Tissue Characteristics at Microthreaded Implants: An Experimental Study in Dogs

The Microtomographic Evaluation of Marginal Bone Resorption of Immediately Loaded Scalloped Design Implant With Various Microthread Configurations in Canine Mandible: Pilot Study

This study was undertaken to evaluate the effect of microthread geometry of scalloped design implant on marginal bone resorption. Four types of scalloped design titanium implant specimens were prepared. The type 1 implant had a machined scalloped collar, type 2 had a sandblasted and acid-etched scalloped collar, type 3 had horizontal microthreads, and type 4 had parabolic microthreads, which are parallel with the scalloped conical margin. Two implants of a type were randomly installed immediately after extraction in the mandible of a beagle dog. Definitive prostheses were delivered immediately after surgery. After 12 weeks of healing, the dog was sacrificed and microtomography was performed. Type 4 specimens showed a marginal bone loss pattern definitively analogous to the scalloped margin. In this preliminary study, microthread geometry affected the marginal bone resorption pattern of scalloped design implants. However, additional specimens and more controlled conditions should be applied in future studies to confirm these results.

Effect of conical configuration of fixture on the maintenance of marginal bone level: preliminary results at 1 year of function

OBJECTIVES

To evaluate and to compare the effect of the conical neck design on marginal bone loss around the fixtures, when both implants were provided with micro-threads to the top of the fixture.

MATERIALS AND METHODS

Two types of implant, one with a straight shape (S) and the other with a conical neck design (C) provided with a retentive element to the top of the fixture, were placed adjacent to each other in the partially edentulous areas of 12 patients. Bone loss around each implant was analyzed after 1 year of functional loading. The bone losses after loading were compared using Wilcoxon's signed-rank test.

RESULTS

The mean marginal bone losses (S, 0.05 + or - 0.09 mm; C, 0.07 + or - 0.14 mm) were not statistically significant between the two groups (P=0.578).

CONCLUSIONS

There was no significant difference between conical and straight neck implants in terms of marginal bone loss after 1 year of loading.

Longitudinal changes in tooth/single-implant relationship and bone topography: an 8-year retrospective analysis

PURPOSE

To evaluate longitudinal changes in tooth/implant relationship and bone topography at single implants with a microthreaded, conical marginal portion (Astra Tech ST® implants, Astra Tech AB, Mölndal, Sweden).

MATERIAL AND METHODS

Thirty-one subjects with single implant-supported restorations in the esthetic zone were included. Radiographs obtained at crown installation and 1, 5, and 8 years of follow-up were analyzed with regard to changes in (1) bone level at the implant and adjacent teeth and (2) vertical position of adjacent teeth relative to the single implant.

RESULTS

The mean marginal bone loss amounted to 0.1 mm at both implants and adjacent teeth during the 8 years of follow-up. Regression analysis failed to identify significant explanatory factors for observed variance in bone level change at the adjacent tooth surfaces. Vertical change in position of the teeth relative to the implants was more frequent and significantly greater in incisor compared with premolar tooth region but not associated with gender or age.

CONCLUSIONS

The marginal bone level at teeth adjacent to single implants with a microthreaded conical marginal part was not influenced by horizontal and vertical tooth-implant distances. Continuous eruption of adjacent teeth may result in infraocclusal positioning of a single-implant restoration.

Effect of microthreads and platform switching on crestal bone stress levels: a finite element analysis

BACKGROUND

The aims of this study were to investigate the effects of implant microthreads on crestal bone stress compared to a standard smooth implant collar and to analyze how different abutment diameters influenced the crestal bone stress level.

METHODS

Two-dimensional finite element imaging was used to create a cross-sectional model of an implant (5-mm platform and 13 mm in length) placed in the premolar region of the mandible. The two tapered implant models consisted of one with microthreads at the crestal portion and the other with a smooth neck. The implant model was reverse-engineered to resemble a commercially available microthread implant. Abutments of different diameters (4.0 mm: 20% platform switching; 4.5 mm: 10% platform switching; and 5.0 mm: standard) were loaded with a force of 100 N at 90 degrees vertical and 15 degrees oblique angles. Finite element analysis was used to analyze the stress patterns in bone, especially in the crestal region.

RESULTS

Upon loading, the microthread implant model had 29% greater stress (31.61 MPa in oblique and 9.31 MPa in vertical) at the crestal bone adjacent to the implant than the smooth-neck implant (24.51 and 7.20 MPa, respectively). When the abutment diameter decreased from 5.0 to 4.5 mm and then to 4.0 mm, the microthread model showed a reduction of stress at the crestal bone level from 6.3% to 5.4% after vertical loading and from 4.2% to 3.3% after oblique loading. The smooth-neck model showed a reduction of stress from 5.6% to 4.9% after vertical loading and from 3.7% to 2.9% after oblique loading.

CONCLUSIONS

Microthreads increased crestal stress upon loading. Reduced abutment diameter (i.e., platform switching) resulted in less stress translated to the crestal bone in the microthread and smooth-neck groups.

Osteotome sinus floor elevation using Choukroun's platelet-rich fibrin as grafting material: a 1-year prospective pilot study with microthreaded implants

OBJECTIVES

The aim of this prospective study was to document, radiographically, changes in the apical bone levels on microthreaded implants placed in subsinus residual bone height, according to a bone-added osteotome sinus floor elevation technique with platelet-rich fibrin (PRF) as grafting material.

STUDY DESIGN

Implants were placed using PRF as grafting material in the bone-added osteotome sinus floor elevation (BAOSFE) technique. The survival rate at abutment tightening (6 to 12 weeks of healing) and at 1 year was calculated. The radiographic analysis determined on consecutive radiographs: 1) the mean residual bone height (RBH) under the maxillary sinus at implant placement; and 2) the change in endosinus bone level. Mean and standard deviation were used to assess the endosinus bone changes in the mesial and distal implant sides at 1 year.

RESULTS

Between December 2004 and June 2005, 20 consecutive patients were included in the study after bone height measurement by periapical radiographs. Patients included 14 women (70%) and 6 men (30%) with a mean age of 54.8 +/- 11.1 years, range 35 to 73 years; they were treated with 35 Astra Tech implants (Astra Tech Dental Implant System; Astra Tech, Mölndal, Sweden) fulfilling the inclusion criteria. The mean healing time before abutment tightening was 8.3 +/- 1.4 weeks (range 6-12 weeks); by this time, 1 implant was mobile and was removed. At 1 year, all implants were clinically stable and the definitive prostheses were in function, resulting in a survival rate of 97.1%. Nineteen implants (55%) were 11 mm long, 6 implants (17%) were 9 mm, 5 implants (14%) were 8 mm, and 5 implants (14%) were 13 mm. The RBH was measured after implant placement on the radiographs on both implant sides. The mean RBH was 6.5 +/- 1.7 mm: 6.3 +/- 1.3 on the mesial side and 6.7 +/- 2.0 mm on the distal side. Measurements of the changes in the endosinus level on the mesial and distal sides showed that all implants gained endosinus bone. The mean endosinus gain was 3.2 +/- 1.5 mm: 3.5 +/- 1.4 mm on the mesial side and 2.9 +/- 1.6 mm on the distal side. The lowest bone gain was 0.9 mm and 0.1 mm on the mesial and distal sides, respectively. The highest gain was 5.8 mm and 5.2 mm on the mesial and distal sides, respectively.

CONCLUSIONS

The BAOSFE procedure with PRF as grafting material can lead to an endosinus bone gain. Despite a limited RBH, a healing period of 2-3 months was found to be sufficient to resist a torque of 25 N.cm applied during abutment tightening. At 1 year, formation of a new recognizable bone structure delimiting the sinus floor was identified radiologically and led to a predictable implant function.

Commentary: Two-Piece Implants With Turned Versus Microtextured Collars

Implant companies have been promoting two-piece implants with microtextured collars in the interest of hard tissue preservation and/or soft tissue integration. However, this rationale may not be justified. Based on comparative studies currently available, it is unclear whether microroughened implant necks reduce crestal bone loss. A possible effect may be overruled by the establishment of a biologic width or by other factors influencing crestal bone remodeling. In addition, the orientation and attachment of the collagen fibers in the peri-implant mucosa are a little different because the surface roughness varies at the level of the implant neck. The clinician should be cautious when using these modified implants because the impact of microtextured collars on the initiation and progression of peri-implant pathology is currently unknown.