The primary challenge faced by reconstructive dentistry today is achieving superior aesthetic results while preserving as much of the biological structures involved as possible. Thanks to modern materials and procedures, clinicians and dental technicians can now recreate both aesthetics and function in a more predictable and efficient way.

One of the main clinical complications of fixed prosthodontics on natural teeth is unsatisfactory aesthetic results due to the apical migration of the gingival margin. The Biologically Oriented Preparation Technique (BOPT) offers a solution, enabling clinicians and dental technicians to manipulate the surrounding dental tissues, altering their shape and gingival architecture regardless of prior dental or gingival limitations.

The development of new materials and equipment, coupled with a better understanding of soft tissue biology, has paved the way for the resurgence and advancement of a revolutionary concept in prosthodontics: vertical preparation – preparation without a defined finish line (like a chamfer or shoulder) and instead it uses a feather-edge or knife-edge margin.

Do you want to discover the secrets of seamless gingival integration and biological stability with BOPT and learn everything about this concept from choosing the right burs to mastering digital impressions and advanced cementation protocols? Then join our course “VertiPrep + BOPT Concept” and perfect your skills in aesthetic rehabilitation, temporary prosthetics, and fixed restorations!

The Problem of Apical Gingival Migration

Apical migration of the gingiva is linked to various factors, including:

Inadequate quality and quantity of keratinized gingiva (recessions are more common in thin biotypes).
Response to trauma during prosthodontic procedures (preparation, gingival retraction). Chronic inflammation due to prosthetic errors (over-contouring, violating biological width).
Poor oral hygiene and trauma from brushing.

With the BOPT approach, the anatomy of the tooth eruption from the gingiva can be transferred to the artificial crown, ensuring that the gingiva can adapt and take form around the new contours and profiles. The contours of the crown produced using BOPT may seem overly exaggerated from the traditional definition of "hypercontouring," but clinically, there is no excess contour. Instead, there is a “new contour” and a new Orthopedic Cement-Enamel Junction.

Clinically, BOPT is applied by adjusting the finish line geometry during preparation, which is key for ensuring a natural, seamless integration with the surrounding tissues. The traditional horizontal preparation involves creating a well-defined line that is replicated in the impression and the working model. In contrast, the vertical preparation approach, as seen in BOPT, allows the dental technician to determine the final boundary based on the surrounding gingival tissues, ensuring a more flexible and less invasive result.

Previously, horizontal finishing lines (Subgingival Horizontal Preparation Technique) have been the standard in crown preparation, widely regarded as the gold standard by the academic world. In traditional crown preparation, horizontal lines are preferred when the clinical and anatomical crowns align well, and the periodontal condition is healthy. These edges are placed near the cementoenamel junction. Vertical preparation is more conservative and is ideal when the clinical crown does not match the anatomical crown due to periodontal disease, allowing for a more minimalistic approach.

Advocates of the Subgingival Horizontal Preparation Technique preparation approach highlight several advantages:

Prevention of undercuts
Prevention of overhanging restoration margins
Respect for biological width
Ease in defining the finish line for dental technicians
Simplified communication between clinician and laboratory

On the other hand, these same proponents have often pointed to the drawbacks of vertical preparation:

Inevitable undercuts
Overhanging restoration edges
Uncontrolled burr penetration into the gingival sulcus, leading to disruption of biological width
Difficulty for dental technicians in defining the finish line
Increased complexity in clinician-laboratory communication

As a result, the academic community has largely dismissed vertical preparation as unfeasible.

However, Subgingival Horizontal Preparation Technique is associated with gingival recession and increased probing depth (>3 mm) over time, higher rates of plaque retention due to a defined finishing line that may trap bacteria, and less gingival stability over the long term. Since SHPT involves placing the crown margin below the gingival crest, which can irritate the gingiva and lead to recession over time, which exposes the crown margin, compromising aesthetics and increasing the risk of root sensitivity. Moreover, invasive subgingival placement can interfere with the biologic width, leading to bone resorption and loss of attachment.

These disadvantages have led to the growing popularity of vertical preparation techniques in the BOPT concept. Over the years, a small group of proponents – referred to as “verticalists” – have introduced two primary approaches to vertical preparation:

Preparation without a true shoulder but with a bevel
Preparation without any visible boundary definition

Bevel preparations were popular during the "golden era" of prosthodontics, as working with gold allowed minimal thickness at the crown's edge. Regardless, one fact remained uncontested: preparation without a shoulder is the most conservative method for preserving tooth structure and the simplest way to prevent gaps between the restoration and the tooth's hard tissues.

Key Features of Vertical Preparation in BOPT concept:

No Defined Finish Line:
- The preparation ends with a feather-edge that gradually tapers off without a distinct margin.
- This allows the restoration to adapt seamlessly to the tooth and gingival tissues.
Rotary Curettage:
- During preparation, a slight gingival displacement occurs using the bur, which acts as a rotary curettage.
- This helps to create a clean interface between the tooth and gingiva, promoting better tissue healing and adaptation.
Soft Tissue Adaptation and Stability:
- By avoiding a defined finish line, the gingiva can naturally adapt to the restoration.
- This promotes gingival thickening and stability of the gingival margin, reducing the risk of recession over time.
Feather-Edge Margin:
- The gradual tapering of the preparation ensures minimal removal of tooth structure.
- It enhances the fit and marginal adaptation of the crown, reducing gaps that could lead to plaque accumulation.

Vertical preparations are beneficial for various clinical scenarios, including:

Replacing old crowns with improper gingival architecture or biologically compromised conditions.
Endodontically treated or young, live teeth that require restoration to address color, shape, or erosion.

Vertical Preparation and the Periodontium

This preparation method is "biologically friendly" to the soft tissues, particularly the periodontium. By using specialized burs, it is possible to preserve the biological width during preparation.

Biological width consists of the following components:

Junctional epithelium
Connective tissue attachment
The gingival sulcus

The only structure that must not be violated during preparation is the connective tissue attachment, which is key to maintaining periodontal health. The junctional epithelium is not as vital structurally and can be replaced with other materials, as long as they are smooth, clean, and free from periodontal disease.

The BOPT Technique: Step-by-Step

The BOPT technique begins with gentle probing of the periodontal sulcus to assess the attachment level using a periodontal probe. Next, the preparation itself is completed with a flame-shaped bur, ensuring that the natural contours of the tooth are followed to remove undercuts and provide proper crown seating. At this stage, the clinician creates a preparation that allows for a crown margin that is 0.3 mm at the edge, 0.5 mm along axial walls, and 1 to 1.5 mm on the occlusal surface, thus ensuring adequate mechanical resistance.

Once the preparation is finished, the bur interacts with both the internal tooth wall and the epithelial attachment of the gingiva, removing the old cementoenamel junction. A temporary crown with a new contour and margin is placed, ensuring it doesn't extend beyond 0.5-1 mm into the gingival sulcus, maintaining biological width.

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Healing and Stabilization

After placement of the temporary crown, the healing process begins, stabilizing the gingival tissue around the new profile. Within a few weeks, the gingiva adapts, thickening and attaching to the new contour, establishing a stable interface between the gingiva and the prosthetic crown.

The Role of the Dental Technician

The dental technician plays a crucial role in creating the final crown profile. By marking the finish line on the working model using a red pencil and following the gingival contour, they can define the new crown margin. Depending on the aesthetic needs, the finish line can be positioned either coronally or apically within the sulcus, ensuring a perfect fit without damaging the epithelial attachment.

The Benefits of Vertical Finishing Lines

Biomechanical considerations in tooth preparation are intimately tied to the ferrule effect, a concept often misunderstood in dental practice. The ferrule is not merely a residual structure but refers to a mechanical effect that enhances the strength and longevity of the restoration.

The ferrule effect involves the crown serving as a "bracelet" around the tooth, holding it in place. For the ferrule to function optimally, the crown material must have a higher modulus of elasticity than the tooth tissues, and it should not reduce the remaining tooth structure excessively.

The major issue with horizontal preparation is that it often reduces vital tooth structure, particularly in the cervical area. This reduction compromises the ferrule effect, making the restoration more prone to failure, especially under stress. The ultimate risk is the concentration of stress at the margin, which can lead to fractures or dislodgement of the restoration.

Biological and Clinical Benefits of Vertical Preparation

BOPT presents numerous advantages both biologically and clinically:

Biological Benefits: Enhanced gingival thickness, increased stability of the gingival margin over time, and the ability to position the gingival margin at different levels according to aesthetic needs.
Clinical Benefits: Easier and quicker to perform, predictable aesthetic results (achieves a seamless transition between the restoration and the gingiva, avoiding visible crown margins), preservation of tooth structure, and effective bonding with minimal invasiveness, the lack of a defined margin simplifies impression techniques and enhances the accuracy of fit.

What is Gingitage retraction technique? How does it differ from traditional retraction techniques? Why is it essential for achieving precise margins and optimal aesthetics in ceramic restorations? Discover the answers to these questions and more in our lesson “Vertical preparation for all-ceramic restorations”. You will also learn the value of vertical geometry and its impact on finish line precision, how to effectively use metal-free ceramics and choose the right materials, including cubic zirconia and lithium disilicate and more!

The BOPT method offers a streamlined, minimally invasive approach to prosthodontic procedures. By working with the surrounding gingival tissues and ensuring a new, more natural Cementoenamel Junction, both clinicians and dental technicians can achieve high-quality aesthetic results while maintaining optimal periodontal health. This method not only preserves more of the natural tooth structure but also ensures long-term stability of the gingiva, making it a superior alternative to traditional preparation techniques.

Professional articles about dentistry: Dental mechanics in prosthodontics