In traditional prosthodontics, a range of techniques has been described to establish the OVD.44 Whereas objective methods use facial dimension measurements, subjective methods rely on esthetics, resting arch position, and closest speaking space. There is no consensus on the ideal method to obtain the OVD. Therefore, this dimension is part art form and part science.
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.44 The practitioner then subtracts 3 mm from the measurement to determine the OVD. Two observations conflict with this approach. First, the amount of freeway space is highly variable in the same patient, depending on factors such as head posture, emotional state, presence or absence of teeth, parafunction, and time of recording (greater in the morning). 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. However, it should be evaluated after the OVD is established to ensure a freeway space exists when the mandible is at rest.
Silverman stated that approximately 1 mm should exist between the teeth when making an “S” sound.45 Pound further developed this concept for the establishment of centric and vertical jaw relationship records for complete dentures.46 Although this concept is acceptable, 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 were related to the original OVD, these patients would not be able to pronounce the “S” sound because their teeth would be more than 11 mm apart. But to say the letter “S” with the correct sound, the teeth must be approximately 1 mm apart (regardless of the OVD). Therefore, the speaking space should not be used as the only method to establish OVD. However, after the OVD has been determined, the speaking space should be observed, and the teeth should not touch during sibilant sounds. On occasion, a short adjustment period of a few weeks may be required to establish this criterion.
After the position of the maxillary incisor edge is determined, the OVD influences the esthetics of the face in general. Facial dimensions are objective (because they are measured) and directly related to the ideal facial esthetics of an individual. They can be easily assessed regardless of the clinician's experience. This objective evaluation is usually the method of choice to initially evaluate the existing OVD or establish a different OVD during prosthetic reconstruction. In addition, it may be performed without the need for additional diagnostic tests.43
Facial measurements can be traced back to antiquity, when sculptors and mathematicians followed the golden ratio for body and facial proportions as described by Plato and Pythagorus.47 The golden ratio relates to the length and widths of objects in nature as 1 to 0.618.48 It was observed that biologic features follow this ratio.49 Architectural proportions often follow the golden ratio, because it is considered the most esthetically appealing to the human eye. Leonardo da Vinci later contributed several observations and drawings on facial proportions, which he called divine proportions.50 He observed the distance between the chin and the bottom of the nose (i.e., OVD) was a similar dimension as (1) the hairline to the eyebrows, (2) the height of the ear, and (3) the eyebrows to the bottom of the nose—and each of these dimensions equaled one third of the face (Figure 33-36).
FIGURE 33-36 Leonardo da Vinci used measurements to aid in drawing a face. The occlusal vertical dimension was similar to the hairline to eyebrow length and the height of the ear.
Many professionals, including plastic surgeons, oral surgeons, artists, orthodontists, and morticians, use facial measurements to determine OVD.51,52 Misch reviewed the literature and found that many different sources reveal many correlations of features that correspond to the OVD14,43,53:
1. The horizontal distance between the pupils54
2. The horizontal distance from the outer canthus of one eye to the inner canthus of the other eye
3. Twice the horizontal length of one eye
4. Twice the horizontal distance from the inner canthus of one eye to the inner canthus of the other eye
6. The horizontal distance from one corner of the lip to the other following the curvature of the mouth (cheilion to cheilion)54
7. The vertical distance from the external corner of the eye (outer canthus) to the corner of the mouth
8. The vertical height of the eyebrow to the ala of the nose50
9. The vertical length of the nose at the midline (from the nasal spine [subnasion] to the glabella point)51
10. The vertical distance from the hairline to the eyebrow line50
11. The vertical height of the ear50
12. The distance between the tip of the thumb and the tip of the index finger when the hand lays flat with the fingers next to each other (Figure 33-37).
FIGURE 33-37 Leonardo da Vinci described “divine proportions” in the following way: A, “The distance between the chin and the nose, and hairline and the eyebrows are equal to the height of the ear and to one-third of the face height.” B, In addition, the facial height (from the chin to hairline) is often equal to the length of the hand, and the distance from the chin to the bottom of the nose is the same length as the distance between the tip of the thumb and the tip of the index finger. (From Misch CE: Contemporary implant dentistry, ed 2, Mosby, 1999, St Louis.)
All of these measurements do not correspond exactly to each other but usually do not vary by more than a few millimeters (with the exception of the vertical height of the ear and the length of the index finger) when facial features appear in balance. An average of several of these measurements may be used to assess the existing OVD. In a clinical study by Misch, the OVD was often slightly larger than the facial measurements listed (more in men than women) but was rarely a smaller dimension.53
To determine facial measurements and their relationship to the desired OVD, the dentist first should evaluate the superior two thirds of the face and establish the face in general as facial balance (Figure 33-38). For example, when the horizontal distance between the pupils of the eyes is within 2 mm of the vertical distance from the outer canthus of the eye to the corner of the mouth, the midface is within facial balance. When the eyebrow to ala of the nose is similar to the hair line (in women) to eyebrow, the superior third of the face has balance. When these measurements are similar, the rest of the measurements are usually similar, including the bottom of the nose to the bottom of the chin (i.e., OVD). Therefore, the position by facial measurement is an objective starting point. Most often a male patient has an OVD that is slightly larger than the other facial dimensions. The subjective criteria of pleasing esthetics may then be considered after the facial dimensions are within balance with each other.
FIGURE 33-38 The superior two thirds of the face is first evaluated to see if it is in facial balance.
Facial measurements as a start to determine OVD offer significant prosthetic advantages. These are objective measurements rather than subjective criteria (e.g., resting jaw position or swallowing). After the dentist has determined the initial OVD, the dentist may use the wax rim to evaluate speech, swallowing, and resting jaw position. In addition, the esthetic requirements may mandate slightly decreasing the OVD and making the patient appear more Angle's class III or slightly increasing the OVD and making the jaw relationship more Angle's class II.
An anterior cantilever on implants in the edentulous mandibular arch may correct an Angle's skeletal class II, division I jaw relationship. The maxillary anterior teeth support the lower lip at rest in both Angle's skeletal class I and class II relationships. A traditional complete mandibular denture cannot extend beyond the anatomical support or neutral zone of the lips without decreasing stability of the prosthesis. However, with implants, the mandibular denture teeth may be set in a more ideal esthetic and functional position.14
The anterior cantilever in the Angle's skeletal class II mandible depends on an adequate implant number and A-P distance between the splinted implants. To counteract the anterior cantilever effect, the treatment plan should provide increased implant support by increasing the surface area by number, size, design, or A-P implant position. In these cases, a removable type 4 (RP-4) prosthesis, designed to prevent food impaction, may facilitate daily care compared with a fixed type 3 (FP-3) prosthesis.
Because no absolute method exists to determine OVD that can be used assuredly for all individuals, the facial measurements for balance are attractive because they require no radiographs or other special measuring devices. The maxillary and mandibular wax rims are evaluated at the OVD position (Figure 33-39). A closed-mouth centric relation bite registration is then made. Because the mandibular prosthesis is implant supported, the bite registration is usually more easily obtained compared with a soft tissue–supported mandibular denture.
FIGURE 33-39 A maxillary base plate and wax rim opposing a mandibular base plate and wax rim verification jig. The maxillary midfacial line, high lip line, canine position, and occlusal vertical dimension are evaluated before obtaining a closed-mouth bite registration record.
Mandibular Incisor Edge Position
After the maxillary incisal edge, the posterior plane of occlusion and the OVD are deemed clinically acceptable, the position of the lower anterior teeth is evaluated. Because the maxillary anterior teeth are first set in the wax rim, the mandibular teeth positions are set in relation to these teeth. In a maxillary denture, no anterior contact in centric relation occlusion is designed with the mandibular implant prosthesis.55,56 Centric stops or pressure from the tongue and muscle positions usually prevent continued extrusion of mandibular anterior natural teeth. However, this is not necessary when the anterior teeth are supported by implants or are part of a denture.
The occlusal position of complete maxillary and mandibular dentures during function is often anterior to the recorded centric relation occlusion.15 As a result, the anterior teeth occlude before the posterior teeth. When the mandibular implant prosthesis is more secure than the maxillary denture, the maxillary prosthesis loses the valve seal retention and may be dislodged during mandibular excursions in the absence of posterior contacts, which occurs not only during the incision of food but also during parafunction. Inadequate valve seal and instability of the maxillary denture also can contribute to gagging.
Maxillary anterior prosthetic teeth most always are positioned facially off the anterior supporting bone to satisfy phonetic and esthetic requirements. The moment forces created by the mandibular anterior teeth of the implant prosthesis may cause instability of the maxillary prosthesis, and therefore the anterior teeth should not come in contact with the maxillary denture. Most often, the horizontal overjet of the anterior teeth is about 2 mm. This overjet permits functional movements of the mandibular overdenture or fixed prosthesis without immediate anterior tooth contacts that may dislodge the maxillary denture and protects the premaxilla from excess forces (Figure 33-40).
FIGURE 33-40 The maxillary anterior teeth are first positioned in the wax rim. The mandibular anterior teeth do not occlude with the maxillary teeth. A horizontal overjet of approximately 2 mm is sufficient.
A vertical overbite of 2 mm with the maxillary anterior teeth often is used to position the mandibular anterior teeth. During mandibular excursions, the maxillary and mandibular anterior teeth contact because the mandible moves down and forward (the condyle slides along the glenoid fossa). In this way, the patient still is able to bite through a sandwich or piece of meat. The resulting anterior guidance is about 15 degrees, which is less than the ideal with natural teeth, where incisal guidance is desired. This position is compatible with the use of a bilateral balanced occlusion scheme when using posterior anatomic teeth. Hence, the maxillary anterior teeth are positioned first primarily by esthetics and secondarily speech. The mandibular anterior teeth are then positioned (after the OVD is established) primarily related to occlusion and function.
The tips of the maxillary canines align with the center of the incisive papilla and are closer to the resorbed residual ridge compared with the maxillary anterior incisors. Therefore, anterior contacts in centric occlusion may be present at the distal aspect of the maxillary canine.
After the maxillary and mandibular anterior teeth are set on the wax rims, the dentist determines the amount of incisal guidance, which determines the steepness of the compensating curve for a balanced occlusion. The greater the anterior guidance, the greater the posterior compensating curve. To establish anterior guidance with a minimal curve is easier to develop bilateral balance. Therefore, setting a shallow incisal guide for phonetics, esthetics, and function of the anterior teeth offers significant advantages.
Posterior Tooth Form
The form of the posterior teeth may be classified as anatomical (30-degree cusp angle), semianatomical (10- to 20-degree cusp angle), or nonanatomical (flat). In most complete denture designs, the posterior tooth form is determined by the resorption process of the posterior mandible. When abundant bone is present, an anatomic tooth form is used. When severe atrophy is present, a flat tooth form is used57,58 (Figure 33-41).
FIGURE 33-41 The posterior mandibular bone volume often determines the posterior tooth form in complete dentures. The more abundant the bone (left), the more anatomic the tooth form. The less bone present (right), the flatter the tooth form.
The anatomical tooth form presents considerable esthetic advantages for the maxillary denture, especially in the premolar positions. In addition, the steeper cusp forms are more efficient at penetrating the bolus of food compared with anatomical forms.59 In addition, the use of maxillary posterior anatomical teeth allows the creation of a vertical overbite in the anterior region of the mouth for improved esthetics and bilateral balance of occlusion. The cusp angles on the posterior teeth allow posterior occlusal contact in protrusion. When flat, nonanatomical teeth are used in the posterior regions, the dentist must eliminate the vertical overbite in cases in which the jaw relationship does not provide an adequate horizontal overjet.60 Therefore, the maxillary posterior denture teeth should have relatively steep cusp angles.
When a maxillary denture opposes an implant prosthesis, the maxillary posterior teeth should use a 20- to 33-degree cusp angle for improved esthetics and function. The mandibular posterior teeth should be 10 to 20 degrees (less than the maxillary teeth). This will enhance the occlusal setup suggested by the author (medial-positioned, lingualized occlusion) (Figure 33-42). Steep cusp angles in the mandible may cause destabilizing horizontal forces, as summarized by Ortman in his statement “the flatter the ridge, the flatter the cusp angles.”61 However, cusp angles are not a consideration for mandibular implant overdentures or fixed prosthesis because the attachment system overrides the functional concerns of tooth form.
FIGURE 33-42 The maxillary posterior teeth use an anatomic tooth form for esthetics and function. The mandibular posterior teeth should use a more nonanatomical tooth form.
Posterior Tooth Position
The mandibular edentulous posterior ridge resorbs in a medial direction as it transforms from division A to B bone volume but then resorbs laterally from division B to C and then to D27 (see Figure 33-42). In complete dentures, the dentist often first determines the position of the mandibular posterior teeth. Occlusal concepts aiming at denture stability often position the mandibular teeth perpendicular to the edentulous ridge.15,16 This positions the central fossa of the posterior mandibular teeth more medial than that of the natural teeth predecessors in division B bone but more facial in division C and even more facial in division D compared with the natural tooth position. Mandibular dentures in the neutral zone record the tongue position and result in a more buccal position of the denture teeth in resorbed arches.62 The maxillary denture teeth then are positioned farther facially than the original natural teeth if the dentist maintains a normal cusp–fossa relation.
Under ideal circumstances, the maxillary residual ridge is the primary stress-bearing region for a maxillary denture.15 The denture teeth are set closer to this structure than to any other supporting region. Placement of the denture teeth directly over the edentulous posterior crest reduces moments of force and improves support under vertical forces. In division A bone of the premolar and molar regions, the dentist often can place teeth over the crest of the ridge.
The maxillary edentulous posterior ridge resorbs in a medial direction as it transforms from division A to B, division B to C, and division C to D (Figure 33-43). In most complete denture concepts, the maxillary teeth are usually positioned to follow the mandibular teeth (which are positioned more buccal as the residual ridge resorbs) and increasingly are cantilevered off the maxillary bone support. Consequently, when the mandibular teeth are positioned over bony support (or when neutral muscular zones are used), maxillary denture teeth are always lateral of the resorbing bony support, and the condition is compounded in cases of advanced maxillary atrophy (division C or D bone) (Figure 33-44). The maxillary posterior teeth are also involved in esthetics, especially the premolar region. The more lateral tooth placement eliminates the buccal space during smiling and negatively affects esthetics compared with the position of the natural teeth.
FIGURE 33-43 The mandible resorbs first to the lingual and then to the facial. The maxilla resorbs toward the midline.
FIGURE 33-44 In this maxillary denture, the posterior teeth were set in relationship to the mandibular teeth, which were set over the existing division D bone. The posterior teeth are cantilevered buccally, off the bony base of the maxilla, which causes instability and poor esthetic appearance of the denture.
Gysi first introduced the basic concept of lingualized occlusion.63 Later Payne reported on a modified posterior setup of Farmer and suggested that the maxillary buccal cusps of posterior teeth should be reduced so only the lingual cusps would be in contact.64 Pound and Murrell discussed a similar concept but reduced the buccal cusp of the mandible rather than the maxilla, so the maxillary teeth remain more esthetic and introduced the term lingualized occlusion.57,58
Consistent in the philosophy of Payne and Pound was the belief that the palatal cusp should be the only area of maxillary tooth contact. This lingualized occlusion has since been renamed lingual contact occlusion.65 These occlusal schemes were designed to narrow the occlusal table and improve mastication, reduce forces to the underlying mandibular bone, simplify the denture teeth setup, prevent cheek biting, and help stabilize a lower denture (Figure 33-45).
FIGURE 33-45 The posterior maxillary anatomic teeth occlude the lingual cusp with the central fossa of the mandibular non-anatomic tooth.
Mandibular implant overdentures or fixed prostheses gain stabilization and retention through the implant support system. They are not tissue supported, so the occlusal scheme and tooth position may differ from traditional denture techniques. The author has suggested that the technique of Payne and Pound be modified further when one fabricates a maxillary denture opposing a stable implant-retained prosthesis.12–14 Because the mandibular prosthesis is stable, the dentist may then position the teeth in the most favorable manner for upper denture stability and support.
Pound placed the lingual cusp of the mandibular posterior teeth between two lines drawn from the canine to the buccal and lingual sides of the retromolar pad (Pound's triangle)57,58 (Figure 33-46, A). The tooth position originally suggested by Pound helps stabilize a mandibular denture. However, an implant-supported mandibular prosthesis does not require such a tooth position to enhance lower denture stability. Misch evaluated the position of the lingual cusps of mandibular molars in 30 patients and skulls with proper jaw relationship and occlusion compared with the lingual cusp position referred to by Pound14 (Figure 33-47). In all patients, the position of the posterior lingual cusps extended medial to a line drawn from the canine to the medial aspect of the retromolar pad. In other words, it is more medial than Pound's position and more medial than the underlying mandibular bone. In the majority of patients, the lingual cusps extended 2 mm more lingual beyond the line, but in about 10%, they extended to 3 mm, and another third were 1 mm more lingual to the line. Therefore, Misch has suggested that for mandibular implant prostheses, denture teeth may be set medial to the retromolar pad in a position similar to natural teeth (Figure 33-46, B).
FIGURE 33-46A, Pound's triangle is created by drawing two lines from the mesial aspects of the canine to each side of the retromolar pad. The lingual aspects of the mandibular teeth then are positioned within this triangle. B, Misch proposed drawing a line from the distal aspect of the canine to the medial aspect of the retromolar pad. The central fossae of the mandibular posterior teeth are then positioned just buccal to this line, and the lingual surfaces are lingual of this line. (Redrawn from Misch CE: Contemporary implant dentistry, ed 2, St Louis, 1999, Mosby.)
FIGURE 33-47 The lingual position of the mandibular posterior teeth was evaluated in 30 patients and skulls with natural teeth. In all patients, the lingual contours of the mandibular teeth were 1 to 3 mm lingual of Pound's most medial line.
The more medial the posterior denture teeth, the more vertical the occlusal forces generated over the maxillary bone, thus reducing tipping and enhancing the upper denture stability during function. Therefore, the central fossa of the mandibular posterior teeth is suggested to be positioned on a line drawn from the tip of the mandibular canine to the lingual aspect of the retromolar pad. The mandibular posterior teeth are placed so that the central fossa is over this line and the lingual cusps extend medial to the line.66 Although this position places the denture tooth more medial than previous denture tooth position techniques, the lingual cusps in both arches are in similar location to that of the original teeth.
The maxillary posterior teeth are then positioned so the mandibular buccal cusp occludes with the maxillary central fossa, with a horizontal overjet of the maxillary buccal cusps. This positions the maxillary posterior teeth closer to the natural tooth position because they follow the more naturally positioned mandibular teeth.
The occlusal centric contacts follow the guidelines of lingualized occlusion described by Payne, Pound, and Murrell.64,57,58,Only the lingual cusps of the maxillary posterior teeth are in contact during centric occlusion (Figure 33-48). Because the primary occlusal contact is the lingual cusp of the maxillary teeth rather than the buccal cusp of the mandibular teeth, this acts as an additional stabilizing factor for the maxillary denture, directing forces closer to the maxillary residual ridge. In addition, the narrower occlusal table (because only one cusp occludes) decreases the force required to penetrate food and simplifies the occlusal adjustment process.
FIGURE 33-48A, Only the lingual cusps of the maxillary anatomical posterior teeth occlude with the mandibular teeth. This brings the occlusal contact closer to the crestal bone support and helps stabilize the denture. B, The mandibular teeth have occlusal contact in the central fossa: the buccal cusps are reduced in height, with no occlusal contact in centric occlusion.
Bilateral balance occlusion has fallen out of favor in many denture philosophies because the occlusal concept is difficult to obtain, and is not practical during function—“enter bolus, exit balance.”67 However, the maxillary and mandibular teeth are set in bilateral balance occlusion. This concept further stabilizes the maxillary denture during parafunction. It also helps protect the premaxilla from the maxillary denture rotating up and loss of posterior seal. Because the anterior teeth do not occlude in centric occlusion, this also protects the premaxillary bone.
When the maxillary denture opposes an implant prosthesis and is set with incisal guidance, only the anterior teeth occlude in protrusive or mandibular excursions (Figure 33-49). When this concept is used with complete dentures, the mandibular denture goes up in the back and down in the front. Because the patient is used to an unstable lower denture, it is not a major concern. However, when the restoration is a maxillary denture opposing an implant-supported mandibular prosthesis, the maxillary denture falls from the back and up in the front. The valve seal is lost, and the denture has no retention. As a consequence, bilateral balance is the occlusal concept necessary to avoid this complication (Figure 33-50).
FIGURE 33-49 When only the anterior teeth occlude in mandibular functional movements, the mandibular implant prosthesis is stable. Therefore, the maxillary denture will rotate up in the anterior and down in the posterior. The valve seal will separate and the maxillary denture will lose retention.
FIGURE 33-50 The maxillary denture has bilateral balance to keep the prosthesis stable during function. This picture illustrates opposing prostheses during a mandibular right excursion with occlusal contacts of the anterior and posterior teeth.
As the crown height increases, an increasing moment force is applied to the maxillary teeth when set facial to the residual ridge. This increased moment force is difficult to avoid in the anterior maxilla because specific tooth position is required for proper esthetics and phonetics. However, setting the teeth and the occlusal contacts in the posterior regions toward the midline and raising the posterior plane of occlusion minimize these forces and instability. The maxillary second molar may even be set in crossbite to improve further the vertical force component over the severely atrophic division D posterior maxilla. Raising the posterior occlusal plane to the upper third of the tragus, medial position of the teeth, lingual contact occlusion, and bilateral balance occlusion help stabilize the weakest member of the removable prostheses, the maxillary denture (Figure 33-51).
FIGURE 33-51A, A maxillary denture wax-up opposing a mandibular implant fixed prosthesis. Only the lingual cusps of the maxillary denture occlude into the central fossae of the mandibular teeth. B, A right excursion of the mandible has bilateral balance occlusion. C, The final maxillary denture and mandibular fixed prosthesis in the mouth.