Abstract
Statement of problem
A typical conversion process of a complete-arch immediate loading protocol entails
preparing holes in a complete denture for connection to interim copings, which reduces
the strength of the prosthesis. The excellent mechanical properties of milled polymethyl
methacrylate (PMMA) disks may provide interim prostheses with improved strength.
Purpose
The purpose of this in vitro study was to measure the flexural strength and failure
load of simulated acrylic resin immediate implant-supported interim prostheses fabricated
by conventional processing and computer-aided manufacturing.
Material and methods
A master patient model was created with an acrylic resin base and 2 BioHorizons Internal
4.5-mm-diameter implants placed with a 21.5-mm span and multiunit abutments (MUA)
tightened to place. Two groups with different prosthodontic designs were used: one
represented the standard fixed prosthesis with support at each end (noncantilever,
NC), and the other group represented the cantilever portion of the prosthesis (cantilever,
C). Two connection designs of prosthesis blocks to MUA abutments were evaluated: one
with typical holes in the prosthesis for capturing interim copings and one with a
low-profile coping. For the heat-processed PMMA groups (HP/NC and HP/C), wax patterns
were milled, and heat-polymerized denture base PMMA prostheses were processed. The
milled PMMA groups (M/NC and M/C) were milled from a tooth-shaded PMMA disk for the
prosthesis blocks. The milled low-profile groups (Mlp/NC and Mlp/C) had identical
dimensions except that connection to the low-profile coping was designed with a cement
space and a narrow diameter screw access hole and was milled from a PMMA disk. The
failure load (N) of the cantilever prostheses was recorded, and for NC groups, the
3-point flexural strength formula (MPa) was calculated. The Weibull modulus, characteristic
strength, and summary statistics were computed, and the groups were statistically
analyzed with ANOVA and the post hoc Tukey test (α=.05).
Results
The mean flexural strengths (MPa) were HP/NC=91.35 ±18.92; M/NC=143.94 ±36.79; Mlp/NC=117.06
±13.86. Significant differences were found among groups (P<.001). Mean failure loads (N) and Weibull modulus (WM) of cantilever prosthesis strengths
were for HP/C=512.66, WM=5.597; M/C=695.06, WM=4.875; Mlp/C=254.97, WM=1.797 (P<.001).
Conclusions
Implant fixed interim structures milled from high-density PMMA blanks had a 35% higher
flexural strength for both the standard prostheses and the cantilever prostheses than
heat-processed denture base PMMA. The low-profile coping design was stronger than
the heat-processed material, and the failure point was relocated from the lateral
walls to the cervical margin area.
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Article info
Publication history
Published online: June 19, 2021
Footnotes
Supported by Tylman Research Grant 2016-2017 Awardee, American Academy of Fixed Prosthodontics. Tylman Third Place Award at the American Academy of Fixed Prosthodontics. Chicago, Ill, February 2018.
Identification
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© 2021 by the Editorial Council for the Journal of Prosthetic Dentistry.
