|Year : 2018 | Volume
| Issue : 2 | Page : 155-159
Comparative evaluation of the dimensional accuracy of cast partial denture frameworks fabricated by conventional technique and light-cure wax technique: An in vitro study
Rijuta Virmani, Anandkumar G Patil, Raghunath Patil, Prashant A Karni
Department of Prosthodontics and Crown and Bridge, KAHE's KLE V K Institute of Dental Sciences, Belagavi, Karnataka, India
|Date of Web Publication||18-May-2018|
Dr. Anandkumar G Patil
Department of Prosthodontics and Crown and Bridge, KAHE's KLE V K Institute of Dental Sciences, Belagavi - - 590 010, Karnataka
Source of Support: None, Conflict of Interest: None
BACKGROUND: Removable partial dentures are an economical way of replacing lost structures, especially in cases where FPD or implants are not possible. Metal alloys by the conventional lost-wax technique are the most common way of fabricating such dentures which can be done by using either conventional casting wax or light-cure wax.
PURPOSE: The objective of this study is to evaluate and compare the dimensional accuracy of cast partial denture frameworks fabricated using conventional casting wax and light-cure wax.
MATERIALS AND METHODS: This in vitro studied was carried out in the Department of Prosthodontics and Crown and Bridges, and Department of Oral Pathology and Microbiology, KAHE's KLE VK Institute of Dental Sciences, Belagavi. A total of 30 samples were included in the study divided into two groups as follows: Group 1: cast partial denture frameworks fabricated using conventional casting wax and Group 2: cast partial denture frameworks fabricated using light-cure wax. A partially edentulous Kennedy's Class III Mod 1 metal die was created, which was then duplicated using a silicone duplicating material to form a master mold. 15 refractory (phosphate bonded investment) and 15 stone (Type III gypsum) casts were poured according to the manufacturer's instructions onto which conventional casting wax and light-cure wax was adapted, respectively, followed by subsequent investing and casting using cobalt–chromium alloy. The final frameworks were finished and polished and checked for dimensional accuracy by assessing the dimensional fit and the linear dimensional change. The dimensional fit was evaluated by measuring the gap between the palatal major connector and the palatal portion of the metal die at five different points: at midline, at 5 mm, and at 10 mm on either side of the midline, by interposing pattern resin between the two and checking thickness under a stereomicroscope. The linear dimensional change was assessed by calculating the difference of the distance between two specific points on the die and the frameworks. The data were subjected to independent t-test (P < 0.05).
RESULTS: The dimensional fit of the Group 1 frameworks using conventional casting wax was 748.25 μm and Group 2 using light-cure wax was 794.02 μm. The result was statistically insignificant. The linear dimensional changes observed for Group 1 and Group 2 were 0.78 mm and 0.63 mm, respectively. The result was statistically insignificant.
CONCLUSION: There was no significant difference between the dimensional accuracies of the cast partial denture frameworks fabricated using conventional casting wax and light-cure wax. Hence, the light-cure wax fabrication method can be considered as an alternative for the cast partial denture framework fabrication, as it is simple and much less time-consuming.
Keywords: Cast partial denture frameworks, conventional casting wax, dimensional accuracy, light-cure wax
|How to cite this article:|
Virmani R, Patil AG, Patil R, Karni PA. Comparative evaluation of the dimensional accuracy of cast partial denture frameworks fabricated by conventional technique and light-cure wax technique: An in vitro study. Indian J Health Sci Biomed Res 2018;11:155-9
|How to cite this URL:|
Virmani R, Patil AG, Patil R, Karni PA. Comparative evaluation of the dimensional accuracy of cast partial denture frameworks fabricated by conventional technique and light-cure wax technique: An in vitro study. Indian J Health Sci Biomed Res [serial online] 2018 [cited 2020 Feb 25];11:155-9. Available from: http://www.ijournalhs.org/text.asp?2018/11/2/155/232689
| Introduction|| |
Partial edentulism is a common problem associated with the general population, the majority of which seek a replacement. This partial edentulism brings its own set of problems, such as drifting and migration of teeth in the edentulous spaces, supraeruption of opposing teeth, loss of vertical dimension, and impaired ability to masticate. Thus, early replacement and rehabilitation of lost structures become the ultimate goal of prosthodontic therapy.
Various types of prosthetic options are available for rehabilitation of partially edentulous arches, which include removable partial dentures (RPD), a tooth-supported fixed partial denture (FPD), as well as implant-supported FPDs. In certain situations, especially with a long length of the edentulous span, excessive ridge resorption, or due to financial constraints, it contraindicates a FPD treatment, or when a patient has a guarded prognosis for their periodontal condition. RPDs are also a good and an economical way of replacing lost structures.
Methods used in the fabrication of cast partial dentures can be either conventional lost-wax technique or the latest method of digital-based manufacturing.
Conventional lost-wax technique for cast partial denture frameworks uses a conventional casting wax, which is adapted on the refractory cast which has to be made by process of duplication of the blocked out master cast where the refractory cast along with the wax pattern is invested for the lost-wax technique. The other method uses the recently introduced light-cure wax that can be adapted directly on the master cast without the need for duplication as it can be removed and directly invested without distortion after curing it in the light-cure chamber. The final accuracy of the casting can be affected by the multiple steps involved with the conventional casting wax. Thus, the purpose of this study was to determine and compare the dimensional accuracy of the casted frameworks between the two different types of groups, that is, the conventional pattern casting wax and light-cure wax.
| Materials and Methods|| |
The study was carried out with the null hypothesis that there is no statistically significant difference in the cast partial denture frameworks fabricated by conventional casting wax and light-cure wax.
A total of 30 samples (cast partial denture framework) divided into two groups as follows: Group 1-Conventional casting wax (Bego, GmbH and Co. KG), Group 2-Light-cure wax (LiWa, Willmann and Pein GmbH), were selected for the study.
A metal die [Figure 1] simulating Kennedy's Class III, modification 1 clinical situation was created onto which four depressions at specific locations equidistant from the midline were made for the assessing linear dimensional change, from which a silicone mold was eventually made. 15 refractory casts using phosphate bonded investment (Wirovest. Bego, GmbH and Co. KG) and 15 master casts using type III dental stone were poured from the silicone mold. The refractory casts were then subsequently hardened at 250°C and dipped in cast hardening solution onto which the casting wax was adapted. The light-cure wax was adapted directly onto the master cast coated with the isolating liquids and polymerized in the light-curing chamber (LiWa Light with light source-2 PL-S 9W, Willmann and Pein GmbH) for 4 min, which was removed and polymerized again for 4 min to cure the intaglio surface. Investing and casting of both the wax patterns were then carried out, using phosphate bonded investment and cobalt-chromium alloy (Girochrom, Amann Girrbach AG), respectively. After casting, the frameworks were retrieved, evaluated and then finished and polished.
The dimensional accuracy was measured in terms of dimensional fit and linear dimensional change. The dimensional fit was checked by assessing the gap between the palatal major connector and the palatal portion of the metal master die. Pattern resin (GC Corporation), was mixed and once it reached a dough stage it was finger adapted on the intaglio surface of the framework which was seated and proper seating of the framework on the master die was ensured, and excess was removed. Following polymerization, the framework was removed, and the thickness of pattern resin was checked at five different points: at midline, at 5 mm, and at 10 mm on either side of the midline under a stereomicroscope (×10, Labomed, SZ-790, SL. No. 97036). The linear dimensional change was checked by measuring the distance using a digital caliper (0–150 mm, Mitutoyo, Japan, 150199) between the 2 extreme depressions on the metal die and the same distance of the corresponding elevations on the frameworks. The difference between the two yielded the linear dimensional change.
| Results|| |
The data obtained was subjected to statistical analysis using SPSS software version 19 (IBM Corp: Armonk, NY). Independent t-test was used to draw a comparison between the mean scores of the two groups for dimensional fit as well as linear dimensional change.
Group 1 and Group 2 denote the cast partial denture frameworks fabricated by conventional casting wax and the light-cure wax, respectively.
Comparison of both the study groups was carried out using independent t-test. The comparison showed a significant result for Group 2 as compared to Group 1 in the region 5 mm right of the midline (P = 0.0279*). However, an overall comparison indicated an insignificant difference (P = 0.0619) [Table 1].
|Table 1: Comparison of dimensional fit between the metal die and the framework of conventional wax patterns and light cure wax patterns|
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Group 1 and Group 2 denote the cast partial denture frameworks fabricated by conventional casting wax and the light-cure wax, respectively.
Comparison between the two groups with respect to mean linear dimensional change after subjecting to independent t-test indicated an insignificant result (P = 0.2043) [Table 2].
|Table 2: Comparison of the mean linear dimensional change between frameworks fabricated with conventional and light cure waxes|
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| Discussion|| |
The results of the current study supported the null hypotheses in that the pattern material, whether conventional wax or light cure, had no statistically significant effect on the dimensional accuracy of the final frameworks.
Most common method for fabrication of RPD employs the use of metal alloys for construction of a metallic framework due to their strength, hardness, less bulk, and good thermal conductivity. The routinely followed technique uses an adaptation of conventional casting wax on refractory casts that are obtained through a duplicating procedure. The accuracy of fit of dental castings is of utmost importance when it comes to the success of any prosthodontic treatment such as crowns, inlays, and onlays, and posts and cores as well as overdenture copings, and cast partial denture frameworks. One of the main causes of dental casting inaccuracy is a distortion of wax patterns used for these dental restorations which are detrimental to the accuracy of fit of the completed casting in the patient's mouth and may cause a major problem in the overall success of the prosthodontic or restorative treatment for the patient.
The procedure for fabrication of frameworks using conventional casting wax can be quite cumbersome, time-consuming, and the multiple steps involved may intensify the inherent dimensional inaccuracy of the wax. Improper fit in these frameworks can cause discomfort to the patient, resulting in delayed adaptation to the denture and dissatisfaction. Since delivery of occlusal forces to the palatal tissues is to be expected, part of the function of the denture is jeopardized. Furthermore, the intimate contact between the metal connectors and the palatal tissues, in addition to their wide mucosal coverage, enhances the support, retention, and stability of the denture.
Various methods and procedures have been advocated, and attempts are ongoing to improve casting accuracy and fit of RPD frameworks. Some of these attempts depend on innovations and developments in the materials used for the fabrication of these frameworks. One of such innovations is the development of light-cure wax.
No studies so far have been performed to evaluate and compare the dimensional fit as well as the linear dimensional change in the castings produced by the two types of frameworks.
Thus, the current study compared the recently introduced light-cure patterns, with the traditional conventional wax patterns for the above-mentioned parameters.
For the validity and reliability of the results, laboratory procedures were performed in one dental laboratory by one clinician to ensure the same laboratory environment and conditions, and to eliminate human error. All materials were used according to the manufacturers' instructions. Other factors apart from wax distortion affecting the casting accuracy such as the effect of type of investment material, burnout temperature, type of alloy, and casting shrinkage were standardized as per the recommendations. Phosphate bonded investment material mixed with special liquid for mold expansion (approximately 2.3%), to compensate for the casting shrinkage of the cobalt–chromium alloy. Phosphate bonded investment material was used for refractory casts as well as, as an investment material to invest the wax patterns as they can withstand high casting temperatures (above 1100°C), which were then kept for burnout after 1 h of mixing  at room temperature until 950°C. Cobalt–chromium alloy was used for all castings. As all the frameworks had to be fitted on the same cast to determine their accuracy for the purpose of standardization, a metal die was constructed for the same to prevent abrasion of the teeth due to the repeated seating of these frameworks on the die. However, as this metallic die does not allow for any tooth movement as may be seen intraorally to compensate for the tight fit of the framework, more amount of distortion could have been observed than on a stone cast or in the mouth.
Following fabrication of frameworks, each framework was checked for a satisfactory seating on the metal die. Visual inspection of the frameworks revealed adequate fit and adaptation in the rest seat area. However, the visible gap was seen for both type of frameworks between the palatal major connector and the mater metal die, indicating a discrepancy in the fit the framework. In this study, pattern resin was used as the interposing material owing to its low polymerization shrinkage, high dimensional stability, and favorable flow, thickness of which was checked under a stereomicroscope (×10 magnification) due to easier accessibility to the instrument. Even though the mean gap found was lesser for the conventional group (748.25 μm) than the light-cure group (794.02 μm), no statistically significant difference was found between the two types of frameworks except at one point, that is 5 mm right to the midline where a statistically significant difference was found (P = 0.0279). This study, however, contradicts the results of the study performed by Mohammad Tarek M. Anan, Mohannad H. Al-Saadi, where, the mean gap value was significantly smaller in the LCMT (light-curing modeling material technique) group compared to the TT (traditional technique) group., As they have used a metal model of a Kennedy class III modification 1 mandibular dental arch and used a digital camera to assess fit, with two edentulous spaces of different spans, short and long, a comparison cannot be drawn between the two studies.
The reason for difference more discrepancy in fit of the light-cure group can be attributed to the stickiness of the light-cure wax compromising the adaptability of this wax.
The results of the current study also showed lesser linear dimensional change in light-cure group (0.63 mm) as compared to the conventional group (0.78 mm) which can be attributed to the fact the light-cure patterns were fabricated directly on the master cast, eliminating the influence of duplicating procedures on the castings;, however, no significant difference between the two types of frameworks was found.
In making a choice between these two materials, it should be considered that conventional wax patterns are easy to handle and do not require the use of any special armamentarium. Light-cure patterns, however, require a special light polymerizing unit and handling of the material can be quite difficult due to their stickiness and thus need precision in adapting them. The polymerized patterns should also be cautiously removed from the cast and handled carefully as excessive force may break them. All of these factors add to the expenses of the final prosthesis. However, light-cure patterns also offer several advantages, as already mentioned earlier. The preference between the two materials, therefore, depends on factors such as time, material and equipment availability, as well as financial factors.
| Conclusion|| |
Within the limitations of the study, it was concluded that there was no statistically significant difference between the dimensional accuracy (dimensional fit, linear dimensional change) of the frameworks fabricated using conventional casting wax and light-cure wax. The dimensional fit obtained was higher with that of the conventional group, whereas the linear dimensional change was observed lesser with the light-cure group; however, the difference was insignificant.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]