4 9 2 Dental Update – December 2001

P R O S T H O D O N T I C S

Abstract: Setting teeth for complete dentures is traditionally done away from the

clinic in the dental laboratory. This has unwittingly given the impression that

arranging tooth position is a mechanical process in which the clinician has little say.

Many technicians are given few instructions, but a detailed prescription is crucial to

the success of the denture. This article describes those considerations the dentist

should address in communicating with the laboratory technician. A ‘denture space’

impression technique is described to assist the dentist in the correct prescription for

posterior teeth placement.

Dent Update 2001; 28: 492–495

Clinical Relevance: The function of the lips, cheeks and other muscles of the oral

tissues influence the optimal tooth position of artificial teeth in complete dentures.

The aim of this paper is to explain the biological forces that influence tooth position,

and describe clinical techniques that can be used to provide denture stability and

retention.

P R O S T H O D O N T I C S

hen providing complete

dentures the base should

always be optimally extended, the

polished surface correctly shaped and

the teeth placed in the most favourable

position. The patient and the dentist

may have conflicting agendas: the

dentist will consider factors promoting

denture stability and retention, and

which provide good aesthetics without

compromising function; the patient may

be more concerned with aesthetics (at

the expense of function) or may prefer a

modified copy of their previous denture

rather than radically different dentures

with significant improvements.

Most edentulous patients have

existing complete dentures, which can

be used as a template. However, if there

is no existing denture, or if a patient has

expressed dissatisfaction with previous

dentures, the dentist may need to use

biometric principles. These use

anatomical landmarks to guide in the

optimal placement of teeth on the

denture.

Using biometric principles, the upper

artificial teeth can best support the lips

and cheeks if they are placed in the

position previously occupied by the

natural teeth. In addition, a peripheral

seal is formed between the denture

flange and the cheeks and lips, which

enhances denture retention and

stability. Pre-extraction photographs and

models can be invaluable guides but, if

they are not available, the dentist must

rely on biological guides to assist in the

optimal placement of the artificial

anterior teeth for function and

aesthetics.

GUIDES TO THE POSITIONOF THE OCCLUSAL PLANEA majority of British dentists consider

the occlusal plane to be parallel to the

interpupillary line and the alar-tragal

line,1 but they differ as to where the

points are located on the relevant

cartilages. The alar-tragal line lies

between the lower border of the ala of

the nose and the upper border of the

tragus of the ear.2 The angulation

relative to the horizontal provided by

the alar-tragal line allows the denture

teeth to articulate in a harmonious

manner, sympathetic to the movement of

the mandibular condyle down the

articular eminence. Other allowances are

built into the set-up by the technician to

provide optimal balanced articulation –

cusp angles, compensating curves and

incisal guidance. The condylar guidance

can be programmed into an adjustable

articulator to allow optimal arrangement

of the teeth.

The alternative viewpoint questions

the need for classical anatomical

articulation because during mastication

most occlusal contacts occur within a

few millimetres either side of retruded

contact position. Further research is

needed to resolve this issue.

Ismail and Bowman3 found that

positioning the occlusal plane at the

level of the upper third of the retromolar

pad brings it close to the level of the

pre-extraction natural dentition. The

lower wax rim, used in the jaw

registration, should be constructed in

the laboratory to the height of the upper

part of the retromolar pad.4 This position

of the plane allows satisfactory

function, as it usually lies mid-way

between the two residual ridges.

Biological Guides to the Positioningof the Artificial Teeth in Complete

DenturesH. DEVLIN AND G. HOAD-REDDICK

W

H. Devlin, PhD, MSc, BSc, BDS, Senior Lecturerin Restorative Dentistry, and G. Hoad-Reddick,PhD, MSc, BDS, Senior Lecturer in DentalEducation, The University Dental Hospital ofManchester.

P R O S T H O D O N T I C S

Dental Update – December 2001 4 9 3

Tuckfield5 recommended placing the

occlusal plane parallel to the crest of the

lower ridge for maximum denture

stability. Although this advice has been

repeated in textbooks, it has not been

thoroughly investigated experimentally.

There is reluctance amongst dentists to

raise the occlusal plane level because it

will cause denture instability if the

tongue is unable to place food

comfortably on the occlusal platform. At

rest, the dorsum of the tongue should lie

at least at the level of the occlusal plane

(Figure 1) or overlying the lingual cusps

to provide denture stability. This

position can be difficult to assess

clinically as the tongue position will

vary according to the denture wearing

experience of the patient. In addition,

patients who tend to retch with dentures

will often retract their tongue on

opening their mouth to guard the

pharynx unconsciously.

Residual ridge resorption is about four

times greater in the mandible than in the

maxilla,6 and in the patient who has been

edentulous for a long time this can

result in the lower denture appearing

large and bulky. Fortunately, the height

of the lower denture can be reduced

slightly because the rest vertical

dimension is diminished following

extraction of the teeth.

The pattern of resorption varies in the

two arches, with bone being lost

laterally in the region of the maxillary

tuberosity and medially in the posterior

lingual region of the mandibular arch.

Thus the upper ridge appears to become

narrower in relation to the lower as

resorption follows its insidious

progress. When the teeth are placed

upon the denture this previous relation

should be borne in mind: if the molar

teeth of the upper denture are placed in

the position previously occupied by the

natural teeth, they might not be placed

over the resorbed ridge crest. Retention

and stability are not compromised

because of the large surface area of the

palate and the peripheral seal of the

denture flange with the cheek.

It is often stated that the lower molar

teeth of the complete denture should be

placed in the ‘neutral zone’, the area

previously occupied by the natural

teeth. This may be an oversimplification

as natural lower molar teeth are often

lingually inclined to such an extent that,

if this situation were replicated in the

dentures, instability would result.

Placing the lower molar teeth over the

residual ridge should provide optimum

stability. If the molar teeth are wide they

may overhang the tongue, and during

tongue movements the dentures will

tend to be unseated. Choosing a narrow

posterior tooth mould will help to

prevent this problem.

THE INCISOR TEETHWith age, the reduction in muscle tone

affects the relation of the upper lip and

the incisor teeth. As a result the amount

of upper central incisor showing below

the upper lip reduces from an average of

2 mm. The exact length of visible tooth

will vary with different jaw relationships

and lip lengths, but is generally more in

younger patients; older patients may

prefer to keep the upper incisor edges

level with the resting lip. The incisal

edges of the upper incisors should

follow the curve of the lower lip when

smiling.

The upper incisors are positioned to

provide lip support, which is generally

accepted to require an average

nasolabial angle of 90o. However,

Brunton and McCord7 showed the

nasolabial angle in their dentate

subjects averaged about 110o, therefore

a slightly more obtuse angle may be

necessary. If the lip is not adequately

supported, the delicate shape of the

philtrum is lost. It is the crowns of the

incisors which should support the lip: if

the flange is thickened to provide

support, not only will the lip be

effectively shortened, but also the area

directly beneath the nose will appear

swollen.

THE CANINE TEETHA coronal plane passes through the tip

of the maxillary canine and the posterior

part of the incisive papilla. When the

patient is viewed from the front, a

vertical line drawn from the inner

canthus of the eye to the alar cartilages

on each side passes through the

maxillary canine tips. The canine

eminence should be considered when

the denture is being waxed up to

provide support for the correct shape of

the angle of the mouth.

BIOMETRIC GUIDELINESThe palatal gingival vestige is a raised

fibrous ridge on the palate. It is

considered a remnant of the palatal

gingivae, and is often used as a guide to

the position of the maxillary artificial

teeth.8,9 Using the palatal gingival

vestige as a fixed-point, measurements

of the average horizontal bone loss

following extraction of the maxillary

teeth allows the pre-extraction position

of the teeth to be determined on the

edentulous cast. The labial surface of

Figure 1. The occlusal plane of the lowercomplete denture is level with the upper part ofthe retromolar pad. The occlusal plane is lowenough for the tongue to position food on theocclusal platform of the lower teeth.

Figure 2. The prominent palatal gingival vestigepresent in a 14-year-old patient with anodontia.Clearly the palatal gingival vestige cannot be theremnant of the palatal gingival margin. (Arrowsindicate a structure resembling the palatalgingival vestige.)

4 9 4 Dental Update – December 2001

P R O S T H O D O N T I C S

the incisors and canines are placed 6

and 8 mm, respectively, labial to the

palatal gingival vestige, with the buccal

surface of the premolars 10 mm and that

of the molars 12 mm buccal to the

vestige. However, this palatal fibrous

ridge is present in patients with

congenital absence of development of

the teeth and associated periodontium

(Figure 2). In addition, the palatal

gingival vestige can be identified in

newborn infants (Figure 3) before the

eruption of teeth. The palatal gingival

vestige cannot therefore be used as an

absolute guide to positioning of teeth in

the arch.

The incisive papilla may likewise be

used as a reference point. The tips of

the central incisor teeth are generally

placed 8–10 mm in front of the central

point of the papilla. The position of the

incisal edges of the anterior teeth

relative to the incisive papilla can be

positioned accurately using a

Schottlander Alma Gauge (Davis,

Schottlander and Davis Ltd., Letchworth

Garden City, Herts, UK). The vertical

metal pointer is placed over the incisive

papilla and a horizontal scale used to

measure the distance in front of the

papilla (Figure 4).

THE DENTURE SPACEIMPRESSION

With the Finished AcrylicDentureThere are many techniques which

attempt to define the ‘denture space’

(that area of stability where the lower

denture extension is in harmony with the

surrounding musculature). Wright10

described a technique in which a low-

viscosity silicone material is applied to

the polished and fitting surfaces of the

denture, which is then inserted into the

patient’s mouth (Figure 5). Functional

movements, such as chewing or

speaking, are performed until the

silicone has set. The tongue will remove

the paste where the flange is too thick or

where the teeth are positioned too far

lingually. Areas of overextension are

highlighted (Figure 6). The silicone can

be easily peeled off, as no adhesive is

used, and after the necessary denture

adjustments have been carried out, the

procedure is repeated.

Defining the Denture SpaceDuring Denture ConstructionTo ensure that the teeth do not conflict

with the surrounding muscular

environment, a light-cured acrylic

baseplate can be constructed with a

posterior vertical flange, or stop, at the

correct occlusal vertical dimension.

Attached to the baseplate are wire

loops, which retain a putty silicone

impression material (Figure 7). The putty

is moulded by the patient (Figure 8) with

the upper trial denture in place. In the

laboratory, indices are constructed

around the impression so that, when the

silicone is removed, the space for the

denture teeth is identified. The resultant

impression of the denture space can be

copied in wax and the teeth set within its

confines.

DISCUSSIONCertain changes occur in ageing of the

facial tissues, which can affect facial

contour and which are not accounted for

in the biometric denture principles. For

Figure 3. A structure resembling the palatalgingival vestige is present in neonatal childrenbefore the eruption of the teeth (arrows indicatea structure resembling the palatal gingivalvestige).

Figure 4. The Schottlander Alma Gauge isused to determine the optimal position of theincisal edges of the upper anterior teeth.

Figure 5. Silicone impression material is appliedto the denture and the patient performsfunctional movements.

Figure 6. The denture is removed when thesilicone impression material has set. Acrylic visibleon the denture periphery may indicateoverextension.

Figure 7. An acrylic baseplate is constructed,with wire loops to retain the impression material.

P R O S T H O D O N T I C S

Dental Update – December 2001 4 9 5

Figure 8. With the upper trial denture in place,the silicone putty is moulded by the patienttalking and swallowing. When set, the denturespace impression is removed and copied in waxin the laboratory. The technician is requested toposition the artificial teeth in the wax template.

instance, Pellacani and Seidenari11 used

ultrasound to show that facial skin of

elderly people was thicker than that of

younger individuals in most areas. In

addition, there is a wide variation in the

amount of facial skin adipose tissue in

the healthy population that must tend to

invalidate the application of fixed

measurements to tooth position.

The rigid application of rules to the

positioning of teeth can prevent the

development of satisfactory alternative

tooth arrangements. For example,

patients with a prominent pre-maxilla

may request that the upper artificial

incisors are positioned more palatally

than indicated by their pre-extraction

position and the labial flange of the

denture either omitted or reduced in

thickness.

The dentist can adopt two main

treatment strategies when providing

replacement complete dentures.

� In the first, the patient receives a

denture based on biometric

principles where the anatomical

guides are used to position the

artificial teeth for optimum function.

� With the second treatment strategy,

the dentist copies the good features

of the patient’s existing dentures

and incorporates improvements

where there are deficiencies in

existing denture design. These can

be related to the biometric

principles described earlier in this

paper, which influence the optimal

position of artificial teeth in

complete dentures.

Both treatment strategies are

appropriate in particular circumstances.

REFERENCES

1. Williams DR. Occlusal plane orientation incomplete denture construction. J Dent 1982;10: 311–316.

2. Hobkirk JA. Complete Dentures. Bristol:Wright, 1986.

3. Ismail YH, Bowman JF. Position of theocclusal plane in natural and artificial teeth. JProsthet Dent 1968; 5: 407–411.

4. Celebic A, Valentic-Peruzovic M, Kraljevic K,Brkic H. A study of the occlusal planeorientation by intra-oral method(retromolar pad). J Oral Rehab 1995; 22:233–236.

5. Tuckfield WJ. The problem of the mandibulardenture. J Prosthet Dent 1953; 3: 8–28.

6. Tallgren A. The effect of denture wearing onfacial morphology. A 7 year longitudinal study.Acta Odontol Scand 1969; 25: 563–592.

7. Brunton PA, McCord JF. An analysis ofnasolabial angles and their relevance totooth position in the edentulous patient. EurJ Prosthodont Restor Dent 1993; 2: 53–56.

8. Likeman PR, Watt DM. Morphologicalchanges in the maxillary denture bearingarea. A follow-up 14 to 17 years after toothextraction. Br Dent J 1974; 136: 500–503.

9. Watt DM, Likeman PR. Morphologicalchanges in the maxillary denture bearingarea following extraction of teeth. Br Dent J1974; 136: 225–235.

10. Wright SM. The polished surface contour: anew approach. Int J Prosthodont 1991; 4: 159–163.

11. Pellacani G, Seidenari S. Variations in facialskin thickness and echogenicity with site andage. Acta Derm Venereol 1999; 79: 366–369.

ABSTRACT

A NEW ASPECT OF PRACTICE

MANAGEMENT?

How Can You Protect Yourself from

Employee Dishonesty? J.M. De St

Georges and D. Lewis Jr. Journal of the

American Dental Association 2000;

131: 1763–1764.

It has been reported that 40% of

American dental offices will suffer

fraud or embezzlement by an

employee. The average amount of

these losses is a staggering $105,000.

Most dentists have suffered this loss

in silence, but it is reported that more

are now seeking redress through the

courts.

This brief article highlights the

concerns and suggests some ways to

protect against such actions. A full

practice audit is both costly and time-

consuming. It is cheaper and simpler

to ask an accountant to design a brief

self-audit for you to use. The third,

and cheapest, option is to carry out

immediate, cursory and random audits.

It is suggested that 15 patient record

cards should be drawn at random each

week. Experience shows that, if the

financial details on these cards

matches the day-books and banking

details, there is probably, although not

definitely, not a problem.

The authors suggest other ways of

checking and preventing fraud,

including a very interesting table of

the common characteristics of

embezzlers. It would appear that the

best, longest-employed and most

hard-working member of the team

could be the prime suspect!

Peter Carrotte

Glasgow Dental School

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