RATIONALE FOR CHOICES OF OCCLUSALSCHEMES FOR COMPLETE DENTURESSUPPORTED BY IMPLANTS

Fotoula Nikolopoulou, DDS, MD,Dr Odont, MPH

Pagona Ktena-Agapitou, DDS,Dr Odont

KEY WORDS

Complete denture supportedby implants

Occlusal materialsOcclusal schemesOcclusal forces

Fotoula Nikolopoulou, DDS, MD,Dr Odont, MPH, is a lecturer at theDental School, University of Athens,Paparseni 50 TK 11522, Athens, Greece(e-mail: fotoulan@pitt.edu; fnikolop@dent.uoa.gr). Address correspondence toDr Nikolopoulou.

Pagona Ktena-Agapitou, DDS, DrOdont, is an assistant teacher at theMedical School, University of Athens,Ipsilantou 160, Piraeus, Greece.

This review of occlusal considerations for implant-supported com-

plete dentures reflects the majority opinion of authors according to

clinical observations and research-documented evidence. Occlusal

concepts are presented for the implant-supported complete dentures

regarding analysis of loads applied to dental implants, location and

number of implants, occlusal materials, and occlusal scheme.

INTRODUCTION

It is known that naturalteeth have periodontal lig-ament receptors thatprotect the teeth and pe-riodontium from excessiveocclusal forces, which can

cause trauma to supporting tis-sues and bone. Although manyfactors are involved in the neuro-muscular reflex actions in naturalteeth, there are no specific defensemechanisms against occlusalforces in implant-supportedcomplete dentures.1 Complica-tions (prosthetic or bony sup-port) reported in follow-upstudies underline occlusion as adetermining factor for successor failure.2

For implant placement andfabrication of implant-supportedcomplete dentures, several factorsare important: the number andposition of implants, the availableimplant surfaces for load trans-mission on the jaw bone, therelation of the length of the super-structure to the implant body, and

the establishment of correct occlu-sion.3 The choice of an occlusalscheme for implant-supportedcomplete dentures is often contro-versial. Almost all guidelines arebased on those developed withnatural teeth, and there are nopublished clinical studies com-paring the occlusal theories.

This study reviews the occlu-sal concept choices for implant-supported complete dentures re-garding analysis of loads appliedto dental implants, location andnumber of implants, occlusal ma-terials, and occlusal scheme.

ANALYSIS OF LOADS APPLIED TO

DENTAL IMPLANTS

A dental implant is subjectedto mechanical forces because ofthe loading placed on the pros-thesis. Forces are described ascompressive, tensile, and shear.Compressive forces tend to main-tain the integrity of an implant.In general, the implant-supported

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CLINICAL

complete dentures best accommo-date compressive forces, whereasshear and tensile forces tend todistract or disrupt an implantinterface.4

The manner in which a force isdistributed over a surface is re-ferred to as mechanical stress.5

The magnitude of stress is de-pendent on 2 variables: force mag-nitude and cross-sectional area.A dentist can control the forcemagnitude, which depends oncantilever length and offset loads.The cross-sectional area is definedas the surface that participatessignificantly in load bearing andstress dissipation. It can be opti-mized by (1) increasing the num-ber of implants for the edentulousarea and (2) selecting an implantgeometry that has been carefullydesigned to maximize the func-tional cross-sectional area.5

Two main types of loadingshould be considered: axial forceand bending force. The axial forceis more favorable because itdistributes the stress throughoutthe implant. Posterior implant-supported complete dentures aresubjected to bending moments,which are generated by func-tional and parafunctional move-ment patterns of the mandible.

According to the theoreticalstudies that have been reportedby some authors, bending mo-ments lead to higher stress levelsin implant components and thesupporting bone than do com-pressive and tensile forces.6–9

Under lateral loads, all implantsexhibit very high levels of stressin the head and neck region withcompressive stress on one sideand tensile on the other. Theyare gradually diminished inapical and lateral directions.10–14

For better function of implant-supported complete dentures, ithas been suggested that the im-plants should have the followingconstruction:

� Root-shaped implants, becauseof their cylindrical shape, min-imize transmission of stressesto supporting bone better thanblade-shaped implants.

� Implant necks should be en-larged. Implants with narrowor constricted necks should beavoided.15,16

LOCATION AND NUMBER

OF IMPLANTS

There are basically 2 types ofimplant-supported overdentures:tissue borne and implant borne.The tissue-borne overdenture isattached to implants that areplaced in the anterior area of themaxillary and mandibular arch.At least 2 implants are requiredfor this overdenture. In the man-dible, the bar and clip are themost commonly used types ofattachments. These attachmentsnot only provide support andretention of the denture in theanterior area, but also allow stressbreaking when the area of thedenture is loaded. In the maxilla,bars and clips are not generallyused. These attachments preventcomplete seating of the prosthesisonto tissues in the area where theimplants are placed, impedethe achievement of seal aroundthe periphery of the denture, andresult in loss of retention ofdentures. This overdenture de-sign is dependent on soft tissuesupport.17,18

The width of the arch playsa role in determining the positionof the implants and the distancebetween the implants.19 Patientswith a tapered mandibular archare not considered good candi-dates for a 2-implant bar andclip system because the bar willoccupy the tongue space. If thebone is of good quality and im-plants are of sufficient length,attachments can be placed over

individual implants without theuse of a splinting bar.20 Theocclusion for this type of over-denture should include contactsin centric relation and in eccentricpositions.20

An implant-borne overden-ture relies on the implants to bearthe full occlusal loading. Thisprosthesis requires the use ofa sufficient number of implantsto accommodate the load that isplaced on the prosthesis.20 Theminimum number of implantsrequired is 4 in the mandibleand 6 to 8 in the maxilla.

The number and the locationof implants reflect the quality andquantity of bone. It is importantto avoid cantilevers on the max-illary arch. Symmetric placementof implants in the tuberosity,canine, and incisor regions isrequired,21 and the type of occlu-sal scheme should be balancedand lingualized. The implantscarry all the occlusal loading.22

OCCLUSAL MATERIALS

The materials that are used for theocclusal surface of the prosthesisaffect the transmission of forcesand maintenance of occlusal con-tacts. Occlusal materials may bedetermined by aesthetics, impactforce, chewing efficiency, wear,fracture, and interarch space.23–25

Occlusal loading of osseointe-grated implants is believed to bean important factor in the long-term success of implant-supportedcomplete dentures.26

Branemark and his associ-ates27 proposed a protocol forocclusal development based onphysics and clinical results.Acrylic resin was the material ofchoice for the occlusal surfaces.The resiliency of acrylic resin wassuggested as a safeguard againststress and microfracture of theimplants.28,29 In contrast with the

Fotoula Nikolopoulou, Pagona Ktena-Agapitou

Journal of Oral Implantology 201

foregoing studies, Ismail and hisassociates30 revealed that thefunction of the resin teeth as ashock absorber was not valid.

It has been suggested thatmetal occlusal surfaces may bepreferred in order to minimizewear and prolong the accuracyand longevity of occlusal schemes.5

Porcelain teeth in both arches isthe material most often selectedwhen there are parafunctionalhabits and marginal interarchspace.31,32 Improved compositeresin materials are available thatwear less than acrylic and arevery similar to enamel; however,the long-term fracture potentialof these materials on implantshas not yet been established.33

OCCLUSAL SCHEME

The goal of any prostheticprocedure must include the es-tablishment of a functional oc-clusion.34 Many authors havedeveloped guidelines for occlu-sion over dental implants. Al-though all authors appear toagree on a balanced occlusion,there are no clinical experimentaldata to support these assump-tions.35–37 Balanced occlusion innatural dentition is not neededbecause the periodontal ligamentsupports each tooth indepen-dently. Numerous articles havedescribed occlusal schemes foredentulous patients.

Parr and Loft38 reviewed thevarious occlusal schemes, whichrange from full anatomic bal-anced to neutrocentric occlusion.These different occlusal schemeswere developed to function onunstable denture bases. Occlu-sion and articulation of implant-supported complete dentures mustreduce stress on the implants.39

The occlusion should distrib-ute the forces evenly among theimplants. The vertical dimension

of occlusion should be madecompatible with a patient’s freespace and evaluated carefully.Adequate interarch space is need-ed to accommodate the prosthesisand allow for adequate hy-giene.40,41

For tissue-supported overden-tures, balanced occlusion is sug-gested with simultaneous contactof the artificial teeth. In edentu-lous patients, there is more lee-way in control of the incisalguidance. The role of condylarguidance also varies with the typeof developed occlusion. If a bal-anced occlusion is desired, a 3-point contact balance between theworking and nonworking sidesis achieved. No attempt shouldbe made to obtain a full balancedocclusion.20

A full balanced scheme ofocclusion can be developed withany of the various cusp types ofartificial teeth with a compensat-ing curve.42 If there is mandibularresorption, a flat plane type ofocclusion should be developed.This is accomplished by the use of08 teeth in the opposing arches.20

A lingualized type of occlusion ispreferred in order to eliminate orreduce lateral stress. The teethwith the greater cusp degree areplaced in the maxillary arch,allowing for the lingual cusps ofthe maxillary posterior teeth toglide from central fosse and ontothe buccal and lingual inclinesof the buccal and lingual cuspsof the mandibular teeth. Thisocclusal scheme is based on theuse of the maxillary lingual cuspas the ‘‘stamp cusp,’’ which oc-cludes with a shallow mandibu-lar central fosse. A lingualizedocclusion can also be accom-plished by the use of cusped teethin the maxillary arch and 08 teethin the mandible.43,44

The occlusion chosen forimplant-supported complete den-tures should be a balanced occlu-

sion ensuring that there is nointerference with jaw movementsinto eccentric positions.45 A lin-gualized occlusion provides anexcellent alternative to a fullybalanced scheme.46

DISCUSSION

In addressing the subject of den-tal implants, a dentist must con-sider not only the surgical phaseof placing the implants, but alsothe entire treatment sequence,especially the prosthodontic re-habilitative procedures. Manyimplant failures can be attributedto improper occlusal design,which can concentrate stresses inthe bone and lead to rapid boneresorption.47 Certain rules arerecommended to establish properocclusal design: (1) cusp designsshould be made so that the stressis directed along the long axis ofthe implant, (2) lateral stressesshould be avoided, (3) the widthof the occlusal table should beno wider than the width of theimplant root, and (4) cusp heightshould be minimized in order todecrease lateral stress. Sometimesthe occlusal table should be flat,providing only centric func-tion.15,48

Lingualized occlusion can bepreferred in tissue-borne andimplant-borne overdentures. Theadvantages of this occlusion arethat the penetration of the bolusof the food is accomplished withless occlusal force and that theopposing incline surfaces of thetooth provide buccolingual sta-bility and eliminate the potentialfor lateral interferences in excur-sive movements.44,49

REFERENCES

1. Gibbs CH, Suit SR. Movements ofthe jaw after unexpected contact with ahard object. J Dent Res. 1973;52:810–814.

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2. Isidor F. Histological evaluation ofperi-implant bone at implants subjectedto occlusal overload or plaque accumu-lation. Clin Oral Implants Res. 1997;8:1–9.

3. Engelman MJ, Sorensen JA, Moy P.Optimum placement of ossointegrationimplants. J Prosthet Dent. 1998;59:467–473.

4. Reilly DT, Burstein AH. The elasticand ultimate properties of compact bonetissue. J Biomech. 1975;8:393–405.

5. Misch EC. Contemporary ImplantDentistry. 2nd ed. St Louis, Mo: Mosby;1999:303–313, 603–626.

6. Rangert B. Mechanical and bio-mechanical guidelines for the use ofBranemark system. General principles.Aust Prosthodont J. 1993;7(suppl):39–44.

7. Glantz PO, Rangert B, Svenson A,et al. On clinical loading of osseointe-grated implants. A methodological andclinical study. Clin Oral Implants Res.1993;4:99–105.

8. Rangert B, Jemt T, Jomeus L. Forcesand moments on Branemark implants. IntJ Oral Maxillofac Implants. 1989;4:241–247.

9. Ko CC, Kohn DH, Hollister SJ.Micromechanics of implant/tissue inter-faces. J Oral Implantol. 1992:18:220–230.

10. Morgan MJ, James DF, Pilliar RM.Fractures of the fixture component ofan osseointegrated implant. Int J OralMaxillofac Implants. 1993;8:409–414.

11. Phillips K, Mitrani R. Implantmanagement for comprehensive occlusalreconstruction. Compend Contin Educ Dent.2001;22:235–238.

12. Cehreli M, Duyck J, De CoomanM, et al. Implant design and interfaceforce transfer. Clin Oral Implants Res.2004;15:249–257.

13. Brunski JB. Biomechanical as-pects of oral/maxillofacial implants. IntJ Prosthodont. 2003;16(suppl):30–32, dis-cussion 47–51.

14. Brunski JB, Puleo DA, Nanci A.Biomaterials and biomechanics of oraland maxillofacial implants: current statusand future developments. Int J OralMaxillofac Implants. 2000;15:15–46.

15. Fagan M, Ismail J, Meffert R,Fagan J. Implant Prosthodontics Surgicaland Prosthetic Techniques for Dental Im-plants. Chicago, Ill: Yearbook Med;1990:217–229.

16. Bergman B. Evaluation of theresults of treatment with osseointegratedimplants by Swedish National Board ofHealth and Welfare. J Prosthet Dent.1983;50:114–115.

17. Adrian E, Krantz W, Ivanhoe J.The use of processed silicone to retain theimplant-supported tissue-borne overden-ture. J Prosthet Dent. 1992;67:219–222.

18. Wismeijer D, van Waas M, KalkW. Factors to consider in selecting anocclusal concept for patients with im-plants in the edentulous mandible.J Prosthet Dent. 1995;74:380–384.

19. Mericske-Stem R. Clinical evalu-ation of overdenture restorations sup-ported by osseointegrated titaniumimplants: a retrospective study. Int J OralMaxillofac Implants. 1990;5:375–383.

20. Block M, Kent J, Guera L. Im-plants in Dentistry. Philadelphia, Pa: WBSaunders; 1997:94–189, 112–212.

21. Osier J. Biomechanical load anal-ysis of cantilevered implant systems.J Oral Implantol. 1991;17:40–47.

22. Winkler S, Monasky GE. Theedentulous mandible opposing maxillarynatural teeth: treatment considerationsutilizing implant overdentures. ImplantDent. 1993;2:44–47.

23. Cibirka RM, Razzoog ME, LangBR, Stohler CS. Determining the forceabsorption quotient for restorative mate-rials used in implant occlusal surfaces.J Prosthet Dent. 1992;67:361–364.

24. Bidez MW, Misch CE. Forcetransfer in implant dentistry: basic con-cepts and principles. J Oral Implantol.1992;18:264–274.

25. Misch CE, Bidez MW. Implantprotected occlusion. Int J Dent Symp.1994;2:32–37.

26. Skalak R. Biomechanical consid-erations in osseointegrated prostheses.J Prosthet Dent. 1983;49:843–848

27. Branemark P, Zarb G, Albrekts-son T. Tissue Integrated Prostheses. Chica-go, Ill: Quintessence; 1985:11–19, 117–128,156–162.

28. Davis DM, Rimrott R, Zarb G.Studies on frameworks for osseointe-grated prostheses: part 2. The effectof adding acrylic resin or porcelainto form the occlusal superstructure. IntJ Oral Maxillofac Implants. 1988;3:275–280.

29. Brunski JB. Biomaterials and bio-mechanics in dental implant design. IntJ Oral Maxillofac Implants. 1988;3:85–97.

30. Ismail Y, Kukunas S, Pipko D,et al. Comparative study of variousocclusal materials for implant prostho-dontics. J Dent Res. 1989;68:962.

31. Mahalick JA, Knap FJ, Weiter EJ.Occlusal wear in prosthodontics. J AmDent Assoc. 1971;82:154–159.

32. Monasky GE, Taylor DF. Studieson the wear of porcelain enamel andgold. J Prosthet Dent. 1971;25:299–306.

33. Rabinowitz E. Friction and Wearof Materials. New York, NY: Wiley Co;1965:113–123.

34. Parker MW. The significance ofocclusion in restorative dentistry. DentClin North Am. 1993;37:341–351.

35. Chapman RJ. Principles of occlu-sion for implant prostheses: guidelinesfor position, timing and force of occlu-sal contacts. Quintessence Int. 1989;20:473–480.

36. Hobo S. Twin-tables techniquefor occlusal rehabilitation: part I—mech-anism of anterior guidance. J ProsthetDent. 1991;66:299–303.

37. Schulte JK, Peterson TA. Im-plants: occlusal and prosthetic consider-ations. CDA J. 1987;15:64–72.

38. Parr GR, Loft GH. The occluasalspectrum and complete dentures. Com-pend Contin Educ Dent. 1982;3:241–250.

39. Bocklage R. Biomechanical as-pects of monoblock implant bridges forthe edentulous maxilla and mandible:concepts of occlusion and articulation.Implant Dent. 2004;13:49–52.

40. Lundqvist S, Carlsson GE. Max-illary fixed prostheses on osseointegrateddental implants. J Prosthet Dent. 1983;50:262–270.

41. Caswell W, Clark A. Dental Im-plant Prosthodontics. Philadelphia, Pa: JBLippincott; 1991:305–315.

42. Guerra LR, Finger IM, Block MS.Tissue-supported implant overdentures.Implant Dent. 1992;1:69–77.

43. Lang BR, Razzoog ME. Lingual-ized intergration. Tooth molds and anocclusal scheme for edentulous implantpatients. Implant Dent. 1992;1:204–211.

44. Reitz J. Lingualized occlusionin implant dentistry. Quintessence Int.1994;25:177–180.

45. Winkler S, Monasky GE. Theedentulous mandible opposing maxillarynatural teeth: treatment considerationsutilizing implant overdentures. ImplantDent. 1993;2:44–47.

46. Kopp CD. Overdentures and os-seointegration. Case studies in treatmentplanning. Dent Clin North Am. 1990;34:729–739.

47. Lundgreen D, Laurell L, Falk H,Bergendal T. Occlusal force pattern dur-ing mastication in dentitions with man-dibular fixed partial dentures supportedon osseointegrated implants. J ProsthetDent. 1987;58:197–202.

48. Jackson BJ. Occlusal principlesand clinical applications for endosseousimplants. J Oral Implantol. 2003;29:230–234.

49. Sadowsky S. The implant-supportedprosthesis for the edentulous arch: de-sign considerations. J Prosthet Dent.1997;78:28–33.

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