Internal adaptation of fixed prosthodontics at shoulder preparation level evaluated by horizontal sections

AIM

The precision of fixed prosthodontic restorations is fundamental for clinical success: well-fitting crowns reduce the risk of recurrent caries and periodontal disease. The aim of this study is to evaluate the internal fit of fixed prosthodontics at the shoulder preparation level by examining horizontal sections.

METHODS

Twenty-four extracted teeth were resin-embedded and prepared on the platform of an iso-parallelometer with a 90 degrees shoulder with a rounded internal angle. Auro Galva Crown (AGC) copings were cemented in place. The preparations were observed by 3 different assessors at 8 points, first externally and then internally at 2 levels by grinding the specimen perpendicular to the long axis at 0.5 mm and at 0.2 mm from the margin of the preparation. A correction factor was calculated to derive real values from measured values. The results were analyzed using a linear regression with robust standard errors, accounting for within-subject correlation introduced by multiple measurements. Shrout-Fleiss Intraclass Correlation Coefficient (ICC) for Inter-Rater Reliability were calculated at each stage.

RESULTS

Internal measurements at 0.5 and 0.2 mm from the margin provided data similar to the external margin data. Average inter-assessor differences were in the range of 2 mm. ICC ranged from 0.93 for the 0.5 mm level to 0.97 for the external level.

CONCLUSIONS

External measurements effectively predict the internal precision at the shoulder level. Horizontal perimarginal sections allow the fit to be studied through the evaluation of a great number of points. Traditional vertical sections for the evaluation of internal fit enable only a few points to be observed. This internal observation method may be suitable for testing new materials.

Overdentures on natural teeth: a new approach

AIM

The study presents a new type of copings for overdentures on natural teeth.

METHODS

A new type of custom-made copings was prepared on 10 extracted teeth and their marginal fit was observed microscopically by means of a mechanical device, and software was employed to measure the gap.

RESULTS

The marginal fit evaluation gave satisfactory values with mean values of the gap measurements below the clinically accepted limits (mean gap: 25.3 microm; minimum 7.3 microm, maximum 56.5 microm).

CONCLUSIONS

The advantages of these new copings are: the rapidity of their preparation; the protection of the root canal treatment, because the coping with this chair-side method is prepared and cemented in one session; the low costs.

[The surgical verification of the periodontal probe and endoral radiography in assessing the bone substance loss in periodontal disease. A proposal for optimizing the methods]

It is difficult to compare levels of bone loss in periodontal disease measured by periodontal probe and X-ray and to verify them versus surgical techniques. In fact, there are relatively few published reports on the subject. To this purpose the Authors describe their personal experience using plates equipped with guide tracks and center-film boxes with personalized bites. The suitability of the two methods (probe, intraoral X-ray) to determine levels of bone loss similar to those revealed by surgical verification was assessed on the basis of an analysis of the respective bone loss in 44 sites surrounding 19 dental elements. This method, which is accurate but time-consuming, demonstrated an broadly analogous underestimate (approx. 20%) using both preoperative probe and X-ray techniques in comparison to the true level of bone loss measured during surgery.