J Periodontal Implant Sci.  2018 Jun;48(3):152-163. 10.5051/jpis.2018.48.3.152.

Oral tissue response to soft tissue expanders prior to bone augmentation: in vitro analysis and histological study in dogs

• Yoo JM
• Ben Amara
• Kim MK
• Song JD
• Koo KT

• KMID: 2414928
• DOI: http://doi.org/10.5051/jpis.2018.48.3.152

Abstract

PURPOSE
To determine whether the swelling and mechanical properties of osmotic self-inflating expanders allow or not the induction of intraoral soft tissue expansion in dogs.
METHODS
Three different volumes (0.15, 0.25, and 0.42 mL; referred to respectively as the S, M, and L groups) of soft tissue expanders (STEs) consisting of a hydrogel core coated with a silicone-perforated membrane were investigated in vitro to assess their swelling behavior (volume swelling ratio) and mechanical properties (tensile strength, tensile strain). For in vivo investigations, the STEs were subperiosteally inserted for 4 weeks in dogs (n=5). Soft tissue expansion was clinically monitored. Histological analyses included the examination of alveolar bone underneath the expanders and thickness measurements of the surrounding fibrous capsule.
RESULTS
The volume swelling ratio of all STEs did not exceed 5.2. In tensile mode, the highest mean strain was registered for the L group (98.03±0.3 g/cm), whereas the lowest mean value was obtained in the S group (81.3±0.1 g/cm), which was a statistically significant difference (P < 0.05). In addition, the S and L groups were significantly different in terms of tensile strength (1.5±0.1 g/cm for the S group and 2.2±0.1 g/cm for the L group, P < 0.05). Clinical monitoring showed successful dilatation of the soft tissues without signs of inflammation up to 28 days. The STEs remained volumetrically stable, with a mean diameter in vivo of 6.98 mm, close to the in vitro post-expansion findings (6.69 mm). Significant histological effects included highly vascularized collagen-rich fibrous encapsulation of the STEs, with a mean thickness of 0.67±0.12 mm. The bone reaction consisted of resorption underneath the STEs, while apposition was observed at their edges.
CONCLUSIONS
The swelling and mechanical properties of the STEs enabled clinically successful soft tissue expansion. A tissue reaction consisting of fibrous capsule formation and bone loss were the main histological events.

Keyword

Alveolar ridge augmentation; Histology; Tissue expansion

MeSH Terms

Alveolar Ridge Augmentation
Animals
Dilatation
Dogs*
Hydrogel
In Vitro Techniques*
Inflammation
Membranes
Tensile Strength
Tissue Expansion
Tissue Expansion Devices*
Hydrogel

Figure

• 

  Figure 1 Unswollen self-infiltrating osmotic expander used in the study, enveloped in its silicone shell.

• 

  Figure 2 (A) A vertical incision measuring 1.5 cm in length was performed in the buccal mucosa of the edentulous area and a subperiosteal pocket was prepared using a periosteal elevator. (B) After a subperiosteal pouch was created, the expander was inserted carefully under the periosteum. (C) The expander was fixed by a bone screw on the alveolar bone. (D) Before the vertical incision was sutured.

• 

  Figure 3 The 3 types of expanders used in the present study (S, M, L from left to right) in their unswollen (A) and swollen states (B).

• 

  Figure 4 Gross healing of STE sites (A) immediately, (B) at 1 week, (C) at 3 weeks, and (D) at 4 weeks after surgery. STE: soft tissue expander.

• 

  Figure 5 Photomicrograph of the active expansion area at 28 days postoperatively, showing E, P, B, and F (scale bar=500 μm). White arrowheads indicate new bone formation secondary to the raising of the periosteum. Yellow arrowheads indicate zone of bone loss underneath the tissue expander. E: expanded hydrogel and silicone, P: raised periosteum, B: mature bone, F: peripheral fibrous capsule.

• 

  Figure 6 Photomicrographs of the fibrous capsule at the interface between the soft tissue and the STE (A) and at the bone/STE interface (B) (scale bar=50 μm). Yellow arrowheads indicate blood vessels within the collagen-rich tissue of the peripheral capsule. White arrowheads show osteoclast-like cells within lacunar craters at the bone surface. STE: soft tissue expander.

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