Abstract

Endosseous implant dentistry has become a predictable clinical modality. The role of the restorative dentist is to minimize overload to the crestal bone by utilizing implant occlusal principles. The prosthetic stages of treatment should follow a disciplined sequence. This article reviews occlusal principles and clinical applications for long-term success of endosseous implants.

OCCLUSAL PRINCIPLES AND CLINICALAPPLICATIONS FOR ENDOSSEOUS IMPLANTSCLINICALBrian J. Jackson, DDSKEY WORDSPeriodontal ligamentStressImplant-protected occlusionOrientation jigBrian J. Jackson, DDS, privately practicesdentistry in Utica, New York. Addresscorrespondence to Dr Jackson, 2534 GenesseeStreet, Utica, NY 13502 (e-mail:Slajacburdds@aol.com).230 Vol. XXIX/No. Five/2003Endosseous implant dentistry has become a predictable clinical modality. Therole of the restorative dentist is to minimize overload to the crestal bone byutilizing implant occlusal principles. The prosthetic stages of treatment shouldfollow a disciplined sequence. This article reviews occlusal principles and clinicalapplications for long-term success of endosseous implants.e eses. p ted r lant-suppo p im e ccess sed Tvidence-bafieldsuhave demorates,nstrancotedurimprovethe long-terosthrm prognosisntial esse are rs ese Th 8,9 ces. ce th o lin ip disc c eti prapirosthd rate. The surgiescalfanderedrviuction of stressfactoat the peri-implanttooe th w dentistry is growing at a adjacent to the implant will allo nsity e e th r p im to l field e th in l lanto pIhNTRODUCTIONe utilizaogytion of oral imofFinalloadingy, the utilizaovetiondof progressivof boneefaging more widespread use by thedental profession. Although the surgicalaspect of the field has expandedinto many high-profile areas (ie, immediateimplant placement, distractionosteogenesis, and the orthodontic anchorageimplant), it is the prostheticaspect that is most critical for longtermsuccess. More specifically, the occlusalconsiderations for implant-supportedprostheses make a major contributionto ensure predictable results.1The responsibilities of the surgeonand the restorative dentist are to minimizeocclusal overload to the bone atthe implant interface.2-7 First, a properdiagnosis is made that will lead to asatisfactory treatment plan. Second, asurgical template must be developed toinsure ideal implant placement. Third,a passive interim prosthesis of adequateretention and form with an acceptableocclusal scheme is required.METHODSImplant-protected occlusion principlesshould be observed during all reconstructivestages of treatment.10,11 First,the natural dentition must be evaluatedfor occlusal prematurities and adjustedprior to implant reconstruction (Figures1 and 2). The natural dentitionshould be equilibrated to minimize eccentricinterferences and to establish aharmonious centric occlusion. Second,the final implant abutments andcrowns should be evaluated prior tothe patient's appointment (Figures 3and 4). The abutment should demonstrateproper axial taper and an intraocclusalspace for sufficient metalframework and porcelain application.Centric occlusion, lateral excursions,and protrusive movements should beevaluated from the articulated stonemodels. It is essential that the dentalBrian J. JacksonFIGURES 1-8. FIGURE 1. Centric occlusion. FIGURE 2. Articulated diagnostic modelscentric occlusion. FIGURE 3. Implant abutmentaxialtaper. FIGURE 4. Implant abutmentinterocclusal distance. FIGURE 5. Implant-supported crownreduced buccal-lingual dimension. FIGURE6. Gingival sulcusnormal. FIGURE 7. Periapical radiographhealing collar attached to implant. FIGURE 8. Periapical radiographabutmentimplant.Journal of Oral Implantology 231IMPLANT-PROTECTED OCCLUSION APPLICATIONSlaboratory be guided in their understandingof the elements of implant occlusion.The soft-tissue model, heightof the abutment, and buccal-lingual dimensionof the crown or bridge shouldbe inspected prior to the final placementof the prosthesis (Figure 5). Thesoft-tissue implant model should correspondto the clinical sulcus probingdepths to ensure a clinically acceptableemergence profile. The buccal-lingualdimension of the crown or bridgeshould be reduced in comparison withthe natural tooth it replaces. At the implant-supported crown placement procedureappointment, the soft and hardtissues surrounding the endosseousimplant must be evaluated (Figures 6and 7). The soft tissues should not exhibitsigns of inflammation such asredness, edema, and purulent discharge.The hard tissues should exhibitminimal crestal bone loss (,2 mm) atthe preocclusal load stage. A radiographof the implant-abutment interfaceis an essential benchmark for futurebone protection (Figure 8). A standardrepeatable radiographic technique(ie, X-ray cone positioningdevice) should be employed to confirmthe preload crestal bone levels andcomplete abutment seating. Implantabutments should be hand tightened,their positions confirmed using anacrylic orientation jig and verified witha radiograph prior to final screw tighteningwith a calibrated torque wrenchto 30 Ncm. The acrylic orientation jigserves to confirm that the abutmentplacement on the working model correspondswith the same position intraorally(Figures 9 and 10). The orientationjig is instrumental in theplacement of the implant abutmentsinto their correct positions. The role ofthe acrylic jig is most useful whenmultipleabutments with numerous hexagonalsides are part of the implant reconstruction(Figures 11 and 12). Afterabutment placement, the interproximalcontact points for the implant-supportedcrowns can be adjusted and the occlusioncorrected. It is essential to establishonly axial occlusal contacts on232 Vol. XXIX/No. Five/2003implant crowns, which will increasethe compressive axial forces and decreaseshear/tensile or angled forces.Endosseous implants should have zeroto minimal contacts during centric occlusionand lateral and protrusiveexcursions. Protrusive movementsshould permit the anterior teeth to disoccludethe posterior implants. If theanterior components are implants, 2 ormore should be splinted together. Oncompletion of the occlusal equilibration,the final restoration is cementedwith temporary cement and a radiographis taken (Figure 13). The radiographshould be evaluated and residualcement removed with a nonmetalinstrument to avoid scratching of endosseousimplants.DISCUSSIONIt is critical for the practitioner to appreciatethe differences between naturalteeth and endosseous implants inregard to the application of stress. Themost significant difference is createdby the periodontal ligament and itsunique properties. This vital structureunique to natural teeth allows forstress distribution, mobility, occlusaltrauma tolerance, and proprioception.Endosseous implants lack a periodontalligament, thereby lacking the propertiesof that structure. The periodontalligament allows forces to be dissipatedaway from the crest and toward theapex of the tooth. The endosseous implantdemonstrates no significantmovement, which results in greaterforces being directed at the crest of thesurrounding bone. Because there is noshock-absorber effect, as is seen withnatural teeth, implants subjected to excessiveocclusal loads will demonstratemicroscopic stress fractures, fatigue,cement breakdown, and screw loosening.The proprioreceptive properties ofthe periodontal ligament assist in themonitoring of centric and excursiveforces. Natural teeth exhibit pain sensations,which are considered to be aprotective mechanism. Endosseous implantshave no proprioreceptive mechanismto signal excessive force. Theymay experience a slow, dull pain thatdelivers a delayed reaction to the hostsite. These factors may contribute tolong-term problems that will jeopardizethe survival of implants. It is essentialthat the implant dentist viewthe occlusal forces as the weakest linkin the dental implant system.12Researchers and clinicians appreciatethat natural teeth and endosseousimplants have distinctive shape differences.Natural teeth present with verydifferent cross-sectional shapes comparedwith the circular shape of implants.The varying morphology of naturalteeth is influenced by their positionsin the arch. They are designed towithstand occlusal trauma by appropriatedistribution of forces. The circularshape of endosseous implantsmakes them less effective during eccentricjaw movements. If one comparesthe cross-section of a molar to awide-body implant, there are signifi-cant differences in the total surface areasof each.The major objective of an implantologistis to develop an implant occlusalscheme that will recognize and utilizenatural tooth movement. Movementof natural teeth may be from 8 to28 mm. Endosseous implants demonstratevirtually no movement.13,14Therefore, for the patient with a toothand implant-borne reconstruction, attentionmust be paid to the occlusalscheme. Implant protective occlusion(IPO) is developed from a concept thatrefers to a specially designed occlusalplan.15 The IPO is a medially positioned,lingualized occlusion adaptedto natural resorptive patterns. Its primarygoal is to direct occlusal loads tothe implant bodies within the physiologiclimits of each patient. It aims atdecreasing the forces of occlusal contactsand increasing the number of implants,and their diameters. Thus, ifthey are subjected to angled loads, unfavorablecrown-implant ratios or supportingthe cantilever portions of prostheses,they will be able to respondmore successfully.FIGURES 9-13. FIGURE 9. Intraoral abutment placement. FIGURE 10. Intraoral acrylic abutment orientation jig (1 unit). FIGURE 11. Acrylicabutment orientation jig (2 units). FIGURE 12. Acrylic abutment orientation jig (3 units). FIGURE 13. Periapical radiographfinal restoration,implant, abutment, porcelain-fused-to-metal crown.The management of angled forcesand abutments is an essential aspect ofimplant prosthodontics. Angled forcesincrease the amounts and types ofstress, converting them to a higher levelof shear. Angled abutments also exhibitproblems due to their inability todirect forces along the long axes. As aresult, it is essential to revise implantnumbers, sizes, and locations to optimizeocclusal force distribution. Theneed for surgical ridge augmentationmay be indicated in order to improvethe labial placement of implants.Occlusal table width is a critical parameterthat the restorative dentistBrian J. Jacksonmust assess. The width of the occlusaltable may be related to the width of theimplant body. It influences the amountof force needed for mastication, buccallingualridge lap dimensions, and porcelainfracture. Wide occlusal tables oftencause offset contacts during masticationand parafunction. Therefore,Journal of Oral Implantology 233IMPLANT-PROTECTED OCCLUSION APPLICATIONSthe buccal-lingual dimensions shouldbe minimized in order to reduce theforce required to penetrate a bolus offood. This feature will diminish thelevels of stress to the supporting bone.Another beneficial factor is to increasethe total surface area of the implants.This will reduce stress to thebone and can be accomplished by usingwider implants and/or splintingstandard-size implants together. Ofbenefit would be to change from afixed prosthetic reconstruction to a removabledesign. This is particularlycritical when treating a patient whohas a parafunctional habit (ie, bruxism).The utilization of cantilevers ispracticed in implant dentistry. Becauseocclusion is so critical for long-termsuccess, it should be designed, whenfeasible, to direst forces through theimplant bodies and away from any distalcantilevers. This will reduce compressiveforces on the distal cantilevers,as well as minimize shear andtensile forces on the more anterior implantabutments. Contact must beavoided at the distal aspects of cantileversduring lateral excursions. Particularattention should be made to theendosseous implant anterior-posterior(A-P) spread, which will determine thelength of the cantilevers.16 As the A-Pspread increases, so can the length ofthe cantilevers. A general rule on cantileverlength is 1.5 3 the A-P spread.CONCLUSIONThe role of the restorative dentist is tounderstand the responsibilities to minimizeocclusal overload and its deleteriouseffects. The importance of a properdiagnosis leading to a treatmentplan providing adequate support must234 Vol. XXIX/No. Five/2003be appreciated and the differences betweennatural teeth and dental implantsunderstood, which would allowthe development of an implant-protectedocclusion. More specifically,treatment plans containing angledabutments, wide occlusal tables, lessthan optimal cumulative surface areas,and cantilevers should be alleviated orminimized prior to initiation of therapy.These principles will encouragepredictable, satisfactory results.ACKNOWLEDGMENTThe author wishes to acknowledgeMelanieFink and Anita Jones for their assistancein the preparation of this article.REFERENCES1. Misch CE. Occlusal considerationsfor implant-supported prostheses.In: Misch CE, ed. Contemporary ImplantDentistry. St. Louis, Mo: Mosby;1993:705-733.2. Cranin AN. Atlas of Oral Implantology.New York, NY: Georg ThiemeVerlag; 1993:18-52.3. Brunski JB. Influence of biomechanicalfactors at the bone-biomaterialinterface. In: Davies JE, ed. The Bone-Biomaterial Interface. Toronto: Universityof Toronto Press; 1991:391-405.4. Brunski JB. Biomechanics ofdental implants. In: Block MS, Kent JN,eds. Endosseous Implants for MaxillofacialReconstruction. Philadelphia, Pa: Saunders;1995:22-39.5. 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