Panoramic radiographs or bite-wing radiographs usually are taken earlier presenting a larger number of unerupted teeth. Shimabukuro et al. (2014) reported the highest frequency of PEIR in unerupted mandibular third maxillary molars (n= 10, 3.09 % of all mandibular molars), followed by maxillary third molars (n=6, 1.55 %), which is in accordance with the results of Demirtas et al. (2016a), whereas in the study of Ngamsom et al. (2024) mandibular molars had the highest prevalence (18.6 %) followed by supernumerary teeth (17.6 %), maxillary molars (13.3 %), and maxillary canines (11.6 %).

In two studies using bite-wing radiographs the prevalence of PEIR was reported as to be 6.4 % and 3.3 % of subjects and 1.6 % and 0.48 % of unerupted teeth, respectively (Seow et al. 1999a,b). Comparing bite-wings and panoramic radiographs, bite-wings revealed a prevalence of 6 % of subjects and 2 % of teeth, panoramic views of 3 % of subjects and 0.5% of teeth. In two studies of this group (Seow et al. 1999a, 1996), the most affected teeth were mandibular first permanent molars, maxillary first permanent molars, mandibular second permanent premolars, and mandibular second permanent molars.

The reported prevalence of PEIR varies considerably, depending on the age groups studied and the radiographic techniques used. In some studies, premolars and second and third molars appear to be the most frequently affected teeth; however, this may be partly due to a methodological issue - these teeth are often still unerupted at the time of the first radiographic examination, making their crowns invisible in bitewing radiographs. (AlBatayneh et al. 2014, Özden & Acikgoz 2009, Uzun et al. 2015). After eruption, reliable radiographic diagnosis and clear differentiation between PEIR and post-eruptive external resorption are often no longer feasible. There are no systematic studies on the prevalence of PEIR in deciduous teeth (Fig. 1a- b).

Most studies have reported no associations between PEIR and gender, ethnicity, general health status, or history of water fluoridation (Özden & Acikgoz 2009, Uzun et al. 2015). Shimabukuro et al. (2014) found a significantly higher prevalence in women (subjects: 2.89 % vs. 1.26 %; teeth: 0.54 % vs 0.17 %). In a study comparing CBCT to panoramic radiographs third molars were affected most frequently (59.5 %), interestingly, 51.9 % of PEIR lesions were detected in ectopically positioned teeth (Demirtas et al. 2016). In a comparative study of Australian and Saudi Arabian populations the presence of PEIR was associated with delayed dental development (Al-Tuwirqi & Seow 2017).

In a recent study on the prevalence of PEIR in orthodontic patients 49 of 3,143 patients (1.56 %) showed radiographic signs of PEIR . In a radiographic follow-up after 36 (+/-8.1) months 89.1 % of the PEIR lesions showed no increase in size (Gurdanetal.2023).

Classification

The first classification of PEIR has been proposed by Seow et al. (1999a) and comprised three groups: degree I= <1/3 relative dentine thickness, degree II= 1/3 relative dentine thickness, degree III= >1/3 relative dentine thickness. Couchene et al. (2020) later used this classification to classify respective treatment options as collected in a systematic review of case reports on PEIR treatment.

Özden and Acikgoz (2009), Demirtas et al. (2016a), and Manmontri et al. (2017) used an extended five-score classification of PEIR based on the radiographic extension of the resorptive defect: score 1: < 1/3 of dentine thickness, score 2: >1/3 but <2/3; score 3: >2/3 without enamel defect; score 4: defect extending into enamel; score 5: defect extending into the pulp chamber.

Yüksel et al. (2023) recently suggested a new classification for PEIR based on the evaluation of panoramic images of 64,546 patients of a Dept. of Dentomaxillofacial Radiology. Teeth with PEIR were detected in 164 cases with a mean patients` age of 51.4 +- 15.6 years, 33.5 % were male, 66.5 % were female, 25 patients presented with multiple PEIR. The most affected teeth were maxillary third molars.

PEIR was classified as follows according to location and size/extension into 15 groups:

Enamel; dentine < 1/3; dentine 1/3 – 2/3; dentine > 2/3; enamel and dentine < 1/3; enamel and dentine 1/3 -2/3; enamel and dentine > 2/3; dentine and root < 1/3; dentine and root 1/3 - 2/3; dentine and root > 2/3; enamel, dentine and root < 1/3; enamel, dentine and root 1/3 – 2/3; enamel, dentine and root > 2/3; root, enamel and root. From their detected lesions most were classified as affecting enamel and dentine 1/3- 2/3 (group 6) and >2/3 (group 7).

The clinical implications and therapeutic consequences of these classifications remain unclear and have not been discussed by the authors.

Etiology

Over the decades there have been a number of different and controversial theories on the etiology of PEIR. Seow et al. (2000) suggested that PEIR should be regarded as an entity of occult caries resulting from a pre- or posteruptive process. While in this hypothesis the etiology of preeruptive resorption remains unclear, undermining fissure caries is made responsible for posteruptive defects. Unfortunately, this theory cannot explain the finding of vital granulation tissue in preeruptive lesions and missing carious dentine in posteruptive defects. Seow (2000) with regard to the literature figures the prevalence of occult caries to be 0.8 to 50 percent dependent on the investigated persons age, which is differing from the figures on PEIR.

The “fluoride bomb-theory” is based on the finding that fluorides in high concentrations will remineralize initial defects or slow down progress of caries in enamel, namely in deep and narrow fissures while carious destruction can progress in the underlying dentine (Seow 2000).

In the dental literature, several further attempts to explain the development of pre-eruptive intracoronal resorptions can be found (Al-Batayneh & AlTawashi 2020, Omar et al. 2015, Seow 2003):

• pulpal and periradicular inflammation of the deciduous teeth with destruction of the epithelium around the permanent tooth germ; this theory would not explain intracoronal resorption in deciduous teeth.

• caries: it seems unlikely that caries-inducing microorganisms will colonize a tooth before eruption into the oral cavity. There is no case report mentioning carious destruction of the tooth surface of a non- or just-erupted tooth.
• caries: it seems unlikely that caries-inducing microorganisms will colonize a tooth before eruption into the oral cavity. There is no case report mentioning carious destruction of the tooth surface of a non- or just-erupted tooth.
• dentinal defects
• enamel defects (hypoplastic or hypomineralized enamel)
• idiopathic origin
• external resorptions

It also has been hypothesized that - similar to external invasive resorptions – a defect in mineralization at the enamel-cementum-junction might be present (see Figs. 4 and 15). Following a yet unknown trigger, clastic cells could invade the crown via this defect and resorb the dentine.

It also has been supposed that defects in the inner enamel epithelium during tooth development could induce resorptions via the direct contact between connecting tissue and enamel. The resorbing cells probably are recruited from undifferentiated cells from the dental papilla or the surrounding bone (Omar et al. 2015, Spierer Weil & Fuks 2014). The resorbed dentine is replaced by a granulomatous tissue, besides which regularly structured dentine and an uninflamed pulpal tissue are found. It is well-known from studies on external invasive cervical resorption that the dental pulp is well-protected against resorption by a so-called “pericanalar resorption-resistant sheet“ (PRRS) (Patel et al. 2009, Chen et al. 2021).

Systemic etiological factors have not been identified so far, but an association with local developmental defects and irregularities, namely ectopic tooth position (13-28% of teeth with PEIR), delayed dental development, or supernumerary teeth has been proposed (Al-Batayneh & AlTawashi 2020, Seow 2003). Ectopic position of a tooth may be associated with increased pressure to a tooth germ, resulting in damage of the integrity of the enamel epithelium (Ngamsom et al. 2024). A defect in the enamel epithelium during crown development allowing ingrowth of connective tissue with direct contact to coronal dentine and thus initiating intracoronal resorption actually is held as the most plausible theory (Al-Batayneh & AlTawashi 2020, Omar et al. 2015, Seow 2003).

Summarizing, it can be stated that the etiology of PEIR remains unclear; ingrowth of resorptive cells through a defect in the cemento-enamel junction followed by resorption of the incompletely mineralized coronal dentine seems to be the most probable reason. An internal origin seems unlikely, as in the vast majority of case reports, a vital pulp and a closed coronal hard tissue barrier have been present. Whether pre-eruptive intracoronal resorption (PEIR) and invasive cervical resorption - now more accurately termed external cervical resorption (ECR) - share similarities or differences, and whether PEIR may represent a variant of ECR, has not yet been discussed or investigated.

Clinics and diagnostics

As dental resorption typically progresses without

clinical symptoms, PEIR is most often detected incidentally. Lesions that develop before tooth eruption are only identified when radiographs of the affected region are taken; however, at that stage of dental development, there is usually no indication for radiographic examination. The resorption develops after formation of the tooth crown (Seow 2003) and usually progresses slowly (Omar et al. 2015). Following eruption into the oral cavity resorption in most cases continues to progress slowly and without symptoms. Posteruptively, the tooth crown presents intact without visible lesions. Additional bacterial contamination via carious or non-carious enamel defects can increase the speed of resorption and the defect visibly and radiographically may resemble a carious lesion. Some authors (AlBatayneh & ATawashi 2020, Omar et al. 2015, Demirtas et al. 2016a) suppose that a number of case reports on so-called “hidden caries” rather developed from intracoronal resorptions, in which after eruption into the oral cavity and bacterial invasion a caries developed. Pain or clinical symptoms usually do not appear before inflammation or infection of the pulp develop (Omar et al. 2015).

Periapical and bitewing radiographs detect more cases of PEIR than panoramic radiographs. Cone- beam computed tomography (CBCT) appears to be superior, providing greater diagnostic accuracy and detailed information on the three- dimensional extent of the resorption and potential involvement of the dental pulp. In 733 patients 3.1 % radiographically were diagnosed as presenting PEIR compared to 9.5 % in the CBCT (Demirtas et al. 2016b). The outcome of studies using CBCT among others depends on the voxel size. Nevertheless, the indication for using CBCT to diagnose pre-eruptive pathologies with such low prevalence or incidence is generally not justified in this age group. (AlBatayneh & AlTawashi 2020, Demirtas et al. 2016a, Ari 2014).

Usually, one single tooth is involved (AlBatayneh & AlTawashi 2020), but resorptive decay of several teeth also has been reported (Özden & Acikgoz 2009, Uzun et al. 2015, Demirtas et al. 2016a).

In the radiograph - panoramic, single tooth-, or bitewing-radiographs - typically a clearly defined lesion with sharp borderlines in the dental crown is visible – usually at or near the cemento-enamel junction extending into the coronal dentine (AlBatayneh & AlTawashi 2020). Caries and internal inflammator y resorptions should be considered as differential diagnoses. The clearly defined borderlines may help to exclude a “hidden caries“, which typically presents diffuse borders. An internal inflammatory resorption starts from chronic pulpal inflammation; usually a communication between the resorption lacuna and the dental pulp can be diagnosed radiographically. As development of pulpal inflammation is unlikely to appear before tooth eruption, an internal resorption can be excluded as differential diagnosis. An external cervical invasive resorption (ECR), characterized by the invasion of resorptive cells through a cemental defect and a finger-like progression of dentine resorption without involving the dental pulp, cannot be excluded as a differential diagnosis. It is possible that PEIR, whose etiology also remains unclear, represents a subtype of ECR. On the other hand, it can be argued that many of the factors proposed as causes of ECR - such as feline viruses or the use of certain wind instruments - are unlikely to be relevant to the development of PEIR. In case of late, post-eruptive detection of PEIR, breakdown of the occlusal enamel surface and the underlying dentine already may have occurred, combined with secondary carious decay, which may result in a misdiagnosis as “hidden caries” (AlBatayneh & AlTawashi 2020, Omar et al. 2015, Gurdan et al. 2023). The important role of orthodontists and paediatric dentists in early and timely diagnosis of PEIR must be stressed (Walton 1980, Rankow et al. 1986).

Histology and Microbiology

Only limited and partly contradictory information

is available regarding the histology and microbiology of pre-eruptive resorption. Reports have described uninflamed but necrotic tissue, as well as cases involving infected or inflamed tissue and bone. Repeatedly, resorptive cells (multinuclear cells, osteoclasts, macrophages, giant cells, chronic inflammatory cells) have been found (AlBatayneh & AlTawashi 2020, Omar et al. 2015, Spierer Weil & Fuks 2014, Rankow et al. 1986). There has been no histological proof for the presence of cariously affected dentine in PEIR defects (Spierer Weil & Fuks 2014, Seow 1999, Seow et al. 1999b, Alon et al. 2023).

Management

Not surprisingly, no evidence-based treatment strategies for PEIR are currently available (Chouchene et al. 2020); existing recommendations are primarily based on case reports. Depending on the clinical situation - including the nature of the resorption (progressive or stationary) and the timing of diagnosis (pre- or post-eruptive) - the following treatment objectives may be considered as generally accepted:

Non-erupted teeth

In order to prevent progression of the resorption utmost early treatment would be beneficial, nevertheless this is limited by the option to get access to the lesion and - especially in children - by the patient’s compliance. In case of a small lesion distant from the pulp, a wait-and-control-approach seems practicable until eruption allows treatment (Holan et al. 2017, Manmotri et al. 2017). Repeated radiographic control is necessary to distinguish between stationary and progressive resorption. In case of a progressive resorption approaching the pulp, immediate surgical treatment should be the treatment of choice (Spierer Weil & Fuks 2014, Holan et al. 1994, Le et al. 2020).

Some authors recommend surgical exposure by removal of the gingiva covering a still unerupted permanent second molar; dependent on the stage of eruption incision of the soft tissue covering the crown may be sufficient (Holan et al. 1994, Davidovich et al. 2005, Spierer Weil & Fuks 2014).

Erupted teeth

Depending on the patient`s age and compliance this procedure sometimes has to be performed under general anaesthesia or inhalation sedation (Spierer Weil & Fuks 2014, see Case 2). In case of invasive treatment of only partially erupted teeth placement of rubber dam may present problems or even be not possible.

1. Complete removal of the granulation tissue: this may require a large access cavity severely compromising the stability and fracture resistance of the affected tooth, resulting even in crown fractures (Counihan & O’Connell 2012). Spoon excavators are recommended for removal, assisted by copious irrigation with sodium hypochlorite.

2. As the dental pulp in the majority of cases obviously is not involved and still is covered – and protected – by a layer of sound dentine, maintaining pulp vitality should be the primary aim of treatment in order to assure completion of root development.

3. In case of exposition of the dental pulp, treatment should aim at maintaining at least partial vitality of the pulp in order to allow further root growth. Treatment options may include pulpotomy or regenerative endodontic treatment (RET).

4. If maintaining vitality of an irreversibly inflamed pulp is not possible, regenerative pulp treatment, (RET) or apical closure using appropriate biocompatible and osteoconductive materials could be the treatment of choice. It has been shown in a number of case reports that maintaining a completely or partially vital pulp can be achieved by pulp capping or pulpotomy (Spierer & Weil 2014, Counihan & O’Conell 2012)

5. The external access to the coronal dentine, typically located at the cementoenamel junction, should be carefully identified during removal of granulation tissue and sealed tightly to prevent reinvasion by resorptive cells and recurrence of the lesion.

6. The sometimes massive decay of the coronal dental hard tissues requires proper restoration, as to assure chewing function and prevent further loss of hard tissue. This may require restoration with a full crown or a paediatric stainless steel crown even at young age.

7. In cases of extreme, non-restorable tooth destruction by PEIR, extraction and orthodontic closure of the gap or replacement of the tooth by tooth transplantation can be considered (Counihan & O’Connell 2012).

The treatment protocol has to take into consideration size, location, and progression of the resorptive lesion and the extent of coronal tooth destruction as well as the age and compliance of the patient, the estimated date of eruption, and the strategic value of the tooth involved.

When PEIR is diagnosed before eruption of a tooth, radiographic and clinical controls in 6-months (large lesions) or 12-months-intervals (small lesions) are recommended.

Treatment options include monitoring and treatment after (partial or complete) eruption (AlBatayneh & AlTawashi 2020. Uzun et al. 2015, Le et al. 2020, Gurdan et al. 2023, Manmotri et al. 2017), as increase in size of the defects has been shown to develop slowly (Gurdan et al. 2023) or the lesion even may be stagnant (Manmotri et al. 2017). Additional treatment options are surgical exposition of the tooth and (at least temporary) restoration before complete eruption, as well as extraction of non-restorable teeth (Grundy et al. 1984, Omar et al. 2015, Counihan et al. 2012, AlBatayneh et al. 2014, Ignielzi et al. 1990, Ilha et al. 2018).

Chouchene et al. (2020) summarized treatment options for PEIR in a flow-chart but explicitly stressed, that there is no consensus on PEIR treatment in the literature.

Case reports

Case 1

A ten-year old Caucasian girl was referred from a local paediatric dentist for diagnostics and treatment of an atypical intracoronal lesion in the erupting symptomatic second right mandibular premolar with no signs of occlusal caries.

Medical history was non-contributory. Dental history revealed hypomineralization of all permanent first molars and of tooth 11. Several weeks earlier, she had presented to the dental office with her parents, reporting severe pain in the region of tooth 45 and a foul taste of pus during the night. According to the paediatric dentist’s report a massive swelling of the buccal soft tissues in the left mandibular premolar region had been present at that time (Fig. 2a).

Following inspection and taking a radiograph (Fig. 2b) the patient was referred to an endodontist for further treatment.

At her presentation in the endodontic office the patient was free of pain, palpation and percussion did not provoke pain, there was no swelling around the erupting tooth 45, and neither pus nor exudate could be expressed.

The tooth responded positive to sensibility testing with cold. No caries was diagnosed, the tooth was not mobile, percussion was uneventful and probing depths were in a physiological range.

As the root tip was not visible on the referring dentist’s radiograph a new single tooth radiograph was taken (Fig. 2c), revealing incomplete root development with a wide root canal and a wide apical opening, but with no signs of periapical inflammation.

A diagnosis of pre-eruptive intracoronal resorption was established. After informing the patient’s parents and obtaining informed consent, a decision was made to prepare a coronal access cavity to inspect the lesion. Although the young patient was noticeably anxious and demonstrated limited compliance, treatment under general anaesthesia was deemed unnecessary.

Following anaesthesia a coronal access was prepared under relative tooth isolation with cotton rolls, as rubber dam could not be fixed securely on the only partially erupted tooth crown. Immediately after penetration of the intact and caries-free enamel heavy bleeding was noted (Fig. 3a), no carious dentine was detected. The cavity was filled with heavily bleeding granulomatous tissue (Fig. 3b), which was gradually removed using rose- head burs and a spoon excavator, accompanied by irrigation with 3% sodium hypochlorite. During the procedure, the dental pulp was exposed. Initial attempts at bleeding control with copious irrigation using 3% sodium hypochlorite were unsuccessful; however, hemostasis was ultimately achieved at the root canal orifice following complete preparation and cleaning of the pulp chamber. Inspection under the dental operating microscope revealed no residual granulation tissue or ongoing bleeding within the pulp chamber. No portal of entry for the resorptive process was identified, and the mesial cavity wall—where a portal had been suspected— appeared intact, with no signs of perforation.

The exposed non-bleeding pulp tissue was covered with a layer of Biodentine (Septodont, Niederkassel, Germany) (Fig. 3c). Following adhesive coronal restoration (Fig. 3d) a final radiograph was taken to check placement of the Biodentine (Fig. 3e).

At the 1-year recall, the patient reported being completely free of signs and symptoms throughout the entire period, which was confirmed by clinical examination. Eruption of the tooth had progressed, and the crown had nearly reached the occlusal plane (Fig. 3f). The pulp showed a weak response to sensibility testing with cold, while percussion and palpation did not provoke any symptoms. Due to the patient’s pronounced gag reflex, a satisfactory periapical radiograph could not be obtained. However, a panoramic radiograph (Fig. 3g) demonstrated continued root development, including increases in root length and wall thickness, progressive apical closure, and no signs of periapical inflammation. Additional resorptive defects in other teeth were not detected on the panoramic radiograph. The comparison of the preoperative and the recall radiograph, the positive response to sensibility testing, and the ongoing tooth eruption confirm the positive course of the vital pulp treatment.

The 3-year control confirmed completely asymptomatic clinical findings and completion of root development with no signs of periradicular inflammation (Fig. 3h).

Case 2

In a two-and-a-half-year-old girl, shortly after the eruption of her mandibular right second primary molar, a deep coronal defect was observed in an otherwise completely caries-free dentition. Granulation tissue was visible within the fissure of the affected tooth (Fig. 4a). No previous (pre-eruptive) radiographs were available. The lesion did not show typical signs of carious destruction, but a rather granular appearance. The corresponding radiograph (Fig. 4b) shows a defect at the mesial cemento-enamel junction, probably the portal of entry of the resorptive tissue, and diffuse calcification-like structures inside the pulp-chamber. The pulp space still seemed to be protected by a thin layer of dentine, apically no inflammatory lesion was visible. Radiography and treatment were performed under general anaesthesia. As the pulp was exposed a pulpotomy was performed, no carious dentine was present. The tooth was restored with a preformed stainless steel-crown (Fig. 4c). At the one-year control the tooth presented asymptomatic, radiography still was not possible. One year later, the girl presented with a loose crown, the radiograph (Fig. 4d) demonstrated the fracture of the crown, probably due to the thin walls remaining after removal of the granulation tissue. The tooth was still asymptomatic.

Discussion

Pre-eruptive invasive coronal resorption (PEIR) resembles a rare and poorly investigated pathology. Due to the low incidence and the limited number of published cases, the etiology still is unclear, but parallels and similarities with external invasive cervical resorption (ECR) are obvious: the portal of entry for the resorptive cells at the cemento-enamel junction, and the still vital dental pulp, which is protected by the unmineralized and therefore unresorbed predentine.

Whereas external invasive cervical resorption (EICR) often extends circumferentially around the pulp chamber and progresses in a finger-like manner along the root canal toward the apex, the extension of pre-eruptive intracoronal resorption (PEIR) appears to be confined to the coronal portion of the pulp chamber. PEIR starts at the cemento-enamel junction or on the occlusal plane in deep fissures. In a classical scanning-electron microscopic study on extracted teeth, four different tissue formations were identified at the cemento-enamel junction:

- Enamel, overlapped by cementum

- Direct neighbourship between enamel and cementum

- Cementum overlapped by enamel

- No contact between enamel and cementum with a gap of exposed dentine between both (Neuvald & Consolaro 2000).

In one single tooth, several different formations may be present. The depth of occlusal fissures may not be completely mineralized, allowing ingrowth of tissue.

Radiographically, the intracoronal defect in the present cases extended to the cemento-enamel junction, but clinically no macroscopically detectable communication with the periodontal space was found. Also, the etiology of the resorption- inducing trigger remains unknown. Whether factors like hypoxia or ischemia, both discussed as probably relevant in the etiology of external resorptions are involved in the development of PEIR, also remains unclear.

Due to its early development before eruption of the tooth, the caries-free appearance of the dental crown and the absence of clinical symptoms, PEIR usually is detected only by chance. As first radiographs, mostly panoramic radiographs, in young patients frequently are taken by orthodontists these colleagues could play an important role in early detection and timely treatment of this pathology. With regard to dental invaginations, evaginations, and other dental malformations, raising awareness and providing information to orthodontists and paediatric dentists would be beneficial. Since the etiology of these conditions remains unknown, no preventive strategies have been established. However, it has been recommended that all available radiographs be carefully examined - including panoramic radiographs of unerupted teeth and bitewing radiographs of erupted teeth - to facilitate the early detection of intracoronal lesions. Nevertheless, treatment options for intracoronal defects detected in unerupted teeth remain uncertain.

In the case presented, the resorptive defect was detected relatively late—after eruption had already begun—when the first radiograph was taken due to tooth pain. As root formation was still incomplete, an attempt was made to preserve pulp vitality, despite a large pulp exposure during removal of the resorptive tissue. Remarkably, three years later, the treatment has proven successful. However, due to the patient’s young age and limited compliance, the procedure had to be performed under suboptimal conditions, without the use of a rubber dam. Ongoing follow-up is necessary to monitor the continued development of the tooth and the long-term maintenance of pulp vitality.

Conclusions

Pre-eruptive intracoronal resorption (PEIR) is a rare condition affecting the developing dentition, typically discovered incidentally and often misdiagnosed as “hidden caries.” Early detection - primarily through radiographic examination - and timely intervention can significantly improve the prognosis of the affected teeth, potentially enabling the preservation of pulp vitality and continued root development.

Acknowledgments

The authors deny any conflicts of interest. Both authors equally contributed to the manuscript.

Due to the young patients` age and their limited compliance not all of the figures and radiographs could be taken in optimal quality.