title: Ablative Potential of Er:YAG Laser in Dentin: Quantum Versus Variable Square Pulse.
abstract: OBJECTIVE
  The primary objective of this study was to compare the dentin ablation volume and ablation rate of quantum square pulse (QSP), using two different pulse energy settings plus a new digitally controlled dental laser handpiece (X-Runner), with those of variable square pulse (VSP), using three different pulse durations. The secondary objective was to examine, by scanning electron microscopy (SEM), the surface effects of ablation with the different Er:YAG laser modes on the dentin surfaces.
  
  
  BACKGROUND
  The available literature has limited data on the efficiency of different operating modes, pulse durations, and the new digitally controlled handpiece of the Er:YAG laser on human dentin.
  
  
  METHODS
  Freshly extracted human molars (n = 72) were divided into two experimental groups (n = 36 each): (1) QSP group, and (2) VSP group. Each group was randomly divided into three subgroups (n = 12 each). In the QSP group, preparations in dentin were performed using 250 and 500 mJ of pulse energy with the conventional handpiece, and with the X-Runner handpiece set at 250 mJ pulse energy. In the VSP group, cavity preparations were performed using three pulse variables: super short pulse (SSP), micro short pulse (MSP), and short pulse (SP). Cavity preparations were made in dentin at time intervals of 1, 2, and 5 sec. A laser triangulation profilometer was used to determine cavity volumes. Surface analysis of the ablated dentin specimens was performed by SEM.
  
  
  RESULTS
  For time intervals of 1 and 2 sec, ablated volume and ablation rate for QSP-500 mJ were significantly higher than for all other groups (p < 0.0001). For the 5-sec time interval, X-Runner and QSP-500 mJ were the most efficient in dentin ablation (p < 0.0001). Dentin surfaces were free of smear layer in all groups.
  
  
  CONCLUSIONS
  The most efficient modes of dentin ablation in the study were the QSP-500 mJ and X-Runner groups. Dentin surfaces were free of smear layer in all groups.
authors.affiliation: 1 Department of Endodontics and Restorative Dentistry, School of Dental Medicine , Zagreb, Croatia .
authors.forename: Anja
authors.initials: A
authors.lastname: Baraba
authors.affiliation: 2 Department of Restorative Sciences and Biomaterials, Boston University Henry M Goldman , School of Dental Medicine, Boston, Massachusetts.
authors.forename: Dan
authors.initials: D
authors.lastname: Nathanson
authors.affiliation: 1 Department of Endodontics and Restorative Dentistry, School of Dental Medicine , Zagreb, Croatia .
authors.forename: Jurica
authors.initials: J
authors.lastname: Matijevic
authors.affiliation: 3 Department of Oral surgery, School of Dental Medicine , Zagreb, Croatia .
authors.forename: Dragana
authors.initials: D
authors.lastname: Gabric
authors.affiliation: 1 Department of Endodontics and Restorative Dentistry, School of Dental Medicine , Zagreb, Croatia .
authors.forename: Ivana
authors.initials: I
authors.lastname: Miletic
mesh_terms: D003737:Dental Cavity Preparation / Q000295:instrumentation*; D003804:Dentin / Q000528:radiation effects*; D006801:Humans; D066298:In Vitro Techniques; D053844:Lasers, Solid-State; D008855:Microscopy, Electron, Scanning; D008963:Molar