jaw muscles in older overdenture patients

Or ig ina l a r t i c l e

Jaw muscles in older overdenture patients

James P. Newton1, Frank C. McManus1 and Stephen Menhenick2

1Oral Physiology Research Group, The Dental School, University of Dundee, Dundee, UK; 2Department of Diagnostic Radiology, Ninewells

Hospital, Dundee, UK

Gerodontology 2004; 21; 37–42

Jaw muscles in older overdenture patients

Objective: To determine, using computer tomography (CT), whether the retention of a small number of

teeth in the older adult used to support overdentures could affect the cross-sectional area (CSA) and X-ray

density of two jaw closing muscles.

Design: Cross-sectional study of a group of older patients subdivided into dentate, edentulous and those

wearing overdentures supported by two to five teeth.

Subjects: The sample consisted of 24 subjects aged 55–68 years.

Outcome measures: CSA and X-ray density of two jaw closing muscles, masseter and medial pterygoid

were measured and evaluated using CT.

Results: There were no significant differences between left and right jaw muscles, but the CSA of the

masseter muscles were significantly larger than the medial pterygoid muscles. The CSA of the masseter and

medial pterygoid muscles was significantly smaller in edentulous subjects compared with dentate subjects

but no significant difference was observed between subjects wearing overdentures and those with a natural

dentition. No significant differences were observed with the X-ray density between different muscles or

dental states.

Conclusion: The retention of a small number of teeth in the older adult used to support overdentures

appears to sustain the CSA of two jaw closing muscles and therefore could enhance these patients’ mas-

ticatory ability compared with those who were edentulous.

Keywords: jaw muscle, computed tomography, cross-sectional area, overdentures.

Accepted 8 December 2003

Introduction

In the older adult, continued muscle function is a

major requirement for the maintenance of oral

functions such as speech and mastication. Previous

studies have shown that the replacement of the

natural dentition by partial or complete dentures

influences the level of masticatory force and

chewing efficiency that can be utilized by these

patients1–6. However, it is worth noting that some

complete denture wearers themselves often regard

their masticatory function as satisfactory7,8.

Although many studies have shown a reduction in

maximal bite force, it has been suggested that, with

careful prosthetic maintenance, immediate denture

wearers can have bit force levels that approach

those recorded for dentate individuals9–11. It

has also been suggested that the retention of a

small number of teeth to be used as overdenture

abutments might prove to be advantageous in the

wearers of complete dentures12. This is supported

by clinical observations and limited evaluation

studies that have shown increased bite force and

electromyographic activity levels13. Further

increases have been observed when the denture(s)

have been retained by means of precision attach-

ments14,15.

The maximum force that a muscle can produce

is determined to a great extent by its cross-

sectional area (CSA) and with the development of

computed tomography (CT) and magnetic reson-

ance imaging, cross-sectional images of whole

muscle groups can be obtained with a great

degree of reproducibility. These techniques have

been used to show that the cross-sectional image

of a muscle is representative of its physiological

� 2004 The Gerodontology Association, Gerodontology 2004; 21: 37–42 37

cross-section16 and more particularly, for changes

in whole muscle groups with age17. Studies on

two jaw closing muscles, the masseter and the

medial pterygoid, have shown that there are sig-

nificant changes with age and dental state18–21.

There is also a decrease in the X-ray density with

advancing age and this has been interpreted to

indicate a progressive increase in the amount of

fat and fibrous tissue18–19. These non-invasive

techniques have also been used to evaluate

potential changes in salivary function of the par-

otid gland in an ageing population22 and

derangement of the temporomandibular joint23.

The purpose of this study was to determine,

using CT, whether the retention of a small number

of teeth in the older adult, used to support over-

dentures, could affect the CSA and X-ray density of

two jaw closing muscles, the masseter and medial

pterygoid.

Methods

Subjects

Data were collected from 24 male subjects,

55–68-years old (mean 61.2 ± 4.9 years), all of

whom gave informed consent, these being divi-

ded into three groups of eight; dentate, edentu-

lous, and those wearing a lower complete acrylic

overdenture opposed by an upper complete ac-

rylic denture. In this later group, specific teeth,

two to five in number and normally canines with

or without premolars, had been retained, root-

treated and modified with their root surfaces used

to support and retain the lower denture for

a mean (±SEM) of 11.5 ± 0.8 years (range

8–13 years). No precision attachments of any

form had been used in this group during the

provision and wearing of the complete dentures.

The dentate group consisted of individuals with a

reproducible occlusal relationship, who had

retained 20 or more of their natural dentition and

were able to maintain a satisfactory level of oral

hygiene. The edentulous group had been

successfully wearing upper and lower complete

dentures for a mean (±SEM) of 13.0 ± 1.3 years

(range 10–16 years). All subjects in the study

had been maintained on a regular basis with

particular regard to oral and denture hygiene and

care of their appliances.

Computed tomography examination

The CT examination was performed using a

Tomoscan 350 whole body scanner (Philips) with

scanning factors of 400 mA, 120 kV and a scan

speed of 1.2 s. Each section was representative of a

slice of tissue 6 mm thick. The scan plane selected

was made with the head in a symmetrical position

and this had the advantage that the scans of the left

and right of both muscles could be obtained sim-

ultaneously18.

CSA and X-ray density measurements

These were carried out using conventional light

pen software by which the contours of the muscles

were drawn on the television screen. The regions

encircled were then analysed for the average value

of CT numbers (Hounsfield Units) encompassed

and their area in squarecentimetre. This latter

measurement was also repeated on a hard copy of

the scan so that the values obtained could be

independently validated18.

Results

Sections of both muscles approximately perpen-

dicular to the fibre direction were readily identified

at defined scan planes (Fig. 1) and there was close

agreement between the results for the cross-sec-

tional area obtained directly from the scanner and

from the hard copy examined. The model for the

analysis of the data from this study was a nested

analysis of variance with crossover, with the

dependent variable being the muscle cross-sec-

tional area. A comparison of the left and right sides

in each subject showed no significant differences

but within each group, the CSA of the masseter

muscles were significantly larger than the medial

pterygoid muscles (p < 0.001).

In the dentate group, the mean (±SEM) CSA of

the masseter and medial pterygoid muscles were

4.30 ± 0.20 and 3.12 ± 0.13 cm2, respectively

(Fig. 2), these being similar to values previously

obtained for an age- and sex-matched cohort18,19.

However, where the natural teeth had been lost

and replaced by complete upper and lower den-

tures, the CSA of both muscles was significantly

reduced (p < 0.001): in masseter by 27% to

3.16 ± 0.07 cm2 and in medial pterygoid by 21% to

2.46 ± 0.11 cm2 (Fig. 2). These values confirm

observations in an edentulous group of a similar

age and sex matched cohort found in a previous

study19. When some of the natural dentition had

been retained and the root surfaces used to support

a lower complete denture, CSA values of

4.24 ± 0.22 and 2.99 ± 0.17 cm2 were obtained for

the masseter and medial pterygoid muscles,

respectively. These values were not significantly

� 2004 The Gerodontology Association, Gerodontology 2004; 21: 37–42

38 J.P. Newton et al.

different from those observed in the group of sub-

jects with a natural functioning dentition.

With respect to the X-ray density of the muscle

tissue, it is well known that there is an

approximately parallel relationship with the CT

numbers in the region of soft tissue and fat. In

this study, it was observed that the density values

of left and right muscles were not significantly

different (paired t-test) and that both masseter

and medial pterygoid muscles had similar values

indicating similar levels of fat and fibrous tissue

(Table 1). When comparing the different groups

of subjects using an analysis of variance with

crossover, the dentate and overdenture groups

were not significantly different from each other

and these were not significantly different from

those subjects who had lost all their natural

dentition (Table 1). However, there was a trend

for an overall decrease in the density in the

edentulous subjects which has been observed in

other studies24.

Discussion

Many of our patients are retaining some of their

natural dentition much later in life25 and that has

enabled them to maintain a more satisfactory level

of oral function and quality of life, although pre-

senting the profession with significant restorative

problems. However, there may come a time when

significant decisions have to be taken with regard

to the transition from a situation involving some of

the natural dentition to a fully artificial one.

Included in the edentulous population is a group of

individuals who consistently present with difficul-

ties in adjusting to and wearing complete den-

tures26. Obviously, if this can be foreseen, a suitable

period of preparation for the transition could be

utilized, and with careful planning, clinicians could

modify their approach to care and patients could

adopt more realistic expectations.

Removal of the last remaining teeth, particularly

in the lower jaw, should not be undertaken

without careful consideration of all the options

Figure 1 Comparison of computed

tomograms taken at the same scan

plane under the same scan factors in

dentate (A), edentulous (B) and

overdenture (C) subjects. A line

diagram is included to indicate the

muscles involved in the study (D).

Table 1 Comparisons of the density in Hounsfield Units

of the masseter and medial pterygoid muscles in the

dentate, edentulous and overdenture groups of subjects

(n ¼ 8 for each group). Values are given as means (±SEM).

Dentate Edentulous Overdenture

Masseter 53.3 ± 2.5 49.1 ± 2.9 54.6 ± 1.4

Medial pterygoid 50.0 ± 1.9 49.6 ± 3.9 53.4 ± 1.9


Jaw muscles in older overdenture patients 39

available. Clinical observations suggest that the

retention of a number of modified teeth and the

provision of overdentures gives improved support,

stability and better masticatory function27. Over-

dentures should always be considered as a pre-

ferred alternative to the provision of immediate

complete dentures, especially where the amount of

remaining alveolar bone is poor28. Retained over-

denture abutments not only transmit more detailed

sensory information through their mechanore-

ceptors, but also ensure the maintenance of

the surrounding alveolar bone providing a more

predictable outcome for the older patient29–31.

A part of the integral treatment to facilitate the

provision of overdentures may involve root canal

therapy of the strategic teeth, which are to be

retained. In some cases where there is radiographic

evidence of considerable secondary dentine present

in the pulp chamber, some decoronated roots may

not appear to require this form of treatment.

However, such a procedure may produce minute

micro-exposures allowing the ingress of organisms,

which has the potential for infection of the pulp

tissue. The most common loss of abutment teeth

subsequent to the provision of overdentures was

that of vital teeth developing periapical lesions. The

high incidence of complex canal anatomy in lower

anterior teeth may also be a deterrent to the root

treatment of overdenture abutment teeth. In

addition, problems can be encountered in older

patients that may be caused as a consequence of

the compromised health of the patient or by stress

changes within the dental pulp or both. As a result,

root canal therapy on this group of individuals

tends to have a greater degree of difficulty than in a

younger age group30,32,33.

When planning the retention of teeth as over-

denture abutments, consideration must be given to

the potential effects of root surface caries and gin-

gival health of the surrounding tissue. It has been

shown that there is a wide variation in caries

development with annual increments of between

10 and 40% but that this can be completely

inhibited by a daily application of chlorhexidine-

fluoride gel32. Covering the root surface and sealing

the root canal is essential to maintain the health of

the tooth and although a variety of materials are

used, research has not clearly indicated a superior

material34. However, more recently, in vitro studies

have indicated that fluoride-releasing glass iono-

mer may be an appropriate material for protecting

the root surface of abutment teeth35.

In addition, periodontal disease continues to be a

major problem36, even where a high degree of

patient co-operation is obtained37. However, even

if the prognosis of the remaining dentition is poor,

their retention to provide support and retention for

a transitional overdenture should be seriously

considered as it allows the patient time to develop

skills necessary for denture wearing38. In addition,

when teeth are subsequently lost, the overdenture

is easily modified and the patient can continue with

minimal dental disruption.

Evidence would suggest that the retention of a

small number of teeth to be used as overdenture

abutments, enhances the retention and stability of

the denture and improves the oral function of these

patients. In some cases, this can be for a long period

of time and should always be considered as a

potential treatment in our older patients. This study

would therefore provide support for the provision

0

1

2

3

4

5

Dentate Overdenture Edentulous

Cro

ss-s

ecti

on

al a

rea

(cm

2 )C

ross

-sec

tio

nal

are

a (c

m2 )

0

1

2

3

4

5

Dentate Overdenture Edentulous

(a)

(b)

Figure 2 A comparison of the cross-sectional areas of

the masseter (a) and medial pterygoid (b) muscles of 24

subjects subdivided into dentate, edentulous and over-

denture groups (n ¼ 8 for each group). Values are given

as means (±SEM).



of overdentures, as an important stage in the

treatment of the older adult in their transition from

a natural to an artificial dentition enhancing the

potential use of retained natural teeth at a later age.

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Correspondence to:

Dr JP Newton, Unit of Restorative Dental Care,

The Dental School and Hospital,

Dundee DD1 4HR, UK.

Tel.: 01382 635980

Fax: 01382 225163

E-mail: [email protected]



jaw muscles in older overdenture patients

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