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Retrieval of the resilient element in an osseointegrated implant system
Retrieval implant
of the resilient system
R. K. K.
Qw,
BDS,
MSc,”
and
K. H.
element Ho,
BDS,
in an osseointegrated
FDSRCPSb
Facuky of Dentistry, National University Hospital, Singapore A fractured apical fragment of dental implant cylinder is difficult implant will be compromised if Two methods of retrieving the internal threads of the implant 1992;68:93-5.)
the
resilient intramobile element within the IMZ to remove. The continued usefulness of the the fractured intramobile element is not removed. apical fragment without causing damage to the cylinder are described. (J PROSTHET DENT
T
he IMZ dental implant system (Interpore International, Irvine, Calif.) is one of several osseointegrated implant systems available for oral rehabilitation.lW5 It incorporates a resilient component, made of polyoxymethylene material, known as the intramobile element. It functions to retain the prosthesis and provide stress distribution.2, 4, 6 The components of the IMZ dental implant system are illustrated in Fig. 1. The resilient intramobile element is retained in the implant cylinder by its external screw threads. It also has an internal threading system to receive the bridge-fastening screw. The clinical life span of the resilient intramobile element is approximately a year, after which time replacement is recommended.2, 4 The intramobile element may undergo fatigue and fracture (often due to overloading), resulting in loosening of the prosthesis. Complete recovery of the fractured fragments is necessary. The coronal section of a fractured intramobile element can be retrieved from the implant cylinder by using standard IMZ instruments.2 However, the retrieval of the fractured apical section is difficult since standard instruments are unsuitable for this purpose. Attempted retrieval may cause accidental damage to the internal threads of the implant cylinder. The risk is increased if the fractured apical section is short and threaded deeply within the implant cylinder. Failure to retrieve the apical section also may prevent the continued use of the implant as a restorative abutment. The purpose of this article is to describe two methods of retrieval of the fractured apical section of the resilient intramobile element retained within the IMZ dental implant cylinder.
LEVEL
OF FRACTURE
The intramobile element, approximately 11 mm long, has internal and external screw threads (Fig. 1). Internal
aAssociate Professor, Department of Restorative Dentistry. bAssociate Professor, Department of Oral and Maxillofacial Surgery. IO/l/36541 THE
JOURNAL
OF PROSTHETIC
DENTISTRY
IME + FS
END ‘OF
INTERNAL
IMPLANT
1. Diagram shows prosthetic restoration (fixed partial denture or denture) constructed on implant. Resilient intramobile element (IME) is interposed between prosthesis and implant. Internal and external screw threads are shown in scalloped outline. Apical end of internal threads is as illustrated. Below this level the intramobile element consists of solid core with only external threads. Prosthesis is retained by fastening screw (FS) threaded into intramobile element. Transepithelial implant element (TIE) is coronal attachment to implant above alveolar bone, providing support for soft tissue cuff. Fig.
screw threads extend from the coronal and toward the apex for a distance of 7.5 mm, leaving the apical 3.5 mm fragment of the intramobile element as a solid core. The level of fracture will determine whether the apical fragment contains part of the internal threads. For convenience, a fracture line at 6 mm or less from the coronal end of the intramobile element will leave a hollow apical section with at least 1.5 mm of internal threads. This length of internal threads allows a retrieving instrument to engage and retrieve the fractured apical fragment. A lower level fracture occurring at 7.5 mm or more from the coronal end of 93
OW AND
Fig. 2. Small screwdriver (SD) is used to retrieve hollow threaded apical fragment of resilient intramobile element. Original fastening screw (FS) has thread size that matches internal threads of resilient element. Working end (arrow) of screwdriver should thus be wider than diameter of fastening screw.
HO
Fig. 3. Instruments used in retrieval of apical solid core of resilient intramobile element. Left to right: Original fastening screw, modified fastening screw, and Kodex drill bit. (Original fastening screw could not be used for this purpose but is shown for comparison.)
the intramobile element leaves a totally solid apical fragment without any internal screw threads. This poses considerable difficulty in its retrieval.
RETRIEVAL OF HOLLOW APICAL SECTION
THREADED
A small screwdriver (Fig. 2) was designed and fabricated for retrieving the hollow apical fragment. The tip of the screwdriver consists of a single rectangular blade with sharp side edges. The width of the blade is slightly larger than the internal diameter of the resilient intramobile element. When the screwdriver is pressed into the hollow apical fragment, the sharp sides of its blade engage the internal threads of the fragment. The screwdriver is then rotated to unwind the apical fragment from its position in the implant cylinder.
RETRIEVAL
OF SOLID
APICAL
SECTION
To retrieve the solid apical section, a pinhole 1.5 to 2 mm deep is made at the center of the element’s resilient core. The pinhole is made with a regular Kodex drill (0.027 inch diameter, Whaledent International, New York, N.Y.), operated at low speed. A half round bur may be used to create an initial indentation in tbe core. This indentation helps to localize and prevent accidental slipping of the drill. The pinhole should parallel the long axis of the intramobile element or that of the implant cylinder so that the retrieving instrument can be centrally located within the implant cylinder. 94
Fig. 4. Modified fastening screw is firmly engaged to apical fragment of resilient intramobile element. Coronal section of resilient element is shown on right side of fastening screw. The retrieving instrument is a modified IMZ fastening screw (Fig. 3). The distal end of the fastening screw is trimmed to form a taper 2 mm in length, with three flat sides making a triangular cross section. The distal tip is further trimmed to a fine point to fit the pinhole. The fastening screw is located over the pinhole and tapped firmly into position. The triangular-shaped distal end of the fastening screw forms an antirotational device. With the fasJULY
1992
VOLUME
68
NUMBER
1
RETRIEVAL
OF RESILIENT
IMPLANT
ELEMENT
tening screw firmly engaged (Fig. 4), the apical sectioncan be unwound from the implant cylinder with a manually controlled contra-angled handpiece(KaVo, Biberach, Germany) fitted with a torque driver key and a short-shanked screwdriver tip (Nobelpharma, Goteborg, Sweden). After retrieval of the fractured fragment, a new intramobile element may be inserted. DISCUSSION The situation of the fractured solid resilient apical fragment is similar to that of a fractured gold abutment screw of the Brinemark implant system.3,7,8 In the Branemark system,the coronal surface of the broken screwis grooved horizontally before using a screwdriver to remove it3 Grooving, however, may causeaccidental damageto the internal threads of the IMZ implant cylinder. The resilient intramobile element is advantageous in that it allows wider distribution of forces exerted on the implant system during function.2,4,6 Becauseof its resilience,it alsoreducesundue bending of the fastening screw, thereby decreasingits potential to fracture-in contrast to a screwattachment to a rigid inner core.2a g To increasethe clinical longevity of the intramobile element, standard biomechanicaldesignrequirementsof the implant prosthesis should be observed. Implant design should take into consideration the expected extent of the interocclusal forces present in relation to the structural limitation of the resilient implant component. When high interocclusalforcesare present, an overengineeredimplant designis preferred.2-4 The threaded inner core of the intramobile element is hollow and should be reinforced throughout its entire internal length (7.5 mm). This is achieved by ensuring that the fastening screw engagesthe full length of the internal threads of the intramobile element. An overshortenedfastening screwmay leave someof the inner threads unused. This renders the section weak and likely to fracture. Loosening of the screwjoints or forced tightening of the screw threads may also predisposethe intramobile element to stressfracture.l*
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
CONCLUSION This article has described two methods of retrieving a fractured intramobile element without damagingthe IMZ dental implant cylinder. Incomplete retrieval of the resilient element or concomitant damageto the threads of the implant cylinder may compromiseits continued use as a restorative abutment. Wearegratefulto Mr. K. Nadarajanfor kindly fabricatingone of the instruments. REFERENCES 1. Smith DE, Zarb GA. Criteria for success of osseointegrated endosseous implants. J PROSTHET DENT 1989;62:567-72. 2. IMZ implant system technique manual. Irvine, Calif.: Interpore International, 1987. 3. Brdnemark P-I, Zarb G, Albrektsson T. Tissue-integrated prostheses. Chicago: Quintessence Publishing Co, 1985. 4. Babbush CA, Kirsch A, Mentag PJ, Hill B. Intramobile cylinder (IMZ) two-stage osteointegrated implant system with the intramobile element (IME): Part I. Its rationale and procedure for use. Int J Oral Maxillofac Implants 1987;2:203-16. 5. Jemt T, Lekholm U, Adell R. Osseointegrated implants in the treatment of partially edentulous patients: A preliminary study on 876 consecutively placed fixtures. Int J Oral Maxillofac Implants 1989;4:211-7. 6. Benzing U, Weber H, Geis-Gerstorfer J, Kirsch A. The mechanical load on IMZ implants. Fundamental problems of measurement technique and data collection. J Dent Implant 1987;3:858-61. 7. Sones AD. Complications with osseointegrated implants. J PROSTHET DENT 1989;62:581-5. 8. Gregory M, Murphy WM, Scott J, Watson CJ, Reeve PE. A clinical study of the Brlnemark dental implant system. Br Dent J 1990;168:1823.
9. McGlumphy EA, Campagni WV, Peterson LJ. A comparison of the stress transfer characteristics of a dental implant with a rigid or a resilient internal element. J PROSTHET DENT 1989;62:586-93. 10. Rangert B, Jemt T, Jarneus L. Forces and moments on Branemark implants. Int J Oral Maxillofac Implants 1989;4:241-7. Reprint
requests
to:
DR. RICHARD K. K. Ow DEPARTMENT OF RESTORATIVE DENTISTRY FACULTY OF DENTISTRY, NATIONAL UNIVERSITY OF SINGAPORE NATIONAL UNIVERSITY HOSPITAL LOWER KENT RIDGE RD. SINGAPORE 0511 SINGAPORE
95
of the resilient system
R. K. K.
Qw,
BDS,
MSc,”
and
K. H.
element Ho,
BDS,
in an osseointegrated
FDSRCPSb
Facuky of Dentistry, National University Hospital, Singapore A fractured apical fragment of dental implant cylinder is difficult implant will be compromised if Two methods of retrieving the internal threads of the implant 1992;68:93-5.)
the
resilient intramobile element within the IMZ to remove. The continued usefulness of the the fractured intramobile element is not removed. apical fragment without causing damage to the cylinder are described. (J PROSTHET DENT
T
he IMZ dental implant system (Interpore International, Irvine, Calif.) is one of several osseointegrated implant systems available for oral rehabilitation.lW5 It incorporates a resilient component, made of polyoxymethylene material, known as the intramobile element. It functions to retain the prosthesis and provide stress distribution.2, 4, 6 The components of the IMZ dental implant system are illustrated in Fig. 1. The resilient intramobile element is retained in the implant cylinder by its external screw threads. It also has an internal threading system to receive the bridge-fastening screw. The clinical life span of the resilient intramobile element is approximately a year, after which time replacement is recommended.2, 4 The intramobile element may undergo fatigue and fracture (often due to overloading), resulting in loosening of the prosthesis. Complete recovery of the fractured fragments is necessary. The coronal section of a fractured intramobile element can be retrieved from the implant cylinder by using standard IMZ instruments.2 However, the retrieval of the fractured apical section is difficult since standard instruments are unsuitable for this purpose. Attempted retrieval may cause accidental damage to the internal threads of the implant cylinder. The risk is increased if the fractured apical section is short and threaded deeply within the implant cylinder. Failure to retrieve the apical section also may prevent the continued use of the implant as a restorative abutment. The purpose of this article is to describe two methods of retrieval of the fractured apical section of the resilient intramobile element retained within the IMZ dental implant cylinder.
LEVEL
OF FRACTURE
The intramobile element, approximately 11 mm long, has internal and external screw threads (Fig. 1). Internal
aAssociate Professor, Department of Restorative Dentistry. bAssociate Professor, Department of Oral and Maxillofacial Surgery. IO/l/36541 THE
JOURNAL
OF PROSTHETIC
DENTISTRY
IME + FS
END ‘OF
INTERNAL
IMPLANT
1. Diagram shows prosthetic restoration (fixed partial denture or denture) constructed on implant. Resilient intramobile element (IME) is interposed between prosthesis and implant. Internal and external screw threads are shown in scalloped outline. Apical end of internal threads is as illustrated. Below this level the intramobile element consists of solid core with only external threads. Prosthesis is retained by fastening screw (FS) threaded into intramobile element. Transepithelial implant element (TIE) is coronal attachment to implant above alveolar bone, providing support for soft tissue cuff. Fig.
screw threads extend from the coronal and toward the apex for a distance of 7.5 mm, leaving the apical 3.5 mm fragment of the intramobile element as a solid core. The level of fracture will determine whether the apical fragment contains part of the internal threads. For convenience, a fracture line at 6 mm or less from the coronal end of the intramobile element will leave a hollow apical section with at least 1.5 mm of internal threads. This length of internal threads allows a retrieving instrument to engage and retrieve the fractured apical fragment. A lower level fracture occurring at 7.5 mm or more from the coronal end of 93
OW AND
Fig. 2. Small screwdriver (SD) is used to retrieve hollow threaded apical fragment of resilient intramobile element. Original fastening screw (FS) has thread size that matches internal threads of resilient element. Working end (arrow) of screwdriver should thus be wider than diameter of fastening screw.
HO
Fig. 3. Instruments used in retrieval of apical solid core of resilient intramobile element. Left to right: Original fastening screw, modified fastening screw, and Kodex drill bit. (Original fastening screw could not be used for this purpose but is shown for comparison.)
the intramobile element leaves a totally solid apical fragment without any internal screw threads. This poses considerable difficulty in its retrieval.
RETRIEVAL OF HOLLOW APICAL SECTION
THREADED
A small screwdriver (Fig. 2) was designed and fabricated for retrieving the hollow apical fragment. The tip of the screwdriver consists of a single rectangular blade with sharp side edges. The width of the blade is slightly larger than the internal diameter of the resilient intramobile element. When the screwdriver is pressed into the hollow apical fragment, the sharp sides of its blade engage the internal threads of the fragment. The screwdriver is then rotated to unwind the apical fragment from its position in the implant cylinder.
RETRIEVAL
OF SOLID
APICAL
SECTION
To retrieve the solid apical section, a pinhole 1.5 to 2 mm deep is made at the center of the element’s resilient core. The pinhole is made with a regular Kodex drill (0.027 inch diameter, Whaledent International, New York, N.Y.), operated at low speed. A half round bur may be used to create an initial indentation in tbe core. This indentation helps to localize and prevent accidental slipping of the drill. The pinhole should parallel the long axis of the intramobile element or that of the implant cylinder so that the retrieving instrument can be centrally located within the implant cylinder. 94
Fig. 4. Modified fastening screw is firmly engaged to apical fragment of resilient intramobile element. Coronal section of resilient element is shown on right side of fastening screw. The retrieving instrument is a modified IMZ fastening screw (Fig. 3). The distal end of the fastening screw is trimmed to form a taper 2 mm in length, with three flat sides making a triangular cross section. The distal tip is further trimmed to a fine point to fit the pinhole. The fastening screw is located over the pinhole and tapped firmly into position. The triangular-shaped distal end of the fastening screw forms an antirotational device. With the fasJULY
1992
VOLUME
68
NUMBER
1
RETRIEVAL
OF RESILIENT
IMPLANT
ELEMENT
tening screw firmly engaged (Fig. 4), the apical sectioncan be unwound from the implant cylinder with a manually controlled contra-angled handpiece(KaVo, Biberach, Germany) fitted with a torque driver key and a short-shanked screwdriver tip (Nobelpharma, Goteborg, Sweden). After retrieval of the fractured fragment, a new intramobile element may be inserted. DISCUSSION The situation of the fractured solid resilient apical fragment is similar to that of a fractured gold abutment screw of the Brinemark implant system.3,7,8 In the Branemark system,the coronal surface of the broken screwis grooved horizontally before using a screwdriver to remove it3 Grooving, however, may causeaccidental damageto the internal threads of the IMZ implant cylinder. The resilient intramobile element is advantageous in that it allows wider distribution of forces exerted on the implant system during function.2,4,6 Becauseof its resilience,it alsoreducesundue bending of the fastening screw, thereby decreasingits potential to fracture-in contrast to a screwattachment to a rigid inner core.2a g To increasethe clinical longevity of the intramobile element, standard biomechanicaldesignrequirementsof the implant prosthesis should be observed. Implant design should take into consideration the expected extent of the interocclusal forces present in relation to the structural limitation of the resilient implant component. When high interocclusalforcesare present, an overengineeredimplant designis preferred.2-4 The threaded inner core of the intramobile element is hollow and should be reinforced throughout its entire internal length (7.5 mm). This is achieved by ensuring that the fastening screw engagesthe full length of the internal threads of the intramobile element. An overshortenedfastening screwmay leave someof the inner threads unused. This renders the section weak and likely to fracture. Loosening of the screwjoints or forced tightening of the screw threads may also predisposethe intramobile element to stressfracture.l*
THE
JOURNAL
OF
PROSTHETIC
DENTISTRY
CONCLUSION This article has described two methods of retrieving a fractured intramobile element without damagingthe IMZ dental implant cylinder. Incomplete retrieval of the resilient element or concomitant damageto the threads of the implant cylinder may compromiseits continued use as a restorative abutment. Wearegratefulto Mr. K. Nadarajanfor kindly fabricatingone of the instruments. REFERENCES 1. Smith DE, Zarb GA. Criteria for success of osseointegrated endosseous implants. J PROSTHET DENT 1989;62:567-72. 2. IMZ implant system technique manual. Irvine, Calif.: Interpore International, 1987. 3. Brdnemark P-I, Zarb G, Albrektsson T. Tissue-integrated prostheses. Chicago: Quintessence Publishing Co, 1985. 4. Babbush CA, Kirsch A, Mentag PJ, Hill B. Intramobile cylinder (IMZ) two-stage osteointegrated implant system with the intramobile element (IME): Part I. Its rationale and procedure for use. Int J Oral Maxillofac Implants 1987;2:203-16. 5. Jemt T, Lekholm U, Adell R. Osseointegrated implants in the treatment of partially edentulous patients: A preliminary study on 876 consecutively placed fixtures. Int J Oral Maxillofac Implants 1989;4:211-7. 6. Benzing U, Weber H, Geis-Gerstorfer J, Kirsch A. The mechanical load on IMZ implants. Fundamental problems of measurement technique and data collection. J Dent Implant 1987;3:858-61. 7. Sones AD. Complications with osseointegrated implants. J PROSTHET DENT 1989;62:581-5. 8. Gregory M, Murphy WM, Scott J, Watson CJ, Reeve PE. A clinical study of the Brlnemark dental implant system. Br Dent J 1990;168:1823.
9. McGlumphy EA, Campagni WV, Peterson LJ. A comparison of the stress transfer characteristics of a dental implant with a rigid or a resilient internal element. J PROSTHET DENT 1989;62:586-93. 10. Rangert B, Jemt T, Jarneus L. Forces and moments on Branemark implants. Int J Oral Maxillofac Implants 1989;4:241-7. Reprint
requests
to:
DR. RICHARD K. K. Ow DEPARTMENT OF RESTORATIVE DENTISTRY FACULTY OF DENTISTRY, NATIONAL UNIVERSITY OF SINGAPORE NATIONAL UNIVERSITY HOSPITAL LOWER KENT RIDGE RD. SINGAPORE 0511 SINGAPORE
95