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A 5-y Randomized Trial to Compare 1 or 2 Implants for Implant Overdentures S.R. Bryant, J.N. Walton and M.I. MacEntee J DENT RES published online 27 October 2014 DOI: 10.1177/0022034514554224 The online version of this article can be found at: http://jdr.sagepub.com/content/early/2014/10/24/0022034514554224
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research-article2014
JDRXXX10.1177/0022034514554224JDR Clinical Research SupplementJDR Clinical Research Supplement
Research Reports: Clinical
A 5-y Randomized Trial to Compare 1 or 2 Implants for Implant Overdentures
Journal of Dental Research 1–8 © International & American Associations for Dental Research 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0022034514554224 jdr.sagepub.com
S.R. Bryant1, J.N. Walton1, and M.I. MacEntee1
Abstract The hypothesis of this 5-y randomized clinical trial was that there would be no significant difference in the satisfaction of edentulous participants with removable complete overdentures attached to 1 or 2 mandibular implants. Secondary aims were to test changes in satisfaction between and within the groups from baseline to 5 y and differences between the groups in implant survival and prosthodontic maintenance over 5 y. Each of the 86 participants (mean age, 67 y) was randomly allocated to receive either 1 implant in the midline (group 1) or 2 implants in the canine areas (group 2) attached to a mandibular overdenture opposing a maxillary complete denture. Satisfaction was self-assessed by participants on a visual analog scale at baseline prior to implants, as well as at 2 mo and 1, 3, and 5 y with implant overdentures, whereas implant survival and prosthodontic maintenance were assessed by clinical examination. After 5 y, 29 participants in group 1 and 33 in group 2 were available, with most dropouts due to death. Satisfaction with the implant denture after 5 y was significantly (P < 0.001) higher than at baseline in both groups and remained with no significant difference (P = 0.32) between the groups. No implants failed in group 1 but 5 failed before loading in 4 participants in group 2. Most participants required maintenance or occasionally denture replacement, and although differences between the groups were not statistically significant, group 1 experienced almost twice as many fractured dentures usually adjacent to the implant attachment. We conclude that there were no significant differences after 5 y in satisfaction or survival of implants with mandibular overdentures retained by 1 implant or 2 implants. Additional research is required to confirm longterm treatment effectiveness of single-implant dentures and the implications of prosthetic maintenance with implant overdentures (ClinicalTrials.gov: NCT02117856). Keywords: implant-supported dental prosthesis, single-implant denture, complete denture, edentulous mandible, dental implant, standard of care
Introduction Implant dentures have substantially higher financial costs than conventional complete dentures (MacEntee and Walton 1998), although 2 consensus conferences concluded that a mandibular overdenture supported by 2 implants is the “minimum standard” of treatment for edentulous patients (Thomason et al. 2012). Others believe that this standard disregards those who cannot afford 2 implants and implies that anything less is negligent care (Owen 2009). Indeed, there is no evidence for a single standard of care for edentulous mandibles with or without implants (Fitzpatrick 2006) or a link between the number of implants and complications or satisfaction with overdentures (Roccuzzo et al. 2012). Cordioli et al. (1997) monitored 15 patients for 5 y, each with a mandibular overdenture attached with a ball abutment and rubber O-ring to 1 midline implant, and the patients remained comfortable and without an implant failure. Liddelow and Henry (2007) reported similar success for 28 patients 1 y after most had
immediate placement of mandibular overdentures on a single midline implant. Walton et al. (2009) reported results from the first year of this randomized clinical trial, allocating 1 or 2 implants in the anterior mandible to retain overdentures with ball abutments and gold matrices about 6 weeks after implant placement. No implants in the 1-implant group failed; however, 5 failed in the 2-implant group, all before connecting the dentures to the implants. At 1 y, most participants were satisfied in both groups, and there were no statistical 1
Division of Prosthodontics and Dental Geriatrics, Department of Oral Health Sciences, University of British Columbia, Canada A supplemental appendix to this article is published electronically only at http://jdr.sagepub.com/supplemental. Corresponding Author: R. Bryant, Division of Prosthodontics and Dental Geriatrics, Department of Oral Health Sciences, University of British Columbia, British Columbia, Canada V6T 1Z3. Email: [email protected]
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differences in satisfaction or prosthetic maintenance, whereas the 1-implant group required significantly less time and financial costs for the initial treatment. Kronström et al. (2010) also allocated participants randomly to receive 1 or 2 mandibular anterior implants with ball patrices and O-ring matrices to connect overdentures immediately after placing the implants. Three (18%) participants in the 1-implant group and 6 (32%) in the 2-implant group lost implants during the first year. Others reported that time and costs are similar to maintain different attachment systems for implant overdentures (Cehreli et al. 2010), although the evidence remains inconclusive given the various ways that data have been reported (Bryant et al. 2007). We conclude from the available evidence that implant survival, participant satisfaction, and ongoing maintenance of overdentures on 1 or 2 implants are similar for at least 1 y, and the singleimplant has lower initial costs.
Hypothesis We now aim to test the null hypothesis that there is no significant difference in participant satisfaction after 5 y between the 1-implant and 2-implant mandibular overdenture groups. Our secondary aims are to assess changes in satisfaction between and within each group over 5 y and differences in implant survival and prosthetic maintenance between groups.
Materials and Methods This randomized clinical trial compared outcomes between edentulous participants treated with either 1 or 2 endosseous implants placed in the anterior mandible to retain a complete lower denture. The trial was approved by the University’s Clinical Research Ethics Board (Certificate H02-70082) with written informed consent from all participants. Recruitment, randomization, and clinical and analytical methods have been described in detail previously (Walton and MacEntee 2008; Walton et al. 2009). Between 2002 and 2006, 86 healthy completely edentulous participants were enrolled from a screening of 220 volunteers (Fig. 1) by a prosthodontist and an oral surgeon following established inclusion and exclusion criteria (Table 1). The anterior mandible required at least 10 mm of bone height,1 as determined by the surgeon using panoramic and lateral cephalometric radiographs. Existing dentures were acceptable if aesthetically satisfactory to the participant and technically acceptable (Online Supplemental Table) to the prosthodontist following international guidelines (Owen 2006; Walton et al. 2009). The dentures had semi-anatomical acrylic teeth with bilateral balanced occlusion. Participants were stratified by sex and ridge resorption, then distributed randomly to 2 groups within stratified blocks of participants to receive 1 (group 1) or 2 (group 2)
implants (Walton et al. 2009). The blocks were generated from a random-number table by a statistician and administered by a research assistant drawing each participant’s assignment from the appropriate stratification envelope immediately before implant surgery. Ridge resorption was classified as either “normal” when the ridge crest was visible bilaterally above the mental foramina or “severe” when the crest was at or below either foramen. Nonetheless, all of the ridges were at least 10 mm high to accommodate either a 10-mm or 12-mm implant. Participants were informed of their treatment assignment when seated for surgery. The staff were absent when participants answered questionnaires and instructed not to make evaluative comments on treatment options or outcomes to the participants. Each participant received an implant (Solid Screw, SLA surface; Straumann Canada, Burlington, ON, Canada) either in the mandibular midline or bilaterally in the mandibular canine areas. A soft reline (Coe Comfort; GC Corporation, Tokyo, Japan) was added to the denture about 10 days after surgery, and participants were prescribed a soft diet until the denture was attached to the implants. Approximately 6 weeks later, a 2.25-mm ball patrix (Straumann-ITI Spherical Stud Retentive Anchor; Straumann Canada) was screwed onto each implant and the denture was relined with laboratory-processed acrylic resin (Ivoclar Vivadent, Mississauga, Canada) to incorporate the retentive matrix (Straumann-ITI Gold Matrix; Straumann Canada) into the denture. Standard recommendations were given on denture and oral hygiene and on not wearing the dentures at night. Participants were assessed at baseline prior to implants, as well as at 2 mo and 1, 3, and 5 y with implant overdentures, to record satisfaction with treatment and monitor the implants, peri-implant tissues, dentures, and attachments, while maintenance events were recorded as they occurred. Maintenance events included matrix or patrix adjustments, reattachments or replacements, denture-base fractures, relining or rebasing, and fabrication of new dentures. Implant status was judged by the presence or absence of clinical mobility, pain or suppuration, and the extent (none, mild, moderate, or severe) of peri-implant inflammation adapted from Löe and Silness (1963). The mucosal height was measured vertically from the abutment shoulder using a periodontal probe at the midfacial and both proximal surfaces. We also assessed the dentures to specific criteria (Online Supplemental Table) and the attachment components between the dentures and implants. Satisfaction was measured on a 10-cm uninterrupted visual analog scale (VAS) representing a continuum of feelings, with “unsatisfied” at one end and “satisfied” at the other. Each participant made a global assessment of his or her satisfaction by marking X on the line at a point identifying his or her response to the following question: “How would you evaluate your ‘overall satisfaction’ with your lower denture?” A research assistant, blinded to the treatment group
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A 5-y Randomized Trial to Compare Implants for Implant Overdentures
Assessed for eligibility (n=220) Excluded (n=134)
Enrollment
Did not meet inclusion criteria (n=62) Declined to participate (n=70) Met criteria but died before treatment (n=2)
Allocation
Stratified and Randomized (n=86)
Allocated for 1 implant (n=42)
Analysis
Follow-up
Received allocated intervention (n=42) - no failed implants
Allocated for 2 implants (n=44) Received allocated intervention (n=44) - 1 failed implant replaced (n=2) - 2 failed implants replaced (n=1) - 1 failed implant not replaced (n=1)
Lost to follow-up (n=13) Deceased (n=8) Unknown reasons (n=5) Withdrew from study (n=0)
Lost to follow-up (n=11) Deceased (n=6) Unknown reasons (n=4) Withdrew from study (n=1) - discomfort from maxillary denture (n=1)
Analyzed (n=29) Excluded from analysis (n=13) - lost to follow-up (n=13)
Analyzed (n=33) Excluded from analysis (n=11) - lost to follow-up (n=11)
Figure 1. Flow diagram of the enrollment, allocation, follow-up, and analysis of participants.
assignment, translated the mark into a number by superimposing a template with 100 numbered intervals.
Sample Size and Analysis The original null hypothesis was based on the assumption that the proportion of participants in 1 group identifying a “substantial increase” in VAS satisfaction would exceed the proportion in the other group by at least half, which was equivalent to an odds ratio of 2, and corresponded to an increase of ≥0.67 from baseline measurements. Our original sample size was estimated on the minimum number of participants required to provide an 80% probability of detecting an odds ratio of 2 or greater for participant satisfaction in the 1-sided nonparametric Wilcoxon Mann-Whitney ranks procedure (α = 0.05) (Noether 1987). Consequently,
we aimed to enroll 43 participants per group: 38 plus 5 per group for dropouts (Walton et al. 2009). We found that nearly one-third of the participants had a baseline VAS score above 75, so they could not experience the “substantial increase” anticipated in the original hypothesis. Consequently, we tested the null hypothesis that there was no significant difference after 5 y in the VAS scores between groups, and as secondary aims, we evaluated the changes in satisfaction from baseline to 5 y between and within groups. The VAS is a subjective ordinal measurement that usually responds similarly to parametric and nonparametric tests (Maxwell 1978). Consequently, with SPSS Statistics (version 21.0; SPSS, Inc., an IBM Company, Chicago, IL), we compared between groups for differences in satisfaction at 5 y and for differences in the change from baseline to 5 y (independent samples Student’s t test and
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Journal of Dental Research
Table 1. Inclusion and Exclusion Criteria for Participants (Walton et al. 2009). Inclusion criteria •• Functional in English or with a responsible adult who can translate •• Able to consent to the treatment provided •• Available for the duration of the study •• Edentate and with at least 6 months’ experience with conventional complete dentures •• Using complete dentures that are aesthetically satisfactory to the patient and technically acceptable to the prosthodontist •• Physically and psychologically suitable for implant surgery Exclusion criteria •• 44) drop in satisfaction scores during the trial. The nonsignificant tendency in both groups for slightly decreasing satisfaction after the large initial improvement (Fig. 2) has been observed previously with implant overdentures (Timmerman et al. 2004). In contrast, others (Naert et al. 2004) did not find such a tendency over time, but their study protocol may well have involved a more frequent maintenance schedule. The tendency for more variability of VAS scores in group 1 (Fig. 2) might be due to more maintenance events in this group, although the satisfaction for most participants remained relatively high in both groups, suggesting that maintenance events may have caused relatively little dissatisfaction. Overall, prosthetic maintenance as a source of dissatisfaction remains unclear as none of the 9 very dissatisfied outliers (≤20) at 5 y had fractured or replaced dentures, while most participants, including these 9, had attachments adjusted, reattached, or replaced. Others have found that subjective perceptions of implant dentures did not relate to differences in the maintenance requirements of different attachment designs (Merickse-Stern et al. 2009). Further prospective investigations are needed, possibly with a mixture of deductive and inductive methods, to identify and explain the behaviors and beliefs initiating and sustaining dissatisfaction with implant overdentures. The fractured overdentures in 19 participants were associated more frequently with group 1, possibly because of stress over the single implant in the midline. Fractures occurred usually adjacent to the implant attachments in both groups and in participants with either “normal” or “severe” mandibular resorption. Goodacre et al. (2003) reported fewer fractures of 2-implant dentures than we found in either group in our study, but these studies frequently used new rather than relined existing dentures, which might explain the difference. Furthermore, they used data pooled from studies of various designs and follow-up periods in their review and cautioned specifically against comparisons on incidence rates. Five participants (none with “severe” ridge resorption) accounted for about half of the 35 fractured dentures (2 in group 1 had 4 fractures each and 3 in group 2 had 3 fractures each), possibly due to parafunctional habits or the cross-sectional thickness of the denture, although we did not measure these characteristics. Attempts to strengthen overdentures by embedding metal frameworks have been unsuccessful (MacEntee et al. 2005; Gonda et al. 2007; Gonda et al. 2010), although attachment systems other than the one used in this trial might help (Cordioli et al. 1997). We agree that tooth loss can be a major disability for which mandibular complete dentures offer little respite (MacEntee et al. 1997; Fiske et al. 1998). Owen (2009) argues that an acceptable “standard of care” in prosthodontics must address economic resources and that the cost of implants does challenge the recommendations of the consensus conferences on
7
minimal standards of care for edentulous mandibles. We propose therefore that the outcome of this trial supports the need for further exploration of the cost of implant dentures with the possibility that 1-implant compared with 2-implant overdentures offer a more accessible and cost-effective option for managing edentulous mandibles.
Conclusions There was no statistical difference after 5 y in overall satisfaction or survival of implants with mandibular overdentures retained by 1 or 2 implants. However the 1-implant group had a tendency for more prosthetic maintenance with more fractured dentures. The decreased power of the analysis due to 28% of dropouts suggests that further research is needed to determine the effectiveness of the single implant beyond 5 y and to reduce the tendency for implant dentures to fracture. Author Contributions S.R. Bryant, contributed to conception, design, data acquisition, analysis, and interpretation, drafted and critically revised the manuscript; J.N. Walton, contributed to conception and design, critically revised the manuscript; M.I. MacEntee, contributed to conception, design, data acquisition, and interpretation, drafted and critically revised the manuscript. All authors gave final approval and agree to be accountable for all aspects of the work.
Acknowledgments The study was funded by the ITI Foundation (grants 222 and 6352009), the Canadian Institutes of Health Research (grant 58954), and Straumann Canada Ltd. None of the supporting agencies for this trial had any influence on its design, analysis, or reports of outcomes. The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.
Note 1. The 1-y report indicated erroneously that 6 mm was the minimum bone height (Walton et al. 2009).
References Awad MA, Feine JS. 1998. Measuring patient satisfaction with mandibular prostheses. Community Dent Oral Epidemiol. 26(6):400–405. Bryant SR, MacDonald-Jankowski D, Kim K. 2007. Does the type of implant prosthesis affect outcomes for the completely edentulous arch? Int J Oral Maxillofac Implants. 22(Suppl):S117– S139. (Published erratum appears in Int J Oral Maxillofac Implants. 2008;23(1):56.) Cehreli MC, Karasoy D, Kokat AM, Akca K, Eckert SE. 2010. Systematic review of prosthetic maintenance requirements for implant-supported overdentures. Int J Oral Maxillofac Implants. 25(1):163–180. Cohen ME. 2001. Analysis of ordinal dental data: Evaluation of conflicting recommendations. J Dent Res. 80(1):309–313.
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Cordioli G, Majzoub Z, Castagna S. 1997. Mandibular overdentures anchored to single implants: a five-year prospective study. J Prosthet Dent. 78(2):159–165. Fiske J, Davis DM, Frances C, Gelbier S. 1998. The emotional effects of tooth loss in edentulous people. Br Dent J. 184(2):90–93; discussion 79. Fitzpatrick B. 2006. Standard of care for the edentulous mandible: a systematic review. J Prosthet Dent. 95(1):71–78. Gonda T, Ikebe K, Dong J, Nokubi T. 2007. Effect of reinforcement on overdenture strain. J Dent Res. 86(7):667–671. Gonda T, Maeda Y, Walton JN, MacEntee MI. 2010. Fracture incidence in mandibular overdentures retained by one or two implants. J Prosthet Dent. 103(3):178–181. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. 2003. Clinical complications with implants and implant prostheses. J Prosthet Dent. 90(2):121–132. Heine SJ, Lehman DR, Peng K, Greenholtz J. 2002. What’s wrong with cross-cultural comparisons of subjective Likert scales: the reference-group problem. J Pers Soc Psychol. 82(6):903–918. Kronström 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(1):181–188. Liddelow GJ, Henry PJ. 2007. A prospective study of immediately loaded single implant-retained mandibular overdentures: preliminary one-year results. J Prosthet Dent. 97(6, Suppl):S126–S137. Locker D. 1998. Issues in measuring change in self-perceived oral health status. Community Dent Oral Epidemiol. 26(1):41–47. Löe H, Silness J. 1963. Periodontal disease in pregnancy: I. Prevalence and severity. Acta Odontol Scand. 21:533–551. MacEntee MI, Hole R, Stolar E. 1997. The significance of the mouth in old age. Soc Sci Med. 45(9):1449–1458. MacEntee MI, Walton JN. 1998. The economics of complete dentures and implant-related services: a framework for analysis and preliminary outcomes. J Prosthet Dent. 79(1):24–30. MacEntee MI, Walton JN, Glick N. 2005. A clinical trial of patient satisfaction and prosthodontic needs with ball and bar attachments for implant-retained complete overdentures: three-year results. J Prosthet Dent. 93(1):28–37.
Maxwell C. 1978. Sensitivity and accuracy of the visual analogue scale: a psycho-physical classroom experiment. Br J Clin Pharmacol. 6(1):15–24. Mericske-Stern R, Probst D, Fahrländer F, Schellenberg M. 2009. Within-subject comparison of two rigid bar designs connecting two interforaminal implants: patients’ satisfaction and prosthetic results. Clin Impl Dent Relat Res. 11(3):228–237. Naert I, Alsaadi G, Quirynen M. 2004. Prosthetic aspects and patient satisfaction with two-implant-retained mandibular overdentures: a 10-year randomized clinical study. Int J Prosthodont. 17(4):401–410. Noether GE. 1987. Sample size determination for some common nonparametric tests. J Am Statistical Assoc. 82:645–647. Owen CP. 2006. Guidelines for a minimum acceptable protocol for the construction of complete dentures. Int J Prosthodont. 19(5):467–474. Owen CP. 2009. Standards of care: good or evil? Int J Prosthodont. 22(4):328–330. Roccuzzo M, Bonino F, Gaudioso L, Zwahlen M, Meijer HJ. 2012. What is the optimal number of implants for removable reconstructions? A systematic review on implant-supported overdentures. Clin Oral Implants Res. 23(Suppl 6):S229–S237. Thomason JM, Kelly SA, Bendkowski A, Ellis JS. 2012. Two implant retained overdentures: a review of the literature supporting the McGill and York consensus statements. J Dent. 40(1):22–34. Timmerman R, Stoker GT, Wismeijer D, Oosterveld P, Vermeeren JI, van Waas MA. 2004. An eight-year follow-up to a randomized clinical trial of participant satisfaction with three types of mandibular implant-retained overdentures. J Dent Res. 83(8):630–633. Tsakos G, Allen PF, Steele JG, Locker D. 2012. Interpreting oral health–related quality of life data. Community Dent Oral Epidemiol. 40(3):193–200. 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(4):331–339. Walton JN, MacEntee MI. 2008. Screening and enrolling subjects in a randomized clinical trial involving implant dentures. Int J Prosthodont. 21(3):210–214.
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A 5-y Randomized Trial to Compare 1 or 2 Implants for Implant Overdentures S.R. Bryant, J.N. Walton and M.I. MacEntee J DENT RES published online 27 October 2014 DOI: 10.1177/0022034514554224 The online version of this article can be found at: http://jdr.sagepub.com/content/early/2014/10/24/0022034514554224
Published by: http://www.sagepublications.com
On behalf of: International and American Associations for Dental Research
Additional services and information for Journal of Dental Research can be found at: Email Alerts: http://jdr.sagepub.com/cgi/alerts Subscriptions: http://jdr.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav
>> OnlineFirst Version of Record - Oct 27, 2014 What is This?
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554224
research-article2014
JDRXXX10.1177/0022034514554224JDR Clinical Research SupplementJDR Clinical Research Supplement
Research Reports: Clinical
A 5-y Randomized Trial to Compare 1 or 2 Implants for Implant Overdentures
Journal of Dental Research 1–8 © International & American Associations for Dental Research 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0022034514554224 jdr.sagepub.com
S.R. Bryant1, J.N. Walton1, and M.I. MacEntee1
Abstract The hypothesis of this 5-y randomized clinical trial was that there would be no significant difference in the satisfaction of edentulous participants with removable complete overdentures attached to 1 or 2 mandibular implants. Secondary aims were to test changes in satisfaction between and within the groups from baseline to 5 y and differences between the groups in implant survival and prosthodontic maintenance over 5 y. Each of the 86 participants (mean age, 67 y) was randomly allocated to receive either 1 implant in the midline (group 1) or 2 implants in the canine areas (group 2) attached to a mandibular overdenture opposing a maxillary complete denture. Satisfaction was self-assessed by participants on a visual analog scale at baseline prior to implants, as well as at 2 mo and 1, 3, and 5 y with implant overdentures, whereas implant survival and prosthodontic maintenance were assessed by clinical examination. After 5 y, 29 participants in group 1 and 33 in group 2 were available, with most dropouts due to death. Satisfaction with the implant denture after 5 y was significantly (P < 0.001) higher than at baseline in both groups and remained with no significant difference (P = 0.32) between the groups. No implants failed in group 1 but 5 failed before loading in 4 participants in group 2. Most participants required maintenance or occasionally denture replacement, and although differences between the groups were not statistically significant, group 1 experienced almost twice as many fractured dentures usually adjacent to the implant attachment. We conclude that there were no significant differences after 5 y in satisfaction or survival of implants with mandibular overdentures retained by 1 implant or 2 implants. Additional research is required to confirm longterm treatment effectiveness of single-implant dentures and the implications of prosthetic maintenance with implant overdentures (ClinicalTrials.gov: NCT02117856). Keywords: implant-supported dental prosthesis, single-implant denture, complete denture, edentulous mandible, dental implant, standard of care
Introduction Implant dentures have substantially higher financial costs than conventional complete dentures (MacEntee and Walton 1998), although 2 consensus conferences concluded that a mandibular overdenture supported by 2 implants is the “minimum standard” of treatment for edentulous patients (Thomason et al. 2012). Others believe that this standard disregards those who cannot afford 2 implants and implies that anything less is negligent care (Owen 2009). Indeed, there is no evidence for a single standard of care for edentulous mandibles with or without implants (Fitzpatrick 2006) or a link between the number of implants and complications or satisfaction with overdentures (Roccuzzo et al. 2012). Cordioli et al. (1997) monitored 15 patients for 5 y, each with a mandibular overdenture attached with a ball abutment and rubber O-ring to 1 midline implant, and the patients remained comfortable and without an implant failure. Liddelow and Henry (2007) reported similar success for 28 patients 1 y after most had
immediate placement of mandibular overdentures on a single midline implant. Walton et al. (2009) reported results from the first year of this randomized clinical trial, allocating 1 or 2 implants in the anterior mandible to retain overdentures with ball abutments and gold matrices about 6 weeks after implant placement. No implants in the 1-implant group failed; however, 5 failed in the 2-implant group, all before connecting the dentures to the implants. At 1 y, most participants were satisfied in both groups, and there were no statistical 1
Division of Prosthodontics and Dental Geriatrics, Department of Oral Health Sciences, University of British Columbia, Canada A supplemental appendix to this article is published electronically only at http://jdr.sagepub.com/supplemental. Corresponding Author: R. Bryant, Division of Prosthodontics and Dental Geriatrics, Department of Oral Health Sciences, University of British Columbia, British Columbia, Canada V6T 1Z3. Email: [email protected]
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Journal of Dental Research
differences in satisfaction or prosthetic maintenance, whereas the 1-implant group required significantly less time and financial costs for the initial treatment. Kronström et al. (2010) also allocated participants randomly to receive 1 or 2 mandibular anterior implants with ball patrices and O-ring matrices to connect overdentures immediately after placing the implants. Three (18%) participants in the 1-implant group and 6 (32%) in the 2-implant group lost implants during the first year. Others reported that time and costs are similar to maintain different attachment systems for implant overdentures (Cehreli et al. 2010), although the evidence remains inconclusive given the various ways that data have been reported (Bryant et al. 2007). We conclude from the available evidence that implant survival, participant satisfaction, and ongoing maintenance of overdentures on 1 or 2 implants are similar for at least 1 y, and the singleimplant has lower initial costs.
Hypothesis We now aim to test the null hypothesis that there is no significant difference in participant satisfaction after 5 y between the 1-implant and 2-implant mandibular overdenture groups. Our secondary aims are to assess changes in satisfaction between and within each group over 5 y and differences in implant survival and prosthetic maintenance between groups.
Materials and Methods This randomized clinical trial compared outcomes between edentulous participants treated with either 1 or 2 endosseous implants placed in the anterior mandible to retain a complete lower denture. The trial was approved by the University’s Clinical Research Ethics Board (Certificate H02-70082) with written informed consent from all participants. Recruitment, randomization, and clinical and analytical methods have been described in detail previously (Walton and MacEntee 2008; Walton et al. 2009). Between 2002 and 2006, 86 healthy completely edentulous participants were enrolled from a screening of 220 volunteers (Fig. 1) by a prosthodontist and an oral surgeon following established inclusion and exclusion criteria (Table 1). The anterior mandible required at least 10 mm of bone height,1 as determined by the surgeon using panoramic and lateral cephalometric radiographs. Existing dentures were acceptable if aesthetically satisfactory to the participant and technically acceptable (Online Supplemental Table) to the prosthodontist following international guidelines (Owen 2006; Walton et al. 2009). The dentures had semi-anatomical acrylic teeth with bilateral balanced occlusion. Participants were stratified by sex and ridge resorption, then distributed randomly to 2 groups within stratified blocks of participants to receive 1 (group 1) or 2 (group 2)
implants (Walton et al. 2009). The blocks were generated from a random-number table by a statistician and administered by a research assistant drawing each participant’s assignment from the appropriate stratification envelope immediately before implant surgery. Ridge resorption was classified as either “normal” when the ridge crest was visible bilaterally above the mental foramina or “severe” when the crest was at or below either foramen. Nonetheless, all of the ridges were at least 10 mm high to accommodate either a 10-mm or 12-mm implant. Participants were informed of their treatment assignment when seated for surgery. The staff were absent when participants answered questionnaires and instructed not to make evaluative comments on treatment options or outcomes to the participants. Each participant received an implant (Solid Screw, SLA surface; Straumann Canada, Burlington, ON, Canada) either in the mandibular midline or bilaterally in the mandibular canine areas. A soft reline (Coe Comfort; GC Corporation, Tokyo, Japan) was added to the denture about 10 days after surgery, and participants were prescribed a soft diet until the denture was attached to the implants. Approximately 6 weeks later, a 2.25-mm ball patrix (Straumann-ITI Spherical Stud Retentive Anchor; Straumann Canada) was screwed onto each implant and the denture was relined with laboratory-processed acrylic resin (Ivoclar Vivadent, Mississauga, Canada) to incorporate the retentive matrix (Straumann-ITI Gold Matrix; Straumann Canada) into the denture. Standard recommendations were given on denture and oral hygiene and on not wearing the dentures at night. Participants were assessed at baseline prior to implants, as well as at 2 mo and 1, 3, and 5 y with implant overdentures, to record satisfaction with treatment and monitor the implants, peri-implant tissues, dentures, and attachments, while maintenance events were recorded as they occurred. Maintenance events included matrix or patrix adjustments, reattachments or replacements, denture-base fractures, relining or rebasing, and fabrication of new dentures. Implant status was judged by the presence or absence of clinical mobility, pain or suppuration, and the extent (none, mild, moderate, or severe) of peri-implant inflammation adapted from Löe and Silness (1963). The mucosal height was measured vertically from the abutment shoulder using a periodontal probe at the midfacial and both proximal surfaces. We also assessed the dentures to specific criteria (Online Supplemental Table) and the attachment components between the dentures and implants. Satisfaction was measured on a 10-cm uninterrupted visual analog scale (VAS) representing a continuum of feelings, with “unsatisfied” at one end and “satisfied” at the other. Each participant made a global assessment of his or her satisfaction by marking X on the line at a point identifying his or her response to the following question: “How would you evaluate your ‘overall satisfaction’ with your lower denture?” A research assistant, blinded to the treatment group
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A 5-y Randomized Trial to Compare Implants for Implant Overdentures
Assessed for eligibility (n=220) Excluded (n=134)
Enrollment
Did not meet inclusion criteria (n=62) Declined to participate (n=70) Met criteria but died before treatment (n=2)
Allocation
Stratified and Randomized (n=86)
Allocated for 1 implant (n=42)
Analysis
Follow-up
Received allocated intervention (n=42) - no failed implants
Allocated for 2 implants (n=44) Received allocated intervention (n=44) - 1 failed implant replaced (n=2) - 2 failed implants replaced (n=1) - 1 failed implant not replaced (n=1)
Lost to follow-up (n=13) Deceased (n=8) Unknown reasons (n=5) Withdrew from study (n=0)
Lost to follow-up (n=11) Deceased (n=6) Unknown reasons (n=4) Withdrew from study (n=1) - discomfort from maxillary denture (n=1)
Analyzed (n=29) Excluded from analysis (n=13) - lost to follow-up (n=13)
Analyzed (n=33) Excluded from analysis (n=11) - lost to follow-up (n=11)
Figure 1. Flow diagram of the enrollment, allocation, follow-up, and analysis of participants.
assignment, translated the mark into a number by superimposing a template with 100 numbered intervals.
Sample Size and Analysis The original null hypothesis was based on the assumption that the proportion of participants in 1 group identifying a “substantial increase” in VAS satisfaction would exceed the proportion in the other group by at least half, which was equivalent to an odds ratio of 2, and corresponded to an increase of ≥0.67 from baseline measurements. Our original sample size was estimated on the minimum number of participants required to provide an 80% probability of detecting an odds ratio of 2 or greater for participant satisfaction in the 1-sided nonparametric Wilcoxon Mann-Whitney ranks procedure (α = 0.05) (Noether 1987). Consequently,
we aimed to enroll 43 participants per group: 38 plus 5 per group for dropouts (Walton et al. 2009). We found that nearly one-third of the participants had a baseline VAS score above 75, so they could not experience the “substantial increase” anticipated in the original hypothesis. Consequently, we tested the null hypothesis that there was no significant difference after 5 y in the VAS scores between groups, and as secondary aims, we evaluated the changes in satisfaction from baseline to 5 y between and within groups. The VAS is a subjective ordinal measurement that usually responds similarly to parametric and nonparametric tests (Maxwell 1978). Consequently, with SPSS Statistics (version 21.0; SPSS, Inc., an IBM Company, Chicago, IL), we compared between groups for differences in satisfaction at 5 y and for differences in the change from baseline to 5 y (independent samples Student’s t test and
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Journal of Dental Research
Table 1. Inclusion and Exclusion Criteria for Participants (Walton et al. 2009). Inclusion criteria •• Functional in English or with a responsible adult who can translate •• Able to consent to the treatment provided •• Available for the duration of the study •• Edentate and with at least 6 months’ experience with conventional complete dentures •• Using complete dentures that are aesthetically satisfactory to the patient and technically acceptable to the prosthodontist •• Physically and psychologically suitable for implant surgery Exclusion criteria •• 44) drop in satisfaction scores during the trial. The nonsignificant tendency in both groups for slightly decreasing satisfaction after the large initial improvement (Fig. 2) has been observed previously with implant overdentures (Timmerman et al. 2004). In contrast, others (Naert et al. 2004) did not find such a tendency over time, but their study protocol may well have involved a more frequent maintenance schedule. The tendency for more variability of VAS scores in group 1 (Fig. 2) might be due to more maintenance events in this group, although the satisfaction for most participants remained relatively high in both groups, suggesting that maintenance events may have caused relatively little dissatisfaction. Overall, prosthetic maintenance as a source of dissatisfaction remains unclear as none of the 9 very dissatisfied outliers (≤20) at 5 y had fractured or replaced dentures, while most participants, including these 9, had attachments adjusted, reattached, or replaced. Others have found that subjective perceptions of implant dentures did not relate to differences in the maintenance requirements of different attachment designs (Merickse-Stern et al. 2009). Further prospective investigations are needed, possibly with a mixture of deductive and inductive methods, to identify and explain the behaviors and beliefs initiating and sustaining dissatisfaction with implant overdentures. The fractured overdentures in 19 participants were associated more frequently with group 1, possibly because of stress over the single implant in the midline. Fractures occurred usually adjacent to the implant attachments in both groups and in participants with either “normal” or “severe” mandibular resorption. Goodacre et al. (2003) reported fewer fractures of 2-implant dentures than we found in either group in our study, but these studies frequently used new rather than relined existing dentures, which might explain the difference. Furthermore, they used data pooled from studies of various designs and follow-up periods in their review and cautioned specifically against comparisons on incidence rates. Five participants (none with “severe” ridge resorption) accounted for about half of the 35 fractured dentures (2 in group 1 had 4 fractures each and 3 in group 2 had 3 fractures each), possibly due to parafunctional habits or the cross-sectional thickness of the denture, although we did not measure these characteristics. Attempts to strengthen overdentures by embedding metal frameworks have been unsuccessful (MacEntee et al. 2005; Gonda et al. 2007; Gonda et al. 2010), although attachment systems other than the one used in this trial might help (Cordioli et al. 1997). We agree that tooth loss can be a major disability for which mandibular complete dentures offer little respite (MacEntee et al. 1997; Fiske et al. 1998). Owen (2009) argues that an acceptable “standard of care” in prosthodontics must address economic resources and that the cost of implants does challenge the recommendations of the consensus conferences on
7
minimal standards of care for edentulous mandibles. We propose therefore that the outcome of this trial supports the need for further exploration of the cost of implant dentures with the possibility that 1-implant compared with 2-implant overdentures offer a more accessible and cost-effective option for managing edentulous mandibles.
Conclusions There was no statistical difference after 5 y in overall satisfaction or survival of implants with mandibular overdentures retained by 1 or 2 implants. However the 1-implant group had a tendency for more prosthetic maintenance with more fractured dentures. The decreased power of the analysis due to 28% of dropouts suggests that further research is needed to determine the effectiveness of the single implant beyond 5 y and to reduce the tendency for implant dentures to fracture. Author Contributions S.R. Bryant, contributed to conception, design, data acquisition, analysis, and interpretation, drafted and critically revised the manuscript; J.N. Walton, contributed to conception and design, critically revised the manuscript; M.I. MacEntee, contributed to conception, design, data acquisition, and interpretation, drafted and critically revised the manuscript. All authors gave final approval and agree to be accountable for all aspects of the work.
Acknowledgments The study was funded by the ITI Foundation (grants 222 and 6352009), the Canadian Institutes of Health Research (grant 58954), and Straumann Canada Ltd. None of the supporting agencies for this trial had any influence on its design, analysis, or reports of outcomes. The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.
Note 1. The 1-y report indicated erroneously that 6 mm was the minimum bone height (Walton et al. 2009).
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