Effect of Different Condylar Guidance Registration Records on Balanced Occlusion of Complete Denture

Introduction

Bilateral  balanced occlusion in complete dentures is a preferred occlusal scheme that approved for setting denture teeth for the conventional complete dentures. It helps to reserve the supporting residual alveolar ridge and improve stability of dentures. Bilateral  balanced occlusion provides teeth contacts at both sides working and balancing sides, at the same time with and allows better distribution of masticatory forces. ⁽¹⁾

One of the most essential considerations in the oral prosthetic rehabilitation of any patient is the inclination of the condylar path Successful treatment of edentulous patients is based on providing coordination between occlusal surfaces of artificial teeth and the condylar path which plays a significant role in reestablishment of stomatognathic system’s function and preservation of alveolar bone.. ^(2-5)

Accurate simulation of the condylar path of patient on an articulator (condylar guidance) with the help of its facebow system creates harmonious tooth contacts without occlusal interferences during mandibular movements. ^(6,7)

Condylar guidance should be recorded accurately, inappropriate recording of the condylar guidance can lead to occlusal interferences, thus leading to an increase in valuable chairside time. These consequences lead to poor patient satisfaction and a disharmonious occlusion. ^{(8, 9)}

The condylar guidance inclination in semi-adjustable articulators is adjusted either by protrusive (horizontal) or lateral interocclusal registrations recorded with a suitable recording medium. ^{(10, 11)}

Semi-adjustable articulators are widely used to simulate certain mandibular movement and condylar pathways due to their ease in programming. They are classified as Arcon and Non-Arcon types which differ in structure of mechanical joint. In Arcon articulator mechanical condyles are in the lower part of the articulator, which corresponds to the mandible, and artificial fossa articularis are in the upper part of articulator, which corresponds to the maxilla. In non-Arcon type of articulator, the position of joint parts is reversed. ⁽¹²⁾

Face-bow is an essential accessory of semi-adjustable articulators for transferring the maxillary cast. Through facebow, maxillary and mandibular casts are mounted in relation in close proximity to the condylar hinge axis and to the temporomandibular joints producig more accurate occlusal contacts in centric and eccentric positions. ^{(13, 14)}

An accurate registration  of condylar guidance and it’s transfer to semi adjustable  articulator is important during complete denture construction. It should simulate the mandibular positions or movements of the patient within the  range of the normal functional contact of the teeth. Thus the condylar elements of the articulator must be adjusted that they approximate the condylar guiding factors within the tempomandibular joint. These adjustments of the condyalr elements of the articulators are made by means of interocculusal  eccentric records. ⁽¹⁵⁾

Several extra oral and intra oral methods are used to clinically record condylar guidance. Interocclusal protrusive wax records, Lucia jig, leaf gauge and intra oral tracers are the most commonly used intra oral methods. Varying inclinations have been reported with repeated registrations, between operators, between recording materials, and between articulators. Extra oral methods are generally illustrated by Gysi and McCollum and mainly used in edentulous patients. ⁽¹⁶⁾

The condylar guidance inclination in semi-adjustable articulators is set either directly by the hinge axis records and pantographic records to the articulatoror indirectly by the interocclusal records to the articulator or by radiographic methods. ⁽¹⁷⁾

Gothic arch tracing is the most popular graphic method and is considered as the ideal method in programming the articulator. It is one-dimensional graphic tracing method which can be applied intra orally and extra orally to record lateral condylar guidance. Intraoral Gothic arch tracing is a favorable method of obtaining consistent positions of the mandible in motion (retrusive, protrusive, and lateral) at a comfortable vertical dimension of occlusion. This is based on the idea of attaching a stylus known as central bearing pointer to one occlusal rim and a plate known as central bearing plate to other rim. The stylus traces or marks the path in the plate as the mandible produces excursive movements from the centric position. The tracing presented a shape of arrowhead or “gothic arch”. ⁽⁷⁾

Studies have shown that radiographic methods can record condylar guidance more accurately than other methods as radiographic measurement involves stable bony landmarks and does not rely on the operator or patient’s neuromuscular control. Recently, cone beam computed tomography CBCT has made them more accurate, safer, and cheaper resulting in widespread application in prosthodontics. CBCT being a more advanced cutting  edge technology provide three dimensional multiplanes sections without superimposition. ⁽¹⁸⁾

To achieve a successful conventional complete dentures fabrication, occlusion needs to be carefully considered as it plays a role in providing uniform distribution of masticatory forces, better retention and stabilization of denture bases. ⁽¹⁹⁾

This clinical study is oriented towards evaluating the effect of different horizontal and lateral condylar guidance registration methods on balanced occlusion of complete denture.

Subjects and Methods

Twelve completely edentulous patients were selected from the outpatient clinics of the Removable Prosthodontic Department, Faculty of Dental Medicine for Girls, Al-Azhar University. All Twelve patients were involved in the study. All patients were free from any oral or debilitating systemic disease, temporomandibular joint disorders such as: clicking, limitation of opening or mandibular movement, muscles spasm or tenderness and mandibular deviation were excluded and with moderately resorbed maxillary and mandibular alveolar ridge that was covered with firm, thick, healthy and compressible mucosa free from any signs of inflammation or ulceration. The patients were in the age of 60- 70 years, have Angle’s class I jaw relation. Before starting the study; all procedures were illustrated to the patients, patients accepted the dental treatment and written consent was obtained from all the patients regarding procedure with approval of the Research Ethics Committee (REC) of Faculty of Dental Medicine for Girls, Al-Azhar University.

Medical and dental history were taken from the patient including asking the patient about the cause and timing of teeth loss. Clinical examination to each patient’s TMJ, ridge, mucosa, lips, muscles and skin were carried out.

All the twelve patients reieved complete dentures constructed for all the patients,a complete denture for each patient. Primary impressions of upper and lower arches were made using alginate impression material which were poured with dental plaster to obtain the study casts then secondaryimpressions were made using green stick compound for border molding and zinc oxide and eugenol impression material for the impression. Jaw relation and facebow transfer were done and maxillary master cast was mounted on an Arcon semi-adjustable (Bio-art articulators Whip Mix corporation,USA).

Centric relation record was recorded using inter occlusal wax record then upper record block was separated from the lower record block and was kept in cold water then protrusive interocclusal wax record was recorded by adding 4 mm of softened wax to the lower occlusion block. Patient was asked to protrude the mandible about 6mm and close the record blocks together in that position. The protrusive interocclusal wax records also were separated from each other and kept in cold water.

The lower cast was mounted to the lower member of the articulator using the centric interocclusal wax record. The horizontal condylar guidance was adjusted on the articulator using the protrusive interocclusal wax record. Protrusive interocclusal wax record was applied to the occlusion blocks on semi-adjustable articulator to adjust horizontal condylar guidance of both sides.

Lateral condylar guidance calculated from horizontal values by Hanau equation: L= H/8+12 where L =Lateral condylar Guidancr and H = Horizontal condylar guidance

Artificial teeth (Vita, Germany) were arranged to balanced articulation. Denture was waxed up, tried at the patient mouth. Plaster index was made by removing the lower cast from the articulator and return the  upper waxed-up denture to the upper cast on the articulator.

A remounting platform was attached to the lower member of the articulator. Plaster was mixed and placed over the remounting plate and the upper member of the articulator with the upper waxed denture was closed on the plaster. After setting of plaster the articulator was opened and any excess plaster than 2-3 mm in the teeth imprint was removed. Waxed up denture was processed into heat cured acrylic resin, finished and polished.

Remounting clinically of finished denture applied on Arcon semi-adjustable (Bio-art articulators) . The adjustment of the occlusion for the finished denture was made by using centric, protrusive and lateral records without teeth contact. The occlusal interference was removed until even contacts through the arch were achieved. To eliminate any cuspal interference in protrusive and lateral excrusions and to establish an even fully bilateral balanced occlusal contact.

The denture was duplicated for expermintal work. The twelve patients received their finished dentures and only one duplicate denture used for measurement of the horizontal and lateral condylar guidance for the experimental work. Mix of silicon impression material was poured in the fitting surface of the denture then flasking. Duplicated denture was checked for proper extension, retention, stability and fine adjustment of occlusion was carried out inside the patient’s mouth.

Methods of registration of Horizontal condylar guidance:

In this study, horizontal condylar angel was calculated using three methods: interocclusal wax record method, Graphic tracing method and Cone Beam Computerized Tomography CBCT scan method.

1-      Interocclusal wax record method (protrusive record was used to record horizontalcodylar guidance angle on articulator )Fig. 1

Figure (1): interocclusal wax record method

2-   Graphic tracing method:

Quick set recorder was used to trace and measure the protrusive pathway. The orbital was palpated and a point opposite to it was marked on a the patient’s face. The reference line (axis-orbital line) drawn on the patient’s face. The flag holder frame of the quick set recorder was adjusted in width to allow positioning of each flag as close as possible to the patient’s head. A graphic card was attached to each flag. Bite fork of the quick set recorder was attached to lower denture and were inserted into the patient’s mouth and fixed to the mandible by mandibular clamp.

The patient’s jaw was guided into the most retruded position, and then the toggle assembly was tightened. A lead holder with sharpened lead was placed onto each pointer. The patient was seated in a comfort upright position and was instructed to protrude the mandible (Maximum protrusion) to trace the condylar path on the graphic cards. The recording papers were placed two times and protrusive movement was repeated each time to produce three graphical recordings of the horizontal condylar path on each side.

Enlarged photocopies (10 times magnification) of the graphic tracings were used to determine the condylar angle mathematically. Four arbitrary points (1-4) were selected on each curve to include the whole curve. From points (2-4) horizontal lines were drawn (parallel to the axis-orbital plane) and from points (1-3) vertical lines were dropped into the horizontal lines. Fig. 2

Figure (2): Graphic tracing method

The slope of the angles (a, b and c) was calculated from the following equation:

The angles were calculated by reversing its slope using a scientific calculator (Casio, FX-82C, Japan). The mean of the three values for each curve was calculated and the mean of the three curve angulations was considered as the condylar inclination of this side.

3-   Cone Beam Computerized Tomography (CBCT) scanning method:

CBCT CRANEX 3Dx machine was used in this study. Two images were taken for each patient; one in centric position and another one in protrusive position. The patient was placed on the machine in upright position and the field of view was adjusted guided by laser lines. Then the patient was asked to close his mouth in centric occlusion then moves his mandible protrusively. Three dimentional images the outline of condyles in both centric and protrusive positions are digitally delineated.

Both images were superimposed together in three dimensions. Frankfort line drawing from the deepest point of inferior orbital rim to the highest point of the external auditory meatus. The protrusive condylar path was obtained by drawing a line tangent to the condyles in maximum intercuspation and in protrusive position. The angle between two tanged lines was measured. This procedure was made twice for each balancing condyle of the same patient and the mean angle was obtained and tabulated. The measured angles tabulated for each patient then applied on the articulators to record the balanced occlusion. Fig. 3

Figure (3): Cone Beam Computerized Tomography (CBCT) scanning method

Methods of registration of lateral condylar guidance:

1-   Hanau Equation:

Obtained from the protrusive interocclusal record, record the horizontal condylar guide angles then calculate the lateral condylar guide angles through the equation

L= H/8+12 where L =Lateral condylar Guidancr and H = Horizontal condylar guidance

and adjust them on the articulators.

2-   Gothic arch tracing method:

The carrier of the Gothic arch was attached to the occlusal surface of the lower duplicated denture by auto-polymerizing acrylic resin, the tracing pointer was adjusted to be centrally across a line joining the position premolars while the tracing plate was attached to the occlusal surface of the upper duplicated denture and covered with thin film of blue soft wax to produce the tracing. The upper and lower dentures with the tracer attached to them, were inserted into the patient’s mouth while the tracing point was adjusted to keep the occlusal surface of the upper and lower denture slightly apart.

The patient was instructed to perform protrusive-retrusive, right- retrusive and left-retrusive movements while the tracing point kept in contact with the tracing plate. Then dentures removed from patient’s mouth and the arrow that was traced should be clearly identified to record lateral condylar path.  The tracing arrow over the tracing plate was scanned and printed by the computer then magnified 10 times. Both angles right and left between the protrusive and lateral right and left condylar paths were measured using the protractor to the nearest 0.5 degree. The left and right lateral condylar guidance were derived from the following formula: L=1.06 BP – 45.

 Where L was the lateral condylar angle and BP was the angle between the lateral border paths of the patient and the protrusive path. Fig. 4

Figure (4): Gothic arch tracing method

3-   Cone beam Computed Tomography scanning:

CBCT CRANEX 3Dx machine was used in this study. The patient was placed on the machine and FOV was adjusted guided by laser lines. Cone beam CT was applied on the patient while placed on the machine in upright position looking forward rested his chin on the chin rest, then the patient was guided to close his mouth in centric occlusion then moves his mandible laterally. After the patient exposure, the images were acquired in a process called (image acquisition) on a computer connected to the cone beam machine, Finland where these images are called (basis images) which performed using a third-party software Ondemand3D ver.1.0.10.

Both images (centric & lateral balancing condyle) were superimposed together in three dimensions (Axial, coronal & Sagittal) as follows: Centric image was set as the primary image & the lateral working image was set as a secondary image. Each image was given a specific color different from the other image to differentiate between the primary & secondary images during the fusion process. Image fusion was performed by first obtaining the same plane in both, centric & lateral images in the axial plane roughly. The lateral condylar path was obtained for the balancing condyle by drawing a line tanged the most highst point of the condyle in maximum intercuspation and in lateral position. The angle between two tanged lines was measured.

This procedure was made twice for each balancing condyle of the same patient and the mean angle was obtained and tabulated.  For the working condyle the Bennett movement was measured by measuring the amount of working condyle movement laterally from the maximum intercuspation to the lateral position. The measured angles tabulated for each patient then applied on the articulators to record the balanced occlusion.

Duplicated denture was prepared for the study including remounting on Arcon articulator following the same method for clinical remounting of the original denture. Occlusal adjustment was carried out to establish even bilateral occlusal contact and remove any interference in protrusive and lateral relation.

Each articulator was locked in centric relation and both maxillary and mandibular second molars were removed from the denture. Metal tubes with internal diameter 0.44 mm. was cemented in place of the upper second molar area facing One cm square metal plates were luted in the lower second molar position by autopolymerizig acrylic resin. One square cm recording papers were attached to the metal plates.

For the right side, Lateral condylar guidance was adjusted to the value calculated from the hanau equation. The left horizontal and lateral condylar guidance were adjusted to zero degree. The right horizontal condylar guidance of the articulator was adjusted three times using the angles determined by the Interocclusal wax record, Graphic tracing method and CBCT radiographic method.

The upper bow of the articulator was moved backward and to the left (working side) till the upper buccal and lower buccal cusps were in a line then the centric lock was locked. Using an indelible pencil, a mark was marked on the incisal table to determine the position of the incisal pin at cusp to cusp position. This mark used to adjust the amount of lateral movement in subsequent records and measurements.

Mesiodistal and buccolingual perpendicular lines were drawn and passes approximately through the center of recording paper. After each horizontal condylar guidance adjustment, a metal needle with 0.22 mm pointed end was inserted inside the metal tube in the maxillary second molar at the right side from the above downwards till it was indenting the recording paper placed on the plate at the lower second molar area.

The distance from each indentation to the mesiodistal and buccolingual lines and from the indentation to the meeting point of the mesiodistal and buccolingual perpendicular lines, were measured by a digital caliper, and were record. The measurements of the buccolingual distance were considered +ve if the indentation was to the buccal to the mesiodistal line and –ve if it was to the lingual. Also, the measurements of the mesiodistal distance were considered +ve if the indentation was mesial to the buccolingual line and –ve if it was to distal. The same procedures of right side record and measurements were followed for the left side. Fig. 5

Figure (5): Metal tubes luted centrally in the area of upper second molar

Statistical analysis:

Numerical data was explored for normality by checking the data distribution, calculating the mean and median values and using Kolmogorov Smirnov and Shapiro-Wilk tests. The results of Kolmogorov-Smirnov test indicated that most of data were normally distributed (parametric data), they were represented by mean and standard deviation (SD) values: therefore, paired-t- test was used to compare between results. The significance level was set at p ≤ 0.05 for all tests. Statistical analysis was performed with IBM® SPSS® (SPSS Inc., IBM Corporation, NY, USA) Statistics Version 26 for Windows.

Results

1)      Bilateral balanced occlusion contact measurements with different horizontal condylar path inclination records using Arcon semiadjustable articulator:

Mean, Standard deviation (SD) values of balanced contact measurements with different horizontal condylar path inclination records and results of paired-t- test for articulator records were presented in table (1) and fig. 6

Table (1): Mean, Standard deviation (SD) values of balanced contact measurements with different horizontal condylar path inclination records for Arcon articulator

ns; non-significant (p>0.05)

Figure (6): Bar chart showing average values of balanced contact measurements with different horizontal condylar path inclination records for Arcon articulator

2- Bilateral balanced contact measurements with different lateral condylar path inclination records using Arcon semi adjustable articulator:

Mean, Standard deviation (SD) values of balanced contact measurements with different lateral condylar path inclination records and results of paired-t- test for Arcon articulator records were presented in table (2) and fig. 7

Table (2): Mean, Standard deviation (SD) values of balanced contact measurements with different lateral condylar path inclination records for Arcon articulator

Figure (7): Bar chart showing average values of balanced contact measurements with different lateral condylar path inclination records for Arcon articulator

Discussion

The more accurate the articulators used in simulating mandibular movements; the more complex they have become in design. Fully adjustable articulators simulate mandibular movement most accurately. However, their usefulness is limited due to the complexity of record making and articulator adjustment. Semi-adjustable articulators are adjusted using individual static records, the reliability of which has been always been favorable. These articulators do not simulate the patient's temporomandibular joint (TMJ) anatomy and are based on average condylar settings. ⁽¹¹⁾

In clinical practice, protrusive interocclusal records are the most commonly method used to adjust different types of semi-adjustable articulators for measuring the horizontal condylar guidance; because it is simple, easy, quick, not expensive and does not require specialized devices or machinery. Protrusive interocclusal wax record was obtained at 6 mm of protrusive movement; as the horizontal condylar guidance changes with the degree of protrusion, so it was important to keep the distance of protrusion the same during registration of all protrusive interocclusal records.⁽²⁰⁾

Hanau concluded that there was a definite relationship between the inclinations of the horizontal and lateral control settings. It was found the lateral settings to consistently range around 15°. Stern insisted that the “Formula” was never exact. Hanau supposed more accurate records could be made once all the teeth were set. It was further proposed that remounts and equilibrations were necessary to refine the occlusion. That would suggest a step backward to an average value instrument. Based on the results, it should be considered reassessing the current recommended average settings and use of the Hanau's formula for programming the semi-adjustable articulators through further research ⁽²¹⁾.

levels of variability were seen in condylar guidance between the protrusive interocclusal wax method and other methods. Measurements of the extraoral tracing of the horizontal condylar path lower values  than the protrusive interocclusal wax method with no significant difference . This aligns with Dos Santos J ⁽²²⁾.

Compared to clinical methods, radiographic method is more accurate and an alternative method of ascertaining Horizontal condylar guidance values.Recently, The 3D multiplanar sections obtained from a CBCT scan provide an improved anatomic overview of the condyle and its pathway without the superimpositions inherent in 2D radiographic images.⁽²³⁾

This study in tended to achieve bilateral balanced occlusion of the conventional complete denture as balanced occlusion can help in better chewing efficiency, maintaining the stability of the denture and ensure even pressure on the residual ridge. ⁽²⁴⁾

Gothic arch methods have been used to record centric relation and condylar guidance but there are certain disadvantage of this technique. Certain limitations of the Gothic arch technique including it requires good ridge anatomy, experienced dentist and this method is time consuming, the effect of tissue resiliency, stable denture bases, patient co-operation and neuromuscular co-ordination, insufficient inter ridge dimension. Gothic tracer was found as delicate technique may exhausting patient due to excessive mandibular movement to produce head arrow tracing in accurate form. ⁽²⁵⁾

Horizontal and latreal condylar guidance values obtained from CBCT scan were lower  than values obtained from protrusive interocclusal wax method with no significant difference.

Our results agreed with some studes, that found SCGA values obtained from CBCT measurements were higher than those from protrusive occlusal records. Similar results were tested by Naqash TA et al.⁽²⁶⁾

The present study is inconsistent with the previous studies showing that protrusive interocclusal methods of recording horizontal condylar angles have lower level of reproducibility and are subject to variation of instrument, operator, and occlusal records. One important reason for this inconsistency may be that, horizontal condylar angle changes with the degree of protrusion, and the intra-oral record represents only one point along the condylar path.⁽²⁷⁾

As regards studying the effect of using these horizontal  and latral condylar registration methods on bilateral balance occlusion, it was found that there was no significant difference.

Conclusion

This study seeks to discover whether the different registration methods of horizontal and lateral condyle guidance have an effect on the bilateral balanced occlusion of complete dentures or not.

Horizontal and lateral condylar guidance angles were measured using three different methods for each; The horizontal condylar guidance was measured using the protrusive interocclusal wax record method, Graphic tracing method and Cone Beam Computed Tomography CBCT scan method. The lateral condylar guidance was measured using Hanau equation calculated from protrusive interocclusal records method, Gothic arch tracing method and Cone beam computed tomography CBCTscan method.

The results of this study showed that there was no statically significant difference in bilateral balanced occlusion when using different horizontal and lateral condylar guidance registration methods during construction of complete denture.

Within the limitation of this study, it can be concluded that, an Arcon semi-adjustable system with the wax protrusive record  and Hanau equation may be the most practical way to obtain the desired relative horizontal  and lateral condylar angle respectively.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflict of Interest

The authors declare no conflict of interest.