The effect of premature extraction of primary molars on spatial conditions and formation of malocclusion – a systematic review

INTRODUCTION

Despite increasing dental awareness of patients and their parents, as well as well-documented scientific reports on the role of deciduous teeth in the normal development of the stomatognathic system [1-3], the problem of tooth decay and premature loss of primary teeth has not lost its relevance. According to national epidemiolog-ical studies carried out in 2012 in Poland as a part of the “Monitoring of oral health” program, only 14.4% of 6-year-old children had dentition that was free of caries [4]. In the group of 6-year-old children there was also a very low index of conservative treatment equal to 0.23 (where 0 means no teeth with caries were treated, and 1 means all teeth that had been decayed were treated) [5]. In addi-tion to the direct complications of caries, such as pulpitis, abscesses or fistulas, loss of hard tissues of the deciduous teeth before the period of their physiological exfoliation implies significant problems in the area of developing occlusion [3, 6, 7]. At the same time, only 40.8% of the adult respondents were aware of the relationship between the loss of numerous deciduous teeth and the risk of permanent teeth movement and crowding [5].
The consequences of space deficiency due to early loss of deciduous molars often complicate the process of orthodontic treatment of the existing malocclusion and in many cases are the only indication for treatment. However, scientific reports are not consistent with the extent of complications and the time of their occurrence, raising in some cases the question about the necessity of using preventive measures in the form of space main-tainers.

OBJECTIVES

The aim of the study was to analyze the reports of the scientific literature regarding the influence of premature loss of deciduous molars on formation of occlusal disorders.

MATERIAL AND METHODS

The literature review was performed in PubMed, EMBASE and Scopus databases in July 2017. English and Polish-language journals were taken into account without specifying the time frame. The index word used was “premature primary tooth loss”. Only original articles were searched and as a criterion for inclusion in the study, the compliance of the information with the specific work objectives was evaluated.

RESULTS

Basing on the conducted research, 78 articles that qualified for further analysis were obtained. Works in a language other than Polish and English as well as articles not directly related to the subject of the review were excluded, obtaining 18 articles. Two articles from professional literature not present in the searched databases but consistent with the subject and methodology were also included (“Space reduction after the premature loss of a second molar-retrospective study” and “Mandibular dental arch dimensional changes following prematurely lost deciduous molars”), obtaining a total of 20 works, which are presented in Tables 1-4. The oldest of the selected articles is from 1965, the latest from 2017. Eleven papers are based on longitudinal studies (Tables 1 and 3), 9 are cross-sectional studies (Table 2), of which 7 are retrospective studies and the remaining 2 are systematic reviews of the literature. Five of the selected articles describe issues related only to premature loss of the upper first deciduous molars. In 1 article only consequences of early loss of lower first deciduous molars were examined and the effects of loss of both upper and lower first deciduous molars were also observed in 1 study. In 5 articles, the consequences of loss of both the first and second primary molars were investigated, while in the remaining 5 loss of deciduous molars and canines was considered. In 1 study, only the effect of losing secondary primary molars was studied.
Research groups were heterogeneous in terms of nationality, gender, size (the smallest group included 9 people, the largest 519 participants), age (from 4.1 to 15 years) and even social origin.
The most frequently used method involved measurements performed on models (14 works), while in other cases the data for analysis was obtained from a clinical examination.
In the group 519 Icelandic children in the dental maturity phase DS02, DS1 and DS2, examined during an epidemiological study in 1979, in 141 (27%) there was a lack of at least one deciduous tooth caused by the necessity of early extraction [8]. Statistically, the premature loss was more often related to the lower arch. Polish research from 1988 showed absence of deciduous molars in 48% of children aged 5.5-6.5 years and in 49% at the age of 5.6-7.5 years [9]. “Monitoring of oral health” carried out in Poland in 2012 indicates a reduction of this percentage to 6.1% (in 6-year-old children) [4]. A study of 5-10-year-old children from Yemen (2016) reports on missing primary teeth in 40.54% of participants [10]. It also confirms greater frequency of premature extraction in the lower arch, where the second deciduous molar was missing the most often.
The number of studies performed to investigate the consequences of premature loss of primary first mo-lars tells a lot about controversy related to this issue. It is commonly accepted that the loss of a deciduous tooth due to non-physiological reasons, especially before the period of appearance of a permanent successor in the oral cavity, carries the risk of loss of space in the dental arch. In the analyzed articles most of the attention was paid to the loss of the first upper molars.
Northway observed mesial inclination of the second deciduous molar as a consequence of extraction of the upper first deciduous molar, followed by eruption of the first premolar in a more mesial position than on the control side [11, 12]. As a result, permanent canines erupted in a buccal position, so correlation with the formation of malocclusion and the necessity of orthodontic intervention is noticeable. However, this state-ment is in contradiction with Park’s study [13], where no significant changes were observed in the inclination of the second upper deciduous molar, the first permanent molar and deciduous canine, and average space loss (0.57 mm) was not statistically significant. It should be emphasized that all participants of Park’s study had a class I molar relation. Lin also did not observe changes in the position of the upper molars, but he noticed distal dislocation of the primary canines with reduction of the D+E space by 1.08 mm after 6 months and 0.82 mm after 12 months [14, 15]. After 81 months in 88.9% of cases crowding on the extraction side was not observed at the stage of permanent dentition [16]. Despite the loss of space, according to the authors of the study, existing changes are not clinically significant and there is no need to use a space maintainer, provided that the first per-manent molar is erupted, or will appear in the mouth in the nearest future. Macena also did not observe signifi-cant changes in the upper dental arch after measuring the space in the extraction site and the length of the arch and comparing it to the control side [17]. Alexander expanded the study to examine the correlation between the amount of space lost after extraction and molar relation and type of face [18]. Assessing the ratio of the length of the section determined by the skin points zygion to the section nasion-gnathion, he distinguished the leptoprosopic face (ratio 0.75 or less), mesoprosopic face (ratio 0.76-0.79) and euryprosopic face (ratio 0.8 or greater). The largest loss of space in the maxilla oc-curred in the case of the cusp-to-cusp relationship and leptoprosopic face (1.75 mm), while the lowest occurred in patients with class I and meso-/euryprosopic face type (0.11 mm), which may suggest that normal intercuspation and moderate and wide face type minimize the risk of losing space.
A less obvious correlation exists in the case of the lower arch. Kumari in his study focused on premature extraction of lower first deciduous molars, showing the greatest loss of space after the first 4 months (1.69 mm), resulting mainly from the distal drift of canines [19]. Interestingly, after 8 months of extraction, the loss of space was only 1.22 mm. Also these authors question the necessity of using a space maintainer in the case of extraction of the first primary molar in the mandible. A different opinion is represented by Al-Dulayme, who observed distal displacement of the lower canine in the 1 mm range, as well as mesial migration of second deciduous molar and first permanent molar (2 mm) [20]. In addition, the first permanent molar in-clined lingually. Due to the intensification of observed changes, this author recommends the use of space main-tainers also in the case of premature loss of the first molar in the mandible.
Magnusson in an epidemiological study of Icelandic children recorded the largest loss of space at the extraction site after premature loss of second deciduous molars [8]. Northway measuring the distance D+E on average 5.9 years after extraction of the primary tooth observed a 3.7 mm loss of space after premature extrac-tion of the second deciduous molar in the maxilla and 3-4 mm after extraction of the lower second deciduous molar in the mandible when compared to the control side [11]. In both cases, the main cause of space deficiency was mesial drift of the first permanent molar, which in the upper arch led to distal molar relation, and in the lower arch to mesial relation. The most significant changes took place during the first year after extraction. In addition, in the case of the upper arch, a correlation was observed between the time of loss of the deciduous tooth and the extent of mesial drift, where early extraction caused more intensive mesialization of the first permanent mo-lar. As a consequence of reducing the D+E distance it is probable that the upper and lower second premolar will erupt in the incorrect position or will not erupt. Pokorna during at least a 6-month observation period after second deciduous molar extraction reported an average loss of space of 2.9 mm in the upper arch and 2.4 mm in the lower arch [21]. A different mechanism of formation of changes was also noted: the first lower permanent molar after premature loss of the second mandibular deciduous molar tipped mesially, while the upper one ro-tated mesially 8.1 degrees on average. Premature loss of the second molar also changed the relation within the first permanent molars on the extraction side towards class II in the case of tooth loss in the upper jaw and class I and III in the case of premature tooth loss in the mandible. The magnitude of the shifts remained unaf-fected either by the height of the cusps of the first permanent molar or the vertical skeletal jaw relation. Al-Dulayme observed in the measurements performed from 6 to 12 months after extraction of the second de-ciduous molar in the mandible both mesial migration of the first permanent molar (2 mm) and distal drift of the primary canine and first primary molar (1 mm) [20]. Slightly different results were obtained by Macena et al. during 10-month observation of Brazilian children [17]. Premature loss of the second deciduous molar resulted only in 1.2 mm of space loss in the lower arch and 0.7 mm in the upper arch, and the largest changes occurred during the first 3 months after extraction.
Posen reports on the correlation between the age of deciduous tooth loss and the time of eruption of the permanent successor [22]. According to the author, extraction of the primary molar at the age of 4-5 years causes delayed eruption of premolars, while in the case of extraction at the age of 8-10 years, eruption of the permanent successor is significantly accelerated. Kerr observed separate phenomena for the mandible and maxilla [23]. Premature loss of upper deciduous molars resulted in faster eruption of premolars than on the control side, while in the case of primary lower molars, early extraction led to delayed eruption of permanent successors.
There are few reports directly related to the relationship between premature loss of deciduous teeth and the need for orthodontic treatment in permanent dentition. Bhujel observed a positive correlation between the need for orthodontic treatment determined by the IOTN index and premature extraction of primary teeth [24]. Results of the study suggest that each prematurely removed deciduous tooth increased the need of orthodontic treatment by 18%. According to Miya­moto’s work, children who lost at least one primary tooth before the age of 9 were treated three times more often than children from the control group [25]. Younger age of the patient at the moment of tooth extraction predisposed to formation of a more severe disorder, but there was no difference between the consequences of losing first and second molars.

DISCUSSION

Comparison of the research results quoted in the above review faces numerous difficulties, due to discrepan-cies in the age of the participants, type of teeth lost, as well as chosen research methods and reference points required to perform linear measurements. Nevertheless, the authors agree in terms of higher frequency of premature extraction in the lower arch, where the second primary molar was lost the most often [8-10]. This coincides with reports on the prevalence of caries in deciduous dentition, where a higher risk exists in the case of the lower molars, especially the second ones. Increased susceptibility to dental caries of these teeth probably results from the specific anatomy of their occlusal surface characterized by deeper fossils and fissures and leads to their loss more frequently than in the case of earlier erupting first molars [26]. Summing up the findings from cited studies about the premature loss of first deciduous molars, it can be assumed that a space maintainer should be considered in patients with an unerupted first permanent molar or cusp-to-cusp contact, because mesial forces acting during permanent teeth eruption tend to accelerate space loss within the dental arch [18]. In addi-tion, there is a greater risk of unfavorable spatial changes in the lower arch, which may occur both as a result of the mesial migration of the posterior teeth and even more significant distal drift of the anterior teeth [19, 27]. This phenomenon can be explained by the influence of forces arising during eruption of permanent incisors on the distal shift of deciduous canines. It means that resulting changes also depend on the dental age at the time of tooth loss [13].
In the case of the upper jaw, taking into account measurements performed on models, there was no loss of space due to mesialization of posterior teeth and only distal drift of primary canines occurred, so the need for space maintainers in the maxillary arch is often negated [13-16]. At the same time Northway noted in 11 out of 13 cases vestibular retention of a permanent canine, which occurred as a result of loss of space in the arch due to more mesial eruption of the first premolars than on the control side [11, 12].
The second deciduous molars, determining the position of eruption of the first permanent molars and being more responsible for maintaining leeway space, seem to play an even more important role in formation of correct occlusion. According to the opinion of some authors, extraction of a second deciduous molar before first permanent molar eruption may even lead to complete closure of the space as a result of its mesial migra-tion [28]. However, the amount of space lost should be related to the dimension of leeway space, which is larger in the mandibular arch. In this context, some authors consider loss of the lower second deciduous molars to be less burdened with negative consequences and suggest greater need for space maintainers in the upper jaw [21].
The mechanism of losing space after second deciduous molar extraction in the maxilla and mandible that often leads to the retention of second premolars is explained by both mesial shift of the first permanent mo-lar and more distal eruption of the first premolar in comparison with physiological teeth exfoliation [11]. Moreo-ver, changes in the sagittal plane are accompanied by transverse displacements: mesial rotation of the upper first permanent molar (although the magnitude of the rotations varies among studies from 0.67° ± 3.51° to 8.1° ± 5.8°) [21, 29] and lingual inclination of the lower first permanent molar resulting in reduction of posterior width of the lower arch [20]. Most of the cited studies refer to measurements performed within the period of dental maturity DS2 M1, where the only erupted permanent teeth are the first molars and central and lateral incisors. This may lead to underestimation of the role of loss of deciduous molars in the formation of occlusion due to the omission of changes occurring during eruption of permanent successors in the resistance zones, such as varia-tion of the inclination of the first premolar, or accelerated or delayed eruption of permanent teeth in the area of premature loss. It seems to be impossible to demonstrate actual changes occurring after premature loss of primary molars in the context of existing scientific reports due to ethical reasons. Each case of premature loss of a deciduous tooth should be recorded and individually assessed in terms of orthodontic treatment needed to maintain a sufficient amount of space or restore missing space. The decision about leaving the patient without any orthodontic intervention may be justified only in the case of satisfactory spatial conditions or planned ex-traction treatment in the future.

CONCLUSIONS

Premature loss of deciduous teeth in many cases has a detrimental influence on forming occlusion. The most frequently reported complications include loss of space leading to vestibular canine eruption and retention or palatal/lingual eruption of a second premolar. Other observed disorders are change in molar relation, mesial rota-tion of the upper first permanent molar and mesial tipping of the lower one. Delayed or premature eruption of permanent successors is also the result of early extraction of primary teeth. The severity of disturbances de-pends on many variables, including child’s age at the time of extraction, initial amount of space in the dental arch (spacing/crowding), and the type and amount of teeth extracted. Available reports do not provide precise guidelines regarding indications for application of space maintainers. Each case requires individual evaluation and selection of a treatment method consistent with current scientific reports.

CONFLICT OF INTEREST

The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publica-tion of this article.

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