Clinical Oral Implants Research

Clinical and radiographic evaluation of early loaded narrow-diameter implants: 3 years follow-up

Authors


Abstract

Objective

To evaluate the clinical reliability of narrow implants placed in a one-stage procedure and early loaded in the upper and lower incisor region.

Material and methods

This is a prospective, single-arm, multicenter study in which patients with missing natural dentition in upper lateral and lower incisor positions were enrolled. Eligible implants (OsseoSpeed™ TX 3.0S, DENTSPLY Implants) were of three different lengths and of 3.0 mm in diameter. One-stage surgery was performed and healing abutment connection took place. Placement of the permanent single crown took place after a 6–10 weeks healing period. Clinical and radiographic checks were performed at implant placement, loading, and at the 6, 12, 24, and 36 months follow-up visits.

Results

A total of 69 subjects with 97 implants have been included in this study. From surgery to 36 months follow-up, 5.6% of the implants showed bone loss of more than 1 mm, while no bone loss at all were observed for 57.3% of the implants. The mean marginal bone level change from surgery to the 6, 12, and 36 months follow-up visits was −0.27, −0.11, and −0.09 mm, respectively. The total survival rate after 3 years is 95.5%.

Conclusions

The data presented show stable marginal bone levels as well as healthy soft tissue around OsseoSpeed™ TX 3.0S implants, after 3 years of function. An interesting finding from this investigation was that a longer healing period before crown placement and loading contributed to statistically significant less marginal bone loss between loading and the 1-year follow-up visit (Galindo-Moreno et al. 2012). This finding, associated with a stable probing pocket depth and a stable crown–gingiva distance, using a one-stage surgical procedure helps to maintain the integrity of the peri-implant soft tissues. Narrow implants can be considered as a valid solution in the treatment of the localized narrow bony defects in the anterior area with reduced spaces between the natural teeth.

The replacement of lateral incisors in the maxillary jaw and central or lateral incisors in the mandible with standard-diameter implants is very often challenging because of the lack of available space or due to an unfavorable anatomy of the residual alveolar ridge. When accepting the concept of prosthetically guided implantology, the placement of an implant in a narrow ridge often leads to dehiscences or fenestrations of the implant neck and body (Romeo et al. 2006), thus making a regenerative procedure mandatory to guarantee a successful outcome of the treatment. Besides this, the placement of an implant closer than 1.5 mm to the adjacent tooth may result in loss of proximal bone height during healing (Tarnow et al. 2000), or affectation of the adjacent teeth, by damaging its periodontal ligament (Comfort et al. 2005).

Reduced diameter implants can represent an option in the rehabilitation of the alveolar narrow ridges. First of all, the term narrow implant needs to be clarified. A narrow implant has a diameter <3.4 mm (Quek et al. 2006), but a distinction between narrow implant and mini-implant (diameter <3 mm) (Jofre et al. 2010) has to be made. Fur-thermore, indications for small-diameter implants have to be discussed with regard to their potential limitations. It has been stated that a 3.3-mm diameter screw-shaped implant presents 25% less resistance to fracture when compared to a similar standard-diameter (3.5–4.0 mm) implant (Olate et al. 2010). It has also been reported that increasing implant diameter resulted in as much as a 3.5-fold reduction in crestal bone strain (Petrie & Williams 2005). An implant with larger diameter contributes to limit the maximum stress/strain between the bone and the implant (Qian et al. 2009). From these considerations, it can be anticipated that the marginal bone loss could augment when placing narrow implants, and even more so in the anterior area.

On the other hand, in a retrospective study on narrow implants (≤3.5 mm diameter), a 12-year cumulative implant survival rate of 98.1% and 98.5% for the implant and subject-based analysis, respectively, was observed (Lee et al. 2012). The conclusion was that narrow implants could be safely used for narrow alveolar ridges or narrow mesiodistal spaces on the basis of their high survival rate. A review involving studies on implants with 3.5-mm diameter or less as a support for overdentures, randomized clinical trials, retrospective or prospective cohort design in humans, a follow-up of at least 5 months after implant placement, reported an survival rate over 90%, including eight studies reporting a 100% survival rate (Sohrabi et al. 2012). Failures were more often reported in shorter narrow implants (≤13 mm) compared with longer ones (>13 mm). The authors concluded that survival rates for narrow implants are similar to those reported for standard-diameter implants, and the failure rate seemed to be higher in shorter narrow implants.

The aim of the present study was to evaluate implant survival, marginal bone level change, and soft tissue stability of single-tooth replacement in the anterior maxilla and mandible with limited bucco-lingual or mesio-distal space by the use of a narrow OsseoSpeed™ TX 3.0S implants (DENTSPLY Implants, Mölndal, Sweden).

Materials and methods

This prospective, single arm, multicentre study was conducted with specific eligibility criteria. Subjects missing a single tooth in position 12, 22, 32, 31, 41, or 42 (FDI) were included to the study, and patients were recruited at six different study sites in Denmark, Germany, Italy, Spain, Sweden, and the United Kingdom, where approval from each local ethics committee was obtained. The study was registered on http://www.clinicaltrials.gov from the US National Institutes of Health, identified as NCT 00646113, from March 25, 2008.

The recruited patients had to fulfill the following criteria: good general health, absence of dental or periodontal disorders, smoking ≤10 cigarettes per day, single tooth absence with healthy neighboring teeth in normal occlusion, recipient sites for implants that had healed for 2 months following tooth extraction. One study implant per patient was placed. However, for patients missing both contra laterals, both the sites were allowed to be treated with study implants and thus followed in the study. According to the protocol inclusion criteria, only patients deemed by the investigator to have a bone height and width suitable for 3.0-mm diameter study implant were enrolled. When patients not meeting the study criteria were enrolled in error, they were excluded from the study and all efficacy analyses.

All subjects received both oral and written information regarding the study and signed a written consent before undergoing any treatment. The recruited subjects had to fulfill the following criteria: good general health, smoking less than 10 cigarettes per day, absence of dental and oral pathologies, single-tooth loss with neighboring teeth in normal occlusion, recipient sites for implants healed at least since 2 months after extraction. Only one study implant was placed in each subject with the exception for subjects having a missing contralateral. In these cases, both positions were allowed to be treated with study implants. The OsseoSpeed™ TX 3.0S cylindrical implants used in the study present a fluoride-modified moderately rough surface with minute threads so-called MicroThread™ at the implant neck and platform shift built in the internal conical connection to the abutment called Conical Seal Design™ (DENTSPLY Implants). A total of 72 subjects were consented in the study (Fig. 1). Three subjects were excluded from the trial, one subject was under 18 years of age, one subject was missing the canines, and one subject did not turn up for placement of the study implant. In this analysis, 69 subjects with a total of 97 implants were included, 36 men and 33 women, mean age 32 years. The surgeon placed 11, 13, and 15 mm long implants depending on the surgeon's preferences and anatomical space (Table 1). The reason for the edentulism in the test area was agenesia in 62 subjects, endodontic disease in 14, periodontal disease in 11, root fracture in 8, non-restorable caries in 1, and unknown in 1 instance. Eleven subjects were smokers, ten reported a previous history of periodontitis, and seven of the subjects were recorded as bruxists.

Table 1. Distribution of implants per length
Implant length (mm)No.
1145
1339
1513
Total97
Figure 1.

Flowchart showing the number subjects enrolled, included, and reaching the 36 months control.

Surgical and prosthetic procedures

All the subjects received antibiotic prophylaxis (2 g amoxicillin or 600 mg clindamycin) 1 h before surgery. After giving local anesthesia, a mid-crestal incision was performed in the edentulous area and two vertical release incisions were made at the neighboring teeth, on the buccal side. After exposing the ridge, the implants were placed according to the procedures described in the surgical implant system manual. No grafting procedure was allowed, except covering visible implant threads with autogenous bone chips harvested during surgery. Flaps were sutured around connected healing abutments. Subjects received postoperative instructions and were recommended to rinse with chlorhexidine, 0.1 or 0.12%, twice a day for 10 days after surgery.

Sutures were removed 7–13 days after implant surgery. In 22 occasions, subjects requested to have a temporary restoration, not connected to the implant, placed after surgery (Table 2). Implant level impressions were taken 5–7 weeks postoperatively. Three-mm TiDesign™ straight or 15° angled abutments were placed according to the procedures described in the implant manual for cement-retained restorations (Dentsply Implants). The permanent crown (metal ceramic or all-ceramic) was cemented on to the abutment 6–10 weeks after surgery.

Table 2. Number of temporary restorations performed
Temporary RestorationNo.
Yes22
No47
Total69

Clinical and radiological examinations

Clinical and radiological evaluations were carried out at implant placement, crown placement, and at 6, 12, 36 month follow-up visits. Intraoral X-rays were taken according to the parallel technique using the study sites equipment and an independent experienced radiologist at the University of Gothenburg analyzed all the radiographs. The marginal bone levels were evaluated as the distance from the mesial and distal interproximal bone-implant contact to the reference point on the implant (the junction between the machined bevel and the top of the MicroThread) and presented as a mean of these two values. The condition of the peri-implant mucosa was evaluated by probing the pocket depth (PPD). Bleeding on probing (BoP) was recorded as Yes/No on four sides of each restoration. Maintenance of the soft tissues in the buccal area was checked by measuring the gingival zenith score, defined as the distance from the most apical aspect of the buccal gingival margin to the incisal edge of the crown.

Statistical analysis

For the statistical analysis, the patients were divided into groups, based on criteria such as bone quantity, bone quality, smoking history, healing time, drilling protocol, implant length, and grafting. When testing, if the expected value of a parameter was equal between the groups, the Student's t-test was used.

If a change in value of a parameter over time was statistically significant, a Wilcoxon signed-rank test was used. All tests were two-sided, and a P-value <0.05 discussed as statistically significant even though no adjustment for multiple comparisons was made. Microsoft Office Excel 2003 software was used for the statistical evaluation.

Results

All subjects were treated with one or two OsseoSpeed™ TX 3.0S implants in positions 12, 22, 31, 32, 41, or 42 (FDI). Most commonly, the study implants were placed in the maxilla (Fig. 2). The bone quality and quantity were assessed according to Lekholm and Zarb's classification (Lekholm & Zarb 1985), and most implants were placed in bone quantity B and bone quality 2 bone (Table 3). Four implants were lost at three different study sites. Three of the implants were lost due to insufficient healing and one due to infection. One subject lost an implant and withdrew the consent to participate in the study despite having a second study implant. The four implants were lost during the healing period prior to loading resulting in a cumulative implant survival rate of 95.9% after 3 years. No implant failures were reported between loading and the 36 months follow-up (100% survival rate after loading). According to this, the implant failure rate per year of the presented study was 4.1% in the first year (Galindo-Moreno et al. 2012) and 0.0 in the second and third years. One subject encountered fracture of both contra lateral abutments (due to offset bucco-lingual placement of the implants), while another subject experienced fracture of one of the lateral abutments (due to excessive occlusal loading). The fractured abutments were replaced by ATLANTIS™ customized abutments (DENTSPLY Implants).

Table 3. Distribution of bone quality and quantity according to Lekholm and Zarb
Bone qualityBone quantityTotal
ABCDE
  1. a

    Figures within parenthesis represent implant failures.

11    1
22028 (3a)13  61
3922 (1a)1  32
4 3   3
Total3053140097
Figure 2.

Implant distribution per study position.

The mean marginal bone level changed from surgery to crown placement by −0.34 mm. At the 6 months follow-up visits, some of the marginal bone was recovered, to be almost totally regained after 12 months, see previous published data (Galindo-Moreno et al. 2012) and levels were maintained at 3 years. Hereof, the mean marginal bone level changes from surgery to the 6, 12, and 36 months follow-up visits were −0.27, −0.11, and −0.09 mm, respectively (Fig. 3). Evaluating the bone level changes from the time of loading (6–10 weeks after implant placement), the mean marginal bone level change to 36 months follow-up consisted of a gain of 0.33 mm bone. This increase was statistically significant (= 0.0005, two-sided Wilcoxon signed-rank test). Mean probing depth increased from 2.0 mm (SD = 0.7) at crown placement to 2.2 mm (SD = 1.0) after 36 months. Bleeding on probing was reported in 34–47% of the subjects during the course of the study (Fig. 4). Mean gingival zenith score remained unchanged throughout the study period with a baseline figure of 8.9 mm (SD = 1.7) at crown placement and a 3-year figure of 8.8 mm (SD = 1.9) (Fig. 5). The changes in probing depth, bleeding on probing, and gingival zenith score from loading to 36 months follow-up were not statistically significant.

Figure 3.

Marginal bone-level alterations from surgery to the 36 months visit.

Figure 4.

Bleeding on probing from loading to the 36 months follow up.

Figure 5.

Gingival Zenith Score from loading to the 36 months follow up.

Discussion

Narrow implants were planned for the rehabilitation of narrow ridges or when space between adjacent teeth was considered limited. Replacing lateral maxillary incisors or mandibular incisors as well as the creation of support to overdentures in extensive narrow edentulous ridges in the mandible represents an ideal indication for narrow-diameter two-piece implants. When talking about narrow implants, only implants with a diameter of 3–3.4 mm should be considered (Quek et al. 2006). A careful distinction between narrow implants and mini-implants is mandatory to evaluate the real survival rates (Avila et al. 2007). Traditionally, narrow implants have presented lower survival rates when compared to standard-diameter implants (Winkler et al. 2000; Albrektsson et al. 2007). A recent meta-analysis has highlighted that implants with a diameter narrower than 3.3 mm or lower show a failure rate 3.92 times larger than regular implants (Ortega-Oller et al. 2013). Nevertheless, some authors reported better results (Saadoun & Le Gall 1996; Andersen et al. 2001; Renouard & Nisand 2006 and Romeo et al. 2006). Other studies reported similar or higher survival rates, ranging from 90 to 100%, for narrow implants when compared to standard diameter ones (Block & Kent 1993; Hallman 2001; Zinsli et al. 2004; Cordaro et al. 2006; Degidi et al. 2008; Lee et al. 2012; Sohrabi et al. 2012). The results from the present study are in accordance with these studies, showing 95.5% total survival rate and 100% survival rate after loading of the implants.

Marginal bone loss is an important indicator for the health of the tissue surrounding dental implants. Looking at the available literature, some studies investigated the possibility of implant diameter impact on the cortical bone surrounding the implant neck. One investigation using a three-dimensional finite elements analysis showed that increased implant diameter could result in up to 3.5-fold reduction in crestal strain (Petrie & Williams 2005). Another study reported that the use of narrow implants as a terminal support for three-unit fixed partial dentures resulted in an increase in stress and strain around the supporting implants in comparison with the support from two standard-diameter implants (Cehreli et al. 2006). One of the goals of the present investigation was the evaluation of the influence of the narrow implant diameter onto the marginal bone level change. The data collected shows that a recovery of the mean marginal bone level occurred from implant placement to the 1-year follow-up, and this recovery was confirmed by the mean marginal bone levels reported from the 3 years follow-up visit. In the present study, no correlations between marginal bone loss and smoking, implant length, bone quality, and bone grafting were observed.

The stability of the gingival margin is another key factor. Literature is poor of long-term studies evaluating the behavior of the peri-implant soft tissues, particularly in the esthetic area. De Rouck et al. (2008) and Cosyn et al. (2011) showed that a remarkable papilla reduction and mid-facial recession in the early phases of healing with immediate implant placement can be appreciated. On the other hand, after 3 years in function, papilla regeneration in the same subjects can be appreciated as well as some reduction in mid-facial recession. The long-term study from Dierens et al. (2013) evaluating the alterations of the soft tissues levels and esthetics over a 16–22 year period in periodontally healthy subjects, failed to prove a significant mid-facial recession at the implant restoration, while gingival levels at the adjacent natural teeth demonstrated a significant recession. The three-year results from the present study show no significant changes in mean gingival zenith score from crown placement to the 36 months follow-up. This finding confirms the data from the mentioned articles.

Besides this, good clinical behavior in terms of bone preservation and soft tissues maintenance, it is important to highlight that no implant failures have been occurred in the study subjects after occlusal loading. Logically, longer follow-up periods might obtain an increased failure rate, and consequently, longer follow-up offers more reliability as regard as survival rate. Many studies fail to report the moment when a clinical failure happens, the reader assuming that these failures happened at the end of the observational time. This practice brings confusion regarding the real results of the studies, where failures should be expressed in failure rates per year. So, this study has taken carefully in consideration this aspect, reporting exactly the moment of the failures, because it offers a better understanding of the implants behavior. According to this, the implant failure rate per year of the presented study was 4.1% in the first year (Galindo-Moreno et al. 2012) and 0.0% in the second and third years .

To summarize, the scientific literature is full of studies reporting data on the outcome of narrow-diameter implants placed in different indications. Satisfying results from different studies (Mericske-Stern et al. 2001; Zarone et al. 2006) even in the long-term period (Vigolo et al. 2004; Lee et al. 2012; Sohrabi et al. 2012) and not only for single-tooth replacement, but also for full arch rehabilitations (Zinsli et al. 2004; Cho et al. 2007).

This study, in accordance with previous studies (Zarone et al. 2006), underlines the advantageous use of narrow implants for single-tooth restorations in the upper lateral incisor and the lower incisor regions where tooth space and ridge form is compromised. Further clinical follow-ups will highlight the behavior of this implant design in the long term.

Conclusions

This study evaluated the thirty-six months clinical and radiological behavior of Osseospeed™ TX 3.0S implants placed into narrow one tooth defect ridges in the anterior area. The data collected from all the study sites participating in the trial show the stability of the marginal bone levels as well as of the soft tissues around implants and confirm that narrow-diameter implants can be considered as an effective solution in the treatment for localized anterior narrow ridges and reduced tooth spaces.

Acknowledgements

The investigators express their gratitude to Mr Robert Corbè for his support, guidance, and professionalism during the study.

Disclosure

This international multicenter study was sponsored by Dentsply Implants. However, none of the researchers involved have economical interest in neither the product related to this study nor the sponsoring company.

Ancillary