¶ Chapter 5 — OCCLUSION PATTERNS ASSOCIATED WITH BASIC MANDIBULAR POSITIONS AND MOVEMENTS
Reference Edition
This chapter is part of the Air Force Dental Laboratory Manual (2005) – Digitally Restored Edition.
This edition preserves the original publication while correcting OCR errors, restoring formatting, reconstructing damaged tables where necessary, and improving digital readability.
The technical content has not been rewritten, modernized, expanded, or altered.
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¶ Section 5A — Basic Terminology
¶ 5.1. Overview
5.1.1. Occlusion is defined as the “the static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth.” Articulation is defined as “the contact relationship between the occlusal surfaces of the teeth during function.”
5.1.2. Many patterns of tooth contact are possible. Part of the reason for the variety is the mandibular condyle’s substantial range of movement within the temporomandibular joint. Some of the more vital terms and fundamental occlusion patterns associated with the basic mandibular positions and movements are described in this chapter.
¶ 5.2. Maximum Intercuspation (MI)
Maximum intercuspation is the complete intercuspation of the opposing teeth independent of condylar position.
5.2.1. It is important to understand the value of MI in the natural dentition. The MI position is a highly reproducible guide for restoring the shape of badly broken down natural teeth. It is also a guide for aligning and shaping artificial teeth for partially edentulous arches.
5.2.2. A dentist checks the height of all kinds of restorations by asking the patient to bring opposing teeth into MI. A technician routinely makes restorations on casts that have been related to each other in MI. When a natural dentition has grossly deteriorated or when all teeth have been extracted, one of the best means a dentist had for accurate, reproducible positioning of the lower jaw in relation to the upper is gone.
5.2.3. Restorative challenges, like making complete dentures or rehabilitating an entire natural dentition, require the dentist to make an educated guess. He or she must determine just where the lower jaw was located when the natural teeth contacted in correct MI. The problem is two-fold; properly orientating the lower jaw vertically and properly positioning the lower jaw horizontally.
¶ 5.3. Centric Relation
Centric relation is a maxillomandibular relationship in which the condyles articulate with their respective discs in the anterior-superior position of the glenoid fossa against the articular eminences.
5.3.1. For most people, when their teeth are in MI, the condyles are situated 1.25 mm plus or minus 1 mm forward of centric relation. When surfaces of teeth are grossly deteriorated or when all teeth are lost, there is no way of telling exactly where the normal MI position placed the condyles in the glenoid fossae. In these cases, the dentist uses the highly reproducible centric relation position to horizontally orient the lower jaw for prosthesis construction procedures.
5.3.2. How do we rationalize the probability that the condyles were not in centric relation when the patient had a full complement of sound natural teeth in good MI? Fortunately for dentistry, most patients function well when the centric relation position is used to horizontally orient the lower jaw to the upper. For example, denture teeth are purposely assembled to come together in MI when the condyles are in centric relation. The dental laboratory technician’s ability to fabricate any restoration or prosthesis in centric relation requires an accurate jaw relation record in centric relation.
¶ 5.4. Centric Occlusion
Centric occlusion is the occlusion of teeth when the mandible is in centric relation (Figure 5.1). This position may or may not coincide with MI.
Figure 5.1. Centric Occlusion.
¶ 5.5. Vertical and Horizontal Overlap
Vertical overlap is the extension of the maxillary teeth over mandibular counterparts in a vertical direction when the dentition is in MI (Figure 5.2). Horizontal overlap is the projection of teeth beyond their antagonists in a horizontal direction.
Figure 5.2. Vertical and Horizontal Overlap.
¶ 5.6. Angle’s Classification
E. H. Angle (1899) developed a classification of the normal and abnormal relationships of maxillary to mandibular teeth (Figure 5.3). Angle defined three classes; I, II, and III. These classes are based on a person’s profile, the position of the mesiobuccal cusp of the upper first molar relative to the buccal developmental groove of the lower first molar, and the upper anterior to lower anterior tooth relations in terms of vertical and horizontal overlap.
Figure 5.3. Angle’s Classification.
Class I or Normal
Class II or Retrognathic
Class III or Prognathic
5.6.1. Class I. In this class, the patient’s profile is characterized as normal. The mesiobuccal cusp of the upper first molar falls in the buccal groove of the lower first molar when the teeth are in MI. In the anterior area, the normal range of horizontal overlap is 0 to 2 mm and the average range of vertical overlap is 1 to 5 mm.
5.6.2. Class II. In this class, the patient’s profile is deficient in chin length and characterized as a retruded (retrognathic) profile. The mesiobuccal cusp of the upper first molar falls anterior to the buccal groove of the lower first molar in MI. In the anterior area, horizontal overlaps in excess of 10 mm are not uncommon. Vertical overlaps, where the lower incisors make indentations in the gingiva of the palate, happen occasionally. In any event, the most significant feature about the anterior tooth relationships in Angle’s Class II is the marked horizontal overlap. There are two subdivisions of Angle’s Class II as follows:
5.6.2.1. Class II, Division 1 (II/1)
In Class II/1 malocclusions, the maxillary incisors have a normal labiolingual inclination or are too labially inclined.
5.6.2.2. Class II, Division 2 (II/2)
In Class II/2 malocclusions, two or more maxillary incisors are tipped palatally.
5.6.3. Class III. In this class, the patient’s profile is excessive in chin length and characterized as a protruded (prognathic) profile. The mesiobuccal cusp of the upper first molar falls posterior to the buccal groove of the lower first molar in MI. In the anterior area, the upper and lower anteriors are usually edge to edge (0 mm of vertical and horizontal overlap). Negative vertical and horizontal overlaps are possible. (The lingual surfaces of the lower anteriors are forward to and extend up over the incisal edges of the upper anteriors.)
¶ Section 5B — Cusp Position in Maximum Intercuspation (MI)
¶ 5.7. Types of Cusps
From a functional point of view, there are two types of cusps—stamp cusps and shearing cusps.
5.7.1. Stamp Cusps (Lingual of the Upper and Buccal of the Lower)
Another name for a stamp cusp is occlusal vertical dimension holding cusp. This is because stamp cusps act to maintain a constant distance between the upper and lower jaws when the teeth are in MI.
5.7.2. Shearing Cusps (Buccal of the Upper and Lingual of the Lower)
By exclusion, shearing cusps are cusps other than stamp cusps. That is, shearing cusps do not maintain the vertical distance between the upper and lower jaws when the teeth are in MI.
¶ 5.8. Cusp Relationships With Opposing Teeth
When teeth come into MI (Class I, II, or III), the stamp cusps in one arch hit in fossae or across occlusal embrasures of the teeth in the opposite arch. Two basic varieties of stamp cusp arrangements are used in making prosthodontic restorations; the cusp-to-occlusal embrasure pattern (paragraph 5.9) and the cusp-to-fossae pattern (paragraph 5.10).
¶ 5.9. Cusp-to-Occlusal Embrasure Pattern
Variations of this pattern are frequently seen in natural dentitions. This type of cusp placement was originally established for complete denture setups. It is basically a one tooth to two teeth relationship of all of the teeth except the mandibular central incisor and the last maxillary molar. In MI, most of the mandibular buccal cusps are in embrasure contact with the maxillary teeth, and almost all of the maxillary lingual cusps are in a fossa relationship with the mandibular teeth.
5.9.1. Stamp Cusp Impacts.
5.9.1.1. Look at Figure 5.4 as you read the information in Table 5.1 on contact locations of mandibular buccal cusps on maxillary teeth in a cusp-embrasure occlusion. You can see that all of the mandibular buccal cusps are in an embrasure contact relationship with the maxillary teeth, except the distobuccal (DB) cusps of the mandibular first and second molars and the distal (D) cusp of the mandibular first molar.
Figure 5.4. Cusp-to-Embrasure Tooth Orientations (Mandibular Buccal).
5.9.1.2. Look at Figure 5.5 as you read the information in Table 5.2 on contact locations on mandibular teeth by the maxillary lingual cusps in a cusp-embrasure occlusion. All of the maxillary lingual cusps are in a fossa relationship except the distolingual (DL) cusps of the maxillary first and second molars.
Table 5.1. Contact Locations of Mandibular Buccal Cusps on Maxillary Teeth.
| ITEM | A | B |
| Mandibular Buccal Cusps | Contact Areas on Maxillary Teeth | |
| 1 | First premolar | Embrasure between canine and first premolar |
| 2 | Second premolar | Embrasure between first and second premolars |
| 3 | First molar (MB cusp) | Embrasure between second premolar and first molar |
| 4 | First molar (DB cusp) | Central fossa of maxillary first molar |
| 5 | First molar (D cusp) | Distal fossa of maxillary first molar |
| 6 | Second molar (MB cusp) | Embrasure between first and second molars |
| 7 | Second molar (DB cusp) | Central fossa of maxillary second molar |
Figure 5.5. Cusp-to-Embrasure Tooth Orientations (Maxillary Lingual).
Table 5.2. Contact Locations of Maxillary Lingual Cusps on Mandibular Teeth.
| ITEM | A | B |
| Maxillary Lingual Cusps | Contact Area on Mandibular Teeth | |
| 1 | First premolar | Distal fossa of lower first premolar |
| 2 | Second premolar | Distal fossa of lower second premolar |
| 3 | ML cusp of first molar | Central fossa of lower first molar |
| 4 | DL cusp of first molar | Embrasure between first and second molars |
| 5 | ML cusp of second molar | Central fossa of lower second molar |
| 6 | DL cusp of second molar | Embrasure distal to lower second molar |
5.9.2. Shearing Cusp Positions.
5.9.2.1. All of the maxillary buccal cusp tips are in a buccal embrasure relationship with lower teeth. (Exceptions are the mesiobuccal cusp of the maxillary first molar in the buccal developmental groove of the mandibular first molar, distobuccal cusp of the maxillary first molar resting over the distobuccal developmental groove of the mandibular first molar, and the mesiobuccal cusp of the maxillary second molar in the buccal developmental groove of the mandibular second molar.)
5.9.2.2. All of the mandibular lingual cusp tips are in a lingual embrasure relationship with the upper teeth. (Exceptions are the distolingual cusp of the mandibular first molar situated in the lingual developmental groove of the maxillary first molar and the distolingual cusp of the mandibular second molar in the lingual developmental groove of the maxillary second molar.
¶ 5.10. Cusp-to-Fossa Pattern
5.10.1. Placement. This type of cusp placement locates all mandibular buccal cusps into the fossae of their maxillary counterparts. Also, all maxillary lingual cusps are positioned in the fossae of their mandibular antagonists. Under ideal conditions, it is a tooth-to-tooth relationship; that is, each mandibular posterior tooth contacts one maxillary opponent. Although the cusp-to-fossa pattern is extensively used to restore teeth in fixed prosthetic dentistry, it is rarely seen in the natural dentition.
5.10.2. Three Advantages. A cusp-to-fossa relationship has three significant advantages over a cusp to embrasure relationship. First, it better directs forces over the long axes of the teeth. Second, it helps stabilize individual teeth in their respective positions in the dental arches. Finally, a cusp-to-fossa relationship reduces food impaction in the proximal area because there are no cusp tips striking in the embrasures to force the teeth apart.
5.10.3. Stamp Cusp Impacts.
5.10.3.1. Look at Figure 5.6 as you read the information in Table 5.3 on contact locations in the maxillary fossae by the mandibular buccal cusps in a cusp-fossa occlusion.
Figure 5.6. Cusp-to-Fossa Tooth Orientations (Mandibular Buccal).
5.10.3.2. Look at Figure 5.7 as you read the information in Table 5.4 on contact locations in the mandibular fossae by the maxillary lingual cusps in a cusp-fossa occlusion.
5.10.4. Shearing Cusp Positions.
5.10.4.1. The maxillary molar buccal cusps are located over mandibular buccal developmental grooves. Maxillary premolar buccal cusps are situated over specially formed notches in the distal cusp ridges of mandibular premolar buccal cusps. NOTE: Notches are also placed in the mesial cusp ridges of maxillary premolar buccal cusps.
Table 5.3. Contact Locations of Mandibular Buccal Cusps on Maxillary Fossae.
| ITEM | A | B |
| Mandibular Buccal Cusp | Contact Areas on Maxillary Teeth | |
| 1 | First premolar | Mesial fossa of maxillary first premolar |
| 2 | Second premolar | Mesial fossa of maxillary second premolar |
| 3 | First molar (MB cusp) | Mesial fossa of maxillary first molar |
| 4 | First molar (DB cusp) | Central fossa of maxillary first molar |
| 5 | First molar (D cusp) | Distal fossa of maxillary first molar |
| 6 | Second molar (MB cusp) | Mesial fossa of maxillary second molar |
| 7 | Second molar (DB cusp) | Central fossa of maxillary second molar |
Figure 5.7. Cusp-to-Fossa Tooth Orientations (Maxillary Lingual).
Table 5.4. Contact Locations of Maxillary Lingual Cusps on Mandibular Fossae.
| ITEM | A | B |
| Maxillary Lingual Cusps | Contact Areas on Mandibular Teeth | |
| 1 | First premolar | Distal fossa of mandibular first premolar |
| 2 | Second premolar | Distal fossa of mandibular second premolar |
| 3 | First molar (ML cusp) | Central fossa of mandibular first molar |
| 4 | First molar (DL cusp) | Distal fossa of mandibular first molar |
| 5 | Second molar (ML cusp) | Central fossa of mandibular second molar |
| 6 | Second molar (DL cusp) | Distal fossa of mandibular second molar |
5.10.4.2. The buccally located maxillary and mandibular notches reduce the possibility of lateral movement interference during working excursions. Natural teeth do not show such notching.
5.10.4.3. As previously stated, the cusp-to-fossa type of MI is frequently incorporated into fixed prosthodontic restorations. All such restorations start as wax patterns (wax simulations of natural teeth surfaces). Within limits, this means stamp cusps can intentionally be waxed into fossae and cusp arms can be notched for better lateral excursion clearance. Mandibular shearing cusps are positioned to avoid collision with maxillary stamp cusps in working excursions.
5.10.4.4. In MI, the distolingual cusp of the mandibular first molar is situated in the lingual developmental groove of the maxillary first molar. The distolingual cusp of the mandibular second molar is in the lingual developmental groove of the maxillary second molar. The positions of the other mandibular shearing cusps are somewhat more variable. Therefore, the mandibular lingual cusp position has to conform to the working excursion rule (no opposing cusp collisions). Notching maxillary and mandibular cusp arms on the lingual aspect of posterior teeth is just as acceptable as it was on the buccal.
¶ 5.11. Applying the Cusp-Fossa Philosophy to Prosthesis Fabrication
5.11.1. Cusp-fossa contacts are of primary value in restoration problems that directly or indirectly involve natural teeth; for example, single castings, fixed partial dentures, RPDs, and natural teeth opposing a complete denture. (The idea is to reproduce cusp-fossa contacts if they were there originally.)
5.11.2. It may be possible to change cusp-embrasure contacts to the more desirable cusp-fossa variety by appropriately carving wax patterns. There are no particular advantages to developing cusp-fossa contacts for opposing complete dentures.
¶ 5.12. Crossbite
5.12.1. Normally, the buccal cusps of the lower teeth and the maxillary lingual cusps are the occlusal vertical dimension holding (stamp) cusps. In MI, the buccal cusps of the maxillary posteriors horizontally overlap the buccal cusps of the mandibular teeth, and horizontal overlaps in the anterior area are the rule.
5.12.2. A crossbite exists when either or both of the following tooth relationships are present in MI. The normal stamp cusp and shearing cusp relationship found in related cases are reversed and/or the normal horizontal and vertical overlap relationship found between upper and lower anterior teeth are reversed.
5.12.3. A crossbite can occur between a single upper and the opposing lower tooth, a few upper and the opposing lower teeth, or throughout the dentition.
¶ Section 5C — Mandibular Movements
¶ 5.13. Vertical Dimension
Vertical dimension is any measurement of vertical distance made between the upper and lower jaw. A mandible can travel and stop anywhere on a path between maximum opening and closure. If a vertical measurement is to have meaning, it should identify a place along the potential path of travel the dentist and the patient can find on demand. The term vertical dimension with no further description of conditions is meaningless.
¶ 5.14. Occlusal Vertical Dimension
Occlusal vertical dimension is the vertical distance between the upper and lower jaws when natural teeth or denture teeth are in MI. The presence of teeth (natural or artificial) controls how far the mandible can travel vertically toward the upper jaw. When teeth are badly worn or gone, “stops” at the correct occlusal vertical dimension do not exist. A reliable guideline is needed to estimate where the vertical movement of the mandible toward the upper jaw should stop so the dental restorations can be made accordingly.
¶ 5.15. Physiologic Rest Position
A physiologic rest position is a measurement of vertical dimension made between the jaws when the muscles controlling the mandible are relaxed. The occlusal vertical dimension in most people with a natural dentition is 2 to 4 mm less than the physiologic rest measurement. This 2 to 4 mm allows the patient to have the teeth apart and out of function when relaxed.
¶ 5.16. Estimates of the Occlusal Vertical Dimension
The principle behind speech sound (phonetic) occlusal vertical dimension estimates is simple. In a normal natural dentition, teeth barely miss contacting when “s” and “ch” sounds are spoken. The vertical dimension a person uses to form these sounds stays about the same throughout adulthood, even though the dental arches might show severe wear or complete tooth loss. NOTE: The physiologic rest position and phonetic occlusal vertical dimension estimate are two reproducible positions on the mandible’s vertical path of travel frequently used by dentists to estimate what the correct occlusal vertical dimension might have originally been.
¶ 5.17. Errors in the Occlusal Vertical Dimension
5.17.1. Open Occlusal Vertical Dimension.
5.17.1.1. The patient’s upper and lower jaws are being held too far apart when natural or artificial teeth meet in MI. Fixed prostheses (such as single crowns, multiple crowns, or fixed partial dentures) can be responsible for this problem when natural teeth are present. An improperly made removable prostheses could cause an open occlusal vertical dimension in people with few or no teeth.
5.17.1.2. An open occlusal vertical dimension usually results from making an inaccurate occlusal vertical dimension estimate or from an error in the construction of the prosthesis. Some of the more common symptoms associated with an open occlusal vertical dimension are soreness of the muscles of mastication, inability to pronounce “s” and “ch” clearly, and teeth making contact noises while the person is talking.
5.17.2. Closed Occlusal Vertical Dimension.
5.17.2.1. In the case of a closed occlusal vertical dimension, the patient’s jaws are too close together when natural or artificial teeth hit in MI. Possible generalized reasons for such overclosure are as follows: severe wear of natural or artificial chewing surfaces, marked resorption of the residual ridges in a person who has been wearing the same set of complete dentures for years, an erroneous estimate of the correct occlusal vertical dimension during prosthesis construction procedures, or a technical error.
5.17.2.2. Some clues that the occlusal vertical dimension is closed too far are as follows. reduced biting power, excessive space between the teeth when the patient is in physiologic rest position, or a great deal of space visible between upper and lower teeth while “s” sounds are spoken. (Teeth should barely miss.)
¶ 5.18. Types of Mandibular Movements
5.18.1. The mandible is capable of many different, subtle kinds of movements. When the mandible moves, the condyles most certainly move with it, but the type and direction of condylar movements are not necessarily the same in each joint.
5.18.2. Basic mandibular movements consist of hinge (paragraph 5.19), translatory (paragraph 5.20), and lateral movements (paragraph 5.21). Most of the time a typical mandibular movement is a smooth, fluid blend of two or three of these motions.
¶ 5.19. Hinge Movements
Hinge movements consist of either opening or closing motions on a horizontal axis common to both condyles (Figure 5.8).
Figure 5.8. Rotational Movement Around a Hinged Axis.
¶ 5.20. Protrusion or Retrusion (Translatory) Movements
5.20.1. These movements are called translatory (sliding) movements although, in protrusion, incisal guidance causes hinge movement to occur at the same time. In protrusion, both condyles leave their fossae and move forward upon the articular eminences. When the mandible retrudes, both condyles leave the eminences and move back into their respective fossae.
5.20.2. The full envelope of hinge and translatory movements as viewed in the midsagittal plane appears in Figure 5.9. Based on the research of Dr. Ulf Posselt, the picture represents the mandible’s range of vertical and anteroposterior movement, which is three dimensional. Observe that the teeth are slightly separated, with the edge of the lower incisor at the “a” position in the diagram. Although the diagram happens to be superimposed over a lower incisor, it applies to any point on the body of the mandible. The features of this diagram , as marked in Figure 5.9, are as follows:
5.20.2.1. Number 1--contact between upper and lower teeth when the condyles are in centric relation.
5.20.2.2. Number 2--MI.
5.20.2.3. Number 3--edge-to-edge incisor contact.
5.20.2.4. Number 4--closure to a negative horizontal and vertical overlap between upper and lower incisors.
5.20.2.5. Number 5--maximum protrusion.
5.20.2.6. Letter a--physiologic rest position.
5.20.2.7. Letter b--maximum opening.
5.20.2.8. Path 2ab--path of habitual opening. (NOTE: The physiologic rest position is a place on this path.)
5.20.2.9. Path 1cb--most retruded path of opening the mandible is capable of taking. From “1” to “c,” the condyles are in centric relation and the mandible is making a pure opening
movement. The pure hinge opening in the centric relation position can last for as far as one inch, as measured between the edges of the upper and lower central incisors. Between “c” and “b,” the mandible continues to open, but is also translated forward. This means the condyles leave the fossae and move on to the eminences.
5.20.2.10. Path 5b--most protruded path of opening the mandible is capable of taking. NOTE: Although Paths 2ab, 1cb, and 5b in Figure 5.9 are described as “opening” paths, they are also “closing” paths.
Figure 5.9. Anteroposterior and Vertical Movements.
¶ 5.21. Right and Left Lateral Movements
The side to which the mandible moves is called the working side; the side opposite the working side is called the nonworking side. The condyle on the working side is called the working or rotating condyle. By ex clusion, the other condyle becomes the nonworking or orbiting condyle. A general description of lateral mandibular motion (Figure 5.10) is as follows:
5.21.1. As the mandible moves to the side, the cusps and incisal edges of the opposing teeth must clear one another. Also, the eminence on the nonworking side is probably lower than the fossa on the working side. The conclusion is that the mandible opens, at least slightly, to make a lateral movement.
5.21.2. The working side condyle rotates in its fossa (Figure 5.10-A).
5.21.3. The nonworking (or balancing) side condyle translates forward and medially down its eminence and produces a protrusion of the nonworking side. Because the nonworking condyle follows a limited arc of travel around the working condyle, the nonworking condyle is said to be orbiting the working condyle (Figure 5.10-B).
5.21.4. There is a total shift (or mandibular translation [MT]) or sideshift of the mandible and its condyles toward the working side (Figure 5.10-C). Two fundamental kinds of MT, progressive and immediate, can occur.
5.21.4.1. Progressive MT is characterized as the working condyle rotating and moving laterally while the balancing condyle moves forward and medially, all as a single integrated movement.
5.21.4.2. Immediate MT takes place prior to the working condyle’s rotation or the balancing condyle’s translation. It occurs immediately prior to the occurrence of progressive MT once the lateral excursion begins.
5.21.4.3. MT of the mandible takes different directions of travel from person to person (and sometimes from right to left sides in the same person).
5.21.5. The Bennett angle (lateral condylar inclination) is the angle the orbiting condyle makes when a sagittal plane passes through its fossa, as viewed in the horizontal plane. The orbiting path’s angle to the sagittal plane averages 12 to 15 degrees. This angle is the combined result of the balancing (nonworking) condyle advancing medially, plus any sideshift that takes place.
Figure 5.10. Typical Lateral Movement.
Legend:
A - Working or Rotating Condyle
B - Balancing or Orbiting Condyle
C - Sideshift or Bennett Movement
¶ 5.22. Arrow Point or Gothic Arch
5.22.1. When test lateral movements are made with the casts of a patient’s mouth mounted in an articulator (a device that simulates mandibular motion), the maxillary and mandibular stamp cusps move out of MI and follow predictable routes across opposing chewing surfaces.
5.22.2. The incisal edges of lower anterior teeth also travel well-defined paths as they pass over the lingual surfaces of upper anterior teeth. The intersection of a stamp cusp’s working excursion and its nonworking excursion produces a Gothic arch or arrow point. The MI position is at the apex.
5.22.3. Stamp cusp routes are diagrammed in Figure 5.11. The arrow points generated by maxillary stamp cusps crossing mandibular chewing surfaces are directed forward. Arrow points generated by mandibular stamp cusps and incisal edges on maxillary tooth surfaces are directed backward.
5.22.4. When the arrow point patterns in the mouths of a number of patients are analyzed, the findings indicates the angle inside an arrow point changes from tooth to tooth and from person to person.
5.22.5. What are some of the major factors that affect the size of the included angle? The farther away a tooth is located from the condyles, the greater the angle within the arrow point. As the distance between the condyles increases, the Gothic arch angle decreases (and vice versa). As the amount of mandibular translation increases, an arrow point’s included angle gets larger.
5.22.6. Persons having mostly progressive MT have working and nonworking paths that intersect at a precise point. Persons having immediate MT show comparative blunting or rounding at the intersection of the working and nonworking paths.
Figure 5.11. Stamp Cusp Arrow Point Tracings.
5.22.7. This information emphasizes that every stamp cusp has a specific working and nonworking track for leaving the MI position, the tracks proceed in directions unique to each cusp, and no obstruction (interference) to a stamp cusp’s lateral movement should appear along those tracks.
5.22.8. When chewing surfaces are fabricated for a prosthesis on an articulator, the alignment of occlusal ridges and grooves will be dictated by the lateral movements of stamp cusps in and out of MI (Gothic arch tracks). If the ridge and groove alignments, as developed in the articulator conflict with the patient’s true lateral movements after the prosthesis is delivered, then unanticipated, harmful cusp collisions could possibly occur. The following questions should be answered to develop properly aligned ridges and grooves for the chewing surfaces of a prosthesis.
5.22.8.1. How closely does the articulator simulate the patient’s actual MT?
5.22.8.2. Is the maxillary cast positioned (articulated) on the articulator the same way the maxilla relates to the glenoid fossae?
5.22.8.3. Does the articulator’s intercondylar distance match the patient’s distance?
¶ 5.23. Occlusal Disharmony
The disastrous effect of occlusal disharmony is best explained by comparing the temporomandibular joint and mandibular movement with the lever systems.
5.23.1. Classes of Lever Systems. Each lever system consists of a rigid bar in contact with a fulcrum, one point on the bar for the application of force and another point on the bar for the application of a load. There are three classes of lever systems; Class I, II, and III as follows:
5.23.1.1. Class I Lever System. As shown in Figure 5.12, a Class I lever system consists of a rigid bar across a fulcrum . Force applied to one end of the bar moves a load on the other end (like pliers or a crowbar). This is a very efficient system because the working force transmitted to the load can be multiplied simply by moving the fulcrum closer to the load and further away from the point of applied force.
5.23.1.2. Class II Lever System. A Class II lever system consists of a rigid bar with a fulcrum at one end, a load in the middle, and a force applied to the other end. A wheelbarrow is an example of a Class II lever system (Figure 5.12). This system is less efficient than the Class I lever system because the load is shared between the fulcrum and the applied force.
5.23.1.3. Class III Lever System. A Class III lever system consists of a rigid bar with a fulcrum placed at one end, a load applied to the other end, and working force applied in the middle like a tree pruner or drawbridge (Figure 5.12). The normal mandibular jaw is a Class III lever system in both the anteroposterior and cross-arch directions. This system is less efficient than either the Class I or II systems because more force must be applied to do the same amount of work.
Figure 5.12. Lever Systems.
5.23.2. Nondestructive Lever System (Figure 5.13).
5.23.2.1. When people chew on the right or left side or bite with their anterior teeth, a Class III lever system normally develops (Figure 5.13-A).
In this system, the teeth closest to the point of applied force receive the greatest impact. The teeth farther away from the point of applied force receive a progressively lesser amount of force. This explains why people tend to lose their anterior teeth last, even though the teeth are comparatively weak by structural design. Because the anterior teeth feel decreased muscular force, they receive less stress.
5.23.2.2. The posterior teeth (Figure 5.13-B) are close to the point of applied force in both the anteroposterior and cross-arch directions. Consequently, they transfer more of the applied force to the load and are under more functional stress than the anterior teeth. They are well able to support the added stress because the large surface area of their multiple root structure stabilizes them and transfers the functional stresses more evenly to the alveolar ridges.
Figure 5.13. Nondestructive Lever System.
5.23.3. Destructive Lever System (Figure 5.14).
Faulty occlusal contacts can change the nondestructive Class III lever system to a destructive Class I or II lever system by changing the relationship of the fulcrum and working points as follows:
5.23.3.1. Class III to Class I Lever System. If a posterior nonworking contact occurs during the protrusive biting function, the fulcrum point moves from the temporomandibular joint to the point of faulty contact (Figure 5.14-A). The closing muscle force vector (P) is now posterior to the tooth fulcrum (F). The work (W) is still done in the area of the anterior teeth. This condition is particularly harmful because it results in incisal stress not in line with the long axis of the working (anterior teeth).
5.23.3.2. Class III to Class II Lever System. If a high-lateral nonworking contact occurs when the mandible is moved to the side to chew food, the normal Class III lever system will be changed to the Class II lever system (Figure 5.14-B). In this instance the work (W) is still being done on the working side, but the premature nonworking contact (B) triggers a more forceful closure of the muscles (P) on the nonworking side. This changes the normal Class III lever system to the destructive Class II lever system and puts an unusual amount of stress on the teeth with the undesired contact.
Figure 5.14. Destructive Lever System.
¶ Section 5D — Functional Articulations
¶ 5.24. Lateral and Translating Excursions
5.24.1. Angle’s classification deals with three basic ways that teeth come into MI. However, there are at least seven ways that natural or artificial teeth actually function in lateral and translating excursions. Four of the functional articulation schemes occur in surveys of people who have natural teeth. Technicians intentionally organize the other three patterns when they construct complete dentures (see Chapter 7).
5.24.2. There are very distinctive characteristics that set the functional articulation schemes apart from one another. The individual patterns of articulation are based on contact differences between upper and lower teeth during working, nonworking, and protrusive excursions. The following paragraphs 5.25 through 5.28 show the functional articulations found in people having natural teeth.
¶ 5.25. Group Function (or Unilateral Balanced Articulation)
The tooth contact characteristics of unilateral balanced articulation are as follows:
5.25.1. Anterior Teeth. In MI, anterior teeth have a horizontal overlap of 1 to 2 mm as well as vertical overlap and 1 to 2 mm.
5.25.2. Working Side. The upper and lower anterior teeth on the working side touch. The lingual inclines of maxillary buccal cusps should be in even contact with the buccal inclines of the mandibular buccal cusps.
5.25.3. Nonworking Side. There is no contact between upper and lower teeth.
5.25.4. Protrusive. There is edge-to-edge contact between upper and lower anteriors. Posterior contact may or may not be present. It varies from person to person.
¶ 5.26. Mutually Protected Articulation (or Anterior-Guided Articulation)
In a mutually protected articulation, the anterior teeth are at least partly responsible for causing separation between opposing posterior teeth on the working side and during protrusive excursions. This movement protects the posterior teeth during excursions. The anteriors characteristically show moderate to steep vertical overlap and minimal horizontal overlap. The posterior teeth take the occlusal load when the teeth are at MI. This protects anterior teeth and completes the mutual protected articulation.
5.26.1. Anterior Teeth. In MI, anterior teeth have a horizontal overlap of 0.0 to 0.5 mm and a vertical overlap of 2 mm or more.
5.26.2. Working Side. The upper and lower anterior teeth on the working side make contact. There is no contact between upper and lower posteriors.
5.26.3. Nonworking Side. No contact develops between upper and lower teeth on the nonworking side.
5.26.4. Protrusive. When the anteriors contact edge to edge, there is no posterior tooth contact.
5.26.5. Canine-Guided Articulation. This form of articulation is a common variety of anterior-guided articulation where the only teeth making contact on the working side are the upper and lower canines. All other features of anterior-guided articulation are unchanged.
¶ 5.27. Delayed Anterior-Guided Articulation
This form of articulation shows group function and anterior guided articulation in the same working movement.
5.27.1. Anterior Teeth. In MI, anterior teeth have a horizontal overlap of 1 to 2 mm and a vertical overlap of 2 mm or more. (Delayed anterior-guided articulation has the horizontal overlap characteristic of group function and vertical overlap associated with anterior-guided articulation.)
5.27.2. Working Side. The working movement begins with the opposing posterior teeth on one side sliding across one another in group function. The last part of the movement shows anterior guided articulation. That is, sufficient contact develops between upper and lower anterior teeth to cause separation of opposing posteriors.
5.27.3. Nonworking Side. There is no contact between upper and lower teeth.
5.27.4. Protrusive. There is edge-to-edge contact between upper and lower anteriors. There is no posterior tooth contact.
¶ 5.28. Asymmetrical Pattern of Articulation
This pattern of articulation shows group function going to one working side and anterior-guided articulation going to the other.
5.28.1. Anterior Teeth. In MI, the anterior teeth have a horizontal overlap of 0.0 to 0.5 mm on the anterior guided side and 1 to 2 mm of horizontal overlap on the group function side. The anterior teeth in MI have a vertical overlap of 2 mm or more on the anterior-guided side and a vertical overlap of 1 to 2 mm on the group function side.
5.28.2. Working Sides. One working side demonstrates tooth contact patterns characteristic of group function; the other shows tooth contacts found in anterior-guided articulation.
5.28.3. Nonworking Sides. There is no contact between upper and lower teeth on either nonworking side.
5.28.4. Protrusive. Protrusive contacts are so variable that no general pattern can be described. NOTE: The single consideration common to all forms of articulation in the natural dentition is the absence of nonworking side contacts. Nonworking contacts involving natural teeth routinely cause pain in the interfering teeth and the temporomandibular joint. These contacts also cause destruction of a tooth’s bone support.
¶ 5.29. Christensen’s Phenomenon
Christensen’s phenomenon is the space that occurs between opposing occlusal surfaces during mandibular protrusion (Figure 5.15). The anterior teeth are responsible for the disclusion of the posterior teeth during the protrusive movement.
Figure 5.15. Christensen’s Phenomenon.
¶ 5.30. Major Determinants of Articulation
Major determinants of articulation include the occlusal plane, occlusal curve, condylar angle or direction, and incisal guide angle, as follows:
5.30.1. Occlusal Plane. The occlusal surfaces of the premolars and molars of both the upper and lower jaws in opposition establish the occlusal plane (Figure 5.16).
Figure 5.16. Occlusal Plane.
5.30.2. Occlusal Curve. The occlusal curve consists of the following two parts:
5.30.2.1. Anteroposterior Curve. The anteroposterior curve is the anatomic curve established by the occlusal alignment of the teeth (from the canine through the buccal cusps of the posterior teeth), when viewed from the side. It also is called the Curve of Spee (Figure 5.17).
5.30.2.2. Curve of Wilson. The Curve of Wilson is the lateral component of the occlusal curve when viewed from the anterior (Figure 5.17).
Figure 5.17. Occlusal Curve.
5.30.3. Condylar Angle of Direction. The angle or direction of the condyle as it traverses the contours of the glenoid fossa dictates the cusp height of teeth. A steep eminence inclination would permit longer cusps; a shallow eminence inclination would require shorter cusps.
5.30.4. Incisal Guide Angle. The incisal guide angle of an articulator is determined by the amount of horizontal and vertical overlap the anterior teeth exhibit. As the overlap increases, the length of the cusp may be longer. Consequently, as the overlap decreases, the cusp length must be shorter. The condylar inclination and anterior guidance may be dependent on each other. The anterior guidance in a healthy occlusion is approximately 5 to 10 degrees steeper than the condylar inclination, which allows for separation of the posterior teeth during a protrusive movement. (See Christensen’s Phenomenon in paragraph 5.29.)
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