Journal of Functional Biomaterials Review Methods to Improve Osseointegration of Dental Implants in Low Quality (Type-IV) Bone: An Overview Hamdan S. Alghamdi Department of Periodontics and Community Dentistry, College of Dentistry, King Saud University, Riyadh 11545, Saudi Arabia; [email protected]; Tel.: +966-11-467-7732 Received: 2 November 2017; Accepted: 9 January 2018; Published: 13 January 2018 Abstract: Nowadays, dental implants have become more common treatment for replacing missing teeth and aim to improve chewing efficiency, physical health, and esthetics. The favorable clinical performance of dental implants has been attributed to their firm osseointegration, as introduced by Brånemark in 1965. Although the survival rate of dental implants over a 10-year observation has been reported to be higher than 90% in totally edentulous jaws, the clinical outcome of implant treatment is challenged in compromised (bone) conditions, as are frequently present in elderly people. The biomechanical characteristics of bone in aged patients do not offer proper stability to implants, being similar to type-IV bone (Lekholm & Zarb classification), in which a decreased clinical fixation of implants has been clearly demonstrated. However, the search for improved osseointegration has continued forward for the new evolution of modern dental implants. This represents a continuum of developments spanning more than 20 years of research on implant related-factors including surgical techniques, implant design, and surface properties. The methods to enhance osseointegration of dental implants in low quality (type-IV) bone are described in a general manner in this review. Keywords: dental implants; osseointegration; bone regeneration; surface modifications 1. Introduction Dental implants have become a more common treatment for replacing missing teeth [1]. Consequently, in clinical dentistry, dental implants aim to increase patient satisfaction in terms of improved chewing efficiency, physical health, and esthetics. The global dental implant market is anticipated to grow steadily from US$3.4 billion in 2011 to US$6.4 billion in 2018 [1]. The favorable clinical performance of dental implants has been attributed to their firm bone integration. In 1965, Brånemark introduced the term “osseointegration” to describe the successful outcome of bone-to-implant integration [2]. Clinically, the process of osseointegration reflects the mechanical anchorage of a dental implant into the jaw bone that persists under all normal conditions of oral function. Overall, bone regeneration related to dental implants in a healthy condition is a complex process and can take up to several weeks. A few days after implantation, several biological events (bone regeneration) are regulated by several growth and differentiation factors that are released in the implant vicinity [3,4]. The process of bone regeneration is formed either on the implant surface (i.e., de novo bone formation, contact osteogenesis) or from the surrounding bone towards the implant surface (i.e., distance osteogenesis) [5]. Finally, bone remodeling occurs by replacing immature with mature bone at the implant site, providing biological (mechanical) stability, which is secondary to primary fixation obtained during implant insertion. Although the survival rate of dental implants over a 10-year observation has been reported to be higher than 90% in totally edentulous jaws [6], dental implants do fail in some patients. There are many reasons for dental implant failure including an inappropriate diagnosis and treatment J. Funct. Biomater. 2018, 9, 7; doi:10.3390/jfb9010007 www.mdpi.com/journal/jfb J.J. Funct. Funct. Biomater. Biomater. 20182018, 9,, 97, 7 2 2of of 7 8 many reasons for dental implant failure including an inappropriate diagnosis and treatment plan, inadequateplan, inadequate information information on the patient’s on the patient’s medical medicalhistory, history,or lack of or experience lack of experience and surgical and skills surgical to placeskills dental to place implants dental correctly implants [7]. correctly Most importantly, [7]. 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In addition,In addition, proliferation proliferation and and activity activity of mesenchymal of mesenchymal cells cells and and osteoblastogenesis osteoblastogenesis seem seem affected affected [11]. [11 ]. AlthoughAlthough research research on on osteoporosis osteoporosis is ongoing, is ongoing, including including prevention prevention and andtreatment treatment modalities, modalities, the knowledgethe knowledge on bone-biomaterial on bone-biomaterial regeneration regeneration in osteoporotic in osteoporotic bone boneremains remains limited. limited. However, However, the searchthe search for improved for improved bone bone regeneration regeneration in challenged in challenged conditions conditions has has helped helped propel propel the the continuing continuing evolutionevolution of of modern modern dental dental implants. implants. This This represents represents a acontinuum continuum of of developments developments spanning spanning more more thanthan 20 20 years years of of research research on on implant implant related-factors related-factors including including surgical surgical techniques, techniques, implant implant design, design, andand material material and and surface surface properties. properties. Figure 1. Lekholm & Zarb classification: Type I, the entire bone is composed of very thick cortical Figure 1. Lekholm & Zarb classification: Type I, the entire bone is composed of very thick cortical bone;bone; Type Type II, II, thick layer ofof corticalcortical bone bone surrounds surrounds a corea core of of dense dense trabecular trabecular bone; bone; Type Type III, thinIII, thin layer layerof cortical of cortical bone bone surrounds surrounds a core a ofcore trabecular of trabecular bone ofbone good of strength;good strength; and Type and IV,Type very IV, thin very layer thin of layercortical of cortical bone with bone low with density low density trabecular trabecular bone of bone poor of strength. poor strength. To explain the above-mentioned problem better, the remedies to enhance bone–implant To explain the above-mentioned problem better, the remedies to enhance bone–implant integration integration in low quality (Type IV) bone are described in a general manner in this review. in low quality (Type IV) bone are described in a general manner in this review. 2. Design of Dental Implants and Primary Stability 2. Design of Dental Implants and Primary Stability Over the last few decades, several implant-design concepts have been developed and are Over the last few decades, several implant-design concepts have been developed and are commercially available. Dental implants mostly possess a threaded cylindrical- or conical(root)- commercially available. Dental implants mostly possess a threaded cylindrical- or conical(root)-design design (Figure 2). The design parameters primarily affect load (i.e., stress/strain) distribution in the (Figure2). The design parameters primarily affect load (i.e., stress/strain) distribution in the bone bone tissue, resulting in a proper implant fixation