Factors that determine cusp angulation

Factors

that

determine

cusp angulation

Honorato Villa A., D.D.S.* National University, Mexico City, Mexico

T

he factors that determine the cuspal inclines of posterior teeth required for balanced occlusion were stated by Rudolph Hanau and are known as the laws of occlusion1 These five factors include the angulation of the cusp which is determined by the combined action of the other four. The five factors are (1) the condylar guidance, (2) the occlusal plane, (3) the angulation of the cusp, (4) the compensating curve, and (5) the incisal guidance. POSITIVE

AND

NEGATIVE

FACTORS

The condylar and incisal guidances are positive factors, because they influence cuspal angulation in a positive way. When the inclination of the condylar and incisal guidances increases, the cuspal angulation increases. The occlusal plane and the compensating curve are negative factors, because when the inclination of the occlusal plane or the compensating curve is increased, the cuspal inclines are affected in a negative way; that is, cuspal amgulation clecreases. These factors and their influence on cuspal angulation are represented in the sagittal plane in Fig. 1. EFFECT OF CONDYLAR

AND

INCISAL

GUIDANCES

The influence of the condylar guidance is 100 per cent at the location of the guide itself. This percentage decreases progressively until it is 0 at the location of the incisal guide (Fig. 1) . The influence of the incisal guidance is 100 per cent at the location of the guide itself. This percentage decreases progressively to 0 at the site of the condylar guide (Fig. 1). If the first molar is placed midway between the condylar and incisal guidances, the required protrusive inclines of this molar will receive a 50 per cent influence from the condylar guidance and a 50 per cent influence from the incisal guidance. If the condylar guidance is 30°, the dotted line from the condylar guide shows that *Professor

522

of Complete

Dentures.

Volume 23 Number 5

Factors

&COtfLAR8$JIDE ,-_-.--

-

.-_ 60 _---

70 t--

-

-

-----

:;w

-3

-

of cusp angulation

30 ,-

-

2s

-

A/L

523

-0

P IlO - -15 --20

-

-

25

CUSP AWL

I I 0

10

20

30

40

50

I 60

70

80

90

100%

Fig. 1. The condylar guide is represented in the upper left-hand corner. The incisal guide is represented in the lower right-hand corner. The effect of the condylar guide diminishes as the in&al guide is approached. As the occlusal plane is raised or as the compensating curve is increased, the inclination of the cusp is decreased.

the influence in the midline is 15O. If the incisal guidance is lo’, the dotted line from the incisal guide shows the influence in the midline is 5’. So, the addition of 15’ and 5’ indicates that the protrusive incline required of the first molar is 20’. The second molar receives more influence from the condylar guidance and less influence from the incisal guidance. The bicuspids receive less influence from the condylar guidances and more influence from the incisal guidances. The incisal path also is influenced by the combined action of the condylar and incisal guidances. The percentage is proportional to the distance of the anterior teeth from the guides. EFFECT OF OCCLUSAL

PLANE

AND

COMPENSATING

CURVE

The inclination of the occlusal plane has a negative influence on cuspal inclines. When the occlusal plane is horizontal, its influence will be 0. When the inclination

of the occlusal

plane

is 5’,

then

this amount

must

be deducted

from

the

When the inclination of the occlusal plane is -5’, then this amount must be added to the influence of the ,guidances. The compensating curve also has a negative influence. As the compensating

influence

curve

of the guidances.

increases,

the required

cuspal

inclines

decrease.

524

Villa A.

C.G.

J. Pros. Dent. May, 1970

CG.

LATERAL MOVEMENT

Fig. 2. The condylar guides (C. G.) are depicted in the upper corners. The incisal guide (I. G.) is centered at the bottom. The working inclines remain 0” in inclination as the working condyle merely rotates. The balancing inclines are affected by both the incisal and condylar guidances.

EFFECT OF FACTORS ON WORKING AND BALANCING INCLINES The influence of the condylar and incisal guidances on the working and balancing inclines of the teeth is demonstrated in Fig. 2. The Bennett movement (B. M.) is considered to be 0. Therefore the influence of the condylar guidance on the working side from the condylar guide to the incisal guide is always 0. The per cent influence of the incisal guidance is determined by its inclination. The influence of the incisal guidance decreases as the condylar guide is approached. The working inclines will be equal to 0 plus the percentage of the effect of the incisal guidance. The balancing side inclines will be equal to the percentage of the condylar guidance plus that of the incisal guidance, as in the protrusive movement.

SUMMARY The influence of the factors of occlusion on the degree of cuspal inclines was described. The effect of altering the condylar and incisal guidances on the inclines of the posterior teeth was determined in combination with the effect of altering the occlusal plane and the compensating curve.

Reference 1. Hanau, Buffalo,

R. L.: Full Denture 1930, R. L. Hanau.

ALVARO OBREGON No. 123 “EDIFICIO CUAUHTEMOC” DESP. 802 50. PISO MEXICO 7, D. F.

Prosthesis-Intraoral

Technique

for

Articulator

Model

H,