The Influence of Implant Inclination on Retention and Peri-implant Stresses of Stud-Retained Implant Overdentures During Axial and Nonaxial Dislodgments: An In Vitro Study.

PURPOSE: The purpose of this study was to evaluate the influence of implant inclination on retention and peri-implant stresses of stud-retained implant overdentures during axial and nonaxial dislodgments. MATERIALS AND METHODS: Mandibular acrylic models (n = 4) received two implants in the canine areas with 0-, 5-, 10-, and 20-degree lingual inclinations. Dentures were attached to the implants with stud connectors. Four strain gauges were bonded at buccal, lingual, mesial, and distal surfaces of each implant to monitor strains around implants. Retention values (Newton) and peri-implant stresses (microstrains, µs) were recorded during axial (vertical) and nonaxial (anterior, posterior, and lateral) dislodging. A general linear model was used to compare retention forces and implant stresses between implant inclinations and dislodging direction. In addition, a linear regression model was used to test correlation of implant stresses with confounding factors. RESULTS: The highest retention and implant stresses were noted with 0 degrees, followed by 5 and 10 degrees (without difference), and the lowest values were noted with 20 degrees. Anterior dislodging was associated with the highest retention and implant stresses, followed by vertical dislodging, then lateral dislodging, and posterior dislodging. Peri-implant stresses significantly correlated with dislodging direction and retention forces. Every 1 N of increase in retention forces causes 19.17 µs increase in implant stresses. Anterior dislodging was associated with the highest predicted stress values (846.0 µs), and the lowest stress values (143.41 µs) were associated with posterior dislodging. CONCLUSION: Retention forces and peri-implant stresses decreased as lingual implant inclination increased during axial and nonaxial dislodging of stud-retained implant overdentures. Peri-implant stresses were significantly correlated with dislodging direction and retentive forces.

Retentive Properties of O-Ring and Locator Attachments for Implant-Retained Maxillary Overdentures: An In Vitro Study.

PURPOSE: To evaluate and compare retentive properties of O-ring and Locator attachments for implant-retained maxillary overdentures. MATERIALS AND METHODS: Four implant analogs were inserted in canine and second premolar areas of an acrylic edentulous maxillary model. A metal-reinforced experimental acrylic overdenture was constructed and connected to the analogs using either O-ring (group I) or Locator (group II) attachments. Locators were divided into 3 subgroups according the degree of retention of the patrix nylon insert: Locator extra-light retention (group IIa), Locator light retention (group IIb), and Locator medium retention (group IIc). Vertical and oblique (lateral, anterior, and posterior) dislodging forces were measured at the beginning of the study (initial retention) and after 540 cycles of denture insertion and removal (final retention). RESULTS: For vertical, lateral, and anterior dislodging, group IIc recorded the highest initial and final retention, and group I recorded the lowest retention. For posterior dislodging, group I recorded the highest retention, and group IIa recorded the lowest retention. For group II, vertical dislodging recorded the highest initial and final retention, and lateral dislodging recorded the lowest retention. For group I, posterior dislodging recorded the highest initial and final retention, and lateral dislodging recorded the lowest retention. For all dislodging forces (except posterior dislodging), the highest retention loss was recorded in group I, and the lowest retention loss was recorded in group IIa. CONCLUSION: Locator medium attachment was associated with favorable retention during axial (vertical) and nonaxial (anterior and lateral) dislodging compared to other types of Locator inserts and O-ring attachments after a simulated 6-month period of overdenture use.

The effect of implant diameter on strain around implants retaining a mandibular overdenture with Locator attachments: An in vitro study.

This study evaluated the effect of implant diameter on strain around implants retaining mandibular overdentures with Locator attachments. Three mandibular acrylic resin models were constructed with 2 implants inserted in canine areas and classified according to implant diameter into 3 groups: large (4.2 mm), medium (3.7 mm), and small (3.3 mm) diameter implants. Duplicate dentures were connected to the implants with Locator attachments. Four strain gauges were bonded to the acrylic resin at mesial, distal, buccal and lingual surfaces of each implant and strain was measured at loading and non-loading sides during 1st premolar and 1st molar loading. Small and large diameter implants recorded the highest and the lowest strain, respectively. Buccal and lingual sites recorded the highest strain, and mesial site recorded the lowest. First premolar loading recorded significant higher strain than first molar loading. The largest possible implant diameter is recommended to minimize strains around implants retaining mandibular overdentures with Locator attachments.

Circumferential bone loss around splinted and nonsplinted immediately loaded implants retaining mandibular overdentures: A randomized controlled clinical trial using cone beam computed tomography.

STATEMENT OF PROBLEM: Circumferential marginal bone around 2 splinted and nonsplinted immediately loaded implants in the edentulous mandible has not been previously investigated. PURPOSE: The purpose of this randomized controlled clinical trial was to assess circumferential bone loss around splinted and nonsplinted immediately loaded implants retaining mandibular overdentures, using cone beam computed tomography (CBCT). MATERIAL AND METHODS: Thirty participants with complete edentulism were allocated to 2 groups and received 2 implants in the canine region of the mandible. Implants were either left nonsplinted (with ball attachment [BA]) or splinted (with bar attachment [RA]). Mandibular overdentures were connected to the implants 1 week later. CBCT was used to evaluate vertical bone loss (VBL) and horizontal bone loss (HBLo) bone loss at the distal (D), buccal (B), mesial (M), and lingual (L) sites of each implant upon overdenture insertion (baseline, T0), 1 year (T1) and 3 years (T3) after insertion. Repeated measures ANOVA was used for statistical analysis (α=.05). RESULTS: No significant difference in the survival rate (93.3% for BA and 100% for RA) was found between groups (P=.156). VBL and HBLo increased significantly at T3 compared with T1 for both groups (P<.005). After 3 years, VBL were 1.36 ±0.57 mm and 1.0 ±0.44 mm and HBLo were 0.88 ±0.48 mm for BA and 0.77 ±0.53 mm for RA. At T1 and T3, BA had more significant VBL than RA (P<.001), while HBLo did not differ significantly between groups. For both groups, a significant difference was found in VBL and HBLo between implant sites (P<.001). The B site recorded the highest VBL, and the L site recorded the lowest VBL. The M and D sites recorded the highest HBLo, and the B and L sites recorded the lowest HBLo. CONCLUSIONS: Two nonsplinted immediately loaded implants retaining mandibular overdentures were associated with significantly higher vertical and horizontal circumferential bone loss than those associated with splinted implants after a follow-up of 3 years.

Strains around distally inclined implants retaining mandibular overdentures with Locator attachments: an in vitro study.

PURPOSE: The aim of the present study was to evaluate, by means of strain gauge analysis, the effect of different implant angulations on strains around two implants retaining mandibular overdenture with Locator attachments. MATERIALS AND METHODS: Four duplicate mandibular acrylic models were constructed. Two implants were inserted in the canine regions using the following degrees of distal inclinations: group I (control); 0°, group II; 10°, group III; 20°, and group IV; 30°. Locator pink attachments were used to connect the overdenture to the implants and Locator red (designed for severely angled implants) was used for group IV (group IVred). For each group, two linear strain gauges were attached at the mesial and distal surfaces of the acrylic resin around each implant. Peri-implant strain was measured on loading and non-loading sides during bilateral and unilateral loading. RESULTS: For all groups, the mesial surfaces of the implants at loading and non-loading sides experienced compressive (negative) strains, while the distal implant surfaces showed tensile (positive) strains. Group IV showed the highest strain, followed by group III, group II. Both group I and group IVred showed the lowest strain. The strain gauges at the mesial surface of the loading side recorded the highest strain, and the distal surface at non-loading side showed the lowest strain. Unilateral loading recorded significantly higher strain than bilateral loading. CONCLUSION: Peri-implant strains around two implants used to retain mandibular overdentures with Locator attachments increase as distal implant inclination increases, except when red nylon inserts were used.