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A comparative study of two techniques for recording centric relation
Reviews and abstracts
Vo/ume 87 Number 6
words, this induces a tripod situation that would create a problem of undesired molar eruption. -The appliance holds back the mandible and minimizes the possibilities of occlusal interference to avoid a reflexive forward posturing of the mandible. -If the mandible is almost in the maximal opening position already (because of the wide-open construction bite), it has limited functional range and possibilities. With limited condylar movement, intermittent occurrence of negative intracapsular pressure would be minimal. The author states that the conclusions reached and the hypotheses proposed are purely theoretical and need to be tested. Thus, he proposes further experiments to change the intracapsular environment so that the reduced functional pressure normally observed would no longer occur. What would be the consequences? A second possible experiment would be to grow condylar cartilage in organ culture while it is being subjected to intermittent atmospheric pressure diminution. This would also provide more information on the possible role of atmospheric pressure changes in condylar growth. T. M. Graber
Zur Frage der Underschiedlichen Effektivitiit der Starren und Elastisch-Beweglichen Apparate in der Tlglichen Praxis (The Question of the Relative Effectiveness of the Rigid and Elastic Movable Appliances in Daily Practice) Hugo Stockfisch Fortschr,
Kieferorthop,
45:251,
1984
The question as to whether to carry out treatment in the mixed dentition with rigid or elastic bimaxillary appliances (with or without headgear) is an important one, according to the author, in determining the ultimate treatment result. In his experience, the rigid activator inhibits mandibular movement by muscularly directed forces and allows only isometric contractions. The elastic appliances, however, allow free directional movement of the orofacial musculature and have the greater potential of stimulating favorable changes in the stomatognathic system. The author points out that more than 25 years ago, electromyographic studies showed that the rigid activator, with an average bite opening, in no way increases the muscle tone during sleep. Muscle tone increases only with active mandibular movements or a true functional appliance. In contrast to the
517
myotonic, myostatic rigid activators, the mobile elastic appliances induce a higher level of muscle activity. The author concludes that elastic appliances are thus superior for the treatment of deep-bite problems as well as open-bite and mouth-breathing problems. T. M. Graber
Cumulative Electromyography of the Human Masseter Muscle During Fatiguing Isometric Contractions Lars V. Christensen .I. Oral
Rehabil.
llt341-49,
1984
In man, it is known that a single bout of tooth clenching at maximum, voluntary strength gives rise to fatigue of the contracting muscles in 30-30 seconds. It was the aim of this study to examine certain EMG events encircling the onset of fatigue of the human masseter muscle during short periods of tooth clenching. Six adult males performed maximum voluntary clenching (MVC) for 10, 20, 30, and 40 seconds and, after 15 minutes, again for 40, 30, 20, and 10 seconds. The electrical currents were sampled for the masseter muscle during the isometric exercises, using integrated and cumulative surface electromyography. Subjective masseter fatigue was present after 30 and 40 seconds of MVC clenching, accompanied by changes in myoelectrical activity. Strength testing of the masseter muscle, before and after endurance testing, showed that the strength increased by a significant 16% following two endurance tests. This observation was explained by a posttetanic potentiation and/or a differentiated use of motor units in the fatigued muscle. It is concluded that brief MVC isometric activity, or strength testing, is not a reliable measure of fatigue in the masseter muscle when cumulative electromyography is used. Prolonged MVC isometric activity, or progressive endurance testing, monitors reliably the onset and progression of masseter fatigue, however. T. M. Graber
A Comparative for Recording
Study of Two Techniques Centric Relation
G. Heilsing, A. Isberg-Helm, and J. McWilliam Dentomnxillofoc.
Rndiol.
12: S-l?.
19X.7
In the treatment of TMJ dysfunction problems, optimal occlusal relations are deemed advisable. How to achieve this goal, however, is still shrouded in controversy and confusion in many instances. The clinical establishment of centric relation is one aspect of par-
518 Reviews and abstracts ticular concern. A major requirement of any techique is its repeatability. Currently, much discussion exists about two different techniques. The one-handed push-back technique is intended to record the most retruded position of the condyles in their fossae. Despite claims of superior repeatability, some clinicians claim that this approach produces a downward and backward condylar displacement. However, an alternative technique of bimanual manipulation is claimed to produce the uppermost, rearmost position. Whether either is the more physiologic approach to centric relation is questionable. The bimanual adherents claim that their approach is better. However, the authors of this research project were concerned only with the repeatability of each technique. In this study, radiographic comparison of both condylar positions failed to reveal any significant difference. Clinically, however, the primary tooth contacts achieved with the bimanual technique tended to be more posterior, and most subjects could detect this difference. It is obvious that the clinician must determine which technique is most biologically compatible, and he should then stay with that one technique. T. M. Graber
A Laminagraphic Study of the Alterations in the Temporomandibular Joint Following Activator Treatment Liselot Birkebaek, Birte Melsen, and Sven Terp Eur. J. Orthod.
6: 257-266,
1984
The exact effect of activator treatment has been a subject of wide discussion and considerable controversy. Although most clinicians agree on the dentoalveolar changes, the exact effect on the temporomandibular joint (condyle, fossa, etc.) is still the subject of continuous debate and ongoing research. The purpose of the present study was to develop a standardized method of laminagraphy and to apply this to an evaluation of the changes in the temporomandibular joint following activator treatment. Twenty-three children (fifteen boys and eight girls) made up the sample. Metallic implants were inserted in both jaws before treatment. Fifteen of the patients, each of whom had a Class II molar relationship with a large overjet, were treated with a Harvold type of activator, worn I2 to 14 hours per day. Construction bite was taken edge-to-edge sagittally, and at least 2 mm beyond the freeway space vertically. One profile and two laminagraphic radiographs were taken before and after 10 ,months, via a standardized technique. TMJ changes were described according to a coordinate system related to the cranial base. Alveolodental as well
as condylar growth increments and direction were re lated to the metallic implants. It was shown that a major part of the activator effect could be ascribed to an anterior displacement of the mandible, caused by an increase in the amount and change in direction of condylar growth, as well as to remodeling of the articular fossa. This clinical study corroborates the extensive laboratory findings of Petrovic, Stutzmann, and associates. T. M. Graber
lndikation Funktionskieferorthoptidischer Geriite (Indications for Functional Jaw Orthopedic Appliances) G. P. F. Schmuth Fortschr.
Kieferorthop.
44: 428.437,
1984
Functional appliances are indicated primarily in cases of orofaciai dysfunction (abnormal perioral muscle activity, hyperactive mentalis function, hypofunction of upper lip, tongue posture and function abnormalities, sucking habits, bruxism). This applies to the deciduous and mixed dentition, as well as the adult dentition, when certain gnathologic procedures must take precedence. Functional appliances are indicated for the correction of a mesio- or distocclusion before and during the mixed-dentition period. In the adult they lead to a change in the habitual closing movement of the mandible which can be therapeutically beneficial. In cases of eccentric bruxism, functional appliances are particularly appropriate in preventing unilateral overload of the temporomandibular joint. Bite raising (stimulating eruption of selected teeth) can be achieved in conjunction with sagittal correction. In anterior open bite resulting from sucking habits, successful therapy is possible, provided there is not a marked skeletal component. When there is a question of tooth sacrifice, the capabilities of functional appliances for limited expansion must be considered. This is valid for both transverse and sagittal dimensions. Other criteria must also be taken into account. If marked mesial drift of the teeth cannot be controlled, then extraction therapy may be the only solution to the problem. Functional appliances that are used before or during the mixed-dentition period should be suspended as soon as the buccal occlusion and excessive overjet are corrected. Only a very small amount of relapse will occur at this time. Unfortunately, functional therapy previously has not always recognized the need for this interim cessation of active guidance and thus was correctly criticized because of the lengthy therapy and potential proclination of lower incisors. Artistic positioning on the teeth, par-
Vo/ume 87 Number 6
words, this induces a tripod situation that would create a problem of undesired molar eruption. -The appliance holds back the mandible and minimizes the possibilities of occlusal interference to avoid a reflexive forward posturing of the mandible. -If the mandible is almost in the maximal opening position already (because of the wide-open construction bite), it has limited functional range and possibilities. With limited condylar movement, intermittent occurrence of negative intracapsular pressure would be minimal. The author states that the conclusions reached and the hypotheses proposed are purely theoretical and need to be tested. Thus, he proposes further experiments to change the intracapsular environment so that the reduced functional pressure normally observed would no longer occur. What would be the consequences? A second possible experiment would be to grow condylar cartilage in organ culture while it is being subjected to intermittent atmospheric pressure diminution. This would also provide more information on the possible role of atmospheric pressure changes in condylar growth. T. M. Graber
Zur Frage der Underschiedlichen Effektivitiit der Starren und Elastisch-Beweglichen Apparate in der Tlglichen Praxis (The Question of the Relative Effectiveness of the Rigid and Elastic Movable Appliances in Daily Practice) Hugo Stockfisch Fortschr,
Kieferorthop,
45:251,
1984
The question as to whether to carry out treatment in the mixed dentition with rigid or elastic bimaxillary appliances (with or without headgear) is an important one, according to the author, in determining the ultimate treatment result. In his experience, the rigid activator inhibits mandibular movement by muscularly directed forces and allows only isometric contractions. The elastic appliances, however, allow free directional movement of the orofacial musculature and have the greater potential of stimulating favorable changes in the stomatognathic system. The author points out that more than 25 years ago, electromyographic studies showed that the rigid activator, with an average bite opening, in no way increases the muscle tone during sleep. Muscle tone increases only with active mandibular movements or a true functional appliance. In contrast to the
517
myotonic, myostatic rigid activators, the mobile elastic appliances induce a higher level of muscle activity. The author concludes that elastic appliances are thus superior for the treatment of deep-bite problems as well as open-bite and mouth-breathing problems. T. M. Graber
Cumulative Electromyography of the Human Masseter Muscle During Fatiguing Isometric Contractions Lars V. Christensen .I. Oral
Rehabil.
llt341-49,
1984
In man, it is known that a single bout of tooth clenching at maximum, voluntary strength gives rise to fatigue of the contracting muscles in 30-30 seconds. It was the aim of this study to examine certain EMG events encircling the onset of fatigue of the human masseter muscle during short periods of tooth clenching. Six adult males performed maximum voluntary clenching (MVC) for 10, 20, 30, and 40 seconds and, after 15 minutes, again for 40, 30, 20, and 10 seconds. The electrical currents were sampled for the masseter muscle during the isometric exercises, using integrated and cumulative surface electromyography. Subjective masseter fatigue was present after 30 and 40 seconds of MVC clenching, accompanied by changes in myoelectrical activity. Strength testing of the masseter muscle, before and after endurance testing, showed that the strength increased by a significant 16% following two endurance tests. This observation was explained by a posttetanic potentiation and/or a differentiated use of motor units in the fatigued muscle. It is concluded that brief MVC isometric activity, or strength testing, is not a reliable measure of fatigue in the masseter muscle when cumulative electromyography is used. Prolonged MVC isometric activity, or progressive endurance testing, monitors reliably the onset and progression of masseter fatigue, however. T. M. Graber
A Comparative for Recording
Study of Two Techniques Centric Relation
G. Heilsing, A. Isberg-Helm, and J. McWilliam Dentomnxillofoc.
Rndiol.
12: S-l?.
19X.7
In the treatment of TMJ dysfunction problems, optimal occlusal relations are deemed advisable. How to achieve this goal, however, is still shrouded in controversy and confusion in many instances. The clinical establishment of centric relation is one aspect of par-
518 Reviews and abstracts ticular concern. A major requirement of any techique is its repeatability. Currently, much discussion exists about two different techniques. The one-handed push-back technique is intended to record the most retruded position of the condyles in their fossae. Despite claims of superior repeatability, some clinicians claim that this approach produces a downward and backward condylar displacement. However, an alternative technique of bimanual manipulation is claimed to produce the uppermost, rearmost position. Whether either is the more physiologic approach to centric relation is questionable. The bimanual adherents claim that their approach is better. However, the authors of this research project were concerned only with the repeatability of each technique. In this study, radiographic comparison of both condylar positions failed to reveal any significant difference. Clinically, however, the primary tooth contacts achieved with the bimanual technique tended to be more posterior, and most subjects could detect this difference. It is obvious that the clinician must determine which technique is most biologically compatible, and he should then stay with that one technique. T. M. Graber
A Laminagraphic Study of the Alterations in the Temporomandibular Joint Following Activator Treatment Liselot Birkebaek, Birte Melsen, and Sven Terp Eur. J. Orthod.
6: 257-266,
1984
The exact effect of activator treatment has been a subject of wide discussion and considerable controversy. Although most clinicians agree on the dentoalveolar changes, the exact effect on the temporomandibular joint (condyle, fossa, etc.) is still the subject of continuous debate and ongoing research. The purpose of the present study was to develop a standardized method of laminagraphy and to apply this to an evaluation of the changes in the temporomandibular joint following activator treatment. Twenty-three children (fifteen boys and eight girls) made up the sample. Metallic implants were inserted in both jaws before treatment. Fifteen of the patients, each of whom had a Class II molar relationship with a large overjet, were treated with a Harvold type of activator, worn I2 to 14 hours per day. Construction bite was taken edge-to-edge sagittally, and at least 2 mm beyond the freeway space vertically. One profile and two laminagraphic radiographs were taken before and after 10 ,months, via a standardized technique. TMJ changes were described according to a coordinate system related to the cranial base. Alveolodental as well
as condylar growth increments and direction were re lated to the metallic implants. It was shown that a major part of the activator effect could be ascribed to an anterior displacement of the mandible, caused by an increase in the amount and change in direction of condylar growth, as well as to remodeling of the articular fossa. This clinical study corroborates the extensive laboratory findings of Petrovic, Stutzmann, and associates. T. M. Graber
lndikation Funktionskieferorthoptidischer Geriite (Indications for Functional Jaw Orthopedic Appliances) G. P. F. Schmuth Fortschr.
Kieferorthop.
44: 428.437,
1984
Functional appliances are indicated primarily in cases of orofaciai dysfunction (abnormal perioral muscle activity, hyperactive mentalis function, hypofunction of upper lip, tongue posture and function abnormalities, sucking habits, bruxism). This applies to the deciduous and mixed dentition, as well as the adult dentition, when certain gnathologic procedures must take precedence. Functional appliances are indicated for the correction of a mesio- or distocclusion before and during the mixed-dentition period. In the adult they lead to a change in the habitual closing movement of the mandible which can be therapeutically beneficial. In cases of eccentric bruxism, functional appliances are particularly appropriate in preventing unilateral overload of the temporomandibular joint. Bite raising (stimulating eruption of selected teeth) can be achieved in conjunction with sagittal correction. In anterior open bite resulting from sucking habits, successful therapy is possible, provided there is not a marked skeletal component. When there is a question of tooth sacrifice, the capabilities of functional appliances for limited expansion must be considered. This is valid for both transverse and sagittal dimensions. Other criteria must also be taken into account. If marked mesial drift of the teeth cannot be controlled, then extraction therapy may be the only solution to the problem. Functional appliances that are used before or during the mixed-dentition period should be suspended as soon as the buccal occlusion and excessive overjet are corrected. Only a very small amount of relapse will occur at this time. Unfortunately, functional therapy previously has not always recognized the need for this interim cessation of active guidance and thus was correctly criticized because of the lengthy therapy and potential proclination of lower incisors. Artistic positioning on the teeth, par-