The fallacy of facial measurements of occlusal height in edentulous subjects

An intraoral method of verifying interocclusal distance for completely edentulous patients

This article describes a method of verifying the interocclusal distance of edentulous patients by using acrylic resin wafers of different thicknesses. The wafers are attached to the occlusal surface of the maxillary wax occlusal rim in the first premolar region to facilitate intraoral verification of the proposed interocclusal distance. This method is straightforward and reduces the registration of an incorrect interocclusal distance.

Individual mandibular movement registration and reproduction using an optoeletronic jaw movement analyzer and a dedicated robot: a dental technique

BACKGROUND

Fully adjustable articulators and pantographs record and reproduce individual mandibular movements. Although these instruments are accurate, they are operator-dependant and time-consuming. Pantographic recording is affected by inter and intra operator variability in the individuation of clinical reference points and afterwards in reading pantographic recording themselves. Finally only border movements can be reproduced.

METHODS

Bionic Jaw Motion system is based on two components: a jaw movement analyzer and a robotic device that accurately reproduces recorded movements. The jaw movement analyzer uses an optoelectronic motion system technology made of a high frequency filming camera that acquires 140frames per second and a custom designed software that recognizes and determines the relative distance at each point in time of markers with known geometries connected to each jaw. Circumferential modified retainers connect markers and do not cover any occlusal surfaces neither obstruct occlusion. The recording process takes 5 to 10 s. Mandibular movement performance requires six degrees of freedom of movement, 3 rotations and 3 translations. Other robots are based on the so-called delta mechanics that use several parallel effectors to perform desired movements in order to decompose a complex trajectory into multiple more simple linear movements. However, each parallel effector introduces mechanical inter-component tolerances and mathematical transformations that are required to transform a recorded movement into the combination of movements to be performed by each effector. Bionic Jaw Motion Robot works differently, owing to three motors that perform translational movements and three other motors that perform rotations as a gyroscope. This configuration requires less mechanical components thus reducing mechanical tolerances and production costs. Both the jaw movement analyzer and the robot quantify the movement of the mandible as a rigid body with six degrees of freedom. This represents an additional advantage as no mathematical transformation is needed for the robot to reproduce recorded movements.

RESULTS

Based on the described procedure, Bionic Jaw Motion provide accurate recording and reproduction of maxillomandibular relation in static and dynamic conditions.

CONCLUSION

This robotic system represents an important advancement compared to available analogical and digital alternatives both in clinical and research contexts for cost reduction, precision and time saving opportunities.

Clinical considerations for increasing occlusal vertical dimension: a review

The purpose of this article is to discuss the clinical considerations related to increasing the occlusal vertical dimension (OVD) when restoring a patient's dentition. Thorough extraoral and intraoral evaluations are mandatory to assess the suitability of increasing OVD. In the literature, multiple techniques have been proposed to quantify OVD loss. However, the techniques lack consistency and reliability, which in turn affects the decision of whether to increase the OVD. Therefore, increasing OVD should be determined on the basis of the dental restorative needs and aesthetic demands. In general, a minimal increase in OVD should be applied, though a 5 mm maximum increase in OVD can be justified to provide adequate occlusal space for the restorative material and to improve anterior teeth aesthetics. The literature reflects the safety of increasing the OVD permanently, and although signs and symptoms may develop, these are usually of an interim nature. Whenever indicated, the increase in OVD should be achieved with fixed restorations rather than a removable appliance, due to the predictable patient adaptation. The exception to this is for patients with TMD, where increasing the OVD should still be achieved using removable appliances to control TMD-associated symptoms before considering any form of irreversible procedure.

Reliability and comparison of two facial measurements to detect changes of occlusal vertical dimension in complete denture wearers

BACKGROUND

Facial measurements are frequently used to determine OVD. However, the reliability of neither the method nor the chosen landmarks has been cleared yet.

OBJECTIVE

This study compares the reliability of two facial measurements, subnasal (SN) to chin (C) and tip of the nose (TN) to C, for determining occlusal vertical dimension (OVD).

MATERIALS AND METHODS

Thirty edentulous subjects with adequate neuromuscular co-ordination, without signs and symptoms of temporomandibular disorders and who had been wearing complete dentures for at least 5years were enrolled. A modified central bearing device was used to alter the OVD and facial measurements were made with a digital caliper. Student's t-test was used to compare the two measurements. Interobserver and intraobserver reliability were evaluated with Spearman's rho correlation test.

RESULTS

TN-C distance had an improved correlation with the changes in intraoral alterations than SN-C distance. While the means of the changes in facial measurements were in good agreement with the intraoral alterations, the ranges were wide. Both interobserver and intraobserver reliability of the measurements were high.

CONCLUSION

While facial measurement is not a good predictor of OVD, TN-C distance appears to be more reliable than SN-C distance.

A comparison of the accuracy of two methods used by pre-doctoral students to measure vertical dimension

STATEMENT OF PROBLEM

Measuring vertical dimension is a soft-tissue measurement. Therefore, inaccuracy may occur.

PURPOSE

The purpose of this study is to compare the accuracy of the Willis gauge method with the caliper method.

MATERIALS AND METHODS

The Willis gauge measures the distance between the septum of the nose and the chin. The caliper method measures the distance between reference points on the tip of the nose and the chin. Twenty predoctoral students applied both methods 10 times in measuring the rest vertical dimension (RVD) and the occlusal vertical dimension (OVD) of a single edentulous patient. The measurements obtained from one experienced clinician were selected as controls for the interocclusal distances (IOD) for the Willis and the caliper methods, respectively. One-sided t tests and a 1-sided nonparametric test were used to determine significant differences between the 2 methods (alpha=.05).

RESULTS

The variances in the RVD values for the Willis gauge method were higher than for the caliper method for most students. A Wilcoxon signed rank test showed that the accuracy of the OVD measurements for the caliper method was significantly better than for the Willis gauge method (P=.001). This was not the case for the RVD measurements (P=.073). The average IOD for the Willis method was significantly higher than the control IOD (P=.026). The average IOD for the caliper method was not significantly larger than the control (P=.1303).

CONCLUSION

This study showed that the use of the caliper method by predoctoral students was a significantly more reliable method of measuring the OVD for the patient evaluated.

Mandibular rest position: a reliable position influenced by head support and body posture

This prospective study was designed to establish how the positions of the molars and the condyles are related to incisor position in the mandibular rest position and how their positions are altered by changing head posture. Measurements of the mandibular rest position were taken on 24 men (age range, 23 to 35) with normal Class I occlusion, skeletal patterns, and temporomandibular joint function. The movements of 5 landmarks (lower incisor, and condyles and molars bilaterally) were tracked from maximum intercuspation into 4 independent rest positions (upright supported, upright unsupported, supine supported, and supine unsupported) using an optoelectric (Optotrak; Northern Digital, Waterloo, Ontario, Canada) computer system. The positions were based on minimal electromyographic and verbal instructions to swallow, lick the lips, and say "Mississippi." The results showed significant (P <.01) movements of the incisors, the molars, and the condyles into each of the 4 rest positions. Movements of the molars and the condyles into the supported upright posture and the unsupported upright posture differed slightly but significantly because of greater movement into the supported posture. Patterns of mandibular movement were entirely different between the upright and the supine rest positions; the mandible rotated anteriorly in the supine position and posteriorly in the upright position. We concluded that movement into the mandibular rest position from the intercuspal position is not a simple opening rotation of the mandible, and that the pattern of movement is influenced by head support and body postures.

Vertical dimension. Part 1: comparison of clinical freeway space

This study was conducted in order to compare the clinical freeway space measurements using three simple methods commonly used by dentists in their practices. The study was performed in 15 young healthy subjects with natural dentition and bilateral molar support. Artificial landmarks (adhesive tape) were placed on the more prominent parts of the nose and chin of each subject. Vertical dimension of occlusion (VDO) was measured in the intercuspal position. Postural vertical dimension (PVD) was measured in the following functional conditions: after swallowing saliva, after pronouncing the word "Mississippi", and in a relaxed postural mandibular position (RPMP). Then, the clinical freeway space value in each functional condition was obtained by subtracting VDO from PVD value. Significant differences among clinical freeway space values using three different methods were observed (ANOVA). A significantly higher clinical freeway space value was found using phonetics method than after swallowing and with the mandible in a relaxed postural position (Bonferroni multiple comparison test). No significant differences between swallowing and relaxed methods were found. These results seem to suggest that the measures of clinical freeway space depend upon the method used.

Regulation of mandibular postures: mechanisms and clinical implications

This review argues that (1) the habitual mandibular position is constantly variable and so cannot be considered as a craniomandibular reference point, (2) there is no unique centric relation, (3) mandibular posture greatly depends on head posture, (4) clinical evaluation of the occlusal vertical dimension is mostly empirical, and (5) neither the vertical dimension at rest nor the centric relation can be determined by means of existing instrument-based clinical methods. However, some physiological conditions exist that facilitate the recording of craniomandibular position.

Influence of lower lip support on recording of vertical dimension in edentulous patients

The purpose of this investigation was to assess the influence of differences in design of the occlusion rim on recorded vertical dimension in complete denture therapy. Edentulous patients were studied with an opto-electronic method when the vertical dimension of rest was established with and without labial support of the occlusion rim. As no significant differences were found, the results did not support the hypothesis that the contour of the lip support will influence the recorded physiological rest position. However, a significant difference between intra and extraoral placement of the point of measurement was found.

Relationship of occlusal vertical dimension to the health of the masticatory system

Changes in occlusal vertical dimension have been claimed to cause masticatory system disorders. Early articles on this subject were mainly limited to clinical case reports, and the more recent clinical studies have been flawed by the lack of control groups, blind evaluation, and by poor definition of criteria for evaluating the health of the masticatory system. Research with humans and animals has shown that if increases in occlusal vertical dimension are not extreme and the appliance used covers most of the dentition, there is a good possibility of adaptation. Current scientific knowledge does not support the hypothesis that moderate changes in occlusal vertical dimension are detrimental to the masticatory system.

The unreliability of facial measurements in the determination of the vertical dimension of occlusion in edentulous patients

The aim of this research was to test the reliability of skin markers in the determination of the V.D.O. in edentulous patients during prosthetic rehabilitation. Two resin baseplates were constructed: on the upper one a modified pin of the Central Bearing Point registration device was fixed with impression compound. The height of the pin could be altered by rotating the pin directly in the patient's mouth with a probe. Two lead spheres were inserted on the resin base-plate as bone markers, and two others were fixed to the skin as markers, one above (end of nose) and one below (point of chin) the oral commissure. Five lateral cephalometric radiographs were exposed for each patient, raising the V.D.O. by 1.2 mm on each occasion. Statistical analysis of measurements made on the resulting radiographs showed a very strong correlation between bone markers and pin position, whereas great variation and considerable differences were found between skin markers and bone as well as measurements.

The mandibular rest position and electromyography--a review

The objective of clinical methods for the establishment of the rest position of the mandible is to establish a position at which masticatory muscle activity is minimal. Several methods are in clinical use but these methods may not elicit a position which is coincident with the lowest level of muscle activity as determined electromyographically.

The relative movements of the chin and the mandible during chewing

The suitability of the soft tissue over the chin as a reference point in studies of mandibular performance during chewing was investigated. The movements of reference diodes (LEDs), one on the chin and the other attached to the lower front tooth, were registered simultaneously using the Selspot system and analysed in relation to the reference system in this method. With respect to chewing rhythm, the conformity of the behaviour of the two diodes-or the two tissue locations-was good, thus allowing the conclusion that the chin reference point is suitable for analysing chewing rhythm. Vertical displacement and velocity were less marked with the chin reference than with the tooth reference, however, indicating that the skeletal part of the mandible moves within the tissues envelope. The difference in movement at maximal opening was significant, the magnitude of the difference being between 12 and 20%. Lateral displacement seemed to be of similar magnitude, although a tendency towards larger movements of the chin point than of the tooth was found.

Interocclusal distance measurement comparing chin and tooth reference points

In a group of nine dentate students with a mean age of 23.1 years, a comparison of their interocclusal distances was determined using tooth and chin reference points. This determination was made with two reference LEDs, one attached to a lower tooth and the other attached to a point on the chin. These two LEDs were registered simultaneously using the Selspot system and analyzed with the use of a computer. Three different methods were used to establish the interocclusal distance: a phonetic method, a relaxation method, and a swallowing method. Independent of the method selected, there was a greater interocclusal distance recorded by the tooth-attached reference LED. This study indicates that, in the clinical determination of interocclusal distance, where a chin reference is used the dentist should be aware of this difference--especially when lip activity is involved.

Change in recurrent headache and mandibular dysfunction after treatment with new complete dentures

The changes in headache and mandibular dysfunction were studied in a group of forty-three complete denture wearers 6 months after treatment with new complete dentures. All patients completed a questionnaire and all were subjected to clinical examination of the function of the masticatory system. Eleven of the seventeen patients with recurrent headache reported less frequent headache 6 months after treatment and nine reported that the headache was less severe. There was also a statistically significant reduction of clinical signs of dysfunction of the masticatory system.

A clinical study of rest position using the Kinesiograph and Myomonitor

The clinical study was designed to study the vertical dimension of rest position and mandibular closure to maximum intercuspation of the teeth before, during, and after relaxation procedures on 14 subjects with stable dentitions. The findings call attention to the potential of both the Myomonitor and the Kinesiograph for research and clinical use, to the physiologic need for flexibility of the vertical dimension of rest position, and to the importance of measuring all three dimensions when examining the rest position.

Short-term changes in the perception of comfortable mandibular occlusal positions

In search of a new clinical method for determining the occlusal height of full dentures, the perception of the comfortable zone was studied in fifteen edentulous patients. In each experimental session perceptual changes were recorded from forty-four consecutive applications of a screw jack per subject. Two stages in perceptual acuity were found. An initial stage, in which only minor variations occurred among the final screw adjustments which the subjects made when they assessed the borders of the comfortable zone. In the ensuing stage greater variations emerged, indicating a deterioration in the ability of the subjects to discriminate.