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Tooth Wear Literature Index – Ramfjord and Ash, Occlusion, Ed. 4


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Date

Publication

Title

Point 1

Point 2

Point 3

Ramfjord and Ash

1995, W. B. Sanders, 01

Occlusion – 4th Ed, p iii

Preface

Diverging lines of thought are pointed out and readers are invited to think rather than to disagree either on the basis of prevailing winds of changing ideologies or vested research interests.

The concept of occlusion presented in this book strongly supports the idea that the teeth, which are actively involved in function and parafunction, are integral parts of the masticatory system and susceptible to primary and secondary interactive influences.

Lately, a trend has developed that tends to obfuscate the role of occlusion in the disorders of the masticatory system. Primarily, this notion stems from the publications of nonclinicians and researchers who do little if any clinical research, but concentrate on basic neurosciences. Their thrust is that clinical phenomena that have not been confirmed experimentally are hearsay.


Ramfjord and Ash

1995, W. B. Sanders, 02

Occlusion – 4th Ed, p iv

That the specific role of occlusion in the etiology and treatment of disorders of the masticatory system has not been established “scientifically” does not by any means allow the conclusion that occlusion has nothing to do with such disorders.

Un fortunately, a good experimental animal for studies of occlusion is not available and retrospective studies without meaningful measurement systems and with numerous variables, encourage a wide range of circumspect interpretations.

Of much greater interest are a few prospective clinical studies with altered occlusion as the only variables. These studies have documented that even minor changes in occlusion may induce disorders in the masticatory system that may vary from individual to individual and that psychic factors influence such disturbances as well.

The success rate depends on the ability to stay within the tolerance level of the patient in therapy based on the understanding, compassion and skill level of the clinician. There is, however, preponderating clinical agreement that masticatory system disorders may be alleviated to a various extent by occlusal therapy.

As all clinicians know, casts and articulators do not a diagnosis make; they are a clinical convenience and nothing more. (emphasis mine – rgp)

Ramfjord and Ash

1995, W. B. Sanders, 03

Occlusion – 4th Ed, p 1

Ch 1, Anatomy, physiology and Pathophysiology of Occlusion

As broadly defined the subject f occlusion is not limited to the occlusal contact relationships of the teeth; it also encompasses neuromuscular and psycho-physiologic areas that may reflect disturbances that occur as the result of, or are the cause of occlusal dysfunction

The masticatory system is a functional unit composed of the teeth; their supporting structures; the jaws; the TMJ’s; the muscles involves directly or indirectly in mastication (including the muscles of the lips and tongue [neck-rgp]); and the vascular and nervous systems supplying the tissues.

Other muscles of the head and neck are also necessary for parafunctions such as swallowing, respiration and speech (parafunction may also refer to clenching and bruxism)



Functional and structural disturbances in any one of the components of the masticatory system may be reflected by functional or structural disorders in one or more of its other components; (emphasis mine – rgp) e.g., pain in the TMJ may cause a restriction if mandibular movement.

Ramfjord and Ash

1995, W. B. Sanders, 04

Occlusion – 4th Ed, p 2-3

The human TMJ is a complex ginglymoarthroidal (hinge and glide) articulation with limited capability of diarthrosis (free movement).

The condyle is perpendicular to the ascending ramus of the mandible and is oriented with a long axis 10 – 30 degrees distal to the frontal plane.

Therefore, Simple (x-ray) techniques with standardized angulation provide a meaningless basis for comparison of joint spaces and distances.

Both the condyle and the articular surface of the temporal bone are covered with a dense fibrous connective tissue, with irregular cartilage-like cells. The number of cells increases with age and stress on the joint.

Ramfjord and Ash

1995, W. B. Sanders, 05

Occlusion – 4th Ed, p 7, 9, 10

Thus for anatomical reasons, the condyle cannot normally be move to any appreciable extent up and back; though it may be moved down and back.

To what extent the adult TMJ undergoes morphologic changes subsequent to changes in occlusal relations of the teeth is a highly controversial subject.



All living bones undergo physiologic remodeling in their internal structures with changes in functional demands and aging and there is no question that such remodeling also takes place in the mandible and temporal bone.

The controversy related to the articulating joint surfaces concerns the possibility of physiologic adaptive remodeling in response to changes in occlusion



Deductive studies based on autopsy results never establish cause and effect relationships. These studies produce only speculative, hypothetic associations in favor of functional remodeling of the TMJ, and they have been made to sound very convincing.

No morphologic adaptive changes were found in the bony joint surfaces of adult monkeys in response to gross changes in occlusion. However, several investigators have reported that some changes have occurred in very young animals in response to similar changes of occlusion.



A number of other experimental studies have subjected the TMJ’s of adult rhesus monkeys to various gross alterations in occlusal relations….However, occlusal forces brought about rebuilding of bone in the neck of the condyle. (After reviewing the studies mentioned, the time frames ere short, 4 months, and boney adaptation or accommodation could not have occurred in that time frame. Examination of multiple dry specimen with digital scans show a decided propensity to adapt toward less steep guidance as the teeth wear. This takes years. – rgp)

Ramfjord and Ash

1995, W. B. Sanders, 06

Occlusion – 4th Ed, p 10, 11

It has been found that the condylar path becomes slightly les steep with age in a large number of patients with functional disturbances of occlusion.

There appears to be no correlation between the type of occlusion and the shape of the TMJ’s. In general, it appears that changes in TMJ morphology may be a result of pathologic rather than physiologic processes.

In all studies of occlusal disharmony and TMJ morphology, there has been striking evidence of periodontal trauma and subsequent movement of teeth. Accommodating to the disharmonies accomplished through tooth movement, which changes the occlusion, rather than causing adaptive changes in the joints. (What about wear f the occluding surfaces? – rgp)

The clinical significance of these research findings to the practice of dentistry should be adaptation of th occlusion to the TMJ’s rather than adaptation of the TMJ’s to the occlusion. (OBI)



) It also points to the TMJ as the natural landmarks fro diagnosis and alignment of the occlusion. (Does not indicate that a restrained CR-CRO occlusion is correct or that CRO=CO(MIP) occlusion is desirable. – rgp)

The basic movements described earlier; however, include only a part of the complex functional and nonfunctional movements of th mandible. It should be recognized that the various types of positions and movements are influence by condylar guidance, tooth contacts, ligaments(?), and muscles involved in complex neuromuscular mechanisms

Ramfjord and Ash

1995, W. B. Sanders, 07

Occlusion – 4th Ed, p 23

Chewing –

The action of masticatory muscles during chewing, as reflected in jaw-tracking devices and EMG, varies between subjects in ampli­tude, onset timing, and duration of the chewing cycle; however, there is a similarity between muscle actions that can be recognized. Such variation is in part related to occlusal contact relations and musculoskeletal morphology.




Starting from the static intercuspal position, where jaw movement pauses for 194 ms in the chewing cycle, muscle activity begins in the ipsilateral inferior head of the lateral pterygoid muscle approximately halfway through the period of tooth contact. This activity is followed closely by the action of the contralateral inferior lateral pterygoid muscles. Both superior and inferior parts of these muscles are active during the opening phase. Early in the opening phase, the digastric muscles become active and remain so until the maximum opening position is reached. During the opening phase, the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid muscles are inactive

At the initiation of jaw closing the inferior heads of the lateral pterygoid muscles cease their functioning and activity is initiated in the contralateral medial pterygoid muscle. Activity in this muscle may be moderate or nonexistent during the closing phase. The contralateral medial pterygoid muscle controls the upward and lateral positions of the mandible, is more active in wider strokes during early closing, and ceases activity during the intercuspal phase. The ipsilateral and contralateral medial pterygoid muscles are active at the onset of intercuspation when the chewing stroke is narrow, i.e., has a minimal lateral component.


Activity increases in the anterior and posterior temporalis muscles, in the deep and superficial masseter muscles, and in the ipsilateral medial pterygoid muscle up to the peak 20 to 30 ms before the onset of the intercuspal position when activity declines to the middle of the intercuspal period. The contralateral medial pterygoid declines in activity at the onset of intercuspation. There appears to be reciprocal action between the inferior head of the lateral pterygoid muscle and the medial pterygoid muscle in some subjects.


Ramfjord and Ash

1995, W. B. Sanders, 08

Occlusion – 4th Ed, p 23

Clenching -

During maximal intercuspal clenching, where forces are directed vertically, posteriorly, anteriorly, or to the right or left, the elevator muscles activate differently. In vertical efforts (clenching in centric occlusion), most of the elevator muscles are acti­vated maximally; however, in some subjects the medial pterygoid muscle activity is low. The variation between subjects appears to be related to occlusal contacts and musculoskeletal morphology.

The inferior head of the lateral pterygoid produces little activity or only 25 per cent of maximum activity compared to the superior head.


Muscle activity decreases with lessening numbers of posterior teeth and drops dra­matically when only the incisors are in contact. The digastric muscle is only slightly active during vertical effort with intercuspal clenching, but it is more active during vertical incisive clenching.

When clenching in the intercuspal position is directed anteriorly, the activity of the anterior temporal muscles is reduced to a low level and activity ceases in the posterior muscles. The deep masseter muscle decreases activity and the superficial masseter muscles maintain maximum activity as do the medial pterygoid muscles and the inferior heads of the lateral pterygoid muscles.




In maximum effort with the mandible in an eccentric position so that the canines are edge-to-edge (no posterior contacts), the ipsilateral temporal muscle is less active than in the maximal intercuspal clench and the contralateral temporal muscle is silent. The ipsilateral masseter muscle is more active than the contralateral masseter muscle; and the medial pterygoid muscle, as well as the inferior head of the lateral pterygoid muscles, are maximally contracting. However, the activity of the ipsilateral medial pterygoid muscle is lower than its contralateral counterpart, and the inferior head of the lateral pterygoid is silent. The EMG activity of the ipsilateral pterygoid muscle is dependent upon the anterior placement of the mandible. An increase in anterior placement results in an increase in the activity of the ipsilateral medial pterygoid muscle.


During clenching on anterior teeth (vertical, incisive, clenching) the activity of the anterior and posterior temporal muscles ceases; however, both the medial pterygoid muscle and the inferior head of the lateral pterygoid muscle are maximally active. The superior head of the lateral pterygoid may be active or silent. The deep and superficial masseter muscles are active, but less so than with intercuspal vertical clenching.”


Ramfjord and Ash

1995, W. B. Sanders, 09

Occlusion – 4th Ed, p 29

Clinical Determined Rest Position and Resting Range -

Accept for minor changes with age, malocclusion and loss of teeth, the relative stability of the clinically determined rest position is generally accepted Although most definitions of rest position, as the relate to vertical dimensions, imply a balance in the tonicity of the elevator and depressor muscles, the rest position is not always indicative of muscle harmony. It has been found that the interocclusal distance averaged 1.7 mm in the clinically determined rest position, whereas the avenge distance was 3.29 mm with an additional resting range of 11 mm when determined electro-myographically on the basis of minimal muscle activity.




Thus, at least for the temporal, masseter, and digastric muscles, there is a resting range rather than a definite mandibular rest position of minimal muscle activity. The observation that the clinically determined rest position often does not coincide with the range of minimal muscle activity suggests that the neuromuscular mechanisms underlying clinical rest position are more complex than was formerly thought.

Electromyographic Rest Position -

The EMG rest position occurs with relative coincidence of vertical dimension of clinically determined rest position, and minimal muscle activity as determined electromyographically. It has been shown electromyographically that in order to obtain balanced resting muscle activity in persons with occlusal interferences, it is often necessary to open the jaw beyond the clinical rest position. Also, it has been observed clinically that occlusal interferences have an increasing tendency to trigger abnormal muscle activity if the interocclusal space is decreased. An increase in interocclusal space seems to increase the muscle tolerance to occlusal interferences and, in extreme cases, to alter the clinical rest position without a change in resting muscle activity.




Interocclusal Space in Clinical Rest Position -

An important aspect of clinical rest position of the mandible is the interocclusal or ‘freeway” space that is usually present between the occlusal surfaces of the maxillary and mandibular teeth when antigravity tonus is maintained. The width this space varies somewhat with the type of occlusion, and also with hypotonicity or hvpertonicitv of the mastication muscles. In the anterior part of the mouth it is commonly found to be 1 to 3 mm: however, it may be much wider (8—10 mm or more) without any indication of a disturbance of the function and health of the masticatory system, and therefore may qualify, as biologically normal. Both rest position and interocclusal space can be changed by raising or lowering310 the occlusal vertical dimension.


Ramfjord and Ash

1995, W. B. Sanders, 10

Occlusion – 4th Ed, p 29

A strong warning should be made against the application of avenge values (for example. 2 mm of interocclusal space) to individuals. A deviation from this avenge may not validly indicate alteration of an occlusion. “Loss of vertical dimension,” based on a wider than average interocclusal space, is often used as an unverified and faulty premise justifying dental procedures that result in harm to the patient.


PAIN: NEUROPHYSIOLOGY AND CLINICAL CORRELATIONS

Pain is an unpleasant sensory and emotional experience. It not only has a sensory discriminative dimension, which provides some information relative to the location, quality, intensity, and duration of the noxious stimulation; but it also has an affective, motivating, and cognitive dimension.




This dimension relates to past and ongoing sensory experiences including stress, anxiety, and feelings about pain that can modulate the pain experience. Thus, pain is a multidimensional experience that can be modulated by cognitive, emotional, and motivational influences.

Peripheral Nociceptive Mechanisms -

Noxious stimuli excite certain types of receptors that are present in the orofacial tissues. Information from these sense organs is carried by afferent nerve fibers that are found in superficial and deep tissues of the craniofacial structures including the TMJ’s and teeth.


Ramfjord and Ash

1995, W. B. Sanders, 11

Occlusion – 4th Ed, p 30, 32

Nociceptors and Afferents

There are three principal classes of nerve fibers that provide the necessary input to the brain for pain perception.” These afferent fibers terminate in endings (nociceptors) in the peripheral tissues. The cutaneous (facial) nociceptive afferent fibers (primary neurons) include: (I) A-delta afferent fibers activated only by intense mechanical stimuli; (2) A-delta nociceptive afferents that respond to intense heat and mechanical stimuli: and (3) C polymodal afferents that respond to intense mechanical, thermal, and chemical stimuli. Free nerve endings are present in nearly all the orofacial tissues and are associated with the small-diameter. myelinated (A-delta) and unmyelinated (C) fiber afferents.




Some primary afferents (e.g.. neurons with cell bodies in the gasserian ganglion) respond very well to certain kinds of sensory stimulation but poorly to others. Within a population of these afferents which are defined by conduction velocity (indirectly by size), are a variety of individual afferents that respond to various specific natural stimuli. Some unmyelinated C fiber primary afferents associated with free nerve endings respond to touch; others to noxious stimuli, warmth and other stimuli. Thus, even when innervation is related only to unmyelinated primary afferents such as in the cornea of the eye, there is a sufficient variety of specific afferents to mediate all sensations generally perceived.


TMJ

Afferents supplying the TMJ and craniofacial muscles include Group III and IV fibers, as well as faster-conducting afferents. Group Ill fibers include A-delta fibers and Group IV include C fibers. Although there are many free nerve endings in the TMJ, there are apparently only a few of the more specialized receptors. The central zone of the meniscus and other articular surfaces are not inner-capsule is the most innervated part of the TMJ. Information is carried from the TMJ primarily by the auriculotemporal branch of the mandibular nerve, but the masseter and temporal nerves may also carry these fibers although their contribution is much less. Largely because free nerve endings and Group Ill and IV fibers are associated with nociception in other areas of the body, it seems reasonable that TMJ afferents would have the same physiologic properties.




Modulation of Nociception

Modulation of nociception may be discussed on the basis of peripheral and central mechanisms. Alteration of the activity of trigeminal brain stem neurons can occur, for example, through inflammation or by deafferentation, Modulation of pain transmission may also occur through descending influences from higher brain centers that involve endogenous pain-suppressive neurochemical mechanisms and the presence of nociceptive neurons in the brain stem. The gate control theory of pain perception proposed that large fiber afferents (carrying tactile information) activate cells in the substantia gelatinosa which interact with the input of small fibers (carrying nociceptive informa­tion) to inhibit (presynaptic) transmission IT) neurons.



Ramfjord and Ash

1995, W. B. Sanders, 12

Occlusion – 4th Ed, p 32, 33

The theory provides for the “gating’ mechanism to be modulated by descending central controls. Periodic revisions have been necessary to bring the theory into line with the circuitry, and physiology has been re­quired to account for both the complexity of the processing involved and the influences of descending inhibition. Yet, stimulation of an adequate number of large fibers relative to small fibers can reduce pain perception.


Peripheral Modulation
Peripheral modulation of nociception appears to involve three interactive systems:

(1) products of tissue damage, (2) the axon reflex, and (3) sympathetic-sensory influences.9~




Substances released during tissue damage such as histamine, prostaglandins, and many other mediators of inflammation cause sensitization of nociceptive nerve endings and also probably change transduction mechanisms. The result is activation of nociceptors by innocuous stimuli causing ordinary sensory experiences (such as touch) to be perceived as painful (hyperalgesia) and moderately painful experiences to be greatly magnified.


Another effect of inflammatory mediators is the stimulation of nociceptive endings to release neuropeptides. Neuropeptides are highly concentrated in the dental pulp.298 When a peripheral nociceptor is activated by painful stimulation, the stimulus-evoked impulse spreads centrally into other peripheral endings of the same nerve where substance P is released.

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