The relationship between maximal jaw opening and size of skeleton: a cephalometric study

Correlations of temporomandibular joint morphology and position using cone-beam computed tomography and dynamic functional analysis in orthodontic patients: A cross-sectional study

Objective

To correlate temporomandibular joint (TMJ) morphology and position with cone-beam computed tomography (CBCT) images, Joint Vibration Analysis (JVA), and Jaw Tracker (JT) to develop a radiation-free, dynamic method for screening and monitoring the TMJ in orthodontic patients.

Methods

A total of 236 orthodontic patients without symptoms of TMJ disorders who had undergone CBCT were selected for the JVA and JT tests in this cross-sectional study. TMJ position and morphology were measured using a three-dimensional analysis software. JT measurements involved six opening-closing cycles, and JVA measurements were performed using a metronome to guide the mouth opening-closing movements of the patients. The correlations among the three measuring devices were evaluated.

Results

Abnormalities in condylar surface morphology affected the mandibular range of motion. The cut-off value results show that when various measurement groups are within a certain range, abnormalities may be observed in morphology (area under the curve, 0.81; P < 0.001). A 300/< 300 Hz ratio ≥ 0.09 suggested abnormal morphology (P < 0.05). Correlations were observed among the maximum opening velocity, maximum vertical opening position, and joint spaces in the JT measurements. Correlations were also observed between the > 300/< 300 Hz ratio, median frequency, total integral, integral < 300 Hz, and peak frequency with joint spaces in the JVA measurements.

Conclusions

JT and JVA may serve as rapid, non-invasive, and radiation-free dynamic diagnostic tools for monitoring and screening TMJ abnormalities before and during orthodontic treatment.

Prediction of condylar movement envelope surface based on facial morphology

The present study aimed to predict the envelope surfaces from facial morphology. Condylar envelope surfaces for 34 healthy adults were formed and simplified as sagittal section curves. Cephalometric and maximum mandibular moving distances measurement were performed on the participants. There was no statistically significant difference (p = 0.763) between the left and right maximum lateral movements. There was a statistically significant difference in the mandibular body length between the sexes. The envelope surfaces were divided into type 1 with H_p2 ≥ 1/3 H_p1 and type 2 with H_p2 < 1/3 × H_p1. SNA and SNB for type 2 were significantly greater than those for type 1 (p < 0.001). Therefore, the participants were divided into four groups based on gender and envelope surface morphology. The curves could be fitted using the second-order Fourier function (R-square ≥0.95). Six facial parameters were selected and a matrix was used to map facial morphology to the envelope surface. Individual sagittal curves were predicted using the matrix and facial parameters, and the envelope surface was predicted using the curve and the condyle model. Deviation analysis for the predicted envelope surface using the actual envelope as a reference was carried out (root mean square = 0.9970 mm ± 0.2918 mm). This method may lay a foundation for the geometric design of artificial fossa components of temporomandibular joint replacement systems. It may improve prosthesis design without flexible tissue repair and guide the movement of the artificial joint head.

Body Mass Index and Age Affect Maximum Mouth Opening in a Contemporary American Population

PURPOSE

Although a standard cutoff value of less than 35 mm in the maximum mouth opening (MMO) has been used to diagnose trismus, this value does not account for natural demographic variations. The present cross-sectional study investigated the effects of age, weight, height, body mass index (BMI), and gender on the MMO in a healthy, heterogeneous population.

MATERIALS AND METHODS

A volunteer sample from multiple sites in Cincinnati, Ohio, without any reported head and neck pathologies or current dental prostheses and with intact natural incisors were included. The main outcome measure was the average MMO. Key demographic information was collected from each participant. Multivariate regression analysis was completed on the factors of age, gender, weight, and height. One-way analysis of variance was completed for binned categories of BMI.

RESULTS

Data from 330 participants (age range, 18 to 86 years; mean, 42.13 ± 18.53 years; 171 men, 159 women) were collected. The range of MMO was 31 to 71 mm. Age, height, and weight were significant predictors of the MMO, and the final model accounted for ∼20% of the variation in the MMO [adjusted r², 0.208; F(3,326) = 29.731; P = .001]. On average, individuals with a greater BMI had a greater MMO (BMI, ≤25 kg/m², 50.57 ± 7.16 mm; BMI >25 but ≤30 kg/m², 51.58 ± 7.13 mm; BMI >30 kg/m², 53.53 ± 9.84 mm).

CONCLUSIONS

In a heterogeneous population of healthy adults, natural variations in age, height, and weight significantly affected the MMO.

Morphological and masticatory performance variation of mouth behavior groups

Food texture preference and product acceptance are hypothesized to be influenced by mouth behavior. Recent work identified four mouth behavior (MB) groups that describe most consumers in the United States: Chewers, Crunchers, Smooshers, and Suckers. While these behavioral preferences are thought to play a significant role in food selection and purchasing decisions, it is unknown how closely they relate to body and oral cavity measures as well as masticatory apparatus performance. Our objectives were twofold: to determine whether MB groups are related to (a) morphological variation in body, head, and oral cavity size and (b) masticatory apparatus performance (i.e., maximum jaw gape, maximum bite forces at the incisors and first molar). Measurements were collected following an online MB assessment (JBMB Mouth Behavior Typing Tool) where participants self-identified as one of the four types of consumers. As expected, univariate associations were observed between masticatory performance and overall body as well as oral cavity size. These relationships did not persist when assessed with multivariate methods. MB groups did not differ by body, head, or oral cavity measurements; maximum gape; or maximum bite force. Because of small sample sizes for Smooshers and Suckers-a reflection of their limited prevalence in the U.S. population-we interpret the results for these groups with caution. We can more confidently conclude based on our sample that Chewers and Crunchers do not differ in size, bite force, or maximum gape, suggesting other factors primarily drive food texture choice and preference in these individuals.

Spray and stretch technique and its effects on mouth opening

STATEMENT OF PROBLEM

Mandibular mouth opening through passive stretching may be an awkward and painful experience for patients with orofacial pain. Whether a spray technique would reduce such discomfort is unclear.

PURPOSE

The purpose of this clinical study was to determine whether the use of a spray technique would be an effective method of increasing maximal mouth opening (MMO) without passive stretching to avoid patient discomfort.

MATERIAL AND METHODS

A sample of 61 participants, 33 men and 28 women, without orofacial pain was selected from a general dental office, and a sample of 60 participants, 30 men and 30 women, was selected from a cohort of over 750 patients with orofacial pain from an oral surgery department. The presence of orofacial pain in the patient group was verified and recorded by means of palpation of the temporomandibular joints (TMJs) and masticatory, neck, and shoulder muscles. All participants in the study were instructed to open their mouth maximally to permit insertion of a TMJ equilateral triangle and the measurement of their MMO twice. Then, the participants were informed that a vapocoolant would be sprayed twice on both cheeks from the mandibular angle to the temple area. After spraying, the participants were requested to open their mouth maximally, and again the interincisal distance was measured twice. For analysis of the variables, a 2-way ANOVA was used with estimates for group effects and a correction for sex. A covariance model was used to test the effect of age (α=.05).

RESULTS

Testing for age revealed an effect for both study groups (P=.032), but not for sex (P=.074). Testing baseline values of maximal mouth opening for the studied groups revealed no significant difference (P=.175), although for sex, it did (P=.008). The relative gain as a percentage of increase in mouth opening led to similar results, comparable with the values of the absolute increase in magnitude (P<.001 for the study groups and P=.090 for sex). Testing the effect of age in a covariance model did not lead to a significant result (P=.73).

CONCLUSIONS

The spray and stretch technique increased maximal mouth opening in most participants, more so in participants with orofacial pain than in the control group and more in women than in men. Pain from passive stretching can be prevented.

Assessment of the TMJ Dysfunction Using the Computerized Facebow Analysis of Selected Parameters

The Purpose of the Paper. Qualitative and quantitative analysis of selected parameters of mandible movements, electronically registered in patients with temporomandibular joint dysfunction and healthy ones. Material. Function test of the mandible movements was conducted in 175 patients. Gender distribution was 143 women and 32 men, aged 9 to 84. Methods. The studied population, after accurate clinical examination, was divided into age groups with the range of five years. All the patients had Zebris JMA computerized facebow examination done, according to the generally accepted principles and procedures. Results. Mean values of mouth opening calculated to 45.6 mm in healthy group and 37.6 mm in TMJ dysfunction group. Mean length of condylar path amounted to 39 ± 7% of the maximum value of mouth opening in the group of healthy people, 44 ± 11% in the case of muscle-based disorders, and 35 ± 11% with joint-based. The mean value of the condylar path inclination oscillated in the range of 25° to 45°. Conclusions. The ratio of length of the condylar path to the size of mouth opening may be a significant value characterising the type and degree of intensification of the TMJ dysfunctions.

The effect of interincisal opening, cavity location and operator experience on the energy delivered by a light-curing unit to a simulated dental restoration

BACKGROUND

Curing of resin-based composites depends on the delivery of adequate total energy, which may be operator dependent. Aim To determine the effect of interincisal opening, cavity location and operator experience on the total energy delivered to simulated cavity preparation sites.

DESIGN

Three cohorts were included: junior dental nurses, senior dental nurses and qualified dentists (N=5, each cohort). Each operator (participant) followed the same procedure and light-cured two simulated restorations in a MARC patient simulator using a Demi light-curing unit for 20 seconds in each of the following situations: left upper second molar (UL7), interincisal opening at both 25 mm and 45 mm; upper central incisor (UR1), interincisal opening at 45mm. The light energy delivered by each operator in each situation was recorded. Five readings for each operator were taken at each interincisal distance. Statistical comparisons of delivered energy (J/cm2) between interincisal openings, location and groups in the total energy delivered were performed using the Kruskal-Wallis nonparametric test: alpha = 0.05.

RESULTS

Less total energy was delivered to the posterior cavity at 25mm (12.0 +/- 5.3 J/cm2) than at 45mm (16.9 +/- 5.6 J/cm2) by all operators (P < 0.05). At 45 mm, less total energy was delivered to the posterior cavity compared to the anterior cavity (25.1 +/- 7.4 J/cm2; P < 0.05). There was no statistically significant difference between junior nurses and qualified dentists (P > 0.05) but there was a significant difference in the total energy delivered between senior nurses (20.1 +/- 7.8 J/cm2) and junior nurses (17.5 +/- 7.6 J/cm2) and between senior nurses and qualified dentists (16.6 +/- 8.7 J/cm2) (P < 0.05).

CONCLUSIONS

Interincisal mouth opening, location of the cavity and operator experience affected the total energy delivered to cavities in a simulated clinical environment.

Natural head position and growth of the facial part of the skull

The aim of this study was to determine any correlation between natural head position and cranio-cervical growth direction and if natural head position influences facial growth direction. One hundred sixty (160) cephalometric radiographs were examined and cranio-cervical inclinations determined (angles: NS-Ver, NS-OPT, NS-CVT). On the basis of the NS-ML angle, radiographs were divided into two groups: mandibular anteriorotation and posteriorotation. On the basis of the SGo/NMe index, two groups were formed: short-faced and long-faced subjects. The angles NS-Ver, NS-OPT, and NS-CVT describe cranio-cervical inclination. Subjects with anterior mandible growth do position their heads more vertically and have a shorter face, and those with posterior mandible growth tilt their heads more backwards and have a longer face. An adaptive head position can be a factor in altering the direction of facial growth. Determination of head position and mandible growth direction can be an important indicator in patients with TMD treatment.

Biomechanics of the mandible and growth extension

BACKGROUND AND OBJECTIVE

One way of determining the direction of growth of the mandible is to consider the temporomandibular joint and movement of the mandible as a four-joint gear system, regarding growth then as an extension of the gear system. Our aim was to examine any correlations between the type of biomechanical growth extension and change in the maxilomandibular relation after Class II therapy.

SUBJECTS AND METHODS

A total of 130 lateral cephalograms-before and after orthodontic treatment-were available from 65 adolescent class II patients with open bite or deep bite. The two lateral cephalograms from each patient were superimposed on the occlusal plane. Cephalometric values and the vertical base point deviation were determined from biomechanical analyses, together with three distances and three angles.

RESULTS

No correlation between the cephalometric data and distances or angles were observed. Although there were no significant differences in the distances, we did note significant differences in all three angles (p < 0.05).

CONCLUSION

If gear system extension during growth is considered, this can be interpreted as meaning that the occlusal plane of those patients with an initially open bite dropped during treatment, but that it rose in patients with an initially deep bite.

Correlation between 3-dimensional facial morphology and mandibular movement during maximum mouth opening and closing

PURPOSE

The purpose of this study was to analyze the relationship between mandibular movement and facial morphology parameters measured using 3-dimensional CT data.

MATERIALS AND METHODS

We have developed a mandibular movement tracking and simulation system. The mandibular movement data were acquired from 22 subjects (6 males and 16 females), 3 who had no clinical facial deformities and 19 who had orthofacial deformities. The subjects voluntarily performed maximum mouth opening and closing movements. Three-dimensional maximum linear movements of selected points (bilateral condylions, infradentale, and pogonion) were calculated to represent mandibular movement. Facial morphology values were measured 3-dimensionally from CT data and bilateral morphological values were divided into 2 groups according to the mandibular deviation, the deviated side, and counter-deviated side groups. Correlation coefficients were calculated to evaluate the relationship between mandibular movements and facial morphology.

RESULTS

Maximum linear movements of all selected points on the mandible were positively correlated with sella-nasion-point A (SNA) and sella-nasion-point B (SNB). Movements of the infradentale and pogonion were significantly correlated with ramus inclination, lateral mandibular body angle, ramus length, and mandibular body length. Condylar movement was positively correlated with lateral mandibular body angle and mandibular body length. Multiple stepwise linear regression analysis was performed to evaluate the model predicting the effect of morphological values on mandibular movement. Condylar movement was associated with the SNA (R(2) value = 0.32 for the deviated side, R(2) value = 0.26 for the counter-deviated side), and movement of the infradentale was associated with both SNA and ramus length (R(2) value = 0.57). Movement of the pogonion could be predicted by SNA, mandibular length, and condylar head length (R(2) value = 0.65).

CONCLUSION

The 3D facial morphology values were associated with variations in mandibular movement, and morphological parameters contributed to predicting the movement of the mandible with different degrees.

Variations in cyclic mandibular movements during treatment of Class II malocclusions with removable functional appliances

The aim of the study was to establish whether juveniles with a Class II malocclusion change the neuromuscular control of mandibular movements during the course of orthodontic treatment with removable functional appliances (RFAs). Neuromuscular control can be indirectly evaluated by recording cyclic planar mandibular movements which were freely carried out by the patients (28 girls, 14 boys, aged 11.1 ± 1.1 years at the start of treatment) and measured with an ultrasonic device before, during, and after Class II functional appliance therapy, with either an activator or a bite jumping plate. The cyclic movements represented simultaneous rotations of the mandible around a maxillary and mandibular fixed axis (MFHA) and could be characterized by μ(α)-diagrams (μ = swing angle of MFHA, α = mouth opening angle) and path length (L) of the MFHA. The μ(α)-diagrams clearly divided into four parts: movement representing protrusion, mouth opening, and two parts of backward closing as known from Posselt diagrams. Parameters from the Posselt and μ(α)-diagrams were checked by one-factor analysis of variance on a 5 per cent significance level for group dependency. For one-third of the patients investigated, no significant changes were seen in any parameter pre- or post-therapy. However, patients showing an initially large mouth opening capacity or a very short condylar path changed their neuromuscular control to that of Class I subjects. Analysis of μ(α)-diagrams provides the possibility of assessing changes in the neuromuscular control of the mandible during Class II treatment.

The relationship between vertical craniofacial morphology and the sagittal path of mandibular movements

The aim was to investigate the relationship between the vertical craniofacial morphology and the sagittal path of mandibular movements. The study was carried out in 40 subjects who were free of temporo-mandibular disorders. Mandibular movements and maximal jaw opening (MO) were recorded by means of a jaw tracking device. The opening-closing angle (OCA) was defined as the angle between the horizontal plane and the opening-closing path of movements. Vertical craniofacial morphology was assessed on prophile cephalograms by means of the Frankfort Mandibular Plane Angle (MP). The OCA did not differ between males and females (P>0.05). OCA and MP were negatively correlated (r=-0.62; P<0.001). MO was significantly greater in males that in females (P<0.05). MO was negatively correlated to MP (-0.44<r<-0.49; P<0.05). The findings suggest that the low-angle subjects exhibit a more vertical path of the mandibular movements than that of high-angle subjects. Differences in the sagittal path of jaw movements may be partly ascribed to anatomical factors.

Condylar motion in patients with reduced anterior disc displacement

The influence of reduced anterior disc displacement on condylar motion has not been fully examined in young adults. Reduced anterior disc displacement was hypothesized to inhibit condylar motion. Using a six-degrees-of-freedom jaw-tracking system, we recorded bilateral condylar motion during maximum open-close jaw movement and gum-chewing on both sides in ten young adults with unilateral reduced anterior disc displacement and in ten control subjects without temporomandibular disorders. The bilateral condylar motion during both maximum open-close jaw movement and chewing on the disc-displacement side was inhibited in the test group. The condylar motion on the disc-displacement side during chewing on the non-disc-displacement side was also inhibited in the test group. These results suggest that the limitation of condylar motion on the disc-displacement side may influence condylar motion on the non-disc-displacement side during maximum open-close jaw movement, and mastication on the disc-displacement side in young adults.

Rotational and translational loading of the temporomandibular joint

Following an introduction to the functional properties of a three-dimensional instantaneous helical axis pertaining to circular (rotatory) and linear (translatory) motions of the mandible, this feasibility study applied the concept of a mandibular average finite helical axis to the maneuver of cyclic opening and closing of the mouth in three healthy subjects. Through the accelerations and decelerations of a mandibular incisor point (instead of a mandibular condylar point) as well as the laws of physics, the kinetic reaction forces and reaction pressures in the upper and lower cavities of the temporomandibular joint (TMJ) were estimated over opening-closing distances of five and ten mm from centric occlusion. The translatory reaction pressures in the upper TMJ cavity (17-29 mm Hg) exceeded the rotatory reaction pressures in the lower TMJ cavity (5-12 mm Hg). The estimated reaction pressures were in close agreement with synovial fluid pressures measured in vivo in the TMJ of humans and pigs, and the biologic significance of frequent and/or prolonged increased TMJ hydrostatic pressures is discussed.

Linear and angular measurements of the mandible during maximal mouth opening

PURPOSE

There are numerous reports of the translatory movement of the condyle in maximal mouth opening; however, the rotatory movement is less well understood. The purpose of this study was to investigate the rotatory condylar movement and the factors associated with it in normal subjects.

PATIENTS AND METHODS

To study the role of facial morphology in maximal mouth opening, linear and angular measurements of the mandible in both the closed and maximal open positions were made by means of cephalometry. Dental students, 29 men and 31 women with no functional disorders of the masticatory system, were investigated.

RESULTS

When the mouth was fully opened, the linear measurement of condylar movement was 20.5 +/- 4.0 mm in men and 18.1 +/- 2.5 mm in women, and the angular measurements of the rotation of the mandibular ramus were 39.1 +/- 5.9 degrees in men and 36.3 +/- 4.3 degrees in women. These differences were statistically significant (P < .01).

CONCLUSIONS

During condylar movement and rotation of the mandible, mandibular length and the inclination of the mandibular ramus in the former, and the inclination of the mandibular ramus, the mandibular angle and the position of the condyle in the latter, were important factors.