Tissue-Level Versus Bone-Level Dental Implants: A Comparative Review for Contemporary Prosthodontic Practice

INTRODUCTION

Since the introduction of osseointegrated implants, two principal macro-design philosophies have shaped clinical practice: the bone-level (BL) implant, restored via a separate abutment connected at or below the crestal bone, and the tissue-level (TL) implant, which incorporates a smooth transmucosal collar that positions the implant-abutment junction (IAJ) coronal to the bone crest, at or near the mucosal surface.¹ The BL concept, popularized by the Brånemark two-stage submerged protocol, was later joined by the one-stage transmucosal design championed by the ITI (International Team for Implantology) system, which allowed non-submerged healing and permitted soft tissue attachment directly against a machined implant collar.² Both approaches have matured into contemporary implant families with strong long-term survival data, and the choice between them remains one of the more frequently debated design decisions in restorative implant dentistry.

For the prosthodontist, the distinction is not purely academic. The location of the IAJ influences the depth of biologic width formation, the restorative envelope available for abutment selection, the ease of impression-making, and the long-term stability of the peri-implant soft tissue margin — all of which affect esthetic and functional outcomes. This review synthesizes the biologic and clinical evidence comparing TL and BL implants and translates it into practical guidance for case selection and prosthetic planning.

1. Design Philosophy and Terminology

Bone-level implants are designed to be placed with the implant platform positioned at or slightly below the alveolar crest, typically in a two-piece configuration in which a separate abutment is connected after a healing period (submerged) or immediately (non-submerged). This design allows the clinician to select abutment height, angulation, and emergence profile independently at the time of restoration, and to reposition the restorative platform relative to the soft tissue margin as needed.

Tissue-level implants feature a machined, smooth-surfaced transmucosal collar — typically 1.8 to 2.8 mm in height — that is manufactured as part of the implant body itself and spans the distance from the crestal bone to the mucosal surface. The prosthetic connection therefore sits coronal to the soft tissue, simplifying impression-making and abutment connection and reducing the number of implant-abutment interfaces exposed to the peri-implant sulcus. Historically, TL implants have been favored for single-stage protocols and for sites where minimizing surgical steps and chairside complexity is prioritized.

2. Biologic Rationale: Biologic Width and the Implant-Abutment Junction

Regardless of macro-design, a biologic width of soft tissue — comprising a junctional epithelium and a zone of connective tissue attachment — forms apical to the IAJ once an implant is exposed to the oral environment.³ Histologic work by Hermann, Buser, Cochran, and colleagues demonstrated that this dimension is relatively consistent (approximately 3 to 4 mm) but that its location relative to the bone crest differs depending on whether the IAJ is one-piece (TL) or two-piece with a microgap (BL).⁴ Around two-piece implants, the presence of a microgap at the IAJ harbors a persistent inflammatory cell infiltrate, and the bone appears to remodel apically to re-establish an adequate biologic dimension away from this microgap — a process implicated in the classic 1.5 to 2.0 mm of early crestal bone loss historically described around submerged, matched-platform BL implants.⁵ One-piece TL implants, lacking a crestal microgap, tend to show a more coronal soft tissue margin and a biologic width dimension that more closely resembles that of a natural tooth, with the bone remodeling pattern occurring around the smooth collar rather than at the crest itself.

This biologic difference is the mechanistic basis for much of the comparative crestal bone research discussed below, and it also underlies the development of platform switching as a bone-preserving modification of the BL design.

3. Platform Switching and Its Influence on Crestal Bone

Platform switching — connecting a narrower-diameter abutment to a wider-diameter implant platform — was introduced by Lazzara and Porter as a means of horizontally repositioning the IAJ inward, away from the outer edge of the implant platform.⁶ This shifts the inflammatory cell infiltrate and the resulting biologic width formation medially and away from the crestal bone, and has been associated radiographically with reduced vertical bone loss compared to matched-diameter BL restorations. Because platform switching is a restorative concept rather than a macro-design feature, it can, in principle, be applied to some BL systems but not to conventional one-piece TL implants, whose collar diameter is fixed. This has made platform-switched BL implants a frequent comparator in more recent literature examining crestal bone stability, and several reviews now suggest that platform-switched BL designs may narrow or reverse the traditional bone-preservation advantage once attributed mainly to TL implants.

4. Comparative Evidence on Marginal Bone Loss

The comparative literature on marginal bone loss (MBL) between TL and BL implants is extensive but heterogeneous, reflecting differences in implant systems, abutment connections (matched versus platform-switched), loading protocols, and follow-up duration.

An early systematic review by Vouros et al. found comparable clinical and radiographic outcomes between BL and TL implants placed in pristine bone, with no clinically meaningful difference in survival.⁷ A subsequent meta-analysis reported a pooled difference of only 0.05 mm in MBL favoring TL implants, a difference that did not reach statistical significance.⁸ In contrast, a systematic review and meta-analysis by van Eekeren and colleagues found that implants placed with the platform above the crest (TL) exhibited approximately 0.29 mm more crestal bone resorption than epicrestal (BL) implants, suggesting a modest advantage for the BL design in that analysis.⁹

More recent systematic reviews have generally reinforced the impression that differences are small and inconsistent in direction. A 2020 systematic review of radiological outcomes across 20 studies and nearly 3,000 implants found no consistent difference in implant success or survival between TL and BL groups, with only a minority of individual studies reporting a statistically significant MBL difference in either direction.¹⁰ A meta-analysis focusing specifically on platform design concluded that BL implants restored with platform-switched abutments tended to show better marginal bone stability than either TL implants or BL implants with matched-diameter abutments, though heterogeneity across the included trials was substantial.¹¹ A more recent (2024) update using pooled data through April of that year likewise reported statistically significant differences in MBL in most of the studies analyzed, while explicitly noting that the magnitude of these differences was unlikely to be clinically meaningful in most cases.¹²

Taken together, the weight of current evidence suggests that (a) both TL and BL implants are capable of maintaining stable crestal bone over the short-to-medium term; (b) platform-switched BL designs may offer a small, statistically detectable advantage over matched-platform BL or conventional TL implants; and (c) the clinical significance of these differences, on the order of a few tenths of a millimeter, remains uncertain and is unlikely by itself to dictate implant selection in most cases.

5. Peri-Implant Soft Tissue Health and Peri-Implantitis Outcomes

Beyond crestal bone, peri-implant soft tissue stability and the incidence of peri-implantitis are important long-term outcome measures. A recent systematic review and meta-analysis comparing TL and BL implants found comparable implant survival and peri-implantitis risk over 1 to 5 years of observation, with no statistically significant difference in probing pocket depth or marginal bone level change between designs.¹³ Notably, TL implants showed numerically lower rates of peri-implantitis and implant failure, and smaller increases in probing depth at 12 and 24 months, although these trends did not reach statistical significance. This is consistent with the biologic rationale that a smooth, one-piece transmucosal collar may reduce the surface area available for microbial colonization at the peri-implant sulcus compared with a two-piece IAJ situated closer to or below the soft tissue margin, particularly in patients with a history of periodontitis or suboptimal plaque control.

6. Prosthetic and Restorative Considerations

From a restorative standpoint, the two designs impose different demands and offer different advantages:

Impression-making and workflow: TL implants present a fixed transmucosal collar at a known, consistent level, which can simplify conventional and digital impression techniques and reduce the number of components requiring verification at try-in. BL implants require an additional abutment-level impression or scan step, but this also allows the restorative margin to be customized chairside.

Restorative flexibility: Because the BL abutment is selected and seated at the time of restoration, the prosthodontist retains flexibility to adjust emergence profile, angulation correction, and transmucosal height according to the final soft tissue contour — an advantage in sites with unpredictable healing or when the definitive restorative plan evolves after implant placement. TL implants, by contrast, fix the transmucosal height at the time of surgery, which requires more precise presurgical planning of soft tissue thickness.

Component inventory and cost: TL restorations often require fewer distinct components (no separate abutment in simpler cases), which can reduce inventory complexity and cost in high-volume or resource-limited settings. BL systems typically require a wider abutment library to accommodate variable soft tissue depths and angulations.

Esthetic zone management: In thin or scalloped biotypes, the fixed collar height of TL implants can be a limitation if the soft tissue level does not match the implant's transmucosal dimension, whereas BL implants with custom or angulated abutments allow more precise soft tissue emergence sculpting — an advantage frequently cited for anterior esthetic cases.

Platform switching access: Only BL systems can take advantage of platform-switched abutment connections, which may confer the crestal bone preservation benefit discussed above; this is not achievable with a conventional one-piece TL collar.

7. Surgical and Site-Specific Considerations

Site-specific anatomy and soft tissue characteristics remain important co-determinants of implant selection. TL implants are frequently favored in posterior sites with adequate keratinized tissue and predictable ridge morphology, where single-stage, non-submerged healing shortens treatment time and simplifies surgical re-entry. BL implants, owing to their restorative flexibility, are more readily adapted to variable soft tissue thickness, immediate placement/immediate provisionalization protocols, and esthetically demanding anterior sites where abutment angulation and emergence profile must be customized. Mucosal thickness itself has also been identified as an independent factor influencing crestal bone stability irrespective of implant macro-design, reinforcing that soft tissue phenotype should be assessed independently of the TL/BL decision.

8. Clinical Decision-Making in Full-Mouth and Partial Rehabilitation

In the context of full-mouth or multi-unit implant rehabilitation, several practical factors typically guide the choice between TL and BL systems: the need for angulation correction across multiple implants (favoring BL abutment flexibility), the desirability of a simplified one-stage protocol in medically compromised or elderly patients (favoring TL), the esthetic demand of the visible zone (favoring BL with custom abutments), and the clinician's and laboratory's familiarity with a given implant system's prosthetic library. In practice, many contemporary implant systems now offer both TL and BL platforms with shared prosthetic components, allowing the clinician to select the macro-design most appropriate to each individual site within the same rehabilitation rather than committing to a single design throughout the arch.

9. Limitations of the Current Evidence

Much of the comparative literature is limited by heterogeneity in implant systems, abutment connections, follow-up duration, and outcome reporting, which complicates direct pooling across studies. Randomized, head-to-head trials with matched implant surface characteristics, standardized loading protocols, and follow-up beyond five years remain relatively scarce. Furthermore, because platform switching can confound comparisons between BL and TL designs, future studies would benefit from clearly stratifying results by abutment connection type in addition to macro-design.

CONCLUSION

Tissue-level and bone-level dental implants both achieve predictable, high long-term survival, and current evidence does not support a clinically decisive advantage of one design over the other in terms of marginal bone loss or peri-implant health. Design selection should instead be individualized according to soft tissue phenotype, restorative space, esthetic demand, need for angulation correction, and the surgical protocol best suited to the patient. A sound understanding of the biologic rationale underlying each design — particularly the role of the implant-abutment junction and platform switching in biologic width formation — equips the prosthodontist to make this decision on a site-by-site basis rather than by default preference.

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