Preclinics of Conservative Dental Medicine · MU Sofia

20. Pin retained restorations – anatomical aspects, armamentarium, placement technique.

Explains where pinholes can safely be placed in dentin for pin-retained restorations, covering line angles as preferred sites, furcations and the pulp as danger zones, and how many pins to use and how deep and long they should be. Includes a table of the Thread Mate System armamentarium, a step-by-step placement sequence, guidance on bending pins, and remedies for broken drills, loose pins, pulp penetration and root perforation.

Inside: 6 sections · 1 labelled picture · 1 table · 17 flashcards · 7 min

Topic 20 of 53 in the MU Sofia syllabus for Preclinics of Conservative Dental Medicine (Dental Medicine, Year 3). The free AceMed note covers it in 6 sections, about 863 words (7 min of reading), with 17 flashcards.

In this note

  1. Introduction
  2. Anatomical aspects: where the pinhole goes
  3. Armamentarium
  4. Placement technique
  5. Mistakes and their management
  6. Key points

Introduction

A pin-retained restoration is a large amalgam (or a composite core) held partly by small metal pins screwed into dentin when too little crown is left for a conventional preparation. This topic covers where a pin can go safely, the instruments and the steps; most failures – perforation, a broken drill, a loose pin – come from a pinhole in the wrong place or direction (indications and pin types: topic 19).

Anatomical aspects: where the pinhole goes

The pinhole must lie entirely in sound dentin: close enough to the outer surface to stay clear of the pulp, far enough from it not to perforate the root or craze the enamel.

Place the pinhole no closer than 0.5–1 mm to the DEJ or 1–1.5 mm to the external root surface, whichever is greater, and drill it parallel to the adjacent external surface of the tooth.

Near the CEJ, where enamel is thin, the root-surface distance decides; higher in the crown the DEJ decides. Check root form and pulp size on a periapical radiograph and feel the root contour with a periodontal probe.

Safe sites and danger zones

  • Line angles (mesiobuccal, distobuccal, mesiolingual, distolingual): the root is convex and the dentin thickest here – the preferred pin sites.
  • Furcations: mid-buccal and mid-lingual in mandibular molars; mid-buccal, mesial and distal in maxillary molars.
  • Root concavities, e.g. the mesial surface of the maxillary first premolar.
  • The pulp: horns under the cusps, large pulps in young teeth, any pinhole angled inwards.
  • Enamel and the DEJ: a pin there crazes or splits off the enamel.

Number, depth and length

  • Number: usually one pin per missing axial line angle (roughly one per missing cusp) – as few as possible, since each pin stresses dentin and weakens the amalgam.
  • Depth into dentin: about 2 mm. Deeper adds little retention and raises the risk of perforation.
  • Length into the restoration: about 2 mm; a longer pin weakens the amalgam. The pin stays inside the future contour, well covered by amalgam.
  • Spacing: spread the pins out, with room to condense amalgam around each; crowded pins craze dentin.

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