Variation of the ultrasonic response of a dental implant embedded in tricalcium silicate-based cement under cyclic loading

Abstract

The use of tricalcium silicate-based cement (TSBC) as bone substitute material for implant stabilization is promising. However, its mechanical behavior under fatigue loading in presence of a dental implant was not reported so far because of the difficulty of measuring TSBC properties around a dental implant in a nondestructive manner. The aim of this study is to investigate the evolution of the 10 MHz ultrasonic response of a dental implant embedded in TSBC versus fatigue time. Seven implants were embedded in TSBC following the same experimental protocol used in clinical situations. One implant was left without any mechanical solicitation after its insertion in TSBC. The ultrasonic response of all implants was measured during 24 h using a dedicated device deriving from previous studies. An indicator I based on the temporal variation of the signal amplitude was derived and its variation as a function of fatigue time was determined. The results show no significant variation of I as a function of time without mechanical solicitation, while the indicator significantly increases (p<10⁻⁵, F=199.1) at an average rate of 2.2 h⁻¹ as a function of fatigue time. The increase of the indicator may be due to the degradation of the Biodentine–implant interface, which induces an increase of the impedance gap at the implant surface. The results are promising because they show the potentiality of ultrasonic methods to (i) investigate the material properties around a dental implant and (ii) optimize the conception of bone substitute materials in the context of dental implant surgery.

Introduction

The use of bone substitute biomaterials in the context of dental implant surgery has become a common technique used for edentulous patients with poor bone quality. Different biomaterials have been used as bone substitute material such as autogenous (Khoury et al., 2007, Rickert et al., 2012), allogeneic (Waasdorp and Reynolds, 2010) and xenogeneic (Simion and Fontana, 2004, Taschieri et al., 2010) bone grafts as well as different synthetic biomaterials (Davies et al., 2010).

Autogeneous bone graft has good clinical performances but constitutes a relatively invasive surgical procedure. Allogeneic bone graft can be considered as a good alternative because of the greater amount of material available and the possibility of using local anesthesia only. However, allograft requires a longer period for bone regeneration and the risk of rejection and infection may be higher (Jones, 2008). Therefore, xenogeneic bone graft has been employed using biomaterials such as coral or animal bone tissue, which are easier to handle (Simion and Fontana, 2004, Eppley and Dadvand, 2006). Another option lies in using synthetic biomaterials which may be easier to produce (Shigeishi et al., 2012) and injectable (Gauthier et al., 1999). Different biomaterials of synthetic origin have been developed such as calcium phosphate ceramic (Morimoto et al., 2012) and bioglass (Kenny and Buggy, 2003, Trindade-Suedam et al., 2010). Among the different calcium phosphate ceramics, β-tricalcium phosphate (Podaropoulos et al., 2009), hydroxyapatite material (Kenny and Buggy, 2003, Shigeishi et al., 2012) and a mix of both (Yamada et al., 1997) have been used as bone substitute materials in the context of dental implantology (Miyamoto et al., 2012). When bone graft, calcium phosphate ceramic and bioglass are used, relatively important healing time (four to nine months) is needed to allow bone remodeling and to secure implant insertion (Brook and Hatton, 1998, Larsson et al., 2012), while modern dental implant treatments aim at a rapid strong and long-lasting attachment between implant and bone for optimal performances.

Interestingly, tricalcium silicate-based cements (TSBCs) (such as Biodentine (Koubi et al., 2012, Koubi et al., 2012)), which are used in the clinic in the context of restorative and endodontic procedures for dentinal tissue replacement (O'Brien, 2008), could be used as bone substitutes in the context of dental implantology because it combines adapted mechanical properties (Golberg et al., 2009, Sawyer et al., 2012), biocompatibility (Camilleri et al., 2012, Leiendecker et al., 2012), with bioactive properties (Laurent et al., 2008, Laurent et al., 2012, Koubi et al., 2012, Koubi et al., 2012). Another advantage of Biodentine lies in the relatively low duration necessary to prepare the mixture before application (only 9–12 min; Golberg et al., 2009; are necessary for material preparation), thus rendering its clinical use relatively easy. TSBC are adapted to be used as bone substitute material in the context of dental implantology because of their adhesive properties with calcified tissues (Kenny and Buggy, 2003), which increase as a function of time due to their chemical composition (Watanabe et al., 2006). Beside adapted adhesive and elastic properties, bone substitute materials must also have adapted fatigue behavior (Davidson, 2006, Wong et al., 2011) in order to sustain actual biomechanical solicitations. However, the fatigue behavior of TSBC in the presence of mechanical stresses generated by dental implants remains unexplored due to the difficulty of measuring the evolution of mechanical properties of materials around the implant interface. A better understanding of the evolution of the cement biomechanical properties around the implant surface could lead to a better conception of bone graft substitute materials.

Different methods have been developed in the past to monitor the evolution of material properties around a dental implant. Dental surgeons use empirical methods based on palpation and patient sensation (Krafft et al., 2012) but these methods suffer from a lack of precision and standardization. Histomorphometry is the gold standard to assess osseointegration and stability of an implant (Franchi et al., 2007), but it is a destructive method and cannot be used to assess mechanical properties. Classical radiography (Frederiksen, 1995) and X-ray microcomputed tomography (Akca et al., 2006) have been suggested for the evaluation of the implant fixture, but resolution problems due to diffraction phenomena (Shalabi et al., 2007) around the implant interface prevent from using X-ray based approaches to measure the interface properties, which is the important parameter for the success of the surgical intervention. The Periotest (Bensheim, Germany) (Schulte et al., 1983) and Osstell (Gothenburg, Sweden) (Meredith et al., 1997) methods are biomechanical approaches clinically used for the assessment of implant stability. However, Periotest (Aparicio et al., 2006) and Osstell (Pattijn et al., 2007) measurements are dependent on the orientation and the fixation of the devices, leading to reproducibility limitations that may prevent from reliable quantitative evaluation of implant stability. More recently, an alternative nondestructive method based on the ultrasonic response of the implant has been developed by our group to assess the biomechanical properties around the implant (de Almeida et al., 2007, Mathieu et al., 2011a, Mathieu et al., 2011b). Ultrasonic techniques have the advantage to be sensitive to the bone-implant interface properties (Mathieu et al., 2011b, Mathieu et al., 2011b, Mathieu et al., 2012a, Mathieu et al., 2012b, Mathieu et al., 2012c).

The aim of this study is to investigate the evolution of the ultrasonic response of an implant embedded in TSBC and subjected to fatigue stresses. The variation of the implant ultrasonic response could lead to important information on the evolution of the biomaterial biomechanical properties around the implant.