Year : 2009 | Volume
: 20 | Issue : 4 | Page : 492--495
Fabrication of fixed partial dentures using functionally generated path technique and double casting
E Prashanti1, Suresh Sajjan2, Jagan Mohan Reddy3,
1 Department of Prosthodontics, Manipal College of Dental Sciences, Mangalore, India
2 Department of Prosthodontics, Vishnu Dental College, Bheemavaram, India
3 Department of Prosthodontics, Vaidehi Dental College & Hospital, Bangalore, India
Department of Prosthodontics, Manipal College of Dental Sciences, Mangalore
Harmonious occlusion is a critical requirement for successful oral rehabilitation. Conventional techniques of construction have been unsuccessful in producing a prosthesis that can be inserted without intraoral occlusal adjustment. This article discusses the use of functionally generated path technique with double casting to fabricate fixed partial dentures. The merits of this approach and the technique involved are discussed in detail.
|How to cite this article:|
Prashanti E, Sajjan S, Reddy JM. Fabrication of fixed partial dentures using functionally generated path technique and double casting.Indian J Dent Res 2009;20:492-495
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Prashanti E, Sajjan S, Reddy JM. Fabrication of fixed partial dentures using functionally generated path technique and double casting. Indian J Dent Res [serial online] 2009 [cited 2020 Jul 4 ];20:492-495
Available from: http://www.ijdr.in/text.asp?2009/20/4/492/59453
In natural articulation, the mandibular teeth move over the maxillary teeth in a harmonious manner. The cusps move in the fossae and grooves between the opposing cusps and, normally, there is no interference during the various mandibular movements. Interference or a premature contact can initiate a wave of disturbance that spreads throughout the stomatognathic system and can even affect the musculoskeletal system. Any prosthesis that is prepared should not disturb the harmony of occlusion or it may jeopardize the situation. The anatomical articulator simulates the mandibular movements and assists in developing a prosthesis suitable for the existing occlusal condition. However, it cannot duplicate the whole stomatognathic system. Intricacies in the use of a fully adjustable articulator precludes its use in routine clinical practice.
An alternative method to reproduce a precise occlusion that was developed way back in the 1930s and is now becoming popular is the functionally generated path (FGP) technique.  The original technique was described by Meyer for obtaining the 'functional occlusal path' for complete dentures  and fixed partial dentures  fabricated by a direct or indirect technique. Later, this technique was adapted for use in complete occlusal rehabilitation by Mann and Pankey. ,,, Meyer suggested that 'no occlusal adjustment in the mouth should be necessary if the technique is carried out correctly.  Recently, FGP has also been used for the fabrication of implant-retained fixed partial dentures.  This case report describes the use of FGP with double casting for fabricating a fixed partial denture.
A 26-year-old male patient who required a three-unit fixed partial denture for replacement of a missing first molar reported to the Department of Prosthodontics. At the initial appointment, a preliminary impression was made using irreversible hydrocolloid impression material (Imprint; Dental Products of India Ltd., Mumbai, Maharashtra, India) and the diagnostic casts were mounted on a semi-adjustable articulator (Hanau WideVue; Waterpik Technologies Inc., Fort Collins, CO, USA) using a facebow transfer (Hanau Spring-Bow, Waterpik Technologies, USA). Protrusive records were made using polyether bite registration paste (RamitecTM; 3M ESPE, Germany). The patient was trained to close in maximum intercuspation position (MIP) and perform various eccentric movements (right lateral, left lateral, and protrusive). This was carried out to accustom the patient to the various movements that would have to be performed later for recording the FGP. The tooth preparation for the abutment teeth, gingival displacement, final impression making, and master die preparation was done following the principles given by Schillingburg.  Wax pattern (Inlay wax type II-Harvard, Gusswachs, Normal Hart, Johannesburg, Berlin, Germany) was made with 1-mm occlusal clearance and retentive beads of wax (Renfert, Hilzingen, Germany) were placed. These beads would aid in the retention of the pattern resin during functional generation of the occlusal morphology in the next step [Figure 1].  After the base casting was obtained, it was sandblasted and checked for accuracy of fit on the model and in the mouth[Figure 2].
Generation of functionally generated path
Before generating the occlusal morphology we ensured that the base casting had adequate occlusal clearance and proper fit on the prepared teeth. The occlusal morphology was generated using pattern resin (GC Corporation, Tokyo, Japan) following the technique described by Dawson.  Pattern resin was mixed according to the manufacturer's instructions and applied on the occlusal surface of the metal coping with retentive beads. The patient was instructed to close the mouth in MIP and then perform right lateral, left lateral, and protrusive movements in succession, ending in the MIP. The excess pattern resin was trimmed off using an acrylic trimmer. The occlusal surface was examined for any exposure of the metal and if this was present the metal in the area was trimmed, pattern resin was added in that area, and the movements were performed once again.
Once the occlusal morphology was perfected, the MIP contacts were marked using 50-ìm blue articulating papers (Products Dentaires S.A., Vevey, Switzerland). Zinc oxide powder (Dental Products of India, Mumbai, India) was sprinkled and brushed onto the occlusal surface to form a thin, uniform coat, and the patient was instructed to perform the eccentric movements as before. All eccentric contacts became visible with the wiping away of the zinc oxide powder. Care was taken not to grind the MIP contacts that were registered in blue. The wiped out areas were trimmed using an acrylic trimmer to eliminate all eccentric interferences and the FGP patterns were completed [Figure 2]. The pattern, along with the base casting, was invested and double casted  [Figure 3].
The casting was placed in the oral cavity (before occlusal correction) to check whether it felt comfortable. At the same time the occlusion was checked to identify any high points in the casting. It was observed that there was absolutely no occlusal error identified in the MIP position. Only minimal eccentric interferences were identified and could be eliminated by selective grinding of the casting. The time taken for metal trimming was drastically reduced to 5 min. The patient reported absolute comfort with the prosthesis. The final prosthesis was cemented using glass ionomer cement (GC Fuji II, GC Corporation, Japan) [Figure 3] and [Figure 4].
The FGP technique is simple and can produce excellent results. Because of its simplicity it is sometimes derided by those dentists who do not use it. Simplicity should not be confused with inaccuracy; the technique is capable of producing very accurate results, but it demands great care and meticulous attention to detail. 
Dawson describes the FGP technique as an extremely sophisticated and practical method of capturing the precise border pathways that the lower posterior teeth follow. The technique has a distinct advantage in that it is able to record all dimensions of such border movements at the correct vertical as they are directly influenced by both condylar guidance and incisal guidance.  The procedure can provide accuracy with fairly simple instrumentation and can be used in combination with almost any laboratory method for waxing posterior restorations. It can be used either in the actual fabrication of the restorations or as a three-dimensional check-bite technique.  There are certain prerequisites for the use of FGP for the restoration of missing teeth; , these are as follows:
Presence of an optimal occlusion.Appropriate anterior guidance. Elimination of posterior interferences prior to making the restoration. No missing or broken down opposing teeth. Badly rotated, carious, or poorly restored teeth in the opposing arch will not provide the occlusal pathways needed for shaping the occlusal surface and hence FGP should be avoided in these cases.
The patient in this case report satisfied the above mentioned prerequisites. We used the double casting technique, which is better than the conventional casting in that it includes an error compensation step.  This technique enables achievement of a highly precise occlusion by eliminating the inherent dimensional errors of the indirect (conventional) method.
In the double casting method, the errors which occur due to distortion of occlusal registration material, incorrect mounting, improper impression of the opposing arch, discrepancy between teeth and master die, and wax pattern distortion can all be addressed before the occlusal surfaces are fabricated on the base casting. Therefore, the errors that could affect the final accuracy of occlusion of double-cast restorations include only those errors that are related to investing and castings and the polishing procedures. 
Even for carefully constructed conventional fixed partial dentures, a comparatively long time is needed for clinical adjustment. Experience has shown that metal trimming is a tedious job and in the attempt to correct the interferences most of the occlusal morphology may be lost.
In the present case, the time taken for occlusal correction was almost negligible. This may be because the occlusal morphology was being generated directly in the patient's mouth and thus was closer to the normal anatomy of the tooth. Hence, the time taken for correction was also drastically reduced. This has a definite role to play in patient satisfaction and confidence.
For more than 60 years, dentistry has recognized functional path articulations as a viable way of developing occlusion. The present technique has certain advantages over the conventional functional path technique;  these are as follows:
A cast fixed partial denture with retentive beads was used as a stable base in the present case report. Hence a functional path tray was not required and the problems associated with the tray, including inaccurate seating and distortions, were avoided. To overcome the drawbacks of using inlay wax  for generating FGP, pattern resin was used in the present case; this has better dimensional stability compared to the waxes. These resins not only complement waxes but could even, in whole or in part, replace them.  The occlusal morphology was developed and corrected directly in the patient's mouth. The discrepancies which can result due to differences between the teeth in the mouth and that in the master dies could thus be avoided. A functional core used routinely for the conventional FGP technique was not utilized in the present technique. Hence, the discrepancies which may result from the functional core becoming slightly degraded during waxing and metal adjustment were avoided. Further, the use of the opposing functional core to adjust maximum intercuspation and to remove eccentric interferences presupposes that it will be necessary to use the patient's mandibular movements to make final adjustments to the prosthesis. Moreover, eccentric interferences were removed in the patient's mouth directly.
As with any technique, the FGP technique also has certain disadvantages. Some of the limitations of this technique are as follows:
The operator needs to have a good knowledge of occlusion and of mandibular movements; otherwise it may lead to an incomplete generation of FGP.The occlusal details are not similar to the ideal anatomical configuration although the surface is functionally ideal.This technique cannot be used in cases with short clinical crowns and unfavorable occlusal morphology of the opposing teeth.The FGP technique cannot be used in patients having attrited teeth.Patients lacking proper neuromuscular control cannot be selected for this technique.In patients having disharmony in occlusion (malocclusions like deep bite and crossbite) and temporomandibular joint dysfunction, the FGP technique is destined to fail.Good laboratory support is a basic requirement, without which successful results are difficult to achieve.
If the FGP technique is carefully done, only minimal occlusal adjustments are required during the clinical try-in stage, which is a major advantage over the conventional technique. Multicenter clinical trials with long follow-up periods should be conducted to confirm the results obtained in present case report.
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