Abstract
Statement of problem
Studies assessing the comparative denture base adaptation performance of the pour technique for various palatal vault depths are sparse.
Purpose
The purpose of this in vitro study was to investigate the denture base adaptation performance of the pour technique compared with other conventional fabrication techniques (light-polymerization, injection, compression molding) for shallow and deep palatal vault depths.
Material and methods
Edentulous maxillary study models with 2 palatal vault depths were prepared. Based on the power analysis, the sample size of each conventional fabrication technique was 12 (N=96). After denture bases for each technique had been fabricated on the casts according to the manufacturers’ recommendations, the casts and the intaglio surfaces of the denture bases were scanned by using a laboratory scanner (InEos X5). The standard tessellation language (STL) files of the casts and the intaglio surfaces of acrylic resin bases were transferred into a software program (Romexis, version 5.0), and the software superimposed each cast and its corresponding denture base scan with the reference pyramids semi-automatically. After superimposition, the mean gap distances (mm) were calculated by using the software and recorded from the identified 4 specific regions (denture border apex, palate, ridge crest, and posterior palatal seal). A statistical analysis was performed by using the 3-factor factorial ANOVA. Post hoc comparisons among the subgroups were performed by using the Tukey HSD test.
Results
Two- and 3-way interactions among palatal vault depth, polymerization technique, and location variables were statistically significant ( P <.05). For shallow palatal vault depth, injection and pour polymerization techniques demonstrated similar mean gap distances irrespective of location ( P >.05). The light-polymerization technique showed the highest mean gap distances among the tested polymerization techniques in all regions except for the posterior palatal seal area ( P <.05).
Conclusions
The pour technique showed similar denture base adaptation to compression molding and injection. Light-polymerization exhibited the highest mean gap distance between the denture base and the cast for both palatal vault depths for most of the locations. A deep palatal vault depth led to inferior denture base adaptation performance for light-polymerization in the ridge crest and compression molding in the posterior palatal seal location.
While innovative techniques have been developed for the fabrication of complete dentures, cost efficiency and ease of production are still important factors. Therefore, the pour technique is a viable alternative for clinicians and dental technicians for its acceptable denture adaptation performance, decreased processing time, and cost of fabrication.
Since the late 1930s, polymethyl methacrylate (PMMA) has been used as a base material for complete dentures. , Fabrication techniques for complete dentures have included compression molding (pack and press), fluid resin (pour) technique, and injection molding, , with compression and injection molding being the most commonly used polymerization methods. The pour technique has the advantage of decreased processing time; however, disadvantages including denture tooth movement during polymerization and lack of bonding between denture teeth and the base material have been reported. By combining the advantages of heat-polymerization with the reduced processing time of the pour technique, injection molding may increase the accuracy and stability of the denture bases; however, this technique is more expensive than the other conventional processing techniques. Additional polymer materials instead of PMMA have been used as denture base, and urethane dimethacrylate (UDMA)-based, visible light-polymerized resin (Eclipse; Dentsply Sirona) has been claimed by the manufacturer to have advantages including no residual methyl methacrylate monomer, ease of manipulation and fabrication, and increased dimensional accuracy compared with conventional heat-polymerized PMMA. , In recent years, computer-aided design and computer-aided manufacturing (CAD-CAM) methods have become popular for the fabrication of complete dentures, although traditional processing still dominates.
The palatal vault depth, classified as shallow, medium, and deep, may affect denture base adaptation. , Sekar et al compared the palatal adaptation of denture bases produced by injection or compression molding for the shallow and deep palatal vaults. They reported that the fabrication technique and material choice play a bigger role than the shape of the vault when evaluating the palatal adaptation of the denture.
The dimensional stability and adaptation of denture base materials have been evaluated by using different techniques. , , Recently, laser and contact scanners have become popular for measuring the dimensional changes of denture bases with the help of different software programs to analyze the processing deformation. ,
Data evaluating the effect of the pour technique and palatal vault depth differences on the performance of complete denture base adaptation are lacking. The purpose of this in vitro study was to compare the denture adaptation of the pour technique with that of conventional light-polymerization, injection molding, and compression molding fabrication techniques for shallow and deep palatal vaults. The null hypotheses were that the pour technique would have similar denture adaptation performance to the other fabrication techniques and that the palatal vault depth would not affect the adaptation of the complete denture base.
Material and methods
Two identical edentulous maxillary study models in Type A residual ridge morphology according to the American College of Prosthodontists classification were prepared and then modified to obtain 2 types of palatal depth configurations by using the method suggested by Avci and Iplikçioğlu. The vertical distances at which the midpoint of the line connects the hamular notches and crosses the palatal vault of the duplicated study models were adjusted to 12 mm for shallow and 20 mm for deep palatal form. The palatal vault depths of the models were modified by adding baseplate wax on the palatal surfaces of the casts so that only the palatal depth was changed, and the ridge configuration was maintained. After adjusting the palatal depth of the models, 3 reference pyramids were added, 2 on the crest of the ridges over each tuberosity and 1 on the anterior crest of the ridge at the midline. These pyramids were used to superimpose the scans of the casts and the corresponding denture bases and to ensure that the measurements were made at the same locations.
Two rubber molds (Klas Dental) were obtained from 2 modified study models with deep and shallow palatal depths to reproduce the models. Based on the power analysis with a 0.8 power factor and 0.01 significance level, the sample size of each test group was 12 (N=96). Definitive casts were poured in Type IV gypsum (Elite Stone; Zhermack). The casts were allocated into 8 test groups according to 2 palatal depths and 4 fabrication techniques ( Table 1 ).
| Palatal Vault Depth | Fabrication Technique | Product Information | n |
|---|---|---|---|
| Deep and Shallow | Injection | IvoBase Hybrid; Ivoclar Vivadent AG | 12+12 |
| Deep and Shallow | Compression molding | Integra Heat Cure Acrylic; Birlesik Grup Dental | 12+12 |
| Deep and Shallow | Pour | Futura Basic Cold; Schütz Dental GmbH | 12+12 |
| Deep and Shallow | Light-polymerization | Eclipse; Dentsply Sirona | 12+12 |
Each definitive cast was allowed to dry completely for 24 hours and was scanned by using a laboratory scanner (InEos X5; Dentsply Sirona) to generate a standard tessellation language (STL) file. For fabrication of the bases, 2 layers of 1-mm modeling wax (Jewellery normal modeling wax; Cera Reus) were adapted on each cast, , and the thickness of the wax was verified by using a scored periodontal probe. This procedure was repeated for all specimens except for the light-polymerization group, where a sheet of UDMA-containing baseplate (Eclipse Resin Materials-Upper Baseplate Resin; Dentsply Sirona) was manually adapted on the cast and polymerized immediately by using a visible light source unit (Eclipse Junior VLC curing unit; Dentsply Sirona). The intaglio surfaces of each completed acrylic resin base were coated with a thin layer of scanning preparation spray (CEREC Optispray; Dentsply, Sirona) by using a uniform dosage and particle size of 40 to 60 μm. Then, the intaglio surfaces of the acrylic resin bases were digitized by using a laboratory scanner (InEos X5; Dentsply Sirona). The STL files of the casts and the intaglio surfaces of acrylic resin bases were transferred into a software program (Romexis, v5.0; Planmeca) to superimpose each cast and its corresponding denture base scan semi-automatically on to the reference pyramids. After superimposition, 4 specific regions of interest were defined as the denture border apex, palate, ridge crest, and posterior palatal seal. The measurements between the cast and the denture base were made at 500 points for each acrylic resin base by using an overlay guide to verify the location of the measurements. The mean gap distances (mm) were automatically calculated by using the software and recorded by an observer (K.O.) from the identified regions. The surface matching and measurements provided the basis for the evaluation of discrepancies along with the acrylic resin bases.
Statistical analysis was performed by 3-factor ANOVA. Two between-group variables (palatal vault depth and fabrication technique) and 1 within-group variable (measurement location) were used. As the triple interactions were significant ( P <.05), post hoc comparisons among the subgroups were performed by using the Tukey HSD test.
Results
The 3-factorial ANOVA showed that 2- and 3-way interactions among the palatal vault depth, polymerization technique, and location variables were statistically significant ( P <.05) ( Table 2 ). The results of post hoc analysis for deep palatal vault depth are shown in Table 3 . Light-polymerization showed the highest mean gap distance among the tested polymerization techniques in all regions except for the posterior palatal seal area ( P <.05). At the denture border apex and palate, the gap distances obtained for injection, compression molding, and pour techniques were not statistically different from each other ( P >.05). In the ridge crest area, the mean gap distance of injection was significantly lower than that of the other polymerization techniques ( P <.05). At the posterior palatal seal region, compression molding showed the highest mean interface gap distance, while the injection technique showed the lowest mean value among the tested polymerization techniques ( P <.05).
| Source | SS | df | MS | F | P |
|---|---|---|---|---|---|
| Palatal vault depth | 0.465 | 1 | 0.465 | 4.471 | .035 |
| Technique | 68.544 | 3 | 22.848 | 219.491 | <.001 |
| Location | 1.885 | 3 | 0.628 | 6.036 | .001 |
| Depth×technique | 3.914 | 3 | 1.305 | 12.535 | <.001 |
| Depth×location | 0.962 | 3 | 0.321 | 3.079 | .028 |
| Technique×location | 19.602 | 9 | 2.178 | 20.923 | <.001 |
| Depth×technique×location | 8.869 | 9 | 0.985 | 9.467 | <.001 |
| Error | 36.850 | 354 | 0.104 | — | — |
| Total | 925.303 | 386 | — | — | — |
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