Effect of the Use of Die Lubricant on the Marginal Fit of Wax Patterns.

The aim of this study was to evaluate the effect of die lubricant on the fit of wax patterns. An ivorine tooth was prepared to receive full-coverage metal-ceramic restoration with 360° shoulder finish line. The tooth was duplicated 40 times using additional silicone. The impression was poured with Type IV dental stone. These 40 dies were divided into 2 groups 20 each. Group A: The patterns were fabricated with the use of die lubricant. Group B: The patterns were fabricated without the use of die lubricant. Later, these patterns were sequentially checked for the marginal fit on the stereomicroscope. The readings from the stereomicroscope were tabulated; independent Student's t-test was used to compare the marginal fit between Group A and Group B. The mean gap on all four tooth surfaces in Group A (with use of die lubricant) was more compared to Group B (without use of die lubricant).
CONCLUSION: Die lubricant definitely has their effect on fit of the wax pattern which later might be duplicated in the casting. Copyright:

INTRODUCTION

It is the natures rule that we constantly evolve, and become a better version of what we are today.

Prosthodontics is not an exception to this rule, in which we strive to give the patient a prosthesis which is as close to the nature as possible. In doing so, we evaluate the prosthesis on many grounds such as mechanical, esthetic, and longevity.

Marginal fit of a restoration is one of the important parameters of a restoration from the success point of view.

The minimization of crown and fixed partial denture marginal gaps is an important goal in prosthodontics. Smaller marginal gaps produce less gingival irritation[12] and cement washout,[34] improving the clinical outcome and longevity of the restoration. The absolute value of the vertical marginal gap deemed to be clinically acceptable has been debated in the literature with proposed values ranging from 39 to 120 μm.[5] A definitive value has not been identified as the benchmark for clinical acceptability because clinical identification and quantification of the gap can be difficult[6] depending on location[5] and instrumentation used.[78]

Appropriate marginal fit is required for successful restoration. Despite the technological advancements in terms of the improvement of casting techniques, die fabrication,[9] waxing pattern[10] and coping fabrication,[11121314] a discrepancy remains between the restoration's margin and the cervical edge of the prepared tooth. This discrepancy will be taken up by cement which are used for luting, this cement has variable degradation rate in oral cavity. This degradation eventually will result in the formation of gap between the restoration and the tooth surface which will lead to accumulation of plaque that will harbor microbes which might lead to an eventful sequence of caries or poor periodontal health. To avoid this, the marginal fit should always be in the prescribed value of 120 μ.

It is the natures rule that we constantly evolve, and become a better version of what we are today. Die lubricants are applied uniformly all over the prepared die surface. Therefore, they are bound to have their effect on the marginal fit of the restoration. Our aim for this study is to evaluate the effect of application of wax separators on the marginal fit of wax patterns.

The null hypothesis for our study was that there is no effect of die lubricant on the fit of wax patterns.

MATERIALS AND METHODS

An ivorine tooth was mounted and prepared with diamond points to receive a full-coverage metal-ceramic preparation. A 360° shoulder finish line was obtained.

The ivorine tooth was later duplicated 40 times with additional silicone. The impression of the tooth was later poured into Type IV dental stone to obtain 40 identical dies.

The 40 dies then were randomly divided into two groups:

Group A: Wax patterns were fabricated with the use of die lubricant

Group B: Wax patterns were fabricated without the use of die lubricant.

A total of 40 dies were used in the study. Die hardener was sequentially applied on all the dies.

Later, all the dies were coated with two layers of die spacer which was applied 1 mm away from the finish line. Pico-Fit (Renfert, Hilzingen, Germany) die spacer system was used in the study [Figure 1].

Figure 1

Die lubricant

The dies in the Group A were then coated with the die lubricant, pico-sep (Renfert, Hilzingen, Germany) system was used in the study [Figure 2].

Figure 2

Application of Die Lubricant

All the patterns for coping were fabricated for Group A and B [Figure 3].

Figure 3

Group A and Group B (wax patterns)

The patterns were later removed and placed back on the die once. Later, the patterns were checked for the marginal under a stereomicroscope for the marginal fit [Figure 4].

Figure 4

Wax pattern under stereomicroscope

RESULTS

Gap on surfaces with the use of die lubricant on buccal surface ranged between 78.1 and 315 μ with a mean of 159.1 μ. On distal surface, gap ranged between 59.4 and 294.4 μ having a mean of 127.6 μ. Lingual tooth surface had gap between 65.3 and 241.4 μ with a mean of 140.5 μ. While on the mesial surface, the gap was within 54.5–176.8 μ having a mean of 132.7 μ.

95% CI of mean indicates that statistically, that there is a 95% chance of the mean will be lying within the range of lower and upper limit [Table 1]

Table 1

Descriptive findings of gap (μ) in Group A (n=20) at tooth surfaces

Tooth surfaces	Minimum	Maximum	Mean	95% CI of mean
Buccal	78.1	315.0	159.1	130.2-187.9
Distal	59.4	294.4	127.6	101-154.2
Lingual	65.3	241.4	140.5	121.4-159.6
Mesial	52.5	176.8	132.7	115.5-149.9

CI: Confidence interval

With the use of die lubricant, the 95% confidence limit of a mean gap on the buccal surface was 130.2 to 187.9 μ; on the Distal surface, it was 101 to 154.2 μ; on the lingual surface, it was 121.4 to 159.6 μ; and on the mesial surface, the gap was 115.5 to 149.9 μ [Table 2].

Table 2

Descriptive findings of gap (μ) in Group B (n=20) at tooth surfaces

Tooth surfaces	Minimum	Maximum	Mean	95% CI of mean (range)
Buccal	9.8	195.0	45.6	26.2-65.1
Distal	9.8	88.4	37.7	28.1-47.2
Lingual	9.8	72.8	32	24-40
Mesial	9.8	83.8	37.1	26.7-47.6

CI: Confidence interval

In Group B, the gap on tooth surfaces without use of die lubricant on the buccal surface was within 9.8–195 μ range with a mean gap of 45.6 μ. On the distal surface, the gap was within 9.8–88.4 μ having a mean of 37.7 μ. On the lingual tooth surface, the gap ranged between 9.8 and 72.8 μ with 32 μ mean. On the mesial surface, the gap was within 9.8–83.8 μ having a mean gap of 37.1 μ.

Without the use of die lubricant, the 95% confidence limit of the mean gap on buccal tooth surface was 26.2–65.1 μ; on the distal tooth surface, it was 28.1–47.2 μ; on the lingual surface, it was 24–40 μ; and on a mesial tooth surface, the gap was 26.7–47.6 μ.

The mean gap on all four tooth surfaces in Group A (with use of die lubricant) was more compared to Group B (without use of die lubricant).

The mean gap in Group A was more than Group B with a mean difference of 113.4 μ on buccal surface, 90 μ on the distal tooth surface, 108.5 μ on lingual, and 95.5 μ on the mesial surface [Table 3].

Table 3

Comparison of gap (μ) in between Group A and Group B - independent sample test

Surfaces	Mean±SD		t	P	Mean difference	95% CI of the difference (LB-UB)
	Group A	Group B
Buccal	159.1±61.6	45.6±41.6	6.824	<0.001	113.4	79.8-147.1
Distal	127.6±56.8	37.7±20.4	6.664	<0.001	90.0	62.6-117.3
Lingual	140.5±40.9	32.0±17.1	10.959	<0.001	108.5	88.5-128.6
Mesial	132.7±36.8	37.1±22.3	9.930	<0.001	95.5	76.1-115.0

CI: Confidence interval, LB: Lower bound, UB: Upper bound, SD: Standard deviation

There was a statistically very highly significant (P < 0.001) difference of mean gap between Group A and Group B on all four tooth surfaces, being greater in Group A than Group B.

95% CI of the mean difference on the gap in between Group A and Group B ranged within 79.8–147.1 μ on the buccal tooth surface, 62.6–117.3 μ on the distal tooth surface, 88.5–128.6 μ on the lingual surface, and 76.1–115 μ on the mesial surface.

On statistical comparison of the mean gap on tooth surfaces in between with die lubricant (Group A) and without die lubricant (Group B):

There is a mean difference with a gap in Group A more than Group B, which is statistically very highly significant (P < 0.001)

95% times (cases) the greater mean difference of gap of Group A will be lying within the lower and upper limit.

DISCUSSION

The result of the study indicates that there was a statistically significant difference between marginal fit of patterns fabricated with die lubricant and without die lubricant. Thus, we reject the null hypothesis which states that there is no difference between Group A and Group B.

Conventional casting procedure has a number of steps which are very critical, if not handled properly they can lead to the introduction of discrepancies which are later duplicated in the final restoration.

Since the time of its introduction, the lost-wax technique has been a very technique sensitive procedure. None of the steps should be fallen short of perfection to get the best result.

In the study, we have fabricated the patterns and tried to check for the fit immediately. However as we have used pattern wax for the fabrication of wax patterns, they are bound to introduce some discrepancies due to the release of internal stress.

Some of the readings can be attributed to such discrepancies. Inlay pattern wax is used to fabricate wax patterns on the die. Inlay pattern wax when used with adherence to the principles of pattern fabrication can be the pattern material of choice to produce a casting with minimal marginal and internal discrepancy which is user-friendly and cost-effective.[15]

With the introduction of newer technology, we have tried to overcome the short comings of the previous techniques. Introduction of CAD/CAM in mid-1980's was one of the pioneer step in dentistry. CAD/CAM has simplified a number of steps for fabrication of a restoration, and we are able to consistently produce restoration of better quality every single time.

Studies done by Tamac et al.,[16] Han et al.,[17] Kokubo et al.,[18] Yuksel and Zaimoglu,[19] and Beuer et al.[20] have consistently shown that it is possible to fabricate restoration by CAD/CAM which have a marginal fit well below the acceptable value of 120 μ.

CONCLUSION

Thus, we can conclude that die lubricants definitely have their effect on fit of the wax patterns; with the introduction of new technology, we can overcome these shortcomings.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.