| Abstract|| |
Objective: The objective of the study is to determine if extraction of permanent teeth, for orthodontic purpose, causes a change in third molar angulation and also to determine if extraction of permanent teeth causes an increase in eruption space available for third molars. Methods: This systematic review includes retrospective cohort studies which evaluated the change in third molar angulation or eruption space available for third molars among orthodontic patients treated by a fixed appliance with either extraction or nonextraction protocol. Search engines used were MEDLINE, IndMED, Web of Science, Cochrane, EMBASE, and Google Scholar from the year 1975 to 2015. Separate data collection forms were used to extract data from the studies. The Cochrane Risk of Bias Assessment Tool was used to assess the studies included in the systematic review. Results: Fifteen studies included in the systematic review proved that third molar angulation and eruption space improved in patients treated with extraction treatment modality. However, two studies concluded that change in third molar angulation and eruption space occurred irrespective of the type of treatment involved. Conclusion: The angulation and eruption space of third molar improved following extraction of premolar or molar. Nonextraction treatment modality did not cause any adverse effects.
Keywords: Extraction, third molar, third molar impaction
|How to cite this article:|
Kamalakannan D, Anathanarayanan V, Padmanaban S. Effect of extraction or nonextraction orthodontic treatment modality on favorability of eruption of impacted third molars. Indian J Dent Res 2019;30:428-36
|How to cite this URL:|
Kamalakannan D, Anathanarayanan V, Padmanaban S. Effect of extraction or nonextraction orthodontic treatment modality on favorability of eruption of impacted third molars. Indian J Dent Res [serial online] 2019 [cited 2019 Aug 24];30:428-36. Available from: http://www.ijdr.in/text.asp?2019/30/3/428/264108
| Introduction|| |
The need of the third molars for mastication has been reduced due to the transition of consumption of diet from coarse, gritty foods to soft, and refined foods., Therefore, taking a cue from the form and function theory,, the jaws may not be developing enough to accommodate the third molars, which are subsequently getting impacted. Third molar impaction is the most common among all other tooth impactions in the oral cavity. This is also in concordance with the Butler's field theory.
The initial appearance of third molars on routine radiographs is seen from 5 to 16 years of age,, whereas the time of eruption of third molars ranges from 18 to 24 years., This long duration in calcification and eruption may also play a role in subsequent impaction of third molars. The factors which influence the impaction of third molars have been dealt with various studies. Deficient mandibular growth, absence of interproximal attrition in modern-day man, limited retromolar space, and direction of condylar growth  are few among the many factors which affect third molar eruption.
Before the dawn of antibiotics, extraction of impacted teeth was in practice to prevent complications such as infection. However, it was concluded, in a consensus development conference  that the third molars should be removed only for pathological reasons. This calls for the need to investigate the factors and methods which promote eruption of third molars. One of the ways to facilitate eruption of third molars is by therapeutic extractions of other permanent teeth, which is one of the common methods of gaining space in orthodontic treatment planning. The influence of permanent teeth extraction on third molar eruption has been presented and discussed in the orthodontic literature.,, However, the effect is still inconclusive and controversial. Therefore, in light of the inconsistent outcomes in the literature, this systematic review is proposed to first qualitatively evaluate the studies on the influence of permanent teeth extraction on third molar eruption, and thereby, try to evaluate the effect of therapeutic extraction of permanent teeth on third molar eruption.
Aims and objectives
The aim of this systematic review is to evaluate the effect of extraction treatment modality on the favorability of third molar eruption.
The following are the objectives which will be met at the end of this systematic review:
- To determine if extraction of permanent teeth causes a change in third molar angulation
- To determine if extraction of permanent teeth causes an increase in eruption space available for third molars.
| Methods|| |
The studies which satisfied the following eligibility criteria were included in the systematic review:
- Patients: orthodontic patients treated with fixed orthodontic appliance involving either extraction or nonextraction treatment modality and having pre- and postorthodontic treatment records
- Intervention: extraction of permanent teeth (premolar, first, or second molars)
- Control: nonextraction therapy
- Outcome: change in third molar angulation or eruption space
- Study type: retrospective cohort.
The design of each study was assessed using the Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0.
Language restrictions were not applied. Unpublished data were not taken into consideration for the review. Studies published from 1975 to 2015 were sought for review.
The literature for this review was searched independently by two authors, in the following database: MEDLINE (1975–2015), IndMED, Web of science (1975–2015), Cochrane (1975–2015), EMBASE (1975–2015), and Google scholar (1975–2015) using the keywords – extraction therapy, third molar impaction, orthodontic treatment, orthodontic patients, premolar extractions, orthodontic, and third molar. Gray literature was sought from GreyNet and OVID.
The following search strategies (with limits) were used in MEDLINE-((extraction therapy) AND third molar impaction) AND orthodontic treatment, ((orthodontic patients) AND third molar impaction) AND premolar extraction, ((orthodontic) AND third molar) AND extraction
Search results from all the databases were assessed. Duplicate records of the same report were excluded from the study. Titles and abstracts were examined to remove the reports that were obviously irrelevant. Full texts of the potentially relevant studies were sought. Individual studies were assessed for compliance on the proposed eligibility criteria. The articles which did not satisfy the eligibility criteria were excluded for the respective reasons. The reports included for review were used to proceed with data collection.
Data collection process and data items
Data were extracted independently by two authors using a data collection form. Details from the articles were collected on the variables such as study method, participants, intervention (extraction/nonextraction), and outcome (third molar impaction). This process was also discussed with the third author to prevent interobserver disagreement.
Risk of bias assessment
Risk of bias assessment was done using A Cochrane Risk of Bias Assessment Tool: for Non-Randomized Studies of Interventions (ACROBAT-NRSI), Version 1.0.0, 24 September 2014.
The studies included in the systematic review showed heterogeneity, therefore, meta-analysis could not be considered.
| Results|| |
This systematic review was executed based on the PRISMA, 2009 statement. The result of the search strategy is described in [Table 1]. Published literature pertaining to the review was accessed through various database including MEDLINE, COCHRANE, Google Scholar, IndMED, Web of Science, and EMBASE, and a total of 4707 results were obtained. The latter three databases did not throw up any results. A total of 4508 Gray literatures were discovered from OVID and GreyNet. The search was further extended by cross-searching the reference articles in the databases and 10 more studies were retrieved.
The identified articles were then screened and 86 studies were filtered out after reading the title and abstract. Among these records, 29 duplicates were eliminated to obtain 43 studies. At this juncture, inclusion criteria were applied to assess for eligibility, as a result of which 26 studies were eliminated. Ultimately, after streamlining the search, 17 studies were included for this systematic review and subjected to data collection.
The study design of each article, before data collection, was assessed independently by the two authors using Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0. All the articles included were retrospective cohort studies. Each article was described based on following premises such as participant information; pre- and posttreatment records of orthodontically treated patients, sample size, age, and sex; intervention; tooth extraction ( first premolar, second premolar, or first molar); control group with nonextraction treatment; and outcomes; third molar eruption assessed by parameters such as change in angulation of third molar, eruption space, and Pell and Gregory classification.
The results of the study characteristics are presented in [Table 2].
Risk of bias for individual studies
Risk of bias for each study was assessed using ACROBAT-NRSI, Version 1.0.0, and presented in [Table 3]. Majority of the studies subjected to qualitative analysis ,,,,,,,,,, showed a low risk of bias. One study  showed the moderate risk of bias and five studies ,,,, proved to have a serious or critical risk of bias.
Results of individual studies
Results of individual studies are presented in [Table 4]. In all the studies, the outcomes of the intervention, that is, the favorability of third molar eruption, were described based on two parameters; change in third molar angulation and eruption space available for the third molars. Only 5 out of the 17 studies evaluated both these parameters.,,,, The remaining studies estimated either one of these.,,,,,,,,,,,,
Among the studies included in the systematic review, the majority of them proved that there is a significant change in the angulation of third molar pre- and posttreatment, involving extraction modality. However, these studies, with the exception of a few,,,,,,,,,, were of low levels of evidence.,,, Two studies have proved that change in angulation was observed irrespective of the type of treatment involved.,
| Discussion|| |
Summary of evidence
Records from various databases were screened and excluded based on the exclusion criteria formulated for our review. The most obvious exclusion involved those which did not have a control group as the research question primarily involved a comparison between the extraction and nonextraction group.
Most of the studies involved extractions of either first or second premolars, as it is the most frequent orthodontic treatment modality,,,,,,,,,,,,,,, although a couple of studies did experiment with the extraction of first molar and their influence on third molar eruption., As mentioned previously, the possibility of third molar eruption, postextraction, was assessed by the change in angulation of the same or by determining the eruption space available after the intervention (extractions).
The authors differed from each other in terms of utilizing different reference planes for the measurement of angulation of third molars. Bayram et al., Mihai et al. and Saysel et al.,, Staggers et al. and Türköz and Ulusoy,, and Artun et al. evaluated angulation of third molars with reference to the occlusal plane, which was formed by joining the cusp tips of second molar and first premolar. The limitation of using the occlusal plane as a reference is that it can be altered during treatment. Artun et al. in addition also used mandibular and palatal planes for the assessment. The mandibular plane remodels with age, hence, the palatal plane is more ideal as a reference plane due to minimal remodeling changes. However, the Frankfurt horizontal plane is an even more stable reference plane when compared to the others. In Gohilot's study, long axis of third molar was assessed with reference to Frankfurt horizontal plane. Interorbital and intertuberosity lines were used as reference lines by Janson et al. and Livas et al., Intertuberosity line had to be used in some patients because the orbital region was cut during exposure. Horizontal reference plane, perpendicular to the midline bisector, proposed by Elsey and Rock, was constructed to measure the third molar angulation in two studies., The long axis of second and third molars was used to assess the change in the third molars following treatment by two studies., The percentage inclusion of mandibular third molar in the ramus was described by Tarazona et al. to evaluate third molar angulation.
As far as eruption space was concerned, it was measured between the most distal point of second molar and Xi by Salehi and Danaie, distal point of second molar to Z point in a couple of other cases., Richardson  calculated the change in the distance between the distal end of the first molar and the junction between ramus and body of the mandible. In a study by Kim et al., upper and lower third molar movement was measured by superimposition on averaged occlusal plane; upper and lower eruption space was measured from the distal surfaces of the crown of the upper and lower first molar to the pterygoid vertical and anterior border of ascending ramus, respectively.
The quantum of increase in the third molar eruption space is much greater following extraction than nonextraction treatment modality as proved by Richardson. Turkoz et al. proved that third molar impaction rate significantly decreased following extraction treatment. Among the extraction group, the majority of the studies involved extraction of premolars, for instance, the studies by Jain and Valiathan  and Salehi and Danaie  who found an increase in the angulation of the developing third molar. Favorable mesiodistal angulation and increased eruption of third molars were observed in maxillary premolar extraction cases by Janson. Kim et al. proved that maxillary and mandibular third molar impaction significantly reduced following extraction of the premolar. Rare instances of first molar extraction and its influence on third molar eruption were studied by Bayram et al. and Livas et al. which showed a significant increase in angulation of third molars.
Anchorage requirements used in orthodontic treatment were not mentioned in most of the included studies except, Celikoglu et al., Jain and Valiathan, and Gohilot et al. where they excluded cases which required anchorage preparation. Pretreatment status of the third molars was not mentioned in the studies. Age matching should have been considered so that the participants have the same potential for resorption on the anterior border of the ramus.
The hypothesis that therapeutic extraction of teeth closer to third molars would more likely result in their eruption is proved in the study by Celikoglu et al. where there was an increase in the angulation and eruption space of mandibular third molars in the group which underwent therapeutic extractions of the second premolars in comparison with the other group which underwent first premolar extractions. This hypothesis was emphasized by Bayram et al. and Livas et al. by obtaining a favorable change in angulation and eruption of third molar after extracting first molar.
Interarch variability was observed in some of the studies. Comparatively, more favorable change in angulation was observed in maxillary third molars when compared to mandibular third molars.,,, Mihai et al. and Saysel et al., proved that mandibular third molar position improved more when compared to maxillary third molar following premolar extraction.
The sole study which proved no significant change in angulation of third molar between groups involving extraction of premolar and nonextraction treatment was conducted by Staggers et al. and Tarazona et al., They proved that third molar angulation was altered irrespective of the type of orthodontic treatment (extraction or nonextraction).
Although the change in angulation and eruption space will give an insight to the probable subsequent eruption of an impacted third molar, only long-term follow-up studies which actually assess the eventual eruption of third molars will be higher in the hierarchy of evidence. Among the studies selected, six studies had a long-term follow-up, out of which four studies which had a low risk of bias, showed subsequent eruption of third molars.
As stated by Jung et al. 2014, third molar development is faster in males than in females. Most the studies included in this systematic review, comprised adequate sample size with an increased female predilection, and reported no significant influence of gender on the eruption of third molar.,,,,,
Studies have reported no correlation between third molar impaction and growth pattern., Therefore, growth pattern is not considered to be a confounding factor.
All the studies included in the systematic review were only retrospective cohort studies. The paucity of study designs like a randomized controlled trial proved to be a limitation. It was concluded that five studies ,,,, showed a serious-to-critical risk of bias because of the risk of confounding. The authors had not used an appropriate analysis method that adjusted for all critically important confounding domains. Among those five studies, a couple of studies either reported with missing data  or did not have any information regarding the intervention status at the time of intervention. The study by Livas et al., which had a moderate risk of bias, provided no information on the balance of critical cointerventions across groups. Varied outcomes across the studies can be attributed to a lack of standardization in the treatment mechanics following extraction. This may predispose the third molar to a change in angulation. Such drawbacks, hence, prove the need for further research on the effect on third molar impaction due to extraction therapy, preferably clinical trials.
| Conclusion|| |
Based on the limitations and the high risk of bias in some of the studies, following conclusions can be drawn:
- The angulation of third molar improved following extraction of premolar or molar
- However, the improvement in angulation does not imply upright position of third molars in the oral cavity
- Eruption space of third molars improved significantly in extraction group
- Nonextraction treatment modality did not cause any adverse effects
- Lack of studies with higher levels of evidence, especially randomized control trials implies the need for further research on the same.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Dhanyashri Kamalakannan
Department of Orthodontics and Dentofacial Orthopedics, Faculty of Dental Sciences, Sri Ramachandra Medical College and Research Institute, Deemed to be University, No.1, Ramachandra Nagar, Chennai, Tamil Nadu - 600 116
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4]