• ISSN 16748301
  • CN 32-1810/R
Volume 33 Issue 2
Mar.  2019
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Citation:

Maxillary denture flange and occlusal discrepancies of Vertex ThermoSens in comparison with conventional heat-cured denture base materials

  • Corresponding author: Ibrahim M. Hamouda, imh100@hotmail.com
  • Received Date: 2016-10-14
    Accepted Date: 2017-10-15
  • This study was conducted to investigate the maxillary denture bases and occlusal discrepancies using the Vertex Thermosens in comparison with the conventional polymethyl-methacrylate materials. Twenty maxillary denture bases were prepared from the Vertex ThermoSens and a conventional heat-cured denture base materials. Acrylic maxillary second molars were arranged in their respective positions on the ridge. After curing of both types of denture bases, they were deflasked with their respective master casts. Reference points were prepared for measurements of the antero-posterior and cross-arch dimensions at the denture borders using caliper device. Furthermore, the teeth discrepancies were measured between reference points in the ligual aspect of the second maxillary molars. The recorded data was analyzed using SPSS statistical software version 20. The results showed initial shrinkage of both denture bases in the antero-posterior and cross-arch dimensions immediately after decasting. This contraction was compensated gradually during storage in water up to 2 weeks. Regarding the variable time, there was a significant difference between the tested materials. Moreover, the results revealed occlusal discrepancies and shifting of teeth inward immediately after decasting, followed by outward movement after storage in water for 2 weeks. Regarding the variables time and materials, there were significant differences. Both materials exhibited inward shrinkage in the antero-posterior and cross-arch dimensions immediately after decasting. Both denture bases showed inward shifting of teeth immediately after decasting, followed by outward movement after storage in water up to 2 weeks.
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  • [1] Anusavice KJ. Phillip's science of dental materials[M]. 12th ed. St. Louis:Elsevier, 2006:485-489.
    [2] Chandu G, Hema B, Mahajan H, et al. A comparative study of retention of complete denture base with different types of posterior palatal seals- an in vivo study[J]. Clin Cosmet Investig Dent, 2014, 6:95-100.
    [3] Craig RG. Craig's restorative dental materials[M]. 11thed. Mosby, St. Louis, Missouri:Elsevier, 2006:23-517.
    [4] Hamouda IM, El-Shokouki AH, Gomaa AM, et al. Effect of arch form and water sorption on the palatal base adaptation of probase hot versus the conventional heat cured acrylic resin[J]. Int J Dentistry Oral Sci, 2016, 3(2):193-199.
    [5] Abuzar MA, Jamani K, Abuzar M. Tooth movement during processing of complete dentures and its relation to palatal form[J]. J Prosthet Dent, 1995, 73(5):445-449. doi: 10.1016/S0022-3913(05)80073-3
    [6] McCartney JW. Flange adaptation discrepancy, palatal base distortion, and induced malocclusion caused by processing acrylic resin maxillary complete dentures[J]. J Prosthet Dent, 1984, 52(4):545-553. doi: 10.1016/0022-3913(84)90343-3
    [7] Vertex Dental BV. The Netherlands[EB/OL]. www.vertexthermosens.com.
    [8] Geerts GAV, Stuhlinger ME, Nel DG. A comparison of the accuracy of two methods used by pre-doctoral students to measure vertical dimension[J]. J Prosthet Dent, 2004, 91(1):59-66. doi: 10.1016/j.prosdent.2003.10.016
    [9] Takamata T, Arakawa H, Inoue Y, et al. Dimensional accuracy of acrylic resins denture bases:Literature review[J]. Matsumoto Shigaku, 1989, 15:27-37.
    [10] Becker CM, Smith DE, Nocholls JI. The comparison of denture base processing techniques. Part 1. Material characteristics[J]. J Prosthet Dent, 1977, 37(4):450-459. doi: 10.1016/0022-3913(77)90147-0
    [11] Babu S, Manjunath S, Vajawat M. Effect of palatal form on movement of teeth during processing of complete denture prosthesis:An in-vitro study[J]. Contemp Clin Dent, 2016, 7(1):36-40. doi: 10.4103/0976-237X.177101
    [12] Negreiros WA, Xediekconsani RL, Mesquita MF, et al. Effect of the flask contention methodon the displacement of maxillary denture teeth[J]. Braz J Oral Sci, 2008, 7:1493-1496.
    [13] Pasam N, Hallikerimath RB, Arora A, et al. Effect of different curing temperature on the distortion at theposterior peripheral seal[J]. Ind J Den Sea, 2012, 23(3):301-304.
    [14] Arora S, Sangur R, Dayakra HR. Comparative study on the fit of maxillary complete denture bases at the posterior palatal border made by heat cure acrylic resin processed on high expansion stone[J]. Int J Dent Clin, 2011, 3(1):18. doi: 10.4103/2231-0754.115768
    [15] Macedo VC, Cotes C, Cabrini RR, et al. Influence of polymerization technique and resin type in denture misfit[J]. J Dent App, 2014, 1:124-126.
    [16] Jang DE, Lee JY, Jang HS, et al. Color stability, water sorption and cytotoxicity of thermoplastic acrylic resin for non metal clasp denture[J]. J Adv Prosthodont, 2015, 7(4):278-287. doi: 10.4047/jap.2015.7.4.278
    [17] Miéssi AC, Goiato MC, dos Santos DM, et al. Influence of storage period and effect of different brands of acrylic resin on the dimensional accuracy of the maxillary denture base[J]. Braz Dent J, 2008, 19(3):204-208. doi: 10.1590/S0103-64402008000300005
    [18] Ladha K, Tiwari B. Processing induced tooth displacement and occlusal changes in complete dentures-an overview[J]. Periodon Prosthodon, 2015, 1:1-8.
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Maxillary denture flange and occlusal discrepancies of Vertex ThermoSens in comparison with conventional heat-cured denture base materials

    Corresponding author: Ibrahim M. Hamouda, imh100@hotmail.com
  • 1. Maxillofacial and Oral Rehabilitation Department
  • 2. Conservative Dentistry, Faculty of Dentistry, Umm Al-Qura University, Makkah Al Mukarramah 21955, Kingdom of Saudi Arabia
  • 3. Dental Biomaterials, Faculty of Dentistry, Mansoura University, Mansoura 35516, Egypt

Abstract: This study was conducted to investigate the maxillary denture bases and occlusal discrepancies using the Vertex Thermosens in comparison with the conventional polymethyl-methacrylate materials. Twenty maxillary denture bases were prepared from the Vertex ThermoSens and a conventional heat-cured denture base materials. Acrylic maxillary second molars were arranged in their respective positions on the ridge. After curing of both types of denture bases, they were deflasked with their respective master casts. Reference points were prepared for measurements of the antero-posterior and cross-arch dimensions at the denture borders using caliper device. Furthermore, the teeth discrepancies were measured between reference points in the ligual aspect of the second maxillary molars. The recorded data was analyzed using SPSS statistical software version 20. The results showed initial shrinkage of both denture bases in the antero-posterior and cross-arch dimensions immediately after decasting. This contraction was compensated gradually during storage in water up to 2 weeks. Regarding the variable time, there was a significant difference between the tested materials. Moreover, the results revealed occlusal discrepancies and shifting of teeth inward immediately after decasting, followed by outward movement after storage in water for 2 weeks. Regarding the variables time and materials, there were significant differences. Both materials exhibited inward shrinkage in the antero-posterior and cross-arch dimensions immediately after decasting. Both denture bases showed inward shifting of teeth immediately after decasting, followed by outward movement after storage in water up to 2 weeks.

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Introduction
  • Heat-cured and self-cured acrylic resins have been the common materials for denture base construction. Unfortunately, all resins used in dentistry undergo shrinkage during processing. Poor fitted dentures were evident as a result of shrinkage[1].

    The major objective for construction of complete dentures is to obtain a denture base that conforms the supporting tissues to a high degree of accuracy[2]. The properties of the denture bases are generally more important to the performance of the denture as it controls retention, mechanical properties, and biocompatibility[3]. It is believed by many authors that intimate tissue contact and peripheral seal of the denture base comprise the most critical retentive factors[2].

    Complete dentures are affected by the dimensional changes of the acrylic resins. These changes occur during or after processing. Volumetric shrinkage and the linear shrinkage are the main factors affecting denture stability. Linear shrinkage exerts significant effects on denture base adaptation and cuspal interdigitation[1].

    The magnitude of linear shrinkage is determined by measuring the distance between two predetermined reference points in the second molar regions of a complete tooth arrangement. Following polymerization of the denture base resin and removal of the prosthesis from the master cast, the distance between these reference points is measured once again. The difference between pre- and postpolymerization measurements is recorded as linear shrinkage[1].

    There are several modifications of denture base materials, including the conventional acrylic resins, high impact resins, glass fibers-reinforced resins and metallic-reinforced resins. Recent advances of polymethyl methacrylate had been used for denture base construction. "ProBase Hot" was introduced as a new denture base material which is supposed to set up a higher standard of quality for the processing properties, accuracy of fitness, and stability of shape than heat cured denture base materials[4]. Finally, the latest form of denture base materials is the VertexTM ThermoSens thermoplastic material.

    There was a little information in the literatures about the Vertex ThermoSens denture base materials. The null hypothesis of this study was that Vertex ThermoSens material is superior in maxillary denture flange adaptation and occlusal stability to the conventional denture base material. Therefore, the aim of this study was to investigate the discrepancies of the maxillary denture base and occlusal plane of dentures made from the newly introduced Vertex ThermoSens in comparison with the conventional polymethyl-methacrylate denture base materials.

Materials and methods
  • Twenty identical maxillary stone casts were produced from a standard metallic mold. The maxillary residual ridge was free of any obvious ridge undercuts or surface irregularities and had a smooth U-shaped, well-formed arch. The master casts were divided into two groups, 10 casts each. The first group was assigned for construction of 10 denture bases from the conventional heat-cured acrylic resin as a control group (compression molding technique). The second group was assigned for construction of 10 denture bases from the newly introduced Vertex ThermoSense denture base material (injection molding technique).

    Baseplate wax was constructed on one master cast using one sheet of wax 2 mm thick (Tru Wax, Dentsply International Inc., York, PA, USA). Anatomic acrylic maxillary second molars were arranged in their respective positions on the ridge (Dentsply International Inc., York, Pa.). The wax base thickness was preserved as 1.25 mm. Small amounts of wax were added to fix the teeth in their respective positions[5]. Two wax sprues with 10 mm diameter were attached on the back of tuberosities. The system (model, base plate wax and teeth) was duplicated using polyvinyl siloxane (Silastic E; Dow Corning, Midland, Mich, USA) to prepare 20 identical denture base wax. After silicon curing, waxed denture base and model has been removed. This silicon was used as a standard template for next waxed denture base specimens. The teeth of the same sizes were arranged in their respective positions in the silicone mold. This silicone mold was placed on 20 stone casts where the teeth and model were fitted in location. Molten base plate wax was poured through the sprues and after cooling the wax replicas of denture were obtained.

    The waxed denture bases were invested with dental plaster and dental flasks using compression molding technique. Stone cap were prepared over the cusps of the maxillary teeth. Waxed denture bases were washed up in boiling water for 10 minutes. The flasks were opened and wax was eliminated. After removing the wax with boiling water and separating medium application, the first group was constructed from heatpolymerized resin, and Major.base 20 (Major Prodotti Dentari S.p.A. Italy) were packed according to the manufacturer, s instructions. The powder/liquid was mixed at a ratio (3:1) andpacked, and the flasks were dipped in boiling water at 100 ℃ for 30 minutes. The flasks were cooled slowly and the denture bases were deflasked with their respective casts in position. While the denture bases remained in their position, the casts were trimmed from the cast-base to expose the border of the denture flanges.

    The second group was constructed from Vertex ThermoSens (Vertex ThermoSens, Vertex-Dental, Netherlands) according to the manufacturer, s instructions. This system used special metallic flasks with posterior wax sprue for injection of the material inside the plaster molds. VertexTM ThermoSens is based on injection technique, with an automatic or manual injection machine. The model and flasks were prepared according to the standard procedures of the dental technique. Since there is no chemical bonding between synthetic acrylic teeth and Vertex ThermoSens, a mechanical bonding must be obtained. For injection of the Vertex ThermoSens into the flask, wax sprue should be used. The main sprue was about 9.5 mm and side sprues was 4.5 mm[6]. The material was heated at 270 ℃–280 ℃ within 18 minutes and injected automatically at a pressure of 8.5 bar. The flasks were cooled slowly and the dentures were deflasked with their respective casts.

    The models were trimmed to expose the denture borders at the regions of the tuberosities, labial frenum notch and the postdam. To assess the anterior-posterior dimensional changes, two reference points were prepared in the midline at the fitting surface of the bases. The first point located at the labial frenum notch (point A) and the second point in midline of the postdam (point B). Also, two reference points (C and D) were prepared in the internal surface of the buccal pouch part of the border of the denture flange (Fig. 1)[6].

    Figure 1.  The antero-posterior reference points (A-B) and the right to left (C-D, flange-flange) reference points

    The lengths between A, B, C and D points were standardized in all dentures by using metallic bar. The distances between these points in the fitting surface were measured by dial caliper (Mitutoy, Us Ms00 13, 500 series, Japan). The caliper has two jaws where one is fixed and the other is movable. The sliding jaw was moved by pressing the thumb on the bump on the bottom. The caliper was used for reading of the distance between centers of these points in antro-posterior direction (A and B) and right-left direction (C and D) and the results were recorded. The unit of measurement was the millimeter with precision of 0.01. The distances were measured before deflasking, while the dentures were still on their models, after removal of the denture from their casts, and 1 week and 2 weeks of water storage after decasting.

    Immediately after the stone casts were deflasked with the dentures still in place, reference notches were prepared in the lingual aspect of the most distal molar tooth on either side of the arch (Fig. 2). With a caliper device, the molar-molar (M-M) cross arch linear distance was measured. The dentures were removed from their casts, the M-M cross arch linear distance was again measured[5]. Measurements were done after storage in water for 1 and 2 weeks.

    Figure 2.  Reference points for molar-molar measurements

Statistical analysis
  • The recorded data were analyzed using 2-way ANOVA and LSD tests to detect the significant differences between the two tested materials at the different periods.

Results
  • The results of the antero-posterior dimensions (A-B) are presented in Table 1. The statistical analysis of the results using 2-way ANOVA showed a significant difference between the conventional heat-cured acrylic resin and the Vertex ThermoSens regarding the anteroposterior dimensions (P≤0.001). Both denture base materials showed significant shrinkage in the anteroposterior (A-B) dimensions after decasting (P≤0.05). Both denture bases exhibited gradual expansion in the antro-posterior dimension during the 2 weeks of water immersion. There were no significant differences between the tested materials in the antro-posterior dimension (P>0.05). Regarding the time factor, there were significant differences between the different testing periods in the antro-posterior dimension (P≤0.05).

    Materials Before decasting After decasting 1 week storage in water 2 week storage in water F-value P-value
    Major. base 20 42.46±0.60a 42.17±0.50b 42.38±0.50a 42.62±0.60a 454, 316.5 P≤0.001
    Vertex ThermoSens 42.48±0.40a 42.17±0.80b 42.36±0.50a 42.54±0.60a
    The mean difference is significant at the 0.05 level. The means with different superscripted letters are significantly different.

    Table 1.  The antero-posterior dimensions (mm) at different periods