2010 RWISO Journal - Roth Williams International Society of ...

Effect of Gnathologic Positioner Wear on Maximum
Intercuspation CR Disharmony
Wesley M. Chiang, DDS, MS ■ Theodore Freeland, DDS, MS
■ Richard Kulbersh, DMD, MS, PLC ■ Richard Kaczynski, BS, MS, PhD
We S L e y m. ch i a n G , ddS, mS
■ MA Candidate, Orthodontic Dept.,
University of Detroit Mercy School
of Dentistry
The o d o R e FR e e L a n d, ddS, mS
tdfortho@freelandorthodontics.com
■ Adjunct Professor, Orthodontic
Dept., University of Detroit Mercy
School of Dentistry
■ Director Roth/Williams USA;
■ Private Practice, Gaylord, MI
Ric h a R d Ku L b e R S h, dmd, mS, PLc
■ Program Director, Orthodontic
Dept., University of Detroit Mercy
School of Dentistry
Ric h a R d Ka c z y n S K i , bS, mS, Phd
■ Statistician, Dept. of Psychiatry,
Yale University School of Medicine
Introduction
Centric relation (CR) refers to a physiologic position of the
mandible when the condyles are located in the superoanterior
position in the articular fossae, fully seated and resting
against the posterior slopes of the articular eminences with
the discs properly interposed. 1 It is a reproducible position
that is obtained independent of the occlusion by manipulating
the mandible in a purely rotary movement about the
transverse horizontal axis. 2
Orthodontic treatment is aimed at achieving static goals
from Andrews’ six keys to normal occlusion and the functional
scheme of mutually protected occlusion recommended
by Stuart and Stallard. 3,4 In the 1970s, Roth introduced gna-
Summary
The goal of a gnathological approach in orthodontics is to achieve a functional
occlusion, in which the mandible can close into maximum intercuspation (MI) without
deflecting the condyles from centric relation (CR). Gnathologic positioners are
used at the end of orthodontic treatment to settle the occlusion while maintaining
MI-CR harmony. The objective of this prospective study was to examine the effect
of gnathologic positioners on MI-CR discrepancy for patients treated with the Roth
gnathological approach.
Methods.The sample consisted of 26 consecutively finished cases in a gnathologically
oriented practice. All cases were treated with a gnathological treatment approach,
using the Roth prescription straight-wire appliance. A gnathologic positioner was
delivered at the time of debonding and was worn for a period of 2 months. Pre- and
postpositioner records were taken. These included a maximum-intercuspation wax
bite; a two-piece Roth power centric CR bite registration; and upper and lower models
mounted using a true hinge transfer and CR bite. The control group consisted of 8
randomly selected finished cases in the orthodontic clinic at the University of Detroit
Mercy and was retained with Hawley retainers. MI-CR discrepancy was measured
with a condylar position Indicator (CPI).
Results. Results indicate a statistically significant improvement in MI-CR discrepancy
in the right horizontal, right vertical, left vertical, and transverse planes after 2 months
of gnathologic positioner wear. The amount of condylar distraction in these 4 measurements
showed statistically significant improvement and came within the envelope
of susceptibility.
Conclusions.The positioner and control groups tend to change differently over time
in the vertical and horizontal planes, with the positioner group improving and the
control group getting worse. In the transverse plane, gnathologic positioners improve
the result of orthodontic treatment with respect to condylar axis distraction.
thological concepts into orthodontic treatment. 5,6,7 The goal
of a gnathological approach in orthodontics is to achieve a
functional occlusion, in which the mandible can close into
maximum intercuspation (MI) without deflecting the condyles
from CR. 8 Dr. Roth believed that a large discrepancy
between MI and CR can lead to breakdown in the stomatognathic
system, because the condyles are distracted from
the glenoid fossae when the teeth come into occlusion. Signs
and symptoms of occlusal disharmony include temporomandibular
joint pain-dysfunction syndrome, occlusal wear and
bruxism, excessive tooth mobility associated with periodontal
disease, and movement or relapse of tooth positions. 9
Occlusal discrepancies, if associated with joint compression,
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