Radiographic assessment of lower third molar eruption in different anteroposterior skeletal patterns and age-related groups

Abstract

Objective: To analyze radiographic predictors for lower third molar eruption among subjects with different anteroposterior skeletal relations and of different age groups. Materials and Methods: In total, 300 lower third molars were recorded on diagnostic digital orthopantomograms (DPTs) and lateral cephalograms (LCs). The radiographs were grouped according to sagittal intermaxillary angle (ANB), subject age, and level of lower third molar eruption. The DPT was used to analyze retromolar space, mesiodistal crown width, space/width ratio, third and second molar angulation (a, c), third molar inclination (b), and gonion angle. The LC was used to determine ANB, angles of maxillar and mandibular prognathism (SNA, SNB), mandibular plane angle (SN/MP), and mandibular lengths. A logistic regression model was created using the statistically significant predictors. Results: The logistic regression analysis revealed a statistically significant impact of b angle and distance between gonion and gnathion (Go-Gn) on the level of lower third molar eruption (P , .001 and P , .015, respectively). The retromolar space was significantly increased in the adult subgroup for all skeletal classes. The lower third molar impaction rate was significantly higher in the adult subgroup with the Class II (62.3%) compared with Class III subjects (31.7%; P , .013). Conclusion:The most favorable values of linear and angular predictors of mandibular third molar eruption were measured in Class III subjects. For valid estimation of mandibular third molar eruption, certain linear and angular measures (b angle, Go-Gn), as well as the size of the retromolar space, need to be considered. (Angle Orthod. 2015;85:577-584.)

Impaction of mandibular third molars after orthodontic treatment by the edgewise method: a retrospective study

“…6,24 Other associated Class II skeletal characteristics are an acute gonial angle and a narrow mandible. 6 Likewise, it is expected that the space-to-width ratio in Class III patients will attain the values needed for eruption of the lower M3, thus acting as a protective factor against impaction, 9 even though this was not confirmed by our results. This disagreement may be attributed to how we evaluated the sagittal relationship, in which we observed the dental relationship, versus how other studies evaluate dental and skeletal relationships.…”

“…These include amount of pretreatment crowding, 30 pattern of mandibular and condylar growth, available retromolar space and residual mandibular growth in Class III patients. 9 The clinical implications of our findings might guide clinical actions and improve the understanding M3 impaction behavior. In sum, mesioangulation of M3 and a pronounced overbite before orthodontic treatment are predictive dental and occlusal characteristics of future disturbances regarding M3 eruption, and indicate orthodontic treatment with premolar extraction in borderline cases.…”

“…6 In addition, vertical condylar growth may also lead to limited anterior remodeling of the mandibular ramus, leading to not enough space for a lower M3 to erupt. 7,8,9 Several authors have defended the principle of premolar extraction to improve the position and angle of an impacted M3, thereby favoring its complete euption. 10,11012,13 A critical appraisal of the literature finds that the main limitations of these studies are related to the unrepresentativeness of the sample, non-standardized use of the type of appliance and orthodontic mechanics, methodological differences regarding evaluations and different follow-up times.…”

A Class II patient with bimaxillary protrusion and mandibular inclined third molars treated with orthodontic anchoring screws: A case report

“…Recently, orthodontic anchoring screw has been generalized, and absolute anchorage can be achieved without active patient cooperation [6]. In a prior study, skeletal Class II patients showed a higher percentage of the impaction rate of third molars (62.3%) than did skeletal Class III patients (31.7%) [7]. They are mainly extracted because of incomplete eruption.…”

The Frequency of Mandibular Third Molar Impaction in Different Types of Vertical Skeletal Faces

“…2 Studies have reported third molar as one of the most commonly impacted tooth accounting for 98% of tooth impactions. 3,4 Mandibular third molar has more tendency for impaction as compared to maxilla. 5 It was noted that 3 to 4 years of ageis the time when crypt formation ofthird molar begins, while calcification starts at the age of 7 to 10 years.…”