Among the 46 subjects we had 14 subjects who complete all the treatment procedure and data collection. The mean masticatory performance prior the surgery on the defect side was 22.6% and 38.6% on the non-defect side, then decreased to 7.8% and 25.3% postsurgically. Restoration with the conventional prosthesis significantly improved performance to 20% on the defect side and 32% on the non-defect side. Following treatment with the implant-supported prosthesis masticatory performance improved significantly to 31.4% on the defect side and 39.5% on the non-defect side. At the entry level the MP was 22and38% very low
Implants in Irradiated Tissues Table of Contents Radiation effects and impact on osseointegration Changing methods of radiation delivery and the impact of chemoradiation Patient selection criteria Animal studies Human data Osteoradionecrosis Role of HBO Timing of implant placement Irradiation of existing implants
Osseointegration Success requires primary implant anchorage and immobilization, the formation of a clot between the surface of the implant and the osteotomy site, release of growth factors, angiogenesis and migration of osteoprogenitor cells to and deposition of bone on the surface of the implant and in the osteotomy site.OsteoblastsMineral deposition Non-collagenous matrix Collagen matrix
Osseointegrated Implants These biologic processes may be compromised or absent in patients exposed to high dose radiation and as a result anchorage of implants in bone is probably mechanical as opposed to biological. In addition, long term function of osseointegrated implants is dependent on the presence of viable bone that is capable of remodeling and turnover as the implant is subjected to stresses associated with supporting, retaining, and stabilizing prosthetic restorations. These processes are compromised or perhaps entirely lacking in heavily irradiated bone.
Radiation effects Reduced vasculature Lamellar bone Loss of osteoprogenitor • Loss of central artery in Haversian systems cells • Death of osteocytes Marrow undergoes fatty and fibrous degeneration Periosteum becomes acellular and loss of vasculature Trabecular bone Root surface Marrow
Radiation effectsThese tissue changes lead to: Lamellar bone • Loss of central artery in Compromised remodeling Haversian systems • Death of osteocytes Response to infection is compromised ie osteoradionecrosis Continuing osteolytic activity Root Trabecular bone surface Marrow
Why are these changes important? Anchorage may be mechanical as opposed to biologic Response to infection is compromised Remodeling apparatus is not fully functional Response to occlusal forces is compromised Osteolytic activity continues and compromises the density of the boneRoot Trabecular bonesurface Marrow
Continued osteolytic activity The density of bone is diminished because bone resorption continues secondary to the presence of isolated osteoclasts making it more difficult to achieve primary stability of the implant.
Remodeling apparatus – Osteolytic Activity This patient received 70 Gy to the mandible for an anterior floor of mouth Sq Ca. Note the dramatic change in the prominence of the cortical Preradiationplates (arrows) and the differences in trabecular patterns between preradiaton and postradiation radiographs. Osteolytic activity seems more prominent in patients treated with chemoRT Postradiation
Remodeling apparatus – Osteolytic Activity Postradiation Hence in irradiated sites initial stabilization of the implants is more difficult to achieve In edentulous patients the irradiated mandible is more susceptible to fracture
Remodeling apparatus – Osteolytic Activity Patient received 60 Gy. The mandible fractured through the left posterior implant site (arrow) two weeks following implant placement. It was reduced and repaired as shown with eventual healing. An implant assisted overlay denture was later fabricated and used successfully by the patient.
The tissue changes are dose dependent and the dose depends in part upon:Mode of therapy CRT (Conventional radiation therapy) IMRT (Intensely modulated radiation therapy) BrachytherapyIn edentulous patients the preferred implantsites are: Symphyseal region of the mandible Premaxilla The mode of therapy will determine the dose delivered to these regions and dose is the best predictor of long term success and the risk of ORN.
Changing methods of radiation deliveryConventional radiation therapy (CRT) 200 cGy per fraction Bilateral opposed equally weighted fields Total doses Source: www.beaumonthospital.com 7000 cGy definitive dose 5000-6000 cGy post opIntensity modulated radiation therapy (IMRT) This technique uses multiple radiation beams of non-uniform intensities. The beams are modulated to the required intensity maps for delivering highly conformal doses of radiation to the treatment targets, while limiting dose normal tissue structures. Source: www.beaumonthospital.com
IMRT dosimetry diagramsNote the hot spot on anterior mandible (oval). With IMRT the dose distribution is not uniform.
(CRT) Chemoradiation (IMRT) Source: www.beaumonthospital.com Source: www.beaumonthospital.com • Used in combination with CRT or IMRT • Full course of concomitant chemoradiation is theoretically equivalent to an additional 7-10 Gy (Kashibhatla, 2006; Fowler, 2008).Consequences (particularly with CRT): The biologically equivalent dose (BED) is raised leading to more short term and long term side effects (mucositis, fibrosis, trismus,velopharyngeal incompetence, osteoradionecrosis etc).
Implants in Irradiated TissuesIssues to consider Potential benefit to the patient What are the objectives and wishes of the patient? Risk – reward ratio? Risk of osteoradionecrosis? Morbidity? Short term success rates? Long term success rates?
Risk vs Reward Edentulous Maxillectomy Patients As indicated by the following data, without implants to help retain and stabilize the complete denture-obturator prosthesis, mastication is not restored With the retention provided by the implants mastication levels are restored to presurgical levels of function (Garrett et al, 2008). The risk of osteoradionecrosis secondary to implant placement is very low. Since the risk is minimal and the rewards are significant we do not hesitate to recommend the use of implants in patients with palatal defects that have been irradiated.
Masticatory Performance Maxillectomy N=5 (‘0’ score if not able to chew) 50 46.2 45 40.5% performance 40 35 30 Defect 25 Intact 20 15.6 15 8.2 8.8 10 6.2 6.6 8.1 5 0 Entry Post-Surgery Post-CP Post-IP Garret et al, 2008 *p<0.01
Masticatory Performance Maxillectomy N=5 (‘0’ score if not able to chew) * * 50 46.2 45% performance 40.5 40 35 30 Defect 25 Intact 20 15.6 15 8.2 8.8 10 6.2 6.6 8.1 5 0 Entry Post-Surgery Post-CP Post-IP Garret et al, 2008; Garrett et al, 2009 *p<0.01
Tongue-Mandible Defects Reconstructed with Free Flaps Patients with dentition on the unresected side As indicated from the following data you can see that patients retain their ability to masticate effectively on the nonresected side after mandibular reconstruction. Implant placement on the fibula side does not add substantially to their mastication efficiency. In addition if the tongue is restored with the flap the patient lacks the sensory and motor innervation to control the food bolus on the resected side. The risk reward ratio is not as favorable and therefore in most such situations we therefore recommend a conventional RPD when the implant sites have been heavily irradiated.
Tongue-Mandible Defects Reconstructed with Free Flaps - Edentulous PatientsThe functional benefit derived from implant placement inirradiated edentulous patients depends on several factors, themost important being the status of tongue function. If the tongue and/or mandible has been resected and reconstructed and the bulk, mobility and control of the reconstructed tongue results in reasonable tongue function, the placement of implants may significantly improve mastication performance particularly if the denture bearing surface has been compromised or is not ideal.
Tongue-Mandible Defects Reconstructed with Free Flaps - Edentulous Patients Patient had hemiglossectomy and reconstruction of tongue with a free flap and received 55 Gy post operatively. Tongue bulk is restored and tongue mobility is excellent Without implants use of a lower complete denture would have been problematic. The dose is low. The risk reward ratio is favorable and therefore in such patients implants were placed to stabilize and retain the denture.Note: The patient must masticate on the sensate unresected side.
Facial Prostheses – Quality of retention Quality of lifeWhen patients present with facial defects implant retention improvespatient satisfaction and frequency of use (Chang et al, 2005).With large combination facial defects adhesive retention is ineffective and implant retention is required for most patientsAlthough the implant loss rates are high the benefits are great particularly in patients with large facial defects such as this one.Therefore, we recommend the placement of implants in most patients with large facial defects even though the implant sites have been irradiated.
Frequency of Wear Facial Prostheses Chang et al, 2005 Adhesive Implant 120 95 100 100 89 88 80 *63% Wearing 60 44 40 20 3 0 0 Home Work Social Never
Implants in Irradiated TissuesBiologic viability (animal studies) Hum and Larsen, (1990) Weinlander et al, (2006) Nishimura et al, (1996) Asikainen et al, (1993) Ohrnell et al, (1997) Jacobsson et al, (1988)
Implants in Irradiated TissuesBiologic viability (animal studies) Asikainen, 1998 Dogs received either 4000, 5000, or 6000 cGy Two months later TPS screw type implants were inserted Four months later the implants were loaded Success rates: 4000 cGy group – 100% 5000 cGy group – 20% 6000 cGy group – 0 %
Implants in Irradiated Tissues Weinlander et al, (2006) Dogs were partially edentulated Following a suitable healing period three implants wereplaced on each side All seven dogs received radiation therapy, starting threeweeks post implantation on one side of the mandible,consisting of a dose equivalent to 5000 cGy delivered in 4fractions during a 2 week period
Methods – Histomorphometric Calculations A scanning electron microscope was used to image the background electron density of the three elements – bone, soft tissue and implant. The histometry calculation yielded volume and boundary fractions for the implant, bone and soft tissue components. Weinlander et al, 2006
Bone contact area in control specimens 80 70 60 50 40 Bone 30 Appositional Index % 20 10 0 Machined Plasma HA Surface Spray Coated Weinlander et al,
Bone contact area in irradiated tissue 70 60 50 40 Bone 30 Appositional 20 Index % 10 0 Machined Plasma HA Surface Spray Coated Weinlander et al, 2006
Nishimura et al,1996 Dosage of Radiation Therapy AdministeredA rabbit tibia model was used in this study. The rat tibia wereexposed to equivalents of the following doses and implants wereplaced 3 months following completion of radiation treatments.Polyfluorochrome labeling was performed three months afterimplant placement and the animals sacrificed 2 days later, (cGy) 4000 5800 4600 6400 5200 7000
Nishimura et al, 1996 Results Normal 5200 cGy 5800 cGyThree months after implant placement the tissue samples wereharvested and were evaluated with light and fluorescentmicroscopy. Fluorochrome labeling documented a steadydecrease in biologic activity at the higher doses.
Nishimura et al, 1996 Results Normal bone Irradiated boneAt lower doses irradiated specimens had morewoven bone at the bone implant interface than didthe normal specimens at the time of sacrifice.
Additional animal studies (summaries) Jacobsson et al (1988) - Reduction in bone formation capacity, an increase in bone resorption and a reduction in the number of capillaries. Ohrnell et al (1997) - Fibrosis of the bone marrow, bone resorption, less bone adjacent to the implants and an overall reduction in the remodeling capacity of bone. Hum and Larsen (1990) - The bone contact area for irradiated specimens was significantly less than nonirradiated specimens
Summary of tissue changes affecting osseointegration based on animal studies At higher doses (70 Gy) virtually little or no bone will be deposited on the implant surface. Anchorage is primarily mechanical as opposed to biologically driven. At lower doses a greater component of woven bone is seen in the interface. Compromise of the remodeling apparatus may preclude this woven bone from being replaced with lamellar bone Death of osteocytes, loss of osteoprogenitor cells and the basic multi-cellular unit of the remodeling apparatus (BMU) compromises the remodeling of bone at the bone implant interface and compromises the bone’s response to occlusal load.
Summary of tissue changes affecting osseointegration based on animal studies• Poor blood supply in the marrow predisposes to infection and implant loss• At lower doses radiation induced tissue effects significantly reduced the bone appositional index as compared to controls and probably compromise implants load bearing capacity.
Disclaimer No animal model truly reflects human biology. Lower formvertebrates are more tissue and vascular tolerant of radiationdamage than humans.Using the mathematical biologic equivalent of human dosesin a single administration or using fewer fractions with largedoses, serves a mathematical purpose but does notguarantee biologically equivalent outcomes. Animal studies have yet to be reported assessing the impact of chemoradiation on osseointegration.
Anticipated outcomes in humans based on animal studies Because anchorage is essentially mechanical as opposed to biologic, the load carrying capabilities of osseointegrated implants in irradiated bone will be less than seen in nonirradiated bone. The success rates of osseointegrated implants in irradiated bone should be less than that seen in nonirradiated bone. The higher the dose, the more profound the tissue changes and the lower the success rates.
Anticipated outcomes in humans based on animal studies In the mandible at higher doses (above 6500 cGy with conventional fractionation) the risk of osteoradionecrosis is most likely quite significant. Because of essentially mechanical anchorage and compromise of the remodeling apparatus of bone, late implant failures should be expected, even in good quality bone sites such as the anterior mandible
Anticipated outcomes in humans based on animal studies Persistent osteoclastic activity secondary to residual functioning osteoclasts leads to bone which is less dense, and therefore initial anchorage and stabilization may be difficult to achieve in irradiated sites. Because of the compromised remodeling apparatus and impaired anchorage, long term clinical observations will be needed to properly assess the success-failure rates of implants in irradiated tissues
Human studies Yerit et al, 2006 Roumanas et al, 1997 (Maxilla) Roumanas et al, 2002 (Craniofacial sites) Nimi et al, 1998 (Maxilla) Esser et al, 1997 (Mandible, maxilla) Granstrom et al, 1994 (Craniofacial sites) Granstrom, 2005 (All sites)
Implants in irradiated mandibleYerit et al, 2006 (Pt base 1990-2003)* Patients – 71 Dose 5000 cGY Number of implants - 316 Implant survival • Nonirradiated – 95% • Irradiated sites – 72% *HBO was not used
Implants in irradiated mandibleYerit et al, 2006 (Pt base 1990-2003)*Success rates – Irradiated sites -154 implants) 93% at 1 year 90% at 2 years 84% at 5 years 72% at 8 years followup. The survival rates for the 84 implants placedSuccess rates - nonirradiated residual mandibular sites (84 implants) 99% at one year 99% at 2 years 99% at 5 years 95% at 8 years followup
Implants in irradiated mandibleEsser and Wagner, 1997 Post op dose (CRT) – up to 6000 cGy Opposed mandibular fields – Symphysis? Pts - 58 (from 1985-1995) Implants placed – 221 Implants lost – 32 Before loading - 18 After loading -17 Success rate 84.2%Granstrom, 2005 63% survival rate for 15 implants placed in the mandible *HBO was not used
Implants in the irradiated maxillaPredictability-Maxilla % Roumanas et al, 1997* 55 Nimi et al, 1998* 63 *Without HBO
Implants in edentulous maxillectomy patients Patients Number of implants Success Treated placed uncovered buried failed %Irradiated 13 50 29 3 10 55.2Non-Irradiated 10 35 25 3 2 80.0Totals 23 85 54 6 12 66.7Roumanas et al, 1997Failures in the irradiated group tend to be late, after the implants have been loaded.
*Roumanas et al, 2002 Implants in irradiated tissues Craniofacial sites* Implant Pts Implants Implants Implants Implants Survival sites placed uncovered buried failed rates (%) Auricular 2 6 6 0 0 100 Nasal 4 Piriform 8 6 0 1 83 Glabella 2 2 0 2 0 Orbital 6 19 15 0 11 27 Overall 12 35 29 0 14 52Failures in the irradiated group tend to be late, after the implants have been loaded. loaded
Implants in the Irradiated Supraorbital RimSuccess is poor and failures are late because: Mostly cortical bone • Blood supply from periosteum and is compromised • Anchorage is primarily mechanical More radiation absorption Compromised remodeling
Implant failures -Irradiated sites Case reportFlange exposure Eventually led to loss of implants This patient received more than 6000 cGy to the implant sites
Implant failures – Irradiated sites Auricular defects Flange exposure led to loss of implants three years post insertion Noteexposed bone (ORN) (arrows)
Risk of osteoradionecrosisEsser et al, 1997.In this retrospectiveanalysis, 2 patients out60 (3.4%), developedosteoradionecrosis, bothin the mandible. Allpatients received 6000cGy with CRTpostoperatively viaopposed mandibularfields.
Risk of osteoradionecrosisGranstrom (2009) 10 out of 116 patients – 8.6% Dose • Mean 79 Gy • 4 had two courses of radiation • 23- 145 Gy Sites • Mandible • Orbit • Mastoid • Frontal bone
Osteoradionecrosis Case report This patient received 6600 cGy for a squamous carcinoma of the lateral tongue. Three years later implants were placed. Three years after implant placement the patient developed an infection associated with left posterior implant.Eventually, the patient developed an osteoradionecrosis, apathologic fracture of the mandible and subsequently themandible was resected.
Osteoradionecrosis - Mastoid Note exposed bone (ORN) (arrows) The necrosis eventually resolved with conservative measures and the two inferiorly positioned implants failed.
Implants in irradiated mandible Role of hyperbaric oxygenThe data is all retrospective, but based on the reports ofGranstrom et al (1993, 2005), there appears to be anadvantage. Success rates appear to be higher and the risk ofosteoradionecrosis may be reduced depending upon thedosage to the implant sites. • 63% survival rate for 15 implants placed in the mandible without HBO • 100% survival rate for 30 implants placed in the mandible with pre-operative HBO therapy.
Impact of HBOGranstrom 2005 -- All sites – 25 years Implants placed Implants lost ORNWithout HBO 291 117 5With HBO 340 29 0
Impact of HBO Periosteal blood supply improvement vs revascularizing the marrow and repopulating it with stem cells? It is not known which of these two phenomenon is most important Success rates improved over the short term particularly in ideal sites such as the anterior mandible Experience in the orbit Late failures with short implants even with HBO
Impact of HBO - MaxillaImplants can be inserted with little or no risk of osteoradionecrosis regardless of dose as long as the dosage is within customary therapeutic levels.The use of hyperbaric oxygen can be justified onlyon the basis of improving success rates.
Time from irradiationImpact of time – After cancerocial doses of radiation do the tissues recover? At cancericidal doses the irradiated tissues do not recover. With time the irradiated tissues continue to deteriorate and become less vascular, more fibrotic etc. The longer the time from radiotherapy the poorer the results (Granstrom, 2005)
Implants in Irradiated TissuesRecommendations Patient selection Edentulous patients receive the most benefit Consider risk – reward ratio Determine tumor status – 80% of recurrences occur within the 1st year Check the dosimetry of the radiation
Implants in Irradiated TissuesRecommendations Longer implants are recommended Use more implants than the usual number Splint implants together with rigid frameworks Implant assisted tissue bar designs are preferred with overlay dentures No cantilevers HBO or pentoxyfilline-tocopherol protocol recommended to improve success rates and reduce risk of ORN
Implants in the irradiated mandibleDoses 5500 cGy and below Implants can be inserted with little or no risk of osteoradionecrosis Success rates will be probably be 15-20% lower than normalDoses between 5500 and 6500 cGy Individual patient factors such as fractionation, tissue responses, clinical findings, dental history etc. impact the decision. Success rates not well documentedDoses above 6500 cGy The risk of osteoradionecrosis becomes significant and implants should not placed unless HBO is given. In such patients the success rates have been in the 75-80% range with little osteoradionecrosis seen.
Implants in the irradiated edentulous mandibleAt doses above 55 Gyanchorage is probably primarilymechanical as opposed tobiologic.Without HBO long termsuccess rates may beproblematic (Granstrom, 2005; Yeritet al, 2006)Therefore if implants are usedwe recommend: Four implants splinted together with a implant assisted overlay denture. In this design the “Hader” segment anteriorly serves as the axis of rotation. The resilient “ERA” attachments posteriorly allow the prosthesis to rotate around the Hader segment when posterior occlusal forces are applied.
Implants in the irradiated mandible Patient had hemiglossectomy and reconstruction of tongue with a free flap and received 55 Gy post operatively. Without implants use of a complete denture would have been problematic.
Implants irradiated maxillary sites Risk of osteoradionecrosis is negligible unless the doses are extremely high (above 7500 cGy) Success rate has generally been less than the mandible presumably because less bone density and depends on: Dose to bone Load biomechanics, etc. Quality and quantity of bone Implant length For maxillectomy patients Splint implants together with rigid frameworks Tissue bars should be implant assisted
Implants - Irradiated craniofacial sitesFloor of nose Little biomechanical stress Success rates will probably be 60-80% depending on the doseMastoid Little biomechanical stress but implants are short Success rates will probably be 60-80% depending on the doseSupraorbital rim All cortical bone Success rates will be very low, long term, probably less that 25%
CRT - Implants in irradiated patients vs implants in the radiation field Check fields and dose Fields are often reduced in size as treatment progressesImplants can be placed in the anterior mandible and anterior maxilla in suchpatients and the success will be equivalent to normal non irradiated patients
CRT - Implants in irradiated patients vs implants in the radiation field These implants were positioned anterior to the field of radiation (note the pattern of hair loss).
Radiation delivery factors - IMRTCheck dosimetry Dose varies considerably and there may be hot spots in unusual areas3 fields 5 fields 7 fields
Irradiation of Existing Implants - BackscatterThese implantswere irradiated 2years followingplacement. Notethe exposure ofthe implant Dose enhancement of about 15%flanges. within 1 mm of implant surface (Schwartz et al, 1978:;Wang et al,1996).
Irradiation of existing implants- BackscatterImplants were placed simultaneous with tumorresection and reconstruction of this large body-symphyseal defect with a fibula free flap. Thepatient received 6000 cGy post operatively.
Irradiation of existing implants- BackscatterSeveral months later and just after delivery of thetissue bar, the tissues on the labial surfaces of theimplants dehisced and the bone overlying the implantssequestrated leading to loss of the implants.
Irradiation of existing implants- BackscatterFollowing loss of the implants, the mucosarecovered the area. The graft remained viable andmandibular continuity was maintained.
Irradiation of Existing ImplantsOptions• Do nothing• Remove the prosthesis and close the wound (Granstrom et al, 1993)• Remove the bridge and place healing abutments on the implants (No data is available but our experience has led us to favor we favor this option)
Irradiation of Existing ImplantsRemove the prosthesis and close the wound (Granstrom et al, 1993)In this patient the fixed partial denture was removed and the implants surgically buried beneath the mucosa. However they soon became exposed to the oral cavity
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider conside Dose to bone anchoring the implants Mandible vs maxilla Target volume/fields Chemoradiation or radiation alone Hygiene access - Beware of posterior ridge laps Patient compliance issues
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider conside Dose to bone anchoring the implants If the implants are located in the mandible and the dose t the implant sites exceeds 65 Gy the risk of ORN is significant and replacing the prosthesis may predispose to a high level of risk.
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider Mandible vs maxilla Since the risk of ORN in the maxilla is very low and the morbidity is minimal reinserting an implant retained prostheses in the maxilla carries very low risk.
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider conside Target volume/fields Implants sites out of the field of radiation when CRT is used receive virtually no radiation and implant sites beyond the clinical tumor volume when IMRT is used will receive lower dose. Therefore prostheses can be reinserted in these situations in both the mandible and maxilla with little or no risk of ORN.
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider conside Chemoradiation or radiation alone ChemoRT raise the BED (biologically equivalent dose by 700 – 1000 cGy. The implant sites are in the mandible and exposed to these dose levels replacement of the prosthesis may predispose to a high risk of developing an ORN
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider conside Hygiene access and patient compliance issues Beware of posterior ridge laps of fixed implant supported prostheses in the mandible in the marginally compliant patient. These patient are at high risk for periimplantitis and ORN.
Irradiation of Existing ImplantsRemove the bridge and replace with healing abutments Minimizes backscatterFollowing completion of radiation therapy should we replace the bridge, tissue bar etc.? Factors to consider consideIn summary in the mandible if the BED (biologicallyequivalent dose) to the implant sites exceeds 6500 cGy wedo not recommend placing the prosthesis back into position inmost patients because compromised hygiene and the risk ofa peri-implant soft tissue infection may lead to anosteoradionecrosis (see slide #56).In the maxilla and craniofacial sites the prosthesis can bereinserted with little risk to the patient.
Placement of implants in patients to receive postoperative radiation. Should the clinician place these implants at the time of tumor ablation or wait until after the radiation treatments have been completed?We consider this issue from two perspectives: Quality of implant anchorage and prospects for long term success Risk of osteoradionecrosis
Quality of implant anchorage and prospects for long term successThis issue is debatable but from this perspective it is probably best to placeimplants at the time of tumor ablation. Given the bio-reactivity of the micro-rough or nano-enhanced surfaces the implants will become very wellanchored in bone by 6 weeks – the period of time usually employed to allowthe surgical wounds to heal prior to commencing postoperative radiationtreatments. Admittedly the dose enhancement effect will render this bonenonvital and the implant anchorage becomes primarily mechanical.If one delays implant placement until radiation treatments are completedthe postoperative doses used today (usually 60 Gy and above) will alsorender the anchoring bone relatively nonvital and the implant anchorage willalso be primarily mechanical as opposed to biologic.The implant anchorage of the former will be considerably better than thelater approach.
Risk of osteoradionecrosis In the mandible the risk of ORN secondary to dose enhancement may be significant If there is the chance that the postop BED to mandibular implant sites will exceed 6500 cGy it is probably best to defer.
Nano-enhanced and genetically engineered implant surfaces Will these phenomenon be clinically significant in the irradiated patient? Probably not. Anchorage is mechanical as opposed to biologic. The macro-surface topography, the quality of bone and the skill of the surgeon are the most critical factors. The major problem in the irradiated patient isloss of vasculature and fibrosis and with it the lossof osteoprogenitor cells (mesenchymal stem cells)in the marrow.
Dental development Levels as low as 2500 cGy effect tooth development (Gorlin and Meskin, 1963; Pietrokovski and Menczel, 1966; Dahllof et al, 1994; Kaste et al, 1994) Changes reflect a variety of defects that indicate the several stages of development existing during the course of radiotherapy This patient is 16 years of age. He received 3600 cGy of radiation when he was 4 years of age for treatment of a rhabdomyosarcoma.
Dental development Levels as low as 2500 cGy effect tooth development (Gorlin and Meskin, 1963; Pietrokovski and Menczel, 1966; Dahllof et al, 1994; Kaste et al, 1994) Changes reflect a variety of defects that indicate the several stages of development existing during the course of radiotherapyAre these patients candidates for implants? Yes! If t dose is below 4000 cGy.
Early Radiation to the Enamel Organ Implant supported fixed partial dentureThis patient was irradiated as a young child fora rhabdomyosarcoma. She received slightly lessthan 40 Gy along with several courses ofchemotherapy which arrested the developmentof her permanent dentition.Eventually all her teeth were lost or extractedand several implants were placed in the maxillaand mandiblePFM fixed prostheses were then fabricated
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