Effects of increased occlusal vertical dimension on the jaw-opening reflex in adult rats

ObjectiveMalocclusion with deep overbite and facial esthetics improve when facial height is intentionally increased during orthodontic extrusion of the posterior teeth. Thus, a better understanding of post-treatment stability of increased occlusal vertical dimension (iOVD) in adult patients is important. We focused on the jaw-opening reflex (JOR), which plays an important role in the control of jaw movements during mastication, and investigated the effects of iOVD on the JOR in rats with an electrophysiological technique.DesignOne hundred and twenty 13-week-old male Wistar rats were randomly divided into control and experimental groups. Rats in the experimental group received a 2-mm buildup of composite resin on the maxillary molars at 13 weeks of age. The JOR was induced by low-intensity electrical stimulation of the left inferior alveolar nerve. The electromyographic responses were recorded from the digastric muscle at 13, 14, 15, 17, 19, and 23 weeks of age. JOR properties including latency, duration, and peak-to-peak amplitude were measured and compared between the groups.ResultsThe latency of the JOR was significantly longer and the peak-to-peak amplitude was significantly smaller in the experimental group than in the control group from 14 to 19 weeks of age, while the reflex duration was not significantly different. Intra-group comparisons of the latency and peak-to-peak amplitudes among rats 14–19 weeks of age were significantly different between the experimental group and the control group.ConclusionsiOVD affected the latency and amplitude of the JOR but not the duration. The JOR adapted after 10 weeks of iOVD.     

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提要：颞下颌关节紊乱病（TMD）是口腔临床常见病之一，其治疗方法众多。咬合板作为一种保守、可逆的治疗方法被广泛应用在TMD的治疗上。然而，各类咬合板治疗TMD的疗效尚不完全明确，本文结合近年来国内外文献对其进行综述。     

Does altering the occlusal vertical dimension produce temporomandibular disorders? A literature review

The purpose of this review was to present a comprehensive review of the scientific evidence available in the literature regarding the effect of altering the occlusal vertical dimens‐ion (OVD) on producing temporomandibular disorders. The authors conducted a PubMed search with the following search terms ‘temporoman‐dibular disorders’, ‘occlusal vertical dimension’, ‘stomatognatic system’, ‘masticatory muscles’ and ‘skeletal muscle’. Bibliographies of all retrieved articles were consulted for additional publications. Hand‐searched publications from 1938 were included. The literature review revealed a lack of well‐designed studies. Traditional beliefs have been based on case reports and anecdotal opinions rather than on well‐controlled clinical trials. The available evidence is weak and seems to indicate that the stomatognathic system has the ability to adapt rapidly to moderate changes in occlusal vertical dimension (OVD). Nevertheless, it should be taken into consideration that in some patients mild transient symptoms may occur, but they are most often self‐limiting and without major consequence. In conclusion, there is no indication that permanent alteration in the OVD will produce long‐lasting TMD symptoms. However, additional studies are needed.     

升高患者咬合垂直距离的修复计划

咬合垂直距离(occlusal vertical dimension,OVD)在临床上指牙尖交错位(intercusp position)时面下1/3的高度.狭义的OVD被定义为由升颌肌群重复收缩所决定的牙萌出空间,即肌力决定牙列空间[1].各种原因导致肌张力增大,将威胁牙列空间,导致牙列萌出不足或异常磨耗.而肌张力的维持取决于中枢神经系统的控制[2].     

Effect of occlusal vertical dimension on swallowing patterns and perioral electromyographic activity

Abnormal swallow patterns have been associated with specific dentofacial traits, such as an anterior open bite, but the cause–effect relationship between swallowing and malocclusion remains highly controversial. The aim of this research was to determine the effects of acute change in occlusal vertical dimension (OVD) on intraoral pressure swallow patterns and perioral electromyographic activity (EMG) during swallowing. Ten volunteers (five female, five male; 27–32 years) repeated standardised swallowing tasks as the OVD was progressively increased using mandibular trays of different heights. Standardised swallowing tasks were performed repetitively with each tray in place. Individual swallowing waveforms were quantitatively and qualitatively analysed. Peak pressure, swallow duration, time to peak pressure and lip EMG peak activity were assessed for each swallow. Data were analysed using mixed‐model analysis. As OVD increased, lip peak pressure during swallowing increased almost threefold (+2·1 kPa; P ≤ 0·001), whereas swallow duration increased by 12·7 per cent (+160 ms; P = 0·01) at lip level and by 26·4 per cent (+270 ms; P < 0·001) at tongue level. Perioral muscle activity during swallows increased by 43·7 per cent (P ≤ 0·01) up to the OVD where resting lip seal was not attainable. Swallowing waveforms varied markedly between individuals, but interindividual waveforms were only minimally affected. The adaptive response and the waveform similarities associated with OVD variation supports the existence of a central control mechanism for swallowing, which may be modified by peripheral inputs.     

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.     

Role of occlusal vertical dimension in spindle function

Several studies have suggested the jaw-muscle spindle as the receptor responsible for regulating and maintaining the occlusal vertical dimension (OVD). However, to challenge this assumption, we hypothesized that long-term changes in OVD could affect the sensory inputs from jaw-muscle spindles. In this study, we investigated changes in masseter muscle spindle function under an increased OVD (iOVD) condition. Responses of primary and secondary endings of masseter muscle spindles to cyclic sinusoidal stretches were investigated. Twenty barbiturate-anesthetized female Wistar rats were divided into control and iOVD groups. Rats in the iOVD group received a 2.0-mm composite resin build-up to the maxillary molars. After iOVD, masseter muscle spindle sensitivity gradually decreased. Primary and secondary spindle endings were affected differently. We conclude that iOVD caused reduction in masseter muscle spindle sensitivity. This result suggests that peripheral sensory plasticity may occur following changes in OVD. Such changes may provide a basis for physiological adaptation to clinical occlusal adjustments.     

一种新的咬合垂直距离升高动物模型建立方法及评价

目的探讨大鼠咬合垂直距离升高（iOVD）动物模型的可重复更好的建模方法，及OVD升高对大鼠牙体牙周、颞下颌关节及全身体重的影响。方法60只成年Wistar大鼠．平均分为对照组和iOVD组（双侧上颌后牙戴1．5mm咬合板）．运用修复技术完成iOVD咬合板的制作和黏结，分别在实验3天、1周、2周、3周、4周处死动物。观察项目包括体重分析、头侧位X线片、头颅标本解剖、下颌磨牙区骨段及髁状突组织学切片观察等。结果两组大鼠体重增长差异无统计学意义（P〉0．05）。头侧位X线片示iOVD组大鼠髁突位置前移。上切牙腭侧磨耗面发生改变。iOVD组大鼠磨牙根分又区牙槽骨及髁状突中后区软骨出现组织学形态改建。结论采用修复技术可成功建立成年期大鼠咬合垂直距离升高动物模型．咬合板的戴入引起了牙体牙周组织和颞下颌关节髁状突软骨的组织适应性改建．但对全身营养摄入无影响。     

低位咬合伴颞下颌关节结构紊乱患者的咬合重建治疗临床效果分析

目的：对低位咬合伴颞下颌关节结构紊乱患者进行咬合重建修复,分析其临床效果。方法：观察14例符合条件患者治疗前、暂时性胎垫治疗后、永久性修复治疗后临床症状、关节间隙及肌电图的变化。结果：（1）暂时性胎垫及永久性修复治疗后临床症状和关节间隙与治疗前相比,结果均有统计学意义（P〈0．05）。（2）静息状态下胎垫治疗及永久性修复后,颞肌前束（TA）和咬肌（MM）肌电活动减弱,有统计学意义（P〈0．05）;但在最大紧咬状态下胎垫治疗后肌电活动变化无统计学意义（P〉0．05）,而永久性修复后肌电活动显著增强,变化有统计学意义（P〈0．05）。结论：咬合重建缓解了颞下颌关节相关症状,永久性修复较暂时性修复达到了更为理想的咬合接触状态,咬合过程中咀嚼肌的功能得到了充分的发挥。     

Response properties of the jaw--closing muscle spindle during decreased occlusal vertical dimension in rats

The masseter-muscle spindle is regarded as being highly adaptable to increases in the occlusal vertical dimension (iOVD), it is hypothesized that spindle function would adapt to a decrease in occlusal vertical dimension (dOVD) as well. Seventy-five 5-week-old female Wistar rats were divided into Control (n = 25) and Experimental (n = 50) groups; those in the Experimental group received a 2.0-mm composite resin build-up to the maxillary molars. The Experimental group was divided into the resin-removal group (n = 25, build-up resin was removed) and the non resin-removal group (n = 25) 8 weeks later; i. e., when the animals were 13 weeks old. Electrophysiological recordings were obtained from masseter-muscle spindle afferents in 13, 14, 15, 19, 21-week-old rats (n = 5 rats each) under general anesthesia Masseter-muscle spindle sensitivity was significantly lower in the resin-removal group 1 week after resin-removal and for the rest of the observation period. The present results indicate that masseter-muscle spindles may not completely adapt to dOVD and may affect jaw function.     

Effects of increased occlusal vertical dimension on daily activity and myosin heavy chain composition in rat jaw muscle

Mammalian skeletal muscles change their contractile-protein phenotype in response to mechanical loading and/or chronic electrical stimulation, implying that the phenotypic changes in masticatory muscles might result from new masticatory-loading conditions. To analyze the effects of increased occlusal vertical dimension (OVD) on daily activities and fibre-type compositions in jaw muscles, we measured the total duration of daily activity (duty time) and the myosin heavy chain (MyHC) compositions in the masseter and digastric muscles of freely moving control and bite-opened rats. In the control state, the duty time of the digastric muscle was higher than that of the masseter muscle at activity levels exceeding 5 and 20% of the day's peak activity. The opposite was true at activity levels exceeding 50 and 80% of the day's peak activity. The MyHCs consisted of a mixture of fast and slow types in the digastric muscle. The masseter consisted of mostly fast-type MyHC. The increment of OVD increased not only the duty time at activity levels exceeding 5, 20, 50 and 80% of the day’ peak activity in both muscles but also the proportion of MyHC IIa in the masseter muscle and MyHC I in the digastric muscle at the expense of that of MyHC IIb. These results suggest that the increment of OVD changes masseter and digastric muscles towards slower phenotypes by an increase in their daily activities.     

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.     

The effect of increasing occlusal vertical dimension on face height

PURPOSE: This study evaluated the effect of increasing occlusal vertical dimension (OVD) on the face height in completely dentate young adults. MATERIALS AND METHODS: Faces of 22 subjects were photographed in a standardized manner in an anterior view. Sequential photographs were taken at intercuspation and clinical rest position, with four complete arch maxillary occlusal overlays increasing OVD in interincisal increments of 2, 4, 6, and 8 mm. Objective measurements were made from the photographs using facial reference markers. Ten observers made subjective evaluations of the resulting changes in face height using the sequential photographs randomly presented. RESULTS: Measurements of the facial markers showed that on increasing OVD, a corresponding change in lower face height was 50% of the interincisal increase in intercuspation and 40% for clinical rest position. ANOVA for repeated measures showed a statistically significant effect of the intraoral increase in OVD on lower face height. However, subjective results showed that observers were not capable of detecting changes in face height caused by an intraoral increase in OVD (2 to 6 mm intrinsically). ANOVA for the difference between dentists and nondentists showed a minimal, but significant, difference between the two groups, with dentists erring slightly less. CONCLUSION: Attempts to alter face height by changing OVD within the range of 2 to 6 mm for esthetic reasons may not be visually distinguishable.