I. Introduction
In 1951, a titanium spiral osseointegrated implant was introduced by Brånemark. Afterwards, research and development on materials and surface treatments were performed, and various types of implants were subsequently released. In particular, wide implants are useful for various purposes, but a lot of controversy remains over their clinical prognosis.
Implants are classified into narrow, standard, and wide implants according to their implant diameters. Al-Johany et al.1 defined narrow, standard, and wide diameters as 3.0 to 3.75 mm, 3.75 to 5 mm, and 5 mm or more, respectively. Among wide implants, fixtures with a diameter of 6 mm or more are defined as ultra-wide implants.
Clinically, wide implants have a variety of advantages. Compared to narrow implants, wide implants have increased contact between the bone and the implant surface, resulting in increased osseointegration2 and force distribution causing the force applied to the crest area to be greatly reduced, which is dynamically advantageous after prosthetic loading3. In addition, by using a wide implant, cortical engagement is obtained and load can be applied to the implant immediately4. From the biomechanical perspective of improving the high initial stability and stress distribution of the supporting bone, wide implants can be used to replace non-integrated fixtures in molars regions. However, if the bone width is insufficient, bony dehiscence may occur frequently due to the excessive pressure applied to the buccal bone with resulting gingival recession5. According to Will and Drago6, the 120 year survival rate of implants with diameters of 7 mm is 97.6%. Similarly, according to Wadhwa et al.7, the 6-year survival rate of implants with a diameter of 6 mm or more is 97.29%, higher than the standard diameter.
To date, many clinical studies have been published on implants greater than 5 mm but less than 6 mm in diameter, but clinical studies on long-term survival, success rate, and marginal bone loss (MBL) in ultra-wide implants greater than 6 mm in diameter remain sparse. The purpose of this paper is to evaluate the long-term survival rate, success rate, and MBL of 6-mm- and 7-mm-diameter ultra-wide implants and to investigate the variables that affect clinical outcomes.
II. Patients and Methods
This retrospective clinical study was conducted after receiving approval from the Institutional Review Board (IRB) of Seoul National University Bundang Hospital (IRB No. B-2208-774-111).
From January 2008 to December 2010, 81 subjects underwent dental implant placement therapy at the Department of Oral and Maxillofacial Surgery of Seoul National University Bundang Hospital. Eighty-eight ultra-wide implants with diameters of 6 mm and 7 mm were placed in 81 patients. Among them, 1 case was excluded due to the inability of follow-up checks because prosthetic treatment was not conducted at this hospital, 1 case was excluded due to the inability for evaluation because radiographs were not taken at the time of the final observation, and 14 cases within 12 months of the follow-up period after prosthetic loading were excluded from the study. As a result, a retrospective clinical study was conducted on 78 implants placed in 71 patients.
The reasons for using ultra-wide implants were as follows: First, an ultra-wide implant was selected as the initial choice due to poor bone quality. Second, if an implant with a diameter of 5 mm or less was attempted during surgery, but initial fixation was not obtained, an ultra-wide implant was used. Third, an ultra-wide was used for replacement after the removal of failed implants.(Table 1)
All patients underwent surgeries performed by one oral and maxillofacial surgeon, and primary stability was measured during the initial surgery, while secondary stability was measured for ultra-wide implants during the second surgery. All of the patients visited the hospital for a regular one-year check-up and underwent clinical examinations and periapical radiographs. Clinical examinations evaluated pocket depth, suppuration, and pus. MBL values were evaluated with periapical radiographs.
Resonance frequency analysis (RFA) was used to measure implant stability (primary and secondary). In this study, the implant stability quotient (ISQ) was measured and RFA was evaluated using an Osstell Mentor (Gothhenburg, Sweden), an integration diagnostic tool. The ISQ figure was recorded between 0-100 with the manufacturer statement of successful implants being above 65 ISQ, while values below 50 ISQ were the criterion for failure or risk of failure of the implant. Among the placed implants, primary stability was not measured for five implants and secondary stability was not measured for two implants.
The mean age of the patients was 54.2 years old with 39 males and 32 females. The age group in which implants were placed was the largest in their 50s, followed by those in their 60s and 40s.(Table 2) The mean healing period was 22 weeks after implant placement before prosthetic loading. The mean follow-up period for patients was 97.8 months. The healing period was set as the period from the time of surgery to second therapy or initial impression taking for prosthesis fabrication. The final observation period was set as the period from the time of prosthetic loading to the time of the final visit. The diameter and length of the implant, the implant site (upper/lower jaw), surgery stage, and the presence of additional surgical procedures (guided bone regeneration [GBR] and sinus lift) were evaluated.(Table 3)
The success and survival of the implants and MBL according to the variables were evaluated.
1. Success
The criteria for success were set as follows: (1) Implant exhibiting no mobility, (2) periapical radiograph showing no radiolucency around the implant, (3) MBL within 1 year of prosthetic loading was less than 1.5 mm, and subsequently less than 0.2 mm per year, and (4) no clinical findings such as inflammation, bleeding, pus, and suppuration.
2. Survival
The criteria for survival were set as follows: (1) Implant persistence at the implanted site until the final observation time.
3. Marginal bone loss
A periapical radiograph that was taken immediately after prosthetic loading was used as the baseline, and MBL was measured by calculating the bone loss of the mesial and distal aspects in the periapical radiograph taken one year after prosthetic loading and at the final observation time. The magnification rate was calculated by measuring the length of the actual implant, the length of the implant measured on periapical radiograph, and the MBL observed on periapical radiograph. (Fig. 1)
MBL=MBL on periapical radiograph×Actual implant lengthImplant length on periapical radiograph
One-way ANOVA analysis was used to evaluate the statistical significance of MBL according to the patient’s sex, implant site, and diameter. Independent sample t-tests were used to determine the statistical significance of MBL according to the reason for ultra-wide implants, length, additional surgery, primary implant stability, and secondary implant stability.
Kaplan–Meier analysis was used to determine the significance of the success and survival rates related to the variables (age, sex, site, diameter, length, additional surgery, reason for ultra-wide implant, implant primary stability, and implant secondary stability). All data were evaluated using IBM SPSS Statistics (ver. 28.0.1; IBM, Armonk, NY, USA), which tested the significance of any association at a 95% confidence level.
VI. Discussion
The ultra-wide implants used in this study were SuperLine (Dentium, Suwon, Korea), which has characteristics of SLA (sandblasted, large‐grit, acid‐etched) surface treatment, an internal connection, 6.0- or 7.0-mm diameter, tapered shaped, and are used when bone quality is poor or the placement of standard diameter implants has failed.
Since wide implants increase initial stability through stress distribution while engaging bone, they are selected as initial implants when bone quality is poor. In this study, 59 implants were placed for that reason, while three implants were used as replacements of implants that were less than 5 mm in diameter and failed to achieve initial stability. According to the characteristics of the ultra-wide implants exhibiting high initial stability, the ultra-wide implants placed in the study by Hattingh et al.2 were immediately loaded after molar tooth extraction. Ultra-wide implants are sometimes called a ‘rescue implant’ if the existing implant has failed and the ultra-wide implant is used for alternative purposes8. In this study, 16 cases of ultra-wide implants were placed after removing the failed implants. If the previous implant failed and was removed, the range of bone defects increased. If implant placement was possible immediately, primary stability could be secured during the placement of 6-mm- and 7-mm-diameter ultra-wide implants. According to Hattingh et al.9, ultra-wide implants reduce the need for bone augmentation compared to standard diameter implants. In this study, 29 implants were used without GBR9.
In the mean 97.8-month follow-up period of ultra-wide implants used in this study, the long-term survival rate was 92.3% with an 83.3% success rate. MBL was 0.2 mm one year after prosthetic loading and 0.54 mm in the mean 97.8-month follow-up period. In Hattingh et al.’s study9 where 580 cases of 7-mm-diameter ultra-wide implant were placed in molar sockets, the 10-year survival rate was 95.17%. In Ku et al.’s study10 where 58 cases of 6-mm or wider diameter ultra-wide implant were placed, the survival rate in the mean 46.25-month follow-up period was 98.28%. In addition, MBL was 0.018 mm and 0.045 mm on mean for 12 months and 24 months after prosthetic loading, respectively, and MBL was 0.14 mm during the follow-up period of 46.25 months.
In this study, ultra-wide implants exhibited a low success rate (83.3%) and survival rate (92.3%). According to Ketabi et al.8, greater torque force is needed when placing large-diameter implants, and a bone thickness of 1.8-2 mm is required on the buccal and lingual/palatal sides. The success of ultra-wide implants may have been affected due to insufficient bone thickness and density, as they were placed in cases of poor bone quality or as replacements for failed implants. Furthermore, previous studies support the significant lower survival rate when replacing implants in failed locations. According to Chrcanovic et al.11, the survival rate of the first implant was 94%, but after removing and replacing the failed implant, the survival rate was 73%. Similarly, according to Agari and Le12, the survival rate of the first implant was 95.4%, but after re-implanting in the location of the failed implant, the survival rate was 77.4%, exhibiting a significant difference. The low survival rate of ultra-wide implants can be explained by the fact that it was placed as a replacement for a failed implant.
Among age, sex, site, diameter, length, additional surgery (GBR or sinus lift), and reason for using ultra-wide implants, none exhibited an effect on the success rate of wide implants. Ting et al.13 reported that patients’ age, implant length, and site did not have an influence on the success rate of implants. Meanwhile, Termeie et al.14 concluded that narrow implants have lower success rates because the narrower the diameter, the greater the stress on the implant. In this study, success rates were higher in wider implants with 91.9% in 6-mm-diameter implants and 93.75% in 7-mm-diameter implants, but no statistical significance was observed. Bazrafshan and Darby15 proposed that implant success rates with or without GBR exhibited no statistical significance, mirroring our study.
Primary implant stability is mainly related to mechanical stability, which represents engagement in the cortical bone16. Primary implant stability has a statistically significant correlation in 5-year implant success rate. The success rate was 61% in cases of less than 60, 91.2% in more than 70, and 100% in between 60 to 70.
Table 4 presents the failed cases shown in this study. Six implants failed in the maxilla, 7 in the mandible, 5 in males, and 8 in females. Eight implants underwent GBR, while 5 did not. Diameter, additional surgery such as GBR or sinus lift, and implant site did not exhibit a statistically significant correlation with implant failure.
As a result of evaluating the factors affecting implant survival rate, none of the variables among age, sex, site, diameter, length, additional surgery (GBR or sinus lift), and reason for using ultra-wide implants had an influence on the survival rate of ultra-wide implants. This was similar to the result of the Cobo-Vázquez et al.17 study of 92 implants which proposed that primary implant stability did not have an effect on implant survival rate. Furthermore, according to Huwiler et al.18, primary implant stability was affected not only by the bone volumetric density, but also by the thickness and density of the alveolar bone cortical layer, a good indicator of mechanical anchorage at the time of placement.
However, implant success rates exhibit a significant correlation between secondary implant stability. The success rate was 100% in ISQ values of 70 or more and 87.5% in ISQ values between 60 and 70. This result is similar to Rodrigo et al.’s study19 which measured implant stability after implant placement, before prosthetic loading, and divided implants into group of ISQ values above and below 60. The success rate of implants with ISQ values above 60 was 99.1% and below 60 was 97.2%. Implant secondary stability referred to the degree of osseointegration with bone remodeling and formation on the implant surface20. In other words, as the bone-implant contact ratio increased, secondary stability increased. Therefore, implants can resist prosthetic loading, which is beneficial to long-term survival.
None of the variables affected the MBL of ultra-wide implants. Deger et al.21 reported that the difference in MBL according to the diameter and length of the implant did not exhibit a statistical significance. The main cause of implant loss was occlusion overload with small stresses applied to the apical aspect of implants. Therefore, the effect of implant length was insufficient. In other words, it can be determined that the effect of the length of the implant on crestal bone strain is minimal.
According to Ibañez et al.22, they obtained the same result found in the current study where the implant site is not a variable affecting MBL. There was no difference in MBL depending on the presence of additional surgery. According to Park et al.23, in the implant group with sinus lifts, 3.15±2.50 mm of MBL was observed, while 3.15±2.61 mm of MBL was observed in the group without sinus lifts, exhibiting no difference in MBL. Likewise, the findings from Zumstein et al.24 were consistent with the results of a study in which MBL did not exhibit a statistically significant correlation between GBR and the lack of GBR.
Through long-term observation of ultra-wide implants (diameters of 6 mm or more), this study investigated the survival rate, success rate, and MBL of ultra-wide implants. However, one limitation was that the sample size was small. Due to the characteristics of most retrospective studies, the evaluation of systemic diseases and smoking can be inaccurate. In addition, if patients have one or more systemic diseases, it is not possible to determine whether medical treatment is done well. Therefore, systemic diseases were not set as variables.