Impaction of Primary Second Molar and Permanent Second Premolar – Report of a Rare Case

The purpose of this manuscript is to present an unusual case about impaction of primary mandibular second molar disrupting the second premolar leading to its disto-angular impaction in a 28-year-old Indian male patient. The presence of this dental variation was accidentally diagnosed following a radiographic examination that was taken for some other dental reason. There were no associated signs and symptoms related to this condition. Occurrence of primary molar impaction is a rare phenomenon and hence reporting such rare conditions is of great importance to enrich existing literature and also to frame new guidelines related to diagnosis, classification, clinical features and different treatment modalities rendered.

Keywords: Ankylosed primary molar, Impaction, Primary molar, Submerged molar, Second premolar variations

Dental literature shows various conditions related to eruption phenomenon of human teeth which may include eruption failure, impaction, ectopic eruption and intraosseous tooth migration or transmigration [1-5]. Impaction of teeth is described as “any tooth that fail to erupt into a normal functional position and remains unerupted beyond the time at which it should normally erupt [6]. Compared to permanent dentition, occurrence of impaction involving primary teeth is relatively a rare condition. The exact ethology behind this condition is not known however, various hypothesis have been proposed consisting presence of odontomas, cysts, eruption failure, ankylosis and obstructions in eruption pathway. Most of the time, impaction involved the primary second molars followed by central incisors [7]. Early detection, diagnosis and treatment of this condition is highly essential as the impaction of a primary tooth cause displacement of the succedaneous permanent tooth and also disturb the growth of the permanent dental arch. When primary molar gets impacted, the position of the permanent premolar gets disturbed resulting in varied location of the tooth like below the roots of primary molar or beside the primary molar either mesial or distal to it or sometimes seen located above the primary molar at the occlusal aspect of primary molar. Primary molar impaction also causes ectopic eruption and deviation in the eruption pathway of the related tooth [6-8].

Literature search showed reports on this eruption phenomenon occurring more commonly in children and usually detected in age group ranging from six to 12 years following a radiographic examination to rule out clinical absence of a primary molar. The present case reported here is unique as the condition existed even at the age of 28 without evidence of any root resorption in the roots of primary molar or with absence of signs and symptoms arising from the impacted second premolar. Therefore, the present case was recorded and manuscript was drafted to show case an occurrence of unusual dental variations occurring in human teeth.

A 28-year-old male patient reported to a private dental clinic complaining of bad breath from past few months. Patient was moderately built and well-nourished with good behaviour. There were no associated signs and symptoms of any systemic, metabolic and syndromic conditions. Intraoral examination showed presence of heavy amount of calculus covering all teeth including both maxillary and mandibular teeth. All permanent teeth were present and erupted except for the mandibular right third molar and left second premolar. The oral health status was poor. In the lower arch spacing was observed between canine and first premolar on the left side. As second premolar was clinically missing and there was no history of previous extraction of any tooth in this region, to rule out its presence or absence, patient was subjected to radiographic examination. Following examination of the radiograph, an unusual dental finding was observed. On left side of the mandibular arch, the primary second molar was impacted, drifted distally located in a distal inclination and placed below the level of the cervical margin of the adjacent first premolar and first molar within the alveolar bone (Figure 1).  Below this impacted second primary molar, the permanent second premolar was also impacted in disto-angular position. The root of this premolar was completely formed and was placed buccally with crown facing lingually. The root of this premolar was located close to the mandibular canal with its apical one third part crossing the mandibular canal (Figure 1). On right side of the mandibular arch, the third molar appeared to be congenitally missing. No other dental findings were observed. Finally, the case was diagnosed as a case of idiopathic impaction of primary second molar in association with disto-angular impaction of the second premolar. As patient was not having any signs or symptoms associated with these two impacted teeth and as the premolar root was close to the mandibular canal and considering the consequences, difficulties of surgical procedures, no treatment was carried out and the patient was kept under regular observation.

Figure 1: Panoramic radiograph showing impaction of primary left second molar (red arrow) and disto-angular impaction of left second premolar (yellow arrow).

It is been reported that the incidence of primary tooth impaction is twice as common in the mandible as in the maxilla and the most commonly affected teeth are mandibular second molars. Similar to the reported previous cases, in the present case too, the mandibular primary second molar was impacted disrupting the second premolar eruption leading to its impaction [6].

Matsumaya et al [6] recently published two cases on severe impaction of the primary mandibular second molar. In one case, recorded in a 7-year-old female child patient, the mandibular primary second molar was impacted and located in mesiolingual inclination within the alveolar bone. The developing second premolar with only crown portion formed was placed in mesial inclination and located between the apical side of the mandibular right first primary molar and the occlusal part of the primary second molar. Small calcium deposits were evident lingual to the impacted mandibular right second primary molar which were diagnosed on Computed tomography scan. In this case, authors extracted the impacted second primary molar and also removed calcium deposits. However, following periodic observation, the second premolar did not erupt clinically. Later when the child was 10 years of age, authors performed fenestration followed by immediate traction of the unerupted premolar, which later successfully erupted into normal occlusion. In another case, reported in 6-year-old female child, the mandibular second molar was impacted and located in distal inclination. Sagittal reconstruction computed tomography scan showed that the root apex of the impacted primary molar was extremely close to the mandibular canal and mandibular plane. Moreover, the impacted second primary molar was surrounded by X-ray permeable regions with clear boundaries in panoramic radiograph and CT [6]. Based on this finding, authors in this case did not extract the impacted primary second molar in order to avoid injuring the mandibular canal and neighbouring dental germs. The patient was kept under regular observation and in later stages when the patient attained 16 years, the second premolar erupted normally into occlusion with slight inclination. However, the primary second molar remained impacted. Contrast to this, in the case reported here, although patient attained 28 years, the second premolar was remained impacted [6]. Therefore, this shows the position of the premolar tooth germ is an important determining factor in concluding whether it will erupt or not. If the premolar tooth germ is located occlusal or beside to the impacted primary second molar there are more chances for eruption of the premolar. If the premolar tooth germ is located below the roots of impacted second primary molar, the possibility of premolar eruption is absolutely nil. The impacted primary second molar acts as an obstruction to the eruption pathway of the second premolar. The most characteristic finding observed in the second as reported by Matsuyama [6] was the position of the second premolar which was located on the occlusal side of the impacted mandibular second primary molar. Therefore, eruption of second premolar was possible in this case.

In 2024, Nagaveni NB and Ashwini KS examined panoramic radiographs of Indian children aged from 3 to 15 years for presence of impacted primary molars [7]. Author found a prevalence of five cases during two years period with all five cases occurred in the mandible. Among five cases, one case involved the first primary molar (20%) and another four cases involving the second molar (80%). Four cases occurred on the left side (80%) and one on the right side (20%). Three cases were observed in boys (60%) and two cases in girls (40%). Based on these recorded cases and from reported previous cases author gave a new classification system on the level of primary mandibular molar impaction (Table 1). According to this classification, primary molar impaction can be classified into three types as type I, II and III. Therefore, in this retrospective study author recorded two cases of Type III – extremely severe (40%), two as severe – type II (40%), and one as type I – moderate (20%). When condition of the succedaneous second premolar was assessed, two patients exhibited distal drifting of the second premolar tooth bud towards the second primary molar.  In one case, malformed second premolar was erupted clinically and, in another case, odontoma formation was noticed and in one case second premolar was erupted buccally [7]. Based on new classification, in the present case, the level of impaction was categorised as moderate (Type I), as the impacted primary mandibular second molar was placed below the level of cervical third of adjacent erupted teeth within the alveolar bone. A recent another retrospective analysis revealed more occurrence of primary molar impaction on the left side compared to right [8]. The similar observation was found in the present case too.

Table 1: New classification system on the level of primary mandibular molar impaction (given by Nagaveni NB) [7]

Kjaer et al [8] examined radiographs of arrested eruption of primary molars and reported that permanent successors were located on the occlusal side of the unerupted primary molar in 4 of 29 cases. A survey of the literature revealed only a few reported cases in which a permanent tooth germ was placed over the impacted primary molar [8-11].

Eruption of human tooth occurs in different stages [12]. Early in the presumptive stage, the successional permanent teeth develop lingual to and near the occlusal level of their primary predecessors. At the end of this stage, the premolars are located under the roots of the primary molars. The change in position of the tooth germ is primarily not the result of apical movement of the permanent tooth germs, but of the eruption of the primary tooth and the coincident increase in the height of supporting tissues [12]. During development, the dental germ of the lower second premolar originates from the successional tooth band at the lingual side of the dental germ of the mandibular second primary molar. As a cause of positional reversal, inhibition of presumptive movement of the primary molar may occur and results in displacement of the succedaneous permeant premolar [12]. Due to above assumed hypothesis, the different location of second premolar was observed in various published cases.

Till date, there have been relatively few reports of impaction and tooth eruption failure in primary teeth compared to permanent teeth. Reports of exact prevalence of primary molar impaction in different ethnic people is not found in the dental literature. This shows requirement of future prospective studies including large sample size encompassing different population across the globe.