A preliminary report from on physiological bone remodeling on KS versus TSIII implants for molar rehabilitations: a split-mouth, multicenter randomized controlled trial

Introduction

Dental implants are widely used to restore the function and aesthetics of missing teeth. While early success focused on osseointegration and survival, modern criteria now include minimally invasive surgery, natural aesthetics, stable occlusion, peri-implant health, patient satisfaction, and overall prosthetic success (1). The definition of “success” has shifted from purely clinical outcomes to a patient-centered model, where perceived function and aesthetics are key (2–7). Long-term result stability is now essential and is addressed through integrated treatment plans that place the patient at the center of care (3,8). Despite these advances, implant complications remain common. Mechanical issues (e.g., screw loosening, chipping, fractures) and biological problems (e.g., mucositis, peri-implantitis) can jeopardize implant survival and tissue health (4,9). A crucial element in preventing such complications is the stability of the implant–abutment connection, which serves as a key interface responsible for load transmission, mechanical integrity, and bacterial sealing. In this context, the TSIII implant, a bone-level implant with an SLA surface and 11° conical internal connection, was selected as the control due to its well-documented clinical reliability; a five-year prospective case series reported a mean marginal bone loss of 0.41 ± 0.30 mm, confirming its long-term stability (7) However, implant manufacturers have invested heavily in developing advanced connection systems that address these challenges effectively (10) Among recent innovations, the KS implant system (Osstem Implant, Seoul, South Korea) features an internal 15-degree tapered connection combined with a superhydrophilic, bioabsorbable apatite nano-coating (BA surface) applied over a clinically validated sandblasted and acid-etched surface (SA surface). The BA coating is designed to gradually dissolve during the bone remodeling phase, progressively exposing the SA surface beneath and promoting the formation of dense, load-bearing lamellar bone. The innovative implant–abutment interface allows for greater angular compensation, improved prosthetic fit, and enhanced structural resistance to masticatory forces. According to manufacturer data and in vitro studies, (7) the KS system improves functional stress absorption and distribution, while the increased thickness of the coronal implant walls contributes to enhanced fracture resistance. These features make it particularly suitable for use in narrow alveolar ridges and clinical scenarios requiring narrow-diameter implants, expanding treatment possibilities for patients with limited bone availability. The modified tapered connection ensures stable mechanical engagement through friction between conical surfaces, significantly reducing micromovements and bacterial microleakage—two critical factors in the prevention of marginal bone loss (7).

Moreover, the broader contact area between prosthetic components facilitates more effective load distribution, supporting long-term mechanical stability. The reduction in micromovements, coupled with enhanced mechanical stability, lowers the risk of crestal bone resorption and reduces the likelihood of screw loosening over time. The friction-fit mechanism also enhances prosthetic retention, making it a preferred solution in contemporary implantology (11).

Concurrently, there is increasing interest in minimally invasive implant surgery, which is appreciated by patients for reduced surgical trauma and postoperative discomfort, and by clinicians for simplified handling and procedural efficiency. In this context, the combination of narrow implants and modified Morse taper connections has demonstrated considerable promise, allowing implant placement in anatomically challenging areas while maintaining mechanical integrity and biological stability (12).

In light of recent clinical evidence and ongoing technological advancements in implant dentistry, it is essential to assess the performance of newly developed implant systems using rigorous scientific methodologies. Among the many factors influencing long-term implant success, the implant–abutment connection plays a central role in ensuring biomechanical stability, preservation of marginal bone, and maintenance of peri-implant tissue health (13).

The aim of this research is to compare, through a randomized study, the clinical and radiographic outcomes of two different implant systems (TSIII and KSIII) used in molar regions, both manufactured by the same company (Osstem Implant), but characterized by distinct implant–abutment connection designs and diameters. The null hypothesis (H₀) is that there are no significant differences between the two implant systems in terms of clinical and radiographic outcomes. The null hypothesis will be tested against the alternative hypothesis (H₁) that significant differences exist between the two systems. The present manuscript is reported according to the CONSORT guidelines.

Materials and methods

Surgical and prosthetic procedure

In the test group, Osstem KS BA implants (4.0 mm diameter, 15° internal taper connection, Osstem Implant) were placed. In the control group, Osstem TSIII BA implants (4.5 mm diameter, conventional 11° internal connection, Osstem Implant) were used (Figure 1). All patients underwent radiographic examination (periodical radiograph with paralleling technique) and professional oral hygiene treatment before surgery.

After enrollment, patients were instructed to rinse with 0.2% chlorhexidine mouthwash (Corsodyl, GlaxoSmithKline, Verona, Italy) for 1 minute, twice daily, starting 3 days before surgery and continuing for 1 week postoperatively. Prophylactic antibiotics included 2 g of amoxicillin–clavulanic acid or 600 mg clindamycin (for penicillin-allergic patients) 1 hour before surgery, followed by 1 g of amoxicillin (or 300 mg clindamycin) every 12 hours for 5 days.

All surgeries were performed under local anesthesia with articaine hydrochloride and adrenaline 1:100,000 (Orabloc, Pierrel, Milan, Italy). After crestal incision and full-thickness flap elevation, implant sites were prepared either freehand or with the aid of a surgical guide. Manufacturer’s recommended protocols were followed (Osstem Implant). Bone quality was assessed subjectively. The first site was randomly assigned to receive either the KS (test) or TSIII (control) implants (Osstem Implant). Implants were placed at the crestal level or up to 2 mm subcrestally, based on anatomical conditions. Healing abutments were immediately connected if primary stability was ≥30–35 Ncm. On the contrary, cover screw would be place and second stage surgery planned. Flaps were closed with Vicryl 4.0 (or equivalent). Baseline periapical radiographs were taken with paralleling technique, for each study implant to prevent the risk of systematic error in performing periapical radiographs. Two to three months post-placement, either digital or conventional impressions were taken. Within one month, monolithic zirconia crowns bonded to titanium links were delivered after testing implant stability. Occlusal contacts were adjusted for light contact with the opposing dentition. Clinical photographs and radiographs were taken. Oral hygiene instructions were reinforced. Patients were enrolled in a maintenance program with six-month intervals. At each visit, professional oral hygiene sessions and clinical evaluations were performed, with particular attention to implant stability and occlusion. In addition, periapical radiographs were taken annually. According to the study protocol, patients were followed for research purposes for up to 5 years. Radiographs of both treatments are reported in figures 2–5. At each center, a single experienced clinician performed all surgical and prosthetic procedures, with optional assistance from a second clinician (e.g., a prosthodontist). All interventions and follow-ups were conducted at the respective sites using standardized materials and protocols to ensure consistency.

Results

A total of 42 patients with 87 implants (44 KS BA [test group] and 43 TS III BA [control group]) were followed and data analyzed. CONSORT flow diagram is reported in Figure 6.

The mean age at the time of implant placement was 50±12.1 years old. Twenty-seven patients were male and 15 female. Nine patient were moderate smokers. No drop-outs were recorded, however, at the time this manuscript has been written, only 27 patients with 53 implants (27 KS BA [test group] and 26 TS III BA [control group]) completed the six month (after prosthesis delivery) follow-up. Several deviation from the original protocols were recorded and showed in the table 1.

No drop-outs were recorded. Overall, there were no failures of implants or prostheses, and no complications were encountered. Marginal bone levels (MBL) were evaluated at implant placement, crowns delivery and six month later. At implant placement, the mean MBL was 0.03±0.09 mm in the TS group and 0.04±0.13 mm in the KS group. At prosthesis delivery (3 months later), mean MBL was 0.32±0.27 mm in the TS group and 0.18±0.32 mm in the KS group. The marginal bone loss between baseline and prosthesis delivery was 0.26±0.24 mm in the TS group and 0.16±0.30 mm in the KS group. The difference between groups was statistically significant with lower value for KS group (0.10±0.23 mm; P=0.029). At the 6-month follow-up (9 months after implant placement), the mean MBL was 0.34±0.27 mm in the TS group and 0.21±0.32 mm in the KS group. The difference from baseline (implant placement) was 0.29±0.25 mm in the TS group and 0.19±0.30 mm in the KS group. The difference between groups was statistically significant with lower value for KS group (0.09±0.24 P=0.034). All the data are reported in table 2.

TS = Test Group, KS = Control Group, MBL = Marginal Bone Level.

Patient satisfaction was assessed at the 6-month follow-up through a structured questionnaire. All 27 patients who completed the follow-up responded positively to all three questions. Specifically, 100% of patients reported being fully satisfied with the functional outcome and aesthetic result. All except one indicated they would undergo the same therapy again (96.3%). No patient expressed uncertainty, dissatisfaction, or regret regarding the treatment received.

Discussion

This multicenter RCT compared clinical and radiographic outcomes of two Osstem implant systems—KS (4.0 mm, 15° internal taper, single platform) and TSIII (4.5 mm, 11° internal connection, dual platform)—for molar replacement in the maxilla and mandible. The primary aim of this study was to assess the clinical performance and complication rates when using a narrower 4.0 mm implant for molar rehabilitation. The null hypothesis was partially rejected. No statistically significant differences were found when comparing primary outcomes (implant and prosthesis survival rates and complications) and patients’ satisfaction. The secondary aim was to asses whether the novel tapered connection of the KS implant would lead to reduced marginal bone loss (MBL) compared to the TSIII implant. In this contest, the null hypothesis—asserting no significant differences between the two systems regarding marginal bone levels—was rejected. A statistically significant difference in marginal bone loss was observed at the time of prosthetic delivery (P = 0.029), with the KS group demonstrating superior bone preservation. This trend toward greater bone stability in the KS group was maintained at the 6-month follow-up and reached statistical significance (P = 0.034), suggesting consistent clinical benefits.

It is important to clarify that the KS implant should not be considered an evolution of the TS system, but rather a distinct design with specific mechanical and clinical advantages. One of the most clinically relevant findings of this study is the favorable performance of the 4.0 mm KS implant in posterior regions—an anatomical context where traditional protocols often recommend a minimum implant diameter of 4.5 mm. These results support the safe and effective use of narrower-diameter implants in molar areas, aligning with evidence from high-strength titanium-zirconium alloy implants, which have also demonstrated success in similar posterior applications 14,15).

Another key advantage of the KS system is its unified prosthetic platform, which eliminates the distinction between mini and regular platforms. This feature simplifies the clinical workflow, particularly in multi-unit or full-arch rehabilitations, by streamlining prosthetic component selection and reducing the likelihood of technical errors. The platform uniformity also facilitates prosthetic planning and inventory management.

From a prosthetic standpoint, the 15-degree internal taper connection of the KS implant provides enhanced angular compensation, improving prosthetic fit in cases involving non-parallel implant placement—often a challenge in complex anatomical scenarios. Compared to standard 11-degree connections, the increased taper angle may allow for better management of divergent implant axes. Nevertheless, as with most internal connection systems, it is advisable to either place the definitive abutment at the time of surgery or use abutment converters to optimize the mechanical seal and minimize soft tissue disruption during subsequent prosthetic phases. Despite its wider taper angle, the KS connection exhibits mechanical behavior similar to that of a Morse taper connection, due to its high-precision friction fit and enhanced mechanical stability. This interface may support subcrestal placement of up to 3 mm in specific clinical scenarios. Recent biomechanical studies have highlighted the importance of implant macrogeometry in promoting mechanical engagement and biological integration. In particular, tri-oval implant designs have demonstrated superior stability in bone surrogate models and finite element analyses, showing improved stress distribution, primary stability, and preservation of peri-implant bone under load compared to traditional round designs (16–18) While the KS system does not share the same tri-oval macrodesign, its internal friction-fit and tapered connection appear to produce comparable clinical advantages in terms of marginal bone preservation and implant stability, particularly in narrow diameter applications.

In the present study, the KS implant’s reduced physiological marginal bone remodeling during biological width formation implies a potential for deeper placement, which could further enhance soft tissue support. Although the differences are statistically significant at both crown delivery and the 6-month follow-up, the overall results may be considered clinically negligible. However, the observed reduction of approximately 40% could be a critical factor in maintaining physiological bone remodeling as close to zero as possible. This may potentially lead to a reduction in biological and technical complications over long-term follow-up (19).

While current manufacturer guidelines recommend crestal-level or 1–2 mm subcrestal positioning, future studies may explore the biological behavior and clinical benefits of placing KS implants at depths of 2–3 mm, similar to other high-stability platforms. Such an approach could further improve soft tissue integration and long-term aesthetics, especially in patients with thin biotypes or compromised gingival architecture (20–23). Preliminary findings from this study also suggest that the KS system may be particularly advantageous in challenging clinical scenarios—such as in patients with limited bone volume or in posterior maxillary and mandibular regions—where the ability to use a reduced-diameter implant with high mechanical resistance can minimize or even eliminate the need for bone grafting procedures. The observed equivalence in clinical performance between the 4.0 mm KS and 4.5 mm TSIII implants in load-bearing posterior sites further supports the feasibility of this approach.

The main limitation of this study are some deviation from the original protocol. Patients 1, 2, 3, 5, and 6 at Center #6 did not follow the intended split-mouth randomization. These cases were retained to avoid additional bias related to center-specific experience with one implant system. Re-randomization was also avoided to minimize delays and increased costs. Similar pragmatic approaches have been documented in multicenter clinical trials to maintain feasibility without compromising overall study integrity (24).

Other limitations include the relatively short follow-up period (6 to 9 months post-placement) and the modest sample size. While adequate for preliminary comparisons, these constraints prevent definitive conclusions about long-term success and biological stability. Future follow-ups involving larger cohorts and extended observation periods (3 to 5 years) will be critical for confirming these early findings. In addition, spit-mouth design has the distinct advantage of removing a lot of inter-subject variability from the estimated treatment effect. Methods of statistical analyses for split-mouth design have been well developed. However, little work is available on sample size consideration at the design phase of a split-mouth trial (25, 26).

This results of the present study must to be interpreted as preliminary report. The minimal marginal bone remodeling observed in this preliminary report supports the potential for further investigations into the subcrestal placement of KS implants. Nonetheless, further randomized controlled trials are required to validate these findings.

Conclusions

Within the limitations of this study, the reduced-diameter KS implant demonstrated significantly lower marginal bone loss compared to the TSIII implant, with no complications observed in either group. These results suggest superior peri-implant tissue stability with the KS system in molar sites. Long-term, large-scale clinical trials are warranted to validate these findings and further elucidate the clinical benefits of the KS implant design.

Funding

Osstem Implant donated the materials used for the research; however, the company never interfered with the evaluation of the research, data collection and writing of the manuscript.

Institutional Review Board Statement

All data were evaluated at the Department of Medicine, Surgery, and Pharmacy, University of Sassari, Italy. The research protocol has been approved (approval code: XXX) and registered in ClinicalTrial.gov (NCT05843981). The study followed the principles of the 2013 Helsinki Declaration and Good Clinical Practice guidelines. All medical data were anonymized to protect patient identity. Written informed consent was obtained from all participants for data collection and treatment. Each center obtained approval from the local ethics committee, where required.

Informed Consent Statement

Written informed consent was obtained from all participants for data collection and treatment.

Conflicts of Interest

Most of the authors are key opinion leader for the company (Osstem Implant). However, all the authors declare no conflict of interest in this research.