This article was published in Quintessence International, Vol 31, No 4 (April 2000).

Functional and Biologic Considerations for Reconstruction of the Dental Occlusion

Definition and epidemiologic studies.

There are 3 critical interfaces between muscle and bone in the masticatory system: the temporomandibular joint, the periodontium, and the dental occlusion. According to Moyers and Wainright,1 the dental occlusion is the most critical interface and is determined by bone growth, dental development, and neuromuscular maturation. Structurally, the relationship of the buccal cusps of the mandibular posterior teeth and the lingual cusps of the maxillary posterior teeth against the opposing fossa and marginal ridges maintain the distance between the maxilla and mandible after growth is complete. By definition, vertical dimension of occlusion is the distance between the mandible and maxilla when the opposing teeth are in contact.2

Functional occlusion of the dentition occurs within the border movements of the mandible and, generally, begins with the mandible in a physiologic rest position. The clinical rest position is highly variable and can be influenced by a number of factors including cranial-cervical position, the presence or absence of dentures,3 speech,4 and stress.5 The term rest position is also somewhat of a misnomer, since the jaw muscles in this position do not necessarily display their least amount of electromyographic (EMG) activity.6 This rest, or postural, position is generally in the range of 2 to 4 mm relative to the intercuspal position.7 In this position, the mandibular condyles are in an acquired centric position, anteriorly positioned along the condylar translation pathway. In this regard, most clinicians agree that the postural position should not be used as a starting point in the determination of the vertical dimension of occlusion.

In 1934, Costen described a symptom complex that included loss of dental occlusal support, ear symptoms (such as pain and tinnitus), and sinus pain. Since that description, others have demonstrated beneficial effects of occlusal therapy on auditory symptoms in some patients.8,9 However, Schwartz10 was unable to confirm the relationships described in Costens syndrome. On the other hand, Agerberg11 has reported that the number of missing teeth was directly correlated with increasing symptoms of mandibular dysfunction. These findings are consistent with the report of Pullinger et al12 that occlusal factors do contribute to specific subclassifications of temporomandibular disorders (TMD). In this regard they reported 5 occlusal conditions that reached significant levels of association with TMD: anterior open bite, overjet greater than 6 to 7 mm, occlusal slides from retruded contact position greater than 2 mm, unilateral maxillary crossbites, and missing posterior teeth. Mejersjö and Carlsson13 suggested that the lack of posterior occlusal support is not an etiologic factor and does not affect treatment outcomes for most patients.

However, they were quick to point out that such an occlusal deficiency may lead to osteoarthrosis and increased pain due to overload in these joints. Under these circumstances, DeBoever and Carlsson14 considered the lack of molar support as a perpetuating factor for TMD.

Rivera-Morales and Mohl15 presented a review of the literature regarding the adaptability of the occlusal vertical dimension. They concluded that postural rest position has a considerable range of adaptability to increases in the occlusal vertical dimension. However, the range of comfort varied considerably among individuals and even within a single individual under different conditions. The hypothesis that increased vertical dimension will cause an increase in masticatory muscle hyperactivity is not supported by the literature. However, the implication that increased EMG activity would be the natural response to encroachment on the postural position, and that this would relate to increased muscle pain, may be invalid. Stohler16 has shown that the injection of saline into the elevator muscles of the jaw, which resulted in increased pain, caused a decrease in EMG activity and a decrease in the bite force. The increased tenderness to palpation Christensen17 noted in all of the masticatory muscles could explain the decrease in EMG activity in the elevator muscles that were tested by Carlson et al.18 These findings support the need to determine the psychobiologic status of each individual patient as accurately as possible through the history, clinical exam, and appropriate investigations. Such information will help to establish a working hypothesis with regard to the adaptive capacity of each patient and the potential impact of altering the vertical dimension of occlusion on the biologic system.

Determinants of vertical dimension of occlusion. Although a static relationship in principle, the vertical dimension of occlusion is initially determined by the interaction of the genetic growth potential of the craniofacial tissues, environmental factors, and the dynamics of neuromuscular function during growth. Maintenance of the vertical dimension of occlusion is principally related to the interaction of environmental factors and the dynamics of neuromuscular function throughout the aging process. According to Moyers and Wainright,1 craniofacial morphology, growth, and dental morphology account for much of the variability in dental occlusion. The correlations among these 3 factors increase up to the age of 12 years. These concepts are consistent with those of Lavergne and Petrovic,20 who emphasize the relationship among 3 tiers of influences on the development of the occlusion: (1) the magnitude of tissue and cell growth; (2) the spatial ordering of the facial skeleton; and (3) the dental occlusion as it affects the rate, amount, and direction of mandibular growth.

Environmental factors play a particular role in the development of the vertical dimension of the facial skeleton and ultimately the vertical dimension of occlusion. Function of the upper respiratory system has been shown in a number of studies to play a particular role in this regard. Upper respiratory obstruction has been shown to cause changes in masticatory muscle recruitment patterns that correlate with changes in facial soft tissue that precede facial skeletal adaptations.20 Linder-Aronson21 suggests that, for certain subjects, mandibular retrognathism, increased vertical facial height, open bite, and crossbite may be due to chronic environmental factors such as airway obstruction, and that treatment should be directed at eliminating or reducing the environmental effects on jaw position and dental occlusion.

Biologic adaptation.

Once growth is complete, maintenance of the vertical dimension of occlusion is determined by the adaptive capacity of the biologic system to insult or injury. Adaptive responses can occur within the temporomandibular joint (TMJ), the periodontium, and the dental occlusion. In most cases, it is the soft tissues of the TMJ and periodontal ligament that initially respond to acute micro- and macrotrauma. The fluid compartments that are maintained within the extracellular matrix rapidly shift in response to variations in strain patterns. The first response within the TMJ to compressive forces is a shift in the fluids within the disc and retrodiscal tissues. Once the strain is relieved, the fluid will return to its original position and the morphology of the tissues is maintained. However, prolonged strain with these tissues will result in an alteration of the architecture of the collagen and noncollagen proteins and ultimately a change in tissue morphology.

Strains beyond the levels of adaptation for the soft tissues will then result in morphologic adaptive changes within the cartilage and bone that may be apparent radiographically. Strains beyond the adaptive capacity of the tissues will result in degeneration, a loss in vertical support, and structural changes that have the potential to impact the vertical dimension of occlusion. Using a 3-dimensional model of the mandible and TMJ articulation, strain patterns within the TMJ have been shown to increase with an increase in the vertical face height.22 Ito et al23 has demonstrated superior repositioning of the mandibular condyle with anterior splints in the absence of posterior occlusal contact. In a study reported by Araki et al,24 the reduction of the crowns of the maxillary molars resulted in degenerative changes in the mandibular condyles. Vertical adaptive responses have been outlined by McNamara25 as adaptive changes within muscle, alterations in the central nervous system, changes at the muscle-bone interface, and changes within bone and cartilage. Enlow et al26 and Harper et al27 have previously attributed adaptive changes within the TMJ to extracapsular forces.

Okeson28 states that orthopedic stability exists when the stable intercuspal position of the teeth is in harmony with the musculoskeletally stable position of the condyles in the fossae. As the discrepancy between an orthopedically stable TMJ and maximum intercuspation of the teeth increases, there is an increased risk for intracapsular TMJ disorders to occur. The concept of orthopedic stability takes into consideration the temporomandibular joint, the integrity of the masticatory muscles and ligaments, and the skeletal-dental relationships. Loss of occlusal vertical dimension may be due to attrition of the dentition, which may be acute (iatrogenic) or chronic and may involve parafunctional activities. A decrease in the vertical dimension of occlusion may also be associated with internal derangement of the TMJ or osteoarthrosis. However, there is no epidemiologic evidence to suggest that dental attrition is necessarily associated with signs or symptoms of TMD.

Clinical implications.

It is difficult to resolve the opinion of DeBoever and Carlsson14 that precision-mounted study casts are not necessary as an adjunct to the diagnosis of TMD or that occlusal reconstruction is not indicated in the treatment of TMD. Although occlusal reconstruction may not be the definitive treatment for a particular TMD, it is appropriate to establish a sound structural and balanced functional base as an adjunct to overall patient management. Rivera-Morales and Mohl29 outline guidelines for the restoration of vertical dimension that include the careful mounting of study casts to a semiadjustable articulator using jaw-relation records. This process is then followed by diagnostic waxup and diagnostic occlusal adjustment on additional or duplicated mounted casts. In this regard, it is prudent to accurately assess the status of the structural occlusion in conjunction with the dynamics of the functional occlusion using sophisticated mounting procedures.

Such information could contribute to a better understanding of the potential for addressing structural issues and provide information regarding factors relating to the adaptive capacity of the patient. The goal of occlusal reconstruction should be to achieve a structural balance to facilitate physiologic adaptation and rehabilitation.

Nitzan30 reported that intra-articular pressures in the human TMJ were significantly reduced after placement of an interocclusal appliance. Although a reduction in intra-articular pressure may relieve pain resulting from intracapsular derangement and inflammation of the retrodiscal tissues, it is not necessarily correlated with a reduction in pain of extracapsular origin. As Dawson31 points out, condylar access to centric relation is not dependent on vertical dimension, and increasing the vertical dimension does not unload the joints if the starting point is a centric relation position. This message is critical and requires an understanding of the relationship of the dental occlusion and condylar position within the TMJ.

For any given patient, the mandibular condyle can be in 1 of 3 positions within the TMJ. The first position, classically defined as centric relation, implies that the condyle within the fossa is in its most superior position against the eminence with the disc properly aligned. This position does not depend on tooth position or vertical dimension. The second possible position is an acquired centric position. In this position the condyle and disc are properly aligned; however, this assembly is positioned anteriorly along the translation pathway. Finally, the condyle may be in a deranged reference position within the fossa. In this position the condyle may be in its most superior position against the eminence; however, the disc is not properly interposed between the condyle and fossa. The latter 2 positions may very well contribute to an alteration of the normal occlusion, and the vertical dimension of occlusion is affected by each of these condylar positions. It is important to define the status of this centric reference position prior to initiation of occlusal therapy.

The current gold standard for the diagnosis or treatment of TMD has been suggested by Clark et al32 to be a global history and clinical examination. Although none of the ancillary investigations or imaging techniques has proven diagnostic validity,33,34 the additional information and documentation may provide a quantifiable starting point and a basis for the assessment of treatment outcomes. In this regard, along with conventional radiographic and magnetic resonance imaging of the TMJ, functional analysis using condylar movement tracking devices may be useful as a means of quantifying the range of condylar translation and analyzing the pattern of the translation pathway.35 Condylar movement analysis can be used subsequently as a method for assessment of treatment outcomes.36

In many cases it is possible to increase the vertical dimension of occlusion if 2 foundational principles are maintained. First, the starting point for reconstruction of the vertical dimension of occlusion must be with the mandibular condyles in centric relation. Second, reconstruction must be within the range of neuromuscular adaptation for each individual patient. The difficulty is determining both of these parameters on an individual patient basis, accurately recording the centric reference point and transferring this information to an instrument that simulates the patient1s functional occlusion. The prudent course under these circumstances is to take a diagnostic approach and formulate a hypothesis based on information from the history, clinical examination, and investigations of condylar position and status of the neuromuscular envelope. This hypothesis can then be tested using reversible intervention modalities such as occlusal splints, removable prostheses, or fixed transitional crowns prior to definitive alteration of the vertical dimension of occlusion. The need for modification of the initial hypothesis may become evident, or definitive treatment may be initiated. The critical message for the clinician who has the ultimate responsibility for this decision-making process is to establish frequent outcome assessment protocols and to approach the practice of dentistry as a clinical scientist.

References

1. Moyers RE, Wainright RL. Skeletal contributions to occlusal development. In: McNamara JA Jr (ed). The Biology of Occlusal Development, monograph 7, Craniofacial Growth Series. Ann Arbor, MI: Univ of Michigan Press, 1977.

2. Molligoda MA, Abuzar M, Berry DC. Measuring diurnal variation in the dispersion of occlusal contacts. J Prosthet Dent 1988;60:235-238.

3. Gattozzi JG, Nichol BR, Somes GW, Ellinger CW. Variations in mandibular rest positions with and without dentures in place. J Prosthet Dent 1976;36:159.

4. Pound E. Controlling anomalies of vertical dimension and speech. J Prosthet Dent 1976;36:124.

5. Rugh JD, Johnson RW. Vertical dimension discrepancies and masticatory pain/dysfunction. In: Solberg WK, Clark G (eds). Abnormal Jaw Mechanics. Chicago: Quintessence, 1984:117-133.

6. Rugh JD, Drago CJ. Vertical dimension: A study of clinical rest position and jaw muscle activity. J Prosthet Dent 1981;45:670-675.

7. Okeson JP. Management of Temporomandibular Disorders and Occlusion, ed 4. St Louis: Mosby, 1998:98-101.

8. Rubinstein B, Carlsson GE. Effects of stomatognathic treatment on tinnitus: A retrospective study. Cranio 1987;5:255.

9. Ash MM, Ash CM, Ash JL, Ash GM. Current concepts of the relationship and management of temporomandibular disorders and auditory symptoms. J Mich Dent Assoc 1990;72:550-555.

10.Schwartz L. Disorders of the Temporomandibular Joint. Philadelphia: Saunders, 1952.

11.Agerberg G. Mandibular function and dysfunction in complete denture wearersA literature review. J Oral Rehabil 1998;15:237-249.

12.Pullinger AG, Selligman DA, Cornbein JA. A multiple regression analysis of the risk and relative odds of temporomandibular disorders as a function of common occlusal features. J Dent Res 1993;72:968.

13.Mejersjö C, Carlsson GE. Analysis of factors influencing the long-term effect of treatment of TMJ-pain dysfunction. J Oral Rehabil 1984;11:289-297.

14.DeBoever JA, Carlsson GE. Etiology and differential diagnosis. In: Zarb GA, Carlsson GE, Sessle BJ, Mohl ND (eds). Temporomandibular Joint and Masticatory Muscle Disorders, ed 2. Copenhagen: Munksgaard, 1994.

15.Rivera-Morales WC, Mohl N. Relationship of occlusal vertical dimension to the health of the masticatory system. J Prosthet Dent 1991;65:547-553.

16.Stohler CS. Clinical perspectives on masticatory and related muscle disorders. In: Sessle BJ, Bryant PS, Dionne RA (eds). Temporomandibular Disorders and Related Pain Conditions. Progress in Pain Research and Management, vol 4. Seattle: IASP Press, 1995.

17.Christensen LV. Pain from the jaw muscles in children and adults. In: Graber LW (ed). Orthodontics, state of the art; essence of the science. St Louis: Mosby, 1986:28-47.

18.Carlson C, Okeson JP, Falace DA, Nitz AJ, Anmderson D. Stretch-based relaxation and the reduction of EMG activity among masticatory muscle pain patients. J Craniomandib Disord 1991;5:205-212.

19.Laverne J and Petrovic AG. Pathogenesis and treatment conceptualization of dentofacial malrelations as related to the pattern of occlusal relationship. In: Dixon AD, Sarnat BG (eds). Normal and Abnormal Bone Growth: Basic and Clinical Research. Progress in Clinical and Biological Research, vol 187. New York: A. Liss, 1985.

20.Miller AJ, Vargevik K. Neuromuscular changes during long-term adaptation of the Rhesus monkey to oral respiration. In: McNamara JA Jr, Ribbens JA (eds). Naso-Respiratory Function and Craniofacial Growth, monograph 9, Craniofacial Growth Series. Ann Arbor, MI: Univ of Michigan Press, 1979.

21.Linder-Aronson S. Naso-Respiratory Function and Craniofacial Growth. In: McNamara JA Jr, Ribbens JA (eds). Naso-Respiratory Function and Craniofacial Growth, monograph 9, Craniofacial Growth Series. Ann Arbor, MI: Univ of Michigan Press, 1979.

22.Tanne K, Tanaka E, Sakuda M. Stress distributions in the TMJ during clenching in patients with vertical discrepancies of the craniofacial comples. J Orofacial Pain 1995;9:153-160.

23.Ito T, Gibbs CH, Marguelles-Bonnet R, Lupkiewicz SM, Young HM, Lundeen HC, Mahan PE. Loading on the temporomandibular joints with five occlusal conditions. J Prosthet Dent 1986;56:478-484.

24.Araki A, Yokoyama T, Murakamu H, Ito Y, Maeda H, Kameyama Y. Effect of decreased vertical occlusion on mandibular condyle of senescence-accelerated mouseP8 [abstract 706]. J Dent Res 1999;78:194.

25.McNamara JA. The role of muscle and bone interaction in craniofacial growth. In: McNamara JA Jr (ed). Control Mechanisms in Craniofacial Growth, monograph 3, Craniofacial Growth Series. Ann Arbor, MI: Univ of Michigan Press, 1975.

26.Enlow DH, Harvold EP, Latham RA, Moffett BC, Christeansen RL, Hausch HG. Research on control of craniofacial morphogenesis: An NIDR state-of-the-art workshop. Am J Orthod 1977;74:509-530.

27.Harper RP, Bell WH, Hinton RJ, Browne R, Cherkashin AM, Samchukov ML. Reactive changes in the temporomandibular joint after mandibular midline osteodistraction. Br J Oral Maxillofac Surg 1997;35:20-25.

28.Okeson JP, Management of Temporomandibular Disorders and Occlusion, ed 4. St Louis: Mosby, 1998:160.

29.Rivera-Morales WC, Mohl ND. Restoration of the vertical dimension of occlusion in the severely worn dentition. Dent Clin North Am 1992:36:651-664.

30.Nitzan DW. Intraarticular pressure in the functioning human temporomandibular joint and its alteration by uniform elevation of the occlusal plane. J Oral and Maxillofac Surg 1994;52:671-680.

31.Dawson PE. Evaluation, Diagnosis, and Treatment of Occlusal Problems, ed 2. St Louis: Mosby, 1989.

32.Clark GT, Tsukiyama Y, Baba K, Simmons M. The validity and utility of disease detection methods and of occlusal therapy for temporomandibular disorders. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;83:101-106.

33.Widmer CG, Lund JP, Feine JF. Evaluation of diagnostic tests for TMD. Can Dent Assoc J 1990;18:53-59.

34.Mohl ND, Ohrbach R. The dilemma of scientific knowledge versus clinical management of temporomandibular disorders. J Prosthet Dent 1992;67:113-120.

35.Romanelli GG, Harper RP, Mock D, Pharoah MJ, Tenenbaum HC. Evaluation of temporomandibular joint internal derangement. J Orofacial Pain 1993;7:254-262.

36.Harper RP. Analysis of temporomandibular joint function after orthognathic surgery using condylar path tracings. Am J Orthod Dentofacial Orthop 1990;97:480-488.

For reprints contact:

Dr Richard P. Harper,

Department of Oral and Maxillofacial Surgery/Pharmacology, Baylor College of Dentistry,

3302 Gaston Avenue,

Dallas, Texas 75246.

E-mail: rharper@tambcd.edu

Objective vs Subjective Methods for Determining Vertical Dimension of Occlusion

Occlusal vertical dimension is defined as the distance measured between two points when the occluding members are in contact.1 In a denture wearer it is initially established with a maxillary and mandibular base plate and wax rim; in a dentate person it is evaluated prior to reconstruction and usually maintained. The determination of occlusal vertical dimension (OVD) is not a precise process, and many professionals arrive at this dimension through various means.2 Many determine OVD with subjective means, such as the use of resting interocclusal distance, and speech-based techniques using sibilant sounds. Niswonger proposed the use of the interocclusal distance (freeway space), which assumes that the patient relaxes the mandible into the same constant physiologic rest position.3 The practitioner then subtracts 3 mm from the measurement to determine the OVD. There are 2 aspects that often make this incorrect. First, the amount of freeway space is highly variable in the same patient, depending on several factors including head posture, emotional state, presence or absence of teeth, parafunction, and time of recording. Second, interocclusal distance at rest varies 3 to 10 mm from one patient to another. As a result, the distance to subtract from the freeway space is unknown for a specific patient. Therefore, the physiologic rest position should not be the primary method to evaluate OVD.

Silverman5 stated that approximately 2 mm should exist between the teeth when the S sound is made. Pound6 further developed this concept for the establishment of centric and vertical jaw relationship records. While this standard is accurate, it does not correlate to the original OVD of the patient. Denture patients often wear the same prosthesis for more than 14 years and during this time lose 10 mm or more of their original OVD. Yet, all of these patients are able to say Mississippi with their existing prosthesis. If speech was related to the original OVD, these patients would not be able to pronounce the S sounds because their teeth would be more than 12 mm apart. Patients with temporomandibular joint dysfunction with surgical increases in OVD and patients with severe atrophy with long-term dentures demonstrate that OVD may vary more than 20 mm, yet most of them are able to speak clearly.

Facial measurements to determine OVD can be traced back to antiquity, where sculptors and mathematicians followed the golden proportion, later specified as a ratio of 1.618:1. Later, Leonardo da Vinci (1452-1519) in his book Anatomical Studies contributed several observations and drawings on facial proportions and the lower one third of the face, which he called divine proportions. He wrote: The distances between the chin and the nose and between the hairline and the eyebrows are equal to the height of the ear and a third of the face. The distance from the outer canthus of one eye to the inner canthus of the other eye is equal to the height of the ear and to one third of the face height. In addition, he said facial height (from chin to hairline) is equal to the height of the hand, and the nose is the same length as the thumb (and also the same length as the distance between the tip of the thumb and the tip of the index finger). Many professionals, including oral surgeons, plastic surgeons, artists, orthodontists, and morticians, use facial or body measurements to determine OVD. A review of the literature confirms that facial measurements can be compared and help to establish the original OVD.

The original occlusal vertical dimension is most often similar to the following dimensions:

1. The horizontal distance between the pupils7

2. The vertical distance from the external corner of the eye (outer canthus) or the pupil to the corner of the mouth7

3. The vertical distance from the eyebrow to the ala of the nose

4. The vertical length of the nose at the midline (from subnasion to glabella)7

5. The distance from one corner of the lips to the other (cheilion to cheilion), following the curvature of the mouth (more often in Caucasians)7

6. The distance from the eyebrow line to the hair line (in females) (da Vinci)

7. The distance from the outer corner of one eye (outer canthus) to the inner corner (inner canthus) of the other eye (da Vinci)

8. The vertical height of the ear (da Vinci)

9. The distance between the tip of the thumb and the tip of the index finger when the fingers are pressed together (da Vinci)

10.Twice the length of one eye

11.Twice the distance between the inner canthus of both eyes

12.The distance between the outer canthus and the ear (da Vinci)

Facial measurements, as a start to determine OVD, offer significant prosthetic advantages.8,9 These are objective measurements rather than subjective criteria (such as resting jaw position or swallowing). With so many measurements available, the clinician may take the average of 5 or more (especially when they are within a 1 to 2 mm range). Once the initial OVD is determined, the wax rim or acrylic temporaries may be used to evaluate speech, swallowing, and resting jaw position. Since there is no absolute method to determine OVD for all individuals, the facial and finger measurements are attractive because they require no radiographs or other special measuring devices.

Since OVD is not a specific measurement for the majority of patients, it may be slightly modified in the transitional stages of treatment and evaluated relative to patient acceptance and the condylar disc assembly. Esthetic requirements may mandate a slight decrease in OVD to make the patient appear more Class III, or a slight increase to make the jaw relationship more Class II. The latter is often useful in maxillary implant reconstruction cases because a slightly open OVD usually places a more axial direction of load on premaxillary implants in centric relation occlusion. Maxillary anterior implants are often placed more palatally than the roots of the natural teeth. A decrease in OVD is often used for mandibular anterior implants opposing natural dentition because a more closed OVD places a more axial force direction on these implants. Crestal stresses on bone are reduced when an axial load is applied to implants.10 In addition, bone is strongest in compression, 30% weaker in tension, and 65% weaker in shear. A 30-degree off-axis load reduces the strength of bone by 10% to 20%, and a 60-degree off-axis load reduces bone strength 30% to 50%.11 Furthermore, an axial load decreases the stresses to the abutment screw, which decreases the risk of screw loosening.9 During the last 2 decades, I have slightly altered OVD to improve force direction on anterior implants. Only 3 patients have expressed difficulty adjusting to the OVD, which in all cases was slightly more open than facial measurements indicated.

Facial and body parts often have dimensions that are consistently similar to each other. The original OVD is similar to at least 12 other dimensions on the face and hands and may be objectively determined in most patients. The condylar disc assembly position is maintained in a broad range of OVD. As a result, this dimension may be slightly modified to improve appearance, help stabilize a denture,9 or improve the direction of force on an implant.

References

1. Academy of Prosthodontics. The glossary of prosthodontic terms, ed 6. St Louis: Mosby, 1994.

2. Sharry JJ. Complete Denture Prosthodontics. New York: McGraw-Hill, 1968.

3. Niswonger ME. The rest position of the mandible and centric relation. J Am Dent Assoc 1934;21:1572-1582.

4. Tallgren A. Changes in adult face height due to aging, wear and loss of teeth and prosthetic treatment. Acta Odontol Scand Suppl 1957;24(15):1-122.

5. Silverman MM. Accurate measurement of vertical dimension by phonetics and the speaking centric space, Part I. Dent Dig 1951;57:265.

6. Pound S. Let /s/ Be your guide. J Prosth Dent 1977;38:482-489.

7. McGee GF. Use of facial measurements in determining vertical dimension. J Am Dent Assoc 1947;35(1):342-350.

8. Misch CE. Vertical occlusal dimension by facial measurement. Continuum, Misch Implant Institute Newsletter, 1997:Summer.

9. Misch, CE. Maxillary denture opposing an implant prosthesis. Misch CE (ed). Contemporary Implant Dentistry. St. Louis: Mosby, 1999.

10.Misch CE, Bidez MW. Implant protected occlusion: A biomechanical rationale. Comp Cont Dent Educ 1994;15:1330-1343.

11.Reilly DT, Burstein AH. The elastic and ultimate properties of compact bone tissue. J Biomech 1975;8:393.

For reprints contact:

Dr Carl E. Misch,

751 Chestnut, Suite 2,

Birmingham, Michigan 48009.

Fax: 248-642-3794.