Indian Journal of Multidisciplinary Dentistry

: 2018  |  Volume : 8  |  Issue : 2  |  Page : 124--127

Fusion and agenesis: Considerations in primary, mixed, and permanent dentition

Praveen Kumar Reddy Karnati1, Anand Siddappa Tegginamani2, Prashant Choudhary3, Priyank Seth1,  
1 Department of Orthodontics, Faculty of Dentistry, SEGi University, Kota Damansara, Selangor, Malaysia
2 Department of Oral Pathology, Faculty of Dentistry, SEGi University, Kota Damansara, Selangor, Malaysia
3 Department of Pedodontics, Faculty of Dentistry, SEGi University, Kota Damansara, Selangor, Malaysia

Correspondence Address:
Dr. Praveen Kumar Reddy Karnati
C-3-5, Casa Indah 2, Tropicana Indah, 47810 Petaling Jaya, Selangor


Tooth anomalies tend to become a challenge in the contemporary world with their diversified and gradual raise in prevalence due to genetic aberrations, trauma, and environmental influences. Fusion, one among the varied tooth anomalies is seen both in primary and permanent dentition either in maxillary or mandibular arches, makes its significance unique by altered pulp canal anatomy internally. Tooth size arch length discrepancies with increased caries risk externally and altered response to physiological resorption if permanent tooth is dichotomized from the same dental lamina internally, are more concerning areas. The present case report discloses a unilateral fusion of primary lateral incisor with canine and agenesis of permanent lateral incisor alleviating the eruption dogmata with a provision of physiological space maintainer in retaining the missing permanent lateral incisor till the late mixed dentition period.

How to cite this article:
Karnati PK, Tegginamani AS, Choudhary P, Seth P. Fusion and agenesis: Considerations in primary, mixed, and permanent dentition.Indian J Multidiscip Dent 2018;8:124-127

How to cite this URL:
Karnati PK, Tegginamani AS, Choudhary P, Seth P. Fusion and agenesis: Considerations in primary, mixed, and permanent dentition. Indian J Multidiscip Dent [serial online] 2018 [cited 2020 Jun 6 ];8:124-127
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Individual tooth anomalies are common both in primary and permanent dentition with fusion being seldom among but widely distributed around the globe. The prevalence is indeterminate with sex distribution and branching out by inherited-congenital, syndromic-non syndromic, maxillary-mandibular, anterior-posterior, unilateral-bilateral, and complete-incomplete expressions. Primary dentition is mostly affected by 0.5% than permanent dentition 0.1%, among are the Caucasian children 1.6%, North Chinese 1.52%, Mongoloid 3%, Japanese children 4.1%, and South Chinese children 4.1%, predominating.[1],[2],[3],[4],[5],[6],[7],[8] The proportion of permanent successor anomalies is reported up to 50% following primary double tooth, including congenitally missing permanent successor, supernumerary morpho diversification, and repeated double teeth formation.[9],[10]

Twinning is more common with primary canine and lateral incisor which also associates with other anomalies such as a supernumerary tooth or peg-shaped succedaneous permanent tooth.[9],[10],[11] The present case report discusses one such classic incidence of fusion of primary lateral incisor with canine and agenesis of permanent lateral incisor, elaborating on interdisciplinary considerations to retain functional occlusion for the permanent dentition.

 Case Report

A 9-year-old Malaysian Chinese origin boy in his early late mixed dentition accompanied by both the parents, had reported to the clinic with a chief complaint of forwardly placed upper and lower front teeth. His parents gave a history of thumb sucking habit which he discontinued a couple of years back. The medical history was noncontributory with no familial genetic predisposition. On examination, he was quite normal with the extra-oral features except for the pronounced nasolabial angle. The intraoral picture was accordingly with the chronologic age mirroring the dental age. Oral hygiene was fair with the international caries detection and assessment system (ICDAS) 5 in 73, ICDAS 3 in 83, 85, and ICDAS 2 in 54, 64, and 84 [Figure 1].{Figure 1}


Interarch relationship disclosed normal buccal occlusion with anterior developing deep bite and increased overjet. Discrepancy with narrow arches, proclined and protruded maxillary anterior teeth with rotations, and a lower dental midline shift towards the right side necessitated to think of space distribution. The absence of primate and developmental spaces reflected the early shift in establishing Class-I molar relation in the mandibular arch in spite of missing 42 and incisor liability in the maxillary arch [Figure 2]. The upper incisor crowding had reflected arch form deficiency than tooth material deficiency and require arch development in the anterior region beyond broadbent phenomenon at this age to alleviate one of the potential for canine impaction. Fusion of 82 with 83 was clearly evident with pronounced developmental grove, a Type II, clinically. Periapical radiograph displayed obliterated coronal pulp chamber with prominent dual pulp chambers and medial radioopacity extending beyond the coronal pulp into the radicular pulp that was resorbed as a result of the chronological process [Figure 3]a, [Figure 3]b, [Figure 3]c.{Figure 2}{Figure 3}


Clinical considerations in primary dentition

Fusion leads to irregularities in crown morphology which attracts more food accumulation and making self-cleansing as well as mechanical cleaning difficult, leading to caries development. A periodic follow-up for preventive measures is better considered.[3]

Clinical considerations in the mixed dentition

In this condition, fusion acts as a transient physiological space maintainer between the early and late mixed dentition transition, walling the 2 years of inter-transition period as the succedaneous 42 is genetically missing. A lingual-bonded cantilever space maintainer, fixed on 32 and sliding onto 4l, loaded with medium open coil spring of 50 g force, was planned to counter the space loss from chronologically delayed permanent canine tooth eruption. This attachment also regains the missing 42 space once the 43 erupts to its functional position, simultaneously establishing midline along with differential growth of jaw [Figure 4].{Figure 4}

Agenesis will steer the anterior arch width deficiency leading to increased overjet, overbite, and posterior arch length discrepancy leading to superclass-I molar relation due to the utilization of leeway space and more mesial migration of permanent canine, in the absence of other factors. This type of malocclusion is due to tooth material loss of approximately 5.5 mm in the late first-transition period (7–8 years).

This space is preserved by the combined width of fusion tooth, i.e., of 82 with 83 throughout the first transition and inter-transition period for about 4 years (6–10 years), which can also be called as physiological space maintainer.[12] Later, the primary canine undergoes physiologic root resorption due to the erupting permanent canine (43) at the early second-transition period.

As the dental eruption sequence generally follows 6123457 in the mandible, the simple mechanical intervention will be sufficient to regain the 42 space by regainer appliance preventing mesial migration of posterior teeth (4, 5, and 6) of the same quadrant and encouraging 43 to erupt mesially. Later, distalization of 43 will be done once adequate labio-lingual cortical width for prosthetic replacement of 42 is achieved. At the end of the second-transition period (13–14 years), simultaneous establishment of midline by preventing mesial displacement of contralateral teeth resulting in midline deviation can also be achieved.

In conjecture, if the primary lateral incisor and canine are with their successors, then fusion can complicate the physiological processes as the chronological root resorption for primary lateral and canine are at different ages. Premature exfoliation of fusion tooth due to resorption can also encourage early eruption of permanent teeth. Other clinical problems being, retarded resorption with the ectopic eruption of permanent teeth or eruption failure due to lack of space.[8]

An interdisciplinary approach[6] can effectively manage problems-associated with fusion during this phase.

Clinical considerations in permanent dentition

In the mandible, agenesis of 42 can lead to Bolton's discrepancy that can compromise the required 77.2% lower anterior tooth material with 100% of upper anterior tooth material to have normal overjet and overbite. The increased overjet and overbite is multifactorial in this case. It was due to genetically deficient tooth material and thumb sucking habit: relatively narrow maxilla, and upward deformation of the premaxilla with proclination of maxillary incisors [Figure 2].

An interdisciplinary approach can effectively manage problems associated with fusion during this phase by orthodontic treatment plan including prosthesis placement.[9]


Comprehensive case history, clinical examination, and radiographic interpretation are the prime criteria for a diagnosis. The clinician should possess sound knowledge with experience in critically understanding and managing such conditions in establishing functional occlusion.

Learning objectives

This article provides information on:

Estimation of the dental development relating to chronological shedding and eruption of the tooth by preventing transverse arch width as well as sagittal arch length discrepancies, in special conditions that lead to bolton's discrepancy leading to increased overjet and overbite, can be assessedPlanning guided space regaining procedures to facilitate prosthetic restoration of the missing permanent tooth and midline discrepancy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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