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Development of a new endosseous dental implant. Part II: Human studies
MAXILLOFACIAL PROS~?S”:CS TEMPOROMANDl1EKJLAR JOI-Y’r
. DENTAL
IMPL.ANTS
SFC TIC 1N I i)lTOl
1. KENNtTH
ADISMAN
KtJNALD
I’. L~ESIARDI~S
Development of a new Part II: Human studies M. 8. Weiss, Rush-Preshwerian
S
D.D.S.,”
and W. Rostoker,
St. Luke‘s
ince the initiation
I\ledic,al
(trnter,
endosseous
University
of the animal experiments
of Illinois,
in
1. Would good oral hygiene increase the success rate? experience
pain
implant.
Ph.D.** and
1969, results using endosseous dental implants have indicated a satisfactory benefit-risk ratio. Therefore, pilot human studies using endosseous dental implants were initiated in July 1975. Over 2,000 prospective volunteers were screened by telephone; 250 of these were examined. The study was designed to verify that the techniques and knowledge gained in the animal experience could be transferred to and reproduced in humans. In addition, only a human study would be able to provide answers to the following questions:
2. Does the patient tion?
dental
postimplanta-
3. To what extent is the pain experienced? 4. Is the amount of pain controllable? The ultimate goal of any implant is to be a freestanding unit that can restore masticatory function. A free-standing implant offers a definite improvement over the conventional fixed partial denture, which requires the preparation of two natural teeth. The baboon study revealed that it is possible to achieve a free-standing unit under less than ideal conditions.’ Five human studies were conducted to determine the viability of the fiber-metal dental implant as a tooth replacement for (1) a fixed partial denture replacement, (2) a single tooth replacement, (3) a stabilized
““22-39,3,82/OofJ6R-i+ ,3$01.X1/0 to 19R2Ttre C. V. MC+ Co.
Chicago,
III.
crown (implant crown attached to an ad,jacenttooth with an inlay SupporL
or crown),
FIXED PARTIAL The fixed partial
and
(4)
an overdenture
DENTURE STUDY
denture study was conducted first because it was anticipated that it would have the highest and most predictable success rate. In addition, the amount of damage caused by failure of the implant would be minimal. The implant was used as a terminal abutment for a fixed partial denture, and the anterior
abutment was a crowned natural tooth. The goal was to insert implants in volumeer
patients with missing molar teeth in a quadrant where the remaining premolar tooth had healthy periodontal tissue. The plan was to place the implant in the site of the missing teeth. The patients in this study had either missing molars or missing molars and premolar teeth. The fixed partial dentures replaced the missing teeth in hnth the mandible and maxillae. ‘l‘hc patients for this study were selected carefully to meet rertain criteria. One important criterion was that they would be available for observation for at least 5 years. Their selection was based on their history of employment and residence in the same places for cxtcndcd periods of time. Othrr criteria were age, general health, oral hygiene, and evidence of good dental rare. A wide range in the age of the patients was selected since it would help determine if age was a variable related to a successful implantation. The final major criterion was to determine through radiographic examination the position nf the maxillary sinus and the mandibular canal in relation to the edentulous alveolar rrcst Patirnts in the sludy were closely supervised so that a failure of the implant would be recognized early and removal could be accomphshed with a mmimum of permanent damage to the mandible or maxillae. Fail-
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t diameter
+ 4mm
1/2mm 16.0 mm 1 Fig. 1. Radiographic templates.
2mm
Mandibular
canal
Fig. 3. Cross-sectionof implant in relation to mandibular canal and alveolar crest.
Mandibular canal Fig. 2. Lateral view of implant in relation to alveolar
crest and mandibular canal.
ure was determined by radiographic evidence of bone loss, clinical signs of periodontal-type pockets around the implant, and pain. Following implantation, long-cone radiographswere usedand a millimeter grid superimposedon the film.* The radiographs were made monthly to record the bone level surrounding the implant. This was correlated with the clinical signs of mobility and gingival inflammation, A failure was defined asan implant that had lost half of its bony support as seenon the radiographs, had over 4 mm of periodontal pocketson three nf its four sides, and had a Class 3 mobility. Class 3 mobility was defined as the condition of an implant exhibiting over 1 mm lateral movementin a buccolingual direction and being depressible in its socket. Continued gingival inflammation resulting in a lateral abscesswas also considered a failure. Failed implants were removed immediately. The patients selected for the initial study were screenedthoroughly. A complete dental examination was given each patient, including the making of diagnostic casts and periapical full-mouth and panoramic radiographs, A comprehensivemedical history
634
was recorded to properly evaluate any complicating systemicproblems. Patients were informed of the exact nature of the study and their part in it. To aid in the explanation of the proceduresinvolved, a seriesof large color plates depicting each phase of treatment was shown to each patient. The patients were required to read the printed informed consent form. This covered the entire course of treatment, the risks involved, and possible damage to the oral apparatus. The patient signed the consent form in the presenceof a witness, reread. and initialed it. DIAGNOSTIC
EVALUATION
Proper diagnosisfor patient selection. as is customary with any procedure. is of the utmost importance. The information recorded during the dental examination as well as the answers given on the medical questionnaire should be evaluated carefully. Dental implants are not indicated for patients with rampant caries or active periodontal disease,or for those exhibiting signs of excessive bruxism. If the patient is deemedacceptable,the size and positioning of the implant(s) must be determined. The site of the anticipated implant should be measured with calipers. The buccolingual thicknessof the residual ridge should be at least 8 mm to accommodate a 4 mm (in diameter) implant or 8.7 mm IO accommodate a 4.76 mm implant. At this point in the treatment, the diameter of the implant is determined. INTRAORAL
RADIOGRAPHS
The intraoral radiographs are usedto examine the previously selectedimplant site. If the root outline of the absent tooth can still be seen, an alternate site
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Fig. Fig. Fig. Fig.
IMPLANT
4. 5. 6. 7.
Round bur at low speedis used to enter cortical plate. Tapered drill with plastic sleeve that controls depth of penetration End cutting drill also has plastic sleeve. Hand reamer.
should be chosen.Through experience, it appearsthat 6 months to 1 year should elapse between tooth removal and implant placement. If the film reveals an overly dense trabeculation at the proposed site, the location should be rejected. The radiographic template (Fig. 1) is placedover the intraoral film. Generally, the intraoral film is to scale and has zero magnification. The zero magnitude template of the appropriate diameter selected is used. There should be 2 mm of bone mesialand distal to the implant meshwork. The inferior surfaceof the implant should be 2 mm above the mandibular canal or 2 mm below the maxillary sinus.The superior surface should be 0.5 mm below the crest of the residual ridge (Figs. 2 and 3). The appropriate height of the implant is selectedusing these determinants. PANORAMIC
RADIOGRAPHS
Although the panoramic radiographs are slightly magnified, they provide a good overall view of the relationship of the implant to the mandible or maxilla. The appropriate diameter of the implant on the template is placed over the panoramic film, and its position is checkedagain. In someinstances,more than one implant size should be checked against the intraoral films.
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A summary of the indications and contraindications include: Indications. The patient should be in good general health, and there should be no rampant caries present. The patient should be free of periodontal diseaseand have good oral hygiene. There must he sufficient investing bone for the implant to sear properly, and there should be edentulousregions in the posterior part of the mouth. Contraindications. Infection is an absolute contraindication, as are hypertension (uncontrolled), poor oral hygiene or periodontal disease,excessively hard bone or torus in the region of the anticipated implant site, insufficient bone height or width for implantation, recent extraction sitesor areasin which the root outline can be seen on the radiographs, edentulous regions anterior to the canine teeth, systemic,diseasessuch as uncontrolled diabetes, and hvpertcnsi\‘i~ pntitnts as indicated by bruxism. SURGICAL
PROCEDURE
The implant site is prepared through the use of precisely sized drills and reamers IO rre;tie accurate dimensionsfor the implant. FolIowine, loctalanesthesia. an incision is made to the bone along the crest of the residual ridge over the proposed implant site. A
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Fig. Fig. Fig. Fig. Fig. Fig. Fig.
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8. Replica of implant is placed into prepared site. 9. Seating instrument. 10. Implant seated. 11. Mucosa is sutured around implant. 12. Four weeks postoperative. 13. Implant fixed partial denture in function. 14. Preoperative photograph of proposed site.
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full-thickness flap is reflected to expose the bone. Then, a round bur in a slow-speed handpiece is used to enter the cortical plate at the proposed implant site (Fig. 4). The bur is cooled during use with a flow of saline directed at the bur head. A tapered drill is used to create the depth of the implant site using the previous opening as a guide. A plastic sleeve on the shank of the drill limits the penetration to the predetermined depth (Fig. 5). The debris is flushed out of the site with saline solution. A four-fluted end cutting drill of a corresponding size to the implant diameter and length is used in the slow-speed handpiece to flatten the base of the implant site. The end cutting drill also has a plastic sleeve so that accurate depth of the implant site can be achieved (Fig. 6). A hand reamer is inserted into the prepared site and rotated manually to assure that the symmetry of the hole matches that of the implant (Fig. 7). A replica of the implant made of solid metal but slightly smaller in diameter is placed into the site (Fig. 8). If the replica seats properly, the sterile implant is placed into the site with the aid of the seating instrument under hand pressure or with a light tap of a mallet (Figs. 9 and 10). When properly seated, the superior surface of the implant should be 0.5 mm below the level of the alveolar crest. The mucosa is repositioned and sutured (Fig. 11). The patient is provided oral tetracycline, 1 gram per day for 5 days, and put on a soft diet for the same period of time. Radiographs are made of the implant, and intraoral photographs are made of the implant site.
PATIENT
FOLLOW-UP
The patient is seen 1 week postoperatively and the sutures removed. Weekly visits are made for 4 weeks or until the implant is stable (Fig. 12). At each visit, the patient undergoes the following examination: (1) intraoral radiograph of the implant site with a millimeter grid superimposed on the film, (2) determination of the pocket depth around the implant, (3) evaluation of clinical symptoms of pain and inflammation, and (4) determination of the mobility of the implant by lateral and downward finger pressure. The implant site is photographed in color to record the condition of the soft tissue. When the implant is stable and symptom-free, treatment with fixed partial dentures is initiated. This is usually at least 4 weeks postinsertion. Full-arch impressions are made and sent to the dental laboratory with occlusal registrations and a stone cast of the
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Fig. 15. Postoperative radiograph
opposite arch. Edentulous sitesare restored with gold and porcelain veneered pontics. The abutments, the implant and natural teeth, are restored with porcelainfused-to-gold crowns. An anatomicarticulator is usedin the fabrication of the fixed partial denture (Fig. 13). After the fixed partial denture is cemented to the abutments, the patient is seenand reexamined weekly for the first month, then monthly for the first year. The examination is the sameone performed at the time of suture removal. A monthly comprehensive review is made of all data on all patients. When it is deemed necessary,consultantsalso review the data. Experts in the fields of periodontics, oral pathology, and fixed partial prosthodontics are available for consultation.
EXAMPLES OF THE FOUR TYPES OF RESTORATIONS Fixed partial denture Patient No. 5 in the study was a 34-year-old man with a full complement of teeth except for the lower right molars (Fig. 14). The decision to insert an implant (4 X 10 mm) in the edentulous spaceof the lower right secondmolar was basedon the measurement of the diagnostic casts and radiographs. The implant was inserted July 11, 1975 (Fig. 15). Four weeks postoperatively the tissue was well healed and the implant solid (Fig. 16). A crown preparation was made on the lower right second premolar, and an impression was made to fabricate a fixed partial denture using the implant as the distal abutment. The fixed partial denture was made on an anatomic articulator and inserted September3,1975. The fixed partial denture has been in function for over 5 years with no deterioration of the soft tissuesas recorded on September 4, 1980 (Figs. 17 and 18).
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Fig. 16. Four weeks postoperative. Fig. 17. Five-year photograph of implant prosthesis.
Fig. 18. Five-year postoperative radiograph of implant. Fig. 19. Preoperative panoramic radiograph. Fig. 20. Postoperative radiograph of implant.
Patient No. 9 in the study was a 35-year-old woman with a full complement of teeth except for the upper right molars and premolars (Fig. 19). Study of the radiographs and diagnostic casts indicated that a 4.76 x 6 mm implant should be placed in the upper right first molar edentulous site. The surgery was performed on September 3, 1975 (Fig. 20). The gingival tissue was extremely thick, and removal of excess gingival tissue was necessary to expose the implant post (Fig. 21). The fixed partial denture was fabricated with the mesial abutment crown on the upper right canine, and the implant was used as the
638
distal abutment. Two pontics replaced the upper right first and second premolars (Fig. 22). The fixed partial denture was in function for over 5 years with no evidence of bone loss or tissue breakdown as of November 10, 1980 (Fig. 23).
Single
tooth replacement
Patient No. 55 in the study was a 26-year-old man with a full complement of teeth except for the lower right first molar. Examination of diagnostic casts and radiographs indicated that a 4.76 X 8 mm implant could be used in the edentulous space. Because of
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Fig. 21. Excessgingiva was removed to expose implant
Fig. 22. Implant prosthesisin function. mechanical difficulty during surgery on August 19, 1977, a 4.76 X 5 mm implant was substituted (Figs. 24 and 25). The free-standing implant crown was placed in function on January 11, 1978 (Figs. 26 and 27). The free-standing implant crown was functioning well after 42 months with no deterioration of the soft tissue and no bone loss.
Stabilized
single
tooth
Patient No. 113 in the study was a 5%year-old woman with a full complementof teeth except for the lower left first molar. Using the usual diagnostic method of measuring the diagnostic casts and radiographs, a 4 x 8 mm implant was decided upon and surgically placed in the edentuloussite of the lower left first molar on April 6, 1979 (Figs. 28 and 29). The adjacent lower left secondmolar had a broken amalgam restoration and was badly tilted mesially. A normal contact could not be achieved with the proposed implant crown. Therefore, a mesial-occlusal-distal onlay was made for the lower left second molar, attached to the implant crown, and cemented to the natural tooth and implant in one unit on July 18,1979. The stabilized crown has been functioning with no bone loss or tissue change for 10 months (Figs. 30 and 31).
Stabilized
overdenture
Patient No. I35 in the study was a completely edentulous 62-year-old man who had tried unsuccessfully to wear a lower denture. He was treated with upper and lower dentures that were adjusted for comfort. Two implants 4.76 X 6 mm were surgically placed on August 6, 1979, in the sitesof the lower right canine and first molar. The lower denture was relieved over the implant posts so the denture could be worn during the healing period. On September20,1979, two 4.76 x 6 mm implants were surgically placed in the sitesof the lower left first molar and canine. The lower
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denture was relieved to accommodate the implant posts.When the implants had completely healed (Fig. 32), gold copings were made that fit the implant post (Fig. 33). The four copings were made parallel to one another and were cemented to the implant posts. Autopolymerizing acrylic resin was added to the implant post spacesin the lower denture, placed over the implant copings, and allowed to polymerize while the patient closed in centric occlusion (Fig. 34). The denture has been worn comfortably, stabilized by a friction fit betweenthe gold copingson the implant post and the acrylic resin. The patient eats normally and has good functional occlusion.The implants have been in place for 17 months with no apparent bone resorption and the soft tissue in normal condition (Fig. 35).
LOSS OF THE IMPLANT A variety of circumstancescould be held responsible for loss of several dental implants. However, one important factor becameclear: there was only a small amount of alveolar bone loss. The site filled in with normal bone in a short period of time following the removal of the implant, and there was no permanent defect. To illustrate this point, patient No. 17 in the study, a 59-year-old man who had undergone periodontal therapy, lost an implant. He was edentulous in the lower left quadrant, missingthe lower left molars and second premolar. The remainder of the dentition was in good repair. One implant 4 x 6 mm was placed in the site of the lower left secondmolar. The implant fixed partial denture consistedof one pontic between the crown on the lower left first premolar and the implant crown. The prosthesisbecamemobile 1 month after insertion, and the mobility increased until the inrraoral radiograph showedexcessivebone loss around the implant (Fig. 36). The implant prosthesis was removed 6 months after it was placed, leaving a bony defect (Fig. 37). The removal was uneventful; thr implant was
639
Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. 640
23. 24. 25. 26. 27. 28. 29. 30.
Five-year postoperative radiograph of implant. Postoperative intraoral view of implant post. Postoperative radiograph of implant. Crown in place on implant. Radiograph of implant with crown in place. Postoperative intraoral photograph of implant Postoperative radiograph of implant. Stabilized implant crown. JUNE
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surrounded with connective tissue, which facilitated its removal. The site healed quickly and filled in with normal bone within 6 months with no apparent defect on the alveolar crest (Figs. 38 and 39). The histologic section of a failing implant in a baboon illustrates the mechanism of bone destruction and replacement by cells of inflammation (Fig. 40). If the bone is resorbed quickly in response to sudden trauma, it is replaced with granulation tissue, possibly resulting in some suppuration. However, if the causes of resorption are less severe, such as traumatic occlusion in eccentric movements, the bone may be replaced with fibrous connective tissue. When the source of the trauma is corrected in such instances, the resorption of the bone ceases. The causes of failure of this implant fixed partial denture were the result of a poor diagnosis. The natural lower left first premolar abutment was periodontally involved with some loss of supporting bone and should not have been used alone as a fixed partial denture abutment. In addition, the implant used was comparatively short, considering that the size of the implant fixed partial denture was excessively large due to the interdental space. If two natural teeth had been used jointly as abutments and a longer implant or two implants used, the resuhant implant fixed partial denture may have been successful. In spite of the failure of this implant prosthesis, it does illustrate the point that the risk to the patient was negligible. The strength of this implant system is that, even when the implant is lost, the implant site always heals well with no residual defect in the bone or soft tissue. ANALYSIS
OF IMPLANT
RESULTS
As of November 1981, the extended clinical trial program had involved the implantation of 216 tooth root prostheses. Of these, 37 (17%) were never placed into function because they were inadequate to receive a prosthesis. A total of 162 implants have been put into function and have involved the following: 46 fixed partial dentures, 2 free-standing fixed partial dentures, 35 free-standing single crowns, 41 stabilized single crowns, 21 to stabilize complete dentures, and 5 to stabilize removable partial dentures. An additional 17 implants have not been put into function because (1) it was too early for 10 and (2) the patients were lost to follow-up for 7. The portion of the clinical studies that has the greatest longevity is the fixed partial denture study (Fig. 41). Although this is the first human clinical study attempted following the animal studies, 83% of the implants have been successful. The few implants Tttt!
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Fig. 31. Eighteen-month implant.
postoperative
radiograph
of
that were lost to the study were due to instrumentation or traumatic occlusion, such as bruxism. The next human study was the free-standing single tooth replacement (Fig. 42). The success rate was significantly lower (54%) and can be attributed to a number of factors. One was the mechanics of preparing the implant site; the bur shank had to bc lengthened because the natural teeth on either side of the site blocked the handpiece from cutting to the proper depth. Another recurring problem was the inability to produce an implant crown in normal contact with the adjacent natural teeth. Due to the edentulous space, the natural teeth drifted and tilted, and it became difficult to create normal contacts. resulting in food impaction and gingival irritation. In spite of the adverse factors, a significant number of free-standing implant crowns (19) have been functioning for 3% years with no sign of deterioration of the bony support. This study showed that a free-standing implant crown can be successful but only if conditions are ideal. When it became apparent that the free-standing implant crown could only be used in ideal situations, a second implant study was initiated using a restoration in the ad,jacent tooth to “stabilize” the implant crown. Many of the volunteer patients who needed a single tooth replacement presented with a defective filling in the adjacent natural tooth. The stabilized single crown study consisted of 41 patients with the implant crown attached to an inlay or crown on the adjacent natural tooth. This study has been successful <83’S), with most of the implants over 2 years in longevity (Fig. 43). Two other studies, the overdenture and the removable partial dentures supported by implants, have been successful but are not statistically relevnnt because the number of implants is small and the study was conducted over a relatively short span of time. These studies are being expanded since the suc‘cess rate has been excellent. 641
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Fig. 32. Intraoral photograph of implant posts. Fig. 33. Parallel gold copings cemented on implant posts. Fig. 34. Denture base modified to receive gold copings.
Fig. Fig. Fig. Fig. 642
35. 36. 37. 38.
Seventeen-month postoperative panoramic radiograph of implants. Radiograph of failing implant prosthesis. Radiograph of implant site following removal of implant. Radiograph of implant site 6 months after post removal. JUNE
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IMPLANT
Fig. 39. Photograph of implant site 6 months after post removal. Fig. 40. Histologic section of failing implant (baboon): a, implant inflammation; and c, osteoclastic activity on bone margin.
wire;
h, cells of
FIXED
182
BRIDW
S?‘W)Y
176 170 s
167 157
AS
157 46
140
38
FIXED FIXED
Of
NOVEMSER.1981/
BR(DGES
ARE
ER1DGES
ARE
COMPLETED
i
SUCCESSFUL
136 135
83%
i
SUCCESS __--
RATE
--j
/
132 107 107 99 97 96 95 92 92 92 85 75 73 71 27 28 25 24 23 21 20 19 18 17
-
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IMPLANT LONGEVITY (years) Fig. 41. Fixed partial THE
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DENTISTRY
denture
study. 643
FREE
f
53 --
6 F d
::. 48
STANDING
SINGLE
CROWN
STUDY
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;; 45 42 40 38 37 36 35 33 32
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l 0
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IMPLANT
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LONGEVITY
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5
(years)
Fig. 42. Free-standing single crown study, These results should be tempered by the experimental nature of the clinical trial program. In many patients, the individual “failures” represent identifiable features that, when recognized, need not be repeated and belong to an important list of contraindications. For example, of the 37 implants deemedinappropriate to place in function, six were placed in the first year of the program. The main reasonfor six of the failures was the inability to deepenthe implant site so that all the wire meshwork was covered. Other reasons for failure were heavy, densecortical plate bone in the site of the implant, which was usually caused by the presenceof a torus mandibularis in the region. Two of the patients had retained deciduousteeth, which were removedjust prior to implantation; both implants were lost. In all the studies, 35 implants were lost prior to being placed in function within the first year. Of the implants that were in function, those lost were attrib644
uted to: (1) bruxism, (2) hypertensive patient, (3) broken soldered joint on fixed partial denture, (4) periodontally involved natural tooth abutment, (5) excessivelylarge pontics due to large interdental space, and (6) long-term viral infection that incapacitated the patient for 6 months. As in any clinical experiment, it becameobvious that certain patients and oral conditions are not suitable for the use of endosseous dental implants. SUMMARY The development of an endosseousimplant has followed a logical and formal plan. 1. Extensive experiments with animals provided preliminary statistics of successful function, extensive histologic studies, evaluation of biocompatibility, and a preliminary assessment of contraindications. 2. Carefully developedand controlled clinical study of human subjects with frequent examinations and JUNE
1982
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IMPLANT
STABtLtZEO
StNC%LE CROWN
41 STABlLtZEO
CROWNS
STUOY
COMPLETED
134 sTABLlzEo:;;;g;;;
j
.-107
0
100 .-99 . 99 98 98 98 98 62 89 80 84 80 00 77 77 75 74 74
l 4 3 0 0 0 0 0
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IMPLANT LONSWTY Fig. 43. Stabilized
detailed records of both successes and failures again provided new basesfor contraindications. The statisticson the clinical study are satisfactory in their results, although they should be regarded as having a somewhat conservative slant. This is because implant failures becamea learning basefor improved procedures. The program so far has been limited to a single implant designthat, with size variants, will serve most applications. However, it is not feasible to modify the design in terms of dimensions for application in the anterior portion of the mouth. A designfor this purpose is established on paper and will become a future additional development. THE
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single
4
(yews)
crown
study.
REFERENCES 1.
2.
Rqmnt
Weiss, M. B., and Rostoker, W.: Uevetopmem of a new endosseous dental implant. Part I: Animal studies. J PRIXTHET DENT 46646 . . 1981 Weiss, M. B., and Ronen, E.: New device to quantitate alveolar bone loss. Oral Surg 44:322, 1977.
reque.st.5
DR. MARVIN RUSH
600
tcr:
B. WEISS
UNIVERSITY s. PAULINA
ROOM 433-A.4.F. CHIcAC;O, IL 60612
645
. DENTAL
IMPL.ANTS
SFC TIC 1N I i)lTOl
1. KENNtTH
ADISMAN
KtJNALD
I’. L~ESIARDI~S
Development of a new Part II: Human studies M. 8. Weiss, Rush-Preshwerian
S
D.D.S.,”
and W. Rostoker,
St. Luke‘s
ince the initiation
I\ledic,al
(trnter,
endosseous
University
of the animal experiments
of Illinois,
in
1. Would good oral hygiene increase the success rate? experience
pain
implant.
Ph.D.** and
1969, results using endosseous dental implants have indicated a satisfactory benefit-risk ratio. Therefore, pilot human studies using endosseous dental implants were initiated in July 1975. Over 2,000 prospective volunteers were screened by telephone; 250 of these were examined. The study was designed to verify that the techniques and knowledge gained in the animal experience could be transferred to and reproduced in humans. In addition, only a human study would be able to provide answers to the following questions:
2. Does the patient tion?
dental
postimplanta-
3. To what extent is the pain experienced? 4. Is the amount of pain controllable? The ultimate goal of any implant is to be a freestanding unit that can restore masticatory function. A free-standing implant offers a definite improvement over the conventional fixed partial denture, which requires the preparation of two natural teeth. The baboon study revealed that it is possible to achieve a free-standing unit under less than ideal conditions.’ Five human studies were conducted to determine the viability of the fiber-metal dental implant as a tooth replacement for (1) a fixed partial denture replacement, (2) a single tooth replacement, (3) a stabilized
““22-39,3,82/OofJ6R-i+ ,3$01.X1/0 to 19R2Ttre C. V. MC+ Co.
Chicago,
III.
crown (implant crown attached to an ad,jacenttooth with an inlay SupporL
or crown),
FIXED PARTIAL The fixed partial
and
(4)
an overdenture
DENTURE STUDY
denture study was conducted first because it was anticipated that it would have the highest and most predictable success rate. In addition, the amount of damage caused by failure of the implant would be minimal. The implant was used as a terminal abutment for a fixed partial denture, and the anterior
abutment was a crowned natural tooth. The goal was to insert implants in volumeer
patients with missing molar teeth in a quadrant where the remaining premolar tooth had healthy periodontal tissue. The plan was to place the implant in the site of the missing teeth. The patients in this study had either missing molars or missing molars and premolar teeth. The fixed partial dentures replaced the missing teeth in hnth the mandible and maxillae. ‘l‘hc patients for this study were selected carefully to meet rertain criteria. One important criterion was that they would be available for observation for at least 5 years. Their selection was based on their history of employment and residence in the same places for cxtcndcd periods of time. Othrr criteria were age, general health, oral hygiene, and evidence of good dental rare. A wide range in the age of the patients was selected since it would help determine if age was a variable related to a successful implantation. The final major criterion was to determine through radiographic examination the position nf the maxillary sinus and the mandibular canal in relation to the edentulous alveolar rrcst Patirnts in the sludy were closely supervised so that a failure of the implant would be recognized early and removal could be accomphshed with a mmimum of permanent damage to the mandible or maxillae. Fail-
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t diameter
+ 4mm
1/2mm 16.0 mm 1 Fig. 1. Radiographic templates.
2mm
Mandibular
canal
Fig. 3. Cross-sectionof implant in relation to mandibular canal and alveolar crest.
Mandibular canal Fig. 2. Lateral view of implant in relation to alveolar
crest and mandibular canal.
ure was determined by radiographic evidence of bone loss, clinical signs of periodontal-type pockets around the implant, and pain. Following implantation, long-cone radiographswere usedand a millimeter grid superimposedon the film.* The radiographs were made monthly to record the bone level surrounding the implant. This was correlated with the clinical signs of mobility and gingival inflammation, A failure was defined asan implant that had lost half of its bony support as seenon the radiographs, had over 4 mm of periodontal pocketson three nf its four sides, and had a Class 3 mobility. Class 3 mobility was defined as the condition of an implant exhibiting over 1 mm lateral movementin a buccolingual direction and being depressible in its socket. Continued gingival inflammation resulting in a lateral abscesswas also considered a failure. Failed implants were removed immediately. The patients selected for the initial study were screenedthoroughly. A complete dental examination was given each patient, including the making of diagnostic casts and periapical full-mouth and panoramic radiographs, A comprehensivemedical history
634
was recorded to properly evaluate any complicating systemicproblems. Patients were informed of the exact nature of the study and their part in it. To aid in the explanation of the proceduresinvolved, a seriesof large color plates depicting each phase of treatment was shown to each patient. The patients were required to read the printed informed consent form. This covered the entire course of treatment, the risks involved, and possible damage to the oral apparatus. The patient signed the consent form in the presenceof a witness, reread. and initialed it. DIAGNOSTIC
EVALUATION
Proper diagnosisfor patient selection. as is customary with any procedure. is of the utmost importance. The information recorded during the dental examination as well as the answers given on the medical questionnaire should be evaluated carefully. Dental implants are not indicated for patients with rampant caries or active periodontal disease,or for those exhibiting signs of excessive bruxism. If the patient is deemedacceptable,the size and positioning of the implant(s) must be determined. The site of the anticipated implant should be measured with calipers. The buccolingual thicknessof the residual ridge should be at least 8 mm to accommodate a 4 mm (in diameter) implant or 8.7 mm IO accommodate a 4.76 mm implant. At this point in the treatment, the diameter of the implant is determined. INTRAORAL
RADIOGRAPHS
The intraoral radiographs are usedto examine the previously selectedimplant site. If the root outline of the absent tooth can still be seen, an alternate site
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Fig. Fig. Fig. Fig.
IMPLANT
4. 5. 6. 7.
Round bur at low speedis used to enter cortical plate. Tapered drill with plastic sleeve that controls depth of penetration End cutting drill also has plastic sleeve. Hand reamer.
should be chosen.Through experience, it appearsthat 6 months to 1 year should elapse between tooth removal and implant placement. If the film reveals an overly dense trabeculation at the proposed site, the location should be rejected. The radiographic template (Fig. 1) is placedover the intraoral film. Generally, the intraoral film is to scale and has zero magnification. The zero magnitude template of the appropriate diameter selected is used. There should be 2 mm of bone mesialand distal to the implant meshwork. The inferior surfaceof the implant should be 2 mm above the mandibular canal or 2 mm below the maxillary sinus.The superior surface should be 0.5 mm below the crest of the residual ridge (Figs. 2 and 3). The appropriate height of the implant is selectedusing these determinants. PANORAMIC
RADIOGRAPHS
Although the panoramic radiographs are slightly magnified, they provide a good overall view of the relationship of the implant to the mandible or maxilla. The appropriate diameter of the implant on the template is placed over the panoramic film, and its position is checkedagain. In someinstances,more than one implant size should be checked against the intraoral films.
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A summary of the indications and contraindications include: Indications. The patient should be in good general health, and there should be no rampant caries present. The patient should be free of periodontal diseaseand have good oral hygiene. There must he sufficient investing bone for the implant to sear properly, and there should be edentulousregions in the posterior part of the mouth. Contraindications. Infection is an absolute contraindication, as are hypertension (uncontrolled), poor oral hygiene or periodontal disease,excessively hard bone or torus in the region of the anticipated implant site, insufficient bone height or width for implantation, recent extraction sitesor areasin which the root outline can be seen on the radiographs, edentulous regions anterior to the canine teeth, systemic,diseasessuch as uncontrolled diabetes, and hvpertcnsi\‘i~ pntitnts as indicated by bruxism. SURGICAL
PROCEDURE
The implant site is prepared through the use of precisely sized drills and reamers IO rre;tie accurate dimensionsfor the implant. FolIowine, loctalanesthesia. an incision is made to the bone along the crest of the residual ridge over the proposed implant site. A
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8. Replica of implant is placed into prepared site. 9. Seating instrument. 10. Implant seated. 11. Mucosa is sutured around implant. 12. Four weeks postoperative. 13. Implant fixed partial denture in function. 14. Preoperative photograph of proposed site.
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full-thickness flap is reflected to expose the bone. Then, a round bur in a slow-speed handpiece is used to enter the cortical plate at the proposed implant site (Fig. 4). The bur is cooled during use with a flow of saline directed at the bur head. A tapered drill is used to create the depth of the implant site using the previous opening as a guide. A plastic sleeve on the shank of the drill limits the penetration to the predetermined depth (Fig. 5). The debris is flushed out of the site with saline solution. A four-fluted end cutting drill of a corresponding size to the implant diameter and length is used in the slow-speed handpiece to flatten the base of the implant site. The end cutting drill also has a plastic sleeve so that accurate depth of the implant site can be achieved (Fig. 6). A hand reamer is inserted into the prepared site and rotated manually to assure that the symmetry of the hole matches that of the implant (Fig. 7). A replica of the implant made of solid metal but slightly smaller in diameter is placed into the site (Fig. 8). If the replica seats properly, the sterile implant is placed into the site with the aid of the seating instrument under hand pressure or with a light tap of a mallet (Figs. 9 and 10). When properly seated, the superior surface of the implant should be 0.5 mm below the level of the alveolar crest. The mucosa is repositioned and sutured (Fig. 11). The patient is provided oral tetracycline, 1 gram per day for 5 days, and put on a soft diet for the same period of time. Radiographs are made of the implant, and intraoral photographs are made of the implant site.
PATIENT
FOLLOW-UP
The patient is seen 1 week postoperatively and the sutures removed. Weekly visits are made for 4 weeks or until the implant is stable (Fig. 12). At each visit, the patient undergoes the following examination: (1) intraoral radiograph of the implant site with a millimeter grid superimposed on the film, (2) determination of the pocket depth around the implant, (3) evaluation of clinical symptoms of pain and inflammation, and (4) determination of the mobility of the implant by lateral and downward finger pressure. The implant site is photographed in color to record the condition of the soft tissue. When the implant is stable and symptom-free, treatment with fixed partial dentures is initiated. This is usually at least 4 weeks postinsertion. Full-arch impressions are made and sent to the dental laboratory with occlusal registrations and a stone cast of the
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Fig. 15. Postoperative radiograph
opposite arch. Edentulous sitesare restored with gold and porcelain veneered pontics. The abutments, the implant and natural teeth, are restored with porcelainfused-to-gold crowns. An anatomicarticulator is usedin the fabrication of the fixed partial denture (Fig. 13). After the fixed partial denture is cemented to the abutments, the patient is seenand reexamined weekly for the first month, then monthly for the first year. The examination is the sameone performed at the time of suture removal. A monthly comprehensive review is made of all data on all patients. When it is deemed necessary,consultantsalso review the data. Experts in the fields of periodontics, oral pathology, and fixed partial prosthodontics are available for consultation.
EXAMPLES OF THE FOUR TYPES OF RESTORATIONS Fixed partial denture Patient No. 5 in the study was a 34-year-old man with a full complement of teeth except for the lower right molars (Fig. 14). The decision to insert an implant (4 X 10 mm) in the edentulous spaceof the lower right secondmolar was basedon the measurement of the diagnostic casts and radiographs. The implant was inserted July 11, 1975 (Fig. 15). Four weeks postoperatively the tissue was well healed and the implant solid (Fig. 16). A crown preparation was made on the lower right second premolar, and an impression was made to fabricate a fixed partial denture using the implant as the distal abutment. The fixed partial denture was made on an anatomic articulator and inserted September3,1975. The fixed partial denture has been in function for over 5 years with no deterioration of the soft tissuesas recorded on September 4, 1980 (Figs. 17 and 18).
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Fig. 16. Four weeks postoperative. Fig. 17. Five-year photograph of implant prosthesis.
Fig. 18. Five-year postoperative radiograph of implant. Fig. 19. Preoperative panoramic radiograph. Fig. 20. Postoperative radiograph of implant.
Patient No. 9 in the study was a 35-year-old woman with a full complement of teeth except for the upper right molars and premolars (Fig. 19). Study of the radiographs and diagnostic casts indicated that a 4.76 x 6 mm implant should be placed in the upper right first molar edentulous site. The surgery was performed on September 3, 1975 (Fig. 20). The gingival tissue was extremely thick, and removal of excess gingival tissue was necessary to expose the implant post (Fig. 21). The fixed partial denture was fabricated with the mesial abutment crown on the upper right canine, and the implant was used as the
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distal abutment. Two pontics replaced the upper right first and second premolars (Fig. 22). The fixed partial denture was in function for over 5 years with no evidence of bone loss or tissue breakdown as of November 10, 1980 (Fig. 23).
Single
tooth replacement
Patient No. 55 in the study was a 26-year-old man with a full complement of teeth except for the lower right first molar. Examination of diagnostic casts and radiographs indicated that a 4.76 X 8 mm implant could be used in the edentulous space. Because of
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Fig. 21. Excessgingiva was removed to expose implant
Fig. 22. Implant prosthesisin function. mechanical difficulty during surgery on August 19, 1977, a 4.76 X 5 mm implant was substituted (Figs. 24 and 25). The free-standing implant crown was placed in function on January 11, 1978 (Figs. 26 and 27). The free-standing implant crown was functioning well after 42 months with no deterioration of the soft tissue and no bone loss.
Stabilized
single
tooth
Patient No. 113 in the study was a 5%year-old woman with a full complementof teeth except for the lower left first molar. Using the usual diagnostic method of measuring the diagnostic casts and radiographs, a 4 x 8 mm implant was decided upon and surgically placed in the edentuloussite of the lower left first molar on April 6, 1979 (Figs. 28 and 29). The adjacent lower left secondmolar had a broken amalgam restoration and was badly tilted mesially. A normal contact could not be achieved with the proposed implant crown. Therefore, a mesial-occlusal-distal onlay was made for the lower left second molar, attached to the implant crown, and cemented to the natural tooth and implant in one unit on July 18,1979. The stabilized crown has been functioning with no bone loss or tissue change for 10 months (Figs. 30 and 31).
Stabilized
overdenture
Patient No. I35 in the study was a completely edentulous 62-year-old man who had tried unsuccessfully to wear a lower denture. He was treated with upper and lower dentures that were adjusted for comfort. Two implants 4.76 X 6 mm were surgically placed on August 6, 1979, in the sitesof the lower right canine and first molar. The lower denture was relieved over the implant posts so the denture could be worn during the healing period. On September20,1979, two 4.76 x 6 mm implants were surgically placed in the sitesof the lower left first molar and canine. The lower
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denture was relieved to accommodate the implant posts.When the implants had completely healed (Fig. 32), gold copings were made that fit the implant post (Fig. 33). The four copings were made parallel to one another and were cemented to the implant posts. Autopolymerizing acrylic resin was added to the implant post spacesin the lower denture, placed over the implant copings, and allowed to polymerize while the patient closed in centric occlusion (Fig. 34). The denture has been worn comfortably, stabilized by a friction fit betweenthe gold copingson the implant post and the acrylic resin. The patient eats normally and has good functional occlusion.The implants have been in place for 17 months with no apparent bone resorption and the soft tissue in normal condition (Fig. 35).
LOSS OF THE IMPLANT A variety of circumstancescould be held responsible for loss of several dental implants. However, one important factor becameclear: there was only a small amount of alveolar bone loss. The site filled in with normal bone in a short period of time following the removal of the implant, and there was no permanent defect. To illustrate this point, patient No. 17 in the study, a 59-year-old man who had undergone periodontal therapy, lost an implant. He was edentulous in the lower left quadrant, missingthe lower left molars and second premolar. The remainder of the dentition was in good repair. One implant 4 x 6 mm was placed in the site of the lower left secondmolar. The implant fixed partial denture consistedof one pontic between the crown on the lower left first premolar and the implant crown. The prosthesisbecamemobile 1 month after insertion, and the mobility increased until the inrraoral radiograph showedexcessivebone loss around the implant (Fig. 36). The implant prosthesis was removed 6 months after it was placed, leaving a bony defect (Fig. 37). The removal was uneventful; thr implant was
639
Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. 640
23. 24. 25. 26. 27. 28. 29. 30.
Five-year postoperative radiograph of implant. Postoperative intraoral view of implant post. Postoperative radiograph of implant. Crown in place on implant. Radiograph of implant with crown in place. Postoperative intraoral photograph of implant Postoperative radiograph of implant. Stabilized implant crown. JUNE
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surrounded with connective tissue, which facilitated its removal. The site healed quickly and filled in with normal bone within 6 months with no apparent defect on the alveolar crest (Figs. 38 and 39). The histologic section of a failing implant in a baboon illustrates the mechanism of bone destruction and replacement by cells of inflammation (Fig. 40). If the bone is resorbed quickly in response to sudden trauma, it is replaced with granulation tissue, possibly resulting in some suppuration. However, if the causes of resorption are less severe, such as traumatic occlusion in eccentric movements, the bone may be replaced with fibrous connective tissue. When the source of the trauma is corrected in such instances, the resorption of the bone ceases. The causes of failure of this implant fixed partial denture were the result of a poor diagnosis. The natural lower left first premolar abutment was periodontally involved with some loss of supporting bone and should not have been used alone as a fixed partial denture abutment. In addition, the implant used was comparatively short, considering that the size of the implant fixed partial denture was excessively large due to the interdental space. If two natural teeth had been used jointly as abutments and a longer implant or two implants used, the resuhant implant fixed partial denture may have been successful. In spite of the failure of this implant prosthesis, it does illustrate the point that the risk to the patient was negligible. The strength of this implant system is that, even when the implant is lost, the implant site always heals well with no residual defect in the bone or soft tissue. ANALYSIS
OF IMPLANT
RESULTS
As of November 1981, the extended clinical trial program had involved the implantation of 216 tooth root prostheses. Of these, 37 (17%) were never placed into function because they were inadequate to receive a prosthesis. A total of 162 implants have been put into function and have involved the following: 46 fixed partial dentures, 2 free-standing fixed partial dentures, 35 free-standing single crowns, 41 stabilized single crowns, 21 to stabilize complete dentures, and 5 to stabilize removable partial dentures. An additional 17 implants have not been put into function because (1) it was too early for 10 and (2) the patients were lost to follow-up for 7. The portion of the clinical studies that has the greatest longevity is the fixed partial denture study (Fig. 41). Although this is the first human clinical study attempted following the animal studies, 83% of the implants have been successful. The few implants Tttt!
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Fig. 31. Eighteen-month implant.
postoperative
radiograph
of
that were lost to the study were due to instrumentation or traumatic occlusion, such as bruxism. The next human study was the free-standing single tooth replacement (Fig. 42). The success rate was significantly lower (54%) and can be attributed to a number of factors. One was the mechanics of preparing the implant site; the bur shank had to bc lengthened because the natural teeth on either side of the site blocked the handpiece from cutting to the proper depth. Another recurring problem was the inability to produce an implant crown in normal contact with the adjacent natural teeth. Due to the edentulous space, the natural teeth drifted and tilted, and it became difficult to create normal contacts. resulting in food impaction and gingival irritation. In spite of the adverse factors, a significant number of free-standing implant crowns (19) have been functioning for 3% years with no sign of deterioration of the bony support. This study showed that a free-standing implant crown can be successful but only if conditions are ideal. When it became apparent that the free-standing implant crown could only be used in ideal situations, a second implant study was initiated using a restoration in the ad,jacent tooth to “stabilize” the implant crown. Many of the volunteer patients who needed a single tooth replacement presented with a defective filling in the adjacent natural tooth. The stabilized single crown study consisted of 41 patients with the implant crown attached to an inlay or crown on the adjacent natural tooth. This study has been successful <83’S), with most of the implants over 2 years in longevity (Fig. 43). Two other studies, the overdenture and the removable partial dentures supported by implants, have been successful but are not statistically relevnnt because the number of implants is small and the study was conducted over a relatively short span of time. These studies are being expanded since the suc‘cess rate has been excellent. 641
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Fig. 32. Intraoral photograph of implant posts. Fig. 33. Parallel gold copings cemented on implant posts. Fig. 34. Denture base modified to receive gold copings.
Fig. Fig. Fig. Fig. 642
35. 36. 37. 38.
Seventeen-month postoperative panoramic radiograph of implants. Radiograph of failing implant prosthesis. Radiograph of implant site following removal of implant. Radiograph of implant site 6 months after post removal. JUNE
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Fig. 39. Photograph of implant site 6 months after post removal. Fig. 40. Histologic section of failing implant (baboon): a, implant inflammation; and c, osteoclastic activity on bone margin.
wire;
h, cells of
FIXED
182
BRIDW
S?‘W)Y
176 170 s
167 157
AS
157 46
140
38
FIXED FIXED
Of
NOVEMSER.1981/
BR(DGES
ARE
ER1DGES
ARE
COMPLETED
i
SUCCESSFUL
136 135
83%
i
SUCCESS __--
RATE
--j
/
132 107 107 99 97 96 95 92 92 92 85 75 73 71 27 28 25 24 23 21 20 19 18 17
-
16
0
15
-
14
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13
Q
12
0
11
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.
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Q
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7
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.
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,
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,
L
,_1.~_L_LA--L-L_II--.L-l 4
5
6
7
IMPLANT LONGEVITY (years) Fig. 41. Fixed partial THE
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FREE
f
53 --
6 F d
::. 48
STANDING
SINGLE
CROWN
STUDY
0 *
0 0 0
;; 45 42 40 38 37 36 35 33 32
0 3 0 .
l 0
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0 0 0 4 0
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,I., 1
.l.. 2
IMPLANT
.I 3
LONGEVITY
.‘.I 4
5
(years)
Fig. 42. Free-standing single crown study, These results should be tempered by the experimental nature of the clinical trial program. In many patients, the individual “failures” represent identifiable features that, when recognized, need not be repeated and belong to an important list of contraindications. For example, of the 37 implants deemedinappropriate to place in function, six were placed in the first year of the program. The main reasonfor six of the failures was the inability to deepenthe implant site so that all the wire meshwork was covered. Other reasons for failure were heavy, densecortical plate bone in the site of the implant, which was usually caused by the presenceof a torus mandibularis in the region. Two of the patients had retained deciduousteeth, which were removedjust prior to implantation; both implants were lost. In all the studies, 35 implants were lost prior to being placed in function within the first year. Of the implants that were in function, those lost were attrib644
uted to: (1) bruxism, (2) hypertensive patient, (3) broken soldered joint on fixed partial denture, (4) periodontally involved natural tooth abutment, (5) excessivelylarge pontics due to large interdental space, and (6) long-term viral infection that incapacitated the patient for 6 months. As in any clinical experiment, it becameobvious that certain patients and oral conditions are not suitable for the use of endosseous dental implants. SUMMARY The development of an endosseousimplant has followed a logical and formal plan. 1. Extensive experiments with animals provided preliminary statistics of successful function, extensive histologic studies, evaluation of biocompatibility, and a preliminary assessment of contraindications. 2. Carefully developedand controlled clinical study of human subjects with frequent examinations and JUNE
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STABtLtZEO
StNC%LE CROWN
41 STABlLtZEO
CROWNS
STUOY
COMPLETED
134 sTABLlzEo:;;;g;;;
j
.-107
0
100 .-99 . 99 98 98 98 98 62 89 80 84 80 00 77 77 75 74 74
l 4 3 0 0 0 0 0
’ ’
0 0 0 0 a 0 0
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0 0 0
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3
IMPLANT LONSWTY Fig. 43. Stabilized
detailed records of both successes and failures again provided new basesfor contraindications. The statisticson the clinical study are satisfactory in their results, although they should be regarded as having a somewhat conservative slant. This is because implant failures becamea learning basefor improved procedures. The program so far has been limited to a single implant designthat, with size variants, will serve most applications. However, it is not feasible to modify the design in terms of dimensions for application in the anterior portion of the mouth. A designfor this purpose is established on paper and will become a future additional development. THE
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single
4
(yews)
crown
study.
REFERENCES 1.
2.
Rqmnt
Weiss, M. B., and Rostoker, W.: Uevetopmem of a new endosseous dental implant. Part I: Animal studies. J PRIXTHET DENT 46646 . . 1981 Weiss, M. B., and Ronen, E.: New device to quantitate alveolar bone loss. Oral Surg 44:322, 1977.
reque.st.5
DR. MARVIN RUSH
600
tcr:
B. WEISS
UNIVERSITY s. PAULINA
ROOM 433-A.4.F. CHIcAC;O, IL 60612
645