Immediate loading of short dental implants after sinus floor augmentation
Eduardo Anitua examines the factors influencing success when immediately loading short implants following a transcrestal sinus lift.
Short implants (less than 8mm in length) offer predictable outcomes to the implant surgeon. However, there is a paucity in the long-term evaluation of immediately-loaded short implants.
This case report examines the outcome of a missing tooth restored with a single-unit short implant. The 7.5mm long implant was inserted after transcrestal sinus floor augmentation and was immediately loaded. The follow-up time was nine years with a successful outcome in terms of implant and prosthesis survival and marginal bone stability.
The immediate loading of short implants could be a predictable alternative in the transalveolarly augmented maxillary sinus floor.
Since the first publication on immediate loading of dental implants, an increasing number of research and systematic reviews have been published.
In 2000, a review of the available clinical and experimental studies accepted the idea of immediate implant loading. It recommended the type of fixation that minimises implant micro-movements (Szmukler-Moncler et al, 2000).
The data compiled for the immediate loading of dental implants shows similar survival rates as delayed loading. The insertion torque is one of the most influential parameters in the treatment success (Szmukler-Moncler et al, 2000; Benic et al, 2014; Esposito et al, 2013; Norton, 2011; Su et al, 2014). The recommended values range between 30Ncm and 45Ncm for single-unit prostheses. A minimum of 20Ncm for multiple prosthesis, or an implant stability quotient between 60-65.
The successful performance of immediate loading generated the question about the possibility of immediate function.
In 2014, a meta-analysis concluded that the functionalisation protocol does not significantly affect implant survival or crestal bone loss (Su et al, 2014).
In a systematic review, implant and prostheses had different survival outcomes. This was according to the anatomical area (maxilla, mandible, anterior and posterior). Immediate implants with immediate loading have a higher failure rate in posterior areas than anterior areas. This was highlighted when estimated together in different published studies (0.54% – 0.45% respectively) (Lang et al, 2012).
Implants in the maxilla have also been shown to have a higher annual failure rate (0.73%). Compared with those inserted in the mandible (0.50%) (Lang et al, 2012).
Short dental implants
The use of short dental implants may limit the need for bone augmentation. The predictability of short implants has been assessed recently. This was covered in a survey of randomised clinical trials of implants placed in augmented sinus (Thoma et al, 2015).
Short (a length of 8mm or less) implants offer predictable survival rates and result in three times fewer intraoperative complications than long implants (Lang et al, 2012).
Short implants placed in a posterior partial edentulism have demonstrated a high initial survival rate – similar to long implants (Atieh et al, 2012).
From all the above, shorter dental implants may be the preferred treatment in atrophic alveolar bone as they have been associated with lower biological complications, decreased morbidity, costs and surgical time (Atieh et al, 2012).
The predictability of immediate implant loading and short implants have raised questions. Such as, whether the immediate loading of short implants is predictable as well.
In a recent work published by our study group about this topic, the authors concluded that the immediate loading of short implants is not a risk factor for treatment success. This could be related to good bone quality and the achievement of adequate primary stability (Anitua et al, 2016).
A 43-year-old female patient attended the dental clinic complaining of pain in the posterior area of the upper left jaw. After careful clinical examination, the upper left first molar was diagnosed with vertical root fracture and tooth extraction was decided upon. The patient accepted the treatment plan.
Atraumatic tooth extraction was performed, preserving the socket walls. The extraction socket was then treated with Endoret (PRGF). For that, peripheral venous blood was extracted by venipuncture into 9ml extraction tubes containing sodium citrate as anticoagulant (BTI Biotechnology Institute S, Vitoria, Spain).
The blood-containing tubes were centrifuged in a BTI system centrifuge. The plasma column was then separated into two fractions with one having the highest platelet concentration. Ten minutes before surgery, the Endoret (PRGF) was activated with calcium ions. This initiates growth factor release from the platelets and the formation of a fibrin scaffold.
The Endoret (PRGF) clot was used to fill the extraction socket and the fibrin membrane was used to cover the extraction socket. Monofilament 5/0 nylon sutures with one or more cross-stitches were then applied (Figure 1).
Figures 2 and 3 show the correct healing and clinical evolution of the extraction socket.
At one month, complete regeneration of the socket was observed and the planning of the dental implant was set.
In order to make a proper treatment plan, the patient underwent a standard diagnostic protocol consisting of clinical examination and the study of the diagnostic wax-up and cone-beam computerised tomography (CBCT) scan (Figure 4).
This author has described the technique for transcrestal sinus floor elevation elsewhere (Anitua et al, 2015). Briefly, conventional drills working at low speed (150 rpm) without irrigation were used to prepare the implant site. A frontal cutting drill was then introduced to prepare the last 1mm of the implant alveolus. When a window (half of the sinus floor) was created, a well-retracted F1 plug was introduced. A blunt hand instrument was introduced to push the fibrin membrane apically and to simultaneously elevate the Schneiderian membrane.
The area below the Schneiderian membrane was grafted by Endoret (PRGF) clot. Before installation, the dental implant was embedded in Endoret (PRGF) and the surgical motor was set at 25Ncm. The implant was finally seated manually by a calibrated torque wrench. The final insertion torque was 70Ncm and the inserted dental implant was 6mm in diameter and 7mm in length. Bone loss at the mesial point was 0.2mm and 0.2mm at the distal point.
Immediate loading was performed 24 hours after the surgery with a personalised definitive abutment and a cemented crown (Figure 5). After completing the surgical and prosthetic phases, the patient was reviewed at six and 12 months during the observation period of the study.
Survival of the implant
Implant success was defined according to the criteria suggested by Buser et al (1994) and modified by Albrektsson and Zarb (1998).
Survival of the implant was evaluated positively when the implant was present at the end of the follow-up period, irrespective of conditions. In follow-up appointments the data of prosthetic and implant-related complications were recorded (abutment screw loosening, abutment screw fracture, loss of retention of the permanent crown or fracture of veneer material). Survival of the prosthesis and success of the prosthetic treatment were considered when the following criteria were fulfilled (Lang et al, 2012).
During the follow-up period (nine years), the single-implant restoration was free of prosthesis- or implant-related complications.
The immediate loading of short implants in posterior areas was not a risk factor for implant survival and marginal bone stability in this case. Cannizzaro et al (2012) reported the four-year outcomes of immediate versus early loading of 6.5mm long single implants in a controlled randomised split-mouth clinical trial.
The insertion torque was greater than 40Ncm in both groups. The implant success rate was 96.7% for both groups.
In another randomised controlled clinical trial, the one-year outcome of immediate loading of 5mm long implants by a fixed cross-arch prosthesis was compared to those of 11.5mm long implants (Cannizzaro et al, 2015).
The insertion torque of most of the implants in this study was greater than 50Ncm. Two short implants and one long implant failed. The differences did not reach statistical significance.
In a recent study about the rehabilitation of the edentulous maxilla, the survival rate of immediately-loaded short implants (between 7.0mm- 8.5mm in length) was 95.7% (Malo et al, 2015). However, most of the implants (68 of 74) were placed at the position of the lateral incisor.
The use of Endoret (PRGF) as a biomaterial for tissue regeneration can result in bone regeneration of the extraction socket and the space underneath the Schneiderian membrane. In this case, the healing of the extraction socket has permitted early implant insertion, shortening the time required for treatment. Plasma rich in growth factors represents a biological technique for the localised release of proteins. As well as autologous growth factors. These are present in the patient’s own plasma and platelets, to stimulate haemostasis and tissue regeneration.
The use of plasma
The use of plasma rich in growth factors has been reported to improve the osseointegration and the implant stability quotient at 12 weeks after placement (Anitua et al, 2009; Quesada-Garcia 2012). Furthermore, increasing implant diameter is more effective than implant length in decreasing the stress transmitted to the peri-implant bone (Anitua et al, 2010).
The use of platelet rich plasma in maxillary sinus augmentation reportedly has favourable effects. Particularly on soft tissue healing and postoperative discomfort reduction (Del Fabbro et al, 2013).
The activation of plasma rich in growth factors with calcium ions triggers the formation of fibrin scaffold and the release of autologous growth factors (Anitua et al, 2012; Torres et al, 2010). A positive effect on soft tissue healing has been observed during bone augmentation surgery.
The use of fibrin membranes has been effective in preventing titanium mesh exposure. Also, in minimising the risk of failure due to graft infection (Torres et al, 2010). Del Fabbro et al (2013) indicated that the using of platelet-derived growth factors during the early phases of healing (three to six months) could be beneficial. Plasma rich in growth factors could increase the bone formation. Supported by an organic bovine xenograft (Del Fabbro et al, 2013; Torres et al, 2010; Taschieri et al, 2015; Torres et al, 2009).
The immediate loading of short implants inserted in posterior areas, supporting unitary prosthesis, was not a risk factor for implant or prosthesis success in this case.
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