Effect of ring length and diameter on effective radial setting expansion

The Effect of Casting Ring Liner Length and Prewetting on the Marginal Adaptation and Dimensional Accuracy of Full Crown Castings

Aim:

To evaluate the effect of varying cellulose casting ring liner length and its prewetting on the marginal adaptation and dimensional accuracy of full veneer metal castings.

Materials and Methods:

The master die was milled in stainless steel to fabricate the wax pattern. Sixty wax patterns were fabricated with a uniform thickness of 1.5 mm at an occlusal surface and 1 mm axial surface, cervical width at 13.5 mm, and 10 mm cuspal height. The samples were divided into six groups (n = 10). Groups I and II samples had the full-length cellulose prewet and dry ring liner, respectively. The groups III and IV had 2 mm short prewet and dry cellulose ring liner, respectively, whereas groups V and VI were invested in 6 mm short ring liner. The wax patterns were immediately invested in phosphate bonded investment, and casting procedure was completed with nickel-chrome alloy. The castings were cleaned and mean score of measurements at four reference points for marginal adaption, casting height, and cervical width was calculated. The marginal adaption was calculated with Imaje J software, whereas the casting height and cervical width was determined using a digital scale. The data was subjected to one-way analysis of varaince and Tukey post hoc statistical analysis with Statistical Package for the Social Sciences version 20 software.

Results:

The group II had the best marginal adaption with a gap of 63.786 μm followed by group I (65.185 μm), group IV (87.740 μm), and group III (101.455 μm). A large marginal gap was observed in group V at 188.871 μm. Cuspal height was more accurate with group V (10.428 mm), group VI (10.421 mm), and group II (10.488 mm). The cervical width was approximately similar in group I, group III, and group V. Statistically significant difference was observed in Tukey post hoc analysis between group V and group VI with all the other groups with regards to marginal adaptation.

Conclusion:

The dry cellulose ring liners provided better marginal adaptation in comparison to prewet cellulose ring liners. Accurate cuspal height was obtained with shorter ring liner in comparison to full-length cellulose ring liners.

Effect of ring liner and casting ring temperature on the dimension of cast posts

STATEMENT OF PROBLEM

If a post does not fit passively, binding with the radicular tooth structure occurs, possibly increasing the risk for root fracture. Therefore, it is necessary to fabricate slightly undersized cast posts to allow for passive fit and cement placement. Shrinkage of the mold cavity may be a desired effect during the casting of posts.

PURPOSE

This study evaluated the influence of: (1) a cellulose ring liner, and (2) a lower casting temperature of the metal ring, on the dimensions of a cast post.

MATERIAL AND METHODS

Eighty plastic posts were divided in 4 equal groups (group 1, 815 degrees C, liner; group 2, 815 degrees C, no liner; group 3, 600 degrees C, liner; and group 4, 600 degrees C, no liner), invested in phosphate-bonded investment and cast with a noble alloy. Posts were measured at 2 locations, the tip and base, before and after casting.

RESULTS

Investing in a lined metal ring and using a casting ring temperature of 815 degrees C (group 1) resulted in markedly oversized posts (tip: +25.8 microm; base: +20.3 microm). The absence of the cellulose liner in the casting ring (group 2) decreased the expansion of the investment producing slightly oversized castings (tip: +9.75 microm; base: +4.52 microm). Lined rings that were heated to a final temperature of 600 degrees C (group 3) produced posts that were oversized (tip: +16.65 microm; base: +11.05 microm). Final casting ring temperature of 600 degrees C and the absence of a cellulose liner (group 4) resulted in posts slightly undersized (tip: -4.1 microm; base: -2.2 microm).

CONCLUSION

The use of 2 casting ring temperatures (815 degrees C or 600 degrees C) and the influence of a ring liner were investigated. Decreasing the casting ring temperature from 815 degrees C to 600 degrees C and the absence of a ring liner significantly decreased the dimensions of a cast post.

Effect of wet and dry cellulose ring liners on setting expansion and compressive strength of a gypsum-bonded investment

Effective setting expansion of gypsum-bonded investments is influenced by many variables. The purpose of this study was to determine the effect of using either water-saturated or dry cellulose ring lining material on (1) the fit of castings on a steel die and (2) the compressive strengths of investment cores using either type of liner. The mean gingival space in the water-saturated liner group was 0.241 +/- 0.048 mm and was 0.071 +/- 0.029 mm in the dry liner group (p < 0.001). The compressive strengths of investment cores from the dry liner group were 36.5% greater than those of cores from the water-saturated liner group. The results demonstrated that the use of dry liners may improve the fit of castings to dies.

Effect of denture wax-pattern position on radial setting expansion

Th dynamics of the setting expansion of gypsum-bonded investment is complicated by many variables and not well understood. The purposes of this study were to examine the fluid mechanics of the flow of investment during setting and to determine if the presence of wax patterns influences effective setting expansion. Mesial-occlusal-distal (MOD) inlay wax patterns were invested at six different radial positions and four different axial positions in plastics casting rings. Total expansion was determined by using xeroradiography. Combined results of radial expansion data at different axial and radial locations within casting rings suggest that expansion of gypsum-bonded investment may represent a variant of the laminar flow of a viscous fluid.