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Biomechanical considerations in implant prosthodontics
MAXILLOFACIAL SECTION
PROSTHETICS
l
DENTAL IMPLANTS
EDITORS
I. KENNETH ADISMAN
RONALD P. DESJARDINS
Biomechanical considerations in implant prosthodontics Anthony W. Rinaldi, D.D.S.,* Harvey J. Goldberger, D.M.D.,** Ernest B. Mingledorff, D.D.S.,**’ Carolanne Craig, D.D.S.,**** and David Donatelli, D.D.S.***** Temple University, School of Dentistry, Philadelphia, Pa.
I
mplants can provide the partially edentulous patient with favorable support for a fixed prosthesis. To successfully design a prosthesis supported by an implant abutment(s), the dentist must consider the same biomechanical principles that are applied to fixed prosthodontics. l-3 Span deflection and the Class I lever, two biomechanical principles that apply to the selection and placement of implants as well as the design of a fixed prosthesis, will be considered.
DEFLECTION= (LENGTH)~ LENGTH= L = 1 MFLECTION = Lt3) = lt3) DEFLECTION= 1
SPAN DEFLECTION The deflection of a beam is directly proportional to the cube of its length (Fig. 1).3s4A fixed prosthesis with one pontic, L = 1, will deflect with a magnitude of 1. A fixed prosthesis with two pontics, 2L = 2, will deflect eight times that of a prosthesis with one pontic (Fig. 2). A fixed prosthesis with three pontics, 3L = 3, will deflect 27 times that of a prosthesis with one pontic (Fig. 3). The deflection of a beam is indirectly proportional to the cube of its depth (Fig. 4).3,4A fixed prosthesis with half the average occlusogingival depth will deflect eight times that of a prosthesis of average width and comparable length (Fig. 5). A fixed prosthesis with one third the average occlusogingival depth will deflect 27 times that of a prosthesis of average width and comparable length (Fig. 6). Because an endosteal implant is rigid in bone, torque
Fig. 2. If length of a beam is doubled, deflection is eight times greater.
*Clinical Professor and Course Director, Postgraduate Fixed Partial Prosthodontics. **Postgraduate candidate, Department of Fixed Partial Prosthodontics. ***Professor and Chairman, Department of Fixed Partial Prosthodontics. ****Instructor Department of Fixed Partial Prosthodontics. *****Postgraduate candidate, Department of Removable Prosthodontics.
transmitted through the implant is greater than force transmitted through a natural abutment cushioned by its periodontal ligament. To decrease its deflection, the dentist must increase the rigidity of an implantsupported prosthesis (Figs. 7 and 8). The increased rigidity will minimize torque generated to the supporting structures and reduce cement wash.
220
Fig. 1. If length of a beam is 1, deflection is 1.
DEFLECTION= (LENGTH)' DEFLECTION= (2Lj3 DEFLECTION= (2j3 = 8
AUGUST
1983
VOLUME
50
NUMBER
2
IMPLANT
PROSTHODONTICS
DEFLECTION= (LENBTH)~ DEFLECTION= (3L13 DEFLECTION= (3j3 = 27
Fig. 3. If length of a beam is tripled,
deflection
is 27
times greater.
Fig. 7. Span deflection abutments.
transmits
torque
to implant
(Dmd3
1
DE~H =D-
OEFLECTICH-
1
.1
(113
Fig. 4. If depth of a beam is 1, deflection
DEPTH =
__
is 1.
Fig. 8. Torque is decreased by decreasing span length or increasing span depth.
D
2 DEFLECTION= 1
Fig. 5. If depth of a beam is halved, deflection
= 8
is eight
times greater.
DEFLECTION=
1
Fig. 9. A natural abutment in fulcrum position creates a Class I lever.
(kPTd3 DEPTH =
D 3
DEFLECTIDN=
1
= 27
t3
Fig. 6. If depth of a beam is one third, 27 times greater.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
deflection
is
CLASS I LEVER SYSTEM Pier abutments create a Class I lever system (Fig. 9). x4 Implants can be used to provide added support and to counteract span deflection. However, this application of implants also creates a Class I lever (Fig. 10).
221
RINALDI
ET AL
Fig. 12. Use of a double-headed implant to reduce a Class I lever.
Fig. 10. An implant abutment in fulcrum also creates an accentuated Class I lever.
position
n
aA4 z
L
I
Fig. 13. Effects of a Class I lever reduced with nonrigid connector. Fig. 11. Class I lever effect is reduced with a nonrigid connector.
The movement about the fulcrum can cause cement wash and transmit torque to the other abutments. When the pier abutment is a natural tooth, stress at the fulcrum can be reduced with a nonrigid connector (Fig. 11).5s6Because implants are more rigid in bone than natural abutments, accentuated fulcrums are created when implants are used in the pier position. This situation may be changed if either an alternate blade design or a semiprecision attachment is used (Figs. 12 and 13).5,6 SUMMARY The dentist who uses implants in conjunction with natural abutment teeth should apply the same princi222
a
ples and guidelines that have proved themselves in fixed and removable prosthodontics. This article reviewed the basic biomechanical principles of span deflection and Class I lever systems as they may apply to fixed prosthodontics with and without implant abutments.
REFERENCES 1. Perel, M. L.: Prosthetic adaptations for dental implants. In Babbush, C.: Implants. Dent Clin North Am 24~401, 1980. 2. Perel, M. L.: Prosthodontic consideration of dental implants. In Perel, M. L., editor: Dental Implantology and Prostheses. Philadelphia, 1977, J. B. Lippincott Co., pp 139-154. 3. Shillingburg, H. T., Hobo S., and Whitsett, L.: Fundamentals of Fixed Prosthodontics, ed 2. Chicago, 1981, Quintessence Publishing Co., pp 25-30.
AUGUST
1983
VOLUME
50
NUMBER
2
IMPLANT
PROSTHODONTICS
Reprint ?wpJfJ to:
4.
Smyd, E. S.: Mltchanics of dental structures: Guide to teaching dental engineering at undergraduate level. J PROSTHET DENT 2:668, 1952. 5. Shillingburg, H. T., and Fisher, D. W.: Nonrigid connectors for fixed partial dentures. J Am Dent Assoc 87:1195, 1973. 6. Markley, M. R..: Broken-stress principle and design in fixed bridge prosthesis. J PROSTHET DENT 1:416, 1951.
DR. ANTHONY W. RINALDI TEMPLE UNIVERSITY SCHOOL OF DENTISTRY PHILAUELPHIA, PA 19140
ARTICLES TO APPEAR IN FUTURE ISSUES Surgical and prosthodontic edentulous patient
reconstruction
of the severely handicapped
Roger Masella, D.D.S., M.S.D., and Paul Mercier, D.D.S., F.R.C.D.(C)
Clinical evaluation of the mandibular Robert E. McKinstry,
D.M.D.,
staple bone plate
and Mohamed A. Aramany, D.M.D.,
The anterior fixed provisional
MS.
restoration: A direct method
Steven D. Miller, D.D.S.
Determination
of the accuracy of laminated wax interocclusal wafers
Philip L. Millstein,
D.M.D.,
Interfacial
M.S., and R. Ernest Clark, Ph.D.
bonding strengths of paired composite systems
F. J. Miranda, D.D.S., M.Ed., M.B.A., M. G. Duncanson, Jr., D.D.S., Ph.D., and W. E. Dilts, D.M.D.
Stress-relaxation testing. Part IV: Clasp pattern dimensions and their influence on clasp behavior H. F. Morris, D.D.S., M.S., K. Asgar, Ph.D., J. S. Brudvik, D.D.S., S. Winkler, D.D.S., and E. P. Roberts
Marginal leakage of contemporary
cementing agents
Michael L. Myers, D.M.D., Robert S. Staffanou, D.D.S., M.S., John H. Hembree, Jr., D.D.S., and William B. Wiseman, D.D.S.
A method of studying the effect of adhesives on denture retention R. K. K. Ow, B.D.S., M.Sc., and E. M. Bearn, L.D.S., M.D.S.
The use of graphoanalysis
for complete denture patient evaluation
P. J. Potgieter, B.Ch.D., M.Sc., and P. D. Carey, B.D.S., H.D.D.,
M.Dent.
Statistical study of the angle formed by the lateral part of the mandibular condyle and the horizontal plane G. Preti, M.D., D.D.S., C. Bruscagin, M.D., D.D.S., R. Scotti, M.D., D.D.S., and E. Cardesi, M.D., D.D.S.
An indirect technique for fabricating a crown under an existing clasp Edwa.rd R. Raskin, D.D.S. THE JOURNAL
OF PROSTHETIC
DENTISTRY
223
PROSTHETICS
l
DENTAL IMPLANTS
EDITORS
I. KENNETH ADISMAN
RONALD P. DESJARDINS
Biomechanical considerations in implant prosthodontics Anthony W. Rinaldi, D.D.S.,* Harvey J. Goldberger, D.M.D.,** Ernest B. Mingledorff, D.D.S.,**’ Carolanne Craig, D.D.S.,**** and David Donatelli, D.D.S.***** Temple University, School of Dentistry, Philadelphia, Pa.
I
mplants can provide the partially edentulous patient with favorable support for a fixed prosthesis. To successfully design a prosthesis supported by an implant abutment(s), the dentist must consider the same biomechanical principles that are applied to fixed prosthodontics. l-3 Span deflection and the Class I lever, two biomechanical principles that apply to the selection and placement of implants as well as the design of a fixed prosthesis, will be considered.
DEFLECTION= (LENGTH)~ LENGTH= L = 1 MFLECTION = Lt3) = lt3) DEFLECTION= 1
SPAN DEFLECTION The deflection of a beam is directly proportional to the cube of its length (Fig. 1).3s4A fixed prosthesis with one pontic, L = 1, will deflect with a magnitude of 1. A fixed prosthesis with two pontics, 2L = 2, will deflect eight times that of a prosthesis with one pontic (Fig. 2). A fixed prosthesis with three pontics, 3L = 3, will deflect 27 times that of a prosthesis with one pontic (Fig. 3). The deflection of a beam is indirectly proportional to the cube of its depth (Fig. 4).3,4A fixed prosthesis with half the average occlusogingival depth will deflect eight times that of a prosthesis of average width and comparable length (Fig. 5). A fixed prosthesis with one third the average occlusogingival depth will deflect 27 times that of a prosthesis of average width and comparable length (Fig. 6). Because an endosteal implant is rigid in bone, torque
Fig. 2. If length of a beam is doubled, deflection is eight times greater.
*Clinical Professor and Course Director, Postgraduate Fixed Partial Prosthodontics. **Postgraduate candidate, Department of Fixed Partial Prosthodontics. ***Professor and Chairman, Department of Fixed Partial Prosthodontics. ****Instructor Department of Fixed Partial Prosthodontics. *****Postgraduate candidate, Department of Removable Prosthodontics.
transmitted through the implant is greater than force transmitted through a natural abutment cushioned by its periodontal ligament. To decrease its deflection, the dentist must increase the rigidity of an implantsupported prosthesis (Figs. 7 and 8). The increased rigidity will minimize torque generated to the supporting structures and reduce cement wash.
220
Fig. 1. If length of a beam is 1, deflection is 1.
DEFLECTION= (LENGTH)' DEFLECTION= (2Lj3 DEFLECTION= (2j3 = 8
AUGUST
1983
VOLUME
50
NUMBER
2
IMPLANT
PROSTHODONTICS
DEFLECTION= (LENBTH)~ DEFLECTION= (3L13 DEFLECTION= (3j3 = 27
Fig. 3. If length of a beam is tripled,
deflection
is 27
times greater.
Fig. 7. Span deflection abutments.
transmits
torque
to implant
(Dmd3
1
DE~H =D-
OEFLECTICH-
1
.1
(113
Fig. 4. If depth of a beam is 1, deflection
DEPTH =
__
is 1.
Fig. 8. Torque is decreased by decreasing span length or increasing span depth.
D
2 DEFLECTION= 1
Fig. 5. If depth of a beam is halved, deflection
= 8
is eight
times greater.
DEFLECTION=
1
Fig. 9. A natural abutment in fulcrum position creates a Class I lever.
(kPTd3 DEPTH =
D 3
DEFLECTIDN=
1
= 27
t3
Fig. 6. If depth of a beam is one third, 27 times greater.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
deflection
is
CLASS I LEVER SYSTEM Pier abutments create a Class I lever system (Fig. 9). x4 Implants can be used to provide added support and to counteract span deflection. However, this application of implants also creates a Class I lever (Fig. 10).
221
RINALDI
ET AL
Fig. 12. Use of a double-headed implant to reduce a Class I lever.
Fig. 10. An implant abutment in fulcrum also creates an accentuated Class I lever.
position
n
aA4 z
L
I
Fig. 13. Effects of a Class I lever reduced with nonrigid connector. Fig. 11. Class I lever effect is reduced with a nonrigid connector.
The movement about the fulcrum can cause cement wash and transmit torque to the other abutments. When the pier abutment is a natural tooth, stress at the fulcrum can be reduced with a nonrigid connector (Fig. 11).5s6Because implants are more rigid in bone than natural abutments, accentuated fulcrums are created when implants are used in the pier position. This situation may be changed if either an alternate blade design or a semiprecision attachment is used (Figs. 12 and 13).5,6 SUMMARY The dentist who uses implants in conjunction with natural abutment teeth should apply the same princi222
a
ples and guidelines that have proved themselves in fixed and removable prosthodontics. This article reviewed the basic biomechanical principles of span deflection and Class I lever systems as they may apply to fixed prosthodontics with and without implant abutments.
REFERENCES 1. Perel, M. L.: Prosthetic adaptations for dental implants. In Babbush, C.: Implants. Dent Clin North Am 24~401, 1980. 2. Perel, M. L.: Prosthodontic consideration of dental implants. In Perel, M. L., editor: Dental Implantology and Prostheses. Philadelphia, 1977, J. B. Lippincott Co., pp 139-154. 3. Shillingburg, H. T., Hobo S., and Whitsett, L.: Fundamentals of Fixed Prosthodontics, ed 2. Chicago, 1981, Quintessence Publishing Co., pp 25-30.
AUGUST
1983
VOLUME
50
NUMBER
2
IMPLANT
PROSTHODONTICS
Reprint ?wpJfJ to:
4.
Smyd, E. S.: Mltchanics of dental structures: Guide to teaching dental engineering at undergraduate level. J PROSTHET DENT 2:668, 1952. 5. Shillingburg, H. T., and Fisher, D. W.: Nonrigid connectors for fixed partial dentures. J Am Dent Assoc 87:1195, 1973. 6. Markley, M. R..: Broken-stress principle and design in fixed bridge prosthesis. J PROSTHET DENT 1:416, 1951.
DR. ANTHONY W. RINALDI TEMPLE UNIVERSITY SCHOOL OF DENTISTRY PHILAUELPHIA, PA 19140
ARTICLES TO APPEAR IN FUTURE ISSUES Surgical and prosthodontic edentulous patient
reconstruction
of the severely handicapped
Roger Masella, D.D.S., M.S.D., and Paul Mercier, D.D.S., F.R.C.D.(C)
Clinical evaluation of the mandibular Robert E. McKinstry,
D.M.D.,
staple bone plate
and Mohamed A. Aramany, D.M.D.,
The anterior fixed provisional
MS.
restoration: A direct method
Steven D. Miller, D.D.S.
Determination
of the accuracy of laminated wax interocclusal wafers
Philip L. Millstein,
D.M.D.,
Interfacial
M.S., and R. Ernest Clark, Ph.D.
bonding strengths of paired composite systems
F. J. Miranda, D.D.S., M.Ed., M.B.A., M. G. Duncanson, Jr., D.D.S., Ph.D., and W. E. Dilts, D.M.D.
Stress-relaxation testing. Part IV: Clasp pattern dimensions and their influence on clasp behavior H. F. Morris, D.D.S., M.S., K. Asgar, Ph.D., J. S. Brudvik, D.D.S., S. Winkler, D.D.S., and E. P. Roberts
Marginal leakage of contemporary
cementing agents
Michael L. Myers, D.M.D., Robert S. Staffanou, D.D.S., M.S., John H. Hembree, Jr., D.D.S., and William B. Wiseman, D.D.S.
A method of studying the effect of adhesives on denture retention R. K. K. Ow, B.D.S., M.Sc., and E. M. Bearn, L.D.S., M.D.S.
The use of graphoanalysis
for complete denture patient evaluation
P. J. Potgieter, B.Ch.D., M.Sc., and P. D. Carey, B.D.S., H.D.D.,
M.Dent.
Statistical study of the angle formed by the lateral part of the mandibular condyle and the horizontal plane G. Preti, M.D., D.D.S., C. Bruscagin, M.D., D.D.S., R. Scotti, M.D., D.D.S., and E. Cardesi, M.D., D.D.S.
An indirect technique for fabricating a crown under an existing clasp Edwa.rd R. Raskin, D.D.S. THE JOURNAL
OF PROSTHETIC
DENTISTRY
223