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ASSESSMENT OF ORTHODONTIC TREATMENT BY PAR INDEX.

Byline: ASMA SHAFIQUE, ABIDA IJAZ and SADIA IQBAL

Abstract

This cross sectional study was carried out to assess the results of orthodontic treatment provided at Lahore Medical and Dental College. Preand post treatment casts and orthodontic files of last 40 finished orthodontic cases were utilized to study the treatment results by using PAR index. Preand post-treatment PAR score was calculated for each patient. All patients who received complete orthodontic treatment were included in the study. One investigator assessed all the components of the PAR Index. ANOVA was used to compare point reduction in PAR score in various malocclusion groups. The degree of correlation between various variables was assessed through Pearson Correlation Coefficient. The results showed that there was100% improvement in upper and lower anterior segment. Class II div I malocclusion displayed maximum improvement in comparison to other malocclusions.

There was a significant positive correlation between pretreatment PAR and point reduction in PAR score. Weighted pretreatment PAR was found to be a significant positive predictor of point reduction.

Key words: PAR index, Outcome assessment, Orthodontics treatment

INTRODUCTION

Quantitative evaluation of Orthodontic diagnosis is considered to be a difficult task due to its subjective nature.1,2 On the contrary, several indices have been presented for quantitative assessment of severity of malocclusion and evaluation of treatment need.3,4

These indices provide valid and reproducible system of measurement. The Peer Assessment Rating (PAR) index was introduced by Richmond in 1990 to assess the severity of malocclusion.5 It provides a cumulative score for occlusal disharmonies and identifies a deviation between normal occlusion and malocclusion. It has been weighted according to the judgment of orthodontists and general dentists.6 The malocclusion is quantified based on five criteria of variable weightings: upper and lower anterior segment alignment (x1), left and right buccal occlusion (x1), overjet (x6), overbite (x2), and centerline (x4). Pretreatment and post treatment study casts are used for and comparison. This comparison is used to judge treatment efficacy in correction of malocclusion.1,7,8 Reduction in the total score and percentage reduction are used to measure changes in PAR index.

According to Richmond et al. 6 30 percent or more reduction in weighted PAR score is required for a case to be considered as improved. Similarly, if there is reduction of 22 points in total PAR score, it is considered to be greatly improved. Some other studies have reported that great improvement can be considered if a change in PAR score is equal or greater than 70 percent.9 Nomogram is a graphic representation of these criteria.6

Richmond et al considered that an acceptable occlusion is characterized by PAR score of 10 or less. An ideal occlusion, on the other hand is characterized by a PAR score of 5 or less.6,7

PAR index has various applications. It has been used to evaluate treatment standards among general dentists and orthodontic specialists, to assess severity of malocclusion3,10 to compare treatment outcomes using different types of fixed appliances and to study post treatment relapse.7,11,12,13 It is also used in studies assessing the effectiveness and outcomes of orthodontic treatment in private practices, graduate and undergraduate clinics.1,2,9

Despite of the fact that it is proved to be a reproducible, valid and objective index for scoring occlusal change for the entire mouth, it has several limitations.14

This is principally because of the high weight assigned to overjet. Additionally, application of one weighting system to all types of malocclusions may give rise to difficulties because of the variation in occlusal features in different malocclusion.15

PAR index is now used to assess orthodontic treatment need as a valid and reliable index. However, numerous factors such as decalcification of enamel, facial profile, root resorption, and treatment stability are not assessed through PAR index. 16,17

The present study was conducted to:

1 Assess the quality of orthodontic treatment provided at Lahore Medical and Dental College, by using PAR index.

2 Determine the significant factors contributing to point reduction in PAR index.

3 Determine the correlation between probable factors affecting point reduction in PAR.

MATERIALS AND METHODS

A cross sectional study was carried out at the Lahore medical and dental college, Lahore. Preand post-treatment records including orthodontic files and study casts of last 40 consecutively finished cases representing different malocclusion categories were evaluated. All patients receiving fixed appliance therapy at our Orthodontic clinic were included in the study. Single arch treatment cases and retreatment cases (treatment after relapse) were excluded from the study.

The total PAR score comprises of sum of scores of seven individual traits: alignment of upper and lower anterior segment, right and left buccal occlusion, overjet, overbite and centerline. A single investigator, who was calibrated in the use of PAR index, calculated both preand post-treatment weighted PAR scores according to British weightings system advocated by Richmond et al.6 and labeled them as wPAR1 and wPAR2 respectively. A digital caliper (Mitutoyo, Kawasaki, Japan), with accuracy closed to 0.1 mm, was used to measure all parameters on the initial and final casts. Information regarding patients' age, gender, angle's malocclusion, duration of active treatment, extraction or non-extraction was collected from their files. The data were recorded on a data sheet especially designed for this study.

Descriptive statistics including means, minimum and maximum were calculated for all variables which included age, duration of treatment, pre-treatment PAR score, post treatment PAR score, angles class (maloc-clusions) and percentage reduction in PAR score. The percentage PAR reduction indicates the improvement and hence success of treatment. This is determined by the formula: T1-T2/T1 x 100% where T1 is the pretreatment score, T2 is the post treatment score. Cases were divided into three categories i.e. "Greatly improved", "improved" and "worse or no different" based on PAR score reduction, according to criteria mentioned by Richmond et al.6,7 In addition means of all individual PAR attributes for WPAR 1 and WPAR 2 were also calculated. ANOVA was used to compare point reduction in PAR score in various malocclusion groups. Pearson Correlation Coefficient was used to assess the degree of correlation between all variables.

A linear regression model was formulated to see the significant effect of independent variables on dependent variable i.e. point reduction. The independent explanotories were: pre-treatment PAR score (wPAR1), age at treatment start (years), treatment duration (months), extraction and malocclusion based on Angle's classification. A stepwise regression model was calculated to evaluate most significant contributory individual factors to the changes in point reduction. SPSS 15 was used for all statistical analyses and p <0.05 was considered as statistically significant.

RESULTS

A correlation matrix was used to investigate the dependence between multiple variables at the same time (Table 4). A significant positive correlation was found between the pretreatment PAR and point reduction in PAR score. Case category had significant negative correlation with point reduction and weighted pretreatment PAR. There is a weak but significant correlation between point reduction and age and pretreatment and post treatment PAR. No significant correlations were found among other variables i.e. age, gender, malocclusion groups, appliance type, duration of treatment and extraction/ non extraction groups. Multiple linear regression shows a significant regression equation i.e: F=5/34=43, P < 0.001 with R2 of.866=86%. Weighted pretreatment PAR is only significant positive predictor and predicts 91% of the variance in point reduction, p is < 0.001, as shown in Table 6 .

DISCUSSION

The results revealed that there was 100 % correction in upper and lower anterior segment followed by more than 85% correction in lower left, upper left, upper right, and right buccal segments respectively.

TABLE 1: MEAN WEIGHTED PRE TREATMENT AND POST TREATMENT INDIVIDUAL PAR SCORE.

###Pre###Post treat###Per-

###treat###Mean###centage

###Mean###improve-

###ment

upper right###.65###.08###87%

segment

upper ant seg-###2.75###0.00###100%

ment

upper left seg-###.55###.08###85.45

ment

lower right###.50###.15###70%

segment

lower ant seg-###1.97###.00###100%

ment

lower left seg-###.43###.02###95%

ment

right buccal###1.05###.18###87%

segment

left buccal seg-###1.13###.30###73%

ment

overjet###9.45###2.10###77%

overbite###2.78###1.50###46%

centre line###1.50###.32###78%

Furthermore, there was moderate correction in lower right, left buccal; over jet and midline i.e. 70-78 % . Overbite was the only variable that ended up with less than 50 % correction, (Table 1). In a study conducted by Kemal et al. 18 highest pretreatment and post treatment PAR scores were found to be in mandibular incisor extraction group and lowest PAR scores were found in non extraction groups. They considered that retraction in extraction space results in anterior deep bite leading to raised post treatment PAR scores. Extraction pattern might be a reason of overbite being the least successful variable in present study as thirteen out of forty cases were treated with single arch premolar extractions and three cases were treated with single lower incisor extraction only.

In accordance to present study, Holman et al.19 achieved more than 85 percent corrections in upper anterior segment, over jet and midline in extraction and non extraction groups. On the contrary, they were able to achieve better correction in overbite (71%) and less improvement in left buccal and right buccal occlusion (60%). This disparity might be due to difference in study design as they used American weighting system. Daniel et al.20 had more consistent results with present study. However, they were least successful in correction of anteroposterior relationships in buccal segments, which they attributed to their assessment criteria instead of treatment mechanics.

TABLE 2: IMPROVEMENT CATEGORIES IN MALOCCLUSION GROUPS

Malocclusion###class I###class II div 1###class II div###class II sub###class III###Total

###2###div

Greatly improved###4###12###0###3###0###19

Improved###7###10###1###1###1###20

Not improved/worsened###0###1###0###0###0###1

Total###11###23###1###4###1###40

TABLE 3: DESCRIPTIVE STATISTICS OF PAR INDEX BEFORE (T1) AND AFTER TREATMENT (T2) IN MALOCCLUSION GROUPS.

###Class I###Class II div 1###Class II div 2###Class II Sub Div###Class III

###T1###T2###T1###T2###T1###T2###T1###T2###T1###T2

Mean###21.1###5###20.6###4.75###11###4###29###6.25###12###5

Max###37###14###36###12###11###4###45###12###12###5

min###7###O###8###5###0###0###11###0###0###0

TABLE 4: PERCENTAGE REDUCTION IN MALOCCLUSION GROUPS.

###Class I###Class II div###Class II div###Class II Sub###Class III###P value

###1###2###Div

% Red.###76.3%###77%###63.6%###78.4%###58.3%###0.85

TABLE 5: CORRELATION MATRIX

###Age###Type of###Weighted###Weighted###Point re-###Total###Arch ex-

###maloc-###pre-treat###post treat###duction in###time du-###traction

###clusion###PAR###PAR###weighted###ration

###PAR

type of maloc- R2###.111

clusion###p###.497

weighted pre- R2###-.299###.067

treat PAR###p###.060###.682

weighted post R2###.067###.063###.313

treat PAR###p###.683###.699###.049

point reduc-###R2###-.324###.066###.920###-.079

tion in weight-

ed PAR###P###.041###.685###.000###.630

total time du- R2###-.178###.070###.172###.310###.041

ration###P###.272###.670###.317###.051###.802

arch###ex-###R2###.246###-.225###.064###.094###.015###.098

traction###p###.126###.163###.694###.562###.925###.546

case category R2###.381###-.074###-.811###.050###-.882###.122###.007

###p###.015###.650###.000###.758###.000###.455###.964

TABLE 6: RESULTS OF MULTIPLE LINEAR REGRESSION ANALYSIS CONSIDERING POINT REDUCTION IN WEIGHTED PAR AS THE DEPENDENT VARIABLE.

S.No###Variable###P value

1###Age of patient###.226

2###Type of malocclusion###.865

3###Weighted pretreat PAR###.000

4###Total time duration###.075

5###Arch extraction###.457

We were able to highest percentage PAR reduction (78%) in Class II sub division malocclusion, followed closely by Class II division 1 and Class I malocclusion (77% and 76 % respectively). Lowest reduction was noted in Class III malocclusion (58%), (Table 4). These results are consistent with the results achieved by Gasgoos.16 However, the statistical relation between percentage reduction and malocclusions in both studies was insignificant. Treatment of Class II Division 1 group was found to be most successful by Birkeland et al.21 It was followed closely by Class II Division 2 malocclusion. In contrast to present study, their study design did not include class II sub division as a separate category. Fidler et al22 also found a high percentage reduction and better long term results in Class II malocclusion group.

Interestingly, in contrast to present tudy, treatment of Class II division 2 malocclusion was declared to be most successful with 80.8 % PAR score reduction and was closely followed by Class II division 1 malocclusion. The disparity can be explained by the fact that our mean pretreatment PAR score of class II division 2 group was less in comparison to the rest of class II malocclusion categories. This eventually led to less mean PAR reduction in that group. Contrary to all these findings, Willems et al.18-23 reported high success rate in Class III group when absolute values were considered but the difference among three groups was statistically insignificant. High percentage reduction in Class II group was attributed to its high pre-treatment PAR score by some authors17,23,24 who advocated that this could be a result of over rated over jet and overbite frequently seen in this group.

Interestingly however, class I malocclusion had maximum pre treatment mean PAR score in the present study. This was due to presence of impacted teeth, cross bite, overbite and center line shift in most patients of class I group.

Correlation matrix was used to evaluate the correlation of different variables (Table 5). There was a significant positive high correlation between the pretreatment PAR and point reduction in PAR score. This is in accordance to various other studies.24-27 It implies that more pronounced treatment changes will be observed in more severe malocclusion. On the contrary, Woods et al.28 found an insignificant correlation pretreatment PAR and post treatment corrections. This lack of correlation could be attributed to the fact that they employed variable treatment plans in order to treat different malocclusions. Point reduction was also found to be positively correlated to gender and experience of operators by Firestone et al25 and Holman et al.19 The relationship of these variables was not considered in present study. In accordance to Reidmann and Berg26, a weak but significant correlation of treatment duration was found with pre and post treatment PAR.

This suggests that greater reduction in PAR score is expected in patients having high pre-treatment PAR score and more complex cases take more time to finish.14,29 In contrast to our findings some authors attributed their lack of correlation to the early termination of treatment due to which fine detailing was not possible in severe cases of Class II division 1 sample.2,11,30 The present study however, found no correlation between age and duration of treatment (Table 6). This is in agreement to results by Gasgoos.17 Similarly, extractions did not significantly influence any other variable in present as well as other studies.19,25

CONCLUSIONS

1. 100% correction was achieved in upper and lower anterior segment crowding, whereas, least improvement was observed in overbite.

2. Class II division I malocclusion exhibited maximum improvement and was found to be the most frequently encountered malocclusion.

3. A significant positive correlation exists between pretreatment PAR score and point reduction.

4. Weighted pretreatment PAR is only significant positive predictor of point reduction in PAR score.

REFERENCES

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19 Holman JK, Hans MG, Nelson S, Powers MP. An assessment of extraction versus nonextraction orthodontic treatment using the peer assessment rating (PAR) index. The Angle Orthodontist. 1998 Dec;68(6):527-34.

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21 Birkeland K, Furevik J, Boe OE, Wisth PJ. Evaluation of treatment and post-treatment changes by the PAR Index. European Journal of Orthodontics. 1997 Jun;19(3):279-88.

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28 Woods M, Lee D, Crawford E. Finishing occlusion, degree of stability and the PAR index. Australian orthodontic journal. 2000 Mar;16(1):9-15

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30 O'Brien KD, Robbins R, Vig KW, Vig PS, Shnorhokian H, Weyant R. The effectiveness of Class II, division 1 treatment. American Journal of Orthodontics and Dentofacial Orthopedics. 1995 Mar 1;107(3):329-34.
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Author:Shafique, Asma; Ijaz, Abida; Iqbal, Sadia
Publication:Pakistan Oral and Dental Journal
Article Type:Report
Date:Sep 30, 2018
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