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Treatment outcomes with implant-supported overdentures: Clinical considerations
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Treatment outcomes with implant-supported overdentures: Clinical considerations Regina Mericske-Stern, DDS, PhDa School of Dental Medicine, University of Bern, Switzerland Three indications for implant-supported overdentures are defined, namely, the edentulous maxilla, the edentulous mandible, and the compromised situation. These indications for overdentures are related to three patient groups: (1) a younger segment of patients among the older population with maxillary complete dentures, (2) elderly completely edentulous patients who request better stabilization of the mandibular denture, and (3) patients with acquired or congenital defects. The aim of this article is to discuss treatment strategies and clinical considerations with respect to three specific indications for overdentures. (J Prosthet Dent 1998;79:66-73.)
A
daptation to wearing complete dentures is a complex process and must be considered from both somatic and psychologic standpoints. Incorporating a foreign body in the oral cavity may be a difficult task. Documentation on success and failure with complete dentures is sparse and not reliable, because the correlation between a favorable shape of the residual ridge, the technical accuracy of the dentures, and the ease of adaptation to wearing dentures is low.1,2 Motor skills tend to decrease with increasing age. The difficulties of wearing dentures has been attributed to deficiencies of the denture-bearing tissues, reduced salivary flow, vulnerable tissue, and severe ridge resorption. Patients may also have an aversion against a foreign body in the oral cavity. For many patients, the wearing of complete dentures also means to be old and socially handicapped. Problems with adaptation to complete dentures are observed with a higher incidence for mandibular dentures than for maxillary dentures. Historically, surgeons focused on improving the structure of the residual mandibular ridge by various preprosthetic surgical techniques and less frequently the maxillary ridge. These techniques appear to be more invasive than the surgery for osseointegrated implants, and there is no scientific evidence of its success and usefulness. The use of implants to substitute for missing teeth was systematically developed by Brånemark et al.3,4 Since the 1980s, several studies have demonstrated the reliability of this treatment modality.5-7 The clinical concept of this treatment consisted of inserting five to six implants into the edentulous mandible to provide support and retention for a fixed prostheses, which was retrievable by the dentist only. While the Brånemark groups focused on fixed prostheses, Schroeder et al8-10 developed the ITI implant system to deal with the problems of unilateral distal extension situations. He suggested that overdentures supported by four implants should be used in situations of Presented at the annual meeting of the Academy of Prosthodontics, Halifax, Nova Scotia, Canada, May 1997. a Associate Professor, Department of Removable Prosthodontics. 66
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complete edentulousness. However, reliable studies to support this method were not available. In the last few years, interest in overdenture therapy for the edentulous jaw has rapidly increased as is evidenced by the number of studies published since 1990.11-20 This may be due to the fact that a greater segment of the population is elderly and complete edentulousness is postponed to an older age. Social change, evolution in dentistry, and changes in prosthetic techniques have lead to patients demanding more in terms of esthetics, function, and oral comfort, which is also true for complete edentulousness.21,22 More patients have access to therapy with implants and the contraindications are few. Essentially, they are as follows: 1. The patient is comfortable with complete dentures and has no complaints. 2. The residual ridge is not adequate for the standard placement of implants. 3. The abuse of drugs. 4. General health conditions do not allow a minor surgical intervention. 5. Therapy with immunosuppressive, long-standing intake of corticosteroids. 6. Metabolic disease not under control. Three groups of patients are identified for whom overdentures would be indicated: (1) a younger segment of elderly patients with edentulous maxilla, who feel uncomfortable with a complete denture and are demanding of a stable prosthesis and high oral comfort; (2) elderly patients who require stabilization of the mandibular complete denture; and (3) patients with congenital or acquired oral and maxillofacial defects in need of oral rehabilitation. The purpose of this article is to discuss specific clinical aspects of these implant-supported overdenture situations.
MAXILLARY OVERDENTURES: THE DEMANDING PATIENT Treatment of the edentulous maxilla with implants is challenging and presents inherent problems that have VOLUME 79 NUMBER 1
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been presented in anecdotal clinical reports on maxillary fixed prostheses.23,24 Problems include divergent and buccally directed implant axes, long teeth, open interdental spaces, insufficient lip support, and incongruence of implant location and tooth position. Such adverse morphologic effects can be more easily eliminated by the use of maxillary implant-supported overdentures instead of fixed, screw-retained prostheses.22 Thus overdentures may become a favored and advantageous treatment option; however, it is likely that they are not a true alternative to fixed prostheses in terms of economics or time-saving procedures.25,26 In treatment planning the maxilla with implants, one usually has to consider the options of both fixed and removable prostheses. The current treatment strategy has been that overdentures were selected as a substitute for failing fixed prostheses.27 In fact, there are no reliable long-term results of patients treated with maxillary overdentures as planned cases; as a consequence, treatment principles for maxillary overdentures are not well-defined. The following statements are the basis of diagnostic and therapeutic criteria: 1. The minimal number of implants is preferably four. 2. Implants should be evenly distributed throughout the arch. 3. Patients who belong to a younger segment of the edentulous population frequently ask for fixed prostheses. 4. The opposing mandible is dentate or reconstructed with fixed prostheses. 5. A standard surgical protocol for implant placement cannot be followed because of deep sinus or thin narrow ridges. 6. Therapy with overdentures is more consistent with optimum placement of the implants with regard to bone quality and quantity. 7. Overdentures may better resolve esthetic and speech problems. 8. The labial flange of the overdenture provides lip support. 9. The overdenture may have a horseshoe design, and thus be more acceptable to the patient. Such therapeutic criteria imply that a more specific patient selection protocol is necessary for maxillary overdentures. Because the dental literature on maxillary implants shows a tendency for an increased failure rate20,26,28,29 when compared with mandibular implants, the placement of four or more implants with a minimum length of more than 6 mm and splinted with a bar is strongly suggested (Fig. 1, A). A rigid connection of the denture to the bar is recommended to reduce high bending moments as they were observed in comparison to fixed prostheses.30 A full diagnostic tooth arrangement or set-up on mounted casts is the crucial first step of the treatment planning to establish vertical dimension of occlusion, esthetic anterior tooth position, and JANUARY 1998
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Fig. 1, A, Maxillary jaw with four implants and connecting bar. Denture has horseshoe design. B, Orientation index of tooth set-up, positioned on maxillary cast for tissue volume analysis. C, Design and esthetics of maxillary overdenture are of high quality. Esthetics match implant-supported mandibular fixed prosthesis.
other morphologic aspects. The orientation index obtained from the diagnostic set-up is helpful for assessment of tissue volume dimensions (Fig. 1, B). If a properly designed and esthetically acceptable complete denture already exists, the denture could be used for diagnostic purposes. The final decision with regard to the best prosthetic design (fixed or removable) is made on the basis of such presurgical critical assessment. The combination of radiographic analysis and the diagnostic set-up is also used for fabricating a surgical template. 67
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Table I. Percentage distribution of main systemic diseases at time of implant placement Systemic health problems
Heart, Circulatory system, CVI Musculoskeletal system Allergies, Asthma Tumors (malignant) Neurologic disease Metabolic disease Eyes Others
Fig. 2. Two mandibular ITI-implants splinted with bar for overdenture connection. Overdenture has complete denture design.
Clinical experience has demonstrated that the soft tissue may be managed successfully in single tooth replacement.31,32 Recreating a well-contoured soft tissue border around implants over an entire dental arch to be a routine clinical outcome has not yet been documented. Further, in situations of advanced bone resorption, the problem of elongated teeth may not be able to be resolved. Therefore, for morphologic and esthetic reasons, the buccal flange of an overdenture can be useful and individual patients needs can be satisfied with this type of prosthesis (Fig. 1, C). Development of hyperplastic tissue beneath the denture base can also be a problem with implant-supported overdentures.25,33 Hyperplasia is more frequently found under maxillary overdentures than mandibular overdentures. Shrinkage of the tissue has been observed if a change is made to a fixed prosthesis design. In some situations, the denture base appears to facilitate phonation. It has also been reported that speech problems are more frequently encountered with fixed prostheses. The horseshoe design of the complete maxillary overdenture has been reported to be wellaccepted by the patients. Rigid bars, such as the U-shaped Dolder bar, have also been shown to provide good stability and optimum retention.
MANDIBULAR OVERDENTURES AND THE ELDERLY PATIENT In contrast to maxillary overdentures, treatment outcomes with mandibular overdentures appear to be more successful and are better documented, particularly for elderly patients.12,13,15-19,22,34 Completely edentulous elderly patients can benefit from implant-supported overdentures when they lose their teeth at an advanced age and are not capable of adapting to wearing complete mandibular dentures or when, after having had dentures for many years, they begin to lose their motor skills and are no longer able to wear complete dentures. Loss of teeth in advanced age can present a poor prog68
Percentage
46% 13% 11% 10% 8% 7% 3% 2%
nosis for learning new muscular patterns and can result in problems, for both the patient and dentist. In the 1980s, the standard protocol described by Schroeder6-8 was the placement of four implants. In 1985 this treatment strategy changed, based on the hypothesis that only two and sometimes three implants were adequate for overdenture support.35,36 Principles of treatment with mandibular implant-supported overdentures rely on the following clinical considerations12,35: (1) most elderly patients should be eligible for overdenture therapy, (2) two implants should be sufficient to support an overdenture prosthesis, (3) three implants can be placed if the minimum length of each implant is less than 8 mm, and (4) a standard surgical procedure should be applied in most situations. The implant-retained overdenture should reduce stress on patients and tissues, and it is a treatment modality that should be less time-consuming, less expensive, will minimize risks on patients and tissues, and becomes a true alternative to fixed prostheses (Fig. 2). Ten years ago age was considered to be an exclusion criterion for implantation. Today, there is evidence that elderly patients would benefit from implants and that the effectiveness of mandibular implant-supported overdentures is high. There is no evidence of adverse effects of aging that negatively affect treatment outcomes. These include compromised systemic health, advanced mandibular atrophy, reduced healing capacity of the bone particularly with osteoporotic bone, soft tissue problems, lack of attached keratinized mucosa due to advanced atrophy, lack of good hygiene and adequate maintenance, and biomechanic considerations if only two implants are used for denture support. With increasing age, systemic health problems are more frequently encountered, however, there is rarely evidence of a negative impact of health problems on implants.37,38 In a recent survey of 125 elderly patients with an average age of 69 years, 67% of the patients had systemic health problems at the time of implant surgery, and at least two medications were prescribed for each patient (Table I). During an observation period of 3 to 12 years, deterioration of general health was observed in 23% of all patients, but only 3% of patients exhibited VOLUME 79 NUMBER 1
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Fig. 3. Peri-implant parameters recorded during observation period of 5 years. Little and insignificant changes were observed. PLI, Plaque index; BI, bleeding index; PD, probing depths; LA, loss of attachment.
improvement in health conditions. The clinical parameters rarely changed over the entire observation period. Only a few implants failed and a correlation between failure and poor systemic health was not observed. Similar observations had been reported in a comparative study of two implant centers.10 After a long period of edentulousness, mandibular atrophy is often advanced. However, bone height itself may not be a predictor of bone quality and resorption of mandibular ridges is not necessarily an indicator for osteoporosis. A study of mandibular implants that used the Periotest (PT) instrument (Siemens, Bensheim, Germany) demonstrated that a shift to more negative PT values in the first year of implant loading,39 which may indicate an increase in bone implant contact. Histomorphometric analysis of bone specimens obtained from these patients revealed a strong correlation between dense cortical bone and advanced atrophy. Controversy exists about the effect of atrophy of the jaw bone by osteoporosis and the healing capacity of the bone.40,41 Although osteoporosis is diagnosed in one part of the body, usually in the dorsal spine, this does not necessarily mean that other parts of the skeleton are equally osteoporotic. It is not yet clear whether mandibular or maxillary bone is more susceptible to osteoporotic atrophy.42,43 Minor soft tissue problems, particularly hypertrophic tissue beneath the bar, may also be encountered. Improvement of hygiene or hygiene techniques may be helpful. Although plaque seems to accumulate more quickly underneath overdentures,11 results of a 5-year longitudinal study13 indicate that over time little change was found with regard to the peri-implant parameters (Fig. 3). When proper recall and maintenance are provided for implant patients, favorable results are seen. It has been observed that a high level of compliance is found among patients with implants, particularly among elderly patients.13 Because of the advanced mandibular atrophy, many implants are not located in attached keratinized mucosa. From this previous study,13 it was conJANUARY 1998
Fig. 4. Ranges of maximum and minimum chewing forces (in Newtons), recorded five retention devices, are given in all three dimensions; different scales of three diagrams. X-axis, lateral (+) and mesial () direction; y-axis, anterior (+) and posterior () directions; z-axis, vertical direction (+, down, -, up).
cluded that the absence of keratinized attached mucosa around the implant neck did not jeopardize the health of the implants, which appears to be supported by others.44 Cross-sectional and longitudinal results of microbiologic studies on edentulous patients with implantsupported overdenture further suggest that the oral microbiota does not exhibit unfavorable shifts in the composition of the oral bacteria.45 Little is known about forces that are directed onto implants during function under in vivo conditions. In vitro measurements cannot predict force transmission in vivo.46 Biomechanical considerations, such as loading and force distribution onto two implants, produces controversy regarding the best retention mechanism (rigid or stressbreaking) and the best retention device for overdenture connection (single anchors or bar splints).47-49 A study was designed to evaluate a measuring method in vitro and in vivo for three-dimensional force measurements on 69
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be selected according to the specific clinical and individual needs of the patient.
ORAL DEFECTS AND THE COMPROMISED PATIENT
Fig. 5. A, Maxillary jaw with cleft lip and palate in 45-year-old man after loss of remaining teeth. Wearing of complete denture is impossible without support of implants. B, Six implants were evenly distributed throughout arch. Because of slightly divergent implant axis, three separate bar segments were fabricated. C, Horseshoe denture design.
implants.50 The comparative measurements of various functional forces and maximum forces, with five attachment devices with a rigid or stress-breaking retention mechanism, demonstrated intraindividual and interindividual variations.51-53 However, the influence of the retention device and mechanism on force magnitudes and force directions in all three dimensions was much less evident than it was expected (Fig. 4). On the basis of these findings, it was suggested that the retention device 70
In situations of congenital or acquired intraoral defects, the anatomic-morphologic oral conditions may lead to the inability of wearing complete dentures. Acquired oral defects are caused by trauma and are also frequently the result of resection of malignant tumors, whereas congenital defects are mainly lip and palate clefts. Implant prosthodontic techniques have enabled the development of successful treatment strategies for structural, functional, and esthetic rehabilitation of these compromised patients. Again, in many situations therapy with overdentures is more favorable than with fixed prostheses and may be the only practicable way of managing these patients for various reasons (Fig. 5, A, B, and C). Because the life-span of patients with tumors is often highly reduced and for more than 50% is less than 5 years, efficient, practical implant prosthetic procedures are needed. The following criteria should determine the treatment option of overdentures for compromised situations: 1. Removable prostheses allow for inspection of the surgical site. 2. The implants must be placed where adequate bone is available. 3. The denture base replaces lost hard and soft tissues. 4. Esthetic demands may better be fulfilled with overdentures. 5. Lip and facial support can be provided by a labial denture flange. 6. Speech problems may be resolved. 7. Oral hygiene is facilitated. 8. Changes of the denture design are possible, if necessary. The previously described clinical aspects and specific indications of overdenture therapy for the maxillary and mandibular jaws are the same for compromised patients, although it may be more difficult to accomplish. Esthetics and function are favorable and promising with overdentures; however, bone and skin grafts, immediate implant placement during grafting procedures, poor alignment of the implants due to reduced bone quantity, irradiation, and reduced salivary flow are factors that may alter the predictability of implant prostheses for compromised patients. Thick skin grafts around implants probably do not form an adequate soft tissue attachment and will produce increased probing depths. Again, a strict maintenance protocol must be followed by these patients. Divergent and nonparallel implant axes are more frequently observed if implants are immediately placed with bone grafts and may pose problems for fabricating bar-splints. Although favorable results have been VOLUME 79 NUMBER 1
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reported for a few patients,54 the failure rate of implants appears to be increased if the implants are placed in irradiated bone.55 According to comparative results, therapy with hyperbaric oxygen enhances the survival rate of the implants.55,56 Furthermore, it seems that rigid bar-splints for overdenture support provide better stability than single attachments that are more prone to failure. Because an increased failure rate of implants is observed in irradiated patients, overdentures are the treatment modality of choice primarily because of the conversion of the prostheses to dentures if implants are lost.
DISCUSSION The recent literature on implantology exhibits an increasing number of articles on implant overdentures. The indications for overdentures should be considered in light of these recent, but contradictory, findings. Treatment outcomes with overdentures were compared with fixed prostheses and evaluated by subjective and objective assessments. General tendencies were observed and the contradictory results need to be subjected to critical analysis. Several studies exhibit a surprisingly high failure rate (> 20%) for maxillary overdentures.20,26,57 This failure rate is significantly increased in comparison with fixed prostheses or mandibular implants. Implant losses in the maxilla were associated with severe resorption, poor bone quality and short implants (≤ 7 mm).25,26,28,33 A critical analysis of the treatment outcomes revealed that the indication for overdentures was often made in an emergency situation.27 Maxillary overdentures were a substitute for failing fixed prostheses and were prescribed in situations with poor bone26 when adequate placement of implants to support fixed prostheses was not possible. Otherwise, it was observed that, if properly planned, the marginal bone surrounding the implants was maintained with overdentures, even in severely resorbed ridges at the same level as with fixed prostheses.58 With fixed, screwretained prostheses, speech problems were frequently reported,25,33,59 in contrast to overdentures. In more than 70% of the patients, speech problems were associated with hearing problems,59 which are frequently encountered in elderly patients and thus complicate phonation with the new prosthesis design. Therefore this might prolong the adaptation period. In contrast to maxillary overdentures, the recent literature exhibits a high success rate for mandibular overdentures, with different implant systems and a varying number of implants.17-20,60,61 This is somewhat surprising because the mandibular overdenture seems to be indicated for the oldest groups of patients with implants. Although implants can facilitate easy adaptation to wearing complete dentures because of fixation and stabilization of the denture, a prolonged adaptation phase must be expected for some very old patients (> 80 years) if they demonstrate impaired psychomotor skills.62 The sucJANUARY 1998
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cessful use of a few, usually two implants, was clearly demonstrated,12,13,36 but has not become the standard clinical protocol. If the choice of prostheses is offered, namely, fixed or implant-supported overdentures, elderly patients more than 50 years of age would prefer the overdenture.63,64 Subjective needs, such as ease of handling, hygiene procedures and oral comfort, may also determine success and individual preferences. The observation that preference was made for long rigid bars for overdenture support63,64 was not confirmed by other investigators.65 Controversial results were also obtained for denture service that became necessary during the maintenance phase. Although one study reported that implant-supported overdentures required frequent services,14 findings of another study indicate that much less service was needed when compared with fixed prostheses.66 In this context, it should be noted that treatment outcomes with different implant systems that use a different philosophy of prosthetic construction and design should not be directly compared. Biologic and biomechanic aspects of implant-supported mandibular overdentures must be discussed. Radiographic assessment of edentulous patients provided with interforaminal implants resulted in a slightly higher resorption rate of the posterior jaw bone if overdentures were used67 instead of fixed prostheses. However, mandibular overdentures occluding with maxillary dentures seem to reduce the negative impact of load transmission onto the maxilla when compared with fixed mandibular prostheses.68 The suggestion that overdentures are a favorable treatment option for elderly patients is supported. In vivo force measurements in three dimensions with two mandibular implants revealed that bars contribute to load sharing between the two implants.51 More information is needed regarding the effect of multiple implants (three or four implants) splinted with a bar in terms of force distribution.
CONCLUSION The high success rate, usefulness, and reliability of mandibular overdentures has been demonstrated. It is necessary that maxillary overdentures also become a wellestablished and reliable treatment option for the edentulous patient. Implantology, though a rather young and fast developing area, is a well-documented discipline in dentistry. Variations in results of different indications for implant placement may be dependent on the use of a specific implant system. Therefore this variable must be considered if efficacy and effectiveness of implant overdentures are further discussed. REFERENCES 1. Berg E. The influence of some anamnestic, demographic, and clinical variables on patient acceptance of new complete dentures. Acta Odontol Scand 1984;42:119-27.
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2. Berg E. A 2-year follow-up study of patient satisfaction with new complete dentures. J Dent 1988;16:160-5. 3. Brånemark PI, Adell R, Breine U, Hansson BO, Lindström J, Ohlsson Å. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg 1969;3:81-100. 4. Brånemark PI, Zarb GA, Albrektsson T. Tissue-integrated prostheses. Chicago: Quintessence; 1985. 5. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part I: surgical results. J Prosthet Dent 1990;63:451-7. 6. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part II: the prosthetic results. J Prosthet Dent 1990;64:53-61. 7. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part III: problems and complications encountered. J Prosthet Dent 1990;64:185-94. 8. Schroeder A, Pohler O, Sutter F. Tissue reaction to an implant of a titanium hollow cylinder with a titanium surface spray layer. [in German] SSO Schweiz Monatssschr Zahnheilk 1976;86:713-27. 9. Schroeder A, Stich H, Straumann F, Sutter F. The accumulation of osteocementum around dental implant under physical loading. SSO Schweiz Monatsschr Zahnheilk 1978;88:1051-8. 10. Schroeder A, van der Zypen E, Stich H, Sutter F. The reactions of bone, connective tissue, and epithelium to endosteal implants with titanium-sprayed surfaces. J Maxillofac Surg 1981;9:15-25. 11. Quirynen M, Naert I, van Steenberghe D, Teerlinck J, Dekeyser C, Theuniers G. Periodontal aspects of osseointegrated fixtures supporting an overdenture. A 4-year retrospective study. J Clin Periodontol 1991;18:719-28. 12. Mericske-Stern R, Zarb GA. Overdentures: an alternative implant methodology for edentulous patients. Int J Prosthodont 1993;6:203-8. 13. Mericske-Stern R, Steinlin Schaffner T, Marti P, Geering AH. Peri-implant mucosal aspects of ITI implants supporting overdentures. A five-year longitudinal study. Clin Oral Implants Res 1994;5:9-18. 14. Cune MS, de Putter C, Hoogstraten J. Treatment outcome with implantretained overdentures. Part Iclinical findings and predictability of clinical treatment outcome. J Prosthet Dent 1994;72:144-51. 15. Cune MS, de Putter C, Hoogstraten J. Treatment outcome with implantretained overdentures. Part 2: patient satisfaction and predictability of subjective treatment outcome. J Prosthet Dent 1994;72:152-8. 16. Cune MS, de Putter C. Comparative evaluation of some outcome measures of implant systems and suprastructure t ypes in mandibular implantoverdenture treatment. Int J Oral Maxillofac Implants 1994;9:548-55. 17. Batenburg RH, van Oort RP, Reintsema H, Brouwer TJ, Raghoebar GM, Boering G. Overdentures supported by two IMZ implants in the lower jaw. A retrospective study of peri-implant tissues. Clin Oral Implants Res 1994;5:207-12. 18. Wismeyer D, van Waas MA, Vermeeren JI. Overdentures supported by ITI implants: a 6.5-year evaluation of patient satisfaction and prosthetic aftercare. Int J Oral Maxillofac Implants 1995;10:744-9. 19. Spiekermann H, Jansen VK, Richter EJ. A 10-year follow-up study of IMZ and TPS implants in the edentulous mandible using bar-retained overdentures. Int J Oral Maxillofac Implants 1995;10:231-43. 20. Jemt T, Chai J, Harnett J, Heath MR, Hutton JE, Johns RB, et al. A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants. Int J Oral Maxillofac Implants 1996;11:291-8. 21. Vigild M. Benefit related assessment of treatment need among the elderly. Gerodontology 1993;10:10-4. 22. Zarb GA, Schmitt A. Implant prosthodontic treatment options for the edentulous patient. J Oral Rehabil 1995;22:661-71. 23. Carlsson B, Carlsson GE. Prosthodontic complications in osseointegrated dental implant treatment. Int J Oral Maxillofac Implants 1994;9:90-4. 24. Hallman M, Carlsson B. Surgical correction of malpositioned implants. A case report. Clin Oral Implants Res 1996;7:316-9. 25. Jemt T. Failures and complications in 391 consecutively inserted fixed prostheses supported by Brånemark implants in edentulous jaws: a study of treatment from the time of prostheses placement to the first annual checkup. Int J Oral Maxillofac Implants 1991;6:270-6. 26. Jemt T. Implant treatment in resorbed edentulous upper jaws. Clin Oral Implants Res 1993;4:187-94. 27. Palmqvist S, Sondell K, Swartz B. Implant-supported maxillary overdentures: outcome in planned and emergency cases. Int J Oral Maxillofac Implants 1994;9:184-90. 28. Enquist B, Bergendal T, Kallus T. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. Int J Oral Maxillofac Implants 1988;3:129-34.
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29. Jemt T, Book K, Linden B, Urde G. Failures and complications in 92 consecutively inserted overdentures supported by Brånemark implants in severely resorbed edentulous maxillae: a study from prosthetic treatment to first annual check-up. Int J Oral Maxillofac Implants 1992;7:162-7. 30. Jemt T, Carlsson L, Boss A, Jörnéus L. In vivo load measurements on osseointegrated implants supporting fixed or removable prostheses: a comparative pilot study. Int J Oral Maxillofac Implants 1991;6:413-7. 31. Gerber DA, Belser UC. Restoration-driven implant placement with restoration generated site development. Compend 1995;16:796-904. 32. Hess D, Buser D, Dietschi D, Grossen G, Schönberger A, Belser UC. Aesthetichr Einzelzahnersatz mit ImplantatenEin Team-Approach. Implantologie 1996;3:245-56. 33. Jemt T. Fixed implant-supported prostheses in the edentulous maxilla. A five-year follow-up report. Clin Oral Implants Res 1994;5:142-7. 34. Zarb GA, Schmitt A. Osseointegration for elderly patients: the Toronto study. J Prosthet Dent 1994;72:559-68. 35. Mericske-Stern R, Geering AH. Implants in total prosthetics. Anchorage of a total prosthesis in the edentulous lower jaw using 2 implants with angle attachments. Schweiz Monatsschr Zahnmed 1988;8:870-6. 36. Mericske-Stern R. Clinical evaluation of overdenture restorations supported by osseointegrated titanium implants: a retrospective study. Int J Oral Maxillofac Implants 1990;5:375-83. 37. Cune MS, de Putter C, Hoogstraten J. Characteristics of 5410 edentulous implant candidates and the treatment they receive. Community Dent Oral Epidemiol 1995;23:110-3. 38. Mericske-Stern R, Boretti G, Geering AH. Systemic health and quality of life in elderly patients f itted with mandibular implants. J Dent Res 1997;76:277[abstract 2105]. 39. Mericske-Stern R, Milani D, Mericske E, Olah A. Periotest measurements and osseointegration of mandibular ITI implants supporting overdentures. A one-year longitudinal study. Clin Oral Implants Res 1995;6:73-82. 40. Roberts WE, Simmons KE, Garetto LP, DeCastro RA. Bone physiology and metabolism in dental implantology: risk factors for osteoporosis and other metabolic bone diseases. Implant Dent 1992;1:11-21. 41. Dao TT, Anderson JD, Zarb GA. Is osteoporosis a risk factor for osseointegration of dental implants? Int J Oral Maxillofac Implants 1993;8:137-44. 42. Soikkonen K, Ainamo A, Xie Q. Height of the residual ridge and radiographic appearance of bony structure in the jaws of clinically edentulous elderly people. J Oral Rehabil 1996;23:470-5. 43. Von Wowern N, Kollerup G. Symptomatic osteoporosis: a risk factor for residual ridge reduction of the jaws. J Prosthet Dent 1992;67:656-60. 44. Wennström JL, Bengazi F, Lekholm U. The influence of the masticatory mucosa on the peri-implant soft tissue condition. Clin Oral Implants Res 1994;5:1-8. 45. Mombelli A, Mericske-Stern R. Microbiological features of stable osseointegrated implants used as abutments for overdentures. Clin Oral Implants Res 1990;1:1-7. 46. Glantz P-O, Rangert B, Svensson A, Stafford GD, Arnvidarson B, Randow K, et al. On clinical loading of osseointegrated implants. A methodological and clinical study. Clin Oral Implants Res 1993;4:99-105. 47. Meijer HJ, Kuiper JH, Starmans FJ, Bosman F. Stress distribution around dental implants: influence of superstructure, length of implants, and height of mandible. J Prosthet Dent 1992;68:96-101. 48. Mericske-Stern R, Geering AH, Buergin WB, Graf H. Three-dimensional force measurements on mandibular implants supporting overdentures. Int J Oral Maxillofac Implants 1992;7:185-94. 49. Meijer HJ, Starmans FJ, Steen WH, Bosman F. Location of implants in the interforaminal region of the mandible and the consequences for the design of the superstructure. J Oral Rehabil 1994;21:47-56. 50. Mericske-Stern R, Assal P, Buergin W. Simultaneous force measurements in 3 dimensions on oral endosseous implants in vitro and in vivo. A methodological study. Clin Oral Implants Res 1996;7:378-86. 51. Mericske-Stern R, Piotti M, Sirtes G. 3-D in vivo force measurements on mandibular implants supporting overdentures. A comparative study. Clin Oral Implants Res 1996;7:387-96. 52. Mericske-Stern R. Force Distribution on implants supporting overdentures: the effect of distal bar extensions. A 3-D in vivo study. Clin Oral Implants Res 1997;142-51. 53. Mericske-Stern R. Biomechanics and implants. Which is the best denture anchorage on implants in the edentulous mandible: an in vivo study. Schweiz Monatsschr Zahnmed 1997;107:602-13. 54. Taylor TD, Worthington P. Osseointegrated implant rehabilitation of the previously irradiated mandible: results of a limited trial at 3 to 7 years. J Prosthet Dent 1993;69:60-9.
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55. Granström G, Bergström K, Tjellström A, Brånemark PI. A detailed analysis of titanium implants lost in irradiated tissues. Int J Oral Maxillofac Implants 1994;9:653-62. 56. Granström G, Jacobsson M, Tjellström A. Titanium implants in irradiated tissue: benefits from hyperbaric oxygen. Int J Oral Maxillofac Implants 1992;7:15-25. 57. Hutton JE, Heath MR, Chai JY, Harnett J, Jemt T, Johns RB, et al. Factors related to success and failure rates at 3-year follow-up in a multicenter study of overdentures supported by Brånemark implants. Int J Oral Maxillofac Implants 1995;10:33-42. 58. Palmqvvist S, Sondell K, Swartz B, Svenson B. Marginal bone levels around maxillary implants supporting overdentures or fixed prostheses: a comparative study using detailed narrow-beam radiographs. Int J Oral Maxillofac Implants 1996;11:223-7. 59. Lundqvist S, Lohmander-Agerskov A, Haraldson T. Speech before and after treatment with bridges on osseointegrated implants in the edentulous upper jaw. Clin Oral Implants Res 1982;3:57-62. 60. Cune MS, de Putter C. A single dimension statistical evaluation of predictors in implant-overdenture treatment. J Clin Periodontol 1996;23:425-31. 61. Buser D, Mericske-Stern R, Bernard JP, Behneke A, Behneke N, Hirt HP, et al. Long-term evaluation of non-submerged ITI implants. Part 1: 8-year life table analysis of a prospective multi-center study with 2359 implants. Clin Oral Implants Res 1997;8:161-72. 62. Jemt T. Implant treatment in elderly patients. Int J Prosthodont 1993;6:456-61. 63. De Grandmont P, Feine JS, Raché R, Boudrias P, Donohue WB, Tanguay R, et al. Within-subject comparisons of implant-supported mandibular prostheses: psychometric evaluation. J Dent Res 1994;73:1096-104.
Noteworthy Abstracts of the Current Literature
64. Feine JS, de Grandmont P, Boudrias P, Brien N, LaMarche C, Taché R, e al. Within-subject comparisons of implants-supported mandibular prostheses: Choice of prosthesis. J Dent Res 1994;73:1105-11. 65. Geertman ME, van Waas MA, vant Hof MA, Kalk W. Denture satisfaction in a comparative study of implant-retained mandibular overdentures: a randomized clinical trial. Int J Oral Maxillofac Implants 1996;11:194-200. 66. Hemmings KW, Schmitt A, Zarb GA. Complications and maintenance requirements for fixed prostheses and overdentures in the edentulous mandible: a 5-year report. Int J Oral Maxillofac Implants 1994;9:191-6. 67. Jacobs R, Schotte A, Van Steenberghe D, Quirynen M, Naert I. Posterior jaw bone resorption in osseointegrated implant-supported overdentures. Clin Oral Implants Res 1992;3:63-70. 68. Jacobs R, van Steenberghe D, Nys M, Naert I. Maxillary bone resorption in patients with mandibular implant-supported overdentures or fixed prostheses. J Prosthet Dent 1993;70:135-40. Reprint requests to: DR. R. MERICSKE -STERN DEPARTMENT OF R EMOVABLE PROSTHODONTICS UNIVERSITY OF BERN FREIBURGSTRASSE 7 CH-3010 BERN SWITZERLAND Copyright © 1998 by The Editorial Council of The Journal Prosthetic Dentistry. 0022-3913/98/$5.00 + 0. 10/1/87063
Effect of hydroxyapatite particle size on myoblasts and fibroblasts Sun JS, Tsuang YH, Chang WHS, Li J, Liu HC, Lin FH. Biomaterials 1997;18:683-90.
Purpose. After surgery, the bone and soft tissues around integrated biomaterials can be adversely affected by implant-related factors acting over a period of years. This study was designed to test the mechanism of biologic effects of various sized hydroxyapatite (HA) particles on myoblasts and fibroblasts. Material and Methods. HA powders were sintered, ground, and separated with mesh into various grain sizes of about 0.5 to 3.0 µm, 37 to 63 µm, 177 to 250 µm, and 420 to 841 µm. HA particles were spherical in shape, and trace elements that might be connected with biocompatibility were detected by atomic absorption analysis. Before use, they were processed by dry heat sterilization (130° C, 40 minutes). Confluent rat myoblast or fibroblast cultures were seeded into six tissue culture wells (seeding density of 1 × 105 cells per well). These cultures were mixed with 0.1% (1 mg ml-1) of various sized HA particles for 1 hour, 2 hour, 1 day, 3 days, and 7 days to test their effects on the cell culture. The production of transforming growth factor-β1 and prostaglandin E2 in the culture medium was analyzed by enzyme linked immunosorbent assay methods. Results. The results showed that adding HA particles into a cell culture can decrease the cell count significantly. The transforming growth factor-β1 (TGF-β1) concentrations in the culture medium decreased significantly on addition of HA particles. When calculated as a ratio to the cell number, the TGF-β1 titre increased most significantly in the groups of medium-sized particles. The prostaglandin E2 (PGE2) concentration in the medium increased significantly. The changes in TGF-β1 and PGE2 concentrations with the smallest particles were most significant and persisted longer. The inhibitory effects of the HA particles on the cell culture were mediated by the increased synthesis of PGE2. Conclusions. HA supplied for clinical use is larger than the largest amount used in this experiment and results on the effect of various sized HA particles on myoblasts do not mean that the same result will occur in the block form. The study does illustrate the in vivo effect of the degradation product of HA on the adjacent ingrowing myoblasts and suggests that caution should be exercised before considering the use of HA products that could easily break down into a fine powder. 34 References.ME RAZZOOG JANUARY 1998
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Treatment outcomes with implant-supported overdentures: Clinical considerations Regina Mericske-Stern, DDS, PhDa School of Dental Medicine, University of Bern, Switzerland Three indications for implant-supported overdentures are defined, namely, the edentulous maxilla, the edentulous mandible, and the compromised situation. These indications for overdentures are related to three patient groups: (1) a younger segment of patients among the older population with maxillary complete dentures, (2) elderly completely edentulous patients who request better stabilization of the mandibular denture, and (3) patients with acquired or congenital defects. The aim of this article is to discuss treatment strategies and clinical considerations with respect to three specific indications for overdentures. (J Prosthet Dent 1998;79:66-73.)
A
daptation to wearing complete dentures is a complex process and must be considered from both somatic and psychologic standpoints. Incorporating a foreign body in the oral cavity may be a difficult task. Documentation on success and failure with complete dentures is sparse and not reliable, because the correlation between a favorable shape of the residual ridge, the technical accuracy of the dentures, and the ease of adaptation to wearing dentures is low.1,2 Motor skills tend to decrease with increasing age. The difficulties of wearing dentures has been attributed to deficiencies of the denture-bearing tissues, reduced salivary flow, vulnerable tissue, and severe ridge resorption. Patients may also have an aversion against a foreign body in the oral cavity. For many patients, the wearing of complete dentures also means to be old and socially handicapped. Problems with adaptation to complete dentures are observed with a higher incidence for mandibular dentures than for maxillary dentures. Historically, surgeons focused on improving the structure of the residual mandibular ridge by various preprosthetic surgical techniques and less frequently the maxillary ridge. These techniques appear to be more invasive than the surgery for osseointegrated implants, and there is no scientific evidence of its success and usefulness. The use of implants to substitute for missing teeth was systematically developed by Brånemark et al.3,4 Since the 1980s, several studies have demonstrated the reliability of this treatment modality.5-7 The clinical concept of this treatment consisted of inserting five to six implants into the edentulous mandible to provide support and retention for a fixed prostheses, which was retrievable by the dentist only. While the Brånemark groups focused on fixed prostheses, Schroeder et al8-10 developed the ITI implant system to deal with the problems of unilateral distal extension situations. He suggested that overdentures supported by four implants should be used in situations of Presented at the annual meeting of the Academy of Prosthodontics, Halifax, Nova Scotia, Canada, May 1997. a Associate Professor, Department of Removable Prosthodontics. 66
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complete edentulousness. However, reliable studies to support this method were not available. In the last few years, interest in overdenture therapy for the edentulous jaw has rapidly increased as is evidenced by the number of studies published since 1990.11-20 This may be due to the fact that a greater segment of the population is elderly and complete edentulousness is postponed to an older age. Social change, evolution in dentistry, and changes in prosthetic techniques have lead to patients demanding more in terms of esthetics, function, and oral comfort, which is also true for complete edentulousness.21,22 More patients have access to therapy with implants and the contraindications are few. Essentially, they are as follows: 1. The patient is comfortable with complete dentures and has no complaints. 2. The residual ridge is not adequate for the standard placement of implants. 3. The abuse of drugs. 4. General health conditions do not allow a minor surgical intervention. 5. Therapy with immunosuppressive, long-standing intake of corticosteroids. 6. Metabolic disease not under control. Three groups of patients are identified for whom overdentures would be indicated: (1) a younger segment of elderly patients with edentulous maxilla, who feel uncomfortable with a complete denture and are demanding of a stable prosthesis and high oral comfort; (2) elderly patients who require stabilization of the mandibular complete denture; and (3) patients with congenital or acquired oral and maxillofacial defects in need of oral rehabilitation. The purpose of this article is to discuss specific clinical aspects of these implant-supported overdenture situations.
MAXILLARY OVERDENTURES: THE DEMANDING PATIENT Treatment of the edentulous maxilla with implants is challenging and presents inherent problems that have VOLUME 79 NUMBER 1
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been presented in anecdotal clinical reports on maxillary fixed prostheses.23,24 Problems include divergent and buccally directed implant axes, long teeth, open interdental spaces, insufficient lip support, and incongruence of implant location and tooth position. Such adverse morphologic effects can be more easily eliminated by the use of maxillary implant-supported overdentures instead of fixed, screw-retained prostheses.22 Thus overdentures may become a favored and advantageous treatment option; however, it is likely that they are not a true alternative to fixed prostheses in terms of economics or time-saving procedures.25,26 In treatment planning the maxilla with implants, one usually has to consider the options of both fixed and removable prostheses. The current treatment strategy has been that overdentures were selected as a substitute for failing fixed prostheses.27 In fact, there are no reliable long-term results of patients treated with maxillary overdentures as planned cases; as a consequence, treatment principles for maxillary overdentures are not well-defined. The following statements are the basis of diagnostic and therapeutic criteria: 1. The minimal number of implants is preferably four. 2. Implants should be evenly distributed throughout the arch. 3. Patients who belong to a younger segment of the edentulous population frequently ask for fixed prostheses. 4. The opposing mandible is dentate or reconstructed with fixed prostheses. 5. A standard surgical protocol for implant placement cannot be followed because of deep sinus or thin narrow ridges. 6. Therapy with overdentures is more consistent with optimum placement of the implants with regard to bone quality and quantity. 7. Overdentures may better resolve esthetic and speech problems. 8. The labial flange of the overdenture provides lip support. 9. The overdenture may have a horseshoe design, and thus be more acceptable to the patient. Such therapeutic criteria imply that a more specific patient selection protocol is necessary for maxillary overdentures. Because the dental literature on maxillary implants shows a tendency for an increased failure rate20,26,28,29 when compared with mandibular implants, the placement of four or more implants with a minimum length of more than 6 mm and splinted with a bar is strongly suggested (Fig. 1, A). A rigid connection of the denture to the bar is recommended to reduce high bending moments as they were observed in comparison to fixed prostheses.30 A full diagnostic tooth arrangement or set-up on mounted casts is the crucial first step of the treatment planning to establish vertical dimension of occlusion, esthetic anterior tooth position, and JANUARY 1998
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Fig. 1, A, Maxillary jaw with four implants and connecting bar. Denture has horseshoe design. B, Orientation index of tooth set-up, positioned on maxillary cast for tissue volume analysis. C, Design and esthetics of maxillary overdenture are of high quality. Esthetics match implant-supported mandibular fixed prosthesis.
other morphologic aspects. The orientation index obtained from the diagnostic set-up is helpful for assessment of tissue volume dimensions (Fig. 1, B). If a properly designed and esthetically acceptable complete denture already exists, the denture could be used for diagnostic purposes. The final decision with regard to the best prosthetic design (fixed or removable) is made on the basis of such presurgical critical assessment. The combination of radiographic analysis and the diagnostic set-up is also used for fabricating a surgical template. 67
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Table I. Percentage distribution of main systemic diseases at time of implant placement Systemic health problems
Heart, Circulatory system, CVI Musculoskeletal system Allergies, Asthma Tumors (malignant) Neurologic disease Metabolic disease Eyes Others
Fig. 2. Two mandibular ITI-implants splinted with bar for overdenture connection. Overdenture has complete denture design.
Clinical experience has demonstrated that the soft tissue may be managed successfully in single tooth replacement.31,32 Recreating a well-contoured soft tissue border around implants over an entire dental arch to be a routine clinical outcome has not yet been documented. Further, in situations of advanced bone resorption, the problem of elongated teeth may not be able to be resolved. Therefore, for morphologic and esthetic reasons, the buccal flange of an overdenture can be useful and individual patients needs can be satisfied with this type of prosthesis (Fig. 1, C). Development of hyperplastic tissue beneath the denture base can also be a problem with implant-supported overdentures.25,33 Hyperplasia is more frequently found under maxillary overdentures than mandibular overdentures. Shrinkage of the tissue has been observed if a change is made to a fixed prosthesis design. In some situations, the denture base appears to facilitate phonation. It has also been reported that speech problems are more frequently encountered with fixed prostheses. The horseshoe design of the complete maxillary overdenture has been reported to be wellaccepted by the patients. Rigid bars, such as the U-shaped Dolder bar, have also been shown to provide good stability and optimum retention.
MANDIBULAR OVERDENTURES AND THE ELDERLY PATIENT In contrast to maxillary overdentures, treatment outcomes with mandibular overdentures appear to be more successful and are better documented, particularly for elderly patients.12,13,15-19,22,34 Completely edentulous elderly patients can benefit from implant-supported overdentures when they lose their teeth at an advanced age and are not capable of adapting to wearing complete mandibular dentures or when, after having had dentures for many years, they begin to lose their motor skills and are no longer able to wear complete dentures. Loss of teeth in advanced age can present a poor prog68
Percentage
46% 13% 11% 10% 8% 7% 3% 2%
nosis for learning new muscular patterns and can result in problems, for both the patient and dentist. In the 1980s, the standard protocol described by Schroeder6-8 was the placement of four implants. In 1985 this treatment strategy changed, based on the hypothesis that only two and sometimes three implants were adequate for overdenture support.35,36 Principles of treatment with mandibular implant-supported overdentures rely on the following clinical considerations12,35: (1) most elderly patients should be eligible for overdenture therapy, (2) two implants should be sufficient to support an overdenture prosthesis, (3) three implants can be placed if the minimum length of each implant is less than 8 mm, and (4) a standard surgical procedure should be applied in most situations. The implant-retained overdenture should reduce stress on patients and tissues, and it is a treatment modality that should be less time-consuming, less expensive, will minimize risks on patients and tissues, and becomes a true alternative to fixed prostheses (Fig. 2). Ten years ago age was considered to be an exclusion criterion for implantation. Today, there is evidence that elderly patients would benefit from implants and that the effectiveness of mandibular implant-supported overdentures is high. There is no evidence of adverse effects of aging that negatively affect treatment outcomes. These include compromised systemic health, advanced mandibular atrophy, reduced healing capacity of the bone particularly with osteoporotic bone, soft tissue problems, lack of attached keratinized mucosa due to advanced atrophy, lack of good hygiene and adequate maintenance, and biomechanic considerations if only two implants are used for denture support. With increasing age, systemic health problems are more frequently encountered, however, there is rarely evidence of a negative impact of health problems on implants.37,38 In a recent survey of 125 elderly patients with an average age of 69 years, 67% of the patients had systemic health problems at the time of implant surgery, and at least two medications were prescribed for each patient (Table I). During an observation period of 3 to 12 years, deterioration of general health was observed in 23% of all patients, but only 3% of patients exhibited VOLUME 79 NUMBER 1
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Fig. 3. Peri-implant parameters recorded during observation period of 5 years. Little and insignificant changes were observed. PLI, Plaque index; BI, bleeding index; PD, probing depths; LA, loss of attachment.
improvement in health conditions. The clinical parameters rarely changed over the entire observation period. Only a few implants failed and a correlation between failure and poor systemic health was not observed. Similar observations had been reported in a comparative study of two implant centers.10 After a long period of edentulousness, mandibular atrophy is often advanced. However, bone height itself may not be a predictor of bone quality and resorption of mandibular ridges is not necessarily an indicator for osteoporosis. A study of mandibular implants that used the Periotest (PT) instrument (Siemens, Bensheim, Germany) demonstrated that a shift to more negative PT values in the first year of implant loading,39 which may indicate an increase in bone implant contact. Histomorphometric analysis of bone specimens obtained from these patients revealed a strong correlation between dense cortical bone and advanced atrophy. Controversy exists about the effect of atrophy of the jaw bone by osteoporosis and the healing capacity of the bone.40,41 Although osteoporosis is diagnosed in one part of the body, usually in the dorsal spine, this does not necessarily mean that other parts of the skeleton are equally osteoporotic. It is not yet clear whether mandibular or maxillary bone is more susceptible to osteoporotic atrophy.42,43 Minor soft tissue problems, particularly hypertrophic tissue beneath the bar, may also be encountered. Improvement of hygiene or hygiene techniques may be helpful. Although plaque seems to accumulate more quickly underneath overdentures,11 results of a 5-year longitudinal study13 indicate that over time little change was found with regard to the peri-implant parameters (Fig. 3). When proper recall and maintenance are provided for implant patients, favorable results are seen. It has been observed that a high level of compliance is found among patients with implants, particularly among elderly patients.13 Because of the advanced mandibular atrophy, many implants are not located in attached keratinized mucosa. From this previous study,13 it was conJANUARY 1998
Fig. 4. Ranges of maximum and minimum chewing forces (in Newtons), recorded five retention devices, are given in all three dimensions; different scales of three diagrams. X-axis, lateral (+) and mesial () direction; y-axis, anterior (+) and posterior () directions; z-axis, vertical direction (+, down, -, up).
cluded that the absence of keratinized attached mucosa around the implant neck did not jeopardize the health of the implants, which appears to be supported by others.44 Cross-sectional and longitudinal results of microbiologic studies on edentulous patients with implantsupported overdenture further suggest that the oral microbiota does not exhibit unfavorable shifts in the composition of the oral bacteria.45 Little is known about forces that are directed onto implants during function under in vivo conditions. In vitro measurements cannot predict force transmission in vivo.46 Biomechanical considerations, such as loading and force distribution onto two implants, produces controversy regarding the best retention mechanism (rigid or stressbreaking) and the best retention device for overdenture connection (single anchors or bar splints).47-49 A study was designed to evaluate a measuring method in vitro and in vivo for three-dimensional force measurements on 69
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be selected according to the specific clinical and individual needs of the patient.
ORAL DEFECTS AND THE COMPROMISED PATIENT
Fig. 5. A, Maxillary jaw with cleft lip and palate in 45-year-old man after loss of remaining teeth. Wearing of complete denture is impossible without support of implants. B, Six implants were evenly distributed throughout arch. Because of slightly divergent implant axis, three separate bar segments were fabricated. C, Horseshoe denture design.
implants.50 The comparative measurements of various functional forces and maximum forces, with five attachment devices with a rigid or stress-breaking retention mechanism, demonstrated intraindividual and interindividual variations.51-53 However, the influence of the retention device and mechanism on force magnitudes and force directions in all three dimensions was much less evident than it was expected (Fig. 4). On the basis of these findings, it was suggested that the retention device 70
In situations of congenital or acquired intraoral defects, the anatomic-morphologic oral conditions may lead to the inability of wearing complete dentures. Acquired oral defects are caused by trauma and are also frequently the result of resection of malignant tumors, whereas congenital defects are mainly lip and palate clefts. Implant prosthodontic techniques have enabled the development of successful treatment strategies for structural, functional, and esthetic rehabilitation of these compromised patients. Again, in many situations therapy with overdentures is more favorable than with fixed prostheses and may be the only practicable way of managing these patients for various reasons (Fig. 5, A, B, and C). Because the life-span of patients with tumors is often highly reduced and for more than 50% is less than 5 years, efficient, practical implant prosthetic procedures are needed. The following criteria should determine the treatment option of overdentures for compromised situations: 1. Removable prostheses allow for inspection of the surgical site. 2. The implants must be placed where adequate bone is available. 3. The denture base replaces lost hard and soft tissues. 4. Esthetic demands may better be fulfilled with overdentures. 5. Lip and facial support can be provided by a labial denture flange. 6. Speech problems may be resolved. 7. Oral hygiene is facilitated. 8. Changes of the denture design are possible, if necessary. The previously described clinical aspects and specific indications of overdenture therapy for the maxillary and mandibular jaws are the same for compromised patients, although it may be more difficult to accomplish. Esthetics and function are favorable and promising with overdentures; however, bone and skin grafts, immediate implant placement during grafting procedures, poor alignment of the implants due to reduced bone quantity, irradiation, and reduced salivary flow are factors that may alter the predictability of implant prostheses for compromised patients. Thick skin grafts around implants probably do not form an adequate soft tissue attachment and will produce increased probing depths. Again, a strict maintenance protocol must be followed by these patients. Divergent and nonparallel implant axes are more frequently observed if implants are immediately placed with bone grafts and may pose problems for fabricating bar-splints. Although favorable results have been VOLUME 79 NUMBER 1
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reported for a few patients,54 the failure rate of implants appears to be increased if the implants are placed in irradiated bone.55 According to comparative results, therapy with hyperbaric oxygen enhances the survival rate of the implants.55,56 Furthermore, it seems that rigid bar-splints for overdenture support provide better stability than single attachments that are more prone to failure. Because an increased failure rate of implants is observed in irradiated patients, overdentures are the treatment modality of choice primarily because of the conversion of the prostheses to dentures if implants are lost.
DISCUSSION The recent literature on implantology exhibits an increasing number of articles on implant overdentures. The indications for overdentures should be considered in light of these recent, but contradictory, findings. Treatment outcomes with overdentures were compared with fixed prostheses and evaluated by subjective and objective assessments. General tendencies were observed and the contradictory results need to be subjected to critical analysis. Several studies exhibit a surprisingly high failure rate (> 20%) for maxillary overdentures.20,26,57 This failure rate is significantly increased in comparison with fixed prostheses or mandibular implants. Implant losses in the maxilla were associated with severe resorption, poor bone quality and short implants (≤ 7 mm).25,26,28,33 A critical analysis of the treatment outcomes revealed that the indication for overdentures was often made in an emergency situation.27 Maxillary overdentures were a substitute for failing fixed prostheses and were prescribed in situations with poor bone26 when adequate placement of implants to support fixed prostheses was not possible. Otherwise, it was observed that, if properly planned, the marginal bone surrounding the implants was maintained with overdentures, even in severely resorbed ridges at the same level as with fixed prostheses.58 With fixed, screwretained prostheses, speech problems were frequently reported,25,33,59 in contrast to overdentures. In more than 70% of the patients, speech problems were associated with hearing problems,59 which are frequently encountered in elderly patients and thus complicate phonation with the new prosthesis design. Therefore this might prolong the adaptation period. In contrast to maxillary overdentures, the recent literature exhibits a high success rate for mandibular overdentures, with different implant systems and a varying number of implants.17-20,60,61 This is somewhat surprising because the mandibular overdenture seems to be indicated for the oldest groups of patients with implants. Although implants can facilitate easy adaptation to wearing complete dentures because of fixation and stabilization of the denture, a prolonged adaptation phase must be expected for some very old patients (> 80 years) if they demonstrate impaired psychomotor skills.62 The sucJANUARY 1998
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cessful use of a few, usually two implants, was clearly demonstrated,12,13,36 but has not become the standard clinical protocol. If the choice of prostheses is offered, namely, fixed or implant-supported overdentures, elderly patients more than 50 years of age would prefer the overdenture.63,64 Subjective needs, such as ease of handling, hygiene procedures and oral comfort, may also determine success and individual preferences. The observation that preference was made for long rigid bars for overdenture support63,64 was not confirmed by other investigators.65 Controversial results were also obtained for denture service that became necessary during the maintenance phase. Although one study reported that implant-supported overdentures required frequent services,14 findings of another study indicate that much less service was needed when compared with fixed prostheses.66 In this context, it should be noted that treatment outcomes with different implant systems that use a different philosophy of prosthetic construction and design should not be directly compared. Biologic and biomechanic aspects of implant-supported mandibular overdentures must be discussed. Radiographic assessment of edentulous patients provided with interforaminal implants resulted in a slightly higher resorption rate of the posterior jaw bone if overdentures were used67 instead of fixed prostheses. However, mandibular overdentures occluding with maxillary dentures seem to reduce the negative impact of load transmission onto the maxilla when compared with fixed mandibular prostheses.68 The suggestion that overdentures are a favorable treatment option for elderly patients is supported. In vivo force measurements in three dimensions with two mandibular implants revealed that bars contribute to load sharing between the two implants.51 More information is needed regarding the effect of multiple implants (three or four implants) splinted with a bar in terms of force distribution.
CONCLUSION The high success rate, usefulness, and reliability of mandibular overdentures has been demonstrated. It is necessary that maxillary overdentures also become a wellestablished and reliable treatment option for the edentulous patient. Implantology, though a rather young and fast developing area, is a well-documented discipline in dentistry. Variations in results of different indications for implant placement may be dependent on the use of a specific implant system. Therefore this variable must be considered if efficacy and effectiveness of implant overdentures are further discussed. REFERENCES 1. Berg E. The influence of some anamnestic, demographic, and clinical variables on patient acceptance of new complete dentures. Acta Odontol Scand 1984;42:119-27.
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2. Berg E. A 2-year follow-up study of patient satisfaction with new complete dentures. J Dent 1988;16:160-5. 3. Brånemark PI, Adell R, Breine U, Hansson BO, Lindström J, Ohlsson Å. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg 1969;3:81-100. 4. Brånemark PI, Zarb GA, Albrektsson T. Tissue-integrated prostheses. Chicago: Quintessence; 1985. 5. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part I: surgical results. J Prosthet Dent 1990;63:451-7. 6. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part II: the prosthetic results. J Prosthet Dent 1990;64:53-61. 7. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part III: problems and complications encountered. J Prosthet Dent 1990;64:185-94. 8. Schroeder A, Pohler O, Sutter F. Tissue reaction to an implant of a titanium hollow cylinder with a titanium surface spray layer. [in German] SSO Schweiz Monatssschr Zahnheilk 1976;86:713-27. 9. Schroeder A, Stich H, Straumann F, Sutter F. The accumulation of osteocementum around dental implant under physical loading. SSO Schweiz Monatsschr Zahnheilk 1978;88:1051-8. 10. Schroeder A, van der Zypen E, Stich H, Sutter F. The reactions of bone, connective tissue, and epithelium to endosteal implants with titanium-sprayed surfaces. J Maxillofac Surg 1981;9:15-25. 11. Quirynen M, Naert I, van Steenberghe D, Teerlinck J, Dekeyser C, Theuniers G. Periodontal aspects of osseointegrated fixtures supporting an overdenture. A 4-year retrospective study. J Clin Periodontol 1991;18:719-28. 12. Mericske-Stern R, Zarb GA. Overdentures: an alternative implant methodology for edentulous patients. Int J Prosthodont 1993;6:203-8. 13. Mericske-Stern R, Steinlin Schaffner T, Marti P, Geering AH. Peri-implant mucosal aspects of ITI implants supporting overdentures. A five-year longitudinal study. Clin Oral Implants Res 1994;5:9-18. 14. Cune MS, de Putter C, Hoogstraten J. Treatment outcome with implantretained overdentures. Part Iclinical findings and predictability of clinical treatment outcome. J Prosthet Dent 1994;72:144-51. 15. Cune MS, de Putter C, Hoogstraten J. Treatment outcome with implantretained overdentures. Part 2: patient satisfaction and predictability of subjective treatment outcome. J Prosthet Dent 1994;72:152-8. 16. Cune MS, de Putter C. Comparative evaluation of some outcome measures of implant systems and suprastructure t ypes in mandibular implantoverdenture treatment. Int J Oral Maxillofac Implants 1994;9:548-55. 17. Batenburg RH, van Oort RP, Reintsema H, Brouwer TJ, Raghoebar GM, Boering G. Overdentures supported by two IMZ implants in the lower jaw. A retrospective study of peri-implant tissues. Clin Oral Implants Res 1994;5:207-12. 18. Wismeyer D, van Waas MA, Vermeeren JI. Overdentures supported by ITI implants: a 6.5-year evaluation of patient satisfaction and prosthetic aftercare. Int J Oral Maxillofac Implants 1995;10:744-9. 19. Spiekermann H, Jansen VK, Richter EJ. A 10-year follow-up study of IMZ and TPS implants in the edentulous mandible using bar-retained overdentures. Int J Oral Maxillofac Implants 1995;10:231-43. 20. Jemt T, Chai J, Harnett J, Heath MR, Hutton JE, Johns RB, et al. A 5-year prospective multicenter follow-up report on overdentures supported by osseointegrated implants. Int J Oral Maxillofac Implants 1996;11:291-8. 21. Vigild M. Benefit related assessment of treatment need among the elderly. Gerodontology 1993;10:10-4. 22. Zarb GA, Schmitt A. Implant prosthodontic treatment options for the edentulous patient. J Oral Rehabil 1995;22:661-71. 23. Carlsson B, Carlsson GE. Prosthodontic complications in osseointegrated dental implant treatment. Int J Oral Maxillofac Implants 1994;9:90-4. 24. Hallman M, Carlsson B. Surgical correction of malpositioned implants. A case report. Clin Oral Implants Res 1996;7:316-9. 25. Jemt T. Failures and complications in 391 consecutively inserted fixed prostheses supported by Brånemark implants in edentulous jaws: a study of treatment from the time of prostheses placement to the first annual checkup. Int J Oral Maxillofac Implants 1991;6:270-6. 26. Jemt T. Implant treatment in resorbed edentulous upper jaws. Clin Oral Implants Res 1993;4:187-94. 27. Palmqvist S, Sondell K, Swartz B. Implant-supported maxillary overdentures: outcome in planned and emergency cases. Int J Oral Maxillofac Implants 1994;9:184-90. 28. Enquist B, Bergendal T, Kallus T. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. Int J Oral Maxillofac Implants 1988;3:129-34.
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29. Jemt T, Book K, Linden B, Urde G. Failures and complications in 92 consecutively inserted overdentures supported by Brånemark implants in severely resorbed edentulous maxillae: a study from prosthetic treatment to first annual check-up. Int J Oral Maxillofac Implants 1992;7:162-7. 30. Jemt T, Carlsson L, Boss A, Jörnéus L. In vivo load measurements on osseointegrated implants supporting fixed or removable prostheses: a comparative pilot study. Int J Oral Maxillofac Implants 1991;6:413-7. 31. Gerber DA, Belser UC. Restoration-driven implant placement with restoration generated site development. Compend 1995;16:796-904. 32. Hess D, Buser D, Dietschi D, Grossen G, Schönberger A, Belser UC. Aesthetichr Einzelzahnersatz mit ImplantatenEin Team-Approach. Implantologie 1996;3:245-56. 33. Jemt T. Fixed implant-supported prostheses in the edentulous maxilla. A five-year follow-up report. Clin Oral Implants Res 1994;5:142-7. 34. Zarb GA, Schmitt A. Osseointegration for elderly patients: the Toronto study. J Prosthet Dent 1994;72:559-68. 35. Mericske-Stern R, Geering AH. Implants in total prosthetics. Anchorage of a total prosthesis in the edentulous lower jaw using 2 implants with angle attachments. Schweiz Monatsschr Zahnmed 1988;8:870-6. 36. Mericske-Stern R. Clinical evaluation of overdenture restorations supported by osseointegrated titanium implants: a retrospective study. Int J Oral Maxillofac Implants 1990;5:375-83. 37. Cune MS, de Putter C, Hoogstraten J. Characteristics of 5410 edentulous implant candidates and the treatment they receive. Community Dent Oral Epidemiol 1995;23:110-3. 38. Mericske-Stern R, Boretti G, Geering AH. Systemic health and quality of life in elderly patients f itted with mandibular implants. J Dent Res 1997;76:277[abstract 2105]. 39. Mericske-Stern R, Milani D, Mericske E, Olah A. Periotest measurements and osseointegration of mandibular ITI implants supporting overdentures. A one-year longitudinal study. Clin Oral Implants Res 1995;6:73-82. 40. Roberts WE, Simmons KE, Garetto LP, DeCastro RA. Bone physiology and metabolism in dental implantology: risk factors for osteoporosis and other metabolic bone diseases. Implant Dent 1992;1:11-21. 41. Dao TT, Anderson JD, Zarb GA. Is osteoporosis a risk factor for osseointegration of dental implants? Int J Oral Maxillofac Implants 1993;8:137-44. 42. Soikkonen K, Ainamo A, Xie Q. Height of the residual ridge and radiographic appearance of bony structure in the jaws of clinically edentulous elderly people. J Oral Rehabil 1996;23:470-5. 43. Von Wowern N, Kollerup G. Symptomatic osteoporosis: a risk factor for residual ridge reduction of the jaws. J Prosthet Dent 1992;67:656-60. 44. Wennström JL, Bengazi F, Lekholm U. The influence of the masticatory mucosa on the peri-implant soft tissue condition. Clin Oral Implants Res 1994;5:1-8. 45. Mombelli A, Mericske-Stern R. Microbiological features of stable osseointegrated implants used as abutments for overdentures. Clin Oral Implants Res 1990;1:1-7. 46. Glantz P-O, Rangert B, Svensson A, Stafford GD, Arnvidarson B, Randow K, et al. On clinical loading of osseointegrated implants. A methodological and clinical study. Clin Oral Implants Res 1993;4:99-105. 47. Meijer HJ, Kuiper JH, Starmans FJ, Bosman F. Stress distribution around dental implants: influence of superstructure, length of implants, and height of mandible. J Prosthet Dent 1992;68:96-101. 48. Mericske-Stern R, Geering AH, Buergin WB, Graf H. Three-dimensional force measurements on mandibular implants supporting overdentures. Int J Oral Maxillofac Implants 1992;7:185-94. 49. Meijer HJ, Starmans FJ, Steen WH, Bosman F. Location of implants in the interforaminal region of the mandible and the consequences for the design of the superstructure. J Oral Rehabil 1994;21:47-56. 50. Mericske-Stern R, Assal P, Buergin W. Simultaneous force measurements in 3 dimensions on oral endosseous implants in vitro and in vivo. A methodological study. Clin Oral Implants Res 1996;7:378-86. 51. Mericske-Stern R, Piotti M, Sirtes G. 3-D in vivo force measurements on mandibular implants supporting overdentures. A comparative study. Clin Oral Implants Res 1996;7:387-96. 52. Mericske-Stern R. Force Distribution on implants supporting overdentures: the effect of distal bar extensions. A 3-D in vivo study. Clin Oral Implants Res 1997;142-51. 53. Mericske-Stern R. Biomechanics and implants. Which is the best denture anchorage on implants in the edentulous mandible: an in vivo study. Schweiz Monatsschr Zahnmed 1997;107:602-13. 54. Taylor TD, Worthington P. Osseointegrated implant rehabilitation of the previously irradiated mandible: results of a limited trial at 3 to 7 years. J Prosthet Dent 1993;69:60-9.
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55. Granström G, Bergström K, Tjellström A, Brånemark PI. A detailed analysis of titanium implants lost in irradiated tissues. Int J Oral Maxillofac Implants 1994;9:653-62. 56. Granström G, Jacobsson M, Tjellström A. Titanium implants in irradiated tissue: benefits from hyperbaric oxygen. Int J Oral Maxillofac Implants 1992;7:15-25. 57. Hutton JE, Heath MR, Chai JY, Harnett J, Jemt T, Johns RB, et al. Factors related to success and failure rates at 3-year follow-up in a multicenter study of overdentures supported by Brånemark implants. Int J Oral Maxillofac Implants 1995;10:33-42. 58. Palmqvvist S, Sondell K, Swartz B, Svenson B. Marginal bone levels around maxillary implants supporting overdentures or fixed prostheses: a comparative study using detailed narrow-beam radiographs. Int J Oral Maxillofac Implants 1996;11:223-7. 59. Lundqvist S, Lohmander-Agerskov A, Haraldson T. Speech before and after treatment with bridges on osseointegrated implants in the edentulous upper jaw. Clin Oral Implants Res 1982;3:57-62. 60. Cune MS, de Putter C. A single dimension statistical evaluation of predictors in implant-overdenture treatment. J Clin Periodontol 1996;23:425-31. 61. Buser D, Mericske-Stern R, Bernard JP, Behneke A, Behneke N, Hirt HP, et al. Long-term evaluation of non-submerged ITI implants. Part 1: 8-year life table analysis of a prospective multi-center study with 2359 implants. Clin Oral Implants Res 1997;8:161-72. 62. Jemt T. Implant treatment in elderly patients. Int J Prosthodont 1993;6:456-61. 63. De Grandmont P, Feine JS, Raché R, Boudrias P, Donohue WB, Tanguay R, et al. Within-subject comparisons of implant-supported mandibular prostheses: psychometric evaluation. J Dent Res 1994;73:1096-104.
Noteworthy Abstracts of the Current Literature
64. Feine JS, de Grandmont P, Boudrias P, Brien N, LaMarche C, Taché R, e al. Within-subject comparisons of implants-supported mandibular prostheses: Choice of prosthesis. J Dent Res 1994;73:1105-11. 65. Geertman ME, van Waas MA, vant Hof MA, Kalk W. Denture satisfaction in a comparative study of implant-retained mandibular overdentures: a randomized clinical trial. Int J Oral Maxillofac Implants 1996;11:194-200. 66. Hemmings KW, Schmitt A, Zarb GA. Complications and maintenance requirements for fixed prostheses and overdentures in the edentulous mandible: a 5-year report. Int J Oral Maxillofac Implants 1994;9:191-6. 67. Jacobs R, Schotte A, Van Steenberghe D, Quirynen M, Naert I. Posterior jaw bone resorption in osseointegrated implant-supported overdentures. Clin Oral Implants Res 1992;3:63-70. 68. Jacobs R, van Steenberghe D, Nys M, Naert I. Maxillary bone resorption in patients with mandibular implant-supported overdentures or fixed prostheses. J Prosthet Dent 1993;70:135-40. Reprint requests to: DR. R. MERICSKE -STERN DEPARTMENT OF R EMOVABLE PROSTHODONTICS UNIVERSITY OF BERN FREIBURGSTRASSE 7 CH-3010 BERN SWITZERLAND Copyright © 1998 by The Editorial Council of The Journal Prosthetic Dentistry. 0022-3913/98/$5.00 + 0. 10/1/87063
Effect of hydroxyapatite particle size on myoblasts and fibroblasts Sun JS, Tsuang YH, Chang WHS, Li J, Liu HC, Lin FH. Biomaterials 1997;18:683-90.
Purpose. After surgery, the bone and soft tissues around integrated biomaterials can be adversely affected by implant-related factors acting over a period of years. This study was designed to test the mechanism of biologic effects of various sized hydroxyapatite (HA) particles on myoblasts and fibroblasts. Material and Methods. HA powders were sintered, ground, and separated with mesh into various grain sizes of about 0.5 to 3.0 µm, 37 to 63 µm, 177 to 250 µm, and 420 to 841 µm. HA particles were spherical in shape, and trace elements that might be connected with biocompatibility were detected by atomic absorption analysis. Before use, they were processed by dry heat sterilization (130° C, 40 minutes). Confluent rat myoblast or fibroblast cultures were seeded into six tissue culture wells (seeding density of 1 × 105 cells per well). These cultures were mixed with 0.1% (1 mg ml-1) of various sized HA particles for 1 hour, 2 hour, 1 day, 3 days, and 7 days to test their effects on the cell culture. The production of transforming growth factor-β1 and prostaglandin E2 in the culture medium was analyzed by enzyme linked immunosorbent assay methods. Results. The results showed that adding HA particles into a cell culture can decrease the cell count significantly. The transforming growth factor-β1 (TGF-β1) concentrations in the culture medium decreased significantly on addition of HA particles. When calculated as a ratio to the cell number, the TGF-β1 titre increased most significantly in the groups of medium-sized particles. The prostaglandin E2 (PGE2) concentration in the medium increased significantly. The changes in TGF-β1 and PGE2 concentrations with the smallest particles were most significant and persisted longer. The inhibitory effects of the HA particles on the cell culture were mediated by the increased synthesis of PGE2. Conclusions. HA supplied for clinical use is larger than the largest amount used in this experiment and results on the effect of various sized HA particles on myoblasts do not mean that the same result will occur in the block form. The study does illustrate the in vivo effect of the degradation product of HA on the adjacent ingrowing myoblasts and suggests that caution should be exercised before considering the use of HA products that could easily break down into a fine powder. 34 References.ME RAZZOOG JANUARY 1998
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