Clinical Research Associates

            Seven post types and two controls were tested. Each post group consisted of five posts, 13 mm in length and approximately 1.5-1.6 mm in diameter. Human maxillary incisors were prepared for post placement by removing the crown at the facial CEJ and preparing a conservative root canal. A small sample size of 5 was used for each test due to a lack of good central incisors available for testing purposes. The teeth were embedded in an ethyl methacrylate resin 2 mm apically from the facial CEJ. The posts were cut to a length of 13 mm and set 9 mm deep, leaving 4 mm raised above the facial CEJ. The posts were clinically prepared for placement per manufacturer’s instructions (see post preparation instructions).

            The post preparations were drilled per manufacturer’s instructions and the posts were cemented using Panavia 21 (J. Morita). A 5 mm diameter buildup (Core Paste - Den-Mat) was applied to a height of approximately 5 mm. Each sample was allowed to set at approximately 30° C for 2-4 minutes. The samples were then checked for flaws and placed into a 37° C water bath for 30-60 minutes. The Core Paste Alone with No Post Buildup control was prepared the same way except no post was used and the dual cure paste was also syringed into the prepared post hole. The samples were then thermocycled 5000 cycles in 5° and 55° C distilled water (dwell time = 15 seconds, transfer time = 10 seconds). After thermocycling, the buildup was trimmed to a height of 4 mm so the head of the post was visible occlusally. A flat surface was prepared on the lingual aspect of the buildup at a 45° angle to the occlusal tip of the post. The samples were then tested for shear strength by applying a compressive force with a 5 mm diameter ball probe positioned on the 45° surface at the tip of the post.    See full method for further testing details.   The method of failure of each post type was recorded and the percentage of buildup and/or tooth failures was deterimined.

            In addition, three groups of five samples were constructed of each post type to compare fatigue cycling (applying an on/off load of 5 to 50 Newtons at a frequency of 1.4 times per second) with a 24 hour soak (37° C tap water for 24-hours).  The samples were then tested by applying a load at a 45° angle to the post tip like previous samples.  See full method for more details.

            Costs per post were based on the ‘suggested retail refill cost’. To determine the cost per post, the suggested retail cost of the refill kit was divided by the total number of posts found in the refill kit.

As seen from ‘Graph 1. Strength of Post Types’, all post types performed statistically the same or better when compared to the Core Paste only control. Core Paste was statistically the same as "posts" made of Ribbond polyethylene fibers and All-Bond 2 D/E Bonding Resin. Ribbond posts were the only post type that did not perform better than the Core Paste control. Ribbond followed a different method of placement than the traditional rod type posts. A 1.6 mm diameter post hole was prepared and two 2 mm wide pieces of Ribbond were cut 34 mm in length and coated with All-Bond 2 D/E Bonding Resin. The ribbons were folded in half and the folded end was inserted down the 9 mm canal leaving the four loose ends (apx. 8 mm long) protruding from the canal. These loose ends were doubled over creating four loops which were worked into the core buildup. Strength numbers for Ribbond were statistically worse than for the other post types. This performance could be due to the fact that the test system evaluated the post types mainly in compression. Fiber reinforcement generally doesn’t improve a system in compression, only in tension. Clinically, however, tensile stresses are also important.

All the traditional rod type posts performed statistically the same or better than the human tooth control. Ribbond and the Core Paste only controls were statistically weaker than the human tooth control. The metal posts had the best strength values, but the overlapping statistical bars prohibit stating that metal posts are better than non-metal posts. See ‘Graph 1. Strength of Post Types.’

Human teeth were cut to mimic the size of the core buildup (4 mm diameter & 4 mm height) and acted as the upper control. They all fractured apically from the probe contact point into the root. A lower control was constructed consisting of a Core Paste buildup placed over a 1.6 mm diameter post hole. The Core Paste was also syringed down the post hole. When broken, this control fractured the root (see picture below). In addition to the root fracture, the core buildup was also sheared off the tooth. All traditional rod post types experienced a fracture of the core buildup from the post to some degree, whereas with Ribbond the ball probe penetrated and crushed the core buildup. Five of five Ceraposts fractured just below the CEJ, whereas no other posts fractured or bent visibly. The metal posts tended to fracture the root more often (47% overall-see picture below) than the non-metal post types, except for AesthetiPost which had 60% tooth breakage (see picture below) which was unexplainable. Caution must be taken when comparing breakage rates of teeth due to the sample size. The sample size was due to a lack of central maxillary insicors available for testing. Tooth breakage rates were: Cerapost-20%; C-Post-20%; and Ribbond-0% as shown in ‘Chart 1. Method of Failure According to Post Type’ below.

D. Yield Strengths of Fatigue Cycled & 24-Hour Water Soaked Posts

Data were analyzed using AOV and Fisher’s LSD (p<0.05).

The non-metal posts, Carbon, Carbon / Quartz Matrix, & Ceramic, were all statistically weakened when stored in 37° C H₂O for 24-hours before breaking, compared to the baseline controls. The Ceramic, Carbon / Quartz Matrix, and Carbon posts were weakened 34%, 33%, and 18% respectively. See ‘Graph 3. Baseline Vs. Water Soaked Posts’. This weakening of the posts due to water, however, may not be significant when comparing the overall yield strength of the posts in general compared to each other. For example, the ceramic post, even when weakened due to water storage, was still statistically stronger than any of the post types tested.

Graph 3. Baseline Vs. Water Soaked Posts

Chart 2. Suggested Retail Cost per Post

Since the overall post strength for the post types are similar, other aspects need to be analyzed. A collection of attributes, have been combined in ‘Chart 3. Miscellaneous Attributes for each Post Type’.

A. All posts with their Core Paste buildup, except Ribbond, exhibited statistically better strength than a similar size core buildup with no post. Ribbond was statistically the same as a similar size core buildup with no post.

B. All posts, except Ribbond and the Core Paste control, exhibited statistically the same or slightly better strength than the control incisor teeth that were cut down to a similar size as the core buildup. Ribbond and the Core Paste control were statistically weaker than the control incisor.

C. Human teeth (control) fractured apically from the point of applied pressure down the root. The Core Paste buildups with no post (control) also typically fractured the root and the core buildup was also sheared off the tooth. For every post system, except Ribbond, the core buildup fractured from the post, whereas the Ribbond core buildup was slowly crushed. The metal posts tended to fracture the root more often (47%) than the non-metal posts (33%) except for AesthetiPost which fractured the foot in 60% of the tests. Ribbond under stress did not cause any tooth fractures but was weaker overall than other posts.

D. Fatigue cycling did not affect any posts, but a water soak weakened all the non-metal posts. Even after soaking in water, however, the ceramic post was still statistically stronger than all other posts.

E. Metal posts cost the least and C-Posts cost 15-30% more. AesthetiPosts cost 40-60% more than a metal post. Cerapost cost the most at 3x more than a metal post.

F. Other attributes for the posts are described in ‘Chart 4. Advantages and Disadvantages for each Post Type’ below.

Chart 4. Advantages and Disadvantages for Various Post Types