title: Prospective randomized controlled clinical study comparing two dental implant types: volumetric soft tissue changes at 1 year of loading.
abstract: OBJECTIVE
  To evaluate the volumetric changes occurring from prosthesis insertion to the 1-year follow-up (FU) using one- and two-piece dental implants.
  
  
  METHODS
  Sixty patients were randomly assigned to receive one-piece or two-piece implants. Casts were obtained at baseline (insertion of final reconstruction) and at 1 year of loading. Finally, 33 pairs of casts (BRA = 18, STM = 15) were deemed appropriate for volumetric analysis of the peri-implant tissues. If the patients had more than one implant, one was randomly selected for analysis. Casts were scanned to obtain stereolithography (STL) files. Baseline and 1-year FU digital models were superimposed with an image analysis program. Linear and volumetric measurements were performed including (i) crown height changes (CHCs), (ii) volumetric changes, and (iii) changes in tissue thickness at three levels below the mucosal margin on the buccal side of the implants (at 1,3, and 5 mm). The Mann-Whitney U-test and the paired t-test were used to analyze the data between the two groups using the patient as the unit of analysis.
  
  
  RESULTS
  No significant baseline differences were observed between the one- and two-piece groups for the linear measurements. The mean CHCs in the two-piece group amounted to 0.02 mm (SD ± 0.32), whereas the one-piece group exhibited a change of -0.17 mm (±0.57). The mean volume changes (VCs) were -0.12 mm (±0.27) (two-piece group) and -0.03 mm (±0.29) (one-piece group). With regard to the changes in tissue thickness, the two-piece group presented a change of -0.15 mm (±0.20) at 1 mm, -0.06 mm (±0.20) at 3 mm, and -0.2 mm (±0.51) at 5 mm. The respective values for the one-piece group were -0.03 mm (±0.35), 0.01 mm (±0.28), and -0.01 mm (±0.51) at the three levels. None of the differences in linear measurements between baseline and the 1-year FU reached significance. Positive correlations were seen for tissue thickness changes at 1 and 3 mm for both groups (P < 0.05). Significant positive correlations were found for VCs and tissue thickness at 1 mm for the two-piece group and for VCs and tissue thickness at 1,3, and 5 mm for the one-piece group (P < 0.05).
  
  
  CONCLUSIONS
  Within the first year of loading, minimal changes occur with regard to tissue thickness, crown height, and facial volume for both implant types.
authors.affiliation: Section of Periodontology, Faculty of Odontology, University Complutense of Madrid, Madrid, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Sanz Martin
authors.affiliation: Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center of Dental Medicine, University of Zurich, Zurich, Switzerland.
authors.forename: Goran I
authors.initials: GI
authors.lastname: Benic
authors.affiliation: Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center of Dental Medicine, University of Zurich, Zurich, Switzerland.
authors.forename: Christoph H F
authors.initials: CH
authors.lastname: Hämmerle
authors.affiliation: Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center of Dental Medicine, University of Zurich, Zurich, Switzerland.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Thoma
mesh_terms: D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D005881:Gingiva / Q000502:physiology; D006801:Humans; D011446:Prospective Studies
chemical_list: D015921:Dental Implants
keywords: crown; dental implants; denture; fixed; humans; partial; soft tissue; volumetric analysis