Association between mandibular third molar formation and retromolar space

Third molar angulation and retromolar space after functional orthodontic treatment : Evaluation of panoramic radiographs after monoblock or Herbst appliance

PURPOSE

The aim of this respectively cohort study was to evaluate the lower second and third molars and canine angulations, retromolar space and occlusal relationships after functional orthodontic treatments with the monoblock or Herbst appliance using panoramic radiographs.

METHODS

Pre- and posttreatment cephalometric and panoramic radiographs of 133 patients (mean age 13.89 ± 1.14 years) treated non-extraction with monoblock (n: 44), Herbst (n: 45) and fixed orthodontic appliances (control group; n: 44) were included to the study. Dental and skeletal measurements were performed on cephalometric radiographs. The angle between the third and second molars, and canines with the lower border of the mandible and the occlusal plane, gonial angle, the angle between the third and second molars and the retromolar space width were assessed on pre- and posttreatment panoramic radiographs. Paired and independent t tests were used for the statistical analysis of the data for intragroup and intergroup comparisons.

RESULTS

Functional treatment with both the monoblock and the Herbst appliances resulted in improvement of skeletal class II relationships. Retromolar space significantly increased in the functional appliance groups compared to the control group (p ≤ 0.001), but improvement of the angulations of posterior teeth was significant only in the monoblock group (p ≤ 0.001).

CONCLUSION

While both the Herbst and monoblock appliances led to an increase in retromolar space, monoblock treatment resulted in more favorable angulation of the third molars compared to the Herbst treatment.

Correlation of mandibular third molar orientation and available retromolar space with arch length discrepancy in subjects with different growth pattern

Aim and Objective

To evaluate, compare, and correlate the mandibular third molar orientation and available retromolar space with arch length discrepancy in subjects with skeletal class II malocclusion and different growth pattern.

Material and Method

A total of 250 patients (age >18 yrs) having skeletal class II malocclusion (based on YEN angle and WITS appraisal) were divided into two groups. Both the groups (Group I with erupted mandibular third molars {N = 150} and Group II with impacted mandibular third molars {N = 100}) were subdivided into subgroups IA (n = 71), IB (n = 19), IC (n = 71) and Group IIA (n = 54), IIB (n = 30) and IIC (n = 16) for normo-, hypo- and hyperdivergent growth patterns, respectively (based on Jarabak ratio and Sn-Go-Gn angle). Four parameters, that is, retromolar space, width of third molar, third molar angulation, and mandibular incisor angulation were measured on orthopantomogram whereas arch length discrepancy was calculated with the help of lateral cephalogram and study model. Intragroup, intergroup comparisons (using unpaired Student's 't' test), and Pearson's correlation coefficient for assessed parameters were obtained.

Result

Third molar angulation and retromolar space were significantly higher in Group I than in Group II (hyperdivergent pattern of Group II had highest value). The width of third molar was less than retromolar space in Group II and vice versa for Group I. Mandibular incisor angulation and arch length discrepancy were more in Group II than in Group I, but difference was statistically nonsignificant. Strong positive correlation was observed for mandibular third molar angulation and available retromolar space in normo- and hyperdivergent growth patterns.

Conclusion

Lack of retromolar space along with increased amount of arch length discrepancy and mandibular incisor angulation is responsible for increased chances of third molar impaction in some subjects with class II malocclusion.

Radiographic Features of Mandibular Second Molars with Eruption Disturbances: A Retrospective Study

We aimed to establish the characteristics and potential etiological risk factors of eruption disturbances in mandibular second molars (MM2). We retrospectively enrolled patients with eruption disturbances in MM2. A total of 143 MM2 with eruption disturbances from 112 patients (mean age 17.45 ± 6.35) were included in this study. Panoramic radiographs were employed to determine the risk factor, angulation type, impaction depth, tooth development stage, and associated pathology. The novel classification method of MM2 was based on impaction depth and angulation. Of 143 MM2, 137 and 6 were diagnosed with impaction and retention, respectively. Insufficient space was the most frequent risk factor for eruption disturbances. There were no significant differences between retention and impaction regarding sex, age, or side. The most frequent impaction type was Type I. The most frequent angulation of impacted MM2 was mesioangular. Impacted MM2 with shallower depth were more frequently associated with the presence of first molar undercut. Impaction types did not differ according to age, side, development stage, or distance from the MM1 distal surface to the anterior border of the ramus. Dentigerous cysts were associated with earlier MM2 development stages and greater MM2 depth. In conclusion, MM2 impaction types differed according to the risk factor, angulation type, MM1 undercut, and presence of cysts. Early MM2 development stage and greater MM2 depth were risk factors for MM2 eruption disturbances with cysts.

Three-dimensional analysis of the relationship between mandibular retromolar space and positional traits of third molars in non-hyperdivergent adults

BACKGROUND

The anatomical position of the mandibular third molars (M3s) is located in the distal-most portions of the molar area. In some previous literature, researchers evaluated the relationship between retromolar space (RS) and different classifications of M3 in three‑dimensional (3D) cone-beam computed tomography (CBCT).

METHODS

Two hundred six M3s from 103 patients were included. M3s were grouped according to four classification criteria: PG-A/B/C, PG-I/II/III, mesiodistal angle and buccolingual angle. 3D hard tissue models were reconstructed by CBCT digital imaging. RS was measured respectively by utilizing the fitting WALA ridge plane (WP) which was fitted by the least square method and the occlusal plane (OP) as reference planes. SPSS (version 26) was used to analyze the data.

RESULTS

In all criteria evaluated, RS decreased steadily from the crown to the root (P < 0.05), the minimum was at the root tip. From PG-A classification, PG-B classification to PG-C classification and from PG-I classification, PG-II classification to PG-III classification, RS both appeared a diminishing tendency (P < 0.05). As the degree of mesial tilt decreased, RS appeared an increasing trend (P < 0.05). RS in classification criteria of buccolingual angle had no statistical difference (P > 0.05).

CONCLUSIONS

RS was associated with positional classifications of the M3. In the clinic, RS can be evaluated by watching the Pell&Gregory classification and mesial angle of M3.

A longitudinal assessment of sex differences in the growth of the mandibular retromolar space

OBJECTIVE

To assess longitudinal variation in patterns of retromolar space growth, with regard to sex and cervical vertebrae maturation.

DESIGN

We utilized serial lateral cephalograms from three craniofacial growth studies (Denver, Iowa, Oregon), measuring retromolar space and cervical vertebrae maturation in 99 subjects (56% male) from 8 to 18 years of age for each subject. Repeated measures ANOVA and a linear mixed effects model were used to assess retromolar space growth through time.

RESULTS

Our analyses revealed an average increase in retromolar space of 8.73 mm from 8 to 18 years. While t-tests failed to find differences in retromolar space growth between males and females at the measured age points, repeated measures ANOVA and linear mixed effects models revealed modest differences in growth trends between sexes, with females having more growth earlier but a younger age of deceleration of growth (between 12 and 14 years of age).

CONCLUSIONS

Our results confirm large increases in retromolar space through growth, reaching an average of 1.38 mm/year around puberty. Importantly, we add to the conversation regarding sex differences, showing differences in timing of growth. This highlights the importance of using longitudinal data and analytical approaches to address questions of this nature.

Mandibular retromolar space in adults with different sagittal skeletal patterns

OBJECTIVES

To analyze the mandibular retromolar space among normal-divergent adult patients with different sagittal skeletal patterns by cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

CBCTs of a total of 120 normal-divergent adult patients were investigated. Patients were categorized into the following three groups according to their ANB angle: skeletal Class I (48 patients), skeletal Class II (36 patients), and skeletal Class III (36 patients). Four different planes parallel to the mandibular occlusal plane were used to measure the retromolar space. The retromolar space was measured by two reference lines and then compared between different sagittal skeletal patterns groups. The incidence of root contact with the inner lingual cortex was compared among the three groups.

RESULTS

The retromolar space of the Class III patients was significantly larger than that of Class I patients and Class II patients. Compared with Class I and Class III patients, Class II patients had a smaller retromolar space and higher incidence of contact with the inner cortex of the mandible.

CONCLUSIONS

Class III patients had a larger retromolar space than Class I patients and Class II patients in four different planes. The mandibular retromolar space should be evaluated by CBCT in patients who need mandibular molar distalization.

Assessment of lower third molar space: A comparative radiographic study

Objective:

The aim of this study was to assess lower third molar space using four different radiographic reconstructed Cone Beam Computed Tomography (CBCT) images: orthopantomogram, lateral cephalogram, multiplanar CBCT and a newly introduced three-dimensional (3D) simulation technique.

Methods:

The CBCT scans of 32 individuals (20.97 ± 2.152 years) with a total of 50 lower third molars were collected and analyzed. The ratio between the necessary space and available space for lower third molars was calculated on each radiographic reconstructed image. Repeated-measure analysis of variance followed by multiple comparison tests were used.

Results:

The mean ratio was significantly smaller with cephalograms (0.611 ± 0.263), followed respectively by orthopantomograms (0.756 ± 0.221), multiplanar CBCT (0.789 ± 0.191) and 3D simulation technique (0.807 ± 0.193) (p < 0.001). The lowest mean difference was recorded between multiplanar CBCT and 3D simulation technique (0.017). Intra class correlation coefficient was strong (>0.90) for all techniques except cephalograms.

Conclusions:

The assessment of the lower third molar space differs according to the adopted imaging technique. 3D simulation technique is a useful novel technology that allows an exploration of the crown in many different dimensions and orientations, giving more predictable results than the conventional methods.

The prediction of impacted versus spontaneously erupted mandibular third molars

Background

To evaluate the predictive capacity of orthodontists and oral maxillofacial surgeons (OMFSs) in anticipating the process of impaction or eruption of lower third molars (L3Ms) through the examination of serial panoramic radiographs.

Methods

Sixty-eight lower third molars (L3Ms) were analyzed in 34 orthodontically treated patients without extraction. Twenty-seven OMFSs and 27 orthodontists were randomized in order to analyze the radiographs. Initially, the evaluators issued the prognosis for the L3Ms in XR1, a posterior for the XR1 + XR2. Concordance of the diagnosis was examined using Kappa statistics, and the differences between the groups of evaluators were examined using the chi-square test at p<0.05.

Results

When examining XR1 in cases where the teeth erupted spontaneously, the prognostic accuracy rate for OMFSs and orthodontists was similar, 63 and 65.7%, respectively (p=0.19). When evaluating XR1 + XR2, the accuracy among orthodontists (60%) was similar to that reported for XR1 (p=0.19), while OMFSs presented a reduction in the accuracy (55.3%, p<0.0001). When the L3Ms remained impacted, accuracy in XR1 was lower than in spontaneously erupting L3Ms, although similar between OMFSs (50.1%) and orthodontists (49.1%). Furthermore, for impacted L3Ms, when examining XR1 + XR2, the OMFSs presented a significant higher accuracy (71.8%, p <0.0001).

Conclusions

Orthodontists and OMFSs seem unable to predict spontaneous eruption or impaction of the lower third molars from single or longitudinal x-rays. When adding a second longitudinal x-ray, orthodontists and more significantly OMFSs tend to indicate more extractions.

Changes in third molar position after Class II subdivision malocclusion treatment with asymmetric extractions

INTRODUCTION

This study aimed to assess the changes in third molars angulation and their available space after Class II subdivision malocclusion treatment with asymmetric premolar extractions.

METHODS

The sample consisted of 37 patients (17 male, 20 female and mean age 13.18 ± 1.99 years) in group 1 (Type 1 Class II subdivision) and 25 (10 male, 15 female, mean age 13.56 ± 2.46 years) in group 2 (Type 2 Class II subdivision). In group 1, extractions were performed in the two maxillary quadrants and in the Class I mandibular quadrant. In group 2, extraction was performed in the Class II maxillary quadrant. Panoramic radiographs were used to evaluate third molar angulations and their available space pre- and post-treatment. Radiographic measurements were performed with Dolphin^® Imaging 11.9. Paired t tests were used for intragroup comparison between stages and sides.

RESULTS

In Type 1, there were similar improvements in third molar angulations and increases in the space available on the extraction quadrants in the maxillary arch. In the mandibular arch, there was significantly greater improvement in angulation and greater space availability in the extraction quadrant after treatment. In Type 2, there was significantly greater improvement in angulation and available space for the maxillary third molar on the extraction quadrant. In the mandibular arch, there was a similar improvement in the available space for the third molars.

CONCLUSIONS

After treatment, both groups presented better angulation and significantly greater space for third molar eruptions on the extraction quadrants, when compared to the homologous non-extraction quadrants.

Effects of Angle class II correction with the Forsus fatigue resistant device on mandibular third molars : A retrospective study

PURPOSE

The goal was to evaluate the effects of Angle class II malocclusion treatment using the Forsus fatigue resistant device (FRD, 3M, St. Paul, MN, USA) on the position and angulation of mandibular third molars and retromolar space.

PATIENTS AND METHODS

In all, 58 class II patients (mean age 13.6 ± 1.8 years) treated with the FRD (FRD group) were compared with 51 class I patients (mean age 13.5 ± 1.6 years) who underwent orthodontic treatment (control group). A total of 109 mandibular third molars in the FRD group and 91 in the control group were evaluated. Changes in the retromolar space, angulation of the second (ɣ) and third molars (β), and the angle between these teeth (α) were assessed with panoramic radiographs taken at the beginning and the end of the treatment. Data were statistically analyzed.

RESULTS

At the end of the treatment, there were significant increases in ɣ and β in the FRD group and ɣ in the control group (p < 0.05). The decrease in α in the FRD group and increase in the control group were not significant (p > 0.05); however, this change led to a small significant change between the groups (p < 0.05). The retromolar space significantly increased in the FRD group compared to the control group (p < 0.05). No significant correlation was found between retromolar space and third molar uprighting in any of the groups (p > 0.05).

CONCLUSION

Class II correction with FRD led to mesialization of the lower arch which provided an increase in the retromolar space. Little improvement in the uprighting of the third molars occurred.

Quantitative evaluation of retromolar space in adults with different vertical facial types

OBJECTIVE

To investigate the differences in mandibular retromolar space among skeletal Class I subjects with different vertical divergence using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

A total of 123 skeletal Class I patients (aged 20-40 years) were categorized into hypodivergent, normodivergent, and hyperdivergent groups based on S-N/Go-Me and facial height index (FHI). Mandibular retromolar space was measured at four planes parallel to the occlusal plane along the sagittal line and molar cuspal line, respectively. The mandibular retromolar space was compared among the three vertical groups.

RESULTS

The hyperdivergent group had a significantly smaller mandibular retromolar space compared with the other two groups, while the hypodivergent group had the largest retromolar space. In addition, the hyperdivergent group had a larger number of subjects whose roots contacted the lingual cortex of the mandibular body.

CONCLUSIONS

The hyperdivergent group tends to exhibit the smallest mandibular retromolar space and highest risk of cortex contact. Clinicians should keep in mind that successful molar distalization requires sufficient retromolar space, especially for hyperdivergent subjects, which should be verified with CBCT.

The ability of orthodontists and maxillofacial surgeons in predicting spontaneous eruption of mandibular third molar using panoramic serial radiographs

OBJECTIVE

To evaluate the skill of orthodontists and oral/maxillofacial surgeons (OMFS) in providing a prognosis of mandibular third molars spontaneously erupted, through follow-up panoramic analysis.

METHODS

22 orthodontic patients treated without extraction, presenting spontaneously erupted mandibular third molars (n = 44) were analyzed through panoramic serial radiographs. The first panoramic radiograph was obtained just after orthodontic treatment (PR1), in patients aging from 13 to 19 years. A second panoramic radiograph (PR2), was obtained in average two years later. The radiographs were randomly analyzed by 54 specialists, 27 orthodontists and 27 OMFS, to obtain the opinion about the approach to be adopted to these teeth in PR1. Then, another opinion was collected by adding a serial radiograph (PR1+2).

RESULTS

The concordance of the answers was moderate for OMFS (Kappa 0.44; p< 0.0001) and significant for orthodontists (Kappa 0.39; p< 0.0001). In the analysis of the first radiograph (PR1) of the spontaneously erupted molars, OMFS indicated extraction in 44.5% of cases, while orthodontists indicated in 42%, with no difference between groups (p= 0.22). In PR1+2 analysis, orthodontists maintained the same level of extraction indication (45.6%, p= 0.08), while surgeons indicated more extractions (63.2%, p< 0.0001).

CONCLUSIONS

Orthodontists and OMFS were not able to predict the eruption of the third molars that have erupted spontaneously. Both indicated extractions around half of the third molars. A follow-up analysis, including one more radiograph, did not improve the accuracy of prognosis among orthodontists and worsened for OMFS.

Effect of extraction or nonextraction orthodontic treatment modality on favorability of eruption of impacted third molars

Objective

The objective of the study is to determine if extraction of permanent teeth, for orthodontic purpose, causes a change in third molar angulation and also to determine if extraction of permanent teeth causes an increase in eruption space available for third molars.

Methods

This systematic review includes retrospective cohort studies which evaluated the change in third molar angulation or eruption space available for third molars among orthodontic patients treated by a fixed appliance with either extraction or nonextraction protocol. Search engines used were MEDLINE, IndMED, Web of Science, Cochrane, EMBASE, and Google Scholar from the year 1975 to 2015. Separate data collection forms were used to extract data from the studies. The Cochrane Risk of Bias Assessment Tool was used to assess the studies included in the systematic review.

Results

Fifteen studies included in the systematic review proved that third molar angulation and eruption space improved in patients treated with extraction treatment modality. However, two studies concluded that change in third molar angulation and eruption space occurred irrespective of the type of treatment involved.

Conclusion

The angulation and eruption space of third molar improved following extraction of premolar or molar. Nonextraction treatment modality did not cause any adverse effects.

Posterior Available Space for Uprighting Horizontally Impacted Mandibular Second Molars Using Orthodontic Microimplant Anchorage

Treatment of horizontally and deeply impacted mandibular molars is challenging for both orthodontists and oral surgeons because of the limited access and anchorage control. We report on two patients who had horizontally and mesially impacted mandibular second molars (MM2s). Both patients were treated by a surgical orthodontic approach, and the crowns of the impacted teeth were brought into the arches by closed forced eruption. Mesially impacted MM2s were uprighted with orthodontic microimplants, inserted in the retromolar area, and then moved into their ideal position. The first patient was in an active growing stage, while the second patient was beyond the active growing stage. Therefore posterior available space (PAS) should be analyzed before treatment of impacted MM2s to prevent periodontal problems after uprighting of impacted teeth. If PAS is not enough for uprighting impacted MM2s, alternative treatment should be considered based on the stage of growth.

Effects of facemask therapy on the mandibular retromolar space. A follow-up study

Objectives:

To evaluate the mandibular retromolar space after facemask therapy and a follow-up period.

Methods:

This retrospective study was conducted between May and September in 2014. The sample consisted of pre-treatment (T1), post-treatment (T2), and follow-up(T3) panoramic radiographs of 19 skeletal and dental Class III patients (7 female, 12 male; mean age: 10.5 years) treated with facemask and a removable intraoral upper appliance in the Faculty of Dentistry Gazi University, Ankara, Turkey. Each patient’s lower arches were evaluated as right and left segments. As third molars were congenitally absent in 3 segments, a total of 35 segments were evaluated. The average treatment time was one year. The average follow-up period was 2.4 years. The positions, angulations, dental maturations of lower third molars, and mandibular retromolar spaces (DJ) were assessed. Friedman’s 2-way Analysis of Variance, multiple-comparison, Pearson’s correlation, and Chi-square tests were used for statistical evaluation. A p<0.05 was considered as significant.

Results:

The angulation of the first molar (¡) increased significantly only in the follow-up period (T3). Mandibular retromolar spaces were increased significantly during all periods. The most commonly determined position of the third molar, by Winter’s classification, was vertical angulation in all periods. Moderate and significant correlations were found between third molar angulation(ß) and DJ at T2 and T3. Significant correlations were also found between DJ and Demirjian classification stages during all periods.

Conclusion:

Facemask therapy did not have an adverse effect on the mandibular retromolar space during treatment and follow up periods.

Treatment with facemask and removable upper appliance versus modified tandem traction bow appliance: the effects on mandibular space

Objective

The aim of this study was to evaluate and compare the mandibular arch posterior space changes in Class III patients treated with facemask (FM) with removable upper appliance or modified tandem traction bow appliance (MTTBA).

Methods

Pre- and post-treatment and pre- and post-observation lateral cephalograms of 76 subjects with skeletal and dental Class III malocclusion from the period 2000-10 years formed the materials of this study. In the first group, 25 patients (10 girls, 15 boys; mean age: 10 years, 1 month) were treated with MTTBA. The average treatment time was 12 months. In the second group, 26 patients were treated (13 girls, 13 boys; mean age: 10 years, 4 months) with a Delaire-type FM. The average treatment time was 13 months. The remaining 25 children (9 girls, 16 boys; mean age: 9 years, 8 months) were observed without treatment for 10 months. ANOVA, Duncan, and paired t-tests were used for statistical evaluation.

Results

Although ramus width and mandibular posterior space increased significantly in all groups, no significant differences were found among the groups. Significant increase in tipping of lower molar (L6/GoMe) in the MTTBA group showed a significant difference compared with the FM and control groups. Significant retroclination of the lower incisors (L1/NB) in the MTTBA and FM treatment groups was significantly different compared with the control group. Retroclination of lower incisors in the MTTBA group was significantly greater than that in the FM group.

Conclusions

FM and MTTBA treatment approaches did not affect the dimensions of posterior space.

Limitations

To generalize the results of this study, long term evaluation by considering the third molar position should be done.

Influence of orthodontic premolar extraction therapy on the eruption of the third molars: A systematic review of the literature

BACKGROUND

Through a systematic literature review, the authors assess the effect of premolar extractions on third-molar (M3) eruption considering eruption rate, retromolar space, and molar angulation.

TYPES OF STUDIES REVIEWED

The authors performed a systematic search using MEDLINE and Web of Science databases up through April 2017 to identify quality studies available comparing M3 eruption between a group with premolar extraction and a group without premolar extraction.

RESULTS

Twelve comparative retrospective cohort studies met all the inclusion criteria. The authors found in 5 studies comparing the rate of M3 eruption that there were significantly higher results in the group with extractions. They found in 5 studies comparing the evolution of the retromolar space significantly higher results in the group with extractions. Lastly, concerning the uprighting of the M3 during treatment, the authors found only 2 studies showing significant differences between the 2 groups, each time in favor of the group with extractions.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

The dental literature on premolar extraction related to the eruption of the M3 is composed of average-quality retrospective studies. Premolar extraction significantly improves the chances of M3 eruption, but the level of evidence of comparative retrospective cohort studies is low. Clinicians must continue to rely on their judgment regarding premolar extraction on a case-by-case basis until the evidence is stronger. Retrospective studies with standardized protocols and more detailed methodologies are required to obtain higher levels of evidence.

Third-molar mineralization as a function of available retromolar space

OBJECTIVE

To test in the maxilla and mandible for an association between stage of third-molar (M3) mineralization and space in the jaws for M3 eruption. Mineralization is hypothesized to be delayed not only for impacted M3s but also for M3s with eruption space less than their mesiodistal crown diameter.

MATERIAL AND METHODS

Retrospective cone beam computed tomography (CBCT) scans of 37 females and 32 males aged 17-24 years, for a total sample of 197 upper and lower M3s, were used to assess the status of M3 eruption and measure the M3 crown diameter (CD) relative to the length of the retromolar space (RS). Stage of M3 mineralization was then compared between impacted and erupting M3s as well as between two conditions of relative eruption space (RS/CD ≥ 1 versus RS/CD < 1) using Mann-Whitney U tests.

RESULTS

Impacted M3s were at significantly earlier (delayed) stages of mineralization compared to erupting M3s. Mineralization was also delayed for M3s with eruption space less than their mesiodistal crown diameter (e.g. RS/CD < 1). A moderate positive correlation between stage of M3 mineralization and space was seen in both jaws, and was stronger in the mandible.

CONCLUSION

Our study shows for the first time that stage of M3 mineralization is associated not only with impaction but also with amount of retromolar space, and that these associations are consistent in upper and lower jaws. Present findings underscore that M3 mineralization stage may be a clinically useful predictor of M3 impaction that thus merits further investigation.