Effect of biomechanical disturbance of the temporomandibular joint on the prevalence of internal derangement in mandibular asymmetry

The aim of the present study was to elucidate the relationship between biomechanical changes of the temporomandibular joint (TMJ) and internal derangement (ID) symptoms in mandibular asymmetry. Posteroanterior cephalograms (PA) of 140 patients with TMJ ID associated with mandibular asymmetry were used to investigate the inclination of the frontal occlusal plane (FOP), and were analysed in conjunction with the results of a report providing information on ID symptoms. A three-dimensional (3D) finite element model (FEM) of the entire mandible was created to investigate the distribution of TMJ forces during clenching. The inclination of the FOP was modified to simulate various degrees of vertical asymmetry. The stresses on the TMJ on the ipsilateral and contralateral sides were analysed and their values were compared with those of the standard model. The results showed that the symptomatic sides were significantly related to the degree of inclination of the FOP. Increasing its angulation resulted in a decrease of the symptoms on the ipsilateral side and an increase of those on the contralateral side. The analysis showed that stress-distribution patterns and overall stresses of the articular disc were influenced by the angulation of inclination of the FOP. These mechanical changes exhibited a distinct relationship with the prevalence of ID in the patients. These results suggest that disturbances in the stresses either in amount or direction due to occlusal inclination can be responsible for ID. Therefore, an attempt to establish a flat occlusal plane is an important orthodontic treatment objective in maintaining the normal health and structure of the TMJ.     

Changes in condylar path inclination during maximum protrusion between the ages of 6 and 12 years

The purpose of this study is to quantify the changes in sagittal condylar path inclination during mandibular protrusion between the ages of 6 and 12 years. A total of 172 children (82 males and 90 females) ranging in age from 6.5 to 12.9 years were divided according to their chronological age into five subgroups with mean ages of 7.1, 8, 9, 10 and 11.4 years respectively. The control group consisted of 41 adults with a mean age of 28 years. All subjects had a normal temporomandibular joint function and neutral occlusion. Five maximum protrusion-retrusion movements were recorded with six degrees of freedom in each subject using an ultrasound (JMA) jaw-tracking system. Initially, condylar path inclination angle (CPIA) was calculated stepwise for each millimetre distance, for the first 10 mm of protrusive tracing path on both sides. A single mean value was then assigned for the entire protrusive path. One-way analysis of variance proved to be significant among the five subgroups of children. Linear regression analysis showed that condylar path had a tendency to become steeper with age, although it was statistically weak. The data indicated that the mean CPIA is 43 degrees -44 degrees at the age of seven, increases annually by 1.2 degrees -1.3 degrees and reaches an average of 49 degrees -50 degrees by the age of 12 at which time it attains around 83-85% of its adult level. In subgroup V, the female population had significantly steeper condylar path on the left-hand side than the male population. Condylar path inclinations indicated a symmetrical growth pattern of the articular eminence.     

Bone level changes at axial- and non-axial-positioned implants supporting fixed partial dentures. A 5-year retrospective longitudinal study

AIM: The aim of this study was to retrospectively analyze the potential influence of implant inclination on marginal bone loss at freestanding, implant-supported, fixed partial dentures (FPDs) over a 5-year period of functional loading. MATERIAL AND METHODS: The material comprised 38 periodontally treated, partially dentate patients with a total of 42 free-standing FPDs supported by implants of the Astra Tech System. Mesio-distal inclination of the implants in relation to a vertical axis perpendicular to the occlusal plane was measured with a protractor on standardized photographs of the master cast. The two tail quartiles of the distribution of the implants with regard to the implant inclination were defined as axial-positioned (mean 2.4 degrees; range 0-4 degrees) and non-axial-positioned implants (mean 17.1 degrees; range 11-30 degrees), respectively. For FPDs supported by two implants, both the mesial-distal and buccal-lingual inter-implant inclination was measured. The primary outcome variable was change in peri-implant bone level from the time of FPD placement to the 5-year follow-up examination. Comparison between axial- and non-axial-positioned implants was performed by the use of a Mann-Whitney U-test. Spearman's correlation analysis was used to analyze relationships between inter-implant inclination (mesial-distal and buccal-lingual) and 5-year bone level change on the FPD level. RESULTS: The 5-year mean bone level change amounted to 0.4 mm (SD 0.97) for the axial and 0.5 mm (0.95) for non-axial-positioned implants (P>0.05). For the FPDs supported by two implants, the mean inter-implant inclination was 9.2 degrees (1-36 degrees) in the mesial-distal direction and 6.7 degrees (0-24 degrees) in the buccal-lingual direction. Correlation analysis revealed lack of statistically significant correlation between inter-implant inclination (mesial-distal and buccal-lingual) and 5-year bone level change (r=-0.19 and r=-0.32, respectively). CONCLUSION: The study failed to support the hypothesis that implant inclination has an effect on peri-implant bone loss.     

Study of the inclination angle between the edentulous upper and lower alveolar ridge in the sagittal plane

Angle of inclination between the upper and lower edentulous alveolar ridge in the sagittal plane was examined on 72 patients (55 woman and 17 men) in centric occlusion. Photos were taken by a special camera (Polaroid MACRO 5 SLR) of the functional casts mounted in average value articulators, on a special squared-film, from the left and right side. The angle between the lines connecting mesially the midline of the alveolar ridge, distally the highest point of the tuber alveolar maxillae and the line drown through the stop-lines, respectively was measured on both sides with 1 degree precision. Distally open angle (max. 7 degrees) was found in 11% of the examine group. The alveolar ridge lines were parallel in only 3% of the cases. Mesially open angle (max. 20 degrees) was found at 86%. Statistical analysis has shown, that there is a significant difference between men and women as well as the left and right side.     

Malposition of unerupted mandibular second premolar in children with cleft lip and palate

OBJECTIVE: To determine whether distoangular malposition of the unerupted mandibular second premolar (MnP2) is more frequent in children with unilateral clefts of the lip and palate. MATERIALS AND METHODS: This retrospective study examined panoramic radiographs from 45 patients with unilateral clefts of the lip and/or palate who had no previous orthodontics. A control sample consisted of age- and sex-matched patients. The distal angle formed between the long axis of MnP2 and the tangent to the inferior border was measured. The mean, standard deviation, and range were calculated for the angles measured in the cleft and the control groups. The significance of the differences between the means was evaluated by the paired t-test. The angles of the cleft and noncleft sides were also measured and compared. RESULTS: The mean inclination of the MnP2 on the cleft side was 73.6 degrees , compared with 84.6 degrees in the control group. This difference was highly significant statistically (P < .0001). The difference in angles from the cleft and noncleft sides was 0.7 degrees , not statistically significant. A significant association was found between clefting and distoangular malposition of the developing MnP2, suggesting a shared genetic etiology. This association is independent of the clefting side, ruling out possible local mechanical effects. CONCLUSION: Clinicians should be aware of the potential for anomalous development of MnP2 in children with clefts.     

Implant angulation: a measurement technique,implant overdenture maintenance,and the influence of surgical experience

PURPOSE: The purposes of this study were to develop a technique to measure the angulation between two implants and between each implant and reference planes, to analyze the relationship between the maintenance (adjustments and repairs) of ball-attachment mandibular implant overdentures and implant angulation, and to see if there is any correlation between surgeon experience and implant orientation. MATERIALS AND METHODS: Final casts of 41 patients who had received two-implant ball-attachment mandibular overdentures were used to measure implant angulations using digital photographs and plane geometry. The measured angles were compared with the number of adjustments and repairs of the prostheses and analyzed by surgeon experience for any trends. RESULTS: No significant relationships were found between number of adjustments and repairs and the interimplant angles. However, there was a significantly higher number of repairs when the lingual inclination of an implant was > or = 6.0 degrees (P = .033) or if the facial inclination was < 6.5 degrees (P = .036). Less experienced surgeons had a significantly greater tendency to place implants that diverged from each other in the frontal plane (P = .045) and with a facial or lingual inclination in the sagittal plane (P = .035). CONCLUSION: While interimplant angulation did not appear to affect prosthesis maintenance, individual implants with a lingual inclination > or = 6 degrees and a facial inclination < 6.5 degrees were associated with significantly more prosthesis repairs. There was a tendency for implants placed by less experienced surgeons to demonstrate greater inclination.     

Comparison of condylar guidance setting obtained from a wax record versus an extraoral tracing: a pilot study

STATEMENT OF PROBLEM: Protrusive condylar angles can be determined by use of wax protrusive records (WPR), pantographic tracings (PT), and occlusal wear facets. These methods generate different angles in the same patient. PURPOSE: The purpose of this study was to compare the condylar inclination angles found by use of the WPR in a Hanau articulator with those found by use of the Whip-Mix PT quick-set recorder. The occlusal wear facet method was not part of this study. MATERIAL AND METHODS: Ten subjects were chosen at random from a dental school patient population. All subjects had a majority of maxillary and mandibular teeth present and according to the examination criteria used in the school's Division of Occlusion, they were healthy with no signs/symptoms of temporomandibular disorders. The WPR was accepted when it was evident that the patient had protruded straight forward at least 6 mm anterior to centric relation, as shown on the Hanau articulator by the condylar spheres having moved anteriorly an equal distance of 6 mm on both sides. The condylar inclination on the articulator was adjusted accordingly. The PT was used according to the manufacturer's directions, which included the use of an intraoral clutch adapted to the mandibular arch, connected to an extraoral facebow with bilateral inscribing pointers. A holder frame was adapted to the face with bilateral flags where the inscribing pointers traced the protrusive movement of the jaw. All the readings were in degrees. No control was used in this project. To test whether there was a significant difference between the 2 independent samples, a Mann-Whitney U test was performed (P=.01). RESULTS: The mean results for the WPR were as follow: right side (28.1 degrees, SD 8.94); left side (31.50 degrees, SD 9.73). For the PT, results were: right side (41.10 degrees, SD 7.53); left side (35.5 degrees, SD 6.43). When right and left side protrusive condylar angles were combined, the values were: WPR (29.80 degrees, SD 9.25); PT (38.30 degrees, SD 6.98). The differences on the right condylar values were significant (P=.01). There was no statistical difference on the left side. CONCLUSIONS: Within the limitations of this study, it was concluded that the PT technique yielded greater values for the protrusive condylar inclination than the WPR.     

Radiographic identification of nonthreaded endosseous dental implants

STATEMENT OF PROBLEM: The identification of dental implant bodies in patients without available records is a considerable problem due to increased patient mobility and to the large number of implant systems with different designs. PURPOSE: The purpose of this study was to document features that would help dentists identify non-threaded implant bodies from their radiographic images. MATERIAL AND METHODS: More than 50 implant manufacturers were contacted and asked to provide implants with dimensions as close as possible to 3.75 mm (diameter) x 10 mm (length). Forty-four implants were donated, 16 of which were identified as non-threaded. Radiographs were made of these implants at 0 degrees, 30 degrees, 60 degrees, and 90 degrees horizontal rotation combined with -20 degrees, -10 degrees, 0 degrees, +10 degrees, and +20 degrees vertical inclination relative to the radiographic beam and film. A total of 20 images per implant were taken and examined to identify consistent, unique features that would aid in implant identification. At a 20 degrees vertical inclination, vital features of implants were distorted enough to be deemed unrecognizable. Therefore, only those observations made from radiographs between -10 degrees and +10 degrees vertical inclination were used for implant identification purposes. RESULTS: All implants could be recognized from radiographs made between -10 degrees and +10 degrees vertical inclination. A series of tables and flowcharts describe the implants according to their identifying features. CONCLUSION: Information from this study should help dentists identify non-threaded endosseous implants from their radiographic images.     

Radiographic identification of threaded endosseous dental implants

STATEMENT OF PROBLEM: The identification of dental implant bodies in patients without available records is a considerable problem due to increased patient mobility and to the large number of implant systems with different designs. PURPOSE: The purpose of this study was to document features that would help dentists identify threaded implant bodies from their radiographic images. MATERIAL AND METHODS: More than 50 implant manufacturers were contacted and asked to provide implants with dimensions as close as possible to 3.75 mm (diameter) x 10 mm (length). Forty-four implants were donated, 28 of which were identified as threaded. Radiographs were made of these implants at 0 degrees, 30 degrees, 60 degrees, and 90 degrees horizontal rotation combined with -20 degrees, -10 degrees, 0 degrees, +10 degrees, and +20 degrees vertical inclination relative to the radiographic beam and film. A total of 20 images per implant were taken and examined to identify consistent, unique features that would aid in implant identification. At a 20 degrees vertical inclination, vital features of implants were distorted enough to be deemed unrecognizable. Therefore, only those observations made from radiographs between -10 degrees and +10 degrees vertical inclination were used for implant identification purposes. RESULTS: All implants could be recognized from radiographs made between -10 degrees and +10 degrees vertical inclination. A series of tables and flowcharts describe the implants according to their identifying features. CONCLUSION: Information from this study should help dentists identify threaded endosseous implants from their radiographic images.     

A comparison of 3 methods of face-bow transfer recording: implications for orthognathic surgery.

PURPOSE: The purpose of this study was to compare the occlusal plane inclination of models mounted using 3 different systems for face-bow transfer with the actual occlusal plane inclination as measured on a cephalometric radiograph. PATIENTS AND METHODS: Twenty-two subjects were enrolled in this study. Three alginate impressions of the maxillary dentition were taken, and 3 stone dental models were produced for each subject. Face-bow recordings were obtained on each subject using the SAM Anatomical Face-bow (Great Lakes Orthodontics Products, Ltd, Tonawanda, NY), the Erickson Surgical Face-bow (Great Lakes Orthodontics Products, Ltd) and a new technique developed by one of the authors (J.G.). For each subject, the dental models were mounted on a SAM articulator using each of the 3 face-bow recordings. Finally, a lateral cephalometric radiograph was obtained for each subject. The occlusal plane inclination was measured on the models and on the cephalometric radiographs. Differences among groups were tested using a 1-way analysis of variance. Bonferroni test was used for post hoc comparison between different pairs of groups. RESULTS: The average occlusal plane inclination using the SAM Anatomical Face-bow was 7.8 degrees +/- 4.2 degrees greater than the actual-a difference that was statistically significant. The mean occlusal plane inclination of the models obtained using the Erickson Surgical Face-bow was 4.4 degrees +/- 2.2 degrees greater than the actual-a difference that was also statistically significant. The mean occlusal plane inclination of the models obtained by the new technique was only 0.9 degrees +/- 1.2 degrees greater than the actual; this difference was not statistically significant. CONCLUSIONS: The new mounting technique is more accurate than the conventional SAM Face-bow or the Erickson Face-bow for reproducing the actual occlusal plane inclination.     

Statistical study of the angle formed by the lateral part of the mandibular condyle and the horizontal plane

The angle between the LCA and frontal plane and the inclination of the lateral part of the mandibular condyle and the horizontal plane were measured in a sample of the skulls used in the study. Correlation between the two angles was found to be almost insignificant. Fifty-eight percent of the TMJs had an inclination of the lateral part of the condyle less than 15 degrees. The maximum value for this angle was found to be 45 degrees, and the minimum was -6 degrees.     

A comparison of protrusive interocclusal records to pantographic tracings

The rationale for recording protrusive mandibular movement is to accurately adjust an articulator. Techniques to record condylar inclination include radiographic interpretation, extraoral tracings, and intraoral recording materials. This study compared the protrusive settings on an articular adjusted by a pantograph to protrusive settings recorded by two intraoral recording materials, one a polyvinyl siloxane material and one a laminated, metalized wax. Pantographs were completed for 20 patients by using a kinematic hinge axis and conventional pantographic techniques. The patients also had three protrusive interocclusal records made with two intraoral registration materials completed and averaged. The average condylar inclination recorded with a pantograph (29.5 degrees) was greater than the recording by either intraoral registration material. Standard deviations ranged from 4.1 degrees to 6.6 degrees. An analysis of variance showed that the condylar inclination recorded by wax was statistically less than recorded with a pantograph. A comparison between the pantograph and the polyvinyl siloxane displayed no statistically significant difference in recording condylar inclination.     

Vertical forces in labial and lingual orthodontics applied on maxillary incisors--a theoretical approach

Theoretical and experimental biomechanical analyses explain most labial orthodontics (LaO); however, lingual orthodontic (LiO) biomechanical principles are rarely introduced. The objective of this study was to apply basic biomechanical considerations in understanding the influence of maxillary incisor inclination and to compare the effect of labial vs lingual intrusive/extrusive forces on tooth movement. Basic anatomic and geometric hypotheses were assumed, ie, tooth length (crown and root), location of the center of resistance, and crown thickness. Incisor inclination as related to a perpendicular line to the occlusal plane (OP) varied between -35 degrees (retroclination) and 45 degrees (proclination). A 0 degrees inclination was defined as a tooth position with its long axis perpendicular to the OP. The buccolingual moment for characterizing root movement was calculated for an applied force perpendicular to the OP. The results showed that when using LaO, an extrusion force resulted in labial root movement from a retroclination of 20 degrees up to a proclination of 45 degrees. In LiO, labial root movement occurred only when the tooth was proclined more than 20 degrees. In all other tooth inclinations, lingual root movement occurred. The opposite tooth movement occurred when an intrusive force was applied. Application of a vertical force has different clinical effects on tooth movement with labial and lingual appliances. Application of a lingual force is more complicated, and its effect on tooth movement depends on bracket position and initial tooth inclination.     

Critical assessment of a device to measure incisor crown inclination.

The aims of this study were to critically assess the use of a disposable device--the tooth inclination protractor (TIP)--to record incisor crown inclination and to compare its reliability and validity with that of traditional cephalometric radiographic analysis. The sample comprised 30 dental students with lateral cephalometric radiographs and dental casts. Four examiners were trained and calibrated to digitize radiographs and to use intraoral (on patients and dental casts) and extraoral (on dental casts) TIPs. The following angles were measured on the radiographs: maxillary incisor to maxillary plane, mandibular incisor to mandibular plane, maxillary incisor to occlusal plane, and mandibular incisor to occlusal plane. Measurements were also made with the TIP: maxillary incisor to occlusal plane and mandibular incisor to occlusal plane. All techniques were reliable between examiners. There were statistically significant systematic differences between the TIP and the radiographic assessments. The following differences were found. The TIP tended to record maxillary incisor crown inclination an average of 14 degrees less than maxillary incisor to maxillary plane. The TIP tended to record mandibular incisor crown inclination as similar to mandibular incisor to mandibular plane. The TIP recorded mandibular crown inclination 19 degrees less than mandibular incisor to occlusal plane. The disposable TIP was shown to be a simple, inexpensive, reliable, and valid method of assessing incisor inclination.     

Temporomandibular joint internal derangement in mandibular asymmetry. What is the relationship?

The purpose of this study was to clarify the contributing factors and their influences on temporomandibular joint internal derangement (TMJ ID) symptoms in subjects with mandibular asymmetry. Postero-anterior (PA) cephalograms of 187 pre-orthodontic treatment subjects (aged 18-45 years, mean 23.9 years) were used to investigate the inclination of the frontal occlusal (FOP) and frontal mandibular (FMP) planes to determine vertical asymmetry. Mandibular dental midline shift (DMS) and mandibular midline shift (MMS) were studied to determine transverse asymmetry. The degree of asymmetry was analysed in conjunction with the results from self-administered TMJ ID history forms. A prevalence of TMJ ID was most related to the inclination of the FMP (P < 0.01), with the symptoms being notably higher when the cant was greater than 3 degrees. The symptomatic side was related only to the inclination of the FOP and FMP. Symptoms confined to the ipsilateral side were primarily found in subjects with mild asymmetry, whereas symptoms on both sides and those on the contralateral side were greater in those with moderate and severe asymmetry, respectively. No significant correlation was found for DMS and MMS. The results suggest that the degree of asymmetry in the vertical dimension is significantly correlated with TMJ ID symptoms.     

Hemodynamics in the pulp of abutment teeth after their preparation for metal-ceramic denture restoration at various degree of lateral wall convergence

Reaction of the pulp to degree-by-degree changes (from 3 to 18 degrees) in inclination of lateral walls of abutment teeth during preparation for cermet dentures was studied by the functional diagnosis methods (electroodontodiagnosis, rheodentography) in 50 patients with intact abutment teeth. Changes in dental pulp electric conductivity and hemodynamics depended on the inclination angle formed during preparation. The optimal safe angle of the lateral wall inclination was determined to be 3-12 degrees. Increase of the angle (> 12 degrees) can lead to traumatic pulpitis.     

Adequacy of mandibular premolar position despite early loss of its deciduous molar

The mandibular second premolar (MnP2) tooth is one of the most commonly impacted teeth. Early loss of its deciduous predecessor has long been suggested to be a factor in the etiology of the MnP2 impaction. In this study, panoramic roentgenograms were used to measure the angular position of the unerupted MnP2 in 85 children. The study was carried out to test whether early loss of the lower second primary molar (dM2) correlates with MnP2 malpositions that are measurably greater than those from a control sample. The results show a small and statistically insignificant difference between the mean angles in cases with (79.6 degrees) and without (83.2 degrees) dM2. To eliminate individual factors, e.g., genetics, 2 sides of the same patient, with and without dM2, were compared. The group with the missing dM2 on one side showed higher angle differences, compared with the control group. However, the differences were still small (approximately 4 degrees) and statistically insignificant. Our findings do not show a significant influence of early loss of dM2 on the inclination of the unerupted MnP2, suggesting that environmental factors may be of less significance, compared with genetic ones.     

Assessments of inclinations of the mandibular fossa by computed tomography in an Asian population

This study aims to evaluate the inclinations of right and left sides the mandibular fossa in Asian population using computed tomography (CT) images and determine its effects according to the parameters of gender, age, and asymmetry. CT images of the heads of 198 Asian subjects [95 females aged 44.2 ± 20.7 years, range 11–88 years; and 103 males aged 44.5 ± 19.7 years, range 15–98 years] were selected. The following eight parameters characterizing the inclinations of the mandibular fossa were measured by medical imaging software: anterior and posterior inclinations on the left and right sides on a sagittal view, and medial and lateral inclinations on the left and right sides on a coronal view. The anterior inclination was significant steeper in males than in females on both the left and right sides. A moderate positive correlation was found between age and anterior inclinations on the left and right sides. None of the other parameters were significantly affected by age or gender. None of the parameters differed significantly between the right and left sides of the mandibular fossa in males, females, or all subjects. The anterior inclination of the mandibular fossa was affected by aging and gender becoming steeper in Asians males than females. Besides, there were no asymmetry in the right and left side inclinations of the mandibular fossa.