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J Dent Res 83(8): 630-633, 2004
© 2004 International and American Associations for Dental Research

RESEARCH REPORT
Clinical

An Eight-year Follow-up to a Randomized Clinical Trial of Participant Satisfaction with Three Types of Mandibular Implant-retained Overdentures

R. Timmerman1,2, G.T. Stoker1,2,3, D. Wismeijer2, P. Oosterveld1, J.I.J.F. Vermeeren2, and M.A.J. van Waas1

1 Free University, Department of Oral Function. Academic Centre for Dentistry Amsterdam, Dental School;
2 Amphia Teaching Hospital, Department of Special Dental Care and Maxillofacial Prosthodontics, Breda, The Netherlands;

3 corresponding author, Hogeweg 5, NL-3212 LG Simonshaven, The Netherlands, geertstoker{at}wxs.nl


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Studies have shown that mandibular implant overdentures significantly increase satisfaction and quality of life of edentulous elders. Improved chewing ability appears to have a positive impact on nutritional state. Therefore, it is important to determine the best design of this prosthesis over the long term. In this randomized controlled trial, three groups of edentulous participants with atrophic mandibles wore 3 types of implant overdentures. During an eight-year follow-up, only seven of the 110 participants had dropped out of this study. Almost all participants were still satisfied with their overdentures. Participant satisfaction concerning retention and stability of the mandibular overdenture had decreased significantly in the two-implant ball attachment group, whereas the opinion of participants in the single- and triple-bar groups was still at the same level. The long-term results suggest that a mandibular overdenture retained by 2 implants with a single bar may be the best treatment strategy for edentulous people with atrophic ridges.

KEY WORDS: randomized controlled clinical trial • participant satisfaction • implant-retained overdentures • treatment strategies • long-term research


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS & METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Approximately 19% of the inhabitants of the Netherlands above 16 years of age are edentulous (Meijer et al., 1999). Fifteen percent of those wearing complete dentures have various complaints (Van Waas, 1990), including loss of retention and stability of the mandibular denture and pain in the denture-bearing areas of the mandible (Boerrigter et al., 1995). In the dental literature, only a few studies have been carried out to address the question of which treatment strategy with a mandibular implant-retained overdenture is the most effective for persons with these kinds of complaints: a tissue-retained overdenture on 2 implants with ball attachments, a combined tissue-implant-retained overdenture on 2 implants with a single bar, or an implant-retained overdenture on 4 implants with a triple bar. Most other studies were either not randomized clinical trials or had a rather short evaluation time (Jemt et al., 1996; Mericske-Stern, 1998; Meijer et al., 1999; Naert et al., 1999; Sadowsky, 2001). The design of this randomized controlled clinical trial was as a long-term evaluation study in compliance with the quality assessment of randomized controlled trials of oral implants (Esposito et al., 2001) and as evaluated by the Cochrane Institute (Coulthard et al., 2004).

This report presents the evaluation after 8 yrs. It is part of the Breda Implant Overdenture Study (BIOS), a randomized clinical trial (RCT) involving 110 totally edentulous participants with denture problems and who received 3 different treatment strategies from 1991 to 1993. The study was designed to investigate differences among the 3 previously mentioned treatment strategies in terms of clinical parameters, participants’ experience, and treatment efficiency. The design incorporated a long-term follow-up. The 19-month results have been published previously (Wismeijer et al., 1997a,b, 1999). At that time there were no differences among the three groups in satisfaction or in clinical and radiological parameters. The aim of this part of the study was to evaluate participants’ satisfaction 8 yrs following delivery of the prostheses.


   MATERIALS & METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
One hundred and ten edentulous participants with atrophic mandibles and persistent problems with their conventional complete dentures were referred by their dentists to the Department of Oral and Maxillofacial Surgery and/or the Department of Special Dental Care and Maxillofacial Prosthodontics of the Ignatius Teaching Hospital in Breda in the period 1991–1993. They were treated with one-stage ITI dental implants and overdentures. Participants with a history of pre-prosthetic surgery (e.g., augmentation procedures and vestibuloplasty), those who had previously been treated with dental implants, and those who were unsuitable for dental implant treatment because of their medical condition were excluded from this study. All potential participants were informed about the three different treatment strategies, as well as the possible benefits and risks of the treatment. They were asked if they would agree to undergo any of these treatment strategies without prior knowledge of which one would be chosen. If they agreed, the intake prosthodontist completed a questionnaire (age, sex, the edentulous period of the mandible and the maxilla, the number of previously worn mandibular and maxillary dentures, the age of the mandibular denture, and the symphysial bone height measured on a lateral headplate). Through a computerized random allocation procedure that was carried out by an independent third party (Zielhuis et al., 1990), participants were randomized into three groups. One group received an implant-retained overdenture on 2 implants with ball attachments (group I), one group received an implant-retained overdenture on 2 implants with a single bar (group II), and the final group wore an implant-retained overdenture on 4 implants with a triple bar (group III). The oral and maxillofacial surgeon and the prosthodontist were bound to the treatment allocation, and all the participants were treated accordingly.

Two or 4 titanium ITI dental implants were installed in the symphysial area of the mandible with the participant receiving local anesthesia. The surgical procedure was performed according to a standard protocol by one oral and maxillofacial surgeon. In group I with ball attachments, a Dalla Bona matrix (Cendres et Métaux, Switzerland) was used. The bars connecting the 2 or 4 implants in the other two groups were egg-shaped Dolder bars (CMST53012P20, Cendres et Métaux). The dentures were manufactured by a prosthodontist according to a standardized protocol with an optimal fit and balanced occlusion (Wismeijer et al., 1995). None of the overdentures was fitted with a pre-cast metal reinforcement. All participants received a recall appointment once a year at the Department of Oral and Maxillofacial Surgery, once a year at the Department of Special Dental Care, and at least twice a year with the oral hygienist for oral hygiene instructions and aftercare.

At baseline, 19 mos, and 8.3 years after delivery of the prostheses, participants completed a 46-item questionnaire focusing on several aspects of denture satisfaction and social functioning. It consisted of specific items on comfort and chewing with the mandibular and maxillary denture, and general items such as speech, aesthetics, retention, mastication, and social functioning. Factor analysis revealed 9 underlying factors related to the functional and social aspects of satisfaction (Wismeijer et al., 1997b).

Power analysis according to Cohen (1988) was used for sample size calculations for a between-subjects design study. With a significance level of 0.05, a power of 0.80, and a treatment effect among three groups (f2) of 0.085, a total of 96 participants had to be included. An additional 14 participants were included to maintain the statistical power despite an expected dropout of participants over time. The pre-treatment comparability of the three treatment groups was examined by analysis of variance (one-way ANOVA). The baseline data were subjected to factor analysis with Varimix rotation to explore the structure of the questionnaire. Calculated Crohnbach’s coefficients assessed the reliability of the factors. Mean factor scores were calculated with a range from 1 to 5. The data were analyzed according the intention-to-treat principle (Antczak-Bouckoms and Chalmers, 1988). Response differences on individual items were tested with a Friedman chi-square test. The treatment effects were evaluated by multivariate analysis of variance (MANOVA).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Of the 110 participants included at baseline, 103 were available for the eight-year evaluation. Three participants had died; four were unreachable for reasons of hospitalization and relocation. Eight participants did not complete the questionnaire, and eight other participants did not respond to one or two questions at one of the time points. For the multivariate analysis group, we used mean substitution for the scale score to be able to include these participants in the analysis. At the start of the study, the age of the participants ranged between 39 and 87 yrs (mean, 59.0); 30 participants were male, and 73 female. The number of participants in each treatment group is shown in Table 1Go.


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  		Table 1. Number of Participants Evaluated According to Allocation
 
For the items related to pain, satisfaction with retention, and general satisfaction, the longitudinal effect was tested with the Friedman Chi-square test for K-related samples. The results of these tests are given in Table 2Go. The responses to these items showed no differences among the three treatment groups at the eight-year evaluation. All longitudinal effects (‘baseline’ compared with ‘19-month post-treatment’ and ‘8 yrs post-treatment’) show significant differences. In the 19-month and eight-year evaluations, the tests demonstrate a significant difference in satisfaction among the three groups for retention and stability of the mandibular overdenture. The participants of group I were less satisfied after 8 yrs than at 19 mos. The Friedman test for K-independent samples was significant (p = 0.008).


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  		Table 2. Test Results Comparing the Three Treatment Groups at the Eight-year Follow-up, and the Longitudinal Effect of Baseline vs. Eight Years and 19 Months vs. Eight Years
 
Table 3Go gives the cross-tabulation of the responses with respect to satisfaction with the retention and stability of the mandibular overdenture at the 19-month and eight-year follow-ups. The majority of the participants were satisfied or very satisfied at both follow-up time points. Nonetheless, the number of participants whose satisfaction scores decreased is larger (n = 21) than the number whose scores increased (n = 10). Seven participants moved from the positive end of the scale to the negative end during the follow-up, whereas one showed a reverse score pattern.


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  		Table 3. Comparison of the 19-month and Eight-year Follow-ups for Satisfaction with the Retention of the Mandibular Denture
 
The means and standard deviations for the 9 satisfaction factor scores for the three groups at each evaluation time point were calculated (Table 4Go). The multivariate test for treatment effect did not show significant differences among the three groups (F18,170 = 1.53, p = 0.09). As expected, analysis of the data also shows that the participants were more satisfied after treatment than at baseline. The ANOVA showed that this effect is significant (F18,70 = 66.97, p = 0.00). The interaction between evaluation period and treatment group was not significant (F36,150 = 1.06, p = 0.39). The latter result implies that there are no differences among the groups in change of satisfaction over time.


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  		Table 4. Means of the Satisfaction Factor Scores for the Three Treatment Groups at Baseline and 19-month and Eight-year Follow-ups
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS & METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Satisfaction with treatment is a highly complex phenomenon influenced by numerous factors, and not strictly related to the stomatognathic system (Al Quran et al., 2001). Yet, participant satisfaction is one of the highest goals in the treatment of edentulous individuals. All three mandibular implant-retained overdenture treatment strategies have significantly increased the scores for general denture satisfaction, for satisfaction with the functioning, retention, and stability of the denture, and for social functioning. The results of this evaluation after 8 yrs give a strong indication that the positive treatment effects found for mandibular implant overdentures are not of a passing nature, but are stable for years.

Treatment of edentulous individuals with implant-retained overdentures appears to be very effective in terms of reduction of denture complaints. This outcome might be positively influenced by the careful maintenance and a strict re-call protocol (Wismeijer et al., 1997a, b, 1999).

There is a worldwide consensus that a mandibular two-implant overdenture should be the first choice of care for edentulous individuals (Feine et al., 2002). This study shows that having more than 2 implants does not lead to a more satisfied individual in terms of denture and social function. Results of this study suggest that retention and stability of the mandibular overdenture, rather than the degree of retention by implants, drive participant satisfaction. This, however, is not in agreement with the results of a study of Tang et al.(1997). Their subjects chose the long-bar overdenture retained by 4 implants in preference to the two-implant hybrid overdenture. A reason for this difference might be because all subjects were aware that they had 4 implants which could be used to support a long-bar overdenture.

Eight yrs after treatment, participants with 2 implants and ball attachments were found to be less satisfied with the retention and stability of the mandibular overdenture than were those with the splinted implants. These results differ from our results after 19 mos and the short-term results of others (Naert et al., 1997, 1999; Burns, 2000; Van Kampen et al., 2002). This unexpected change in between-group differences may be due to the gathering of data over a long term. The reason for this decrease in satisfaction might be that the overdentures in this group are still mainly tissue-retained. In this report, not all gathered clinical data from this RCT have been taken into account.

The participants in this study were treated in a general hospital and not in an academic center or university clinic. The latter represents a relatively protective treatment setting; therefore, the results of this study are more representative for the general dental practice.

Proper randomization has been carried out. Participants were distributed over the three treatment groups by a balancing randomized procedure (Zielhuis et al., 1990). The randomization procedure allowed for three identical treatment groups to be recruited (Wismeijer et al., 1997b). The dropout rate in this study was very low due to a strict re-call protocol. Even after 8 yrs, the study has a high statistical power for comparison between and within subjects over time.

Eight yrs after treatment, participants’ general satisfaction with mandibular implant-retained overdentures and their opinion about phonetics, aesthetics, and social functioning over time are high and not dependent on treatment strategy. Only the score on the item ‘retention and stability of the overdenture’, for the participants with overdentures on 2 implants with ball attachments, decreased over time. The results of this study suggest that a mandibular overdenture retained by 2 implants interconnected by a single bar might be the best treatment strategy with proven stability in the long term. This conclusion differs from that drawn after an evaluation period of 19 mos and suggests that research of this nature should be carried out over a long term.


   ACKNOWLEDGMENTS
 
This project was supported by a grant from the ITI Foundation for the Promotion of Oral Implantology, Switzerland. This grant did not, in any way, create a conflict of interest in the conduct of this study.

Received December 29, 2003; Last revision May 3, 2004; Accepted May 25, 2004


   REFERENCES
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 ABSTRACT
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 MATERIALS & METHODS
 RESULTS
 DISCUSSION
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Al Quran F, Clifford T, Cooper C, Lamey PJ (2001). Influence of psychological factors on the acceptance of complete dentures. Gerodontology 18:35–40.[Medline]

Antczak-Bouckoms A, Chalmers TC (1988). The importance of design and analysis in clinical trials. J Oral Implantol 14:36–42.[Medline]

Boerrigter EM, Stegenga B, Raghoebar GM, Boering G (1995). Patient satisfaction and chewing ability with implant-retained mandibular overdentures: a comparison with new complete dentures with or without preprosthetic surgery. J Oral Maxillofac Surg 53:1167–1173.[ISI][Medline]

Burns DR (2000). Mandibular implant overdenture treatment: consensus and controversy. J Prosthodont 9:37–46.[Medline]

Cohen J (1988). Statistical power analysis for the behavioural sciences. New York: Academic Press.

Coulthard P, Esposito M, Jokstad A, Worthington HV (2004). Interventions for replacing missing teeth: surgical techniques for placing dental implants (Cochrane Review). In: The Cochrane Library. Issue 2. Chichester, UK: John Wiley & Sons, Ltd.

Esposito M, Coulthard P, Worthington HV, Jokstad A (2001). Quality assessment of randomized controlled trials of oral implants. Int J Oral Maxillofac Implants 16:783–792.[ISI][Medline]

Feine JS, Carlsson GE, Awad MA, Chehade A, Duncan WJ, Gizani S, et al. (2002). The McGill consensus statement on overdentures. Montreal, Quebec, Canada, May 24–25, 2002. Int J Prosthodont 15:413–414.[Medline]

Jemt T, Chai J, Harnett J, Heath MR, Hutton JE, Johns RB, et al. (1996). A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants. Int J Oral Maxillofac Implants 11:291–298.[Medline]

Meijer HJ, Raghoebar GM, Van’t Hof MA, Geertman ME, Van Oort RP (1999). Implant-retained mandibular overdentures compared with complete dentures; a 5-years’ follow-up study of clinical aspects and patient satisfaction. Clin Oral Implants Res 10:238–244.[ISI][Medline]

Mericske-Stern R (1998). Treatment outcomes with implant-supported overdentures: clinical considerations. J Prosthet Dent 79:66–73.[ISI][Medline]

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Naert I, Gizani S, Vuylsteke M, van Steenberghe D (1999). A 5-year prospective randomized clinical trial on the influence of splinted and unsplinted oral implants retaining a mandibular overdenture: prosthetic aspects and patient satisfaction. J Oral Rehabil 26:195–202.[ISI][Medline]

Sadowsky SJ (2001). Mandibular implant-retained overdentures: a literature review. J Prosthet Dent 86:468–473.[ISI][Medline]

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