Retromolar Space Research Articles

Facteurs prédictifs de l’éruption des dents de sagesse

We studied the prognosis of upper and lower third molar evolution. Seventy-eight patients were included after a clinical examination, dental casts, panoramic and lateral cephalometric radiographs on inclusion (T1) and two years after (T2). Five parameters were studied: retromolar space (RMS) between the third molar (M3) and the anterior ridge of the ramus; RMS/M3 crown diameter ratio, distances (PTV-M(1)) and (X(i)-Mi(2)); and third molar angle with occlusal plane. They were noted at T1 and T2. The gain of retromolar space from T1 to T2 reached 1.2 to 2.2mm without extraction, 2 to 2.7mm with PM extraction, and 4.5 to 6.8mm with M1 extraction. The "RMS/M3 diameter" ratio increased in the maxilla from 0.6 to 0.8 and from 0.5 to 0.8 in the mandible (P=0.01) between T1 and T2. PTV-M1 increased significantly from 17.1 to 19.9mm (P<0.001), and Xi-M2i increased significantly from 18.5 to 22.4mm (P<0.001) between T1 and T2. The extraction of premolars has little influence on the variation of the retromolar space; conversely first molar extraction increases that space. Prognosis techniques for the evolution of third molars are helpful when considering avulsion.

The use of buccal fat pad (BFP) as a pedicled graft in cleft palate surgery

The buccal fat pad (BFP) as pedicled graft was originally used in reconstructing medium sized intraoral defects. Promising results concerning the use of BFP in cleft palate surgery have been published recently. The aim of this article is to report on the use of BFP as a pedicled graft in cleft palate surgery and to discuss promising results for this reconstructive surgical concept. A retrospective evaluation of 24 patients who had BFP pedicled flaps used for the prevention and repair of Type III (Pittsburgh Fistula Classification) cleft palate fistulas, to obstruct the retromolar space of Ernst and in case of wide clefts, from 2005 to 2010, was conducted. In all cleft palate patients, the recipient area fully epithelialized within 4 weeks or less. No recurrence was seen and the donor site healed well without aesthetic or significant functional impairment. This series confirms the excellent and predictable healing of BFP intraorally and the minimal morbidity associated with the use of such grafts. The results of this study allow the authors to recommend that the BFP pedicled flap is considered as a reliable alternative procedure to expand the therapeutic options. The BFP graft provides an advantage in reconstructive cleft palate surgery.

Retromolar fibreoptic orotracheal intubation in a patient with severe trismus undergoing nasal surgery

A considerable challenge arises when passage of an endotracheal tube between the teeth is impossible because of severe trismus and the presence of concomitant contraindications to nasotracheal intubation. We report a novel technique to circumvent the need for tracheostomy by using the retromolar space for oral fibreoptic intubation. A 50-yr-old female with a history of pharyngeal cancers treated with surgery and radiotherapy presented for right dacryocystorhinostomy. She had undergone left dacryocystorhinostomy after nasotracheal intubation one week earlier. This time, orotracheal intubation was requested since surgery would involve the right nostril and left nasal intubation might dislodge the recently placed nasolacrimal tube. Due to severe trismus, the patient's interincisor distance was only 9mm, and it was impossible to pass a 6.0mm endotracheal tube through that gap. A flexible bronchoscope loaded with a 6.0mm tracheal tube was inserted through the retromolar space into the pharynx and maneuvered through the vocal cords for endotracheal intubation. The retromolar space is located between the last molar and the ascending ramus of the mandible. Even with complete mandibular occlusion, it is usually able to accommodate a 7.0mm endotracheal tube. Despite its hidden location, it can be used successfully for orotracheal fibreoptic intubation. With practice, the expertise achieved in performing this technique will confer a much needed option for securing the airway in this challenging situation.

Mandibular third molar space in different antero-posterior skeletal patterns

Retromolar space has long been identified as a major factor in the aetiology of mandibular third molar impaction. The aims of this study were to compare mandibular third molar space between the different antero-posterior (A-P) skeletal patterns, between erupted and impacted third molars in the different A-P skeletal patterns, and to report on the status of third molar eruption/impaction among the studied subjects. A total of 432 mandibular third molars in 270 subjects (132 females and 138 males) were investigated from dental pantomograms (DPTs) and lateral cephalograms (LC). The average age for the total sample was 20.80 ± 2.03 years. The subjects were divided into three groups according to their ANB angle as follows: skeletal Class I (144 third molars in 90 subjects), skeletal Class II (145 third molars in 95 subjects), and skeletal Class III (143 third molars in 85 subjects). Each group was subdivided into impacted and erupted subgroups. DPT and LC were traced and the following variables were measured: retromolar space width, third molar width and angulation, β angle, second molar angulation, mandibular length, and gonial angle. Independent t-test, analysis of variance, and chi-square test were used for statistical analysis. Retromolar space width in the Class III subjects was smaller than in the Class I subjects (P < 0.05). Mandibular third molars were recorded as impacted in 26, 32, and 42 per cent of the Class I, II, and III subjects, respectively (P < 0.001). The impacted groups had a reduced retromolar space width, increased β angle, and reduced third molar angulation in all A-P skeletal patterns. Class III subjects showed increased mandibular third molar impaction with reduced retromolar space width.

Mandibular cephalometric characteristics of a Saudi sample of patients having impacted third molars

To evaluate the cephalometric characteristics of mandibles of Saudi patients having impacted third molars and to compare them to those of patients having normally erupted third molars. One hundred and twenty-one Saudi adult subjects (59 females and 62 males; age: 20-40 years) were divided into two groups based on the status of the mandibular third molars: (1) impaction group and (2) normal group. Means and standard deviations of 21 cephalometric measurements related to mandibular geometry were measured and compared between the two groups using the unpaired t-test. Males and females in the impaction group were also compared with their equivalent subgroups in the normal group using the unpaired t-test. Anteroposteriorly, space distal to second molar, ramal width and mandibular body length were significantly less in the impaction group than in the control group. In addition, posterior teeth were more upright in the impaction group. Vertically, posterior alveolar height was significantly less in the impaction group. The Y-axis was significantly increased in the impaction group. The significance of these measurements was variable between males and females. Third-molar impactions in the Saudis living in the Western region of Saudi Arabia were more likely to occur when inadequate retromolar space is present. This can be attributed to certain mandibular skeletal and dental features, among which the increased width of mandibular ramus and backward inclination of posterior teeth seem to be the most influencing factors in both sexes.

Some morphological features related to mandibular third molar impaction

Objective: The aim of this study was to evaluate the effect of some morphological features of the mandible and mandibular permanent molars on impaction of mandibular third molars with panoramic measurements in a Turkish patient group. Study design: Standardized panoramic radiography variables compiled from 140 patients retrospectively were evaluated. Predictive variables included mesio-distal crown width and inclination of the mandibular molars, vertical and horizontal surface dimension between distal surface of the lower second molar tooth and anterior surface of its ramus, length and width of the mandible ramus and corpus, angle of the mandible gonion, the number of the lower third molar roots, and angulations of roots of the lower third molars. Results and Conclusions: According to the data obtained in this study, the vertical height of the anterior border of the ramus, length of the posterior basal corpus, mesio-distal diameters of the first, second and the third molars, 1/3 root angle of the third molar, number of third molar roots, inclination of the first molar to increase, vertical height of the posterior border of the ramus, vertical height of alveolar crest, and height and the width of the retro-molar space to decrease are all in direct proportion to the possibility of impaction of the third molar.

Neandertal mandibles from the Sima de las Palomas del Cabezo Gordo, Murcia, southeastern Spain

The Middle Paleolithic levels of the Sima de las Palomas have yielded eight partial mandibles (Palomas 1, 6, 7, 23, 49, 59, 80, and 88). Palomas 7, 49, 80, and 88 are immature, and Palomas 49, 59, 80, and 88 are among the latest Neandertals (approximately 40,000 cal BP). Palomas 1 is geologically older (approximately 50,000-60,000 cal BP), and the other three were found ex situ. The mandibles exhibit a suite of characteristics that align them with the Neandertals among later Pleistocene humans, including symphyseal morphology, symphyseal orientation, corpus robusticity, distal mental foramen position, retromolar space presence, wide immature dental arcade, and high-coronoid process with an asymmetrical mandibular notch. However, Palomas 6 lacks a retromolar space, Palomas 59 has a narrow lateral corpus, and Palomas 80 has a mesial mental foramen and open mandibular foramen. The Palomas mandibles therefore help to document that the late Middle Paleolithic of southern Iberia was the product of Neandertals. They also reinforce the presence of variability in both metric and discrete aspects of Neandertal mandibular morphology, both within and across samples, some of which may be temporal and/or geographic in nature.

A Review of Intraoperative Airway Management for Midface Facial Bone Fracture Patients

In craniofacial trauma patients, oral route endotracheal intubation may thwart the accuracy of dental occlusion and nasotracheal intubation carries the risk of intracranial invasion in skull base fracture cases. Between November 2005 and June 2006, patients receiving facial bone fracture operations at Kaohsiung Medical University Hospital were enrolled in this study. Intraoperatively, the endotracheal tube was pushed to either the retromolar space or the missing tooth space and secured by two 4.0 silk stitches. Then, surgeons could perform the usual procedure to explore the fracture sites, check the occlusion and correct the deviated nose without limitation. Also, for better understanding the time needed for various intubation techniques, a time-measuring study was performed. Ninety-one patients were treated by this method. Most of them were satisfied with the result of occlusion and nasal contour. Only 2 patients received second surgery to correct nasal deformity. One hundred seventeen anesthesia procedures were checked. In average, an experienced anesthesiologist could successfully intubate a patient in less than 105 seconds. The advantages and reported complications of different intubation methods were discussed. This retromolar position and tooth fixation technique allowed surgeons to correct the dental occlusion and nasal deformity simultaneously. It has served well for zygoma fracture, maxilla fracture, and Le Fort II fracture patients. It is worthy of consideration in management of middle face trauma patients involving occlusion change and nasal deviation.

Correlation Between the Pattern of Facial Growth and the Position of the Mandibular Third Molar

The purpose of this study was to examine the correlation between variables that determine the position of the third molar (M3) and correlation between the pattern of facial growth and examined variables. Material for the study consisted of 130 panoramic radiographs and lateral radiographs of subjects' heads in whom orthodontic therapy had been started. Analysis of the position of the mandibular M3 and its relation to the bone and other teeth were determined by 4 variables: evaluation of the space for both M3, spatial relation between the second molar and M3, vertical position of the M3 in relation to the alveolar ridge, and inclination of the germ of the M3. In boys, significant correlation was determined on the right side of the jaw, between the retromolar area and the vertical position of M3. Significant correlation was determined in girls, between the retromolar area and the vertical position of M3 on both sides, retromolar area and M3 inclination on the left side, and retromolar area and spatial relation of M3 on the right side. Analysis of correlation between facial growth pattern and 4 variables that determinate the position of M3 showed positive correlation only for the lower right M3 inclination in subjects with anterior facial rotation. The present study showed that the amount of retromolar space for the position of the M3 is not a sign of its normal development. No significant differences were determined between the position of M3 and type of facial growth.

Co-relation of variables as determined from panoramic radiograph and evaluating their significance in eruption of permanent mandibular third molar

Purpose of the Study: Purpose of the study is to investigate whether the variables associated with the permanent mandibular third molar (PMM3) and arch dimensions could be co-related and significantly differentiated between a fully erupted and mesially impacted PMM3 among a set of Indian population. Study Design: A standardized panoramic radiograph was taken of subjects of age 21 years and above. Patients with missing tooth from mandibular arch, subjects undergoing or having history of orthodontic treatment, subjects having disto-angular, horizontal or vertical impacted PMM3 were excluded from the study. Subjects were divided into 2 groups: (1) mesially impacted PMM3 and (2) vertically erupted PMM3. Following measurements were taken from acetate paper tracing of standardized panoramic radiograph: (1) Angulation of long axis of PMM3 to permanent mandibular second molar (theta) (2) Angulation of PMM 3 to base of mandible (theta 2) (3) Gonial angle (theta 3) (4) Mesio-distal width of PMM 3 (5) Retro molar space. From these measurements Ganss ratio (retro molar space /PMM3 crown width.) was calculated. Results and Conclusion: Results revealed that angle theta 1, angle theta 2, retro molar space and Ganss ratio were positively co-related and highly significant variables associated with the mesially and vertically erupted teeth as measured on panoramic radiograph. Using these variables a long-term study can be carried out to predict the ultimate position of lower third molar in the arch so that if there is a probability of the tooth being impacted at a later age, a prophylactic germectomy can be performed at an early age.

Third molar availability in Class II subdivision malocclusion

In this study, we compared retromolar available space and third molar angulation between the Class I and Class II sides in patients with Class II subdivision malocclusion. Two samples were obtained from 46 subjects grouped according to the following characteristics: group 1 comprised 29 subjects (17 male, 12 female) with Class II subdivision malocclusion at a mean age of 14.73 years. Group 2 was the control to assist in the asymmetry evaluation and included 17 subjects (11 female, 6 male) with normal occlusion at a mean age of 21.73 years. Corrected oblique radiographs of each patient side were obtained to evaluate right and left retromolar available space and third molar angulation. The retromolar space and third molar angulations in the Class I and Class II sides in each group were compared with paired t and Wilcoxon tests. Asymmetry between the Class I and Class II sides of the Class II subdivision malocclusion group was compared with asymmetry between the right and left sides of the normal occlusion group with independent t and Mann-Whitney tests. The results demonstrated significant differences between the Class I and Class II retromolar available spaces in the Class II subdivision malocclusion group. Significant angular asymmetry between these sides was observed only for the mandibular third molars. However, when retromolar space asymmetry and third molar angular asymmetry were compared between the Class II subdivision malocclusion and the normal occlusion groups, there were significant differences only for retromolar space asymmetry. Patients with Class II subdivision malocclusion have asymmetric amounts of maxillary and mandibular retromolar available space and asymmetric angulation of the mandibular third molars between the Class I and Class II sides.

Retromolar space analysis in relation to selected linear and angular measurements for an Iraqi sample

Radiographic diagnosis of the presence, position, and degree of third molar formation is a crucial part of integral treatment planning for the development of this tooth. Shortage of eruption space between lower second molar and the ramus has long been identified as a major factor in the etiology of lower third molar impaction. The purpose of the present investigation was to evaluate the validity of some angular and linear measurements made on digital panoramic imaging to be used as a reference for early prediction of lower third molar eruption or impaction. Digital panoramic imaging was done on 50 individuals with full dentition and a class I occlusal relationship. The sample was divided into full-eruption and marginal-eruption groups. Nine variables (linear measurements and angles) were measured for every individual to determine the minimal and maximal values of each variable and these variables were correlated to each other using Pearson's correlation equation. Lower eruption space measurements for the marginal-eruption group were smaller by more than 3 to 4 mm than that of the full-eruption group. The beta-angle, the angle formed between the long axes of lower second and third molars, showed a marked increase in their values (9 degrees to 10 degrees) when the marginal-eruption group is compared to the full-eruption group. Third molar angle (alpha-angle), beta-angle, and gonial angle together with lower eruption space measurements are the variables that should be taken into consideration when early prediction of lower third molar eruption is performed.

An Evaluation of the Retromolar Space for Oral Tracheal Tube Placement for Maxillofacial Surgery in Children

The eruption of the first and second permanent molar teeth may influence the size of the retromolar space. In this study we evaluated the adequacy of the retromolar space for retromolar intubation and any effect of eruption of the first and second permanent molar teeth on this space in children. Children 3-15 yr of age, undergoing surgery other than facial surgery were included for evaluation of the retromolar space. After standard oral tracheal intubation, the endotracheal tube was shifted to the retromolar space and the mandible was slowly closed to achieve centric occlusion. At the same time, any increase in airway resistance or decrease in oxygen saturation was noted. In the second part of the study, the feasibility of retromolar intubation in pediatric patients undergoing maxillofacial surgery with intraoperative maxillomandibular fixation was assessed. There was enough space for endotracheal tube placement in the retromolar region. The eruption of the first and second permanent molar teeth did not affect intubation. It was possible to achieve centric occlusion in 79 of 80 children with the endotracheal tube positioned in the retromolar space. Retromolar intubation was successfully accomplished in six pediatric patients undergoing maxillomandibular fixation and maxillofacial surgery. The retromolar space can be safely used for intubation in children when intraoperative maxillomandibular fixation, and simultaneous access to the nose and oral cavity are needed.

Panoramic radiographic predictors of mandibular third molar eruption

Third molar (M3) eruption can be problematic. According to some orthodontic surgeons, the teeth are capable of aggravating the average crowding level in the dental arch. The question is whether it might be possible to give a prognosis for ultimate M3 position in the arch and make an early decision to extract or retain them. The purpose of the study was to determine which measurements made on panoramic tomograms might facilitate prognosis for M3 position in the dental arch over the years. The investigation involved 64 patients who had been enrolled to the study group 10 years earlier, ie, in 1993, when an analysis had been carried out regarding M3 effect on dental arch crowding. At that time panoramic tomograms had been taken, and dental casts made. The procedures were repeated in 2003. The following measurements were taken at baseline (1993) and at the end of the study (2003): (1)/the retromolar space to lower third molar crown width, (2) third molar angulation to the base of the mandible, and (3) third molar to second molar inclination. At some defined values of the Ganss ratio, and M3 inclination to mandibular base and second molar, it is possible to predict potential lower third molar alignment in the dental arch using a panoramic radiograph.

Retromolar intubation – a simple alternative to submental intubation

There are special considerations when securing the airway peri-operatively in patients with panfacial trauma. Orotracheal intubation is not feasible when intra-operative intermaxillary fixation is planned for restoration of dental occlusion [1]. Nasotracheal intubation, an alternate technique of securing airway, is contra-indicated in certain conditions such as fracture of the base of the skull or fracture of the naso-orbital-ethmoid complex [2]. In such patients, submento-tracheal intubation has been described as an alternative to short-term tracheostomy for securing the airway peri-operatively [3, 4]. Disadvantages of submento-tracheal intubation include superficial wound infection, haemorrhage, trauma to the sublingual ducts and orocutaneous fistula [4]. Retromolar intubation is a non-invasive technique and avoids both submento-tracheal intubation and tracheostomy in the majority of patients. In 15 patients with panfacial trauma, where orotracheal intubation was not feasible and nasotracheal intubation contra-indicated, retromolar intubation was attempted to avoid tracheostomy. First, orotracheal intubation was performed with a flexometallic tracheal tube using a standard general anaesthesia technique. The orotracheal tube was then placed in the retromolar space behind the last upper and lower erupted molar teeth. The tube was then fixed by a wire ligature to the molar/premolar tooth along the upper or lower maxilla in a ‘figure of eight’ fashion. (The fixation should not be too tight as the flexometallic tube wire can be deformed). Retromolar intubation was successful in 12 patients and intra-operative intermaxillary fixation was easily carried out. At the end of the surgical procedure the wire fixation was cut and mouth opening was adequate. The wire ligature around the tracheal tube was removed and the tube moved back to a standard orotracheal position, and the trachea then extubated. In three patients, the retromolar space was inadequate and the tracheal tube could not be placed there. In these patients submento-tracheal intubation was performed. The adequacy of the retromolar space can be determined by introducing an index finger into the patient's mouth and asking him or her to close the mouth. No compression on the finger indicates an adequate space. The technique of Martinez et al. [5] to increase the retromolar space by extraction of the third molar tooth and performing a semilunar osteotomy involves destruction of the bony anatomy. This bone may otherwise have been useful for fixation devices and the technique is impractical [6]. If necessary, a tracheal tube smaller than the standard size for the patient can be used for retromolar intubation. One minor disadvantage of this is that the tube can interfere with the surgical field.

Quantitative analysis of human mandibular shape using three‐dimensional geometric morphometrics

Human mandibular morphology is often thought to reflect mainly function, and to be of lesser value in studies of population history. Previous descriptions of human mandibles showed variation in ramal height and breadth to be the strongest difference among recent human groups. Several mandibular traits that differentiate Neanderthals from modern humans include greater robusticity, a receding symphysis, a large retromolar space, a rounder gonial area, an asymmetric mandibular notch, and a posteriorly positioned mental foramen in Neanderthals. Nevertheless, the degree to which these differences are part of modern human variation and/or are related to size and function remains unclear. The aim of this study was to document geographic and functional patterning in the mandibular shape of recent humans, to assess the effects of allometry on mandibular form, and to quantitatively evaluate proposed "Neanderthal" mandibular traits through comparison with samples of geographically diverse recent humans. Data were collected in the form of three-dimensional coordinates of 28 landmarks. Unlike previous studies, this analysis found that modern human mandibular shape exhibits considerable geographic patterning, with some aspects of mandibular morphology reflecting a climatic gradient, and others, a functional specialization. Population history is also reflected in mandibular form, albeit relatively weakly. Proposed "Neanderthal" traits were found to separate Neanderthal from modern human mandibles successfully in the statistical analysis. Of these, the retromolar gap was found to be related to increased mandibular size in modern humans. The status of this trait as a Neanderthal autapomorphy should therefore be treated with caution.

Possibilty of the lower third molar eruption: Radiographic analysis

To assess the possibility of the eruption of the lower third molar on the basis of the measured parameters: retromolar space, mesiodistal crown width of a molar and the third molar angulation. The investigation included 104 patients both sexes (43 boys, and 61 girls), 16 to 25 years old (mean age, 18 years). It was performed using the orthopanthomographic radiographs analysis of those patients. Each radiograph was covered by tracing paper, and the contoures of the following anatomic details were drawn: a) the crown and root contours of third molars, upper and lower central incisors, distal molars in occlusion, anterior edge of ramus mandible, b) lines: 1. the occlusal plane, 2. the line of retromolar space, 3. the mesiodistal crown width of third molar, 4. the axial shaft of the third molar and the distal angle between occlusal plane and the axial shaft of the third molar. The values were measured with an orthodontic caliper: the diameter of retromolar space, diameter of mesiodistal width, the value of distal angle between occlusal plane and axial shaft of molar. A favourable angulation of the lower third molar (more than 60 degrees) was found in, boys (left 27.90%, right 32.55%), girls (left 39.34%, right 37.77%). A favourable relationship between the diameters of mesiodistal width of the third molar and retromolar space was found in, boys, (left 13.59%, right 16.27%), girls, (left 8.19%, right 14.75%). A favourable relationship between the diameters of mesiodistal width of the third molar and the retromolar space and the angulation was found in boys, (left 9.30%, right 11.62%), girls, (left 6.56%, right 9.83%). There was not any statistically significant difference found between the relation of the retromolar value, third molar mesiodistal diameter, or of the third molar angulation to the left and the right side nor of their mutual relations in comparing boys and girls. A favourable prognosis was found in 9.33% of the patients.

Prediction of maxillary third molar impaction in adolescent orthodontic patients.

The purpose of this study was to identify risk factors for maxillary third molar impaction in adolescent orthodontic patients. Radiographs made before treatment (T1) and after treatment (T2) and at a minimum of 10 years postretention (T3) of 132 patients that allowed accurate diagnosis of impaction vs eruption of one or both maxillary third molars were evaluated. Although univariate logistic regression revealed that the decision to extract premolars reduced the risk of impaction by 76% (P < .01), this parameter was not included in the final prediction model at T1. Multiple logistic regression analyses revealed that third molar impaction could be predicted at T1 according to the size of the retromolar space and the amount of mesial molar movement that will occur during active appliance therapy, reducing the risk of impaction by 22% and 34% for every millimeter increase in distance, respectively (P < .01). At T2, multiple logistic regression revealed that the odds of impaction were more than 60 times higher (P < .01) if the third molar was angulated mesially as compared with less than 30 degrees distally relative to the occlusal plane and almost five times (P < .05) higher if the third molar was angulated more than 30 degrees distally as compared with less than 30 degrees distally. Similar analyses at T2 showed 29% reduced risk of impaction for every millimeter increase in retromolar space and 18% reduced risk for every degree increase in angle MP/SN (P < .01).

Third molar influence on dental arch crowding

The aim of the present study was to measure the dental arches in order to assess the potential influence of third molars on lower incisor crowding. Changes in dental arch dimensions were assessed in 47 patients (36 females, 11 males) three years following either removal of the third molars or deciding to leave them in situ. A dental pantomogram (DPT) was taken at the start of the study and plaster study models were obtained at both the beginning and end of the observation period. The study models were used to measure crowding, and to prepare photocopies for linear measurements of the dental arch (length and width). Using the DPT, the ratio of retromolar space to the width of the crown of the third molar was calculated using the method originally described by Olive and Basford and later modified by Ganss (Ganss ratio). The results showed that the measurements of crowding and arch length and width had changed in 12 lower and two upper dental arches. The relationship between these results and the Ganss ratio was statistically significant. Calculation of the Ganss ratio may therefore assist investigations into the development of dental arch crowding and also help determine the indications for third molar removal.

Prevalence of third molar impaction in orthodontic patients treated nonextraction and with extraction of 4 premolars

The purposes of this study were to confirm that premolar extraction treatment is associated with mesial movement of the molars concomitant with an increase in the eruption space for the third molars and to test the hypothesis that such treatment reduces the frequency of third molar impaction. Lateral cephalograms, panoramic or periapical radiographs, and study models made before (T1) and after (T2) treatment and a minimum of 10 years postretention (T3) of 157 patients were selected from the postretention sample at the Department of Orthodontics of the University of Washington, Seattle. Treatment for 105 patients included the extraction of 4 premolars; the other 53 were treated nonextraction. These patients represented all the extraction and nonextraction patients in the sample who had at least 1 third molar at T1 or T2 and who showed evidence of full eruption or closure of the root apex at T2 or T3. Student t tests showed higher scores for third molar impaction (P < .01), less mesial movement of the molars from T1 to T2 (P < .01), and smaller retromolar space at T2 (P < .001) in both arches of the nonex patients than in the ex patients. Similarly, molar movement was more mesial from T1 to T2 in the maxilla (P < .01) and in the mandible (P < .05), and the retromolar space was larger in both arches (P < .001) of the patients with eruption than in those with impaction of the third molars. Our results suggest that premolar extraction therapy reduces the frequency of third molar impaction because of increased eruption space concomitant with mesial movement of the molars during space closure. (Am J Orthod Dentofacial Orthop 2003;123:138-45)