To compare the stability of apically tapered and straight (non-tapered cylindrical) implants at the time of immediate placement and to histologically evaluate the healing outcomes after 6 weeks.
The second maxillary incisors were extracted bilaterally in nine dogs. After randomization, apically tapered and straight implants with a 3.3 mm shoulder diameter were inserted into the extraction sockets. The implant stability quotient (ISQ) of the implants were recorded after placement. Peri-implant defects on the buccal aspect were filled with deproteinized bovine bone mineral and covered with resorbable type I/III porcine collagen matrix. After 6 weeks of healing, sections were prepared for histological and morphometric analysis.
All implant sites healed uneventfully. The apically tapered implants had significantly higher ISQ values compared to straight implants at placement (p = 0.009). The histomorphometric outcomes 6 weeks following implant placement in both experimental groups were similar, except in the apico-palatal region. Apically tapered implants demonstrated significantly less percentage bone-to-implant contact (p = 0.035) in the apico-palatal region. At both implant types, substantial corono-apical resorption of the buccal bone wall was noted in the coronal 2 mm of the implant.
Apically tapered implants had significantly higher ISQ values at immediate placement compared to straight implants. The healing outcomes and remodeling of the buccal bone wall were similar for both implant designs. In the apico-palatal region, there was less %BIC at the implant surface at apically tapered implants compared to straight implants.

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