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implant protective occlusion in prosthodontics

The document presents an extensive overview of occlusal considerations for implant-supported prostheses, emphasizing the importance of meticulous planning in the rehabilitation process. Key topics include various occlusal schemes, mechanical stress and its effects on bone, and guidelines for maximizing implant longevity through optimal occlusal load management. The conclusion stresses the need for careful design to minimize risks associated with implant prosthetics.

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OCCLUSAL CONSIDERATIONS FOR IMPLANT- SUPPORTED PROSTHESIS PRESENTED BY DR. RAJ SALVI GUIDED BY DR. JYOTI TEMBHURNE DR. MANISH CHAUHAN
CONTENTS  INTRODUCTION  OCCLUSAL SCHEMES  IMPLANT PROTECTIVE OCCLUSION(IPO)  OCCLUSAL CONSIDERATIONS FOR FIXED IMPLANT PROSTHESIS Premature occlusal contacts Implant body orientation Force direction and bone mechanics Prosthetic angled loads Posterior crown cusp angle
Mutually protected articulation Cantilevers and IPO Crown height and IPO Posterior implant crown contour Posterior occlusal contact positions Timing of occlusal contacts Design to the weakest arch  CONCLUSION
INTRODUCTION  Rehabilitation using implant supported prosthesis involves multiple steps and meticulous planning.  Once surgical placement is done, the long term success of implant has been associated to restorative dentist’s knowledge of prosthetic dentistry.  The mechanical setting in which implant function, mechanical stress/ strain > bone loss. 1) Misch CE: Early crestal bone loss etiology and its effect on treatment planning for implants, Postgrad Dent 3:3–17, 1995. 2) Isidor F: Loss of osteointegration caused by occlusal load of oral implants, Clin Oral Implants Res 7:143–152, 1996.
 Occlusal setting determines the mechanical stress.  The treatment plan > design, number and position > occlusal load on implant.  Implant rehabilitation is occlusal scheme that minimizes risk factors and allows the restoration to function in harmony with the rest of the stomatognathic system. 1) Isidor R: Histological evaluation of peri-implant bone at implants subjected to occlusal overload or plaque accumulation, Clin Oral Implants Res 8:1–9, 1997. 2) Rangert B, Krogh PH, Langer B, et al: Bending overload and implant fracture: a retrospective clinical analysis, Int J Oral Maxillofac Implants 7:40–44, 1995.
Why do we read so much about stress..??? Dental Implant Prosthetics, Carl E Misch, 2nd edition.
Attachment Proprioception Load bearing characteristic Fulcrum to lateral forces Modulus of elasticity Movement (primary & secondary) Anatomy and cross section Surrounding bone
Occlusal schemes Balanced Mutually protected Group function O c c l u s i o n Osseointegration and occlusal rehabilitation, Sumiya Hobo.
Balanced occlusion The bilateral simultaneous anterior and posterior occlusal contact of teeth in centric and eccentric positions. The glossary of prosthodontic terms. J Prosthet Dent 2005; 94:10–92.
Mutually protected occlusion An occlusal scheme in which the posterior teeth prevent excessive contact of the anterior teeth in maximum intercuspation and the anterior teeth disengage the posterior teeth in all mandibular excursive movements.  Posterior teeth protect the anterior teeth in centric position  Incisors protect the canine and posterior teeth during protrusive movement  canines protect the incisors and posterior teeth during lateral movements Osseointegration and occlusal rehabilitation, Sumiya Hobo.
Group functional occlusion Multiple contact relationship between maxillary and mandibular in lateral movements on working side, where by simultaneous contact of several teeth acts as a group to distribute occlusal forces.  Often encountered in elderly patients.  Provides a harmonious balance to structures of stomatognathic system.
OCCLUSAL SCHEME IN IMPLANT PROSTHESIS The implant-protective occlusion (IPO) concept refers to an occlusal plan specifically designed for the restoration of endosteal implants, providing an environment for reduced biomechanical complications and improved clinical longevity of both the implant and prosthesis. medial-positioned; lingualized occlusion 1) Misch CE, Bidez MW: Implant protected occlusion: a biomechanical rationale, Compend Contin Dent Educ 15:1330– 1343, 1994. 2) Misch CE: Occlusal considerations for implant-supported prostheses. In Misch CE, editor: Contemporary implant dentistry, St Louis, 1993, Mosby. 3) Misch CE: Medial positioned lingualized occlusion. In Misch Institute manual, Birmingham, Mich, 1991. GOAL: Maintain occlusal load within physiologic and biomechanical limit.
Electromyograms demonstrated that the implant patient has similar muscle activation on heavy occlusion on working and nonworking sides as patients with natural dentition. Therefore, it appears logical to derive implant occlusion from occlusal principles for the natural dentition. Gartner JL, Mushimoto K, Weber HP, et al: Effect of osseointegrated implants in the coordination of masticatory muscles: a pilot study, J Prosthet Dent 84:185–193, 2000 Where do we derive the idea of implant occlusion??
Principles Of Implant Protected Occlusion
OCCLUSAL CONSIDERATIONS FOR FIXED IMPLANT PROSTHESIS  Maximum intercuspation  Centric occlusion  This may or may not coincide in a patient As a general rule, the more teeth to be replaced or restored , the more likely the patient is restored to CO.
PREMATURE OCCLUSAL CONTACTS  Stress= force/area  No premature contacts on implant system  Localized lateral loading.  Even a small premature contact, magnitude a stress increases proportionately {S = F/A}  Inclined plane > the horizontal component > the shear stresses Dental Implant Prosthetics, Carl E Misch, 2nd edition.
 In parafunction > duration and magnitude of occlusal forces  The elimination of premature contact is more critical than in natural teeth because of lack of proprioception and the implant inability to move and dissipiate forces. Dental Implant Prosthetics, Carl E Misch, 2nd edition.
1) cervical abfraction and recession present 2) buccal cusp inclines needs to be adjusted.
IMPLANT BODY ORIENTATION  Forces (vectors) defined, based on magnitude and direction.  Occlusal forces are 3 dimensional with components directed along one or more clinical coordinate axes  Same magnitude of force can have dramatical effects based on the direction of load. Dental Implant Prosthetics, Carl E Misch, 2nd edition. PERPENDICULAR TO CURVE OF SPEE AND WILSON IN NATURAL DENTITION
• Implants are designed for long axis loads • Implants axial load > compressive force > stresses are concentcrestal level. • Forces at an angle > shear stress >10 times Implant bodies should be positioned perpendicular to curve of spee and Wilson as in natural dentition to reduce the shear stresses on implant system and prevent the crestal bone loss, abutment screw loosening and implant component fracture
FORCE DIRECTION AND BONE MECHANICS Anisotrophy of bone- it refers to the character of bone whereby its meachanical properties depend on the direction in which bone is loaded and the type of force applied. BONE IS STRONGER IN COMPRESSION, 30% WEAKER IN TENSION, 65% WEAKER IN SHEAR Porcelain and titanium are also weaker in shear component of load IPO attemps to eliminate all shear loads to implant system
Angled load  compressive stresses  Tensile on opposite Because bone is weaker to tensile and shear forces, the risks to the bone are increased due to : (1) the amount of increasing stress (2) type of stress is changed to more tensile and shear conditions. Greater the angle of load to implant long axis, greater the compressive, tensile and shear stresses
A 12-degree angled force increases the force to the implant system by 18.6%.
• Force (shear, tensile) is detrimental; • Not only is the bone weakest to shear loads, but forces physiologic limit of compressive and tensile strengths of bone. IPO attempts to eliminate lateral or angled loads to an implant-supported prosthesis because the magnitude of the force increases and the strength of the bone decreases. Reilly DT, Burstein AH: The elastic and ultimate properties of compact bone tissue, J Biomech 80:393–405, 1975.
The risk of crestal bone loss is increased with an angled implant
PROSTHETIC COMPLICATIONS OF SHEAR FORCES 1. Porcelain is weaker and may fracture 2. Cement retained prosthesis may dislodged 3. Abutment screw may become loose 4. Crestal bone loss 5. Implant component fracture
SOLUTION TO ANGLED LOADS??  Reduction in the force magnitude;  Additional surface area of implant support  Implant with greater diameter  Additional implant wherever possible  Splinting;  Reduce occlusal contacts  Elimination of all lateral and horizontal loads Duyck J, Van Oosterwyck H, Vander Sloten J, et al: Magnitude and distribution of occlusal forces on oral implants supporting fixed prostheses: an in vivo study, Clin Oral Implants Res 11:465–475, 2000
POSTERIOR CROWN CUSP ANGLE • Greater cusp angle > more esthetics and increased food chewing efficiency • Occlusal contact on angled cusp > increased angle load and makes it premature contact even if it is not • Solution 1. Occlusal contact on flat surface 2. Increased fossa by 2-3 mm 3. Recounturing of opposing cusp Miyata T, Kobayashi Y, Araki H, et al: The influence of controlled occlusal overload on peri-implant time. 4. A histologic study , Int J Oral Maxillofac Implants 17:384–390, 2002.
MUTUALLY PROTECTED ARTICULATION  The bite force in the posterior region is 200 – 250 psi. and anterior region is 25-50 psi.  In mutually protected occlusion: 1. 2/3rd of temporalis and masseter don’t contract when posterior teeth don’t occlude 2. TMJ and teeth complex forms class 3 lever. (nutcracker) 3. Anterior show more physiologic lateral movement Ideal vertical overbite- 4-5 mm Minimum incisal guidance- 23-25 degrees
MUTUALLY PROTECTED ARTICULATION  Protrusive mandibular movement - central and lateral incisors disocclude the posteriors  Lateral excursions- canine (central and lateral when possible) disocclude the posteriors  CO- posterior and canine occlude, when central and lateral are natural they may also occlude, (when central and lateral are implants they should not occlude if opposing dentition is also implant supported)
When single missing canine  No protrusive contact , if at all necessary give light contact  Lateral excursion > give slight contact on lateral incisor  Under heavy bite it might contact as same intensity as lateral inciosor
CANTILEVERS AND IPO  A cantilever on two implants may be considered a class 1 lever.  When the implants are 10 mm apart, with a 20-mm cantilever, a mechanical advantage of 2 is created.  Therefore, the load on the cantilever will be multiplied by 2 on the far implant, and the implant close to the cantilever receives the total stress of the two loads. Compressive Tensile and shear Compressive
 The greater the force on the cantilever, the even greater the forces on the implants because the cantilever is a force magnifier.  The greater the length of the cantilever, the greater the loads on the implants. To reduce the amount of force that is magnified by the cantilever, the occlusal contact force may be reduced on the cantilevered prosthesis No lateral load is applied to the cantilever crown
CROWN HEIGHT AND IPO  The implant crown height is often greater than the original natural anatomical crown.  If the implant is loaded on the long axis, crown height does not magnify the force.  However, crown height is a force magnifier (vertical cantilever) when any lateral load, angled force, or cantilever load is applied. Dental Implant Prosthetics, Carl E Misch, 2nd edition.
Note: the crown height is not a force magnifier (lever) when there is no cantilever or lateral load.
POSTERIOR IMPLANT CROWN CONTOUR  A buccal or lingual cantilever > offset load.  The greater the offset, the greater the load to the implant system.  WIDER ROOT FORM implants can accept a broader range of vertical occlusal contacts while still transmitting lesser forces at the permucosal site under offset loads.  Narrower implant bodies are more vulnerable to occlusal table width and offset loads. Dental Implant Prosthetics, Carl E Misch, 2nd Therefore, in IPO, the width of the occlusal table is related directly to the width of the implant body
 Post implants inserted under central fossa  Restoring the normal crown contour on narrow implant causes buccal cantilever> risk of porcelain fracture Occlusal table should be narrower to improve • Sulcular home care • Improves axial loading • Decreases the risk of porcelain fracture
Mandibular posterior crowns • Mandibular implant crowns should be reduced from buccal to reduce the stamp offset • Cheek biting is prevented by increasing buccal overjet • Lingual contour similar to natural tooth to prevent tongue biting • No lingual cusp contact
Maxillary post crown  In esthetic zone preserve buccal cusp contour and horizontal overlap is similar to natural tooth  Prevents cheek biting  Reduce lingual cusp contour (stamp cusp) to reduce the offset load When teeth are out of esthetic zone, 1. Bl dimension should be smaller 2. Centre of implant in ridge centre 3. Contact only on stamp cusps 4. Reduce width of central fossa crowns may be designed for crossbite
POSTERIOR OCCLUSAL CONTACT POSITIONS  Ideal contact points  The ideal occlusal contacts per tooth should have minimum offset loads to the implant body, the central fossa is the logical primary occlusal contact position. Dental Implant Prosthetics, Carl E Misch, 2nd edition.
 The ideal primary occlusal contacts therefore will reside within the diameter of the implant within the central fossa.  Secondary occlusal contacts should remain within 1 mm of the periphery of the implant to decrease moment loads.  Occlusal contact on mesial or distal is a cantilever load While occlusal contact on buccal or lingual is an offset load
Primary centric contact (red) Secondary centric contacts (green) Occlusal contacts on the cusp angles instead of the central fossa. Increase in the magnitude of shear stress.
TIMING OF OCCLUSAL CONTACTS  Because of the inherent differences between teeth and implants, the “timing” of occlusal contacts is extremely important to the force distribution.  Studies have shown implant patients to have far less awareness of occlusal interferences  Goal: to eliminate the mobility differences between teeth and implants.  This will allow for an even distribution of occlusal load and prevention of premature contacts and increased loads. Randolph R. Principles of Implant Occlusion: Part 2 – Recommendations for Single Implant Prostheses, Glidewell 2017.
Natural tooth • Vertical primary tooth movement= 5-28 microns • Vertical secondary tooth movement= 3-5 microns • Horizontal movement- 68- 108 microns Implant • No vertical primary movement • Vertical secondary movement of 5 microns under heavy load • Horizontal movement under heavy load is 10-55 microns
Step 2: Heavy force bite into centric relation with shimstock in between. Resistance upon removal. Goal: Heavy force exerted equals to PDL compression. Thus an even contact between tooth and implant. Step 1: Light force bite into centric relation with Shimstock less than 25u) in between. All contacts removed. Shimstock retrieval be unobstructed. Goal: Great force on natural teeth which coincides with PDL compression. This “timed” contact will account for the mobility differences between the teeth and implants.
DESIGN TO THE WEAKEST ARCH  The weakest component philosophy is used when one opposing segment is at more risk of complications than an opposing area.  Goal of ipo 1. Identify the weakest link 2. Design prosthesis and occlusal scheme to protect it  The amount of force distributed to a system can be reduced by stress relieving components that may dramatically reduce impact loads to the implant support.  The soft tissue of a conventional complete removable prosthesis opposing implant prosthesis is displaced more than 2 mm and is an efficient stress reducer.  Lateral loads do not causes great crestal load to the implants because the opposing prosthesis is not rigid. Dental Implant Prosthetics, Carl E Misch, 2nd
 The weakest component philosophy also applies to axial occlusal contacts in implant body in the presence of cantilevers and offset loaded areas.  During excursion, Absence of contacts on posterior cantilevers and anterior offset pontics is recommended which minimizes the loads on the terminal implant abutments.  When cantilever pontics are in both arches, they should oppose each other.  If cantilever pontic is present only in one arch it is better for mandibular cantilever pontics to oppose maxillary implants than the reverse situation.
Mutually protected occlusion with shallow anterior guidance when opposing natural dentition > No working and balancing contact on cantilever > Infraocclusion in cantilever segment (100 mm) Freedom in centric (1–1.5 mm) Bilateral balanced occlusion using lingulized occlusion Monoplane occlusion on a severely resorbed ridge Anterior guidance with natural dentition Group function occlusion with compromised canines Centered contacts, narrow occlusal tables, flat cusps, minimized cantilever Cross bite posterior occlusion when necessary Natural tooth connection with rigid attachment when compromised support Anterior or lateral guidance with natural dentition Light contact at heavy bite and no contact at light bite Centered contacts (1–1.5 mm flat area) No offset contacts Increased proximal contact Longer healing time Progressive loading by staging diet and occlusal contacts/materials Full arch fixed prosthesis Overdenture Posterior fixed prosthesis Single implant prosthesis Poor quality of bone/ grafted bone
CONCLUSION  Any complex engineering structure typically will fail at its weakest link, and dental implant structures are no exception.  Thus, all treatment planning decisions for IPO should be based on careful consideration of (1) identifying the weakest link in the overall restoration and (2) establishing occlusal and prosthetic schemes to protect that component of the structure.
The IPO concept addresses several conditions to decrease stress to the implant system, including implant body angle to occlusal load, cusp angle of crowns, mutually protected articulation, cantilever or offset distance, crown height, crown contour, the timing of occlusal contacts, and protection of the weakest component.
Occlusion concept for different types of osseointegration prostheses - Hobo Osseointegration and occlusal rehabilitation, Sumiya Hobo.
References  Dental Implant Prosthetics, Carl E Misch, 2nd edition.  Osseointegration and occlusal rehabilitation, Sumiya Hobo.  Gartner JL, Mushimoto K, Weber HP, et al: Effect of osseointegrated implants in the coordination of masticatory muscles: a pilot study, J Prosthet Dent 84:185–193, 2000.  Miyata T, Kobayashi Y, Araki H, et al: The influence of controlled occlusal overload on peri-implant time. 4. A histologic study , Int J Oral Maxillofac Implants 17:384–390, 2002.  Duyck J, Van Oosterwyck H, Vander Sloten J, et al: Magnitude and distribution of occlusal forces on oral implants supporting fixed prostheses: an in vivo study, Clin Oral Implants Res 11:465–475, 2000.  Randolph R. Principles of Implant Occlusion: Part 2 – Recommendations for Single Implant Prostheses, Glidewell 2017.
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