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[Class II--vertical dimension].

The vertical dimension and its implication in the etiology of the class II are described. This dimension is analysed at the level of the cranial base, the maxillary and mandibular bones and alveolar processes. Then, the facial architecture as a whole is considered and particularly the key position of the upper molar. The dorsal and low position of these teeth in the hyperdivergent cases is fundamentally different from the one they occupy in the hypodivergent cases. The therapeutic approach is completely different in both cases and is illustrated by means of three deep overbite and three open bite cases.

Alveolar Process

Vertical dimension: a dynamic concept based on facial form and oropharyngeal function.

Craniofacial vertical dimension is a more accurate measure of facial proportion than mere measurement of the mid and lower part of the face. Craniomaxillary dimension is skeletally determined, whereas facial height of the lower part of the face is partly dependent on the vertical dimension of occlusion. Alterations in the vertical dimension of occlusion can dramatically affect the esthetics of the soft facial tissue. The "Golden Proportion" quantitatively defines ideal measured relationships and encourages a scientific appreciation of beauty. Faces with deficiencies in lower facial balance (brachyfacial) often exhibit insufficient height of the occlusal plane. The scientific literature has suggested a pliability of skeletal muscle allowing for physiologic variance in vertical facial height. Temporomandibular joint compliance is demonstrated with elevations in resting muscle length. Facial balance and location of the occlusal planes are the primary determinants for establishing an appropriate vertical dimension of occlusion.

Electromyography

A preliminary investigation into the effect of increased occlusal vertical dimension on mandibular movement during speech.

Current methods of determining whether a patient will accommodate to an increased occlusal vertical dimension rely on a largely subjective assessment of the mandibular rest position and capacity to adapt whilst wearing a temporary appliance. The purpose of this preliminary study was to establish if mandibular movement during speech may provide an objective criterion in the assessment of adaptation to increases in occlusal vertical dimension. The closest speaking space, measured as the vertical distance between an incisor point and centric occlusion, as determined during pronunciation of sibilant speech sounds was chosen to depict mandibular movement. The closest speaking space was determined using a Sirognathograph for six young adult subjects and varied from a mean of 1.0 to 3.3 mm. An acrylic splint covering the entire occlusal surface of the lower arch, designed to increase the occlusal vertical dimension by 4 mm in the incisor region, was then cemented on each subject's mandibular arch. The closest speaking space was again determined after 5 days continuous wear of the splint and the mean values found to have decreased to a range of 0.0-1.0 mm. The differences between the mean values for the closest speaking space for each subject before and after splint wear were statistically significant. It was postulated that this method may lead towards an objective basis for deciding if patients will adapt to an increase in occlusal vertical dimension.

Adaptation, Physiological

Occlusal vertical dimension changes in visible light-cured resin.

On a twenty standard, identical edentulous upper and lower casts, an identical upper and lower waxed-up sets of dentures were constructed with same vertical dimension of occlusion. These waxed up dentures were divided into two equal groups. For group I, the dentures sets were processed in compression molding heat-cured acrylic resin denture base material. For group II, the denture sets were processed in visible light-cured denture base material. After processing the vertical dimension of occlusion was measured for every denture set in both groups. It was found that there was an increase in the vertical dimension of occlusion on group I and a decrease in the vertical dimension of occlusion in group II. Regardless of the direction of the changes in the vertical dimension of occlusion, it was found that there was a significant difference between the dimensional changes in both groups and the dimensional changes in the denture bases of group I was more than group II by 54.5%.

Acrylic Resins

The relationship of vertical dimension of atypical swallowing with complete dentures.

A number of subjects were studied cineflourographically during swallowing, and their vertical dimensions of occlusion were clinically evaluated. The subjects who had reduced vertical dimensions of occlusion were older than those with normal vertical dimensions, their dentures were older, their total years with complete dentures were more, and the tendency to swallow without opposing tooth contact was greater. The cumulative evidence indicates that such aberrant muscle activity might contribute to the regressive changes found in complete denture wearers.

Aged

Rest vertical dimension determined by electromyography with biofeedback as compared to conventional methods.

This study was undertaken to determine if electromyography with biofeedback can be utilized to produce a more reliable determination of rest vertical dimension than conventional methods such as phonetics and swallowing. It was found that: 1. Electromyography with biofeedback appeared to produce a more consistently reliable determination of rest vertical dimension than conventional methods when used with edentulous subjects. 2. Determinations of rest vertical dimension by individual dentists using phonetics and swallowing had wide variations in two of the five patients in a range of up to 6 mm. An error of this magnitude could easily cause an intrusion upon the interocclusal distance and resultant failure of treatment. Since this study was limited to five patients, a more expanded study is necessary to determine the validity of electromyography vs. conventional methods for determining rest vertical dimension. Both methods have questionable aspects in relation to the time of day, patient's understanding of each technique, and past dental history. However, the most critical problem of the electromyographic technique is the feasibility of its use in a private practice in light of the excessive cost of the required equipment.

Biofeedback, Psychology

Preservation of occlusal vertical dimension in overdentures.

The preextraction record is used to reestablish the occlusal vertical dimension in immediate and in later overdentures. A colored dot on the denture can be used to verify the occlusal vertical dimension after the dentures have been inserted.

Dental Records

An experimental study of increased vertical dimension in the growing face.

Five juvenile rhesus monkeys were used in an experiment designed to study the structural adaptations in the craniofacial complex that resulted from increases in vertical dimension. The bite was opened 2,3,10, or 15 mm. by means of cast bite splints cemented on the maxillary arch. Adaptations were monitored in these animals by means of serial cephalometric radiography with metallic implants. The results of this study indicate that any change in the vertical dimension of the face results in specific structural adaptations throughout the craniofacial complex. The most significant adaptation occurred in the maxillary region, in which the normal downward displacement of this region was decrease and the anterior displacement was increased. Adaptation were less evident in the mandible, except in those animals in which a severe bite opening was produced; resorption in the region of the gonial angle was evident. Dentitional adaptations were of secondary importance. This study demonstrates that the maxillary complex is a very plastic structure which responds to changes in bite opening and altered muscle length. The clinician should be aware of the changes that result from various alterations of vertical dimension to make sure that these changes are not antagonistic to his over-all treatment goal. He may also take advantage of these changes when designing treatment strategies for certain clinical cases.

Animals

A new method for positioning the maxillary anterior arch, orienting the occlusal plane, and determining the vertical dimension of occlusion.

A new method for positioning the maxillary anterior arch, orienting the occlusal plane, and establishing the vertical dimension of occlusion in edentulous patients is described. The procedure uses a newly developed registration pin assembly that is fixed to the maxillary acrylic resin baseplate. The vertical dimension of occlusion is determined by having the patient swallow. This approach eliminates the tedious and time-consuming process of trimming the occlusion wax rims. The accuracy of the new method is currently being evaluated.

Deglutition

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.

Aged

Vertical dimension increases in the adult rhesus monkey: a pilot study.

Tooth impaction, increased muscle activity, and histologic changes in the bone of the temporomandibular joint have been reported following attempts to increase the vertical dimension of occlusion. The purpose of this research was to study the effects of increases in the vertical dimension of occlusion on bone density at five levels of the mandible in the adult rhesus monkey, and to assess dentoalveolar changes by lateral cephalometric radiographs and mounted diagnostic casts. Mandibular cobalt chromium splints measuring 3 mm in height at the first molar, providing even occlusal contact to the maxillary anterior and posterior teeth, were cemented in place on two monkeys. Five similar monkeys without splints were used as controls. Computed tomograms were completed to evaluate bone density bilaterally at five levels of the mandible after 3 months of splint wear. Pretreatment and posttreatment lateral cephalometric radiographs and mounted diagnostic casts were completed to assess tooth impaction. Periodontal ligament (PDL) thickening and mobility of molars and premolars were evaluated before splint placement and after splint removal. There was no statistically significant difference in the bone density levels of the animals with splints compared with the controls. Minimal dentoalveolar changes were observed.

Animals

Regressive formula to determine vertical dimension in the edentulous.

The distances between the cephalometric points of 380 patients with complete natural dental arches were measured. A correlation between the bizygomatic, nasion-subnasal and subnasal-gnathion distances and the vertical dimension was established and a mathematical formula was derived to enable determination of both the physiologic rest position and vertical dimension at centric occlusion in edentulous patients.

Cephalometry

The inapplicability of formulae to determine vertical dimension.

The accuracy and precision of certain external cephalometric measurements were investigated on a subject presenting optimal conditions, using ten operators. Due to difficulties in identifying landmarks and tissue compressibility, the standard deviation of a measurement for ten replications ranged from 0 . 3 to 1 . 7 mm, while the "between operators" standard deviation was no better than 2 . 0 mm. Measurement accuracy was also poor: that of primary interest, subnasale-gnathion, had a bias of the order of 7 mm, judged by a radiographic determination. A minimum denture success rate of 97% is equated with a standard deviation of 1 mm in the design freeway space. A recently published regression equation for predicting occlusal vertical dimension has a minimum error of prediction of 5 . 8 mm and thus is considered an inadequate predictive tool. The errors demonstrated in facial measurements suggest that using formulae to predict occlusal vertical dimension is unlikely to produce clinically acceptable results.

Cephalometry

Control of vertical dimension during maxillary orthognathic surgery. A clinical trial comparing internal and external fixed reference points.

The accuracy of vertical control during maxillary orthognathic surgery was assessed in 45 patients, comparing the use of traditional internal measurements across the osteotomy lines (15 subjects) with measurements between the incisor teeth and an external reference point consisting of a bone screw placed at nasion (two groups of 15 subjects each). Although use of a fixed external reference point can significantly decrease positioning error (p < 0.001), considerable care is required during application of rigid fixation to maintain the correct vertical dimension.

Bone Plates

A comparative study of two methods for the orientation of the occlusal plane and the determination of the vertical dimension of occlusion in edentulous patients.

The aim of this study was to compare two methods used to orientate the occlusal plane (OP) and to determine the vertical dimension of occlusion (VDO). In method A the VDO was established by means of the rest position, the minimal speaking distance, and the patient's profile. Method B used a newly developed registration pin assembly. The VDO was registered using a silicone occlusion rim and the swallowing technique. The results were compared to the values of the new dentures. Three standardized lateral radiographs were taken at the VDO obtained with methods A, B, and at that of the final dentures. On each radiograph the orientation of the OP to the Camper plane and the VDO were measured by two investigators independently. The results indicated no statistically significant differences between the mean VDO with method A and B compared with the new dentures (P greater than 0.05). With both methods it was not possible to orientate the OP parallel to the Camper plane. None of the occlusal planes of the new dentures were parallel either. Their OP diverged on average by 7 degrees dorso-caudally. The time spent with method B to orient the OP and to determine the VDO was significantly lower than with method A (17-50 min).

Adult

Variability of the nasion-subnasal, subnasalgnathion, and bizygomatic distances of individuals of 6, 7, 11, and 15 years of age and their importance in the determination of the vertical dimension.

A study of the cephalometric points which represent the height and width of the face was undertaken in the city of Piracicaba on 576 boys and girls aged 6, 7, 11, and 15 years. Analysis of the data shows that the measurements increased progressively and proportionately with age and the importance of the cephalometric points in the determination of the vertical dimension in occlusion.

Adolescent

Alteration of vertical dimension and its effect on head and neck posture.

Previous research has shown a relationship between head posture and rest position of the mandible. Should this relationship really be an interrelationship? Does a change in mandibular posture alone also alter head and neck posture? The purpose of this article is to demonstrate how a change in mandibular posture, specifically an increase in vertical dimension, contributes to craniovertical extension leading to suboccipital compression and upsetting the postural balance between the head and neck. A model of physiologic equilibrium is presented for the craniomandibular articulation.

Adaptation, Physiological