Restoration of posterior quadrants

Restoration of posterior quadrants

• 1.
  John Beumer IIIDDS, MS Robert F. Faulkner, DDS Kumar C. Shah DDS, MS Division of Advanced Prosthodontics, UCLA Restora(on  of  posterior  quadrants   Pa(ent  selec(on,  and  treatment  planning   This  program  of  instruc(on  is  protected  by  copyright  ©.    No  por(on  of  this   program  of  instruc(on  may  be  reproduced,  recorded  or  transferred  by  any  means   electronic,  digital,  photographic,  mechanical  etc.,  or  by  any  informa(on  storage  or   retrieval  system,  without  prior  permission.  
• 2.
  Table of Contents Treatmentoptions –  RPD’s –  Fixed dental prostheses –  Endodontic therapy Implant biomechanics –  Number of implants per unit –  Staggered vs. linear configurations –  Length, implant diameter –  Cantilevers –  Occlusal factors –  Parafunctional activity –  Strategies to avoid biomechanical related problems Anatomic limitations and the role of preprosthetic surgery –  Grafting –  Distraction osteogenesis –  Socket augmentation and ridge preservation –  Placement of implants into fresh extraction sites
• 3.
  Implants vs RPD’s v Cost   v Mas(ca(on  efficiency  (Kapur  et  al,  1987,   1989.  1991a,  1991b,  1997)     Implants may not always be the best choice for the patient
• 4.
  RPD’s and Implants Positionand lengths •  Implant site most favored – 1st molar position •  Lengths vary but in recent times some clinicians have reported successful outcomes when using implants as short as 6 mm in length (Gates et al, 2012). In  extension  base  RPD’s  (Kennedy  Class  I  and  II)  to   supplement  the  support,  stability  and  reten(on  provided   by  the  exis(ng  den((on.        
• 5.
  RPD’s and Implants • Unanticipated implant failures •  Poor quality bone •  Unfavorable biomechanics
• 6.
  Endodontics vs Implants v Highlevel of predictability v Extraction of the tooth and replacement with an implant is based on volume and integrity of tooth structure remaining v Cost advantages to endo plus restoration v Esthetics – Retention of bone and soft tissue
• 7.
  Conventional fixed vsimplants o  Predictable  when  abutments  in  good   condi(on  (Pietursson  et  al,  2007;   Walton,  2009)   o  Cost  effec(ve   o  Implants  preferred  when  abutments   are  virgin  or  near  virgin     15 year follow-up
• 8.
  Things can gowrong with implants Biomechanics – Partially Edentulous Patients !  Because of the curve of Spee and the distal angulation of the implants, the occlusal loads (arrow) are nonaxial. !  Note the bone loss around the implants. Linear configurations in the posterior region, such as in this patient, are particularly vulnerable to the effects of nonaxial loading, particularly brachycephalic individuals. Nonaxial loads and implant overload in posterior quadrants Semi-precision attachments usion of the natural tooth abutment ears after delivery the patient noticed the premolar o intrude. Exam revealed that the screw retaining the ad become loose, hence the rotation of this crown. Bruxism - Case Report This is a five year followup x-ray of a patient with an implant supported fixed partial denture. Closer exam revealed both implants to be fractured . The patient was a heavy bruxer. Six months later he presented with significant bone loss around both implants. Bruxism - Case Report This is a five year followup x-ray of a patient with an implant supported fixed partial denture. The patient was a heavy bruxer. Six months later he presented with significant bone loss around both implants. Implant overload Bone loss Implant fractures Peri-implantitis Impaction of cement Implant loss
• 9.
  How can weavoid these complications? Biomechanics – Partially Edentulous Patients !  Because of the curve of Spee and the distal angulation of the implants, the occlusal loads (arrow) are nonaxial. !  Note the bone loss around the implants. Linear configurations in the posterior region, such as in this patient, are particularly vulnerable to the effects of nonaxial loading, particularly brachycephalic individuals. Nonaxial loads and implant overload in posterior quadrants Semi-precision attachments usion of the natural tooth abutment ears after delivery the patient noticed the premolar o intrude. Exam revealed that the screw retaining the ad become loose, hence the rotation of this crown. Bruxism - Case Report This is a five year followup x-ray of a patient with an implant supported fixed partial denture. Closer exam revealed both implants to be fractured . The patient was a heavy bruxer. Six months later he presented with significant bone loss around both implants. Bruxism - Case Report This is a five year followup x-ray of a patient with an implant supported fixed partial denture. The patient was a heavy bruxer. Six months later he presented with significant bone loss around both implants. Implant overload Bone loss Implant fractures Peri-implantitis Impaction of cement Implant loss
• 10.
  Implant Biomechanics and TreatmentPlanning Why should we be concerned with implant biomechanics when we develop a plan of treatment? Because if we are not, we risk implant overload and prosthesis failures such as fracture and screw loosening. Implant overload can lead to bone loss around implants and eventually implant failure.
• 11.
  Bone  is  a  dynamic  structure.    Excessive  loads  lead  to   a  resorp(ve  remodeling  response     Hoshaw et al (1994) observed a resorptive remodeling of the bone around implants subjected to excessive axial loads (300N). Bone loss was observed at the crest around the neck of the implant and in the zone of bone adjacent to the body of the implant   Brunski et al, 2000   Recent studies by Myata et al (1998, 2000, 2008) and Nagasawa et al, (2013) have reconfirmed Hoshaw and Brunski’s original hypothesis Is it possible to overload the bone anchoring an osseointegrated implant?
• 12.
  Implant Overload -Basic Mechanism v Excessive  occlusal  loads,  off  angle  loads,   bending  moments   v Resul(ng  microdamage  (fractures,  cracks,   and  delamina(ons)   v Resorp(on  remodeling  response  of  bone  is   provoked   v Increased  porosity  of  bone  in  the  interface   zone  secondary  to  remodeling   v Vicious  cycle  of  con(nued  loading,  more   micro-­‐damage,  more  porosity  un(l  failure  
• 13.
  Implant overload l  Implant  alignment  must  consider  the  curve  of  Spee  and  the   curve  of  Wilson   l  In  both  situa(ons  the  implants  will  be  exposed  to  bending   moments  and  predispose  to  implant  overload.   Occlusal force
• 14.
  Implant  overload   • In posterior quadrants when implants are aligned in a linear fashion they should be aligned consistent with the curve of Spee and the curve of Wilson Curve of Wilson
• 15.
  Implant Biomechanics    What  is  the  load  bearing  capacity  of    osseointegrated   implant  supported  restora(ons?         Is  the  load  carrying  capacity  of  implant  prostheses   influenced  by  the  quality  of  the  bone  sites?           What  factors  control  the  magnitude  of  the  loads  that   are  delivered  through  the  implant  into  the  surrounding   bone?     What  loads  should  implant  borne  restora(ons  be   designed  to  resist?  
• 16.
                  Karnak The Great Wall Pont  de  Gard   You must over engineer your implant restorations, particularly when restoring posterior quadrants with linear configurations in order achieve predictable long term results. Implant Biomechanics
• 17.
  Implant  Biomechanics   LOADBEARING CAPACITY 1.  Quality  of  bone  site       2.  Quality  of    bone                      implant  interface   3.  Implant  microsurfaces        Machined  vs    microrough    vs    nano-­‐enhanced    surfaces   4. Implant  Number and Arrangement Linear vs Curvilinear  Length and diameter  Angulation ANTICIPATED LOAD (Affected by)  Occlusal factors Cusp angles Width of occlusal table Guidance type Anterior guidance Group function  Cantilever forces Connection to natural dentition Size of occlusal table Cantilevered prostheses  Parafunctional habits (bruxism)  Brachycephalics
• 18.
  Load  bearing  capacity   Implant  number  and  arrangement   •  Both  the  number  and  arrangement  of   implants  affect  the  load  carrying   capacity  of    any  par(cular  implant   supported  restora(on.       •  Curvilinear  arrangements  withstand   more  load  than  linear  arrangements  
• 19.
  Load  bearing  capacity      Linear  vs  Curvilinear   o  Curvilinear  arrangements    have  the    greatest    load   bearing  capacity.   o  Cross  arch  stabiliza(on  
• 20.
  Load  bearing  capacity   Linear  vs  Curvilinear     v Curvilinear  arrangements  such  as  seen  in  this  pa(ent  are   very  predictable   v This  PFM  fixed  prosthesis  is  12  years  post  inser(on.   Occlusion: Group function 12 year follow-up12 year follow-up
• 21.
  Load  bearing  capacity   Linear  vs  Curvilinear    Linear configurations restoring the cuspid region, such as the patient on the right, are unpredictable, whereas curvilinear implant arrangements such as shown on the left are very predictable. Predictable Not predictable
• 22.
  Maxilla vs Mandible Bonequality v The  size  and  shape  of  the  trabeculae   is  different  in  the  mandible  as   compared  to  the  mandible.     v This  may  be  one  of  the  reasons  why   the  load  carrying  capacity  of  implant   supported  prostheses  restoring   posterior  quadrants  in  the  mandible   appears  to  be  superior  to  those  in  the   maxilla.   Courtesy  Dr.  C.  Stanford  
• 23.
  Number of Implantsper Unit Posterior Maxilla  When  restoring  posterior  quadrants  with  implants  we  are  forced  to  use   linear  arrangements  by  anatomic  necessity.    Therefore  in  most  instances:     *The third implant dramatically improves the biomechanics of the restoration  One  implant  for   each  dental  unit.    At  least  three  where   possible  in  extension   areas.   One dental unit = premolar
• 24.
  Number of Implantsper Unit Posterior Maxilla The distal implants failed 30 months after loading in both these patients because of implant overload.
• 25.
  Number of Implantsper Unit Posterior Maxilla o  The distal implant failed 30 months after loading in both these patients because of implant overload. o  The patient was a bruxer
• 26.
  Number of Implantsper Unit Posterior Maxilla These implants failed 66 months after loading because of implant overload. Group function was used to restore this patient. Result:  Application of excessive lateral forces  Implant failure Another problem: Cusp angles too steep and the occlusion was tripodized
• 27.
  Number of Implantsper Unit Posterior Maxilla Space allowed only two implants to be placed in this patient. However, note anterior guidance. Design the occlusion to minimize the delivery of nonaxial forces
• 28.
  Number of Implantsper Unit Posterior Maxilla Only two implants were placed. Note anterior guidance
• 29.
  Bone Augmentation –Horizontal Deficiencies  Predictable    Less  occlusal  force    Fixa(on  of  the  grae  is  easy  to    accomplish    The  blood  supply  to  the  grae  is    usually  quite  good        
• 30.
  Bone Augmentation Vertical Defects Less  predictable   Problems:    Tension  on  the  wound  secondary  to    closure  of    (ssue  flaps    Poor  blood  supply    Difficulty  in  achieving  fixa(on   Result:    Relapse  (resorp(on)  rate  is  75%  
• 31.
  Sinus Augmentation Advantages  over  onlay  gra7s    Resorp(on  probably  less  than  25%   Challenge    Elevate  the  sinus  membrane  without  perfora(on   Sinus membrane Bone graft Bone of the residual allveolar ridge
• 32.
  Sinus  Augmenta(on   • Implants can be placed simultaneous when there is 4-5 mm over the sinus and primary immobilization of the implants can be achieved •  Otherwise implant placement delayed for 6-9 months
• 33.
  Sinus augmentation      Predictable  (Jensen  et  al,   1997;    Aghaloo  and  Moy,   2007)      Sources  of  grae  material   include  chin,  ramus,  and    iliac   crest  some(mes  mixed  with   bone  subs(tutes.   Complica(ons    Loss  of  grae  material    Blockage  of  the  os(um    Incomplete  eleva(on  of  the   sinus  prevent  normal  sinus   drainage  
• 34.
  PRE-OP 4M POST-OP 2M POST-OP
• 35.
  Sinus augmention This patientwas restored following a sinus lift and graft. Autogenous chin bone was used. She is 10 years post treatment and doing well. Note: Best results achieved when there is 4-5 mm of normal bone over the sinus before the procedure
• 36.
  Sinus augmentation § This  pa(ent  was  restored  following    a             bilateral  sinus  lie  and  grae.     §   Freeze  dried  bone  was  used  to  grae  the  lee   maxillary  sinus.       § The  implants  placed  in    this  grae  failed  18   months  following  delivery  of  the  implant   supported  fixed  par(al     denture.  
• 37.
  Crestal  Augmenta(on   Augmenta(on  of  ver(cal  defects  in  posterior  mandibular   quadrants  with  free  autogenous  bone  graes    has  been   unpredictable.  Following  surgery  the  relapse  rate  is  about  75%  and   further  bone  loss  is  also  seen  aeer  loading.    Why?   a)  Tension  on  the  wound  upon  closure   b)  Poor  blood  supply     c)  Difficulty  is  achieving  proper  fixa(on  of  the  grae    
• 38.
  Pterygoid implants •  Asan alternative to sinus augmentation •  Success rates in excess of 90% Courtesy Dr. A. Pozzi
• 39.
  *Removable Partial Dentures* Removablepartial dentures properly designed and fabricated provide the patient with masticatory function equivalent to that obtained with an implant supported fixed partial dentures (Kapur, et al, 1992) and this service should be offered to the patient before grafting is considered.
• 40.
  Number of Implantsper Unit Posterior Mandible Two is sufficient for most patients Why? v The trabecular bone is more dense v Cortical layer is thicker
• 41.
  Number of Implantsper Unit Posterior Mandible v There is bone over the nerve for only short implants v Bone quality is poor v When restoring four dental units Three are recommended when:
• 42.
  Number of Implantsper Unit Posterior Mandible Three implants were used to restore four units in this patient
• 43.
  Posterior Mandible –Limiting Factors v Inferior alveolar nerve(arrow) v Insufficient bone over the nerve to permit placement of a 10 mm or longer implant v Uni-cortical anchorage (arrow)
• 44.
  Many patients suchas this one, present with moderate to severe resorption precluding placement of implants unless the inferior alveolar nerve displaced. Posterior Mandible – Limiting Factors
• 45.
  Displacement of theInferior Alveolar Nerve  This  procedure  enables  placement  of  implants  of  sufficient  length  with  bicor(cal  anchorage.      Although  the  risk  of  nerve  injury  is  rela(vely  small  the  morbidi(es  associated  with  injury   may  be  severe.        Therefore,  these  issues  must  be  thoroughly  discussed  with  the  pa(ent  before  proceeding   with  the  procedure.  
• 46.
  Crestal Augmentation Augmenta(on  of  ver(cal  defects  in  posterior  mandibular  quadrants  with  free   autogenous  bone  graes  (A)  has  been  unpredictable.  Following  surgery  the  relapse  rate   is  about  75%  and  further  bone  loss  is  also  seen  aeer  loading  (B).    Why?    a)  Tension  on  the  wound  upon  closure    b)  Poor  blood  supply      c)  Difficulty  is  achieving  proper  fixa(on  of  the  grae     BA Presently,  distrac(on  osteogenesis  is  the  only  reasonably   predictable  method  for  enhancing  this  site  ver(cally.    
• 47.
  Mandibular Onlay Grafting
 Patients= 13 Total grafts = 21 •  Follow-up: 3 mos – 72 mos Avg. = 26 mos •  Avg. height gained with block graft = 4.21 mm •  Avg. height of graft remaining on f/u = 1.05 mm •  Overall, 75% of initial graft height was lost •  Complication(s) –  6 of 21 sites demonstrated wound dehiscence •  28.6% complication rate
• 48.
  Distraction Osteogenesis §  4-5mm of bone required over the nerve §  Distract 1mm per day §  Relapse rate is 25 % §  Wait 6 months for consolidation before implant placement
• 49.
  Horizontal vs verticalaugmentation Predictable
• 50.
  Use of ShortWide Diameter Implants in the Posterior Mandible This practice has not been predictable. The short implants are particularly prone to occlusal overload and bone loss. This is a 2 and 7 year follow-up x-ray of two 6 mm diameter implants.
• 51.
  Use  of  Short  Wide  Diameter    Implants  in  the  Posterior  Mandible   The implants failed 15 years after insertion.
• 52.
  If implants ofadequate length cannot be used, consider removable partial dentures Mastication efficiency of distal extension RPD’s is equivalent to implant supported fixed partial dentures.
• 53.
   When in doubtadd the 3rd implant in posterior quadrant cases.  Minimize the length and width of the occlusal table Linear  configura(ons Over engineer your cases
• 54.
  Over-engineer your linearquadrant cases v When in doubt re: the quality of the implant site bone, history of parafunction etc., add the third implant
• 55.
  Over-engineer your linearquadrant cases v Minimize the width of the occlusal surfaces. They should be no wider than a premolar Note: The buccal-lingual dimension is excessive However,  there  is  a  flaw  in  the  design  of    this  case.     What  is  it?  
• 56.
  Staggered vs linearconfiguration in posterior quadrants This has been studied using a photoelastic model by Itoh, et al, 2003 Staggered implant configuration 1.5 mm 1.5 mm 1.5 mm Straight line implant configuration
• 57.
  Staggered vs linearconfiguration Staggered implant configuration 1.5 mm 1.5 mm 1.5 mm Straight line implant configuration Itoh and Caputo, et al 2003 Is  it  biomechanically  more  favorable?     v Yes,  par(cularly  with  specific   chewing  cycles.  Nonlinear   arrangements  resist  lateral  forces   more  effec(vely   v Is  the  improvement  clinically   significant?  This  is  unknown  
• 58.
  Staggered vs linearconfiguration Staggered implant configuration 1.5 mm 1.5 mm 1.5 mm Straight line implant configuration Probably not. In the posterior quadrants you can’t get enough stagger to make much of a difference biomechanically. Itoh and Caputo, et al 2003 Is  it  feasible  in  the  posterior  quadrants?  
• 59.
  Implants in CompromisedSites  Posterior maxilla  Posterior mandible over the inferior alveolar nerve in partially edentulous patients  Craniofacial application Theore(cally  perhaps.               However  we  need  well   designed    clinical    outcome   studies  to  determine   predictability   Can  we  use  shorter  implants?  
• 60.
  Length and diameterof Implants v Short implants, such as this 7 mm screw shaped implant, demonstrate unfavorable stress distribution patterns as seen in this study performed with finite element analysis. Longer implants distribute stresses more favorably. v Given the bone anchorage achieved with modern surfaces, failures are most likely to occur in the trabecular bone v Failure rates approach 25% for machine surface implants 7 mm in length (Wyatt and Zarb, 1998; Winklet et al, 2000) Avoid the use of implants less than 10 mm in length and 4mm in diameter when restoring posterior quadrants. Cho et al, 1993
• 61.
  • Two year followupdata from Moy and Sze,’93 • Note the high failure rates with the 7 mm and 10 mm implants in the posterior maxilla. Length  and  diameter  of  Implants  
• 62.
  Implant length vsdiameter Using a photoelastic model, Caputo et al, 2002 attempted to determine whether increasing the diameter of the implant or increasing the length of the implant had a significant impact on stress distribution. They concluded that: Does increasing the diameter compensate for the lack of sufficient length?
• 63.
  Implant length vsdiameter Lingual load Axial load Buccal load  Most equitable load transfer with axially directed loads.  Under comparable loading conditions, the stresses transferred by the wide diameter implant were only slightly lower than the same length narrow implant.  For implants tested, increased length was more important than diameter in stress reduction. Caputo  et  al,2002  
• 64.
  Implant length vswidth § Failure rates of short wide diameter implants approaches 20%. 2 years 8 years Cho,In  Ho  et  al,   1992   14 years
• 65.
  Implant  length  vs  width   l  Over-­‐prepara(on  and/or  over  hea(ng  of  the  osteotomy  site.    This   may  precipitate  early  loss  of  bone,  par(cularly  around  the  neck  of   the  implant.     l  Implant  overload.   l  Insufficient  trabecular  bone  encasing  the  implant  on  its  buccal   and  lingual  aspect  leading  to  progressive  bone  loss.        
• 66.
  Ideal Implant Diameter 4-5mm in diameter Less than 4 mm the rate of implant fracture is unacceptably high Implants 3.75 mm in diameter have a 5-7% fracture rate More than 5 mm the higher the failure rate. Implants 6 mm in diameter have a 20% failure rate Implants 4-5 mm in diameter have a less than 5% failure rate
• 67.
  Implant Angulation –Posterior vs Anterior v  Implants in the posterior quadrants should be placed so that occlusal loads can be directed axially in the posterior quadrants. v  In the anterior region, anatomic necessity precludes implant placement perpendicular to the occlusal plane. v  However, the forces used to incise the bolus are only about ¼ of those used posteriorly to masticate the bolus. For this and other reasons implant overload is rarely seen in the anterior regions.
• 68.
  v Nonaxial loads resultin load magnification. Kinni et al (1987), using photoelastic analysis and Cho et al (1993), using finite element analysis, demonstrated that nonaxial loads concentrated potentially clinically significant stresses around the neck and at the tip of the implant. Implant angulation Cho,In  Ho  et  al,  1992  
• 69.
  Curve of Wilson Implant  Angula(on     Curve of Wilson Curve of Spee
• 70.
  Implant angulation v Implant  alignment  must  consider  the  curve  of   Spee  and  the  curve  of  Wilson   Nonaxial  loads  and  implant  overload  in  posterior   quadrants  
• 71.
  Implant  Angula(on     CAC-­‐CAM    technologies  permit:   l Development  of  virtual  diagnos(c  wax-­‐ups   l Surgical  drill  guides  which  permit  controlled   direc(onal  drilling  as  opposed  to  free  hand  drilling  
• 72.
  Implant  Angula(on     •  Controlled directional drilling is preferred because it results in few errors in implant angulation and position as opposed to free hand drilling
• 73.
  Implant  Angula(on     •  CAD-CAM can also be used to design and mill custom abutments and prototype restorations
• 74.
  Cantilevers and LinearConfigurations in Posterior Quadrants •  They are particularly detrimental and are therefore contraindicated when using linear configurations to restore posterior quadrants. They cause subject the implants to bending, load magnification and overload the bone around the implant adjacent to the cantilever. Mesial  and  distal  canClevers  
• 75.
   They  are  well  tolerated  when   implant  supported  restora(ons   are  used  to  restore  the   edentulous  mandible,  so  long   as:   –  The  can(levered  sec(on  is  within  a   reasonable  limit   –  The  implants  are  arranged  in  a   reasonable  arc  of  curvature.   –  Rigid  frameworks  with  cross  arch   stabiliza(on  are  used   Cantilever forces Cantilever section
• 76.
  Cantilevers – ImplantOverload •  Note the bone loss around the dental implants adjacent to the cantilever. Restorations designed in this fashion, especially in the posterior maxilla, have a poor prognosis.
• 77.
  Limit buccal, lingualand cantilevers The occlusal tables are excessively wide in this case. Buccal and lingual cantilever forces may lead in selected patients to: Prosthesis failures • Porcelain fractures • Screw fractures Implant overload and bone loss
• 78.
  Occlusal Anatomy andBiomechanics v Narrow occlusal table Goal: Reduce the buccal - lingual cantilever effect
• 79.
  Avoid  buccal  and  lingual  can(levers     The occlusal table must be narrowed to avoid buccal and lingual cantilevers. Molars should be no wider than premolars as shown in these two examples.
• 80.
  Solitary implants restoringsingle molars – Cantilever effect When the food bolus is applied to the marginal ridge (B), the restoration is easily tipped because the crown is supported by such a narrow platform. Result: Cantilever forces lead to screw loosening, implant fracture and overload the bone anchoring the implant. BA
• 81.
  Fracture Implant fractured after30 months of function Solitary implants restoring single molars Cantilever effect
• 82.
  Single tooth restorationsin the molar region – Cantilever effect This implant was too short and too narrow to withstand occlusal loads and bone loss caused by the resorptive remodeling response led to its loss. 4 mm diameter implant Mesial  canClever  
• 83.
  Single Tooth RestorationsDistal Extension Defects
• 84.
  Distal Extension Defects
• 85.
  Restoration of singlemolar sites - Solutions In this patient a wide diameter implant was used to restore the first molar.  Eliminate  the  can(lever  by  using      Wide  diameter      Mul(ple  implants  
• 86.
  Restoration of singlemolar sites Custom abutment Lingual set screw In  this  pa(ent,    two  4  mm  diameter  implant  were  used  to   restore  the  first  molar.    The  width  of  the  occlusal  table  was   limited  to  the  width  of  the   natural  premolar,     thereby  elimina(ng  any   possible  buccal  or     lingual  can(levers.  
• 87.
  Restoration of singlemolar sites Note:   Hygiene access for proxy brush   Note width of occlusal table
• 88.
  Splinted vs Nonsplinted Pa(ent  presented  with  a  failed  endodon(cally  treated    #30.    This   tooth  was  extracted  and  the  space  restored  with  an  implant.     Several  years  later  the  endodon(c  therapy  on  #29  failed  and  this  too   was  replaced  with  and  implant  restora(on.      
• 89.
  Splinted  vs  Nonsplinted   •  These  implants  were  not  splinted   •  Note  the  anterior  group  func(on   •  Mandibular  bone  sites  favorable   •  Pa(ent  did  not  demonstrate  evidence   of  parafunc(onal  ac(vity   •  Long  implants  
• 90.
  Splinted  vs  Nonsplinted   From a theoretical biomechanical perspective splinted designs are more favorable than unsplinted designs, but whether this difference is clinically significant has yet to be determined with properly desinged clinical outcome studies.
• 91.
  Criteria for splinting • If the patient shows signs of parafunctional activities. •  If the quality of bone anchoring the implants is questionable (type IV bone, or if the implants are in grafted sites). •  Misangled implants ie, implants that are not perpindicular to the plane of occlusion. •  If relatively short implants have been employed (less than 10 mm in length). •  If the patient presents with or is to be restored with group function. Linear configurations of implants lack cross arch stabilization and are less able to resist bending moments (nonaxial loads) and implant angulations that are not ideal result in the application of bending moments. •  All maxillary posterior quadrant cases.
• 92.
  l When  implants  of  10  in  length  or  longer  are  placed.   l When  the    quality  of  bone  is  good.     l Implants  placed  with  perfect  angula(on     (perpendicular  to  the  plane  of  occlusion)   l Absence  of  parafunc(onal  ac(vity.   Nonsplinted  designs  are  used  when  restoring  posterior   quadrants  only  in  the  mandible  and  under  the  following   circumstances:  
• 93.
  Connecting Implants toNatural Dentition How do you minimize cantilever forces? Semiprecision (nonrigid) vs rigid attachments
• 94.
  Connecting Implants toNatural Dentition Posterior  implant  apached  to  anterior  abutment   Rigid  apachment     Nonrigid  apachment   Nishimura  et  al,  1999   Loads applied in the pontic area
• 95.
  Connecting Implants toNatural Dentition Rigid  vs  non  rigid  apachments    No  difference  as  long  as  the  nonrigid  (semi-­‐precision)   apachments  remain  fully  seated    
• 96.
  Semi-precision Attachments Problems v Intrusion ofthe natural tooth leading to: v Cantilever affect v Load magnification v Resorptive remodeling response v Bone loss (arrows) Semi-precision attachment
• 97.
  Semi-precision attachments Intrusion ofthe natural tooth abutment •  Eleven years after delivery the patient noticed the premolar began to intrude. Exam revealed that the screw retaining the molar had become loose, hence the rotation of this crown.
• 98.
  Rigid Attachments* Intrusion isprevented with rigid attachments Screw retained tube lock attachment *Shared support
• 99.
  Rigid Attachments* Screw  retained  tube  lock  apachment   *Shared support
• 100.
  Occlusal Anatomy andBiomechanics •  Narrow occlusal table •  Flat cusp angles •  Lingualize or buccalize