An evuludon

of terminal

neuromuscular

positisn

Part II. Duplicate Gerald

N. Graser,

hi

pdfion and in edenWkws patiw3ts.

manQibutar

D.D.S.,

cktures*

MS.**

Eastman Dental Center, Rochester, N. Y.

A

discrepancy between the terminal hinge position (THP) and the neuromuscular position (NMP) for edentulous patients was reported in Part I of this investigation. The next question that arises is, of what clinical significance is this discrepancy in jaw relations for edentulous patients ? One of the best methods of analyzing this problem is to use duplicate dentures, one denture fabricated to the terminal hinge position and the other to the neuromuscular position. Denenl was one of the first to use duplicate dentures. He fabricated two sets of complete dentures for one edentulous patient, one set using the apex of the Gothic arch (needlepoint) tracing and the other set in the “comfortable” position. He concluded that the patient does not accept dentures fabricated with the mandible in the most retruded position. Lammie, Perry, and Crumm2-4 studied the effect of complete dentures occluding maximally in six different positions. They used one maxillary denture and six mandibular dentures for one patient. The NMP was 1.0 mm. anterior to the THP for this subject. Electromyographic results showed maximal power only with the denture fabricated to the NMP, with little difference in chewing between the THP and the NMP dentures. They found a briefer chewing stroke and a reduced masticator-y pressure with the denture fabricated to the THP. These two clinical studies alone in the literature compare the THP to the NMP in edentulous patients. However, only one subject was used in each, thereby limiting the applicability of the results. The purpose of the second part of this study was to determine whether or not a denture fabricated to the NMP could be as functional as one fabricated to the THP. Read

before

the Academy

From a thesis submitted degree of Master of Science, *Part

I, J. PROSTHET.

**Instructor.

12

of Denture by the University DENT.

36:

Prosthetics, author in partial of Rochester. 491-500,

1976.

Minneapolis, fulfilment

Minn. of the

requirements

for

the

ES”:

THP

Fig.

METHOD

AND

1. Duplicate

mandibular

dentures

and NMP

with

single

in edentulous

maxillary

patients

13

denture.

MATERIALS

Six subjects in good health and with a favorable prognosis for stability and retention of denture bases were selected. They were patients at the Eastman Dental Center, Department of Prosthodontics, and in need of new complete dentures. They were not told that they were to participate in a research project. Final maxillary and mandibular impressions were made, and heat-cured acrylic resin bases were fabricated. A selected hinge axis, 13 mm. ahead of the foot of the tragus along the tragus-canthus, was used for a face-bow transfer and related to a Hanau model H-2 articulator.* A THP recording was made at the desired vertical dimension of occlusion using manual guidance. Then the mandibular base and mounting cast were mounted on the articulator. The THP was verified in three dimensions by using Centric Check Points,* machined to 0.001 inch. The position was considered correct when substantiated by the author and another dentist. The NMP was established by placing three large metal cups on the lower points in such a manner that they were at the same vertical dimension of occlusion and then by filling them with baseplate wax. The subject was seated upright without a head support and asked to open and close his jaws once in a relaxed manner. When three exactly duplicated NMP records were obtained, the distance between this point and the THP was measured. A minimal difference of 0.28 mm. and a maximal one of 2.77 mm. were used for this study. The completed mandibular base was previously duplicated as described in Part I. This second base and mounting cast were placed on the articulator at the NMP in the same manner as the first. *Hanau

Engineering

Company,

Buffalo,

N. Y.

14

.I. l’mthet. Dent. January, 1977

Graser

Table

I. THP

and NMP-Duplicate

mandibular

Sex

Years edentulous

THPNMP discrepancy (mm.)

70

F

21

1.15

None

II

50

F

2

2.17

None

III IV

35 80

M F

5 30

2.45 1.86

None Soreness of prominent genial tu-

Subjeer

Age (yrs.)

I

Discomfort

denture

study

Maslicatory effectiveness

Subjecr observations

NMP denture better With time, could function at first with both effectively Both fine initially; Approximately I month NMP denture better after insertion, THP denwith time ture caused maxillary denture to loosen, especially while eating No preference No preference No preference No preference after soreness relieved

bercle with

V

51

F

6

I .21

THP denture None

VI

74

M

3

0.28

None

No preference Definite preference for NMP denture initially; slight preference for NMP with time

Slight preference for THP denture, as it seemed to fill out lower lip more Definite preference for NMP denture initially; slight preference for NMP with time

Then the denture was completed in the following manner. After the try-in, 30 degree porcelain posterior teeth were used to increase the perceptiveness of the subject to positional discrepancies. Two identical molds of mandibular teeth were selected. The first set was arranged at the THP in cross-tooth and cross-arch balanced occlusion. The second set was placed in the NMP and completely balanced in a similar manner. The mandibular anterior teeth were arranged to resemble the first setup as closely as possible. The waxing of both mandibular dentures was completed so that they looked alike. The maxillary and the two mandibular dentures were processed and finished according to the standard technique of the Department of Prosthodontics, Eastman Dental Center (Fig. 1) . At the next appointment, the maxillary denture and one of the mandibular dentures were inserted. The subject was not told that two mandibular dentures had been fabricated. Adjustments were made until the subject was comfortable, but at no time was the occlusion adjusted. The maxillary denture was not adjusted unless a gross sore spot existed. Once the subject was comfortable with the first mandibular denture, the other denture was substituted without the knowledge of the subject. The sequence of mandibular denture insertion was reversed for every other subject. When this denture needed no more adjustment, the first mandibular denture was reinserted. Without telling the subjects about the substitutions, the procedure was repeated at intervals for several weeks. Finally, the subjects were told about the fabrication of

THP

Fip. 2. THP cusp

mandibular denture of the maxillary first molar

Fig. 3. NMP mandibular denture cusp of the maxillary first molar

and NMP

in edentulous patients

15

is located at the NMP. Note the relation of the mesial to the buccal groove of the mandibular first molar.

buccal

is located at the THP. Note the relation of the mesial to the buccal groove of the mandibular first molar.

buccal

the two mandibular dentures and asked whether Then they were allowed to take both mandibular to determine which one they preferred and why. necessary adjustments, patient observations, and by the author and another dentist. A study was perience of the subjects for possible correlations.

or not they had realized this fact. dentures home for several weeks The information on discomfort and masticatory experience was noted made of the dentures and the ex-

RESULTS None of the six subjects was aware that two mandibular dentures had been fabricated until told. When they were allowed to change from one mandibular denture to the other every 3 days for several weeks, they made their own observations. The first subject appeared to function better with the denture fabricated to the NMP, but in time, he could wear either one comfortably, and after several weeks, he had no preference. The second subject did well with both dentures initially but approximately 1 month later, complained about the looseness of the maxillary denture when she used the one fabricated to the THP. This subject had a definite preference for the NMP denture. The third subject found no difference between the two dentures and had no preference. The fourth subject had soreness of a prominent genial tubercle after wearing the THP denture but had none with the NMP denture. This subject observed no other differences and had no preference. The fifth subject had no soreness from either denture. After interchanging them for several weeks, she had a slight preference for the THP denture, because it seemed to fill out her lower lip a little more. Shortly after being told of the two dentures, the sixth subject believed that he had a definite preference for the NMP denture. After using them for several more weeks, his preference for the NMP denture was only slight (Table I). Thus, three subjects had no preference, one subject had a slight preference for the THP denture for esthetic reasons only, one subject had a slight preference for the NMP denture because of increased mandibular denture stability, and one subject had a definite preference for the NMP denture because of looseness of the maxillary denture when wearing the THP mandibular denture,

16

Graser

.I. Prorthet. Janualy,

Dent. 1977

DISCUSSlON

Duplicate mandibular dentures were used to assess the clinical effect of the THP and the NMP upon the ability of the subject to function with a prosthesis. The anterior force directed on the maxillary denture when the THP denture was closed in the NMP by the subject (Figs. 2 and 3) may have been the reason for the looseness of the maxillary denture for that subject, and the posterior force on the mandibular denture may have caused the sore genial tubercle for another. However, definite clinical conclusions cannot be drawn from the subjective data on the limited number of subjects. It can be stated, however, that these subjects were able to function at least as well with dentures fabricated to the NMP as with those fabricated to the THP. The finding that a patient can function with a denture fabricated to the NMP as well as, and in some instances better than, with one fabricated to the THP is somewhat in agreement with Denen.’ He reported that the patient preferred the dentures fabricated to the NMP and concluded that the patient would not accept dentures built to the most retruded position. However, he had fabricated only two sets of dentures with the patient’s knowledge and had used only one patient. Lammie and associates’-* found little difference in the patient’s comfort and ability to chew between two mandibular dentures, one fabricated to the NMP and the other to the THP. They also used only one subject who knew at the start of the study that different dentures were to be evaluated. There are several clinical implications of the findings from this research. Individual variation requires consideration when establishing occlusion for edentulous patients. Trying to establish maximal intercuspation at the most retruded point for all subjects without allowing freedom of closure at the same vertical position can cause denture problems, as observed with two subjects, and possibly even more serious long-range changes in the supporting structures. Although the differences between two recordings of the NMP,,-,, on different occasions were statistically significant, a 0.10 mm. difference should not rule out its clinical use. On the contrary, it is necessary to observe the NMP for each subject. The occlusion can be established in a special manner. Subjects with poor repeatability in the NMP may require the THP location as a reference position, but the anterior freedom provided will correspond to the THP-NMP discrepancy both anteroposteriorly and mediolaterally. Subjects with a minimal discrepancy between the positions (i.e., less than 1 mm.) and good reproducibility could have the occlusion established at either position, allowing freedom in all possible directions. Subjects with a large discrepancy (i.e., 1 mm. or more) and good reproducibility at the NMP require maximal intercuspation established at this point with anterior and mediolateral freedom up to approximately 0.50 mm. Then they can be allowed a short retrusive movement equal to the discrepancy between THP and NMP, since some use of the THP has been found.” Dentist guidance for subjects with poor repeatability can be useful. The dentist can help to stabilize the mandibular base and/or provide guidance of the mandible in NMP with minimal or no posterior pressure. This procedure allows for a closer approxrmation to the NMP. Ingervall and associates” and Federick? found that as

THP

and NMP

in edentulous patients

17

posterior pressure is increased, a more retruded position is found. To eliminate this variable and arrive more nearly at an NMP, no posterior pressure should be used. Hickey and associates8 have concluded there is a need for freedom of cusp movement in the NMP because of the variation and the amount of condylar movement found in their study. Schuyler” also has emphasized that it is essential to provide both anteroposterior and mediolateral freedom in jaw position. These observations agree with the results of this study. Freedom is necessary not only because of variability in jaw closure from time to time but also because of changes in jaw position as a result of posture and head position. The difference in position caused by posture has been documented by Helkimo, Ingervall, and Carlssomn.‘” Therefore, it does not appear that use of a singIe jaw position with point contact will produce the most stable occlusion for edentulous patients. For each patient, it is necessary to exactly locate where maximal intercuspation should occur and to determine how broad the area (anteroposterior and mediolateral) around it should be. The NMP method can be used clinically for edentulous patients if several records are made to determine a position anterior to THP, and a record that lies within this variation is selected. This procedure will give a record identifying individual differences from the THP anteroposteriorly and mediolaterally for each patient. Freedom anterior and mediolateral to the NMP record should be established to allow for variation in closure, with posterior freedom equal to the discrepancy between THP and NMP being optional. The need for verifying jaw relations is as important as the method itself because of the amount of individual variation among dentists and patients. SUMMARY

AND

CONCLUSION

The purpose of Part II of this study was to determine whether or not a denture fabricated to the neuromuscular position (NMP) could be as functional as one fabricated to the terminal hinge position (THP) . Two mandibular dentures were fabricated for each of six edentulous subjects, one to the THP and one to the NMP, along with only one maxillary denture each. The subjects had no prior knowledge of the two mandibular dentures in order to determine the clinical significance of a difference in the two positions. These results were evaluated by clinical methods. It was concluded that the NMP is clinically acceptable for intercuspation of artificial teeth on complete dentures. References 1. Denen, H. E.: Movements and Positional Relations of the Mandible, J. Am. Dent. Assoc. 25: 548-552, 1938. 2. Lammie, G. A., Perry, H. T., and Crumm, B. D.: Certain Observations on a Complete Denture Patient. Part I. Method and Results, J. PROSTHET. DENT. 8: 786-795, 1958. 3. Lammie, G. A., Perry, H. T., and Crumm, B. D.: Certain Observations on a Complete Denture Patient. Part II. Electromyographic Observations, J. PROSTKET. DENT. 8: 929939, 1958. 4. Lammie, G. A., Perry, H. T., and Crumm, B. D.: Certain Observations on a Complete

18

.I. Prosthet. Dent.

Graser

January.

lqii

Denture Patient. Part III. Considerations of the Results From a Neuromuscular Viewpoint, J. PROSTHET. DENT. 9: 34-43, 1959. 5. Pameijer, J. H. N., Brion, M., Glickman, I., and Roeber, F. W.: Intraoral Occlusal Telemetry. Part V. Effect of Occlusal Adjustment Upon Tooth Contacts During Chewing and Swallowing, J. PROSTHET. DENT. 24: 492-497, 1970. 6. Ingervall, B., Helkimo, M., and Carlsson, G. E.: Recording of the Retruded Position of the Mandible With Application of Varying External Pressure to the Lower Jaw in Man, Arch. Oral Biol. 16: 1165-1171, 1971. 7. Federick, D. R.: A Correlation Between Force and Distalization of the Mandible in Obtaining Centric Relation, Thesis, Boston University, Boston, Mass., 1972. 8. Hickey, J. C., Woelfel, J. B., and Stacy, R. W.: Mandibular Movements in Three Dimensions, J. PROSTHET. DENT. 13: 72-92, 1963. 9. Schuyler, C. H.: Freedom in Centric, Dent. Clin. North Am. 13: 681-686, 1969. 10. Helkimo, M., Ingervall, B., and Carlsson, G. E.: Variation of Retruded and Muscular Position of the Mandible Under Different Recording Conditions, Acta Odontol. Stand. 29: 423-437, 1971. 1501

EAST AVE. N. Y. 14610

ROCHESTER,

ARTICLES

TO APPEAR

IN FUTURE

ISSUES

Porcelain shade stability after repeated flring Nasser Barghi, D.D.S., and Joel Goldberg, D.M.D. The comparison of denture-base Curtis M. Becker, D.D.S., M.S.D., B.E., M.A.Sc., Ph.D. lingual Melchor

flange Bocage,

design Odont.Dr.,

in

Dale

complete and Jaime

Subjective reactions to dentures Larry D. Campbell, D.D.S.

major

processing E. Smith,

dentures Lehrhaupt,

of an enzyme Connor, M.D.Sc.,

denture Charles

M.

Parts I and II and Jack I. Nicholls,

Odont.Dr.

connector

designs

Scanning electron microscope study of in restoration finishing techniques Kai Chiu Chan, D.D.S., M.S., John W. Edie, Ph.D. An evaluation James N. E. Taylor, M.D.S.

techniques. D.D.S., M.S.D.,

marginal MS.,

for

removable

adaptation Ph.D.,

cleanser Schoenfeld,

and

D.D.S.,

Carl

partial

of

amalgam

W. &are,

Ph.D.,

and

D.D.S.,

Ross

L

An evaluation of terminal hinge position and neuromuscular position in edentulous patients. Part II. Duplicate mandibular dentures.

An evuludon of terminal neuromuscular positisn Part II. Duplicate Gerald N. Graser, hi pdfion and in edenWkws patiw3ts. manQibutar D.D.S., c...
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