Tooth Eruptions and Dental Impactions

Volume 4, Issue 2 US $6.00

Editor: Allan G. Farman, BDS, PhD (odont.), Tooth Eruption and Dental Impactions DSc (odont.), Diplomate of the American Board of Oral and By Dr. Allan G. Farman rence in females. [6]. Natal and Maxillofacial Radiology, Professor of neonatal teeth are occasionally Radiology and Imaging Sciences, A broad range of variation exists reported in patients having syn- Department of Surgical and Hospital in the normal eruption times of dromes such as pachyonychia Dentistry, The University of primary and permanent teeth in congenita, Hallerman-Streiff syn- Louisville School of Dentistry, humans. However, normality is drome, and Wiedemann- Louisville, KY. usually associated with bilateral Rautenstrauch syndrome, the latter symmetry. Furthermore, cases where being associated with premature Featured Article: eruption time is grossly beyond the aging [7-14]. Radiographic inspection Tooth Eruptions and Dental extremes of normalcy may be is not necessary. Impactions considered to represent a pathologi- Premature eruption of a perma- cal state [1]. Radiography plays an nent tooth sporadically may follow In The Recent Literature: important part in determining the premature loss of the overlying Premolar Extraction normality of tooth eruption with primary tooth. This can readily be regard to position and time se- assessed using panoramic radio- Impacted Teeth quence. This is particularly important graphs [15]. Caries and restorations in patients whose teeth are undetect- in primary teeth have also been Impacted Canines able by clinical means, such as associated with premature eruption those with delayed eruption or of their successors [16]. A study of Learning Objectives: impaction. Impaction is the impeding 4,468 Flemish children indicate that Gain understanding of the role of of the eruption by tooth, bone, or the emergence of the maxillary and radiography in determining the pathosis, so the eruption of the tooth mandibular premolars was acceler- normality of tooth eruption with is rendered unlikely. ated by 2-8 months when its prede- regard to positions and time cessor had been decayed or restored sequence. Premature Eruption but had not been extracted. Very Occasionally, one or two primary early eruption of a permanent tooth Learn about the role of panoramic teeth – natal teeth – are present at following agenesis of its primary radiography in identifying and birth or, in the case of neonatal predecessor has also been reported monitoring premature eruption, retarded eruption and dental teeth, erupt within the first month of [17]. Cases of premature eruption impactions. life [2]. Eighty-five per cent of such involving the whole permanent premature teeth are mandibular dentition have been associated with Learn the proper use of panoramic primary central incisors, 11 % are Proteus syndrome [18]. radiography, its benefits and primary maxillary incisors, and 4 % limitations, in reviewing impactions. are primary posterior teeth [2]. Retarded Eruption Generally such teeth are well-formed Delay in dental eruption affecting and normal in all respects. They the whole of one or both dentitions should be retained despite nursing has been associated with various difficulties [3]. Although anecdotally systemic conditions, including there may be a familial occurrence, rickets, cretinism, and cleidocranial most cases defy explanation [4]. A dysplasia [1]. Neonatal illness and study of 34,457 infants born in postnatal nutrition as well as degree southern Finland (1997-2000) deter- of premature birth have been found mined an incidence of 1:1000 for to affect the timing of primary tooth natal and neonatal teeth and found eruption [19]. Fibromatosis gingivae no association with environmental may either slow or camouflage pollutants [5]. Other studies have put eruption due to enlarged hyperplastic the incidence of natal and neonatal gingival tissues with dense connec- at between 1:700 and 1:3,500 live tive tissue [20]. If the cause is local births with a predilection for occur- (e.g. fibromatosis gingivae, supernu- “Where there is a systemic cause to delayed eruption, lack of eruptive force can be permanent, and there is no known remedy. Such unimpeded unerupted teeth are termed embedded.”

merary tooth, or odontoma), treat- Fig. 1: Multiple unerupted regular permanent ment of the primary condition should and supernumerary teeth in a patient having promote eruption. Excessive delay in cleidocranial dysplasia. eruption should be evaluated using either panoramic or intraoral radiographs. Panoramic radiology will provide the best overview so long as the patient can cooperate for the full exposure time. Where there is a systemic cause to delayed eruption (e.g. cleidocranial dysplasia), lack of eruptive force can be permanent, and there is no known remedy [21,22]. Such unimpeded unerupted teeth are termed embedded (Fig. 1). In such cases, periodic panoramic radiography is useful to evaluate the possible development of associated pathoses, including Fig. 2: Molar impaction classification according to dentigerous cysts. angulation of the impacted third (and in the case of the horizontal impaction illustrated here – A variety of conditions have supernumerary/fourth) molar tooth. been associated with temporary delayed eruption – or delayed dental development. These include low birth weight [23], HIV infection in child- hood [24,25], Silver-Russell syndrome [26], Kabuki syndrome [27], osteopetrosis [28], and pycnodysostosis [29]. A study of 70 HIV infected children aged 5 months to 13 years found that delay in tooth eruption is most closely linked to severity of symptoms rather than to CD4 depletion [25].

Dental Impactions Impacted teeth may be defined Mesioangular Vertical as those teeth prevented from eruption due to a physical barrier within the path of eruption. Any tooth can be impacted; however, teeth in the regular permanent dentition or supernumerary teeth are usually affected. A study of radiographs from 3,874 dental patients aged over 20 years determined the prevalence of impaction to be 17 % [30]; hence, this condition can be considered among the most significant affecting dental care. The most frequently affected regular teeth are the third molars (especially in the mandible) Horizontal Distoangular

2 phy, computed tomography, or cone- beam CT with 3-D reconstruction. Fig. 3: Panoramic radiographs do not show Vertically- bucco-lingual dimensions, so they impacted should be supplemented because maxillary third this dimension is critical for appropri- molar tooth. ate treatment planning. Damage to the contents of the mandibular canal can lead to temporary or permanent paresthesia of the ipsilateral side of the lower lip. While this complication may be unavoidable, it is less likely to occur given appropriate radiographic assessment. A prospective cohort study was performed in Sweden to measure the prevalence of disease in conjunction with mandibular third molars referred for removal [32]. Pericoronitis was found in 64 % of cases, caries in the third molar in 31 %, periodontitis in association with 8 %, caries in the second molar in 5 %, and root and the permanent maxillary from eruption through impingement resorption of the second molar with 1 canines. Cases can occur simply on the anterior ramus or distal % of the molars having pathoses. The due to dental crowding, to space surface of the second permanent odds ratio for disease was highest for reduction following premature molar tooth. With horizontal impac- distoangular molars (5.8) and for loss of primary teeth, or to an tion, the third molar is positioned impactions partially covered by soft errant path of eruption. horizontally within the mandible with tissue (6.7). The odds ratio for the crown directed towards the distal associated pathoses was between 22 Third Molars surface of the second molar. In each and 34 times higher for molars Impacted mandibular third of these angular impactions, the third partially covered by soft tissue than molars are traditionally classified molar can be positioned at various for impactions completely covered by according to position following depths within bone, and in relation to soft or bone tissue. For distoangular the method of Winter [31] (Fig. the mandibular canal. Panoramic molars the odds ratio for associated 2). The most common type of radiographs clearly demonstrate the pathoses was 5 to 12 times higher impaction for mandibular molars mesio-distal and vertical position of than for molars in other positions. is mesioangular. Mesioangular- the impacted tooth, but do not Impacted maxillary third molars impacted mandibular third molars provide details of the bucco-lingual (Fig. 3) may also be mesioangular, lie obliquely in bone with the positioning or angulation. This can be distoangular, vertical, or horizontal in crown slanted in a mesial remedied in most cases by simply position. In the maxilla, no structure direction, generally in contact taking a true occlusal radiograph as critical to surgical success as the with the distal surface of the using a size 2 intraoral x-ray film to mandibular canal is present; hence, ipsilateral second permanent provide details in the third orthogonal pre-surgical assessment using molar. Distoangular impacted plane. This will be sufficient if the panoramic and true occlusal radiogra- third molars lie obliquely in bone tooth is not superimposed over the phy is almost invariably sufficient. with the crown slanted in a distal mandibular canal or intimately Concerning the treatment of direction towards the ramus, the associated with that structure. In the impacted third molars, systematic roots abutting the distal root of few cases where this occurs and reviews have generally concluded the second molar. Vertical extraction is deemed necessary, the that, in the absence of association impaction sees the third molar in case may warrant more advanced with definite pathoses, it is best not normal angulation, but prevented imaging using conventional tomogra- to extract these teeth [33,34]. Fur-

3 ther, there is little evidence that retention of third molars has any effect on anterior crowding that might undermine orthodontic treatment [35]. Nevertheless, univariate analysis based on removal of 354 mandibular third molars identified increased patient age as a factor that predicted the surgical difficulty of third molar extractions, so delay could have a price if extraction is eventually needed [36]. Other factors ascribed to increased surgical difficulty included bony impaction, depth of tooth within bone, horizontal angulation, proximity Fig. 4: Impacted maxillary to the inferior alveolar canal, male canines. Note that the right gender, and obesity [36]. When it is canine appears to have a relatively decided not to extract impacted third wide crown indicating palatal molars, periodic panoramic radio- location of the crown; however, the graphs should be made to assure that root appears relatively narrow in no conditions develop that warrant comparison with those of the regular teeth indicating a facial/labial location. subsequent surgical intervention. All bets are off for the impacted left That periodic re-evaluation may canine due to its rotation. be preferred to extraction of third molars in adolescence is supported by a study of 2,857 third molars in different locations. The most the erupted regular dentition. assessed at age 18 years, and where important considerations are the This is due to panoramic image 93 % were able to be clinically followed relationship of the affected tooth to layer theory. Objects that are up at age 26 years [37]. Approxi- the erupted regular teeth, especially displaced facially with respect to mately 55 % of the teeth that were not whether the position of the crown the regular dentition will appear considered impacted by age 18 had and roots of the impacted tooth is narrowed horizontally, whereas erupted by 26 years. Of the teeth palatal or facial. This determines the those that are palatally displaced considered impacted at age 18, 34 % surgical access to the maxillary will appear magnified in horizon- had fully erupted by age 26. Of the canine impaction for surgical orth- tal dimension (Fig. 4). Hence, if maxillary teeth that were categorized odontics or removal. the crown or root of the im- as “impacted” at age 18 years, 36 % In more than 60 % of cases of pacted canine appears broader had fully erupted by age 26, whereas impacted canines it is possible to horizontally in the panoramic 26% of the mandibular teeth had done decide whether the crown of the image than do the regular tooth so (p <.01). Excluding horizontally- impacted tooth is facial or palatal crowns or roots, the affected impacted third molars, a substantial using palpation [39]; however, for the tooth portion is displaced proportion of impacted teeth did erupt remaining one-third, radiographic palatally, whereas if it appears fully. It can be concluded that radio- assessment is needed to effect narrowed, it is facially posi- graphically-apparent impaction in late localization. It was emphasized tioned. This presupposes that adolescence should not be sufficient above that the panoramic radiograph the impacted tooth is morpho- grounds for their prophylactic removal should not be relied on for the logically normal in terms of size. in the absence of other clinical assessment of the facio-lingual It is suggested that localization indications. position of mandibular third molars. In of impacted canines using the anterior maxilla, however, it is panoramic radiographs be Canines possible, by using a single panoramic supplemented using standard Impacted permanent maxillary radiograph, to make some inferences parallax methods employing canines occur in 1-2 % of the popula- regarding the facio-palatal positioning periapical or occlusal radio- tion [38]. These impactions can occur of the impacted tooth with respect to graphs made at different vertical

4 “Both regular and supernumerary teeth completely impacted and embedded in bone can occasionally undergo resorption of the root, or crown, or both.”

Supernumerary Teeth Fig. 5: Any tooth can be impacted. A detailed overview of supernumerary teeth was made in a previous issue of Panoramic Imaging News (Volume 3; Issue 1). Many supernumerary teeth are impacted or lead to impaction of regular teeth. While these can be detected using panoramic radiography even in the anterior segment the panoramic radiograph does not provide a means of determining the facio-lingual relationship of such teeth to the regular dentition. Supernumerary Impacted Impacted Impacted nd teeth vary too widely in size and Premolar Incisor2 Molar morphology for any panoramic assessment of position because of the effects of tooth magnification with panoramic radiographs. Resorption of Impacted Teeth Both regular and supernumerary teeth completely impacted and embedded in bone can occasionally undergo resorption of the root, or crown, or both. In a study of 226 impacted teeth showing resorption, 78 % were in the maxilla, and of the maxillary cases, 60 % were canines [44]. Examination of panoramic radiographs of 11,598 patients (average age 47 years) revealed Fig. 6: Detail of resorption of 1,756 patients having 3,702 im- an impacted pacted teeth with an average reten- mandibular tion period approximately 27 years. third molar In these cases, internal resorption tooth. was found in 16 (0.43 %) [45] (Fig. 6). Pathosis and Impaction beam angulations for the purpose severely impacted teeth, with A retrospective study of patients of verification [40,41]. younger patients requiring the hospitalized for infections associated Unlike the case of the third most time [42]. Successful with partially-erupted third molars molar, there are important outcomes are typical [43]. from 1985-94 showed the incidence esthetic reasons for retaining the of serious orofacial infections maxillary canine and bringing it Other Regular Teeth associated with partially-erupted third into harmonious alignment with Regular teeth other than the molars to be 0.016 cases per year the rest of the dentition. Most mandibular third molars and per 1000 patients at risk [46]. The cases will be treated by forced canines are less frequently same investigation determined the orthodontic eruption, often impacted (Fig. 5). The third most incidence of large third-molar- following surgical exposure commonly impacted teeth are the associated cystic lesions requiring [42,43]. Treatment time is usually premolars in both the mandible hospitalization to be 0.016 cases per two to three years with more and maxilla. year per 1000 patients at risk [47].

5 “ Within the jaws, teeth are occasionally displaced so that they are mispositioned in the dental arch (transposition), or erupt into even more dramatically anomalous positions.”

The presence of mandibular third molar impactions has also been found to be a significant predisposing factor for mandibular angle fractures during injury [48]. Cause-and-effect, or sequence of events, can be difficult to determine. In some cases, impacted teeth develop dentigerous cysts [45,49,50] (Fig. 7). Upon panoramic follow-up, these have been reported to have regressed, only infrequently [49]. Surgical removal of the cystic lesion is the current treatment of choice. Following formation of the cyst, the Fig. 7: Dentiger- ous cyst associated affected tooth can be displaced with horizontally considerably as the cyst grows. Of positioned impacted 3,702 impacted teeth retained over an mandibular third molar. The average period of approximately 27 dentigerous cyst forms within the years, dentigerous cystic changes dental follicle space and shows attachment at the enamel-cemental junction. occurred in about 30 (0.81%) [45]. A variety of additional pathoses can cause – or be associated with – Fig. 8: Several impaction and displacement of teeth different pathoses can be associated (Fig. 8). These include the ameloblas- with dental toma, odontogic keratocyst, odonto- impactions and tooth mas, adenomatoid odontogenic tumor displacement. [50-53] and, less commonly, Examples shown here ameloblastic fibroma [54] and other are of ameloblastoma, ameloblastic cysts and neoplasms. fibroma, odontogenic Ectopic Dental Eruption keratocyst, and a malignant neoplasm, Within the jaws, teeth are occa- Ameloblastoma Ameloblastic Fibroma mesenchymal sionally displaced so that they are chondrosarcoma. All mispositioned in the dental arch four of these (transposition), or erupt into even examples displace more dramatically anomalous posi- unerupted teeth. All tions. The prevalence of ectopic four need histologic analysis of tissue eruption of the first permanent molars specimens to derive in a group of 4,232 Thai students, age the correct diagnosis. 6 to 9 years was found to be 0.75% [55]. Transposition has been reported also in the anterior arches [56-57]. Teeth appearing perfectly normal can also be formed at distant sites in the body, such as the ovaries in terato- Odontogenic Keratocyst Mesenchymal Chondrosarcoma mas [58], but, needless to state, follow in watching or removing appar- tion only in the vertical and panoramic radiography does not work ently impacted third molars, it is mesio-distal planes, so additional in such situations! indisputable that the panoramic radiographs might be necessary Concluding Remarks radiograph provides a valuable means to establish bucco-lingual relation- While there is some controversy of assessing these teeth. The pan- ships between teeth and associ- concerning the correct strategy to oramic radiograph provides informa- ated anatomic structures.

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7 In The Recent Literature: Orthodontics: Premolar extraction The results support the hypothesis that and periodontal diseases were reduces the probability of third molar premolar extraction reduces the commonly seen in relation to the impaction. frequency of third molar impaction due impacted third molars, yet cystic Kim TW, Artun J, Behbehani F, Artese to increased eruption space afforded by pathoses and root resorption were F. Prevalence of third molar impaction mesial movement of the molars during rarely observed. in orthodontic patients treated space closure. nonextraction and with extraction of 4 Impacted canines: The probability premolars. Am J Orthod Dentofacial Impacted teeth: Panoramic radio- of impaction of a maxillary canine Orthop 2003;123:138-145. [From the graphs revealed impacted teeth in is very high when the canine Department of Orthodontics, College more than 28 % of the study popula- overlaps the midline of the lateral of Dentistry, Seoul National University, tion in Hong Kong. incisor. Seoul, Korea.] Chu FC, Li TK, Lui VK, Newsome PR, Warford JH Jr, Grandhi RK, Tira Chow RL, Cheung LK. DE. Prediction of maxillary canine This study tested the hypothesis that Prevalence of impacted teeth and impaction using sectors and premolar extraction treatment is associated pathologies—a radio- angular measurement. Am J associated with mesial movement of the graphic study of the Hong Kong Orthod Dentofacial Orthop. 2003; molars concomitant with an increase in Chinese population. Hong Kong Med J 124:651-655. [From the Depart- the eruption space for the third molars, 2003;9:158-163. [From Prince Philip ment of Orthodontics and thereby reducing the frequency of third Dental Hospital Faculty of Dentistry, Dentofacial Orthopedics, Univer- molar impaction. Panoramic or periapi- The University of Hong Kong.] sity of Missouri, USA.] cal radiographs, lateral cephalograms, and study models made before (T1) and The records of 7,486 patients were Maxillary canine impaction has an after (T2) treatment and a minimum of examined and a total of 2,115 (28 %) incidence of 1 in 100 in the general 10 years postretention (T3) of 157 patients were determined to have at population. Because patients with patients were selected from the least one impacted tooth. The preva- canine impactions generally have Department of Orthodontics of the lence of impacted teeth was high, with a relatively long orthodontic treatment University of Washington, Seattle. predilection for impacted third molars in times, early identification of Treatment for 105 patients included the mandible. As more than 50% of impaction is of importance to the extraction of four premolars; the other maxillary third molars had erupted in orthodontist. In this investigation, 53 (controls) had been treated without patients having impacted mandibular angulation of the unerupted canine extraction. Student t tests were applied third molars, this created potential was measured from panoramic to the data for statistical comparison. trauma to the pericoronal tissues radiographs and added to sector For the controls, third molar impaction overlying the impacted mandibular third location to see whether the was found to be more common than in molars. Roughly one-third of patients combination of these factors could patients who had undergone premolar with dental impaction reported associ- predict impaction more accurately extraction (p <.01), there was less ated symptoms. Of a total of 3,853 than sector alone. Logistic regres- mesial movement of the molars from T1 impacted teeth, mandibular third molars sion analysis determined that once to T2 (p <.01), and a smaller retromolar were the most frequent (83 %), followed the canine overlaps the midline of space was found on average at T2 (p by maxillary third molars (16 %), and the lateral incisor, there is a greater <.001) in both arches. Moreover, molar maxillary canines (1 %). Some 8 % of than 0.87 chance of impaction. movement was more mesial from T1 to mandibular second molars associated Sector location was found to be the T2 both in the maxilla (p <.01) and in the with impacted third molars had peri- better predictor of impaction, with mandible (p <.05), and the retromolar odontal bone loss of more than 5 mm angulation providing little supple- space was larger in both arches (p on their distal surfaces. Caries were mentary predictive value. <.001) of the patients with eruption than also found on the distal surface of 7% of in those with impaction of third molars. the associated second molars. Caries ©2004 Panoramic Corporation (4-04)

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