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The Effect of Skeletal Form on Second Molar Impaction

McKeon, Kathleen (2021) The Effect of Skeletal Form on Second Molar Impaction. Master's Thesis, University of Pittsburgh. (Unpublished)

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Background: Mandibular second molar impaction, while still a relatively rare condition, has been increasing in frequency over recent years. There are a few theories about what might be causing these impactions, including, lower arch crowding1, genetics2, and use of appliances that preserve E-space3, such as lower lingual holding arches and lip bumpers4. A potential contributor to second molar impaction that has not been studied is skeletal form. The purpose of this study was to examine the relationship of gonial angle to the impaction of mandibular second molars. Secondary goals were to compare second molar tooth size, space available, ramus to molar width, and the angle between the occlusal plane and posterior border (OP-PR) of the mandible in patients with impacted second molars and those without. Hypothesis: Patients with mandibular second molar impaction are more likely to have a smaller gonial angle when compared with patients that do not have impaction. Materials and Methods: Panoramic radiographs were collected from two private orthodontic offices. Those with impactions were designated to the experimental group, while those without were designated to the control group. Measurements were made on each of the radiographs and compared between experimental and control groups. Results: No statistically significant difference was found in gonial angle between impacted and non-impacted groups. Statistically significant differences were found for space available ratio, ramus to molar width ratio, and OP-PR angle between the two groups. Conclusions: There was a clinically significant difference in the tooth size to space available ratio between the two groups with the second molar accounting for 126% of the space available in the impacted group and only about 80% of the space available in the non-impacted group. A clinically significant difference was also found in OP-PR between the two groups, with the impacted group averaging 72.43º, and the non-impacted group averaging 66.39º. These findings may be of use to clinicians when treatment planning for patients that have the potential to develop second molar impactions.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
McKeon, Kathleenkrm142@pitt.edukrm142
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairBurnheimer, Johnjmb334@pitt.edujmb334
Committee MemberMortimer, Robertrrm7@pitt.edurrm7
Committee MemberShah, Nileshnhs3@pitt.edunhs3
Date: 7 July 2021
Date Type: Publication
Defense Date: 14 May 2021
Approval Date: 7 July 2021
Submission Date: 25 May 2021
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 36
Institution: University of Pittsburgh
Schools and Programs: School of Dental Medicine > Dental Science
Degree: MDS - Master of Dental Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: second molar impaction gonial angle
Date Deposited: 07 Jul 2021 19:09
Last Modified: 07 Jul 2021 19:09


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