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Treatment plan and biological consideration of implants
- 1. Biomechanics, Treatment Planning, and Prosthetic Considerations of implants Dr. Diana Abo El Ola
- 2. IF Loading- bearing capacity of implant < anticipated loads during function FAILURE in osseointegration . -NATURAL TEETH are more adapted to forces (y??) Any movement of OSSEOINTEGRATED IMPLANT (direct bone contact) loss of osseointegration fibrous encapsulation failure(no adaptation to excessive forces).
- 3. ā¢ Control & distribution of stress F. ā¢ The Q & Q of available bone. ā¢ Maintenance of bone apposition. ā¢ Bone Support under functional loading. Is a Critical factor Controlled by Controlled by
- 4. If applied loads exceed load-bearing capacity Mechanical failure ā¢ Screws that secure the restorationļØmay bend, loosen, or fracture ā¢ Fracture of the implant Biologic failure ā¢ ļ©bone loss around the implant ļØļ§ļÆļ osseointegration
- 5. Load-Bearing Capacity Is influenced by: 1.The quality of the bone-implant interface. 2.The no and size (Length & Width) of implants. 3.The arrangement & angulation of implant position. ā¢The bone appositional index : ā¢Is the % of bone-to-implant contact ā¢It is the most important factorļØ to consider when evaluating the load-bearing capacity of implant. ļŖ bone density ļŖbone-implant contact (low bone apposition index) ļŖ support & resistance to occ. loads.
- 6. 1-Quality of bone Most dense bone is 1- Anterior mand.(Thick cortical plate +dense trabecular) 2- Anterior Max. (Dense cortical plate + dense trabecular) 3- Posterior mand. (Thin cortical plate + thin trabecular) 4- Posterior Max.(thin cortical plate + least dense trabecular(fine) Ant. Mand. Index=65-90% Post. Max. index=30-60%
- 7. Implant Surface with altered microtopography (surface modification) Higher bone appositional index than machined surfaces + facilitate biologic process of bone formation. Enhance bone apposition in poor Q & Q bone.
- 8. ā¢ Lack of bone height/anatomic str.?? Long Implant Reduce bone-implant contact & bone apposition index Solution: (use short wide implant toļ© load bearing area) Or (elevation of sinus floor or bone augmentation) Surf. modification (microtopigraphy)ā¦higher bone apposition index b.Size of implant(W &L) 2-a.Number of implants One implant for every missing tooth BUT In mand : use fewer implants, y??
- 9. 3-a.Implant Arrangement 1-In linear fashion unfavorable response 2-In nonlinear (curvilinear or staggered) configuration more stable & resists torqueing F. ( created by off-center contacts & lateral loads). Implant supported FPD ļ cause NON AXIAL LOADSļ LOAD MAGNIFICATION(overload F.) ļ implant- bone interface (esp. coronal part?? )or microdamage (fracture-cracks) ļ FAILURE In case of ā¢ Implant- with a cantilevered ponticļ transfer nonaxial Forcesļ creating a torqueing forces ļ load magnification ļ BONE LOSS.
- 10. b. Implant Angulation ā¢ It affects the transfer of occusal forces to implants and surrounding bone. If loads are applied at an angle ā„200 to the long axis of the implant(Non-axial loads ) LOAD MAGNIFICATIONā¼ concentrated stresses around the neck of the implant Resorptive remodeling ā¼ coronal bone loss. N.B Short implant +improper positioned and angulation in poor quality bone=OVERLOAD=FAILURE ā¢ Excessive distal angulationsā¼ created non-axial loading ā¼ bone loss.
- 12. ļ§ Multiunit implant restorations ā¦..splinted to share the loads. ļ§ Open embrasure spacesā¦ā¦ facilitate OHI (avoid tipping F.) ļ§ Wide diameter implants ā¦..especially for molar replacement. ļ§ Standard diameter (4 mm implants)ā¦ best for premolar replacement. 1. Limiting the width of the occlusal table 2. Flattening the cusp angles 3. Avoiding cantilevered restorations 4. Restoring the anterior guidance
- 13. Not advisable because: 1. Implants & teeth function differently. 2. It may cause screw loosening and intrusion of natural teeth. 3. It may create a cantilever effect on the implant.
- 14. 1. A rigid connection should be done, either with screw-retained attachments or with secured permanent cement. 2. Tooth preparation should allow good retention. 3. Teeth should be periodontally healthy & stable. 4. The occlusal scheme should be good. ā¢If implant is to be connected to teeth authors say:
- 15. Summary to Avoid Implant Overload
- 16. Place implants perpendicular to the occ. Plane.(not flat)(curve of Spee & Wilson ) Use 1 implant for each tooth being replaced in curved manner. Avoid the use of cantilevers & linear manner.
- 17. Flattening the cusp angles & decrease width of occ. table. Avoid use of short implants(less than 10mm) and distal angulation Avoid connecting implants to teeth. If needed, use a rigid attachment.
- 18. Treatment plan for implant placement
- 19. RX PLAN FOR
- 20. Adv. ā¢Poor ridge form ā¢Lack of max. post. support with an intact mand. Ant. Teeth leads to a condition called ā combination syndrome ", as in closure ļØ causes a āhammer and anvilā type of destruction of the ed. ant. maxilla. ā¢Patient cannot tolerate palatal coverage .(psychologically- taste and texture sensation-avoid gag reflex-presence of torus ) Complete denture Implant assisted overlay denture Implant support fixed prosthesis Disadv: The max. sinusā© limits the height of bone available for implant. Options for a dentist
- 21. Only 4 implant 1. Lower cost 2. Hygiene accessibility 3. Improve speech 4. The labial flange support lip (if lost ) ā¢ 6 or more implants arranged in arc of curvature with at least 2 cm of A-P spread. ā¢ Long crowns due to ļŖST height+ lack of lip support. Implant-supported fixed prosthesis ā If the A-P spread is inadequate to provide support, a full- palatal-coverage overlay denture is recommended.
- 22. Treatment Planning with Dental Implants Edentulous Mandible RX PLAN FOR
- 23. ā¢ The 2 implantāassisted overdenture is the treatment of choice. Adv. ā¢ The implants provide stability and retention while bearing minimal stress from occ. Loads ā¢ It is more critical to have //implants, y?? for proper path of insertion and to dec. stress.
- 24. ā¢ 4-6 implants arranged in an arc of curvature with at least 1 cm of A-P spread. ā¢ Masticatory efficiency is slightly better. ā¢ It tends to stop bone resorption of the posterior Mandible. Fixed implant supported prothesis vs implant over denture
- 25. Partially Edentulous Patients Multiple Tooth Sites RX PLAN FOR
- 26. The same rule(one implant for every missing tooth)
- 27. RX PLAN FOR
- 28. In post region , The most common problem āwith external hex- headed implant. Tipping of restoration during functionļØ loosening of the screw. because the diameter of the implant head is much smaller the size of the occlusal surface ļ§ Controlled by narrowing the dimension of restoration,ā B Li width & not the MD dimension because of the contacts. In ant. And premolar area Single implants ļØhigh success rate.
Editor's Notes
- NATURAL TEETH are more adapted to forces dt presence of PDL which allows slight physiologic movement during function
- Control and distribution of stress for preservation of the ābiologicā connection The Q & Q of bone available to support implants play an important role in: Stress distribution Maintenance of bone apposition Support under functional loading
- Osseointegrated dental implants provide a predictable means of replacing missing teeth and restoring dental function. It is now clear that a thorough understanding of implant biomechanics is essential if implant-retained restorations are to be employed predictably. The load-bearing capacity of implants supporting the restoration must be greater than the anticipated loads during function. If applied loads exceed load-bearing capacity, it may lead to mechanical and/or biologic failure. In the case of mechanical failure, screws that secure the restoration may bend, loosen, or fracture. The most devastating type of mechanical failure is fracture of the implant. In the case of biologic failure, a resorption-remodeling response of the bone around the implant(s) is provoked, leading to progressive bone loss.[10,18] In some cases, bone loss around the implant progresses until the implant is no longer supported and osseointegration is lost. The function and support of implant-retained restorations is quite different from tooth-retained restorations. Teeth are suspended within the supporting alveolar bone by a periodontal ligament, which allows slight physiologic āmovementā of teeth in function. If forces are excessive, teeth have the capacity to adjust or move in response to the applied forces. In the absence of inflammatory periodontal disease, teeth will adapt to these forces without appreciable bone loss. Orthodontic movement of teeth through alveolar bone is the ultimate example of the capacity of teeth to adapt to excessive applied forces. As orthodontic forces move a tooth, bone resorbs in response to pressure and forms in response to tension applied by the āattachedā periodontal ligament fibers. Osseointegrated dental implants, by definition, are in direct contact with the alveolar bone without intervening soft tissues; there is no periodontal ligament and should movement occur, it would indicate a loss of osseointegration (e.g., fibrous encapsulation).[9] Excessive forces are destructive. Thus it is crucial to have a good understanding of the biomechanical properties and the limitations of dental implants to ensure proper treatment planning that will sustain the anticipated occlusal forces.
- Load-Bearing Capacity The load-bearing capacity of implants is influenced by several factors, including the number and size of implants, the arrangement and angulation of implant positions, and the quality of the bone-to-implant interface (Box 76-1). The bone appositional index (percentage of bone-to-implant contact) may be the most important factor to consider when evaluating the load-bearing capacity of any given implant(s). Less bone density and lower bone-to-implant contact provide less support and resistance to occlusal loading. As an example, consider the bone support of implants in the posterior maxilla; the bone quality is particularly poor as compared with the anterior mandible. The trabecular bone is less dense and the cortical bone layer is thin in the posterior maxilla. As a result, the bone appositional index in the posterior maxilla is significantly less than what can be achieved in the anterior mandible, where the trabecular bone is typically dense with a thick cortical bone layer. The bone appositional index for implants in the posterior maxilla typically ranges from 30% to 60%, whereas the bone appositional index for implants placed in the anterior mandible typically ranges from 65% to 90% (Figure 76-1).
- D1ā¦.dense cortical bone(ant . And post .mand) D2ā¦.dense porous with dense trabecular( ant. And post. Mand) D3ā¦.thin porous with fine trabucular (ant . Maxilla and post maxilla) D4ā¦ā¦fine trabecular (post. Maxilla)
- Acid etched implants have harder and denser bone
- Anatomic strā¦ā¦.inf. Alveolar nereve(mand.) ,mental foramen (premolar area),max. sinus ā¦ā¦ā¦ā¦dec. height of implantā¦ā¦affect bone appostional index Wider implants rather than longer implants registered lower stress value, suggesting that the use of short, wide implants could increase the load-bearing capacity of implants and implant prosthesis. Historically, the use of longer (>7 mm) implants has been advocated as the result of reported higher rates of failure for shorter (ā¤7 mm) implants.[17,20,29,39] Logic suggests that biomechanical stress around āshortā implants leads to greater bone loss and a higher rate of implant failure. On the other hand, Pierrisnard[37] showed that the maximum implant stress increased somewhat with implant length and bicortical anchorage, encouraging use of short implants in selected cases. He also states that the low anchorage stiffness of short implant might reduce the mechanical stress to the implant because of the flexibility of the bone. Using the finite element analysis (FEA), Pierrisnard and colleagues[36] showed that greater implant length did not positively affect the way stresses were transferred to the implant but found that increasing implant diameter reduced the intensity of stress along the length of the implant. Iplikcioglu and Akca[19] using the same method observed that wider implants rather than longer implants registered lower stress value to the whole system, suggesting that the use of short, wide implants could increase the load-bearing capacity of implants and implant prosthesis. Baggi and colleagues also used FEA to show that increases in implant width reduced stress more than increases in length[5] (Box 76-2). These āroughnessā implant surfaces appear to have a significant effect on bone anchorage: Surfaces with an altered microtopography achieve higher bone appositional indices than the machined surfaces Facilitate the biologic processes of bone formation, resulting in greater deposition of bone onto the surface of the implant Bone deposited on the surface of acid-etched implants appears to be harder and denser and may be more resistant to resorptive remodeling
- Bone loss occurs Esp. around The cornal part of the implant ā¦ā¦there is no PDL + adjcent bone has the poor capacity to repair as it has different density of bone compared to apical lesion When implants are arranged in a linear fashion, the biomechanics with respect to anticipated bone response are quite unfavorable compared with a configuration in which the implants are arranged in a nonlinear (curvilinear or staggered) fashion Arranging implants in a nonlinear configuration creates a more stable base that is more resistant to the torquing forces created by off-center contacts and lateral loads Therefore every attempt should be made to position posterior implants with the long axis directed toward the opposing stamp cusp and aligned perpendicular to the occlusal plane. Then, occlusal forces can be directed down the long axis of the implant, which is tolerated far better than nonaxial forces. The restoration is also simpler and more cost effective to fabricate, since angled or custom abutments are not required. Cantilever contraindicated for unilateral posterior. Implant-supported restorations with a cantilevered pontic transfer nonaxial occlusal forces to the adjacent implant and surrounding bone resulting in bone loss. Occlusal forces directed to the pontic created torquing forces around the implant adjacent to the cantilever. As a result, load magnification caused bone loss around the neck of the implant closest to the cantilever (Figure 76-4). Excessive distal angulations, which also created nonaxial loading and bone loss were also recognized problems. These implants often exhibit signs of overload (i.e., progressive and irreversible bone loss around neck of implant) when nonaxial occlusal loads are applied to the prosthesis
- The angulation of implants in relation to the plane of occlusion and the direction of the occlusal load is an important factor in optimizing the transfer of occlusal forces to implants and surrounding bone. Axial loads are tolerated well. Minor discrepancies in angulation are probably not clinically significant, but if loads are applied at an angle of 20 degrees or more to the long axis of the implant, load magnification can result, provoking a resorptive remodeling response of the adjacent bone. Nonaxial loads lead to implant overload through load magnification at the bone-to-implant interface, which in turn precipitates a resorptive remodeling response of the bone around the neck of the implants. This concept is supported by numerous finite element analysis (FEA) studies, which clearly demonstrate that nonaxial forces significantly increase the stress concentration to the cortical bone around the neck of the implant
- Strategies to Avoid Implant Overload Multiunit implant restorations should be splinted to maximize implant support (sharing the loads), and emergence profiles should be developed with open embrasure spaces to facilitate oral hygiene (Figure 76-16). It is important to āengineerā implant-retained restorations well. In fact, some advocate āover engineeringā to avoid failures. Implants should be adequate number, size and position to sustain the anticipated occlusal loads. Implants with smaller diameters have a lesser capacity to support bending forces than do implants with larger diameters. Implants with a minimum of 4 mm diameter should be used in areas expected to sustain greater occlusal loads (i.e., the posterior regions). Wider-diameter implants can be used when adequate bone and space exists (Figure 76-17). Thus, when the residual ridge and site permits, wide diameter implants should be used for molar replacement. Standard diameter (4 mm) implants may be best for premolar replacement since it approximates the premolar size and will provide a better emergence profile. In the case of multiple implant restorations, when ridge width permits, offsetting the implant location is encouraged. Narrow occ table- reduce buccal width ā flatten the cusps
- Splinting to natural teethā¦..they have different mobility level during function Connecting Implants to Teeth In general, it is advisable to keep implant-supported restorations separate from natural teeth because implants and teeth function differently and connecting them can lead to complications such as screw loosening and intrusion of natural dentition. Teeth have the capacity to move under functional occlusal loads while implants do not. Connecting implants to teeth may create a cantilever effect on the implant.[8,27,30,31] Furthermore, designing the restoration so that it is independent of the natural dentition simplifies the biomechanics. In contrast to this widely accepted view, a recent critical review of the literature suggests that these concerns may have been overstated.[13] There are situations that may warrant connection of implants to teeth. Several authors have shown (animal and human research) that success is possible when specific guidelines are followed.* Specifically, if implants are to be connected to the natural dentition, it should be done in a rigid manner, either with screw-retained attachments or with copings secured by permanent cement. Tooth preparation should allow good retention, teeth should be periodontally healthy and stable, and the occlusal scheme should be good. Gulbransen[15] showed that if implants are connected to the natural dentition with a rigid system of attachment, the implant failure and complication rates were dramatically reduced. It appears that the intrusion problem (and other complications) is increased when implants and natural teeth are connected with ānonrigidā and āsemirigidā attachments. In addition, the well-documented phenomenon of intrusion of the natural tooth abutment associated with the use of semiprecision attachments is prevented.[14]
- Edentulous Maxilla Prosthetic options for the patient with an edentulous maxilla include a conventional complete denture, an implant-assisted denture or an implantsupported fixed prosthesis. For many patients, a conventional complete denture does not provide the comfort and quality of life that they desire. An implant-assisted or implant-supported prosthesis can provide stability comfort and restore confidence to the patient, especially in patients with one or more of the following conditions: 1 Poor ridge form with a marginally stable conventional maxillary denture. Two or four implants provide greater stability and security of a maxillary denture in function when the maxillary ridge is severely resorbed and lacks resistance to lateral forces. 2 Lack of posterior support with an intact mandibular anterior dentition. Implants in the maxilla can offset the potentially destructive effects on the premaxillary region when a mandible with natural anterior teeth and missing posterior teeth opposes an edentulous maxilla. In this situation the lack of posterior support leads to a condition often referred to as combination syndrome, in which overclosure of the anterior teeth causes a āhammer and anvilā type of destruction of the edentulous anterior maxilla (Figure 76-6). 3 Palatal coverage is not tolerated. Some patients prefer a palateless denture, which may enhance their sensations of taste and texture or may simply provide a psychologic advantage. Some patients prefer a palateless denture because the proximity of the denture with the soft palate induces a gag reflex. Patients with large palatal tori (see Figure 53-19, A) can also benefit from a palateless maxillary denture. Minimum of four implants with adequate anterior-posterior (A-P) spread allows the fabrication of an implant-assisted overdenture without palatal coverage.
- Most patients are best served with an implant-assisted overlay denture. Lower cost, improved hygiene access, and predictable speech articulation are additional benefits that favor the use of an overlay denture in the edentulous maxilla over an implant-supported fixed prosthesis. The four-implantā assisted, palateless overlay denture ideally addresses the needs of most patients (Figure 76-8). Many patients who are edentulous in the maxilla have lost a significant amount of structure in the premaxillary region resulting in a lack of support for the upper lip. An implant-assisted maxillary overdenture is preferred over an implant-supported fixed prosthesis because the labial flange can provide the needed lip support. The usual resorption pattern of the alveolus places the gingival margin of a fixed restoration too far superiorly, too far palatally, or both. Even if the patient has a low enough smile line to hide the appearance of long crowns and deficient soft tissue height (Figure 76-9), a lack of lip support just beneath the nose can be unsightly with fixed prostheses. The design of a maxillary implant-retained prosthesis is greatly influenced by the anatomy of the maxilla. Most notably, the maxillary sinus limits the height of bone available for implant placement in the posterior region. As a result, implant placement is confined to the anterior region, and the A-P spread that can be achieved is often limited (Figure 76-7). If the A-P spread is inadequate to provide support, a full-palatal-coverage overlay denture is recommended.
- The two-implantāassisted overdenture is now the treatment of choice for patients with an atrophic, edentulous mandible. Implant-assisted overlay dentures are designed so that most of the masticatory load is borne by the primary denture-support areas (i.e., retromolar pad, buccal shelf). A common practice is to place two implants in the anterior mandible with a connecting bar. One or two clips retain the denture to the bar (Figure 76-10). When occlusal forces are applied, the denture rotates around the bar (anterior axis of rotation) and depresses slightly in the posterior aspect, directing the forces to the primary denture-bearing areas (Figure 76-11). The implants provide stability and retention while bearing minimal stress from occlusal loads. Individual attachments secured to each implant offer a simple prosthetic alternative (Figure 76-12) to the bar and clip design. However, it is more critical for implants with individual attachments to be parallel to one another to facilitate a proper path of insertion and to minimize stress during prosthetic seating and function. The first pic shows bar attached to 2 implants in ed. Mand.,clip allows denture to rotate around the bar when patient applies forces posteriorly and load is absorbed by posterior part of the mand.
- The mastication efficiency provided by a fixed versus removable prosthesis does not appear to be significant Cantilieverin is twice the AP spread in mandibles while is half AP spread in maxilla
- Currently, it is imperative to āengineerā the treatment of unilateral, posterior segments with an implant used to support each missing tooth that will be restored. If space and available bone permits, it is desirable to use a minimum of three implants to replace three missing posterior teeth in the maxilla. The same rule (one implant for every missing tooth being restored) applies to replacing teeth with implants in the posterior mandible as well. However, greater bone density (i.e., thickness of cortical bone) in the posterior mandible sometimes permits the use of fewer implants. A three-unit bridge supported by two implants in the posterior mandible is widely accepted (Figure 76-14). However, the decision to restore three missing teeth supported by two implants should always be made with consideration for the quantity and quality of bone available to support the implants (i.e., effective load-bearing capacity of the implants). Roughness of implant have significant effect on anchorage even in poor quality of bone Height of implant in maxilla sovledby autogenous bone graft and augmentaion and sinus lifting while in posterior man. Just use width of 10 mm with length less than 10mm
- The most common problem observed, particularly when external hex-headed implants were used, was loosening of the screw retaining the restoration.This problem results because the diameter of the head of the implant is much smaller than the size of the occlusal surface. The buccolingual width of the crown can be minimized by narrowing the dimension of the restoration, but there is less control over the mesiodistal dimension because contacts need to be established and the space is most often filled. Consequently, a mesiodistal cantilever, albeit small, is created. Tipping of the restoration during function eventually leads to stretching and loosening of the screw that secures the crown to the implant fixture. If hex-headed implants are used, the use of wide-diameter implants greatly diminishes the screw-loosening complication (Figure 76-15). The larger platform reduces the potential for tipping forces to stretch or break the screw. Internal connection implants are far less susceptible to screw loosening.