“A simple or complex articulator is an instrument that helps the dentist apply their knowledge and experience to a clinical problem. Thus, the dentist is the critical factor for the effective application of this device in dentistry”1.
Definition
Articulators are instruments used to replicate the static and dynamic three-dimensional (3D) relationships between the patient’s maxilla and mandible in the dental clinic or laboratory. With an acceptable degree of accuracy, they can reproduce the positions of centric relation (CR) and maximal intercuspal position (MIP) and the patient’s mandibular movements. However, they have limitations in terms of faithfully simulating the multidirectional excursive and incursive movements controlled by the patient’s neuromuscular system that occur in biologic structures with some resilience and flexibility [Figure 8-01A,B].
[Figure 8-01A,B] Articulators are able to reproduce the position of centric relation (CR), maximal intercuspal position (MIP), and the patient’s mandibular movements with an acceptable degree of accuracy [A]. However, their limitations in terms of faithfully simulating the multidirectional excursive and incursive movements controlled by the patient’s neuromuscular system should be recognized [B].
Despite the clinical benefits related to the accuracy of the results and the scientific validation regarding their use, many professionals do not routinely use articulators2, impairing the quality of functional diagnoses and the predictability of treatments.
Indications
Functional analysis
The articulator assembly allows a detailed analysis of how much the occlusion deviates from the therapeutic reference model. These findings should be interpreted in conjunction with other signs and symptoms in a stomatognathic system in a pathologic state to decide whether the patient could benefit from changes in the existing occlusal pattern and whether the case should be monitored for a period of time or treated immediately. Unfortunately, such a decision is not always straightforward due to the multiple factors involved3.
Several occlusal aspects can be analyzed with models mounted on the articulator in CR or in the adapted centric position (ACP)4 such as the alignment of the occlusal plane, the magnitude and direction of vertical and horizontal mandibular deviations from premature contacts, and the effectiveness of the functional guidance.
TREATMENT PLANNING
Study models mounted on an articulator are essential for treatment planning in the most diverse dental specialties such as orthodontics, dental prosthodontics, restorative dentistry, and orthognathic surgery. Through the practical use of an articulator, it is possible to plan the necessary occlusal changes to correct the morphologic deficiencies found in the previous examinations such as, for example, an improvement of the occlusion by orthodontic movement or selective grinding, or by adding restorative material.
With the use of a facebow, an articulator also allows a more precise acquisition of complementary esthetic information to be added to the clinical examination, in addition to the analysis of photographic images and videos and their integration with the functional aspects through the diagnostic wax-up.
COMMUNICATION
The articulator is a useful tool to communicate the present occlusal issues with the interdisciplinary team and discuss some potential solutions. In addition, it is valuable for patient education as it is possible to demonstrate and explain to the patient the factors that can be impacting their masticatory system.
Execution
Models mounted on the articulator are used for making the diagnostic wax-up, mock-ups, or tooth preparation guides with silicone putty matrices, guides for implant installation, interocclusal splints, temporary prostheses, and final prostheses.
Deficiencies in the analysis of study models not mounted on AN articulator
The analysis of plaster models not mounted on an articulator provides limited and “static” occlusal diagnostic information. The manual and free articulation of the models allows the observation of the existing intraarch relationships such as dental morphologies, alignment of the occlusal planes, asymmetries, inclinations, misalignments, and extrusions. However, it does not allow the precise classification of the patient’s interarch relationship and the evaluation of the functional and dynamic components of the occlusion from the CR, in addition to not relating the dental arches to the patient’s face. Also, depending on the number of missing teeth and their location, as in bilateral edentulous spaces, for example, it is not possible to achieve an accurate intercuspation of the models in a manually articulated MIP.
Types of articulators5–7
- Non-adjustable articulator
- Semi-adjustable articulator
- Fully adjustable articulator
Non-adjustable articulator
The non-adjustable articulator (NAA) is the simplest articulator. It is unable to acceptably represent the patient’s functional movement pattern, and the location of its rotation axis is arbitrary and inferior to the clinical reality. In addition, it has a restricted mandibular closing arch, generating clinically relevant changes in the position of the centric contacts and the direction of the fossae and ridges of the prosthetic restorations. Some devices cannot reproduce lateral or protrusive movements with acceptable accuracy, and such characteristics demand significant occlusal adjustments in the mouth when the VDO is changed. Due to these limitations, this device can only be used to fabricate single-unit posterior restorations in which the anatomy of neighboring teeth provides a suitable anatomical reference pattern in a conformative approach to treatment. Examples of this articulator are the hinged articulator and the quick-fixing articulator [Figure 8-02A–C].
[Figure 8-02A–C] Models of non-adjustable articulators (NAAs).
Semi-adjustable articulator
The semi-adjustable articulator (SAA) is the most commonly used articulator in dental clinics and laboratories. It can reproduce centric positions and jaw movements but without replicating condylar trajectories and mandibular kinematics in an identical manner to the patient [Figure 8-03A–C].
[Figure 8-03A–C] The semi-adjustable articulator (SAA) allows acceptable reproduction of centric positions and jaw movements but without replicating condylar trajectories and mandibular kinematics in an identical manner to the patient.
The difference between the NAA and the SAA is depicted in [Figure 8-04].
[Figure 8-04] The NAA has a randomly located rotation axis, a restricted jaw closure arch, and an inability to reproduce lateral and protrusive movements with acceptable accuracy. This leads to clinically relevant changes in the centric contact position and the fossae and ridges of the prosthetic restoration. The SAA has a rotation axis with a location and dimension closer to the clinical reality, reducing the differences between the mandibular opening and closing arch in the patient and the articulator.
Some of the characteristics of the SAA should be understood in order to minimize its limitations6,8. The location of the rotation axis of the articulator is not equivalent to the natural axis. However, it maintains a distance of 100 to 110 millimeters (mm) from the interincisal point, which is close to the clinical reality, thus reducing the differences between the opening and closing trajectories between the articulator and the patient. These discrepancies will influence the positioning of the cusps and the relationship of the incisal edges of the restorations. Performing the intermaxillary registration in the planned VDO limits this problem5.
In addition, the shape of the articular eminences of the SAA is usually flat and rigid, and the intercondylar distance is approximate in size. Therefore, distortions in occlusal morphology related to the direction of fossae, marginal ridges, and functional guidance should be refined in the mouth through an accurate occlusal adjustment. Some models of SAAs recommended by the author are shown in [Figure 8-05A–E].
[Figure 8-05A–E] Recommended models of SAAs: Bio-Art A7 Plus (Bio Art, Brazil) [A], SAM 3 (SAM Präzisionstechnik, Germany) [B], Artex CR (Amann Girrbach, Austria) [C], Whip Mix 4640 (Whip Mix, USA) [D], and Panadent 1610AR (Panadent, USA) [E].
Fully adjustable articulator
The fully adjustable articulator (FAA) is capable of reproducing mandibular movements as fully as possible from the patient’s “real” mandibular rotation axis9 [Figure 8-06A–D]. Its utilization is complete when it has adjusted according to the pantographic tracings of the mandibular border movements [Figure 8-07A,B]. Depending on the device, it is possible to record condylar and incisal trajectories, Bennett movements and angles, Fischer angles, and the patient’s intercondylar distance. Thus, the use of this type of articulator will allow the development of an occlusal morphology fully compatible with the posterior and anterior determinants of occlusion, resulting in a fewer number of clinical adjustments, even in cases of alteration of the vertical dimension of occlusion (VDO).
[Figure 8-06A–D] Examples of fully adjustable articulators (FAAs): Stuart Gnathological Computer Model 73 (Dental CE Stuart, USA) [A], Denar Mark II (Whip Mix) [B], Gamma Reference SL (Gamma Dental, Austria) [C], and KaVo PROTARevo (KaVo Dental, Germany) [D].
[Figure 8-07A,B] Different pantographic recording equipment complements the mounting of patient models in the FAA.
However, this type of articulator usually requires considerable investment and a substantial amount of time for learning and even for assembling each case. In addition, the procedures for its use are quite sensitive to the technique, allowing for errors and inaccuracies. The pantographic device for recording the terminal rotation axis and the pin that marks the condylar tracings can interfere with the mandibular movements, causing involuntary, restricted, or inconsistent tracings10–12.
Arcon versus non-arcon
There are two types of adjustable articulator designs. The first, called non-arcon–type articulators, have the balls that represent the condyles coupled to the upper frame of the articulator, with the condylar trajectory contained in the lower frame. In an arcon-type design, the condylar ball is coupled to the lower frame of the articulator and the condylar trajectory to the upper frame, which provides a more faithful representation of the anatomical relationships.
Despite the didactic interest regarding their historic evolution, non-arcon–type articulators, e.g. Hanau 96H2 (Whip Mix) and Dentatus Articulator Type ARH (Dental Specialties, Sweden), are not commonly used nowadays. They allow greater control during handling for the diagnostic wax-up or for the assembly of teeth in complete dentures, both in centric contacts and in laterality and protrusive movements, as the axes of their respective trajectories rigidly support their condylar balls. However, the non-anatomical design of non-arcon–type articulators causes the angle between the condylar guidance, the occlusal plane, and the dental guidance to change according to the VDO alteration or the excursive movements. In arcon-type articulators, e.g. Bio-Art A7 Plus (Bio Art), SAM 3 (SAM Präzisionstechnik), Artex CR (Amann Girrbach), Whip Mix 4640 (Whip Mix), and Panadent 1610AR (Panadent), the relationship between the condylar guidance, the occlusal plane, and the dental guidance remains constant, anatomically similar to what occurs in the mouth [Figure 8-08A–D].
[Figure 8-08A–D] Arcon-type articulators more faithfully represent the patient’s mandibular dynamics, with fixed mechanical fossae angulations in their upper frames. In these devices, the angle between the lines that tangent the condylar guidance and the maxillary occlusal plane remain the same both with the dental arches separated (simulating the presence of the intermaxillary registration) [A] and together (MIP position) [B]. In non-arcon–type articulators, the mechanical fossae are fixed in the lower frames, and the condylar balls are located in the upper frames, causing the angle described above to change, becoming less accentuated in the MIP than in the position in which the registration was used [C,D]. (Modified from Shillingburg et al13.)
Another aspect to be considered is that, in arcon-type articulators, the condylar balls follow a forward and downward movement during protrusion, as in the mouth. In non-arcon–type articulators, the balls are directed backward and upward in these same movements, increasing the distance between the condylar balls and the anterior teeth at the end of the movement. The extent to which these differences are significant for the diagnosis or treatment planning cannot be specified7,17. However, it is suggested to give preference to arcon-type articulators due to their similarity with the physiologic conditions of the patient [Figure 8-09A–D].
[Figure 8-09A–D] Likewise, in arcon-type articulators, the distance from the condylar ball to the anterior teeth remains constant during the different mandibular movements [A,B]. In non-arcon–type articulators, lateral and protrusive movements are performed with the condylar ball moving in a posterior direction, causing the distance from the balls to the anterior teeth to increase [C,D]. (Modified from Shillingburg et al13.)
Facebow
The facebow is the instrument used to record the spatial relationship of the maxilla with certain anatomical landmarks on the patient’s face or skull and to allow the transfer of this relationship to the articulator18 [Figure 8-10A–I]. The facebow guides the 3D relationship of the plaster model and the rotation axis of the SAA, and incorporates esthetic and functional information for the diagnosis, treatment planning, and execution of the prosthetic work.
[Figure 8-10A–I] Inaccuracies in transferring the position of the individual’s occlusal plane can cause esthetic and functional problems when performing a diagnostic wax-up or positioning artificial teeth in a complete denture. A combination of horizontal reference lines could sometimes be used as a parameter. A mock-up or temporary restoration is recommended to confirm the alignment and harmony of the planned smile.
The dentist should assemble the articulator with the facebow in all indicated cases to provide predictability to the treatment [Figure 8-11]. Inaccuracies in the sagittal or frontal inclination of the models can cause esthetic and functional problems when performing a diagnostic wax-up or positioning artificial teeth in a complete denture19. Such esthetic flaws can be amplified according to the number of restorations needed or the patient’s asymmetries20.
[Figure 8-11] The facebow should be parallel to the interpupillary line when symmetric. If this is not the case, a combination of horizontal reference lines can be used, such as the eyebrow line, the interpupillary line, and the intercommissural line, in addition to an arbitrary mean horizontal axis related to the horizon.
Significant errors in the morphology of new restorations can potentially be created if a facebow is not used, especially concerning VDO alterations performed by increments in the height of the articulator’s incisal pin21. The magnitude of these errors tends to increase according to the difference between the position of the patient’s real rotation axis and the articulator’s axis, and the amount of VDO increase necessary5. In this author’s opinion (more details in Chapter 11), in cases where there is an indication of an increased VDO, the intermaxillary registration should be performed in a previously planned dimension according to the esthetic, functional, and structural requirements.
Horizontal references considered for facebow assembly
Side view
Many SAAs are designed to use the Frankfurt plane as a sagittal reference for the facebow. Although this plane has been defined as a horizontal skeletal reference from studies with isolated skulls18, it generally causes anteroposterior inclinations of the models on the articulator that are more accentuated than those seen when the patient is observed with the head in an upright position22 [Figure 8-12]. According to some authors19,23–26, this difference in angulation can generate esthetic and functional consequences concerning the analysis and planning of the length and inclination of the anterior teeth, the direction of the occlusal plane, and the relationship of the maxillary anterior teeth with the patient’s lips.
[Figure 8-12] In this case, the horizontal frame of the facebow is parallel to the interpupillary line.
For these reasons, using an esthetic reference plane9,23 based on the patient with the head in an upright position and gazing straight ahead at a theoretical point on the horizon has been suggested [Figure 8-13]. Thus, the DLT will have a perspective of the models on the articulator that is similar to how the patient is observed in their daily activities. However, the deliberate use of the esthetic plane as a reference should be considered concerning the necessary adaptations for positioning the facebow based on references outside the articulator manufacturers’ specifications, which can generate anomalies in the positioning of the models.
[Figure 8-13] The Frankfurt plane is traditionally suggested to align the facebow in the lateral view while transferring the maxillary dental arch position from the patient to the articulator. This plane usually results in anteroposterior inclinations of the models on the articulator that are more accentuated than those observed in the patient with the head upright.
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Frankfurt plane |
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A plane that begins at the lower part of the bony margin of the orbit and continues to the highest point of the bony margin of the external auditory meatus (porium). As these posterior references occur at the bone level, they are clinically replaced by the superior border of the tragus. |
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Esthetic plane |
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Also called the arbitrary plane, this plane begins 18 mm below the inferior part of the bone margin of the orbit and continues to the external auditory meatus19. It is recommended to mark this anterior point on the patient’s face with a dermatograph pencil and use the plastic auricles of the facebow inserted into the external auditory meatus. The esthetic plane forms an angle of about 819 to 925 degrees to the Frankfurt plane. |
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Camper’s plane |
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Also called ala-tragus, this plane begins at the lower part of the nose ala and continues to the upper border of the tragus. The Camper’s plane presents a high degree of parallelism with the occlusal plane and is usually used as a reference for assembling teeth in complete dentures. The Camper’s plane forms an angle of about 6.5 degrees to the esthetic plane and 15.5 degrees to the Frankfurt plane25. |
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Axis-orbital plane |
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This begins at the lower part of the bony margin of the orbit and continues to a hypothetical line that passes through the condyles. It is generally used as a reference in fully adjustable articulators, and the demarcation and stabilization of the facebow at these posterior points are critical in these devices. The axis-orbital plane forms an angle of about 5 degrees to the Frankfurt plane and 13 degrees to the esthetic plane19. |
Frontal view
For the transferal of esthetic and functional information, it is critical that the facebow is parallel to the interpupillary line when symmetric. When this line is asymmetric, a combination of horizontal reference lines can be used such as the eyebrow line, the interpupillary line, and the intercommissural line25, in addition to an arbitrary horizontal axis related to the horizon26 [Figure 8-14]. The transposition of the perspective in the upright head position to the laboratory bench is an essential requirement for fabricating new indirect restorations20.
[Figure 8-14] Using a lateral esthetic reference plane based on the patient with an upright head position creates a perspective of the models on the articulator similar to how the patient is observed in their daily activities. However, one should consider whether such a procedure will not cause an anomalous positioning of the models in articulators built to use different references.
Facial asymmetries that compromise the accurate transfer of information should be recognized and compensated20. When the external auditory meatus positions are asymmetric, a manual correction in the frontal arch alignment can improve esthetic communication4,20. However, the magnitude of this correction should be analyzed prudently and individually so that it does not impact the patient’s functional relationships. In this author’s experience, the minimal inaccuracies potentially generated by this local adjustment in the alignment of the facebow are susceptible to adjustments in the resulting prosthesis.
Assembly of the mandibular model in relation to the maxillary model
The relationship between the mounted maxillary and mandibular models is the key factor for the accuracy of the assembly27–30, with a direct influence on the accuracy of occlusal morphology and treatment predictability. Errors in the intermaxillary relationship of the models will generate negative consequences such as failures in diagnosis, treatment planning, and execution, which will be a source of frustration for all those involved in the treatment due to the waste of time, energy, and financial resources.
Mounting the patient models in CR is a good norm for diagnosis and treatment because it constitutes a posterior limit position on the SAA. If the treatment planning defines the working position as the MIP, the articulator will allow such movement in the anterior direction. If the models are mounted in MIP, the articulator cannot reach the CR. Thus, mounting the models in CR does not necessarily mean that the patient will be treated in CR, but that the restorations can be planned so as not to interfere with this position.
Condylar guidance angle and Bennett angle adjustment
Using mean values for articulator adjustment has proven to be effective for most clinical situations4. The values found in the literature31,32 range from 25 to 75 degrees for the condylar guidance angle, with a mean of 45 degrees to the axis-orbital plane, and values of 7 degrees for the Bennett angle.
Thus, for those dentists and DLTs who mount the maxillary models using the Frankfurt plane, mounting values with 30 degrees of inclination for the condylar guidance angle and 15 degrees for the Bennett angle are suggested4. For those using the esthetic plane, values of 20 degrees for the condylar guidance angle and 15 degrees for the Bennett angle are suggested. These differentiated values concerning the mean constitute a safety factor4 in planning restorative treatments to guarantee the disclusion of posterior teeth during functional movements.
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