Inclination Of Molars Research Articles

The change in inclination of impacted mandibular third molars

The change in inclination of impacted mandibular third molars

Relationship between facial types and tooth and bone characteristics of the mandible obtained by CT scanning.

The purpose of this study was to evaluate relationships between morphological characteristics of vertical sections of the mandibular body and facial type. Of the correlation coefficients between tooth and bone inclination and facial type parameters, facial height index (FHI) was negatively associated with second premolar (P2), first molar (M1), and second molar (M2) inclinations. The angle represented by Frankfort horizontal plane to mandibular plane (FMA) was negatively associated with bone inclination of the M2 section. The buccal cortical bone was thicker in short-faced individuals than in the average and long-faced groups, while lingual cortical bone thickness of the M1 and M2 sections was greater. The basal cortical bone thickness of the L1 section was greater in the short-faced group, and the inclinations of the P2, M1, and M2 axes were significantly smaller. Teeth in the short-faced group inclined more lingually than in the average- and long-faced groups. The results of this study provide evidence that a significant but complex relationship exists between structures of the mandibular body and facial types. The morphological features that relate to masticatory function and facial types are associated with cortical bone thickness of the mandibular body and the buccolingual inclination of the first and second molars.

Third molar impaction in extraction cases treated with the Begg technique.

The aim of this study was to investigate the differences between two groups of patients with either erupted or impacted mandibular third molars before and after orthodontic treatment. All patients were treated with Begg appliances following extraction of the four first premolars. The erupted group consisted of 14 subjects and the impacted group 13 subjects. Lateral cephalometric films, peri-apical radiographs, orthopantomographs and orthodontic casts of each subject were taken before and after treatment. Thirteen measurements were carried out on the lateral cephalometric radiographs. The results revealed slightly more vertical growth and a smaller mandibular arc angle in the erupted group at pre-treatment, and also a more upright lower third molar position and slightly greater distance between the distal point of the lower second molars and the centre of ramus (Xi) in the same group. In the course of treatment, mandibular third molars seemed less likely to erupt when the condyle grew vertically. The lesser resorption on the anterior border of the ramus might have played a part in this finding. In addition, a greater mesial inclination of the mandibular third molars might be an indication of the tendency for these teeth to be impacted in the present study.

Comparative Study of Vertica1 Sections of the Jomon and Modern Japanese Mandibles.

The purposes of this study are to compare the characteristics of mandibular internal structures between Neolithic Jomon and modern Japanese, and to investigate the relationship between internal structures of the mandible and the standing position of the teeth in both populations with the use of CT scanning. The data for this study were obtained from 40 male Japanese and 39 male Jomon dry adult skulls housed in the Department of Anthropology and Prehistory, the University Museum of the University of Tokyo. For each specimen, a lateral radiograph of the skull and four CT scan sections of the mandibular body were available.The lingual inclination of mandibular molars of Jomon was weaker than that of modern Japanese, and mandibular cortical bone of Jomon was thicker than that of modern Japanese mainly because Jomon had strong masticatory function. Although the dental arch breadth of Jomon was larger than that of modern Japanese, there was no significant difference in the mandibular body breadth in molar regions. It was suggested that overall size of mandibular body of Jomon was almost the same as that of modern Japanese, but the larger dental arch breadth resulted from upright position of molars.

COMPARISON of DENTOFACIAL CHANGES with RIGID ACRYLIC BONDED and HAAS TYPE BANDED RAPID MAXILLARY EXPANSION DEVICES

SUMMARY: The aim of this study was to describe and compare the dentofacial changes obtained with the Haas type banded and rigid acrylic bonded RME therapies. Lateral and posteroanterior radiographs, and dental casts of 30 growing children who had unilateral or bilateral posterior crossbite were analysed. The study groups consisted of 21 cases treated with acrylic bonded and 9 cases treated with Haas type banded RME appliances. Results revealed that lower nasal width, basal maxillary width and intermolar width were increased in both groups. Increase in the inclination of the upper molars in the transversal direction was more in the banded group compared to the bonded group (p < 0.05) Overbite was markedly reduced in the banded group (-2.51 mm), while slightly decreased in the bonded group (-0.61 mm), and the difference between the two groups was statistically significant (p < 0.01). The findings of this study suggest that the rigid acrylic bonded RME appliance may be an acceptable alternative compared to t...

Class II subdivision treatment with tip-back moments.

Unilateral tip-back mechanics are challenging because of a number of undesirable side-effects associated with their use during orthodontic treatment. The purpose of this paper is to review the differential diagnosis and treatment planning of Class II subdivision malocclusions and present a treatment strategy based on a careful biomechanical analysis of the clinical situation. Emphasis is placed on the correction of molar axial inclination using unilateral tip-back moments in the treatment of dental asymmetries. Appliance design and treatment sequencing are also discussed.

Effect of non-erupted 3rd molars on distal roots and supporting structures of approximal teeth. A radiographic survey of 202 cases.

Root resorption of 2nd molars in proximity to non-erupted 3rd molars has been widely reported. The purpose of this study was to determine the prevalence of root resorption in second molars adjacent to non-erupted third molars. Its association to age and gender of the patient, location and inclination of the non-erupted third molar and to distal bone support of the 2nd molars was analyzed. A radiographic survey of 202 periapical radiographs taken in patients with clinically missing third molars was conducted. 3 examiners independently evaluated the radiographs and only those cases where at least 2 observers agreed were included in this report. Statistical analysis was performed on 186 radiographs. Associations were analyzed with the Pearson chi 2 test. Radiographic evidence of root resorption was found in 45 2nd molars (24.2%) of which 12 (6.5%) showed moderate to complete root resorption. Non-erupted tooth apical position and mesio-inclination of 60 degrees or more relative to the distal root of the second molar were significantly associated with root resorption (p = 0.01368 and p = 0.0194, respectively). Resorption was positively associated with age of patient (p = 0.00606). These results may support early extraction of impacted 3rd molars especially in cases with a mesio-angulation of 60 degrees or more and an apical location in proximity to the distal root of the 2nd molar.

Significance of the cant of the posterior occlusal plane in class II division 1 malocclusions.

In studying a group of fifty adult females with Class II division 1 malocclusion, it was evident that the skeletal problems of this malocclusion involved small, retruded mandibles accompanied by backward rotation. This skeletal pattern was considered to be influenced by the vertical dimension of the upper dentition in the buccal segment for mandibular function. The anterior and the posterior occlusal planes were examined to gain a detailed assessment of the relationship between the dental and the skeletal patterns. The findings indicated that the steep cant of the posterior occlusal plane was strongly correlated with the following: 1. Small, retruded mandible with backward rotation as the skeletal pattern. 2. Short vertical height of the upper second molars and distal inclination of the upper molars as the dental pattern. The increased vertical height of the lower second premolars was found to be related to backward rotation of mandible. In treating skeletal Class II malocclusions, this study indicated that control of the vertical dimension of the posterior teeth is extremely important.

骨格性反対こう合者の外科的矯正治療に伴う臼歯こう合の前頭面変化

The purpose of this study was to examine molar occlusal changes in the frontal dimension and their effects on the anterior overjet and overbite following surgical orthodontic treatment.The subjects were 14 adult patients with mandibular protrusion treated with sagittal splitting ramus osteotomy. Serial sets of gnathostatic models and lateral cephalograms were used for analysis. Materials were taken at the stages of first examination, end of active treatment, and in retention (more than two years after the end of active treatment).Buccolingual inclination of the upper and lower first molar, lateral overjet and overbite, and inter molar distance in both arches were measured on the three-dimensional graphics of the dental model produced by the noncontact three-dimensional measuring unit. The anterior overjet and overbite were also measured on the lateral cephalometric radiographs. Changes of molar inclination, inter molar distance and molar occlusion during the treatment period and the retention period were analyzed, and a correlation between changes of molar occlusion and those of anterior overjet and overbite in the retention period was examined.The results were as follows:1. There was a significant correlation between the changes of molar inclination during the treatment period and those in the retention period (upper lst molar; r=-0.71, p<0.01, lower lst molar; r=-0.58, p<0.05). These results suggested a relapse tendency of molar inclination in the retention period. However, no significant correlation was found in the changes of upper and lower inter molar distance between treatment period and retention period, and lateral overjet and overbite on both sides remained stable in most of the cases in the retention period. It was suggested that the molar occlusion in the retention period was characterized by the relapse tendency of the molar inclination without the changes of the inter molar distance.2. In the retention period, the changes of the anterior overbite had significant correlations with the lateral overjet (r=0.65, p<0.05) and the lateral overbite (r=0.64, p<0.05).It was concluded that the change of the molar occlusion played an important role for long-term stability of the occlusion after surgical orthodontic treatment.

Cross-sectional tomography: A diagnostic technique for determining the buccolingual relationship of impacted mandibular third molars and the inferior alveolar neurovascular bundle

Twenty-two patients with 31 impacted mandibular third molars were examined with a new, precise, cross-sectional tomographic technique to assess the radiographic size, shape, branching pattern, location, and degree of cortication of the mandibular canal, and the inclination of impacted mandibular third molars in the buccolingual plane. The mandibular canal, including bifid canals, was accurately identified in 30 cases (96.8%). The cross-sectional appearance of the canal was an uncorticated, or partially corticated, radiolucent oval that measured on average (± SD) 2.9 ± 0.7 × 2.5 ± 0.6 mm in diameter. It was located more frequently (45.2%) on the buccal aspect of the impacted mandibular third molar. About 60% of the mandibular canals notched the inner cortical plate of the mandible or the third molar root surface. Cystic expansion and quantification of cortical bone destruction were readily assessed by this technique. It was concluded that diagnostic information obtained from cross-sectional tomograms significantly aids the oral and maxillofacial surgeon during the preoperative diagnostic workup and that the radiation risks are comparable to those of other accepted localization techniques.

Eruption of mandibular third molars after second-molar extractions: A radiographic study

The purpose of the present study was to analyze the posteruptive contact relationship and inclination of mandibular third molars after extraction of second molars and to determine whether predictors could be formulated for the dental relationships observed. In all, 140 mandibular quadrants were evaluated from 95 sets of panoramic radiographs taken at the time of second molar extraction (T1) and at the time of final evaluation (T2). For analysis of a consecutive sample of patients, a subsample of 25 sets of radiographs from all the patients who had received such treatment during one calendar year was also quantified. Subjective evaluation indicated that 46% of the sites examined had satisfactory tooth contact relationship between the first and third molars at T2. Third-molar impaction was found in 4% of the sites in the subsample of 25 consecutively treated patients. Measurements of crown axis inclination revealed that the third molar invariably erupted into a mesially tilted position. The first molar showed only minor distal tipping between T1 and T2. Inclination of the third molar bud at the time of second molar extraction was not found to be a useful predictor for posteruptive third molar position. The clinical significance of these results and the need for studies regarding a rationale for mandibular second molar extraction are discussed.

Factors influencing the anterior component of occlusal force

We hypothesized that the anterior component of occlusal force (ACF) generated by mandibular molars was a function of molar inclination, height of the transverse condylar axis above the occlusal plane, steepness of the occlusal plane, gape, molar root dimensions, interproximal tooth contact force when not biting, and bite force. Our research aim was to identify those biomechanical factors which determine ACF. Mandibular second molars were axially loaded with a 90 N force (10 mm second molar gape) in 15 subjects, and the resulting ACF was measured at the mandibular first molar-second premolar contact using a recording technique based on interproximal frictional forces. Morphologic measurements were obtained from lateral cephalometric radiographs of each subject and included: Frankfort mandibular plane angle, occlusal plane angle, angles formed by the longitudinal axis of the second molar and the occlusal and mandibular planes, perpendicular distance from the top of the condyle to the occlusal plane, and second molar root width and root length. For ten subjects, ACF resulting from axial loads of 50, 100, 150, and 200 N was measured. For ten subjects, ACF resulting from an axial load of 50 N and second molar gapes of 10 mm, 14 mm, 18 mm, and 22 mm were measured. ACF increased with increasing gape and increased proportionally to increasing bite force. Correlation and stepwise regression analyses revealed that ACF varies with interproximal tooth contact force when not biting (contact ‘tightness’) and molar root width (model R 2 = 0.71, p < 0.01). The hypothesis that ACF is a function of bite force, gape, molar root width, and interproximal contact tightness has been supported, and the hypothesis that ACF is a function of molar inclination, occlusal plane steepness, condylar axis height, and root length was rejected.

若年発症顎関節症の歯科学的研究 上顎臼歯部冠軸に関する検討

The subjects were 39 female patients with juvenile TMJ arthrosis (T group) and 30 healthy females (N group) who visited the Dept. of Oral Surgery in the Dental Clinics of Nagoya University Hospital, Dept. of Oral Surgery in the Dental Clinics of Fujita-Gakuen Health University Hospital and the Clinics of the Lion Foundation for Dental Health during a period of 3 years and one month from April 1983 to April 1986. The following evaluations were made: 1) U 5 to occlusal plane angle, 2) U 6 to occlusal plane angle, 3) U 7 to occlusal plane angle, 4) U 5 to U 6 angele, 5) U 7 to U 6 angle, 6) U 5 to FH plane angle, 7) U 6 to FH plane angle, 8) U 7 to FH plane angle, and 9) FH plane to occlusal plane angle. The following results were obtained: 1. U 7 to occlusal plane angle in the T group (82.0±6.5) was significantly smaller than that in the N group (85.7±8.2). 2. U 7 to FH plane angle in the T group (113.0±6.8) was significantly larger than that in the N group (108. 4±8.5). 3. Significant differences between the T group (15. 2±4.2) and the N group (15.0±4.0) were not seen in terms of the FH plane to occlusal plane angle. 4. In conclusion, a majority of the T group patients showed a centrifugal inclination of the upper second molar.

Prediction of lower third molar impaction from the frontal cephalometric projection.

The purpose of the present investigation was to analyse the eruption path of the lower third molar (M3), as seen in the frontal cephalometric projection, in an effort to contribute to an improved prediction of impaction. A total of 31 subjects (23 boys and 8 girls) representing 41 erupting (Group I) and 18 impacting (Group II) lower third molars were included in the study, the cases were drawn from a larger sample, who had been followed with annual observations and measurements from childhood until adult age. On the frontal head films the inclination of third molars was measured annually from the time of complete crown calcification until the inclination of M3 was stable. Based on the longitudinal data on M3 inclination, individual and mean curves were produced for both groups. The relationship between eruption/impaction of M3 and skeletal and dental development was analysed. The eruption pattern for Group I and Group II was markedly different. The difference seemed to be more pronounced, than in previous studies based on the lateral cephalometric projection. The dental development stage produced the earliest and most significant separation of the mean curves for the two groups. In extreme cases, reliable prediction would seem possible, based on the inclination observed in a single frontal head film at the time of appearance of the bifurcation.

Development of human first and second permanent molar, with special reference to the distal protion of the dental lamina

Serial sections of pre- and postnatal human jaws were examined to document the development of the first and second permanent molars and related dental laminae. The results are summarized as follows: 1. The first permanent molar develops as an epithelial thickening on the distal extension of the dental lamina in the 100–110 mm fetus, reaches the capstage in the 140 mm fetus and the succeeding lamina (abortive successor) is defined in the 195–215 mm fetus. The lateral enamel strands are more extensive in the mandible than in the maxilla. The connecting bridge is nothing more than the epithelial connection of the most ligual of the lateral enamel strads. 2. At birth the dental lamina ends on the mesial part of the first permanent molar, attached to it through the lateral enamel strands and the connecting bridge. In the maxilla the attachment through the former is almost lost. 3. In the latter half of the first year, with the reduction of the distal inclination of the first permanent molar, the dental lamina separates from it and extends distally. There is no doubt that the first permanent molar belongs to the first dentition. 4. The degenerative successor of the first permanent molar is discernible even in the specimens with later stages of the second permanent molar. Therefore, the second permanent molar also seems to belong to the first dentition.

Monozygotic triplets with discordance for some traits

The results of a clinical, occlusal and radiographic study of three monozygotic male triplets aged seven years nine months, showed they all had concordance, or a very high degree of similarity, with respect to incompetent lips, class II division 1 malocclusion, bi-maxillary protrusion, deep overbite and the development of the third molars. One of the triplets, however, had a complete unilateral crossbite on the right side due to a pronounced buccal inclination of the upper deciduous molars and the first permanent molar together with a lingual inclination of the corresponding lower teeth. Two of the triplets had mirror image congenital absence of one of the lower second premolars although they were all present in the third child. This discordance for missing premolars could be due to a gene mutation during the process of gene recombination or to a difference in gene expressivity. However, the abnormal inclination of the upper and lower molars which caused the unilateral crossbite could not be satisfactorily explained.

顎態模型計測による歯槽基底および歯列弓の経年的変化に関する研究 : 口蓋点を計測基準として

Using the serial gnathostatic models longitudinally taken over a period of about three years from 37 males and 32 females from 6 to 17 years of age, and using a new measuring method established in which the palatal vault was set as the standard point for measuring. The length and width of the maxilla and mandible apical bases and the dental arches, and changes in tooth inclination were examined longitudinally for four groups consisting of normal occlusion, maxillary protrusion, anterior cross bite, and crowding. Changes in maxillo-mandibular horizontal relation were also examined. Results are summarized as follows : 1. The horizontal changes with growth of point 'a', which is the anterior point of the maxillary apical base, was minimal for each group. However, the horizontal changes with growth of point 'b', which is the anterior point of the mandibular apical base, varied. As a result, the horizontal distance between the points 'a' and 'b' increased for the maxillary protrusion and decreased for the anterior cross bite. 2. The difference in the length of the dental arches between the maxilla and mandible was stable for normal occlusion, whereas the difference decreased for the maxillary protrusion and for anterior cross bite, but increased for crowding. 3. The width of the apical bases and of the dental arches increased to the age of 17 but no distinct difference was indicated between normal occlusion and malocclusion for both maxilla and mandible. 4. As to the changes in molar inclination, distal tipping decreased in the maxilla, medial tipping decreased in the mandible, and buccal tipping decreased, for each group. No significant difference was indicated between normal occlusion and malocclusion.

Quantitative evidence for the helicoid relationship between the maxillary and mandibular occlusal surfaces

A method for measuring the transverse inclination of molar teeth is described which enabled significant differences (P less than 0.001) between the three molars to be demonstrated for a sample of English Modern (n 24) and Romano-British (n20) skulls. No significant differences between the transverse molar inclinations were found for the Bronze Age (n 10) or the Neanderthal (n 8) sample.

Factors that affect the alignment of the mandibular incisors: A longitudinal study

Measurements on lateral cephalograms and study casts at two stages of dental development were used to study the influence of different variables upon the alignment of the mandibular incisors. In Stage I the only permanent mandibular teeth clinically visible were the incisors and the first molars. In Stage II all permanent teeth anterior to the first molars were in occlusion. The study casts of 150 subjects were classified subjectively in both stages as having crowding or proper alignment of the incisors. According to the frequency of the groups (Table I), the probability that a subject without crowding in Stage I will not have crowding in Stage II is 82 per cent and the probability that a subject with crowding in Stage I will have crowding in Stage II is 89 per cent. The error when these criteria are used is approximately 15 per cent. The axial inclination of the permanent mandibular incisors relative to the inclination of the first molars and the size of the first molars are strongly related to the presence of crowding of the mandibular incisors. This article points out that incisor crowding is not merely a tooth-arch size discrepancy but a discrepancy among many variables.

Open-Bite Malocclusion, Its Causes and Treatment

In relation to an impacted third molar, which is the most frequently impacted tooth, external root resorption (ERR) or dental caries can be seen on the distal surface of the adjacent second molar. The purpose of this study was to investigate the risk factors for ERR in second molars associated with impacted third molars using cone-beam computed tomography (CBCT).In this cross-sectional study, the presence of ERR on the adjacent second molar was investigated retrospectively on sagittal and axial CBCT slices of patients who underwent CBCT examination for diagnostic reasons (surgical removal of third molars, orthodontic assessments, and so on) between 2013 and 2017 at the Necmettin Erbakan University Faculty of Dentistry, Konya, Turkey. The primary outcome variable was ERR (yes or no). Predictor variables included demographic (age and gender) and radiographic (impacted tooth angulation and tooth type) parameters. Given that there are multiple observations per patient (1 to 4 impacted teeth), 1 third molar per patient was selected at random for study inclusion. Statistical analysis was performed using descriptive statistics, the Mann-Whitney U test, and the Pearson χ2 test. Logistic regression analysis was used to determine the risk factors for ERR in second molars. The Cohen κ test was used to test intraobserver agreement. The significance level was set at P < .05.Two hundred patients were analyzed, and of the 200 impacted third molars evaluated, 42 (21%) showed ERR. The severity of resorption increased with aging (P < .05). Logistic regression analysis indicated that tooth type and inclination of the third molars could predict the occurrence of ERR associated with an impacted third molar (P < .05).Mesioangular and horizontal inclinations and impacted mandibular third molars posed a greater risk of ERR lesions in adjacent second molars than other inclinations (distoangular and vertical) and maxillary third molars.