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Management of misangulated implants for a maxillary overdenture with spherical abutments: A clinical report
Management of misangulated implants for a maxillary overdenture with spherical abutments: A clinical report Avinash S. Bidra, BDS, MS,a and John R. Agar, DDS, MAb University of Connecticut Health Center, Farmington, Conn. Misangulated and malpositioned implants pose a significant challenge for the prosthodontic treatment of edentulous patients. Most reports of maxillary overdenture patients have described the use of a bar to splint malaligned implants, followed by successful fabrication of the prosthesis. Few reports have discussed the use of individual abutments in such situations. This clinical report describes the successful use of spherical/ball abutments for the management of 4 malaligned implants in the edentulous maxilla for an overdenture. The rationale and technique for the use of spherical abutments for overdenture fabrication in such situations are described. (J Prosthet Dent 2011;106:209-213) There are few evidenced-based guidelines for the design and number of implants necessary for maxillary implant-supported overdentures.1 For the palateless/horseshoe design, the placement of 4 implants has been recognized as a popular treatment.1 The implants are either splinted by a bar or have individual abutments for retention. The literature is not clear about the superiority of using a bar versus individual abutments. However, it is known that maxillary implantsupported overdentures have been associated with higher rates of implant failures than other implant-supported prostheses.2 Therefore, in patients with a history of implant failure, the complete palatal coverage overdenture may be more advantageous than a palateless/horseshoe design. Complete palatal coverage can provide additional support for the overdenture and ensure against future fabrication of a new prosthesis if implants strategic to the horseshoe design fail to osseointegrate. This also helps to eliminate any dramatic shift in prosthesis acclimatization or patient dissatisfaction. Improper angulation of implants is one of the most difficult problems to overcome in the fabrication of implant-supported prostheses.3,4 It often arises from poor treatment planning,
unfavorable anatomy, poor communication within the treatment team, lack of a surgical guide, an inaccurate surgical guide, or instability of the surgical guide during surgery.5 Previous reports on malaligned implants in the maxilla have focused primarily on the use of a bar for the correction of unfavorable angulations.6-8 Few reports in the literature have described the use of individual abutments.9,10 A bar may be the preferred choice for situations with severe malalignment and when prosthetic space is available; however, when malalignment is not so severe, the use of a bar may not be the best option because of 1) the requirement for additional prosthetic space; 2) increased treatment expense and time;
3) technique sensitivity; 4) difficulty in oral hygiene maintenance underneath the bar; and 5) difficulty in the future reline, repair, and maintenance of the prosthesis. Wiemeyer et al11 described in detail the concept of using spherical abutments for non-parallel implants to obtain a favorable path of insertion and removal and predictable retention. The premise of their report was that the parallel orientation of retentive matrices could engage an equal amount of undercut on spherical abutments, even if implants were divergent to each other. The authors stated that complete seating and predictable retention of a removable prosthesis was possible for implants that varied
1 Illustration of concept that parallel orientations of retentive matrices can engage equal amount of undercut on spherical abutments, even when implants diverge by up to 60 degrees to each other or 30 degrees to vertical axis. Figure adapted from Wiemeyer et al.11
Assistant Professor and Maxillofacial Prosthodontist, Department of Reconstructive Sciences. Professor and Prosthodontics Program Director, Department of Reconstructive Sciences.
a
b
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Volume 106 Issue 4 as much as 60 degrees between each other or 30 degrees from the vertical axis (Fig. 1). Furthermore, placement and withdrawal of a matrix that could be rotated 3-dimensionally (3-D) on a spherical abutment can exhibit the same retentive properties, regardless of its orientation. This concept has also been reported in 2 recent studies of spherical abutments.12,13 This mechanism is not possible for attachment systems such as ERA (APMSterngold, Attleboro, Mass) or Locator (Zest Anchors, Inc, Escondido, Calif ), which do not allow 3-D rotational movement between patrix and matrix. The purpose of this clinical report was to describe the management of 4 misangulated implants by using spherical/ball abutments, for the fabrication of a maxillary overdenture.
CLINICAL REPORT A 75-year old woman presented for the fabrication of an implant-supported maxillary overdenture because she was dissatisfied with the retention of her maxillary complete denture. The patient had been edentulous in the maxilla and partially dentate in the mandible for several years. She was satisfied with her mandibular partial removable dental prosthesis. An analysis of the patient’s history revealed that 4 implants had been placed in the maxilla by an oral and maxillofacial surgeon approximately 6 months before presentation (Fig. 2). Two months after implant surgery, the left posterior implant failed to osseointegrate, and a new implant was placed in its position. The clinical
exam revealed that the implants were asymmetrically distributed across the maxillary arch. The palatal vault was shallow with a flat contour and lacked undercuts for retention. A panoramic radiograph confirmed misalignment of the implants and also revealed the level of bone around the implants (Fig. 3). The implants were of various lengths and the posterior implants appeared to be encroaching into the maxillary sinuses. Healing abutments were removed and none of the implants demonstrated mobility, bone loss, or clinical signs of any infection. Therefore, clinically they were deemed to be successfully osseointegrated. All implants were 4.3 mm in diameter (RP-Replace Select; Nobel Biocare, Yorba Linda, Calif ) and appeared to be nonparallel to one another.
2 Pretreatment occlusal view of maxilla with 4 implants unevenly distributed across arch.
3 Panoramic radiographic image showing angulations of implants. Posterior implants appear to encroach into maxillary sinuses.
4 Placement of impression copings for implant-level impression reveals amount of divergence among implants.
5 Maxillary definitive cast with implant analogs and cobalt chromium metal base. Note metal stops in tripod arrangement for accurate orientation and retentive loupes and meshwork for acrylic resin retention.
The Journal of Prosthetic Dentistry
Bidra and Agar
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October 2011 Based on the clinical situation and patient’s expectations, a treatment plan was developed to fabricate an implant-supported overdenture in the maxilla with complete palatal coverage. The patient was satisfied with her existing mandibular prosthesis and declined any treatment for the mandible. The fit of the metal framework was good and mandibular denture teeth showed minimal wear. A preliminary impression was made in irreversible hydrocolloid (Jeltrate Dustless; Dentsply, York, Pa), and a custom tray (Triad; Dentsply) was fabricated on the diagnostic cast. As it was understood that there would be issues with implant angulations, a decision was made to make an implantlevel impression (Fig. 4). After border molding procedures, an implant-level impression was made using polyether impression material (Impregum Pen-
tasoft; 3M ESPE Dental Products, St. Paul, Minn). A definitive maxillary cast was fabricated using type IV dental stone (Die-Stone; Heraeus Kulzer, South Bend, Ind). Placement of guide pins (Nobel Biocare) into implant analogs revealed the extent of divergence between various implants ranging from 40 to 60 degrees. Therefore, 4 spherical abutments and corresponding matrices were used for support and retention of the planned maxillary overdenture. A metal base was fabricated on the definitive cast using a cobalt-chromium alloy (Wironium; Bego, Lincoln, RI). The metal base was repositioned on the cast using the tripodized metal stops and cyanoacrylate resin (Duro Super Glue; Loctite Corp, Cleveland, Ohio) (Fig. 5). Autopolymerizing resin (Repair Material; Dentsply) was used to complete the record base, and an
occlusal rim was fabricated. Standard prosthodontic principles14 were then followed and maxillary denture teeth were arranged. The maxillary trial denture was evaluated intraorally, to the satisfaction of the patient and the clinician. A cross-sectional putty matrix (Trixa Laboratory Matrix Putty; Dentsply) placed over the notches of the definitive cast confirmed the presence of adequate space for the prosthetic components, acrylic resin and denture teeth.15 The trial denture was invested in a denture flask according to standard dental laboratory procedures.14 At the wax-elimination stage, the autopolymerizing resin was removed by heating it. Four spherical abutments of 2.25 mm in diameter and 3 mm in cuff height (Ball AbutmentTitanium, Nobel Biocare) were hand tightened on the implant analogs (Fig. 6A). Four corresponding matrices
A
B
C 6 A, Placement of spherical abutments on implant analogs at wax elimination stage of denture fabrication. Note lack of parallelism among various abutments. B, Retentive matrices placed on spherical abutments rotated in 3 dimensions and verified for parallelism with surveyor. C, Type III dental stone used to block out undercut and stabilize matrices before denture processing. Note parallelism among various matrices and slight anterior inclination for ease of insertion and removal.
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Volume 106 Issue 4
7 A, Insertion and final torque of spherical abutments. B, Maxillary occlusal view of definitive prosthesis.
8 Intaglio surface of prosthesis at 3-year follow-up showing integrity of original matrices. (Preci-Clix White Females; Preat Corporation, Santa Ynez, Calif ) were then placed on the spherical abutments. The matrices were pivoted on the spherical abutments in all 3 dimensions to attain parallelism. A surveyor was used to confirm the parallelism11 (Fig. 6B). The selected path of insertion was directed slightly towards the anterior region, to facilitate easier insertion and removal of the prosthesis. A mix of type III dental stone (Modern Materials Denstone; Heraeus Kulzer) was used to block out undercuts below the retentive matrices. The mix of stone was carefully placed beneath the matrices and was locked into place by mechanical retention, as the stone set around the undercut regions (Fig. 6C). The stone served to: 1) stabilize the position of the matrices and counteract the forces of denture processing;
2) prevent acrylic resin from entering into the undercuts. The metal base was then returned to the definitive cast using the tripodized metal stops and glued with cyanoacrylate resin for better stability during denture processing. The denture was then processed in heat-polymerized acrylic resin (Lucitone; Dentsply), according to standard dental laboratory procedures.14 The matrices were incorporated into the denture during processing, and the final denture was finished and polished. The spherical abutments were then screwed intraorally into the implants, at the manufacturer recommended torque of 35Ncm, and the overdenture was inserted (Fig. 7). The path of insertion and removal was acceptable to the clinician and the patient, and the denture exhibited good retention over the spherical abut-
The Journal of Prosthetic Dentistry
ments. The intimate fit of the denture over the maxillary tissues was confirmed with pressure-indicating paste (Pressure Indicator Paste; Mizzy Inc, Cherry Hill, NJ). Final occlusal adjustments were made to conform to the planned lingualized occlusal scheme. The patient was given postoperative instructions for the maintenance of the prosthesis, implants, and surrounding tissues, and was placed on a 6-month follow-up program. At a 3-year follow-up, no complications were noted with respect to the implants or the prosthesis (Fig. 8). No adjustments or replacement of the retentive components were performed during the 3-year period. The retention of the overdenture remained excellent with the original matrices, and the patient was comfortable with the prosthesis.
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October 2011 DISCUSSION Different prosthodontic treatment options were considered for the 4 implants in this patient. They included: removable overdenture supported by a single milled or cast bar; removable overdenture supported by 2 separate bars; screw-retained fixed prosthesis in metal-acrylic resin or metal-porcelain; cemented fixed prosthesis in metal-resin or metal-porcelain and single screw-retained metal substructure with individually cemented crowns. Fixed prosthetic options were eliminated because of increased expense, and removable overdenture options supported by a bar were ruled out because of lack of sufficient prosthetic space. Furthermore, the use of a bar would have significantly increased the technique sensitivity and treatment expense for the patient. An argument can be made against using complete palate coverage for the overdenture, even though 4 implants were available for retention and support. However, the authors believed that because of the patient’s history of implant failure in the left posterior region, she was better suited to complete palatal coverage as her prosthesis would not require a remake if she were to experience any future implant failures. Additionally, only a few short-term retrospective studies in the literature show evidence for the use of a palateless/horseshoe overdenture supported by 4 implants.16,17 A metal base was used for complete palatal coverage because of its advantages of improved fit with underlying tissues, good thermal conductivity, reduced palatal bulk, and superior comfort for the patient.14 The use of metal bases has also been shown to eliminate fractures in the body of the maxillary overdenture prosthesis.18 In addition, the use of a
Bidra and Agar
metal base in this patient significantly reduced the amount of acrylic resin required for final denture processing and thus minimized the amount of distortion of the overdenture. This allowed good fit of the matrices over the spherical abutments. However, the posterior palatal seal area consisted of acrylic resin rather than metal to allow easier postinsertion adjustments in this region.
SUMMARY This clinical report described the management of 4 malaligned implants in the edentulous maxilla with spherical abutments and corresponding matrices. Even though implants were divergent, the use of spherical abutments allowed the matrices to be rotated in 3 dimensions and to be aligned parallel to each other during denture processing. This facilitated a favorable path of insertion and removal and good retention of the overdenture prosthesis. The use of spherical abutments may be preferred over the use of a bar in situations with divergent implants and limited prosthetic space.
REFERENCES 1. Sadowsky SJ. Treatment considerations for maxillary implant overdentures: a systematic review. J Prosthet Dent 2007;97:340-8. 2. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications with implants and implant prostheses. J Prosthet Dent 2003;90:121-32. 3. Lewis S, Avera S, Engleman M, Beumer J. The restoration of improperly inclined osseointegrated implants. Int J Oral Maxillofac Implants 1989;4:147-52. 4. Drago CJ. Prosthodontic complications related to compromised implant placement. J Oral Maxillofac Surg 1994;52:15-22. 5. Bidra AS. Surgical and prosthodontic consequences of inadequate treatment planning for fixed implant-supported prosthesis in the edentulous mandible. J Oral Maxillofac Surg 2010;68:2528-36.
6. Asvanund C, Morgano SM. Restoration of unfavorably positioned implants for a partially endentulous patient by using an overdenture retained with a milled bar and attachments: a clinical report. J Prosthet Dent 2004;91:6-10. 7. Lee JH, Frias V, Woo C, Maiberg R. Fixed prosthesis with a milled bar for correcting misangled implants: a clinical report. J Prosthet Dent 2007;97:129-32. 8. Moeller MS, Duff RE, Razzoog ME. Rehabilitation of malpositioned implants with a CAD/CAM milled implant overdenture: a clinical report. J Prosthet Dent 2011;105:143-6. 9. Dario LJ. A maxillary implant overdenture that utilizes angle-correcting abutments. J Prosthodont 2002;11:41-45. 10.Schneider AL, Kurtzman GM. Restoration of divergent free-standing implants in the maxilla. J Oral Implantol 2002;28:113-6. 11.Wiemeyer AS, Agar JR, Kazemi RB. Orientation of retentive matrices on spherical attachments independent of implant parallelism. J Prosthet Dent 2001;86:434-7. 12.Gulizio MP, Agar JR, Kelly JR, Taylor TD. Effect of implant angulation upon retention of overdenture attachments. J Prosthodont. 2005;14:3-11. 13.Ortegón SM, Thompson GA, Agar JR, Taylor TD, Perdikis D. Retention forces of spherical attachments as a function of implant and matrix angulation in mandibular overdentures: an in vitro study. J Prosthet Dent 2009;101:231-8. 14.Zarb GA, Bolender CL. Prosthodontic treatment for edentulous patients. 12th ed. St. Louis: Mosby; 2004. p. 207, 263, 396-400. 15.Bidra AS. Consequences of insufficient treatment planning for flapless implant surgery for a mandibular overdenture: a clinical report. J Prosthet Dent 2011;105:286-91. 16.Naert I, Gizani S, van Steenberghe D. Rigidly splinted implants in the resorbed maxilla to retain a hinging overdenture: a series of clinical reports for up to 4 years. J Prosthet Dent 1998;79:156-64. 17.Kiener P, Oetterli M, Mericske E, MericskeStern R. Effectiveness of maxillary overdentures supported by implants: maintenance and prosthetic complications. Int J Prosthodont 2001;14:133-40. 18.Smedberg JI, Nilner K, Frykholm A. A sixyear follow-up study of maxillary overdentures on osseointegrated implants. Eur J Prosthodont Restor Dent 1999;7:51-6. Corresponding author: Dr Avinash S. Bidra University of Connecticut Health Center 263 Farmington Avenue, L6078 Farmington, CT 06030 Fax: 860-679-1370 E-mail: [email protected] Copyright © 2011 by the Editorial Council for The Journal of Prosthetic Dentistry.
unfavorable anatomy, poor communication within the treatment team, lack of a surgical guide, an inaccurate surgical guide, or instability of the surgical guide during surgery.5 Previous reports on malaligned implants in the maxilla have focused primarily on the use of a bar for the correction of unfavorable angulations.6-8 Few reports in the literature have described the use of individual abutments.9,10 A bar may be the preferred choice for situations with severe malalignment and when prosthetic space is available; however, when malalignment is not so severe, the use of a bar may not be the best option because of 1) the requirement for additional prosthetic space; 2) increased treatment expense and time;
3) technique sensitivity; 4) difficulty in oral hygiene maintenance underneath the bar; and 5) difficulty in the future reline, repair, and maintenance of the prosthesis. Wiemeyer et al11 described in detail the concept of using spherical abutments for non-parallel implants to obtain a favorable path of insertion and removal and predictable retention. The premise of their report was that the parallel orientation of retentive matrices could engage an equal amount of undercut on spherical abutments, even if implants were divergent to each other. The authors stated that complete seating and predictable retention of a removable prosthesis was possible for implants that varied
1 Illustration of concept that parallel orientations of retentive matrices can engage equal amount of undercut on spherical abutments, even when implants diverge by up to 60 degrees to each other or 30 degrees to vertical axis. Figure adapted from Wiemeyer et al.11
Assistant Professor and Maxillofacial Prosthodontist, Department of Reconstructive Sciences. Professor and Prosthodontics Program Director, Department of Reconstructive Sciences.
a
b
Bidra and Agar
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Volume 106 Issue 4 as much as 60 degrees between each other or 30 degrees from the vertical axis (Fig. 1). Furthermore, placement and withdrawal of a matrix that could be rotated 3-dimensionally (3-D) on a spherical abutment can exhibit the same retentive properties, regardless of its orientation. This concept has also been reported in 2 recent studies of spherical abutments.12,13 This mechanism is not possible for attachment systems such as ERA (APMSterngold, Attleboro, Mass) or Locator (Zest Anchors, Inc, Escondido, Calif ), which do not allow 3-D rotational movement between patrix and matrix. The purpose of this clinical report was to describe the management of 4 misangulated implants by using spherical/ball abutments, for the fabrication of a maxillary overdenture.
CLINICAL REPORT A 75-year old woman presented for the fabrication of an implant-supported maxillary overdenture because she was dissatisfied with the retention of her maxillary complete denture. The patient had been edentulous in the maxilla and partially dentate in the mandible for several years. She was satisfied with her mandibular partial removable dental prosthesis. An analysis of the patient’s history revealed that 4 implants had been placed in the maxilla by an oral and maxillofacial surgeon approximately 6 months before presentation (Fig. 2). Two months after implant surgery, the left posterior implant failed to osseointegrate, and a new implant was placed in its position. The clinical
exam revealed that the implants were asymmetrically distributed across the maxillary arch. The palatal vault was shallow with a flat contour and lacked undercuts for retention. A panoramic radiograph confirmed misalignment of the implants and also revealed the level of bone around the implants (Fig. 3). The implants were of various lengths and the posterior implants appeared to be encroaching into the maxillary sinuses. Healing abutments were removed and none of the implants demonstrated mobility, bone loss, or clinical signs of any infection. Therefore, clinically they were deemed to be successfully osseointegrated. All implants were 4.3 mm in diameter (RP-Replace Select; Nobel Biocare, Yorba Linda, Calif ) and appeared to be nonparallel to one another.
2 Pretreatment occlusal view of maxilla with 4 implants unevenly distributed across arch.
3 Panoramic radiographic image showing angulations of implants. Posterior implants appear to encroach into maxillary sinuses.
4 Placement of impression copings for implant-level impression reveals amount of divergence among implants.
5 Maxillary definitive cast with implant analogs and cobalt chromium metal base. Note metal stops in tripod arrangement for accurate orientation and retentive loupes and meshwork for acrylic resin retention.
The Journal of Prosthetic Dentistry
Bidra and Agar
211
October 2011 Based on the clinical situation and patient’s expectations, a treatment plan was developed to fabricate an implant-supported overdenture in the maxilla with complete palatal coverage. The patient was satisfied with her existing mandibular prosthesis and declined any treatment for the mandible. The fit of the metal framework was good and mandibular denture teeth showed minimal wear. A preliminary impression was made in irreversible hydrocolloid (Jeltrate Dustless; Dentsply, York, Pa), and a custom tray (Triad; Dentsply) was fabricated on the diagnostic cast. As it was understood that there would be issues with implant angulations, a decision was made to make an implantlevel impression (Fig. 4). After border molding procedures, an implant-level impression was made using polyether impression material (Impregum Pen-
tasoft; 3M ESPE Dental Products, St. Paul, Minn). A definitive maxillary cast was fabricated using type IV dental stone (Die-Stone; Heraeus Kulzer, South Bend, Ind). Placement of guide pins (Nobel Biocare) into implant analogs revealed the extent of divergence between various implants ranging from 40 to 60 degrees. Therefore, 4 spherical abutments and corresponding matrices were used for support and retention of the planned maxillary overdenture. A metal base was fabricated on the definitive cast using a cobalt-chromium alloy (Wironium; Bego, Lincoln, RI). The metal base was repositioned on the cast using the tripodized metal stops and cyanoacrylate resin (Duro Super Glue; Loctite Corp, Cleveland, Ohio) (Fig. 5). Autopolymerizing resin (Repair Material; Dentsply) was used to complete the record base, and an
occlusal rim was fabricated. Standard prosthodontic principles14 were then followed and maxillary denture teeth were arranged. The maxillary trial denture was evaluated intraorally, to the satisfaction of the patient and the clinician. A cross-sectional putty matrix (Trixa Laboratory Matrix Putty; Dentsply) placed over the notches of the definitive cast confirmed the presence of adequate space for the prosthetic components, acrylic resin and denture teeth.15 The trial denture was invested in a denture flask according to standard dental laboratory procedures.14 At the wax-elimination stage, the autopolymerizing resin was removed by heating it. Four spherical abutments of 2.25 mm in diameter and 3 mm in cuff height (Ball AbutmentTitanium, Nobel Biocare) were hand tightened on the implant analogs (Fig. 6A). Four corresponding matrices
A
B
C 6 A, Placement of spherical abutments on implant analogs at wax elimination stage of denture fabrication. Note lack of parallelism among various abutments. B, Retentive matrices placed on spherical abutments rotated in 3 dimensions and verified for parallelism with surveyor. C, Type III dental stone used to block out undercut and stabilize matrices before denture processing. Note parallelism among various matrices and slight anterior inclination for ease of insertion and removal.
Bidra and Agar
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Volume 106 Issue 4
7 A, Insertion and final torque of spherical abutments. B, Maxillary occlusal view of definitive prosthesis.
8 Intaglio surface of prosthesis at 3-year follow-up showing integrity of original matrices. (Preci-Clix White Females; Preat Corporation, Santa Ynez, Calif ) were then placed on the spherical abutments. The matrices were pivoted on the spherical abutments in all 3 dimensions to attain parallelism. A surveyor was used to confirm the parallelism11 (Fig. 6B). The selected path of insertion was directed slightly towards the anterior region, to facilitate easier insertion and removal of the prosthesis. A mix of type III dental stone (Modern Materials Denstone; Heraeus Kulzer) was used to block out undercuts below the retentive matrices. The mix of stone was carefully placed beneath the matrices and was locked into place by mechanical retention, as the stone set around the undercut regions (Fig. 6C). The stone served to: 1) stabilize the position of the matrices and counteract the forces of denture processing;
2) prevent acrylic resin from entering into the undercuts. The metal base was then returned to the definitive cast using the tripodized metal stops and glued with cyanoacrylate resin for better stability during denture processing. The denture was then processed in heat-polymerized acrylic resin (Lucitone; Dentsply), according to standard dental laboratory procedures.14 The matrices were incorporated into the denture during processing, and the final denture was finished and polished. The spherical abutments were then screwed intraorally into the implants, at the manufacturer recommended torque of 35Ncm, and the overdenture was inserted (Fig. 7). The path of insertion and removal was acceptable to the clinician and the patient, and the denture exhibited good retention over the spherical abut-
The Journal of Prosthetic Dentistry
ments. The intimate fit of the denture over the maxillary tissues was confirmed with pressure-indicating paste (Pressure Indicator Paste; Mizzy Inc, Cherry Hill, NJ). Final occlusal adjustments were made to conform to the planned lingualized occlusal scheme. The patient was given postoperative instructions for the maintenance of the prosthesis, implants, and surrounding tissues, and was placed on a 6-month follow-up program. At a 3-year follow-up, no complications were noted with respect to the implants or the prosthesis (Fig. 8). No adjustments or replacement of the retentive components were performed during the 3-year period. The retention of the overdenture remained excellent with the original matrices, and the patient was comfortable with the prosthesis.
Bidra and Agar
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October 2011 DISCUSSION Different prosthodontic treatment options were considered for the 4 implants in this patient. They included: removable overdenture supported by a single milled or cast bar; removable overdenture supported by 2 separate bars; screw-retained fixed prosthesis in metal-acrylic resin or metal-porcelain; cemented fixed prosthesis in metal-resin or metal-porcelain and single screw-retained metal substructure with individually cemented crowns. Fixed prosthetic options were eliminated because of increased expense, and removable overdenture options supported by a bar were ruled out because of lack of sufficient prosthetic space. Furthermore, the use of a bar would have significantly increased the technique sensitivity and treatment expense for the patient. An argument can be made against using complete palate coverage for the overdenture, even though 4 implants were available for retention and support. However, the authors believed that because of the patient’s history of implant failure in the left posterior region, she was better suited to complete palatal coverage as her prosthesis would not require a remake if she were to experience any future implant failures. Additionally, only a few short-term retrospective studies in the literature show evidence for the use of a palateless/horseshoe overdenture supported by 4 implants.16,17 A metal base was used for complete palatal coverage because of its advantages of improved fit with underlying tissues, good thermal conductivity, reduced palatal bulk, and superior comfort for the patient.14 The use of metal bases has also been shown to eliminate fractures in the body of the maxillary overdenture prosthesis.18 In addition, the use of a
Bidra and Agar
metal base in this patient significantly reduced the amount of acrylic resin required for final denture processing and thus minimized the amount of distortion of the overdenture. This allowed good fit of the matrices over the spherical abutments. However, the posterior palatal seal area consisted of acrylic resin rather than metal to allow easier postinsertion adjustments in this region.
SUMMARY This clinical report described the management of 4 malaligned implants in the edentulous maxilla with spherical abutments and corresponding matrices. Even though implants were divergent, the use of spherical abutments allowed the matrices to be rotated in 3 dimensions and to be aligned parallel to each other during denture processing. This facilitated a favorable path of insertion and removal and good retention of the overdenture prosthesis. The use of spherical abutments may be preferred over the use of a bar in situations with divergent implants and limited prosthetic space.
REFERENCES 1. Sadowsky SJ. Treatment considerations for maxillary implant overdentures: a systematic review. J Prosthet Dent 2007;97:340-8. 2. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications with implants and implant prostheses. J Prosthet Dent 2003;90:121-32. 3. Lewis S, Avera S, Engleman M, Beumer J. The restoration of improperly inclined osseointegrated implants. Int J Oral Maxillofac Implants 1989;4:147-52. 4. Drago CJ. Prosthodontic complications related to compromised implant placement. J Oral Maxillofac Surg 1994;52:15-22. 5. Bidra AS. Surgical and prosthodontic consequences of inadequate treatment planning for fixed implant-supported prosthesis in the edentulous mandible. J Oral Maxillofac Surg 2010;68:2528-36.
6. Asvanund C, Morgano SM. Restoration of unfavorably positioned implants for a partially endentulous patient by using an overdenture retained with a milled bar and attachments: a clinical report. J Prosthet Dent 2004;91:6-10. 7. Lee JH, Frias V, Woo C, Maiberg R. Fixed prosthesis with a milled bar for correcting misangled implants: a clinical report. J Prosthet Dent 2007;97:129-32. 8. Moeller MS, Duff RE, Razzoog ME. Rehabilitation of malpositioned implants with a CAD/CAM milled implant overdenture: a clinical report. J Prosthet Dent 2011;105:143-6. 9. Dario LJ. A maxillary implant overdenture that utilizes angle-correcting abutments. J Prosthodont 2002;11:41-45. 10.Schneider AL, Kurtzman GM. Restoration of divergent free-standing implants in the maxilla. J Oral Implantol 2002;28:113-6. 11.Wiemeyer AS, Agar JR, Kazemi RB. Orientation of retentive matrices on spherical attachments independent of implant parallelism. J Prosthet Dent 2001;86:434-7. 12.Gulizio MP, Agar JR, Kelly JR, Taylor TD. Effect of implant angulation upon retention of overdenture attachments. J Prosthodont. 2005;14:3-11. 13.Ortegón SM, Thompson GA, Agar JR, Taylor TD, Perdikis D. Retention forces of spherical attachments as a function of implant and matrix angulation in mandibular overdentures: an in vitro study. J Prosthet Dent 2009;101:231-8. 14.Zarb GA, Bolender CL. Prosthodontic treatment for edentulous patients. 12th ed. St. Louis: Mosby; 2004. p. 207, 263, 396-400. 15.Bidra AS. Consequences of insufficient treatment planning for flapless implant surgery for a mandibular overdenture: a clinical report. J Prosthet Dent 2011;105:286-91. 16.Naert I, Gizani S, van Steenberghe D. Rigidly splinted implants in the resorbed maxilla to retain a hinging overdenture: a series of clinical reports for up to 4 years. J Prosthet Dent 1998;79:156-64. 17.Kiener P, Oetterli M, Mericske E, MericskeStern R. Effectiveness of maxillary overdentures supported by implants: maintenance and prosthetic complications. Int J Prosthodont 2001;14:133-40. 18.Smedberg JI, Nilner K, Frykholm A. A sixyear follow-up study of maxillary overdentures on osseointegrated implants. Eur J Prosthodont Restor Dent 1999;7:51-6. Corresponding author: Dr Avinash S. Bidra University of Connecticut Health Center 263 Farmington Avenue, L6078 Farmington, CT 06030 Fax: 860-679-1370 E-mail: [email protected] Copyright © 2011 by the Editorial Council for The Journal of Prosthetic Dentistry.