In implant dentistry, the goal of the implant prosthesis is to not only survive but also be able to be stable biologically and functionally. For long-term success, the implant crown or prosthesis should approximate the morphology of a natural tooth.1 If the implant prosthesis deviates from the normal, natural tooth contours, the prosthesis may be predisposed to compromised aesthetics, prosthetic mechanical complications, a loss of ideal soft-tissue architecture, peri-implant disease, and hygiene difficulty.
IDEAL IMPLANT POSITIONING
One of the most critical skills in the practice of implant dentistry is the understanding and the ability to place an implant in the ideal and correct position. Prior to implant placement, a detailed and comprehensive evaluation of the patient’s existing condition should be completed with respect to the intended final prosthesis. The positioning of implants must be carefully treatment planned three-dimensionally (via CBCT) with the goal of the final prosthesis being in harmony biologically, functionally, and aesthetically. Ideally, prior to implant placement, the existing alveolar ridge should be evaluated and treated appropriately for any osseous or soft-tissue deficiencies so that the implant may be inserted in the same position as the natural tooth.
Properly placed dental implants will allow the clinician to insert a prosthesis with ideal contours, thus allowing for an emergence profile that will maintain ideal embrasure spaces and proximal contact areas. According to the The Glossary of Prosthodontic Terms the emergence profile is defined as “the contour of the restoration as it relates to the emergence from circumscribed soft tissues.” A proper emergence profile is crucial in preventing peri-implant disease as it maintains gingival health, prevents plaque (biofilm) retention, maintains adequate thickness of soft tissue, and allows for oral hygiene maintenance. To minimize the risks of these postoperative complications, biological, mechanical, and occlusal principles must be strictly followed. However, in some clinical situations, this is difficult to accomplish because of poor implant placement positioning.
The placement of a dental implant in available bone is comparable to an object in space that is defined by x-, y-, and z-coordinates. In implant dentistry, the x-axis is defined by the mesiodistal plane, the y-axis is the buccolingual dimension, and the z-axis is known as the apicocoronal (the length of the implant body in relation to the osseous crest). In this article, various poor-positioning clinical complications will be discussed with respect to the x-axis.
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1. Insufficient Implant: Tooth (Coronal) Distance
When lack of space between the implant platform and the coronal aspect of the adjacent tooth occurs, numerous complications may result. The implant should be 1.5 to 2.0 mm from the adjacent tooth for proper prosthesis contour, maintenance of crestal bone, and preservation of the soft-tissue drape. Complications include:
• Compromised emergence profile: When inadequate space is present for the formation of a prosthesis emergence profile, aesthetic, hygienic, and soft-tissue complications may arise. Ideally, a straight emergence profile (ie, similar to natural teeth) should be utilized in the final prosthesis to decrease implant morbidity.
• Interproximal bone loss: Because of the lack of space between the tooth and implant, bone resorption is more prevalent due to insufficient blood supply. Studies have shown a correlation between increased bone loss and decreased distance of the implant from the adjacent tooth.2
• Reduced papilla height: Because of interproximal bone loss and compromised space, a lack of or reduction in the size of the tissue papilla will lead to a poor soft-tissue drape and increased peri-implant problems.
• Hygiene difficulties: The ability to keep the prosthesis properly cleaned will be difficult with compromised space. This will result in increased biofilm accumulation, which may lead to increased periodontal complications.
In conclusion, the coronal implant-tooth distance should be approximately 1.5 to 2.0 mm, depending on the specific tooth being replaced (Figure 1).
2. Insufficient Implant: Root (Apical) Distance
Implants placed too close to an adjacent tooth root are usually the result of poor treatment planning (eg, inadequate space), poor surgical technique (eg, improper angulation), or the placement of too wide of an implant body. This may occur more commonly when root dilacerations are present or when a tooth has been orthodontically repositioned to where the tooth root has encroached on the intra-root space. Ideally, 2.0 mm of space should be present between the implant and the natural root apex. Complications include:
• Damage to the adjacent periodontal ligament: Implants positioned too closely to a root may risk damage to the periodontal ligament (PDL) and surrounding structures. This may cause displacement of bone into the PDL space and result in altered blood supply to the adjacent tooth, loss of tooth vitality, apical periodontitis, and internal or external resorption.3
• Loss of implant: Implants that are placed too close to an adjacent tooth may fail due to the increased possibility of infection or bone resorption.
• Loss of tooth: If adequate space is not maintained between a tooth and an implant, the adjacent tooth may be irreversibly traumatized and may be lost to a fracture or to internal or external resorption.
In conclusion, the coronal implant-tooth distance should be approximately 1.5 mm to 2.0 mm, depending on the specific tooth being replaced (Figure 2).
3. Increased Distance Between Implant and Tooth
An implant that is placed too far from a natural tooth poses numerous issues. When an implant is placed more than 2.0 mm from an adjacent tooth, a cantilever effect will usually result on the marginal ridge of the implant crown. This may lead to increased possibility of biomechanical overload and aesthetic issues and resulting bone loss with increased morbidity. Complications include:
• Overcontoured crowns: Because of the excessive space, overcontouring of the final prosthesis is necessary to obtain a contact area with the adjacent tooth. This will result in biomechanical and aesthetic complications.
• Atypical prostheses: Because of the need to obtain interproximal contact, the final prosthesis will be atypical, which may lead to increased difficulty in prosthetic impression, laboratory, and insertion procedures.
• Cantilever effect (biomechanics): The resultant cantilever from a malpositioned implant results in a biomechanical disadvantage with damaging moment forces, leading to bone loss. Cantilevers present on implant prostheses are more problematic than on natural teeth because of the lack of PDLs. The overcontoured crown leads to resultant shear forces, which may lead to component failure (eg, screw loosening, screw fracture, or implant fracture).
• Food impaction: Food impaction is a common complaint from patients with an increased implant-tooth distance because hygiene maintenance is difficult due to overcontoured prostheses and associated soft-tissue complications.
In conclusion, the distance between the implant and tooth should be approximately 1.5 to 2.0 mm (Figure 3).
4. Lack of Implant-Implant Distance
When multiple implants are inserted, care should be exercised to maintain adequate spacing between the implants. Studies have demonstrated that the ideal amount of space between implants is approximately 3.0 mm. Tarnow et al4 have shown that implants placed less than 3.0 mm apart may have adequate stability and function; however, this placement will likely result in crestal bone loss. In this study, implants with greater than 3.0 mm of distance between implants resulted in a 0.45-mm bone loss, while implants positioned less than 3.0 mm apart had over twice the amount—or approximately 1.04 mm—of bone loss.4 Complications include:
• Prosthetic issues: When lack of space is present between 2 implants, numerous prosthetic complications may arise, including an inability to place healing abutments, a lack of space for the placement of transfer copings, and a compromised and unconventional prosthesis.
• Intra-implant bone loss: If insufficient bone is present between implants, bone loss will result due to the lack of blood supply.
• Loss of intra-implant papilla: As bone loss results, the distance between the contact point of the implant prosthesis and the bone level increases. As this distance increases (ie, above 5 mm), the papilla will decrease in size and contour and the formation of a black triangle will result.
• Hygiene difficulty: Difficulty in hygiene will result due to the lack of space between the implants. The resultant poor tissue condition increases the amount of biofilm accumulation, leading to the development of peri-implant disease.
In conclusion, the ideal implant-implant distance is approximately 3.0 mm (Figure 4).
PREVENTION OF POOR POSITIONING
1. Treatment planning: The use of an accurate radiographic modality (CBCT) is paramount in determining the existing available bone, bone density, occlusal relationship, and ideal implant position. In some clinical cases, a study cast and diagnostic wax-up may be utilized.
2. Surgical templates: A CBCT-generated template may be used to accurately place the implants. When an implant is to be placed adjacent to a tooth, a tooth-supported guide is the most accurate guide when compared to bone- or tissue-borne guides.
3. Surgical adjuvants: With freehand implant placement, positioning instruments and devices allow for ideal osteotomy preparation and adherence to implant placement approximately 1.5 to 2.0 mm from an adjacent tooth and 3.0 mm between adjacent implants (Figure 5).
IN SUMMARY
Recently, advances in implant dentistry have created a greater appreciation for the aesthetic and biological results of the implant prosthesis. Implant dentistry has experienced a profound shift from a solely functional approach to a prosthetically and biologically driven approach. Recent studies have shown the prevalence of peri-implant mucositis and peri-implantitis to be approximately 39.7% and 16.7%, respectively.5 A significant component of the increased incidence of peri-implant disease results from poor implant positioning. Therefore, the implant clinician must follow a top-down treatment planning approach, which dictates the implant position be predicated on the intended, ideal prosthesis.
References
- Parkinson CF. Excessive crown contours facilitate endemic plaque niches. J Prosthet Dent. 1976;35:424-429.
- Esposito M, Ekestubbe A, Gröndahl K. Radiological evaluation of marginal bone loss at tooth surfaces facing single Brånemark implants. Clin Oral Implants Res. 1993;4:151-157.
- Margelos JT, Verdelis KG. Irreversible pulpal damage of teeth adjacent to recently placed osseointegrated implants. J Endod. 1995;21:479-482.
- Tarnow DP, Cho SC, Wallace SS. The effect of inter-implant distance on the height of inter-implant bone crest. J Periodontol. 2000;71:546-549.
- Ahn DH, Kim HJ, Joo JY, et al. Prevalence and risk factors of peri-implant mucositis and peri-implantitis after at least 7 years of loading. J Periodontal Implant Sci. 2019;49:397-405.
Dr. Resnik is a leading clinician, educator, researcher, and author in the field of prosthodontics and oral implantology. Dr. Resnik received a specialty degree in prosthodontics and oral implantology from the University of Pittsburgh, along with a Master’s degree in oral implantology/radiology. He is currently the chief of staff and surgical director of the Misch Implant Institute. He also holds faculty positions at the University of Pittsburgh (graduate prosthodontics), Temple University (graduate periodontics), and Allegheny General Hospital in Pittsburgh (oral and maxillofacial surgery). Along with his passion for lecturing and education, Dr. Resnik is also an accomplished author, having published numerous research articles and textbooks across his career. His 2 recent books, Avoiding Complications in Oral Implantology and the Misch’s Contemporary Implant Dentistry, 4th Edition are best sellers in the field of oral implantology. He can be reached via email at resnikdmd@gmail.com.
Disclosure: Dr. Resnik reports no disclosures.
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