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Does a collagen matrix add
dimensional stability in guided
bone regeneration?

    Does a collagen matrix add
    dimensional stability in guided
    bone regeneration?

    Goran I. Benic, Stefan P. Bienz, Young Woo Song, Jae-Kook Cha, Christoph H.F. Hämmerle, Ui-Won Jung, Ronal


    In cases where there is insufficient bone availability to place
    implants, guided bone regeneration (GBR) simultaneous
    with implant placement is commonly used. It is usually
    performed with particulated grafting materials and resorbable
    membranes, as explained by the systematic review published
    in 2019 by Thoma et al. However, both this review and other
    studies showed how the combination of these materials for
    successful regeneration was sometimes not predictable and it
    was not adequate in the case of non-contained bone defects,
    mainly because of their lack of dimensional stability.
    As a result, different materials have been developed to
    increase dimensional stability, such as the soft-type block,
    which consists of a mixture of particles of bone substitutes
    in a collagen matrix. This combination was developed for
    alveolar ridge preservation (ARP) because of its increased
    ability to maintain the augmented space and the ridge
    contours, as was shown in the results of two in vitro studies
    (Mir-Mari et al., 2016, 2017).
    However, there is still not enough evidence from in vivo preclinical
    and clinical studies, especially regarding the long-term
    results when using these materials.



    The aim was to compare the hard-tissue dimensions and
    dimensional stability after guided bone regeneration of periimplant
    defects, using either a soft-type block-bone substitute,
    in which the bone substitute was incorporated into a collagen
    matrix, or a particulated bone substitute.

    Materials & methods

    • This prospective randomised clinical trial included 40 patients
    in need of at least one dental implant and simultaneous bone
    augmentation of peri-implant defects, with a follow-up of six months.
    Conventional inclusion and exclusion criteria for implant therapy were
    applied, and heavy smokers were excluded.
    • Forty patients were randomised into two parallel treatment groups.
    Patients in the control group received a particulate synthetic biphasic
    calcium phosphate (BCP), comprising 60% hydroxyapatite and 40%
    beta tricalcium phosphate (HA/TCP), whereas those in the test group
    received a soft-type block bone in which the same synthetic BCP
    was embedded in a collagen matrix (CM) to improve its dimensional
    • Implants were placed at least two months after tooth extraction,
    leaving peri-implant bone defects that were filled and overaugmented
    with the material during the surgery. Bone dehiscences
    were classified in contained and non-contained defects, and their
    apicocoronal dimension was measured on the buccal implant
    surface. Local antiseptics and systemic antibiotics were prescribed
    during the healing period.
    • Re-entry surgeries were performed six months after implant
    placement, and the residual presence of bone dehiscences was
    measured, along with other clinical parameters.
    • Cone beam computed tomography (CBCT) scans were performed at
    baseline, immediately after implant placement, and after six months,
    and assessed by a blinded investigator. The horizontal dimension
    of the augmented bone at the implant shoulder was evaluated and
    considered as the primary outcome variable for sample calculation.
    • Other radiographic variables such as the vertical and diagonal
    dimension of augmented bone were also evaluated at the various
    time points.
    Does a collagen matrix add
    dimensional stability in guided
    bone regeneration?
    Goran I. Benic, Stefan P. Bienz, Young Woo Song, Jae-Kook Cha, Christoph H.F. Hämmerle, Ui-Won Jung, Ronald E. Jung

    Figure: Complete clinical sequence of each treatment modality with full defect resolution


    Baseline situation after implant placement (a), guided bone regeneration with the selected bone graft (b), collagen membrane stabilised (c),
    complete defect resolution at re-entry surgery (d), and CBCT six months after implant placement (e).


    • Thirty-five subjects were finally included in the six-month analysis
    (17 in the test group and 18 in the control group).
    • With regards to soft-tissue dehiscences, only one was found in each
    • Horizontal hard-tissue dimensional changes, measured by CBCT,
    showed mean augmentation values of 1.15mm (test) and 0.93mm
    (control), with no statistically significant differences.
    • When clinically measuring apicocoronal hard tissue changes at
    the re-entry surgery, 58.8% of the test sites and the 55.6% of the
    control sites, showed a complete vertical defect fill. When assessed
    by CBCT, higher percentages of complete vertical defect fill were
    observed (82.4% for the test group and 88.9% for the control group).


    • Combining both groups, 14 contained and 21 non-contained defects
    were included. At six months, only two of the 14 contained defects
    (7.1%) did not achieve complete vertical fill (both in the control
    group); while 13 out of 21 (61.9%) non-contained defects did not
    achieve complete vertical bone fill, with similar results in both
    groups – 58.3% (test) and 66.7% (control).
    • In both type of defects, there was a reduction in the horizontal
    dimension of the augmented hard tissue, comparing post-operative
    and six-month measurements.
    • The average time after tooth extraction was longer for noncontained
    defects (7.5 months) compared with contained defects
    (3.0 months).


    • Sample: no information about the smoking
    habits of patients (only that heavy smokers were
    excluded); use of the term “active periodontal
    disease”, which does not follow the current
    • Surgical procedure: wide time range after tooth
    extraction, membrane stabilisation could have been
    improved, and a high exposure rate after two and
    four weeks in both groups.
    • Main radiographical outcome variable might not
    be adequate, as clinical measurements show less
    resolution and are not ideal because three different
    CBCTs were needed within six months.
    • Unclear if the lack of statistically significant
    differences in the results resulted from the sample
    size calculation, which was merely empirical,
    based on a superiority trial design. Only 35 patients
    attended the short-term follow-up.

    Conclusions & impact

    • Immediately after wound closure, GBR with a soft-type BCP and
    collagen block combined with a CM and fixation pins lead to superior
    dimensions of augmented hard tissue compared to a particulate graft
    plus CM.
    • However, at re-entry, six months later, this dimensional stability
    favouring the test group was not observed, and no differences were
    found regarding augmented hard-tissue dimensions.
    • The use of either a soft-type collagen-containing block or particulate
    bone grafts in combination with a buccally tacked CM is not a
    predictable alternative in reaching complete resolution of noncontained
    peri-implant bone defects.
    • Neither GBR with a BCP bone graft in a particulate presentation nor
    supported with a collagen matrix creating a soft-type block seem to be
    the ideal treatment option when treating non-contained bone defects
    simultaneous to implant placement.