Abstract

As a result of the progress made in the area of endosseous implants in the last 15 years, the value of the subperiosteal implant has been minimized. Yet endosseous implants are not appropriate for all patients in need of implants. Well-designed subperiosteal implants have been reported to function successfully for many years. Among the relevant factors contributing to the success of this method are implant design, atraumatic surgery, understanding of the involved anatomic structures, accurate impression techniques, and appropriate occlusal adaptations of the final prosthesis. This report reviews the design characteristics of successful subperiosteal implants and the anatomy of the areas upon which subperiosteal implants rest in both mandibles and maxillae based on recent research performed in Rumania.

SUBPERIOSTEAL IMPLANT TECHNOLOGY:REPORT FROM RUMANIAINTERNATIONALIoan Sirbu, DDS (DMSc)KEY WORDSOral implantologyOral subperiosteal implantColonel Ioan Sirbu, DDS (DMSc), is Chief ofthe Oral Implantology Clinic of Carol DavilaUniversity of Medicine and Pharmacy, Facultyof Dentistry, Central Clinical EmergencyMilitary Hospital, Bucharest, Rumania.As a result of the progress made in the area of endosseous implants in the last15 years, the value of the subperiosteal implant has been minimized. Yetendosseous implants are not appropriate for all patients in need of implants.Well-designed subperiosteal implants have been reported to function successfullyfor many years. Among the relevant factors contributing to the success of thismethod are implant design, atraumatic surgery, understanding of the involvedanatomic structures, accurate impression techniques, and appropriate occlusaladaptations of the final prosthesis. This report reviews the design characteristicsof successful subperiosteal implants and the anatomy of the areas upon whichsubperiosteal implants rest in both mandibles and maxillae based on recentresearch performed in Rumania.B cular ripheral struts) on a specified series of es, and the anterior maxilla, partittress- points of castings (the pe- canine pillars, the zygomatic bt n ee betw are lants p im osteal th Plasubpecingriosteale suppoimplants.rtingforces. The best areas to place subpeuhe twrioe termining the success of and thus less resistant to comt of r a t t a p f o antra e- d i s e r majo l p tureNTRODUCTION Ione moraypholorgyolandntex- roundedolderby corticalienbosne,e the ep enlargednressivthin-,traditionally acceptable, dense anatomicsites plays a vital role in the longevityand success of the implant. Finding suchdense areas in maxillae is more challengingthan in areas of the normally densermandibles. Linkow1 has made valuablecontributions to this method.To ensure the success of the procedure,subperiosteal implants shouldbe seated on the densest bone available.The density of the bone is often not appreciatedduring the period immediatelyfollowing tooth extraction. In theposterior maxilla, for example, thebone quality is found to be coarse andcancellous in nature. Although surlyin the dense infranasal rims and upto the anterior nasal spine.Although the first-stage operationrequires an accurate impression, severaltransfer procedures are requiredin order to produce a model uponwhich the implant ''wax-up'' is directlymade. This is the ''refractory'' model,which is created by a series of duplicationprocesses. The accuracy of thecasting is entirely dependent on theskill of the laboratory technician.PATIENT SELECTIONRadiographic studies should includeperiapicals, panoramics, cephalonetric,Journal of Oral Implantology 189SUBPERIOSTEAL IMPLANT TECHNOLOGYFIGURES 1-10. FIGURE 1. Presurgical radiograph. FIGURE 2. Presurgical intraoral aspect. FIGURE 3. Intraoral view of the alveolar ridge afterincision from 1 tuberosity to the other and reflection of the flaps. FIGURE 4. Eight endosseous implants in the anterior maxillary region.FIGURE 5. Postsurgical radiograph. FIGURE 6. An impression of the host maxilla. FIGURE 7. The working model and investment (refractory)model. FIGURE 8. The ''wax-up'' of the left subperiosteal implant. FIGURE 9. Both subperiosteal implants after finishing. FIGURE 10. Theweight of these unilateral subperiosteal implants is 2.4 g.occlusal, and CT scan, and the clinicalexamination must include orofacialand head and neck evaluations. A thoroughphysical examination is requiredto rule out any potential contraindicationsto the surgical procedure. Bloodchemistries should be within normallimits and should include glucose, potassium,calcium, sodium, creatinine,urea, alkaline phosphatase, chloride,and albumen/total protein. Thereshould be no active infections present.190 Vol. XXIX/No. Four/2003Patients with the following conditionsshould be excluded: alcoholism, historyof stroke or myocardial infarctionwithin the past year, valvular prosthesesof less than 18-months' duration,end-stage renal disease, treatment-resistantosteomalacia, generalized osteoporosis,unstable diabetes mellitus,postradiotherapy to the face or neck,significant endocrinopathies, and drugaddiction. Clinician discretion will determinewhether patients with less severeconditions may be candidates forthe target procedure.In this study, 2 clinical cases arepresented. The first patient is a 55-year-old woman with total maxillaryedentulism and a Kennedy class Imandible (Figures 1-16). The secondcase is a 74-year-old woman with Kennedyclass edentulism of both jaws.The remaining teeth are not salvageabledue to severe periodontal disease(Figures 17-29).FIGURES 11-16. FIGURE 11. The second-stage surgery: insertion of the abutments on the anterior implants at the same time as the incisionand reflection of the mucoperiosteum of the subperiosteal implant. FIGURE 12. The placement of the left subperiosteal implant. FIGURE 13.The placement of the right subperiosteal implant. FIGURE 14. Insertion of the abutments and the unilateral subperiosteal implants. FIGURE15. (a) Pre- and (b) postsurgical radiographs after the insertion of the abutments and the unilateral subperiosteal implants. FIGURE 16. (a)Before and (b) after treatment. The prostheses are fixed because the patient presents with excellent oral hygiene.DESIGN CONSIDERATIONSThe peripheral or main struts must bedesigned to accommodate specific anatomicelements so that stability againstvertical and lateral forces will be assured.The involved sites are the anteriornasal spine, the zygomatic buttresses,canine pillars, and the tuberosities.Selection of sites for primary strutplacement must be limited to areaswhere the periosteum is firmly attachedto the bone in order ensure early fixationof the implant. Implant castingsshould be as light as possible. Increasingthe castings' weight contributes todecreasing success of the implant. Thesupporting struts (primary or peripheral)must be no greater than 2 mm inwidth or, if wider, contain fenestrationsthat will lighten the casting as well asoffer additional areas for fiber ingrowth.Struts must not be placed on exostoses,spinous or sharp bone angles,or other points of potential loss of vascularityin order to avoid irritation tothe overlying soft tissues. Secondarystruts, on which there are no abutments,must be at least 0.5 mm thickand 2 mm wide. Thinner widths ofmetal can cause bone resorption, widerwidths may interfere with periostealreattachment, and thicker widths maybe responsible for metal dehiscence.Peripheral struts must be rigid, and ifthis characteristic contributes to greaterwidth, then fenestrations are essential.In areas of high bone density, smallerand less numerous struts may be used.Whenever possible in the anteriorIoan Sirbumaxilla, individual vestibular extensionsshould be used, rather than theconventional type of continuous peripheralstrut. With this design, eachcomponent remains somewhat independent.If a sectional problem arises,the individual portions may be resected,by simply cutting the connector,without jeopardizing the uninvolvedremainder. In instances where secondarystruts are not intimately adapted tobone, vital support areas may be graftedwith hydroxyapatite or harvestedbone.Except for those rare patients withoutstrong occlusal forces, or unusualesthetic demands, acrylic teeth shouldbe chosen. Further, canine protectionshould be avoided and full cuspalguidance sought. It is not advisable toJournal of Oral Implantology 191SUBPERIOSTEAL IMPLANT TECHNOLOGYFIGURES 1730. FIGURE 17. Presurgical radiograph. FIGURE 18. Maxillary edentulous ridge. FIGURE 19. First-stage surgery: host bone afterincision and reflection of the flaps. FIGURE 20. Silicone impression of the bone. FIGURE 21. Duplication of the master cast. FIGURE 22. Theinvestment (refractory) model. FIGURE 23. The ''wax-up'' prepared for investment. FIGURE 24. The unfinished implant after casting. FIGURE25. Placing the implant on the host bone. FIGURE 26. Postsurgical intraoral view. FIGURE 27. Intraoral view of the maxilla after removal ofsutures. FIGURE 28. Radiograph after inserting the final fixed prostheses. FIGURE 29. The patient (a) pre- and (b) postsurgery.192 Vol. XXIX/No. Four/2003restore subperiosteal implants usingfixed prostheses, which can result indifficulty in performing oral hygiene,nonremovability, and lack of resilienceduring occlusion. The ideal occlusalanatomy employs acrylic teeth and utilizes08 cuspal angulations. Anterior incisiveguidance should be kept to aminimum.In maxillae that have undergonesignificant resorption, the sinus, itsmembrane, and the posterior surface ofthe ridge form a triad that must bekept in balance. Bone resorption is arrestedin the posterior maxilla whenthe infrastructure lies over the sinuswall. In the presence of significantbone resorption under a strut component,the region will become filled withdense avascular connective tissue,which may be curetted. If the tissue isdifficult to reach, the overlying strutmay be removed without threat to theentire device.Tripodal implants, as devised byWagner,2 are of benefit in the mandiblewith dehiscent neurovascular bundles.The design embodies 3 separate islets:1 on each side of the posterior mandible,depending on support from the externaloblique ridge, often extendingwell lateral to it and covering some ofthe ramus cortex. The third islet is ananterior component designed to rest onthe symphysis and genial tubercles. Itis necessary to avoid the neurovascularbundles and mylohyoid ridges: the formerbecause of the danger of dysesthesia,and the latter because of the fragileand poorly vascularized nature of theoverlying mucosa. This design is ofsignificant value for patients with exposedor dehiscent canals.SURGICAL PROCEDURESThe first stage of surgery involves takinga direct impression of the bone inorder to create a model of the host'sexposed implant site. The oral cavity issterilized and appropriate anestheticblocks are administered. The periosteumis incised by making a crestal incisionfully around the arch. A verticalanterior relieving incision is requiredto facilitate reflection of the mucoperiostealflaps. A sharp periosteal elevatoris employed in order to reflect theflaps, thereby exposing the vital bearingareas. At this time small bone irregularitiesor protrusions may be correctedwith bone files and rongeur forceps.After suitable retraction of theflaps, using cross tongue dorsum ligatures,an appropriate impression trayis made directly over the bone usingautopolymerizing polymethyl methacrylate.After the muscle is trimmed andtrial seatings performed, an elastomericimpression is made of the potentialbearing site. A counterimpression ismade as well as a centric recording.The cast that is produced in stone fromthe impression is replicated in a refractorymaterial (cristobalite) and mountedon a semianatomical articulator. Theimplant is designed as a wax-up. Themodel is then invested and the implantproduced in a suitable metal. If the implantcan be prepared for insertion onthe same day, a second surgical proceduremay be averted. If that is notpossible, the tissues are irrigated withsaline and the wound loosely closedwith a continuous suture. Appropriateantibiotics and analgesics are provided,and standard home care instructionsare issued.The second stage of surgery isplanned for 28 to 45 days after makingthe impressions in order to permit forplacement of the implant casting. Thepatient is anesthetized using acceptableblocks after sterilization of the oralcavity, and the wounds are reopenedusing the same incision lines. After exposureof the host bone, the sterilizedinfrastructure casting is fitted. Afterthe implant is completely seated, observationshould indicate the preciserelationship of its bearing points to theunderlying cortex. At this point, carefulsuturing of the facial and lingualflaps will complete the procedure. Inthe regions of the abutments, pursestring sutures are required to obtainintimate closure. This is essential in orderto discourage retrograde infectionIoan Sirbuor epithelial inversion. In many instances,a vertical or oblique relievingincision will be required to assureatraumatic reflections and to spare thetissues from traction-induced injuries.The appropriate positions for these incisionsare generally just lateral to themidline in either jaw. If there are smalldefects between casting and bone, hydroxyapatitemay be used to fill them;if there is a lack of retention, smallscrews may be used for primary fixation.When all remedial steps havebeen completed, closure may ensue usinga continuous horizontal mattresssuture with tight pursestrings at theabutment crevices. Postoperative antibioticsand analgesics are prescribed,and home care instructions provided.Postoperative care for implant patientsshould be conducted every day or 2 forthe first 10 days, or at least until thesutures are removed.PROSTHETIC PHASESTen days after placement of the implant,sutures are removed and a temporaryprosthesis may be inserted. Atthe end of 1 month, the final prosthesismay be placed. It should be comprisedof an acrylic base, acrylic teeth, and retentivedevices such as Hader or similarclips. Perfect occlusal relationshipsand balance are mandatory to ensureimplant longevity. It is essential thatthe mucosal surface of the prosthesisdoes not come into contact with thesoft tissues. If the denture becomesanything but completely implantborne,there is significant risk of mucosalulceration, dehiscence, and subsequentimplant loss. Monthly checkupsare required for the first 6 months,and less frequent examinations thereafter.The bite must be rebalancedwhen necessary and additional hygienemeasures employed as needed.DISCUSSIONCurrently in Rumania, the objective insubperiosteal implant treatment is theelimination of the first-stage surgery(ie, direct bone impression). Researchhas focused on bone replication withJournal of Oral Implantology 193SUBPERIOSTEAL IMPLANT TECHNOLOGYthe aid of the CAD-CAM methodbased on CT scanning. Some of the advantagesof this approach are methodsimplification, the ability to obtain asimulation of the jaw bones, and thepossibility of analyzing and using allof the true dimensions. However, inRumania this method has had the disadvantageof a high degree of inaccuracy,with the resulting implants fittingpoorly or not at all.Subperiosteal implants have improvedduring the last few years; thepercentage of success had risen dramaticallythanks to new techniquesand better implant design as well as adeeper understanding of the patternsof bone resorption. Especially importanthas been the development of techniquesand materials that arose fromthe early chromium alloys to the presentuse of titanium, bringing with it194 Vol. XXIX/No. Four/2003the entire array of advantages that thismaterial possesses.CONCLUSIONIn summary, the advantages of subperiostealimplants include the predictabilityof the results and the highsuccess rate. This technique utilizesless invasive surgery and is thereforepreferable to the use of iliac crest ortibial grafts. Alveolar ridges with severeatrophy can be reconstructedprosthetically. Partial subperiosteal implantscan be used with endosseousimplants and even natural teeth withfixed bridges. The surgical techniqueand clinical stages are not complicated,generally being mastered by implantologistsin general dental practice.Disadvantages include the frequentnecessity for 2 surgical procedures andthe initial complexity of the surgicalprocedures. This complexity presumesa certain level of experience that thepractitioner can obtain only over a longperiod of time. The procedures requirespecialized technicians and a titaniumsmelting oven. Finally, removal of subperiostealimplants, although rarely indicated,can present difficulties. Theimportance and potential benefits ofsubperiosteal implants are undeniable,being at this time the only means ofrestoring jaws in situations where endosseousimplants cannot be placed.REFERENCES1. Linkow LI. Implant Dentistry TodayA Multidisciplinary Approach. VolII. Padua, Italy: Piccin Nuova Libraria;1990:961-1034.2. Linkow LI, Wagner JR, ChanavazM. Tripodal mandibular subperiostealimplant: basic sciences, operationalprocedures, and clinical data. JOral Implantol. 1998;24:16-36.