10.59987/ads/2015.3-4.104-109
Purpose. The aim of this study was to evaluate a novel technique of tooth preparation in fixed prosthodontics suitable for dental students and neophyte dentists.
Materials and methods.Twenty-four dental students of the sixth-year class were recruited to verify the predicibility of this technique. Each student prepared two mandibular second premolars on a typodont for a dental crown with a 90° shoulder finishing line. One tooth was prepared using standard procedures taught in the prosthodontic dental course; the other tooth was prepared with the new technique. Three Professors of Prosthodontics of the same University evaluated the result on the basis of 10 criteria.
Results. A statistically significant difference between the two techniques was found in 8 out of 10 criteria. The new technique showed higher values (p&lt;0.05) in 7 criteria, while the conventional technique had better results in just 1 criterion. Moreover, the total sum of values was higher for the new technique (total 41.2±3.98, p&lt;0.05) compared to the conventional technique (total 38.12±5.18,p&lt;0.05).
Conclusions. This study showed that the results were less dependent on manual abilities and personal experience with the novel technique. It could helps dental students and neophyte dentists in their learning curve.
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Annali di stomatologia
prosthodontics
A tooth preparation technique in fixed prosthodontics for students and neophyte dentists
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Original Article
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G. Pompa
2015
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104
Department of Oral and Maxillofacial Sciences, “Sapienza” University of Rome, Italy
1971-1441
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prosthodontics
en
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A tooth preparation technique in fixed prosthodontics for students and neophyte dentists
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                                                                                                    Original article



    A tooth preparation technique in fixed
    prosthodontics for students and neophyte dentists




                                                                                                      i
                                                                                                    al
                                                                                                 on
    Daniele Rosella, DDS1                                  sonal experience with the novel technique. It
    Giancarlo Rosella, MD, DDS2                            could helps dental students and neophyte denti-
    Edoardo Brauner, DDS, PhD1                             sts in their learning curve.
    Piero Papi, DDS1
    Luca Piccoli, DDS, PhD1                                Key words: tooth preparation, fixed prosthodon-




                                                                                       zi
    Giorgio Pompa, MD, DDS1                                tics, dental education, prosthodontics.




                                                                        na
                                                           Introduction
    1   Department of Oral and Maxillofacial Sciences,
        “Sapienza” University of Rome, Italy               Tooth preparation for fixed prosthesis is a common pro-
    2   Private Practitioner, Italy                        cedure in clinical practice, which all general dentists
                                                           should perform correctly. However, it could be difficult to




                                                             er
                                                           obtain always a predictable result, especially for dental
                                                           students or young doctors: they could make mistakes in
    Corresponding author:                                  their learning curve leading to inadequate results.
    Daniele Rosella


                                                     t     Unlike other human substance, dental tissues don’t
    Department of Oral and Maxillofacial Sciences,
    “Sapienza” University of Rome
                                                  In       have regenerative capacity. Therefore, the removal of
                                                           dental biological material should be planned and exe-
    Via Caserta 6                                          cuted with maximum attention (1).
    00161 Rome, Italy                                      The purpose of a fixed prosthodontic therapy may
    E-mail: daniele.rosella@gmail.com                      vary from the restoration of a single tooth to the reha-
                                       ni
                                                           bilitation of the complete occlusion. A single tooth can
                                                           be fully restored both functionally and aesthetically. A
                                                           missing tooth can be replaced by a fixed prosthesis,
                              io

    Summary                                                increasing patient masticatory competence and main-
                                                           taining or improving dental arches function, often ele-
    Purpose. The aim of this study was to evaluate a       vating patient’s self-image (2).
    novel technique of tooth preparation in fixed          Tooth preparation should have specific geometrical cha-
                       iz



    prosthodontics suitable for dental students and        racteristics to provide necessary retention and resistance
    neophyte dentists.                                     to the vertical and lateral forces acting on the restoration.
    Materials and methods.Twenty-four dental stu-          The most important element of retention is the presence
           Ed




    dents of the sixth-year class were recruited to ve-    of two opposing vertical surfaces. The axial walls of the
    rify the predicibility of this technique. Each stu-    preparation should taper slightly to allow the cementation
    dent prepared two mandibular second premolars          of the artificial crown. The more parallel are the axial wal-
    on a typodont for a dental crown with a 90° shoul-     ls the greater is the retention. However, it is impossible to
    der finishing line. One tooth was prepared using       obtain parallel surfaces without producing undercuts.
    standard procedures taught in the prosthodontic        Goodacre et al. (3) suggest an angle of convergence be-
IC




    dental course; the other tooth was prepared with       tween 10 and 20°. Moreover, the occlusocervical length
    the new technique. Three Professors of Prostho-        is another fundamental factor for both retention and re-
    dontics of the same University evaluated the re-       sistance. The longer is the preparation the greater is the
    sult on the basis of 10 criteria.                      retention. Teeth with larger diameter need a greater
C




    Results. A statistically significant difference be-    length to prevent dislodgement (4). Proper occlusal and
    tween the two techniques was found in 8 out of 10      axial reductions are essentials to provide enough space,
    criteria. The new technique showed higher values       allowing a good functional morphology and structural
    (p<0.05) in 7 criteria, while the conventional tech-   durability. Moreover, no more than necessary dental tis-
©




    nique had better results in just 1 criterion. More-    sues should be removed in order not to jeopardize tooth
    over, the total sum of values was higher for the       structure and retention of the restoration (2).
    new technique (total 41.2±3.98, p<0.05) compared       Preston (5) and Miller (6) suggest starting the tooth prepa-
    to the conventional technique (total 38.12±5.18,       ration producing depth-orientation groves on the vestibu-
    p<0.05).                                               lar and incisal surfaces, with a round-end tapered dia-
    Conclusions. This study showed that the results        mond as reference for removing tooth structure. The oc-
    were less dependent on manual abilities and per-       clusal reduction is performed by removing the tooth por-

    104                                                                     Annali di Stomatologia 2015; VI (3-4): 104-109
    A tooth preparation technique in fixed prosthodontics for students and neophyte dentists


    tions between the orientation groves with the same bur.           •   Bur N°2: diamond-coated depth marker of 2 mm
    After the functional cusp bevel is made, a no. 17L bur is             with a round and angled stopping surface;
    used to smooth the planes of the occlusal reduction.              • Bur N°3: cylindrical diamond of 1 mm with no dia-
    Three vertical groves are performed in the vestibular sur-            mond head;
    face with a flat-end tapered diamond. All tissues between         • Bur ANT: football diamond bur. It is the only one




                                                                                                             i
    the depth-orientation channels are removed. The proximal              conventional bur of the kit;




                                                                                                           al
    reduction is performed with a needle narrow diamond,              • Bur N°4: cylindrical bur with the only 2 final mm
    avoiding damage to the adjacent teeth. The lingual and                diamond-coated;
    proximal surfaces are then cut with a torpedo diamond             • Bur N°5: truncated cone diamond bur with no dia-




                                                                                                        on
    (2). Different finishing line may be created. A chamfer is            mond head.
    considered the preferred choice for veneer metal restora-         The innovation of this technique is the easier control
    tion. Several Authors have shown how this finishing line          of depth and direction of the removing procedures. In-
    exhibits the least stress, with the lowest failure rates (7). A   deed, due to flat and no diamond-coated stopping
    shoulder finishing line is used for all-ceramic crowns, mini-     surfaces, the dentist can dominate easier the bur du-




                                                                                               zi
    mizing stresses with its wide and preventing the possibility      ring tooth reduction. Every bur tracks a guide for the
    of the porcelain fracture. However, it is the more destruc-       following one. There are less variables to consider,
    tive finishing line for the tooth tissues. On the other hand,     so the error-probability is lower.




                                                                                  na
    the knife-edge is the more conservative finishing line, but       The technique consists in four phases (Fig. 1):
    it may results in an over-contoured restoration.                  1. First phase: axial and occlusal reduction depths
    The most demanding challenges for prosthodontists                 2. Second phase: reduction
    are the control of depth and direction of tissue remo-            3. Third phase: finishing line preparation




                                                                          er
    val. None of the Authors in the current literature had            4. Fourth phase: tooth surface refining.
    proposed a systematic procedure in which every bur
    of the previous step produces a stopping surface on
    the tooth for the next one.                                       1. Axial and occlusal reduction depths
    The aim of this paper is to present a novel technique


                                                               t
    of tooth preparation in fixed prosthodontics, capable
    to decrease the importance of dentist’s manual skill in
                                                            In        Depth-orientation grooves are placed with the N°1 bur
                                                                      along the vestibular and oral gingival margin of the
    order to obtain a proper result.                                  tooth (Fig. 2A). The round and flat stopping surface of
                                                                      the bur doesn’t allow to go beyond a depth of 1 mm.
                                                                      Anterior teeth: two or three grooves are completed on
                                               ni
    Methods                                                           the incisal surface with the N° 2 bur.
                                                                      Posterior teeth: following the tooth occlusal anatomy,
    Novel technique                                                   the dentist creates longitudinal and trasversal deep
                                    io

                                                                      guide channels on the occlusal surface with the N° 2
    The new technique consists of six burs (Fig.1):                   bur (Fig. 2B). The angled stopping surface of the bur
    • Bur N°1: diamond-coated depth marker of 1 mm                    makes it easier between the cusps. It doesn’t allow
       with a round and flat stopping surface;                        the dentist to go deeper than 2 mm.
                          iz



                                                                      2. Actual reduction
          Ed




                                                                      2.1 Incisal/occlusal reduction

                                                                      Anterior teeth: the tooth incisal reduction is made
                                                                      between the grooves with the N° 3 bur.
                                                                      Posterior teeth: the no diamond head of the N° 3 bur
IC




    Figure 1. Burs and phases of the novel technique.                 is placed at the bottom of the central sulcus on the


                                                                                                 Figure 2. A, Depth-orientation
                                                                                                 groove placed with the N°1
C




                                                                                                 bur along the vestibular gingi-
                                                                                                 val margin of a mandibular
                                                                                                 second premolar. B, Longitu-
                                                                                                 dinal and trasversal deep
©




                                                                                                 guide channels on the oc-
                                                                                                 clusal surface made with the
                                                                                                 N° 2 bur.




    Annali di Stomatologia 2015; VI (3-4): 104-109                                                                          105
    D. Rosella et al.




                                                                                                            i
                                                                                                          al
                                                                                                       on
    Figure 3. A, Vestibular view of a deep guide grove made with the N° 3 bur. B, Interproximal reduction made with the N° 3
    bur orientated perpendicularly to the major axis of the tooth. C, Circumferential axial reduction.




                                                                                               zi
    occlusal surface. The occlusal reduction is made               convention way, it could be practicable to start using
    using as reference the trasversal deep guide chan-             a normal flame bur.




                                                                               na
    nels. An uniform reduction of 2 mm is easily obtained          The N° 3 bur could now easily remove the axial cir-
    just moving the bur in the mesiodistal way.                    cumferential surface through the reference of the
                                                                   axial and the cervical grooves (Fig. 3C).
                                                                   The ANT bur is used in the anterior teeth only to re-
    2.2 Axial reduction                                            duce the occlusal area between the cingolum and the




                                                                     er
                                                                   incisal margin.
    An axial deep guide grove is made with the N° 3 bur. It
    should be directed in a perfectly vertical way and in pa-
    rallel with the tooth major axis. The no diamond head          3. Finishing line preparation
    doesn’t allow to remove dental tissue beyond the 1

                                                            t
    mm depth of the gingival margin groove (Fig. 3A).
                                                         In        The N° 4 bur is used to prepare the finishing line. The
    The same bur is used to separate the tooth from the            smooth proximal portion of the bur allows to use the
    proximal one. The interproximal cut is made with the           axial surfaces of the cast to guide the dentist in the
    N° 3 bur orientated perpendicularly to the major axis          preparation (Fig. 4).
    of the tooth (Fig. 3B). If it isn’t possible, or the dentist
                                            ni
    prefers an approach to the interproximal cut in the
                                                                   4. Tooth surface refining
                                  io

                                                                   The N° 5 bur refines the tooth surface. It is used to
                                                                   round the line angle of the stump and eliminates any
                                                                   undercut (Fig. 5A, B).
                          iz



                                                                   Study sample selection
          Ed




                                                                   Twenty-four students of the 6th years dental school
                                                                   were recruited to test the novel technique. They vo-
                                                                   lunteered for the study by responding to an email
                                                                   sent to the sixth-year class. All participants gave ver-
                                                                   bal and written consent to take part of the study, ac-
                                                                   cording to the World Medical Association’s Declara-
IC




    Figure 4. Vestibular view of the 90° shoulder finishing line
                                                                   tion of Helsinki.
    made with the N° 4 bur.

                                                                                               Figure 5. A, Refining proce-
C




                                                                                               dures made with the N° 5 bur.
                                                                                               B, Final vestibular view of a
                                                                                               mandibular second premolar
                                                                                               prepared with the novel tech-
                                                                                               nique.
©




    106                                                                           Annali di Stomatologia 2015; VI (3-4): 104-109
    A tooth preparation technique in fixed prosthodontics for students and neophyte dentists


    Each student prepared two mandibular second pre-                    33). It also facilitate pouring impressions and in-
    molars (#4.5) on a typodont for a dental crown with a               vesting wax patterns without trapping air bubbles
    90° shoulder finishing line. One tooth was prepared                 and to ease removing casting modules.
    using standard procedures (1, 2) taught in the pro-             9. Surface texture:
    sthodontic dental course; the other tooth was prepa-                The restorations fitting appears better in smooth




                                                                                                             i
    red with the new technique. Prior to the beginning of               tooth preparation (34, 35). The retention of zinc




                                                                                                           al
    the study, the students were given a thirty-minute                  phosphate cement is increased by surface rough-
    training session on how to use the novel technique                  ness (35-41); its effect has not been as definitely
    with the first Author, DR.                                          determined with adhesive cements.




                                                                                                        on
    Three Professor of Prosthodontics (SDC, GP and LP) of           Another criterion was added for the assessment:
    the same University evaluated the result on the basis of        10. Lesion of the proximal teeth.
    9 scientific principles described by Goodacre et al. (3).
    1. Total occlusal convergence (TOC):                            The grading sheet contains ten criteria above-mentio-




                                                                                               zi
        TOC is the angle of convergence formed between              ned, associated with a specific point value and added
        the two opposite axial surfaces of the preparation;         together to generate the total score. These criteria
        it should vary between 10 and 20°.                          appear in rows, while the associated letter grades (A,




                                                                                 na
    2. Occlusocervical dimension:                                   B, C, D and F) appear in columns. There are point
        The minimal size of incisors and premolar pre-              values for letter grades on each criterion: A=5, B=4,
        pared with 10-20° of TOC is 3 mm (8). 4 mm is               C=3, D=2, F=0. The total score is the sum of the all
        the minimal dimension of molars prepared within             points in the columns.
        10-20°of total occlusal convergence (9).                    After each student completed the first tooth, perfor-




                                                                      er
    3. Ratio of occlusocervical/incisocervical dimension            med with a standard procedure, the second Author
        to faciolingual dimension:                                  (GR) has given to everyone an identification number
        For all teeth it should be 0.4 or higher (4).               and each tooth was placed into a sealed envelope.
    4. Circumferential morphology:                                  The identification numbers were assigned progressi-
        Everytime is possible, facioproximal and linguo-

                                                           t        vely from the first student to finish (id n° 1) to the last
                                                        In
        proximal corners of the teeth should be preserved           one (id n° 24). After each student completed the se-
        (10).                                                       cond tooth, performed with the new technique, the sa-
    5. Finish line location:                                        me Author has given to every student an identification
        Whenever possible, a supragingivally finish lines           letter and each tooth was placed in a different sealed
        should be preferred (11-19); when subgingival fin-          envelope. The identification letters were assigned pro-
                                               ni
        ish lines are required, they should preserve the            gressively from the first student to finish (id letter A) to
        epithelial attachment (20-22).                              the last (id letter X) in the same way for the identifica-
    6. Finish line form and depth:                                  tion numbers above-mentioned. Therefore, every stu-
                                    io


        A chamfer finish lines of 0.3 mm is deep enough             dent had a double code with a number and a letter
        for all-metal crowns (23, 24). The different finish         (i.e. 1F). Next, the typodonts were given to the eva-
        line chosen for use with metal-ceramic crowns               luator, who was blinded to the student’s identity.
                          iz



        should not be related to marginal fit but on per-
        sonal preference (25, 26). Although metal-ceram-
        ic finish line depths of 1.0 mm or more is recom-           Statistycal analysis
          Ed




        mended, the optimal depth has not been deter-
        mined. Both chamfer and shoulder can be used                A specific statistical software (IBM SPSS V10 Statis-
        with all-ceramic crowns bonded to the prepared              tics, IBM, Armonk, USA) was used to analyze the da-
        teeth (27, 28). A greater depth than 1 mm is not            ta. Descriptive statistics (mean, frequency, range,
        necessary when a semitranslucent type of all-ce-            standard deviations) were computed for each group
        ramic crown is used (29).                                   of students, a T test was performed with a significant
IC




    7. Axial and occlusal reduction depths                          P value < 0.05.
        All-metal crowns should be reduced at least 0.5
        mm on the axial surface and 1.0 mm on the oc-
        clusal surface. For metal-ceramic crowns, axial             Results
C




        reductions beyond 1 mm can prejudice the resid-
        ual tooth structure external to the pulp (30); a 2.0        A statistically significant difference between the two tech-
        mm of occlusal reduction is generally possible              niques was found in 8 out of 10 criteria: only “surface tex-
        even on a young tooth (2, 23, 24, 31). With all-ce-         ture” and “line angle form” had p value > 0.05.
        ramic crowns, it is not required a greater depth            The new technique showed higher values (p<0.05) in
©




        than 1 mm of axial reduction and 2 mm incisal/oc-           7 criteria, while the conventional technique had better
        clusal reduction with semitranslucent systems               results in just 1 criterion (“lesion of the proximal
        (29).                                                       teeth”).
    8. Line angle form:                                             Moreover, the total sum of values was higher for the
        Line angles of tooth preparations should be                 new technique compared to the conventional tech-
        rounded to reduce stress in the restoration (31-            nique (p<0.05). Data were summarized in Table 1.

    Annali di Stomatologia 2015; VI (3-4): 104-109                                                                          107
    D. Rosella et al.


    Table 1. Assessment criteria.

    Assessment criteria                                 Conventional technique                   New technique                   P value
    Total occlusal convergence                          3.82 ± 0.43                              4.23±0.78                       <0.05
    Occlusocervical dimension                           3.67 ± 0.67                              4.04±0.75                       <0.05




                                                                                                                     i
    Occlusocervical / faciolingual dimension            3.87 ± 0.54                              4.12±0.67                       <0.05




                                                                                                                   al
    Circumferential morphology                          3.64 ± 0.78                              4.25±0.6                        <0.05
    Finish line location                                3.84 ± 0.77                              4.21±0.56                       <0.05
    Finish line form and depth                          3.77 ± 0.69                              4.33±0.63                       <0.05




                                                                                                                on
    Axial and occlusal reduction depths                 3.93 ± 0.52                              4.37±0.62                       <0.05
    Line angle form                                     3.83 ± 0.63                              4.08±0.65                       >0.05
    Surface texture                                     3.81 ± 0.83                              3.78±0.81                       >0.05
    Lesion of the proximal teeth                        3.94 ± 0.57                              3.79±0.56                       <0.05




                                                                                                      zi
    Total                                               38.12 ± 5.18                             41.2± 3.98                      <0.05



    Discussion                                                         cularly for neophyte dentists: they can use it as a trai-




                                                                                      na
                                                                       ning procedure in their learning curve. It could be also
    According to our results, the new preparation techni-              possible the use of the technique in combination with
    que is more predictable than the conventional techni-              other methods. Hence, due to the small size of the
    que for no experienced doctors. The reason is that re-             sample (N students = 24, N teeth = 48), which could be




                                                                         er
    sults are less dependent on manual abilities and per-              affected by selection and information biases, these da-
    sonal experience. This study has shown benefits in                 ta need to be evaluated carefully, however the novel te-
    control of depth and direction of tooth tissue removal             chnique is a valid alternative in the landscape of fixed
    as well as a better definition of the tooth finishing line.        prosthodontic preparation techniques.
    The total occlusal convergence (TOC) is an essential

                                                            t
                                                         In
    criterion to be considered in tooth preparation. Okuya-
    ma et al. (42) made a quantitative evaluation of axial             Conflict of interest
    wall taper in artificial teeth prepared by pre-clinical stu-
    dents. After a fixed prosthodontics course, they have              No potential conflict of interest relevant to the study
    been instructed to reduce 54 artificial teeth for comple-          was reported.
                                               ni
    te cast restorations. Statistically significant higher TOC
    than required have been detected. The greatest diffe-
    rences were produced in the vestibular region with a               References
                                    io


    mean taper value of 21.7° instead of 2-5° required. Si-
    milarly, Aleisa et al. (43) evaluated 355 tooth prepara-            1. Castellani D. La preparazione dei pilastri per corone in metal
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                         iz


                                                                        2. Shillingburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE.
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IC




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©




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                                                                                            na
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    Annali di Stomatologia 2015; VI (3-4): 104-109                                                                                             109
