Eliminating Lower Retention - R. Williams, JCO 1985[1].pdf

retention and relapse

1. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Eliminating Lower Retention
RALEIGH WILLIAMS, DDS, MSD
The frequency with which lower retainers are used after treatment to prevent lower incisor or
cuspid collapse suggests there is little understanding of how to avoid these posttreatment events.
However, several steps can be taken during fixed appliance treatment to eliminate the need for
retention in the lower dentition.
My study of how to achieve post-treatment stability in the lower arch without retention was
begun 21 years ago. For the patients followed, all lower retention was eliminated and constant
observations were made to see what had to be done to create post-treatment stability, especially in
the lower incisors. Six treatment keys have emerged as essential if lower retention is to be
eliminated.
First Key
The incisal edge of the lower incisor should be placed on the A-P line or 1 mm in front of it. This
is the optimum position for lower incisor stability (Fig. 1). It also creates optimum balance of soft
tissues in the lower third of the face for all the variations in apical base differences within the
normal range
1 (Fig. 2).
The angulation of lower incisors has not proven to be relevant to their stability. A lower incisor
angulation of 90° to the mandibular plane, or 65° to the Frankfort plane, may be esthetically
appropriate and stable for those who have optimal Northern European skeletal configurations, but
not for members of other ethnic groups.
Appliance control is required to achieve optimal position of the lower incisor consistently at the
end of treatment. Point A on the upper end of the A-P line can be retracted. Point P, at the lower
end, will move forward or not depending on mandibular growth. With experience, the clinician will
know how each end of this line changes, which procedures will place the lower incisor 1 mm in
front of the line, whether extractions are necessary, and which teeth should be extracted.
2
If the lower incisor is advanced too far beyond the A-P line, relapse and crowding will occur.
Lower incisors that are overly proclined in treatment— beyond one standard deviation— can only
be maintained in such an untenable position with a fixed retainer. When the retainer is removed, the
incisors will move lingually and become crowded.
Second Key
The lower incisor apices should be spread distally to the crowns (Fig. 3) more than is generally
considered appropriate (Fig. 4), and the apices of the lower lateral incisors must be spread more
than those of the central incisors. The Begg technique is geared to achieve the necessary progressive
spreading, but none of the current straightwire systems provides adequate lower incisor slot
angulations to bring about sufficient progressive spreading of lower incisor apices. When the lower
Article Text 1

2. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
incisor roots are left convergent, or even parallel, the crowns tend to bunch up and a fixed lower
retainer is usually needed to prevent post-treatment relapse.
Third Key
The apex of the lower cuspid should be positioned distal to the crown (Fig. 5). The occlusal
plane, rather than the mandibular plane, should be used as a positioning guide. Use of the
mandibular plane might indicate that the apex is not sufficiently distal to the crown, when in fact it
is if the occlusal plane is used. Such a circumstance could occur when there are highly divergent
occlusal and mandibular planes in a steep mandibular plane angle case.
This angulation of the lower cuspid is important in creating post-treatment incisor. stability
because it reduces the tendency of the cuspid crown to tip forward into the incisor area. If this
happens, the lower incisors crowd up, even if their roots are spread and the incisal edges are on the
A-P line or 1mm in front of it. Distal inclination of the lower cuspid should be a standard treatment
objective and is easily accomplished with the Begg or any straightwire technique. Straightwire
systems agree within 4-6° of inclination of the lower cuspids to the occlusal plane.
Fourth Key
All four lower incisor apices must be in the same labiolingual plane (Fig. 6). Spreading the
apices of the lower incisor roots distally causes a strong reciprocal tendency for the crowns to move
mesially. Moreover, as the roots are spread, the contact areas between the incisor crowns move
upward toward the anatomical contact points, which are small, rounded, and near the incisal edge.
Because of the strong mesial pressure on the crowns during the root spreading process, there is a
tendency for these contact points to displace each other labiolingually. This results in a reverse
movement of the apices linguolabially.
The displacement forces are considerably augmented by the increasing width of the lower incisor
crown toward the incisal edge and contact point. This means that provision for the additional space
must be made during the spreading process. Otherwise, labiolingual apical displacement of the
lower incisors will tend to occur, and the degree to which it occurs will affect lower incisor
posttreatment stability.
Experience has shown that the labiolingual apical displacement of the lower incisors can occur
easily if round wires are used during the spreading process, because round wires forfeit labiolingual
control. To maintain labiolingual apical control during the spreading process— using uprighting
springs in the third stage of Begg treatment— an edgewise sectional auxiliary in the incisor region
along with the main round archwire is effective. With the edgewise technique, spreading begins at
the start of treatment, so any labiolingual apical displacements occurring from the initial use of
round wires can be corrected later when rectangular arches are used.
Fifth Key
Article Text 2

3. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
The lower cuspid root apex must be positioned slightly buccal to the crown apex. This is
extremely important because of its influence on post-treatment stability. All sorts of occlusal forces
await their chance to exert lingual pressure on the lower cuspid crown. If the apex of the lower
cuspid is lingual to the crown at the end of treatment, the forces of occlusion can more easily move
the crown lingually toward the space reserved for the lower incisors because of these functional
pressures plus a natural tendency for the crown to upright over its root apex. Even if a lower cuspid
with abnormal lingual position of the apex were supported for many years with a fixed retainer, the
crown would eventually move lingually when the restraint was removed (Fig. 7).
The old concept that lower intercuspid width cannot be increased permanently is only true some
of the time. After treatment, the newly acquired lower intercuspid width will be maintained without
retention if the lower cuspid crowns are moved distally into a wider part of the jaw and if their
apices are moved buccally so they are at least under the crown. If the apex is not moved buccally
along with the crown while distalizing the cuspid, lingual relapse of the crown into the incisor area
is likely.
Until the advent of straightwire brackets with built-in torque, there was a tendency for the old
edgewise bracket to move the lower cuspid apex lingually whenever rectangular wires were used
(Fig. 8). Unless the clinician took the precaution to place appropriate buccal root torque into the
rectangular wire, increased lingual root position of the lower cuspid was bound to result. Lower
fixed retention was then routinely needed to prevent intercuspid distance from diminishing and
incisors from collapsing.
To torque the lower cuspid apex buccally, a Begg clinician can use a simple auxiliary. An
edgewise clinician can place the appropriate torque in the rectangular wire. There is a bewildering
range of lower cuspid buccal root torques in straightwire edgewise brackets, from -11° to + 7°, a
total variation of 18°. Between the lower right and left cuspids, the combined variation can be 36°.
Variations in crown slopes to which the variously torqued brackets are attached compound the
dilemma.
Sixth Key
The lower incisors should be slenderized as needed after treatment. Lower incisors that have
sustained no proximal wear have round, small contact points, which are accentuated if the apices
have been spread for stability (Fig. 4C). Consequently, the slightest amount of continuous mesial
pressure can cause various degrees of collapse in the lower incisor segment.
There are two sources for post-treatment pressure on the lower incisors that may bring about a
shifting or collapse even though all other key treatment requirements have been accomplished. One
source is the molars. Current evidence indicates that natural mesial pressure is limited to the upper
and lower molars. Molar pressure can cause displacement of lower incisor contact points. Removal
of third molars does not eliminate the mesial pressure derived from the first and second molars, and
"there is little rationale, based on present evidence, for the extraction of third molars solely to
Article Text 3

4. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
minimize present or future crowding of lower anterior teeth".
The second source of hidden pressure is an adverse tooth-jaw relationship. Who can say that the
removal of two, four, six, or eight teeth will provide the perfect solution for tooth-jaw discrepancy?
It is conceivable that the right combination to provide balance and stability in some instances
should be the removal of 1¾ teeth or 3¾ teeth. But we can only do our best by removing whole
tooth units when indicated.
Flattening lower incisor contact points by slenderizing or stripping creates flat contact surfaces
that help resist labiolingual crown displacement. This treatment also helps eliminate the need for
lower incisor retention (Fig. 9).
Begg said, "Unless sufficient tooth substance is eliminated from mouths having it in excess,
neither artificial post-treatment retention nor factors inherent in the dental apparatus itself can
prevent relapse after treatment. Even after reduction of tooth substance by extractions, the balance
between jaw accommodation and tooth size may not precisely match, even with competent
treatment, and slenderizing may be necessary."
4
If the post-treatment dentition displays pressure signs by developing irregularities among the
incisors, reduction of incisor width by slenderizing can be the answer. Usually only minimal tooth
structure has to be removed if the root apices have been adequately spread. Occasionally, more than
one slenderizing session may be necessary to bring the tooth mass into harmony with the jaw size
and to eliminate the need for lower incisor retention.
Some post-treatment situations do not seem to have a detrimental effect on lower incisor
stability. One is the depth of the overbite, and another is prodigious mandibular growth that carries
the lower incisors forward against the upper incisors and tips them out. Experience has shown that
neither of these requires the protection of a lower retainer.
Summary
By observing the six treatment keys, it is possible to eliminate lower incisor retention following
fixed appliance therapy. Clinicians who want to eliminate lower retention may find that they have
to increase their extraction percentage in order to achieve the six keys adequately (Fig. 10).
RALEIGH WILLIAMS
Article Text 4

5. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
FIGURES
Fig. 1
Fig. 1 To achieve stability and soft tissue balance in the lower third of the face, optimum position of lower incisal edge
is on or 1 mm in front of A-P line.
Article Text 5

6. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Fig. 2
Fig. 2 A. Moving lower incisor back 4mm to A-P line provided stability without lower retention and improved facial
harmony. B. Lower incisor was moved forward 2mm to produce facial harmony. Because it moved only to A-P line, the
incisor remained stable and no lower retention was needed.
Article Text 6

7. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Fig. 3
Fig. 3 A,B. Convergent lower Incisor roots before being spread distally for stability. C,D. Same case after roots were
spread adequately.
Article Text 7

8. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Fig. 4
Fig. 4 Root apices in typically convergent position (top). Root apices insufficiently spread to assure stability without
retention (middle). Root apices sufficiently spread so that, if other treatment keys are attained, stability of lower incisors
without retention can be expected (bottom).
Article Text 8

9. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Fig. 5
Fig. 5 Apex of lower cuspid positioned distal to crown for protection of lower Incisor stability after treatment.
Fig. 6
Fig. 6 A. Lower incisor apices well aligned in same labiolingual plane. If other treatment keys are attained stability of
lower incisors without retention can be expected. B. Crowns aligned but lower incisor apices not aligned in same
labiolingual plane. Unless this is corrected, there is little likelihood of lower incisor stability.
Article Text 9

10. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Fig. 7
Fig. 7 Faulty lingual position of lower right cuspid apex.
Fig. 8
Fig. 8 Old-style edgewise bracket automatically created lingual positioning of lower cuspid apex unless clinician placed
adequate buccal root torque in rectangular archwire.
Article Text 10

11. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
Fig. 9
Fig. 9 A. Small, round contact points of lower incisors. B. Small size and shape of contact points make it easy for
pressures from the rear, or inadequate space in the jaw, to cause their dislodgment. C. Flattening contact points and
reducing mesiodistal width of lower incisors makes it possible to eliminate lower incisor retention, provided other
treatment keys have been attained.
Fig. 10
Fig. 10 Stable lower incisor segment two years alter treatment and no retention.
Article Text 11

12. JCO on CD-ROM (Copyright © 1997 JCO, Inc.), Volume 1985 May(342 - 349): Eliminating Lower Retention - RALEIGH WILLIAMS, DDS, M
References
1. Williams, R.: The Diagnostic Line, Am. J. Orthod. 55:458-467, 1969.
2. Williams, R.: The Effect of Different Extraction Sites Upon Incisor Retraction, Am. J. Orthod. 69:388, 1976.
3. Laskin, D.S.: Third Molars, Letters to the editor, ADA News, March 26, 1984.
4. Begg, R.R. and Kesling, P.C.: Begg Orthodontic Theory and Technique, W.B. Saunders Co., Philadelphia, 1971, p.
660.
Article Text 12