reliability of pederson scale in surgical extraction of impacted

Research ArticleReliability of Pederson Scale in Surgical Extraction ofImpacted Lower Third Molars: Proposal of New Scale

Mohamed Yasser Kharma,1,2 Salah Sakka,3 Ghassan Aws,2

Basel Tarakji,3 and Mohammed Zakaria Nassani3

1 Dental School, Aleppo University, Aleppo, Syria2 Al Farabi College of Dentistry, Jeddah 45107, Saudi Arabia3 Al Farabi College of Dentistry, Riyadh 11691, Saudi Arabia

Correspondence should be addressed to Mohamed Yasser Kharma; [email protected]

Received 3 April 2014; Revised 29 May 2014; Accepted 4 June 2014; Published 12 June 2014

Academic Editor: Tarek El-Bialy

Copyright © 2014 Mohamed Yasser Kharma et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

The aim of this study was to evaluate the clinical reliability of the Pederson index in preoperative assessment of the difficulty ofsurgical removal of impacted mandibular third molars. Pederson index was found to be unreliable predictor of true difficulty withlow sensitivity and specificity. A new index (Kharma scale), which takes into consideration the anatomical form of tooth roots, isproposed and evaluated both pre- and postoperatively. The results of the evaluation indicate that the new estimating index is morereliable and accurate measure than Pederson scale.

1. Introduction

Surgical extraction of impacted mandibular third molars isa common practice in the field of oral and maxillofacialsurgery. Therefore, establishing objective criteria that canestimate the clinical difficulty of such procedure preopera-tively is very important. This would allow oral surgeons toundertake correct management with minimal complications.

A search in the literature has shown that only few studiesattempted to evaluate elements, which can complicate surgi-cal removal of impactedmandibular third molars [1]. Amongthese studies, Pederson difficulty index (Table 1) which ismainly based upon anatomical and radiographic features,including angulations, depth, and ramus relationship [2].

However, Pederson scale was tested by several studies andwas claimed to be unreliable predictor of true difficulty [3–7]. Other studies were more comprehensive and took intoconsideration other variables than Pederson’s ones such asabnormal root curvature, width of root, and number ofroots [4, 6, 8]. These studies have suggested new indices andclaimed that their suggested criteria are more reliable andaccurate than Pederson’s scale.

In view of the lack of sufficient data, the current study wasundertaken in an attempt to establish scientific standards thatcan be utilized reliably and accurately to assess preoperativelythe level of difficulty of extraction of impacted mandibularthird molars.

2. Subjects and Methods

A successive surgical extraction of 100 impacted lower thirdmolars from a total of 75 patients (40 men, 35 women)has been studied. The operations were undertaken betweenSeptember 2010 and July 2012, by the authors, at the Depart-ment of Oral andMaxillofacial Surgery of Aleppo University,Syria.

2.1. Operative Technique. All extractions were carried outin outpatient department by the same senior surgeons (Dr.Kharma and Dr. Sakka) to remove the operator bias. Astandard protocol under local anesthesia was followed inall studied cases. This included undertaking regional nerve-block anesthesia of the inferior alveolar, lingual, and buccal

Hindawi Publishing CorporationJournal of Oral DiseasesVolume 2014, Article ID 157523, 4 pageshttp://dx.doi.org/10.1155/2014/157523

2 Journal of Oral Diseases

Table 1: Spatial relationship (position of the molar).

Mesioangular 1Horizontal/transverse 2Vertical 3Distoangular 4Depth

Level A: high occlusal level 1Level B: medium occlusal level 2Level C: deep occlusal level 3

Ramus relationship/space availableClass 1: sufficient space 1Class 2: reduced space 2Class 3: no space 3

Difficulty indexVery difficult 7–10Moderately difficult 5–7Slightly difficult 3-4

nerves with a maximum of two capsules of 1.8mL of 2%lidocaine containing 1 : 80,000 epinephrine. In cases whereforceps alonewere not effective, a vestibular flapwas retractedand osteotomy was undertaken using number 8 tungstencarbide round bur with coronal or root resection if necessary.The wound was then sutured with 3/0 silk and the sutureswere removed one week afterwards. Postoperatively patientswere prescribed anti-inflammatory medication and antibio-therapy.

2.2. Evaluation of Operative Difficulty. For each extractionthe level of difficulty was assessed both pre- and post-operatively. Preoperative assessment was estimated frompanoramic radiograph using two scales. The first scale wasthe Pederson’s scale, while the second one was a modifiedversion of Pederson’s scale (Kharma scale), which took intoconsideration anatomical form of tooth roots (Table 2).

Postoperative assessment of the difficulty of each case wasdetermined using Parant scale [9] which takes into accountthe technique required for surgical extraction as shown inTable 3.

2.3. Statistical Analysis. Sensitivity, specificity, and oddsratios were calculated using a nonparametric ranking test(Kendall’s tau-c) and a probability value of more than 0.5 wasaccepted as a significant value using SPSS analysis.

3. Results

Classification of the difficulty of 100 extractions preoper-atively using Pederson score and Kharma scale is shownin Table 4. The results indicate that 15 extractions are verydifficult according to Kharma scale. By contrast, only 12 casesare classified as very difficult by the Pederson scale. Thecorrelation between themwas found to be relatively poorwithan ordinal value of 0.526 (Table 5).

Table 2: Kharma scale/relationship (position of the molar).

Mesioangular 0Horizontal/transverse 1Vertical 2Distoangular 3Depth

Level A: high occlusal level 1Level B: medium occlusal level 2Level C: deep occlusal level 3

Ramus relationship/space availableClass 1: sufficient space 0Class 2: reduced space 1Class 3: no space 2

Roots formConvergent 0Divergent 1Bulbous 2

Difficulty indexVery difficult 7–10Moderately difficult 5–7Slightly difficult 3-4Easy 1-2

Table 3: Criteria of modified Parant scale.

Easy I Extraction requiring forceps onlyEasy II Extraction requiring osteotomyEasy III Extraction requiring osteotomy and coronal sectionEasy IV Complex extraction (roots section)

The data obtained by Pederson score was also comparedwith Parant scale (Table 6). The results showed poor corre-lation between both scales with low ordinal value of 0.328(Table 7). Furthermore, the sensitivity test of both Pedersonand Parant scales was calculated and the results indicateda high sensitivity value of 0.67 for Parant scale while a lowsensitivity value of 0.37 was obtained for Pederson scale(Table 8).

The same set of tests were undertaken for both Parantand Kharma scale (Table 9). The results showed highercorrelation between both scales with an ordinal value of 0.577(Table 10) and high sensitivity value of 0.67 for Kharma scale,while Parant scale has a sensitivity value of 1.61 (Table 11).

4. Discussion

Estimating the difficulty of removing third molars is acommon dilemma [10]. One of the most important funda-mentals in the planning impacted third molars extractionsis evaluation of preoperative surgical difficulty of impactionremoval; this ability to predict the surgical difficulty facilitatesthe design of treatment plan byminimizing complication andimproving the postoperative management of inflammationand pain [11].

Journal of Oral Diseases 3

Table 4: Pederson scale ∗ Kharma scale crosstabulation.

Kharma scaleTotalEasy Slightly difficult Moderately difficult Very difficult

Pederson scaleSlightly difficult 17 18 2 0 37Moderately difficult 4 18 20 9 51Very difficult 0 4 2 6 12

Total 21 40 24 15 100

Table 5

Value Asymp. std. errors Approx. 𝑇 Approx. SigOrdinal by ordinal Kendall’s tau-c .526 .063 8.323 .000𝑁 of valid cases 100

Table 6: Pederson scale ∗ Parant scale crosstabulation.

Parant scale

TotalExtraction byforceps

Extraction requiringosteotomy

Extraction requiringosteotomy andcoronal section

Complexextraction

Pederson scaleSlightly difficult 14 19 2 2 37Moderately difficult 2 24 22 3 51Very difficult 0 8 4 6 12

Total 16 51 28 5 100

Table 7


Table 8: Sensitivity confidence interval section.

Statistic Test Value Lower 96.0% conf. limit Upper 96.0% conf. limitSensitivity (Parant) 1 0.6700 0.5731 0.7544Sensitivity (Pederson) 1 0.3700 0.2818 0.4678

Table 9: Kharma scale ∗ Parant scale crosstabulation.

Parant scale

TotalExtraction byforceps

Extraction requiringosteotomy

Extraction requiringosteotomy andcoronal section

Complexextraction

Kharma scaleEasy 12 9 0 0 21Slightly difficult 4 30 4 2 40Moderately difficult 0 10 14 0 24Very difficult 0 2 10 3 15

Total 16 51 28 5 100

Table 10


4 Journal of Oral Diseases

Table 11: Sensitivity confidence interval section.

Statistic Test Value Lower 96.0% conf. limit Upper 96.0% conf. limitSensitivity (Kharma) 1 0.6700 0.5731 0.7544Sensitivity (Parant) 1 0.6100 0.5120 0.6998

Various indexes have been proposed and are used byclinicians to classify the difficulty of extraction of lowerthird molar. The Pederson index can be utilized for difficultyevaluation before extraction. However, it is not widely usedbecause it often incorrectly identifies a case as difficult[4].

A postoperative indexmodified Parant scale is consideredto be a better alternative to the Pederson scale in terms ofaccuracy and ease of application [12]. But it also shares similarproblems that it does not account for clinical and radiologicalparameters (root number and morphology) [3].

The target of this study was to critic the Pederson scaleand to provide a guideline for the oral surgeon and dentistwho are regularly involved in the extraction of lower wisdomteeth. The new index (Kharma scale) formed and evaluatedin this study uses different important factors which arementioned by different study [10, 13] such as tooth position,root number and morphology. All variables used in the newindex are easily identifiable with orthopantomographs.

In the current study, the significance of the Pedersonscale in preoperatively predicting the surgical difficulty ofthe removal of impacted mandibular molars was evaluatedand compared to both a new proposed scale (Kharma scale)which takes into account root forms and a postoperative dif-ficulty scale that is suggested by Parant scale. The Pederson’sindex has showed poor correlation with both the proposedKharma scale and the Parant scale. By contrast, the evaluationof Kharma scale, in terms of estimating preoperatively thedifficulty of removal of impacted mandibular third molars,with reference to postoperative difficulty indicated by Parantscale has showed a significant correlation.

In our study we included a new parameter and thatwas root morphology which it consider by de Carvalhoet al. as significant predictor of surgical difficulty [10]. Theauthors of this study believe the major difference of thenew index and Pederson index is the incorporation of theroot morphology which should be considered with anypreoperative assessment and as a consequence the accuracyof prediction gets significantly better.

In conclusion, both radiological and clinical informationmust be taken into account. The proposed Kharma scaleshowedmore accuracy and reliability in preoperative estima-tion of the difficulty of surgical extraction of impacted lowerthirdmolars than Pederson scale. However, a further researchmay be required to further evaluate this new index and toprove its superiority.

Conflict of Interests

The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper.

References

[1] A. Bali, D. Bali, A. Sharma, and G. Verma, “Is pederson indexa true predictive difficulty index for impacted mandibular thirdmolar surgery? A meta-analysis,” Journal of Maxillofacial andOral Surgery, vol. 12, no. 3, pp. 359–364, 2013.

[2] L. J. Peterson, “Principles of management of impacted teeth,” inContemporary Oral and Maxillofacial Surgery, L. J. Peterson, E.Ellis, J. R. Hupp, and M. R. Tucker, Eds., Mosby, Chicago, Ill,USA, 4th edition.

[3] M. Diniz-Freitas, L. Lago-Mendez, F. Gude-Sampedro, J. M.Somoza-Martin, J. M. Gandara-Rey, and A. Garcıa-Garcıa,“Pederson scale fails to predict how difficult it will be to extractlower third molars,” British Journal of Oral and MaxillofacialSurgery, vol. 45, no. 1, pp. 23–26, 2007.

[4] H. Yuasa, T. Kawai, and M. Sugiura, “Classification of surgicaldifficulty in extracting impacted third molars,” British Journalof Oral and Maxillofacial Surgery, vol. 40, no. 1, pp. 26–31, 2002.

[5] A. G. Garcia, F. G. Sampedro, J. G. Rey, and M. G. Torreira,“Trismus and pain after removal of impacted lower thirdmolars,” Journal of Oral and Maxillofacial Surgery, vol. 55, no.11, pp. 1223–1226, 1997.

[6] O. M. Gbotolorun, G. T. Arotiba, and A. L. Ladeinde, “Assess-ment of factors associated with surgical difficulty in impactedmandibular third molar extraction,” Journal of Oral and Max-illofacial Surgery, vol. 65, no. 10, pp. 1977–1983, 2007.

[7] A. Garcıa-Garcıa, F. G. Sampedro, J. G. Rey, P. G. Vila, andM. S.Martin, “Pell-Gregory classiffication is unreliable as a predictorof difficulty in extracting impacted lower third molars,” BritishJournal of Oral andMaxillofacial Surgery, vol. 83, no. 6, pp. 585–587, 2000.

[8] A. J. MacGregor, The Impacted Lower Wisdom Tooth, OxfordUniversity Press, Oxford, UK, 1985.

[9] M. Parant, Petite Chirurgie de la Bouche, Expansion Cientifique,Paris, France, 1974.

[10] R. W. de Carvalho, R. C. de Arajo Filho, and B. C. do EgitoVasconcelos, “Assessment of factors associated with surgicaldifficulty during removal of impacted lower third molars,”Journal of Oral and Maxillofacial Surgery, vol. 69, no. 11, pp.2714–2721, 2011.

[11] O. Sefvan Janjua, Z. Baig, A. Manzoor, and T. Abbas, “Accuracyof Pederson and modified Parant scale for predicting difficultylevel of mandibular thirdmolars,”Archives of Orofacial Sciences,vol. 8, no. 1, pp. 9–13, 2013.

[12] J. Barreiro-Torres, M. Diniz-Freitas, L. Lago-Mendez, F. Gude-Sampedro, J. M. Gandara-Rey, and A. Garcıa-Garcıa, “Evalua-tion of the surgical difficulty in lower third molar extraction,”Medicina Oral Patologia Oral y Cirugia Bucal, no. 6, pp. e869–e874, 2010.

[13] N. Komerik, M. Muglali, B. Tas, and U. Selcuk, “Difficulty ofimpacted mandibular third molar tooth removal: predictiveability of senior surgeons and residents,” Journal of Oral andMaxillofacial Surgery, vol. 72, no. 6, pp. 1062.e1–1062.e6, 2014.

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