An unusual case of dens invaginatus on a mandibular second molar: a case report
Article information
Abstract
The present case report describes the endodontic treatment of a type III B dens invaginatus (DI) in a three-rooted mandibular second molar since the invagination invades the root and extends apically. Clinical and cone-beam computed tomography examination of the mandibular second molar showed a broadened coronal morphology, DI, a third root, periapical radiolucency, and compression of a distal root canal by the invagination, which developed an atypical semilunar shape. The tooth was diagnosed with pulpal necrosis, symptomatic apical, and peri-invagination periodontitis. Consequently, three-dimensional virtual reconstruction was conducted to improve anatomical interpretation and case planning and accelerate the intraoperative phase by reducing operator stress and minimizing intraoperative variables. The present case report aims to raise awareness of the existence of DI on the mandibular second molar.
INTRODUCTION
Dens invaginatus (DI), or dens in dente, is a common developmental anomaly described for the first time in humans in 1856 [1]. The term DI appears to be most appropriate, reflecting the invagination of the enamel organ into the dental papilla, with the formation of a pocket preceding the calcification of the dental tissues [2]. To date, there is no concurrence on its etiology [3]. However, both genetic and environmental aspects may be involved. The most affected teeth by this anomaly are the maxillary lateral incisors, frequently bilaterally.
Invagination can reach a varying depth, remaining localized at the level of the crown or extending deeper into the root. In the latter case, because of invagination, endodontic anatomy is modified and can become complex. The depth of the invagination could determine the external morphology of the affected tooth [4].
Clinically, a developmental anomaly should be suspected if the following isolated or simultaneous features are present: palatine or vestibular fissure; cylindrical or conoid-shaped coronal morphology; broadened coronal morphology; micro-dental tooth; and the existence of a cuspal bead [5].
Due to the clinical, radiographic, and histological variability of DI, several classifications have been proposed. Nevertheless, Oehlers’ classification [6], simultaneously assessing the depth of the invagination and its relation- ship to the pulpal tissue and periodontal ligament, is the most commonly used. In type I, the invagination is confined to the crown and ends as a blind sack. Type II extends apically beyond the cementoenamel junction, ending as a blind sack and never reaching the periapi- cal tissues. In type III, the invagination deepens likewise apically beyond the cementoenamel junction. However, it does not terminate as a blind sack. Rather, it com- municates with the periapical tissues through a lateral (type III A) or an apical (type III B) exit port, like a true foramen. Consequently, in type III, microorganisms can easily cause inflammation of the periapical tissues through the invagination canal called peri-invagination periodontitis [6].
The DI incidence varies between 0.3% and 10% [7]. It is often undervalued due to the difficulty of highlighting the change in external tooth morphology, particularly if it is not apparent or due to a quick intraoral clinical examination without clinical symptoms [8]. Therefore, invagination is often accidentally discovered during a radiographic examination and, in some cases, when the tooth is necrotic. Invagination favors the accumulation of organic substances inside it, which, being colonized by the microorganisms of the buccal flora, can cause early caries and later pulpal necrosis if left untreated [7]. Invaginated enamel may be hypomineralized and less thick in some areas or absent, creating additional direct access areas to pulpal tissue [3,9].
If pulpal necrosis develops before the complete formation of the root, the tooth will remain immature [7]. In this regard, early diagnosis followed by prophylactic treatment, consisting of sealing the invagination using composite resins, is fundamental. However, if dental pulp is involved, the treatment plan should include vital pulp therapy, orthograde endodontic treatment, apexogenesis or apexification, pulp regeneration, root-end surgery, intentional reimplantation, or even extraction of the tooth [10]. Treating these anomalies is complicated once irreversible pulpitis or necrosis develops, even if planned correctly.
DI occurrence in mandibular teeth, particularly posterior teeth, is an exceedingly rare phenomenon. Even more extraordinary is its presentation in mandibular second molars, a case that, to our knowledge, has yet to be reported in the existing literature. Most documented DI involves anterior teeth, likely due to the higher diagnostic visibility and the predisposition of anterior regions to developmental anomalies.
This report presents a unique and rare case of DI in a second mandibular molar, contributing to the current understanding of this anomaly’s prevalence and morphological diversity. In contrast to more commonly described cases, the invagination in a posterior mandibular tooth challenges current assumptions about the localization of this anomaly. Given the structural complexity of molars and their functional significance, the clinical implications for treatment and diagnosis are substantial. Furthermore, documenting this case aims to fill a critical gap in the literature and inspire further investigation into the potential for DI to manifest in atypical locations. The rarity of such cases underlines the importance of comprehensive clinical and radiographic assessment, especially in light of recent advances in imaging technologies such as cone-beam computed tomography (CBCT) and three-dimensional virtual reconstruction (3D-VR).
The presentation of DI in the mandibular second molar, as highlighted in this case, adds an important dimension to our understanding of dental anomalies and supports the need for expanding diagnostic criteria to include posterior teeth. This case report not only contributes to the current understanding of DI but also has significant implications for future research and clinical practice. It underscores the necessity of revisiting current epidemiological data on DI to reflect better the potential for its occurrence in a broader range of teeth. It also encourages the development of more extended diagnostic criteria and treatment guidelines.
This report aims to describe a rare case of a type III-B DI in a mandibular second molar with a 2-year follow-up and analyze its management from diagnosis to treatment.
CASE REPORT
The oral surgery department referred an 18-year-old Caucasian male to the endodontic department for treatment evaluation of the mandibular right second molar. The medical history was noncontributory and ethics approval was obtained from the Ethical Committee of Strasbourg Hospital and Medical Faculty before the treatment (No. CE-2024-30). Written informed consent was obtained from the patient for the publication of this report including all clinical images.
According to the clinical picture, the patient had previous episodes of localized pain and swelling related to the right mandibular posterior area. Clinical examination revealed the presence of a widened atypical coronal morphology in tooth number 47, pathological probing of 11 mm and 12 mm at the mesiobuccal and distolingual levels, respectively, no pain or swelling, negative response to the sensitivity tests, and slight tenderness to palpation and percussion.
The crown anatomy of tooth number 47 presented four buccal and three lingual cusps, resulting in a broadened coronal morphology with a trapezoidal shape where the major base was located at the level of the distal ridge. In contrast, the contralateral (tooth number 37) presented two buccal and two lingual cusps with a rectangular shape, the typical mandibular second molar morphology. Noticing the broadened coronal morphology of the 4.7 during clinical examination guided us toward diagnosing the developmental anomaly. However, a broadened coronal morphology can be found in the case of fusion and gemination; in these two cases, the crown should be larger than in the present case. Moreover, the invagination of the enamel was visible upon radiographic examination, which confirmed the fact that this was a case of dens in dente.
A CBCT analysis allowed the clear detection of DI on the 47 with a further third root and apical radiolucency (Figure 1A–C). The diagnosis of 47 was pulp necrosis and symptomatic periodontitis associated with peri-invagination periodontitis.
Preoperative radiographic and clinical view. (A) Axial plane cone-beam computed tomography (CBCT) image highlights the three roots, an atypical distal canal, and the invaginated canal. (B) Coronal plane CBCT highlighting the distal canal. (C) CBCT sagittal plane from left to right highlights the invaginated canal with the visible dens invaginatus, the distal canal, and the third root canal. (D) A preoperative radiograph after the access cavity was carried out urgently. (E, F) Clinical images.
Two weeks later, the patient was scheduled for non-surgical root canal treatment (NSRCT). To plan the NSRCT, a detailed segmentation of the DI was performed using CBCT data, which allowed a 3D-VR of the anatomy of this mandibular second molar with its different tissues. This task was performed with the software Mimics version 24.0 (Materialise, Leuven, Belgium) to aid in minimizing intraoperative variables and managing the treatment correctly (Figure 2), as the CBCT analysis alone did not permit a precise mental previsualization of the anatomy of this second molar.
Preoperative three-dimensional virtual reconstruction. (A–D) Different points of view of the three-dimensional (3D) reconstruction of the cone-beam computed tomography with the affected tooth with grey enamel and yellow roots; the eighth included light blue and the mandible and the remaining teeth in purple. (E) A 3D reconstruction of 4.7 by applying different opacities to the tissues: enamel and invagination in grey; yellow dentin, fuchsia pulp tissue, and dark yellow invaginated canal. (F) A 3D visualization of the fuchsia pulp tissue and the dark yellow invaginated canal. (G) Only 3D visualization of the pulp tissue is needed. (H) Visualization of the invaginated canal only.
On the day of the endodontic treatment, the patient reported that he had been to his private dentist a week earlier because of a painful episode on the causative tooth. The private dentist performed an access cavity and prescribed antibiotic therapy based on amoxicillin 1,000 mg every 12 hours for 1 week. Clinical examination revealed no spontaneous pain or swelling but rather the persistence of the pathological probing, which was detected during the first visit. A preoperative radiograph was taken to examine the current clinical situation (Figure 1D). Although the CBCT’s previous landmarks could not be used to their full extent after the general dentist’s intervention (Figure 1E and F), there were no indications to support performing an additional CBCT.
All procedures were done in conformity with current contemporary practices in endodontics. These included effective local anesthesia, rigorous clinical and radiographic analysis, appropriate rubber dam application, and operating microscopic utilization for precision (OMS 2380; Zumax Medical Co., Ltd., Suzhou, China). The access cavity was redesigned using a # 014 cylindrical diamond bur and an ultrasonic tip with a non-cutting end (Start X1; Dentsply Sirona, York, PA, USA). The canal orifices were quickly localized because the 3D-VR permits anticipating their exact location, considering that the tooth presented a rotation in the distolingual direction and atypical anatomy, with the distal canal being very buccal and kidney-shaped in the axial plane due to the compression created by the invagination (Figure 3A–D).
Intraoperative clinical steps. (A–D) Displays the different stages of access cavity preparation, providing a clear chronological progression of the treatment. (C) The purple arrow indicates the third root canal; the blue arrow is the M canal. (D) Cone-beam computed tomography distance of the invagination from the distal canal. (E) Location of the invagination. (F) The red arrow highlights the clinical localisation of the invagination. (G, H) Postoperative radiographs. (I) Postoperative clinical image.
The pulp chamber was constantly flooded with 6% sodium hypochlorite (NaOCl; COLTENE/Whaledent AG, Altstatten, Switzerland), and root canal shaping was performed for each canal, using a step-down technique [11]; this stage consisted of four sub-steps: (1) initial preflaring, (2) apical scouting, (3) glide path, and (4) shaping. Initial mechanical preflaring was performed using Proglider (Dentsply Sirona) until 2/3 of the estimated radiographic working length (WL) using an endodontic motor (X-smart-IQ motor; Dentsply Sirona) in a continuous clockwise rotation at 300 rpm and 4 Ncm.
Next, a #10 K-file (Dentsply Sirona) easily scouted the canals until WL + 0:5 mm. WL determination was established using an apex locator (Root ZX; J. Morita MFG. Corp., Kyoto, Japan). Then, a mechanical glide path was performed using a Proglider to WL. Following, the shaping phase was performed until the WL, using ProTaper Next X1 (PTX1) and X2 (PTX2) (Dentsply Sirona) with the same motor and setting. Although the two mesial canals were quite thin and curved, the most complicated canal to shape was the distal root canal with its semilunar anatomy. Therefore, it was decided to treat the canal as if it had three separate canal orifices. So, in the most mesial part of the canal, the PTX2 reached WL. While going distally, in the middle and distal part of the semilunar canal, it was decided to shape them using the same file PTX2 but by reaching –2 mm of the WL to avoid deforming the foramen. Throughout the mechanical preparation, 5 mL of 6% sodium hypochlorite was used for each canal between the file changes.
Once the canals were shaped, it was time to locate the invagination. This task was greatly facilitated, once again, by the 3D-VR performed during the analysis phase. Although the use of the operating microscope was indispensable, the visual localization of the invagination, even at high magnification, was not evident, probably induced by the intervention by the patient’s general dentist between the preoperative CBCT and the root canal therapy appointment. Moreover, the application of methylene blue (Cerkamed Group, Nisko, Poland) also proved ineffective in localizing the invagination. Consequently, the localization of DI, using Start X3 ultrasonic tip (Dentsply Sirona) while constantly checking the 3D-VR, was performed successfully at the first attempt (Figure 3E, F). Then, while the pulp chamber was soaked with 6% NaOCl, the walls of the invagination until its apical extension were carefully mechanically cleaned using PTX2.
Next, the final intracanal 3D irrigation phase, including the invagination canal too, was initiated. It started by flushing the canals with sterile water to remove intracanal sodium hypochlorite and avoid chemical interaction with the subsequent irrigating solution [12]. Afterward, for each canal, 5 mL of 17% ethylenediaminetetraacetic acid solution over 120 ± 10 seconds, activated using an Endoactivator (Dentsply Sirona) with the red tip (25/0.04) at 10,000 cycles/min (166 Hz) to dissolve the inorganic component produced by the shaping. Later, each canal was rinsed with 3 mL of sterile water, and the technique of internal heating of NaOCl and ultrasonic/sonic activation (IHAN) was applied to properly clean and disinfect the endodontic system and the invagination canal [13].
Three activation cycles were performed per canal. Each cycle, using fresh NaOCl, consisted of the following steps:
• NaOCl was internally heated for 6 seconds at 180°C using the FI-P handpiece (Woodpecker Medical Instrument Co. Ltd., Guilin, China) with its 35/04 bendable tip. It was positioned 3 ± 1 mm from the WL without touching the canal walls.
• Sonic activation of the heated NaOCl (20 seconds) was performed using an Endoactivator with the red tip placed 1 mm from the WL.
• The activated irrigant was left to act in the canals for 60 seconds.
The canals were then rinsed with 5 mL of sterile water and dried with sterile PTX2 paper points (Dentsply Sirona). Since no problems were encountered during the drying of the canals and invagination, such as purulent exudate or bleeding, the obturation phase was then performed. The mesial and the third root canals were obturated using a carried-based obturation technique, according to the manufacturer’s instructions, using Thermafil 25 (Dentsply Sirona) in combination with AH Plus root canal sealer (Dentsply Sirona). A sealer drop per canal was delivered using a coated paper point at the canal’s entrance and distributed along the canal using a second paper point.
The invagination and the semilunar distal canals were filled using a cold hydraulic condensation technique, with a PTX2 gutta-percha cone (Dentsply Sirona) for the invagination canal and two for the distal canal. Each gutta-percha cone was trimmed 0.5 mm short from the WL with a calcium silicate sealer (Well-Root ST; Vericom, Chuncheon, Korea). In this situation, since the hydraulic condensation technique is a “sealer-based” filling technique, the amount of the sealer introduced into the canal was considerably higher than the previous ones filled with the carrier technique. Calcium silicate sealer was inserted into the canal by direct injection into the middle thirds using disposable tips, fully packing the middle third.
Once the endodontic treatment was completed, an adhesive composite restoration was applied, according to the manufacturer’s instructions, using Prime&Bond active adhesive (Dentsply Sirona) combined with CERAM.x Spectra ST (Dentsply Sirona). Two postoperative radiographs were done (Figure 3G–I), and the patient was advised to take analgesics only if necessary. However, after the endodontic treatment, the patient had no pain or discomfort in the following days.
The first follow-up was performed one month later. The treated tooth was asymptomatic at the first check-up, and the pathological probing disappeared at the 6- and 12-month follow-ups. Upon the 2-year follow-up, the radiographic examination revealed complete healing of the periapical lesion and healthy lamina dura around the tooth, suggesting favorable healing; the patient was asymptomatic, and the tooth, with physiological probing, was negative to percussion and palpation tests (Figure 4).
Radiographic follow-up. (A) Preoperative radiograph. (B) Control X-ray at one year. (C) Two-year follow-up X-ray. (D) Preoperative cone-beam computed tomography (CBCT) and three-dimensional virtual reconstruction (3D-VR) where the lesion is visible. (E) CBCT and 3D-VR after 2 years, where complete tooth healing is noted.
This case report has been written according to Preferred Reporting Items for Case Reports in Endodontics (PRICE) 2020 guidelines [14].
DISCUSSION
DI is considered an anomaly of tooth development originating from an invagination of the enamel tissue that reaches the dental papilla during odontogenesis [15]. DI occurrence in mandibular teeth, particularly posterior teeth, is exceedingly rare. Even more extraordinary is its presentation in mandibular second molars, a case that, to our knowledge, has yet to be reported in the existing literature. Most documented DI involves anterior teeth [16], likely due to the higher diagnostic visibility and the predisposition of anterior regions to developmental anomalies. This report presents a unique and rare case of DI in a second mandibular molar, contributing to the current understanding of this anomaly’s prevalence and morphological diversity.
In contrast to more commonly described cases, the invagination in a posterior mandibular tooth challenges current assumptions about the localization of this anomaly. Given the structural complexity of molars and their functional significance, the clinical implications for treatment and diagnosis are substantial. Furthermore, documenting this case aims to fill a critical gap in the literature and inspire further investigation into the potential for DI to manifest in atypical locations. The rarity of such cases underlines the importance of comprehensive clinical and radiographic assessment, especially in light of recent advances in imaging technologies such as CBCT and 3D-VR.
The presentation of DI in the mandibular second molar, as highlighted in this case, adds an important dimension to our understanding of dental anomalies and supports the need for expanding diagnostic criteria to include posterior teeth. This case report not only contributes to the current understanding of DI but also has significant implications for future research and clinical practice. It underscores the necessity of revisiting current epidemiological data on DI to reflect better the potential for its occurrence in a broader range of teeth. It also encourages the development of more extended diagnostic criteria and treatment guidelines.
Endodontic treatment of teeth with DI is often complicated due to its anatomical complexity, and individualized strategies should be implemented. In the current case, NSRCT was preplanned owing to the aid of 3D-VR of the tooth, which gives each tissue a different color, and 3D printing was unnecessary. Moreover, to visualize all the anatomical variations, more than exploiting CBCT by analyzing axial, frontal, and sagittal planes was required. This approach improved diagnosis, anatomical understanding, and case planning and accelerated the intraoperative phase by reducing operator stress.
The 3D-VR was crucial in locating the exact position of all the canals orifices, including the DI. Furthermore, it aided in visualizing the actual anatomy of the endodontic system, particularly the semilunar or kidney shape of the DI [17,18].
Therefore, 3D-VR using different colors for different tissues could offer several advantages over CBCT and 3D printing when dealing with cases of anomaly of tooth development:
1. Diagnosis, since 3D-VR can highlight subtle distinctions in tissue boundaries and anomalies in a way that CBCT grayscale imaging struggles with. This advantage is particularly important in cases of DI, where identifying the exact point of enamel infolding and its relationship with the surrounding dentin and pulp is crucial to determining the treatment plan. Moreover, the 3D printed models might not have the resolution or visual clarity to detect such fine structural differences.
2. Anatomical understanding is important since the CBCT provides detailed cross-sectional imaging. Still, it often presents grayscale images that can make it challenging to differentiate between tissues, particularly when dealing with fine anatomical details like the invagination of enamel. Conversely, 3D printing on a single-material print often makes distinguishing between different tissue types easier without external markers or color codes. Meanwhile, color-coded virtual reconstruction allows a clearer and more immediate understanding of the tooth’s internal structure.
3. Case planning, since 3D-VR allows clinicians to manipulate, zoom, rotate, and virtually dissect the model. This level of interaction surpasses CBCT, where images are static and require mental reconstruction of the whole tissues. Moreover, virtual models are dynamic compared to 3D printing, which results in a fixed model. Clinicians can adjust transparency settings, isolate specific tissues, or highlight different anatomical features as needed, providing greater flexibility during diagnosis and treatment planning.
4. Speed and cost-effectiveness: since 3D printing can take time and resources, particularly for complex models, virtual reconstructions can be done faster without needing physical materials. This option can be especially beneficial in clinical sites where speed and efficiency are important for diagnosis and treatment planning. Additionally, adjusting or modifying virtual models instantly is more practical than 3D printing, where errors or changes require reprinting, incurring additional costs and delays.
In conclusion, the operator’s stress is generally reduced for the above reasons. Adopting this technology can lead to more predictable and individualized treatment outcomes, ultimately improving patient care in endodontics. Future studies should explore the broader application of 3D-VR across a wider range of DI cases to validate its potential as a routine standard in endodontic practice.
In addition to the 3D-VR, the operating microscope was fundamental in the current clinical case [19,20]. It allowed for the meticulous examination of the pulp chamber’s floor and, consequently, the visualization of all canal orifices. Henceforth, the correct choice of mechanical shaping files, proper irrigation, and appropriate obturation techniques were established in the presented case.
The PTX system was chosen for the shaping phase to benefit from the advantages of an asymmetrical cross-section. This offers better resistance to bending stresses and a kinetic snake-like movement while maintaining excellent centering ability and cutting performance, which is important when dealing with accentuated curvatures. The IHAN technique was preferred during the chemical irrigation phase because it is easy, fast, low-cost, and highly effective [13,19] in pushing the boosted NaOCl deep into all the lateral anatomies, isthmuses, apical deltas, and dentinal tubules [21]. Choosing the proper obturation approach was essential to maximizing the result obtained by the IHAN [22–26].
Therefore, carrier-based obturation managed the curved and complex anatomy of the mesial and third root canals. At the same time, cold hydraulic condensation was chosen to fill the invaginated canal and the distal canal. This approach allowed, on the one hand, to easily manage the wide apex of the invaginated canal and improve the recruitment of periodontal cells in the apical part of the invagination and, on the other hand, to 3D obturate the semilunar canal using two gutta-percha cones in this instance. The two-year follow-up highlights the healing of the case and indicates the protocol used to treat the present case was effective.
CONCLUSIONS
Most documented cases of DI involve anterior teeth; upon reviewing the literature, no cases of DI in mandibular second molars were reported. The potential occurrence of DI in any tooth, including the mandibular second molar, should not be underrated. Furthermore, a careful clinical examination, which includes inspecting the tooth’s surface for unusual pits or fissures, and radiographic analysis, which involves taking multiple angled X-rays to reveal any internal anomalies, could help identify these anomalies early on and intervene only prophylactically.
In the case where NSRCT is required, the management could be quite complicated, bearing in mind that the canal anatomy of these teeth is often modified, and dealing with the invaginated canal is always challenging.
Ultimately, in situations where a precise understanding of the intricate relationship between enamel, dentin, and pulp is critical, 3D-VR with color-coded tissues emerges as a game-changer. It provides a superior alternative to CBCT and 3D printing, offering better visualization of the complex anatomy, dynamic interaction with the model, accurate diagnosis and pretreatment planning, improved patient communication, and cost-effective, flexible enhancement of the clinical workflow. This technology opens up exciting possibilities for the future of dental diagnostics and treatment.
Notes
Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Funding/support
None.
Acknowledgments
The authors thank Doctor Chasson JM, the patient's private dentist.
Author Contributions
Conceptualization: Mancino D. Data curation: Iandolo A, Abdellatif D. Investigation: Mancino D, Bornert F. Methodology: Abdellatif D. Project administration: Mancino D, Haïkel Y. Supervision: Haïkel Y. Visualization: Bornert F. Writing - original draft: Mancino D. Writing - review & editing: Abdellatif D. All authors read and approved the final manuscript.