Implant prosthesis occlusion

differences between natural tooth periodontium and implant bone connection, biomechanics of implants, implant protected occlusion , occlusal principles for single tooth implant prosthetics and implant supported prosthesis on edentulous arch, shortened arch concept, therapeutic occlusion

1. Piyali Bhattacharya Dept of Prosthodontics and Crown & Bridge HIDSAR Implant occlusion

2. I ntroduction Occlusion specific to implants is termed as Implant Protective Occlusion. This scheme reduces the forces at the crestal bone/implant interface. The basis of this concept is formed by the biomechanical principles Occlusal Principles and Considerations for Implants: An Overview , Journal of Academy of Dental Education , Vol 1 (2)| July–December 2014|

3. Five concepts important for an ideal occlusion had been described by Dawson (1974): Stable stops on all the teeth when the condyles are in the most superior posterior position (Centric Relation) An anterior guidance that is in harmony with the border movements of the envelope of function Disclusion of all the posterior teeth on the balancing side. Disclusion of all the posterior teeth in protrusive movements Non-interference of all posterior teeth on the working side with either the lateral anterior guidance or the border movements of the condyles. Occlusal Principles and Considerations for Implants: An Overview , Journal of Academy of Dental Education , Vol 1 (2)| July–December 2014|

4. LOADING ON TEETH VERSUS IMPLANTS Natural tooth Implant Connection PDL fibres Osseointegration or ankylosis Proprioception Periodontal mechanoceptors Osseoperception Tactile sensitivity high low Axial mobility 25-100 micron 3-5 micron Movement phases Two phases- Primary: non linear and complex Secondary: linear and elastic One phase-linear and elastic Movement patterns Primary: Immediate Secondary: Gradual Gradual Fulcrum to lateral force Apical third of the root Crestal bone

5. Natural tooth Implant Load bearing characteristics Shock absorbing function and stress distribution Stress concentration at crestal bone Signs of overloading Thickening of PDL , Fremitus, wear facets, mobility , pain Screw loosening, veneer fracture, crestal bone loss, Implant failure Misch CE. Occlusal considerations for implant-supported prostheses: Implant-protected occlusion . Pp 874-912. Dental Implant Prosthetics (2nd ed ), Misch CE. 2015 . Mosby, Int.

6. 14 considerations for following the IPO scheme that should be judiciously implemented before restoration - Elimination of premature occlusal contacts Premature contacts are defined as occlusal contacts that divert the mandible from a normal path of closure; interfere with normal smooth gliding mandibular movement; and/or deflect the position of the condyle, teeth, or prosthesis Prior to the evaluation of occlusion on implant reconstruction, the occlusion should be evaluated and all occlusal prematurities should be eliminated during maximum intercuspation and centric relation. Verma , et al ., Principles of occlusion in implant dentistry, Journal of the International Clinical Dental Research Organization | Supplement 1 | Vol 7 | 2015

7. Excessive lateral loads arising from premature contact may cause bone loss and implant failure . While restoring an implant, a <25 µm articulating paper is used , the patient occludes in centric relation, the implant prosthesis barely makes contact which the rest of the teeth exhibit greater contact initially. The occlusal contact should remain axial over the implant body and may be of similar intensity on the implant crown and adjacent teeth when under greater bite force . The harmonization under light occlusal loads is followed by adjustment under heavy occlusal load. Verma , et al ., Principles of occlusion in implant dentistry, Journal of the International Clinical Dental Research Organization | Supplement 1 | Vol 7 | 2015

8. 2. Provision of adequate surface area to sustain load transmitted to the prosthesis Increased load can be compensated by increasing the implant width; reducing crown height; ridge augmentation if necessary; increasing the number of implants; or splinting the prosthesis

9. 3. Controlling the occlusal table width The wider the occlusal table, the greater the force developed to penetrate a bolus of food. a restoration mimicking the occlusal anatomy of natural teeth often results in offset load (increased stress), increased risk of porcelain fracture, and difficulties in home care (due to horizontal buccolingual offset/cantilever).

10. 4. Mutually protected articulation During centric occlusion the anterior teeth have only light contact and, are protected by the posterior teeth, during excursion the posterior teeth are protected by the anterior guidance The rationale of mutually protected occlusion is that the forces are distributed to segments of the jaws with an overall decrease in force magnitudes .

11. The steeper the anterior guidance, the greater are the anticipated forces on anterior implants . In case of a single tooth implant replacing a canine, no occlusal contact is recommended on the implant crown during excursion to the opposite side.

12. 5. Implant body orientation and influence of load direction Anisotropy refers to the character of bone whereby the mechanical properties depend on the direction in which the bone is loaded . The greater the angle of the load , the greater is the shear component of the load. The cortical bone is the strongest and most able to withstand compressive forces . Its ability to withstand tensile and shear forces is 30 % and 65% less, respectively. Misch CE. Occlusal considerations for implant-supported prostheses: Implant-protected occlusion . Pp 874-912. Dental Implant Prosthetics (2nd ed ), Misch CE. 2015 . Mosby, Int.

13. The increase in the shear component of stresses is by almost three times, which predisposes the bone to increased crestal bone loss and impairs successful bone growth . The implant body should be placed perpendicular to the occlusal plane and along the primary occlusal contact.

14. A force at a 30-degree angle decreases the bone strength limit by 10% under compression and by 25% under tension whenever lateral / angled loads cannot be eliminated, a reduction in force magnitude or additional surface area of the implant surface is indicated to reduce the risk of bone loss or of implant component fracture.

15. Prosthetic Angled Loads An angled implant body or an angled load on the implant crown increases the amount of crestal stresses on the implant system, transforms a greater percentage of the force to shear force, and reduces bone , porcelain, and cement strength .

16. Solution to Angled Loads A reduction in the force magnitude additional surface area of implant support is indicated A. s urgically : 1.Additional implant next to most angled implant 2.Increased diameter of the angled implant 3.Select implant design with greatest surface area B. Restoratively: 1. Splinting implants together 2. Reducing occlusal load on angled implants 3. Eliminating all lateral or horizontal forces on angled implants Misch CE. Occlusal considerations for implant-supported prostheses: Implant-protected occlusion . Pp 874-912. Dental Implant Prosthetics (2nd ed ), Misch CE. 2015 . Mosby, Int.

17. Crown cusp angle the angle of force to the implant body may be influenced by cusp inclination, which in turn will increase crestal bone stress. The occlusal contact over an implant crown should, therefore, ideally be on a flat surface perpendicular to the implant body. This positioning is accomplished by increasing the width of the central groove to 2-3 mm in posterior implant crowns, which are positioned over the center of the implant abutment.

18. Cantilevers are class-1 levers, which increase the amount of stress on implants. Twice the load applied at the cantilever will act on the abutment farthest from the cantilever, and the load on the abutment closest to cantilever is the sum of the other two components. 10 20 25 lbs 50 lbs 75 lbs For example , a 100-N force on the cantilever equals a 200-N tensile or shear force on the most distal abutment and a 300-N Compressive force on the abutment ( the fulcrum) next to the lever. Cantilevers and IPO

19. Because cement and screws are weaker to tensile loads, the implant abutment farthest from the cantilever often becomes unretained , resulting in the fulcrum abutment’s bearing the entire load. Because the implant is more rigid than a tooth, it acts as a fulcrum with higher force transfer. As a consequence , crestal bone loss, fracture, and implant failure are often imminent after the distal abutment becomes no longer connected to the prosthesis . The greater the length of the cantilever, the greater the mechanical advantage and the greater the loads on the implants.

20. The shorter the distance between the implants, the greater the mechanical advantage and the greater the force on the implant system. The goal of IPO relative to cantilevers is to reduce the force on the pontics of the lever region compared with that over and between the implant abutments . the occlusal contact force may be reduced on the cantilevered portion of the prosthesis t o reduce the amount of force that is magnified by the cantilever. No lateral load is applied to the cantilever portion of the prosthesis whether it is in the posterior or anterior region.

21. Crown height and IPO Crown height does not magnify the stress to the implant system when the force is applied in the long axis of the implant body. An increased crown height acts as a vertical cantilever, a force magnifier when any lateral load, angled force, or cantilever load is applied 15 mm Crown Height 100 N Angled load E.g. A 100-N load at a 12-degree angle increases the lateral or shear force component by 20.79 N. A crown height of 15 mm increases the 20.79-N force to a 311.85–N-mm moment force . 100 N Axial load

22. If a load perpendicular to the curves of Wilson and Spee is applied to an angled implant body, the increase in load is not magnified by the crown height. The angled implant will increase the force. Hence, the angle of load to the occlusal surface is more important to control than the angle of the implant body position .

23. A buccal or lingual cantilever in the posterior regions is called an offset load, and the same principles of force magnification from class 1 levers apply. The greater the offset, the greater the load to the implant system . The ideal occlusal contact is over the implant body which leads to the axial loading of implants . A posterior implant is hence placed under the central fossa of the implant crown Occlusal contact position

24. A marginal ridge contact is also a cantilever load, as the marginal ridge may also be several millimeters away from the implant body. T he moment of force on the marginal ridge may contribute to forces that increase abutment screw loosening. Thus, the ideal primary occlusal contact should reside within the diameter of the implant within the central fossa. The secondary occlusal contact should remain within 1 mm of the periphery of the implants to decrease the moment loads . The marginal ridge contact is not an offset load when located between implants splinted to one another.

25. 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 . As posterior teeth are out of the esthetic zone, the posterior implant crown should have a reduced occlusal width compared with a natural tooth. A wide occlusal table favors offset contacts during mastication or parafunction .

26. Implant crown contour The narrower occlusal contour of an implant crown reduces the risk of porcelain fracture. Also, The narrower posterior occlusal table facilitates daily sulcular home care. Thus, a narrow occlusal table combined with a reduced buccal contour (in the posterior mandible) and a reduced lingual contour (in the posterior maxilla) facilitates daily care, improves axial loading and decreases the risk of porcelain fracture.

27. The posterior mandible resorbs lingually as the bone resorbs from division A to B. As a result, endosteal implants are also more lingual than their natural tooth predecessors. The division C–h and D mandibular ridge shifts to the buccal compared with the maxillary arch. E ndosteal implants typically cannot be inserted because the available bone above the mandibular nerve is inadequate for endosteal implants Mandibular crown contour

28. The lingual contour of the mandibular implant crown is similar to a natural tooth p ermitting a horizontal overjet to exist and push the tongue out of the way during occlusal contacts (just as natural teeth ). In the posterior mandible, as the implant diameter decreases, the buccal cusp contour is reduced which decreases the offset length of cantilever load.

29. Maxillary Posterior Crowns In the esthetic zone (high lip position during smiling), the buccal contour of the maxillary implant crown is similar to a natural tooth . When maxillary posterior implants are in the esthetic zone, they are positioned more facial than the center of the ridge . The ideal functional position for the maxillary posterior implant is under the central fossa when the cervical region is not in the esthetic zone. Hence, the lingual cusp is cantilevered from the implant similar to the buccal cusp of the posterior mandible . Therefore, the reduced lingual contour reduces the offset load to the lingual

30. Design of the prosthesis should favor the weakest arch Usually the maxilla is the weaker of the two arches, predominantly due to less dense bone . To follow the weaker component theory, when cantilevered pontics are in both arches, they should ideally oppose each other. posterior cantilevers in the maxillary arch are less indicated than in the mandible. When maxillary posterior implants support cantilevered anterior teeth and mandibular anterior implants support cantilevered posterior teeth, the occlusal scheme cannot minimize forces on both. In this scenario, the weaker component is usually the anterior maxilla, and reduced force in the region would be appropriate.

31. Summary by Bone Volume Division A bone

32. M axillary natural tooth vs mandibular implant-supported prosthesis in division A bone- Maxillary lingual cusp is the primary contacting cusp. Central fossa of implant crown is broadened by 2-3 mm to receive the contacting cusp of opposing tooth. The lingual cusp of the mandibular implant crown should be out of contact to eliminate offset load. Mandibular buccal cusps are reduced to prevent offset load and cheek bite

33. Mandibular buccal cusp is the primary contacting cusp Central fossa of implant crown is broadened by 2-3 mm to receive the contacting cusp of opposing tooth The lingual cusp of the mandibular implant crown should be out of contact to eliminate offset load . Maxillary buccal cusp maintains esthetics M axillary implant-supported prosthesis vs mandibular natural tooth in division A bone

34. M axillary implant-supported prosthesis vs mandibular implant-supported prosthesis in division a bone Favour the weaker arch when axial loading is not possible Mandibular buccal cusp is the primary contacting cusp Maxillary buccal cusp maintains esthetics Central fossa of implant crown is broadened by 2-3 mm to receive the contacting cusp of opposing tooth Lingual cusp of mandibular crown is maintained and lingual cusp of maxilla is reduced to prevent offset load

35. M axillary implant-supported prosthesis vs mandibular natural tooth in division B C and D bone, might require cross-arch relation of teeth

36. Maxillary lingual overjet prevents tongue overbite Mandibular buccal overjet prevents cheek bite Reduced width of maxillary buccal cusp Primary occlual contact over central fossa over implant body Verma , et al .: Occlusion in implantology , Journal of the International Clinical Dental Research Organization | Supplement 1 | Vol 7 | 2015

37. 12. Parafunctional activity Naert et al. reported that overloading from parafunctional habits such as clenching or bruxism seemed to be the most probable cause of implant failure and marginal bone loss. According to them, shorter cantilevers, proper location of the fixtures along the arch, a maximum fixture length, and night-guard protection should be prerequisites to avoid parafunctional habits or the overloading of implants in these patients. Falk H, Laurell L, Lundgren D. Occlusal interferences and cantilever joint stress in implant-supported prostheses occluding with complete dentures. Int J Oral Maxillofac Implants 1990;5:70-7 .

38. 13.Timing of loading Implant loading can be either delayed (submerged ), progressive bone loading or immediate bone loading . Progressive bone loading is specifically indicated for less dense bones. Progressive bone loading allows a “ development time ” for load-bearing bone and allows bone adaptability to loading via the gradual increase in loading. The concept is based on incorporating time intervals of 3-6 months, avoiding chewing with a soft diet, then progressing to harder food, gradually intensifying the occlusal contacts during prosthesis fabrication ,prosthesis design, and occlusal materials (from resin to metal to porcelain) for poor bone quality conditions

39. 14. Occlusal guidelines for different clinical situations Group function or mutually protected occlusion with shallow anterior guidance is recommended when opposing natural dentition or a full-arch fixed prosthesis. In case of a full-arch fixed prosthesis, if the opposing arch is a complete denture, balanced occlusion is recommended .

40. In case of overdentures , bilateral balanced occlusion. In case of severely resorbed ridges, monoplane occlusion should be used . If the posterior arch is rehabilitated with a fixed prosthesis , Where necessary, the posterior occlusion must be placed in crossbite Occlusal concept when rehabilitating the edentulous mandible with oral implants have been suggested by Quirynen M et al B L

41. In case of the fully edentulous maxilla, whether the mandibular rehabilitation is done on an overdenture supported on two implants or on a mucosal-implant supported overdenture (four implants with a bar attachment ), a balanced occlusal scheme ( bilateral/ lingualized /monoplane ) is recommended . W here a Kennedy class I partially edentulous condition is present in the maxillary arch and mandibular mucosa implant supported (four implants with a bar attachment) or an implant-supported prosthesis is planned for the mandibular arch, balanced occlusion is recommended . Kennedy’s class I in maxillary arch that has been restored with fixed denture prosthesis (FDP) or with implants, and a mandibular implant-supported prosthesis is advised, it is recommended to follow group function or mutually protected occlusion.

42. Modern Concept In Implant Occlusion The current criteria for a healthy or physiologic occlusion as developed by Mohl et al . and Ash and Ramfjord reflect this shift : (a) Absence of pathologic manifestations (b) Satisfactory function (c) Variability in form and function (d) Adaptive capacity to changing situations Fernandes and Chitre : An alternative to management of the partially dentate patient- The SDA Concept, The Journal of Indian Prosthodontic Society | September 2008 | Vol 8 | Issue 3

43. The shortened dental arch (SDA) concept, first discussed internationally by the Dutch prosthodontist Professor Käyser in 1981- shortened dental arches comprising anterior and premolar teeth in general fulfill the requirements of a functional dentition In the original Brånemark implant treatment, a moderate SDA concept was applied- In spite of the lack of complete molar support, excellent long-term functional outcome has been demonstrated subjects with extreme SDA may exhibit functional problems Gunnar E. Carlsson , Dental occlusion: modern concepts and their application in implant prosthodontics, Odontology (2009) 97:8–17

44. How many teeth are required cannot be answered in general but must be evaluated individually with respect to the wide variation in occlusal morphology and individual adaptability present in the population . Comparisons of two options for treatment of SDA, a removable partial denture and small fixed dental prostheses, have demonstrated several advantages for the fixed prostheses in spite of the fact that they did not provide molar support. The patients liked them better than the removable denture,

45. It has also been found that removable partial dentures do not provide better chewing comfort and stability of occlusion or prevent or cure temporomandibular disease ( TMD) problems. In a unilateral SDA, where a removable partial denture is admittedly difficult to fabricate and use, an implant restoration would ideally be the treatment of choice

46. Therapeutic occlusion A therapeutic occlusion has been defined as one modified by various therapeutic measures so that it falls within the parameters of a physiological occlusion . Some general guidelines for a therapeutic occlusion- Acceptable vertical facial height after treatment Acceptable interocclusal distance with the mandible at rest

47. Stable jaw relationship with bilateral contact after relaxed closure leading into maximal intercuspation as well as after retruded closure • Well-distributed contacts in maximal intercuspation , providing axially directed forces • Multidirectional freedom of contact movements radiating from maximal intercuspation • No disturbing or harmful intermaxillary contacts during lateral or protrusive excursions • No soft tissue impingement during occlusal contact

48. Conclusion By application of biomechanical principles such as reducing the cantilever length, passive fitting of prostheses, narrowing the buccolingual / mesiodistal dimensions of the prosthesis, reducing cusp inclination, eliminating excursive contacts, and centering occlusal contacts, these complications can be prevented. Implant occlusion be adjusted periodically and re-evaluated to prevent them from developing potential overloading clinical sequelae , thus providing implant longevity. Occlusal Principles and Considerations for Implants: An Overview , Journal of Academy of Dental Education, Vol 1 (2)| July–December 2014|

49. References Occlusal Principles and Considerations for Implants: An Overview , Journal of Academy of Dental Education , Vol 1 (2)| July–December 2014 Misch CE. Occlusal considerations for implant-supported prostheses: Implant-protected occlusion . Pp 874-912. Dental Implant Prosthetics (2nd ed ), Misch CE. 2015. Mosby, Int. Verma , et al ., Principles of occlusion in implant dentistry, Journal of the International Clinical Dental Research Organization | Supplement 1 | Vol 7 | 2015 Gunnar E. Carlsson , Dental occlusion: modern concepts and their application in implant prosthodontics, Odontology (2009) 97:8–17 Fernandes and Chitre : An alternative to management of the partially dentate patient- The SDA Concept , The Journal of Indian Prosthodontic Society | September 2008 | Vol 8 | Issue 3