compact bone. Third, the relationship of the IO to the endosteum (inner layer of cortex) was judged as either (a) buccal, (b) lingual, or (c) both bucco-lingual; as well as the relationship to the mandibular canal as either (a) present contact without compression and displacement, or (b) absent contact. Finally, each involved dentate region was checked for the presence of an IO-associated root resorption.

[See PDF for image]

Fig. 1

A 35-year-old female with a periapical IO in region 44 on CBCT in the transverse plane. The consecutive CBCT scans were visually compared using an automated software tool to produce an overlay (A) of two comparative CBCT scans at the baseline (B) and follow-up after 12 months (C). By moving a slider bar, this overlay could be accentuated toward each of the scans, the baseline (B) versus the follow-up (C), to visualize potential changes in size and morphology of the lesion (arrows), which did not change. The maximum axial (D) and cranio-caudal (E) diameter (small double arrows) were obtained in the transverse and orthoradial plane, respectively; the oviod IO lesion (D, E) with compact bone density shows lingual endosteum as well as lamina dura attachment (arrows).

Statistical analysis

Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS) software (IBM SPSS Statistics version 29.0 for Microsoft Windows; IBM, Armonk, New York, USA; https://www.ibm.com/support/pages/downloading-ibm-spss-statistics-29/). A p-value ≤ 0.05 was considered to indicate statistically significant results.

For each IO lesion, the dental region and the number of involved regions was noted. At each baseline scan, and at each follow-up scan, as available, the lesional maximum axial and cranio-caudal diameter measurements and morphological appearance (tooth relationship, lesional shape and radiodensity, endosteum and mandibular canal relationship, root resorption) were tabulated, and the lesions were checked for any size and morphology changes in terms of quantity and quality, as well as frequencies over time. Furthermore, a Pearson correlation was calculated to analyze the relationship between the age of the patients and the lesional maximum axial diameter. Finally, the intraobserver and interobserver agreement were evaluated for the assessment of quantitative measurements (continuous variable: maximum axial and cranio-caudal diameter) using the intraclass correlation coefficient, and for qualitative features (categorical variable: tooth relationship, lesional shape and radiodensity, endosteum and mandibular canal relationship, root resorption) using weighted κ statistics.

Results

Based upon the inclusion criteria, 37/441 (8.4%) asymptomatic adult patients were included. There were 19/37 (51.4%) females and 18/37 (48.6%) males, and their mean age at the time of the baseline CBCT scan was 40.5 years (age range, 21.6 to 87.3 years). There were 30 individuals with a solitary IO lesion, six individuals with two IO lesions, and one individual with three IO lesions. Consequently, overall, there were 45 IO lesions that were assigned for evaluation, and that total number did not change within the follow-up period. Furthermore, based upon chart review, 7/37 patients (8/45 lesions) were specifically referred for the CBCT evaluation of IO, and 30/37 patients (37/45 lesions) because of other clinical indications, such as endodontic lesions, cysts, or implant planning in dental regions separate from the IO lesions. None of the included individuals underwent biopsy of the IO, and consequently, there were no histopathological results available. Using the exclusion criteria, 402/441 (91.2%) patients were primarily excluded because of no available follow-up CBCT scan. In addition, two other patients were excluded, with diffusely sclerotic, expansile, unilateral involvement of all dental regions and histopathological findings demonstrating a central osteoma of the mandible.

CBCT follow-up scans

Consisting of 45 lesions in 37 individuals, a total of 99 CBCT scans (45 baseline scans and 54 follow-up scans) were included for evaluation. For follow-up, 38 lesions underwent a singular scan, five lesions underwent two scans, and two lesions three scans. Overall, the mean follow-up period was 19.0 months, with, as per inclusion criterion, a required minimum of 12 months, and a maximum of 96.0 months. In detail, there were 36 scans at 12 months, six at 18, four at 24, one at 30, three at 36, two at 48, one at 60, and one at 96 months, respectively.

Lesional maximum diameter and dentate regions

On CBCT imaging, the mean maximum axial diameter was 8.36 mm (range, 4.0 to 20.8 mm), and the mean maximum cranio-caudal diameter was 8.21 mm (range, 3.5 to 18.0 mm). Of 45 lesions, 40 lesions (88.9%) affected a single region, four lesions (8.9%) two regions, and one lesion (2.2%) three regions, respectively, which accounted for 51 regions involved. This included two incisor, seven canine, 22 premolar, and 20 molar regions, respectively.

Lesional localization and morphological appearance

Of 45 lesions, 26 (57.8%) were found in periapical/periradicular areas with contact with the lamina dura of a single tooth, five (11.1%) in periapical/periradicular areas between two teeth with contact with the lamina dura, and 14 (31.1%) in periapical areas but separated from the lamina dura of the respective teeth (Figs. 1 and 2). Of 45 lesions, the shape was irregular in 32 (71.1%), round or ovoid in nine (20.0%), triangular in three (6.7%), and square in one lesion (2.2%), respectively (Figs. 1 and 2). As by definition, all 45 lesions (100%) showed compact bone radiodensity. Of 45 lesions, both buccal and lingual endosteum contact was present in 24 (53.3%), lingual contact in 13 (28.9%), and buccal contact in eight lesions (17.8%), respectively; contact between the IO and the mandibular canal was present in 15 lesions (33.3%), and absent in 30 (66.7%) lesions (Figs. 1 and 2). Root resorption was found in four of the 37 patients (10.8%), and 45 IO lesions (8.9%), respectively (Fig. 3). The latter four asymptomatic patients underwent only clinico-radiological follow-up but no biopsy, surgical, or endodontic treatment within the respective study-related observational period.

[See PDF for image]

Fig. 2

A 35-year-old asymptomatic female with a periapical IO in region 34, separated from the lamina dura of the tooth on CBCT in the transverse (A) and orthoradial (B) plane. The ovoid IO lesion shows attachment to the buccal endosteum (large arrows) with radiating trabeculae and a direct relationship to the mandibular canal (small arrows) at its course to the mental foramen, which did not change over 12 months of follow-up.

[See PDF for image]

Fig. 3

A 41-year-old asymptomatic female with a periradicular IO in region 46 on CBCT in the transverse (A) and orthoradial (B) plane. There is IO-associated resorption (large arrows) of the distal root of this molar tooth at the apical third (A, B), which did not change over 36 months of follow-up. The mandibular canal (small arrow) shows semicircumferential encasement by the IO lesion (B) with compact bone density occupying almost the entire cancellous bone in this slice. Please note distinct artifacts at the crown level (B), mimicking a defect, due to a restoration of the neighboring tooth.

Lesional changes on CBCT follow-up

None of the 45 IO lesions (0.0%) exhibted any changes in maximum axial or cranio-caudal diameter at the respective follow-up scans, either at the final CBCT scan, or at a scan in the interim. Likewise, none of the 45 lesions (0.0%) showed any changes in terms of morphology (tooth relationship, lesional shape and radiodensity, endosteum and mandibular canal relationship). The finding of root resorption also did not change on follow-up. Detailed consideration of the 7/37 patients specifically referred for CBCT of IO, two of which with root resorption, showed a mean age of 36.6 years and a mean lesional axial diameter of 11.55 mm versus 41.4 years and 7.66 mm, respectively, in the 30/37 patients referred because of other indications. Furthermore, there was a low correlation between the age of the patients and the lesional maximum axial diameter (r= −0.314, p = 0.058).

Reader agreement

For the CBCT image analysis of the IO lesions, there was good to excellent reader agreement for the assessment of the quantitative measurements (ICC), and substantial to perfect agreement for the assessment of the qualitative morphological appearance (weighted κ). This interpretation of the results was performed for the ICC according to Koo et al. and for the weighted κ statistics according to Landis et al., respectively^23,24. The specific results are detailed in Table 1.

Table 1. Intra- and interobserver agreement.

Measurements
Maximum axial diameter	ICC
	Intra – Reader 1	0.897
	Intra – Reader 2	0.870
	Inter	0.808
Maximum cranio-caudal diameter	Intra – Reader 1	0.905
	Intra – Reader 2	0.880
	Inter	0.854
Morphological appearance
Tooth relationship	Weighted κ
	Intra – Reader 1	0.907
	Intra – Reader 2	0.930
	Inter	0.888
Lesional shape	Intra – Reader 1	0.765
	Intra – Reader 2	0.789
	Inter	0.754
Lesional radiodensity	Intra – Reader 1	1.0
	Intra – Reader 2	1.0
	Inter	1.0
Endosteum relationship	Intra – Reader 1	1.0
	Intra – Reader 2	1.0
	Inter	1.0
Mandibular canal relationship	Intra – Reader 1	1.0
	Intra – Reader 2	1.0
	Inter	0.883
Root resorption	Intra – Reader 1	1.0
	Intra – Reader 2	1.0
	Inter	1.0

Discussion

This study sought to investigate the CBCT follow-up of IO in asymptomatic adults, to demonstrate natural changes over time, based upon maximum diameter and visual morphological evaluation. The impetus for this was two-fold. First, the general, ever-growing use of CBCT to evaluate bone lesions, because of its improved diagnostic accuracy, compared to panoramic radiographs, has drawn attention to its use for the diagnosis of IO on CBCT^{17, 18, 19–20,25}. Second, at the same time, the issue remains whether CBCT follow-up of IO does actually aid in its management.

In essence, the basic findings of IO in the current study regarding its predominantly periapical localization, and ovoid or bizzare shape and size, did not substantially differ from various previous imaging studies using radiographs and, more recently, CBCT, which has detailed the characteristics of IO in extenso^{6, 7–8,11,17, 18–19}. Especially here, on follow-up, unchanged root resorption of adjacent teeth was found in four of 45 lesions. Although relatively uncommon and not present in some studies, this finding has been reported in up to ~ 10% of cases^13,26,27. This refers to the complex cascade of noninfective, pressure-induced external surface resorption, and per se, it is usually asymptomatic, without signs of endodontic disease, in vital teeth²⁸. The treatment recommendation is directed at the elimination of the cause of excessive pressure, for example, an impacted tooth or a cystic lesion, whereas endodontic treatment of the affected tooth is primarily not recommended²⁸. However, in the scenario of IO, as presented in this study, watchful waiting based on clinico-radiological follow-up may be justified due to the benign, asymptomatic, non-progressive nature of IO.

Notably, this CBCT study, in adults with a mean age of 40.5 years, did not identify any changes in the size or morphology of IO at a mean follow-up of 19.0 months. Furthermore, there was a low negative correlation (r= −0.314) with a trend toward statistical significance (p = 0.058) between the patients` age and the lesional axial diameter, meaning that an older age may tend to be associated with smaller lesions compared to a younger age. Possibly, this could be due to a selection bias, since patients specifically referred for CBCT of IO were younger (36.6 versus 41.4 years) and had larger IO lesions (11.55 versus 7.66 mm), on average, than those referred because of other indications. Speculatively, it could also be the result of an actual long-term IO decrease with advancing age. The current findings, of course, do not exclude possible changes of IO per se. A previous longitudinal investigation of IO lesions in orthodontically-treated patients, using panoramic radiographs in a follow-up of one to five years after the pre-treatment radiograph, demonstrated a lesional enlargement for the vast majority in adolescence between 10 and 19 years of age, whereas most lesions did not change in adulthood between 30 and 39 years of age¹³. Likewise, another radiographic longitudinal study of IO and condensing osteitis in adults, with a mean age of 44.0 years and a mean follow-up of 10.4 years, found 86% of lesions to be unchanged in size¹². Nevertheless, a few IO lesions may increase or even decrease in adulthood on long-term radiographic follow-up^12,14,29. Although the methods of these previous studies differed quite a bit from this CBCT study in untreated adult individuals, the synopsis of all these observations, including our own investigation, may indicate a common increase of IO during adolescence and a tendency toward unchangeability in adulthood^{12, 13–14,29}. However, it should be qualified that these follow-up studies did not correlate the initial lesional size, location, and extension, nor the time of follow-up, to the observed changes in size^12,14,29. Technically, it has also been recognized that the comparison, and thus follow-up of lesions, may be limited on two-dimensional radiographs subjected to magnification and distortion phenomena¹³.

Clinically, IO may thus represent a straightforward diagnosis. However, diagnosing IO invariably requires the distinction of radiopaque differential diagnoses based upon a combination of clinical and radiological investigation, follow-up, and, in some cases, histological evalution and surgical treatment³⁰. These commonly include condensing osteitis associated with periapical inflammation, less commonly cemento-osseous dysplasia, and rarely, tumors such as cementoblastoma³⁰. Tumorous lesions also include central, and thus medullary osteoma, typically associated with expansion, cortical erosion, and tooth displacement^31,32. For the comparison of radiopaque periapical lesions also refer to Table 2. Moreover, biopsy is usually not recommended nor performed in IO, and histology per se may be insufficient, because “bone in bone” lesions, such as IO, condensing osteitis, and osteomas, may share similar characteristics, and would not be differentiable microscopically³³. This may result in confusing these entities. In particular, central osteoma, although exceptionally rare, may arouse the clinician’s attention due to the nature of its growth, bone expansion, and tooth displacement^31,33. And here is the dilemma, because, as previously described, IO may increase in size during the teen-age years, and this may not allow for differentiation between IO and osteoma³³. Along with this vagueness in definition, some authors have also claimed a distinction between IO and bone islands, the latter specifically presenting without a dental relationship, which, however, was not included in most studies³⁴.

Table 2. Comparison of IO versus other radiopaque differential diagnoses in a periapical location. Please note that this summarizes only the key features of the different lesions and does not review the entities in full detail. The radiological features refer to panoramic radiographs and CBCT.

Lesion	Clinical features	Radiological features	Histological features
Idiopathic osteosclerosis	- Asymptomatic - Incidental imaging finding - Possibly developmental finding in vital, untreated teeth, predominantly in mandible - No associated endodontic lesion - Rarely associated root resorption	- Focal, variably shaped, compact bone density within cancellous bone - Extensions into spongiosa and attachment to endosteum and/or lamina dura	Benign, non-expansile, mature compact bone within cancellous bone, with distinctive thorn-like, thickened trabeculae radiating into surrounding spongiosa
Condensing osteitis (focal sclerosing osteitis)	- May be symptomatic due to associated caries with chronic pulp inflammation and periapical periodontitis - May regress after treatment	Diffuse radiopaque, non-expansile, concentric zone around root apex	Localized bony reaction with sclerotic bone formation secondary to chronic low-grade inflammation
Central (medullary) osteoma	- May be symptomatic with discomfort and pain due to jaw bone expansion, tooth displacement, and inferior alveolar nerve compression - Anywhere in jaw bones	Expansile, uniformly dense “bone within bone” lesion without periosteal reaction or soft tissue component	Rare benign, slowly growing, osteogenic neoplasm of normal mature-appearing bone, either compact, trabecular, or combination of both
Cemento-osseous dysplasia	- Most often asymptomatic and self-limiting, incidental imaging finding, with mandibular predominance and one or multiple lesions - Less frequently pain or swelling	Radiolucent (osteolytic phase), mixed density (cementoblastic phase), or radiopaque lesion (osteogenic phase) with radiolucent rim	- Benign fibro-osseous lesion mainly at dentate regions - Normal bone replaced by fibrous tissue, followed by calcification with osseous and cementum-like tissue
Hypercementosis	- Asymptomatic at one or multiple vital teeth - Incidental imaging finding - Idiopathic or associated with tooth retention, inflammation, trauma, and developmental, genetic, and metabolic disorders	Bulbous, sclerotic root enlargement (club-shaped, “fat root”)	Non-neoplastic, excessive deposition of cementum within periodontal ligament space at lower root third
Cementoblastoma	- Pain, tenderness on palpation - Jaw bone expansion - Affected teeth frequently vital	Expansile, radiodense or mixed-density lesion with a rounded or sunburst appearance, and radiolucent rim, with root resorption	Rare benign, slowly growing, odontogenic neoplasm with masses of hypocellular cementum embedded in fibrovascular stroma with rim of connective tissue

In fact, the follow-up of IO is troublesome to address. Although the clinico-radiological follow-up of IO has been found essential in its management, at present, there are no exact guidelines as to how individuals should be followed. Pragmatically, the radiographic detection of IO might entail further CBCT to confirm IO, and ultimately to prevent any misdiagnosis, which, again, may engender less follow-up examinations. Thus, for the typical asymptomatic incidental presentation of IO without progression, CBCT follow-up may result in over-imaging, which is associated with increased ionizing radiation exposure, as well as intense effort and expense. Notably, mean effective doses from intraoral radiographs, 1.3 µSv, and panoramic radiographs, 17.9 µSv, have been found to be about 1% and 15% of that from CBCT, 121.1 µSv, respectively³⁵. Consequently, since panoramic and periapical radiographs may be generally adequate to delineate IO, these radiographs may be emphasized as the preferred routine follow-up option^12,14,29. Moreover, following The Bone Reporting and Data System (Bone-RADS) of the Society of Skeletal Radiology, IO may reflect Bone-RADS 1, and thus a benign, incidentally encountered solitary sclerotic “leave-me-alone” (“do not touch”) lesion³⁶. In contrast, atypical clinico-radiological findings, such as orthodontic hindrance in children, root resorption, rapid size increase, or emerging pain, may result in individually adapted follow-up^{13, 14, 15–16,26,27}.

The study limitations should also be addressed. First, the number of study patients was limited because of the retrospective setting, and this narrowed the quantity of CBCT scans for evaluation, as well as an analysis of age-related IO patterns. Second, this approach also involved CBCT follow-up to be performed at varying but not uniform time points, which restricted the arrangement of long-term follow-up over several years. Third, based upon clinical practice, the inclusion of patients was based on clinico-radiological findings alone, whereas histological results were generally not available. Consequently, it would have been impossible to identify false-positive cases with absolute certainty. Finally, using diameter measurements and computer-enhanced visual inspection on CBCT resulted in a relatively simple evaluation, reflecting a routine lesional assessment.

Conclusion

CBCT is efficient for the follow-up of incidentally encountered IO lesions by morphometric measurements and qualitative morphological assessment. Here, in asymptomatic adults, on CBCT follow-up scans at 12 months or later, none of the IO lesions presented with any changes in size or morphological appearance. Although this certainly does not exclude potential long-term advancement of IO over several years, the current results underline that IO should be considered a “leave-me-alone” lesion in asymptomatic adults. In those, once the diagnosis of IO has been established, CBCT follow-up should be avoided whenever appropriate to prevent imaging overuse and unnecessary exposure to radiation. Still, the follow-up of IO may be based on an individual-specific approach.

Acknowledgements

The authors acknowledge Ms. Mary McAllister, MA (editor at Johns Hopkins University, Baltimore, Maryland), for her magnificent support in editing the manuscript.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by S. F. N., U. S. N., and M. Z. Statistical analysis was performed by S. F. N. and M. W. The first draft of the manuscript was written by S. F. N. All authors reviewed the mansucript for important intellectual content. All authors read the final manuscript and approved its submission.

Funding

No funding was received.

Data availability

The clinical radiological images analysed during the current study are not publicly available to protect the patients’ privacy but generated study data are available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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