Original study - ZZI 02/2011

Guided vertical bone regeneration by means of roughened
and alkaline treated titanium implant surfaces
A comparison based on a rabbit mandible model

M. Karl1, M.A. Freilich2, B. Wen2, M. Wei3, D.M. Shafer4, L.T. Kuhn2

Introduction: To determine if an alkaline surface treatment would enhance vertical bone growth around sand-blasted, large grit, acid-etched (SLA) titanium implants in a rabbit mandible model.

Material and methods: A total of twelve New Zealand white rabbits received either SLA or alkaline-treated SLA implants placed in transverse orientation in the posterior mandible with the coronal 3 mm of the implants left outside the bone. Three treatment groups (n = 6 implants per group) were studied with or without demineralized bone matrix (DBM) scaffolds as follows: SLA/DBM, alkSLA/DBM or alkSLA alone. The DBM was stabilized by a scaffold retention screw. MicroCT imaging and histological analysis was performed on retrieved specimens after ten weeks of healing to assess new bone formation.

Results: For all parameters, except for bone volume fraction, the highest values were recorded for SLA implants plus DBM scaffolds. Bone-to-implant contact (BIC) in the newly-formed mass of bone above the original bone was not enhanced in the alkaline-treated group as compared to the SLA group (32.0 % ± 13.5 vs. 55.7 % ± 12.8; p = 0.0152). Significantly less new bone formed around alkaline-treated implants when they were placed without DBM scaffolds (e. g. bone height with DBM: 1.9 mm ± 0.3, without DBM: 0.3 mm ± 0.5; p = 0.0312).

Discussion: Alkaline treatment of commercially available SLA implants did not enhance vertical bone regeneration or bone-to-implant contact in combination with DBM in this animal model.

Keywords: vertical bone regeneration; implant surface; demineralized bone matrix; rabbit mandible; alkaline treatment

Introduction

Vertical bone augmentation is often needed in order to create adequate bone height for implant placement [4, 8]. Numerous techniques have been developed, some requiring the use of autogenous bone [18, 25], guided bone regeneration (GBR) using resorbable and non-resorbable membranes with and without particulate bone grafting materials [5, 11] and the use of signalling agents such as bone morphogenetic proteins such as BMP [29, 31], platelet rich plasma [18] and enamel matrix proteins [16, 30]. Significant challenges have also been reported for all of these methods. Donor site morbidity often accompanies the harvesting of autogenous bone, membrane uti-lization can be technique sensitive and result in exposure and sometimes infection [19] and the use of platelet rich plasma and enamel matrix proteins shows inconsistent results [10, 15].

Recently it has been shown that new mandibular bone, with good bone-to-implant contact and bone quality, can be regenerated above the original level of bone, using a partially inserted sand-blasted, large-grit, acid-etched (SLA) titanium implant surrounded by a demineralized bone matrix scaffold [1] stabilized by a scaffold retention screw [12, 13].

Surface modifications of titanium implants are known to influence bone regenerative processes [26, 28], thus it was hypothesized that the amount of new vertical bone formed by the implant construct of Freilich et al. [13] could be increased by enhancing the surface of the implant. The SLA surface used in the Freilich et al. [13] study has been shown to result in higher bond strengths between the implant and bone as compared to smooth metal surfaces [2, 3]. Other techniques, such as calcium phosphate (CaP) coating and alkaline treatment, are alternative options to modify the surface of titanium implants to achieve good surface bioactivity and bond strengths [17, 20, 22, 33]. The two major problems encountered with CaP coatings are degradation of the coatings [22] and interface reactions between titanium and CaP during sintering of the coatings [32]. One approach to by-pass the limitations of CaP coatings is to treat the implant surface with alkaline solutions [33]. The altered implant surface has bioactive characteristics and stimulates the body to deposit CaP on the implant in situ which in turn enhances osseointegration [7, 21, 24, 27, 33].

Alkaline coatings had not been tested previously against SLA directly, thus in the current study, SLA implants were subjected to an additional alkaline treatment, and their capability for generating vertical bone formation was compared to the as-received SLA implants, both in combination with a demineralized bone matrix scaffold. It was hypothesized that besides greater levels of bone-to-implant contact (BIC), alkaline-treated implants would improve quality of the newly formed vertical bone (increase bone density) and increase volume of new bone as compared to SLA.

 

Materials and Methods

Implants and scaffold material

Experimental solid screw implants (8 mm long, 4.1 mm diameter) made of commercially pure titanium were used in all groups (Institut Straumann AG, Basel, Switzerland). The implants were cylindrically shaped except for the coronal-most 3 mm, which exhibited slight taper increasing the diameter to 4.8 mm at the head of the implant. A line was scribed into the implants dividing them into a 5 mm apical part to be anchored in the existing bone and a 3 mm coronal, osteogenic part to be left out of the existing bone. Modified healing abutments 8 mm in diameter with polished surfaces and six oval shaped openings were screwed onto the implants and served as scaffold retention screws. The implants either had an SLA surface or an alkaline-treated SLA surface (denoted as alkSLA) which were placed up to the shoulder of the implants with no polished collar. For the alkaline treatment, the SLA implants were immersed in 10 M NaOH at 80°C for eight hours. The alkaline-treated implants were re-sterilized using E-Beam radiation prior to their use.

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