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Basic and Clinical Research

Removal Rates of Dental Implants Placed in Conjunction With Autologous Bone and Xenogeneic and Synthetic Alloplastic Materials in Finland Between 1994 and 2012

Wolff, Jan DDS, Dr Med Dent*; Pyysalo, Mikko DDS; Antalainen, Anna-Kaisa DDS; Sándor, George K. MD, DDS, PhD§; Helminen, Mika MSc

Author Information
doi: 10.1097/ID.0000000000000320
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Dental implant treatment is a clinically validated and practice-proven therapy for partially edentulous patients and completely edentulous patients.1 Because most of the currently available dental implants can integrate with bone, the success rate of dental implant treatment is high.1

However, many patients undergoing implant treatment require alveolar augmentation because of a lack of bone tissue.2 The use of the autologous bone and bone substitutes for alveolar augmentation purposes has increased tremendously over the last few years because of functional and aesthetic demands.3 A large variety of augmentation materials and surgical techniques are available for alveolar augmentation. During the past decades, autologous bone grafts have been considered to be the gold standard and benchmark for bone substitutes. The major advantage of autologous bone grafts is that they incorporate certain properties that are beneficial when compared with other materials. Autologous bone is an organic cellularized material capable of osteogenesis, osteoinduction, and osteoconduction.4 Autologous bone grafts also provide good biomechanical structural support in procedures requiring the bridging of larger osseous gaps. However, harvesting autologous bone has its disadvantages: secondary donor site surgery, extended operating time, risk of complications, and limited amount of available graft material.5–7 The above shortcomings related to autologous bone have led to the development of 3 categories of augmentation materials, namely: allogeneic, xenogeneic, and synthetic alloplastic materials.8,9

Unlike autologous bone grafts, allogeneic grafts spare donor site morbidity and are readily available from human bone banks. They have become increasingly popular because of their biomechanical properties allowing surgeons to predictably sculptor the bone into any given form.10 To date, the most commonly used allografts in implant dentistry are freeze-dried bone allografts and demineralized freeze-dried bone allografts.11,12 Allografts are osteoinductive and osteoconductive and may be cortical and trabecular in nature. Although allografts are not without controversy because there are inherent risks of disease transmission and immunologic incompatibility, the risk of disease transmission can be virtually eliminated by freezing and irradiating the deceased donor bone.13

Xenografts comprise a large group of materials often used in implant dentistry and are commonly bovine derivatives. Xenografts undergo a series of processing steps to eliminate viable cells.14–16 These include extraction of all organic components, exposure to virucidal agents, and sterilization.16

Alloplastic materials are derived totally from synthetic components and are being used more frequently in implant dentistry.17 Alloplasts such as hydroxyapatite and tricalcium phosphate are resorbable. Alloplasts may be of granular rather than solid block form and vary in pore size, ranging from macroporous to microporous materials.18 Alloplastic materials may be crystalline or amorphous. All these versions of alloplastic materials have different properties and indications.19

The choice of specifically which of the 3 classes of materials is used depends on the location, size, and topography of the bony defect and working characteristics most preferred by the surgeon. To date, very little is known about the pattern of use of the different augmentation materials and the associated survival rate of dental implants placed using such materials.

Finland has a long history of long-term dental implant monitoring, and to the best of our knowledge, it is the only country in the world with a Dental Implant Register.1,20 The Finnish Dental Implant register has become a valuable source of information for the long-term assessment of dental implants even though Finland constitutes only a small part of the global dental implant market. The register provides comprehensive data on the number of implants placed and removed since the establishment of the register in 1994.1 Since the establishment of the registry, dentists in Finland have been obliged to provide detailed information on the placement and removal of all dental implants.

This study focused on data available from the Finnish Dental Implant Register regarding the removal rate of dental implants and their associated augmentation materials. The aim of the study was to determine the pattern of use of bone augmentation materials such as autologous bone or other biomaterials in conjunction with dental implant treatment and to determine whether this was associated with more implant removals than in those implants that were placed without the use of any augmentation materials.

Materials and Methods

A retrospective analysis of removed implants that had been placed using augmentation materials was conducted under section 4(1) of the Act on National Personal Data Registers kept under the Health Care System (556/1989, amendment 38/1993) and section 28(1) of the Finnish Act on the Openness of Government Activities (621/1999). The National Institute for Health and Welfare (THL) granted permission to access raw data in the Finnish Dental Implant Register from April 1994 to April 2012 for this register-based research project. All raw data were provided by THL. All data used in this study were not publicly available and were processed in accordance with the very strict rules and regulations provided by THL to the research team. The project was conducted at the Oral and Maxillofacial Unit, Department of Otorhinolaryngology, Tampere University Hospital and the Science Center, Pirkanmaa Hospital District, Finland.

After accessing and analyzing data provided by THL, it was apparent that data contained some misspelled product names. Some data concerning the time of implant placement or removal had been left out. In some cases, company names had been used instead of brand names. All data were checked and appropriately amended by the research team. The generic names of augmentation materials used in Finland between April 1994 and April 2012 are listed in Table 1.

Table 1
Table 1:
Generic Names of Synthetic and Xenogeneic Materials Used in Finland

The following factors were assessed: total dental implant placements, total implant removals, time from implant placement to removal, implant types, and augmentation materials used in the implant procedures.

Statistical analysis was performed using SPSS (IBM SPSS Statistics for Windows, Version 19.0; IBM Corp, Armonk, NY) and Excel (Microsoft Excel 2010). The differences in removal rates were analyzed with Chi-square tests. The Kruskal-Wallis test was used for comparisons of follow-up time distributions between augmentation groups.


A total of 198,538 dental implants, using 51 different types of dental implants, were placed in Finland between 1994 and 2012 in 110,543 operations. A total of 3318 (1.7%) of the placed implants were removed during the observation period in 2684 (2.4%) implant removal operations. However, it must be noted that some of these removal operations were performed on implants that had been placed before 1994. In this study, only removal operations that had been performed using augmentation materials and that could be linked to implant placement operations performed between 1994 and 2012 were assessed (Fig. 1). Therefore, information concerning the use of augmentation materials was available for 2126 of the removal operations. Augmentation materials were used in 448 (21.1%) of these cases. However, in 72 operations, a combination of 2 or more augmentation materials was used, and these cases were omitted from the results. The final number of operations with valid augmentation information was 2054.

Fig. 1
Fig. 1:
Distribution of dental implant removal times (categorized by days) for augmentation material groups.

The removal rates of implants placed in sites augmented with autologous bone were 2.31%, xenogeneic materials 0.91%, and synthetic alloplastic materials 2.80%. The overall removal rate when augmentations were used was 2.15% and thus a little bit higher (P = 0.008) than the removal rate of 1.87% when no augmentation was used. However, this difference is quite small in practice. The median removal time after implant placement with augmentation was 196.5 days postoperatively (range 0–5831 days). The implant fixtures placed in the augmented sites were 10 mm or longer (94.1%) with 13 mm being the most commonly used length (28.4%).

When reviewing the 2054 removal operations, synthetic materials demonstrated the longest removal times from implant placement (median 264 days, n = 62). Xenogeneic materials demonstrated the shortest removal times from the time of implant placement (median 102 days, n = 28). Compared with these, autologous bone (median 190 days, n = 286) and no augmentation (median 186.5 days, n = 1678) had mediocre removal times (Fig. 1). There were statistically significant (P < 0.001) differences between the removal time distributions of these 4 groups; however, these differences were not large in practice.

Furthermore, the Finnish Dental Implant Register data were analyzed to assess the distribution of the use of the various augmentation materials relative to the implant placement and removal sites in the alveolar processes (Fig. 2). The augmentation materials used at each implant site can be compared to the removal rates of dental implants at the corresponding sites (Fig. 3). In viewing the 2 graphs in Figures 2 and 3, the order of magnitude is higher in the augmentation figure than in the implant removal figure, and there are parallel distributions of the augmentations sites in the jaws corresponding with the implant removals.

Fig. 2
Fig. 2:
Types of augmentation materials used at each site in the mouth with autogenous bone and synthetic and xenogeneic materials.
Fig. 3
Fig. 3:
Removal rates of implants placed at augmented sites related to autogenous bone, synthetic, and xenogeneic materials reported to the register.


The results of this study demonstrate that few augmentation procedures are performed in Finland relative to the total number of dental implants placed. Autologous bone often acknowledged as the gold standard of materials still remains the material of preference among Finnish practitioners placing dental implants. It seems reasonable to assume that not all bone substitutes available on the market perform similarly and it still remains unclear as to which augmentation material is the most effective at this time.17

Interestingly, when accessing the 2054 removal operations, performed in Finland over the past 18 years, the synthetic materials demonstrated the longest removal times (median 264 days, n = 62) after implant placement, whereas the xenogeneic materials demonstrated the shortest removal times (median 102 days, n = 28) after implant placement followed by autologous bone (median 190 days, n = 286). Although the overall implant removal rate was the lowest in the xenogeneic group, 0.91% the implants were surprisingly removed after the shortest period in situ (median 102 days, n = 28). Furthermore, when the removal rates of the xenogeneic group are compared with patients who did not require any augmentation, the implants in the xenogeneic group were removed on average 84 days earlier. This implies that the implants placed in conjunction with xenogeneic materials resulted in the least implant removals but were associated with the most rapid implant removal times after placement. To summarize, removals for implant placements augmented by alloplastic materials occurred late after, whereas those augmented by xenografts seemed to require early removal, and both autogenous augmentations and cases without augmentation had removal rates between those of alloplasts and xenografts.

One of the biggest limitations of this study is the self-reported nature of the implant register. Even though dentists are obliged to register all placed/removed dental implants, a comparison of the number of implants sold to the number of implants placed shows that only approximately 70% of all dental implants are actually registered.1,20 This failure to register placed/removed dental implants is mainly because no sanctions are applied to dentists who do not comply with existing rules. In addition, the register by its nature does not make it possible to assess the specific reasons for implant removals on a case by case basis. Another potential weakness of this study was the recording errors that became apparent after analyzing raw data provided by the registry administrator. There were mistakes in data such as product names that had been misspelled, and in some cases, company names had been used instead of brand names. Although these were easily corrected, this may introduce some forms of bias into the study. Furthermore, implant placements performed during the period 1994–2012 could result in continued further future implant removals.

This register study cautiously attempted to analyze the reported usage of augmentation materials in a jurisdiction with an available registry with large amounts of data. However, the use of register data can have severe limitations, because the investigators are totally reliant on those who have created the register, on the data collection forms used and on the practitioners who complete the registration forms. This study tried to collect data regarding many aspects of augmentation using different augmentation materials. The authors are aware that practitioners might consider using different materials in different circumstances, and these circumstances may affect the success or implant removal rates in the augmented areas. The authors acknowledge the importance of this fact, but due to limitations of the register, they are unable to extend the analysis further in this regard. The authors caution the reader as statistical analysis may not truly represent the clinical scenario as their reporting in a confined register is limited by the design of the forms. Although the analysis of the data may not truly represent the exact clinical scenarios, the value of such a register-based study is to establish trends during the study period rather than to establish cause and effect conclusions.

More in-depth long-term multicenter studies are required to provide further insight into the nature of augmentation procedures and dental implant survival in sites requiring augmentation.21,22 To the best of our knowledge, this is the first register-based study assessing the removal rates of dental implants with different augmentation materials with over 100,000 implant procedures.


Augmentation procedures in combination with dental implants offer good long-term predictable clinical success/survival rates, regardless of the type of graft materials used. Removals for implant placements augmented by alloplastic materials occur late after 201 days, whereas those augmented by xenografts seem to require early removal after 102 days, and both autogenous augmentations and cases without augmentation have removal rates, which reside between alloplasts and xenografts.


The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.


The National Institute for Health and Welfare (THL) granted permission to access raw data in the Finnish Dental Implant Register from April 1994 to April 2012 for this register-based research project.


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alveolar augmentation; autograft; allograft; xenograft

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