Retention Assessment of High Performance Poly-etheretherketone Removable Partial Denture Frameworks Constructed by Various Techniques (in vitro Study).

STATEMENT OF THE PROBLEM: Poly-etheretherketone is a novel material used in the construction of the removable partial dentures frameworks instead of the metal frameworks. This material can be fabricated by various techniques. Most common methods are the injection molding or Computer Aided Design/Computer Aiding Manufacturing (CAD/CAM) milling techniques. The fabrication technique may affect the adaptation of the frameworks by influencing the retention. PURPOSE: To assess the effect of the processing techniques of high performance Poly-etheretherketone either by injection molding (pressing) or CAD/CAM milling techniques on removable partial denture frameworks retention for rehabilitation of upper class I Kennedy classification. MATERIALS AND METHOD: This in vitro study was performed on one epoxy resin model representing the partially edentulous maxillary arch with natural teeth extending from first premolar to first premolar. First premolars and canines were reduced to receive porcelain fused to metal crowns with 0.50mm mesio-buccal retentive undercuts, distal guiding planes and mesial occlusal rest seat on first premolars and cingulum rest seat on canines. Considering the construction technique of frameworks, twenty samples were divided into two groups. In the group I, ten frameworks were fabricated by injection molding, and in the group II, ten frameworks were fabricated by CAD/CAM. The removal and insertion was carried out at 120, 720 and 1440 cycles for both groups, respectively. The retention values were measured by using Universal Testing Machine before cycling and after each interval. RESULTS: Independent t-test showed significant difference on retention at different simulation cycles between groups. Group II exhibited significantly less retention than group I (p< 0.001), while comparing the retention at different cycles within each group by paired sample t-test exhibited significant decrease of retention till the end of the cycling (p< 0.001). CONCLUSION: From the retention point of view, high performance poly-etheretherketone frameworks fabricated by injection molding technique provided a promising method over CAD/CAM technique milling method.

Impact of implants number and attachment type on the peri-implant stresses and retention of palateless implant-retained overdenture.

OBJECTIVES: To evaluate the impact of implants number and attachments type on the peri-implant stresses and retention of maxillary palateless implant-supported overdenture. MATERIALS AND METHODS: Four edentulous maxillary educational acrylic resin models were used. According to the implants number and type of attachment used, four groups were compared: Group I, 2-locator attachments in the canine area; Group II, 2- OT equator attachments in the canine area; Group III, 4-locator attachments in the canine, second premolar area and Group IV, 4-OT equator attachments in the canine, second premolar area. Implants retained palateless overdenture was constructed on each model. Four self-protected linear strain gauges were cemented on each implant. A digital loading device was used to apply compressive loads to measure the resulting peri-implant stresses. Forcemeter and Universal testing machines were used to test the retention of palateless overdenture. RESULTS: A significant difference between the same implant number and distribution with different attachments was found (P = 0.003, P = 0.020), respectively. Least stresses amount was found around the 4-implant locator palateless overdenture, while the highest was found around the 2-implant OT equator palateless overdenture. Nevertheless; the result was that 2-implant locator palateless overdenture recorded insignificant higher retentive forces than the 4-implant OT equator one. CONCLUSIONS: It can be concluded that the implant-retained palateless overdenture with four locator attachments is considered a promising treatment option regarding stress distribution. Using locator attachments, for implant-retained palateless overdenture with either two or four implants considering their superior retentive properties, is advantageous when compared to OT equator attachments.

Clinical evaluation of inter-implant distance influence on the wear characteristics of low-profile stud attachments used in mandibular implant­retained overdentures.

BACKGROUND: This study was aimed to evaluate the influence of inter-implant distance on the wear characteristics of low-profile stud attachments used in mandibular implant retained overdentures. MATERIAL AND METHODS: Forty Completely edentulous participants aged between 50 - 70 years were enrolled in this study. Each patient received 2-implants by 2-stage submerged surgical protocol. Participants categorized into 4-groups. Group I: 19 mm inter-implant distance with Locator retained overdentures; Group II: 19 mm inter-implant distance with OT Equator retained overdentures; Group III: 25 mm inter-implant distance with Locator retained overdentures; Group IV: 25 mm inter-implant distance with OT Equator retained overdentures. The female housings of each attachment were picked up to the mandibular overdenture. 12 month later the male inserts were replaced by new one. The used retentive male inserts were examined by Stereomicroscopic. RESULTS: Stereomicroscopic examination revealed wear were detected on both inner surface and, the core of male inserts. Comparison between the unused and the used Locator and OT equator retentive male inserts at various inter-implant distance revealed highly significant wear changes between them at either 19 mm, or 25 mm inter-implant distance P1= .000, P2=.000 respectively. CONCLUSIONS: After one year of implant overdenture clinical use; both locator and OT equator retentive male inserts revealed significant surface deformities and wear. Wear were more notable on both locator and OT equator retentive male inserts with 25 mm interimplant distance than with 19 mm interimplant distance. Key words:Inter-implant distance, attachments wear, locator retentive male inserts, OT equator retentive male inserts.

Effect of Implant Position and Edentulous Span Length on Stresses Around Implants Assisting Claspless Distal Extension Partial Overdentures: An In Vitro Study.

The aim of this in vitro study was to evaluate the effect of implant position and edentulous span length on stresses around implants assisting claspless distal extension partial overdentures. Four bilateral mandibular distal extension acrylic models were constructed. Two implants were inserted in the distal extension ridges parallel to each other and perpendicular to the ridges. Based on the implant position, models were categorized into two groups: Group I, mesial implants position and Group II, distal implant position. Each group was subdivided into 2 subgroups according to the length of edentulous span: Subgroup a, long span and Subgroup b, short span. Four claspless partial overdentures were fabricated on the models and retained to the implants with ball-and-socket attachments. Three strain gauges were cemented to the acrylic resin at buccal, lingual, and distal sides of each implant. Static unilateral vertical load of 60N was applied in the central fossae of the first molar, and peri-implant stresses were measured on loading and nonloading sides. Distal implant placements recorded significantly higher peri-implant stresses than did mesial implant placements. Long saddle recorded significantly higher stresses than did short saddle. The greatest peri-implant stresses were recorded with distal placement and long saddle at the loading side. At loading and nonloading sides, the mesial placement with a short saddle recorded the lowest strain. For mandibular distal extension partial overdentures, a mesially placed implant combined with short saddle may be preferable to a distally placed implant combined with long saddle, as the former was associated with reduced peri-implant stresses.

Mandibular Kennedy Class I partial denture management by broad stress distribution philosophy (radiographic assessment).

PURPOSE: The objective of this study was radiographic assessment of the premolar teeth abutments alveolar bone resorption in mandibular Kennedy Class I removable partial denture (RPD) utilizing the broad stress distribution philosophy, either designed with multiple circlet clasp or compound Aker clasp. MATERIALS AND METHODS: Twelve patients were enrolled for this study with upper completely edentulous arch against mandibular Kennedy Class I ridges posterior to the second premolar. The patients were divided into two groups according to the type of the clasp assembly design used, where the mandibular Kennedy Class I RPD was designed with multiple circlet clasp and compound Aker clasp assemblies for Groups I and II, respectively. The abutment alveolar bone resorption was evaluated radiographically after 1(st) 6, 2(nd) 6, and 12 months of mandibular Kennedy Class I RPD insertion. RESULTS: Second premolar abutment interdental alveolar bone resorption was significantly increased as compared to first premolar abutment along the interval periods of the study for Group I. The reverse was observed for Group II. Along the interval periods of the study, the alveolar bone resorption at the first premolar abutment of Group II was significantly increased compared to that of Group I while the reverse was observed when comparing the second premolar of Group I with that of Group II. CONCLUSION: Compound Aker clasp is better than the multiple circlet clasp assembly as it reduces abutment alveolar bone resorption regards broad stress distribution philosophy is considered for distal extension cases.

Scanning electron microscopy observations of osseointegration failures of dental implants that support mandibular overdentures.

AIM: : Investigating possible failure causes of mandibular implants after their immediate loading with an overdenture retained with bilateral bar attachments, using scanning electron microscope. PATIENTS AND METHODS: Twenty edentulous male patients were included in the present study. Each patient had 2 fixtures inserted in the canine and the first molar areas on each side of the mandible. After abutments screwing, the 2 fixtures on the same side were splinted with a bar, and immediately loaded with an overdenture. Implants mobility was assessed on weekly basis. Failed implants were removed, and examined by scanning electron microscope. RESULTS: The failed implants, removed after 4 weeks of treatment, showed an intimate contact of mineralized and osteoid tissues with dense collagen-rich matrix in the apical third of implants. Furthermore, newly developed bone was observed at the same area in implants removed after 7 weeks. However, there was no evidence of such growth at the middle and/or cervical thirds in either case. CONCLUSION: Lack of osseointegration at the middle and cervical thirds of the root could be a possible cause of implant failure. Early loading by an overdenture retained with bilateral bars is considered a major contributing factor to incomplete osseointegration of the supporting implants.