Journal of Conservative Dentistry
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Year : 2023  |  Volume : 26  |  Issue : 1  |  Page : 104-107
Evaluation of detrimental effects of impacted Mandibular third molars on adjacent second molars – A retrospective observational study

Department of Conservative Dentistry and Endodontics, HKES's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi, Karnataka, India

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Date of Submission09-Jun-2022
Date of Decision06-Oct-2022
Date of Acceptance13-Oct-2022
Date of Web Publication08-Dec-2022


Context: Mandibular impacted third molars are the most frequently impacted teeth in humans and can predispose the adjacent second molar to an array of detrimental effects such as caries, periodontitis, and cervical resorption thus the aim of this study was to determine the same.
Subjects and Methods: A retrospective observational cross-sectional study involving patients with orthopantomography presenting with impacted lower third molar. The type, depth, and level of impaction, the extent of caries, periodontal changes, and the presence of cervical resorption were assessed.
Statistical Analysis Used: Data were analyzed using SPSS version 21.0. with Chi-square.
Results: Mesioangular impaction was most commonly noted. The pattern of impaction had a direct influence in the formation of carious lesions, cervical resorption, and periodontal ligament (PDL) changes.
Conclusions: Noting the pattern of third molar impaction helps the clinician to forecast problems that may occur on adjacent teeth and initiate necessary prophylactic treatment.

Keywords: Cervical resorption; distal caries; impacted lower third molars; PDL changes

How to cite this article:
Belam A, Rairam SG, Patil V, Ratnakar P, Patil S, Kulkarni S. Evaluation of detrimental effects of impacted Mandibular third molars on adjacent second molars – A retrospective observational study. J Conserv Dent 2023;26:104-7

How to cite this URL:
Belam A, Rairam SG, Patil V, Ratnakar P, Patil S, Kulkarni S. Evaluation of detrimental effects of impacted Mandibular third molars on adjacent second molars – A retrospective observational study. J Conserv Dent [serial online] 2023 [cited 2023 Nov 28];26:104-7. Available from:

   Introduction Top

An impacted tooth is one that fails to erupt into the dental arch within the expected time. The tooth becomes impacted because of adjacent teeth, dense overlying bone or excessive soft tissue prevents eruption.[1] Wisdom teeth may emerge in a nonfunctional or only partly functional position and can affect any tooth, but the impaction rate is much more frequent in mandibular third molars (66%–77%) than in maxillary third molars (40%–60%). The prevalence is influenced by age, gender, ethnicity, and skeletal face type.[2]

Unerupted lower third molar has been associated with various symptoms and pathologies, such as pericoronitis, pain, swelling, cheek ulcerations, odontogenic cysts, benign or malignant tumors, and systemic infections.[3] Impacted third molars can predispose the adjacent second molar to an array of detrimental effects such as pain, swelling, pericoronitis, caries, periodontitis, and resorption.[4]

Therefore, it is essential to detect high-risk patients to establish a strict follow-up protocol allowing for an early diagnosis of pathologies. Thus, the study aimed to evaluate the detrimental effects of impacted lower third molars on the status of second molars. The objective of our study was to investigate whether second molars adjacent to impacted third molars exhibit a greater risk of loss due to dental caries, cervical resorption, or periodontal changes. Further, it also evaluates various other aspects of impaction such as its angulation, depth, level, and the degree of causing the above effects on adjacent teeth. The null hypothesis for the study was that there would be no detrimental effects on second molars due to impacted lower third molars.

   Subjects and Methods Top

A cross-sectional retrospective observational study was carried out after obtaining clearance from the institutional ethical committee board. A total of 400 orthopantomography (OPG) radiographs were collected, out of which 205 OPGs satisfying inclusion and exclusion criteria were selected, constituting a total of 379 impacted mandibular third molars.

Inclusion criteria

  1. OPGs of male and female adult patients having erupted/partially impacted or fully impacted lower third molar with the presence of adjacent second molar
  2. Age ranging between 18 and 60 years.

Exclusion criteria

  1. OPG of traumatic injuries or fractures
  2. No proper clarity/hazy images and benign and malignant cysts tumors.

Methodology: After data collection, the impacted third molars were classified using Winter's classification[5] for angulation, depth of impaction, and space available for eruption distal to the second molar.

Based on the inclination of the long axis of the impacted third molar to the long axis of the second molar, the tooth was classified as mesioangular, distoangular, horizontal, and vertical.

The depth of the impacted third molar was evaluated as:

Level A, if the occlusal line of the third molar is in line with or above the occlusal line of the second molar, Level B, if it is below the occlusal line and above the cervical line of the second molar, and Level C, if the third molar is below the cervical line of the second molar.[6]

Depending upon the space available, it was divided as[7]

Class 1: Sufficient space available for eruption,

Class 2: Space is less than the mesiodistal width of the third molar, and

Class 3: If the tooth is completely embedded in the bone.

The effect of impacted/partially erupted and fully erupted the third molar on adjacent teeth for the presence of caries, cervical resorption, or any PDL changes seen with the adjacent second molar was assessed by two investigators.

Healthy second molars with no such pathologies were also recorded as a part of the study. Cervical resorption of the second molar was recorded by viewing the contact point of the third molar to the second molar whether the attachment is with a crown (occlusal, middle, or apical), root (cervical, middle, or apical), or below the apex. Periodontal status was considered compromised if widening, thinning/thickening, or loss of sharp border of lamina dura, horizontal, or vertical bone loss, involvement of furcation was seen with the second molar and normal if any such findings were not seen.

   Results Top

Statistical analysis

Data were analyzed using Statistical Package for Social Sciences (SPSS) version 21, IBM Inc. Armonk, NY. The Chi-square test was used for the comparison of categorical data among groups. The level of statistical significance was set at P < 0.05.

   Discussion Top

Impacted third molars can predispose the adjacent second molar to an array of detrimental effects such as caries, periodontitis, and cervical resorption. This may lead to loss of hard tissue, pain, discomfort to the patient, and ultimately loss of the tooth.[8]

Mesioangular impaction was the most prevalent type of impaction encountered[9],[10],[11] [Table 1]. Most authors state that a mesioangular tilt is highly associated with the occurrence of pathology, while vertical, distoangular, or ectopic impactions are unlikely to result in the above pathologies.[12]
Table 1: Effect of angulation, level of impaction, and space available for the eruption of mandibular third molar on the occurrence of caries, resorption, and PDL status of adjacent second molar

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Most of the third molars were impacted in line with the occlusal line of the second molar, i.e., Level A (71.80%). The percentage of impacted third molar Level B (10%) and Level C (15.80%) of second molars was less comparable.

Most of the lower third molars belonged to class 1, i.e., 64.10%, 9.00% of them were class 2 whereas 25.9% were class 3.

Among all the pathologies, the prevalence of dental caries is the highest seen[13],[14],[15] in the literature which was in accordance with the study as it showed 16.1% involvement, followed by periodontal involvement (13.2%) and cervical resorption (12.7%) [Table 2]. Mesioangular and horizontal third molars are more likely to be associated with caries development in the adjacent second molars and cause resorption of the adjacent molar.[16] However, fully erupted molars might also be an important risk factor to cause caries (16.9%).
Table 2: Effect of the contact point of impacted lower third molar on second molar

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The influence of the contact point located between the second and third molars on the formation of distal caries on the second molar has been well documented.[17],[18] Third molar contacting the adjacent molar in the middle of the crown (23.1%) showed a higher caries rate than other contact points probably due to difficulty in cleaning leading to higher plaque accumulation and subsequent caries.

The literature suggests a unique pattern of distal caries. Carious lesion present at and below DEJ is termed as distal cervical caries usually seen when the mesial cusp of a partially erupted mesioangular impacted third molar contacts the second molar.[19] Radiographically, it appears as a notch on the enamel surface near the contact point.

Mandibular third molar in mesioangular and horizontal impactions have been reported to cause resorption of the adjacent teeth[20] and this was also observed in the present study. All the second molars that had cervical resorption had direct tooth-to-tooth contact with the impacted third molar while most of the second molars with distal caries did not have tooth-to-tooth contact. This suggests that resorption may be due to possible eruptive movements of the third molar as seen in succedaneous teeth resorption during their normal eruption sequence.

Impacted third molars showed a higher prevalence of PDL involvement than erupted third molars.

Studies suggest that a visible third molar itself might be a risk factor for an anaerobic environment conducive to periodontal disease.[21] However, in our study, the strongest association was found in mesioangular (21.2%), followed by horizontally impacted third molars (16.1%).

The International Caries Detection and Assessment System has presented a new paradigm for the measurement of dental caries, which was developed from the systematic reviews of the literature on the clinical caries detection system and other sources and it could be of great use in the detection of such cases.[22],[23]

Further studies in this direction can be carried out using CBCT which helps in better detection and assessment of three-dimensional pathologies.

   Conclusions Top

Within the limitations of this study, it can be concluded that mesioangularly impacted third molar is the most commonly found impaction and is associated with most of the pathologies on adjacent second molar. However, fully erupted third molar or any other kind of impactions also cause pathologies on adjacent teeth. Hence, one can consider prophylactic extraction of the impacted third molar, if detected in the early stages.


We acknowledge the help from Dr. Arvind Moldi Principal, HKES S N Dental College, Kalaburagi Dr. Pallavi Deshmukh Head of Department of Oral Medicine and Radiology, HKES S N Dental College, Kalaburagi, and Dr. Prashant Kumar, Reader, Department of Oral Pathology, HKES S N Dental College, Kalaburagi, for helping us in data collection (OPGs of patients).

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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Winter GB. The Principles of Exodontia as Applied to the Impacted Third Molar. St. Louis, MO: American Medical Book Co.; 1926.  Back to cited text no. 5
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[PUBMED]  [Full text]  

Correspondence Address:
Dr. Ambika Belam
Department of Conservative Dentistry and Endodontics, HKES's S. Nijalingappa Institute of Dental Sciences and Research, Kalaburagi - 585 105, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcd.jcd_341_22

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