Tilted Implants as an Alternative to Maxillary Sinus Grafting: A Clinical, Radiologic, and Periotest Study

Tilted Implants as an Alternative to Maxillary Sinus Grafting: A Clinical, Radiologic, and Periotest Study Carlos Aparicio, MD, DDS, MS;'+ Pilar Perales, MD, DDS;+ Bo Rangert, Mech Eng, PhDt

A0 ST R ACT

Background: Owing to mechanical and anatomic difficulties, implant treatment in the atrophic maxilla represents a challenge. The maxillary sinus floor augmentation procedure is still not universally accepted because of its complexity and its unpredictability.

Purpose: In this study, a combination of tilted and axial implants was used in patients with severely resorbed posterior maxillae as an alternative to sinus grafting.

Materials and Methods: Twenty-five patients were rehabilitated with 29 fixed partial prostheses supported by 101 Brinemark System' implants. Fifty-nine implants were installed in an axial and 42 in a tilted direction. The average follow-up period was 37 months (range: 21-87 mo post loading).

Results: After 5 years, the implant cumulative success rate was 95.2% (survival: rate 100%) for the tilted implants and 91.3% (survival rate: 96.5%) for the axial implants, and the prosthesis survival rate was 100%. At the fifth year, the average marginal bone loss was 1.21 mm for the tilted implants and 0.92 mm for the axial ones. The mean Periotest@ values (PTV) at loading time were -2.62 and -3.57, and after 5 years the PTVs were -4 .73 and -5.00 for the tilted and the axial implants, respectively. During the follow-up, all prostheses but two were mechanically stable, retightening of 18 abutment screws and of 5 gold screws in 14 prostheses was done, and fracture of two abutment screws and two occlusal surfaces was experienced.

Conclusions: Results indicate that the use of tilted implants is an effective and safe alternative to maxillary sinus floor augmentation procedures.

KEY WORDS: dental implants, maxillary sinus, partial fixed prostheses, Periotest', posterior maxillary segment, screw loosening, tilted implants

n the case of total edentulousness in the maxilla, a I full-arch bridge supported by multiple implants dis- tributes the masticatory loads primarily in axial direction along the maxillary arch.' In the case of a partially edentulous maxilla in the posterior region, the implants have to be placed in a more lineal arrangement, which may increase the risk for bending overload.2 Moreover, bone with less volume and worse quality is often found in these regions, which frequently complicates implant placement and may compromise the prognosis of the

*Department of Biomaterials and Handicap Research University of Goteborg, Sweden; +Private practice, Barcelona, Spain; and 'Nobel Biocare AB, Goteborg Sweden

Reprint requests: Carlos Aparicio, MD, DDS, MS, General Mitre 90 B, 0802 1 Barcelona, Spain; e-rnail: [email protected]

clinical r e s ~ l t s . ~ The presence of the maxillary sinus and limited vertical space are two other obstacles encoun- tered when placing implants in this r e g i ~ n . ~ ? ~ As a consequence, the implants placed in the premolar or molar areas are shorter than the ones located in the incisive or canine areas."8 It is known that shorter implants have a higher failure rate than longer one^.^^^ Thus, the placement of dental implants in the posterior atrophic maxilla usually results in a compromised biomechanical situation with a combination of short implants placed on a straight line in poor quality bone in an area exposed to high loading forces.'('

During the past decades, various alternative clinical procedures have been proposed to place implants in the posterior atrophic maxilla; one of them is the maxillary sinus floor augmentation or the sinus graft procedure.

39

40 <,'liniciil Iniplnnt Dentistry and Related Resenrch, Volitrne 3, Niiniber I , 2001

Numerous grafting materials, including autologous bone taken from different areas, such as the hip, the calvaria, or the chin, have been used."," The clinical results of these techniques are related to the amount of the residual crestal bone. Possible complications are morbidity of the donor site and those related to sinus surgery, such as sinusitis, fistulae, loss of the graft or the implants, and osteomyelitis." Most of the published sinus graft studies are retrospective. In those studies, clinical and biotechnologic treatment concepts are mixed in such a way that the reader can get easily con- fused. At the present time, the maxillary sinus grafting procedure is still not universally a ~ c e p t e d . ' ~ , ~ ~ One attractive approach when treating the posterior maxilla is to use tilted implants to engage as much cortical bone as possible." From a theoretic point of view, the use of tilted implants in the residual crestal bone permits

1. Placement of longer implants, which increases the degree of implant-to-bone contact area and also the implant primary stability. A longer distance between implants, allowing for the elimination of cantilevers in the prosthesis, which results in a better load distribution situation. Placement of implants in residual bone, avoiding more complex techniques, such as sinus lifting or bone grafting procedures.

In this study, the rehabilitation of the extremely resorbed posterior maxilla by means of a prosthesis supported by a combination of axial and tilted implants was evaluated by clinical, radiographic, and Periotestm examinations with a follow-up period of 21 to 87 months.

2.

3.

MATERIALS AND METHODS

Patients

This retrospective study included 25 consecutive (10 male; 15 female) patients with partially edentulous maxillae (Appelgate-Kennedy Class I, 11, and 111). The mean age was 59 years for males and 49 years for females. From June 1991 to June 1998, the patients were treated with implants placed in axial and tilted directions, in relation to the occlusal plane, to support fixed prostheses without distal or mesial cantilevers. The indication for the placement of tilted implants was established because the residual bone quantity was less than 8 nim under the maxillary sinus. Six patients were smokers and eight patients showed signs of wear on the occlusal surfaces. In general, the patients were healthy.

One patient had epilepsy, and another had undergone angioplastic surgery owing to a coronary event and was being treated with acetylsalicylic acid.

The authors recognize that all placed implants are somewhat angulated to the occlusal plane. However, in this study, an implant was considered tilted when the inclination was over 15 degrees with respect to the occlusal plane. The inclination could be in the mesiodistal o r distomesial direction and combined with a buccopalatal angulation.

5 u rg ery

The presurgical examinations of all the patients included a panoramic radiograph. In most cases, the extension of the maxillary sinus and the volume and density of the remaining bone was evaluated by means of maxillary computed tomography. The bone quantity and quality were estimated based on the presurgical radiog- raphy and on the resistance to surgical drilling during surgery and classified according to the index described by Lekholm and Zarb.I7 The data concerning bone quality were 1 patient type I, 7 patients type 11, 13 patients type 111, and 4 patients type IV.

One surgeon treated all the patients in one clinic. The implants were placed using a two-stage surgical approach, according to the method described by Adell et

Of 101 fixtures placed, 42 were with a tilted position in relation to the occlusal plane (Figure 1). Standard Branemark System@ implants (Nobel Biocare AB, Gote- borg, Sweden) 15 mm and 18 mm long with diameters of 3.75 mm and 4 mm were most frequently used (Table 1). Each patient received a minimum of two and a maximum of five implants. One to three of these were tilted implants placed in the tuberosity or pterygoid bone or in the area just mesial to the maxillary sinus (Figure 2 ) . All prostheses were supported by both test (tilted) and control (axial) implants. No implants shorter than 13 mm were used in the tilted group (see Table 1) . The majority of the fixtures were placed without pretapping. All implants reached a high primary stability. Table 2 pre- sents the distribution of implants according to their length and year of placement.

Abutment connection was performed 6 to 8 months after implant placement (average 29 weeks). To give a better orientation to the gold screw or to obtain a better parallelism, 30-degree angulated abutments (Nobel Bio- care AB) were connected to 38 of the 42 tilted implants

Tilted Implants as an Alternative to Maxillnry Sinus Grafting 41

Figure 1. A, Surgical placement of an axial implant following the anterior wall of the maxillary sinus. The mesial axial implant will be the guide for the orientation of the tilted implant. B, Note the tilting of the implant. Once the implant is placed, the emergence point corresponds to the tooth to be replaced.

(90%), whereas Aur-Adapt" abutments (Nobel Biocare AB) were used for the remaining four implants (10%) (Table 3). In the group of the axial implants, Estheti- Conee (Nobel Biocare AB) abutments were used in 87% of the cases and Mirus-Cone" (Nobel Biocare AB) in the rest (13%). A periapical radiograph was used to verify the correct abutment seating

PROSTHETICS

Twenty-nine fixed partial screw-retained prostheses supported by a combination of tilted and axial implants were delivered to the 25 patients. Eleven of the 29 prostheses were supported by four or five implants, fourteen were supported by three implants (Figure 3), and four by two

TABLE 1. Length and Diameter of the Tilted and Axial Implants

Implant Number of length (mm) Implants (%) 3.75 mm 4 mm 5 mm

Diameter

implants (Figures 4 and 5 ) (Tables 4 and 5 ) . Rigid teeth- to-implant connections were used in four prostheses. Seven prostheses included the canine position ( 2 prostheses of 3 implants and 5 of 4 or 5 implants). The prostheses had neither distal nor mesial cantilevers.

The opposing jaw presented a natural dentition or a fixed implant-supported prostheses up to the third molar in six patients, up to the second molar in fourteen

Tilted 42 (100.0) 21 (50) 20 (48) 1 (2) 13 4 (9.5) 2 1 1 (WP) 15 12 (28.5) 8 4 0 18 23 (55.0) 8 15 0 20 3 (7.0) 3 0 0

Axial 59 (100.0) 40 (68) 15 (25) 4 (7) 8.5 1 (2.0) 1 0 0

10.0 4 (8.0) 2 0 2 13.0 8 (13.0) 6 0 2 (WP) 15.0 18 (30.0) 10 8 0 18.0 25 (42.0) 18 7 0 Figure 2. Radiographic images. A, Tilted implants placed in the 20.0 3 (5.0) 3 0 0 tuberosity or pterygoid bone and in the area just mesial to the

maxillary sinus. B, A combination of axial and tilted implants, the latter placed in the area just mesial to the maxillary sinus. WP = wide platform.

42 Clinical Implant Dentistry and Related Research, Volume 3, Number I , 2001

TABLE 2. Distribution of Implants according to Length and Year of Placement

Number of Total length of

Axial Implants (mm) Number of Length of

Tilted Implants Axial Implants Implants Number Of ~i l ted Implants (mm)

Patients Year (11-25) 13 15 18 20 (n = 42) 8.5 10 13 15 18 20 (n I 59) (n = 101)

1991 1

1992 4 1993 4 1994 1 1995 3 1996 4 1997 3 1998 5

1 1 0 0

1 5 0 1 0 1 3 0 0 0 1 0 1 2 2 2 0 0 5 0 1 1 2 0 0 2 1 0 0

2 0 0 1 0 0 0 7 0 1 3 1 2 1 4 0 1 1 1 5 0 1 1 1 0 0 1 0 7 0 0 1 2 3 2 5 0 0 1 3 4 0 4 0 1 0 4 0 0 12 0 0 1 7 10 0

1 8 8 3 8 8 5 18

3 15 12 4 15 13 9 30

patients, up to the first molar in two patients, and up to the second premolar in three patients. Porcelain-fused- to-gold alloy was used as the occlusal material in 22 prostheses (76%). In the remaining seven prostheses (24%), the material was acrylic. To achieve a passive fit of the metallic structures, the technique described by Aparicio was used." In brief, the metallic framework was cemented to modified gold cylinders. An occlusal relation was established with the goal of eliminating, when possible, lateral function and balancing interfer- ence and to ensure slight contacts in occlusion.

Clinical Follow-up

All patients were offered the opportunity to be included in a follow-up protocol consisting of a visit at 1, 3, and 12 months after the placement of the prosthesis and then once every year. At the check-ups, oral hygiene, occlusion, stability of prostheses, or possible mechanical complications were controlled and registered. Each implant was individually tested for mobility, and the Periotest value (PTV) (Seimens AG, Bensheim, Germany) was recorded.20-2z

The implants were evaluated and classified in a four- field table, according to Albrektsson and I ~ i d o r , ~ ~ as follows:

TABLE 3 Glades of AngtiI'it1on of thc 4 2 Ti l ted

Grades of Angulation (Degrees)

I111 p la I1 t 5

Inclination <15 15-25 2 5 3 5 >35

Mesiodistal-distomesial 0 15 20 7 Buccopalatal 15 23 4 0

Success: those implants that meet all the specific criteria for success proposed by Albrektsson and colleagues in 1986.24 Survival: those implants that are stable but where the criteria for success regarding marginal bone loss of less than 1.5 mm during the first year or less than 0.2 mm annually has not been met. Dropout: those implants in patients who did not appear for the scheduled recall for whatever rea- sons, including patient death. Failure: those implants removed for any reason.

The chi-squared test was used for statistical com- parisons between the two groups of axial and tilted implants.

At the check-ups, the prostheses were unscrewed, and the screw tightening was evaluated. A screw was classified as loose if it could be manually retightened.

TABLE 4. Data of Patients and Prostheses

Parameter Number

Patients 25 Edentulism (Class)

I 5 II I5 Ill 5

Prostheses 29 Implants per prostheses

2 4 3 14 4-5 1 1

Resin 7 Porcelain 22

Occlusal material

Figure 3. A , Radiographic image of tilted implants that seem to penetrate the sinus. Band C, Detail of two coronal cuts in the postsurgical scan in which the palatal and pterygornaxillar inclinations of the tilted implants are observed. Note how the implants avoid the maxillary sinus. D, The esthetic result of the rehabilitation does not seem to be affected by the tilting of the implants. Notice how the emergence profile of the implant corresponds to the missing tooth.

The mean loading time (time between the prosthesis connection and the last check-up) was 37 months (range: 21-87 mo). One patient with a three-implant

prosthesis ( 2 axial and 1 tilted) was referred to another center, and the follow-up after the provisional prostheses was interrupted.

Figure 4. Intraoral radiographs. A, At the abutment connection stage. One tilted implant and one axial were placed, avoiding the maxillary sinus, into a type 4 bone. B, At the 5-year follow-up appointment. Note the positive response to nonaxial load of the residual bone around the implants.

44 CIinical Implant Dentistry and Related Research, Volume 3, Number I , 2001

Radiographic Measurements

Implant tilting in the anterior-posterior direction was measured in postsurgical radiographs taken between abutment connection surgery and the placement of the definitive prosthesis. Buccopalatal inclinations with respect to the occlusal plane were measured on the master cast used to build the prosthesis. For the tilted implant group, the mean mesiodistal or distomesial tilting was of 35 degrees and was usually combined with a mean buccopalatal inclination of 15 degrees with some extreme inclinations over 50 degrees (see Figure 2 and Table 3).

Intraoral radiographs were taken, according to the recommendations of Strid,25 at baseline (prostheses placement) and at the check-ups. Measurements were made from the implant abutment junction to the marginal bone level at the mesial and distal aspects of each implant by one observer, and a mean value was calcu- lated to the closest half thread.

The data corresponding to the marginal bone loss were statistically evaluated by one-way multivariate

analysis of variance. The grouping variable was the inclination of the implants to the occlusal plane with two levels: tilted and axial. The dependent variables were the marginal bone loss at mesial and distal.

Periotest Measurements

The stability of each implant was measured, according to Olive and Aparicio,20 after abutment connection, 1 and 3 months after prostheses placement, and at the annual check-ups, using the Periotest method. The abutments were tapped with the Periotest rod on the 2 mm closest to the abutment edge, following the manu- facturer's recommendations. To accomplish this during the follow-up, the gold screws were unscrewed, the prostheses were removed, the measurements were taken, and then the prostheses were placed again. The obtained measurements (PTV) were compared to pre- viously established values for 3.75-mm wide implants placed in the maxilla.20

Figure 5. A, Radiographic image of a two-wall bony defect in the maxillary left premolar-first molar area. B, Panoramic radiograph showing a partial prosthesis without cantilever supported by a combination of axial and tilted implants. Note the length and how the tilted implant is inclined toward a more palatal plane compared to the axially placed implant. C, Clinical occlusal view of the prosthesis showing the emergence point of the gold screws. D, lntraoral radiograph 5 years later. Note the bone level maintenance.

Tilted I n i p l a ~ t s as a n Alternative to Maxillary Siriirs G'rciftirig 45

TABLE 5. Distribution of the Prostheses over Time, Related t o the Number of Implants

Prostheses (n = 29)

2 Implants 3 Implants 4 or 5 Implants Period (yr) (n = 4) (n = 14) (n=11)

1-2 (n = 9) 1 3 5 2-3 (n = 4) 0 2 2 3 4 (n = 4) 0 1 3

4-5 (n = 3) 0 3 0 5-6 (n = 2 ) 0 2 0 6-7 (n = 2) 1 1 0 7-8 (n = 5) 2 2 1

RESULTS

Clinical Follow-up

Two axial implants failed before loading, but no more failures were experienced during the study period (Table 6). One axially placed implant was considered as surviving previous to loading. All the implants from the tilted group reached secondary stability and ful- filled the criteria for success. At second stage, the differences between the two groups were not statistically significant (p > .36). During the first year in function, two implants from each group did not meet the success criteria owing to progressive marginal bone loss, and they were classified as surviving. The bone resorption around these implants was stabilized after the first

TABLE 6. Characteristics of Surviving and Failed Implants

year, reaching the success criteria of no more than 0.2 mm of resorption per year. From a functional stand- point, these surviving implants were successful and performed their function, and the prostheses survival was 100% over the study time. The implant cumulative success rates were 91.3% and 95.2% for the axial and tilted implants, respectively (no statistical difference: p > .78) (Table 7), and the overall cumulative success rate was 93.1%. The implant cumulative survival rates, however, were 96.5% and 100% for the axial and tilted implants, respectively, and the overall cumulative survival rate was 98.25%.

A total of 28 mechanical incidents were detected for 16 prostheses (55.2%). The most frequent event was retightening of the abutment screw 18 times for 14 prostheses, followed by gold screw retightening in five prostheses. However, all the prostheses but two were stable previous to their unscrewing and so remained during the study time. Fracture of the abutment screws and of the occlusal material was observed on two prostheses (Table 8).

In the resin prostheses group, 25% of the retightening occurred 1 year after the placement of the prostheses and 50% between the fourth and seventh year. In the porcelain prostheses group, 67% of the screws were retightened during the first year and 33% between the second and fourth year. No differences were observed between the percentage of screws that had to be retightened in the axial and tilted implant groups. None of the

-

2.4 1.8

- -

-2 -4 Abutment loosening -4 -4 No

PTV Length x Implants per MBL 1st year Implant Type Diameter (rnrn) Prostheses (mm) At Loading 1st Year Prosthetic Problems

I Tilted Postloading

Failed (n = 0) - -

Surviving (n = 2) 18 X 3.75 3 13 X 5.00 (WP) 4

11 Axial Preloading

Failed (n = 2)

Surviving (n = 1 )

Failed (n = 0) Surviving (n = 2) 13 x 3.75 3 2.4 -2 -2 No

15 X 3.75 3 3.2 -3 -3 No

13 X 3.75 13 X 3.75

13 x 5.00 (WP) Postloading

- - - - -

MBL = marginal bone loss; PTV = Periotest value; WP = wide platform.

46 Clinical Implant Dentistry and Related Research, Volume 3, Number 1 , 2001

TABLE 7. Implant Success Rate for Tilted and Axial Implants

Follow-UP Number of Implants Success Rate

Time (yr) At Beginning of Period Dropped Out Failed Surviving During Period (%) Cumulative (%)

Tilted At placement 42 1 0 0 100 100 0-1 41 0 0 2 95.2 95.2 1-2 27 2 0 0 I 00 95.2 2-3 25 1 0 0 100 95.2 3 4 17 2 0 0 100 95.2 4-5 13 2 0 0 100 95.2 5-6 12 2 0 0 100 95.2 6-7 9 1 0 0 100 95.2

Axial At placement 59 2 2 1 95.0 95.0 0-1 54 0 0 2 96.3 91.3 1-2 37 5 0 0 100 91.3 2-3 31 3 0 0 100 91.3 3-4 19 3 0 0 100 91.3 4-5 15 3 0 0 100 91.3 5-6 13 3 0 0 100 91.3 6-7 8 1 0 0 100 91.3

above-mentioned problems made it necessary to replace the prosthesis.

Radiographic Measurements

The average distance from the abutment-implant junction to the bone crest at the placement of the prosthesis was 1.84 mm. Comparison of the results shows that 0.14 mm more bone loss was evident at the tilted implants during the first year of loading. Only minimal changes were observed in the marginal bone height after the first year. Mean bone loss during the first 60

Periotest Measurements

At prosthesis placement, the mean PTV for the tilted implants was -2.62 units (SD = -2.97) and -3.57 units (SD = -1.88) for the axial group, which was statistically significant (Table 10). There were no significant differences observed at the annual check-ups. A decrease of 2.1 1 PTV for the tilted and 1.43 PTV for the axial implants was observed from the time of the placement of the prosthesis to the 5-year follow-up. The decrease was greater in the tilted group.

months of loading was 1.21 mm and 0.92 mm for the tilted and axial implants, respectively (Table 9). Com- DISCUSSION

parative analysis did not demonstrate statistically significant differences between the distal and mesial marginal bone level of either tilted or axial implants.

In this study, 29 prostheses supported by a combination of tilted and axial standard Brinemark implants placed in the posterior maxilla were evaluated. The overall

TABLE 8. Postloading Mechanical Incidents

Resin Prostheses (n = 7) Porcelain Prostheses (n = 22)

Number with Number of Number with Number of Total with Total of Type of Problem Complications (%) Problems Complications (%) Problems Complications (%) Problems

Total Prostheses (n = 29)

~~

7 (100) 21 9 (41) 18 16 (55.2) 39 Gold screw loosening 3 (43) 6 2 (22) 2 5 (31.2) 8 Abutment screw loosening 6 (86 ) 12 8 (89) 15 14 (87.5) 27 Abutment screw fracture 2 (29) 2 0 0 2 (12.5) 2 Occlusal material fracture 1 ~ 4 ) 1 l (11) 1 2 (12.5) 2

TABLE 9. Marginal Bone Loss of Tilted and Axial Implants during Follow-up

0-1 Year 1-2 Years 2-3 Years 3 4 Years 4-5 Years Total

Tilted Implants (n) 40 25 24 17 11 MBL (mm)

Mesial (SD) 0.51 (0.39) 0.31 (0.35) 0.21 (0.37) 0.09 (0.17) 0.07 (0.17) 1.19 Distal (SD) 0.64 (0.71) 0.26 (0.36) 0.17 (0.26) 0.06 (0.16) 0.09 (0.17) 1.22 Mean (SD) 0.57 (0.50) 0.29 (0.32) 0.19 (0.28) 0.08 (0.1 I ) 0.08 (0.12) 1.21

Axial Implants (n) 53 32 28 16 12 MBL (mm)

Mesial (SD) 0.43 (0.50) 0.20 (0.20) 0.10 (0.13) 0.06 (0.10) 0.06 (0.10) 0.85 Distal (SD) 0.43 (0.44) 0.22 (0.28) 0.14 (0.13) 0.06 (0.08) 0.11 (0.13) 0.96 Mean (SD) 0.43 (0.45) 0.23 (0.28) 0.12 (0.10) 0.06 (0.06) 0.08 (0.09) 0.92

Manova test p > .40 p > .14 p > .14 p > .55 p > .86

cumulative success rate (93.1%) and cumulative survival rate (98.25%) were similar to the results published in previous reports,26 in which partial prostheses, mostly with cantilevers, supported by axial implants were followed up during a postloading observation period of 5 years (cumulative success rate: 93.8%). The prostheses survival rate was 100%.

Although not statistically significant, the implant success rate was higher for tilted (95.2%) implants than for axial implants (91.3%), which is in agreement with other authors.16 This is thought to be because longer implants can be placed and anchored with larger cortical bone contact. The tilted implants were all placed in bone sites 8 mm or less high, but most of them were 15 mm or longer. As indicated by the computed tomography (CT) measurements, the mesially tilted implants are packed in their marrow trajectory between the mesial implant that is crossed or contacted by its palatal side, and the cortical of the anterior curve of the palate (see Figure 3). Then, a tricortical anchorage is achieved, that is, the implant is anchored in the cortical bone of the alveolar crest, in the cortical bone of the nasal floor, and in the cortical of the anterior palatal vault. In 11 cases, a reported vibration during the drilling procedure or an increased resistance during the implant placement indicated an additional anchorage of the tilted implant by contact with the mesial implant itself (see Figures 2; 3, A; and 5, B ) .

Studies performed in vitro discourage the use of implants connected to angulated abutments.27 How- ever, these studies analyze the distribution of load forces on the peri-implant bone for single implants, which differs from the present study in which multiple implants supported partial prostheses. In vivo measure-

ments on a tilted implant as part of a multi-implant prosthesis found no load increase to the bone from the tilting.16 Moreover, animal studies that have attempted to examine the effect of nonaxial loading of dental implants have shown that nonaxial loading in the range of the clinical reality is not detrimental to the integration of the

In this clinical study, the tilting of the implants did not seem to affect the marginal bone height (see Table 9). Only minimal differences that are statistically not significant between the two groups of implants can be observed, particularly during the first year after loading (0.14 mm), with a tendency of becoming equal during the following years. After a postloading period of 3 years, no difference between the data obtained by other authors regarding the marginal bone loss of axial implants and the data obtained in this study was o b ~ e r v e d . ~ ' . ~ ~

Measurements of PTV in tilted implants were not affected by the degree of inclination in respect to the

TABLE 10. Variations of Mean Periotest (PTV) Values of Tilted and Axial Implants Depending on Time

Periotest Value (SO)

Check-up Tilted Implants Axial Implants

At placement -2.62 (-2.97) -3.57 (-1.88)

First year -3.54 (-1.47) -4.05 (-1.54)

Second year -4.25 (-1.15) -4.37 (-1.10)

Third year 4 .38 (-1.10) -4.36 (-1.19)

Fourth year 4 .76 (-1.20) -5.10 (-0.74) Fifth year 4.73 (-1.27) -5.00 (-0.85)

48 Clinical Implant Dentistry and Related Research, Volume 3, Number 1 , 2001

remaining bone (see Table 10). The instrument is able to adjust itself to measure implant stability according to a specific inclination of the handpiece to the ground plane. Mean values of PTV at the connection of the prosthesis were -2.62 (SD = -2.97) for tilted implants and -3.57 (SD = -1.88) for the axial implants. This difference in the initial measurement could be explained by a longer angulated abutment compared to the esthetic abutment that is used in the majority of cases. During the following 2 years after the prosthesis placement, PTV values diminished progressively in both groups. Two years after loading, PTV of tilted implants became the same as the PTV of axial implants. After the third year, the stability of the tilted implants was even higher than that of the axial ones.

The mechanical incidents were easily solved without the development of biologic problems. All the prostheses remained stable in place during the observation period, so the prosthetic success rate was 100%. Regard- ing the number of complications, the results of this study agree with those of other authors who have ana- lyzed specific complications in the posterior m a ~ i l l a . ~ ' There were more complications than in other follow-up studies with partially edentulous patient^.^^-^^

Previous authors have reported that the most frequent problem was fracture of resin veneer^,^'-^^ whereas in the present study, i t was retightening of abutment screws, followed by gold screw retightening. In this study, the initial abutment loosening could be a consequence of cement remnants on the gold screw (cement used to achieve passive fit of the frameworks), locking the gold screw to the abutment screw.'' The unscrewing of the contaminated gold screws at prosthesis removal, therefore, might be a cause of the initial abutment screw loosening. However, of the 27 abutment screws that loosened, 11 were on angulated abutments that had no connection between the abutment screw and the gold screw. Difficulties in tightening these abutment screws, because of limited access and the tilting per se, might be a reason for this loosening. No relation was found between screw loosening and the number of implants supporting the prostheses.

In agreement wi th other author^,^' efficacy of porcelain as a restorative material in partial fixed prostheses over implants seems acceptable because of the low occurrence of mechanical problems. This last find- ing is encouraging compared to the high occurrence of problems seen with acrylic prostheses.

Tilted implants were placed when there was not enough bone beneath the maxillary sinus, allowing successful treatment of patients by means of fixed prostheses. This philosophy of placing implants in the preexist- ing bone avoided more complex surgical procedures such as the maxillary sinus bone graft. The treatment principle followed was to make the maximum profit of the available bone, which led to a more simple, more predictable, less expensive, and a less time-consuming treatment compared to the maxillary sinus bone grafting procedure.' '-I5

CONCLUSIONS

Within the limits of the present study, it is concluded that partial edentulism in the posterior part of resorbed maxillae can be successfully treated with fixed prostheses supported by a combination of tilted and axially placed BrAnemark System implants. The results indicate that tilted implants are an effective alternative to the maxillary sinus bone grafting procedure.

ACKNOWLEDGMENTS

The authors acknowledge the work of Prof. Dr. Martin Rios on the statistical analysis and thank Dr. Pep Qui and Ms. M6nica Ruiz for their assistance.

REFERENCES 1.

2.

3.

4.

5.

6.

7.

Rangert B, Krogh PHJ, Langer B, Van Roekel N. Bending overload and implant fracture: a retrospective clinical analysis. Int J Oral Maxillofac Implants 1995; 10:326-334. Rangert B, Sullivan R, Jemt T. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997; 12:360-368. Lekholm U, Adell R, Branemark P-I. Possible complication. In: Branemark P-I, Zarb GA, Albrektsson T, eds. Tissue- integrated prostheses: osseointegration in clinical den- tristry. Chicago: Quintessence, 1985:233-240. Branemark P-I, Adell R, Albrektsson T, Lekholm U, Lind- strom J , Rockler B. An experimental and clinical study of osseointegrated implants penetrating the nasal cavity and maxillary sinus. J Oral Rehabil 1979; 43:497-505. Tatum H. Maxillary and sinus implant reconstruction. Dent Clin North Am 1986; 30:207-229. van Steenberghe D, Lekholm U, Bolender C, et al. The applicability of osseointegrated oral implants in rehabilitation of partial edentulism: a prospective multicenter study of 558 fixtures. Int J Oral Maxillofac Implants 1990; 5:

Naert I, Quirynen M, van Steenberghe D, Darius P. A six- year prosthodontic study of 509 consecutively inserted implants for the treatment of partial edentulism. J. Prosthet Dent 1992; 67:236-245.

272-28 1.

Tilted Implants as an Alterniitive to Maxillary Sinus Grafting 49

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

Friberg B, Jemt T, Lekholm U. Early failures in 4641 consecutively placed Brinemark dental implants: a study from stage 1 surgery to the connection of completed prostheses. Int J Oral Maxillofac Implants 1991; 6:142-146. Lekholm U. The BrAnemark implant technique: a standard- ized procedure under continuous development. In: Laney WR, Tolrnan DE, eds. Tissue integration in oral, orthope- dic, and maxillofacial reconstruction. Chicago: Quintes- sence, 1992: 194-1 99. Rangert B, Sennerby L, Nilson H. Load factor analysis for implants in the posterior maxilla. In: Jensen T, ed. The sinus bone graft. Chicago: Quintessence, 1999: 167-177. Smiler DG, Johnson PW, Lozada JL, et al. Sinus l i f t grafts and endosseous implants. Treatment of the atrophic posterior maxilla. Dent Clin North Am 1992; 36:151-186. Wood RM, Moore DL. Grafting for the maxillary sinus with intraoral harvested autogenous bone prior to implant placement. Int J Oral Maxillofac Implants 1988; 3:209-214. Regeev E, Smith RA, Perrot DH, Pogrel MA. Maxillary sinus complications related to endosseous implants. Int J Oral Maxillofac Implants 1995; 10:451-461. Jensen OT, Shoulman LB, Block MS, lacono VJ. Report of the Sinus Consensus Conference of 1996. Int J Oral Max- illofac Implants 1998; 13(Special Supp1):l I , 29. Tong DC, Kioux K, Drangsholt M, Bierne OR. A review of survival rates for implants placed in grafted maxillary sinuses using meta-analysis. Int J Oral Maxillofac Implants

Krekmanov L, Kahn M, Rangert B, Lindstrom H. Tilting of posterior mandibular and maxillary implants for improved prosthesis support. Int 1 Oral Maxillofac Implants 2000; I5:405-4 14. Lekholm U, Zarb GA. Patient selection and preparation. In: Brinemark P-I, Zarb GA, Albrektsson T, eds. Tissue-integrated prostheses: osseointegration in clinical dentistry. Chicago: Quintessence, 1985: 199-209. Adell R, Lekholm U, Branemark P-I. Surgical procedures. In: Branemark P-I, Zarb GA, Albrektsson T, eds. Tissue- integrated prostheses: osseointegration in clinical dentistry. Chicago: Quintessence, 1985:211-232. Aparicio C. A new method to routinely achieve passive fit of ceramometal prostheses over Brinemark osseointegrated implants: a two-year report. Int J Periodontics Restorative Dent 1994; 14:405419. Olive I , Aparicio C. The Periotest method as a measure of osseointegrated oral implant stability. Int J Oral Maxillofac Implants 1990; 5:390400. van Steenberghe D, Quirynen M. Reproducibility and detection threshold of peri-implant diagnostics. Adv Dent Res 1993; 7:191-195. van Steenberghe D, Tricio J , Naert I, Nys A. Damping char-

1998; 13:175-182.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

acteristics of bone-to-implant interfaces. Clin Oral Imp1 Res

Albrektsson T, lsidor F. Criteria for success and failure of an implant system. Consensus report. In: Lang NP, Karring T, eds. Proceedings of the First European Workshop on Peridontology. Chicago: Quintessence, 1994:243-244. Albrektsson T, Zarb G, Worthington P, Erikson AR. The long-term efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillo- fac Implants 1986; 1:1 1-25. Strid KC. Radiographic results and radiographic procedures. In: BrOnemark P-I, Zarb GA, Albrektsson T, eds. Tissue- integrated prostheses: osseointegration in clinical dentistry. Chicago: Quintessence, 1985:187-198,317-327. Lindh T, Gunne J, Tillberg A, Molin M. A meta-analysis of implants in partial edentulism. Clin Oral Imp1 Res 1998; 930-90. Clelland NL, Gilat A, McGlumphy EA, Brantley WA. A photoelastic and strain gauge analysis of angled abutments for an implant system. Int J Oral Maxillofac Implants 1993;

Celleti R, Pameijer CH, Bracchetti G, Donath D, Persichetti G, Visani I . Histologic evaluation of osseointegrated implants restored in nonaxial functional occlusion with preangled abutments. Int J Periodontics Restorative Dent

Asikainen P, Klemetti E, Vuillenin T, Sutter F, Rainio V, Koti- lainen R. Titanium implants and lateral forces. An experimental study with sheep. Clin Oral lmpl Res 1997; 8:465-468. Miyata T, Kobayashi Y, Araki H, Motomura Y, Shin K. The influence of controlled occlusal overload on peri-implant tissue: a histologic study in monkeys. Int J Oral Maxillofac Implants 1998; 13:677483. Wennerberg A, Jemt T. Complications in partially edentulous implant patients: a 5-year retrospective follow-up study of 133 patients supplied with unilateral maxillary prostheses. Clin lmpl Dent Relat Res 1999; 1:49-56. Jemt T, Lekholm U. Oral implant treatment in posterior partially edentulous jaws: a 5-year follow-up report. Int J Oral Maxillofac Implants 1993; 8:635-640. Lekholm U, van Steenberghe D, Herrmann I, et al. Osseoin- tegrated implants in the treatment of partially edentulous jaws: a prospective 5-year multicenter study. Int J Oral Maxillofac Implants 1994; 9:627-635. Jemt T, Linden B, Lekholm U. Failures and complications in 127 consecutively placed fixed partial prostheses supported by Branemark implants: from prosthetic treatment to first annual checkup. Int J Oral Maxillofac Implants 1992; 7:4044. Carlson B, Carlsson GE. Prosthodontic complications in osseointegrated dental implant treatment. Int J Oral Max- illofac Implants 1994; 9:9&94.

1995; 6:31-39.

8~541-548.

1995; 15~563-573.

Documents

Tilted Implants as an Alternative to Maxillary Sinus Grafting: A Clinical, Radiologic, and Periotest Study