Seminars in Orthodontics VOL 9, NO 2 JUNE 2003

Introduction

T he study of gnathology concerns itself with the harmonious functioning of the jaws

and teeth; stated this way, who would feel com- fortable arguing that "gnatholoD," has no place in orthodontics? Since the formation of the Gna- thological Society in 1926 by McColhun, the study of jaw movement as it is related to occlu- sion was a central focus in reconstructive den- tistry. It was not, however, until the 1970s that Dr Ronald Roth ' proposed the introduction of gna- thological principles, modified for consider- ations of natural teeth, into orthodontic diagno- sis and treatment philosophy. This formally at tempted to m a n y jaw function and tooth fit within a mutually protected functional scheme. Before that time, orthodontic goals were mostly aimed at attempting to achieve an acceptable static occlusion such as later described by An- drews ~ in his 1972 article, "Six Keys to Normal Occlusion," or more recently in "The American Board of Orthodontics (ABO) Objective Grad- ing System for Dental Casts and Panaoramic Radiographs" presented in 2000) Ahhough the ABO required in its case workups tor hoard certification an assessment of the fnnctional oc- clusion, its characteristics and measurement were tbr the most part not formally considered in traditional orthodontic treatment.

Since the mid-1980s, a paradigm shift has occurred from the traditional prima W etiologic cause and effect occlusion views to the new cur- rent view stated as follows: "We have to come to understand the enormous range of structural variability among human masticatol y systems, that what individuals do with their occlusions may be more important than structural relation- ships, and that this system, like all musculoskel- etal systems, often adapts to changing structural and functional demands. We are not implying that therapy, once initiated, should not adhere

Cop),Hgq~t 2003, Elsevier Scie*u'e (U&I). All @dlts te~e~wed. doi: 10.1053/~odo. 2003. 34029

to strict technical standards. However, arriving at a decision of when to treat, and toward what end, deserves a less rigid ontlook at the present time."~

Under these new philosophical consider- ations, interest ii1 and concern about gnatho- logical concepts are considered either unwar- ranted or unnecessa U. It should be noted, however, that even these individuals fnlly recog- nize and appreciate the tact that if fnll-mouth rehabilitation is required, either prosthetically or orthodontically, that traditional gnathologi- cal concepts lend themselves to clinically rele- vant reconstructive techniques that have been empMcally shown to provide acceptable patient o u t c o l n e s .

Central to any flfll-mouth rehabilitation tech- nique, e.itlmr orthodontic or prosthetic, is the concept of a centric relation that is reproduc- ible, stable, and can be obtained independent of the occlusion. It is determined by manipulation of the mandible and is a purely rotary movement about tile transverse horiz(mtal axis) Its use as a therapeutic condylar reference position for re- storing the occlusion is empirically valid and central to diagnosis, treatment planning, aud case completion. '~

In orthodontics, a specialty essentially dealing with full-mouth reconstruction in enamel, cen- tric relation (CR) considerations should also be a central theme for evm T orthodontist. The power centric bite advocated by Roth allows tile condyles to be positioned superior and anterior in the fossa and seated against the posterior slope of the eminence with tile thin avascular portion of the disc interposed and centered. According to Roth, ~ this CR position must be coincident with maximum intercuspation (MI) of the teeth to achieve an ideal flmctional post- orthodontic occlusion.

Tile purpose of the articles in this issue of Semi~a,:~ in Orthodontics is two-fold: illst, to ex- plore the accuracy and reproducibility of various aspects of the gnathological technique, which

Seminars in Orthodontics, Vol 9, No 2 (]u~e), 2003: pp 9;'-95 93

94 Kulbersh, Kaczynski, and Freeland

uses ins t rumentat ion to diagnose, treat, and es- tablish a mutually protected functional scheme; and, second, to ti T and assess whether, in fact, any difference really exists between or thodont ic t rea tment r endered with the utilization of gna- thological ins t rumentat ion using m o u n t e d mod- els or a less rigid approach guided solely by opera tor exper ience and chairside visualization of the occluso-functional end result.

In the first two articles, the authors evaluate the following aspects of gnathological instru- menta t ion used in the Roth or thodont ic tech- nique: the Condylar Position Indicator (CPI, Pa- naden t Corp, Grand Terrace, CA) and the Roth power centric 2-piece Delar blue wax registra- tion bite (Delar Co, Lake Oswego, OR). In the next three articles, the authors assess one central aspect of the gnathological approach: MI-CR co- incidence. In other words, they address whether or not finished or thodont ic cases exhibit greater MI-CR ha rmony if t reated with the gnathological ins t rumentat ion approach using m o u n t e d mod- els, ra ther than the less rigid, operator-visualized nonins t rumenta t ion technique. The third arti- cle by Klar et al explores the MI-CR change f rom pre- to post- t reatment in 200 consecutively treated gnathological cases. Is there a differ- ence? In the next article by Kulbersh et al, MI-CR postor thodont ic t rea tment differences between a gnathological sample versus a non- gnathological control are assessed. Is there a difference between these t rea tment modalities? Pangrazio-Kulbersh et al address the issue of MI-CR pos t t rea tment differences in two-phase functional t reatment , involving a first-stage func- tional appliance reg imen followed by a second stage of fu l l -banded /bonded or thodont ic appli- ances versus one-phase gnathologic-oriented treat- rnent. Do functional appliances used for a phase I t reatment affect the MI-CR outcome? Finally, Free- land and Kulbersh present two cases in which the pat ient 's dysfunctional occlusion is clearly indi- cated by articulator mount ings and fur ther eval- uated through the use of hinge axis and condy- lar position indicator (CPI) recordings. Could one have reached the same t rea tment diagnosis and or thodont ic end result without this gnatho- logically or iented ins t rumentat ion approach? In all instances, the CPI was used to measure con- dylar position change in five dimensions (right x and y, left x and y, and transverse) as affected by interferences at the occlusal level. This informa-

tion was then used with appropr ia te analyses to establish a t rea tment plan as well as to assess the MI-CR outcome postor thodont ic therapy.

Although, the general t rend in current dental t rea tment phi losophy considers the issue of MI-CR disharmony and its relationship to tem- p o r o m a n d i b u l a r j o i n t dysfunction (TMD) prob- lems as unclear, 7 the following quote should be considered: "The most conspicuous lapse of logic is perhaps the s ta tement that the majority of studies show no association between occlusal factors and TMD; therefore, they are not caus- ally linked. The reiteration of such an obvious error in reasoning in articles on TMDs only serves to misdirect research efforts. Absence of evidence is not evidence of absence. TM

It should be noted, first, that based on the work presented here, MI-CR harmony can be improved by or thodont ic therapy using a gna- thological approach tbr diagnosis and t rea tment planning. And, second, that in all the articles presented here assessing pre- t rea tment and post- t rea tment records of gnathological versus nong- nathological therapy, a single statistically signif- icant difference was consistently noted in all s i tua t ions-- the vertical. In fact, were it not tbr the case selection exclusionary parameters (ie, very careful opera tor clinical assessment of MI-CR ha rmony pos tdeband for the uongnatho- logical group and moun ted models showing only 1-2 m m vertical discrepancy at the pin be- fore gnathological positioner) statistically signif- icant differences may well have been noted in more than .just the vertical dimension. It would appear that the vertical dimension cannot be appropriate ly diagnosed unless moun ted mod- els are used. The consistency of this vertical discrepancy difference is worth noting. Its impli- cations with regard to pat ient 's s tomatognathic functional health are not clearly research docu- men ted but warrant fur ther investigation. Cer- tainly, vertical condylar distractions in the order of 2 to 3 m m may not only require t rea tment plan modifications but also potentially affect pa- tient occlusofunctional health. ~

In summary, al though the dental scientific literature has its naysayers regarding the rela- tionship between occlusal dysfunction and TMD, this issue is far f rom resolved. In fact, articles based on good sample size and sound research design cont inue to appear, implicating various aspects of occlusal dysfunction as sus-

Introduction 95

raining or contributing factors in the develop- ment o f TMD problems." It appears prudent as dentists, therefore, to h o n o r the concept of harmonious stomatognathic system function. Ir- respective o f definitive, research-documented, health-related issues, a gnathological approach as advocated by Dr Roth serves another vm T valuable purpose: it sets goals that are necessaD~ and clinically useful when orthodontical ly recon- structing a functional bite.

R i c h a r d K u l b e r s h , D M D , MS

R i c h a r d Kaczynsk i , P H D

Theodore F r e e l a n d , DDS, MS

Guest Editor~

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