Delaying Premolar Extraction for Conservation of Anchorage: A Prospective Case Control Study

Introduction: Anchor loss (AL) is the most common side effect of orthodontic treatment. Anchorage planning is the vital step of every orthodontic treatment. The aim of this study was to evaluate the amount of anchor loss of maxillary first permanent molar in early v/s delayed premolar extraction cases treated using fixed orthodontic mechanotherapy. Materials & Method: Sixty orthodontic patients, having either Class I or Class II Division 1 malocclusion with no or minimal crowding were divided equally into early extraction and the delayed extraction group (30 each). The patients were treated using MBT prescription 022” slot brackets with standard wire sequencing until 0.019”x 0.025” stainless-steel wire. Pre and post levelling study models were used for assessing the amount of space loss using palatal rugae as a stable point from the points marked on the 1st molar (point A on mesiobuccal cusp and point B on the distobuccal cusp). The obtained data was tabulated and was subjected to statistical t test (p<0.05). Result: The distance of point A to the 3rd rugae reduced after treatment by 0.39mm (3.4%) and by 0.48 mm (3.24%) in delayed and early extraction groups respectively. Similarly, the distance from point B was reduced by 0.48 mm (3.24%) and by 1.77mm (6.28%) in delayed and early extraction group respectively. The change in point A and point B in Early extraction cast group was 76% and 71% more respectively than the delayed Extraction cast group. All the findings were statistically significant (p<0.05). Conclusion: Anchor loss is an inevitable after effect following premolar extraction. Greater chances of anchor loss in early extraction group is noted. And delaying premolar extraction in cases with mild crowding (<4mm) can effectively help in anchorage preservation.


INTRODUCTION
teeth, since it is impossible to achieve complete anchorage within the dentures. 3 According to Tweed: "The production of a stable anchorage is most important for successful orthodontic treatment and should be the initial concern of the operator". 4 If not taken care of, the failure to maintain anchorage leads to a phenomenon known as anchor loss.
Anchorage loss (AL) is an inadvertent side effect of orthodontic mechanotherapy. It is defined as the amount of mesial movement of the first permanent molar during premolar extraction space closure.
Driftodontics is a term applicable when some teeth have been removed without any active orthodontic therapy. 5 The posterior teeth also have a tendency to move towards the extraction space. This movement of Orthodontic Journal of Nepal, Vol. 9 No. 2, July-December 2019 48 the molars toward the extraction site is sometimes an undesirable side effect.
Thus, the purpose of this study is to investigate the amount of anchor loss of the 1st permanent maxillary molar in cases treated using early and delayed pattern of 1st premolar extraction following fixed orthodontics treatment. As the amount of research is limited on the current issue, this study is aimed at highlighting the consequences of early extraction treatment so as to provide a sound base for future references.

MATERIALS AND METHOD
The cross sectional study was conducted on a sample of 70 patients of age 12-25 year. The patients were selected by simple random sampling. Two groups were made namely: early extraction group and a delayed extraction group. The early and the delayed extraction groups had 30 patients. The ethical clearance for the study was obtained by the institutional ethical committee. Before carrying out the study, patients were informed about the purpose of the study and the written consent was obtained for the same. The subjects were selected after they fulfilled the selection criterion like patients having Class I or Class II Division 1 malocclusion and who required extraction of first four premolars for the treatment and who had no or minimal crowding.
Seventy patients who visited outpatient department of orthodontics and dentofacial orthopaedics for the treatment were screened for the diagnosis and treatment planning with respect to early and delayed extraction. Of these 70 patients, 10 patients who didn't meet the screening criteria were discarded. These patients were finally allocated to two groups viz: early extraction (group I) and delayed extraction (group II), each having 30 patients. Based on the malocclusion, a comprehensive treatment plan was developed for each patient.
After the allocation in particular groups, group I (early extraction group) underwent extraction of both 1st premolars in the upper arch by a trained personnel.
All the patients were treated using MBT prescription 022" slot bracket system. Standard wire sequencing advocated by MBT system was followed until 0.019"x 0.025" stainless steel wire. With all the arch wires, 0.010" stainless steel ligature wire was used to ensure complete engagement of the wire in the bracket slot. Pre and post levelling study models were taken to evaluate the amount space loss in both the groups.
In the study models, the centre of the 3rd ruga on the maxilla was taken as the reference point from which the anchorage loss was measured using a vernier caliper. The collected data was tabulated and was subjected to statistical analysis using the SPSS software version 21.
Demographic data comparison was done using chi square test. Intragroup comparison was done using paried t test and unpaired t test was used for intergroup comparison.
The measurement of the10 casts were repeated after a week and the obtained data was studied for the intraexaminer variability using the kappa statistics and the kappa for the same was 0.7 showing the moderate agreement.        not have any effect on the maxillary rugal pattern. 5,11,12 Thus, the study was done on dental casts keeping the mid-point of the 3rd palatal ruga as a stable point for the measurement of anchor loss of molar. According to the study done by Su et al maxillary first molars have tendency to tip mesially, and if the molars are distally tipped before treatment, the more they will tip mesially during treatment. 18 Moreover, mesial movement of first maxillary molar during orthodontic treatment is seen more commonly in class II malocclusion and in the premolar extraction cases.

DISCUSSION
These findings support the results of the present study.
Our results indicated that early premolar extraction in the orthodontic treatment was related to anchor loss. This was supported by Geron et al who said that anchor loss was a multifactorial response which varied according to the extraction site (1st or 2nd premolar), appliance used, age, crowding, and horizontal overlap. 19 However anchorage loss at the end is not a single factor dependent phenomenon. It depends on many factors, which can be majorly categorized into primary and secondary. In which primary includes the factors like crowding and mechanics. In secondary factors age, extraction site and overjet are included. 20 Further, the study carries the scope to check the anchorage loss in delayed and early extraction of second premolar cases and it can be further improved by including other variables like overjet and age to check their influence on the anchor loss.