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Year : 2019  |  Volume : 22  |  Issue : 7  |  Page : 936-942

Effects of first permanent molar extractıon on space changes observed in the dental arch using data mining method

1 Department of Dentomaxillofacial Radiology, Faculty of Dentistry, Hatay Mustafa Kemal University, Hatay, Turkey
2 Department of Pedodontics, Faculty of Dentistry, Hatay Mustafa Kemal University, Hatay, Turkey
3 Department of Computer Technologies, Hatay Mustafa Kemal University, Hatay, Turkey

Date of Acceptance01-Mar-2019
Date of Web Publication11-Jul-2019

Correspondence Address:
Dr. G Serindere
Department of Dentomaxillofacial Radiology, Dental Faculty, Hatay Mustafa Kemal University, Hatay
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njcp.njcp_52_19

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Aim: The high incidence of caries in first permanent molars (FPMs) makes premature extraction of these teeth common. The extraction of the permanent teeth results in various changes in the dental arch. The aim of this study was to evaluate space closure, the eruption of second permanent molars (SPMs), and changes in dental arch after extraction of the FPMs. Materials and Methods: Eruption of 83 SPMs was recorded and radiographically developmental stage of these SPMs in the pre-extraction panoramic radiograph was assessed. Space was measured between the distal surface of the second premolar and the mesial surface of SPM. Results: Out of 55 patients, 28 (50.9%) were males and 27 (49.1%) were females. Thirty-seven (44.6%) of 83 teeth belonged to category 1, 17 (20.5%) teeth belonged to category 2, and 5 (6.02%) teeth belonged to category 3. Although category 4 was not found, 24 (28.9%) teeth were observed to be in category 5. Out of all SPMs, 10.8% represented the ''ideal'' stage of Demirjian's dental development, stage E. Conclusion: In patients who had the FPMs extracted before the eruption of the SPM, it is important with regards to the patients' comfort and health to review the patient regularly and to determine any need for orthodontic treatment.

Keywords: First permanent molars, space closure, tooth extraction

How to cite this article:
Serindere G, Bolgul B, Parlar T, Cosgun A. Effects of first permanent molar extractıon on space changes observed in the dental arch using data mining method. Niger J Clin Pract 2019;22:936-42

How to cite this URL:
Serindere G, Bolgul B, Parlar T, Cosgun A. Effects of first permanent molar extractıon on space changes observed in the dental arch using data mining method. Niger J Clin Pract [serial online] 2019 [cited 2020 Jul 5];22:936-42. Available from:

   Introduction Top

A high incidence of caries in the first permanent molars (FPMs) makes premature extraction of these teeth common.[1] Early extraction of FPMs can cause problems like tipping of the adjacent teeth toward extraction area, overeruption of the opposing teeth, shift of the midline toward the extraction space, asymmetric or unilateral chewing habits, and periodontal problems resulting from the loss of alveolar bone in the extraction area.[2],[3]

The restoration of FPMs is preferred if possible. However, if the extraction of FPM is performed between ages 8 and 10 years, these problems can be reduced or even eliminated as the second permanent molar (SPM) spontaneously erupts in place of the FPM.[4] Thilander and Skagius [5] reported this timing in 1970, and it was identified in the Royal College of Surgeons of England guideline as being “when there is radiographic evidence of early dentine calcification within the second molar root bifurcation.”[6] Despite this, Angle in 1907[7] supported a nonextraction policy. He resisted the idea of extraction of FPMs as he thought of these teeth as the “keystones of the dentition.”

Thus, it is important to assess some factors before planning extraction of the FPMs. These factors include the restorative condition of the tooth, the dental age of the patient, the presence and degree of crowding, the occlusal relationship, and condition and position of other teeth.[8]

The aim of this study was to describe the percentage of patients in whom FPM extractions were performed at the “ideal” time of 8--10 years of age in the Faculty of Dentistry and to evaluate the effect of FPM extraction time on the eruption of SPMs.

It is anticipated that the clinical features observed in this study could contribute to the limited literature available on the effects seen on space changes after extraction of FPMs and would provide a much better clinical picture about the treatment in such cases, which is important to prevent the orthodontic problems as well as to advise the patient correctly.

Under these conditions, conventional regression models may not always be a suitable method. The development of computer systems has enabled development of data mining methods. Data mining is essentially used in marketing.[9] However, it is also used for research in medical fields like bioinformatics [10],[11] public health surveillance,[12] and for making clinical decisions.[13] In this study, the space changes after the FPM extraction were evaluated by using data mining. This method approach was preferred due to availability of only a limited number of studies using this method and also the lack of studies on this subject. It was deliberated that this study would prove to be beneficial for further investigations.

   Materials and Methods Top

Once the Ethical Committee approved the study (protocol number 2017/127), a total of 285 patients were recalled for assessment, out of which 55 patients (27 females, 28 males) attended the study (19.3% attendance). Informed consent was obtained from all patients for being included in the study. The patients who had undergone extraction of the FPMs and who had all the desired records, collected in Pediatric Dentistry Department, Faculty of Dentistry, Mustafa Kemal University, were included in the study.

The extraction was performed between an age of 8 and 13 years. The mean evaluation age was 13.75 while the mean extraction age was 11.02. The difference between the age at extraction and evaluation was at least 2.5 years. All the required information was obtained during the clinical examination and from the patient's record files. Gender and age of the patients, side of dentition involved, and a number of the extracted FPMs were considered during observations.

Inclusion criteria were: (1) Patients with extraction age between 8 and 13 years; (2) patients with an acceptable diagnostic quality of the panoramic radiographs.

Exclusion criteria were: (1) Patients lying in the age groups other than the described age range; (2) patients whose panoramic radiographs artefacts; (3) patients with no panoramic radiographs.

A single radiology technician obtained all the panoramic radiographs on the digital panoramic systems with the Planmeca Promax 2D (Planmeca Inc., Helsinki, Finland). Two observers, one of which was a pedodontist having more than 10 years of experience, evaluated all the panoramic radiographs.

Demirjian's dental developmental stages [14] were described as Stage D- crown developed, Stage E- early bifurcation, Stage F- late bifurcation, and Stage G- root development almost complete. Stage E was described as the “ideal time” for extraction [Figure 1].
Figure 1: (a) Second permanent molar at the “ideal” developmental stage with caries of left first permanent molar and (b) post-extraction panoramic radiography of the same patient with spontaneous space closure

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Based on Demirjian's dental developmental stages, the developmental stage of SPMs was retrospectively evaluated in the pre-extraction panoramic radiographs.

Space between the distal surface of the second premolar and the mesial surface of SPM was measured in the post-extraction panoramic radiographs. Space closure was categorized according to the classification given by Teo et al. [Table 1].[4]
Table 1: Evaluation classification of space closure between second permanent molar (SPM) and second premolar based on the study of Teo et al.[4]

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Many researchers have applied data mining tools to extract information from different amounts and types of data. The aim of data mining is to create a model that helps to interpret the data. In this paper, the authors employed data mining techniques (WEKA data mining tools) to analyze the data. WEKA [15] is an open source software which is a collection of machine learning algorithms for data mining. This software contains several data mining tools such as data pre-processing, classification, regression, clustering, association rules, and visualization. WEKA machine learning software evaluates data by using an ARFF (Attribute- Relation File Format) file, which is a text file, introduced by the Machine Learning Project at the Department of Computer Science of the University of Waikato in New Zealand. The csv files generated from excel sheets are converted to arff files for WEKA. WEKA uses arff data format. WEKA provides an explorer window to observe the data. For example, if you select an attribute (eval_age: evaluation age), you can see some statistical information for this attribute in the right side of the explorer window. Moreover, there is a visualize button to examine the data that allows you visualize the data.

   Results Top

A total of 285 patients were called for evaluation. Out of them, SPMs were clinically evaluated and recorded in 55 (19.3% attendance) patients. The number of extracted FPMs was 83. The difference between the age at extraction and evaluation was at least 3 years.

Out of all the extracted 83 FPMs assessed, lower FPMs were removed in 56 cases, whereas upper FPMs were removed in 27 cases. Space closure was observed at the rate of 55.6%, 50%, 40%, and 38.5% for the extracted right and left upper FPMs and extracted right and left lower FPMs, respectively. In 14 patients, two teeth were extracted, bilateral lower FPMs were extracted in 12 of these 14 patients while bilateral upper FPMs were extracted in two patients [Figure 2]a and [Figure 2]b. Space closure in the region of bilateral extraction of the lower and upper FPMs was found to occur at the rate of 16.7% and 50%, respectively. In two patients, right lower and upper FPMs were extracted. In eight patients, left lower and upper FPMs were extracted. In both, extractions of the right and left FPMs, space closure occurred at the rate of 50%. In one patient, all four FPMs were extracted. Space closure that occurred in this patient has been shown in [Figure 3]. The detailed information is shown in [Table 2] and [Figure 4].
Figure 2: (a) Clinical photograph showing bilateral extraction with diastema in the lower jaw. (b) Clinical photograph showing bilateral extraction with diastema in the upper jaw

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Figure 3: Clinical photograph showing spontaneous space closure in a patient who had all first permanent molar extraction

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Table 2: Space closure percentages according to the extraction region

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Figure 4: Percentages of space closure success according to the extraction region

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The space between second permanent premolar and the SPM was measured by two observers, one of them having an experience of more than 10 years. The mean interval of the difference between measurements made by the two observers was 0.26.

In both maxilla and mandible, SPMs in stage G were frequently found while SPMs in Stage D were not observed in any of the arches [Figure 5]. The most common extraction age was 11 years, followed by 10 and 12 years, respectively, whereas the most common evaluation age was 14 years. Category 1 space closure was found in 37 SPMs (44.6%), whereas category 2 space closure was observed in 17 (20.5%) SPMs. Of them, 5 (6.02%) SPMs were evaluated to belong to category 3. Although SPMs belonging to category 4 were not found, 24 (28.9%) teeth were found to belong to category 5. In total, 10.8% SPMs belonged to the “ideal” stage of Demirjian's dental development, that is, stage E [Table 3],[Table 4] and [Figure 6].
Figure 5: Plot of lower and upper SPMs evaluation based on categories 1--5 and stages D-G. The categories is shown on the horizontal axis and the stages is on the vertical axis

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Table 3: Relationship between clinical and radiographic findings and space between second permanent premolar and SPM in upper jaw

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Table 4: Relationship between clinical and radiographic findings and space between second permanent premolar and second permanent molar in lower jaw

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Figure 6: Stages of upper and lower second permanent molars development with categorical information

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   Discussion Top

FPMs are the teeth that are most prone to caries, presumably because of their early exposure to the oral cavity. In more than 50% children over 11 years of age, the FPMs are found to be carious.[16] In Turkey, the general information on the oral health of children has been compiled in two national surveys, those of 1988[17] and 2004.[18] According to these surveys, the prevalence of caries in 6-year-old children in 1988 was 84% while in 5-year-olds it was 70% in 2004. The prevalence of caries in 12-year-old children was 84% in 1988 and 61% in 2004.[17],[18] According to the study of Olatosi et al.,[19] the prevalence of early childhood caries was 21.2% and untreated teeth rate was high below the age of 6 years. Due to the high prevalence of caries in these teeth, FPMs are frequently extracted in our country. In this study, the percentage of patients with FPM extractions performed at the “ideal” time of 8--10 years of age and the effect of FPM extraction time on the eruption of SPM (after extraction of FPMs) has been evaluated.

The decision to extract the FPMs is rarely made because the extraction of FPM has a possibility of making orthodontic treatment more difficult and may require a longer time for treatment. However, in case of poor prognosis of the FPM, the decision of its extraction must be considered. The factors that make its prognosis poor include the presence of large carious lesions and restorations, severe hypoplasia, irreversible pulpitis, and apical lesion in the tooth.[20] In the present study, the reasons for extraction of the FPM included the presence of large carious lesions and apical lesions.

A study done by Thunold in 1970[21] dictates that the ideal extraction time of lower FPM is when the patient is 8--9 years old. By this time, the crown of the lower SPM is radiologically complete or the bifurcations in them become visible. If the extraction of lower FPM is performed at the ideal stage, the SPM on eruption may have a good contact with the second premolar where crowding is usually present otherwise. Spontaneous improvement in crowding may occur at the anterior region of the arch.[22] In addition to this, the third permanent molar can erupt satisfactorily.[23]

If the lower FPM is extracted before the ideal stage, there is a risk of distal drift of the lower second premolar. The lower second premolar may become impacted against the lower SPM and a space between the first and second premolars is thus created. The extraction of the lower second primary molar and the FPM, if performed together, can avoid this problem. Therefore, the lower second premolar erupts freely.[20]

It may satisfactorily move anteriorly after the extraction of upper FPM if upper SPM does not erupt, although there were still be remaining space, if inadequate crowding is present. In case, the upper SPM erupts at the time of the extraction of FPM, tipping and anterior rotation of the SPM may occur.[20] Thus, the possibility of little relief or no spontaneous relief from crowding in the maxillary labial segment may be seen after the extraction of the upper FPM.[21] A general opinion about the effect of FPM extraction on the eruption of the third molar is that the extraction of FPM reduces the frequency of third molar impaction because the space for its eruption increases and the mesial movement of the molars occurs in the course of space closure.[24],[25]

Teo et al.[4] evaluated the position of 236 molar teeth on eruption. Of 236 teeth, 117 were maxillary while 119 were mandibular. In their study, category 1 was frequently found and the “ideal time” (Stage E) was the time in which the extractions were most frequently performed. In the present study, the most frequent extraction time was Stage G, yet, similar to their study, category 1 was the most common category observed. Also, it was found in their study that complete space closure for upper SPMs was more likely to be achieved than that for lower SPMs, which was similar to the reults of the present study.

The study of Teo et al.[26] assessed 66 patients (37 females; 29 males), out of which the FPMs had been extracted at the “ideal time” in 58% of the cases. In the present study, 10.8% of the FPMs were extracted at the “ideal time,” out of which 2 (2.4%) belonged to the maxilla and 7 (8.4%) belonged to the mandible.

In the present study, there was one patient who had all the FPMs extracted, the highest rate of space closure was observed in this patient followed by that upper bilateral FPM extraction, right and left opposing teeth extraction and lastly, the lower bilateral FPM extraction. When bilateral extractions were performed, the rate of space closure was found to be higher in the upper jaw than that in the lower jaw. No statistically significant differences were found between unilateral and bilateral extractions of the upper jaw. On the contrary, the rate of space closure was higher in the unilateral extractions than that in the bilateral extractions of the lower jaw. However, when the opposing tooth was extracted, the rate of space closure was found to be 50% in both the jaws. Once all the FPMs were extracted, the rate of space closure was found to be 100%. These results suggest that the rate of space closure was higher when the opposing tooth was extracted.

However, Teo et al.[4] also reported one limitation of their study that SPMs were assessed and recorded only by a single examiner. They emphasized that an increased validity to the study could be provided if the evaluation was performed by two or more examiners and if the research agreement would have been followed. The advantage of the present study was that it had been evaluated by two researchers.

Although panoramic radiographic technique bears the disadvantages of image magnification and distortion, the angle measurements and the consistency between measurements may be evaluated by continuous use of the same device and settings.[27],[28] Larheim and Svanaes [28] reported that if the patient is properly stabilized during the exposure, the horizontal dimensions may be measured with acceptable reliability. Panoramic radiographs are in use worldwide since a long time and play an important role in dental radiology; therefore, it was speculated that additional radiographs for evaluating the eruption of SPMs after FPM extraction was not required, which was similar to the idea of Bayram et al.[25]

   Conclusion Top

In conclusion, favorable space closure and development of SPM is expected to occur even without orthodontic treatment, although it does not always end up with satisfactory results. Therefore, it is important to perform the extraction in the “ideal time” and the patient must be followed up after extraction for the maintenance of a good patient health. Accordingly, the need for orthodontic treatment can be determined and the patients may appropriately be directed to the necessary departments. Additionally, a few detailed studies on space closure after FPM extraction have been found in the literature, although no study using data mining tools was reported on this subject. The authors opine that this study will be the first of its kind with regards to the detailing as in mandible as well as in the maxilla, as the studies that have been found are mostly on mandibular molar teeth. To the best of knowledge of the authors, this is the first study to use data mining method. Further studies are however needed to evaluate space closure and changes in the dental arch after FPM extractions.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

  [Table 1], [Table 2], [Table 3], [Table 4]


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