Abstract
Statement of problem.
The weight of larger obturators places increased stress on the supportive teeth and bearing tissue and allows gravity to act as a dislodging factor affecting the stability and retention of the prosthesis. However, whether conventionally processed and 3-dimensionally (3D) printed hollow obturators have similar reduced weights compared with solid obturators is unclear.
Purpose.
The purpose of this in vitro study was to evaluate the weight difference between conventionally heat-processed complete denture obturators with and without hollowing and 3D printed obturators with a hollow bulb.
Material and methods.
Obturators were fabricated as conventionally heat-processed solid obturators, conventionally heat-processed with a hollow obturator bulb, and 3D printed with a hollow obturator bulb. Nine obturator prostheses were fabricated for each type of Aramany Class I, Class II, and Class III defect. The weights of each of the 27 obturator prostheses were measured, and a statistical analysis was performed with exact versions of the Kruskal-Wallis test or Wilcoxon Rank Sum test (α=.05).
Results.
Conventionally heat-processed solid obturators were significantly heavier than the conventionally heat-processed hollow (P<.001) or the 3D printed hollow obturators (P<.001). No significant difference (P=.222) was found between the conventionally heat-processed hollow and 3D printed hollow obturators. The decrease in weight was proportional to the size of the defect with the Aramany Class I defect having the largest differences in weight between the different fabrication methods, followed by Class II, and then Class III with a much smaller defect.
Conclusions.
Additive manufacturing could be a suitable alternative to conventional techniques for the fabrication of a closed hollow obturator because of the comparable weights.
An obturator plays an essential role in patients with congenital or acquired tissue openings as a result of oral cancer or maxillary trauma by improving daily functions and overall quality of life.1 Large oronasal defects that require extensions of the prosthesis into a broader opening to improve the seal and retention of the obturator lead to increased prosthesis weight, which may put high stress on the supportive teeth and bearing tissue. 2 Gravity also tends to act as a dislodging factor that affects the stability and retention of a heavy prosthesis, especially in patients who are edentulous with no implant retention.2 Various techniques and materials have been described to fabricate a closed hollow obturator.3–22 Wu et al23 reported that hollowing the obturator for patients with a partial maxillectomy led to an obturator with a weight decreased by 6.55% to 33.06% depending on the size of the defect.
Traditional methods of obturator fabrication required highly skilled laboratory technicians performing time-consuming and technique-sensitive methods.2 The prostheses were often less-than-ideal because of the difficulty of connecting the hollow portion of the obturator to the base or sealing vent holes using autopolymerizing acrylic resin.24 Poor adhesion at the joined parts or air bubbles in the autopolymerizing resin would disrupt the seal and allow saliva, water, and bacteria to enter the hollow section, making it unsanitary and causing malodor, decreasing esthetics, and increasing weight.24 This contamination can also become a source for infection and aspiration pneumonia due to the inner space of the obturator acting as a bacterial reservoir.25
The digital workflow has become established in maxillofacial prosthetics. It allows scanning technologies to be used to capture data, which is imported into a computer-aided design (CAD) software program used to manufacture structures in a suitable material through computer-aided manufacturing (CAM) via subtractive methods (milling) and more recently with additive 3-dimensional (3D) printing.26 A significant advantage of 3D printing is that a single-piece hollow prosthesis can be formed with no joints. In addition, improved control of the overall material thickness, colors, and materials can be customized in specific areas of the printed prosthesis.27,28 Disadvantages of additive manufacturing include the high cost of the machines and software programs, the need for postprocessing and polishing because of the step effect of layered production, the limitations in materials that can be used, and the sensitivity to inconsistencies in the standard tessellation language (STL) file.27,28 Studies evaluating the accuracy and properties of 3D printed hollow obturators are sparse.2,24,29–31
This study aimed to evaluate the weight difference between conventionally heat-processed complete denture obturators with and without hollowing and 3D printed obturators with a hollow obturator bulb. The null hypothesis was that the 3D printed technique would not affect the weight of an obturator prosthesis.
MATERIAL AND METHODS
An edentulous model mold (Nissin Dental Model; Kilgore International Inc) was used to fabricate 3 identical maxillary edentulous casts in Type IV stone (Silky-Rock; Whip Mix Corp). Maxillary defects based on the Aramany classification for partially edentulous maxillectomy arches were drawn and carved out to simulate defects for a Class I (midline resection), Class II (unilateral resection), and Class III (central resection) patient.32 The simulated defect casts were duplicated by using addition vulcanizing duplication silicone (Z-Dupe; Henry Schein) in order to pour multiple casts of the simulated defects for conventional processing (Fig. 1A). Six casts were poured in Type III stone (Denstone, Modern Materials; Kulzer GmbH) for each of the 3 simulated defects (Fig. 1B).
Figure 1.
Fabricating simulated defect casts A, Simulated defect casts duplicated in addition vulcanizing duplication silicone. B, Type III stone casts used for conventional processing.
For the conventionally heat-processed solid obturator group (n=9), 3 duplicate casts were poured in Type III stone (Denstone, Modern Materials; Kulzer GmbH) by using the silicone duplicate matrices of each of the 3 simulated defects. Two sheets of approximately 1-mm-thick baseplate wax (Mizzy Allcezon Base Plate Wax; Keystone Industries) were overlayed and sealed to each cast, providing a wax pattern for the obturator. The defect was also filled with wax to make it flush with the rest of the cameo surface of the wax pattern for the solid obturator (Fig. 2). The casts were flasked, allowed to set, and boiled for wax elimination. After bench cooling, the flasks were separated and packed with a heat-activated polymethyl methacrylate resin (Lucitone 199 Original Shade; Dentsply Sirona). Obturators were then processed using a 2-stage temperature approach to prevent porosity in the center of the bulb area. The first stage of processing was done at 57 °C for 1.5 hours, and the second stage of processing was done at 76 °C for 8 hours. Flasks were allowed to cool completely before the polymerized prostheses were deflasked. The obturators were trimmed and finished using a tungsten carbide bur (H251EF.11.060 HP EF Cutter Carbide; Brassler USA) and polished with a pumice substitute (Dazzle PS; Whip Mix Corp) and a high shine polishing compound (High Shine Polishing Compound; Keystone Industries). Each solid obturator was then labeled using a permanent marker on the intaglio and cameo surfaces with the specimen number, type of fabrication (S = solid conventional), and defect classification (Fig. 3).
Figure 2.
Wax patterns for conventional heat-processing of obturators.
Figure 3.
Conventionally heat-processed solid obturators A, Cameo surface. B, Intaglio surface.
For the conventionally heat-processed hollow obturator group (n=9), a technique was followed similar to that described by Minsley et al.13 Three duplicate casts were poured in Type III stone (Denstone, Modern Materials; Kulzer GmbH) by using the silicone duplicate matrices of each of the 3 simulated defects. Two sheets of approximately 1-mm-thick baseplate wax (Mizzy Allcezon Base Plate Wax; Keystone Industries) were overlayed and sealed to each cast, providing a wax pattern for the obturator. The interiors of the defects were then lined with wax. Flasking and packing was done as described previously. They were then processed at 74 °C for 9 hours. Flasks were allowed to cool completely before the polymerized prostheses were deflasked. The obturators were trimmed and labeled with a permanent marker. The thickness of the walls of the obturator bulb were checked with a digital thickness gauge (iGaging Digital Electronic Thickness Gage; iGaging) to ensure a 2-mm thickness of at least 3 areas and adjusted as necessary (Fig. 4A). A straight tungsten carbide bur (H295E.11.023 HP E-Cutter Carbide; Brassler USA) was modified using a diamond disk (918B.11.220 HP Medium Flexible Coated Double Sided Diamond Disc; Brassler USA) to create a flat head. This modified bur was used to create a recess around the palatal opening of the obturator extension to a 2×2-mm depth and width (Fig. 4B). The interior of the hollow extension was filled with a polyvinyl siloxane laboratory modelling material (Lab-Putty; Coltène) up to the edge of the recess and then coated with petroleum jelly (Vaseline Original; Unilever). Light- and medium-body polyvinyl siloxane (Aquasil Ultra; Dentsply Sirona) were used to make an impression of the obturator opening with a recess for a closure lid. Each impression was labeled to correspond with the respective obturator specimen (Fig. 4C). The impressions were poured in Type III stone (Denstone, Modern Materials; Kulzer GmbH), and wax patterns were made of the lids with baseplate wax (Fig. 4D) and then flasked and processed into heat-activated polymethyl methacrylate resin (Lucitone 199 Original Shade; Dentsply Sirona). The lids were placed over the palatal opening of their respective obturators and trimmed until fully seated. Autopolymerizing polymethyl methacrylate resin (Bosworth TruRepair; Keystone Industries) was then applied to the ledge around the opening of each obturator, and the lids were pressed into position and allowed to bench polymerize. The obturators were then trimmed flush around where the lid was fixed to the base, finished and polished as described previously, and labeled with an “H” (for hollow conventional). (Fig. 5).
Figure 4.
Fabrication steps for conventionally heat-processed hollow obturator A, Thickness of walls of obturator bulb evaluated with digital thickness gauge. B, Recess created around palatal opening of obturators. C, Impression of obturator opening for lid fabrication. D, Wax pattern for processing of obturator lids.
Figure 5.
Conventionally heat-processed hollow obturators A, Cameo surface. B, Intaglio surfa
For the 3D printed hollow obturator group (n=9), each specimen of the completed solid obturator group was scanned with a high-resolution 3D scanner (Artec Space Spider; Artec 3D) to use as a model for printing. Three fiducial markers (DentalMark 2.0 mm; Suremark) were placed on each obturator and then coated with a scanning spray (AESUB white; AESUB) until it appeared matte white. The obturator was placed on a turntable atop a marked reference sheet. The first scan was acquired holding the scanner at a 0.2- to 0.3-m distance while spinning the turntable and simultaneously watching the scanning software program (Artec Studio 16 v16.0.8.2; Artec 3D). The obturator was then turned to the opposite side and another scan was acquired. Additional scans were acquired if a portion of the obturator was not captured. Once both sides of each obturator had been scanned, all scans were aligned by using the fiducial markers as reference points. The scans were then fused and exported in standard tessellation language (STL) file format. Each STL file was imported into an open-source CAD software program (MeshMixer v3.5.474; Autodesk). The “Hollow” feature was selected, and the offset distance was set to 2 mm, which automatically generated a hollow bulb (Fig. 6A). Each obturator base with a hollow bulb was then exported as an STL file and imported into a CAM software program (PreForm v3.26.2; Formlabs Inc) to prepare for 3D printing. Support structures were generated on the cameo surface of the obturator consisting of a raft and Ø1-mm support arms. Up to 3 STL files were imported per print run and then manipulated to a suitable orientation (Fig. 6B). To print the hollow bulb, the obturators were oriented as flat as possible to prevent hydraulic and air pressure build up while printing and to keep the part watertight. The 3D printer with build platform and compatible resin tank (Form 2 with Form 2 Resin Tank LT; Formlabs Inc) was loaded with biocompatible photopolymer denture base resin (Denture Base OP V1 Resin; Formlabs Inc). The prints ranged from 6 to 8 hours depending on the layer height of each unique print run. Once the print was completed, the build platform along with the printed parts attached were moved to the wash unit (Form Wash; Formlabs Inc). The parts were washed for 10 to 20 minutes in 99% isopropyl alcohol (Isopropyl Alcohol Reagent Isopropyl 99% Colorless; Cardinal Health) and left to air dry or dried using compressed air before being removed from the build platform. The support structures were then detached, and touch points removed with a tungsten carbide bur to achieve a smooth finish. A clear glass jar was filled with glycerin (Vegetable Glycerin 100% Pure USP; Momentum Elements) and heated in the polymerization unit (Form Cure; Formlabs Inc) for 2 hours at 80 °C. The part was then submerged in the glycerin for a total of 1 hour at 80 °C, rotating the part halfway through the cycle. The obturators were then finished and polished as previously described and labeled with a “P” (for printed hollow) (Fig. 7).
Figure 6.
Fabrication steps for 3D printed hollow obturators A, Using CAD software program to generate hollow bulb obturator STL file. B, Orienting STL files for 3D printing. CAD, computer-aided design; STL, standard tessellation language; 3D, 3-dimensional.
Figure 7.
Three-dimensionally printed hollow obturators A, Cameo surface. B, Intaglio surface.
The weight of each of the 27 labeled obturators was recorded in grams by using a digital scale (Newton EJ-303 Portable Balance; A&D Co) to the nearest thousandth. The scale was checked to be level and was zeroed before each measurement. Weight differences between the differently fabricated obturators were evaluated statistically with exact versions of the Kruskal-Wallis test or Wilcoxon Rank Sum test (α=.05). Results were diagramed using boxplots.
RESULTS
Statistical analysis revealed significant differences in the weight of the obturator based on the different fabrication method overall (P<.001). Pairwise comparisons revealed a significant difference between the weight of specimens that had been conventionally heat-processed solid and heat-processed hollow obturators (P<.001). A significant difference was found between the weight of specimens that had been conventionally heat-processed solid and 3D printed hollow obturators (P<.001). No significant difference was found between the conventionally heat-processed hollow and 3D printed hollow obturators (P=.222) (Table 1). The conventionally heat-processed solid obturators had the greatest weights with the largest distribution (Fig. 8).
Table 1.
Descriptive statistics and comparisons using exact versions of the Kruskal-Wallis test (overall P value) or Wilcoxon Rank Sum test (pairwise P values) for weight of obturator based on different fabrication methods
| Weight (g) | |||||||
|---|---|---|---|---|---|---|---|
| Fabrication Method |
N | Mean (SD) | Median (IQR) | Overall P |
S versus H P |
S versus P P |
P versus H P |
| H | 9 | 21.469 (2.164) | 21.273 (20.095 - 22.319) | <.001 | <.001 | <.001 | .222 |
| P | 9 | 20.151 (1.082) | 19.772 (19.246 - 20.741) | ||||
| S | 9 | 29.311 (4.686) | 28.894 (24.674 - 32.391) | ||||
H, conventional hollow; IQR, interquartile range; N, number; P, printed hollow; S, conventional solid; SD, standard deviation.
Figure 8.
Box plot showing effect of different fabrication method on weights
As expected, weights were highest in the Aramany Class I defect group and decreased when comparing Aramany Class I with Class III defect groups (Table 2). However, only the comparison between the Aramany Class I and Class III defect groups was statistically significant (P<.05). Examining weight by fabrication methods within each Aramany Class defect showed that the magnitude of the weight differences among the fabrication methods was highest in the Aramany Class I defect group and lowest in the Class III defect group (Table 3). There were significant differences in the weight of the obturator based on the different fabrication methods within the Aramany Class I defect (overall P=.004) and Aramany Class II defect (overall P=.011), but no significant difference for Aramany Class III defect (overall P=.071) (Table 3). Pairwise comparison among the individual defect groups with each defect class was not possible because of the small specimen sizes.
Table 2.
Descriptive statistics and comparisons using exact versions of the Kruskal-Wallis test (overall P value) or Wilcoxon Rank Sum test (pairwise P values) for weight of obturator based on different Aramany Class defects
| Weight (g) | |||||||
|---|---|---|---|---|---|---|---|
| Aramany Defect |
N | Mean ±SD | Med (IQR) | Overall P |
1 versus 2 P |
1 versus 3 P |
2 versus 3 P |
| 1 | 9 | 26.557 ±6.408 | 24.576 (22.117 - 32.391) | .033 | .190 | .024 | .094 |
| 2 | 9 | 23.418 ±4.228 | 21.273 (20.703 - 28.421) | ||||
| 3 | 9 | 20.955 ±2.513 | 19.772 (19.149 - 23.458) | ||||
IQR, interquartile range; N, number; SD, standard deviation.
Table 3.
Descriptive statistics and overall comparisons using exact versions of Kruskal-Wallis test for weight of obturator based on different fabrication methods within each Aramany defect classification group
| Weight (g) | |||||
|---|---|---|---|---|---|
| Aramany Defect | Fabrication Method | N | Mean ±SD | Median (IQR) | Overall P value |
| 1 | H | 3 | 23.946 ±1.421 | 24.576 (22.319 - 24.943) | .004 |
| P | 3 | 21.004 ±1.24 | 21.228 (19.667 - 22.117) | ||
| S | 3 | 34.722 ±2.054 | 35.508 (32.391 - 36.267) | ||
| 2 | H | 3 | 21.111 ±0.356 | 21.273 (20.703 - 21.357) | .011 |
| P | 3 | 20.163 ±0.842 | 20.551 (19.197 - 20.741) | ||
| S | 3 | 28.981 ±0.608 | 28.894 (28.421 - 29.628) | ||
| 3 | H | 3 | 19.349 ±0.669 | 19.149 (18.803 - 20.095) | .071 |
| P | 3 | 19.285 ±0.469 | 19.246 (18.837 – 19.772) | ||
| S | 3 | 24.231 ±0.672 | 24.561 (23.458 – 24.674) | ||
H, conventional hollow; IQR, interquartile range; N, number; P, printed hollow; S, conventional solid; SD, standard deviation.
DISCUSSION
The null hypothesis that the 3D printed technique would not affect the weight of an obturator prosthesis was rejected because the different manufacturing techniques affected the weights of the obturator prostheses. The conventionally heat-processed solid obturators were significantly heavier than either the conventionally heat-processed hollow or the 3D printed hollow obturators (P<.05). However, there was no significant difference in weight between the conventionally heat-processed hollow and 3D printed hollow obturators (P>.05). Further analysis showed that the difference in weight among the fabrications methods was greatest within the Aramany Class I defect group and lowest within the Class III defect group.
While a hollow obturator should be lighter than a solid obturator because of a reduction in material, few studies have compared the weight of solid versus closed hollow obturators. Wu et al23 reported that hollowing the obturator for patients with a partial maxillectomy led to an obturator with a weight decreased by 6.55% to 33.06% depending on the size of the defect. Most articles about hollow obturators have been technical reports describing methods of fabricating a closed hollow obturator.3–22 All these methods are time-consuming and technique sensitive methods with less-than-ideal results.2 Most laboratory technicians find it easier to fabricate an open hollow obturator, but this has the disadvantages of accumulation of mucus, food, and fluids in the bulb, which can lead to bad odor and taste, necessitating constant cleaning or a vent to aid elimination.22 Digital technologies offer promising solutions to the drawbacks encountered with traditional methods.
Few studies have evaluated the accuracy and properties of the 3D printed hollow obturators. Koyama et al24,29 reported that a 2-mm prosthesis thickness was suitable for a hollow obturator in terms of hermeticity and durability. Alfaraj et al30 compared the intaglio surface trueness of obturator prosthesis bases manufactured by different methods and reported that the injection molding technique had better intaglio surface trueness than those made by the compression molding technique or with 3D printers but that 3D printed obturator bases with the same 3D printer had excellent accuracy. Neena et al31 compared 1-piece closed hollow bulb obturators fabricated with CAD-CAM additive manufacturing with those constructed from heat-processed resin and reported that the CAD-CAM obturators constructed by additive manufacturing tended to be oversized when compared with the original design.
Few studies have evaluated the weight difference between obturators fabricated by traditional methods versus digital fabrication. A technical report by Alfaraj et al2 described a digital workflow by using an open-source software program to hollow a digital design of a solid obturator base from a commercially available software program. The authors noted a 24% weight reduction of the hollow obturator base when compared with the solid one.
The present results were consistent with those of a previous study which reported that hollowing the obturator for patients with a partial maxillectomy significantly decreased its weight.23 The conventionally heat-processed solid obturators were significantly heavier than the conventionally heat-processed hollow (P<.001) and the 3D printed hollow obturators (P<.001). No significant difference (P=.222) was found between the conventionally heat-processed hollow and 3D printed hollow obturators. The decrease in weight was proportional to the size of the defect, with Aramany Class I having the largest differences in weight between the different fabrication methods, followed by Class II and then Class III, which specifies a much smaller defect.
Limitations of this study included the small sample size which prevented a formal examination of whether the differences in weight among the fabrication methods were proportional to the Aramany Class defect. Other limitations included the difficulty that was encountered when trying to standardize the thickness of the walls of the conventionally heat-processed hollow obturators. Unpolymerized monomer may have remained in the hollow center, which could have led to deformation or discoloration, and trial and error was needed to determine the optimal orientation of the obturators on the build platform to prevent hydraulic and air pressure build up and keep the part watertight.
Benefits of producing obturators by additive manufacturing include conservation of material which reduces the environmental impact and cost, virtually unlimited ability to design complex structures in 1 fabrication cycle with no joints, straightforward use, and colors and materials that can be customized in specific areas of the print.27,28 Future research should address the consistency of the seals of the hollow obturators (conventionally heat-processed and printed) tested. The weights in the present study could have been skewed if the seals were not completely watertight. Therefore, each hollow obturator was placed in a beaker full of water and demonstrated the ability to float, establishing a complete and stable watertight seal. Future studies need to investigate the long-term seal stability, long-term biocompatibility, durability, and stability of printed resins versus conventional acrylic resin when used for obturators because of different mucosal exposures.
CONCLUSIONS
Based on the findings of this in vitro study, the following conclusion was drawn:
Additive manufacturing of obturators could be a suitable alternative to conventional techniques for the fabrication of a closed hollow obturator due to comparable weights and ease of fabrication with the elimination of joints; this should also help solve the clinical problems such as contamination, malodor, and decreased esthetic properties as a result of saliva and water entering the hollow bulb.
CLINICAL IMPLICATIONS.
Additive manufacturing could be a suitable alternative to conventional techniques for the fabrication of a closed hollow obturator because of comparable weight and more straightforward fabrication.
Acknowledgments
Supported in part by the NIH/NCI Cancer Center Support Grant [P30 CA008748].
Footnotes
Declarations of interest: none.
REFERENCES
- 1.The glossary of prosthodontic terms: Ninth edition. J Prosthet Dent 2017;117: e1–e105. [DOI] [PubMed] [Google Scholar]
- 2.Alfaraj A, Su FY, Lin WS. CAD-CAM hollow obturator prosthesis: A technical report. J Prosthodont 2022; 31: 635–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Benington IC. Light-cured hollow obturators. J Prosthet Dent 1989; 62: 322–25. [DOI] [PubMed] [Google Scholar]
- 4.Birnbach S, Barnhard B. Direct conversion of a solid obturator to a hollow obturator prosthesis. J Prosthet Dent 1989; 62:58–60. [DOI] [PubMed] [Google Scholar]
- 5.Brown KE. Fabrication of a hollow-bulb obturator. J Prosthet Dent 1969; 21: 97–103. [DOI] [PubMed] [Google Scholar]
- 6.Buckner H. Construction of a denture with hollow obturator, lid, and soft acrylic lining. J Prosthet Dent 1974; 31: 95–9. [DOI] [PubMed] [Google Scholar]
- 7.Chalian VA, Barnett MO. A new technique for constructing a one-piece hollow obturator after partial maxillectomy. J Prosthet Dent 1972; 28: 448–53. [DOI] [PubMed] [Google Scholar]
- 8.el Mahdy AS. Processing a hollow obturator. J Prosthet Dent 1969; 22: 682–86. [DOI] [PubMed] [Google Scholar]
- 9.Habib BH, Driscoll CF. Fabrication of a closed hollow obturator. J Prosthet Dent 2004; 91: 383–5. [DOI] [PubMed] [Google Scholar]
- 10.Kocacikli M, Yalug S, Yazicioglu H, Yilmaz C. Fabricating a hollow obturator with visible light-cured resin system. J Prosthodont 2008; 17: 596–8. [DOI] [PubMed] [Google Scholar]
- 11.Matalon V, LaFuente H. A simplified method for making a hollow obturator. J Prosthet Dent 1976; 36: 580–2. [DOI] [PubMed] [Google Scholar]
- 12.McAndrew KS, Rothenberger S, Minsley GE. 1997. Judson C. Hickey scientific writing awards. An innovative investment method for the fabrication of a closed hollow obturator prosthesis. J Prosthet Dent 1998; 80: 129–32. [DOI] [PubMed] [Google Scholar]
- 13.Minsley GE, Nelson DR, Rothenberger SL. An alternative method for fabrication of a closed hollow obturator. J Prosthet Dent 1986; 55: 485–90. [DOI] [PubMed] [Google Scholar]
- 14.Nidiffer TJ, Shipmon TH. The hollow bulb obturator for acquired palatal openings. J Prosthet Dent 1957; 7: 126–37. [Google Scholar]
- 15.Orr MT. The application of a duplication technique in post-surgical prosthodontics. J Oral Rehabil 1986; 13: 163–8. [DOI] [PubMed] [Google Scholar]
- 16.Palmer B, Coffey KW. Fabrication of the hollow bulb obturator. J Prosthet Dent 1985; 53: 595–6. [DOI] [PubMed] [Google Scholar]
- 17.Phankosol P, Martin JW. Hollow obturator with removable lid. J Prosthet Dent 1985; 54: 98–100. [DOI] [PubMed] [Google Scholar]
- 18.Schneider A. Method of fabricating a hollow obturator. J Prosthet Dent 1978; 40: 351. [DOI] [PubMed] [Google Scholar]
- 19.Tanaka Y, Gold HO, Pruzansky S. A simplified technique for fabricating a lightweight obturator. J Prosthet Dent 1977; 38: 638–42. [DOI] [PubMed] [Google Scholar]
- 20.Tasopoulos T, Kouveliotis G, Polyzois G, Karathanasi V. Fabrication of a 3D printing definitive obturator prosthesis: A clinical report. Acta Stomatol Croat. 2017; 51: 53–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Wang RR, Hirsch RF. Refining hollow obturator base using light-activated resin. J Prosthet Dent 1997; 78: 327–9. [DOI] [PubMed] [Google Scholar]
- 22.Buzayan MM. The Hollow Bulb Obturator Fabrication, Where do We Stand in 2017. Periodontics and Prosthodontics. 2017; 03(02). [Google Scholar]
- 23.Wu YL, Schaaf NG. Comparison of weight reduction in different designs of solid and hollow obturator prostheses. J Prosthet Dent 1989; 62: 214–7. [DOI] [PubMed] [Google Scholar]
- 24.Koyama S, Sato N, Mito T, Izumita K, Sasaki K. Hermeticity of a hollow obturator model using CAD and rapid prototyping technologies. J Prosthet Dent 2020; 124: 123–7. [DOI] [PubMed] [Google Scholar]
- 25.Takeuchi Y, Nakajo K, Sato T, Koyama S, Sasaki K, Takahashi N. Quantification and identification of bacteria in acrylic resin dentures and dento-maxillary obturator-prostheses. Am J Dent 2012; 25: 171–5. [PubMed] [Google Scholar]
- 26.Davidowitz G, Kotick PG. The use of CAD/CAM in dentistry. Dent Clin North Am. 2011; 55: 559–70. [DOI] [PubMed] [Google Scholar]
- 27.Masri R, Driscoll C. Clinical Applications of Digital Dental Technology. 1st ed. John Wiley & Sons, Inc.; 2015. [Google Scholar]
- 28.Tian Y, Chen C, Xu X, Wang J, Hou X, Li K, Lu X, Shi H, Lee ES, Jiang HB. A Review of 3D Printing in Dentistry: Technologies, Affecting Factors and Applications. Scanning 2021; 2021: 1–19. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Koyama S, Kato H, Harata T, Sasaki K. A workflow for fabricating a hollow obturator by using 3D digital technologies. J Prosthet Dent 2020; 123: 648–52. [DOI] [PubMed] [Google Scholar]
- 30.Alfaraj A, Yang CC, Levon JA, Chu TG, Morton D, Lin WS. The trueness of obturator prosthesis base manufactured by conventional and 3D printing techniques. J Prosthodont 2022; 31: 221–7. [DOI] [PubMed] [Google Scholar]
- 31.Neena AF, Alshimy AM, Khamis MM, Ekram AM, Digital evaluation of CAD/CAM single-piece obturators, Alexandria Dental Journal 2020; 45: 68–74. [Google Scholar]
- 32.Aramany MA. Basic principles of obturator design for partially edentulous patients. Part I: classification. J Prosthet Dent 1978; 40: 554–7. [DOI] [PubMed] [Google Scholar]