A 3-Year Follow-up Study of Overdentures Retained by Mini–Dental Implants Elena Preoteasa, DMD, PhD1/Marina Imre, DMD, PhD2/Cristina Teodora Preoteasa, DMD3 Purpose: This study evaluated overdentures retained by mini–dental implants (MDIs) as a treatment option for complete edentulism during a 3-year follow-up period. Materials and Methods: This observational clinical study included completely edentulous patients who were treated with MDI-retained overdentures. The MDIs were supplied by the manufacturer. Results: Twenty-three patients received 7 maxillary and 16 mandibular MDI overdentures retained by 110 MDIs. Of the 36 MDIs placed in the maxilla, 8 failed (in two patients), 2 had compromised survival, 3 displayed satisfactory survival, and 23 were successful. Of the 74 MDIs placed in the mandible, 11 displayed satisfactory survival and 63 were successful. The marginal bone loss was more pronounced for the MDIs placed mesially (intercalated), in areas of decreased ridge width and bone density, and with lower values of insertion torque. The overdentures fractured in seven patients; in 4 of them, this corresponded to the implant housing area. Self-reported reasons for patient dissatisfaction included occasional pain under the overdenture (n = 5) and instability of the maxillary antagonist complete denture (n = 4). Conclusion: Based on this research, considering its limitations, it is possible to conclude that survival rates and health status are better for MDI overdentures applied in the mandible than for those applied in the maxilla. The most severe prosthetic complications encountered were overdenture base fracture, matrix detachment, and instability of the maxillary antagonist denture. Int J Oral Maxillofac Implants 2014;29:1170–1176. doi: 10.11607/jomi.3222 Key words: denture, edentulous, mini–dental implants, overdenture
T
he mini–dental implant (MDI) overdenture is a relatively recent treatment option for complete edentulism and is indicated especially for patients who are dissatisfied with their conventional dentures. The MDIs provide only overdenture retention, not support, as there is an occlusal space between the implant abutment attachment and the overdenture. MDI overdentures have several benefits compared to other treatment alternatives. In contrast to the conventional complete denture, this type of overdenture requires an
1Professor,
Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania. 2Lecturer, Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania. 3 PhD Student and Assistant Professor, Department of Scientific Research Methodology, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania. Correspondence to: Elena Preoteasa, Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Str. Ionel Perlea nr. 12, sector 1, 010208 Bucharest, Romania. Email: [email protected]
additionally relatively simple, minimally invasive surgical intervention, but the attachment system and immediate loading of the MDIs ensure increased retention, stability, and function, with improvements in patient satisfaction, comfort, and quality of life.1–3 Standarddiameter implant-supported prosthetic alternatives have shown success, but these are not viable solutions for all edentulous patients. The MDI overdenture may be a more appropriate treatment alternative for the edentulous patient with compromised health and/or a restricted buccolingual dimension of bone. In these cases, MDI placement requires fewer and less invasive surgical interventions (eg, avoidance of bone grafting procedures and decreased clinical time required for implant placement, especially when a minimally invasive flapless technique is used), promoting a lower risk of developing complications and shortening the healing period.4,5 Given the demographic changes in the population, especially the aging trend, there is an increasing need for relevant treatment for the medical problems of older patients, complete edentulism being one of them. The MDI overdenture is one viable treatment alternative for this condition, which seems appropriate to this segment of the population, but scientific evidence regarding clinical outcomes of the MDI overdenture is relatively limited.6 Therefore, more
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information is needed to assess the viability and safety of this treatment concept. The purpose of this study was to evaluate the MDI overdenture as a treatment option for complete edentulism. Treatment outcomes were considered in three dimensions: MDI status, overdenture status, and patient perception and satisfaction. Data were collected after a 3-year follow-up period.
MATERIALS AND METHODS An observational clinical study was conducted and implemented. Patients with complete edentulism who requested treatment at the Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, between April and November 2008 were enrolled in the study. A convenience sample was formed according to the following eligibility criteria. Completely edentulous patients with conventional complete dentures who were dissatisfied with this treatment alternative, or who were untreated but expressed fear and reticence toward conventional dentures, were included. Excluded were those with severe systemic conditions (eg, uncontrolled hypertension, diabetes mellitus) or receiving particular medications (eg, bisphosphonates) because of the risk associated with the surgical procedure of MDI placement and the potential for these conditions and medications to contribute to a poor prognosis. The patients were given information regarding the MDI overdenture, and all chose this treatment alternative and participation in the study on a voluntary basis. From each patient, written informed consent was obtained. Because the role of the MDIs is to improve retention of a prosthetic device, the overdenture design aimed to ensure proper support, retention, and stability. In this respect, complete coverage of the support area, including the anatomical and functional borders, with a complete peripheral seal was chosen. For maxillary dentures, complete palatal coverage with a postpalatal seal was used. Registration of the maxillomandibular relationship aimed to ensure a correct functional vertical dimension of occlusion in centric relation. Premature contacts were checked and eliminated to accomplish the coincidence of centric relation and centric occlusion and obtain bilateral simultaneous stable occlusal contacts in centric occlusion. Principles of lingualized denture occlusion were used; ie, the maxillary lingual cusps articulated with the central fossae of the mandibular occlusal surfaces in centric working and nonworking mandibular positions. Some of the patients presented with previously made complete dentures; their quality was analyzed
and the clinician decided either to keep or replace them. Aspects related to coverage of the support area, denture retention and stability, correct registration of maxillomandibular relationships, type of denture occlusion, the correctness of the arrangement of artificial teeth, material status, and patient perception regarding the denture were evaluated and considered as factors in this decision. The MDIs used were supplied by IMTEC/3M ESPE. These were available in four lengths (10 mm, 13 mm, 15 mm, and 18 mm) and three diameters (1.8 mm, 2.1 mm, and 2.4 mm) and used collared balls as attachments. The number of MDIs placed and their locations and dimensions were chosen based on the individual features of the patient and the judgment of the dentist but considered as closely as possible the manufacturer’s recommendations for this type of implant regarding the minimum number of MDIs that should be placed (four MDIs in the mandible and six MDIs in the maxilla). The MDI overdenture was chosen as a treatment option for mandibular or maxillary complete edentulism. This treatment alternative was indicated for maxillary edentulism when teeth or fixed prosthetic restorations were present in the anterior mandible or when patients had a skeletal Class III relationship with a reverse relation of the edentulous arches. To ensure a good prognosis, several instructions were given to the patients. Amoxicillin with clavulanic acid (Augmentin, SmithKline Beecham) were administered to patients for 5 days, starting 2 hours prior to implant placement. After the surgical intervention, patients were informed that they would probably feel some discomfort and pain that would disappear in a few days; analgesic drugs were recommended if necessary. Also, they were advised to eat soft foods of moderate temperature. The importance of adequate hygiene procedures was highlighted. Patients were taught how to adequately clean the MDIs and the overdenture. Additionally, they were advised to use chlorhexidine products to prevent bacterial and fungal infections. Chlorhexidine digluconate 0.2% solution was recommended (twice daily oral rinses) before surgical implant placement and afterward. For overdenture cleaning, in addition to traditional mechanical cleaning, chemical cleaners (tablets) were recommended. Also, patients with bruxism or xerostomia were advised not to wear the overdenture overnight at least two times per week. The main outcome of this study was the success of the MDI overdenture as a treatment option for the completely edentulous patient. The analysis covered MDI status, overdenture status, and patients’ perceptions regarding this treatment alternative. The study variables, which addressed patient features and treatment specifics, are listed in Table 1.7 Additionally, a The International Journal of Oral & Maxillofacial Implants 1171
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Table 1 Study Variables
Table 2 Health Status of MDIs Placed Location
Patient’s general attributes (age, sex) Data regarding oral and treatment-related features: • Bone information: bone height,* ridge width,† bone density according to Misch classification7* • Treatment variables: Number and locations of MDIs, length and diameter of MDIs, implant insertion torque
MDI health status
MDI status: • Implant health, assessed using the previously described scale • Peri-implant marginal bone loss‡: registered as the maximum number of threads devoid of bone on the mesial and distal implant sides • Implant mobility§ • Self-reported peri-implant bleeding: spontaneous or during brushing • Radiolucency at the apical part of the implant‡
Success
Overdenture status: • Presence of any technical complication that required repair or maintenance: matrix detachment, overdenture fracture or relining Patient perceptions regarding MDI overdenture: • Self-reported reasons for satisfaction/dissatisfaction with this treatment • Frequency of overdenture wearing • Ease of use of MDI overdenture: overdenture placement (insertion), removal, and cleaning *Assessed
with computed tomography; †assessed with a clinical bone compass; ‡assessed with panoramic radiography; §assessed by clinical evaluation.
health scale for the MDI, derived from that proposed by the International Congress of Oral Implantology in Pisa, Italy, at the 2007 Consensus Conference8 and taking into consideration the Albrektsson et al criteria for implant success,9 was used as follows: • Failure: MDIs that were lost or removed for any reason, MDIs that fractured or presented with mobility, marginal bone loss exceeding half of the implant body length, or pain during function • Compromised survival: MDIs still present in the mouth, without an indication to be removed, but with either minimal clinical mobility, severe marginal bone loss (less than half of the implant body length), or sensitivity during function • Satisfactory survival: MDIs displaying no clinical mobility or sensitivity during function, with moderate bone loss (more than two threads, but less than half of the implant body length) • Success: MDIs without clinical mobility or sensitivity during function and marginal bone loss of less than two threads Data collection was conducted before and during surgical placement of the MDIs and after surgery; follow-up appointments were attended weekly during
Maxilla
Mandible
Failed
8
0
Compromised survival
2
0
Satisfactory survival
3
11
23
63
the first month postsurgery, at 3 and 6 months, and at 1, 2, and 3 years postsurgery. Clinical and radiographic (panoramic radiography, computed tomography) methods, together with data obtained through discussions with the patient during recall visits, were used for evaluations. Panoramic radiographs were indicated at 6 months, 1 year, 2 years, and 3 years. Statistical analysis was performed with the Statistical Package for the Social Sciences (version 13.0, SPSS Inc). In addition to descriptive statistics, the chi-square and Mann-Whitney tests were used for comparison between groups.
RESULTS Sample Characteristics
Of the 24 completely edentulous patients initially enrolled, 1 was lost during follow-up. Of the remaining 23 patients, 10 were men and 13 were women; the mean age was 62 years (range, 52 to 76 years). The subjects were treated with 7 maxillary and 16 mandibular MDI overdentures. A total of 110 MDIs were placed (36 in the maxilla and 74 in the mandible). Five or six MDIs were placed in the maxilla and four to six MDIs were placed in the mandible.
MDI Status
Of the 110 MDIs placed, 8 failed, for a survival rate of 92.7%. All MDIs that failed had been placed in the maxilla. Also, all eight failed MDIs had been placed in two female patients and failed within 1 to 2 years after their insertion. In one patient, all five MDIs that had been placed failed, two as a result of MDI fracture. In the other patient, three of five MDIs placed were lost as a result of progressive marginal bone loss. The health status of the MDIs, according to the scale presented, can be summarized as follows: in addition to the 8 failed MDIs, 2 had compromised survival, 14 showed satisfactory survival, and 86 were considered successful. Differences in the health status of maxillary and mandibular MDIs are summarized in Table 2. The other complications that occurred within the 102 MDIs still present at the 3-year follow-up
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examination are listed in Table 3. Almost half of the MDIs registered marginal bone loss > 1 thread and peri-implant bleeding, which appeared most frequently during brushing. Some of the complications had a different distribution depending on location (eg, spontaneous peri-implant bleeding was reported only for MDIs placed in the mandible). Marginal bone loss was more severe in women, in patients with a decreased ridge width, in sites with decreased bone density, around implants with lower insertion torque values, and in MDIs placed toward the midline (mesial/intercalated). MDIs with marginal bone loss of more than one implant thread more frequently presented with radiolucent lesions at the apical part of the implant and were more frequently associated with spontaneous peri-implant bleeding (Table 4).
Overdenture Status
During the 3-year follow-up period, overdenture fractures occurred in seven patients. In the mandible, overdenture fracture sites corresponded more frequently to the implant housing area (n = 4), but fractures also occurred in regions between implants (n = 2). In the maxilla, only one overdenture fractured in the area between implants. Overdenture relining was done in five cases. Two of these were the patients with implant failures. During the 3-year period, detachment of the corresponding matrices from the overdenture base occurred in eight MDIs; clinical prosthetic procedures were required to rectify these problems. Five of these matrices corresponded to mesial MDIs and three to distal MDIs.
Patient Perceptions and Satisfaction
With respect to patients’ perceptions of MDI overdenture treatment during the 3-year follow-up period, they were generally satisfied with the esthetics, retention, and functionality (mastication, phonation). Patients’ complaints were related mainly to occasional pain that was described as appearing under the overdentures or related to soft tissue trauma (n = 5). Some patients perceived instability of the maxillary antagonist denture (n = 4 patients with mandibular MDI overdentures), which was related to difficulties during mastication. Treatment satisfaction was linked to the frequency of overdenture wearing. Twenty patients declared that they wore the overdenture continuously, whereas only three stated that they did not wear it while sleeping. However, the latter patients were not the patients advised to avoid wearing the overdenture during sleep (ie, those with bruxism or xerostomia). The specific recommendation regarding nighttime wearing of the overdentures was generally not followed, with the patients admitting that they followed this advice only for a short time.
Table 3 Complications of MDIs Placed Total (n = 102)
Maxillary (n = 28)
Mandibular (n = 74)
Marginal bone loss 1–2 threads 2–3 threads > 3 threads Total
29 11 5 45
6 4 1 11
23 7 4 34
Apical radiolucency
22
6
16
2
2
0
36 12 48
13 0 13
23 12 35
Complication
Mobility Bleeding During brushing Spontaneous Total
Table 4 Relationships between Patientand Implant-Related Factors and Peri-implant Marginal Bone Loss Peri-implant marginal bone loss Characteristic
< 1 implant > 1 implant thread thread Significance
Patient sex Female Male
23 MDIs 34 MDIs
33 MDIs 12 MDIs
Mean patient age (y)
62.04
60.27
NS†
Mean bone height (mm)
17.23
18.44
NS†
Mean ridge width (mm)
6.23
5.64
28 MDIs 20 MDIs 9 MDIs
9 MDIs 28 MDIs 8 MDIs
Implant length 10 mm 13 mm
11 MDIs 46 MDIs
15 MDIs 30 MDIs
Implant diameter 1.8 mm 2.10 mm 2.40 mm
0 MDIs 26 MDIs 31 MDIs
3 MDIs 14 MDIs 28 MDIs
32.11
27.67
Implant location Mesial (intercalated) Distal
26 MDIs 31 MDIs
33 MDIs 12 MDIs
Apical radiolucency Absent Present
52 MDIs 5 MDIs
28 MDIs 17 MDIs
33 MDIs 22 MDIs
21 MDIs 14 MDIs
2 MDIs
10 MDIs
Bone D2 D3 D4
P = .001*
density 7
Mean implant torque (Ncm)
Peri-implant bleeding Absent Present during brushing Present spontaneously
P = .013† P = .007*
NS*
–
P = .003† P = .005*
P < .001*
P = .014*
*Chi-square
test; †Mann-Whitney test. NS = not statistically significant; – = assumptions not met to apply the corresponding statistical test.
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Regarding the ease of use of MDI overdentures, most patients perceived overdenture insertion as quite easy. Only six patients reported difficulties with this procedure. Regarding overdenture removal, most patients (n = 16) said they perceived it as problematic. Thus, in general, overdenture removal was perceived as being more difficult than overdenture insertion. All patients declared that they perceived cleaning of the overdenture as easy. All of them stated that they cleaned the prosthetic device daily, and some patients (n = 6) reported cleaning their overdenture twice a day.
DISCUSSION Nowadays the MDI overdenture is more frequently seen as an optimal treatment option for completely edentulous patients, as it is extremely well suited to this population of often elderly persons. These persons may have multiple general diseases that limit the ability to undergo complex surgical interventions, they may be less willing to undergo extensive medical procedures, and they may have limited financial resources. A major advantage of the MDI overdenture is related to the possibility of immediate loading of the MDIs, which gives maximum satisfaction to the patient because function is rapidly regained (ability to chew, speak, and interact socially). Regarding the MDIs that are used to stabilize the dentures, this study presented a survival rate of 92.7% within a 3-year follow-up period. The published evidence comprises data similar to this, generally presenting MDI survival rates above 90%.5 Elsyad et al indicated a survival rate of 96% for MDIs placed in the mandible after a 3-year follow-up period,10 and Griffitts et al obtained a survival rate of 97.4% for MDIs placed in the mandible after 13 months.11 In the current study, MDIs placed in the maxilla presented a lower survival rate than those placed in the mandible. These results are concordant with other studies reported in the scientific literature, such as that conducted by Shatkin et al, who achieved survival rates of 95.1% for mandibular MDIs and 83.2% for maxillary MDIs within a 2.9-year follow-up period.12 They also reported that the MDI survival rate depended on implant location: posterior maxillary MDIs had a greater chance of being lost than those placed in the anterior maxilla (posterior 88.9%, anterior 93.3%), whereas similar survival rates were seen for anterior and posterior MDIs placed in the mandible (posterior 96.5%, anterior 96%). This differing behavior of MDIs placed in the maxilla and mandible is likely a consequence of differences in bone features (eg, bone density). This behavior of MDIs may be similar to that observed with conventional dental implants, which also have a higher failure rate in the maxilla.13
In the current study, MDI failures occurred only in the maxilla in two female patients. One of these lost all five MDIs placed. She had reduced bone density (D3 and D4 Misch classification) and hypodivergent facial pattern and had become edentulous only recently (the remaining teeth were the maxillary right canine and premolars). After overdenture placement, the patient complained about phonation deficiencies and perceived some muscular tension and discomfort. Adjustments were made to the overdentures and a gradual improvement was noticed that led to a satisfying outcome after 3 weeks. Positive results were experienced for approximately 1 year. Three months after the 1-year appointment, the patient came to the dentist citing some discomfort related to overdenture wearing; denture stomatitis was noted at that time. Treatment was recommended for this condition, but the patient did not attend follow-up medical appointments. Five months later, she came to the office claiming that all her MDIs had been progressively lost. Radiographic exams showed that two of the MDIs had fractured. The patient stated that she desired only some overdenture adjustments because she was suspected to have other medical problems (osteoporosis and hepatic neoplasm). During this visit, the denture was relined, and an appointment was made to remove the remaining fractured implants, but the patient missed this appointment. The other patient lost three of her five MDIs. She was a highly stressed person with an unbalanced, mainly vegan, diet that included many hard foods. In her case, MDI failure was probably related to a slightly increased vertical dimension of occlusion, which had been chosen because of the decreased available vertical prosthetic space. When the problems began to be noticed, adjustments were made; nevertheless, three implants were lost. After this, two new MDIs were placed, and a positive status of the two surviving MDIs at the 3-year follow-up was noted. During this study, two MDIs failed because of fractures, both in the apical part of the implant. The authors note that this behavior is similar to that of teeth and different from that of conventional implants. Conventional dental implants typically present problems at the connection between the abutment and endosseous implant, most often loosening of the abutment screw or fracture of the implant in this location. Shatkin et al also identified MDI fracture as a complication of MDI overdentures, but they reported that it occurred infrequently (0.8%) during MDI placement.12 Regarding implant fractures, some aspects need to be clarified. Endosseous dental implants seem to fracture less frequently when supporting overdentures, compared to fixed prosthetic devices, as supported by some clinical evidence.14 In contrast, however, according
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to Sánchez-Pérez et al15 and Allum et al,16 narrow implants (defined, respectively, as narrower than 4 mm and 3 mm) have an increased risk of fracture. Taking these aspects together, studies should be implemented to identify the frequency and types of implant fractures associated with MDI overdentures. Peri-implant marginal bone loss and matrix detachment were more frequent for the implants located toward the midline (intercalated), probably indicating that mesially placed implants may be subjected to higher loads than distal implants. The higher strain on mesial MDIs may be explained by their increased role in indirect retention in counteracting tipping forces and overdenture dislodgment during mastication. Also, the presence of MDIs may induce movements of the occlusal and masticatory field anteriorly, which could explain, in the case of mandibular MDI overdentures, the relatively quick appearance of instability of the antagonistic maxillary complete denture. The results of this study indicate that marginal bone loss around MDIs is not influenced by the implant diameter, a finding supported by other studies.17 When a patient’s general health status may prevent complex surgical interventions, small-diameter implants may be considered as the best options for mandibular edentulous patients, who often present a decreased ridge width. However, the authors emphasize that the current results indicate that a decreased ridge width appears to have a tendency to a more pronounced peri-implant marginal bone loss. Also, according to the current results, although self-reported spontaneous peri-implant bleeding was noted rarely, when present it may indicate more severe MDI marginal bone loss. Several overdenture deficiencies were noted during the 3-year follow-up period. Overdenture fractures were found with a moderate frequency (seven overdentures fractured) and can be explained by the increased security in chewing brought about by the overdenture’s increased balance and retention, which favored an increase in muscular activity. The most common location for overdenture base fractures was in the housing area; this is probably related to the relatively thin overdenture base in that region. Overdenture relining is a complication that has been identified in several studies concerning the topic of MDI or conventional implant overdentures and conventional dentures.18,19 Patients were generally satisfied with their MDI overdentures. This might be related to the sample characteristics and study inclusion criteria, ie, volunteers who were dissatisfied with their complete dentures or who expressed fear and reticence regarding conventional dentures, with limited financial means,
who were offered access to this treatment option at a lower cost. Even so, their positive perceptions about this treatment alternative remained constant over time, probably related to the increased retention and comfort associated with the prosthetic device. The main limitation of this study is its relative small sample, but it provides data to help dentists to understand the behavior of MDI overdentures and offers hypotheses that might be tested in larger, randomized controlled clinical trials.
CONCLUSIONS Based on this research and taking its limitations into consideration, the following conclusions regarding mini–dental implant (MDI) overdenture treatment can be drawn. • Survival rates and health status were better for MDIs placed in the mandible than for those placed in the maxilla, indicating that the MDI overdenture may be a more suitable treatment option for mandibular complete edentulism. • Overdenture fracture is a relatively frequent complication that occurred most often in the mandible in sites corresponding to implant housing areas. Consequently, it may be recommended that dentists ensure proper thickness of the overdenture base or reinforce it to prevent this. • In completely edentulous patients, applying an MDI overdenture in the mandible may have a negative impact on the stability of a conventional maxillary denture, and it may be necessary to manage this side effect (eg, to apply a maxillary MDI overdenture) to ensure patient satisfaction. The MDI overdenture, like any other medical treatment, has potential complications. In general, these can be addressed through interventions that have acceptable moderate biologic, financial, and clinical costs (eg, prosthetic interventions such as adjustment or relining of the overdenture’s acrylic base, repairing the fractured overdenture, replacement or change of the matrices of the ball attachments, or insertion of a new MDI in case of MDI failure).
ACKNOWLEDGMENTS The authors thank IMTEC, currently part of 3M ESPE, for their support of this research by providing some of the materials and mini–dental implants. The authors reported no conflicts of interest related to this study.
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11. Griffitts TM, Collins CP, Collins PC. Mini dental implants: An adjunct for retention, stability, and comfort for the edentulous patient. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;100:e81–84. 12. Shatkin TE, Shatkin S, Oppenheimer BD, Oppenheimer AJ. Mini dental implants for long-term fixed and removable prosthetics: A retrospective analysis of 2514 implants placed over a five-year period. Compend Contin Educ Dent 2007;28:92–99. 13. Pikner SS, Gröndahl K, Jemt T, Friberg B. Marginal bone loss at implants: A retrospective, long-term follow-up of turned Brånemark System implants. Clin Implant Dent Relat Res 2009;11:11–23. 14. Gargallo Albiol J, Satorres-Nieto M, Puyuelo Capablo JL, Sánchez Garcés MA, Pi Urgell J, Gay Escoda C. Endosseous dental implant fractures: An analysis of 21 cases. Med Oral Patol Oral Cir Bucal 2008;13:e124–128. 15. Sánchez-Pérez A, Moya-Villaescusa MJ, Jornet-Garcia A, Gomez S. Etiology, risk factors and management of implant fractures. Med Oral Patol Oral Cir Bucal 2010;15:e504–508. 16. Allum SR, Tomlinson RA, Joshi R. The impact of loads on standard diameter, small diameter and mini implants: A comparative laboratory study. Clin Oral Implants Res 2008;19:553–559. 17. Pommer B, Frantal S, Willer J, Posch M, Watzek G, Tepper G. Impact of dental implant length on early failure rates: A meta-analysis of observational studies. J Clin Periodontol 2011;38:856–863. 18. Bortolini S, Natali A, Franchi M, Coggiola A, Consolo U. Implantretained removable partial dentures: An 8-year retrospective study. J Prosthodont 2011;20:168–172. 19. MacEntee MI, Walton JN, Glick N. 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 2005;93:28–37.
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T
he mini–dental implant (MDI) overdenture is a relatively recent treatment option for complete edentulism and is indicated especially for patients who are dissatisfied with their conventional dentures. The MDIs provide only overdenture retention, not support, as there is an occlusal space between the implant abutment attachment and the overdenture. MDI overdentures have several benefits compared to other treatment alternatives. In contrast to the conventional complete denture, this type of overdenture requires an
1Professor,
Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania. 2Lecturer, Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania. 3 PhD Student and Assistant Professor, Department of Scientific Research Methodology, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania. Correspondence to: Elena Preoteasa, Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Str. Ionel Perlea nr. 12, sector 1, 010208 Bucharest, Romania. Email: [email protected]
additionally relatively simple, minimally invasive surgical intervention, but the attachment system and immediate loading of the MDIs ensure increased retention, stability, and function, with improvements in patient satisfaction, comfort, and quality of life.1–3 Standarddiameter implant-supported prosthetic alternatives have shown success, but these are not viable solutions for all edentulous patients. The MDI overdenture may be a more appropriate treatment alternative for the edentulous patient with compromised health and/or a restricted buccolingual dimension of bone. In these cases, MDI placement requires fewer and less invasive surgical interventions (eg, avoidance of bone grafting procedures and decreased clinical time required for implant placement, especially when a minimally invasive flapless technique is used), promoting a lower risk of developing complications and shortening the healing period.4,5 Given the demographic changes in the population, especially the aging trend, there is an increasing need for relevant treatment for the medical problems of older patients, complete edentulism being one of them. The MDI overdenture is one viable treatment alternative for this condition, which seems appropriate to this segment of the population, but scientific evidence regarding clinical outcomes of the MDI overdenture is relatively limited.6 Therefore, more
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information is needed to assess the viability and safety of this treatment concept. The purpose of this study was to evaluate the MDI overdenture as a treatment option for complete edentulism. Treatment outcomes were considered in three dimensions: MDI status, overdenture status, and patient perception and satisfaction. Data were collected after a 3-year follow-up period.
MATERIALS AND METHODS An observational clinical study was conducted and implemented. Patients with complete edentulism who requested treatment at the Department of Prosthodontics, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy, Bucharest, between April and November 2008 were enrolled in the study. A convenience sample was formed according to the following eligibility criteria. Completely edentulous patients with conventional complete dentures who were dissatisfied with this treatment alternative, or who were untreated but expressed fear and reticence toward conventional dentures, were included. Excluded were those with severe systemic conditions (eg, uncontrolled hypertension, diabetes mellitus) or receiving particular medications (eg, bisphosphonates) because of the risk associated with the surgical procedure of MDI placement and the potential for these conditions and medications to contribute to a poor prognosis. The patients were given information regarding the MDI overdenture, and all chose this treatment alternative and participation in the study on a voluntary basis. From each patient, written informed consent was obtained. Because the role of the MDIs is to improve retention of a prosthetic device, the overdenture design aimed to ensure proper support, retention, and stability. In this respect, complete coverage of the support area, including the anatomical and functional borders, with a complete peripheral seal was chosen. For maxillary dentures, complete palatal coverage with a postpalatal seal was used. Registration of the maxillomandibular relationship aimed to ensure a correct functional vertical dimension of occlusion in centric relation. Premature contacts were checked and eliminated to accomplish the coincidence of centric relation and centric occlusion and obtain bilateral simultaneous stable occlusal contacts in centric occlusion. Principles of lingualized denture occlusion were used; ie, the maxillary lingual cusps articulated with the central fossae of the mandibular occlusal surfaces in centric working and nonworking mandibular positions. Some of the patients presented with previously made complete dentures; their quality was analyzed
and the clinician decided either to keep or replace them. Aspects related to coverage of the support area, denture retention and stability, correct registration of maxillomandibular relationships, type of denture occlusion, the correctness of the arrangement of artificial teeth, material status, and patient perception regarding the denture were evaluated and considered as factors in this decision. The MDIs used were supplied by IMTEC/3M ESPE. These were available in four lengths (10 mm, 13 mm, 15 mm, and 18 mm) and three diameters (1.8 mm, 2.1 mm, and 2.4 mm) and used collared balls as attachments. The number of MDIs placed and their locations and dimensions were chosen based on the individual features of the patient and the judgment of the dentist but considered as closely as possible the manufacturer’s recommendations for this type of implant regarding the minimum number of MDIs that should be placed (four MDIs in the mandible and six MDIs in the maxilla). The MDI overdenture was chosen as a treatment option for mandibular or maxillary complete edentulism. This treatment alternative was indicated for maxillary edentulism when teeth or fixed prosthetic restorations were present in the anterior mandible or when patients had a skeletal Class III relationship with a reverse relation of the edentulous arches. To ensure a good prognosis, several instructions were given to the patients. Amoxicillin with clavulanic acid (Augmentin, SmithKline Beecham) were administered to patients for 5 days, starting 2 hours prior to implant placement. After the surgical intervention, patients were informed that they would probably feel some discomfort and pain that would disappear in a few days; analgesic drugs were recommended if necessary. Also, they were advised to eat soft foods of moderate temperature. The importance of adequate hygiene procedures was highlighted. Patients were taught how to adequately clean the MDIs and the overdenture. Additionally, they were advised to use chlorhexidine products to prevent bacterial and fungal infections. Chlorhexidine digluconate 0.2% solution was recommended (twice daily oral rinses) before surgical implant placement and afterward. For overdenture cleaning, in addition to traditional mechanical cleaning, chemical cleaners (tablets) were recommended. Also, patients with bruxism or xerostomia were advised not to wear the overdenture overnight at least two times per week. The main outcome of this study was the success of the MDI overdenture as a treatment option for the completely edentulous patient. The analysis covered MDI status, overdenture status, and patients’ perceptions regarding this treatment alternative. The study variables, which addressed patient features and treatment specifics, are listed in Table 1.7 Additionally, a The International Journal of Oral & Maxillofacial Implants 1171
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Table 1 Study Variables
Table 2 Health Status of MDIs Placed Location
Patient’s general attributes (age, sex) Data regarding oral and treatment-related features: • Bone information: bone height,* ridge width,† bone density according to Misch classification7* • Treatment variables: Number and locations of MDIs, length and diameter of MDIs, implant insertion torque
MDI health status
MDI status: • Implant health, assessed using the previously described scale • Peri-implant marginal bone loss‡: registered as the maximum number of threads devoid of bone on the mesial and distal implant sides • Implant mobility§ • Self-reported peri-implant bleeding: spontaneous or during brushing • Radiolucency at the apical part of the implant‡
Success
Overdenture status: • Presence of any technical complication that required repair or maintenance: matrix detachment, overdenture fracture or relining Patient perceptions regarding MDI overdenture: • Self-reported reasons for satisfaction/dissatisfaction with this treatment • Frequency of overdenture wearing • Ease of use of MDI overdenture: overdenture placement (insertion), removal, and cleaning *Assessed
with computed tomography; †assessed with a clinical bone compass; ‡assessed with panoramic radiography; §assessed by clinical evaluation.
health scale for the MDI, derived from that proposed by the International Congress of Oral Implantology in Pisa, Italy, at the 2007 Consensus Conference8 and taking into consideration the Albrektsson et al criteria for implant success,9 was used as follows: • Failure: MDIs that were lost or removed for any reason, MDIs that fractured or presented with mobility, marginal bone loss exceeding half of the implant body length, or pain during function • Compromised survival: MDIs still present in the mouth, without an indication to be removed, but with either minimal clinical mobility, severe marginal bone loss (less than half of the implant body length), or sensitivity during function • Satisfactory survival: MDIs displaying no clinical mobility or sensitivity during function, with moderate bone loss (more than two threads, but less than half of the implant body length) • Success: MDIs without clinical mobility or sensitivity during function and marginal bone loss of less than two threads Data collection was conducted before and during surgical placement of the MDIs and after surgery; follow-up appointments were attended weekly during
Maxilla
Mandible
Failed
8
0
Compromised survival
2
0
Satisfactory survival
3
11
23
63
the first month postsurgery, at 3 and 6 months, and at 1, 2, and 3 years postsurgery. Clinical and radiographic (panoramic radiography, computed tomography) methods, together with data obtained through discussions with the patient during recall visits, were used for evaluations. Panoramic radiographs were indicated at 6 months, 1 year, 2 years, and 3 years. Statistical analysis was performed with the Statistical Package for the Social Sciences (version 13.0, SPSS Inc). In addition to descriptive statistics, the chi-square and Mann-Whitney tests were used for comparison between groups.
RESULTS Sample Characteristics
Of the 24 completely edentulous patients initially enrolled, 1 was lost during follow-up. Of the remaining 23 patients, 10 were men and 13 were women; the mean age was 62 years (range, 52 to 76 years). The subjects were treated with 7 maxillary and 16 mandibular MDI overdentures. A total of 110 MDIs were placed (36 in the maxilla and 74 in the mandible). Five or six MDIs were placed in the maxilla and four to six MDIs were placed in the mandible.
MDI Status
Of the 110 MDIs placed, 8 failed, for a survival rate of 92.7%. All MDIs that failed had been placed in the maxilla. Also, all eight failed MDIs had been placed in two female patients and failed within 1 to 2 years after their insertion. In one patient, all five MDIs that had been placed failed, two as a result of MDI fracture. In the other patient, three of five MDIs placed were lost as a result of progressive marginal bone loss. The health status of the MDIs, according to the scale presented, can be summarized as follows: in addition to the 8 failed MDIs, 2 had compromised survival, 14 showed satisfactory survival, and 86 were considered successful. Differences in the health status of maxillary and mandibular MDIs are summarized in Table 2. The other complications that occurred within the 102 MDIs still present at the 3-year follow-up
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Preoteasa et al
examination are listed in Table 3. Almost half of the MDIs registered marginal bone loss > 1 thread and peri-implant bleeding, which appeared most frequently during brushing. Some of the complications had a different distribution depending on location (eg, spontaneous peri-implant bleeding was reported only for MDIs placed in the mandible). Marginal bone loss was more severe in women, in patients with a decreased ridge width, in sites with decreased bone density, around implants with lower insertion torque values, and in MDIs placed toward the midline (mesial/intercalated). MDIs with marginal bone loss of more than one implant thread more frequently presented with radiolucent lesions at the apical part of the implant and were more frequently associated with spontaneous peri-implant bleeding (Table 4).
Overdenture Status
During the 3-year follow-up period, overdenture fractures occurred in seven patients. In the mandible, overdenture fracture sites corresponded more frequently to the implant housing area (n = 4), but fractures also occurred in regions between implants (n = 2). In the maxilla, only one overdenture fractured in the area between implants. Overdenture relining was done in five cases. Two of these were the patients with implant failures. During the 3-year period, detachment of the corresponding matrices from the overdenture base occurred in eight MDIs; clinical prosthetic procedures were required to rectify these problems. Five of these matrices corresponded to mesial MDIs and three to distal MDIs.
Patient Perceptions and Satisfaction
With respect to patients’ perceptions of MDI overdenture treatment during the 3-year follow-up period, they were generally satisfied with the esthetics, retention, and functionality (mastication, phonation). Patients’ complaints were related mainly to occasional pain that was described as appearing under the overdentures or related to soft tissue trauma (n = 5). Some patients perceived instability of the maxillary antagonist denture (n = 4 patients with mandibular MDI overdentures), which was related to difficulties during mastication. Treatment satisfaction was linked to the frequency of overdenture wearing. Twenty patients declared that they wore the overdenture continuously, whereas only three stated that they did not wear it while sleeping. However, the latter patients were not the patients advised to avoid wearing the overdenture during sleep (ie, those with bruxism or xerostomia). The specific recommendation regarding nighttime wearing of the overdentures was generally not followed, with the patients admitting that they followed this advice only for a short time.
Table 3 Complications of MDIs Placed Total (n = 102)
Maxillary (n = 28)
Mandibular (n = 74)
Marginal bone loss 1–2 threads 2–3 threads > 3 threads Total
29 11 5 45
6 4 1 11
23 7 4 34
Apical radiolucency
22
6
16
2
2
0
36 12 48
13 0 13
23 12 35
Complication
Mobility Bleeding During brushing Spontaneous Total
Table 4 Relationships between Patientand Implant-Related Factors and Peri-implant Marginal Bone Loss Peri-implant marginal bone loss Characteristic
< 1 implant > 1 implant thread thread Significance
Patient sex Female Male
23 MDIs 34 MDIs
33 MDIs 12 MDIs
Mean patient age (y)
62.04
60.27
NS†
Mean bone height (mm)
17.23
18.44
NS†
Mean ridge width (mm)
6.23
5.64
28 MDIs 20 MDIs 9 MDIs
9 MDIs 28 MDIs 8 MDIs
Implant length 10 mm 13 mm
11 MDIs 46 MDIs
15 MDIs 30 MDIs
Implant diameter 1.8 mm 2.10 mm 2.40 mm
0 MDIs 26 MDIs 31 MDIs
3 MDIs 14 MDIs 28 MDIs
32.11
27.67
Implant location Mesial (intercalated) Distal
26 MDIs 31 MDIs
33 MDIs 12 MDIs
Apical radiolucency Absent Present
52 MDIs 5 MDIs
28 MDIs 17 MDIs
33 MDIs 22 MDIs
21 MDIs 14 MDIs
2 MDIs
10 MDIs
Bone D2 D3 D4
P = .001*
density 7
Mean implant torque (Ncm)
Peri-implant bleeding Absent Present during brushing Present spontaneously
P = .013† P = .007*
NS*
–
P = .003† P = .005*
P < .001*
P = .014*
*Chi-square
test; †Mann-Whitney test. NS = not statistically significant; – = assumptions not met to apply the corresponding statistical test.
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Regarding the ease of use of MDI overdentures, most patients perceived overdenture insertion as quite easy. Only six patients reported difficulties with this procedure. Regarding overdenture removal, most patients (n = 16) said they perceived it as problematic. Thus, in general, overdenture removal was perceived as being more difficult than overdenture insertion. All patients declared that they perceived cleaning of the overdenture as easy. All of them stated that they cleaned the prosthetic device daily, and some patients (n = 6) reported cleaning their overdenture twice a day.
DISCUSSION Nowadays the MDI overdenture is more frequently seen as an optimal treatment option for completely edentulous patients, as it is extremely well suited to this population of often elderly persons. These persons may have multiple general diseases that limit the ability to undergo complex surgical interventions, they may be less willing to undergo extensive medical procedures, and they may have limited financial resources. A major advantage of the MDI overdenture is related to the possibility of immediate loading of the MDIs, which gives maximum satisfaction to the patient because function is rapidly regained (ability to chew, speak, and interact socially). Regarding the MDIs that are used to stabilize the dentures, this study presented a survival rate of 92.7% within a 3-year follow-up period. The published evidence comprises data similar to this, generally presenting MDI survival rates above 90%.5 Elsyad et al indicated a survival rate of 96% for MDIs placed in the mandible after a 3-year follow-up period,10 and Griffitts et al obtained a survival rate of 97.4% for MDIs placed in the mandible after 13 months.11 In the current study, MDIs placed in the maxilla presented a lower survival rate than those placed in the mandible. These results are concordant with other studies reported in the scientific literature, such as that conducted by Shatkin et al, who achieved survival rates of 95.1% for mandibular MDIs and 83.2% for maxillary MDIs within a 2.9-year follow-up period.12 They also reported that the MDI survival rate depended on implant location: posterior maxillary MDIs had a greater chance of being lost than those placed in the anterior maxilla (posterior 88.9%, anterior 93.3%), whereas similar survival rates were seen for anterior and posterior MDIs placed in the mandible (posterior 96.5%, anterior 96%). This differing behavior of MDIs placed in the maxilla and mandible is likely a consequence of differences in bone features (eg, bone density). This behavior of MDIs may be similar to that observed with conventional dental implants, which also have a higher failure rate in the maxilla.13
In the current study, MDI failures occurred only in the maxilla in two female patients. One of these lost all five MDIs placed. She had reduced bone density (D3 and D4 Misch classification) and hypodivergent facial pattern and had become edentulous only recently (the remaining teeth were the maxillary right canine and premolars). After overdenture placement, the patient complained about phonation deficiencies and perceived some muscular tension and discomfort. Adjustments were made to the overdentures and a gradual improvement was noticed that led to a satisfying outcome after 3 weeks. Positive results were experienced for approximately 1 year. Three months after the 1-year appointment, the patient came to the dentist citing some discomfort related to overdenture wearing; denture stomatitis was noted at that time. Treatment was recommended for this condition, but the patient did not attend follow-up medical appointments. Five months later, she came to the office claiming that all her MDIs had been progressively lost. Radiographic exams showed that two of the MDIs had fractured. The patient stated that she desired only some overdenture adjustments because she was suspected to have other medical problems (osteoporosis and hepatic neoplasm). During this visit, the denture was relined, and an appointment was made to remove the remaining fractured implants, but the patient missed this appointment. The other patient lost three of her five MDIs. She was a highly stressed person with an unbalanced, mainly vegan, diet that included many hard foods. In her case, MDI failure was probably related to a slightly increased vertical dimension of occlusion, which had been chosen because of the decreased available vertical prosthetic space. When the problems began to be noticed, adjustments were made; nevertheless, three implants were lost. After this, two new MDIs were placed, and a positive status of the two surviving MDIs at the 3-year follow-up was noted. During this study, two MDIs failed because of fractures, both in the apical part of the implant. The authors note that this behavior is similar to that of teeth and different from that of conventional implants. Conventional dental implants typically present problems at the connection between the abutment and endosseous implant, most often loosening of the abutment screw or fracture of the implant in this location. Shatkin et al also identified MDI fracture as a complication of MDI overdentures, but they reported that it occurred infrequently (0.8%) during MDI placement.12 Regarding implant fractures, some aspects need to be clarified. Endosseous dental implants seem to fracture less frequently when supporting overdentures, compared to fixed prosthetic devices, as supported by some clinical evidence.14 In contrast, however, according
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to Sánchez-Pérez et al15 and Allum et al,16 narrow implants (defined, respectively, as narrower than 4 mm and 3 mm) have an increased risk of fracture. Taking these aspects together, studies should be implemented to identify the frequency and types of implant fractures associated with MDI overdentures. Peri-implant marginal bone loss and matrix detachment were more frequent for the implants located toward the midline (intercalated), probably indicating that mesially placed implants may be subjected to higher loads than distal implants. The higher strain on mesial MDIs may be explained by their increased role in indirect retention in counteracting tipping forces and overdenture dislodgment during mastication. Also, the presence of MDIs may induce movements of the occlusal and masticatory field anteriorly, which could explain, in the case of mandibular MDI overdentures, the relatively quick appearance of instability of the antagonistic maxillary complete denture. The results of this study indicate that marginal bone loss around MDIs is not influenced by the implant diameter, a finding supported by other studies.17 When a patient’s general health status may prevent complex surgical interventions, small-diameter implants may be considered as the best options for mandibular edentulous patients, who often present a decreased ridge width. However, the authors emphasize that the current results indicate that a decreased ridge width appears to have a tendency to a more pronounced peri-implant marginal bone loss. Also, according to the current results, although self-reported spontaneous peri-implant bleeding was noted rarely, when present it may indicate more severe MDI marginal bone loss. Several overdenture deficiencies were noted during the 3-year follow-up period. Overdenture fractures were found with a moderate frequency (seven overdentures fractured) and can be explained by the increased security in chewing brought about by the overdenture’s increased balance and retention, which favored an increase in muscular activity. The most common location for overdenture base fractures was in the housing area; this is probably related to the relatively thin overdenture base in that region. Overdenture relining is a complication that has been identified in several studies concerning the topic of MDI or conventional implant overdentures and conventional dentures.18,19 Patients were generally satisfied with their MDI overdentures. This might be related to the sample characteristics and study inclusion criteria, ie, volunteers who were dissatisfied with their complete dentures or who expressed fear and reticence regarding conventional dentures, with limited financial means,
who were offered access to this treatment option at a lower cost. Even so, their positive perceptions about this treatment alternative remained constant over time, probably related to the increased retention and comfort associated with the prosthetic device. The main limitation of this study is its relative small sample, but it provides data to help dentists to understand the behavior of MDI overdentures and offers hypotheses that might be tested in larger, randomized controlled clinical trials.
CONCLUSIONS Based on this research and taking its limitations into consideration, the following conclusions regarding mini–dental implant (MDI) overdenture treatment can be drawn. • Survival rates and health status were better for MDIs placed in the mandible than for those placed in the maxilla, indicating that the MDI overdenture may be a more suitable treatment option for mandibular complete edentulism. • Overdenture fracture is a relatively frequent complication that occurred most often in the mandible in sites corresponding to implant housing areas. Consequently, it may be recommended that dentists ensure proper thickness of the overdenture base or reinforce it to prevent this. • In completely edentulous patients, applying an MDI overdenture in the mandible may have a negative impact on the stability of a conventional maxillary denture, and it may be necessary to manage this side effect (eg, to apply a maxillary MDI overdenture) to ensure patient satisfaction. The MDI overdenture, like any other medical treatment, has potential complications. In general, these can be addressed through interventions that have acceptable moderate biologic, financial, and clinical costs (eg, prosthetic interventions such as adjustment or relining of the overdenture’s acrylic base, repairing the fractured overdenture, replacement or change of the matrices of the ball attachments, or insertion of a new MDI in case of MDI failure).
ACKNOWLEDGMENTS The authors thank IMTEC, currently part of 3M ESPE, for their support of this research by providing some of the materials and mini–dental implants. The authors reported no conflicts of interest related to this study.
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