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Eugenio Romeo Cristiano Tomasi Igor Finini Paolo Casentini Diego Lops

Implant-supported fixed cantilever prosthesis in partially edentulous jaws: a cohort prospective study

Authors’ affiliations: Eugenio Romeo, Igor Finini, Diego Lops, Department of Prosthodontics, Dental Clinic, School of Dentistry, University of Milan, Italy Cristiano Tomasi, Department of Periodontology, Institute of Odontology, The Sahlgrenska Academy at University of Gothenburg, Sweden Paolo Casentini, Department of Oral Surgery, Dental Clinic, School of Dentistry, University of Milan, Italy

Key words: cantilever fixed prostheses, cantilever length, endosseous implants, ITI implant

Correspondence to: Eugenio Romeo Department of Prosthodontics, Dental Clinic, School of Dentistry University of Milan, Italy Via Beldiletto 1/3 20142 Milano – Italy Tel.: þ 250 319 039 Fax: þ 250 319 040 e-mail: eugenio.romeo@unimi.it

with implant-supported fixed partial dentures (FPD) with cantilever after a mean follow-up

system, opposite denture, peri-implant bone resorption, prospective study Abstract: Background: Reconstructive procedures present a higher rate of biological costs due to the necessity of bone harvest and grafts, use of semipermeable barriers etc. On the hand, implant supported cantilever prostheses could allow a simpler rehabilitation procedure. Aims: The aim of the present study was to assess the clinical outcome of patients treated time of 8 years. Material and methods: The study included 45 consecutive partially edentulous patients treated between January 1994 and August 2006 with 59 partial cantilever fixed prostheses s

supported by 116 ITI implants. The primary outcome variable considered was the presence of complications at the subject and bridge level; the secondary outcome variable was marginal bone loss (MBL). The frequency of complications was analyzed according to cantilever location and opposite dentition and tested by Fisher’s exact test. A multilevel regression model was constructed to analyze the factors influencing MBL with three levels: subject as the highest, and then implant and site. During the follow-up period, 11 implants showed a bone loss exceeding the limit for success, out of which two implants showed an infection of the peri-implant tissue. Results: After an average observation of 8.2 years of cantilever prostheses loading, the implant success and survival rates were 90.5% and 100%, respectively. Besides, the prosthetic success and survival rate were 57.7% and 100%, respectively. Discussion: None of the predictors included in the multilevel model presented a significant impact on the bone loss between baseline and the follow-up examination. Conclusions: The authors concluded that the prognosis of implant-supported FPDs and marginal bone loss at implants were not influenced by the position or the length of the cantilever, the location of the bridge and type of opposite dentition. Implant-supported fixed cantilever prosthesis can be considered a suitable treatment choice.

Date: Accepted 17 May 2009 To cite this article: Romeo E, Tomasi C, Finini I, Casentini P, Lops D. Implant-supported fixed cantilever prosthesis in partially edentulous jaws: a cohort prospective study. Clin. Oral Impl. Res. 20, 2009; 1278–1285. doi: 10.1111/j.1600-0501.2009.01766.x

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Unfavorable local conditions of the residual edentulous ridges may lead to two therapeutic options for a rehabilitation by means of implant-supported fixed partial denture (FPD): (i) pre-implant reconstructive and/ or regenerative procedures; and (ii) treatment of a partially edentulous site with

cantilever fixed prosthesis. As a simple and economical procedure, edentulous ridges next to implants may be reconstructed by means of cantilevers or pontics (Rodriguez et al. 1994; Shackleton et al. 1994; Jimene´z-Lopez et al. 1999; Becker & Kaiser 2000). Especially, if these ridges need aug c 2009 John Wiley & Sons A/S


Romeo et al  Implant-supported fixed cantilever prosthesis in partially edentulous jaws

mentation procedures before or during implant placement, a considerable amount of time and money may be saved. Observations made in studies on humans suggested that a relationship may exist between excessive loading and peri-implant bone loss (Sanz et al. 1991; Quirynen et al. 1992; Rangert et al. 1995). Gunne and colleagues (1997) showed an increase in non-axial loading when cantilever extensions were included in FPD prostheses. Findings from in vitro studies revealed that higher stress concentrations were measured adjacent to implants with extensions compared with implants without extensions (White et al. 1994; Sertgo¨z & Guvener 1996; Stegaroiu et al. 1998; Yokoyama et al. 2004). It was further observed that the enhanced stress occurred mainly at the bone crest adjacent to the distal surface of the implant that was facing the cantilever extension and was dependent on the length of the cantilever segment. Barbier and Schepers (1997) reported from an animal study that the presence of cantilevers in an FPD might stimulate bone remodelling and result in an increased density of the trabecular bone and a thickening of the cortical layer of the adjacent ridge. The authors also described the presence of inflammatory lesions and enhanced numbers of osteoclasts in the tissues surrounding the implant closest to the cantilever unit. Moreover, it is not properly documented whether in an FPD, supported by few implants, the load exerted on the cantilever extension may cause undue bone loss (Akc¸a & Iplikc¸ioglu 2002). A clinical study by Romeo et al. (2003) on implant-supported FPDs reported a correlation between the bone loss around the implant closest to the cantilever and the extension of the cantilever segment. On the other hand, Wennstro¨m et al. (2004) retrospectively analyzed whether the inclusion of distal cantilever extensions increased the amount of marginal bone loss that took place at free-standing, implantsupported FPDs over a 5-year period of functional loading. They enrolled 45 partially dentate patients with a total of 50 free-standing implant-supported FPDs. The primary outcome variable was change in the peri-implant bone level from the time of FPD placement to the 5-year follow-up examination. The comparison between FPDs with and without cantilevers  c 2009 John Wiley & Sons A/S

was performed at three levels: FPD level, implant level and surface level. They failed to demonstrate that the presence of cantilever extensions in an FPD had an effect on peri-implant bone loss. There was also no difference in the observed failure/complication rates of the FPDs. The aim of the present study was to assess the clinical outcome of patients treated with implant-supported FPDs with a cantilever after a mean follow-up time of 8 years.

Material and methods Patient selection

Forty-five patients (18 males and 27 females), ages 42–100 years (mean age 63 years), were treated consecutively from January 1994 to August 2006 by implantsupported FPDs with a cantilever extension and included in the study (Table 1). The other 14 patients (seven males and seven females) were subjected to the same treatment but refused to participate in the follow-up program of the study. These drop-out patients received 16 bridges, 10 with a distal cantilever and six mesial cantilevers supported from a mean number of two implants. A few of these patients attended the Dental Clinic of Biomedical Sciences Institute, S. Paul Hospital, University of Milan, Italy, and a few of them attended a private out-patient regimen. The study protocol was approved by the University of Milan Institutional Ethics Committee. Informed consent was obtained from all subjects. Inclusion criteria were (i) partial edentulism, (ii) absence of local inflammation, (iii) absence of oral mucosal disease, (iv) adequate oral hygiene, (v) recovery time of at least 6 months for patients subjected to tooth extractions, and (vi) adequate bone volume at the implant site (enough for placement of an implant at least 3.3 mm

in diameter and 8 mm in length) evaluated by intraoral periapical radiographs and clinical evaluation. Exclusion criteria were (i) systemic diseases (such as heart, coagulation, and leukocyte diseases or metabolic disorders), (ii) a history of radiation therapy in the head and neck region, (iii) current treatment with steroids, (iv) neurological or psychiatric handicap that could interfere with good oral hygiene, (v) immuno-compromised status, including infection with the human immunodeficiency virus, (vi) severe clenching or bruxism; (vii) smoking habit (415 cigarettes/day); (viii) drug or alcohol abuse; and (ix) inadequate compliance. Sample characteristics

All the 45 patients included in the study were rehabilitated with cantilever implantsupported prostheses and followed yearly for a mean period of 8.2 years from prosthesis installation. Patients’ characteristics are reported in Table 1. A total of 116 implants (Institute Straumann, Waldemburg, Switzerland) supported 59 bridges, yielding a mean number of 1.3 FPD and 2.5 implants/patient and 2 implants/bridge (Table 2). Of the 59 FPDs followed, 32 had a mesial while 27 had a distal cantilever. A natural dentition or teeth-supported bridges were opposite to 45 cantilever FPDs, while the other 14 chewed against another implant-supported bridge. Thirty-three cantilever FPDs were located in the upper jaw. Table 3 presents the distribution of the Table 2. FPDs characteristics Number Cantilever location mesial/distal Mean cantilever length in mm (SD) Jaw (maxilla/mandible) Opposite dentition (natural/ implant) Mean number implants (range)

59 32/27 6.1 (1.3) 33/26 45/14 2 (1–3)

FPDs, fixed partial dentures; SD, standard deviation.

Table 1. Patient sample characteristics Subjects treated Unavailable to follow-up Subjects followed Mean age (Standard deviation) Gender (male/female) Mean years of follow-up (range) Mean number of bridges (range)

59 14 45 64 (13) 18/27 8.2 (1–12) 1.3 (1–3)

Table 3. Distribution of FPDs (n ¼ 59) according to number of implants and cantilever location Number of implants

Mesial cantilever

Distal cantilever

1 2 3

7 23 2

2 20 5

FPDs, fixed partial dentures.

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Romeo et al  Implant-supported fixed cantilever prosthesis in partially edentulous jaws

Table 4. Mean FPDs’ cantilever length (SD) according to cantilever location and jaw Mesial Distal

Upper

Lower

5.6 (1.3) 7.3 (0.8)

4.9 (1) 6.7 (0.9)

FPDs, fixed partial dentures; SD, standard deviation.

Table 5. Distribution of placed implants (n ¼ 116) according to position in the jaw Implant position in the jaw 1 2 3 4

5

6

7 Total

Maxilla 0 1 7 22 27 8 1 66 Mandible 0 0 1 5 14 24 6 50

Table 6. Distribution of placed implants according to length and jaw Implant Maxilla Mandible Total (%) length (mm) 8 10 12 14 Total

11 38 15 2 66

2 41 7 0 50

13 79 22 2 116

(11%) (68%) (19%) (2%) (100%)

Table 7. Distribution of placed implants according to diameter and jaw Implant Maxilla Mandible Total (%) diameter (mm) 3.3 4.1 4.8 Total

12 52 2 66

3 47 0 50

15 99 2 116

(13%) (85%) (2%) (100%)

FPDs according to the number of implants supporting and the location of the cantilever. Most FPDs (n ¼ 43) were supported by two implants. The mean cantilever length was 6.1 mm. Besides, the mean length of the cantilever according to the location in the jaw and direction is reported in Table 4. No statistically significant difference was detected between the locations. The distribution of the implants according to the length, diameter and jaw position is depicted in Tables 5–7. The most frequent position for implants in the upper jaw was at the premolars, while for the lower jaw the second premolar and the first molar were the most common locations. The implants more frequently chosen from the clinicians were 10 mm in length and 4.1 mm in diameter.

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Prosthetic treatment

After a minimum of 3 months from fixture placement, patients were called back for a pre-prosthetic evaluation. After healing screw removal, the abutments were screwed to the implants with a 35 N torque. Solid or OCTA abutments with cast-to parallel gold copings were used for cemented prostheses (41), and OCTA abutments with only castto gold copings were used for screw-retained prostheses (18). All the cantilever prostheses were made of gold alloy and porcelain, and cemented (46) or retained by a titanium screw (13), in agreement with the manufacturer’s instructions. Soldering was never performed. Prostheses fixation was performed by zinc ox phosphate or zinc– eugenol oxide cement (cemented prostheses) and an electronic or manual dynamometer (screw-retained prostheses).

Fig. 1. RX of cantilever fixed prosthesis supported s by Straumann implants – 0 year-load.

Clinical assessment

At follow-up examinations, peri-implant tissues and implant health status were evaluated using the following parameters: (i) suppuration (presence/absence) (Mombelli et al. 1987); (ii) plaque index (score 0– 3) in agreement with Mombelli et al. (1987) and Mombelli and Lang (1994); (iii) probing pocket depth and probing attachment level (Lang et al. 1994); (iv) bleeding on probing (score 0–3) (Mombelli et al. 1987); (v) mobility index (score 0–2) (Mombelli et al. 1987) or by using the Periotest (Siemens AG, Bansheim, Germany); (vi) percussion with evidence of metal (functional ankylosis) or dull sound (fibrous-integration in the area of placed implants) (Esposito et al. 1998); and (vii) persistent pain or paresthesia. All cases showing peri-implant inflammation were treated according to the guidelines suggested by Mombelli and Lang (1998).

Radiographic examination

At follow-up examination, intraoral periapical radiographs were taken and subsequently stored on a PC. The radiographic images were then analyzed with a software program (Image J, NIH, Montgomery County, MD, USA) to measure the following parameters:  

cantilevers’ length. peri-implant bone resorption (Marginal Bone Loss, MBL) referred to implant

Fig. 2. RX of cantilever fixed prosthesis supported s by Straumann implants – last control.

loading. Measurements were made at the mesial and distal side of each implant.

Intraoral periapical radiographs were performed at baseline (time of loading) and at every follow-up evaluation (Figs 1 and 2). The analysis included baseline and the last follow-up examination for each implantsupported FPD. Performing intraoral periapical radiographs and loading them on a PC were considered with data found in the literature. A standardized measurement protocol was adopted (Benn 1990; Weber et al. 1992; Esposito et al. 1993; Bra¨gger 1994; Romeo et al. 2003).  c 2009 John Wiley & Sons A/S


Romeo et al  Implant-supported fixed cantilever prosthesis in partially edentulous jaws

Fig. 3. Measuring setting system: a vertical red line (distance between the implant neck and the most apical point of each fixture, along an ideal line, parallel to the long axis of the same fixture), a vertical yellow line (implant neck height) and a horizontal red line (implant neck diameter) are drawn.

Fig. 4. Cantilever length measuring: A point (the most coronal part of the metal connector), vertical red lines (tangent to the A and B points and perpendicular to the line crossing the occlusal plane of the adjacent teeth), B point (the farthest metal connector point), and yellow line A–B (cantilever length) are drawn.

The measurement system setting was performed by considering the distance between the implant neck and the most apical point of each fixture, along an ideal line running parallel to the long fixture axis (Fig. 3). This procedure was carried out for each intraoral periapical radiograph by analyzing some reference measurements such as (i) implant neck height equal to 2.8 mm or 1.8 mm for Standard and Standard Plus s Straumann implants (Institute Straumann, Waldemburg, Switzerland), respectively, and (ii) implant neck diameter equal to 4.8 mm s for Regular Neck Straumann implants (Institute Straumann, Waldemburg, Switzerland) (Romeo et al. 2003). Figure 4 refers to cantilever length measurement. A single operator performed all measurements (I.F.). Implants and FPDs’ success, survival and failure

Implant success was defined according to the following parameters (Albrektsson  c 2009 John Wiley & Sons A/S

et al. 1986; Buser et al. 1990; Roos et al. 1997; Noack et al. 1999): (i) bone resorption in measurement areas within 1 mm, during the first year after implant placement, and 0.2 mm/year in subsequent years; (ii) no mobility and symptoms concerning abutments and implants; and (iii) probing depth within 3 mm for each implant site (mesial, distal, buccal, and lingual–palatal). Implant survival rate calculation included as survivors: (i) implants supporting functional and asymptomatic prostheses although showing a mean bone loss rate that exceeded the maximum limits established by the present study (within 1 mm during the first year after implant placement, and 0.2 mm/year in subsequent years). (ii) implants showing clinical and radiographic signs of peri-implantitis (subsequently treated). Clinical mobility was mandatory for implant removal. Implants showing mobility were regarded as ‘failures’. Prosthetic failure was defined in the presence of one of the following conditions: (i) prosthetic framework permanent warpage or breakage, (ii) abutment or implantto-abutment connecting screw breakage and (iii) framework-to-abutment fixing screw impairment. Prosthetic complication was attributed to the following events: (i) prosthesis detachment, (ii) abutment–framework screw unscrewing and (iii) porcelain veneer permanent warpage or breakage. An FPD not presenting any of the previous conditions (failure or complication) was defined as a ‘success’ while an FPD presenting any complication was defined as a ‘survivor’.

adopting as a dichotomous event implant loss and implant failure as defined previously. All testing was performed using SPSS 16.0 software package (SPSS inc., Chicago, IL, USA). A multilevel regression model was constructed to analyze the factors influencing MBL at three levels: subject as the highest, and then implant and site. Bridge was excluded from the model as a level as the variance between bridges was not significantly different from zero. The database consisted of 45 subjects, 116 implants and 232 sites. Bone-level changes related to implant margin at the follow-up examination represented the dependent variable. The normality of the residuals at the different levels was also tested. The factors tested in the model were follow-up time at the subject level, cantilever location (mesial or distal) and length, implant location in relation to the cantilever (adjacent or not), opposite dentition type (natural teeth or implant-supported restoration) and jaw at the implant level and location of the site in relation to cantilever (adjacent or not) at the site level. Regression coefficients were estimated using iterative generalized least squares. Nested models were tested for significant improvements in model fit by comparing the reduction in  2LL (  2 log likelihood) with a Chi-squared distribution. A statistical package specifically designed for multilevel modelling (MLwiN 2.10, r Center for Multilevel Modelling, University of Bristol, UK) was used.

Statistical analysis

Success, complications and failures

For description of the data, mean values, standard deviations and frequencies for nominal or ordinal data were calculated at the subject, bridge and implant level. The primary outcome variable considered was the presence of complications at the subject and at bridge level; the secondary outcome variable was MBL. Differences in terms of the frequency of complications between mesial and distal cantilever location and between natural and implant supported opposite dentition were tested using Fisher’s exact test at the bridge level. A life table was computed

Results An 8-year mean follow-up showed the following clinical outcomes (Tables 8 and 9): Table 8. Number and prevalence of patients and implants with or without complication Patients

Implants

Number % Number % No 36 complication Complication 9 Implant 0 failure Total 45

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80

105

90.5

20 0

11 0

9.5 0

100

116

100

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Romeo et al  Implant-supported fixed cantilever prosthesis in partially edentulous jaws

Table 9. Outcome of FPDs Patient

No complication Complication FPD failure Total

FPDs

Cantilever location

Opposite dentition

Number

%

Number

%

M

%

D

%

Natural teeth

%

Implant Fixed Prosthesis

%

25 20 0 45

55.6 44.4 0 100

34 25 0 59

57.7 42.3 0 100

21 11 0 32

65.7 34.3 0 100

13 14 0 27

48.1 51.9 0 100

29 18 0 47

61.7 38.3 0 100

5 7 0 12

41.7 58.3 0 100

FPDs, fixed partial dentures; M, mean; D, drop-out.

Table 10. Life table analysis for implant success Interval (years)

Implants at start of interval

Early failures

Loaded implants

Drop out

Implants under risk

Survivals during interval

Success rate (%)

Cumulative success rate (%)

0–1 1–2 2–3 3–4 4–5 5–6 6–7 7–8 8–9 9–10 10–11 11–12

116 112 112 112 110 107 102 94 85 72 57 45

0 0 0 0 0 0 0 0 0 0 0 0

116 112 112 112 110 107 102 94 85 72 57 45

0 0 0 0 1 4 7 8 13 15 12 0

116 112 112 112 109.5 105 98.5 90 78.5 64.5 51 45

4 0 0 2 2 1 1 1 0 0 0 0

96.6 100 100 98.2 98.2 99 99 98.9 100 100 100 100

96.6 96.6 96.6 94.8 93.1 92.2 91.4 90.5 90.5 90.5 90.5 90.5

Table 11. Life table analysis for implant survival Interval (years)

Implants at start of interval

Early failures

Loaded implants

Drop out

Implants under risk

Failures during interval

Survival rate (%)

Cumulative survival rate (%)

0–1 1–2 2–3 3–4 4–5 5–6 6–7 7–8 8–9 9–10 10–11 11–12

116 116 116 116 116 115 111 104 96 83 68 56

0 0 0 0 0 0 0 0 0 0 0 0

116 116 116 116 116 115 111 104 96 83 68 56

0 0 0 0 1 4 7 8 13 15 12 0

116 116 116 116 115.5 113 107.5 100 89.5 75.5 62 56

0 0 0 0 0 0 0 0 0 0 0 0

100 100 100 100 100 100 100 100 100 100 100 100

100 100 100 100 100 100 100 100 100 100 100 100

 implant complications were recorded for 80% of treated patients and 90.5% of placed implants.  Complications were observed for 11 implants in nine patients, with nine showing radiographic bone resorption and two cases showing clinical signs of peri-implantitis 4 years after implant loading. Causal mechanical therapy and local antibiotic therapy followed by guided bone regeneration were performed. No further pathologic bone loss progression was observed at the subsequent control visits.

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No implant failure was observed. Prosthetic success was recorded for 55.6% of patients and 57.7% of prostheses. Three prosthesis decementations were observed, so that prostheses were fixed again with zinc ox phosphate or zinc– eugenol oxide cement. Besides, 17 patients showed an esthetic veneer fracture for a total of 22 partial prostheses; these FPDs were veneered and put in function again. No prosthetic failure was observed during the follow-up examinations.

Life tables on implant survival and implant success are depicted in Tables 10 and 11. During the follow-up period, 27 patients with 60 implants were considered to be drop-outs. The patients moved elsewhere and could not be reached.

Mean bone loss

In Table 12, the mean bone loss at the FPD level evaluated on the radiographs is reported according to cantilever location and jaw. The bone loss varied between 0.8 mm and 1.2 mm and no statistically significant  c 2009 John Wiley & Sons A/S


Romeo et al  Implant-supported fixed cantilever prosthesis in partially edentulous jaws

Table 12. Mean FPDs’ bone loss in mm (SD) according to cantilever location and jaw Mesial Distal All

Upper

Lower

All

1.2 (0.3) 1.2 (0.5) 1.2 (0.4)

1 (0.2) 0.8 (0.4) 1 (0.3)

1.1 (0.2) 1 (0.5) 1.1 (0.4)

FPDs, fixed partial dentures; SD, standard deviation.

difference was detected between the various groups. Multilevel model

An analysis to explore the covariates influencing the bone loss at the implant site level was performed. It started from an empty modelthat did not include any covariate (Table 13). The model with no covariates included yielded a mean value of 1.1 mm for the bone loss and a total unexplained variance of 0.41 (28% attributed to variation between sites, 42% between implants and 30% between patients). None of the predictors included in the final model (years of follow-up, cantilever location, jaw, cantilever length, opposite teeth and location of the implant referred to cantilever, location of the site referred to cantilever) showed a significant impact on the bone loss between baseline and the follow-up examination. A borderline significance (P ¼ 0.055) was detected using years of follow-up as a covariate, with a mean yearly bone loss of 0.04 mm.

Discussion A meta-analysis performed by Pjetursson and Lang (2008) summarized the results on survival and complication rates of different designs of fixed dental prostheses (FDP) published in a series of systematic reviews. It was concluded that when planning prosthetic rehabilitations, conventional endabutment tooth-supported FDP, solely implant-supported FDP or implant-supported SC should be the first treatment option. Only as a second option, because of reasons such as financial aspects patient-centered preferences or anatomical structures, cantilever tooth-supported FDP, combined tooth-implant-supported FDP or resinbonded bridges should be chosen. On the contrary, different conclusions can be drawn from the present report: data on medium MBL around the implants  c 2009 John Wiley & Sons A/S

Table 13. Multilevel model with marginal bone level as the dependant variable Fixed part Intercept Predictors Follow-up (centered) Cantilever location (mesial) Jaw (upper) Cantilever length (centered) Opposite (teeth) Implant location (close to cantilever) Site (close to cantilever) Random part Subject level variance Implant level variance Site level variance  2 loglikelihood:

supporting a cantilevered fixed prosthesis met the success criteria of Albrektsson et al. (1986), Buser et al. (1990) and Roos et al. (1997) so that the presence of this prosthetic device should not considered as critical in increasing peri-implant bone resorption. Nevertheless, based on post hoc power analysis the authors agreed that a larger sample is required to confirm these results. These evidences agree with the findings of Wennstro¨m et al. (2004): they retrospectively measured the amount of marginal bone loss that took place at free-standing, cantilever implant-supported FPDs over a 5-year period of functional loading. This amount of bone loss was by all standards small and well below the criteria of a proper implant system. It was found that cantilever FPDs had a tendency to show a greater mean peri-implant bone loss and a higher frequency of implants with 1 mm of bone loss than FPDs without cantilevers. Whether this tendency indicated a potential, negative effect on the peri-implant bone stability by the inclusion of the cantilever extensions may be argued, because the small overall amount of bone loss observed may have hampered the possibility to detect a statistically significant difference between cantilever FPDs and FPDs without cantilevers. In fact, factors such as jaw of treatment, abutment length, implant length and type of prosthetic material used (Naert et al. 2001) may influence the amount of bone loss that takes place at endosseous implants. On the contrary, there are no available studies on the behavior of mesial cantilever prostheses as compared with distal cantile-

Empty model

SE

Final model

SE

 1.108

0.07

 0.956

0.245

 0.038  0.151  0.158  0.061  0.033 0.062 0.028

0.02 0.17 0.153 0.063 0.194 0.09 0.044

0.119 0.162 0.110 338.571

0.047 0.037 0.015

0.122 0.173 0.111 344.117

0.049 0.039 0.015

NS NS NS NS NS NS NS

ver prostheses. It can be argued that biomechanical loads applied to the cantilever will be more intensive whether this is mesial or distal (Lundgren et al. 1989; Tashkandi et al. 1996). Hence, different compressive and tensive stress will be transferred to the implant-supported prostheses (considering sites, cantilever length and framework manufacture as being equal). However, the present study reported a nonsignificantly different mean MBL value for distal and mesial cantilever prostheses; the findings reported by Romeo et al. in 2003 were confirmed. Lundgren et al. (1994) showed the importance of receptors situated in opposite dentition. These receptors (mechanoceptors, baroceptors and nociceptors) are capable of perceiving a possible mechanical overload during mastication. Overloads should be controlled by neuromuscolar feedback systems; in cantilever implantsupported prostheses, no control could be exercised over biomechanical forces during mastication. However, in agreement with the results of 2003 (Romeo et al.), the present study does not seem to highlight the importance of these periodontal ligament receptors. In fact, no significant differences of peri-implant bone resorption were found between different types of opposite dentition. On the contrary, the frequency of prosthetic complicances was significantly higher for cantilever prostheses opposed to implant-supported rehabilitations than to natural teeth (58.3% vs. 38.3%). Nevertheless, the statistical power of these evidences could be low; in fact, a more large and significant sample is required to confirm such a finding.

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The present study showed a cantilever prostheses survival rate of 100%: this is consistent with that of 98% obtained by the previous report of. Similar results were published by Shackleton et al. (1994) and Naert (1992) (respectively, 100% and 96.5% for cantilever total fixed prostheses after 7 years). Also, the findings of Albrektsson et al. (1988) were in agreement with these findings (respectively, a survival rate of 99.7% and 96.1% for mandibular and maxillary site). It must be considered that a cantilever fixed prosthesis will guarantee a good medium to long prognosis if a number of rules are observed: cantilever length (Neart et al. 1992; Shackleton et al. 1994; White et al. 1994; Young et al. 1998) and correct prosthesis function and occlusion (Beyron 1973; Skalak et al. 1983; Lundgren et al. 1987; Falk et al. 1989; Taylor 1991; Hobkirk & Psarrios 1992; Stewart et al. 1992; Hoshaw & Brunsky 1993; Benzing et al. 1995; Matsui et al. 1996). The data obtained in the present study on cantilever length are consistent with the limits recommended in the literature (Neart et al. 1992; Shackleton et al. 1994; White et al. 1994; Young et al. 1998). In the current study, the low prosthetic success rate could be explained by longterm prostheses observation; during this follow-up period, a likely abrasion of the residual natural teeth has been followed by a change in the patient occlusion. The effect of this trauma on an implant-supported prosthesis could be an overload on the porcelain veneer. The high number of porcelain fractures (22) reported by the authors could be associated with this comment. The long-term follow-up and the more selective success parameters can ex-

plain the different prosthetic success rates found by Romeo et al. (2003) and in the present report (98% after a 4-year mean follow-up vs. 57.7% after an 8-year mean follow-up). Besides, Romeo et al. (2003) evaluated Straumann and Bra˚nemark implants together, while the present study followed Straumann implants only. A recent systematic review by Berglundh et al. (2002) reported a mean 5-year incidence/patient of 0.24 technical complications calculated for FPDs supported by implants. Further, Bra¨gger et al. (2001) reported, from a 4-to 5-year follow-up of 40 implant-supported FPDs, seven cases of screw loosening and 11 cases of minor porcelain fracture (0.45 incidence/patient). These incidence/patient reports agree with the findings of the present study on cantilever fixed prostheses (12-year prosthetic success of 57.7%). Thus, there could be reasons to suggest that technical (prosthesis related) complications may not constitute a major obstacle in implant-supported restorative therapy involving cantilever extensions, provided that the occlusion as well as the bridge attachments are regularly examined and, if necessary, adjusted. Moreover, the technical complication rate was analyzed by De Boever et al. (2006); 172 fixed reconstructions (317 prosthetic units), made on 283 ITI implants in 105 patients (age range 25–86 years) with a minimum follow-up period of 40 months, were included in the study. The mean evaluation time was 62.5  25.3 months. There were 80 single crowns and 92 different types of FPDs. Fifty-five prosthetic interventions were needed on 44 constructions (25%), of which 88% were in the molar/premolar region. The percentage of complications

that occurred in 3–4 unit FPDs (and in FPDs with an extension) was 35% and 44%, respectively. These evidences agree with the findings of the present study. However, Kreissl and co-workers prospectively evaluated the incidence of the most common technical problems, namely screw loosening, screw fracture, fracturing of veneering porcelain and framework fracture in implant-supported FPDs, and assessed the survival and success rate (event-free survival) after 5 years of function. Two-hundred and five implants were placed and restored with 112 implant-supported FPDs; 23 of these were cantilever FPDs. The overall complication incidence after 5 years was the highest in the group of FPDs with cantilever, which showed the lowest success rate 68.6% when compared with that of FPDs without cantilevers (86.1%). The authors state that a long-term evaluation of these results is required; also, prosthetic success parameter homogeneity could help to compare the study results available in the literature. The study results led to the following conclusions:

posterior edentulism. Journal of Oral Rehabilitation 29: 350–356. Barbier, L. & Schepers, E. (1997) Adaptive bone remodeling around oral implants under axial and non-axial loading conditions in the dog mandible. The International Journal of Oral & Maxillofacial Implants 12: 215–223. Becker, C.M. & Kaiser, D.A. (2000) Implant-retained cantilever fixed prosthesis: where and when. Journal of Prosthetic dentistry 84: 432–435. Benn, D.K. (1990) A review of the reliability of radiographic measurements in estimating alveolar

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(i)

the position or the length of the cantilever did not exert any influence on the prognosis of implant-supported FPDs and on the marginal bone level. (ii) the position of the implant or the site referred to the cantilever did not influence the bone loss at the follow-up examination. (iii) natural teeth or fixed prosthesis on natural teeth opposite dentition is not an a priori improving prognosis factor for implants supporting a cantilevered prosthesis.

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