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Biomechanical aspects of monoblock implant bridges for the edentulous maxilla and mandible concepts of occlusion and articulation

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  • 1. Biomechanical Aspects of Monoblock Implant Bridges for the Edentulous Maxilla and Mandible: Concepts of Occlusion and Articulation Rainer Bocklage, DrMedDent, DUI* mplant treatment consists of 2 components: biology of the jaw bone and mechanics on implants and supraconstruction.1 Connective tissue-integrated implants are inferior than osseointegrated implants, because their mobility is increased during functional loading. However, osseointegrated implants can lose osseointegration by overload on the implant bodies.2,3 For implant placement and fabrication of implant bridgework, several factors are important: the number and position of implants, the available implant surfaces for load transmission on the jaw bone, the relation between length of the supraconstruction to the implant body, and finally, the adjustment of correct occlusion and articulation patterns.4,5 According to the basics of mechanics, a mechanical load causes deformation. The stressed body works against this load with the same force (action ϭ reaction). During loading time, there is a much higher deformation on the mandible (flexion) than on the maxillary arch. Even the distance of implants placed between the mental foramina is diminished during loading. The maximum vertical component of bite force in occlusion in the molar region is 6 to 10 times higher than during natural chewing function. Supraconstructions have to be passive and must fit correctly to the I *Private practice. ISSN 1056-6163/04/01301-049 Implant Dentistry Volume 13 • Number 1 Copyright © 2004 by Lippincott Williams & Wilkins DOI: 10.1097/01.ID.0000116452.45096.E0 The knowledge of forces that influence implants and suprastructure is important for the restorative dentist to realize the surface areas and vertical dimension of fixed restorations. The purpose of the concepts of occlusion is to respect the protection of implants that receive stress transmission and being aware of destructive forces. In cases in which the edentulous maxilla and mandible are provided with large monoblock implant bridges, the author recommends a bilateral balanced group guidance. If biomechanical principles are not respected, implant loss and restoration failure will result. For the first adjustment of occlusion and articulation patterns immediately after implantation, fixed temporaries are placed on the implants. Another 40 to 60 days later, the temporaries are exchanged for definitive implant bridgework. (Implant Dent 2004;13:49 –53) Key Words: biomechanics, forces, overload, group guidance implant abutments. In cases in which they do not fit to the abutments, tension on the cortical bone can be noted in the horizontal plane. In the vertical plane, an addition of tensile forces on the implants is often noticed. To avoid damages to implants, it is important to respect the following rules: small differences of the implant axis in the vertical plane to the other implants (parallelism) and clearness in the concepts of occlusion and articulation. Analysis of cantilever bridges placed on 4 or 6 implants reveals the harmlessness of forces within the supporting polygon.6 Similar axial forces on both posterior cantilevers, however, create undesirable forces: compressive force on the posterior implants and tensile force on the anterior implants. The loading of only one side of the cantilever bridge is very unfavorable. These constructions are rather dangerous and destructive for posterior implants. The implant-supported bridges presented by the author are not fixed cantilever bridges.7 Setting implants in the posterior areas of maxilla and mandible, the monoblock restorations are also supported distally. The occlusion and articulation concept of implant-supported bridges has to establish a centric jaw relation and finally to protect implants from overload and unfavorable forces (compressive, tensile, shear).8,9 CONCEPTS OF OCCLUSION ARTICULATION AND The common purpose of those concepts is a protection of implants. Occlusion and articulation of implantsupported restorations have to reduce stress on the implants.10 For rehabilitation of the edentulous maxilla and mandible with fixed monoblock restorations, the articulation pattern is changed in a bilateral group guidance. In a first step, this change is real- IMPLANT DENTISTRY / VOLUME 13, NUMBER 1 2004 49
  • 2. ized by fixed metal/resin temporaries placed immediately after implantation for 40 to 60 days on the implant abutments.11,12 Applying this procedure shortly after operation, the patient should adapt easily to group guidance. Using natural canine guidance in such cases can cause problems for long-term success of implants. During lateral movement of the mandible, a high compression force is noted in the area of the artificial canine and, as well, a significant compression on the premolar and molar zones of the working side. On the disclusion side, an important tensile force on the implants is evident. Compression on the working side and tensile force on the contralateral side of the arch induce a micromovement of the monoblock bridgework with the unpleasant results of bone loss combined with possible implant loss. Lots of failures are caused by this phenomenon. (As I started the rehabilitation of the edentulous maxilla and mandible with implant-supported fixed bridges in the early 1990s, I had a lot of problems 3 to 4 years after definitive placement of the bridgework because I applied a canine guidance in these cases.) Using unilateral group guidance, the compressive force is distributed on premolars and molars of the working side. Nevertheless, tensile forces are noted on the contralateral side. These forces are less destructive but also dangerous (Fig. 1A). Therefore, the author recommends a bilateral balanced occlusion in such implant cases. This guidance causes better loading transference to the jaw. Under this condition, tensile forces are minimized. The compressive force is distributed over almost the whole arch. During chewing function, the contralateral side is also supported (Fig. 1B). Furthermore, it is important to eliminate the palatal contacts of the upper incisors during protrusive movement. Otherwise, significant tensile forces are noted in the posterior areas on both sides of the upper bridgework. This lever is especially dangerous for implant patients with parafunctional habits (Fig. 1C). Finally, it is recommended to eliminate prematurities on the occlusal table of bridgework during lateral movements. 50 MONOBLOCK IMPLANT BRIDGES monoblock bridge, the natural canine guidance can also be maintained. There are no destructive forces on teeth and implants. CASE PRESENTATIONS Case No. 1 The edentulous maxilla and mandible are provided with implants. The implants are immediately loaded with fixed metal/resin temporaries. Forty to 60 days postoperatively, the definitive monoblock bridges (metal/porcelain) are fabricated. The following aspects are respected: • Centric jaw relation (Fig. 2) • No canine guidance, but a bilateral balanced group guidance (Fig. 3) • Prematurities are eliminated during lateral movements (Fig. 4) • No palatal contacts of the upper incisors in protrusive movements (Fig. 5) Case No. 2 Fig. 1. Effects of compressive and tensile forces on implants of monoblock bridges. (A) Lateral movement in unilateral balanced occlusion: Compressive force (white arrow) in the premolar and molar area causes a tensile force (red arrow) on the contralateral side. (B) Lateral movement in bilateral balanced occlusion: Compressive force (white arrow) in the premolar and molar area causes no tensile force on the contralateral side. (C) Protrusive movement: Compressive forces (white arrows) on the upper incisors cause tensile forces (red arrows) on both sides of the upper bridgework. If the edentulous maxilla is supplied with an ordinary removable prosthesis and the edentulous mandible with an implant-supported monoblock bridge, the canine guidance can be maintained. If in such cases the shearing forces are too high, the upper prosthesis cannot be kept stable on the maxilla. Therefore, these forces are not destructive to the implants in the edentulous mandible. According to clinical observation in the last 15 years, in situations in which implants are tied together with natural teeth to restore the jaw with a The maxilla is restored with a conventional prosthesis. The edentulous mandible is provided with an implant-supported monoblock bridge. In this case, the natural canine guidance is maintained (Fig. 6). Case No. 3 In the upper jaw, implants and natural teeth are tied together with a monoblock bridge. The mandible has conventional bridgework. According to my clinical observation in the last 15 years, canine guidance has no destructive effects on teeth and implants (Fig. 7). RESULTS The occlusion and articulation of an implant-supported suprastructure has to diminish stress on the implants. For the treatment of the edentulous maxilla and mandible with fixed implant bridges, the occlusion pattern has to be changed to a bilateral balanced group guidance. Canine guidance in these cases can cause destructive forces on implants and bridgework. Loss of implants and failure of the restoration are the consequences. The first adjustment should be executed with fixed temporaries
  • 3. Fig. 2. Maxillary and mandibular casts mounted on the articulator. Fig. 5. No palatal contacts of the upper incisors in protrusive movement. Fig. 6. Prosthesis and implant-supported monoblock bridge with natural canine guidance. Fig. 3. A bilateral balanced occlusion of the monoblock bridges is realized. Fig. 7. Monoblock bridge (teeth and implants tied together) in the maxilla and classic bridgework with canine guidance. Fig. 4. Intraoral view of implant-supported bridgework during lateral movement. (metal/resin) on the implants. They are used for 40 to 60 days after operation. Applying the results of occlusion, articulation and vertical dimension the transitional bridges are exchanged for definitive bridgework (metal/porcelain). Beside group guidance, it is important for these bridges to eliminate contacts on the upper incisors during protrusive movement and prematuri- ties on the occlusal table of bridgework during lateral movement.13 In the other implant cases that are presented, the canine guidance is applied similar to natural teeth arches. DISCUSSION In function, the mandible works like a hammer and the maxilla represents the anvil. The forces that influence implants and bridgework are compressive, tensile, and shearing forces. Overload on fixtures leads to an osteolysis around the implants.14,15 The fixtures lose their osseointegration. Without correct articulation, a destructive load transmission is noted on the fixtures. The consequences could be implant loosening and implant fracture. Applying screwretained bridgework, loosening and fracture of the fixation screws are also possible. Implant loosening is often noticed in the porous maxillary bone and fracture in the dense mandibular bone jaw. These observations appear to take place especially in the posterior implant sites of the lower jaw. Working according to the principles of gnathology in placing the condyles in the most retruded position as possible (centric bite), and applying a bilateral balanced occlusion, the mechanical load is transmitted over the suprastructure on all implants. Stress reduction is achieved. A main problem in implantology is bruxism.16 Bruxism is the vertical and horizontal, nonfunctional grinding of teeth. Bruxism is the most common oral habit. The maximum biting force of bruxers is greater than conventional biting forces. The maximum vertical component of bite force in occlusion in the molar region is 6 to 10 times higher than during natural chewing function. In the natural dentition, the maximum force is approximately 400 N, patients with implants approximately 200 N, and patients with conventional prostheses approximately 100 N.17 Bruxism imparts overload on implants. Even by adapting correct occlusion and articulation patterns, the results in these cases are often unfavorable. CONCLUSION A knowledge of forces that affect implants and suprastructure is important for the restorative dentist to realize. This includes the surface areas and vertical dimension of occlusion of fixed restorations. The goal is to prevent destructive forces on implant bridgework and fixtures. In cases in which the edentulous maxilla and mandible are provided with large monoblock implant bridges, the author recommends a bilateral balanced group guidance. IMPLANT DENTISTRY / VOLUME 13, NUMBER 1 2004 51
  • 4. DISCLOSURE The author claims to have no financial interest in any company or any of the products mentioned in this article. REFERENCES 1. Misch CE. Clinical biomechanics in implant dentistry. In: Misch CE, ed. Contemporary Implant Dentistry, 2nd ed. St. Louis: Mosby; 1999:303–316. 2. Weinberg LA. Reduction of implant loading with therapeutic biomechanics. Implant Dentistry. 1998;7:277–285. 3. Adell R, Lekholm B, Rockler B, et al. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Maxillofac Surg. 1981;10: 387–396. 4. Engleman MJ, Sorensen JA, Moy P. Optimum placement of osseointegrated implants. J Prosthet Dent. 1988;59:467– 473. 5. Bahat O. Treatment planning and placement of implants in the posterior maxillae: Report of 732 consecutive No- belpharma implants. Int J Oral Maxillofac Implants. 1993;8:151–157. 6. Misch CE. Chapter 10. Diagnostic casts, preimplant prosthodontics, treatment prostheses, and surgical templates In: Misch CE, ed. Contemporary Implant Dentistry, 2nd ed. St. Louis: Mosby; 1999: 140–141. 7. Bocklage R. Rehabilitation of the edentulous maxilla and mandible with fixed implant-supported restorations applying immediate functional loading: A treatment concept. Implant Dentistry. 2002;11:154– 158. 8. Stuart CE. The geometrics of the gnathic system. J Gnathol. 1982;1:6–13. 9. Kantor M, Silverman S, Garfinkel L. Centric relation recording techniques: A comparative investigation. J Prosthet Dent. 1972;28:593–600. 10. Weinberg LA. Axial inclination and cuspal articulation in relation to force distribution. J Prosthet Dent. 1957;7:804–813. 11. Bocklage R. Advanced alveolar crest atrophy: An alternative treatment technique for maxilla and mandible. Implant Dentistry. 2001;10:30–35. 12. Tarnow DP, Emitiag S, Classi A. Immediate loading of threaded implants at one stage surgery in edentulous arches: Ten consecutive case reports with 1 to 5 year data. Int J Oral Maxillofac Implants. 1997;12:319–324. 13. Stuart CE. Overlap of the upper anterior teeth and its determinants. J Gnathol. 1983;2:3–10. 14. Misch CE. Bone response to mechanical loads. In: Misch CE, ed. Contemporary Implant Dentistry, 2nd ed. St. Louis: Mosby; 1999:317–328. 15. De Lange G, De Putter C. Structure of the bone interface to dental implants in vivo. J Oral Implantol. 1993;19:123–135. 16. Misch CE. Dental evaluation. In: Misch CE, ed. Contemporary Implant Dentistry, 2nd ed. St. Louis: Mosby; 1999: 124–127. 17. Braun S, Hnat WP, Freudenthaler JW, et al. A study of maximum bite force during growth and development. Angle Orthodont. 1996;66:261–264. Reprint requests and correspondence to: Rainer Bocklage, DrMedDent, DUI Langemarkstr.11, D-41539 Dormagen, Germany E-mail: info@drbocklage.de Abstract Translations [German, Spanish, Portugese, Japanese] AUTOR: Rainer Bocklage, Dr. med. dent., DUI. *Privat praktizierender Arzt. Schriftverkehr: Rainer Bocklage, Dr. med. dent., DUI, Langmarkster 11, D-41539 Dormagen. eMail: info@drbocklage.de Biomechanische Aspekte von einteiligen Implantatbrücken für den zahnlosen Oberund Unterkiefer: Konzeptionen zu Zahnreihenschluss und Artikulation ZUSAMMENFASSUNG: Die genaue Kenntnis der auf die Implantate und deren Überbau einwirkenden Kräfte ist für den behandelnden Zahnarzt bei der Wiederherstellungsbehandlung von größter Bedeutung, da nur so die Oberflächenbereiche und vertikalen Ausdehnungen der festen Wiederherstellungsmedien exakt festgelegt werden können. Das Okklusionsprinzip zielt darauf ab, gestressten Implantaten den erforderlichen Schutz zukommen zu lassen und ein Bewusstsein für eventuell vorliegende zerstörerische Kräfte zu entwickeln. Wird ein zahnloser Ober- oder Unterkiefer mittels einteiliger Implantatbrücke wiederhergestellt, empfiehlt der Autor des Artikels den Einsatz einer bilateral austarierten Gruppenführung. Missachtet man bei der Behandlung die normalen biomechanischen Prinzipien, muss als Ergebnis mit Implantatverlust und Fehlschlagen der gesamten Wiederherstellungsbehandlung gerechnet werden. Für die Erstanpassung des Zahnreihenschlusses und der Artikulation unmittelbar nach erfolgter Implantierung werden feste Provisorien auf den Implantaten befestigt. Nach 40 bis 60 Tagen werden diese Provisorien dann durch die endgültigen Implantatbrücken ersetzt. SCHLÜSSELWÖRTER: Biomechanik, Kräfte, Überlastung, Gruppenführung AUTOR: Rainer Bocklage, Dr. med. dent, DUI. *Práctica Privada. Correspondencia a: Rainer Bocklage, Dr. med. dent., DUI, Langemarkster 11, D-41539, Dormagen, Alemania. Correo electrónico: info@drbocklage.de Aspectos biomecánicos de los puentes de implante de un solo bloque para el maxilar y la mandíbula edentulosa: Conceptos de oclusión y articulación ABSTRACTO: En el conocimiento de las fuerzas que influencian a los implantes y la supraestructura es importante que el dentista de restauración tenga en cuenta las áreas de la superficie y la dimensión vertical de las restauraciones fijas. El propósito de los conceptos de oclusión es respetar la protección de implantes que 52 MONOBLOCK IMPLANT BRIDGES
  • 5. reciben la transmisión de tensión y estar al tanto de sus fuerzas destructivas. En casos donde el maxilar y la mandíbula edentulosa se incluyen con puentes de implantes de un solo bloque grande, el autor recomienda una guía grupal equilibrada bilateral. Si los principios biomecánicos no son respetados, resultará en la pérdida del implante y la falla de la restauración. Para el primer ajuste de la oclusión y la articulación inmediatamente luego de la colocación, se colocan en los implantes puentes temporarios fijos. Otros 40 a 60 días después, se cambian los temporarios por el puente definitivo con implantes. PALABRAS CLAVES: biomecánica, fuerzas, sobrecarga, guía grupal. AUTOR: Rainer Bocklage, Doutor em Odontologia, DUI. *Clínica particular. Correspondência para: Rainer Bocklage, Dr. med. dent,, DGI, Langemarkster. 11, D-41539, Dormagen, Germany. e-mail: info@drbocklage.de Aspectos biomecânicos das Pontes de Implante Monobloco para as e Mandíbula: Conceitos de Oclusão e Articulação RESUMO: O conhecimento de forças que influenciam os implantes e a supra-estrutura é importante para o dentista restaurador perceber as áreas de superfície e a dimensão vertical de restaurações fixas. O objetivo dos conceitos de oclusão é respeitar a proteção de implantes que recebem a transmissão de tensão e ser consciente das forças destrutivas. Nos casos em que a e a mandíbula são providas de grandes pontes de implante monobloco, o autor recomenda direção de grupo bilateral e equilibrada. Se os princípios biomecânicos não forem respeitados, o resultado será perda de implante e falhas na restauração. Para o primeiro ajuste de padrões de oclusão e articulação imediatamente após a implantação, próteses temporárias fixas são colocadas nos implantes. Uns 40 ou 60 dias mais tarde, as próteses temporárias são trocados por próteses de implante definitivas. PALAVRAS-CHAVE: biomecânica, forças, sobrecarga, direção de grupo IMPLANT DENTISTRY / VOLUME 13, NUMBER 1 2004 53

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