With continuing research in the field of digital dentistry, various novel technologies have emerged in recent years, one being the three-dimensional (3D) printing technology. Many researchers have explored various parameters of this technology so that its clinical implications can be widened. 3D printing has the potential to revolutionize conventional dentistry in clinical treatment, education, and research with the rapid development of new materials, printing techniques, and machines. ¹

In dentistry, 3D printing technology finds its use in the construction of surgical guides, stents, provisional restorations, resin patterns, dental models, and cast copings. Arguably, one of the procedures that can benefit the most from the recent developments in 3D printing technologies is the fabrication of provisional crowns and bridges. Placement of the provisional restoration is one of the very important steps in the treatment planning of dental implants. Although an important step in implant dentistry, this step is often overlooked and has been underutilized. Provisional restoration is used to evaluate the occlusal function, phonetics, soft tissue contours, and esthetics prior to delivery of the final restoration while maintaining and/or enhancing the condition of the peri-implant hard and soft tissues. ²

Provisional restoration can be fabricated using the conventional chairside method, in the laboratory on working casts, and more recently by the use of digital technology by computer-aided designing/computer-aided milling (CAD/CAM) process or rapid prototyping (RP).

There are some studies which have evaluated and compared the marginal fit and accuracy of the 3D printed provisional restoration with conventionally fabricated restorations, but to the best of our knowledge, no previous study has compared the in vivo effect of provisional restorations fabricated using the 3D printing technique and conventional technique on peri-implant hard and soft tissue parameters.

Therefore, the purpose of this study was to evaluate the influence of full-coverage provisional restorations on hard and soft peri-implant tissues in two workflows, 3D printing versus conventional technique.

Study design

The present study was designed as a randomized controlled trial with a two-group design. A prospective, clinical study was conducted in the department of prosthodontics and crown and bridge involving the subjects selected from November 2018 to June 2019. Ethical clearance was obtained from the institutional ethical committee vide letter number: PGIDS/IEC/2018/11, dated November 30, 2018. Systemically healthy individuals with maintainable oral hygiene were selected based on inclusion and exclusion criteria. After an explanation of proposed study criteria, including alternative treatment options, potential risks, and benefits, signed informed consent was obtained for all subjects prior to the dental implant placement.

Study population

A total of 58 subjects were screened from the outpatient department, based on the chief complaint requiring replacement of the mandibular single posterior tooth.

Inclusion and exclusion criteria

Subjects with age above 18 years and with partially edentulous mandible who were willing for tooth replacement with sufficient bone width and density for implant placement and who gave written consent for the participation in the study were included. Good periodontal health, no systemic disease, and adequate buccolingual, mesiodistal, and interocclusal space at the site of implant placement were also the criteria for inclusion in the study. Those subjects who had an infection around the proposed site of implant placement or had a condition that would interfere with the healing of the soft tissue and bone and in whom, for any reason, surgical procedure was contraindicated were excluded from the present study.

Grouping of the subjects

After examining the patients clinically and radiographically and based on the inclusion and exclusion criteria, 24 subjects (12 males and 12 females) were randomly allocated to the control and test groups each, by using the lottery method.

Group GpIC included subjects with single-stage implant placement and early nonfunctional loading with provisional restorations fabricated by the conventional method, whereas in Group GpIID, fabrication was done by the digital light processing (DLP) 3D printing technique.

Presurgical assessment

A detailed history and clinical examination of patients were carried out. The implant site was assessed clinically. Preoperative records were obtained. Routine hematological (hemoglobin, bleeding time, clotting time, and blood sugar tests) and radiographic investigations were carried out to evaluate patient fitness for implant placement. Cone-beam computed tomography and standardized intraoral periapical (IOPA) X-ray were taken using a long-cone paralleling technique with a customized jig for the evaluation of bone quality and quantity.

Surgical phase

Local anesthesia was administered, and after confirming its effectiveness, incisions were given. A full-thickness mucoperiosteal flap was reflected followed by osteotomy preparation by sequential drilling. Thereafter, torque wrench was used to position the dental implant and the cervical collar of a dental implant was approximated with the margin of the crestal bone. Healing abutment was then positioned. The surgical site was then irrigated with a 0.9% saline solution and sutured. Postoperative instructions were given to the subject regarding diet and oral hygiene, and the medications were prescribed. Subjects were recalled after 24 h for review, and suture removal was done after 7 days.

Prosthetic phase

After a healing period of 10–14 days, the healing abutment was removed, the height of the gingival collar was assessed, and the selection of a suitable implant abutment was done. To transfer the orientation of the implant, a closed-tray transfer implant coping was used. Impression was made using polyvinyl siloxane impression material. After retrieval of the impression from the mouth, the implant analog was positioned over the close-tray transfer coping and secured on the impression. After retrieval of the cast, upper and lower models were articulated using the interocclusal record and a cement-retained provisional implant-supported restoration was fabricated.

Group I (GpIC)

In this group, provisional restoration was fabricated using the indirect method. After the application of die spacer, wax pattern of nonfunctional provisional restoration providing customized contours was fabricated on the abutment, i.e., the prostheses were kept out of occlusion in nonfunctional relationship with the opposing arch. A silicone putty index was made involving at least one tooth on either side of the abutment teeth. A cotton pellet was placed into the temporary abutment screw hole to prevent provisional restoration material from flowing into the screw access hole. As a separating medium, petroleum jelly was applied to the trimmed abutment and cold mold seal was applied on the adjacent teeth. Self-cure acrylic resin was injected into the tissue side of the putty index. After the provisional restoration material was set, the temporary restoration was removed carefully. The excess provisional restoration material was trimmed extraorally. The provisional restoration was relined if required. It was finished and polished and cemented on the implant abutment using a noneugenol temporary cement (Meta Biomed Co., Korea) Figure 1. Figure 1

(a) Prerehabilitation intraoral view depicting missing 36, (b) Maxillary impression and mandibular impression with abutment and laboratory analog, (c) Wax pattern fabricated conventionally on mandibular cast, (d) Postrehabilitation intraoral view after cementation of conventional nonfunctional provisional restoration.

Table 1shows the various parameters regarding the age, gender, location of dental implant, and dimensions of the dental implant. The subjects from Group GpIC1 to GpIC12 received conventionally fabricated provisional restorations. The subjects from Group GpIID1 to GpIID12 received 3D printed provisional restorations.{Table 1}

The intragroup comparison for all the data was done using Wilcoxon signed-rank test [Graph 1] and [Graph 2]. Statistically significant (P < 0.01) intragroup variation in magnitude of MBL and probing pocket depth was noted throughout the study with the lowest values at baseline and highest values at 4 months of the follow-up period. The intragroup variation in mSBI and BOP was statistically significant (P < 0.01) in both the groups from baseline to 2 months of follow-up period without any further statistically significant variation in these clinical parameters from 2 months to 4 months of follow-up period.[INLINE:1][INLINE:2]

The intergroup variation in the MBL Table 2around dental implants restored with conventionally fabricated provisional restoration was greater than around dental implants restored with 3D printed provisional restoration from baseline to 4 months of follow-up, but the difference in the finding was statistically as well as clinically nonsignificant (P > 0.05). The intergroup difference in sulcular probing pocket depth Table 3was found to be statistically as well as clinically nonsignificant (P > 0.05) over a period of 4 months.{Table 2}{Table 3}

The intergroup comparison of mSBI score was found to be statistically nonsignificant (P > 0.05) over a period of 4 months Table 4. Improvement in BOP was found to be greater around dental implants restored with 3D printed provisional restoration than dental implants restored with conventionally fabricated provisional restoration from baseline to 4 months of follow-up Table 5, and the difference in finding was statistically significant (P < 0.05). The mucosal suppuration around dental implants in both the groups was found to be negative and constant over a period of 4 months. There was a statistically nonsignificant difference seen for the responses between both the groups (P > 0.05) for all questions related to patient satisfaction Table 6.{Table 4}{Table 5}{Table 6}

The conventional manual chairside fabrication of provisional restorations is very common and simple, but this method has its drawbacks such as low flexural strength, ³ incorporation of voids during the mixing procedures that could adversely affect the surface texture, low mechanical strength, and less precise fit of the restoration. Hence, other methods of provisional restoration have been explored, studied, and evaluated.

Recent technological advances such as the CAD/CAM method and the 3D printing method have enabled accurate and precise methods to fabricate provisional restorations. The principle on which CAD/CAM unit works is the subtraction of material. However, this method causes unnecessary loss and wastage of materials which is as high as 90%. ⁴ Furthermore, the construction of complex geometrical structures cannot be successfully reproduced. ⁵ 3D printing technology, on the other hand, offers various advantages such as it is time-saving, has high accuracy, and gives precise fitting of the constructions. ⁶ There is no risk of distortions and laboratory mistakes, the production of complex shapes can be done without the use of special tools, and there is almost no wastage of material. ⁶ 3D printed provisional restorations have sufficient mechanical properties to be used intraorally. ⁷ 3D printed resins are unfilled composed of at least 90% methacrylic oligomers which are photo cross-linked, and in the monomer blend, up to3% phosphine oxides are present as photoinitiators. ⁸

There have been many in vitro studies which compared the mechanical properties of conventional provisional restorative material and the 3D printed provisional restoration material and found contrasting results. Park et al. ⁹ concluded in their study that the wear resistance of the 3D printed resin material was in a comparable range to the conventionally fabricated or the milled resin materials. The 3D printing process was found to be suitable for manufacturing dental restorations. On the other hand, Munoz et al. ¹⁰ used the DLP technique to fabricate wax patterns for indirect manufacturing of cast gold crowns and found that the marginal gap was significantly larger for DLP fabricated patterns compared to the milled or manually fabricated wax patterns. Digholkar et al. ¹¹ conducted an in vitro study on provisional crowns fabricated by conventional heat-activated resin, CAD/CAM, and RP. They concluded that the flexural strength values of all the groups were higher than minimal acceptable flexural strength of provisional FDP materials which is 50 MPa. According to Tahayeri et al., ⁷ the modulus of elasticity of 3D printed samples was comparable to jet (the conventional methyl methacrylate resin). The peak stress of 3D printed samples was significantly higher than Jet, and the degree of conversion appeared to be higher than Jet. ⁷

The present study compared the effect of conventional and DLP 3D printed provisional restoration on peri-implant hard and soft tissues. Change in MBL of 0.54 ± 0.52 mm and 0.48 ± 0.52 mm was seen in Group GpIC and Group GpIID, respectively, from baseline to 4 months of follow-up period. The mean crestal/MBL noted in both the groups was within the success criteria of an implant (mean crestal bone loss <1.5 mm within the 1 ^styear of implant loading). ¹² Both the groups showed a similar change in mean MBL at mesial and distal sites ranging from 0.51 mm to 0.55 mm from baseline to 4 months of follow-up.

The change in crestal bone level in the present study is comparable to that noted by Roccuzzo and Wilson ¹³ around early loaded implants. Resorption was about 0.65 mm for the implants loaded after 6 weeks and 0.77 mm for loading within 12 weeks. In addition, Salvi et al. ¹⁴ found resorption of 0.57 mm in implants loaded after 1 week and 0.72 mm in implants loaded after 6 weeks.

Apart from the evaluated hard tissue parameter as mentioned above, soft tissue parameters also play an essential role in the overall success of implant treatment and are usually a significant indicator of implant health. An increase in pocket depth was statistically significant and similar in both the groups from baseline to 4 months of follow-up period (GpIC 0.35 ± 0.32 mm ~ GpIID 0.36 ± 0.33 mm). Gradual increase of 0.21–0.55 mm in probing pocket depth was observed in both the groups from baseline to 4 months of follow-up with the highest increase at distal sites (0.46 mm, 0.55 mm) followed by mesial (0.38 mm, 0.41 mm), lingual (0.34 mm, 0.29 mm), and buccal sites (0.25 mm, 0.21 mm).

According to the study done by Adell et al. ¹⁵ and Buser et al., ¹⁶ peri-implant probing depth (PPD) up to 3 mm is considered “healthy.” Only a slight increase in PPD (<3 mm) and improvement in mSBI in the present study revealed the absence of progressive destruction of connective tissue around implants. The implant mucosa remained in a healthy condition as the patient's maintained good oral hygiene from the beginning of the study.

mSBI and BOP were higher at mesial and distal sites in both the groups followed by lingual and buccal sites. This intersite variation noted in values of mSBI and BOP may be attributed to differences in accessibility of these sites to oral hygiene measures. More bleeding sites resolved in the 3D printed group than the conventional group, but improvement noted in the mSBI was greater in the conventional group. Despite BOP being a diagnosis of peri-implant disease, bleeding, unusual in healthy periodontium, is found in most healthy peri-implant tissues. Therefore, according to Ferreira et al., ¹⁷ it is not clearly defined whether peri-implant BOP could represent a reliable parameter for identifying the presence of peri-implant disease. Some studies suggest that peri-implant mucosa may be more sensitive to probing forces, causing more BOP when compared with teeth. ¹⁸ , ¹⁹

Lesser marginal bone loss and better improvement in BOP observed in the GpIID group than the GpIC group may be attributed to better marginal fit and finish of 3D printed provisional restorations than conventionally fabricated provisional restorations, but the difference in marginal bone loss (0.54 ± 0.52 >0.48 ± 0.52) between the two groups from baseline to 4 months of follow-up was statistically as well as clinically insignificant.

When assessing the various outcomes of dental implantology, it is essential to consider both patient and clinician appraisals. For the oral implant prosthesis longevity, frequency of complications and implant survival are the significant parameters; on the contrary, cost-effectiveness, the social and psychological impact of the treatment, its utility, and benefit are the important factors from a patient's point of view. ²⁰ Nearly, all questionnaires regarding the level of patient satisfaction with implant treatment were scored positive in the present study. There was a statistically nonsignificant difference seen for the frequencies between the groups (P > 0.05) for all questions.

The nonfunctional loading concept was used in the present study. The nonocclusal pattern reduces the masticatory force on implants, and studies have shown that nonocclusal loads for short-span prostheses and single-tooth replacements are important factors for a successful hard and soft tissue outcome. ²¹

The soft tissue attachment onto the implant surface is more delicate than that seen at the natural tooth surface due to the lack of Sharpey's fiber insertion, decreased number of collagen fibers, and altered direction of these fibers. Hence, any residual cement can cause gingival inflammation or peri-implantitis leading to bone loss or implant failure. ²² , ²³ Thus, precaution was taken during cementation to avoid any residual cement after cementation.

To the best of our knowledge, there is no earlier in vivo study in the literature where the influence of provisional restorations on the outcome of clinical parameters has been studied, hence the results of this study could not be compared, being the first study of its kind. In the present study, all the subjects participated until the end of the study, showed good compliance with the study protocol, and maintained good oral hygiene except one case in GpIID and two cases in GpIC. These three cases showed peri-implantitis and were given suitable treatment accordingly. However, healing, in general, was uneventful with minimal discomfort to all the subjects.

Limitations

The marginal bone loss value may have been influenced by the variation in implant dimension in subjects of both the groups. However, the effect of implant dimensions on marginal bone loss has been studied in the past with variable result. According to Monje et al., other variables such as surgical trauma, prosthetic considerations, implant neck design, or patient's habits have a more significant impact on MBL. ²⁴

The present study collected data from a limited pool of patients and as specific site (posterior mandible); therefore, further trials are needed to generalize these results to a broader population and different areas of the mouth.

Both 3D printed and conventionally fabricated provisional restorations have a comparable impact on the clinical parameters related to peri-implant hard and soft tissue health. Therefore, it may be speculated that both can be used during the initial healing period with early nonfunctional loading protocol.

Financial support and sponsorship

This was a self-funded study.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.