Molar-incisor malformation: Eight new cases and a review of the literature

Prevalence and morphological features of molar-root incisor malformation in children attending a specialist paediatric dental unit

BACKGROUND

Molar-root incisor malformation (MRIM) is a rare dental anomaly featuring constricted cervical margins and tapered, narrow root and pulp morphology, often associated with severe toothache and infection.

AIM

The aim of this study was to determine the prevalence of MRIM in children seen in a specialist paediatric dental unit of a tertiary referral hospital and to describe the characteristics of affected individuals.

DESIGN

This study was an audit of children attending from November 2020 to November 2021. Radiographs were used to identify individuals with MRIM, and clinical data were collated. In addition, histology and microcomputed tomography (microCT) imaging were performed on teeth extracted from an affected individual.

RESULTS

The prevalence of MRIM was five cases of 1054 children examined (0.47% or 1:210). The permanent first molars were affected in all five children and the primary second molars in two children; all children had medical comorbidities and multiple exposures to general anesthesia before 4 years of age. In addition, histological and microCT analyses displayed numerous microchannels connecting the pulp chamber to the external surface of the tooth at the furcation.

CONCLUSIONS

Molar-root incisor malformation is an uncommon dental anomaly affecting paediatric patients with multiple comorbidities and is characterized by porosities extending from the pulp chamber to the external tooth surface, predisposing the risk of bacterial ingress from the oral cavity into the pulp chamber. Early detection may prevent atypical odontogenic facial pain and infection.

A Review of Selected Dental Anomalies With Histologic Features in the Pediatric Patient

Unique dental conditions in children include odontogenic cysts and tumors, hereditary dental diseases, developmental anomalies, and lesions associated with the eruption of the primary or permanent teeth. Many of these conditions have long lasting effects on the adult dentition in terms of affecting esthetics, function, and overall quality of life. Inherited dental syndromes affect the dental hard tissues specifically the enamel, dentin, and/or cementum in a generalized manner, involving both primary and permanent teeth. These conditions manifest in altered quality or quantity of the hard tissues, leading to fragility, tooth loss and dental diseases such as caries, periapical pathology, and periodontal disease. This category includes amelogenesis imperfecta, dentinogenesis imperfecta, dentin dysplasia, hypophosphatasia, and hypophosphatemia. Developmental defects such as regional odontodysplasia are defined by involvement of the primary and permanent dentition in a localized manner, identified in early childhood. This review will elaborate on the histologic findings in these selected dental conditions with a discussion on clinical and radiographic findings, as well as molecular features wherever appropriate.

Molar-root incisor malformation - a systematic review of case reports and case series

OBJECTIVES

Molar-root incisor malformation (MRIM) is a seldom reported condition characterised by disturbances in root development of first permanent molars. This systematic review aimed to collate the clinical characteristics of individuals diagnosed with MRIM.

MATERIALS AND METHODS

A systematic search strategy using PubMed, Embase, Web of Science, and SCOPUS databases was performed through to March 2023. Inclusion criteria were case reports or case series including a diagnosis consistent with MRIM. Critical appraisal for all included studies utilised the Joanna Briggs Institute (JBI) critical appraisal checklist for case reports and case series and collation of clinical characteristics was performed in JBI System for the Unified Management, Assessment and Review of Information program.

RESULTS

The search identified 157 studies from which 35 satisfied the inclusion criteria. After full-text review, a total of 23 papers described the MRIM dental anomaly and were included in this paper. A total of 130 reported cases were retrieved, with age ranging 3-32 years, and males affected 1.16:1 females. Presence of neurological conditions, premature birth history, medication, and surgery within first years of life were synthesised and described.

CONCLUSIONS

The aetiology of MRIM is yet to be determined but epigenetic changes from significant medical history in the first years of life are likely to influence the development of this root malformation. First permanent molars were most commonly affected, but clinicians should be aware that permanent central incisors, primary teeth and other permanent teeth may also be affected.

Morphological, histological, and chemical analysis of first permanent molars with molar incisor malformation

PURPOSE

Molar incisor malformation (MIM) is a dental anomaly rendering first permanent molar pulps inflamed/necrotic at a young age. It often affects permanent incisors, primary second molars and less frequently other teeth. The purpose of this study was to investigate the anatomy and histology of MIM in seeking insight into its pathogenesis.

METHODS

Five MIM first permanent molars were examined with micro-computed tomography (micro-CT) for 3D morphology, with scanning electron microscopy for microanatomy, with energy-dispersive X-ray spectrometer (EDS) for chemical composition and for histology with optical microscopy. Composition differences were statistically determined using one-way ANOVA.

RESULTS

Micro-CT confirmed dentin abnormalities in the middle and cervical third of the crown in the form of the radiodense 'cervical mineralized diaphragm' (CMD). This was peripherally intertwined with enamel fjords and projections severely disrupting the integrity of pulp chamber and its continuity with root canals. EDS showed increased Ca in CMD compared to dentin. The histological examination revealed anomalous osteodentin-like hard tissue with denticles in the CMD.

CONCLUSION

An interconnection of anomalous cervical enamel with crown CMD dentin preceded to the severe pulp chamber and root dysplasias in MIM molar teeth.

Management of Severely Aberrant Permanent First Molars in Molar Root-Incisor Malformation Patients: Case Series and a Guideline

Recently, a new type of dental anomaly, a molar–incisor malformation or molar root–incisor malformation (MRIM), was recognized. The disease phenotype is now relatively well characterized; however, its etiology and disease-mechanism need to be elucidated. The affected teeth do not respond well to conventional treatment because of severe malformation and an unusual root structure. In this study, we present the treatment of MRIM cases with the extraction of severely aberrant permanent first molars (PFMs) and suggest that the PFM extractions are performed when it is clear that third molars will develop. The purpose of this report was primarily to present amendments to the guidelines for the treatment of patients with MRIM.

Compositional and micromorphological features of hypoplastic enamel in children’s permanent teeth

Enamel hypoplasia is the most common disease of hard tooth tissues of non-carious origin emerging before their eruption. It develops as a result of a delayed and perverse function of ameloblasts leading to the violation of the processes of formation and mineralization of tooth protein structures. The clinical manifestations of enamel hypoplasia are spots, defects in the form of pits, cup-shaped depressions, grooves on various surfaces of child’s teeth. The work is devoted to a comparative investigation of microstructural and compositional features of intact and hypoplastic enamel in children’s permanent teeth using analytical scanning electron microscopy with energy-dispersive X-ray spectroscopy. The hypoplastic enamel is enriched in organic substance and has an irregular structure without keyhole-shaped prismatic structure. Mineral deposition is indicated for hypoplastic enamel including hydroxyapatite with globular structure and calcite and halite, which might have been caused by the violation of extracellular local environment probably due to the enamel hypoplasia development.