Increase In Occlusal Vertical Dimension Research Articles

An involvement of trigeminal mesencephalic neurons in regulation of occlusal vertical dimension in the guinea pig.

Although the occlusal vertical dimension (OVD) is strictly controlled, the neuronal mechanism of its regulation is still unclear. We hypothesize that neurons in the trigeminal mesencephalic nucleus (MesV) play an important role in the regulation of the OVD, because the MesV receives the projection from jaw-closing muscle spindles and periodontal mechanoreceptors. We measured the temporal OVD change in the guinea pig to study the effects of MesV lesions on the OVD. OVD-raised animals without MesV lesions showed a rapid OVD decrease to the same level as that in naïve controls, followed by an OVD increase after the OVD-raising appliance was removed. In contrast, OVD-raised animals with MesV lesions showed only a slight decrease in the OVD for 15 days after removal of the appliance, and then the OVD increased. The time-course of OVD development in normal-bite animals with MesV lesions was similar to that of naïve controls. These results suggest that MesV neurons are involved in OVD regulation.

Adaptation of Guinea-pig superficial masseter muscle to an increase in occlusal vertical dimension

To study the effect of increased occlusal vertical dimension on the fibre phenotypes of the superficial masseter muscle, the composition of myosin heavy-chains (MHC), myosin light-chains (MLC) and tropomyosin was investigated by sodium dodecyl sulphate–polyacrylamide gel electrophoresis and two-dimensional gel electrophoresis in conjunction with densitometric analysis in normal (control) and bite-opened (5.7 mm increase in the vertical dimension for 1 week) guinea-pigs. The superficial masseter contained two fast-type MHC isoforms, II-1 and II-2, in both the bite-opened and control groups; their relative content (mean±SD, n=7) was 47.8±2.9% and 52.2±2.9%, in the bite-opened and 44.4±3.0% and 55.6±3.0% in control preparations, indicating no significant ( p>0.05) changes in MHC composition in association with the bite opening. On the other hand, significant differences in MLC and tropomyosin composition were found between the two preparations. Although the MLC consisted of three components, LC1f, LC2f and LC3f, in both preparations, their relative content (mean±SD, n=7) was 37.1±2.4%, 49.6±1.6% and 13.2±3.2%, respectively, in the bite-opened and 28.1±3.1%, 50.9±1.6% and 21.0±3.5% in the control preparations, indicating that the bite opening induced a significant ( p<0.0001) increase in the relative content of LC1f at the expense of that of LC3f. Although the tropomyosin consisted of two components, TM- α and TM- β, in both preparations, their relative content (mean±SD, n=7) was 91.8%±1.9% and 8.2±1.9%, respectively, in the bite-opened and 95.9±0.7% and 4.1±0.7% in the control preparations, showing a significant ( p<0.001) increase in the relative content of TM- β in relation to the bite opening. These results indicate that in guinea-pigs an increase in occlusal vertical dimension for 1 week changes the composition of MLC and tropomyosin, with no significant change in MHC, in the masseter muscle. These changes might be required to meet altered functional demands.

A 2-year follow-up of mandibular posture following an increase in occlusal vertical dimension beyond the clinical rest position with fixed restorations.

While resting mandibular posture is continuously changing, repeatable relations of 'physiologic rest position' (PRP) and 'clinical rest position' (CRP) are described in the literature. The PRP is defined as a position of minimal muscle activity and CRP as a more closed clinical reference relation. Relaxed resting posture (RRP) is a repeatable postural range obtained by operator-induced relaxation techniques. This article reports on measurements of mandibular posture in a patient group following an increase in occlusal vertical dimension (OVD) with fixed restorations beyond CRP over 2 years. The relationship of CRP and RRP in the restored and a non-restored control group is compared. The relationship of RRP and corresponding masseteric EMG values to baseline minimal EMG levels is reported for both groups. Resting face height adapted to the increased OVD and remained consistent over 1 and 2 years. The RRP was greater and significantly different from CRP in both groups (P = 0.0001). Results indicated that both CRP and RRP were postural ranges and not specific postural positions. The RRP occurred at minimum baseline EMG levels for both groups and appears to be consistent with physiologic rest position. The possibility of achieving minimal EMG levels at varying interocclusal rest space relations is discussed.

Effect of an increase in occlusal vertical dimension on the rate of cyclic actin-myosin interaction in guinea-pig masseter muscle

To study the effects of increased occlusal vertical dimension on these kinetics, the actin-filament sliding velocity on masseter myosins in an in vitro motility assay and the ATPase activity of masseter myosins from normal (control [and bite-opened (5.6 mm increase in the vertical dimension for 1 week (guinea.-pigs were measured. In control myosin preparations, the average value ( mean ± SD, n = 5) for the actin-filament sliding velocity at 25°C was 4.0 ± 0.3 μm/sec. In bite-opened myosin preparations ( n = 5), it was 3.4 ± 0.3 μm/sec a significant ( p < 0.01) decrease. Myosin ATPase activity was also decreased significantly ( p < 0.01) from 1.0 ± 0.1 to 0.7 ± 0.1 μmol Pi mg per min (mean ± SD, n = 5) after the bite opening. These results strongly suggest that in guinea-pigs an increase in occlusal vertical dimension for 1 week decreases the turnover rate of actin-myosin interaction in the masseter through charges in the myosin isozyme. These changes may result in a slowing of the rate of detachment of myosin cross-bridges from actin filaments.

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.

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.

開口量と下顎伸張反射との関係 こう筋α運動ニューロンの興奮レベル

The purpose of this study is to investigate the relationship between the incisal opening and the amplitude of the jaw-jerk reflex in the human beings.The findings were summerized as follows;1. The amplitudes of jaw-jerk reflexes were decreased according to the increase of incisal opening.2. In all subjects, jaw-jerk reflexes were not evoked at mostly maximum jaw opened.3. The regression lines between the amplitudes of the reflex and the displacements of the incisor elicited by the chin tapping at the different jaw openings suggest two different ways of the decreases of the reflex amplitude. The first is the increase of the threshold of the jaw-jerk reflex circuit and the second is the decrease of the sensitivity of the reflex circuit. The considerable mechanism for these changes of the reflex circuit are as follows;a. The membrane potential changes of α-motoneurons, that is depolarization or hyperpolarization.b. The change of muscle spindles sensitivity which is controlled by γ-motoneuron activity.c. Primary afferent depolarization could change the efficiency of the synaptic transmission from Ia afferents to α-motoneurons.These findings suggest that the increase of occlusal vertical dimension by such as occlusal splints for temporomandibular joint disoders could lead the relaxation of jaw-closing muscles and susseedingly doctors are able to improve the occlusion of the patients easier.

An electromyographic study of masticatory muscle activity at increased occlusal vertical dimension in complete denture wearers

I t is a common clinical experience that patients wearing complete dentures at an increased occlusal vertical dimension (OVD) will suffer discomfort and complain that the dentures feel “too big.” At one time this discomfort was said to be an attempt of the muscles of mastication to return the mandible to its predetermined rest position.’ However, the concept that mandibular rest position is stable throughout life is no longer accepted,“5 but that the mandible can adapt to a rest position at an OVD Provided by the dentures.6 The idea now proposed is that at an increased OVD there is increased muscle activity during function, instead of an attempt to return the mandible to a rest position. This investigation tested this idea by recording the quantitative level of muscle activity occurring during function at increased OVD. The activity levels were recorded on an electromyograph (EMG), and a summation integrator was used to permit accurate measurement of the recorded activity.

ポリエーテルサルホン樹脂の補綴臨床への応用に関する基礎的研究第 1 報

Recently, polyethersulfone resin (PES), substituing for acrylic resin, has been introduced as a denture base material. PES excells in mechanical properties, thermal resistance, and abrasive resistance, and is stable chemically, and has no harmful effect on the oral mucosa. Thus, PES appears to have favorable properties for a denture base material. There are, however, some unclear aspects in its manageability and clinical applications. Therefore, an investigation was made of its plasticity, vertical dimensional change of artificial tooth at molding of the denture, bonding strength of artificial tooth to PES, deformation at molding. The results were as follows : 1. The test portion was selected under the clasp tang where considered to be the most difficult to mold and the feasibility of packing was examined. As a result, it was found that relief of 0.65mm and over would be required to pack under the clasp tang completely. 2. Examination of rising of artificial tooth at molding the denture, the eliminable area changing to 3, 6, and 10mm, showed that increase in the width of eliminable area tended to increase the extent of rise of artificial tooth. Making the width of the eliminable area 3mm, resulted in 0.17 ± 0.09mm rise and the effect on occlusal vertical dimension increase was made small. 3. The bonding material specified for PES did not produce satisfactory bonding strength of artificial tooth to PES. Only when undercut had been given on the base of the artificial tooth, the bonding strength of artificial tooth similared to that to heatcured polymerized resin. 4. A mold shrinkage rate of PES was rather large with 4.4 ± 0.3%.

Histologic changes in rat masticatory muscles subsequent to experimental increase of the occlusal vertical dimension

Histologic changes in various masticatory muscles were studied in Wistar rats from 12 hours to 84 days after an experimental increase of the occlusal vertical dimension. The increases applied (1 to 2 mm) were based on the amount of interocclusal space (1 mm) in the rat. A sequence of tissue reaction from early acute inflammatory destruction of myofibers to healing with myofiber regeneration was most pronounced in the deep masseter muscle of the 2 mm group (12 hours to 21 days). A similar sequence was also observed to a lesser degree in the superficial masseter and anterior temporal muscles, while no changes were detectable in the posterior temporal, medial pterygoid, and anterior digastric muscles of this group. Variable severity of tissue response in different masticatory muscles might be attributable to the amount of stretching of myofibers as a result of an increased occlusal vertical dimension. On the other hand, degenerative atrophy of myofibers in the lateral pterygoid muscle occurred within 2 days with no sign of inflammation, and these condensed myofibers persisted as late as 84 days. Based on these findings, it was suggested that displacement of the mandibular condyle would exert an important influence on the prognosis after an increase in the occlusal vertical dimension. Only a transient acute inflammation occurred in the deep and superficial masseter muscles in the 1 mm group. Except for a small number of condensed myofibers in the lateral pterygoid muscle, degenerative changes of myofibers were not revealed. Therefore, increasing the occlusal vertical dimension within the extent of the interocclusal space might be regarded as appropriate for prosthodontic practices.

Periodontal traumatism produced by sustained increase in occlusal vertical dimension: a histopathological study.

Periodontal traumatism produced by sustained increase in occlusal vertical dimension: a histopathological study.

Near or full occlusal vertical dimension increase of severely reduced interarch distance in complete dentures

The primary purpose of this study was to determine whether a large occlusal vertical dimension increase could be restored immediately with new complete dentures. The increase was recorded with cephalograms and was measured. After a six-month period, a third cephalogram was made to record any change of the occlusal vertical dimension. No destruction of tissue was in evidence by this immediate occlusal vertical dimension increase, and subject acceptance was good.