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Replacement of maxillary and mandibular molars with single endosseous implant restorations: A retrospective study
R e p l a c e m e n t of maxillary and mandibular molars with single e n d o s s e o u s implant restorations: A r e t r o s p e c t i v e study W i l l i a m B e c k e r , D D S , M S D , a a n d B u r t o n E. B e c k e r , D D S b
University of Southern California, Los Angeles, Calif., and University of Texas, Houston, Tex. This r e t r o s p e c t i v e report p r e s e n t s findings on 22 patients w i t h 24 implants replacing single m o l a r s w i t h i m p l a n t - s u p p o r t e d restorations. P a t i e n t s w i t h k n o w n b r u x i s m habits w e r e not considered for s i n g l e - m o l a r implant replacement. The p a t i e n t s u n d e r w e n t f o l l o w - u p for an a v e r a g e of 24 months. The c u m u l a t i v e s u c c e s s rate was 95%, w h i c h reflects the loss of one 5 • 6 mm wide implant. Eleven i m p l a n t s w e r e placed in edentulous ridges, and 13 were placed in extraction sockets. Most of the i m p l a n t s w e r e placed in type B and C bone quantity and type 2 and 3 bone quality. All i m p l a n t s w e r e restored on a b u t m e n t s w i t h nonrotating gold cylinders. The occlusion for all restorations w a s d e v e l o p e d to m i n i m i z e centric contacts and lateral interferences. The f r e q u e n c y of gold r e t a i n i n g - s c r e w l o o s e n i n g w a s o b t a i n e d for 21 patients. The gold retaining s c r e w s l o o s e n e d in eight i m p l a n t s b e t w e e n one and three t i m e s (38%). No incidence of c r o w n or i m p l a n t fracture occurred. Within the limits of this study, r e p l a c e m e n t of single-tooth molars by i m p l a n t - s u p p o r t e d restorations w a s predictable; h o w e v e r , a high incidence of gold s c r e w l o o s e n i n g w a s seen. (J PROSTHET DENT 1995;74:51-5.)
T h e long-term data relating to commercially pure titanium endosseous implants have revolutionized modern dentistry. Implant-supported restorations for fully and partially edentulous patients have exceedingly good longterm success rates. 13 Jemt et al. 4 reported on osseointegrated implants that were restored in mainly bicuspid and anterior teeth positions. Five implants were placed into molar positions. One hundred six implants were placed, and of these, three implants (2.8 % ) were lost. Although the cited studies provided longitudinal evidence of implant survival for fully edentulous, partially edentulous, and single-tooth anterior replacements, no data relating to replacement of molars exist. Rangert and Sullivan 5 recently suggested that molars replaced by one implant may fracture as a result of bending moments. They suggested that wide implants or multiple implants may withstand the occlusal forces on molars better than a single standard 3.75 mm implant. This article presents the retrospective findings of 24 consecutively placed mandibular and maxillary molar single-tooth implants. The patients were evaluated for bone quality and quantity, implant survival, and length of time of loading. Complications related to screw loosening and fracture were also recorded. aPrivate Practice, Tucson, Ariz.; and Assistant Professor, Department of Periodontology, University of Southern California, Los Angeles, Calif. bprivate Practice, Tucson, Ariz.; and Associate Professor, Department of Periodontology, University of Texas, Houston, Tex. Copyright | 1995 by The Editorial Council of THE JOURNALOF PROSTHETICDENTISTRY. 0022-3918/95/$3.00 + 0. 10/1/63630
JULY 1995
Fig. 1. Periapical radiograph of lower left second molar. There is advanced furcation invasion.
MATERIAL
AND METHODS
Twenty-two patients, 16 women and six men, whose ages ranged from 48 to 73 years (average 58.6 years) participated in this study. The patients were referred for periodontal therapy and implant placement for single maxillary or mandibular molars and were considered to be in good general health. At the initial examination a periodontal evaluation was made, and radiographs were taken (Fig. 1). These were supplemented by a panoramic radiograph. Diagnostic casts and clinical photographs were made. Consultations were made with the referring doctor, the patient, and on occasion, the laboratory technician. Patients with known bruxism or clenching habits were not considered for
THE JOURNAL OF PROSTHETICDENTISTRY
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Fig. 2. A. Molar has been removed, socket debrided, and distal socket prepared to receive 13 mm implant. B, Implant installed slightly below crest is entirely within distal extraction socket.
Fig. 3. Five months after implant placement, implant has been exposed with bone surrounding implant.
single-tooth molar implant placement. Alternative treatment plans were discussed with the patients. Once the decision was made to place and implant, surgical guides were fabricated. The patients underwent premedication with either penicillin or erythromycin (2 gm to be taken 2 hours before surgery and 1 gm p/day for 7 days). The patients underwent premedication with light intravenous conscious sedation, and local anesthesia was administered. Incisions for edentulous sites were begun within the sulcus of the adjacent posterior tooth and were extended across the palatal or lingual aspect of the edentulous ridge, terminating one tooth anteriorly. Vertical buccal releasing incisions were made for access, and full-thickness mucoperiosteal flaps were reflected. In the mandible the mental foramen was always identified to prevent injury to the nerve. If the tooth was presented and was to be replaced by an immediate implant, mesial-distal luxation was carefully
52
applied. Once the tooth was loosened, i t was gently removed with forceps. The sockets were debrided with curettes and files. When the tooth was missing, incisions were made lingual or palatal to the crest, and the tissues were reflected to the buccal surface. The implant sites were prepared according to the methods described by Adell and Lekholm. 6 The bone quality and quantity were determined from the preoperative radiographs and were registered in the patient's chart. 7 For extraction sockets the implants were either placed into .the interradicular bone (Fig. 2) or within one of the engaging socket's bony walls in an attempt to engage part of the interradicular bone. Most implants were placed without tapping. Twenty-one standard implants 3.75 mm wide, one implant 4 mm wide, and two implants 5 mm in diameter were placed. In instances where the bone quality was of low density and complete tapping could have overprepared the surgical sites, only the coronal half of the
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F i g . 4. A, I m p l a n t restored on nonrotating a b u t m e n t gold cylinder and in occlusion. B, Radiograph taken at 2-year evaluation. Bone level is at second thread.
T a b l e II. M e t h o d of placement
T a b l e I. I m p l a n t success
Time period
Implant insertion0 (yrs) 0-1 yrs 1-2 yrs
Success rate No. No. within Cumulative of Implants of group success Patients followed Failures (%) r a t e (%)
22
24
0
100
100
Immediate implant placement
Maxilla Mandible
4* 7
3 10
*One implant was lost and replaced. 21" 20 ^
23 22
1 0t
95.7 100.0
95.7 95.7
*One p a t i e n t moved a n d was lost to follow-up. t O n e p a t i e n t died.
socket was tapped. The implants were then placed, cover screws were inserted, and the flaps were closed. The sutures were removed in 7 days. Second-stage surgery was performed 4 to 5 months after healing occurred in the mandible and 6 months after it occurred in the maxilla. A periapical radiograph of the implant site was taken before second-stage surgery was done. The surgical site was anesthetized and flaps were reflected, exposing the implant head and surrounding bone (Fig, 3). T h e cover screws were removed, and either healing a b u t m e n t s or nonrotating a b u t m e n t cylinders were placed onto the implant. The gingival tissues were apically positioned and sutured with interrupted sutures. Periapical radiographs were taken to confirm the complete seating of the a b u t m e n t on the implant. Six to 8 weeks after the second-stage surgery was done, the restorative dentists made impressions and began fabrication of the single-tooth implant crowns. All 24 implants were restored by seven dentists trained in restoring the implant system (Nobelpharma, Chicago, Ill.). The precise restorations were retained with screws, and the occlusal relationships were developed to eliminate lateral and balancing interferences and to ensure only light contacts in centric occlusion (Fig. 4, A). Two weeks after crown insertion, the gold screws were retightened and the occlusion was reevaluated by the dentists. If the gold screw or abut-
J U L Y 1995
Location
Standard implant placement
ment screw was loose, a radiograph was taken to evaluate the complete seating of the a b u t m e n t and crown (Fig. 4, B). If nonworking contacts were noted, they where reduced by occlusal adjustment. Patients were given oral hygiene and appointments for 6 months, and they also underwent annual examinations. The number of implants placed between two adjacent teeth and the number of implants terminally placed in the arch were tabulated. As part of the s t u d y the participating restorative dentists were surveyed to determine whether crowns had fractured or loosened. The frequency of screw loosening was also recorded. RESULTS The results are based on placement of 24 implants in 22 patients. Two patients received two implants each. One patient lost a 5 x 6 m m implant after 6 months of function. This implant was replaced with another 5 mm wide implant and has been functioning for 4 months. One patient died and one patient moved out of the city. The average time of implant function was 24 months. T h e cumulative success rate after 1 year of function was 95.7 % (Table I). Table II describes the number of implants placed in healed edentulous ridges or into extraction sockets. The implant size and arch location are listed in Table III. Eighteen implants were placed in the mandible, and six were placed in the maxilla. Table IV delineates the bone quality and quantity. Eleven implants were placed in alveolar ridges with minimal bone resorption (type B). Nine implants were placed in type 3 bone and indicated the pres-
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BECKER AND BECKER
T a b l e III. Size and location of implants in millimeters Position
10 x 3 . 7 5 m m *
Maxilla Mandible Total
2
3 5
13 • 3.75 m m
15 • 3 . 7 5 m m
10 • 4 m m
2
0
0
It
1
6
11 13
3 3
1 1
0 1
0 1
18 24
6 x 5 mm
8 • 5 mm
Total
*Standard implant diameter is 3.75 m m wide. t o n e 6 m m long x 5 m m wide implant was lost and replaced.
T a b l e IV. I m p l a n t placement according to bone quality
T a b l e V. N u m b e r and frequency of screw loosening for
and q u a n t i t y as determined from preoperative radiographs
21 implants Stable
Quantity Quality
A
B
C
D
E
Total
1 2 3 4 Total
2 0 2 1 5
1 3 5 2 11
0 3 2* 3 8
0 0 0 0 0
0 0 0 0 0
3 6 9 6 24
*One implant was lost and replaced.
ence of a thin cortical plate with a compact trabecular pattern. All implants were restored on single-tooth nonrotating a b u t m e n t s with gold cylinders. The number of implants and frequency of loosening of the gold screws are listed in Table V. Table V is based on information for 22 implants. The gold screws in 13 implants (61.9 %) remained tightened, and three gold screws (14.3%) became loose three times. The a b u t m e n t screw fractured in one p a t i e n t and was retrieved and then replaced. No implant fractures occurred. Twenty implants were placed between two adjacent teeth, and six implants were in terminal positions. DISCUSSION The results of this retrospective analysis represent the first report of replacement of single molars with implantsupported prostheses. The results indicate t h a t maxillary and m a n d i b u l a r molars can be successfully (95.7%) replaced by single, threaded, endosseous implants. Laney et al. s reported the results of t r e a t m e n t for single-tooth replacements for bicuspids and anterior teeth. Ninety-five patients were treated and followed-up, and at 3 years a 97.2% success rate was reported. Parel* has cautioned against the use of one implant to replace single molars. Replacement of a molar with a single implant may present problems of force distribution and stress. Rangert and Sullivan 5 suggest the use of 4 m m wide implants with CeraOne a b u t m e n t s (Nobelpharma, Goth*Parel S. Personal communication, Nobelpharma Team Day. Sidney, Australia, 1993.
54
Maxillary Mandible Total (%)
Loosened once
4 1 9 2 13 (61.9) 3 (14.2)
Loosened twice
Loosened three times
0 2 2 (9.5)
1 2 3 (14.3)
enburg, Sweden) ~for single-tooth implants. This implant is reported to be 30% stronger t h a n the standard 3.75 m m implant and m a y be more resistant to bending forces. 9 With one implant, there is a discrepancy between the implant length and width and the size of the restored crown. P l a c e m e n t of a crown t h a t extends beyond the long axis of the implant could generate cantilevering forces on the crown and implant. These forces could contribute to screw loosening and eventual i m p l a n t fatigue. Ideally, two implants should be used to replace a single molar; however, a molar edentulous space is often bound by natural teeth, which results in insufficient mesial-distal bone width for placement of more than one implant. According to Wheeler 1~ the average mesial-distal width of a maxillary first molar is 7.5 mm, whereas the average width of a mandibular first molar is 8.5 mm. These dimensions provide insufficient space for placement of more than one 3.75 m m wide implant. Several factors may account for the high success rate reported in this study, namely bone quality, bone quantity length of implants placed, and exclusion of patients with bruxism habits. Twelve of the implants were placed at the time of tooth extraction, thereby having the advantage of a large q u a n t i t y of bone volume. Sixteen implants were either 13 m m or 15 m m in length, and 16 implants were placed in either type A or B bone quantity. Laney et al. s placed 65 of the 95 implants in t y p e 2 or type 3 quality bone. Most of the implants (78) in the Laney study were placed in the maxillary arch and ranged from 13 to 18 m m in length. Patients with known bruxism or clenching habits were not considered for single-tooth i m p l a n t replacement in this group of patients. Parafunctional habits may be a risk factor related to implant fracture and screw loosening and may create uncontrolled and excessive occlusal loading forces.
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BECKER AND BECKER
T h e r e s t o r a t i v e dentists were r e q u e s t e d to m i n i m i z e occlusal contacts in centric occlusion. Occlusal tables were narrow to reduce t h e c a n t i l e v e r effect of wide buccolingual restorations.* Occlusal c o n t a c t for p a t i e n t s w i t h 5 • 6 m m i m p l a n t s were m i n i m i z e d . T h e occlusion was e v a l u a t e d by t h e restorative d e n t i s t 2 weeks after crown p l a c e m e n t and at 6 m o n t h s and 1 year. M o s t of t h e i m p l a n t s were placed b e t w e e n a d j a c e n t teeth. T h i s r e l a t i o n s h i p m a y be related to t h e high success rate. T h e a d j a c e n t t e e t h m a y h a v e cont r i b u t e d to m i n i m i z a t i o n of excessive loading on t h e i m p l a n t s and m a y have " p r o t e c t e d " t h e i m p l a n t s during function: J e m t et al.5 r e p o r t e d t h a t 26 % of gold retaining screws b e c a m e loose d u r i n g the first year. L a n e y et al. 8 p r e s e n t e d t h e 3-year follow-up results f r o m t h e s a m e study. A b u t m e n t screw loosening occurred in 10 (10.8 % ) of 92 p a t i e n t s who received e i t h e r single-tooth i m p l a n t - s u p p o r t e d restorations for bicuspids or incisors. T h e incidence of screw loosening in this r e p o r t is greater t h a n t h a t in the previous studies (38%). In this study, if gold screws b e c a m e loose m o r e t h a n twice, t h e y were r e p l a c e d and the occlusion of t h e r e s t o r a t i o n was readjusted. N o reports of crown fract u r e s were made. P l a c e m e n t of C e r a O n e restorations ( N o b e l p h a r m a ) m a y h a v e r e d u c e d t h e incidence of screw loosening. T h e o r e t i cally, t h e C e r a O n e a b u t m e n t has a high p r e t e n s i o n abutm e n t screw that, w h e n p r o p e r l y t o r q u e d , will resist unscrewing. S t u d i e s t h a t v a l i d a t e and d o c u m e n t t h e complications with this type of r e s t o r a t i o n need to be performed. Carlson and Carlsson 11 r e p o r t e d complications f r o m 600 i m p l a n t - s u p p o r t e d prostheses (2709 implants) p l a c e d b e t w e e n 1972 and 1991. C o m p l i c a t i o n s o c c u r r e d least often in single-tooth r e p l a c e m e n t s . CONCLUSION
W i t h i n t h e limits of this r e t r o s p e c t i v e study, replacem e n t of molars w i t h single i m p l a n t - s u p p o r t e d crowns were successful. One i m p l a n t was lost (5 • 6 m m ) , and a 95.7%
THE JOURNAL OF PROSTHETIC DENTISTRY
survival rate resulted. Factors such as b o n e quality, quantity, l e n g t h of i m p l a n t s , and m i n i m i z e d occlusal contacts m a y have c o n t r i b u t e d to t h e favorable success rate. Pat i e n t s with known p a r a f u n c t i o n a l h a b i t s were n o t included in t h i s population. T h e m a i n c o m p l i c a t i o n was loosening of gold retaining screws, which occurred in eight (38 % ) of the 21 i m p l a n t s and in s o m e cases m o r e t h a n once (Table V). We thank Dr. Bo Rangert for his technical assistance in writing this article. REFERENCES
1. Adell R, Lekholm U, Rockier B, Branemark P-I. A 15 year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Maxillofac Surg 1981;10:387-416. 2. Albrektsson T, Dahl E, Enbom L, et al. Osseointegrated oral implants: a Swedish multicenter study of 8139 consecutively inserted Nobelpharma implants. J Periodontol 1988;59:287-96. 3. van Steenberghe D, Lekholm U, Boienden C, et al. The applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: a prospective multicenter study of 558 fixtures. Int J Oral Maxillofac Implants 1990;5:272-81. 4. Jemt T, Laney WR, Harris D, et al. Osseointegrated implants for single tooth replacement: a 1-year report from a multicenter prospective study. In J Oral Maxillofac hnplant 1991;6:29-36. 5. Rangert B, Sullivan R. Preventing prosthetic overload induced by bending. Nobelpharma News 1993;7:5. 6. Adell R, Lekholm U. Surgical procedures. In: Branemark PI, Zarb GA, Albrektsson T, eds. Tissue integrated prosthesis. Osseointegration in clinical dentistry. Chicago: Quintessence Publ, 1985:211. 7. Lekholm U, Zarb GA. Patient selection and preparation. In: Brhnemark PI, Zarb GA, Albrektsson T, eds. Tissue-integrated prosthesis: osseointegration in clinical dentistry. Chicago: Quintessence Publ, 1985;199-209. 8. Laney WR, Jemt T, Harris D, et al. Osseointegrated implants for single-tooth replacement: Progress report from a multicenter prospective study after 3 years. Int J Oral Maxillofac Implant 1994;9:49-54. 9. Rangert B, Forsmalm B. Nobelpharma News 1994;8:7. 10. Wheeler RR. A textbook of dental anatomy and physiology. 2nd ed. Philadelphia: WB Saunders Co, 1950:215-43. 11. Carlson B, Carlsson GE. Prosthodontia complications in osseointegrated dental implant treatment. Int J Oral Maxillfac Implant 1994; 9:90-4. Reprint requests to:
WILLIAMBECKER,DDS, MSD 801 N. WILMOT;B-2 TUCSON,AZ 85711
*Lewis S. Personal communication. Gainesville, Florida, 1993.
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55
University of Southern California, Los Angeles, Calif., and University of Texas, Houston, Tex. This r e t r o s p e c t i v e report p r e s e n t s findings on 22 patients w i t h 24 implants replacing single m o l a r s w i t h i m p l a n t - s u p p o r t e d restorations. P a t i e n t s w i t h k n o w n b r u x i s m habits w e r e not considered for s i n g l e - m o l a r implant replacement. The p a t i e n t s u n d e r w e n t f o l l o w - u p for an a v e r a g e of 24 months. The c u m u l a t i v e s u c c e s s rate was 95%, w h i c h reflects the loss of one 5 • 6 mm wide implant. Eleven i m p l a n t s w e r e placed in edentulous ridges, and 13 were placed in extraction sockets. Most of the i m p l a n t s w e r e placed in type B and C bone quantity and type 2 and 3 bone quality. All i m p l a n t s w e r e restored on a b u t m e n t s w i t h nonrotating gold cylinders. The occlusion for all restorations w a s d e v e l o p e d to m i n i m i z e centric contacts and lateral interferences. The f r e q u e n c y of gold r e t a i n i n g - s c r e w l o o s e n i n g w a s o b t a i n e d for 21 patients. The gold retaining s c r e w s l o o s e n e d in eight i m p l a n t s b e t w e e n one and three t i m e s (38%). No incidence of c r o w n or i m p l a n t fracture occurred. Within the limits of this study, r e p l a c e m e n t of single-tooth molars by i m p l a n t - s u p p o r t e d restorations w a s predictable; h o w e v e r , a high incidence of gold s c r e w l o o s e n i n g w a s seen. (J PROSTHET DENT 1995;74:51-5.)
T h e long-term data relating to commercially pure titanium endosseous implants have revolutionized modern dentistry. Implant-supported restorations for fully and partially edentulous patients have exceedingly good longterm success rates. 13 Jemt et al. 4 reported on osseointegrated implants that were restored in mainly bicuspid and anterior teeth positions. Five implants were placed into molar positions. One hundred six implants were placed, and of these, three implants (2.8 % ) were lost. Although the cited studies provided longitudinal evidence of implant survival for fully edentulous, partially edentulous, and single-tooth anterior replacements, no data relating to replacement of molars exist. Rangert and Sullivan 5 recently suggested that molars replaced by one implant may fracture as a result of bending moments. They suggested that wide implants or multiple implants may withstand the occlusal forces on molars better than a single standard 3.75 mm implant. This article presents the retrospective findings of 24 consecutively placed mandibular and maxillary molar single-tooth implants. The patients were evaluated for bone quality and quantity, implant survival, and length of time of loading. Complications related to screw loosening and fracture were also recorded. aPrivate Practice, Tucson, Ariz.; and Assistant Professor, Department of Periodontology, University of Southern California, Los Angeles, Calif. bprivate Practice, Tucson, Ariz.; and Associate Professor, Department of Periodontology, University of Texas, Houston, Tex. Copyright | 1995 by The Editorial Council of THE JOURNALOF PROSTHETICDENTISTRY. 0022-3918/95/$3.00 + 0. 10/1/63630
JULY 1995
Fig. 1. Periapical radiograph of lower left second molar. There is advanced furcation invasion.
MATERIAL
AND METHODS
Twenty-two patients, 16 women and six men, whose ages ranged from 48 to 73 years (average 58.6 years) participated in this study. The patients were referred for periodontal therapy and implant placement for single maxillary or mandibular molars and were considered to be in good general health. At the initial examination a periodontal evaluation was made, and radiographs were taken (Fig. 1). These were supplemented by a panoramic radiograph. Diagnostic casts and clinical photographs were made. Consultations were made with the referring doctor, the patient, and on occasion, the laboratory technician. Patients with known bruxism or clenching habits were not considered for
THE JOURNAL OF PROSTHETICDENTISTRY
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THE JOURNAL OF PROSTHETIC DENTISTRY
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Fig. 2. A. Molar has been removed, socket debrided, and distal socket prepared to receive 13 mm implant. B, Implant installed slightly below crest is entirely within distal extraction socket.
Fig. 3. Five months after implant placement, implant has been exposed with bone surrounding implant.
single-tooth molar implant placement. Alternative treatment plans were discussed with the patients. Once the decision was made to place and implant, surgical guides were fabricated. The patients underwent premedication with either penicillin or erythromycin (2 gm to be taken 2 hours before surgery and 1 gm p/day for 7 days). The patients underwent premedication with light intravenous conscious sedation, and local anesthesia was administered. Incisions for edentulous sites were begun within the sulcus of the adjacent posterior tooth and were extended across the palatal or lingual aspect of the edentulous ridge, terminating one tooth anteriorly. Vertical buccal releasing incisions were made for access, and full-thickness mucoperiosteal flaps were reflected. In the mandible the mental foramen was always identified to prevent injury to the nerve. If the tooth was presented and was to be replaced by an immediate implant, mesial-distal luxation was carefully
52
applied. Once the tooth was loosened, i t was gently removed with forceps. The sockets were debrided with curettes and files. When the tooth was missing, incisions were made lingual or palatal to the crest, and the tissues were reflected to the buccal surface. The implant sites were prepared according to the methods described by Adell and Lekholm. 6 The bone quality and quantity were determined from the preoperative radiographs and were registered in the patient's chart. 7 For extraction sockets the implants were either placed into .the interradicular bone (Fig. 2) or within one of the engaging socket's bony walls in an attempt to engage part of the interradicular bone. Most implants were placed without tapping. Twenty-one standard implants 3.75 mm wide, one implant 4 mm wide, and two implants 5 mm in diameter were placed. In instances where the bone quality was of low density and complete tapping could have overprepared the surgical sites, only the coronal half of the
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F i g . 4. A, I m p l a n t restored on nonrotating a b u t m e n t gold cylinder and in occlusion. B, Radiograph taken at 2-year evaluation. Bone level is at second thread.
T a b l e II. M e t h o d of placement
T a b l e I. I m p l a n t success
Time period
Implant insertion0 (yrs) 0-1 yrs 1-2 yrs
Success rate No. No. within Cumulative of Implants of group success Patients followed Failures (%) r a t e (%)
22
24
0
100
100
Immediate implant placement
Maxilla Mandible
4* 7
3 10
*One implant was lost and replaced. 21" 20 ^
23 22
1 0t
95.7 100.0
95.7 95.7
*One p a t i e n t moved a n d was lost to follow-up. t O n e p a t i e n t died.
socket was tapped. The implants were then placed, cover screws were inserted, and the flaps were closed. The sutures were removed in 7 days. Second-stage surgery was performed 4 to 5 months after healing occurred in the mandible and 6 months after it occurred in the maxilla. A periapical radiograph of the implant site was taken before second-stage surgery was done. The surgical site was anesthetized and flaps were reflected, exposing the implant head and surrounding bone (Fig, 3). T h e cover screws were removed, and either healing a b u t m e n t s or nonrotating a b u t m e n t cylinders were placed onto the implant. The gingival tissues were apically positioned and sutured with interrupted sutures. Periapical radiographs were taken to confirm the complete seating of the a b u t m e n t on the implant. Six to 8 weeks after the second-stage surgery was done, the restorative dentists made impressions and began fabrication of the single-tooth implant crowns. All 24 implants were restored by seven dentists trained in restoring the implant system (Nobelpharma, Chicago, Ill.). The precise restorations were retained with screws, and the occlusal relationships were developed to eliminate lateral and balancing interferences and to ensure only light contacts in centric occlusion (Fig. 4, A). Two weeks after crown insertion, the gold screws were retightened and the occlusion was reevaluated by the dentists. If the gold screw or abut-
J U L Y 1995
Location
Standard implant placement
ment screw was loose, a radiograph was taken to evaluate the complete seating of the a b u t m e n t and crown (Fig. 4, B). If nonworking contacts were noted, they where reduced by occlusal adjustment. Patients were given oral hygiene and appointments for 6 months, and they also underwent annual examinations. The number of implants placed between two adjacent teeth and the number of implants terminally placed in the arch were tabulated. As part of the s t u d y the participating restorative dentists were surveyed to determine whether crowns had fractured or loosened. The frequency of screw loosening was also recorded. RESULTS The results are based on placement of 24 implants in 22 patients. Two patients received two implants each. One patient lost a 5 x 6 m m implant after 6 months of function. This implant was replaced with another 5 mm wide implant and has been functioning for 4 months. One patient died and one patient moved out of the city. The average time of implant function was 24 months. T h e cumulative success rate after 1 year of function was 95.7 % (Table I). Table II describes the number of implants placed in healed edentulous ridges or into extraction sockets. The implant size and arch location are listed in Table III. Eighteen implants were placed in the mandible, and six were placed in the maxilla. Table IV delineates the bone quality and quantity. Eleven implants were placed in alveolar ridges with minimal bone resorption (type B). Nine implants were placed in type 3 bone and indicated the pres-
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BECKER AND BECKER
T a b l e III. Size and location of implants in millimeters Position
10 x 3 . 7 5 m m *
Maxilla Mandible Total
2
3 5
13 • 3.75 m m
15 • 3 . 7 5 m m
10 • 4 m m
2
0
0
It
1
6
11 13
3 3
1 1
0 1
0 1
18 24
6 x 5 mm
8 • 5 mm
Total
*Standard implant diameter is 3.75 m m wide. t o n e 6 m m long x 5 m m wide implant was lost and replaced.
T a b l e IV. I m p l a n t placement according to bone quality
T a b l e V. N u m b e r and frequency of screw loosening for
and q u a n t i t y as determined from preoperative radiographs
21 implants Stable
Quantity Quality
A
B
C
D
E
Total
1 2 3 4 Total
2 0 2 1 5
1 3 5 2 11
0 3 2* 3 8
0 0 0 0 0
0 0 0 0 0
3 6 9 6 24
*One implant was lost and replaced.
ence of a thin cortical plate with a compact trabecular pattern. All implants were restored on single-tooth nonrotating a b u t m e n t s with gold cylinders. The number of implants and frequency of loosening of the gold screws are listed in Table V. Table V is based on information for 22 implants. The gold screws in 13 implants (61.9 %) remained tightened, and three gold screws (14.3%) became loose three times. The a b u t m e n t screw fractured in one p a t i e n t and was retrieved and then replaced. No implant fractures occurred. Twenty implants were placed between two adjacent teeth, and six implants were in terminal positions. DISCUSSION The results of this retrospective analysis represent the first report of replacement of single molars with implantsupported prostheses. The results indicate t h a t maxillary and m a n d i b u l a r molars can be successfully (95.7%) replaced by single, threaded, endosseous implants. Laney et al. s reported the results of t r e a t m e n t for single-tooth replacements for bicuspids and anterior teeth. Ninety-five patients were treated and followed-up, and at 3 years a 97.2% success rate was reported. Parel* has cautioned against the use of one implant to replace single molars. Replacement of a molar with a single implant may present problems of force distribution and stress. Rangert and Sullivan 5 suggest the use of 4 m m wide implants with CeraOne a b u t m e n t s (Nobelpharma, Goth*Parel S. Personal communication, Nobelpharma Team Day. Sidney, Australia, 1993.
54
Maxillary Mandible Total (%)
Loosened once
4 1 9 2 13 (61.9) 3 (14.2)
Loosened twice
Loosened three times
0 2 2 (9.5)
1 2 3 (14.3)
enburg, Sweden) ~for single-tooth implants. This implant is reported to be 30% stronger t h a n the standard 3.75 m m implant and m a y be more resistant to bending forces. 9 With one implant, there is a discrepancy between the implant length and width and the size of the restored crown. P l a c e m e n t of a crown t h a t extends beyond the long axis of the implant could generate cantilevering forces on the crown and implant. These forces could contribute to screw loosening and eventual i m p l a n t fatigue. Ideally, two implants should be used to replace a single molar; however, a molar edentulous space is often bound by natural teeth, which results in insufficient mesial-distal bone width for placement of more than one implant. According to Wheeler 1~ the average mesial-distal width of a maxillary first molar is 7.5 mm, whereas the average width of a mandibular first molar is 8.5 mm. These dimensions provide insufficient space for placement of more than one 3.75 m m wide implant. Several factors may account for the high success rate reported in this study, namely bone quality, bone quantity length of implants placed, and exclusion of patients with bruxism habits. Twelve of the implants were placed at the time of tooth extraction, thereby having the advantage of a large q u a n t i t y of bone volume. Sixteen implants were either 13 m m or 15 m m in length, and 16 implants were placed in either type A or B bone quantity. Laney et al. s placed 65 of the 95 implants in t y p e 2 or type 3 quality bone. Most of the implants (78) in the Laney study were placed in the maxillary arch and ranged from 13 to 18 m m in length. Patients with known bruxism or clenching habits were not considered for single-tooth i m p l a n t replacement in this group of patients. Parafunctional habits may be a risk factor related to implant fracture and screw loosening and may create uncontrolled and excessive occlusal loading forces.
VOLUME 74 NUMBER 1
BECKER AND BECKER
T h e r e s t o r a t i v e dentists were r e q u e s t e d to m i n i m i z e occlusal contacts in centric occlusion. Occlusal tables were narrow to reduce t h e c a n t i l e v e r effect of wide buccolingual restorations.* Occlusal c o n t a c t for p a t i e n t s w i t h 5 • 6 m m i m p l a n t s were m i n i m i z e d . T h e occlusion was e v a l u a t e d by t h e restorative d e n t i s t 2 weeks after crown p l a c e m e n t and at 6 m o n t h s and 1 year. M o s t of t h e i m p l a n t s were placed b e t w e e n a d j a c e n t teeth. T h i s r e l a t i o n s h i p m a y be related to t h e high success rate. T h e a d j a c e n t t e e t h m a y h a v e cont r i b u t e d to m i n i m i z a t i o n of excessive loading on t h e i m p l a n t s and m a y have " p r o t e c t e d " t h e i m p l a n t s during function: J e m t et al.5 r e p o r t e d t h a t 26 % of gold retaining screws b e c a m e loose d u r i n g the first year. L a n e y et al. 8 p r e s e n t e d t h e 3-year follow-up results f r o m t h e s a m e study. A b u t m e n t screw loosening occurred in 10 (10.8 % ) of 92 p a t i e n t s who received e i t h e r single-tooth i m p l a n t - s u p p o r t e d restorations for bicuspids or incisors. T h e incidence of screw loosening in this r e p o r t is greater t h a n t h a t in the previous studies (38%). In this study, if gold screws b e c a m e loose m o r e t h a n twice, t h e y were r e p l a c e d and the occlusion of t h e r e s t o r a t i o n was readjusted. N o reports of crown fract u r e s were made. P l a c e m e n t of C e r a O n e restorations ( N o b e l p h a r m a ) m a y h a v e r e d u c e d t h e incidence of screw loosening. T h e o r e t i cally, t h e C e r a O n e a b u t m e n t has a high p r e t e n s i o n abutm e n t screw that, w h e n p r o p e r l y t o r q u e d , will resist unscrewing. S t u d i e s t h a t v a l i d a t e and d o c u m e n t t h e complications with this type of r e s t o r a t i o n need to be performed. Carlson and Carlsson 11 r e p o r t e d complications f r o m 600 i m p l a n t - s u p p o r t e d prostheses (2709 implants) p l a c e d b e t w e e n 1972 and 1991. C o m p l i c a t i o n s o c c u r r e d least often in single-tooth r e p l a c e m e n t s . CONCLUSION
W i t h i n t h e limits of this r e t r o s p e c t i v e study, replacem e n t of molars w i t h single i m p l a n t - s u p p o r t e d crowns were successful. One i m p l a n t was lost (5 • 6 m m ) , and a 95.7%
THE JOURNAL OF PROSTHETIC DENTISTRY
survival rate resulted. Factors such as b o n e quality, quantity, l e n g t h of i m p l a n t s , and m i n i m i z e d occlusal contacts m a y have c o n t r i b u t e d to t h e favorable success rate. Pat i e n t s with known p a r a f u n c t i o n a l h a b i t s were n o t included in t h i s population. T h e m a i n c o m p l i c a t i o n was loosening of gold retaining screws, which occurred in eight (38 % ) of the 21 i m p l a n t s and in s o m e cases m o r e t h a n once (Table V). We thank Dr. Bo Rangert for his technical assistance in writing this article. REFERENCES
1. Adell R, Lekholm U, Rockier B, Branemark P-I. A 15 year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Maxillofac Surg 1981;10:387-416. 2. Albrektsson T, Dahl E, Enbom L, et al. Osseointegrated oral implants: a Swedish multicenter study of 8139 consecutively inserted Nobelpharma implants. J Periodontol 1988;59:287-96. 3. van Steenberghe D, Lekholm U, Boienden C, et al. The applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: a prospective multicenter study of 558 fixtures. Int J Oral Maxillofac Implants 1990;5:272-81. 4. Jemt T, Laney WR, Harris D, et al. Osseointegrated implants for single tooth replacement: a 1-year report from a multicenter prospective study. In J Oral Maxillofac hnplant 1991;6:29-36. 5. Rangert B, Sullivan R. Preventing prosthetic overload induced by bending. Nobelpharma News 1993;7:5. 6. Adell R, Lekholm U. Surgical procedures. In: Branemark PI, Zarb GA, Albrektsson T, eds. Tissue integrated prosthesis. Osseointegration in clinical dentistry. Chicago: Quintessence Publ, 1985:211. 7. Lekholm U, Zarb GA. Patient selection and preparation. In: Brhnemark PI, Zarb GA, Albrektsson T, eds. Tissue-integrated prosthesis: osseointegration in clinical dentistry. Chicago: Quintessence Publ, 1985;199-209. 8. Laney WR, Jemt T, Harris D, et al. Osseointegrated implants for single-tooth replacement: Progress report from a multicenter prospective study after 3 years. Int J Oral Maxillofac Implant 1994;9:49-54. 9. Rangert B, Forsmalm B. Nobelpharma News 1994;8:7. 10. Wheeler RR. A textbook of dental anatomy and physiology. 2nd ed. Philadelphia: WB Saunders Co, 1950:215-43. 11. Carlson B, Carlsson GE. Prosthodontia complications in osseointegrated dental implant treatment. Int J Oral Maxillfac Implant 1994; 9:90-4. Reprint requests to:
WILLIAMBECKER,DDS, MSD 801 N. WILMOT;B-2 TUCSON,AZ 85711
*Lewis S. Personal communication. Gainesville, Florida, 1993.
JULY 1995
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