|Year : 2014 | Volume
| Issue : 1 | Page : 8-12
Effect of direct and indirect face-bow transfer on the horizontal condylar guidance values: A pilot study
Aditi Mishra, Jayant Palaskar
Department of Prosthodontics and Crown and Bridge, Sinhgad Dental College and Hospital, Pune, Maharashtra, India
|Date of Web Publication||6-May-2015|
Dr. Aditi Mishra
Department of Prosthodontics and Crown and Bridge, Sinhgad Dental College and Hospital, Sinhgad Institutes, Off Sinhgad Road, Pune - 411 041, Maharashtra
Source of Support: None, Conflict of Interest: None
Aims and Objectives: This study aimed to evaluate the effect of direct and indirect face-bow transfer on the horizontal condylar guidance (HCG) values obtained on the semi-adjustable articulator. Materials and Methods: A total of 15 subjects of age 20-30 years, of either sex were selected. Two sets of maxillary and mandibular casts were obtained. A single arbitrary face-bow record was used for mounting the maxillary casts by direct and indirect transfer for each subject. The mandibular casts were mounted using maximum intercuspation record. Protrusive records were made in Alu wax and used to program the directly and indirectly transferred casts. HCG values obtained from cephalometric records were taken as control. The data was subjected to ANOVA and Bonferroni post hoc test. Results: Mean values of HCG obtained in direct face-bow transfer were 24.93°, indirect transfer −27.66°, and cephalometric analysis −32.73°. One-way ANOVA test indicated that there was a significant difference between all the groups (P < 0.05). Tukey's test with Bonferroni's correction (P < 0.01) was significant for direct and indirect transfer (P = 0.008), and direct transfer and cephalometric readings (P = 0.0046). A nonsignificant difference was found between indirect transfer and cephalometric readings (P = 0.047). Conclusion : There is a statistically significant difference in HCG values obtained from direct and indirect face-bow transfer records. Lateral cephalograms gave higher mean HCG values than those obtained from protrusive records. Mean HCG values obtained from indirect face-bow transfers are significantly more than those obtained from direct transfers and are also closer to the values obtained from the lateral cephalograms.
Keywords: Condylar guidance, facebow transfer, interocclusal records
|How to cite this article:|
Mishra A, Palaskar J. Effect of direct and indirect face-bow transfer on the horizontal condylar guidance values: A pilot study. J Dent Allied Sci 2014;3:8-12
|How to cite this URL:|
Mishra A, Palaskar J. Effect of direct and indirect face-bow transfer on the horizontal condylar guidance values: A pilot study. J Dent Allied Sci [serial online] 2014 [cited 2019 Jan 18];3:8-12. Available from: http://www.jdas.in/text.asp?2014/3/1/8/156518
| Introduction|| |
Condylar guidance by definition (GPT-8)  is the mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa. Success of complex prosthodontic procedures is enhanced by accurate simulation of the condylar path of the patient on an articulator. It enables the clinician to estimate the correlation between the path traced by the condyle during mandibular movements and the morphology of the occlusal surfaces which in turn aids in restoring the occlusion without interferences. 
Many studies have been done on the comparative accuracy of clinical as well as radiographic methods of determining the horizontal condylar guidance (HCG). The condylar guidance inclination in semi-adjustable articulators is set either by protrusive or lateral interocclusal registrations recorded in a suitable recording medium. The same can be determined radiographically by tomographs,  lateral cephalograms,  and pantomographs. 
It has been shown by many studies that methods and materials used to make the arbitrary face-bow records and protrusive records for programming the articulators play a significant role in determining the HCG. However, as claimed by the manufacturer, there is no effect of the type of face-bow transfer, that is, direct and indirect, on the values of HCG.
Direct mounting means that after face-bow registration has been obtained, and the ear-bow halves have been removed from the subject, the face-bow is transferred directly on to the articulator to mount the maxillary cast. With indirect mounting, once the face-bow registration has been obtained, the transfer assembly is removed from the spring-bow and placed on to the articulator using the transfer jig and mounting platform for mounting the maxillary cast. 
The aim of this study was to evaluate the effect of the type of face-bow transfer on the HCG values obtained on the articulator and their comparison with values obtained from a lateral cephalogram of the subject. This study was based on the null hypothesis that type of transfer of arbitrary face-bow has no effect on HCG values obtained on the semi-adjustable articulator.
| Materials and Methods|| |
A total of 15 subjects (dental students at Sinhgad Dental College and Hospital, Pune) within the age group of 20-30 years, of either sex were selected. Inclusion criteria included having a full complement of teeth, class I molar relation and 2-4 mm of overjet. Exclusion criteria included subjects with temporomandibular disorders, any progressive periodontal disease, major restorations, gross attritions, poor general health and lack of adequate neuromuscular control of jaw movements.
Two sets of irreversible hydrocolloid impressions were made for each subject and poured using Dental stone (Kaldent, Kalabhai, India). Split casts were prepared for all maxillary casts. Face-bow record (HANAU™ Spring Bow, Whip Mix Corporation, USA) was made for each subject.
The semi-adjustable articulator (HANAU™ Wide-Vue Articulator, Whip Mix Corporation, USA) has a condylar guidance which is graduated at 5° intervals. In order to obtain more accurate readings, a sectioned modified protractor, graduated at per degree interval, was attached onto the inner side of the graduated markings on the condylar element, in alignment with the markings. An L-shaped extender made from 23 gauge orthodontic wire was attached onto the reference zero line [Figure 1]. The articulator was zeroed according to the Hanau™ manual. 
Direct face-bow transfer
After making the face-bow record, the ear pieces of the spring-bow were used for suspending the bow over the condylar shaft ends of the Hanau™ Wide-Vue articulator. The anterior elevator was adjusted so as to position the top of orbitale pointer on the spring-bow to the underside of the orbitale indicator on the articulator and then was secured by the thumbscrew. The bitefork index was checked to be adequately supported by cast support before placement of the maxillary cast and plaster mounting to the articulator [Figure 2].
Indirect face-bow transfer
After the direct transfer had been completed, the spring-bow was unscrewed from the transfer assembly. The mounting platform was secured on the lower member by the cast support. The transfer assembly was secured onto the mounting platform, and the cast support was raised to support the bitefork index following which the maxillary cast was mounted [Figure 3].
The mandibular casts were then mounted using maximum intercuspation Alu wax record for both direct and indirect transfers. A single protrusive record for each subject was made in Alu wax to program the directly and indirectly transferred casts [Figure 4]. The HCG values obtained from the direct and indirect transfers were noted for each subject [Figure 5] and [Figure 6].
|Figure 5: Horizontal condylar guidance readings from direct face-bow transfer|
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|Figure 6: Horizontal condylar guidance readings from indirect face-bow transfer|
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Lateral cephalograms of the subjects were obtained (Planmeca EC Proline Ceph, Helsinky, Finland; 77 kV and 10 mA.). The outline of the condyle, glenoid fossa and articular eminence (AE) was traced. The Frankfort horizontal plane (FHP) was traced by joining the porion and orbitale. Another line along the posterior slope of AE was drawn, extending from the most antero-superior point on the glenoid fossa to the most convex point on the apex of AE. The angle between FHP and posterior slope of AE was measured to obtain condylar inclination angle as seen in [Figure 7]. HCG values obtained from cephalometric records were taken as control. The data was subjected to ANOVA and Bonferroni post hoc test.
|Figure 7: Horizontal condylar guidance readings from cephalometric tracing|
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| Results|| |
All the statistical analyses were done using Microsoft Excel 2013. Out of the 15 subjects who participated in the study, 8 were males, and 7 were females. Mean values of HCG obtained in direct face-bow transfer were 24.93°, indirect transfer −27.66° and cephalometric analysis-32.73° [Table 1]. One-way ANOVA test indicated that there was a significant difference between all the groups (P < 0.05). Tukey's test with Bonferroni's correction (P < 0.01) was significant for direct and indirect transfer (P = 0.008), and direct transfer and cephalometric readings (P = 0.0046). A nonsignificant difference was found between indirect transfer and cephalometric readings (P = 0.047) [Table 2].
|Table 2: One-way ANOVA and Bonferroni's post hoc test of HCG values obtained from different groups|
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| Discussion|| |
There have been previous studies that compare the accuracy of different clinical methods of recording the HCG and their comparison with readings obtained radiographically. Occlusal interferences may result during mandibular movements if condylar guidance is not taken into account. Clinically, this might lead to an increased chairside adjustment time and arbitrary trimming which can be frustrating for both the patient, as well as the dentist.
Gracis  advocated setting the condylar inclination at lower than average values to ensure disocclusion of the posterior teeth during excursions. Gilboa et al.  contradicted this by stating that if the individual inclination of the eminence is very steep or flat, guidance obtained from average value settings may differ sufficiently to cause problems in achieving particular clinical objectives, such as posterior disocclusionor balanced occlusion.
Several extraoral and intra oral methods are used to clinically record condylar guidance. Extra oral methods are mainly used in edentulous patients. Interocclusal protrusive wax records, jigs, and intra oral tracers are the most commonly used intra oral methods.
Donegan and Christensen  have stated that one important reason for the inconsistency of intra oral methods may be that, regardless of the material used, horizontal condylar angle changes with the degree of protrusion, and the intra-oral record represents only one point along the condylar path.
Ratzmann et al.  have stated that intra oral methods of recording condylar guidance angle have lower levels of reproducibility and are subject to variations of the operator, instrument, and occlusal records.
Radiographs provide an alternative method of ascertaining HCG values. Compared to clinical methods, radiographic measurement has the advantage of using stable bony landmarks and ability of being standardized and repeatable. Studies comparing radiographic and clinical methods like protrusive wax records have also been abundant.
Goyal and Goyal  compared sagittal condylar values of arcon and nonarcon articulators with cephalometric readings and determined the amount of discrepancy in sagittal condylar guidance values between arcon and nonarcon articulators using same protrusive record. The authors concluded that the mean difference in sagittal condylar guidance values obtained from nonarcon and arcon articulators was highly significant indicating a low level of reproducibility.
Tannamala et al.  compared the sagittal condylar angles set in the Hanau articulator by use of an intraoral protrusive record to those angles found using a panoramic radiographic image. The radiographic values were found to be on average 4° greater than the values obtained by protrusive interocclusal record method. The authors concluded that protrusive condylar guidance angles obtained by panoramic radiograph may be used in programming semi-adjustable articulators.
Shreshta et al.  compared condylar guidance measurements made using computed tomography (CT) scans, interocclusal wax records, interocclusal jigs, and intraoral tracer in healthy adults. The results showed that CT scan showed higher HCG values than the clinical methods and among the clinical methods, values obtained from all the methods were comparable.
After a literature search on HCG, it was found that while all possible variations of recording, may it be of instruments, methods of recording, interocclusal records, intra- and inter-operator variability had been studied, the one variable that had been consistently ignored was the effect of type of face-bow transfer, that is, direct and indirect, on the values of HCG.
The Hanau™ Spring Bow manual considers both direct and indirect transfer similar and describes indirect as an alternative to the direct type of transfer. The manual further mentions that indirect transfer offers increased stability when mounting, greater access to the cast, and parallel orientation of the upper and lower members of the articulator. 
In order to have more accuracy regarding the HCG values, the Hanau™ Wide Vue articulator was innovatively modified by adding a sectioned protractor to measure the angle to per degree as compared to the original 5° mark. Furthermore, an L-shaped extender made from 23 gauge orthodontic wire was attached onto the reference zero line so as to extend it.
Alu wax was used to make protrusive interocclusal records which were then used to program the articulators. Same protrusive record was used to program both mountings for a subject. Another factor that added to the objectivity and reduced error was the use of split cast which allowed the observer to accurately ascertain that there was indeed no gap between the two rigid surfaces while programming the articulator.
Lateral cephalograms (Planmeca EC Proline Ceph, Helsinky, Finland) were made for all 15 subjects. Cephalometric tracings were done, and values of HCG were determined by measuring the angle between Frankfurt's horizontal plane and posterior slope of AE. The values obtained were consistently higher than those obtained from both directly and indirectly transferred casts which is in agreement with Christensen and Slabbert,  Shreshta et al.  and Tannamala et al.  who found that radiographically determined angle always showed a greater mean value than that determined by intra-oral records.
However, there can be other variables which might have played a role. As this was designed to be a pilot study, the sample size was just 15. A larger sample size would be able to give us more reliable and insightful conclusions.
| Conclusion|| |
It was the aim of this study to analyze whether there is any difference in mountings obtained by direct and indirect transfer of the same face-bow record as the indirect type of transfer does not directly utilize the anterior point of reference. Within the limitations of this pilot study, it was proved that these two procedures are indeed not exactly similar or an alternative to each other as is stated by the Hanau™ Spring-bow manual.
Within the limitations of this study, the following conclusions were derived.
There is a statistically significant difference in HCG values obtained from direct and indirect face-bow transfer records. Lateral cephalograms gave higher mean HCG values than those obtained from protrusive records. Mean HCG values obtained from indirect face-bow transfers are invariably more than those obtained from direct transfers and are also closer to the values obtained from the lateral cephalograms. More studies need to be done with increased sample sizes so as to have a more detailed insight into the role of the type of transfer on the accuracy of semi-adjustable articulator mountings.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2]