PubMed · 1077339
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A Daniel, C Aouizerat, B Fournier, H Brulin, P Rassat, J Praud. 1976-06-03. [Physiologic dental mobility].. https://pubmed.ncbi.nlm.nih.gov/1077339/
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When single-tooth implants are not appropriate, the use of resin-bonded fixed partial dentures is a preferred treatment option when the abutments are relatively sound. However, the use of resin-bonded fixed partial dentures (RBFPDs) for replacing two or more missing teeth is considered to have a guarded prognosis, as long-span RBFPDs have been shown to be less successful than single pontic prostheses. The use of properly modified nonrigid connectors may well improve the success of long-span RBFPDs by reducing harmful interabutment stresses that appear to be responsible for retainer debonding in long-span RBFPDs. For such long-span prostheses, it is advised that the major retainer have wraparound on at least three surfaces of the abutment or have strategically placed opposing axial grooves or slots. It is considered essential that the connector allow interabutment movement in both the horizontal and vertical planes so that the retainer with the greater resistance and retention form does not stress and possibly debond the minor retainer. The upside-down positioning of the nonrigid connector and the matrix incorporated with the major retainer is considered important for successful maintenance, if a debond should occur due to greater loading on the major retainer, because it can be removed and recemented easily. Clinical cases are described that replace two or more missing teeth using fixed-movable RBFPDs with nonrigid connectors.
The application of the rubber dam (dental dam) is indicated in endodontics and for restorative dental treatments involving the acid-etch technique. The frequency of the technique's use varies significantly according to individual circumstances, and is generally too low given its advantages. One possible reason for many dentists' reluctance to use it could be frustrating results in the past with technically difficult applications. Such conditions arise, for example, when the taut rubber dam sheet exerts too much pull on the rubber dam clamps, causing them (and the entire rubber dam) to come loose. Particularly susceptible here are clamps attached to molars. This undesired tension results from stretching the rubber dam material--a necessary step--for attaching the sheet to the traditional rubber dam frame. As an alternative, a new easy-to-use rubber dam frame (Safe-T-Frame) has been developed that offers a secure fit without stretching the rubber dam sheet. Instead, its "snap-shut" design takes advantage of the clamping effect on the sheet caused when its two mated frame members are firmly pressed together. In this way the sheet is securely attached, but without being stretched. Held in this manner, the dam sheet is under less tension, and hence, exerts less tugging on clamps--especially on those attached to molars. Even in cases where there are no distinct anatomic undercuts, this lack of tension in the sheet eases isolation procedures and permits the use of standard rubber dam clamps. As a further benefit, the frame's raised edging provides a barrier around the sheet, which prevents small amounts of fluids from escaping. This contributes to greater patient comfort.
Intracellular signals generated by mechanical strain profoundly affect the metabolic function of osteoblast-like periodontal ligament (PDL) cells, which reside between the tooth and alveolar bone. In response to applied mechanical forces, PDL cells synthesize bone-resorptive cytokines to induce bone resorption at sites exposed to compressive forces and deposit bone at sites exposed to tensile forces in an environment primed for catabolic processes. The intracellular mechanisms that regulate this bone remodeling remain unclear. Here, in an in vitro model system, we show that tensile strain is a critical determinant of PDL-cell metabolic functions. Equibiaxial tensile strain (TENS), when applied at low magnitudes, acts as a potent antagonist of interleukin (IL)-1beta actions and suppresses transcriptional regulation of multiple proinflammatory genes. This is evidenced by the fact that TENS at low magnitude: (i) inhibits recombinant human (rh)IL-1beta-dependent induction of cyclooxygenase-2 (COX-2) mRNA expression and production of prostaglandin estradiol (PGE2); (ii) inhibits rhIL-1beta-dependent induction matrix metalloproteinase-1 (MMP-1) and MMP-3 synthesis by suppressing their mRNA expression; (iii) abrogates rhIL-1beta-induced suppression of tissue inhibitor of metalloprotease-II (TIMP-II) expression; and (iv) reverses IL-1beta-dependent suppression of osteocalcin and alkaline phosphatase synthesis. Nevertheless, these actions of TENS were observed only in the presence of IL-1beta, as TENS alone failed to affect any of the aforementioned responses. The present findings are the first to show that intracellular signals generated by low-magnitude mechanical strain interfere with one or more critical step(s) in the signal transduction cascade of rhIL-1beta upstream of mRNA expression, while concurrently promoting the expression of osteogenic proteins in PDL cells.