Implant restorations in partially edentulous patients are a predictable option for esthetically and functionally replacing missing dentition. In patients with long-span edentulous situations, which are not conducive for placement of an adequate number of supporting implants, tooth-to-implant–connected prostheses have been described as a possible treatment option.
The advantages of tooth-to-implant–supported prostheses included increased mechanoreception, additional support for the total load on the dentition, increased treatment possibilities for the restorative dentist, reduced cost of teeth replacement, and the elimination of cantilevering.1,2 The bone surrounding the cantilevered fixed partial denture (FPD) is subjected to increased torquing forces that may be associated with the failure of the bone-implant interface or bone loss around the FPD.3 During the first 5 years of function, the tooth-supported cantilever FPDs were reported to have a significantly higher annual failure rate than the tooth-to‐implant–supported FPDs.4 However, the tooth-to-implant–supported prosthesis has disadvantages that included increased need for repair and maintenance1,5,6 and increased periodontal and prosthetic complications.7 Furthermore, the difference in mobility between the teeth and osseointegrated implants may result in excessive stresses on the implant and subsequent marginal bone loss or osseointegration failure.7
Some clinicians advocated nonrigid tooth-to-implant connection to compensate for the difference in mobility,8–10 whereas others advocated a rigid connection because of the decreased frequency of mechanical failures.11,12 However, with the reported increased need for repair and maintenance of these combined prosthesis, some also advocated that implants and teeth should not be connected.1,5,6 Thus, with the absence of clear guidelines and conflicting reports, the clinician is faced with the controversy of whether connecting implants to natural teeth is a treatment option with an adequate success or survival rate.
The aim of this systemic review was to perform a comprehensive overview of systematic reviews and meta-analyses pertaining to fixed dental prostheses that use tooth-to-implant connections to determine whether this is a viable treatment option when restoring the partially edentulous patient.
Is splinting an implant to natural dentition a viable option?
A systematic search was conducted using PubMed, EMBASE, Web of Science, Cochrane Library, and Google Scholar for systematic reviews and meta-analyses of tooth-to-implant–supported FPDs from inception until January 2017. The search keywords included the following: “tooth,” “teeth,” “implant/s,” “denture,” “fixed partial denture/s,” “prostheses and implants,” “splinted,” “supported,” “classification,” “systematic,” and “meta.” The gray literature was also searched on Google Scholar using the advance search to find articles with the words “implant/s, teeth, tooth” and at least one of the words “systematic review” or “meta-analysis.” Hand searching was also conducted on the reference list of identified systematic reviews and meta-analyses.
Inclusion and Exclusion Criteria
- The selected review must be a systemic review or meta-analysis.
- The focused questions or review objectives must pertain to tooth-to-implant–supported FPDs in humans. Tooth-to‐tooth–supported and implant-to‐implant–supported FPDs were excluded.
- Only systematic reviews that reviewed >5 studies were included.
- Based on the AMSTAR checklist,13 only studies scoring greater than 3 of 11 were included.
Screening and Data Extraction
Two reviewers (R.J.F. and M.T.) independently screened the “Title and Abstract.” Articles were selected based on the inclusion criteria. Two reviewers (R.J.F. and M.T.) independently analyzed the full text. The data extraction form was previously pilot-tested before being used independently by 2 reviewers (R.J.F. and M.T.) for data extraction. Disagreements were resolved by discussion with another reviewer (D.P.D.).
Assessment of Quality of Systematic Reviews and Meta-analyses
The selected reviews were rated independently for methodologic quality by 2 reviewers (R.J.F. and M.T.) using the AMSTAR checklist.13 Studies were rated to be of high quality (scoring 8–11 of a total of 11 points), of moderate quality (scoring 4–7 of 11 points), or of low quality (scoring 0–3 of 11).14 Discrepancies was resolved by discussion with another reviewer (D.P.D.). Studies scoring low (less than 3 of 11) were excluded. Table 2 reported details of the selected reviews and their AMSTAR ratings.
The initial search yielded 369 reviews in PubMed, 248 in Web of Science, 49 in EMBASE, 63 in Cochrane Library, and 27 in Google Scholar. After abstract and title screening, 2 reviews were selected from PubMed, 5 from Web of Science, 3 from EMBASE, 2 from the Cochrane Library, 5 from Google Scholar, and 1 from hand searching the reference list of the selected reviews. After elimination of the duplicates, 8 remained for full-text analysis. After full-text analysis, 5 were selected for data extraction (Fig. 1).
The 5 selected reviews (Table 1) also provided meta-analytic data.4,15–18 Of these 5 meta-analyses, 2 analyzed data on the survival rates of combined tooth-to‐implant–supported FPDs, implant-supported FPDs, and implant-supported single crowns.4,16 Only 1 of the 2 meta-analyses further analyzed tooth-supported FPDs and tooth-supported cantilever FPDs.4 None of the reviews analyzed the data for implant-supported cantilever FPDs.
Most of the selected systematic reviews reported on the clinical outcomes of tooth-to‐implant–supported FPDs in more than 1 area. All the articles reported on the survival rates of tooth-to-implant FPDs,4,15–18 4 articles reported on biological complications,4,15,17,18 4 articles reported on technical complications,4,15,17,18 and 4 articles on the intrusion of the abutment tooth.4,15,17,18 The selected reviews scored mostly moderate AMSTAR ratings (Table 1).
All the selected reviews reported on the survival rates of tooth-to-implant FPD (Tables 2 and 3); most reported a 5-year survival rate for tooth-to-implants FPD ranging from 90.1% to 95.5%4,15,18 and a 10-year survival rate ranging from 77.8% to 82.1%.4,15,18 The reported survival of abutment teeth ranged from 89.4% to 100%.15,17,18 The reported survival of abutment implants ranged from 97.5% to 98.0%.15
Four reviews reported on the biological complications (Tables 2 and 3). The most reported complications were periapical lesions and caries. Other biologic complications included tooth fractures, loss of osseointegration, periodontal pathology, and fistulas.17 One review reported the cumulative rate of 11.7% at 5 years for biologic complications involving combined tooth-to-implant–supported FPDs.18
Four reviews reported on technical complications (Tables 2 and 3). The most frequent technical complications include porcelain occlusal fracture4,15,17,18 and screw loosening.4,15,17 Other technical complications included prosthesis remake, facing fracture and replacement of composite plug, cement failure and screw fractures, occlusal interferences requiring adjustment and material replacement, and loss of retention.17
Four reviews reported on tooth intrusion (Tables 2 and 3). Tooth intrusion was reported in abutment teeth from 0.0% to 5.2%.15,18 One review conducted a meta-analysis on the intrusion between the rigid connection group and the nonrigid connection group of the tooth-to‐implant–supported FPDs.17 In the nonrigid tooth-to-implant FPDs, there were conflicting reports of intrusion in abutment teeth.17 However, no intrusion was detected in the abutment teeth of rigidly connected tooth-to-implant FPDs.17
Most of the studies included in the selected reviews4,15–18 were not specific about categorizing the pontic span of the FPDs and included a wide range of FPD span. Most did not include a description of the FPD span of the evaluated FPDs. Only 1 systematic review17 included a description of the span of the FPDs evaluated in their selected studies. Some of the studies included in this systematic review17 reported only short-span FPDs, or only long-span FPDs, or no data on the number of units; although most of the studies reported a mix of short- and long-span FPDs, with the short-span FPDs being the majority. Most of the studies included considered less than 3 units as a short-span FPDs. None of the systematic reviews selected in this overview specifically compare the survival between short-span and long-span FPDs.
Treatment planning difficulties involving long-span edentulous situations that were not conducive for placement of an adequate number of supporting implants included anatomical limitations in the posterior areas or an inadequate bony alveolar housing for implants. Thus, when restoring implant segments in these areas, splinting of dental implants to natural teeth may be the better option.
In the short term, the ranges of the failure rate of tooth-to-implant–supported FPDs reported in this overview of 4.5% to 9.9%4,15,18 was not substantially different from the failure rate of 5.9% reported in a systematic review for solely implant-supported FPDs after 5 years.19 In a review by Goodacre et al,20 this was also not substantially different from the mean implant loss rate of 6% in the maxilla or 6% in the mandible for the solely implant-supported FPDs. In another systematic review by Pjetursson et al,4 the reported 5-year failure rates of 6.2% for solely tooth-supported FPDs and 4.8% for solely implant-support FPDs were also within the reported ranges of the tooth-to-implant–supported FPDs. However, after 10 years, the failure rates reported in this overview were 17.9% to 22.2%4,15,18 for the tooth-to‐implant–supported FPDs. These were much higher than the failure rate of 13.3% reported in the systematic review for solely implant-supported FPDs4,19 and the failure rate of 10.8% reported for solely tooth-supported FPDs.4 Thus, the length of time the tooth-to‐implant–supported FPDs is in function in the mouth seems to be a contributing factor to the clinical failures reported in this overview. The 5-year survival rates of 90.1% to 95% are higher than 10-year survival rates of 77.8% to 82.1%.4,15,18 However, none of the systematic reviews recognized the potential of aging-related medical conditions such as osteoporosis and diabetes, or the effects of medication such as steroids, bisphosphonates, and antineoplastic drugs may account for the observed survival rate decline from 5 to 10 years. Mamalis et al15 evaluated the summary estimate proportion for abutment loss for teeth and implants at 5 years and at 10 years; the study reported statistically higher abutment tooth loss than implant loss, suggesting that the survival rates of the tooth-to‐implant–supported FPDs may be limited by the failure rate of the abutment teeth.
Biological complications can compromise the integrity and stability of tooth-to-implant–supported FPDs, as well as increase the incidence of unscheduled patient appointments. When vital teeth are used as an abutment in either a solely tooth-supported18 or tooth-to‐implant–supported FPDs,17 loss of pulp vitality and caries are frequently reported biological complications.4,17 Caries leading to periapical lesions or caries requiring aggressive abutment preparation leading to pulpal pathosis are dynamic factors that develop over time. Other biological complications like periimplantitis,21 loss of osteointegration, fistulas, and periodontal pockets are also related clinical issues.4,15,17,18
Good oral hygiene is crucial for the longevity of the implant.22 Periimplant complications can include dehiscence, gingival inflammation, and fistulas.23 Brägger et al24 reported that 9.6% of implant for tooth-implant–supported FPD developed periimplantitis after a 5-year observation period. When the same cohort was followed for 10 years, 13.6% of the implants had to be treated for periimplantitis.25 However, this does not consider whether an effective periodontal and implant maintenance protocol was implemented after delivery of the tooth-to‐implant–supported FPD. An effective maintenance program may reduce periimplantitis-related biological complications. Patient factors related to oral hygiene, maintenance compliance, diet, bruxism, and cleansability of the prosthetic design must be considered in implant treatment planning. High caries risk, parafunction, and physical or mental inability to maintain oral hygiene may be contraindications to connecting implants to natural teeth.
Bone loss around implants is also a concern; Naert et al5,6 reported more bone loss around rigidly connected implants than nonrigidly connected implants of tooth-to‐implant–supported FPDs. Naert et al5 also reported higher marginal bone loss around tooth-to-implant–supported FPDs compared with implant-to-implant–supported FPDs after 6 months of loading. However, conflicting results were reported by Gunne et al26 and Lindh et al27; both studies reported more marginal bone loss around implant-to-implant–supported FPDs compared with tooth-to‐implant–supported FPDs.
The most frequently reported technical complications for tooth-to-implant–supported FPDs were porcelain fracture,4,15,17,18 loss of retention, and screw loosening.4,15,17 In tooth-to-implant–supported FPDs, Tsaousoglou et al17 reported occurrence of “porcelain occlusal fracture” at 16.6%. In comparison, Pjetursson et al4 reported that the solely tooth-supported FPDs had significantly lower 5-year risk of ceramic fracture at 2.9% compared with 8.8% for solely implant-supported FPDs. Furthermore, Sadid-Zadeh et al33 reported that the incidence of veneer material fracture for solely implant-supported FPDs was 12.4% over a mean of 5.7 years. Porcelain veneer fracture was also identified as the most common complication for solely implant-supported FPDs.28
For implant restorations using screw retention, Tsaousoglou et al17 reported occurrence of screw loosening for tooth-to-implant–supported FPDs at 15%. And Pjetursson et al4 reported screw loosening at 5.6% for solely implant-supported FPDs compared with 6.9% for tooth-to-implant–supported FPDs. Furthermore, Lang et al18 reported the incidence of abutment or screw loosening at 3.6% at 5 years, which increased to 26.4% at 10 years.
For implant restoration and tooth restorations using cement retention, loss of prosthesis retention or luting cement failure is another technical complication. Pjetursson et al4 reported 5-year rates of loss of retention at 5.7% for solely implant-supported FPDs and at 7.3% for tooth-to-implant–supported FPDs. In general, overall technical complications were within comparable ranges for solely implant-supported FPDs and tooth-to-implant–supported FPDs,4 and the incidence increased with the length of time the prothesis is in function.18
For tooth-to-implant–supported FPDs, rigid connection consists mostly of vertical or horizontal locking screws and nonrigid connection of telescopic crowns or sliding attachments. Nonrigid tooth-to-implant–supported FPDs were reported to encounter significantly more technical complications than rigid tooth-to-implant–supported FPDs.29 Nickenig et al29 reported similar survival outcomes for tooth-to-implant–supported FPDs and implant-to-implant–supported FPDs when rigid connections are used. Therefore, the choice of a rigid connection for tooth-to-implant–supported FPDs connection may be preferred although fabrication of the rigid connection may be technically more demanding.
Furthermore, a meta-analysis by Tsaousoglou et al17 showed that 8.19% of nonrigidly connected teeth intruded compared with none of the rigidly connected teeth. Cordaro et al30 reported similar findings. Fugazzotto et al31 further reported that for rigid tooth-to-implant–supported FPDs, all observed cases of intrusion were associated with lost or broken attachment fixation screws. Similarly, Naert et al6 reported that almost 50% of tooth intrusion were observed in patients with cement failures of abutments for tooth-to‐implant–supported FPDs. Kindberg et al32 also reported that all intrusion detected were associated with loosening or fractures of the rigid connection of the tooth-to-implant–supported FPDs.
This present overview is limited by the heterogeneity of the studies included in the selected systematic reviews. The included studies varied in the type of study (prospective or retrospective), the sample size, the follow-up periods, and the span of the fixed prostheses. However, the selected systematic reviews in this overview were mostly moderate in methodological quality; the number of studies that satisfied the inclusion criteria was low, and the overall quality of evidence of each included study was also low. Other limitations were that most of the selected systematic reviews included only studies published in English, which would not account for outcome differences in other parts of the world where the data were published in different languages. Another limitation was that the selected systematic reviews included mostly studies that were conducted under institutional conditions and may not necessarily translate to services provided under private practice conditions.
When comparing systematic reviews published from 2004 to 20074,18 with systematic reviews published from 2015 to 2016,16,17 some differences were noted. The survival rates reported in the reviews published from 2015 to 2016 were higher than those reported in the reviews from published 2004 to 2007. This may be due to improved FPD designs, reconstruction materials, implant surfaces, and treatment protocols implemented in the past decade. Implant connection design improvement from external connections to internal connections can substantially reduce implant complications. Implant-supported FPDs with external connections had a higher incidence of technical complications at 20.9% compared with implant-supported FPDs with internal connections at 9.3%.33
Other competing treatment options to the tooth-to‐implant–supported FPD included the implant cantilever FPD and the tooth cantilever FPD. The 2-unit and 3-unit implant cantilever studies34–36 reported high patient satisfaction and prosthetic success. However, these other options are not without disadvantages; some studies reported increased stresses on the bone adjacent to the cantilevered FPD.37,38 The increased stresses on the bone may adversely affect the bone-implant interface, contributing to bone loss around the implant, screw loosening, and implant or prothesis fracture.3 Furthermore, Rammelsberg et al39 reported increased risk of complications of the implant cantilever compared with the tooth-to‐implant–supported FPD. The increased stresses on the bone and accompanying complications increased with increasing lengths of the cantilever37,38; thus, in situations where there is a 2-tooth space between an implant and tooth, the tooth-to‐implant–supported FPD may be a better option.
A few systematic reviews and meta-analyses reviewed the survival and success of the cantilever implant prosthesis,3,40,41 and although the survival rate of the cantilever implant FPD was higher than that reported for the tooth-to‐implant–supported prosthesis, none of the published systematic reviews compared both cantilever implant and tooth-to‐implant–supported FPD in their evaluation of the data. Thus, this overview will not compare whether implant cantilever FPD is better than tooth-to‐implant FPD because systematic reviews with that focused question was not available in the literature. There was only 1 systematic review that compared the tooth cantilever FPD with the tooth-to‐implant–supported FPD.4 And this systematic review reported conflicting survival data between 5 and 10 years of the tooth cantilever FPD compared with the tooth-to‐implant–supported FPD. There is no clear data whether one treatment option is better than another; therefore, the implant cantilever FPD, the tooth cantilever FPD, and tooth-to‐implant–supported FPD may be treatment options, given the correct intra-oral conditions.
Currently, there is inconclusive clinical evidence as to whether tooth-to-implant–supported FPDs will have a higher success rate in some areas of the mouth under certain functional conditions, such as opposing dentures instead of natural teeth. All the systematic reviews included in this overview currently does not provide sufficient survival data between anterior and posterior tooth-to-implant–supported FPD, between long- and short-span tooth-to-implant–supported FPD, and between tooth-to-implant–supported FPD opposing natural teeth or dentures. Further clinical trials defining differences between regions of the oral cavity and prosthesis design need to be further evaluated.
The 10-year survival rates for tooth-to-implant–supported FPDs were lower than the 5-year survival rates. The tooth-to-implant–supported FPD survival was limited by the survival of the individual abutment tooth or implant supporting it. Interestingly, the failures and complications of solely implant-supported FPDs, the tooth-to-implant–supported FPDs, and the solely tooth-supported FPDs seen at the 5-year mark were within similar ranges as the tooth-to-implant–supported FPDs. However, at the 10-year mark, the solely implant-supported FPDs and the solely tooth-supported FPDs fared better than the tooth-to-implant–supported FPDs. This is probably due to the biologic and technical complications that can compromise the integrity and stability of the FPDs. These biological and technical complications were more at 10 years compared with 5 years. This recent trend of increased periimplant complications of implants at 10 years compared with 5 years also mimic what was reported when implants are splinted to teeth at the same time points. Another complication, intrusion of the abutment teeth, was reported more in the nonrigidly connected FPDs than in the rigidly connected FPDs. Intrusion may be reduced by using a rigid connection when connecting teeth to implants.
Because the oral environment and conditions of every patient is unique and, thus, when a patient condition precludes other FPD options that have higher survival rates, the tooth-to-implant–supported prosthesis can also be considered a possible option to provide long-term function in the patient's mouth. The purpose of this overview was to help clinicians determine whether tooth-to-implant–supported prosthesis could be a viable treatment option for each patient, after considering survival, complication risks, and unique patient anatomy. Thus, within the limits of this comprehensive overview, tooth-to-implant–supported FPDs can be considered a viable option to provide long-term function in the patient's mouth but should be considered a secondary option after considering other available options with higher long-term survival rates and lower complications. Furthermore, whatever the treatment option chosen, the clinician must also be prepared to manage the possible complications associated with the tooth-to-implant–supported FPDs during the lifetime of the prosthesis.
The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
This is a systematic overview of previously published systematic reviews and meta-analyses. It is neither a human nor an animal study.
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