Unusual Impaction-Rosettes of Multiple Unerupted Molars: Review Article

Background: There is a wide spectrum of syndromes that include dental, oral and craniofacial disorders. Early diagnosis is often crucial for their effective treatment. However, not all syndromes can be clinically identified on time, especially in cases of absence of known family history. Moreover, the treatment of these patients is often complicated because of insufficient medical knowledge and because of the dento-alveolar and craniofacial developmental variations. Objective: The cases of a single impacted tooth are common. But the ones of multiple unerupted permanent molars are a rare phenomenon. They could be either isolated or associated with local or general pathologic factors. When identified, they present a challenging problem for the dentist, or the oral and maxillofacial surgeon. The aim of the article is to review the possible etiology and management modalities in cases of multiple unerupted molars. Results: The Pubmed and Medline database was searched. The information found was presented mainly by case reports. Unfortunately, because of the rarity of this clinical finding and the great clinical diversity, it is difficult to propose clinical procedure protocols. So, we assume, that the real incidence of that condition might be higher than the one mentioned in the literature. Discussion: It seems that due to the rare occurrence of severe complaints, many patients with multiple unerupted molars do not regularly present to their dentists, until other conditions take place. Clinical phenotyping together with reviewed data and evidence-based conclusions will ultimately pave the way for preventive strategies and therapeutic options in the future. This will improve the prognosis for better functional and aesthetic outcome for these patients and lead to a better quality of life. Conclusion: Care of individuals with syndromes affecting craniofacial and dento-alveolar structures is mostly treated by an interdisciplinary team who becomes more frequently involved in the refined diagnostic and etiological processes of these patients. The dentist and the surgical specialist must have a thorough knowledge about the various forms and possible etiology of tooth non-eruption. It can be a sign of various medical conditions. Therefore, detailed and specific investigations are further required, preceding a patient-tailored treatment plan.


Tooth Eruption and Non-eruption
Tooth eruption is a multifactorial process of maturation, whose biological mechanism is still unclear. Among the various hypotheses that have been proposed, are the ones of root growth and periodontal formation, the dental follicle theory and the guidance theory [1,2].
The eruption of some teeth may be delayed, and in almost 20% of the population it does not occur at all. [3,4] Most commonly it involves the mandibular and maxillary third molars (Figure 1), the maxillary canines ( Figure 2) or central incisors/mesiodens ( Figure 3) and the mandibular second premolars (Figure 4). [5,6] The non-eruption of the first and second permanent molars is rarer: 0.03% -2.3%. (Figures 4 and 5) [5,[7][8][9] The prevalence in the normal population is 0.01% in the case of the first permanent molar, and 0.06% in the case of the second one [5].

Classification
According to the classification by Andreasen and Kurol [10], the absence of eruption of the second molar could be caused by three events: impaction, primary retention and secondary retention [11].
Impaction is the cessation of the eruption of a tooth caused by a clinically or radiographically detectable physical barrier (Figure 3), an abnormal tooth direction ( Figure 1 -lower jaw, and Figure 5) or lack of space ( Figure 2). Primary retention (unerupted and embedded teeth) refers to the cessation of eruption before emergence, without a physical barrier in the eruption path and not due to an abnormal position. (Figure 1 -upper jaw, and Figure 4) [2] It is probably caused by a disturbance in the dental follicle which fails to initiate the metabolic events responsible for bone resorption in the eruption path. [12] The radiographies show normal orientation of the molar. (Figure 1 -upper jaw, and A special case of multiple unerupted permanent molars are the "kissing" or "rosetting" molars. Van Hoof was the first who described "rosetting" molars in an intellectually retarded 31-year-old man in 1973. [14] Almost 18 years later, in 1991, Robinson et al. [15] proposed the term "kissing" molars to describe a similar condition in a 25-year-old man. The same year, Nakamura et al. [16] suggested the possible association of "kissing"/"rosetting" molars with MPS (mucopolysaccharidosis) following his radiographic study of three adult cases of MPS. They concluded that "rosetting" molars can occur also as an isolated event. But the possibility of any systemic disease is only suggestive in such cases. [16] Nakamura's associative finding was further corroborated by McIntyre. [17] By definition, "kissing" molars are "impacted mandibular permanent molars that have occlusal surfaces contacting each other while their roots are pointed in the opposite direction, sharing a single follicular space with a continuous cement-enamel junction". [14,15,18] However, the term "kissing phenomenon" has also been used to describe a similar appearance with other impacted teeth. [15,[19][20][21] In the literature, there are controversies regarding the distinction between unusual impaction and rosettes of molars. (Figures 4 -8) It has been suggested that the absence of a contact between the two impacted molars discounts them from being classified as "kissing"/"rosetting" [18,22].

Classification
A classification according to the angle of contact between the two teeth involved in kissing is made to help describe any kissing teeth and to give an impression about the severity of the condition: full kissing (if both teeth facing each other are along the same long axis), partial kissing (there is an obtuse angle between the long axis of crowns of both the teeth - Figure 5) and minimal kissing (if the long axis of both the crowns is at an acute angle to each other - Figure 4) [21].

Unusual Non-eruption -Etiology and Co-morbidity
Multiple unerupted "rosetting" molars may occur either as a disease component or an isolated feature. This condition can be caused by systemic or local etiologic factors. It may be also related to syndromes and metabolic disorders.
Among the local factors involved in the failure of eruption are the inclination (Figures 1, 4-6) and the depth of the molar (Figures 4 and 6), the developmental stage of the root (Figures 4, 6 and 7), malocclusion disturbances of the deciduous dentition, the position of the adjacent teeth (Figures 2 -4), space deficiency in the dental arch, supernumerary teeth (Figures 3 and 8), odontomas or cysts. [6,7,24] According to a study by Baykul et al. [25], 50% of the total cases investigated by them were associated with dentigerous cyst. Moreover, patients with unerupted molars have been reported to have a more frequent occurrence of dismorphological teeth (Figures 3 and 8) and cranial anomalies ( Figure 7) [9,26].
Authors like Sun et al. [27], Sandler et al. [28] and Cho et al. [29] reported that HDF (hyperplastic dental follicles, or its synonym peri-follicle fibrosis), CHDF (calcified hyperplastic dental follicles) and premature calcifications, which are different to HDF, can involve multiple unerupted/impacted teeth. These conditions are extremely rare, with exclusive male predilection. [24] On the other hand, several studies have revealed no gender differences in tooth non-eruption [7,26].
However, heredity is also mentioned as an etiologic factor and a more recent report suggested a genetic tendency as a possible cause. [27] Hata et al. [30] reported dentofacial manifestations of XXXXY syndrome involving molars noneruption. Recently, mutations in PTH1R (parathyroid hormone receptor 1) have been identified in several familial cases of primary failure of eruption. [31,32] In a current study, Shapira et al. [33] investigated genetic traits in molar non-eruption and found that the Chinese -American population had a higher prevalence (2.3%) compared with the Israeli population (1.4%).
Disturbanses in teeth development can be linked with conditions such as mucopolysaccharidoses [16,34], cleidocranial dysostosis [35,36], Gardner syndrome [37] and Yunis-Varon syndrome [38]. Other conditions which can be considered in the differential diagnosis in multiple unerupted teeth are NBCCS (nevoid basal cell carcinoma syndrome) or Gorlin syndrome/ Gorlin-Sedano syndrome [39,40], familial fibrous dysplasia or cherubism. Therefore, in each case with abnormal dental eruption feature, further work-up should be performed, in order to rule out any systemic disorders or syndromes.

Management Strategies
The decision about removal of "rosetting" molars is a surgical challenge for the oral/maxillofacial surgeon. [41] This can be explained by the elevated rates of complications (4.6% to 30.9%) that can be assigned to the removal of impacted teeth [42], such as mandibular fractures during the surgery [43,44] or post-operation [41,[43][44][45], dry socket [43,44] or damage to the alveolar nerve [46][47][48]. On the other hand, the maintenance of these teeth can be connected to other complications, such as reduction of mandible bone tissue, which on its behalf increases the risk of mandibular fractures [46,49], root resorption of adjacent teeth, pericoronaritis, local pain or cystic changes [50]. In order to reduce or prevent these complications, it is mandatory to have a detailed surgical planning, as well as awareness of both the professionals and patients about the nature of the condition. [51] At the moment of surgical planning, the panoramic X-rays often combined with a cone beam computed tomography (CBCT) are considered base-line of the diagnostic process (Figures 4-7) [48].
There is no standard solution in treating of multiple unerupted molars. Different approaches are proposed and should be taken into consideration in each individual case. Extraction of both "kissing"/"rоsetting" molars or only the one of them with/without exposure of the non-extracted tooth are yet the most successful surgical protocol reported in the literature. [8,52] The orthodontic up-righting by different mechanics and devices such as push spring and mini-hook systems are also well applied as an alternative conservative approach. (Figures 5 and 7) [53,54] However, the management plan depends on several local factors, such as: tooth inclination and position, as well as the degree of teeth crowding or follicle collision. These influence not only the treatment but also the prognosis and outcome. The ideal procedure should allow the establishment of a normal functional occlusal relationship.

Meaning of Non-eruption
The eruption of the first and second permanent molars is especially important for the co-ordination of the facial growth and for providing sufficient occlusal support for undisturbed mastication. [1] Early diagnosis and early treatment are the keys for successful correction of molar non-eruption. Therefore, a radiographic examination (ideally during the early mixed dentition period) is recommended. The proper time to treat these types of disorders is between 11 and 14 years while second molar root formation is still incomplete and before the third molars complete their development in close proximity to the second ones. [6,33] Close collaboration between the specialists (surgeons, orthodontists, pediatric dentists, etc.) is mandatory for the successful outcome. Management of such cases is considered very difficult, unpredictable and challenging. It also often requires a complex surgery, which is dependent on experience and great attention to details from the surgeon [17,20].
Unfortunately, because of the rarity of this clinical finding and the great clinical diversity, it is difficult to propose clinical procedure protocols. Many factors such as age, occlusion, the presence of the adjacent molars, the degree of crowding, pathological conditions, the teeth position and their root anatomy, as well as patient cooperation and expectations should be considered, before formulating the final treatment decision and plan. [6,8,26,33,55] Most importantly, the potential risks and complications and the possible benefits of other treatment modalities should be brought to the patient's mind and thoroughly explained, before proceeding with an intervention, on each individual case basis.

Conclusion
In conclusion, the dentist and the surgical specialist, must have a thorough knowledge about the various forms and possible etiology of tooth non-eruption. It can be a sign of various medical conditions. Therefore, detailed and specific investigations are further required, preceding a patienttailored treatment plan.