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Biomechanics/ dental implant courses

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Biomechanics/ dental implant courses

  2. 2. CONTENTS • Introduction • Definition • Types of biomechanics • Importance in field of dental implants • Methods to analyze and visualize stresses in bone • Biomechanics of natural teeth • Elements of mechanical properties • Force delivery and failure mechanism • Clinical moment arms and crestal bone loss • Bone as reactive recipient material • The bone repair mechanism • Endosseous implant • Biomechanical problems of implant-supported prostheses • Effects on treatment planning • Summary and conclusion
  3. 3. Biomechanics is one of the most important considerations affecting the design of framework for an implant –borne prosthesis. In general, the forces that participate in both the masticatory process and parafunction must be considered in the design of the prosthesis. These considerations act as determining factors of the device’s success or failure. INTRODUCTION
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  5. 5. WHAT ARE BIOMECHANICS? Biomechanics is the scientific study of the load-force relationships of a biomaterial in the oral cavity. (Ralph Mc Kinney). GPT-8 It is the relationship between the biologic behavior of oral structures and the physical influence of a dental restoration.
  6. 6. TYPES OF BIOMECHANICS TWO TYPES:- 1) Reactive Biomechanics: is the interaction of isolated biomechanical factors which when combined, produce an accumulative effect. 2) Therapeutic Biomechanics is the clinical process of altering each biomechanical factor to reduce the cumulative response causing implant overload.
  7. 7. IMPORTANCE IN THE FIELD OF DENTAL IMPLANTS: • First, to know the loading (bite forces) exerted on the prosthesis. • Secondly, to know the distribution of the applied forces to the implants and teeth supporting the prosthesis. • Thirdly, the force on each implant must be delivered safely to the bony tissues which in turn depend on the shape and size of the implant. In all these, the aim of biomechanical analysis is to foresee failure of any part of the system, including the prosthesis, the supporting implants and the biological tissues.
  8. 8. METHODS TO ANALYZE AND VISUALIZE STRESSES IN BONE Stress analysis can be performed:- • Experimentally e.g. Stress-optical examination • Theoretically & mathematically with computer simulation e.g. Finite-element method Stress-optical examination Implant to be analyzed is embedded in synthetic resin and stresses induced by loading are made visible by polarized light. Disadvantages are:- 1. Not possible in inhomogeneous structure of bone 2. Limited optical resolution
  9. 9. Finite-element method • The structures to be examined are subdivided into a finite number of elements of similar size that can be connected with each other at corner points, i.e. nodes. • The displacements and stresses at each node caused by loading can be calculated with a computer program. Advantages are:- 1. Allows inclusion of various materials with differing material properties. Most importantly, the inhomogeneous structure of bone, i.e. the subdivision into cortical and cancellous bone, can be taken into consideration. 2. Allows three-dimensional visualization of the calculated displacement and stresses.
  10. 10. BIOMECHANICS OF NATURAL TEETH The tooth is suspended syndesmotically within the alveolar bone by dentoalveolar bundles of collagen fibers. Because of its elasticity there is measurable horizontal, vertical, and rotational tooth mobility. Basically, tooth movement can be subdivided into two phases:- 1. Desmodontal phase:- referred to as the first stage of movement, taking place when a load of up to 100 N acts on the tooth. During this phase, the tooth moves slightly within the socket. Some periodontal fiber bundles are stretched, while others are relaxed. However, the alveolar process does not undergo marked deformation.
  11. 11. 2. Periodontal phase:- commences at loads exceeding 500 N. After the desmodontal phase has passed and the periodontal fiber bundles have been stretched to their full length, these strong forces cause deformation of the entire alveolar process, which subsequently offers more resistance to further tooth deflection. The degree of tooth deflection may vary from one individual to another and ranges between 10 and 50 µm.
  12. 12. Calculations of the stress distribution around natural teeth have shown that physiologic stresses result in a relatively even stress distribution. The exception is in the cervical region of the tooth, where horizontal loading with transfer of the compressive forces into the periodontium results in moderately high tensile stresses, and the lamina dura is affected by axial compressive stresses because of bending of the alveolar bone.
  13. 13. • Mass, is the degree of gravitational attraction the body of matter experiences. • Force was described by Newton. Newton's second law, states that the acceleration of a body is inversely proportional to its mass and directly proportional to the force that caused the acceleration. A α f m Therefore, F = ma • Weight is the gravitational force acting on an object at a Specified location. Weight and Force therefore can be expressed by the same units, newtons (N) or pound force (Ibf) ELEMENTS OF MECHANICAL PROPERTIES
  14. 14. FORCES • Forces may be described by magnitude, duration, direction, type, and magnification factors. • Forces acting on dental implants are referred to as vector quantities; that is, they possess both magnitude and direction. A force applied to a dental implant is rarely directed absolutely longitudinally along a single axis. In fact, forces are three dimensional with components directed along one or more of the three clinical coordinatethree clinical coordinate axesaxes i.e. :-
  15. 15.
  16. 16. Components of Forces (Vector Resolution) A single occlusal contact most commonly result in a three- dimensional occlusal force. The process by which three- dimensional forces are broken down into their component parts is referred to as vector resolution Types of Forces Forces may be described as :- 1. Compressive forces attempt to push masses toward each other. 2. Tensile forces pull objects apart. 3. Shear forces on implants cause sliding forces.
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  18. 18. • Compressive forces tend to maintain the integrity of a bone- to-implant interface, whereas tensile and shear forces tend to disrupt such an interface. • Shear forces are most destructive to implants and bone when compared with other load modalities. • Compressive forces, in general, are best accommodated by the complete implant-prosthesis system.
  19. 19. The implant body design transmits the occlusal load to the bone. Threaded or finned dental implants impart a combination of all three force types at the interface under the action of a single occlusal load. Cylindrical implants are at highest risk for harmful shear loads under an occlusal load directed along the long axis of the implant body. As a result, cylinder implants require a coating to manage the shear stress at the interface through a more uniform bone attachment along the implant length. Compressive forces should typically be dominant in implantCompressive forces should typically be dominant in implant prosthetic occlusion.prosthetic occlusion.
  20. 20. STRESS The manner in which a force is distributed over a surface is referred to as mechanical stress. Thus stress is defined by the familiar relation: Stress = F/A The internal stresses that develop in an implant system and surrounding biologic tissues have a significant influence on the long-term longevity of the implants in vivo. As a general rule of thumb, a goal of treatment planning should be to both minimize and evenly distribute mechanical stress in the implant system and the contiguous bone.
  21. 21. The magnitude of stress is dependent on two variables:- 1. force magnitude and 2. cross-sectional area over which the force is dissipated. Force magnitude • rarely be completely controlled by a dental practitioner. • The magnitude of the force may be decreased by reducing the significant "magnifiers of force“ :- cantilever length, offset loads, and crown height. Night guards to decrease nocturnal parafunction, occlusal materials that decrease impact force, and overdentures rather than fixed prosthesis so they may be removed at night are further examples of force reduction strategies.
  22. 22. Functional cross-sectional area is defined as that surface that participates significantly in load bearing and stress dissipation. It may be optimized by :- (1) Increasing the number of implants for a given edentulous site, and (2) Selecting an implant geometry that has been carefully designed to maximize functional cross-sectional area.
  23. 23. DEFORMATION AND STRAIN Strain is defined as the change in length divided by the original length. For tension and compression, strain expresses a lengthening and a shortening of the body respectively. In shear, the shape change is expressed in terms of a change in angle of one part of the body relative to the other. The deformation and strain characteristics of the materials used in implant dentistry may influence interfacial tissues, and clinical longevity. Elongation (deformation) of biomaterials used for dental implants range from 0% for aluminum oxide (Al2O3) to up to 55% for annealed 316-L stainless steel.
  24. 24. Related to deformation is the concept of strain—a parameter believed to be a key mediator of bone activity. All materials (both biologic and nonbiologic) are characterized by a maximum elongation possible before permanent deformation or fracture results.
  25. 25. STRESS-STRAIN CHARACTERISTICS: A relationship is needed between the applied force (and stress) and the subsequent deformation (and strain). If any elastic body is experimentally subjected to an applied load, a load-vs.-deformation curve may be generated. If the load values are divided by the surface area over which they act and the change in the length by the original length, a classic engineering stress-strain curve is produced.
  26. 26. Such a curve provides for the prediction of how much strain will be experienced in a given material under an applied load. The slope of the linear (elastic) portion of this curve is referred to as the modulus of elasticity (E), and its value is indicative of the stiffness of the material under study. The closer the modulus of elasticity of the implant resembles that of the biologic tissues, the less the likelihood of relative motion at the tissue-to-implant interface. Once a particular implant system (i.e., a specific biomaterial) is selected, the only way to control the strain is to control the applied stress or change the density of bone around the implant.
  27. 27. The greater the magnitude of stress applied, the greater the difference in strain between implant material and bone.
  28. 28. • When two bodies collide in a very small interval of time (fractions of a second), relatively large forces develop. Such a collision is described as impact. • In dental implant systems subjected to occlusal impact loads, deformation may occur in the prosthetic restoration, in the implant itself, or in the interfacial tissue. • The higher the impact load, the greater the risk of implant and bridge failure and bone fracture. • Rigidly fixed implants generates a higher impact force than a natural tooth with its periodontal ligament. Various methods have been proposed to address the issue of reducing implant loads. IMPACT LOADS
  29. 29. Skalak suggested the use of acrylic teeth in conjunction with osteointegrated fixtures Weiss has proposed that a fibrous tissue-to-implant interface provides for physiologic shock absorption in the same manner as by a functioning periodontal ligament. one implant design has attempted to incorporate shock absorption capability in the design itself, by the use of an "intramobile element" of lower stiffness compared with the rest of the implant. Misch advocates an acrylic provisional restoration with a progressive occlusal loading to improve the bone-to-implant interface before the final restoration, occlusal design, and masticatory loads are distributed to the system.
  30. 30. FORCE DELIVERY AND FAILURE MECHANISMS The manner in which forces are applied to implant restorations dictates the likelihood of system failure. If a force is applied some distance away from a weak link in an implant or prosthesis, bending or torsional failure may result from moment loads.
  31. 31. The moment of a force about a point tends to produce rotation or bending about that point. The moment is a vector quantity. Moment Loads = force magnitude X moment armMoment Loads = force magnitude X moment arm This imposed moment load is also referred to as a torque or torsional load and may be quite destructive with respect to implant systems. Moment Loads
  32. 32. Proper restorative design must necessarily include consideration of both forces and the moment loads caused by those forces. 100 N
  33. 33. "Clinical Moment Arms" and Crestal Bone Loss A total of six moments (rotations) may develop about the three clinical coordinate axes. faciolingual plane
  34. 34. Such moment loads induce microrotations and stress concentrations at the crest of the alveolar ridge at the implant-to-tissue interface, which leads to crestal bone loss. Three "clinical moment arms" exist in implant dentistry:- 1. Occlusal height, 2. Cantilever length, and 3. Occlusal width. Minimization of each of these moment arms is necessary to prevent unretained restorations, fracture of components, crestal bone loss, and/or complete implant system failure.
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  36. 36. Occlusal Height Moment Arm Occlusal height serves as the moment arm for force components directed along the faciolingual axis as well as along the mesiodistal axis.
  37. 37. Moment of a force along the vertical axis is not affected by the occlusal height because there is no effective moment arm. Offset occlusal contacts or lateral loads, however, will introduce significant moment arms.
  38. 38. • Large moments may develop from vertical axis force components in cantilever extensions or offset loads from rigidly fixed implants. • A lingual force component may also induce a twisting moment about the implant neck axis if applied through a cantilever length. Cantilever length moment arm
  39. 39.
  40. 40. • An implant with a cantilevers extending1 cm, 2 cm, and 3 cm has significant ranges of moment loads. • A 100-N force applied directly over the implant does not induce a moment load or torque because no rotational forces are applied through an offset distance. • This same 100-N force applied 1 cm from the implant results in a 100 N-cm moment load. • Similarly, if the load is applied 2 cm from the implant, a 200 N-cm torque is applied to the implant-bone region, and 3 cm results in a 300 N-cm moment load. • (Implant abutments are typically tightened with less than 30 N-cm of torque).
  41. 41. The distance from the center of the most anterior implant to the distal of each posterior implant is called the anteroposterior (AP) distance. The greater the A - P distance, the smaller the resultant load on the implant system from cantilevered forces, because of the stabilizing effect of the anteroposterior distance. According to Misch, the amount of stress applied to system is determined by the length of the distal cantilever. Nobel Biocare prosthetic protocol uses four to six anterior implants placed in front of the mental foramen or maxillary sinus and uses a full-arch fixed prosthesis with cantilevered segments.
  42. 42. Replacement of maxillary anterior teeth in a tapered arch form requires more posterior implants than in a square arch form, with less offset loading of mandibular teeth. A tapered arch form permits greater cantilever length than a square arch form in mandibular anterior region.
  43. 43. • The most ideal biomechanical arch form depends on the restorative situation:- • Tapering arch form is favorable for anterior implants with posterior cantilevers. • Square arch form is preferred when canine and posterior implants are used to support anterior cantilevers in either arch. • Ovoid arch form has qualities of both tapered and square arches. • Clinical experiences suggest that the distal cantilever should not extend 2.5 times the A-P distance under ideal conditions. • Patients with severe bruxism should not be restored with any cantilevers.
  44. 44. Occlusal Width Moment Arm Wide occlusal tables increase the moment arm for any offset occlusal loads. Faciolingual tipping (rotation) can be significantly reduced by narrowing the occlusal tables and/or adjusting the occlusion to provide more centric contacts. It can be summarized that a destructive cycle can develop with moment loads and result in crestal bone loss. Unless the bone increases in density and strength , the cycle continues towards implant failure if the biomechanical environment is not corrected.
  45. 45. BONE AS REACTIVE RECIPIENT MATERIAL Meier (1887) assumed that the trajectories within cancellous bone show the same direction as in the femur head. Wolff (1892) gave more clarity to Meier hypothesis and established it as law of nature. Roux (1895) suggested that natural tissues are capable of adapting to changing loading conditions because of a cellular regulation process. Depending on the magnitude of loading ,bone tissue cells either respond by bone formation or bone resorption. Later, Wolff’s hypothesis and Roux’s principle merged into one concept as Wolff’s Law. Today, practically all load related changes in the bone structure areToday, practically all load related changes in the bone structure are grouped together under termgrouped together under term remodelingremodeling and are associated withand are associated with Wolff’s Law.Wolff’s Law.
  46. 46. THE BONE REPAIR MECHANISM Pauwels hypothesis (1960) is based on the observation that bone responds to physiologically relevant long-term loading by increasing bone formation. If bone remains unloaded for the same period of time it will undergo resorption. If a physiologically relevant force acts on the bone, bone tries tobone tries to reduce strainreduce strain by bone apposition or reduction and by changing its cross section and stiffness. This is done by :- • Bone formation or resorption at surface [external or surface remodeling] • Altering the bone mineral content [internal remodeling]
  47. 47. As long as the mechanical stimulus remains within a certain physiologic limit, the system will maintain balance between bone resorption and new bone growth. Stress of 2.48x10N/mm² --- will cause increase in bone growth. Stress ranging 2.5x10 to 6.9x10N/mm2 – will lead to reduction of bone growth. Stress exceeding 6.9x10N/mm² -- will cause cell destruction.
  48. 48. To prevent bone resorption caused by biomechanical factors,forces should be as even as possible and not exceeding a maximum value of 2.5x10 N/mm². The balance can be regulated by both hormonal and mechanical factors. Several theories concern the effect of mechanical loads and repair mechanisms.
  49. 49. ENDOSSEOUS IMPLANT (OPEN IMPLANT SYSTEM) • The biomechanical conditions around an implant differ fundamentally from those around natural teeth. • While natural teeth are anchored within the socket by the fibers of the periodontal membrane, implants may show either direct bone bonding or connective tissue encapsulation.
  50. 50. Direct bone bonding • Can be achieved if implant is allowed to heal into bone in the absence of loading and new bone is oppositioned onto the implant surface. • Ankylotic-healing can be considered as one of the most important aspects of the force transfer mechanisms in osseointegrated implants because it prevents relative movement of implant and bone. • Close apposition of bone to the implant can even be observed in microasperities at the Angstrom level.
  51. 51. Connective tissue encapsulation • occurs if the implant is loaded immediately after having been placed. • Following long periods of function, the bone around endosseous implants can undergo resorption observed as funnel- shaped local areas of cortical bone reduction at the site where the implant enters bone. • Aside from inflammatory causes, bone resorption is mainly due to biomechanical factors.
  52. 52. Will the use of "isoelastic" implants result in more favorable stress conditions in bone than those observed when relatively stiff, conventional dental implants are used? Soltesz and Siegele (1982) as well as Moilgth et al (1989) have shown that :- • The global stress pattern remains the same when the material properties of an implant are changed. • Most stress values only show minor changes, except for the site where the implant enters bone. • The values obtained from implants made of bonelike substances are more than twice as high as those calculated for implants made of stiffer materials. Impact of implant stiffness on stress distribution
  53. 53.
  54. 54. All in all, the use of isoelastic implants cannot be recommended. On the contrary, implants should be as stiff as possible from the biomechanical standpoint, and should have modulus of elasticity of atleast 100,000N/mm². The stiffness of an implant can also be increased by choosing an implant of larger diameter. If the diameter is increased by 30%, implant stiffness will be five times higher, and the stresses around the implant neck are thus reduced.
  55. 55. Impact of implant shape on stress distribution The stress conditions around an implant can also be improved by selecting an appropriate implant shape. Endosteal dental implant designs may be generally considered as blade or root form. The neck design in either implant system (i.e. root form & blade form) is particularly important in the consideration of implant geometry because the physiologic load is transmitted through the neck region to the implant body and the surrounding tissues. As the cross-sectional area of the neck decreases, the stress levels in the neck and the surrounding tissues increases. ( stress= force/area.)
  56. 56. The implant body must exhibit a macrogeometry suitable for force transfer to the surrounding tissues as well as for implantation into a bony site of a particular anatomic size. When viewed from the broad end, blade implants show a relatively favorable stress pattern, when viewed from the front, they exhibit an extremely unfavorable stress pattern, particularly with regard to horizontal forces.
  57. 57. Because force transfer into bone should be as even as possible, implants showing rotational symmetry can be considered more favorable from the biomechanical point of view. However, this imposes size constraints on the geometry of the implantation site. Blade implants are designed to serve in those bony sites which are too narrow to accommodate root form implants. However , they have reduced cross-sectional area available to resist axial loads as compared to root form implants.
  58. 58. Perforations or "vents" in the body of an endosteal dental implant provide a means for bone in growth into the device with resultant stabilization of the implant within the tissues. In blade form implants, vents also serve to increase the amount of cross-sectional area available to resist axial loads.
  59. 59.
  60. 60. Impact of implant surface on stress distribution Osteolytic loosening of an implant may result from selection of a biomechanically unfavorable implant shape. Because endosseous implants lack the natural attachment to bone, this missing periodontal function must be compensated for by minimization of the specific surface pressure (snowshoe principle). This means that implant surface used for force transfer should be as large as possible. To minimize the compressive forces, the implant surface can be enlarged by:- •Applying threads •Plasma flame spray coating •Surface roughening •Acid etching
  61. 61. Another factor that influences the size of the surface area is the length of the implant. Albrektsson et al (1983) revealed a clear correlation between the length of an implant and implant prognosis. Implants with a length of less than 10mm showed a markedly worse prognosis than did implants whose length exceeded 10 mm. This may be due to the fact that short implants have a considerably smaller surface area and are affected by markedly higher moments.
  62. 62. BIOMECHANICAL PROBLEMS OF IMPLANT-SUPPORTED PROSTHESES Connecting implants with natural teeth In a combined tooth-implant prosthesis, force distribution depends on whether, the main load is borne by the tooth or the implant . • If the superconstruction above the implant is affected by vertical loads, load transfer will take place almost exclusively via implant, the natural tooth only being used minimally as support.
  63. 63. Use of an implant with an integrated elastic layer, i.e. an intramobile element can reduce the stresses. From the prosthodontic point of view, whenever possible avoid a rigid connection between implant and tooth and use purely implant-supported superconstructions instead. • lf the same vertical load acts on the portion of the prosthesis above the tooth, the load distribution will differ from the one previously described. In this case, the prosthesis acts as a lever arm. The tooth is affected both by vertical force and torque and can slightly sink into the socket .
  64. 64. Purely implant-supported prostheses Implant-supported prostheses seem to involve fewer biomechanical problems. However, there are many aspects that need to be clarified, because: 1. The prosthesis must follow the arched shape of the mandible. 2. The implants cannot be considered an ideal rigid system. 3. The mandible undergoes functional deformation.
  65. 65. One of the most common indication for implant treatment is the atrophic edentulous mandible. Aside from the widely used bar-joint dentures, fixed implant-supported prostheses with a posterior cantilever are gaining increasing importance. The number of implants to be placed can be calculated from the space available between the two mental foramina and the distance between the implants postulated by Branemark et al (1985). Because the mean distance between the two mental foramina is 47 mm and the distance from the center of one implant to that of the adjacent implant should be 7 mm, up to six implants can be placed.
  66. 66. The author's (Mailath-Pokorny/Solar) own finite-element analyses have shown that :- 1. The maximum shear stress and moments can be observed in the implant closest to the site of force impact and the effects on all other implants can even be ignored. 2. When the distribution and density of stress on a prosthesis supported by four implants are compared with those supported by six implants, the additional procedures needed for placement of the two additional implant do not seem to be justified.
  67. 67.
  68. 68. 3. Prolongation of the cantilever by more than two times the width of a premolar tooth results in unfavorable loading condition because of lever arm effect. It seems to be sensible to use cantilever prostheses whose free end is not longer than two times the width of a premolar tooth. 4. Also, the use of six implants would not improve the unfavorable loading conditions caused by a long cantilever.
  69. 69. EFFECTS ON TREATMENT PLANNING 1) The most common complications in implant dentistry, once the prosthesis is delivered are, bone loss, fracture of occlusal materials or implant components, and unretained restorations. These problems are primarily related to increases in stress. Therefore once the sources of additional force are identified on the implant system, the treatment plan is altered to lower their negative impact on the implant, bone, and final restoration.
  70. 70. 2) Stress can be reduced by using Additional implants, rather than only an increase in implant width or height. This will:- • decrease the number of pontics and the associated mechanics and strains on the prosthesis. • dissipate stresses more effectively to the bone structure, especially in crestal region. • retention of the final prosthesis or superstructure is further improved. • The amount of bone in contact with the implant is also increased as a multiple of the number of implants. • Also, Increase in implant width is preferable to length as lesser stresses transmitted to crestal bone.
  71. 71. Panoramic radiograph of mandibular fixed prosthesis opposing natural dentition. Posterior implants are used as abutments rather than cantilevers to decrease stress on implants and prosthesis. No second molars are provided to decrease stress.
  72. 72. 3) Forces from bruxism are often the most difficult forces to control. Crestal bone loss, unretained abutments, and fatigue stress fractures of implants or prostheses are more likely a result of this condition. The implant treatment plan is modified primarily in two ways when implants are inserted in the posterior region. • Additional implants and occlusal considerations are both primordial. • The elimination of posterior lateral occlusal contacts during excursive movements is recommended when opposing natural teeth or an implant or tooth supported fixed prostheses.
  73. 73. • The anterior teeth may be modified to recreate the proper incisal guidance and avoid posterior interferences during excursions. • Use of a night guard is helpful for the bruxism patient with fixed prostheses. • Anterior-guided disocclusion of the posterior teeth in excursions is strongly suggested in the night guard, which may be designed for the maxilla or mandible.
  74. 74. • A removable partial denture over a healing implant is especially of concern. These patients often have many remaining teeth and higher forces are transmitted to the soft tissue regions that support the restorations. The acrylic between the soft tissue-borne region and metal substructure is usually less than 2 mm thick. • Removing the thin acrylic region over the implant is often not sufficient. Instead, a 6-mm diameter hole through the metal substructure should be prepared. In this manner, a bruxing patient will not load the submerged implant during healing.
  75. 75. 4) The time Intervals between prosthodontic restoration appointments may be increased to provide additional time to produce load-bearing bone around the implants through progressive bone-loading techniques. • Anterior implants submitted to lateral parafunction forces require further treatment considerations. Additional implants are indicated, preferably of greater diameter.
  76. 76. • The excursions are canine guided if natural, healthy canines are present. • Mutually protected occlusion is developed if the implants are in the canine position or if this tooth is restored, as a pontic. • A first premolar may also disocclude the remaining posterior teeth when the patient is in skeletal Class II or when anterior implants are small in size or number
  77. 77. 5) Prosthesis may be designed to improve the distribution of stress throughout the implant system. • Centric vertical contacts should be aligned with the long axis of the implants whenever possible. • The posterior occlusal tables may be narrowed to prevent inadvertent lateral forces, and to leave greater space for the tongue. • Enameloplasty of the cusp tips of the opposing natural teeth is done to improve the direction of vertical forces.
  78. 78. 6) A Lateral tongue thrust is most detrimental if horizontal forces are applied to the implant during the early stages of interface formation. Submerged, two-phase, rigid, fixated implants are indicated.
  79. 79. 7) Inadequate bone height for endosteal implants usually means a higher crown height and extension of the implant substructure. These permucosal abutment posts are subject to increased lateral oral forces. valid treatment alternatives are:- • Myofunctional therapy and/or autogenous bone grafts to modify the bone type. • cantilevered bridges from the anterior teeth or implants. • conventional removable partial dentures.
  80. 80. SUMMARY AND CONCLUSION The most common complications in implant-related reconstruction are related to biomechanical conditions. The manifestation of biomechanical loads on dental implants (moments, stress, and strain) controls the long- term health of the bone-to-implant interface. Knowledge of basic biomechanical principles is thus required for the dentist.
  81. 81. • Biomechanics in clinical dentistry -Angelo. A CapitoAngelo. A Capito • Contemporary implant dentistry - Carl E Misch Ed 2nd.Carl E Misch Ed 2nd. • Oral rehabilitation with implant supported prostheses- Vicente jimenez- LopezVicente jimenez- Lopez • Endosteal Dental Implants -Ralf V McKinney JrRalf V McKinney Jr • Endosseous implants- Georg WatzekGeorg Watzek • Dental implant prosthetics - Carl E MischCarl E Misch REFERENCES
  82. 82.