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Success and survival rates of mandibular overdentures supported by two or four implants: a systematic review.

Introduction

The use of implant-retained dentures has been an alternative for treating the edentulous mandible, since it allows fixation of the prosthesis to the edentulous ridge. (1) This has encouraged dental professionals to display and perform prostheses, such as overdentures retained by implants, as an option to solve the problem of edentulous patients. Treating patients by implant placement is a popular option for restoring function and esthetics, (2) and for improving oral function, masticatory efficiency and individual satisfaction. (3)

There is still some debate regarding the number of implants required to properly support dentures. Studies have shown good results for oral rehabilitation with implant-retained prostheses; however, overdentures with 2 and 4 implants must be compared in the long term, with respect to clinical characteristics, patient satisfaction and ease of care. (4)

In addition to the success rate of osseointegrated implants supporting dental prostheses, the prosthesis itself should also be taken into consideration when determining the overall success of the rehabilitation treatment. (5) Thus, the goal of this systematic review was to demonstrate the variations in success or survival rates of overdentures when 2 or 4 implants are used to treat the edentulous jaw.

Methodology

Search strategy

The search was conducted by 2 reviewers, independently, using electronic databases (Pubmed/ Medline, Embase, Cochrane), and was limited to clinical trials reporting the success of mandibular overdentures on 2 or 4 implants. A broad search was undertaken from January 1980 to January 2013 to identify the studies by title and abstract. The terms "overdenture," "implant-retained," "implant-supported," "success," "dental prosthesis," "complete mandibular denture" and "prosthetic outcome" were combined using "and" or "or," and a total of 967 studies were identified for initial screening.

The titles and abstracts of all reports identified through the electronic searches were assessed by 2 reviewers, and both the inclusion criteria (publications in English, follow-up of at least one year, mandibular overdentures, success rates, survival rates, failure rates or prosthesis function rate of overdentures on two or four implants, and ball and/or bar attachments) and the exclusion criteria (laboratory studies, case reports, and cross-sectional data) were applied. The literature search yielded a total of 967 citations, 951 of which were excluded because they did not meet the inclusion criteria. Any disagreement between the reviewers in the search process was resolved either by reaching a consensus or by including the reference for subsequent review. Hand-searching of the selected journals, as well as searching the references of the selected studies was also performed at this point to include any paper not found in the electronic search. Finally, full-text copies of the remaining 16 studies (Tables 1 and 2) were obtained for a more detailed evaluation. The reasons for excluding another 5 studies are listed in Table 3.

The final studies that were included after passing the second phase of the review process were classified according to the quality assessment of pre-established characteristics, in order to document the methodological strength of each paper. (6) The variables investigated in the quality assessment are listed in Table 4. The sample size was considered adequate when the sample size calculation was presented. Measurement methods were considered valid when a measurement error test was presented. Each study was classified based on the following scores:

* low (0-5 points),

* medium (6-8 points) or

* high (9-10 points).

Results

The database search initially yielded 967 titles. Sixteen studies (7-22) were evaluated initially, but only 11 met the inclusion criteria and were ultimately selected for analysis (7-17) (Figure 1). Methodological issues such as sample size, follow-up, attachment system, quality of assessment and results for implants and prostheses were described (Tables 1 and 2). Studies with unclear methodological issues, such as reports with a different number of implants, were excluded (18-22) (Table 3).

This systematic review included randomized controlled trials, (16) non-randomized controlled trials, (9-12) prospective studies (7,8,13,15,17) and retrospective studies. (14) Randomized clinical trials (RCT) present a better evaluation of treatment results when adequate methods are used. However, since RCTs were uncommon for the topic researched, the clinical guidance provided to dental clinicians would be limited if this review were based solely on RCTs. Thus, it was decided that other study designs of overdentures retained by 2 or 4 implants should be included.

Only one study (10) showed a medium degree of quality and methodological consistency (Table 1); most showed a low degree, and none showed a high degree. The sample size, statistical analysis and confounding factors were the most significant flaws.

The main results evaluated in the studies with overdentures (OD) focused on the influence of the number of implants on OD success. Several data were evaluated, including implant success and survival rates, prosthesis failure and functional rates. Five studies described overdenture performance with 2 implants, (7,9-12) and five reported the use of 4 implants. (13-17) One study (8) showed results for both 2 and 4 implants. In regard to the attachment system, the ball attachment was the most commonly used system for 2 implants, and bars, for 4 implants.

The prosthesis survival rates for 2 implants ranged from 92%10 to 100%. (12) However, when the protocol described by Payne et al. (23) was used to define success rate based on different criteria (success, survival, unknown, loss, retreatment by relining or replacement), the rate ranged from 23%9 to 100%. (12) For other authors, (8,13,14,16,17) individual criteria were used to define the outcomes. As can be observed, these individual criteria are reflected in the results. Authors who used the criteria successfully were stricter and sought to follow predetermined evaluation criteria. In contrast, those who used survival rates, considered only the prostheses that remained in use, despite the fact that complications may have occurred.

High survival rates were observed in the studies with four implants. The results were based on personal evaluation and criteria established by the authors regarding prosthesis function (8,13,15-17) or failures. (14)

Discussion

The parameters for prosthetic success showed great variability among the studies as a result of different methodologies and criteria. This becomes a challenge for significant synthesis and comparison of results. The authors used the terms success and survival as two independent characteristics. Success was defined as rehabilitation that remained unchanged, not requiring any intervention during the entire observation period, and that proceeded under ideal conditions. Survival was defined as the rehabilitation remaining in situ with or without modification and clinical management over the observation period, (24) even when repairs were made. Thus special attention had to be given when comparing the results of each parameter.

The different results were a consequence of different sample sizes, follow-up periods, attachment systems and complications. An adequate evaluation should take into consideration all of these aspects to show the prosthetic success in general, and any conclusions should be addressed carefully before applying them to dental practice.

Considering that randomized, controlled clinical trials present excellent quality, further evaluation should be conducted based on this type of study, to compare appropriate sample sizes with 2 and 4 implants and different attachment systems. It is important to highlight that any unexpected complications requiring clinical intervention should be classified as treatment complications and described in the clinical trials (prospective and retrospective), seeing that a trend was observed to report only positive results.

There were wide-ranging results for overdentures retained by 2 implants based on pre-established criteria. (23) The only study with a 100% success rate was a short-term follow-up, (12) and, most probably, the evaluation period was not long enough to show any complications. Although some authors suggested that failures usually occur during the first year and decrease over time, (9-11,25) medium- and long-term follow-ups are recommended to assess prosthesis performance, (8) in order to determine the real trend.

A minimum of 2 and up to 4 implants are required for rehabilitation with overdentures. (26) Some authors concluded that 2 implants are enough and presented this option as a low-cost alternative. (4,12) However, this alternative has some limitations and a number of complications related to the prosthetic components, (9-11) and also to non-axial load transfer, posterior bone resorption and prosthesis rotation (27) The protocol with 4 implants showed better results and optimum survival rates in four studies. (13,15-17) In two other studies, (8,14) the long-term follow-up results may justify these rates. Four implants provide better stability, and avoid both movement and excessive loading, which may compromise osseointegration. (14)

The attachment system plays an active role in prosthesis success rates, reflected in prosthetic maintenance and complications. Ball attachments revealed complications, such as being time-consuming and incurring costs related to wearing and loosening of matrix and patrix components that had to be changed. They also incur movement in different directions, resulting in damage and ring wear. (9-11) This kind of attachment is used basically with two implants. In contrast, the bar attachment showed better results for rehabilitation with two and four implants. Some studies suggested that implants splinted with bars are a favorable alternative to minimize rotational movement and provide vertical load transfer, (14,16) and to avoid implant micromovement and prosthetic repairs. (28) Bearing this in mind, it is important that these complications be recorded when analyzing prosthesis maintenance during follow-ups.

Walton (10) evaluated the success rate based on pre-established criteria (21) to assess any difference in prosthetic maintenance between ball and bar attachments. After a 3-year follow-up, the bar-clip system exhibited a statistically significant difference in its success rate. The ball attachment required 5 times more repair than the bar system, thus lowering its success rate to 23%.

Other factors are also important in analyzing the results, such as maintenance period, types of complications and failure, time and type of repair, complexity of procedures, and prosthesis design. Although it is difficult to predict the complications, these factors should be considered during treatment planning and be informed to the patient, since they will influence treatment success.

Not only is the success of implants and prosthesis at issue, but the occurrence of complications that must be considered in evaluating the treatment. Biological failures, costs and patient satisfaction regarding function and esthetics should also be included in the final results.

Few studies showed that mandibular overdentures retained by 4 implants are an adequate alternative for an edentulous mandible, based on better success rates and prostheses survival, especially with the bar attachment system.

Conclusion

Given the limitations of this review, mandibular overdentures with 4 implants showed better results with respect to survival and success rates, especially those with a bar connection. Further studies comparing these two treatment types are necessary to improve the scientific evidence in this area. With this in mind, long-term, randomized and appropriately designed clinical studies are recommended.

Acknowledgments

The authors would like to thank Danilo Gonzaga for his critical comments and suggestions.

References

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(2.) Wennerberg A, Albrektsson T. Current challenges in successful rehabilitation with oral implants. J Oral Rehabil. 2011 Apr;38(4);286-94.

(3.) Pera P, Bassi F, Schierano G, Appendino P, Preti G. Implant anchored complete mandibular denture: evaluation of masticatory efficiency, oral function and degree of satisfaction. J Oral Rehabil. 1998 Jun;25(6):462-7.

(4.) Meijer HJ, Raghoebar GM, Batenburg RH, Visser A, Vissink A. Mandibular overdentures supported by two or four endosseous implants: a 10-year clinical trial. Clin Oral Implants Res. 2009 Jul;20(7):722-8.

(5.) Carr AB. Successful long-term treatment outcomes in the field of osseointegrated implants: prosthodontic determinants. Int J Prosthodont. 1998 Sep-Oct;11(5):502-12.

(6.) Jadad AR, Moore RA, Carroll D, Jenkinson C, Reynolds DJ, Gavaghan DJ, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary?. Control Clin Trials. 1996 Feb;17(1):1-12.

(7.) Naert I, De Clercq M, Theuniers G, Schepers E. Overdentures supported by osseointegrated fixtures for the edentulous mandible: a 2.5-year report. Int J Oral Maxillofac Implants. 1988 Fall;3(3):191-6.

(8.) Ferrigno N, Laureti M, Fanali S, Grippaudo G. A long-term follow-up study of non-submerged ITI implants in the treatment of totally edentulous jaws. Part I: Ten-year life table analysis of a prospective multicenter study with 1286 implants. Clin Oral Implants Res. 2002 Jun;13(3):260-73.

(9.) Watson GK, Payne AG, Purton DG, Thomson WM. Mandibular overdentures: comparative evaluation of prosthodontic maintenance of three different implant systems during the first year of service. Int J Prosthodont. 2002 May-Jun;15(3):259-66.

(10.) Walton JN. A randomized clinical trial comparing two mandibular implant overdenture designs: 3-year prosthetic outcomes using a six-field protocol. Int J Prosthodont. 2003 May;16(3):255-60.

(11.) Mackie A, Lyons K, Thomson WM, Payne AG. Mandibular two-implant overdentures: prosthodontic maintenance using different loading protocols and attachment systems. Int J Prosthodont. 2011 Sep-Oct;24(5):405-16.

(12.) De Kok IJ, Chang KH, Lu TS, Cooper LF. Comparison of three-implant-supported fixed dentures and two-implant-retained overdentures in the edentulous mandible: a pilot study of treatment efficacy and patient satisfaction. Int J Oral Maxil lofac Implants. 2011 Mar-Apr;26(2):415-26.

(13.) Donatsky O. Osseointegrated dental implants with ball attachments supporting overdentures in patients with mandibular alveolar ridge atrophy. Int J Oral Maxillofac Implants. 1993 Mar-Apr;8(2):162-6.

(14.) Chiapasco M, Gatti C, Rossi E, Haefliger W, Markwalder TH. Implant-retained mandibular overdentures with immediate loading. A retrospective multicenter study on 226 consecutive cases. Clin Oral Implants Res. 1997 Feb;8(1):48-57.

(15.) Makkonen TA, Holmberg S, Niemi L, Olsson C, Tammisalo T, Peltola J. A 5-year prospective clinical study of Astra Tech dental implants supporting fixed bridges or overdentures in the edentulous mandible. Clin Oral Implants Res. 1997 Dec;8(6):469-75.

(16.) Romeo E, Chiapasco M, Lazza A, Casentini P, Ghisolfi M, Iorio M, et al. Implant-retained mandibular overdentures with ITI implants. Clin Oral Implants Res. 2002 Oct;13(5):495 501.

(17.) Heschl A, Payer M, Clark V, Stopper M, Wegscheider W, Lorenzoni M. Overdentures in the edentulous mandible supported by implants and retained by a dolder bar: a 5-year prospective study. Clin Implant Dent Relat Res. 2013 Aug;15(4):589-99. DOI: 10.1111/j.1708-8208.2011.00380.x. Epub 2011 Aug 11.

(18.) Adell R, Eriksson B, Lekholm U, Branemark PI, Jemt T. Long-term follow-up study of osseointegrated implants in the treatment of totally edentulous jaws. Int J Oral Maxillofac Implants. 1990 Winter;5(4):347-59.

(19.) Johns RB, Jemt T, Heath MR, Hutton JE, McKenna S, McNamara DC, et al. A multicenter study of overdentures supported by Branemark implants. Int J Oral Maxillofac Implants. 1992 Winter;7(4):513-22.

(20.) Hutton JE, Heath MR, Chai JY, Harnett J, Jemt T, Johns R B, et al. Factors related to succes s and failure rates at 3-year follow-up in a multicenter study of overdentures supported by Branemark implants. Int J Oral Maxillofac Implants. 1995 Jan-Feb;10(1):33-42.

(21.) Jemt T, Chai J, Harnett J, Heath MR, Hutton JE, Johns RB, et al. A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants. Int J Oral Maxillofac Implants. 1996 May-Jun;11(3):291-8.

(22.) Fartash B, Tangerud T, Silness J, Arvidson K. Rehabilitation of mandibular edentulism by single crystal sapphire implants and overdentures: 3-12 year results in 86 patients. A dual center international study. Clin Oral Implants Res. 1996 Sep;7(3):220-9.

(23.) Payne AG, Walton TR, Walton JN, Solomons YF. The outcome of implant overdentures from a prosthodontic perspective: proposal for a classification protocol. Int J Prostho dont. 2001 Jan-Feb;14(1):27-32.

(24.) Pjetursson BE, Bragger U, Lang NP, Zwahlen M. Comparison of survival and complication rates of tooth-supported fixed dental prostheses (FDPs) and implant-supported FDPs and single crowns (SCs). Clin Oral Implants Res. 2007 Jun;18 Suppl 3:97-113.

(25.) Turkyilmaz I, Tumer C . Early versus late loading of unsplinted TiUnite surface implants supporting mandibular overdentures: a 2-year report from a prospective study. J Oral Rehabil. 2007 Oct;34(10):773-80.

(26.) Bueno-Samper A, Hernandez-Aliaga M, Calvo-Guirado JL. The implant-supported milled bar overdenture: a literature review. Med Oral Patol Oral Cir Bucal. 2010 Mar;15(2):e375-8.

(27.) Krennmair G, Seemann R, Weinlander M, Piehslinger E. Comparison of ball and telescopic crown attachments in implantretained mandibular overdentures: a 5-year prospective study. Int J Oral Maxillofac Implants. 2011 May-Jun;26(3):598-606.

(28.) Weinlander M, Piehslinger E, Krennmair G. Removable implant-prosthodontic rehabilitation of the edentulous mandible: five-year results of different prosthetic anchorage concepts. Int J Oral Maxillofac Implants. 2010 May-Jun;25(3):589-97.

Isabelle de Sousa Dantas

Mariana Barbosa Camara de Souza

Maria Helena de Siqueira Torres Morais

Adriana da Fonte Porto Carreiro

Gustavo Augusto Seabra Barbosa

Department of Dentistry, Universidade Federal do Rio Grande do Norte--UFRN, Natal, RN, Brazil.

Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.

Corresponding Author:

Isabelle de Sousa Dantas

E-mail: isabelledantas21@gmail.com

http://dx.doi.org/10.1590/S1806-83242013000600012

Submitted: May 13, 2013

Accepted for publication: Sep 28, 2013

Last revision: Oct 14, 2013

Table 1--Results of studies with two implants.

Authors             Sample      Number of   Follow-up
(year)                          implants     (years)

Naert et              43            2          2.5
al. [7] (1988)

Ferrigno et           84            2          10
al. [8] (2001)

Watson et             72            2           1
al. [9] (2002)

Walton [10]       Group 1: 50       2          2-4
(2003)            Group 2: 50

Mackie et             106           2           5
al. [11] (2011)

De Kok et             10            2           1
al. [12] (2011)

                                  Rate for implants

Authors           Attachment     Survival     Success
(year)

Naert et             Bar            -          97.7%
al. [7] (1988)

Ferrigno et          Ball      97.1% (2 and      -
al. [8] (2001)                 4 implants)

Watson et            Ball           -
al. [9] (2002)

Walton [10]          Ball           -
(2003)               Bar

Mackie et            Ball           -
al. [11] (2011)

De Kok et            Ball          100%          -
al. [12] (2011)

                  Rate for prostheses

Authors           Survival   Success    Quality
(year)                                 evaluation

Naert et             -        97.7%       Low
al. [7] (1988)

Ferrigno et        98.8%        -         Low
al. [8] (2001)

Watson et          98.6%     83.3% *      Low
al. [9] (2002)

Walton [10]         92%       23% *      Medium
?(2003)             96%       63% *

Mackie et          96.84%    58.5% *      Low
al. [11] (2011)

De Kok et           100%     100% *       Low
al. [12] (2011)

* Six-field protocol by Payne et al. [23] (2001).

Table 2--Results of studies with four implants.

Authors (year)    Sample   Number of   Follow-up
                           implants     (years)

Donatsky [13]       19         4           1
(1993)

Chiapasco et       194         4         2-13
al. [14] (1997)

Makkonnen et        15         4           5
al. [15] (1997)

Ferrigno et         44         4          10
al. [8] (2002)

Romeo et            20         4           2
al. [16] (2002)

Heschl et           32         4           5
al. [17] (2011)

                                     Rate for implants

Authors (year)    Attachment     Survival            Success

Donatsky [13]        Ball           -                  98%
(1993)

Chiapasco et         Bar            -                 96.9%
al. [14] (1997)

Makkonnen et         Bar          97.4%                 -
al. [15] (1997)

Ferrigno et          Bar       97.1% (2 and             -
al. [8] (2002)                 4 implants)

Romeo et             Bar            -           100% (Immediate
al. [16] (2002)                                  loading) 97.5%
                                              (Conventional loading)

Heschl et            Bar            -                 98.6%
al. [17] (2011)

                  Rate for prostheses

Authors (year)    Survival   Success    Quality
                                       evaluation

Donatsky [13]       100%        -         Low
(1993)

Chiapasco et       98.5%        -         Low
al. [14] (1997)

Makkonnen et        100%        -         Low
al. [15] (1997)

Ferrigno et        97.7%        -         Low
al. [8] (2002)

Romeo et             -        100%        Low
al. [16] (2002)

Heschl et           100%        -         Low
al. [17] (2011)

Table 3--Studies excluded and reason why.

Authors (year)               Exclusion criteria

Adell et al. [18] (1990)     A mean of 6 implants was used

Johns et al. [19] (1992)     A maximum of 4 implants were
Hutton et al. [10] (1995)    placed but only 2 were connected to
Jemt et al. [21] (1996)      the abutments. However, one of the
                             sleepers was activated at some point
                             of the treatment. Thus, 3 implants
                             were evaluated

Fartash et al. [22] (1996)   Individual assessment of success rate
                             for 2 or 4 implants was not reported

Table 4--Characteristics and scores used for quality analysis
of selected papers.

Characteristic                                      Score

Adequate study design: randomized clinical trial,
prospective study, controlled clinical trial,         3
longitudinal study

Clinical trial                                        1

Adequate sample size                                  1

Adequate description of selection process             1

Valid measurement methods                             1

Use of method of error analysis                       1

Blinded measurement evaluation                        1

Valid statistical methods                             1

Confounding factors included in analysis              1
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Article Details
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Author:Dantas, Isabelle de Sousa; de Souza, Mariana Barbosa Camara; Morais, Maria Helena de Siqueira Torres
Publication:Brazilian Oral Research
Article Type:Author abstract
Date:Jan 1, 2014
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