Clin Oral Invest DOI 10.1007/s00784-014-1248-8
REVIEW
The single midline implant in the edentulous mandible: a systematic review Nicole Passia & Matthias Kern
Received: 21 July 2013 / Accepted: 24 April 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Objectives The concept of a single midline implant retaining a complete mandibular denture is controversially discussed among experts. Studies are rare in the literature, and commonly accepted recommendations for this treatment options are not available. This systematic literature review was performed to give an overview over the current literature on the single midline implant therapy for the edentulous mandible and to reveal whether this treatment option might be an alternative to commonly accepted treatment modalities with more implants. Methods A review of the literature published until 24th of May 2013 was conducted to identify in vivo studies on the single midline implant concept with a mean follow-up time of at least 3 months. Results From the electronic search, 11 studies were finally included. After an observation period of 3–60 months, the implant survival rate ranged from 62.5 to 100 %. The most frequent prosthetic maintenance intervention was “activation of the matrix” followed by “repair of fractured denture base.” Conclusions The concept of one single midline implant to retain a mandibular complete denture can be an alternative, especially for elderly patients. Immediate loading of the implants should be avoided, and the way of integrating the matrix into the denture base should be carefully considered.
Keywords Single midline implant . Edentulous mandible . Mandibular complete denture . Implant-supported overdenture . Implant therapy
N. Passia (*) : M. Kern Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University, Arnold-Heller-Str. 16, 24105 Kiel, Germany e-mail: [email protected]
Introduction Despite numerous improved methods for tooth preservation, caries control, and periodontal treatment, edentulism is a present condition in the elderly generation in many countries [1, 2]. Edentulous people are often dissatisfied with the stability of their mandibular complete denture and complain about a reduced masticatory function. As a result, their quality of life is often severely reduced [3, 4]. According to the McGill consensus statement, an implant therapy with two implants in the interforaminal area should be the first choice of treatment for the edentulous mandible [5]. Indeed, mandibular overdentures retained by two implants improve masticatory function and show high implant success rates [6–10], but unfortunately, edentulism is often connected to a low income [11], and many edentulous patients cannot afford a therapy with two or more implants. An implant therapy with one single midline implant to retain a mandibular complete denture might be a lower-cost alternative. This treatment option was for the first time described by Cordioli [12] in 1993. The first 5-year results from a prospective clinical trial were published in 1997 with an implant success rate of 100 % [13]. Oral comfort and function were significantly improved. In 2009, Walton et al., comparing an implant therapy with one or two implants, revealed comparable patients’ satisfaction and maintenance time, with lower treatment time and component cost, when mandibular prostheses were retained by one instead of two implants [1]. However, studies investigating the single midline implant supporting a complete mandibular denture are rare in literature, and no commonly accepted recommendations for this treatment option are available. The aim of this systematic literature review was to give an overview over the available literature on the single midline implant therapy for the edentulous mandible and to reveal whether this treatment option might be an alternative to
Clin Oral Invest
commonly accepted treatment modalities with two or more implants.
Materials and methods Search strategy An electronic database (PubMed) search was performed for English language publications published until 24th of May 2013. Five search terms were used for every search run. These included “single” AND “midline” AND “implant” AND “mandibular” AND “denture,” single, AND “dental” AND implant AND mandibular AND denture, single, AND “median” AND implant AND mandibular AND denture. The search term single was replaced by the search term “one,” the search term denture was replaced by the search term “overdenture” as well as “prostheses,” and the search term midline was replaced by the search term “symphyseal” for further search runs (Table 1). In addition, a manual search was conducted based on the references in the full-text articles selected from the electronic search. The following inclusion and exclusion criteria were defined to select the articles included in this systematic review. Inclusion criteria
Study selection Titles and abstracts found through the electronic and manual search were screened for possible inclusion. Full-text versions of all investigations with possible relevance for this review were selected and screened again. Articles that could not be clearly identified as relevant or not by title or abstract were screened via full text, as well. All studies that met the defined inclusion criteria underwent data extraction. Data extraction For all investigations, the following data were recorded, if available: number and mean age of patients, dental status of the opposing maxilla, healing mode and loading protocol, implant surface, attachment system, observation period, implant survival rate, most frequent prosthodontic maintenance interventions, and patients’ satisfaction. Unfortunately, due to the heterogeneity of the included studies concerning observation time, healing mode, loading protocol, and others, a statistical analysis of the accumulated data was not justifiable [14].
Results – –
English language publications Clinical trials using a single midline implant in the mandible to retain an overdenture Exclusion criteria
– – –
Case reports Review articles In-vitro investigations
The initial database search yielded 938 hits. After eliminating duplicates, 238 titles remained. The manual search revealed no further articles that met the inclusion criteria. After screening the abstracts, 219 articles were excluded because they did not relate to the therapy using a single midline implant to retain a mandibular overdenture. Therefore, 19 articles were selected for full-text screening, of which eight clinical reports were excluded because they did not meet the inclusion criteria
Table 1 Search terms Search run
1 2 3 4 5 6 7 8 9 10 11 12 13
Search terms
Number of obtained references
1
2
3
4
5
Single Single Single Single Single Single One One One One Single Single Single
Midline Dental Median Median Midline Dental Midline Median Median Midline Midline Symphyseal Symphyseal
Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant
Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular
Denture Denture Denture Prostheses Prostheses Prostheses Prostheses Prostheses Overdenture Overdenture Overdenture Overdenture Prostheses
12 236 3 13 12 586 17 26 9 7 11 1 5
Clin Oral Invest
(Fig. 1). So finally, 11 studies were included in this review for further analysis (Table 2). The main reasons for exclusion were in-vitro studies or case reports. Excluded studies and reasons for their exclusion are listed in Table 3. A total of 255 completely edentulous patients were treated with a single implant in the midline of the mandible (Fig. 2). The mean age was 67.9 years. Healing modes, loading protocols, implant systems, and utilized attachment systems are summarized in Table 2, together with observation times, implant survival rates, complications, and patient satisfaction.
Implant survival rate Five of the included studies reported an implant survival rate of 100 % [1, 13, 15–17] (Table 2). Their observation periods ranged from 12 to 60 months. In these studies, immediate loading was avoided, and the implants were left unloaded or moderately loaded due to the healing abutment for at least 2 weeks. Whenever information on the implant surfaces was given, those were modern surfaces, mostly air-abraded and acid-etched. Another study reported also an implant survival rate of 100 % after 36 months of observation, when implants with
First electronic search 938 hits
After eliminating duplicates
air-abraded and acid-etched surfaces were inserted [18]. However, in the same study, an implant failure rate of 37.5 % was revealed when implants with machined surfaces were used. It must be to emphasize that in this study, all implants were loaded immediately. The attachment systems used in the above studies were, in most instances, integrated into the denture base intraorally (Fig. 3). Three of the included studies reported implant survival rates less than 100 % over an observation period of 12 to 36 months [10, 18, 19] (Table 2). In two studies, the implants were immediately loaded, and in one study, the implants were loaded after 6 weeks, following a non-submerged healing protocol. Implant surfaces were TiUnite, machined or not clearly defined. The attachment systems in those studies with failing implants were integrated into the denture base extraorally in the dental laboratory.
Prosthodontic complications/prosthodontic maintenance interventions The most frequent prosthetic maintenance intervention was “activation or exchange of the matrix” due to loss of retention over an observation period between 3 and 60 months. After an observation period of 36 months, Liddelow and Henry described three denture base fractures in the attachment area being the most frequent complication [18]. “Fracture of the denture base” was the second common prosthodontic complication. Most of the fractured dentures were not provided with a metal framework. In a retrospective investigation on the fracture incidence of overdentures retained by one or two implants with no metal reinforcement of the denture base, Gonda et al. [20] reported a fracture rate of 21.4 % in the one-implant group and 9.3 % in the two-implant group after an observation time of at least 17 months. The differences were not statistically significant.
238 titles Patients’ satisfaction
First selection based on abstract screening 19 titels for full- text analysis
11 included studies Fig. 1 Search strategy
Eight of the included studies provided information on the patients’ satisfaction [1, 13, 15–18, 21, 22]. A significant increase in all comfort and functional parameters due to the implant therapy was observed in all clinical trials evaluating these parameters. Cheng et al. [21], comparing two different attachment systems in their investigation, found no significant difference between the two treatment groups regarding overall satisfaction after 3 months of observation. Walton et al., comparing patients’ satisfaction between one and two implants, reported comparable results between the two groups [1]. Treatment time, treatment costs, and maintenance time were significantly reduced in the oneimplant group.
2013
Grover et al. [22]
10/70
15/53–83
42/67
42/68
20/62
21/74.2
ns/el (7 days)
ns/el (10 weeks)
Complete denture
Complete dentures
ns/ll (3 months)
ns/el (6 weeks)
ns/il
ns/il
s/ll (3 months)
6 ns, 5 s/el (2 months)
MTX surface
Air-abraded/ acid-etched
SLActive
25 oxidized surfaces/7 machined surfaces Not listed
TiUnite
Air-abraded/ acid-etched
Air-abraded, acid-etched
SLActive
Not listed
s/llb (4 months)
ns/el (3 weeks)
Not listed
Implant surface
ns/el (6 weeks)
Healing mode/ loading protocol
Complete denture
Complete denture
Complete denture Complete denture
Complete denture
Complete denture
Complete denture
Complete denture
Complete denture
Maxilla
Magnet
Stud (locator), magnetic (Magfit)/io
Gold matrix/io
3
3
At least 17 months
12
36
ball/eo
ball/io
12
18
43.4 (mean)
12
60
12
Observation period (months)
Ball/eo
Ball/N.N.
Retentive anchor with a titanium matrix/eo Ball/io
O-ring/ball/io
Ball/locator/eo
Attachment system/way of integrationa
–
–
–
–
Countering of denture base, followed by adjustment of the matrix No other complications than fracture are investigated –
Fracture of denture base
–
Activation/exchange of the matrix
Activation/exchange of the matrix
Activation/exchange of matrix
Activation of the matrix
Most frequent prosthetic maintenance intervention
100 %
100 % (oxidized surface), 62.5 % (machined surface)
82 %
100 %
100 %
100 %
91.7 % (total, all implant failures in one group) 100 %
Implant survival rate (%)
b
a
At least 3 months after implant placement
Way of integrating the matrix: intraoral/extraoral
s submerged, ns non-submerged, il immediately loaded, el early loaded, ll lately loaded, RCT randomized clinical trial, io intraoral, eo extraoral
2012
2010
Cheng et al. [21]
2010
2010
32/68
2011
Krennmair and Ulm [17] Kronstrom et al. [10] Liddelow and Henry [18]
Gonda et al. [20]
17/53,2
2011
Harder et al. [15]
2009
9/82.2
2012
El-Sheikh et al. [16]
Walton et al. [1]
11/66.7
1997
Cordioli et al. [13]
36/68
2011
Alsabeeha et al. [19]
Number of patients /mean age (N/Y, years)
Year of publication
Included studies
Table 2 Summary of the included literature
Significant improvement in satisfaction and masticatory performance Significant improvement in satisfaction and in masticatory performance
–
Remarkable improvement of all parameters of oral comfort and prostheses function Significant improvement in satisfaction
–
No
No
No (retrospective)
Yes
No
Yes
No
No
No
No
No
–
Remarkable improvement of all parameters of oral comfort and prostheses function Significant increase in all comfort and functional parameters Significant improvement in the oral health-related quality of life Improvement in patients’ subjective satisfaction
RCT comparing 1 vs 2 implants
Patients’ satisfaction
Clin Oral Invest
Clin Oral Invest Table 3 Excluded articles after full-text screening and reasons for exclusion Reference Review articles Alsabeeha et al. [24] Case reports Wolfart et al. [25]
Year of publication
2009 2008
Schneider and Synan [26] 2011 In vitro studies Maeda et al. [27] 2008 Yokoyama et al. [28] 2005 Alsabeeha et al. [29] 2011 Investigations having already been published over a longer observation period Liddelow and Henry [30] 2007 Results having already been published elsewhere Alsabeeha et al. [31] 2010
Discussion This systematic literature review was conducted to give an overview over the current literature on the single midline implant therapy for the edentulous mandible and to reveal whether this treatment option might be an alternative to commonly accepted treatment modalities with two or more implants. Edentulous patients are often dissatisfied with their conventional complete mandibular denture but cannot afford an implant therapy with two or more implants. One single midline implant might be a lower-cost alternative, but there is still no longer-term scientific evidence for the applicability of this treatment option. A number of studies were identified and selected for this review if conform to the applied inclusion criteria. Despite the heterogeneity of the included studies, the concept of one single midline implant retaining a complete mandibular denture showed high implant survival rates as long as modern implant surfaces were chosen and immediate loading was avoided. In those cases, healing mode, either submerged or non-submerged, did not seem to influence implant success.
Fig. 2 Single implant in the midline of the mandible
Fig. 3 Denture base with intraorally integrated matrix
Implants, provided with a healing abutment directly after implant placement, did not show higher failure rates than implants that were allowed to heal submerged, despite the chewing forces they were exposed to [15]. The attachment system did not have any influence on implant success or prosthodontic complications. The most frequent maintenance intervention was activation or exchange of the matrix which is a common intervention when two or more implants are used, as well [23]. The matrix should be regarded as an expendable part, and patients have to be informed about that prior to treatment. It is interesting to see that those investigations with high implant failure rates did not integrate the matrix intraorally but sent the denture base to the laboratory, having taken an impression before. This could have led to inaccuracies and an overload of the implant, especially during function. Therefore, it is suggested that the attachment matrix is integrated into the existing denture base intraorally in occlusion to avoid possible overloading of the implant during healing. Another frequent prosthetic complication was fracture of the denture base with a fracture rate of 21.4 to 36 % during the first 42 months of observation [15, 20]. Fractures occurred predominantly in the area of the attachment system, and most of the fractured denture bases were not reinforced with a metal framework. The matrices of the attachment systems were mainly integrated into already existing denture bases. That might have led to thin resin bases being weak and instable in the attachment area. It might be useful to reinforce thin denture bases in the anterior region with a metal framework. When evaluated, patients’ satisfaction and oral healthrelated quality of life was significantly improved in all studies after the insertion of one single midline implant. The attachment system does not seem to have any influence on patients’ overall satisfaction [21]. However, studies investigating the concept of one single midline implant retaining a complete mandibular denture were conducted only with a small number of patients over a short- to medium-term observation time. Valid data over an observation period of more than 5 years are still missing, and the need for randomized controlled clinical
Clin Oral Invest
trials comparing clinical treatment modalities is obvious from the data revealed by the current review.
Conclusions The concept of one single midline implant to retain a mandibular complete denture can be an alternative, especially for elderly patients. Immediately loading of the implants should be avoided, and the way of integrating the matrix into the denture base should be carefully considered.
References 1. Walton JN, Glick N, Macentee MI (2009) A randomized clinical trial comparing patient satisfaction and prosthetic outcomes with mandibular overdentures retained by one or two implants. Int J Prosthodont 22:331–339 2. Zitzmann NU, Hagmann E, Weiger R (2007) What is the prevalence of various types of prosthetic dental restorations in Europe? Clin Oral Implants Res 18(Suppl 3):20–33 3. Moynihan P, Thomason M, Walls A, Gray-Donald K, Morais JA, Ghanem H, Wollin S, Ellis J, Steele J, Lund J, Feine J (2009) Researching the impact of oral health on diet and nutritional status: methodological issues. J Dent 37:237–249 4. Fiske J, Davis DM, Frances C, Gelbier S (1998) The emotional effects of tooth loss in edentulous people. Br Dent J 184:90–93, discussion 79 5. Feine JS, Carlsson GE, Awad MA, Chehade A, Duncan WJ, Gizani S, Head T, Lund JP, MacEntee M, Mericske-Stern R, Mojon P, Morais J, Naert I, Payne AG, Penrod J, Stoker GT, Tawse-Smith A, Taylor TD, Thomason JM, Thomson WM, Wismeijer D (2002) The McGill consensus statement on overdentures. Mandibular twoimplant overdentures as first choice standard of care for edentulous patients. Montreal, Quebec, May 24-25, 2002. Int J Oral Maxillofac Implants 17:601–602 6. Bergendal T, Engquist B (1998) Implant-supported overdentures: a longitudinal prospective study. Int J Oral Maxillofac Implants 13: 253–262 7. Feine JS, de Grandmont P, Boudrias P, Brien N, LaMarche C, Tache R, Lund JP (1994) Within-subject comparisons of implant-supported mandibular prostheses: choice of prosthesis. J Dent Res 73:1105–1111 8. Gotfredsen K, Holm B (2000) Implant-supported mandibular overdentures retained with ball or bar attachments: a randomized prospective 5-year study. Int J Prosthodont 13:125–130 9. Feine JS, Maskawi K, de Grandmont P, Donohue WB, Tanguay R, Lund JP (1994) Within-subject comparisons of implant-supported mandibular prostheses: evaluation of masticatory function. J Dent Res 73:1646–1656 10. Kronstrom M, Davis B, Loney R, Gerrow J, Hollender L (2010) A prospective randomized study on the immediate loading of mandibular overdentures supported by one or two implants: a 12-month follow-up report. Int J Oral Maxillofac Implants 25:181–188 11. Marcus SE, Kaste LM, Brown LJ (1994) Prevalence and demographic correlates of tooth loss among the elderly in the United States. Spec Care Dentist 14:123–127 12. Cordioli GP (1993) Mandibular overdentures supported by a single implant. Minerva Stomatol 42:469–473
13. Cordioli G, Majzoub Z, Castagna S (1997) Mandibular overdentures anchored to single implants: a five-year prospective study. J Prosthet Dent 78:159–165 14. Needleman IG (2002) A guide to systematic reviews. J Clin Periodontol 29(Suppl 3):6–9, discussion 37-8 15. Harder S, Wolfart S, Egert C, Kern M (2011) Three-year clinical outcome of single implant-retained mandibular overdentures—results of preliminary prospective study. J Dent 39:656–661 16. El-Sheikh AM, Shihabuddin OF, Ghoraba SM (2012) A prospective study of early loaded single implant-retained mandibular overdentures: preliminary one-year results. Int J Dent 2012:236409 17. Krennmair G, Ulm C (2001) The symphyseal single-tooth implant for anchorage of a mandibular complete denture in geriatric patients: a clinical report. Int J Oral Maxillofac Implants 16: 98–104 18. Liddelow G, Henry P (2010) The immediately loaded single implantretained mandibular overdenture: a 36-month prospective study. Int J Prosthodont 23:13–21 19. Alsabeeha NH, Payne AG, De Silva RK, Thomson WM (2011) Mandibular single-implant overdentures: preliminary results of a randomised-control trial on early loading with different implant diameters and attachment systems. Clin Oral Implants Res 22:330– 337 20. Gonda T, Maeda Y, Walton JN, MacEntee MI (2010) Fracture incidence in mandibular overdentures retained by one or two implants. J Prosthet Dent 103:178–181 21. Cheng T, Sun G, Huo J, He X, Wang Y, Ren YF (2012) Patient satisfaction and masticatory efficiency of single implant-retained mandibular overdentures using the stud and magnetic attachments. J Dent 40:1018–1023 22. Grover M, Vaidyanathan AK, Veeravalli PT (2013) OHRQoL, masticatory performance and crestal bone loss with single-implant, magnet-retained mandibular overdentures with conventional and shortened dental arch. Clin Oral Implants Res. doi:10.1111/clr.12111 23. Andreiotelli M, Att W, Strub JR (2010) Prosthodontic complications with implant overdentures: a systematic literature review. Int J Prosthodont 23:195–203 24. Alsabeeha N, Payne AG, De Silva RK, Swain MV (2009) Mandibular single-implant overdentures: a review with surgical and prosthodontic perspectives of a novel approach. Clin Oral Implants Res 20:356–365 25. Wolfart S, Braasch K, Brunzel S, Kern M (2008) The central single implant in the edentulous mandible: improvement of function and quality of life. A report of 2 cases. Quintessence Int 39: 541–548 26. Schneider GB, Synan WJ (2011) Use of a single implant to retain a mandibular overdenture on the compromised atrophic alveolar ridge: a case report. Spec Care Dentist 31:138–142 27. Maeda Y, Horisaka M, Yagi K (2008) Biomechanical rationale for a single implant-retained mandibular overdenture: an in vitro study. Clin Oral Implants Res 19:271–275 28. Yokoyama S, Wakabayashi N, Shiota M, Ohyama T (2005) Stress analysis in edentulous mandibular bone supporting implant-retained 1-piece or multiple superstructures. Int J Oral Maxillofac Implants 20:578–583 29. Alsabeeha NH, Swain MV, Payne AG (2011) Clinical performance and material properties of single-implant overdenture attachment systems. Int J Prosthodont 24:247–254 30. Liddelow GJ, Henry PJ (2007) A prospective study of immediately loaded single implant-retained mandibular overdentures: preliminary one-year results. J Prosthet Dent 97:S126–S137 31. Alsabeeha NH, De Silva RK, Thomson WM, Payne AG (2010) Primary stability measurements of single implants in the midline of the edentulous mandible for overdentures. Clin Oral Implants Res 21: 563–566
REVIEW
The single midline implant in the edentulous mandible: a systematic review Nicole Passia & Matthias Kern
Received: 21 July 2013 / Accepted: 24 April 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract Objectives The concept of a single midline implant retaining a complete mandibular denture is controversially discussed among experts. Studies are rare in the literature, and commonly accepted recommendations for this treatment options are not available. This systematic literature review was performed to give an overview over the current literature on the single midline implant therapy for the edentulous mandible and to reveal whether this treatment option might be an alternative to commonly accepted treatment modalities with more implants. Methods A review of the literature published until 24th of May 2013 was conducted to identify in vivo studies on the single midline implant concept with a mean follow-up time of at least 3 months. Results From the electronic search, 11 studies were finally included. After an observation period of 3–60 months, the implant survival rate ranged from 62.5 to 100 %. The most frequent prosthetic maintenance intervention was “activation of the matrix” followed by “repair of fractured denture base.” Conclusions The concept of one single midline implant to retain a mandibular complete denture can be an alternative, especially for elderly patients. Immediate loading of the implants should be avoided, and the way of integrating the matrix into the denture base should be carefully considered.
Keywords Single midline implant . Edentulous mandible . Mandibular complete denture . Implant-supported overdenture . Implant therapy
N. Passia (*) : M. Kern Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University, Arnold-Heller-Str. 16, 24105 Kiel, Germany e-mail: [email protected]
Introduction Despite numerous improved methods for tooth preservation, caries control, and periodontal treatment, edentulism is a present condition in the elderly generation in many countries [1, 2]. Edentulous people are often dissatisfied with the stability of their mandibular complete denture and complain about a reduced masticatory function. As a result, their quality of life is often severely reduced [3, 4]. According to the McGill consensus statement, an implant therapy with two implants in the interforaminal area should be the first choice of treatment for the edentulous mandible [5]. Indeed, mandibular overdentures retained by two implants improve masticatory function and show high implant success rates [6–10], but unfortunately, edentulism is often connected to a low income [11], and many edentulous patients cannot afford a therapy with two or more implants. An implant therapy with one single midline implant to retain a mandibular complete denture might be a lower-cost alternative. This treatment option was for the first time described by Cordioli [12] in 1993. The first 5-year results from a prospective clinical trial were published in 1997 with an implant success rate of 100 % [13]. Oral comfort and function were significantly improved. In 2009, Walton et al., comparing an implant therapy with one or two implants, revealed comparable patients’ satisfaction and maintenance time, with lower treatment time and component cost, when mandibular prostheses were retained by one instead of two implants [1]. However, studies investigating the single midline implant supporting a complete mandibular denture are rare in literature, and no commonly accepted recommendations for this treatment option are available. The aim of this systematic literature review was to give an overview over the available literature on the single midline implant therapy for the edentulous mandible and to reveal whether this treatment option might be an alternative to
Clin Oral Invest
commonly accepted treatment modalities with two or more implants.
Materials and methods Search strategy An electronic database (PubMed) search was performed for English language publications published until 24th of May 2013. Five search terms were used for every search run. These included “single” AND “midline” AND “implant” AND “mandibular” AND “denture,” single, AND “dental” AND implant AND mandibular AND denture, single, AND “median” AND implant AND mandibular AND denture. The search term single was replaced by the search term “one,” the search term denture was replaced by the search term “overdenture” as well as “prostheses,” and the search term midline was replaced by the search term “symphyseal” for further search runs (Table 1). In addition, a manual search was conducted based on the references in the full-text articles selected from the electronic search. The following inclusion and exclusion criteria were defined to select the articles included in this systematic review. Inclusion criteria
Study selection Titles and abstracts found through the electronic and manual search were screened for possible inclusion. Full-text versions of all investigations with possible relevance for this review were selected and screened again. Articles that could not be clearly identified as relevant or not by title or abstract were screened via full text, as well. All studies that met the defined inclusion criteria underwent data extraction. Data extraction For all investigations, the following data were recorded, if available: number and mean age of patients, dental status of the opposing maxilla, healing mode and loading protocol, implant surface, attachment system, observation period, implant survival rate, most frequent prosthodontic maintenance interventions, and patients’ satisfaction. Unfortunately, due to the heterogeneity of the included studies concerning observation time, healing mode, loading protocol, and others, a statistical analysis of the accumulated data was not justifiable [14].
Results – –
English language publications Clinical trials using a single midline implant in the mandible to retain an overdenture Exclusion criteria
– – –
Case reports Review articles In-vitro investigations
The initial database search yielded 938 hits. After eliminating duplicates, 238 titles remained. The manual search revealed no further articles that met the inclusion criteria. After screening the abstracts, 219 articles were excluded because they did not relate to the therapy using a single midline implant to retain a mandibular overdenture. Therefore, 19 articles were selected for full-text screening, of which eight clinical reports were excluded because they did not meet the inclusion criteria
Table 1 Search terms Search run
1 2 3 4 5 6 7 8 9 10 11 12 13
Search terms
Number of obtained references
1
2
3
4
5
Single Single Single Single Single Single One One One One Single Single Single
Midline Dental Median Median Midline Dental Midline Median Median Midline Midline Symphyseal Symphyseal
Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant Implant
Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular Mandibular
Denture Denture Denture Prostheses Prostheses Prostheses Prostheses Prostheses Overdenture Overdenture Overdenture Overdenture Prostheses
12 236 3 13 12 586 17 26 9 7 11 1 5
Clin Oral Invest
(Fig. 1). So finally, 11 studies were included in this review for further analysis (Table 2). The main reasons for exclusion were in-vitro studies or case reports. Excluded studies and reasons for their exclusion are listed in Table 3. A total of 255 completely edentulous patients were treated with a single implant in the midline of the mandible (Fig. 2). The mean age was 67.9 years. Healing modes, loading protocols, implant systems, and utilized attachment systems are summarized in Table 2, together with observation times, implant survival rates, complications, and patient satisfaction.
Implant survival rate Five of the included studies reported an implant survival rate of 100 % [1, 13, 15–17] (Table 2). Their observation periods ranged from 12 to 60 months. In these studies, immediate loading was avoided, and the implants were left unloaded or moderately loaded due to the healing abutment for at least 2 weeks. Whenever information on the implant surfaces was given, those were modern surfaces, mostly air-abraded and acid-etched. Another study reported also an implant survival rate of 100 % after 36 months of observation, when implants with
First electronic search 938 hits
After eliminating duplicates
air-abraded and acid-etched surfaces were inserted [18]. However, in the same study, an implant failure rate of 37.5 % was revealed when implants with machined surfaces were used. It must be to emphasize that in this study, all implants were loaded immediately. The attachment systems used in the above studies were, in most instances, integrated into the denture base intraorally (Fig. 3). Three of the included studies reported implant survival rates less than 100 % over an observation period of 12 to 36 months [10, 18, 19] (Table 2). In two studies, the implants were immediately loaded, and in one study, the implants were loaded after 6 weeks, following a non-submerged healing protocol. Implant surfaces were TiUnite, machined or not clearly defined. The attachment systems in those studies with failing implants were integrated into the denture base extraorally in the dental laboratory.
Prosthodontic complications/prosthodontic maintenance interventions The most frequent prosthetic maintenance intervention was “activation or exchange of the matrix” due to loss of retention over an observation period between 3 and 60 months. After an observation period of 36 months, Liddelow and Henry described three denture base fractures in the attachment area being the most frequent complication [18]. “Fracture of the denture base” was the second common prosthodontic complication. Most of the fractured dentures were not provided with a metal framework. In a retrospective investigation on the fracture incidence of overdentures retained by one or two implants with no metal reinforcement of the denture base, Gonda et al. [20] reported a fracture rate of 21.4 % in the one-implant group and 9.3 % in the two-implant group after an observation time of at least 17 months. The differences were not statistically significant.
238 titles Patients’ satisfaction
First selection based on abstract screening 19 titels for full- text analysis
11 included studies Fig. 1 Search strategy
Eight of the included studies provided information on the patients’ satisfaction [1, 13, 15–18, 21, 22]. A significant increase in all comfort and functional parameters due to the implant therapy was observed in all clinical trials evaluating these parameters. Cheng et al. [21], comparing two different attachment systems in their investigation, found no significant difference between the two treatment groups regarding overall satisfaction after 3 months of observation. Walton et al., comparing patients’ satisfaction between one and two implants, reported comparable results between the two groups [1]. Treatment time, treatment costs, and maintenance time were significantly reduced in the oneimplant group.
2013
Grover et al. [22]
10/70
15/53–83
42/67
42/68
20/62
21/74.2
ns/el (7 days)
ns/el (10 weeks)
Complete denture
Complete dentures
ns/ll (3 months)
ns/el (6 weeks)
ns/il
ns/il
s/ll (3 months)
6 ns, 5 s/el (2 months)
MTX surface
Air-abraded/ acid-etched
SLActive
25 oxidized surfaces/7 machined surfaces Not listed
TiUnite
Air-abraded/ acid-etched
Air-abraded, acid-etched
SLActive
Not listed
s/llb (4 months)
ns/el (3 weeks)
Not listed
Implant surface
ns/el (6 weeks)
Healing mode/ loading protocol
Complete denture
Complete denture
Complete denture Complete denture
Complete denture
Complete denture
Complete denture
Complete denture
Complete denture
Maxilla
Magnet
Stud (locator), magnetic (Magfit)/io
Gold matrix/io
3
3
At least 17 months
12
36
ball/eo
ball/io
12
18
43.4 (mean)
12
60
12
Observation period (months)
Ball/eo
Ball/N.N.
Retentive anchor with a titanium matrix/eo Ball/io
O-ring/ball/io
Ball/locator/eo
Attachment system/way of integrationa
–
–
–
–
Countering of denture base, followed by adjustment of the matrix No other complications than fracture are investigated –
Fracture of denture base
–
Activation/exchange of the matrix
Activation/exchange of the matrix
Activation/exchange of matrix
Activation of the matrix
Most frequent prosthetic maintenance intervention
100 %
100 % (oxidized surface), 62.5 % (machined surface)
82 %
100 %
100 %
100 %
91.7 % (total, all implant failures in one group) 100 %
Implant survival rate (%)
b
a
At least 3 months after implant placement
Way of integrating the matrix: intraoral/extraoral
s submerged, ns non-submerged, il immediately loaded, el early loaded, ll lately loaded, RCT randomized clinical trial, io intraoral, eo extraoral
2012
2010
Cheng et al. [21]
2010
2010
32/68
2011
Krennmair and Ulm [17] Kronstrom et al. [10] Liddelow and Henry [18]
Gonda et al. [20]
17/53,2
2011
Harder et al. [15]
2009
9/82.2
2012
El-Sheikh et al. [16]
Walton et al. [1]
11/66.7
1997
Cordioli et al. [13]
36/68
2011
Alsabeeha et al. [19]
Number of patients /mean age (N/Y, years)
Year of publication
Included studies
Table 2 Summary of the included literature
Significant improvement in satisfaction and masticatory performance Significant improvement in satisfaction and in masticatory performance
–
Remarkable improvement of all parameters of oral comfort and prostheses function Significant improvement in satisfaction
–
No
No
No (retrospective)
Yes
No
Yes
No
No
No
No
No
–
Remarkable improvement of all parameters of oral comfort and prostheses function Significant increase in all comfort and functional parameters Significant improvement in the oral health-related quality of life Improvement in patients’ subjective satisfaction
RCT comparing 1 vs 2 implants
Patients’ satisfaction
Clin Oral Invest
Clin Oral Invest Table 3 Excluded articles after full-text screening and reasons for exclusion Reference Review articles Alsabeeha et al. [24] Case reports Wolfart et al. [25]
Year of publication
2009 2008
Schneider and Synan [26] 2011 In vitro studies Maeda et al. [27] 2008 Yokoyama et al. [28] 2005 Alsabeeha et al. [29] 2011 Investigations having already been published over a longer observation period Liddelow and Henry [30] 2007 Results having already been published elsewhere Alsabeeha et al. [31] 2010
Discussion This systematic literature review was conducted to give an overview over the current literature on the single midline implant therapy for the edentulous mandible and to reveal whether this treatment option might be an alternative to commonly accepted treatment modalities with two or more implants. Edentulous patients are often dissatisfied with their conventional complete mandibular denture but cannot afford an implant therapy with two or more implants. One single midline implant might be a lower-cost alternative, but there is still no longer-term scientific evidence for the applicability of this treatment option. A number of studies were identified and selected for this review if conform to the applied inclusion criteria. Despite the heterogeneity of the included studies, the concept of one single midline implant retaining a complete mandibular denture showed high implant survival rates as long as modern implant surfaces were chosen and immediate loading was avoided. In those cases, healing mode, either submerged or non-submerged, did not seem to influence implant success.
Fig. 2 Single implant in the midline of the mandible
Fig. 3 Denture base with intraorally integrated matrix
Implants, provided with a healing abutment directly after implant placement, did not show higher failure rates than implants that were allowed to heal submerged, despite the chewing forces they were exposed to [15]. The attachment system did not have any influence on implant success or prosthodontic complications. The most frequent maintenance intervention was activation or exchange of the matrix which is a common intervention when two or more implants are used, as well [23]. The matrix should be regarded as an expendable part, and patients have to be informed about that prior to treatment. It is interesting to see that those investigations with high implant failure rates did not integrate the matrix intraorally but sent the denture base to the laboratory, having taken an impression before. This could have led to inaccuracies and an overload of the implant, especially during function. Therefore, it is suggested that the attachment matrix is integrated into the existing denture base intraorally in occlusion to avoid possible overloading of the implant during healing. Another frequent prosthetic complication was fracture of the denture base with a fracture rate of 21.4 to 36 % during the first 42 months of observation [15, 20]. Fractures occurred predominantly in the area of the attachment system, and most of the fractured denture bases were not reinforced with a metal framework. The matrices of the attachment systems were mainly integrated into already existing denture bases. That might have led to thin resin bases being weak and instable in the attachment area. It might be useful to reinforce thin denture bases in the anterior region with a metal framework. When evaluated, patients’ satisfaction and oral healthrelated quality of life was significantly improved in all studies after the insertion of one single midline implant. The attachment system does not seem to have any influence on patients’ overall satisfaction [21]. However, studies investigating the concept of one single midline implant retaining a complete mandibular denture were conducted only with a small number of patients over a short- to medium-term observation time. Valid data over an observation period of more than 5 years are still missing, and the need for randomized controlled clinical
Clin Oral Invest
trials comparing clinical treatment modalities is obvious from the data revealed by the current review.
Conclusions The concept of one single midline implant to retain a mandibular complete denture can be an alternative, especially for elderly patients. Immediately loading of the implants should be avoided, and the way of integrating the matrix into the denture base should be carefully considered.
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