1. The Anterior component of occlusal force
Part1: Measurement and distribution
Thomas E. Southard, Behrents & Tolley
American Journal of Orthodontics and Dentofacial Orthopedics
December 1989
2. THE ANTERIOR COMPONENT OF OCCLUSAL FORCE
● Occlusal force projected towards front of
mouth
● Result of axial inclination of posterior teeth
● Causing teeth to tip forward during occlusal
loading
● Transmitted through interproximal contacts
3. Objective:
• To design and develop instrumentation to measure the Anterior
component of force generated by a single tooth under axial load and
to quantify the distribution and dissipation of this force
4. Methods and Materials
• ACF calculated from frictional
force measurements
0.0015 inch SS
matrix strip
Tension
trasducer
5. CALCULATION OF INTERPROXIMAL FORCE
1. (u) =known coefficient of dynamic friction between tooth enamel and
matrix material,
1. (IPF)=the interproximal contact force
1. (f)=Frictional force resisting withdrawal with the following equation
IPF = f / 2u
6. Determination of Value of u
● A known IPF was applied between extracted teeth.
● A dental matrix strip was slipped interproximally, and f was measured as the
matrix strip was withdrawn.
● The coefficient of dynamic friction was calculated from the following
relationship: u = f/[2(IPF)].
● With five extracted teeth, the mean value of u was found to be 0.145
7. Bite force transducer design and occlusal load distribution
• Restrict biting to a select
cusp of a single tooth
Functional Cusp-
The mesiobuccal cusp of the mandibular
left second molar or the mesiolingual
cusp of the maxillary
left second molar.
8. • 15 adult volunteers participated
• Intact dentition and healthy periodontal tissue
• No temporomandibular joint dysfunction
11. ACF CALCULATION
For each contact, the IPF (biting) measurements were averaged as were the IPF (not
biting) measurements.
The ACF = IPF (biting) - IPF (not biting).
Because the precise biting force (BF) was rarely 20 pounds, the ACF was calculated and
normalized for a 20-pound load on the second molar with the following formula:
ACF = [IPF(biting) - IPF(not biting)](20/BF).
12. The ACF dissipated by each tooth into its supporting periodontium = ACF
measured at its mesial -ACF distal surfaces.
In instances in which either contact was slipped or restored, the dissipated force
could not be calculated.
The ACF distributions appeared to follow exponential decay functions of the form
13. RESULT
• When a dental matrix strip was inserted into interproximal contacts mesial to the
second molar and withdrawn, frictional force resisting the withdrawal subject was
biting on the second molar > subject was not biting.
• The ACF was not detected mesial to any open contacts.
• Biting with reduced load resulted in an ACF reduction for all subjects tested.
• ACF dissipated increased at increased gape
14. DISCUSSION
• ACF is transmitted only in presence of interproximal contacts
• Simplified force measurements by loading a single posterior tooth on a
select cusp tip
• Neglected the effects of cuspal inclined planes
15. Balance of horizontal forces
During the crushing of food and once maximal
intercuspation is attained, there is a balance
of horizontal forces against the inclined
planes and no net anterior force exists
except that caused by axial loading.
The horizontal
components of
resisting forces
18. • The premolars dissipated most of the force, the canine teeth play a relatively
minor role in dissipating this force but their role increases at wider gapes
GAP - ACF- ACF dissipated by canines
• The ACF progresses anteriorly through proximal tooth contacts and can pass
beyond the dental midline to the contralateral side
19. The anterior component of occlusal force
Part2. Relationship with dental malalignment
Thomas E. Southard, Behrents & Tolley
American Journal of Orthodontics and Dentofacial Orthopedics
January 1990
20. ACF -possible role in causing
1]mesial migration of teeth
2]subsequent dental malalignment
Stallard,Newcomb and Waldron hypothesized that without harmonious arch form and
proper proximal tooth contact,ACF could not be resisted and malalignment would result.
There is a correlation between interproximal forces when the subject was not biting
(contact tightness) and dental malalignment.
21. METHOD AND MATERIAL
3 groups of 5 volunteer subjects were selected on the basis of the extent of
mandibular anterior malalignment
GROUP 1 GROUP 2 GROUP 3
3M, 2F, 26YRS 3M, 2F, 27.6YRS 2M, 3F, 24.2yrs
Irregularity Index<2 mm Irregularity Index >2 mm Irregularity Index of >4 mm.
but <4mm
22. RESULTS
• The mean Irregularity Index for subjects grouped according to mandibular anterior crowding
was
group 1 - 0.94mm (SD = 0.65)
group 2 - 2.82 mm (SD = 0.85)
group 3- 7.1 mm (SD = 2.47)
• Significant correlations were detected between the irregularity of the mandibular anterior
teeth and a number of these forces.
23. • Significant correlation between the magnitude of the mandibular left IPF (not
biting) at contact 5-6 and all other such forces in the left posterior quadrants of
both arches.
24. DISCUSSION
• ACF can cause dental malalignment in persons who clench, brux, or in any other way
load posterior teeth axially for extended periods of time.
• Continuous soft tissue forces as small as 0.0035 pounds are capable of moving teeth,
forces of 0.12 pounds are routinely used to move teeth orthodontically.
• The ACF applied against the canine teeth during a conservative chewing force on the
second molar is typically 8 to 200 times greater than these forces.
• The mandibular canines could tip mesially under their influence and crowd the
mandibular anterior teeth
25. Progression of the anterior component of occlusal force
tangential (ACFt) to curvature of dental arch
26. widened gape.
increased ACF dissipation by mandibular canine
Simultaneous decrease in ACF dissipated by the lateral incisor.
larger ACF values
the ACF vector has even more of a tendency to emerge from the arch at the canines.
Canines may be tipped out of dental alignment
slipped mandibular 2-3 contacts
Vestium congue
27. • Malalignment of the mandibular anterior teeth was found to be related to the
1]magnitude of the anterior component of occlusal force
2]tightness of interproximal contacts in the mandibular posterior segments
• Teeth are squeezed together through interproximal forces, narrowing mandibular
anterior contacts resulting in slippage
Matrix strip was slipped interproximally and withdrawn at approximately
2 to 5 mm/sec Frictional resistance of withdrawal was measured as subject was biting
on left second molar with axial load approximating 20 pounds nd again while subject was not biting.
recessed area in the acrylic tab at the end of the upper bar permitted the generation of an occlusal load at only a single fixed point within the selected arch.The tension and bite force transducers were calibrated with known weights before each experiment.The bite force transducer signal was not subject to detectable temperature drift. Temperature fluctuations caused by respiration resulted in rapid thermal dimensional changes of the tension transducer and subsequent drift of the strain signal. This signal drift was reduced by enclosing the tension transducer in a thin latex encapsulation. The accuracy of this ACF measurement system was within 0.1 pound.
The use of the second molars permitted ready access to mesial contacts for ACF measurements.To obtain a dynamic frictionai force reading,the subject was asked to bite to the 20-pound level and to hold this force as the matrix strip was withdrawn.
Motion was stopped and then started again to provide two IPF (biting) readings . Two readings were then taken while the subject was not biting.
The procedure was repeated for all contacts mesial to the first molars that were neither slipped nor restored.
the process of reducing an amount of force by a consistent percentage rate over a period of time.
We simplified force measurement interpretation by loading a single posterior tooth on a select cusp tip. It may be argued that such an experimental method neglects
the effects of the cuspal inclined planes in ACF generation. ‘I An ACF should be generated as the mandible closes into maximal intercuspation and the distal acing
cuspal inclines of its posterior teeth slide along the mesial-facing cuspal inclines of the maxillary teeth.
during normal chewing on the second molars, mean ACF forces of 5 pounds against the second
premolars and 1 pound against the canines are expected. Even larger forces would be generated with elevated chewing loads or during paranormal activities
such as bruxing or clenching.
For each subject, we measured the interproximal contact force (IPF) for all contacts mesial to the first
molars.Dental models were made for each subject. Using calipers calibrated to tenths of a millimeter, we measured
the anatomic contact point displacements between each of the mandibular anterior teeth. These displacements
were summed to provide the Irregularity Index. Statisitical analyses were performed with the SAS statistical software package.
A correlation between occlusal forces and dental mAlalignment was demonstrated.
This study also revealed a correlation between interproximal forces when the subject was not biting (contact tightness) and dental malalignment.
Correlation analysis was used to quantify the relationship
between all IPF (not biting), ACF, and ACF
dissipation measurements of the left mandibular posterior
quadrant with each of the following: (1) anatomic
contact point displacements between each of the mandibular
anterior teeth; and (2) the sum of the mandibular
anatomic contact point displacements between the left
2-3, left 1-2, and midline 1-1 contacts
As the ACF vector reaches the canine, it progresses tangentially (ACFt) to the curvature of the arch . A lessened component of the ACF continues along the arch to affect the incisors. Significant lateral dissipation of the ACF should occur as the arch turns the corner at the canines, and there should consequently be an increased likelihood of contact slippage at that point.
