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Survey on use of titanium dentures in Tsurumi University Dental Hospital for 11 years
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Journal of Prosthodontic Research 53 (2009) 53–59 www.elsevier.com/locate/jpor
Original article
Survey on use of titanium dentures in Tsurumi University Dental Hospital for 11 years Yasuko Takayama DMD, PhD*, Norio Takishin DMD, PhD, Fujio Tsuchida DMD, PhD, Toshio Hosoi DDS, PhD Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, 2-1-3 Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan Received 19 February 2008; accepted 28 August 2008 Available online 10 January 2009
Abstract Purpose: The purpose of this study was to survey the production of titanium dentures in Tsurumi University Dental Hospital and to study the actual use of titanium dentures in our university. Methods: The survey was based on the metal base dentures produced at Tsurumi University Dental Hospital during an 11-year period between April 1995 and March 2006, with relation to the types of metals used in the dentures, types of dentures, dental condition, and the number of artificial teeth. Results: 1871 metal base dentures were produced in the study period. The dentures consisted of 1290 cobalt–chromium alloy dentures (68.9%), 350 titanium dentures (18.7%) and 231 platinum-added gold alloy dentures (12.3%). Within the titanium denture groups, 132 were complete dentures (37.7%), 55 were complete overdentures (15.7%) and 163 were removable partial dentures (46.6%). JIS type 3 pure titanium was used in the titanium base of 252 dentures (72.0%). The average number of artificial teeth was 10.9, which was the highest among the three types of metal bases, exhibiting significant differences (P < 0.01). Conclusion: Approximately 32 titanium dentures per year on average were delivered at our university and they were applied to almost edentulous arch compared with the other metal base dentures. # 2008 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved. Keywords: Survey; Titanium denture; Cobalt–chromium alloy denture; Platinum-added gold alloy denture; Production
1. Introduction Due to its favorable characteristics, titanium has a wide range of applications in dentistry from implants to crowns and denture bases. The clinical application of titanium for denture bases is one-step further than that of crowns and bridges [1]. Titanium dentures are becoming popular among general clinicians, probably due to the recent availability of titanium casting systems in commercial laboratories. In our university, complete dentures have been fabricated from superplastic titanium alloy since 1987 [2], and by introducing a titanium casting system with a vacuum compression method (GC), we started producing titanium cast denture bases in 1993. Currently, the major metals used in denture casting include cobalt–chromium alloy, titanium (pure titanium, titanium alloy)
* Corresponding author. Tel.: +81 45 581 1001; fax: +81 45 573 9599. E-mail address: [email protected] (Y. Takayama).
and platinum-added gold alloy. Among them, the titanium is considered to be highly biocompatible, light in weight and superior in anti-corrosion and anti-abrasion properties [3–5]. On the other hand, because it is difficult to cast and polish [6– 11], it is not used much despite the above advantages. The purpose of this study was to survey the production of titanium dentures in Tsurumi University Dental Hospital and to reveal the actual use of titanium dentures in our university. 2. Materials and methods We conducted a survey on the metal base dentures fabricated at Tsurumi University Dental Hospital during an 11-year period from April 1995 to March 2006. Based on the laboratory records used in the hospital affiliated with our university, we examined the items shown in Table 1. We added a category of complete overdentures to the type of dentures; however, if stud attachments and copings were used in removable partial dentures, we classified them as removable partial dentures. Moreover, for titanium
1883-1958/$ – see front matter # 2008 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved. doi:10.1016/j.jpor.2008.08.011
54
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
Table 1 Survey items.
Table 2 The number of metal base dentures produced each year.
Installation expected date Clinical record number
Year
Kind of use metal
Platinum-added gold alloy (Au–Pt) Cobalt–chromium alloy (Co–Cr) Titanium (Ti)
Prosthesis
Metal base denture Complete denture (CD) Complete overdenture (COD) Removable partial denture (PD)
Dental condition
Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
The number of artificial teeth Other
Co–Cr
Ti
Au–Pt
Total
n
%
n
%
n
%
n
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
94 83 141 113 119 91 125 149 128 148 99
58.8 60.1 72.3 67.7 66.9 61.1 66.1 83.2 71.9 72.5 73.9
42 29 30 25 33 43 43 17 24 40 24
26.3 21.0 15.4 15.0 18.5 28.9 22.8 9.5 13.5 19.6 17.9
24 26 24 29 26 15 21 13 26 16 11
15.0 18.8 12.3 17.4 14.6 10.1 11.1 7.3 14.6 7.8 8.2
160 138 195 167 178 149 189 179 178 204 134
Average S.D.
117.3 23.3
69.0
31.8 9.1
18.7
21.0 6.2
12.3
170.1 22.8
Attachment Coping Telescopic crown
dentures, we added the types of titanium used in the dentures and each clinician’s reasons for choosing the titanium base, as survey items. The questionnaire for dentists (present prosthetic department staff) included multiple choice questions, but they were asked to describe their reasons when ‘‘others’’ was chosen. 2.1. Data analysis The statistical analysis was performed using a chi-squared test and Kruskal–Wallis test (SPSS Ver. 12.0; SPSS Japan Inc., Tokyo, Japan). The levels of significance used were P < 0.05 and P < 0.01. 3. Results 3.1. Total number of metal base dentures and changes over the period of 11 years 1871 metal base dentures were fabricated at Tsurumi University Dental Hospital during the 11-year period between April 1995 and March 2006. The dentures consisted of 1290 cobalt–chromium alloy dentures (68.9%), 350 titanium dentures (18.7%), and 231 platinum-added gold alloy dentures (12.3%). The number of dentures produced annually is shown in Table 2. The dentures comprised 448 complete dentures (23.9%), 80 complete overdentures (4.3%), and 1343 removable partial dentures (71.8%). 1087 maxillary dentures (58.1%) and 784 mandibular dentures (41.9%) were delivered. The percentage of titanium dentures made each year ranged from 9.5% to 28.9% and approximately 32 titanium dentures on average were delivered each year. 3.2. Features of each metal Of the cobalt–chromium alloy dentures, 288 complete dentures (22.3%), 19 complete overdentures (1.5%), and 983 removable partial dentures (76.2%) were fabricated during the study period. In contrast, the titanium denture group consisted
of 132 complete dentures (37.7%), 55 complete overdentures (15.7%) and 163 removable partial dentures (46.6%). The platinum-added gold alloy denture group consisted of 28 complete dentures (12.1%), 6 complete overdentures (2.6%) and 197 removable partial dentures (85.3%). There was some relationship between the kind of metal used and types of denture (a chi-squared test, P < 0.01). Within each metal-type group, the proportion of the types of dentures fabricated tended to be the same every year. The complete dentures and complete overdentures constituted more than half of the dentures with a titanium denture base. Removable partial dentures were predominantly fabricated with a cobalt–chromium alloy or platinum-added gold alloy base (Fig. 1). In Table 3, dentures are classified according to the site where they were inserted, i.e. maxillary or mandibular, and the proportion of different types of dentures in these two sites was different (a chi-squared test, P < 0.01). In all types of metals, most of the complete dentures were inserted in the maxilla. As for the mandible, the proportion of removable partial dentures was high. Table 4 indicates the dental conditions and the number of artificial teeth. Distal extension missing comprised 63.9% of the cobalt–chromium alloy dentures, while in the platinumadded gold alloy, dentures for bounded missing and distal extension missing corresponded to 21.6% and 63.7%, respectively. In contrast with those figures, edentulous patients and those with a few roots remaining in titanium dentures exhibited a higher percentage of 53.4% and bounded missing was 5.7%. There was some relationship between the kind of metal used and the dental conditions (a chi-squared test, P < 0.01). Similarly, the number of artificial teeth was significantly different among metals groups and highest in the titanium base dentures (Kruskal–Wallis test, P < 0.01). The titanium denture was mostly applied to edentulous or almost edentulous arch with many artificial teeth. 3.3. Titanium types 252 out of 350 titanium dentures were made from JIS type 3 pure titanium (72.0%); 39 were from titanium alloy (Ti–6A1–
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
55
Fig. 1. Annual percentage of each denture.
4V alloy or Ti–6A1–7Nb alloy) (11.1%); and 59 were unknown (16.9%). 3.4. Reasons for selecting titanium We prepared questionnaires to determine the prime reason for selecting a titanium denture, targeting 33 dentists who delivered the titanium dentures. The response ‘‘high biocompatibility’’ accounted for 37.0%, which was the most common reason for selecting titanium, followed by ‘‘light-weight’’ with 23.3% (Table 5). 4. Discussion The metal base dentures produced at our university were predominantly cobalt–chromium alloy dentures, and titanium dentures comprised only 18.7%. Although cobalt–chromium alloy was introduced as a substitute for platinum-added gold alloy, it is now well accepted as a material which can be used in
metal denture bases. Platinum-added gold alloy seemed to comprise a small proportion of denture production because it is often used in conjunction with precision attachments and it is more expensive than other metals. The dentists’ (present prosthetic department staff) evaluations of the titanium dentures were not constant at the time of the investigation. On the other hand, the reliability of cobalt–chromium alloy dentures is high based on the experiences gained from it being used for a long time. In addition, the cost of titanium dentures is higher than that of cobalt–chromium alloy dentures in our hospital. Moreover, platinum-added gold alloy dentures are also very expensive. When a metal base denture is recommended to the patient, the price becomes an important factor. It is easy to recommend the patient a cheaper one. The ratio of each type of metal base denture fabrication in this investigation seemed consistent when pricing was considered. Compared to the cobalt–chromium alloy denture, the titanium denture was likely to be applied in edentulous or almost edentulous arch. It is highly possible that the titanium
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Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
Table 3 The number and percentage of each denture made of different types of metals (the maxilla and mandible). Co–Cr
Ti
Au–Pt
Total
n
%
n
%
n
%
n
%
Maxilla Mandible
754 536
58.4 41.6
230 120
65.7 34.3
103 128
44.6 55.4
1087 784
58.1 41.9
Maxilla Complete denture Complete overdenture Removable partial denture
210 12 532
27.9 1.6 70.5
107 40 83
46.5 17.4 36.1
20 3 80
19.4 2.9 77.6
337 55 695
31.0 5.0 64.0
Mandible Complete denture Complete overdenture Removable partial denture
78 7 451
14.6 1.3 84.1
25 15 80
20.8 12.5 66.7
8 3 117
6.3 2.3 91.5
111 25 648
14.2 3.2 82.6
Table 4 The position and number of artificial teeth in each metal base denture. Co–Cr
Ti
Au–Pt
Total
n
%
n
%
n
%
n
%
Total Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
158 385 440 19 288
12.2 29.8 34.1 1.5 22.3
20 56 87 55 132
5.7 16.0 24.9 15.7 37.7
50 75 72 6 28
21.6 32.5 31.2 2.6 12.1
228 516 599 80 448
12.2 27.6 32.0 4.3 23.9
Maxilla Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
133 209 190 12 210
17.6 27.7 25.2 1.6 27.9
17 29 37 40 107
7.4 12.6 16.1 17.4 46.5
27 30 23 3 20
26.2 29.1 22.3 2.9 19.4
177 268 250 55 337
16.3 24.7 23.0 5.0 31.0
Mandible Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
25 176 250 7 78
4.7 32.8 46.6 1.3 14.6
3 27 50 15 25
2.5 22.5 41.7 12.5 20.8
23 45 49 3 8
18.0 35.2 38.3 2.3 6.3
51 248 349 25 111
6.5 31.6 44.5 3.2 14.2
The number of artificial teeth Average S.D.
8.5 4.1
10.9 4.0
Table 5 Responses to the questionnaire. (1) (2) (3) (4) (5) (6) (7)
Allergic disorders were noted or suspected High biocompatibility Light-weight Interest in new material At patient’s request Easy to explain the advantages Other reasons
9 54 34 26 18 1 4
(6.2) (37.0) (23.3) (17.8) (12.3) (0.7) (2.7)
denture was often chosen to be used in maxillary complete dentures and complete overdentures mainly because it’s lightweight. In particular, in our university, it is often the case that metal structure dentures are designed for complete dentures and complete overdentures (Fig. 2). A metal structure framework designed as a three-dimensional framework, such as a double
6.7 4.3
structure, a T-shaped structure, or a trussed structure could resolve the strength issue [12]. In the double structure design, the occlusal surface consists of cut metal teeth or cut metal backing and a substructure near the alveolar ridge connected by a series of columns. Although metal structure dentures are strong and rigid, they also have the disadvantage of being heavy. As a consequence, titanium dentures may have been purposefully applied in order to reduce the weight. Because we tend to choose cobalt–chromium alloy dentures as the first selection among the metal base dentures, the number of complete dentures made of cobalt–chromium alloy was more than that of titanium. However, for the complete overdentures, the percentage of those made of titanium was rather large. In such cases, metal structure dentures were frequently applied in order to reinforce the dentures. It seemed that titanium was selected to fabricate the denture to be as light as possible.
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
57
Fig. 2. An example of the titanium denture with metal structure. (a) Occlusal view; (b) buccal view; (c) removable partial denture with metal structure.
Fig. 3. Ti–6A1–4V alloy denture showing change of color after 3 years of wearing. (a) Occlusal view; (b) denture basal surface view.
It can also be assumed that the use of titanium denture bases in removable partial dentures is not common because of the fact that titanium cast clasps have not yet obtained sufficient credibility. Au et al. examined the success of titanium removable partial dentures compared with that of cobalt– chromium alloy removable partial dentures in a 2-year clinical follow-up [13]. The results showed a higher incidence of failures in titanium removable partial dentures prior to the 12month review, suggesting the importance of taking its lower rigidity into account when designing removable partial dentures. Moreover, they reported a 91% survival rate for rests and retainers and the dentures were found to be more comfortable (55%) and preferred (64%) than the cobalt– chromium alloy dentures [14]. Many research papers indicated that although the retentive force of titanium clasps was inferior to that of cobalt–chromium alloy clasps, the retentive force was only slightly lower in the titanium clasps [7,10,15–17]. In addition, the long-term retentive resiliency of the pure titanium and titanium alloy clasps suggested suitability of these materials for removable partial dentures [7,10,13–18]. Bridgeman et al. pointed out that porosity was more apparent in the pure titanium and titanium alloy clasps than in those made from cobalt–chromium alloy, but the amount of porosity did not correspond to evidence of fractures or permanent deformation [7]. Moreover, the utility of clasps made of Ti–6A1–7Nb alloy was verified [19,20]. As mentioned above, the credibility of titanium clasps has been confirmed by various studies. However, since our confidence in cobalt–chromium alloy clasps was extremely high, titanium was used less in removable partial dentures. At the beginning of the research period, the reliability of the titanium denture was not enough. Therefore, it
seemed that many dentists had a tendency to choose cobalt– chromium alloy dentures as the conservative selection. Considering the different types of titanium, JIS type 3 pure titanium accounted for the majority of the titanium used in dentures and the proportion of titanium alloy was small. As for the application of titanium, it is yet to be decided whether it is better to use pure titanium, taking advantage of its superior biocompatibility, or to use titanium alloy to maximize its workability. It seems that in our university, the biocompatibility of pure titanium was given more importance. Regarding the titanium alloy, Ti–6A1–4V alloy was used only in the first 3 years and Ti–6A1–7Nb alloy was used subsequently. The alloy was changed because vanadium was reported to be harmful and also changes of color were observed in our university (Fig. 3). In the questionnaires we distributed to clinicians to inquire into the reasons for selecting a titanium denture, biocompatibility and being light-weight were considered as the main reasons. This suggests that their decision was based on a proper understanding of the features of titanium. In fact, titanium was used for those who were diagnosed as or suspected of being allergic to metal in only 6.2% of the cases. ‘‘Patient’s own request’’ comprised 12.3%, which can be attributable to the fact that the patients showed interest in titanium through information obtained from mass communication sources. In our university, approximately 32 titanium dentures per year on average were inserted and they were mostly applied to edentulous or almost edentulous arch, compared with other metal base dentures. Titanium has advantages such as biocompatibility and suitability of laser processing, whereas it also has the problems of adhesiveness to resins [21] and discoloration [22]. However, considering the recent trend to
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Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
Fig. 4. A case of intermixture of various metals in the oral cavity. (a) Intraoral finding; (b) removable partial denture with JIS type 3 pure titanium; (c) the region corresponding to the milling part of the anterior bridge. There was no change of color or corrosion; (d) bridge made from 12% silver–palladium–gold alloy. Discoloration and corrosion were observed in the milling part contacting the titanium denture.
reduce the varieties of metals used in one patient, broader clinical application of titanium should be recommended (Fig. 4). This study was based on the production of titanium dentures in the hospital affiliated to our university. This may be insufficient as an overall survey on the actual use of titanium dentures. In order to understand the nationwide status of titanium denture production, a large-scale survey involving universities and dental laboratories from across the country may be required. Further nationwide surveys on the use of titanium dentures would be desirable. 5. Conclusion We surveyed 1871 metal base dentures fabricated at Tsurumi University Dental Hospital from April 1995 to March 2006. The dentures comprised 68.9% of cobalt–chromium alloy dentures, 18.7% of titanium dentures and 12.3% of platinumadded gold alloy dentures. Complete dentures and complete overdentures accounted for more than half of the titanium dentures and they were mostly used in edentulous or almost edentulous arch. An average of 31.8 titanium dentures (standard deviation 18.7) were produced per year and a tendency for that number to increase was not observed. References [1] Kawazoe T, Suese K. Application of titanium for fixed restorations. J Jpn Prosthodont Soc 1998;42:559–66 [in Japanese]. [2] Onodera S, Hosoi T, Morito M, Miwa E, Okikura Y, Tsuchida F, et al. The clinical evaluation of the metal-based denture using superplastic titanium alloy for upper edentulous patients. J Jpn Prosthodont Soc 1989;33:1381– 7 [in Japanese].
[3] Lautenschlager EP, Monaghan P. Titanium and titanium alloys as dental materials. Int Dent J 1993;43:245–53. [4] Ko¨no¨nen M, Rintanen J, Waltimo A, Kempainen P. Titanium framework removable partial denture used for patient allergic to other metals: a clinical report and literature review. J Prosthet Dent 1995;73:4–7. [5] Tamaki Y, Miyazaki T. Problems on titanium castings for clinical use. J Jpn Prosthodont Soc 1998;42:528–39 [in Japanese]. [6] Miyakawa O, Watanabe K, Okawa S, Nakano S, Kobayashi M, Shiokawa N. Layered structure of cast titanium surface. Dent Mater J 1989;8:175– 85. [7] Bridgeman JT, Marker VA, Hummel SK, Benson BW, Pace LL. Comparison of titanium and cobalt–chromium removable partial denture clasps. J Prosthet Dent 1997;78:187–93. [8] Mori T, Togaya T, Jean-Louis M, Yabugami M. Titanium for removable dentures. I. Laboratory procedures. J Oral Rehabil 1997;24:338–41. [9] Zinelis S. Effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium castings. J Prosthet Dent 2000;84:575–82. [10] Rodrigues RC, Ribeiro RF, de Mattos Mda G, Bezzon OL. Comparative study of circumferential clasp retention force for titanium and cobalt– chromium removable partial dentures. J Prosthet Dent 2002;88:290–6. [11] Eliopoulos D, Zinelis S, Papadopoulos T. The effect of investment material type on the contamination zone and mechanical properties of commercially pure titanium castings. J Prosthet Dent 2005;94:539–48. [12] Ohkubo C, Kurtz KS, Suzuki Y, Hanatani S, Abe M, Hosoi T. Comparative study of maxillary complete dentures constructed of metal base and metal structure framework. J Oral Rehabil 2001;28:149–56. [13] Au AR, Lechner SK, Thomas CJ, Mori T, Chung P. Titanium for removable partial dentures (III): 2-year clinical follow-up in an undergraduate programme. J Oral Rehabil 2000;27:979–85. [14] Thomas CJ, Lechner S, Mori T. Titanium for removable dentures. II. Twoyear clinical observations. J Oral Rehabil 1997;24:414–8. [15] Dharmar S, Rathnasamy RJ, Swaminathan TN. Radiographic and metallographic evaluation of porosity defects and grain structure of cast chromium cobalt removable partial dentures. J Prosthet Dent 1993;69:369–73. [16] Vallittu PK, Kokkonen M. Deflection fatigue of cobalt–chromium, titanium, and gold alloy cast denture clasp. J Prosthet Dent 1995;74:412–9.
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59 [17] Tse ET, Cheng LY, Luk HW, Chu FC, Chai J, Chow TW. Comparison of the retentive characteristics of cobalt–chromium and commercially pure titanium clasps using a novel method. Int J Prosthodont 2006;19:371–2. [18] Iijima D, Yoneyama T, Doi H, Hamanaka H, Kurosaki N. Wear properties of Ti and Ti–6Al–7Nb castings for dental prostheses. Biomaterials 2003;24:1519–24. [19] Mahmoud A, Wakabayashi N, Takahashi H, Ohyama T. Deflection fatigue of Ti–6Al–7Nb, Co–Cr, and gold alloy cast clasps. J Prosthet Dent 2005;93:183–8.
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[20] Al Wazzan KA, Al-Nazzawi AA. Marginal and internal adaptation of commercially pure titanium and titanium–aluminum–vanadium alloy cast restorations. J Contemp Dent Pract 2007;8:19–26. [21] Shimizu H, Kurtz KS, Tachii Y, Takahashi Y. Use of metal conditioners to improve bond strengths of autopolymerizing denture base resin to cast Ti– 6Al–7Nb and Co–Cr. J Dent 2006;34:117–22. [22] Takayama Y, Miura E, Hosoi T, Ishikawa M, Shibuya K. A study on discoloration of Au–Ag–Pd alloy. Part 1. Influence of oral microorganism. J Jpn Prosthodont Soc 2002;46:223–32 [in Japanese].
Journal of Prosthodontic Research 53 (2009) 53–59 www.elsevier.com/locate/jpor
Original article
Survey on use of titanium dentures in Tsurumi University Dental Hospital for 11 years Yasuko Takayama DMD, PhD*, Norio Takishin DMD, PhD, Fujio Tsuchida DMD, PhD, Toshio Hosoi DDS, PhD Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, 2-1-3 Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan Received 19 February 2008; accepted 28 August 2008 Available online 10 January 2009
Abstract Purpose: The purpose of this study was to survey the production of titanium dentures in Tsurumi University Dental Hospital and to study the actual use of titanium dentures in our university. Methods: The survey was based on the metal base dentures produced at Tsurumi University Dental Hospital during an 11-year period between April 1995 and March 2006, with relation to the types of metals used in the dentures, types of dentures, dental condition, and the number of artificial teeth. Results: 1871 metal base dentures were produced in the study period. The dentures consisted of 1290 cobalt–chromium alloy dentures (68.9%), 350 titanium dentures (18.7%) and 231 platinum-added gold alloy dentures (12.3%). Within the titanium denture groups, 132 were complete dentures (37.7%), 55 were complete overdentures (15.7%) and 163 were removable partial dentures (46.6%). JIS type 3 pure titanium was used in the titanium base of 252 dentures (72.0%). The average number of artificial teeth was 10.9, which was the highest among the three types of metal bases, exhibiting significant differences (P < 0.01). Conclusion: Approximately 32 titanium dentures per year on average were delivered at our university and they were applied to almost edentulous arch compared with the other metal base dentures. # 2008 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved. Keywords: Survey; Titanium denture; Cobalt–chromium alloy denture; Platinum-added gold alloy denture; Production
1. Introduction Due to its favorable characteristics, titanium has a wide range of applications in dentistry from implants to crowns and denture bases. The clinical application of titanium for denture bases is one-step further than that of crowns and bridges [1]. Titanium dentures are becoming popular among general clinicians, probably due to the recent availability of titanium casting systems in commercial laboratories. In our university, complete dentures have been fabricated from superplastic titanium alloy since 1987 [2], and by introducing a titanium casting system with a vacuum compression method (GC), we started producing titanium cast denture bases in 1993. Currently, the major metals used in denture casting include cobalt–chromium alloy, titanium (pure titanium, titanium alloy)
* Corresponding author. Tel.: +81 45 581 1001; fax: +81 45 573 9599. E-mail address: [email protected] (Y. Takayama).
and platinum-added gold alloy. Among them, the titanium is considered to be highly biocompatible, light in weight and superior in anti-corrosion and anti-abrasion properties [3–5]. On the other hand, because it is difficult to cast and polish [6– 11], it is not used much despite the above advantages. The purpose of this study was to survey the production of titanium dentures in Tsurumi University Dental Hospital and to reveal the actual use of titanium dentures in our university. 2. Materials and methods We conducted a survey on the metal base dentures fabricated at Tsurumi University Dental Hospital during an 11-year period from April 1995 to March 2006. Based on the laboratory records used in the hospital affiliated with our university, we examined the items shown in Table 1. We added a category of complete overdentures to the type of dentures; however, if stud attachments and copings were used in removable partial dentures, we classified them as removable partial dentures. Moreover, for titanium
1883-1958/$ – see front matter # 2008 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved. doi:10.1016/j.jpor.2008.08.011
54
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
Table 1 Survey items.
Table 2 The number of metal base dentures produced each year.
Installation expected date Clinical record number
Year
Kind of use metal
Platinum-added gold alloy (Au–Pt) Cobalt–chromium alloy (Co–Cr) Titanium (Ti)
Prosthesis
Metal base denture Complete denture (CD) Complete overdenture (COD) Removable partial denture (PD)
Dental condition
Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
The number of artificial teeth Other
Co–Cr
Ti
Au–Pt
Total
n
%
n
%
n
%
n
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
94 83 141 113 119 91 125 149 128 148 99
58.8 60.1 72.3 67.7 66.9 61.1 66.1 83.2 71.9 72.5 73.9
42 29 30 25 33 43 43 17 24 40 24
26.3 21.0 15.4 15.0 18.5 28.9 22.8 9.5 13.5 19.6 17.9
24 26 24 29 26 15 21 13 26 16 11
15.0 18.8 12.3 17.4 14.6 10.1 11.1 7.3 14.6 7.8 8.2
160 138 195 167 178 149 189 179 178 204 134
Average S.D.
117.3 23.3
69.0
31.8 9.1
18.7
21.0 6.2
12.3
170.1 22.8
Attachment Coping Telescopic crown
dentures, we added the types of titanium used in the dentures and each clinician’s reasons for choosing the titanium base, as survey items. The questionnaire for dentists (present prosthetic department staff) included multiple choice questions, but they were asked to describe their reasons when ‘‘others’’ was chosen. 2.1. Data analysis The statistical analysis was performed using a chi-squared test and Kruskal–Wallis test (SPSS Ver. 12.0; SPSS Japan Inc., Tokyo, Japan). The levels of significance used were P < 0.05 and P < 0.01. 3. Results 3.1. Total number of metal base dentures and changes over the period of 11 years 1871 metal base dentures were fabricated at Tsurumi University Dental Hospital during the 11-year period between April 1995 and March 2006. The dentures consisted of 1290 cobalt–chromium alloy dentures (68.9%), 350 titanium dentures (18.7%), and 231 platinum-added gold alloy dentures (12.3%). The number of dentures produced annually is shown in Table 2. The dentures comprised 448 complete dentures (23.9%), 80 complete overdentures (4.3%), and 1343 removable partial dentures (71.8%). 1087 maxillary dentures (58.1%) and 784 mandibular dentures (41.9%) were delivered. The percentage of titanium dentures made each year ranged from 9.5% to 28.9% and approximately 32 titanium dentures on average were delivered each year. 3.2. Features of each metal Of the cobalt–chromium alloy dentures, 288 complete dentures (22.3%), 19 complete overdentures (1.5%), and 983 removable partial dentures (76.2%) were fabricated during the study period. In contrast, the titanium denture group consisted
of 132 complete dentures (37.7%), 55 complete overdentures (15.7%) and 163 removable partial dentures (46.6%). The platinum-added gold alloy denture group consisted of 28 complete dentures (12.1%), 6 complete overdentures (2.6%) and 197 removable partial dentures (85.3%). There was some relationship between the kind of metal used and types of denture (a chi-squared test, P < 0.01). Within each metal-type group, the proportion of the types of dentures fabricated tended to be the same every year. The complete dentures and complete overdentures constituted more than half of the dentures with a titanium denture base. Removable partial dentures were predominantly fabricated with a cobalt–chromium alloy or platinum-added gold alloy base (Fig. 1). In Table 3, dentures are classified according to the site where they were inserted, i.e. maxillary or mandibular, and the proportion of different types of dentures in these two sites was different (a chi-squared test, P < 0.01). In all types of metals, most of the complete dentures were inserted in the maxilla. As for the mandible, the proportion of removable partial dentures was high. Table 4 indicates the dental conditions and the number of artificial teeth. Distal extension missing comprised 63.9% of the cobalt–chromium alloy dentures, while in the platinumadded gold alloy, dentures for bounded missing and distal extension missing corresponded to 21.6% and 63.7%, respectively. In contrast with those figures, edentulous patients and those with a few roots remaining in titanium dentures exhibited a higher percentage of 53.4% and bounded missing was 5.7%. There was some relationship between the kind of metal used and the dental conditions (a chi-squared test, P < 0.01). Similarly, the number of artificial teeth was significantly different among metals groups and highest in the titanium base dentures (Kruskal–Wallis test, P < 0.01). The titanium denture was mostly applied to edentulous or almost edentulous arch with many artificial teeth. 3.3. Titanium types 252 out of 350 titanium dentures were made from JIS type 3 pure titanium (72.0%); 39 were from titanium alloy (Ti–6A1–
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
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Fig. 1. Annual percentage of each denture.
4V alloy or Ti–6A1–7Nb alloy) (11.1%); and 59 were unknown (16.9%). 3.4. Reasons for selecting titanium We prepared questionnaires to determine the prime reason for selecting a titanium denture, targeting 33 dentists who delivered the titanium dentures. The response ‘‘high biocompatibility’’ accounted for 37.0%, which was the most common reason for selecting titanium, followed by ‘‘light-weight’’ with 23.3% (Table 5). 4. Discussion The metal base dentures produced at our university were predominantly cobalt–chromium alloy dentures, and titanium dentures comprised only 18.7%. Although cobalt–chromium alloy was introduced as a substitute for platinum-added gold alloy, it is now well accepted as a material which can be used in
metal denture bases. Platinum-added gold alloy seemed to comprise a small proportion of denture production because it is often used in conjunction with precision attachments and it is more expensive than other metals. The dentists’ (present prosthetic department staff) evaluations of the titanium dentures were not constant at the time of the investigation. On the other hand, the reliability of cobalt–chromium alloy dentures is high based on the experiences gained from it being used for a long time. In addition, the cost of titanium dentures is higher than that of cobalt–chromium alloy dentures in our hospital. Moreover, platinum-added gold alloy dentures are also very expensive. When a metal base denture is recommended to the patient, the price becomes an important factor. It is easy to recommend the patient a cheaper one. The ratio of each type of metal base denture fabrication in this investigation seemed consistent when pricing was considered. Compared to the cobalt–chromium alloy denture, the titanium denture was likely to be applied in edentulous or almost edentulous arch. It is highly possible that the titanium
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Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
Table 3 The number and percentage of each denture made of different types of metals (the maxilla and mandible). Co–Cr
Ti
Au–Pt
Total
n
%
n
%
n
%
n
%
Maxilla Mandible
754 536
58.4 41.6
230 120
65.7 34.3
103 128
44.6 55.4
1087 784
58.1 41.9
Maxilla Complete denture Complete overdenture Removable partial denture
210 12 532
27.9 1.6 70.5
107 40 83
46.5 17.4 36.1
20 3 80
19.4 2.9 77.6
337 55 695
31.0 5.0 64.0
Mandible Complete denture Complete overdenture Removable partial denture
78 7 451
14.6 1.3 84.1
25 15 80
20.8 12.5 66.7
8 3 117
6.3 2.3 91.5
111 25 648
14.2 3.2 82.6
Table 4 The position and number of artificial teeth in each metal base denture. Co–Cr
Ti
Au–Pt
Total
n
%
n
%
n
%
n
%
Total Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
158 385 440 19 288
12.2 29.8 34.1 1.5 22.3
20 56 87 55 132
5.7 16.0 24.9 15.7 37.7
50 75 72 6 28
21.6 32.5 31.2 2.6 12.1
228 516 599 80 448
12.2 27.6 32.0 4.3 23.9
Maxilla Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
133 209 190 12 210
17.6 27.7 25.2 1.6 27.9
17 29 37 40 107
7.4 12.6 16.1 17.4 46.5
27 30 23 3 20
26.2 29.1 22.3 2.9 19.4
177 268 250 55 337
16.3 24.7 23.0 5.0 31.0
Mandible Bounded missing Unilateral distal extension missing Bilateral distal extension missing A few roots remaining Edentulous
25 176 250 7 78
4.7 32.8 46.6 1.3 14.6
3 27 50 15 25
2.5 22.5 41.7 12.5 20.8
23 45 49 3 8
18.0 35.2 38.3 2.3 6.3
51 248 349 25 111
6.5 31.6 44.5 3.2 14.2
The number of artificial teeth Average S.D.
8.5 4.1
10.9 4.0
Table 5 Responses to the questionnaire. (1) (2) (3) (4) (5) (6) (7)
Allergic disorders were noted or suspected High biocompatibility Light-weight Interest in new material At patient’s request Easy to explain the advantages Other reasons
9 54 34 26 18 1 4
(6.2) (37.0) (23.3) (17.8) (12.3) (0.7) (2.7)
denture was often chosen to be used in maxillary complete dentures and complete overdentures mainly because it’s lightweight. In particular, in our university, it is often the case that metal structure dentures are designed for complete dentures and complete overdentures (Fig. 2). A metal structure framework designed as a three-dimensional framework, such as a double
6.7 4.3
structure, a T-shaped structure, or a trussed structure could resolve the strength issue [12]. In the double structure design, the occlusal surface consists of cut metal teeth or cut metal backing and a substructure near the alveolar ridge connected by a series of columns. Although metal structure dentures are strong and rigid, they also have the disadvantage of being heavy. As a consequence, titanium dentures may have been purposefully applied in order to reduce the weight. Because we tend to choose cobalt–chromium alloy dentures as the first selection among the metal base dentures, the number of complete dentures made of cobalt–chromium alloy was more than that of titanium. However, for the complete overdentures, the percentage of those made of titanium was rather large. In such cases, metal structure dentures were frequently applied in order to reinforce the dentures. It seemed that titanium was selected to fabricate the denture to be as light as possible.
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
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Fig. 2. An example of the titanium denture with metal structure. (a) Occlusal view; (b) buccal view; (c) removable partial denture with metal structure.
Fig. 3. Ti–6A1–4V alloy denture showing change of color after 3 years of wearing. (a) Occlusal view; (b) denture basal surface view.
It can also be assumed that the use of titanium denture bases in removable partial dentures is not common because of the fact that titanium cast clasps have not yet obtained sufficient credibility. Au et al. examined the success of titanium removable partial dentures compared with that of cobalt– chromium alloy removable partial dentures in a 2-year clinical follow-up [13]. The results showed a higher incidence of failures in titanium removable partial dentures prior to the 12month review, suggesting the importance of taking its lower rigidity into account when designing removable partial dentures. Moreover, they reported a 91% survival rate for rests and retainers and the dentures were found to be more comfortable (55%) and preferred (64%) than the cobalt– chromium alloy dentures [14]. Many research papers indicated that although the retentive force of titanium clasps was inferior to that of cobalt–chromium alloy clasps, the retentive force was only slightly lower in the titanium clasps [7,10,15–17]. In addition, the long-term retentive resiliency of the pure titanium and titanium alloy clasps suggested suitability of these materials for removable partial dentures [7,10,13–18]. Bridgeman et al. pointed out that porosity was more apparent in the pure titanium and titanium alloy clasps than in those made from cobalt–chromium alloy, but the amount of porosity did not correspond to evidence of fractures or permanent deformation [7]. Moreover, the utility of clasps made of Ti–6A1–7Nb alloy was verified [19,20]. As mentioned above, the credibility of titanium clasps has been confirmed by various studies. However, since our confidence in cobalt–chromium alloy clasps was extremely high, titanium was used less in removable partial dentures. At the beginning of the research period, the reliability of the titanium denture was not enough. Therefore, it
seemed that many dentists had a tendency to choose cobalt– chromium alloy dentures as the conservative selection. Considering the different types of titanium, JIS type 3 pure titanium accounted for the majority of the titanium used in dentures and the proportion of titanium alloy was small. As for the application of titanium, it is yet to be decided whether it is better to use pure titanium, taking advantage of its superior biocompatibility, or to use titanium alloy to maximize its workability. It seems that in our university, the biocompatibility of pure titanium was given more importance. Regarding the titanium alloy, Ti–6A1–4V alloy was used only in the first 3 years and Ti–6A1–7Nb alloy was used subsequently. The alloy was changed because vanadium was reported to be harmful and also changes of color were observed in our university (Fig. 3). In the questionnaires we distributed to clinicians to inquire into the reasons for selecting a titanium denture, biocompatibility and being light-weight were considered as the main reasons. This suggests that their decision was based on a proper understanding of the features of titanium. In fact, titanium was used for those who were diagnosed as or suspected of being allergic to metal in only 6.2% of the cases. ‘‘Patient’s own request’’ comprised 12.3%, which can be attributable to the fact that the patients showed interest in titanium through information obtained from mass communication sources. In our university, approximately 32 titanium dentures per year on average were inserted and they were mostly applied to edentulous or almost edentulous arch, compared with other metal base dentures. Titanium has advantages such as biocompatibility and suitability of laser processing, whereas it also has the problems of adhesiveness to resins [21] and discoloration [22]. However, considering the recent trend to
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Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59
Fig. 4. A case of intermixture of various metals in the oral cavity. (a) Intraoral finding; (b) removable partial denture with JIS type 3 pure titanium; (c) the region corresponding to the milling part of the anterior bridge. There was no change of color or corrosion; (d) bridge made from 12% silver–palladium–gold alloy. Discoloration and corrosion were observed in the milling part contacting the titanium denture.
reduce the varieties of metals used in one patient, broader clinical application of titanium should be recommended (Fig. 4). This study was based on the production of titanium dentures in the hospital affiliated to our university. This may be insufficient as an overall survey on the actual use of titanium dentures. In order to understand the nationwide status of titanium denture production, a large-scale survey involving universities and dental laboratories from across the country may be required. Further nationwide surveys on the use of titanium dentures would be desirable. 5. Conclusion We surveyed 1871 metal base dentures fabricated at Tsurumi University Dental Hospital from April 1995 to March 2006. The dentures comprised 68.9% of cobalt–chromium alloy dentures, 18.7% of titanium dentures and 12.3% of platinumadded gold alloy dentures. Complete dentures and complete overdentures accounted for more than half of the titanium dentures and they were mostly used in edentulous or almost edentulous arch. An average of 31.8 titanium dentures (standard deviation 18.7) were produced per year and a tendency for that number to increase was not observed. References [1] Kawazoe T, Suese K. Application of titanium for fixed restorations. J Jpn Prosthodont Soc 1998;42:559–66 [in Japanese]. [2] Onodera S, Hosoi T, Morito M, Miwa E, Okikura Y, Tsuchida F, et al. The clinical evaluation of the metal-based denture using superplastic titanium alloy for upper edentulous patients. J Jpn Prosthodont Soc 1989;33:1381– 7 [in Japanese].
[3] Lautenschlager EP, Monaghan P. Titanium and titanium alloys as dental materials. Int Dent J 1993;43:245–53. [4] Ko¨no¨nen M, Rintanen J, Waltimo A, Kempainen P. Titanium framework removable partial denture used for patient allergic to other metals: a clinical report and literature review. J Prosthet Dent 1995;73:4–7. [5] Tamaki Y, Miyazaki T. Problems on titanium castings for clinical use. J Jpn Prosthodont Soc 1998;42:528–39 [in Japanese]. [6] Miyakawa O, Watanabe K, Okawa S, Nakano S, Kobayashi M, Shiokawa N. Layered structure of cast titanium surface. Dent Mater J 1989;8:175– 85. [7] Bridgeman JT, Marker VA, Hummel SK, Benson BW, Pace LL. Comparison of titanium and cobalt–chromium removable partial denture clasps. J Prosthet Dent 1997;78:187–93. [8] Mori T, Togaya T, Jean-Louis M, Yabugami M. Titanium for removable dentures. I. Laboratory procedures. J Oral Rehabil 1997;24:338–41. [9] Zinelis S. Effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium castings. J Prosthet Dent 2000;84:575–82. [10] Rodrigues RC, Ribeiro RF, de Mattos Mda G, Bezzon OL. Comparative study of circumferential clasp retention force for titanium and cobalt– chromium removable partial dentures. J Prosthet Dent 2002;88:290–6. [11] Eliopoulos D, Zinelis S, Papadopoulos T. The effect of investment material type on the contamination zone and mechanical properties of commercially pure titanium castings. J Prosthet Dent 2005;94:539–48. [12] Ohkubo C, Kurtz KS, Suzuki Y, Hanatani S, Abe M, Hosoi T. Comparative study of maxillary complete dentures constructed of metal base and metal structure framework. J Oral Rehabil 2001;28:149–56. [13] Au AR, Lechner SK, Thomas CJ, Mori T, Chung P. Titanium for removable partial dentures (III): 2-year clinical follow-up in an undergraduate programme. J Oral Rehabil 2000;27:979–85. [14] Thomas CJ, Lechner S, Mori T. Titanium for removable dentures. II. Twoyear clinical observations. J Oral Rehabil 1997;24:414–8. [15] Dharmar S, Rathnasamy RJ, Swaminathan TN. Radiographic and metallographic evaluation of porosity defects and grain structure of cast chromium cobalt removable partial dentures. J Prosthet Dent 1993;69:369–73. [16] Vallittu PK, Kokkonen M. Deflection fatigue of cobalt–chromium, titanium, and gold alloy cast denture clasp. J Prosthet Dent 1995;74:412–9.
Y. Takayama et al. / Journal of Prosthodontic Research 53 (2009) 53–59 [17] Tse ET, Cheng LY, Luk HW, Chu FC, Chai J, Chow TW. Comparison of the retentive characteristics of cobalt–chromium and commercially pure titanium clasps using a novel method. Int J Prosthodont 2006;19:371–2. [18] Iijima D, Yoneyama T, Doi H, Hamanaka H, Kurosaki N. Wear properties of Ti and Ti–6Al–7Nb castings for dental prostheses. Biomaterials 2003;24:1519–24. [19] Mahmoud A, Wakabayashi N, Takahashi H, Ohyama T. Deflection fatigue of Ti–6Al–7Nb, Co–Cr, and gold alloy cast clasps. J Prosthet Dent 2005;93:183–8.
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[20] Al Wazzan KA, Al-Nazzawi AA. Marginal and internal adaptation of commercially pure titanium and titanium–aluminum–vanadium alloy cast restorations. J Contemp Dent Pract 2007;8:19–26. [21] Shimizu H, Kurtz KS, Tachii Y, Takahashi Y. Use of metal conditioners to improve bond strengths of autopolymerizing denture base resin to cast Ti– 6Al–7Nb and Co–Cr. J Dent 2006;34:117–22. [22] Takayama Y, Miura E, Hosoi T, Ishikawa M, Shibuya K. A study on discoloration of Au–Ag–Pd alloy. Part 1. Influence of oral microorganism. J Jpn Prosthodont Soc 2002;46:223–32 [in Japanese].