J. Dent.





A preliminary investigation into the effect of increased occlusal vertical dimension on mandibular movement during speech* C. A. Burnett and T. J. Clifford Department

of Restorative


The Queen’s University

of Belfast, Northern


ABSTRACT 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 ofO.O-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. KEY WORDS: J. Dent. 1992;

Occlusal vertical dimension, 20:



Closest speaking 30 September



Correspondence should be addressed to: Mr C. A. Burnett, University of Belfast, Belfast BT12 6BP. UK.


INTRODUCTION Silverman (1951a, b) suggested that mandibular position during the pronunciation of sibilant sounds be used to establish occlusal vertical dimension (OVD) on the basis that this is a reflection of function which produces a stable position of the mandible. Silverman (1953) defined the distance between the closest speaking position of the mandible, which is produced during sibilant pronunciation, and the teeth in centric occlusion as the closest speaking space. He believed the closest speaking position of the mandible remained constant for each individual provided it was determined at normal conversational rate and volume with the head upright in relation to the body. Rivera-Morales and Mohl(1991a) recently reported their *Presented at the European Prosthodontic Association. Amsterdam, 1990. @ 1992 Butterworth-Heinemann 0300-5712/92/040221-04



13 December of Restorative

1991) Dentistry,


finding that the variance of the closest speaking space was smaller than the variance of interocclusal space at the mandibular rest position for 26 to 30 subjects. Mandibular rest position has often been referred to as the objective baseline for decisions involving an increase in OVD. However most authorities no longer accept the concept of a constant rest position of the mandible (Tallgren, 1957; Prieskel, 1965; Nairn and Cutress, 1967; Gattozzi et al., 1976). It has been shown that the mandibular rest position adapts to changes in OVD in dentate subjects (Christensen, 1970; Carlsson et al.. 1979). Both these authors showed an increase in the OVD to cause a concomitant increase in the mandibular rest vertical dimension. Indeed in a recent review of the relationship of OVD to the health of the masticatory system (Rivera-Morales and Mohl, 1991b), the authors could find no published studies demonstrating that the


J. Dent. 1992;

20: No. 4

postural rest position of the mandible is fixed and unaffected by a variety of extrinsic and intrinsic factors. If a consistently reproducible and measurable position of the mandible, unaffected by changes in OVD, was to be identified it may provide a basis for the assessment of a patient’s ability to adapt to these changes. This in turn may provide a guide to the original OVD in such situations as severe toothwear or total tooth loss. In seeking an objective method and an alternative to mandibular rest position it would seem worthwhile to establish if the closest speaking space has a role in the determination of OVD. The aim of this preliminary investigation was to measure the closest speaking space and examine the effect of an increase in OVD upon it. If a consistent trend were to be identified the intention would be to expand the investigation to patients who require an increase in OVD as part of their restorative treatment.



Six subjects, all female dental surgery assistants working in the School of Clinical Dentistry, Queens’ University Belfast, voluntarily took part in the investigation. Their ages ranged from 19 to 23 years. All had intact dentitions and reported no history or symptoms of joint or muscular dysfunction. There was no restriction of participants on the basis of skeletal or occlusal relationships. Casts were made of the maxillary and mandibular arches from impressions in irreversible hydrocolloid and mounted on an adjustable articulator in the terminal hinge axis using a wax record. Clear acrylic resin splints were constructed with a flat occlusal surface to cover the mandibular teeth, with limited extension onto the buccal and lingual surfaces. The splints were designed to increase the OVD by 4 mm in the incisor region. This follows the method of Carlsson et al. (1979) except that the incisors were not covered by their splint. The magnetic method of jaw tracking was used to record mandibular movement to determine the closest speaking space. The kinesiograms were made with a Sirognathograph (Siemens A.G., Bensheim, Germany) and the tracings recorded by a single pen XY-recorder (Esterline Angus, type XY 575 OEM) which limits graphic representation to one plane at a time (sagittal, frontal or horizontal). The subjects were placed with the Frankfort plane horizontal, with a firm headrest, and instructions to avoid head movements. They were then asked to close to the retruded axis position, this position having been explained and demonstrated prior to the experiment, and it was recorded as a mark on the tracing paper. The retruded position must be used if the values for the closest speaking space before and after splint wear are to be comparable without introducing sagittal translation of the mandible. They were then asked to recite a series of short phrases of speech and when finished to close again, if this did not coincide with the original the recording was rejected. The speech exercise was to be recited at normal

conversational rate and volume and the participants were given a few minutes to practice and become familiar with it. The exercise, with sibilants underlined, was as follows: I get a bug I like to Iis& Fill the measure I went to c_hurch Look at the bdge Follow the Mis$gppi Ah - sixtv-six Six recordings were taken ofthe individuals performing the exercise, with three being in the frontal plane and three in the sagittal. The occluding splint was then cemented in place for 5 days, using Temp Bond (Kerr USA Romulus, MI, USA) temporary crown cement, after which the recordings were repeated. The passage used as the speech exercise was designed to contain the six sibilants, 2, 4, &-I, &, &r and j, of the phonetic sounds of the English language. According to Silverman (1953) one or more of these sibilants are the sounds which cause the closest speaking position in 90 per cent of cases surveyed. In the other cases where different sounds cause the closest level it is found that the sibilants cause a constant, reproducible position of the mandible in relation to the maxilla. In some subjects it is found that not all the six sibilants cause the closest speaking level but that one or more of the group will. The closest speaking space was determined on the sirognathograph tracing by measuring the distance between the mark for centric occlusion and the nearest pen marking as recorded during the speech exercise and taking the mean from the six recordings. All measurements were made by the same investigator. The mean of the measurement of the closest speaking space for each subject was then compared with that recorded after 5 days wear of the plate using a two-tailed paired t test.

RESULTS Table Z shows the mean closest speaking space determined for each individual. There was a variation between subjects ranging from 1.0 to 3.3 mm. Table 1. Closest speaking space (mm) Standard Subject


: 3 4 5 6

2.00 1 .oo 2.50 3.30 1.40 2.40


f + * f * +

0.04 0.03 0.05 0.05 0.02

Standard deviation 0.12 0.1 1 0.13 0.10 0.09 0.12


and Clifford:

Table II. Closest speaking space (mm) following of occluding splint



1 2 3 4 5 6

0.35 0.20 0.00 0.90 0.30 1 .oo


5 days wear

Standard error

Standard deviation

f 0.05 f 0.04 -

0.05 0.10 -

* 0.02 Ik 0.05 f 0.03

0.1 1 0.10 0.12

Table II shows the closest speaking space as assessed after 5 days’ continuous wear of the occluding splint. On this occasion there was a range in the mean from 0.0 to 1.0 mm. The change in each individual’s mean closest speaking space between the two assessments is shown in Fig. I. A two-tailed paired t test showed a statistically signilicant difference, P > 0.001. between the mean values for the closest speaking space of each subject before and after the splint was worn.

DISCUSSION The results of this study show the closest speaking space of the six subjects to be significantly reduced by 5 days wear of a mandibular occluding splint increasing the OVD by 4 mm in the incisor region. The small variation in the mean standard error of the recordings would suggest that the method used to measure the closest speaking space was both reproducible and accurate. The correct or physiological OVD for any patient is perhaps best described as a range instead of a fixed position. The width of this so called ‘comfort zone’ may vary among individuals and individual adaptive capacity is unknown. As this study involved young adult subjects who had no toothwear or toothloss it could be assumed








Fig. 7. Change in mean closest speaking space between two assessments.

W, CSS; 8, CSS-splint.



and mandibular


in speech


that they had not suffered any change in their original OVD. The increase in vertical dimension produced by the splint was therefore a true increase and not just a relative one. The 4-mm increase produced by the splint would appear to have raised the subjects’ OVD beyond the ‘comfort zone’ as all subjects complained of a variety of symptoms such as headache, sore joints, tired musculature and sore teeth. The great difficulty in dealing with patients who have lost posterior support or have severe toothwear is that we do not know how much, if any, OVD that patient has lost. Current techniques to establish a new OVD in such situations where space is required for placement of restorative materials rely mainly on empirical knowledge. It must be said that the employment of this empirical knowledge has allowed and continues to allow dentists to provide successful treatment. However, research that integrates clinical techniques with standard scientific information should underpin the chosen methods of routine clinical procedure. A significant reduction, or elimination, in the closest speaking space when the OVD is increased by oral appliances. be they occlusal splints, dentures or crowns, may be a positive indication that the OVD is beyond the adaptive capability of that particular patient. Was the 5-day period of the investigation sufficiently long to allow adaptation of the musculature controlling mandibular movement during speech? In a study investigating speech articulation errors associated with increased OVD, in dentate and edentate individuals, Hammond and Beder (1984) reported that the initial gross adaptation was accomplished by the speech mechanism within 5 days. Thereafter, they suggested, any adaptation would represent a process of refinement and tine adjustment. As the design of their splint was similar to that used in this study we may imply that this suggestion reflects upon not only the increase in OVD produced but the oral volume occupied as well. An interesting feature of their study was that they found the -ch and&r sounds to be most frequently misarticulated. Both of these sounds are sibilants and this finding would support that of this study in that increased vertical dimension affected the closest speaking space. A factor limiting the time-span of this type of study is the subjective symptoms suffered by the participants. However none complained of poor speech and the 5-day period is undoubtedly long enough to have shown an interesting trend. if not proof, that a longer experimental period would not show a different result. Experimental work in the treatment of patients in an effort to determine if they will adapt to increases in OVD would need to incorporate a longer period of assessment. The population sample in this preliminary investigation is small but we believe the results show a trend that encourages broader research in an attempt to identify if the closest speaking space is a more constant factor than the mandibular rest position. A study involving male and female subjects with a greater age range and including those with toothwear and partially and completely edentulous patients is planned.


J. Dent.



No. 4

References Carlsson G. E.. Ingervall B. and Kocak G. (1979) Effect of increasing vertical dimension on the masticatory system in subjects with natural teeth. J. Prostbet. Dent. 41, 284-289. Christensen J. (1970) Effect of occlusion-raising procedures on the chewing system. Dent. Practit. 20, 233-238. Hammond R. J. and Beder 0. E. (1984) Increased vertical dimension and speech articulation errors. J. Prosthet. Dent. 52,40 l-406. Gattozzi J.. Nicol B.. Somes G. et al. (1976) Variations in mandibular rest positions with and without dentures in place. J. Prosthet. Dent 36, 159-163. Nairn R. I. and Cutress T. W. (1967) Changes in mandibular position following removal of the remaining teeth and insertion of immediate complete dentures. Br. Dent J. 122, 303-306. Prieskel H. W. (1965) Some observations on the postural position of the mandible J. Prosthet. Dent. 15, 625-633.

Rivera-Morales W. C. and Mohl N. D. (199la) Relationship of occlusal vertical dimension to the health of the masticatory system. J. Prosthet. Dent. 65, 547-553. Rivera-Morales W. C. and Mohl N. D. (1991b) Variability of closest speaking space compared with interocclusal distance in dentulous subjects. J. Prosthet. Dent. 65, 228-232. Silverman M. M. (195la) Accurate measurement of vertical dimension by phonetics and the speaking centric space. Dent. Digest 57, (part I), 261-265. Silverman M. M. (195lb) Accurate measurement of vertical dimension by phonetics and the speaking centric space. Dent. Digest. 57, (part II), 308-311. Silverman M. M. (1953) The speaking method in measuring vertical dimension. J. Prosthet. Dent. 3, 193-199. Tallgren A. (1957) Changes in adult face height due to aging, wear and loss of teeth and prosthetic treatment. Acta Odontol. Stand. 15, (suppl. 24), l-l 12.

Book Reviews Emergencies in Dental Practice. R. Juniper and B. Parkins. Pp. 172. f 14.95.



This slim, soft-backed pocket volume entitled Emergencies in Dental Practice, Diagnosis and Management, deals adequately with the true dental emergency, of which there are few, while comprehensively covering the diagnosis and management of complaints presenting at initial treatment. There are 20 chapters, divided indistinctly into two sections. In the first, and larger, the emphasis is on general practice, beginning with pain, swelling, trauma, haemorrhage and oral mucosa, medical emergencies, HIV infection and child abuse, before ending with specialty emergencies. The latter, and smaller, section repeats these initial chapters but with the relevant additional diagnostic and management information needed for the hospital practice. Since these often start with ‘See Chapter . . .‘, the reader is occasionally left with a finger in both sections, not ideal, I would suggest, at a time when the authors consider ‘the brain ceases to function efficiently’. However, time spent reading and familiarizing oneself with the book before putting it to use is time well spent, since it is packed with sound, practical advice on both diagnosis and management; irrelevant material is kept to a minimum. It is well laid out, chapters are short, and beneath the clear, bold subheadings is a combination of a concise text and lists which enable rapid identification and assimilation of the essential information. This is helped by an adequate and accurate index and the use of simple line diagrams to illustrate the key points. This book should prove a valuable aide-m&moire to all practitioners, especially the newly qualified who will not have extensive clinical experience on which to draw in an emergency. Whether you would trust it to the trauma and insecurity of the white coat pocket, as is the publisher’s hope, at a price of f 14.95 is a matter of conjecture. P. Hardy

Primary Preventive Dentistry, 3rd edition. N. 0. Harris and A. G. Christen. Pp. 560. 1990. Appleton 8 Lange. Hardback, $30.25.


This is the third edition of a text that has become widely used in the USA but has not achieved universal acclamation in the UK. It has certainly been subjected to substantial revision and updating but also to considerable addition and re-emphasis. There is increased emphasis on periodontal disease, patient education and geriatric dentistry. In fact, the range of subjects covered is much wider than in most books on preventive dentistry. Unfortunately, as is the case with many multiauthor publications, there is considerable variation in the quality of the individual chapters, and a degree of repetition. Editorial control has meant that all the contributors have produced a similar format; each chapter begins with a list of learning objectives, and contains groups of selfevaluation questions to check whether the reader has being paying attention, followed by further questions at the end of the chapter with answers and explanations. This certainly facilitates the learning process although some of the questions simply check on the level of the readers’ photographic memory rather than the understanding of the text. The 22 chapters range from factual, informative and well-researched accounts of the development of dental plaque to more erudite concepts of understanding human motivation. There is undoubtedly something here for everyone, but the book does suffer from trying to be too diverse. There are some minor niggles: all illustrations are in black and white, the typeface is variable, and there are numerous typographical errors-my favourite was ‘pre-pubital periodontitis’! However, it is a book to be recommended, not least for its extensive lists of references. It will be useful for all members of the dental team as part of a preventive dentistry reference library. L. N. Shaw

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 ...
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