What Exactly Is Morse Taper?

Discover the intriguing world of Morse Taper, a unique engineering concept that plays a vital role in dental implants. Unravel the mysteries behind Morse Taper's significance in oral healthcare and how it revolutionizes the connection between implants and abutments. Join us on a journey to explore the cutting-edge technology shaping the future of dental implantology!

 

Dental implants play a crucial role in restoring dental defects and losses, widely adopted in clinical dentistry. As implant technology becomes more prevalent, the connection between implants and abutments is garnering increased attention from professionals and scholars due to its long-term impact on implant success. Implant-abutment connections fall into two categories: external connection and internal connection. External connection involves the implant's upper plane protruding 1-2 mm outward, connecting with the corresponding concave portion on the abutment's lower plane. Internal connection, on the other hand, features the implant's upper plane recessing inward, connecting with the abutment's lower plane's outward protruding portion. External connections include hexagon, octagon, and cogwheel connections, while internal connections comprise hexagon, octagon, cogwheel, and taper connections, with the Morse taper connection, also known as the Morse Taper, gaining significant attention in modern dental implantology.

1. Morse Taper Connection Structure

The Morse Taper structure, invented by American engineer Stephen A. Morse in 1864, consists of a cone (referred to as the male taper) fitting into another matching hollow cone (referred to as the female taper), both sharing identical taper angles. In implant-abutment connections utilizing the Morse Taper, internal junctions form through two conical structures, with the male taper located on the abutment connection surface and the female taper on the implant connection surface. These conical structures, with parallel-facing joint portions, exhibit self-locking characteristics, generating substantial frictional forces to aid in stabilization. Common implant systems featuring the Morse Taper structure include Bicon® (1.5°), Ankylos® (5.7°), ITI® (6°~8°), and Astra Tech® (11°), with Bicon® and Ankylos® representing well-known pure Morse Taper connection implants.

Bicon® (Bicon, USA) implants possess a 1.5° taper, relying solely on the Morse Taper structure for stability without the aid of screws, making them widely used in clinical settings, particularly for short implants. During clinical implant procedures, Bicon® implant abutments are seated by tapping, relying entirely on the frictional forces at the connection surface for stabilization, eliminating concerns about screw loosening or breakage. However, Bicon® abutments lack positioning markers for seating. In clinical practice, parallel technique X-rays can be employed to capture periapical X-rays of the implant to determine the proper seating of the Morse Taper connection implant abutment by assessing the presence of low-density shadows between the abutment and implant.

Ankylos® (Dentsply Sirona, Germany) systems feature a 5.7° taper, combining the Morse Taper structure with screw fixation. In clinical practice, a torque wrench is used to tighten the central screw, securing the abutment to the implant, resulting in higher long-term retention rates.

2. Characteristics of Morse Taper Connection

(1) High Stability

The stability of dental implants is a crucial factor influencing their long-term retention rate. In many cases, the connection and stabilization of implants and abutments involve the use of a central screw. The torque applied to this central screw determines the preload on the implant-abutment interface. This preload, in conjunction with the resistance of the implant-abutment connection surface structure, collectively influences the stability of the dental implant. Therefore, torque plays a vital role in maintaining the tightness of the implant-abutment interface. Appropriate torque can reduce screw loosening and marginal opening. Excessive external forces on the implant, surpassing the preload and the frictional forces at the connection surface, can lead to torque loss, resulting in screw loosening or even breakage, affecting implant stability. Morse Taper connection, with its conical matching surfaces creating a self-locking effect, provides high stability.

Mangano et al. conducted a follow-up study on 178 Morse Taper connection implants in 49 patients over a period of 10 to 20 years. The results showed a survival rate (10 years and above) of 97.2%, closely approaching the reported 10-year survival rate for implants (96.7%). Studies by Feitosa et al. comparing Morse Taper, external hexagon, and internal hexagon connection implants under the same insertion torque found that Morse Taper connection implants exhibited significantly higher initial removal torque and less torque loss after fatigue testing compared to external hexagon and internal hexagon connection implants. Therefore, Morse Taper connection implants demonstrated better stability than hexagon connection implants.

(2) Excellent Fit

Micro-gaps at the implant-abutment connection interface can compromise the seal and serve as vulnerable points for microbial invasion. Microbial accumulation can lead to marginal bone destruction, impacting osseointegration, and causing serious complications such as peri-implantitis, potentially resulting in implant failure. Studies have shown that regardless of the connection type, two-piece dental implants exhibit some degree of bacterial contamination at the implant-abutment connection surface. However, different designs of implant-abutment connection interfaces can affect their fit. Morse Taper connection implants show a clear advantage in terms of fit at the implant-abutment connection.

Research by Jaworski and Tripodi confirmed that Morse Taper connection implants exhibited superior fit at the implant-abutment connection compared to external hexagon and internal hexagon connection implants. Studies by do Nascimento, immersing implants of different connection types in saliva for pressure cycling experiments, revealed that Morse Taper connection implants had the fewest microorganisms at the connection interface compared to external hexagon and internal hexagon connection implants.

(3) Minimal Peri-implant Bone Resorption

Peri-implant bone volume, including bone height and thickness, significantly affects the long-term retention and aesthetic outcomes of dental implants. Post-implantation, bone resorption around implants is common, and excessive resorption can lead to the formation of deep peri-implant pockets, implant loosening, or even implant failure. Weng et al. compared bone volume changes in the first 3 months after implantation between external hexagon and Morse Taper connection implants in an animal model, finding that Morse Taper connection implants exhibited significantly less peri-implant bone resorption than external hexagon connection implants. Clinical randomized controlled trials by Pessoa et al. confirmed that Morse Taper connection implants had significantly lower bone resorption one year post-implantation compared to external hexagon connection implants, aligning with the aforementioned results.

Peri-implant bone volume also affects the aesthetic outcome of restorations. Mangano et al. conducted a retrospective study on immediate and delayed implantation in the anterior maxillary region using Morse Taper connection implants. They concluded that Morse Taper connection implants, whether used for immediate or delayed implantation, showed acceptable peri-implant bone resorption levels and exhibited good soft tissue conditions, resulting in favorable aesthetic outcomes. However, it is worth noting that while Morse Taper connection implants may have less peri-implant bone resorption compared to other internal connection implants, there were no significant differences in peri-implant parameters, soft tissue changes, or gingival papilla height around the final implant restoration. Additionally, a minority of literature reports that the connection type at the implant-abutment interface has no effect on peri-implant bone resorption. Therefore, the aesthetic restoration effects of Morse Taper connection implants still require long-term clinical controlled trials for validation.

3. Advances in the Application of Morse Taper Connection Implants

As mentioned earlier, peri-implant bone resorption is an inherent challenge regardless of the implant connection type. Minimizing or preventing bone resorption around the implant post-placement is a critical indicator for ensuring long-term implant retention. Both Morse Taper connection and platform switching techniques are considered effective in reducing bone resorption. Consequently, recent literature reports a combination of Morse Taper connection and platform switching to minimize bone resorption around implants. Platform switching involves using an abutment with a diameter smaller than the implant diameter, positioning the abutment edge inside the top platform edge of the implant rather than aligning it with the platform edge. Studies have demonstrated that using platform switching during implant restoration can reduce peri-implant bone resorption and promote the formation of a cuff of soft tissue around the implant, preventing bacterial infiltration and enhancing long-term restoration outcomes. Implant systems, such as the Ankylos® system, that integrate Morse Taper connection with platform switching are now available in the market.

Romanos et al. conducted a 3-year follow-up on 634 Morse Taper connection implants designed with platform switching, achieving a remarkable implant survival rate of 98.74%. According to a foreign review, neck bone resorption within 1.5 mm in the first year after implantation is considered normal. Studies have shown that Morse Taper connection implants combined with platform switching exhibit favorable bone resorption levels in the first year (0.26~0.56 mm). Romanos et al. compared peri-implant bone conditions two years post-implantation between Morse Taper connection implants with platform switching and those without, finding significantly less bone resorption (< 2 mm) in the Morse Taper connection implant group. These studies suggest that the combination of Morse Taper connection and platform switching has a positive effect on reducing bone resorption around implants. Regarding stress distribution, Liu et al. conducted finite element analysis on Morse Taper connection implants (Ankylos) using platform switching. The study found that stress concentrated mainly at the abutment neck and the connection between the abutment and implant for the implant itself. Around the implant, stress was distributed mainly in the cortical bone, and compared to non-Morse Taper connection implants (Anthogyr) with platform matching, Morse Taper connection implants with platform switching exhibited a more uniform stress distribution with lower stress in the peri-implant bone. However, the maximum von Mises stress values were higher in the abutment neck and the portion where the abutment was inserted into the implant. Regarding aesthetic restoration outcomes, Vinnakota et al. reported on four cases using platform switching with Morse Taper connection implants, indicating ideal aesthetic outcomes for all cases after one year, highlighting the effectiveness of Morse Taper connection and platform switching. Currently, there is a lack of long-term studies on the retention rate and long-term aesthetic outcomes of implants combining these two approaches.

Morse Taper connection falls under the category of internal connection and possesses inherent advantages over external connections, such as resistance to lateral forces and rotational stability. Fatigue-related failures often occur at the abutment and screw fixation sites, allowing for abutment or central screw replacement after fracture. Morse Taper connection implants also provide a greater gingival distance, facilitating later-stage restoration. Additionally, compared to implants with other connection types, Morse Taper connection implants exhibit higher stability, better fit at the connection surface, and less peri-implant bone resorption. However, it's essential to note that Morse Taper connection implants still have some limitations: implants with a small taper are challenging to replace; Morse Taper connection implants without screw-assisted fixation are difficult to determine if fully seated, and the tapping placement method may be intolerable for elderly patients with weakened bone. Moreover, several Morse Taper connection implants have not completely avoided microbial contamination at the implant-abutment connection surface. Therefore, improving the clinical operability of Morse Taper connection implants and harnessing their advantages to prevent bacterial contamination at the connection interface is a future research direction. Simultaneously, more long-term clinical trials are needed to explore the performance of Morse Taper connection implants.