Comparison of Parameters for Programming Adjustable Dental Articulators by Using Wax Eccentric Records and Arcus Digma Device.

OBJECTIVES: Programming of joint mechanism/parameters (sagittal condylar inclination and Bennett angle) of adjustable dental articulators is a prerequisite for performing positions and movements of the mandible. The aim of the study was to test significant differences between the two methods (wax eccentric records and Arcus Digma device) of measuring these joint parameters by using three different dental articulators (SAM 3, Protar 7; and Artex CR).
MATERIALS AND METHODS: Thirty asymptomatic younger (age 25.7 ± 2.9 years) subjects (dental medicine students) divided by gender, with normal occlusion (Angle class I) participated in the study. After taking anatomical impressions of both dental arches, master casts were made of hard dental plaster for each subject. The values of the left and right sagittal condylar inclination and Bennett angle by the two methods of wax eccentric protrusive and lateral records and Arcus Digma device were measured for the purpose of programming the mentioned joint parameters in three different articulator systems.
RESULTS: The average values of the measured parameters of sagittal condylar inclination and Bennett angle of wax eccentric records were higher (ranging from 5ºto 10º) in relation to the values measured by Arcus Digma device. Statistically significant differences found between the measured joint parameters (p <0.025) were influenced by the articulator system design and measurement methods (t-test for dependent samples and MANOVA).
CONCLUSION: The use of Arcus Digma device should be considered reliable and valid for individualized programming of dental articulators, rather than the use of wax eccentric records.

Introduction

The use of dental articulators in everyday dental practice, especially in prosthodontics, is an inevitable and standard process if morphological and functional aspects of occlusion within the masticatory system need to be examined and/or restored. Therefore, it is necessary for every clinician using dental articulators to know which parameters (values of condylar path inclination and Bennett angle) should be set (programmed) in order to simulate kinetics of the masticatory system. It is a common practice to set the mentioned parameters on adjustable dental articulators based on average values. However, there is also a so-called individualized measuring, which is as its name suggests a more accurate parameter measurement. It is a precondition for reproduction and simulation of the mandibular position and mandibular movements in a dental articulator. For individualized parameter measuring clinical methods of wax centric/eccentric records and radiographic technique can be used, as well as dry bone samples and various mechanical and electronic (axiographic) devices ( – ).

Sagittal condylar inclination is defined as the angle between the protrusive condylar path and usually the Frankfort horizontal plane or other horizontal reference planes (e.g. Camper's, axial-orbital, etc.). The average programming of sagittal condylar inclination of semiadjustable dental articulator is based on the type of dental occlusion. An individual with normal occlusion (Angle class I) has a sagittal condylar inclination of 30-35°. In dentate subjects with Angle class II, sagittal condylar inclination is higher, and with Angle class III it is lower. However, it should be noted that these angles should be interpreted bearing in mind the fact that we should determine which horizontal plane is referential (e.g. the difference between the Frankfort horizontal plane and Camper's plane is on average 15°) for the relation of the discus-condyle complex protrusion path towards articular tubercle ( – ). In their study, Ćimić et al. () measured the average value of the sagittal condylar inclination for fully dentate subjects (Angle class I) of 40° in relation to the Camper's plane, by using axiographic ultrasonic devices. They concluded that those values were especially important for adjustable articulator systems programmed in relation to the Camper's plane as reference.

Bennett angle is the angle formed between the sagittal plane and the average path of the non-working (orbiting) condyle as viewed in the horizontal plane during lateral mandibular movements (). Bennett angle comprises two components of the movement: immediate side shift and progressive side shift. Immediate side shift describes the beginning of lateral movement, i.e. non-working condylar movement toward ahead and medial from the position of centric relation, while progressive side shift relates to continuation of lateral movement to its maximum, i.e. to the remaining part of the non-working condyle path during lateral mandibular movement (which is basically the value of Bennett angle). In general, fully adjustable articulator systems have the possibility of setting/programming the mentioned parameters necessary for as accurate as possible simulation of lateral movements in the articulator ( – ).

There are different studies in the scientific literature in which parameters (sagittal condylar path inclination and Bennett angle) of programming adjustable dental articulators are compared by means of wax eccentric protrusive and lateral records, axiographic devices and/or other methods/instruments ( – ). Prasad et al. () compared the average measured values of condylar inclination using an ultrasonic axiograph (SAM Axiograph) and a wax protrusive eccentric record in order to program two articulator systems (SAM and Artex CR). Statistically significant differences were found between two methods used for sagittal condylar inclination measurements in subjects with normal occlusion (Angle class I). They recommend using fully adjustable articulators during instrumental-functional diagnostics of the masticatory system and prosthetic treatment, thus avoiding errors at the level of occlusion and tooth wear. Proschel et al. () made similar conclusions by promoting the use of dental articulators and their individual programming. Fanucci et al. () measured Bennett angles and programmed an adjustable dental articulator by using wax eccentric lateral records and TMJ scans obtained by computerized tomography. They found matching Bennett angle values between the two measuring methods, which makes both methods reliable in clinical conditions.

The purpose of this study was to determine whether there were differences between the values of individualized measuring of the left and right condylar path inclination, and left and right Bennett angle measured using wax eccentric records and Arcus Digma device in order to program various adjustable articulator systems (SAM 3, Protar 7 and Artex CR). The working hypothesis was that there would be no difference in the measured values ​​of the parameters necessary for programming of adjustable dental articulators by using two methods in the examined sample.

Material and Methods

The study included 30 asymptomatic subjects (dental medicine students) divided by gender, with normal occlusal relationship (Angle class I), who had not undergone any orthodontic treatment and with no evidence of clinical signs and symptoms of temporomandibular disorders. An alginate impression of the upper and lower dental arch was taken for each subject (Aroma Fine Plus, GC, Tokyo, Japan) in order to make master casts out of hard dental stone (type IV) (Alpenrock, AmannGirrbach Koblach, Austria). Hard (pink) wax plates (Pinnacle, Dentsply Hanau, Germany) were used for making centric records, protrusive records, and left and right laterotrusive records. A centric wax record was used for precise mounting of master casts onto adjustable dental articulators, whereas protrusive and laterotrusive wax records were used for setting values and adjusting the right and left condylar path inclination and left and right Bennett angle. Three adjustable articulator systems were used in this study: SAM 3 (SAM, SAM Präzisionstechnik Gauting, Germany), Protar 7 (Protar, Kavo Biberach, Germany) and Artex CR (Artex, AmannGirrbach Koblach, Austria) (Figure 1).

Figure 1

Adjustable articulator systems used in this study (SAM 3, Artex CR, and Protar 7).

Centric/eccentric record bases were adjusted to the occlusal surfaces of upper teeth on the upper master cast. The procedure of taking individual records was performed in each subject's mouth in the course of mandibular guidance into centric relation (bimanual manipulation technique), into protrusive position (tete-a-tete) and left and right laterotrusive position (canine guidance). Firstly, an average hinge axis transfer was performed, i.e. transfer of the distance between the upper dental arch and the hinge axis by means of standard (anatomic) face bow, as well as mounting of the upper cast into the upper articulator part. This was followed by the placement of the centric record on the upper dental arch, attachment of the lower master cast and mounting of the cast into the lower articulator part. Afterwards, wax eccentric records (protrusive, left and right laterotrusive records) were placed between dental arches of master casts onto the dental articulator (SAM 3, Protar 7, and Artex CR) in order to adjust and register values of the right and left condylar path inclination (protrusive record), and left and right Bennett angle (right and left laterotrusive records), on the joint mechanism of the dental articulator ().

Apart from this measurement, the same parameters were measured for each subject by means of an ultrasonic axiograph - Arcus Digma device (Arcus Digma II, Kavo, Biberach, Germany) (). Arcus Digma is an electronic device for recording mandibular movements, which is based on three-dimensional ultrasonic measurement. The device consists of the upper and lower arch. The lower arch of the device is fixed to the lower dental arch by means of paraocclusal tray and carries ultrasonic impulse emitters. The upper arch (face bow) has four pairs of ultrasonic impulse sensors. The device measures time discrepancies of emitted and registered ultrasonic impulses. Depending on time difference of ultrasonic intervals, based on the concept of six degrees of freedom, the software calculates the spatial position of the condyle, as well as of the sagittal incisal point or selected occlusal feature. In other words, the device measures the patient's individual mandibular movements, which are then processed by the software in order to obtain mathematical values (graphical and numerical) of these movements. This device has a wide application. It can be used in the field of instrumental functional diagnostics and accurate application of adjustable articulator systems in different groups of patients, such as patients with clinical signs and symptoms of temporomandibular disorders, prosthetic patients, orthodontic patients, etc. This device provides the information necessary for individual programming of articulators that would e.g. enable design and functional prosthetic restorations in prosthetic patients. According to its software features, it is not intended for only one articulator system (Protar), but the data can be obtained also for other systems (SAM, Panadent, Artex CR, Referenz SL, Money Mark II, Stratos 300). The values ​​of the right and left condylar path inclination and right and left Bennett angle for SAM 3, Protar 7 and Artex CR dental articulators were measured in this study.

The measurement process started with placing the kinematic face and paraocclusal tray on the face of the subject (Figure 2). The paraocclusal tray adjustment was performed on the existing lower master casts made of dental stone (used in the first method of wax records), by using light cured resin (Unitray, Polident, Volčja Draga, Slovenia). Each subject was sitting comfortably in a chair (upright posture) as the paraocclusal tray was attached to the lower dental arch using temporary restorative resin (Structur, Voco, Cuxhaven, Germany). It was important to assure for the paraocclusal tray to be firmly attached to the lower dental arch and not to be in contact with the upper teeth in either maximum intercuspation or lateral mandibular movements. The measurements were carried out in the module "Articulator" of Arcus Digma device, with the settings set to individualization of SAM 3, Protar 7 and Artex CR articulator for each individual subject. All measurements were performed according to the manufacturer's instructions for use (average hinge axis situated 10.33 mm in front of the tragus medialis point and 3.66 mm above the line connecting tragus medialis and infraorbital point). Each subject performed three protrusive movements, three left laterotrusive movements and three right laterotrusive movements. The Arcus Digma software calculated the average value of the measured parameters (condylar path inclination angle, Bennett angle) for individualized setting of the selected dental articulators for each subject in this study (, ).

Figure 2

Kinematic face bow with paraocclusal tray of Arcus Digma system for mandibular movements recording.

Results

The study included a total of 30 asymptomatic subjects divided by gender (15 females and 15 males) with normal occlusion (Angle Class I) and with no clinical signs and symptoms of temporomandibular disorders. The subjects were aged between 20 and 34 years (25.7 ± 2.9 years). Table 1 shows descriptive characteristics of the examined variables (values ​​of the left and right condylar inclination measured by performing protrusive mandibular movement and of the left and right Bennett angle measured by performing right and left lateral mandibular movement) using two methods (wax centric/eccentric records and Arcus Digma device) for programming three adjustable articulator systems (SAM 3, Protar and Artex CR). The average values of the measured parameters where wax eccentric records were used showed higher values ​​(ranging from 5° to 10°) in relation to the values ​​measured by Arcus Digma device.

Table 1

Descriptive features of the left and right condylar path inclination/left and right Bennett angle for programming of adjustable articulator systems (SAM 3, Protar 7 and Artex CR) by means of wax centric/eccentric records and Arcus Digma device.

Examined variables	N	Min	Max	x	SD
SAM 3 (wax record) – protrusion left	30	20	55	37.6	11.9
SAM 3 (wax record) – protrusion right	30	20	64	39.2	13.7
SAM 3 (wax record) – Bennett left	30	10	25	17.7	4.2
SAM 3 (wax record) – Bennett right	30	10	26	18.5	3.9
SAM 3 (Arcus Digma) – protrusion left	30	10	66	28.2	13.4
SAM 3 (Arcus Digma) – protrusion right	30	11	70	29.0	13.4
SAM 3 (Arcus Digma) – Bennett left	30	3	17	9.6	3.9
SAM 3 (Arcus Digma) – Bennett right	30	4	18	11.3	3.6
Protar (wax record) – protrusion left	30	22	65	41.3	11.2
Protar (wax record) – protrusion right	30	20	62	41.7	12.8
Protar (wax record) – Bennett left	30	4	35	16.0	7.1
Protar (wax record) – Bennett right	30	6	35	15.7	7.5
Protar (Arcus Digma) – protrusion left	30	10	55	30.3	11.9
Protar (Arcus Digma) – protrusion right	30	8	60	29.4	13.2
Protar (Arcus Digma) – Bennett left	30	4	22	9.5	4.9
Protar (Arcus Digma) – Bennett right	30	4	24	9.3	4.9
Artex CR (wax record) – protrusion left	30	20	61	38.4	11.5
Artex CR (wax record) – protrusion right	30	15	70	38.9	12.8
Artex CR (wax record) – Bennett left	30	6	47	19.2	8.6
Artex CR (wax record) – Bennett right	30	3	45	19.7	9.2
Artex CR (Arcus Digma) – protrusion left	30	14	56	34.0	12.7
Artex CR (Arcus Digma) – protrusion right	30	10	60	34.4	14.3
Artex CR (Arcus Digma) – Bennett left	30	4	21	9.8	4.1
Artex CR (Arcus Digma) – Bennett right	30	4	20	9.3	4.3

The Kolmogorov-Smirnov test showed normal distribution for all variables; hence in further procedures methods of parametric statistical analysis were applied. All variables were tested by Student's t-test for independent samples, with respect to gender. No statistically significant differences for any tested variable were found according to gender (p> 0.05) (Table 2).

Table 2

Examined variables testing with respect to gender (t-test for independent samples).

Examined variables	t-test
	df	P
SAM 3 (wax record) – protrusion left	28	0.655
SAM 3 (wax record) – protrusion right	28	0.876
SAM 3 (wax record) – Bennett left	28	0.228
SAM 3 (wax record) – Bennett right	28	0.682
SAM 3 (Arcus Digma) – protrusion left	28	0.219
SAM 3 (Arcus Digma) – protrusion right	28	0.158
SAM 3 (Arcus Digma) – Bennett left	28	0.226
SAM 3 (Arcus Digma) – Bennett right	28	0.694
Protar (wax record) – protrusion left	28	0.169
Protar (wax record) – protrusion right	28	0.137
Protar (wax record) – Bennett left	28	0.468
Protar (wax record) – Bennett right	28	0.474
Protar (Arcus Digma) – protrusion left	28	0.387
Protar (Arcus Digma) – protrusion right	28	0.223
Protar (Arcus Digma) – Bennett left	28	0.387
Protar (Arcus Digma) – Bennett right	28	0.344
Artex CR (wax record) – protrusion left	28	0.687
Artex CR (wax record) – protrusion right	28	0.452
Artex CR (wax record) – Bennett left	28	0.150
Artex CR (wax record) – Bennett right	28	0.102
Artex CR (Arcus Digma) – protrusion left	28	0.658
Artex CR (Arcus Digma) – protrusion right	28	0.464
Artex CR (Arcus Digma) – Bennett left	28	0.219
Artex CR (Arcus Digma) – Bennett right	28	0.142

df – degrees of freedom, P – significance.

T-test for dependent samples checked pairs of variables that were identical according to the movement (measured angle of the left and right condylar path inclination and Bennett angles) and within one type of articulator (SAM 3, Protar 7 and Artex CR), with respect to the method applied (wax eccentric records and Arcus Digma). Table 3 shows statistically significant differences at the level of p<0.05 for the most of the tested variables, except for the variable pair 9 and 10 (left and right condylar path inclination (protrusive mandibular movement) for Artex CR articulator). The differences of the arithmetic means show that the values measured with Arcus Digma are always lower, except for the variable pair 9 and 10, in which, although the measured values ​​are lower due to sample variance, their statistical significance cannot be proved. The highest statistical differences were found for the variable pair 3 and 4 (left and right Bennett angle for SAM 3 articulators).

Table 3

Correspondence testing between two measurement methods (wax eccentric records and Arcus Digma) with respect to the measured values of programming parameters (left and right condylar path inclination and Bennett angles) and dental articulator type (SAM 3, Protar and Artex CR) - t-test for dependent samples.

		Differences	t	df	P
		95% confidence interval
		Upper
Pair 1	Wax record SAM 3 – protrusion right / SAM 3 Arcus – protrusion right	17.516	2.851	29	.008
Pair 2	Wax record SAM 3 – protrusion left / SAM 3 Arcus – protrusion left	16.616	2.579	29	.015
Pair 3	Wax record SAM 3 - Bennett right / SAM 3 Arcus - Bennett right	9.263	2.579	29	.000
Pair 4	Wax record SAM 3 - Bennett left / SAM 3 Arcus - Bennett left	10.586	7.350	29	.000
Pair 5	Wax record Protar – protrusion right / Protar Arcus – protrusion right	18.232	3.752	29	.001
Pair 6	Wax record Protar – protrusion left / Protar Arcus – protrusion left	16.867	3.902	29	.001
Pair 7	Wax record Protar - Bennett right / Protar Arcus – Bennett right	9.917	3.668	29	.001
Pair 8	Wax record Protar - Bennett left / Protar Arcus - Bennett left	10.058	3.791	29	.001
Paiir 9	Wax record Artex CR – protrusion right / Artex CR Arcus – protrusion right	11.000	1.452	29	.157
Pair 10	Wax record Artex CR – protrusion left / Artex CR Arcus – protrusion left	10.601	1.414	29	.168
Pair 11	Wax record Artex CR – Bennett right / Artex CR Arcus - Bennett right	13.546	6.578	29	.000
Pair 12	Wax record Artex CR - Bennett left / Artex CR Arcus - Bennett left	12.311	6.410	29	.000

t- t-test result; df-degrees of freedom; p-significance.

Apart from the differences between the measured values of condylar path inclination and Bennett angle for each articulator, the purpose of this study was to test the mutual influence of the selected variables individually, combined and in total. Therefore, multivariate analysis of variance for dependent samples (MANOVA) was used. The variables were tested with respect to three parameters: articulator (SAM 3, Protar and Artex CR), measurement method (wax eccentric record and Arcus Digma) and measurement values (left and right condylar path inclination and Bennett angles). The effect of multivariate tests (Table 4) shows that there are statistically significant differences between each individual articulator (p <0.001), measurement method (p <0.001), measured values ​​of the articulator programming parameters (p <0.001), in combination of articulator and measurement methods (p <0.012) and in total for articulator, measurement method and measured parameters (p <0.025). The combinations of articulator and measured parameters (p <0.055) and measurement method and measured parameters (p <0.590) showed no statistically significant differences.

Table 4

Testing of the mutual influence of the selected variables individually, combined and in total – multivariate analysis of variance for dependent samples (MANOVA).

Effect	Test	P
Articulators	Wilkis' Lambda	0.141
Techniques	Wilkis' Lambda	0.000
Movements	Wilkis' Lambda	0.000
Articulators and techniques	Wilkis' Lambda	0.478
Articulators and movements	Wilkis' Lambda	0.002
Techniques and movements	Wilkis' Lambda	0.915
Articulators, techniques and movements	Wilkis' Lambda	0.104

p- significance

Discussion

The average values ​​of the left and right condylar path inclination and the right and left Bennett angle showed a tendency toward higher values using the method of wax eccentric records rather than those using the method with Arcus Digma device for all the three articulator systems used in this study (Table 1). However, the average values for condylar path inclination, considering the type of occlusion (Angle class I) amounted to 34°- 41.7° for wax eccentric records and 28.2°-34.4° for Arcus Digma device. Bennett angles amounted to 15.7°-19.7° for wax eccentric records and 9.3°-9.8° for Arcus Digma. In this study, no statistically significant differences for the tested variables were found according to gender (Table 2), which could have been expected with respect to the selected sample and its age limit. A review of the literature on the average values ​​of condylar path inclination have showed large variations, ​​which, as it can commonly be explained, arose from different study sample sizes, different measurement methods for the condylar inclination according to different referential planes (, , ). With respect to the measured average values of Bennett angle, probably the best study to compare is the study by a group of Croatian authors (), who measured the average Bennett angle of 7.7° in their test group (Arcus Digma device used). It should be noted that the same angle was measured for subjects with Angle class I, but also other subjects with other Angle classes had the same average value of Bennett angle. Average Bennett angle of 7° to 8° was also found in other studies (, ), whereby its value of 15°, which is most often recommended for average articulator programming, represents a higher value of Bennett angle than the value in most individuals. Hobo et al. () argue that in average adjustable articulator programming, where a higher condylar path inclination and a smaller Bennett angle are used, the incidence of interference in excursive movements of the articulator can be increased. Since dental articulators are already widely used in everyday practice, this suggests that they should be individually set/ programmed.

Ratzman et al. () compared the average values of horizontal condylar inclination recorded by means of protrusive interocclusal record and electronic pantograph on a sample of 23 subjects divided by gender. Statistical analysis found a match between these two methods, but it was insufficient in order to be reliably used for dental articulator programming in clinical conditions. The values ​​of condylar path inclination obtained based on protrusive eccentric record, showed a high variance in relation to the values ​​obtained with electronic pantograph. In conclusion, they recommend using a pantograph in relation to protrusive records with the aim of individualized adjustable dental articulator programming.

The results of this study indicate similar tendencies, i.e. statistically significant differences between the measured parameters were found, caused by the influence of different constructions of the dental articulators used in the study (SAM 3, Protar 7 and Artex CR), as well as the measurement method (wax eccentric record and Arcus Digma) (Table 3 and 4). The reason for this may be explained by the fact that wax records relate only to the initial part of protrusive/lateral movement, while in case of Arcus Digma application, TMJ condyles perform movements throughout their range. Angles emerging during these condylar movements form angles that in the application of wax centric records (especially in Bennett lateral movement) have higher values than measured with Arcus Digma device. A recent study by Ćimić et al. () points to the fact that condylar movement in the sagittal direction (which happens during protrusive mandibular movement) is not uniform; indeed, there was a difference between the left and right side of the measured condylar inclination, amounting to over 10°. Their measurements were carried out with Arcus Digma device, and the test group was almost identical as in this study. It included younger subjects with normal occlusion. Another reason could be unequal hinge axis transfer to the selected dental articulators using anatomic (wax centric record) and kinematic face bow (Arcus Digma device). Although for both arches in this study an average hinge axis transfer was used, and not kinematic axis, it should be noted that some articulator systems, especially their anatomic face bows are oriented (placed) on the subject according to different reference planes (e.g. for SAM articulators according to axial-orbital plane, and for Protar articulators according to the Camper's plane). It is known that reference planes are not parallel to each other (differences range on average 10° to 15°). Otherwise, in the scientific literature, the position of the terminal hinge axis is under argument. The prevailing view is that this axis is determined by two points situated in the canter of joint heads of mandibular ramus. However, some authors believe that it is located in the mandibular ramus or even outside of it ().

Conclusion

Based on the results of this study, in younger subjects with normal occlusion (Angle class I), the average values of condylar paths inclination and Bennett angle differed between the two methods used (wax eccentric record and Arcus Digma device) in the same way as parameters necessary for adjustable dental articulator programming. When using multivariate analysis of variance for dependent samples (MANOVA), the average values of the measured parameters are influenced by articulator selection (design) and measurement method, which was confirmed by statistical significance found between the tested variables. The results obtained by using Arcus Digma device corresponded to the data from the scientific literature to a higher extent. This favors Arcus Digma device as a more reliable method for determination of condylar path inclination and Bennett angle, and thus can be considered more valid for individualized dental articulator programming.