Articles - Forum Implantologicum

Article

Feature Article

May 25, 2021 // 17 min read

Implant Shapes and Macro-designs: Advantages and Disadvantages

DOI: 10.3290/iti.fi.45624

Abstract

Every time a dentist places an implant in a patient, a series of decisions are made regarding implant selection. Implant macro- and micro-design are dictated by manufacturers. There are patient-related metrics like anatomical evaluation, restorative intention, time to loading, restorative space and other factors that are important. Dentist-related criteria like brand preference, cost, personal experience, education, exposure to marketing and available inventory also influence the selection.

Obvious differences between implants include their shape, thread pattern, transmucosal design and prosthetic connection, which together comprise their macro-design. Each of these elements can be engineered or manufactured to impact different clinical performance features of the implants such as primary stability, crestal bone stability, implant fracture toughness, abutment selection, ability to implement digital workflow, augmentation requirements and esthetics. Texture, composition and surface treatment also alter implant options but are considered micro-design features not included in this review.

Categorizing and analyzing design features of implants should help clinicians prioritize and select design features that enhance or facilitate treatment decisions for their patients in each clinical situation. Clinicians should be aware of options and, when possible, should deliberately select the most appropriate implant for each specific indication based on these criteria in order to optimize efficiencies and outcomes. It should clearly be recognized that implant selection alone will neither ensure success nor trigger failure in the absence of other surgical and restorative considerations. This paper will review the macro-design features and suggest clinical guidelines for choosing appropriate implants.

Introduction

Dental implants are a predictable treatment option to replace missing teeth from a functional and esthetic perspective (Jung et al. 2012; Jung et al. 2018). The dental implant market has grown exponentially in the last decades. New brands, different materials and designs, each with a goal of long-term success, are available. Osseosource.com (www.osseosource.com) tracks hundreds of dental implant manufacturers with over 2,000 implant designs manufactured worldwide (Jokstad & Ganeles 2018).

The process of osseointegration in implant dentistry requires implants to be sufficiently immobilized in bone for the complex cellular and cytokine mediated sequence of bone formation onto the implant surface to occur. The biomechanical events are well understood and can be influenced by many factors including implant design (Terheyden et al. 2012; Albrektsson et al. 1981). These devices are manufactured to optimize clinical success while focusing on increasing primary stability, crestal bone stability, optimizing clinical and esthetic outcomes and decreasing augmentation requirements. It should also be acknowledged that many of the different features incorporated into many implants may be marketing-related and business-oriented, rather than evidence-based.

Different implant shapes and designs have been manufactured and investigated in the literature. Variations between designs include abutment connection method, platform-switching versus matched diameter abutments, bone level versus tissue level, tapered versus cylindrical designs, thread patterns and others (Abuhussein et al. 2010; Atieh et al. 2018; Jung et al. 2018). However, the implant selection for each case incorporates more than objective implant-related criteria. Patient- or site-related factors such as timing of implant placement and loading protocol, esthetic or non-esthetic zone, hard and soft tissue anatomy, restorative space, availability of restorative components and single or multiple-tooth rehabilitation impact the selection of specific implant designs. The surgeon’s experience is an important determinant as well.

Clinicians should be aware of the favorable and unfavorable features of each implant design for case selection in order to increase treatment success. This article focuses on metallic implant macro-design features.

Fig. 1: Illustration of different tapered implant designs

Fig. 2: Increased apical dehiscence for cylindrical implant compared to tapered implant in the same position in the same ridge. a: Socket with thin buccal plate. b: Cylindrical implant perforating the buccal plate apically c: Tapered implant within the alveolar contours d: Radiograph simulating cylindrical implant with apical perforation e: Radiograph simulating minimal perforation with tapered implant

Fig. 3a: Cylindrical implant caused need for additional grafting. A similarly sized tapered implant was not available at the time of surgery. 10-year result shows that despite this macro-design-induced challenge, excellent esthetic results and tissue stability were achieved. a: surgical placement with significant apical protrusion of the cylindrical implant. b: 10-year clinical result showing stable tissue contours. C: 10-year radiograph showing stable proximal bone levels

Fig. 3b: Cylindrical implant caused need for additional grafting. A similarly sized tapered implant was not available at the time of surgery. 10-year result shows that despite this macro-design-induced challenge, excellent esthetic results and tissue stability were achieved. a: surgical placement with significant apical protrusion of the cylindrical implant. b: 10-year clinical result showing stable tissue contours. C: 10-year radiograph showing stable proximal bone levels

Fig. 3c: Cylindrical implant caused need for additional grafting. A similarly sized tapered implant was not available at the time of surgery. 10-year result shows that despite this macro-design-induced challenge, excellent esthetic results and tissue stability were achieved. a: surgical placement with significant apical protrusion of the cylindrical implant. b: 10-year clinical result showing stable tissue contours. C: 10-year radiograph showing stable proximal bone levels

Fig. 4: Tapered implant is less likely to damage adjacent roots apically, when placed in close proximity. 6-year post-treatment

Fig. 5: Inter-implant spacing with tilted implants is more difficult with cylindrical implants compared to tapered implants and can result in apical collisions unless shorter implants are used, which may reduce primary stability. a: Close approximation of the apices of tapered implants. b: collision of the apices of cylindrical implants of the same size. c: Example of placement using guided surgery with apices in close approximation

Fig. 6: Tapered vs cylindrical initial bone contact depth

Fig. 7: Fractured tapered implant caused by under-drilling the osteotomy and/or over-seating the implant in dense bone

Fig. 8: Implant thread definitions. a: Reverse buttress screw design b: Spiral thread design

Fig. 9a: Surgical placement with apical stabilization

Fig. 9b: Occlusal view showing no coronal retention

Fig. 10: Implant designs and connections

Fig. 11: Implant/abutment external (a), internal (b) and conical (c, d) connections. a, b, c: Bone level implants. d: Tissue level implant

Fig. 12: 8-year-old implant with matching diameter implant and abutment shows 1-2-mm bone loss while adjacent 4-year-old platform-switched implant shows no bone loss

Fig. 13: Implant external (EC), internal (IC) and conical (CC) connections and platform matching (PM) or switch (PS) abutments. a: EC with a PM abutment, observe the bone resorption around the implant due to the proximity of the micro-gap/interface with the bone. b: using the same connection but with a PS abutment, observe the increased horizontal distance from the micro-gap, reducing the marginal bone loss. c: An internal parallel wall connection with a PM abutment, observe the reduced bone loss when compared to EH and PM. d: IC and PS, the horizontal shift of the micro-gap and more stable bone. e: CC with PM, but in this case, the tissue level implant shifts the micro-gap/interface vertically to the soft tissue, observe the minimal bone loss. f: CC with PS in a bone level implant, showing minimal bone alterations

Fig. 14: Adjacent implants in the esthetic zone. a: External hexagon implant connections with platform matching abutments and an inter-implant distance ≤ 3 mm. The saucerization processes were combined, resulting in loss of bone height, and inter-implant papilla, and formation of a black triangle. b: The same implant connection and abutments, but respecting a minimum distance wider than 3 mm, observe the saucerization processes around both implants, separated by a bone crest. c: Conical connections implants with platform-switching abutments, resulting in a minimum bone loss, and presence of inter-implant papilla

Fig. 15a: Final restorations 2 years post-op show excellent esthetics and tissue stability with full inter-implant papilla

Fig. 15b: Radiograph shows inter-implant bone level at or coronal to implant shoulders

Fig. 15c: Abutments removed showing excellent tissue health

Fig. 15d: Abutments in place showing restorative design for cemented restorations

Fig. 16: Well-spaced posterior tissue level implants with inter-implant bony peaks supporting papillas, 23 years post-op

Fig. 17a: Facial view showing maintenance of labial contour and interdental papillas

Fig. 17b: Radiograph showing excellent crestal bone maintenance

Fig. 18a: Facial view showing discoloration and graying of the labial gingiva near the margin

Fig. 18b: Radiograph showing excellent crestal bone maintenance

Fig. 19a: Facial view showing maintenance of labial contour and interdental papillas without gingival color change

Fig. 19b: Occlusal view with crown off showing thickness of labial tissue

Fig. 19c: Radiograph showing excellent crestal bone maintenance

Fig. 20a: Facial view showing good esthetics and tissue stability

Fig. 20b: Radiograph showing excellent crestal bone maintenance

Fig. 21a: Radiograph taken at the time of provisionalization

Fig. 21b: Radiograph taken 6 years after restoration showing excellent maintenance of crestal bone levels, despite unfavorable crown/implant ratio (>2.5)

Fig. 21c: Clinical view showing elongated crowns to fill restorative space

Fig. 22a: Clinical view showing good esthetics and contours

Fig. 22b: Radiograph showing good maintenance of crestal bone height