Vertical dimension of occlusion


The vertical dimension of occlusion (VDO) is the distance between two selected anatomical points on the patient’s face, usually the nasion and chin, with the teeth in the maximal intercuspal position (MIP)1 [Figure 11-01].

The resting vertical dimension (RVD) is the distance between two selected anatomical points on the patient’s face, usually the nasion and chin, when the mandible is in a physiologic resting position. According to studies27, the position of the RVD is not determined by the minimal level of contraction of the elevator muscles but by a combination of low levels of activity of these muscle fibers and the passive viscoelastic tension of the soft tissue, which may vary according to the degree of muscle contraction, posture, and emotional state of the patient [Figure 11-02].

The resting interocclusal space (RIS) is the measure of the difference between the positions of the VDO and RVD1, previously called functional free space (FFS).


Altering the VDO has been one of the most controversial aspects of restorative dentistry. Many controversies were empirically substantiated by articles published almost a century ago that have not been scientifically validated to date. Some authors at that time considered the VDO an immutable dimension during the individual’s life and that its alteration would have the potential to interfere with the physiology of the masticatory system811.

The VDO is of great clinical importance, as it must be understood and managed by every dentist when performing extensive treatments such as complete dentures, removable and fixed partial dentures, orthodontic treatments, and orthognathic surgeries. Vertical changes in the relationship between the maxilla and the mandible have esthetic, functional, structural, and biologic implications, as the initial references of the maxillomandibular relationship, the incisal relationships, and the occlusal plane must be reconstructed in a new dimension in space. Although the literature has shown it to be a predictable procedure when indicated and performed properly6,1218, problems can occur when some limitations are disregarded. Therefore, the clinician must be entirely sure of the therapeutic goals to alter the patient’s VDO from a restorative perspective due to the complexity of the work involved, the irreversibility of some procedures, and the financial aspect of this type of treatment.

This chapter critically analyzes the literature on the VDO to scientifically inform the decision-making process when treatment planning restorative treatments that may require its alteration.

[Figure 11-01] The vertical dimension of occlusion (VDO) is the distance between two selected anatomical points on the patient’s face, usually the nasion and chin, with the teeth in the maximal intercuspal position (MIP).

[Figure 11-02] The resting vertical dimension (RVD) is the distance between two selected anatomical points on the patient’s face, usually the nasion and chin, when the mandible is in a physiologic resting position. The resting interocclusal space (RIS) is the measure of the difference between the positions of the VDO and RVD1, previously called functional free space (FFS).

Establishment of the patient’s initial VDO

The patient’s VDO is established by the growth and development processes of the mandibular ramus, the gonial angle, and the pattern of tooth eruption, being influenced by the mandibular elevator muscles in the stages of primary, mixed, and permanent dentition. Although growth is genetically determined, it can be altered by environmental factors such as mouth breathing, tongue posture, non-nutritive sucking, the interposition of the lips, and neuromuscular dynamic function13,1921.

The growth of the mandibular ramus from the condylar process must be coordinated with tooth eruption so that occlusal contacts are maintained2224. The reduced growth of the mandibular ramus associated with a normal pattern of eruption of the posterior teeth will result in an increased height of the lower third of the face, determining a dolichofacial morphology2527 [Figure 11-03A,B]. On the other hand, the increased growth of the mandibular ramus associated with a normal pattern of eruption of the posterior teeth will result in a shortened lower third of the face, determining a brachyfacial morphology25,28,29 [Figure 11-04A,B].

[Figure 11-03A,B]
Dolichofacial patient:
Reduced growth of the mandibular ramus, associated with a normal eruption pattern of the posterior teeth, will result in an increased height of the lower third of the face.

[Figure 11-04A,B]
Brachyfacial patient:
Increased growth of the mandibular ramus, associated with a normal eruption pattern of the posterior teeth, will result in a shortened lower third of the face.

The strength of the jaw elevator muscle can affect the position of the body of the mandible with its ramus, which is reflected in the gonial angle. Individuals with such powerful muscles tend to have the straightest gonial angle and have the characteristics of brachyfacial individuals. Individuals with less strength in these muscles tend to have a more obtuse gonial angle and dolichofacial characteristics19,24,30.

Literature REVIEW

Most articles published in the scientific literature on increasing the VDO are related to indications or techniques for prosthetic treatments8,21,3148. On the other hand, VDO reduction has indications related to cases of skeletal discrepancies, such as vertical maxillary excess27 and anterior open bite49,50, or where there is a need to replace existing prostheses when the VDO is esthetically or functionally inappropriate.

Among the most commonly accepted techniques to determine the VDO are facial morphologic proportions31-33,51, physiologic8,3436, phonetic3740, cephalometric41,42, neuromuscular52,53, and bioesthetic54.

In 1928, Turner and Fox31 recommended that the VDO be determined according to the external appearance of the face in terms of the conformation of the nasolabial folds and the harmony between the facial thirds. In 1930, Willis32 developed a “bite-gauge” to determine the VDO according to the references published by Ivy33 in 1887. That author proposed that the distance measured from the outer corner of the eye to the labial commissure should be equal to that from the base of the nose to the chin. Niswonger8, in 1934, suggested the use of the RIS to determine the VDO. In 1947, McGee51 proposed using different facial measurements to confirm the VDO such as the distance from the pupil to the stomion, that from the glabella to the subnasale point, and that from one labial commissure to another. Two or three of these measurements would generally coincide and should be used to measure the VDO, recorded from the subnasale point to the gnathion.

In 1951, Pleasure35 stated that the physiologic rest position provides a stable reference for obtaining the VDO, considering a mean RIS of 3 millimeters (mm) between the maxillary and mandibular teeth, with the mandible at rest. Silverman37, in 1951, suggested that phonetics determine the VDO. According to that author, assessing the mandibular position during the pronunciation of certain sounds would identify the smallest vertical dimension of pronunciation. Pound40, also in 1951, reported that phonetic tests were auxiliary methods to obtain a reliable functional and esthetic diagnosis. He suggested the adoption of the “S” sound, claiming that the mandible would have a memory of vertical and horizontal position when the patient uttered this sound.

In 1954, Pyott and Shaeffer41 considered the validity of using radiographs to measure the VDO. The cephalometric analysis would also provide the ideal orientation and position of the occlusal plane of the anterior teeth42. Shanahan36, in 1956, proposed swallowing the saliva to determine the VDO and centric relation (CR) of the patient simultaneously, and to confirm the presence of the RIS by using phonetic tests with the “M” sound. Murphy55, in 1959, reviewed the philosophies of the time on the VDO. He observed that different authors had measured VDO loss using different methodologies without any consensus to establish the most appropriate method.

In 1962, Nagle and Sears43 stated that the VDO is not static throughout life and reflects the individual’s period of growth, development, and maturity. Jankelson53, in 1969, proposed using transcutaneous electrical nerve stimulation (TENS) to determine the VDO. In this technique, electrodes with an electrical current of moderate intensity are applied to the coronoid process to reduce the activity level of the elevator muscles to a minimum and make it possible to obtain a “neuromuscular rest position.” For dentate patients, Lee54, in 1990, proposed that the distance between the cementoenamel junction of the maxillary and mandibular central incisors could serve as a reference for the assessment and “restoration” of the VDO. According to that author, for Angle Class I, this distance was about 18 to 20 mm in a patient without tooth wear, and measurements lower than this would characterize a loss of VDO and would be a justification for treatment.

In 1997, Spear56 stated that no method can accurately determine the VDO of the individual, but that phonetics is a means capable of perceiving whether it has been exceeded. In 2000, Misch44 concluded that the RVD is not a stable and accurate parameter and depends on several factors such as head posture, emotional state, presence or absence of teeth, parafunction, and even measurement time. In 2006, Spear45 observed that the temporary use of an occlusal splint could help to determine the maxillomandibular relationship due to the muscular deprogramming provided, but that it was limited in assessing the feasibility of a new VDO. According to that author, the splint alters the VDO, occlusal contacts, and functional guidance. Its shape does not reproduce the natural contours of the occlusal surface, which may interfere with phonetics6,12,56,57, especially in the case of the maxillary teeth.

The dynamic nature of the dentoalveolar complex has long been recognized58,59, but it is unlikely that the compensatory dentoalveolar eruption occurring in the patient can be clinically quantified [Figure 11-05]. Berry and Poole60, in 1976, related the real loss of VDO to the rate of tooth wear, proposing that the loss would only occur when the degree of wear was more significant than the speed of compensatory dentoalveolar eruption. Despite a coherent theoretical explanation, its clinical occurrence is difficult to estimate. The measurement of the lost dimension seems to be secondary compared with the need to alter it for therapeutic reasons. Thus, it is not the purpose of restorative treatment to find a predefined ideal VDO or to try to reestablish a previous VDO, but rather to plan a VDO that satisfies the esthetic, functional, and biomechanical needs of the patient61.

[Figure 11-05] Mechanism of biologic compensation for dentoalveolar eruption58,59: Occlusal tooth wear can be partially or fully compensated by the lengthening of the dentoalveolar process, not necessarily resulting in a reduction in the VDO.

The dentist should also be aware that, although the most “visible” portions of tooth wear are the incisal and occlusal surfaces, several intra- and interarch changes can occur such as proximal wear, mesial migrations, lingual inclination of the mandibular incisors, proclination of the maxillary incisors, and a decrease in the perimeter of the dental arches54,6266 [Figure 11-06]. In addition, tooth wear can cause a change in the horizontal positioning of the mandible in the direction of the predominant wear pattern. Therefore, any increase in the VDO must be carried out in conjunction with an occlusal reorganization in CR or adapted centric position (ACP)61.

[Figure 11-06] Concomitantly with occlusal wear and compensatory dentoalveolar eruption, other intra- and interarch changes may occur such as proximal wear, mesial migrations, lingual inclinations of the mandibular incisors, proclination of the maxillary incisors, and a decrease in the perimeter of the dental arches54,6266.

The clinician should be aware that wear observed on the incisal edges of the anterior teeth does not necessarily indicate that there has been a reduction in the VDO. In most cases of Angle Class I and Class II patients, the anterior teeth wear out when the patient protrudes the mandible and performs attrition movements in this anterior position due to parafunctional or dysfunctional activities. Angle Class III patients often exhibit wear on the anterior teeth because the edge-to-edge relationship predisposes them to this. The incisal edges gradually wear out, and the mandibular position tends to be subsequently positioned in an anterior direction with the maxilla6 [Figures 11-07A–D and 11-08A,B].

[Figure 11-07A–D] Anterior tooth wear usually occurs due to parafunctional or dysfunctional activity in which the patient protrudes the mandible and performs attrition movements in this anterior position. Thus, the anterior teeth wear initially and progressively, and the posterior teeth will be compromised only when the anterior teeth cannot guide the excursive and incursive movements. Relationship of sound dental arches in MIP [A]. Relationship of the arches in the edge-to-edge position, where the patient performs tooth attrition movements [B]. In the initial phases, only incisal wear of the anterior teeth can be observed [C]. Morphologic changes of the incisal and occlusal surfaces of the anterior and posterior teeth in cases of more severe wear [D].

[Figure 11-08A,B] Incisal and occlusal wear will cause changes in bone and gingival levels, resulting from the mechanism of compensatory dentoalveolar eruption. Bone and gingival architecture of a healthy dentition [A]. Dentoalveolar eruption located in the anterior region due to attrition [B].

A severe degree of attrition in the anterior teeth needs to occur before the posterior teeth are also compromised by significant wear to the point of a reduction in the VDO. As a standard of diagnostic practice, as long as the posterior teeth are present, well positioned, and show minimal signs of wear in relation to the patient’s age, it is unlikely that a loss of VDO has occurred. However, a loss of VDO may be evident in cases of posterior bite collapse or in edentulous patients, causing overclosure of the labial commissures and a facial appearance of pseudoprognathism67,68 due to the anterior rotation of the mandible [Figure 11-09A–C].

[Figure 11-09A–C] Etiologies of VDO alterations: Dentate individual without clinical signs of VDO loss [A]. Modification of the VDO by a posterior collapse of the bite, that is, by the loss of posterior occlusal support and proclination of the maxillary anterior teeth [B]. In edentulous patients, the loss of VDO becomes evident [C].

Another essential aspect to consider is that cellular aging in patients of an advanced age causes loss of support of the skin and lips, generating changes in the facial contour and reduced exposure of the maxillary anterior teeth67,68. Thus, many of the esthetic deficiencies observed in these patients are not solely due to the supposed loss of VDO due to existing tooth wear or loss.

Based on this literature review, it is essential to highlight that many authors have stated, from a clinical point of view, that the VDO should not be seen as a single, static, and immutable point, but rather as a vertical interval4,6,47,48 that could be called a comfort zone48. As none of the techniques described is sufficiently precise or consistent when used in isolation4,6, it is recommended that the clinician make use of a combination of them, together with the clinician’s experience and clinical judgment, to ensure greater precision, according to each patient.

Deciding to alter the VDO

Any VDO alteration demands a significant amount of restorative work in one or both dental arches and a reorganizing approach to the patient’s occlusion. Before performing such an alteration, a methodical clinical examination and an accurate diagnosis are performed to identify the risks associated with the patient’s functional and parafunctional pattern, which will influence the stability, maintenance program, and longevity of the treatment.

In order to provide effective clinical parameters to manage the predictably of the patient’s VDO, the following four fundamental aspects are discussed below:

  1. Indications for altering the VDO.
  2. Consequences of altering the VDO.
  3. Determining the magnitude of the VDO alteration.
  4. Clinical performance of the VDO alteration.

Indications for altering the VDO

The main indications for VDO alteration are:

  • a) Harmonizing dentofacial esthetics.
  • b) Improving incisal and occlusal relationships.
  • c) Providing adequate space for the restorative material.

A) Harmonizing dentofacial esthetics

There is still some confusion among dentists about the real influence of the increase in the VDO in harmonizing the patient’s dentofacial esthetics because, in most prosthetic and restorative treatments, alteration of the VDO is performed together with the modification of the position and exposure of the maxillary anterior teeth.

The isolated increase in the VDO may not provide a notable esthetic improvement in the patient’s face. Gross and Ormianer7 evaluated the ability of dentists to observe esthetic changes in the face according to fractional increases of 2 mm in the VDO. These authors concluded that raters had difficulty perceiving and ordering vertical facial changes up to 8 mm. Increases of such magnitude would make it difficult to establish proper anterior incisal relationships in dentate patients.

Orenstein et al69, using acrylic overlays with increments of 2, 3, 4, and 5 mm in the height of the incisal pin of the articulator, stated that such vertical changes were not correlated with the perception of an increase in the lower third of the patient’s face by the examiners. For these authors, the indication of VDO increase should not be based only on facial esthetics.

It should be considered that in cases of complete dentures and implant-supported and implant-retained fixed full-arch prostheses, “facial rejuvenation” is caused by an increased VDO as well as by greater exposure of the maxillary anterior teeth, repositioning of the orofacial musculature, and improved lip support allowed by the position and arrangement of the artificial teeth and the denture base within the limits of the neutral zone62 [Figure 11-10A,B]. For dentate patients, this benefit is limited by the position of the teeth in the bone and the occlusal relationships. When indicated, it can only be corrected through integrated treatments with orthodontics or orthognathic surgery [Figure 11-11A,B].

[Figure 11-10A,B] The rehabilitation of edentulous patients allows the repositioning of the orofacial musculature and improvement of the lip support through the use of the wax orientation plane, denture base, and alignment of the occlusal plane of the artificial teeth within the limits of the neutral zone.

[Figure 11-11A,B] Facial changes provided by an increase in the VDO are associated with improving lip support and respecting the neutral zone.

B) Improving incisal and occlusal relationships

The exposure of the anterior teeth to the lips at rest and during smile should be carefully evaluated and planned, as it significantly impacts esthetics and function. In general, the greater the need to lengthen the incisal edges for esthetic reasons, the greater the possibility that they will interfere with the patient’s envelope of function, and, consequently, the greater the risk of failure of the restorative materials70.

In dentate patients, the incisal relationships of the maxillary and mandibular anterior teeth are the main factors to be considered when altering the VDO, since any vertical increase or reduction in this region will impact the horizontal relationship between these teeth due to the geometry of the mandibular opening movement15,7173. As the increase in VDO occurs from an eminently rotational movement of the mandible, which causes it to move in an inferior and posterior direction71, the overjet and overbite relationships of the anterior teeth will be simultaneously altered. Depending on the patient’s facial morphologic pattern, it can be established that for every vertical increase of 3 mm in the incisal region, an increase of 2 mm of overjet will also occur in this area45 [Figure 11-12A–D]. Thus, the critical factor to be considered when increasing the VDO is that the increase in overbite may make it impossible to establish appropriate previous relationships.

[Figure 11-12A–D] The Posselt diagram71 demonstrates the alteration of anterior relationships provided by the degree of mandibular opening in patients with different morphologic patterns [A]. In Angle Class I patients, a slight increase in the VDO is allowable in terms of the existing adequate anterior relationships [B]. In Angle Class II patients or patients with severe overbite, it is difficult to increase the VDO because these patients tend to lose the stabilizing anterior occlusal contact point in MIP due to the concomitant increase in overjet [C]. In Angle Class III patients, the relationship of the anterior teeth can be corrected by compensation through an increased VDO [D].

The increase in VDO demands that the patient’s occlusion be reorganized to improve pretreatment three-dimensional (3D) occlusal relationships such as overjet, overbite, angle of functional guidance, occlusal plane, and direction of forces on the teeth and restorations72,74,75. Therefore, to decrease treatment risks, the clinician will have to “negotiate” wisely between the necessary amount of elongation of the incisal edge of the anterior teeth and the angle and contour of the functional guidance [Figures 11-13A,B and 11-14A,B].

[Figure 11-13A,B] The influence of incisal edge elongation on the patient’s envelope of function. An incisal lengthening of a small magnitude of about 1 mm, for example, presents a reduced risk of interference in the mandibular trajectory, both in excursive and incursive movements [A]. In this author’s experience, increasing the overbite by an incisal lengthening of 2 mm or more increases the risk of functional or structural problems [B].

[Figure 11-14A,B] Interrelationship between the increase in VDO and the angle of functional guidance. Within certain limitations, increasing the thickness of the lingual restoration allows for a less inclined disclusion angle, capable of generating less stress on the teeth and anterior restorations72,74,75, in addition to being able to harmonize the behavior of the neuromuscular system.

C) Providing adequate space for the restorative material

An increase in VDO is a biologic ally for restorative treatment. It can generate space for the selected material to restore tooth morphology, often allowing an additive treatment in patients with structural loss due to attrition, biocorrosion, and abrasion. Minimally invasive tooth preparations are made possible with the use of materials with adequate strength and ability to adhere to different substrates. The traditional approach, with indications of surgery to increase the clinical crown, endodontic treatments, and intraradicular retainers, does not present rational reasons for recommendation due to its high biologic and financial cost.

The treatment plan should be carefully tested and adjusted using adhesive mock-ups or temporary cemented restorations that allow a realistic clinical assessment of the proposed changes due to their physiologic contours76. Only after ensuring that all these modifications provide harmonious esthetics, stable masticatory function, adequate phonetics, and comfort, can the dentist proceed with the treatment or perform any irreversible procedures [Figure 11-15].

[Figure 11-15] Due to its potential to generate space for the restorative material, the planned increase in VDO is a biologic ally for the treatment, allowing for more conservative tooth preparation.

Consequences of altering the VDO

Many studies6,7,12,13,1517,20,44,63,64,7789 have investigated the effect of VDO alteration on the temporomandibular joints (TMJs), neuromuscular system, teeth, and phonetics. Most of these studies reported that VDO alteration is safe as long as the clinician understands and respects certain individual variables. Abduo and Lyons16 stated that an increase in the VDO of up to 5 mm is a predictable procedure without harmful consequences. The associated symptoms are limited and tend to resolve within a few weeks. Moreno-Hay and Okeson17 stated that the masticatory system could adapt quickly to moderate changes in the VDO and that mild transient symptoms may occur in some patients without unfavorable effects. Some adaptive response mechanisms have been cited such as resizing the RIS by stretching and reorganizing the muscle fibers, apposition of sarcomeres, and connective tissue at muscle insertions12,79,82,88,89.

Regarding the phonetic aspects, it should be noted that the clarity of pronunciation of the “S” sound is often not related to a VDO increase but to the relationships between the mandibular incisal edges, maxillary incisal edges, and maxillary lingual surfaces. To minimize phonetic problems, Spear56 recommends carrying out some tests during the clinical examination to observe how the patient pronounces the “S” sound. According to Pound90,91, about 75% of patients pronounce the “S” sound with a protruded, slightly lingualized positioning of the mandibular teeth and with these teeth lowered to the maxillary incisal edges, and 20% with a minimally protruded position of the mandibular teeth [Figure 11-16A,B].

[Figure 11-16A,B] Phonetic relationships with the pronunciation of the “S” sound in restorative treatment: Most Angle Class I and Class III patients pronounce the “S” sound with the incisal relationships almost in the edge-to-edge position [A]. Some individuals, usually Angle Class II patients, pronounce the “S” sound in a retruded position [B].

For Spear56, the relationship of the incisal edges seems critical. It must be adjusted in individuals who articulate the “S” sound in a protruded mandibular position, with the maxillary lingual morphology adjusted in those who pronounce the “S” sound in a minimally protruded position. Fine adjustments should be performed weekly while the patient experiences phonetic adaptation difficulties with the mock-up or temporary restorations for up to 4 to 6 weeks. All adjustments should be evaluated in the protruded position and in MIP so that centric contacts are not lost and occlusal stability is not compromised56.

The anterior incisal relationships are adjusted by asking the patient to pronounce hissing sounds, such as “sixty-six,” several times, with an articulating tape positioned in the anterior region. The demarcated areas need to be adjusted and the improvement obtained should be evaluated. It is advisable to make these adjustments gradually and wait at least a week before reassessment and continuation of the treatment.

In order for VDO changes to enable favorable adaptive responses and minimize any negative consequences, all criteria for optimal occlusion62 must be respected such as the establishment of a new maxillomandibular relationship from healthy and stable TMJs and masticatory muscles; axial, bilateral, and simultaneous occlusal contacts; and effective functional guidance in harmony with the patient’s envelope of function [Figure 11-17A,B].

[Figure 11-17A,B] Adjusting the occlusal contacts in the new VDO is essential to provide comfort and functional stability.

Determining the magnitude of the VDO alteration

No single technique or panacea establishes an ideal and unchanging VDO for the patient. The method or combination of methods used should meet the patient’s esthetic, functional, structural, and biologic needs in a minimally invasive way61.

The determination of VDO must be performed with the condyles positioned in CR or ACP, and differently for edentulous as opposed to dentate patients. In edentulous patients, it is recommended to work with the wax orientation planes until the patient presents a facial esthetic with harmony between the horizontal component (provided by the soft tissue support) and the vertical component (provided by the increase in the VDO). Two additional methods can be used to determine whether the RIS seems sufficient: In the first method, with the patient erect and in the resting mandibular position, ask them to pronounce the “M” sound, slowly closing the mouth until the lips touch lightly. Check this measure by asking the patient to try to swallow the saliva presently in their mouth, and observe whether this occurs naturally and is not forced, using a Willis compass or caliper to help measure the changes. In the second method, phonetic tests using the “S” sound can be performed, although such tests are limited at this time by the conformation and volume of the orientation planes. For this author, all these VDO estimates should be considered provisional until the artificial teeth are mounted on the test base and the phonetic and esthetic tests can be performed more realistically.

The techniques used to determine the VDO in edentulous patients have not proven to be accurate, consistent, and reliable for use in dentate patients because the measurements are based on the position of the soft tissue, which is subject to significant variations15. For dentate patients, an increase in the VDO is generally of a smaller magnitude. It can be quantified more precisely according to the references of the teeth in their respective bone bases, using a dry tip caliper or a leaf gauge92 [Figure 11-18A–C]. In this author’s clinical experience, an increase of 1 to 3 mm in the anterior region is adequate and sufficient in most cases.

[Figure 11-18A–C] A practical example of the use of a leaf gauge92 to aid in the previous clinical determination of the VDO by the author: A height of 1 mm is insufficient to restore lost tooth structure and functional guidance [A]. A height of 2.5 mm seems to provide a starting point close to the recommended one to be considered in articulator mounting and occlusal analysis[B]. A height of 4 mm is shown to be too much, as it requires an unnatural thickening of the lingual surfaces of the teeth or elongation of the incisal edges of the mandibular anterior teeth [C].

The ability to determine the changes in occlusal relationships that will result from an increase in VDO will help in planning the amount of tooth structure to be removed or restorative material to be added93. Bohannan and Abrams94, based on personal observations of the mechanics of mandibular closure to its center of rotation, stated that an increase of 1 mm in the occlusal surface of the second molars would correspond to an increase of 3 mm in the central incisors. Kaiser and Schelb95 and Rebibo et al96, through studies on the geometry of mandibular movements, identified that an increase in height of 1 mm in the second molars would lead to an approximate increase of 2 mm in the central incisors and 3 mm in the height of the incisal pin of the semi-adjustable articulator (SAA). This author has practically used this 1:2:3 ratio when treatment planning restorative treatments, with predictable results [Figure 11-19].

[Figure 11-19] The geometry of the height relationship between the posterior teeth, anterior teeth, and incisal pin, according to the increase in VDO. On average, a height increase of 1 mm in the area of the second molars results in an approximate vertical increase of 2 mm in the central incisors and 3 mm in the height of the SAA incisal pin. This is called the 1:2:395,96 ratio.

Following these same parameters, excessive VDO increases in these patients can result in lingual surfaces with thick and unnatural contours, possibly causing functional and phonetic problems [Figures 11-20 to 11-22]. Elongating the mandibular anterior teeth in an incisal direction could reduce the lingual contours, but they are limited due to their unesthetic nature. Another factor to consider is that including mandibular teeth in the treatment planning would make the treatment more complex and costly in biologic, time, and financial terms.

[Figure 11-20] Changes in the lingual anatomy due to a planned VDO increase in Angle Class I patients. Suppose there is a need for a significant increase in VDO in these patients by the restorative treatment alone. In that case, the lingual surface may become thick and abnormally contoured, creating problems with comfort and phonetics. The mandibular teeth can also be elongated to achieve these goals. However, esthetics should be evaluated, mainly because older patients lose lip support and present relevant exposure of the mandibular teeth, especially during phonation.

[Figure 11-21] In Angle Class II patients, increasing the VDO by the restorative treatment can cause the anterior stabilizing occlusal contact to be lost, or leave it positioned on an inclined plane in MIP. Changes in lingual morphology to accommodate such a situation are generally not indicated as they generate an abnormal anatomy. Such cases often have indications for orthodontic treatment, sometimes together with orthognathic surgery.

[Figure 11-22] In Angle Class III patients, increasing the VDO may improve the relationship of the anterior teeth. However, any attempt at prosthetic compensation of skeletal or dental discrepancies should be evaluated in detail with models mounted on the articulator and be discussed with the interdisciplinary team and the patient.

In Angle Class II patients, it is more difficult to establish adequate and stable contacts on the lingual surface of the anterior teeth as the VDO increases. The use of an SAA is strongly recommended to visualize the consequences of the required changes in three dimensions and to plan the most satisfactory way to resolve the functional problems that are generated [Figure 11-21]. These limitations can only be fully corrected through integrated treatments with orthodontics or orthognathic surgery.

On the other hand, the increase in VDO in Angle Class III patients can improve the previous relationships. Compensatory treatment in these patients can be considered as a therapeutic approach. In this author’s opinion, any “prosthetic compensation” should only be recommended as a last resort, after scientifically based guidelines and with patient awareness, as there are trade-offs associated with every therapeutic compensation [Figures 11-22 and 11-23A,B].

[Figure 11-23A,B] Example of prosthetic compensation for VDO alteration for an Angle Class III patient and its benefits in terms of facial profile and occlusal relationships. (Courtesy of Dr. Dickson Fonseca, Brazil.)

In order to provide stability to the treatment and a lower adaptive response from the patient61, it is recommended that an increase in the VDO be restricted to the minimal amount necessary to harmonize dentofacial esthetics, improve occlusal relationships, and provide space for the planned restorations.

The increase in VDO in a single stage can be performed as long as it is based on a previous clinical evaluation of the planned dimension, accurate intermaxillary registration, and careful planning in an SAA6,7. According to this author’s experience, the option to increase the VDO in multiple stages is a laborious task because it requires an accurate adjustment of the complete occlusion with each addition, at the risk of negatively interfering with the patient’s adaptation process.

Clinical performance of THE VDO alteration

The clinical sequence presented below is a synopsis of the treatment planning process for cases that require an alteration in the VDO recommended by this author. It can be executed in an analog mode, with the assembly of the models on an SAA, or in a digital mode utilizing a virtual articulator with the appropriate design software. The specific details of each procedure are discussed in the corresponding chapters.

Assembly of models on a semi-adjustable articulator

After a complete clinical examination, the maxillary study model should be mounted on the articulator with the aid of a facebow or the Kois dentofacial analyzer97 [Figure 11-24A,B]. The mandibular study model should then be assembled from an intermaxillary registration in CR62.

[Figure 11-24A,B] Assembly of study models on the SAA from an intermaxillary registration in CR.

In this author’s opinion, using an anterior occlusal device, such as a Lucia jig98 or Kois therapeutic deprogrammer99, provides a stable anterior stopping point for the intermaxillary registration in a VDO very close to the planned one [Figure 11-25A–C].

[Figure 11-25A–C] The Kois therapeutic deprogrammer99 provides a reproducible and stable position to record the CR position with traditional registration materials and an intraoral scanner. The Kois therapeutic deprogrammer can be manufactured with acrylic resin in the dental laboratory, digitally made from milled blocks of polymethyl methacrylate (PMMA), or printed with acrylic resin materials in a 3D printer61.

Evaluation of the 3D position of the incisal edge of the maxillary anterior teeth in relation to the face and lips

Although there are specific parameters to be considered for smile design100102, this step depends on the dentist’s ability and experience with three-dimensionally positioning the incisal edges of the anterior teeth to provide both lip support and appropriate tooth exposure, with the lips at rest and during smile (more details in Chapter 3) [Figure 11-26A–E]. This author suggests using digital tools that help with smile planning, such as Digital Smile Design (DSD)103,104, with the patient’s face and lips as primary references105,106.

[Figure 11-26A–E] The smile construction planning should be guided by the face105,106 [A]. The Digital Smile Design (DSD) Hands-On App helps the dentist or dental laboratory technician (DLT) to determine the initial morphology of the restorations [B,C]. From the 2D design, restorations can be performed using either an analog [D] or a digital [E] workflow.

Integrating function and esthetics

Initially, only the buccal surfaces of the maxillary teeth are waxed-up in the study model, according to facial references, dental morphology parameters, and the patient’s esthetic wishes103,104. A diagnostic wax-up can be performed through an analog or digital workflow, depending on the clinical case or the preference of the dentist and dental laboratory technician (DLT).

The proposed alterations should be clinically tested through mock-ups or temporary restorations and adjusted until the patient’s approval is obtained regarding the esthetic and functional aspects. In this author’s opinion, the demand for an increase in the VDO is directly related to the increase in the length of the incisal edge of the maxillary anterior teeth. When they are significantly elongated, increased overbite of the anterior teeth and inclination of functional guidance can potentially restrict the patient’s envelope of function71,72. Such restriction increases the risks of treatment, especially in patients with parafunctional activity, in addition to increasing the torque on the supporting teeth and the shear stresses on the restorative material74,75 [Figure 11-27A–C].

[Figure 11-27A–C] Tests and initial esthetic–functional adjustments of the maxillary mock-up in the patient’s mouth. The diagnostic wax-up can be refined and completed upon patient and dentist approval.

Design of the posterior occlusal plane

Once the morphology of the buccal surfaces and the anterior relationships are approved, the wax-up of the lingual and occlusal surfaces of the posterior teeth can be completed. From there, temporary restorations can be pressed, milled, or printed in the dental laboratory and adhesively cemented to the tooth structure [Figure 11-28A–D].

[Figure 11-28A–D] Temporary restorations should be used for a broader esthetic evaluation of the patient. Preoperative photograph [A]. Temporary milled PMMA restorations bonded to the tooth structure [B]. Approval of temporary restorations by the patient regarding esthetic and functional harmony [C]. PMMA block (VIPI Block Trilux, Brazil) [D].

Author’s note

In my opinion, the philosophic discussion about the loss or not of VDO seems to be secondary to the therapeutic advantages of being able to change the VDO to harmonize dentofacial esthetics, improve occlusal relationships, and provide adequate space for the restorative material, with minimal biologic damage. The TMJs and the patient’s neuromuscular system, in the vast majority of cases, will present appropriate adaptive responses to the planned changes, provided that the clinician respects fundamental occlusal principles such as intermaxillary registrations in the CR position and the accurate adjustment of the occlusal contacts in this “new” VDO.

According to the scientific literature and my clinical experience, the planned VDO should not be considered a static and immutable reference point but a flexible measure within a physiologic tolerance range, subject to change to meet the treatment goals.

Subjective and objective clinical parameters should be incorporated into the VDO determination process to increase its predictability. Subjective parameters, such as dentofacial harmony, phonetics, and comfort, should be analyzed and approved by the patient. The 3D position of the maxillary anterior teeth in the proper maxillomandibular relationship will provide lip support and influence decisions regarding the magnitude of the VDO alteration needed to accommodate the various mandibular movements with reduced stress.

The objective parameters will be defined by the need to establish favorable functional relationships for the guidance of mandibular movements without distorting the posterior occlusal contact relationships. It is also necessary to plan the appropriate thickness for the selected restorative material to provide structural longevity to the teeth and restoration.

During restorative treatment, it is highly recommended that the proposed changes to increase the VDO, as well as the position of the incisal edges and the inclination of the occlusal planes, be clinically tested, responsibly and reversibly, through mock-ups or temporary restorations, for the necessary time. Only after ensuring that all these modifications provide harmonious esthetics, stable masticatory function, adequate phonetics, and comfort, can the dentist proceed with the treatment or perform any irreversible procedures such as tooth preparations [Figures 11-29A–F and 11-30A–C].

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May 13, 2024 | Posted by in Esthetic Dentristry | Comments Off on Vertical dimension of occlusion

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