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Strain measurements and fracture resistance of endodontically treated premolars restored with all-ceramic restorations

Seow LL, Toh CG, Wilson NH

J Dent, 2015 Jan;43(1):126-32.
PMID: 25448436 DOI: 10.1016/j.jdent.2014.10.001

OBJECTIVES: The aim of this study was to investigate the recovery of cuspal stiffness and fracture resistance in endodontically treated maxillary premolars restored with bonded ceramic inlays and onlays of various designs.
METHODS: Seventy intact premolars were selected for this study; six cavity designs were investigated: (i) mesio-occlusal-distal (MOD) inlay (I), (ii) MOD inlay with palatal cusp coverage (IPC), (iii) MOD onlay (O), (iv) MOD inlay with pulp chamber extension (IPE), (v) MOD inlay with palatal cusp coverage and pulp chamber extension (IPCPE), and (vi) MOD onlay with pulp chamber extension (OPE). Intact teeth acted as control. Strain gauges were attached to the buccal and palatal surfaces of the teeth to measure cuspal stiffness under static loading. All specimens were eventually subjected to compressive load to failure. Cuspal stiffness and fracture resistance data were analyzed using ANOVA and Tukey test.
RESULTS: The I and IPE restorations restored cuspal stiffness to 75% of the sound tooth value. The O and OPE restored teeth had stiffness values greater than that of a sound tooth. The I, IPC, O, IPE, IPCPE and OPE restored teeth demonstrated fracture strength values of 938N±113 N (s.d.), 1073N±176 N and 1317N±219 N, 893N±129 N, 1062N±153 N and 1347N±191 N respectively.
CONCLUSIONS: Within the limitations of this study, it was concluded that the all-ceramic onlay or inlay with palatal cusp coverage provided best biomechanical advantage in restoring an endodontically treated maxillary premolar tooth.
CLINICAL SIGNIFICANCE: The onlay approach which is more conservative compared to full coverage restoration is considered an appropriate approach to the restoration of endodontically treated maxillary premolars. The addition of a pulpal extension to the all-ceramic restorations, apart from being technically challenging, was not found to offer any biomechanical advantage to the restored teeth.
KEYWORDS: Endodontically treated teeth; Fracture strengths; Inlay; Onlay; Pulp chamber extension; Strains
A finite element analysis of ceramic restorations in endodontically treated premolars

Seow LL, Toh CG, Fok AS, Wilson NH

Am J Dent, 2008 Oct;21(5):331-6.
PMID: 19024261

PURPOSE: To investigate the level and distribution of stresses in endodontically treated maxillary premolar teeth restored using various cavity designs of bonded all-ceramic restorations. The hypothesis tested was that the various all-ceramic approaches, including incorporating a pulp chamber extension in the restoration, had no influence on the stresses in the restored tooth unit.
METHODS: Finite element packages Patran and Abaqus were used for the stress analysis. The cavity designs investigated include: (1) inlay (I); (2) inlay with palatal cusp coverage (IPC); (3) onlay (O); (4) inlay with pulp chamber extension (IPE); (5) inlay with palatal cusp coverage and pulp chamber extension (IPCPE); and (6) onlay with pulp chamber extension (OPE).
RESULTS: In each case, tensile stresses were found to be concentrated subjacent to the occlusal fossa. Peak tensile stress and peak shear stress values along the tooth/restoration interface for IPC, O IPCPE and OPE cavity designs were found to be associated with the axiogingival line angle. Overall, the order of the various forms of restoration investigated in terms of the maximum principal stress (from greatest to lowest) was as follows: IPE > IPCPE > OPE > I > IPC > O.
Remaining tooth structure associated with various preparation designs for the endodontically treated maxillary second premolar

Seow LL, Toh CG, Wilson NH

Eur J Prosthodont Restor Dent, 2005 Jun;13(2):57-64.
PMID: 16011232

Existing literature suggests a relationship between the amount of remaining tooth structure and the fracture resistance of the restored endodontically treated tooth. This study investigated the amount of tooth structure remaining following various tooth preparations used in the restoration of the endodontically treated maxillary second premolar. Illustrations of the maxillary second premolar in buccopalatal, mesiodistal and occlusal sections were drawn to scale. Outlines of various intra- and extracoronal preparations were superim-posed on the illustrations to reveal the amount of tooth tissue remaining in each case. Preparations for a ceramic inlay, inlay with palatal cusp coverage and onlay left 2.0-2.5mm of tooth structure buccally and palatally. Following preparation for a metal-ceramic crown, approximately 1.0mm of tooth structure remained buccally, and between 1.6mm-1.8mm palatally. Preparation for an all-ceramic crown was observed to leave 1.0mm-1.2mm of tooth structure surrounding what remained of the endodontic access cavity. It was concluded that decisions as to the type of definitive restoration to restore the endodontically treated maxillary second premolar may be influenced, amongst other factors, by information on the amount of tooth tissue remaining following preparation.
A survey of current practices among general dental practitioners in Manchester in 2002

Seow LL, Toh CG, Wilson NH

Prim Dent Care, 2003 Jul;10(3):87-92.
PMID: 12929337

AIM: The purpose of this study was to obtain data on current approaches for the restoration of endodontically treated teeth among general dental practitioners (GDPs) in Manchester, United Kingdom.
METHOD: A questionnaire containing 19 single-answer, multiple-choice type questions was mailed to 503 GDPs practising in the Greater Manchester area in January 2002. An explanatory covering letter and a stamped addressed return envelope were enclosed. The data obtained were processed using SPSS statistical software.
RESULTS: Three hundred and fifty-one (70%) of the practitioners responded to the questionnaire. The restoration of root-filled teeth was normally undertaken within 1-2 weeks of completing root canal therapy by 63% of the practitioners. Only 35% of the GDPs used posts routinely in the restoration of root-filled anterior teeth; the corresponding figure for posterior teeth was 15%. While a cast, precious metal post was the preferred choice in the restoration of anterior teeth, the use of prefabricated posts and related techniques predominated in the restoration of posterior teeth. Composite resin was the most popular choice of material for core build-up procedures in anterior teeth. Amalgam tended to be favoured for core build-ups in posterior teeth. The majority of the practitioners (56%) routinely restored root-filled anterior teeth by means of porcelain-fused-to-metal crowns. Seventy-three per cent of the GDPs preferred to restore root-filled posterior teeth by means of a full veneer crown.
CONCLUSIONS: The results of this study suggest that the practitioners surveyed had a sound understanding of the principles involved in the restoration of endodontically treated teeth, with the possible exception of the need to establish a durable coronal seal as soon as possible after the placement of a root filling.