Treatment of edentulous mandible with metal-resin fixed complete dentures: A 15- to 20-year retrospective study.

OBJECTIVES: The purpose of this retrospective study was to report the implant and prosthetic complications of mandibular metal-resin fixed complete dentures (MRFCDs) opposing a maxillary complete removable dental prosthesis (CRDP) in a 15- to 20-year post-placement follow-up period. MATERIAL AND METHODS: Dental records of 24 edentulous patients treated by a mandibular MRFCD and a maxillary CRDP were reviewed. Complications for the implants, MRFCDs, and CRDPs were recorded in four different recall periods: 0-5 years, 5-10 years, 10-15 years, and more than 15 years. The survival and failure times based on Kaplan-Meier statistics were analyzed using Lifetest procedures. Product-limit survival estimates were used for cumulative survival rates (CSRs). RESULTS: The mean service time was 18.5 years. The CSR for the implants and MRFCDs was 91.8% at 16.9 years (confidence intervals: 85.2% and 95.5%) and 80% at 19.6 years (confidence intervals: 44.1% and 94.1%), respectively. The implant failures after 15 years occurred because of a tumor resection. Acrylic resin tooth fracture (45.8% of patients) and wear (75% of patients) were the most common complications with the MRFCD. Retaining screw complications [loosening (8.1% of retaining screws) and fracture (11.3% of retaining screws)] were also common. CONCLUSIONS: The outcomes seen with MRFCD over the long term were favorable. After placement of prostheses, 1 implant loss was observed potentially due to prosthetic/hygiene/periodontal factors. However, potential maintenance complications such as acrylic resin tooth fracture and/or wear and retaining screw loosening and fracture may occur in the long term when a similar design is used for the mandible.

Displacement comparison of CAD-CAM titanium and zirconia abutments to implants with different conical connections.

PURPOSE: To compare the displacements of CAD-CAM zirconia and titanium abutments into different internal connection systems after torquing. METHODS: OsseoSpeed EV and OsseoSpeed TX implants (n=10) were placed in resin blocks. Zirconia and titanium abutments (n=5) were first hand tightened and then tightened to the recommended torque (20Ncm for TX and 25Ncm for EV). Displacements of abutments between screw tightening by hand and torque driver was measured using three-dimensional digital image correlation (3D DIC) technique. Displacements were measured in U (front/back), V (into/outward), W (right/left) directions and 3-dimensionally (3D). ANOVA with restricted maximum likelihood estimation method was used to analyze the data. Bonferroni-corrected t tests was used to determine the statistical differences (α=0.05). RESULTS: 3D displacement of zirconia and titanium abutments was significantly greater in OsseoSpeed EV implant (P<0.001). Displacement of zirconia and titanium abutments was not significantly different within implant systems, 3D (P≥0.386) and in each direction (P≥0.382). In U and V directions, zirconia and titanium abutments displaced significantly more towards negative in OsseoSpeed EV implant (P<0.019). Within the OsseoSpeed TX system, abutments displaced significantly more in V direction compared to the U and W (P≤0.005), and within the Osseospeed EV system, abutment displacements were significantly different amongst directions and displacements in V were the greatest (P<0.001). CONCLUSION: Abutments displaced more in the implant that required higher torque values to tighten the abutment. The amount of displacement in both systems was clinically small. Abutment material did not affect the magnitude of displacement.

Clinician-generated torque on abutment screws using different hand screwdrivers.

STATEMENT OF PROBLEM: Many clinicians use hand screwdrivers to tighten prosthetic and abutment screws. The impact of the screwdriver type, the location of the implant, and the sex of the practitioner on the generated torque is not well understood. PURPOSE: The purpose of this in vitro study was to compare the torque generated by different hand screwdrivers when used in the anterior and posterior regions and to evaluate the correlation between the applied torque and the sex and body mass index (BMI) of the practitioner. MATERIAL AND METHODS: A mandibular typodont with anterior and posterior implants was mounted in a mannequin head. Fifty clinicians (6 prosthodontists, 8 graduate prosthodontic students, and 36 dental students) used their maximum force to tighten the abutment screws in the anterior and posterior regions, using 3 different hand screwdrivers, with handles of different shapes and sizes (small, medium, and large). The torque values generated were measured using torque meters connected to the implants. The generated torque, sex, age, height, and weight were also recorded for each clinician. A generalized linear model was used to find correlations between the different factors and the generated torque (α=.05). RESULTS: Significant differences were observed among the applied torque values when different screwdrivers were used (P<.001). Higher torque values were generated in the anterior region than in the posterior region (P<.001). The interaction of the sex and BMI of the participants significantly affected the generated torque values (P=.044). CONCLUSIONS: The type of screwdriver and location of the implant affected the generated torque. Torque values generated by the large screwdriver were higher than those of small and medium screwdrivers. Higher torque was applied in the anterior region.

An alternative conversion technique for fabricating an interim fixed implant-supported complete arch prosthesis.

The conversion technique enables the immediate loading of implants using an existing or a new complete denture. Acrylic resin is generally used directly intraorally when the conventional conversion technique is used. The technique described suggests picking-up the interim copings and capturing the soft tissue contour with the conversion prosthesis with a polyether impression material when 4 implants are placed with an angled implant protocol. A polyether impression was made to complete an autopolymerized reline jig reline. Acrylic resin was applied on the cast generated from this impression outside the oral cavity. This technique may minimize chair time and maximize the ability of the technician/clinician to adapt the prosthesis to the soft tissue contour.

Effect of Offset Implant Placement on the Stress Distribution Around a Dental Implant: A Three-Dimensional Finite Element Analysis.

There are some anatomical restrictions in which implants are not possible to be inserted in their conventional configuration. Offset placement of implants in relation to the prosthetic unit could be a treatment solution. The aim of this study was to evaluate the effect of the offset placement of implant-supported prosthesis on the stress distribution around a dental implant using 3D finite element analysis. 3D finite element models of implant placement in the position of a mandibular molar with 4 configurations (0, 0.5, 1, 1.5 mm offset) were created in order to investigate resultant stress/strain distribution. A vertical load of 100 N was applied on the center of the crown of the models. The least stress in peri-implant tissue was found in in-line configuration (0 mm offset). Stress concentration in the peri-implant tissue increased by increasing the amount of offset placement. Maximum stress concentration in all models was detected at the neck of the implant. It can be concluded that the offset placement of a single dental implant does not offer biomechanical advantages regarding reducing stress concentration over the in-line implant configuration. It is suggested that the amount of offset should be as minimum as possible.