| Abstract|| |
Aim: The purpose of this study was comparative evaluation of sagittal condylar values of arcon and non-arcon articulators with cephalometric readings and to determine the amount of discrepancy in sagittal condylar guidance values between arcon and non-arcon articulators using same protrusive record.
Materials and Methods: Twenty subjects in the age group of 19-35 years, free from temporomandibular joint dysfunction, and occlusal disharmony, with healthy dentition participated in the study. Hanau H2 (non-arcon type) and Hanau Wide-Vue (arcon type) articulators were programmed for sagittal condylar guidance values using the same protrusive record made in polysiloxane bite registration material with edge to edge degree of protrusion. The resultant values for both the articulators on either side were compared with values obtained from tracing of digital lateral cephalogram using Kodak Dental imaging Window software 18.104.22.168-C program. The tabulated data were subjected to statistical analysis, ANOVA (Fishers 'F' test) for group comparison, Tukey's HSD test for inter-comparison, student's unpaired 't' test for intra-group comparison, and level of significance (P) was calculated using the same.
Results: The mean sagittal condylar guidance values of the three different groups were found to be very highly significant (P=0.001) and highly significant (P=0.002) on the right and left sides respectively. There was a very highly significant difference (P=0.001) and highly significant difference (P=0.003) between the arcon and non-arcon group on the right and left side respectively. No significant difference was found between the arcon and cephalometric group (P=0.284 right, P=0.853 left) and a statistically significant difference was found between the non-arcon and cephalometric group (P=0.049 right, P=0.015 left). On intragroup comparison there was no statistically significant difference in sagittal condylar values on the right and left sides.
Conclusion: The mean difference in the sagittal condylar guidance values obtained from non-arcon and arcon articulators shows a low level of reproducibility, and no significant difference found in mean sagittal condylar values obtained from arcon articulator and cephalometric tracings indicates replication of sagittal condylar guidance value from image of articular eminence.
Keywords: Articular eminence, arcon articulator, cephalometric tracing, non-arcon articulator, sagittal condylar guidance
|How to cite this article:|
Goyal MK, Goyal S. A comparative study to evaluate the discrepancy in condylar guidance values between two commercially available arcon and non-arcon articulators: A clinical study. Indian J Dent Res 2011;22:880
The mandibular condylar path is the path travelled forward and downward by the condyles in the temporomandibular joints during various mandibular movements, and is peculiar to each individual.  As the condyle moves out of centric relation it descends along the articular eminence of the mandibular fossa. The angle at which the condyle moves away from a horizontal reference plane is referred to as condylar guidance.  The double ogee curve of the glenoid fossa will cause the apparent path of the condyle to be different with varying amount of mandibular protrusion. The ideal amount of protrusion for making the record is the exact equivalent of the amount of protrusion necessary to bring the anterior teeth edge to edge. However, the mechanical limitations of most articulators require a protrusive movement of at least 6 mm so the condylar guidance mechanism can be adjusted. 
|How to cite this URL:|
Goyal MK, Goyal S. A comparative study to evaluate the discrepancy in condylar guidance values between two commercially available arcon and non-arcon articulators: A clinical study. Indian J Dent Res [serial online] 2011 [cited 2013 Dec 9];22:880. Available from: http://www.ijdr.in/text.asp?2011/22/6/880/94695
Condylar guidance on articulators is an approximate duplication of the condylar path in patients and reproduced on the instrument with the help of interocclusal records. Three general classes of records are used for transferring maxillomandibular relationships from the patient to the articulator. It may be either directly by the hinge axis records and pantographic records to the articulator  or indirectly by the interocclusal records to the articulator or by radiographic methods. ,, This clinical study is oriented towards comparing two different articulator systems, Hanau H2 (non-arcon type), and Hanau Wide-Vue (arcon type) in reproducing sagittal condylar guidance angulations when programmed using same the protrusive record, and to critically analyze if any discrepancy would occur in the condylar guidance values when compared with cephalometric readings.
| Materials and Methods|| |
Twenty complete dentate subjects in the age group of 19- 35 years with periodontally healthy and caries-free teeth with no sign of alveolar bone loss and pathologic migration were included in the study. Subjects had an Angle's Class I molar relationship with no spacing or crowding of anterior teeth and exhibited an average degree of horizontal and vertical overlap. The presence or absence of the third molar was not considered. Subjects had no signs and symptoms of temporomandibular joint dysfunction. They did not have any kind of prosthesis with minimum or no occlusal restorations and had no history of orthodontic treatment. Subjects had no congenital or developmental deformities and had not undergone any surgical repair in the oro-facial region. Subjects with pathological migration, traumatic occlusion of anterior teeth, temporomandibular joint clicking, crepitation, tenderness, and gross edentulism were excluded. Subjects associated with risk of radiation, like pregnancy, xerostomia, skin reactions, mucositis etc. were excluded. Ethical committee approval was obtained by the Kasturba Hospital Ethics Committee, Kasturba Medical College and Hospital, Manipal, India. (KHEC No. 169/2007) prior to the study. All subjects included in the study were screened through a detailed case history and were well-informed regarding the study design. Written consent from each subject was obtained.
Two sets of alginate impressions (Tropicalgin chromatic, Zhermack, Italy) were made for each subject and were poured immediately in Type III dental stone (Kalabhai, Karskarson Pvt. Ltd.) following the manufacturer's instructions and guidelines, giving two sets of maxillary and mandibular casts for each individual. Auto-polymerizing acrylic resin (DPI-RR, cold cure DPI) was used to fabricate Lucia jig  over the individual maxillary cast. The palatal surface of the jig was trimmed into a flat platform (not an inclined plane); according to Dr. Peter Neff  to permit upward condylar movement without the distalizing effect. It is used to interrupt the reflex action of the muscles and train the patient to close in centric relation position and final adjustments are done intraorally. A bite frame  was used to obtain the centric and protrusive records, which reinforces the registration plates during setting. Two bite frames were fabricated using a 12-gauge wire adapted on the subject's cast, around the maxillary dental arch with half an inch clearance. These were reinforced with heavy ligature wire by spot welding. Using sticky wax, gauze was secured onto the frame to act as a carrier for the bite registration paste.
Face bow registration for both semiadjustable articulator systems (Hanau H2-non-arcon type articulator and manual ear bow, Hanau wide-vue arcon type articulator and spring bow, Waterpik, Fort Collin, USA) was accomplished as per the standard technique following user's instruction manual using axis-orbitale as the reference plane and orbitale as the anterior point of reference. Both articulators were prepared by initial adjustment of 70° sagittal and 0° lateral condylar inclination (Hanau H2) and 30° sagittal and Bennet angles for Hanau wide-vue articulator. Horizontal and lateral incisal guidance was adjusted at 0° for both the articulators. Maxillary casts were secured in place in the compound index, assured for complete seating and mounted with fast-setting plaster for both the articulators. Upon complete set of the mounting, the mounting guide and transfer rod with bitefork index assembly was removed carefully. 'Lucia jig" was used to train the patient to close in centric relation position [Figure 1]. The main function of the jig is to deprogram the subject's habitual closure. This short-circuits the proprioception that directs the engram of closure. The jig was inserted in place and a carbon paper was placed in between the jig and the lower incisors. The subject was instructed to move to the right, left, forward, and backward in order to free jaw movements. The jig was removed and there would be a gothic arch traced on the jig. The tails of the Gothic arch were trimmed off and the apex was slowly reduced into a flat area eliminating any inclined plane effect. The mandible was guided into a retruded position and the jig was trimmed till the just disocclusion was obtained. The procedure was completed in 20 min and the closure of mandibular incisors on the jig was repeated to ensure that the contact was reproduced [Figure 1]. Bite registration addition silicone paste (Futar D Occlusion, Kettenbach, Germany) was syringed onto the bite frame and also on the occlusal surfaces of the lower posteriors. The bite frame was inserted and the subject was guided to close the mandible into the rehearsed position. This centric relation position was held till the material set. The records were removed with the bite frame. This record was used to mount the mandibular cast on the articulators. Similarly, the protrusive record was obtained in edge to edge relationship (6 mm). Bite registration paste was extruded on the custom-made bite frame as well as on the occlusal surfaces of the lower teeth. Bite frame was inserted and the subject was instructed to close his anterior teeth in edge to edge relationship, while bite framework was secured in place. This protrusive record was used to program both the articulators. The procedure for adjustment of sagittal condylar guidance value was repeated three times and values were recorded for each articulator on the right and left side. The average of these three readings was considered sagittal condylar guidance value for that articulator on the right and left side for a particular individual. Digital lateral cephalometric images of each subject were obtained using Kodak 8000 C unit (Eastman Kodak Company, France) with standardized radiographic parameters (78 kv/12 mA/1 sec) following the manufacturer's instructions and guidelines. Obtained images were saved using Kodak Dental imaging software program. Each lateral cephalometric image was traced with a direct digitization process using Kodak Dental imaging Window software 22.214.171.124-C program. Tracings were made for Frankfort horizontal plane by identifying the orbitale and porion, and the two most posterior points were marked on the posterior slope of the articular eminence and two reference lines were drawn respectively by display of white hairline cursor controlled by a graphic mouse. Angle of bisecting these two reference lines was interpreted by using software tool and was considered as cephalometric sagittal condylar guidance value [Figure 2]. All tracings were made three times and interpreted. The average of these three readings was considered as the cephalometric sagittal condylar guidance value for a particular subject. Lateral cephalogram for just one side was taken as referece measurement for both sides. It must be done because referece measurement based on unilateral image directly affects on results in this study. Information from the left side will be useful for a better understanding of the results.
|Figure 1: Lucia jig in place, modified to produce disocclusion for deprogramming the mandible; (a) Right lateral view; (b) Frontal view; (c) Left lateral view|
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|Figure 2: Reference lines digitized on the lateral cephalogram and angles measured using Kodak dental imaging window software 126.96.36.199-C program|
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The data thus obtained were tabulated and subjected to ANOVA (Fishers 'F' test) for group comparison, Tukey's HSD test for inter-comparison, student's unpaired 't' test for intra-group comparison, and level of significance (P) was calculated using SPSS Version 15.0 software program. The results obtained were considered very highly significant when the P value was less than 0.001, highly significant when P<0.01, significant when P<0.05, and were considered non-significant if P value was more than 0.05.
| Results|| |
[Table 1] and [Table 2] show the mean and standard deviation of sagittal condylar guidance values on right side and left side respectively for 20 subjects (N), obtained by non-arcon, arcon articulators, and cephalometric tracings. The mean sagittal condylar guidance values for non-arcon, arcon articulators and cephalometric tracings were 41.25 ± 6.66 degrees, 32.75 ± 6.17 degrees, and 36.05 ± 7.54 degrees on the right side and 43.00 ± 7.67 degrees, 34.75 ± 7.69 degrees, and 36.05 ± 7.54 degrees on the left side respectively [Figure 3]. The mean sagittal condylar guidance values of the three different groups were found to be very highly significant (P=0.001) on the right side and highly significant (P=0.002) on the left side.
|Table 1: Mean sagittal condylar guidance values of the three different groups on the right side (in degrees)|
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|Table 2: Mean sagittal condylar guidance values of the three different groups on the left side (in degrees)|
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|Figure 3: Comparison of mean sagittal condylar guidance values (in degrees) obtained from the three different groups|
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[Table 3] and [Table 4] show the mean difference in sagittal condylar guidance values on the right side and left side respectively. The mean difference in sagittal condylar guidance value between arcon and non-arcon articulators was found to be very highly significant (P=0.001) on the right side whereas on the left side the difference was highly significant (P=0.003). The mean difference in sagittal condylar guidance values between arcon articulator and cephalometric tracing was found to be statistically non-significant with P=0.284 and P=0.853 respectively. A significant difference in mean sagittal condylar guidance values was found between non-arcon articulator and cephalometric tracings on the right side (P=0.049) and left side (P=0.015).
|Table 3: Intercomparison of mean sagittal condylar guidance values of the three different groups on the right side (in degrees)|
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|Table 4: Intercomparison of mean sagittal condylar guidance values of the three different groups on the left side (in degrees)|
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[Table 5] shows intra-group comparison of sagittal condylar guidance values obtained from three different groups. Mean sagittal condylar guidance values obtained from non-arcon and arcon articulators on the right and left sides were statistically not significant with P=0.446 and P=0.37 respectively.
|Table 5: Intragroup comparison of sagittal condylar guidance values of the three different groups on the right and left sides (in degrees)|
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| Discussion|| |
All cases selected were in the age group of 19-35 years. This age group was selected as the cranio-dentofacial growth is accomplished by this age.  The range of sagittal condylar values was 30-55° for the non-arcon articulator and 25-45° for the arcon articulator; these values are in accordance with Payne. 
The semiadjustable articulators used were Hanau H2 (non-arcon type) and Hanau wide-vue (arcon type) with their respective face-bows. Particular articulator systems were used because both of them make use of the orbitale as the anterior point of reference for orientation of the maxillary cast which standardizes the three-plane position of the maxillary cast on both the articulators.  According to Weinberg  the various anterior points of reference used in different face-bows may raise or lower the occlusal plane by ±16 mm and that has no effect on centric occlusion, however, it does have an effect on eccentric condylar readings that may influence cuspal inclines. Thus, the influence of the error induced by face-bow registration could be eliminated in the study. Moreover, in accordance with Gonzalez and Kingery  the axis-orbital plane is the least variable and most reliable and considered best for face-bow registration as it is easy to locate and reproducible.
After the maxillary casts were mounted, the Lucia jig  was used to guide the mandible in the centric relation position and syringeable addition polyvinyl siloxane impression material was used as an interocclusal recording media reinforced with custom-made metal bite frame.  The Lucia jig was considered as it is the most accurate, easily learned and practical method of deprogramming the mandible. Addition polyvinyl siloxane bite registration material was used because the reliability of other recording materials like wax and zinc-oxide impression paste as an interocclusal record has been proved to be low by previous authors and these materials are considered dimensionally stable and highly accurate. The same centric interocclusal record was used to mount the mandibular casts on both the articulators. Protrusive record was also obtained with the same bite registration material in edge to edge relationship (6 mm) to set sagittal condylar guidance on both the articulators. Craddock  believed that it was important to keep the distance of protrusion the same because the sagittal condylar angle changes with the amount of protrusion. Posselt et al.,  also reported that some correlation exists between degree of protrusion that can influence the setting of condylar readings on instruments. The amount of protrusion was the same in the present study as the same protrusive record was used for both the articulators. 
Digital lateral cephalogram was selected to obtain individual sagittal condylar guidance value which was taken as a standard for critical comparison with two groups. According to Davis  digital imaging with interactive computer processing have added benefits of high-quality images, speed of application, low radiation dosage, direct analysis and as accurate as manual technique. Lateral cephalogram reveals accurate morphology of the articular eminence and anatomic landmarks to draw reference planes i.e. Frankfort horizontal plane in single image. Cohen  has suggested that the left and right protrusive condylar paths are the same. Since in the cephalometric technique the right and left sides were not distinguished, these values were considered the same. 
A difference in the sagittal condylar guidance values was noted between both the articulators. The mean sagittal condylar guidance value for the Hanau H2 (non-arcon) on the right side was 41.25 ± 6.66 and on the left side was 43.00 ± 7.67 degrees. The mean value for Hanau wide-vue (arcon) on the right side was 32.75 ± 6.17 and on the left side was a 34.75 ± 7.69 degrees [Table 5]. These values are statistically not significant but clinically condylar guidance values on the right side were slightly less than the left side in both the articulators.
These results are in accordance with the studies done by Arthur  and Gheriani and Winstanley.  This might be due to the topography of the condyle and glenoid fossa which may affect the condylar guidance since it is determined by the distal slope of the articular eminence. Flatter the curvature of condyle, lesser will be the condylar guidance. Despite a normal topography, the guidance may not be correspondingly steep due to the fact that the condylar guidance is also affected by the ligaments, muscles and soft tissues of the temporomandibular joints. This also might be attributed to the masticatory habits related to individual chewing patterns as most of the subjects favor their right side for chewing which could be related to more wear of the right condyle as compared to the left.
While comparison was made between non-arcon and arcon articulators in the present study, the mean difference for condylar sagittal values was 8.50° and 8.25° on the right and left sides respectively and this difference was very highly significant for the right side and highly significant for the left side with lesser values for the arcon articulator [Table 3] and [Table 4]. This difference might be due to the fact that condylar inclination changes in relation to maxillary occlusion in non-arcon articulators as a certain degree of opening of the articulator takes place, whereas in arcon articulators condylar inclination remains constant in relation to the maxillary occlusion plane at any degree of opening of the articulator. According to Shillingburg et al.,  and Rosensteil et al.,  with the non-arcon design condylar inclination of the mechanical fossae changes in relation to the maxillary occlusion plane as the articulator is opened and can lead to errors when a protrusive record of certain thickness is being used to program the articulator. They reported that with a 3-5 mm thickness of interocclusal record there would be a difference of 8° between where the articulator settings are adjusted and a closed position where the articulator is used. These findings are in accordance with the present study. Thus the average thickness of centric and protrusive interocclusal records must be within the range of 3-5 mm depending on the type of the interocclusal record material.
While comparing sagittal condylar guidance values obtained from arcon articulator and cephalometric readings, a mean difference of 3.3° and 1.3° was found on the right and left side respectively, which was statistically not significant [Table 3] and [Table 4]. These findings correlate with the findings of Corbett et al.,  who studied the condylar movements and confirmed that in protrusion, the condylar head follows closely the anatomical form of the articular eminence and represents a very high correlation coefficient and level of significance. Isberg et al.,  reported that a high degree of correlation exists between the protrusive condylar path and the steepness of the articular eminence, and the condylar path is slightly less steep than the steepness of the articular eminence, which may be attributed to the active role played by the soft tissues during condylar movements. Stallard and Stuart  proposed that the muscles operating the mandible hold the condyles against the eminence throughout all condylar movements and these movements are guided by ligaments. Gilboa et al.,  reported a high degree of correlation between articular morphology and panoramic images and suggested that the inclination of the articular eminence in a panoramic image may be of value in setting the condylar guidance in semiadjustable articulators, which supports the present study. The correlation between mean sagittal condylar readings of the arcon articulator and cephalometric readings could be possibly due to the anatomic representation of the articulator design in close approximation with the human temporomandibular joint. This anatomic duplication of the temporomandibular joint on the instrument may be responsible for near accurate replication of mandibular movements. However, a slight difference in values of both these groups could be justified by the active role played by the articular disc, ligaments, and muscles in condylar movements and neuromuscular synchronization during functional mandibular movements.
| Conclusion|| |
On the basis of the findings of this study, it may be concluded that the mean difference in sagittal condylar guidance values obtained from non-arcon and arcon articulators was highly significant indicating a low level of reproducibility. The mean difference in sagittal condylar values obtained from the non-arcon articulator and cephalometric tracings was statistically significant whereas no significant difference was found in the mean sagittal condylar values obtained from the arcon articulator and cephalometric tracings. In the groups studied, there was no significant difference in sagittal condylar guidance values on the right and left sides, however, slightly lesser values were obtained on the right side.
| Acknowledgment|| |
Author wishes to express his paramount gratitude to Dr. Veena Hegde (Professor and Head), Dr. Dhanasekar B. (Associate Professor), and Dr. Aparna I. N. (Professor), Department of Prosthodontics and Maxillofacial Prosthetics, Manipal College of Dental Sciences, Manipal, India, for their constant support and guidance.
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Mukesh Kumar Goyal
Department of Prosthodontics and Maxillofacial Prosthetics, Jan Nayak Ch. Devilal Dental College, Sirsa, Hariyana
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]