12.6 Osseointegration of Dental Implants in a Human Model 12 12.6 Osseointegration of Dental 1998, 2003; Ivanoff et al., 2001, 2003; Romanos Implants in a Human Model et al., 2005; Grassi et al., 2007). The BIC values largely depended on location, implant design, and implant surface characteristics (i.e., topography Giovanni E. Salvi, Dieter D. and chemistry). In single dental implants retrieved Bosshardt, and Niklaus P. Lang from humans after 4, 5, 10, and 12 years in func- tion, the BIC amounted to 78.1%, 83.2%, 77.4%, and 94.1%, respectively (Schenk and Buser, 12.6.1 Background and Scientific Rationale 1998). In one case, four bar-connected titanium Implant placement into alveolar bone induces a plasma-sprayed (TPS) implants retrieved from a cascade of healing events resulting in direct bone 95-year old patient revealed a mean BIC of 76.4% contact with the implant surface. Direct bone-to- after 12 years of functional load (Ledermann et implant contact (BIC) was first described by Per-In- al., 1998). These studies clearly showed that den- gvar Brånemark and coworkers (Brånemark et al., tal implants installed in jawbone of humans 1969, 1977) and histologically demonstrated for become osseointegrated and that osseointegra- the first time by André Schroeder and coworkers as tion of functionally loaded dental implants gener- “functional ankylosis” (Schroeder et al., 1976, ally lasts for many years. Knowledge on the 1978, 1981). Osseointegration is defined as “a sequence of healing events leading to osseointe- direct, structural and functional connection gration of dental implants in humans, however, is between ordered, living bone and the surface of a sparse. A recent series of studies aimed at evaluat- load-bearing implant” (Listgarten et al., 1991). ing histological and molecular levels the rate and Thus, quantification of osseointegration is per- degree of osseointegration at chemically modified formed in histological sections by measuring the at moderately rough, hydrophilic and hydropho- proportion of bone-to-implant contact (BIC) along bic implant surfaces during early phases of healing the external implant surface. To create true BIC val- in a human model (Bosshardt et al., 2011; Donos ues, the analysis needs to be performed along the et al., 2011; Ivanovski et al., 2011; Lang et al., intact tissue-implant interface and without the 2011). The findings of these studies (Bosshardt et presence of aberrations. Therefore, micro-com- al., 2011; Lang et al., 2011) indicated that implant puted tomography (µ-CT) and histomorphometri- placement into alveolar bone induces a cascade of cal analysis of tissues where the implant had been healing events starting with clot formation and removed prior to histological processing may be continuing with bone maturation in contact with considered as inadequate (Butz et al., 2006). the implant surface. From a molecular point of Indeed, in most studies where the BIC was ana- view, osseointegration is associated with a lyzed, ground sections (i.e., histological sections of decrease in inflammation and an increase in oste- undecalcified tissues) were performed. ogenesis-, angiogenesis- and neurogenesis-asso- A number of studies show that titanium implants ciated gene expression during the early stages of with various surface characteristics do osseointe- wound healing (Donos et al., 2011; Ivanovski et grate in human jawbone as demonstrated by al., 2011). histomorphometry. Implants retrieved from Although important findings on the interaction humans represent a very inhomogeneous group of individual cell types and titanium surfaces may of different implant types explanted for various be obtained from in vitro studies, they do not fully reasons including implant failure. Implants reflect the complex mechanisms during tissue retrieved 2 to 10 months following installation integration of implants in vivo. Based on the fact without bone grafting showed BIC values between that wound healing and tissue formation, espe- 7% and 100% (Piattelli et al., 1998, Wilson et al., cially bone formation, may occur at a higher speed 263 Clinical Research Protocols for Indications in Dental Regeneration 1. Study protocol 1. Pre-operative care 1. Histologic processing 1. Statistical analysis 2. Ethical committee approval 2. lmplant placement 2. Descriptive histology 2. Manuscript preparation 3. Application for funding 3. Postoperative care 3. Histomorphometry 3. Manuscript submission 4. Healing time point(s) 4. lmmunohistochemistry 4. Manuscript revision 5. Explantation 5. Gene analysis Phase 1: Planning Phase 2: Surgery Phase 3: Laboratory processing Phase 4: Data analysis and manuscript preparation Fig 12.6-1 The four phases of a clinical study evaluating osseointegration of dental implants in a human model. in experimental animals compared with humans, installation, and by histomorphometric measure- findings from animal experiments may not be ments of the BIC with respect to implant land- transferred directly to the human situation with- marks. Moreover, immunohistochemical and gene out adaptation. analysis techniques may be applied. Hence, it is the aim of this chapter to summarize the steps necessary to conduct a study on osseo- 4. Data Analysis and Preparation of the integration of dental implants in humans. Manuscript The timeframe for performing a clinical study may 12.6.2 Timeline of the Study (Fig 12.6-1) depend on the number of subjects included, the Studies evaluating osseointegration in humans healing time-points chosen and the laboratory should be divided into four phases: techniques applied. One to 2 years may be required, from the planning phase to the final ver- 1. Planning Phase sion of the manuscript. Preparation of the study protocol, including a clear statement of the scientific hypothesis, is to 12.6.3 The Four Phases be carried out. In order to receive financial sup- port, the principal investigator of the study should 1. Planning Phase consider submission of the protocol to institutions and foundations. A clinical study should only be Subject Sample Inclusion Criteria initiated after the protocol has been submitted to Subjects fulfilling the following inclusion criteria and approved by the appropriate ethical or human should be enrolled: subjects committee. • age ≥ 18 years • absence of relevant medical conditions 2. Surgical Phase • absence of regular intake of medications affect- Preoperative care, implant placement, postopera- ing bone metabolism (e.g., bisphosphonates, tive care, healing time-point(s) and explantation. corticosteroids) • smoking ≤ 5 cigarettes/day 3. Laboratory Phase • periodontal health or treated periodontal condi- The events leading to osseointegration should be tions analyzed by a descriptive analysis of histological • absence of mandibular third molars or healed sections at different time-points following implant extraction sockets after third molar extraction 264 12.6 Osseointegration of Dental Implants in a Human Model 12 • presence of sufficient parent bone volume in mercially available implants with respect to Sa and the retromolar area for experimental implant Ra values. installation Moreover, implant surface wettability measured • signed informed consent. with dynamic contact angles (DCA) should be assessed. This would allow the distinction between Exclusion Criteria hydrophobic and hydrophilic implant surfaces. Subjects should not be enrolled, if the following conditions are present: Healing Time-points • uncontrolled medical conditions Early healing periods ranging from 7 days up to 6 • untreated periodontal conditions weeks after implant installation should be planned. • contraindications for oral surgical procedures Healing periods after 6 weeks following implant • pregnant and lactating females installation may no longer provide the dynamic • unwillingness to comply with study protocol. processes during tissue integration. Rather, they represent a stage of homeostasis in which remod- Power Calculation eling processes may take place. A standard normal distribution should be assumed. The probability of a type I error will be set at Test Groups α = 0.05 and of a type II error at β = 0.20 in order A split-mouth study design testing devices with to achieve a study power of 80%. The standard two different materials or surface characteristics in deviations reported in previous similar experi- the same subject may be planned. ments should be used as a reference. Mean values and standard deviations should be 2. Surgical Phase calculated for each variable and group. Normal distribution of the data should be tested. Depend- Preoperative Care ing on the data distribution, either non-parametric In order to avoid an accidental perforation of the or parametric tests should be applied in the statis- lingual cortical plate in the retromolar area, a tical analysis. three-dimensional image may be indicated. Peri-operative complications (i.e., events occur- Experimental Implant Configuration ring during the surgical procedure itself or during The implants used should have a geometry corre- the early stages of wound healing) should be sponding to that of a solid screw implant for clinical avoided by enrolling only subjects fulfilling the use and be made of commercially pure titanium, inclusion criteria. titanium-zirconia alloys or zirconia. A U-shaped cir- The use of prophylactic systemic antibiotics is not cumferential trough should be prepared within the indicated for straightforward implant installation. thread region of the endosseous portion of the implant leaving